WO2003049615A1

WO2003049615A1 - Method and apparatus for establishing an osteoporosis measure

Info

Publication number: WO2003049615A1
Application number: PCT/DK2002/000836
Authority: WO
Inventors: Michael Grunkin; Johan Doré HANSEN
Original assignee: Osteomate Aps
Priority date: 2001-12-10
Filing date: 2002-12-09
Publication date: 2003-06-19
Also published as: AU2002358458A1

Abstract

The present invention relates to a method and a system for establishing a measure relating to skeletal and joint status of an individual, said method comprising establishing a radiation source having a tube head capable of rotating in any angle, meaning that the tube head has at least one degree of freedom in relation to the detector, and a radiation detector for acquisition of an image, positioning a limb of the individual between the tube head and the radiation detector, arranging the tube head in a predetermined distance from the radiation detector, so that the distance between the tube head and the radiation detector is a constant distance independent of the size of the limb, and/or arranging the tube head in a predetermined angle from the radiation detector, so that the radiation path from the tube head is substantially orthogonal to the detector, capturing an image of the limb in the radiation detector, analysing the image detected thereby establishing the measure relating to skeletal and/or joint status of the individual.

Description

Method and apparatus for establishing an osteoporosis measure

The present invention relates to the field of non-invasive measure of bone quality of vertebrates. This measure may be used in the assessment of bone status which, in turn, may be of relevance in the diagnosis of, e.g., osteoporosis and other bone diseases which cause bone fragility and, thus, increase the risk of bone fracture. Furthermore, the measure may be used for assessment of joint status, which, in turn, may be of relevance in the diagnosis of rheumatoid arthritis and other joint diseases.

Background

A bone of a vertebrate consists of a cortical outer layer and a cancellous or trabecular inner structure. The strength of a bone relates to the bone structure including the thickness of the cortical layer.

Osteoporosis is the end result of bone loss. Postmenopausal women over 60 who have had limited or no estrogen replacement therapy at menopause are the major high-risk group. Today, osteoporosis affects more than one third of elderly women in the industrialized part of the world. The prevalence of this disease is still increasing, partly caused by the increase in the proportion of elderly people, but also a more sedentary lifestyle is thought to play an important role.

Also, asthmatics or other lung patients, or rheumatoid arthritis patients, treated with high- dose corticosteroids, lose trabecular bone and experience fractures, as do patients with Cushing's Syndrome. Other disorders including renal failure and certain types of cancer cause bone loss, along with chronic use of drugs such as anticonvulsants, anticoagulants, excess alcohol, and too much thyroid medication. Young women who experience amenor- rhea due to athletic activity, weight loss, stress, or the nutritional deficiency of bulemia or anorexia nervosa lose bone; so do young women who have an early natural or surgical menopause and are not given estrogen replacement therapy. Not all of the patients in all of these groups will develop osteoporosis. However, most of them will lose some bone and thus increase their long-term risk for fractures.

Since the risk of fracture is generally believed to be related to the structural competence of the axial or appendicular skeleton, bone quality measurements such as bone mineral density, cortical thickness or even trabecular connectivity are likely to supply the essential information about fracture risk. Major studies have demonstrated a relationship between low bone mass and increased fracture risk, expressed in terms of odds-ratio. However, if individuals at risk of developing osteoporosis can be identified sufficiently early, preventive measures can be applied. This requires a reliable, inexpensive, safe and widely available method for identification of those at risk.

Furthermore, since the means of preventing osteoporosis are much more efficient than those of treating osteoporosis, identification of individuals at risk of developing this disease is crucial. Only by early prevention of osteoporosis, the individual as well as the socio-economic consequences of the disease may be minimized.

Most commercially available methods for bone density measurement pass a low-intensity beam of x-rays or gamma rays through a patient, and a radiation detector on the other side measures how much of the beam is absorbed. Part of the beam is absorbed by the bone and part by the surrounding soft tissue, and each technique measures these differently.

Quantitative Computed Tomography (QCT) provides a cross-sectional or 3-dimensional image from which the bone is measured directly, independent of the surrounding soft tissue.

Dual energy x-ray absorptiometry (DXA) measures the bone by computing the difference in absorption of low-energy photons and high energy photons by the mixture of soft tissue and bone in the path of the beam, and can generate a 2-dimensional image for localization of the bone. DXA provides a direct measurement of the bone mineral density (BMD - area density in g/cm2). It uses an X-ray source that produces photons of two distinct energies, a photon detector and an interface with a computer system for imaging the scanned areas. While DXA is recognized as the technique of choice in the management of osteoporosis, there are, however, some limitations. It is generally accepted that spine BMD can be significantly affected by the presence of osteophytes, aortic calcifications, degenerative hypertrophy of the facet joints and inter-vertebral disc space narrowing in degenerative disk disease and the measured BMD in the postero-anterior measurement of the lumbar spine may be increased artificially. Furthermore, the technology requires experienced and trained staff to operate the equipment. It is important to remember that BMD explains only about 70-75% of the variability in strength, while the remaining variability could be due to other factors such as accumulated fatigue damage, degradation in bone micro-architecture and the state of bone remodeling. While these techniques are effective for the determination of bone mineral density they represent relatively expensive approaches that give limited information on bone structure.

Single energy x-ray absorptiometry (SXA) computes bone mineral from the increased absorption of the beam as it passes from a constant thickness of soft tissue or water bag into the bone. Localization for SXA is normally done using external landmarks without an image. Radiographic absorptiometry (RA) measures bone density in the fingers relative to an aluminum calibration wedge on the film. Non absorptiometric methods such as ultrasound of bone do not measure bone density directly, but give alternative information about properties of bone such as the speed of sound that are related to bone density and structure. Generally, BMD and measures related to ultrasound are highly correlated

Radiogrammetry, a technique that has been in use for more than 30 years, relies on the measurement of the cortical thickness of bones in the hand (metacarpals) and/or fingers (phalanges). This technique has suffered from relatively poor accuracy and reliability and has largely been supplanted by more recent techniques such as DXA as discussed above.

Recently, advances in computer technology have renewed interest in this old technique. In WO 00/62673 forearm bone mass is estimated from measurements of the cortical width of bones in the hand using computerized digital x-ray radiogrammetry from a single plain radio- graph of the hand and wrist. The BMD estimate is referred to as DXR-BMD.

A measure of the overall bone strength may naturally be obtained from a bone specimen taken from the potential patient and subjected to mechanical testing. However, this requires bone biopsy, which is painful and implies a minor risk of complications and is usually associ- ated with a high precision error. Thus, in order to have a comfortable, cheap, fast and safe screening of the very large group of potential patients (most women after menopause), the estimation of the bone quality should be performed non-invasively using widely available equipment. Most of the equipment discussed above are expensive, and consequently, almost only located and larger hospitals or other centrally placed clinics whereby the individu- als to be tested have to travel far to be examined.

A majority of dentists have an X-ray apparatus for diagnosing various conditions in relation to teeth, alveoles and jaws. Therefore dental X-ray apparatuses are distributed decentralized in the countries, since dentists are available in most cities and towns. This has led to the idea, that osteoporosis and related skeletal diseases could be diagnosed from an X-ray of the mandible. However, dental apparatuses are characterised by a tube head being capable of positioning in any angle and direction, in order to obtain X-rays of all parts of the teeth and jaws, which make them less useful in the diagnosis of osteoporosis, since it is difficult if not even impossible to position the tubehead at a predetermined, reproducible position on the jaw due to lack of anatomical landmarks again leading to difficulties when processing the X- rays for bone analysis. Summary of the invention

The present invention relates to the use of X-ray apparatuses, in particular dental X-ray apparatuses being easily available to the population due to their decentralized position at den- tal clinics when obtaining X-rays of limbs, on which the bone analysis should be based. The present invention provides a system and a method for using dental X-ray systems. Dental X- ray systems for use in the present invention have a radiation source having a tube head capable of rotating in any angle in relation to the detector.

Therefore, in one aspect the invention relates to a method for establishing a measure relating to skeletal and joint status of an individual comprising

establishing a radiation source having a tube head capable of rotating in any angle, and a radiation detector for acquisition of an image,

positioning a limb of the individual between the tube head and the radiation detector,

capturing an image of the limb in the radiation detector,

analysing the image detected thereby establishing the measure relating to skeletal and joint status of the individual.

In a preferred embodiment the tube head is positioned in a fixed position in relation to the limb in order to obtain a more reproducible X-ray at a fixed landmark position of the bone.

Thus the present invention relates to a method for establishing a measure relating to skeletal and joint status of an individual comprising

arranging the tube head in a predetermined distance from the radiation detector, so that the distance between the tube head and the radiation detector, is a constant distance independent of the size of the limb, and/or arranging the tube head in a predetermined angle from the radiation detector, so that the radiation path from the tube head is substantially orthogonal to the detector, capturing an image of the limb in the radiation detector,

Preferably also, the distance between the limb and the radiation detector is kept substantially constant.

By the present invention a means for using dental x-ray apparatuses for obtaining a measure relating to skeletal status is provided.

Another object of the invention relates to a system, suitable for use in the method, namely a system for establishing a measure relating to skeletal and joint status of an individual, comprising

a radiation source having a tube head capable of rotating in any angle,

a radiation detector for acquisition of an image, and

a support having a surface with a recess for receiving the radiation detector.

In yet another aspect the invention relates to a system, suitable for use in the method, namely a system for establishing a measure relating to skeletal and joint status of an individual, comprising

a radiation source having a tube head capable of rotating in any angle,

a radiation detector for acquisition of an image, and

a distance piece for determining a constant predetermined distance between the tube head and the radiation detector

Furthermore, the invention relates to a method for establishing a measure relating to skeletal status of an individual, comprising

establishing an image of a tubular bone having, at any given point, an outer projected width D, and inner projected width d and a cortical layer therebetween, establishing a plurality of points along the length axis on the image of the tubular bone, and for each point calculating at least the outer projected width D, and inner projected width d,

from the calculations identifying at least one landmark for estimating the measure relating to skeletal status of an individual, and

establishing the measure.

Since the projected width of tubular bones typically varies along the length axis of the bone a plurality of points along the length axis are established.

The method may be used on images of tubular bones independent of the method for acquiring the image, however the method is preferably included in the method for determining the skeletal status by use of dental x-ray apparatuses.

Also, the invention relates to a method for establishing a standard reference for a measure M relating to skeletal and joint status of an individual is established by the following steps

selecting a plurality of individuals, wherein the plurality represents at least individuals of different ages, optionally different sexes, and/or different races,

obtaining the measure M relating to skeletal and joint status for each individual by a method as defined above,

arranging the measure M in relation to age thereby establishing a standard reference the measure M.

Furthermore, the invention relates to a method for screening skeletal and joint status of an individual comprising subjecting the individual to a method as described above, and analysing the image detected obtaining a measure M for said individual, and then comparing the obtained measure M with a standard reference. The image detected is preferably analysed by the method as described above.

Drawings

Fig 1 : 3rd proximal finger and its X-Ray image.

Fig 2: Found center points.

Fig 3: Image before and after rotation. Fig 4: Correct oriented image before and after cropping.

Fig 5: Full bone model illustration.

Fig 6: Image before and after longitudinal smoothing.

Fig 7: Simple model for rough outer border estimation. Fig 8: Range from 32 times sub-sampled to full image resolution.

Fig 9: Cross section to fit with model.

Fig 10: Observed cross section log-transformed intensities.

Fig 11 : Sub-pixel accuracy fit of model to log-transformed intensities.

Fig 12: Inner and outer ellipse borders along the bone. Fig 13: Polynomial fits of ellipse borders near measuring position.

Fig. 14: A schematic drawing of a support having a surface wherein two parallel distance pieces are arranged.

Fig. 15: A photo of a hand positioned in the support with distance pieces.

Fig. 16: A photo of a typical dental X-ray apparatus. Fig. 17: A plot of the measure M as a function of age.

Detailed description of the invention

As discussed above the present invention relates to a system and a method for obtaining a measure relating to conditions of the skeletal apparatus, including bones and joints. The measure may thus correlate either to biomechanical properties of the bones, such as failure load and elasticity, wherein the latter is normally measured as Young's modulus, or bone mass or bone density

In particular the invention relates to conditions, such as osteoporosis, osteopenia or hyper- parathyroidism or other bone disorders. The implications caused by these disorder may be termed "intra cortical resorption" also called intracortical porosity, as described in for example "Radiograhpically detectable intracortical porosity" by Meema, H.E. (Acta Radiographica Diagnosis 27 (1986) pp. 165-172, "periosteal resorption", and "endosteal resorption".

The method has the advantage that reproducible information may be derived from in particular phalangeal bones,

The present invention relates to the principle that a measurement of the cortical thickness of a bone is related to the skeletal status, e.g. biomechanical properties and/or BMD. Thereby the invention provides a measure more easily and less expensively obtained yet still being a measure reliably correlating to BMD measured by a gold standard, i.e. DXA-BMD of the hip and spine. Since cortical thickness of a bone is a measure related to the amount of bone, the measure according to the invention identifies individuals at risk of acquiring or having osteoporosis or related bone conditions, and may therefore be used to identify individuals that should be diagnosed more thoroughly, for example by measuring DXA-BMD on the hip and/or spine.

The measure may also on its own identify individuals having a low bone density before a fracture occurs, thus predicting the risk of fracturing in the future, determining the rate of bone loss if the test is conducted at intervals of a year or more, and monitoring the effects of treatment if the test is conducted at intervals of a year or more.

As indicated above, in the present context "the measure relating to skeletal and/or joint status" is not equalled to "bone quantity", such as Bone Mineral Density. In fact, it is contemplated that a better estimate of skeletal status may be obtained by considering pertinent properties of cortical and cancellous bone individually instead of treating these two types of bones similarly, as it is done in standard densitometric methods.

Endosteal and intra-cortical erosion are reflected in the radiographic image as low-frequency variations in the grey-levels. For young normals, erosions are not systematically manifested in the projection radiographs, and hence there is no significant component of low-frequency variability to be measured in the cortical region. With age and disease progression, the degree of cortical resorption is increasing, leading to an increasing amount of low-frequency content in the image.

In addition to measuring the cortical thickness, the present invention may include information regarding the erosions, such as endosteal erosions, and intra-cortical erosions, the latter also being called porosity, vide Meema cited above. In x-rays the porosity is often identified as striations, i.e. longitudinal low-frequency variations as discussed above.

By combining the two measures, the method may more efficiently discriminate between indi- viduals of normal and abnormal skeletal status.

Also by the present invention it is possible to provide information relating to the joints, such as information regarding the distance between the bone ends of a joint, as well as any variations of the bone ends, for example the substantially circular low-frequency variation nor- mally correlated to rheumatoid arthritis. Anatomy

The method according to the invention is suitably adapted for analysing tubular bones, such as radius or ulna of the arm, the metacarpal bones as well as the fingers, or corresponding bones of the distal limbs. Therefore, the limb to be used when establishing the osteoporosis measure is preferably a distal part of the limbs, such as distal arm or distal leg, hand, foot or fingers. In a preferred embodiment the limb is the hand, wherein one or more of the metacarpal bones are examined or one or more of the fingers. In a more preferred embodiment the fingers are examined, such as the third finger. The method may be carried out on both the dominant and the non-dominant hand and/or fingers, however it is preferred that the non- dominant hand and/or fingers are used. Accordingly, the present invention is preferably carried out on the third proximal phalangeal bone of the non-dominant hand.

If e.g. an X-ray image is taken of a hand comprising both a number of phalangeal and/or metacarpal bones and/or a part of the distal radius, the cortical thickness may be determined for one or more of the phalangeal and metacarpal bones as well as at positions in the distal radius.

The present invention provides a measure that does no rely on the assumption that the corti- cal bone has the same thickness around the circumference of the bone at the longitudinal position thereof, since the invention provides a method for estimating the bone cortical thickness independent of the geometry of the bone.

This method has the advantage that absorption data may be derived about the cortical bone (and on the basis thereof about the trabecular bone) which is independent of the manner in which the image was taken, developed, illuminated, scanned, etc - as long these properties are at least substantially the same over the surface of the scanned image.

The present invention uses radiogrammetry in the analysis of the images, i.e. analysis based on the X-ray image as such without absorption data obtained by using for example standard wedges. An X-ray image is a projection of the attenuating properties of the tissue in the direction of the X-ray radiation and is thus a projection of the 3-dimensional distribution of the X-ray attenuating properties of the cortical and cancellous tissue. Thus, even though the bones and the trabecular structures thereof are inherently three-dimensional, the projection of this structure onto two dimensions, such as in a radiographic image, conveys useful information about the spatial distribution of bone.

In another embodiment, bone densitometry is determined by use of radiographic absorptiometry. To correct for the influences of different films, exposure times, voltage setting and film processing, wedges may be used. Preferably two wedges are used, one being tissue equivalent and one being bone equivalent. In a preferred embodiment, the tissue equivalent wedge is made of Exradin A-150 plastic and the bone equivalent wedge is made of Exradin B-100 plastic.

X-ray mass attenuation coefficients are shown below:

A-150 TISSUE-EQUIVALENT PLASTIC

Energy μ/p L P

(MeV) ⁽cmVg⁾ (cm²/g)

1, .OOOOOE-03 2 .259E+03 2 .256E+03

1. .50000E-03 7 .282E+02 7 .267E+02

2, .OOOOOE-03 3 .183E+02 3 .172E+02

3. .OOOOOE-03 9 .652E+01 9, .576E+01

4, .OOOOOE-03 4 .081E+01 4 .021E+01

4, .03810E-03 3 .96SE+01 3, .907E+01

20 K 4, .03810E-03 5 .629E+01 5, .326E+01

5, .OOOOOE-03 3, .069E+01 2. .901E+01

6^", •OOOOOE-03 1. .813E+01 1. .708E+01

8. .00000E-03 7. .914E+00 7. .337E+00

1, .00000E-02 4, .186E+00 3, .771E+00

1, .50000E-02 1. .394E+00 1, .106E+00

2. .OOO00E-02 7, .068E-01 4, .S05E-01

3. .OOO00E-O2 3, .481E-01 1, .378E-01

4. .OOOOOE-02 2, .562E-01 6, .411E-02

5, .OOOOOE-02 2, .198E-01 4, .018E-02

6, .00000E-02 2, .008E-01 3. .095E-02

8. .00000E-02 1, .803E-01 2, .561E-02

1, .OOOOOE-01 1, .680E-01 2, .520Ξ-02

1, .50000E-01 1, .485E-01 2. .736E-02

2, .OOOOOE-01 1, .353E-01 2, .937E-02

3, .OOOOOE-01 1, .173E-01 3, .159E-02

4, .OOOOOE-01 1. .049E-01 3, .245E-02

5, .OOOOOE-01 9, .579E-02 3. .265E-02

6, .OOOOOE-01 8, .857E-02 3, .249E-02

8, .OOOOOE-Ol 7, .777E-02 3, .172E-02

1. .OOOOOE+00 6. .992E-02 3, .070E-02

1, .25000E+00 6. .253E-02 2, .934E-02

1. .50000E+00 5. .691E-02 2. ■805E-02

2, •00000E+00 4. .880E-02 2, .578E-02

3. .OOOOOE+00 3. ■907E-02 2, .247E-02

4. •00000E+00 3. •335E-02 2, .025E-02

5. •00000E+00 2. .958E-02 1, .867E-02

6, •OOOOOE+00 2. .690E-02 1, .751Ξ-02

8. .OOOOOE+00 2. .338E-02 1. .592E-02

1, .OOOOOE+01 2. .117E-02 1. .489E-02

1. .50000E+01 1. .819E-02 1. .346E-02

2. .OOOOOE+01 1. .675E-02 1. .275E-02 B- 100 BONE -EQUIVALENT PLASTIC

Energy -lP _ P (MeV) (cm²/g) (cmVg)

1, .OOOOOE-03 3, .211E+03 3. •203E+03

1, .50000E-03 1, .083E+03 1, .080E+03

2, .OOOOOE-03 4, .878E+02 4. .859E+02

3, .OOOOOE-03 1, .542E+02 1. •530E+02

4, .OOOOOE-03 6, .717E+01 6, , 623E+01

4, .03810E-03 6, .535E+01 6. •442E+01

20 K 4. .03810E-03 2, .251E+02 2, .008E+02

5, .OOOOOE-03 1, .298E+02 1. .178E+02

6, .OOOOOE-03 7, .942E+01 7. •294E+01

8, .OOOOOE-03 3, .619E+01 3. •363E+01

1. .OOOOOE-02 1, .944E+01 1, , 812E+01

1. .50000E-02 6 . •222E+00 5. .694E+00

2, .OOOOOE-02 2 , •798E+00 2. •452E+00

3, .00000E-02 9, .752E-01 7, •337E-01

4, .00000E-02 5, •179E-01 3, •124E-01

5, .00000E-02 3, •506E-01 1. •648E-01

6, .00000E-02 2, •738E-01 1. •014E-01

8. .00000E-02 2, •076E-01 5. •372E-02

1.. .OOOOOE-Ol 1, •793E-01 3, •864E-02

1. .50000E-01 1. •482E-01 3. .031E-02

2, .OOOOOE-Ol 1. •325E-01 2. .984E-02

3, .OOOOOE-01 1. , 135E-01 3, .081E-02

4, •OOOOOE-Ol 1. •012E-01 3. .135E-02

5, •OOOOOE-01 9, •227E-02 3. .145E-02

6, •OOOOOE-01 8, •525E-02 3. .126E-02

8, •OOOOOE-01 7. •481E-02 3. .047E-02

1. •OOOOOE+00 6, •723E-02 2, .947E-02

1, •25000E+00 6. , 012E-02 2. .815E-02

1. .50000E+00 5. •473E-02 2. .691E-02

2. •00000E+00 4, •705E-02 2, .478E-02

3, .00000E+00 3. •799E-02 2. .180E-02

4. •00000E+00 3, •277E-02 1. .989E-02

5, •OOOOOE+00 2, •938E-02 1, .858E-02

6. •OOOOOE+00 2, •703E-02 1, .765E-02

8. •00O0OE+O0 2, •400E-02 1. .644E-02

1. •OOOOOE+01 2. •218E-02 1. .571E-02

1, •50000E+01 1. .987E-02 1. .478E-02

2. •OOOOOE+01 1. .888E-02 1. •438E-02

The wedge(s) is/are placed within the field or view, such as arranged in relation to the distance piece, or may be integrated with the distance piece.

The measure may include information from radiogrammetry, radiographic absorptiometry, or a combination of both. X-ray apparatus

Any x-ray apparatus normally used in dental practice is suitable in the present invention, in particular x-ray apparatuses for intra-oral x-rays. The common feature of all the dental x-ray apparatuses is that they are adapted for x-ray of the jaw of a person, and therefore the tube- head is capable of being movable in any direction in order to be able to emit x-rays to the jaw independent of the position and anatomy of the patient and the position of the radiation detector.

The x-ray apparatus is typically attached to a wall or ceiling by means of a freely moving support arm. Thereby the x-ray apparatus have at least three degrees of freedom in relation to the detector, more often at least four degrees of freedom in relation to the detector, preferably at least five degrees of freedom in relation to the detector. Thus the term "a tube head capable of rotating in any angle" means that the tube head has at least three degrees of freedom in relation to the detector.

Examples of such apparatuses are GX-770, GX-900 and GX 1000 from Dentsply, and Helio- dent DS, Heliodent Vario from Sirona, and Planmeca Dixi®2, Digital.

However, the x-ray apparatus may also be a hand-held apparatus not attached to any support.

As discussed above the reason for using a dental x-ray apparatus is that such apparatuses are widespread throughout the country since most dentists have an x-ray apparatus, and dentists are located even in minor cities and towns. Thus, by using a dental x-ray apparatus it is possible to provide to the patients a method for an osteoporosis measure in their neighbourhood, ideally every time or every second time they visit the dentist for other purposes.

Another advantage of using the dental X-ray apparatus for screening purposes, is that amount of radiation from a dental X-ray apparatus is normally much lower than for other conventional X-ray apparatuses.

Preferably the X-ray apparatus has voltage settings of from 40 to 70 kV.

It is preferred that the X-rays are captured in a constant distance between the tube head and the detector. In this respect precautions have to be taken in relation to dental x-ray apparatus, since the tube head is not fixed in relation to the detector. When performing x-rays of the jaw, the tube head is simply abutting the jaw. However, in order to have x-rays of a limb of a quality that allows osteoporosis measures to be obtained without post-normalisation, such as introducing a scaling factor, it is has been found advantageous to establish a fixed distance between the tube head and the x-ray detector, and pre- ferably also as between the limb and the x-ray detector. Due to the variation of the thickness of fingers, this distance is not obtained if the tube head is positioned directly on the finger. Therefore, the present invention also relates to a method and a system, wherein a distance piece may be provided between the tube head and the x-ray detector.

Distance piece

The distance piece may be formed in any shape suitable. Preferably the distance piece is adapted to the tube head in use.

In the following a non-limiting list of examples of distance pieces is discussed:

In one embodiment the system includes a support having a surface, wherein the detector is arranged in said surface. The support further comprises at least one distance piece, such as a plate arranged substantially orthogonal to the surface. The tube head could then rest on the plate during acquisition of the x-ray. The dimensions of the plate are preferably so that the height of the plate, as measured from the surface, is at least about - 1 cm higher than the average thickness of the limb to be measured, in order to have a suitably low magnification of the object on the radiographic film, vide Fig. 14.

The length of the plate is preferably longer than the width of the tube head in order to provide sufficient support for the tube head. In a preferred embodiment the distance piece is consisting of two plates, each substantially orthogonal to the surface and arranged in parallel with each other. The tube head may then be positioned so that it rests on both plates, and the limb may be positioned between the plates. Thereby a sufficient orientation of the limb is also provided.

In another embodiment the plate as discussed above is replaced by a frame optionally with a network providing the same function, or even just providing the outer contours of the plate, leaving the mid part open.

The distance piece may be attached to a support, either releasably attached, or permanently attached. In yet another embodiment the distance piece is releasably attached to the tube head. In this embodiment the distance piece may be one or more, preferably two or more, pins attached to the tube head, whereby the tube head is provided with a kind of "legs" to stand on when the x-ray is acquired.

It is preferred that the distance piece is not permanently attached to the tube head, since this would impair the normal dental x-rays of the jaw.

The distance piece should preferably be arranged in relation to the detector, so that the ra- diation path from the tube head to the detector is substantially orthogonal.

Alignment

Furthermore, it is preferred that the method and system includes means for aligning the tube head so that the radiation path is substantially orthogonal to the detector, since otherwise distorted images not relatable to the skeletal status may be obtained.

Means for alignment may be combined with the distance piece, so that by using the distance piece the alignment is also provided.

Orientation of limb

In order to obtain a reliable and reproducible osteoporosis measure, it is important to define exact points of measure, since anatomical landmarks, i.e. characteristics, of the bones ex- amined may be difficult to obtain reliably. Therefore, it is necessary to arrange the limb so that its orientation may compensate for the lack of anatomical landmark. In particular when using the phalanges or the metacarpal bones for the measure, the orientation may be provided by using the distance piece as orientation means, or using another means for similar purposes.

Furthermore, it is preferred that the distance between the limb and the detector is constant, which may be arranged by having the limb placed directly on the detector.

Detector

The detector may be any suitable x-ray detector, such as an x-ray film or a digital x-ray detector, such as a CCD. In a preferred embodiment the x-ray film is a conventional dental x- ray film suitable for providing x-rays with even very low intensity. Examples of dental X-ray films are Kodak intra-oral dental films available in three types: Periapical film, for examination of the entire tooth and its surrounding structures, Bite-wing film, for interproximal examination, and Occlusal film, for examination of large areas of the maxilla and the mandible, such as KODAK INSIGHT Dental Film, KODAK ULTRA-SPEED Intraoral Dental Film, and KODAK Intraoral Film Sizes 0, 1 , 2 prepackaged in single and double film packets. Kodak Ektaspeed Plus Dental Film, and Agfa intraoral dental films, such as AGFA M2 COMFORT Dental Film

Examples of CCD for dental X-ray purposes are provided for example by Sirona, such as SIDEXIS intra-oral sensors, and Planmeca Dixi®2 digital sensors from Planmeca.

Naturally, the resolution of the X-ray film or CCD used to obtain the X-ray image will have an effect on the quality of the image data. Thus, it is presently preferred that the resolution of the X-ray film is at least 4 pairs of lines per millimeter, such as at least 5 line pairs per milli- meter. Even though this may be sufficient for obtaining a satisfactory estimation of the bone quality, it is preferred that the resolution of the X-ray film is at least 20 line pairs per millimeter, such as at least 25 line pairs per millimeter, preferably at least 50 line pairs per millimeter. Naturally, a resolution of this preferred size will ensure that a large amount of information is present in the X-ray image.

Image

The term image is used to describe a projection or representation of the region examined, i.e. the term image includes a digital 1 -dimensional, or 2-dimensional representation, as well as n-dimensional representations. Thus, the term image includes a volume of the region, a matrix of the region as well as an array of information of the region.

Scanning

Using X-ray illumination on X-ray films, the X-ray images may easily be used to generate the image data for use in the present invention. As it is preferred to perform the image analysis on a computer, the analogue X-ray image may be digitized and introduced into a computer for example by scanning the X-ray image.

Naturally, it is preferred that the scanning of X-ray images is performed with a sufficiently large resolution in order to ensure that a minimum relevant information of the X-ray image is lost in the transfer to the image data. Thus, it is preferred that the scanning has been performed at a resolution of at least 10 line pairs per millimeter, such as at least 25 line pairs per mm, preferably at least 100 line pairs per mm. Preferably, the scanner scans the x-ray into a higher resolution, such as resolution twice the film resolution.

Furthermore, it is preferred that the resolution of the scanner is better than 4 true bits per pixel, such as better than 6 true bits per pixel, preferably better than 8 bits per pixel.

Since for most embodiments of the present invention, the x-ray films are small, the preferred scanners are flatbed scanners, such as Umax PowerLook III Flatbed Scanner, Umax Power- Look 1100 Flatbed Scanner, and Agfa DuoScan HiD Flatbed Scanner. However, any scanner capable of scanning the x-ray films may be used, such as dedicated dental x-ray scanners.

In another preferred embodiment the detector may be a digital means, such as a CCD, di- rectly transferring information of the image to a computer or other digital means, such as the sensors described above, whereby no scanning is necessary.

Analysis

The digitised data, whether obtained through scanning an x-ray film or directly from a CCD, may then be analysed with respect to obtaining a measure for the skeletal status. The analysis may be carried out at the location of acquisition of the image, or at a centralised location. Therefore, in one embodiment the image may be transferred to a central for analysis, either as hard copy x-rays or as digitised images.

It is therefore within the scope of the present invention, that the system is comprised of at least two units, wherein one unit is performing the steps acquiring the image, and another unit is performing the steps of analysing the image.

This facilitates the use of the system since any dentist may provide the image, have it subjected to analysis decentrally without the need of being capable of conducting this analysis. The result of the analysis may be communicated to the individual being tested directly or via the dentist.

Using either distal radius, fibula, tibia, ulna, a metacarpal, a phalanges, or any bone, preferably a long or a tubular bone, in which two-dimensional image data comprising information relating to the structure of the bone can be obtained, a measure relating to the bone quality or skeletal status may be generated when determining cortical thickness and/or inhomoge- neity, such as porosity. The determination may be carried out by any suitable method. In a preferred embodiment the analysis is carried out by calculating a measure (M) relating to the skeletal status for the individual in question. For all measurements of bones, it is of importance to standardize the landmarks used for choosing the position for measurements. Some prior art measurements for example identify a bone characteristic and then calculate for example a certain percentage of the total bone length from said characteristic to establish a landmark for the measurements. However, in particular for metacarpal bones and phalanges no obvious bone landmarks can be identified.

Therefore, the present invention also relates to a method for establishing a measure relating to skeletal status of an individual, comprising

establishing an image of a tubular bone having an outer projected width D, and inner projected width d and a cortical layer therebetween,

establishing a plurality of points along the length axis on the image of the tubular bone, and for each starting point calculating at least the outer projected width D, and inner projected width d,

from the calculations identifying a landmark for estimating the measure relating to skeletal status of an individual, and

establishing the measure.

Thereby the information of the tubular bone on the image defines the landmark from the image itself, without relying on any specific anatomical characteristic. In the present invention, it has been shown that the landmark of the tubular bone may be the part of the tubular bone having the smallest outer projected width D.

The method relates to measurements of tubular bones, in particular of phalangeal bones, metacarpeal bones, radius and ulna, more preferably of phalangeal bones, and metacarpal bones, most preferred of phalangeal bones.

The outer projected width D and the inner projected width d may be determined by any suitable reliable method from the image of the tubular bone.

In a preferred embodiment at least 10 points along the length axis on the image of the tubular bone, such as at least 50 points along the length axis on the image of the tubular bone, such as at least 100 points along the length axis on the image of the tubular bone, are homogeneously established along the length axis. More preferably the number of points correspond to the number of pixels along the length axis. Normally the points lead to one landmark, from which the measure is established. It may, however, be advantageous to combine measurements from more than one position on the bone, such as at least from 2 landmarks, more preferably at least 3 landmarks.

In one embodiment the outer projected width D and the inner projected width d are determined by means of determining the dimensions and affine transformation of an inner and an outer ellipse corresponding to the tubular bone and a background level corresponding to the surrounding soft tissues, for which the absorption characteristics would be as close as possible to the observed density profile in the image.

In another embodiment the outer projected width D and the inner projected width d are determined by determining the outer and inner edge of the cortical layer, for example by estimating a gradient for outer and inner edge.

Independent of how the outer and inner diameters of the tubular bone are determined, the establishment of the measure is made from these determinations. As discussed above the present invention relates to the principle that a measurement of the cortical thickness of a bone is related to the skeletal status of an individual. Thus, in a preferred embodiment the measure relates to the thickness of the cortical layer of the tubular bone as determined from the outer and inner projected width of the cortical layer. In a more preferred embodiment the thickness of the cortical layer is determined at a predetermined distance from the part of the bone having the smallest outer projected width D, that is within for example 50 pixels from the smallest outer projected width D, such as within 25 pixels from the smallest outer projected width D, more preferably the distance is substantially zero.

The method may be supplemented with an estimate of the porosity of the cortical layer of the tubular bone.

Thus, in a preferred embodiment the method according to the invention provides a measure relating to the skeletal status for the individual in question, wherein the measure is based on

- the thickness of the cortical layer of the tubular bone, preferably measured around the part of the bone having the smallest outer projected width D, and

the porosity of the cortical layer of the tubular bone In the following calculation for a preferred embodiment of the invention is described, namely the affine transformation, which is a mathematical model describing the observed densities in horizontal bone cross sections, composed of three densities:

D_s Density of tissue surrounding the bone including background density. D_B Density of the bone excluding marrow. D_M Density of the bone marrow.

It is assumed that the bone surrounding tissue can vary linearly over the cross section, and that the bone can be approximated with an affine transformed outer and inner ellipses each having individual centers.

Data transformation

An X-Ray beam with intensity l₀ penetrating an object with density D and height H, is attenuated and emerges from the object with a intensity I according to the exponential attenuation law:

I = I₀ x e ,^~-{plD)-H

Formula 1: The exponential attenuation law. Where:

p/D : Object material X-Ray Mass Attenuation Coefficient.

The bone model described below is based on estimation of both bone densities and heights. An initial logarithmic transformation of the scanned radiograph intensities is performed, resulting in:

log(/) = (p /D). ff + log(/₀) Formula 2: Log-transformation of the exponential attenuation law.

Where:

l₀ : Is X-Ray equipment dependent and can be assumed to be constant.

Affine ellipse transformation

The height of an ellipse at a given point x is given by:

Formula 3: The ellipse formula.

Where:

A : Semi major axis of ellipse.

B : Semi minor axis of ellipse.

C : Center of ellipse.

By applying the affine transformation to the ellipse REFFLETFORMAT extends to:

H_mpse>Afme (x) = _mpse (x)-(l-S-{x-C)) Formula 4: The affine transformed ellipse formula.

Where:

S Slope of the transformation. C Center of ellipse.

The above described assumptions results in the following model for the expected observed logarithmic transformed X-Ray intensity at a given point in a horizontal cross section of the bone:

{D_s-H_s)-(l + S_s-x)+ ^_ogW= {D_B -D_s)-H_BtEllipse(x)-(l + S_B -{x-C_B))+ {D_M -D_B)-H_MtE!lipse(x)-(l + S_M -(x-C )

Formula 5: Full bone cross section model.

Where:

Formula 6: Outer ellipse height formula.

Formula 7: Inner ellipse height formula.

And:

D_s Density of tissue surrounding the bone including background density. Η_s Full height of surrounding tissue and the height of the bone. S_s Slope of the surroundings. D_B Density of the bone excluding marrow (Outer ellipse). A_B Semi major axis of outer ellipse. B_B Semi minor axis of outer ellipse. S_B Slope of the outer ellipse height. C_B Center of the outer ellipse. D Density of the bone marrow (Inner ellipse). A_M Semi major axis of inner ellipse.

B|M Semi minor axis of inner ellipse.

SM Slope of the inner ellipse height. CM Center of the inner ellipse.

Standardization of bone orientation

It is advantageous to standardize the bone orientation in the preprocessing step of the algo- rithm. Thereby the later described bone model does not need to take a bone rotation into account.

Initially the actual orientation of the bone in the image has to be determined. This is done by the detection of the outer bone borders. The found outer borders are used to form a set of bone center points, which is then used to estimate a straight bone centerline. As some of the centerline points inevitably deviate significantly from the estimated line, an iterative algorithm which continuously removes outlier points from the estimation is implemented.

The algorithm for iteratively removing outliers is implemented so that in the first step the line is estimated using all points. Thereafter the point deviating most from the estimated line is removed and the line is re-estimated using the remaining points. This process of point exclusion and re-estimation is continued until all included points do not deviate more than one Euclidian pixel distance from the estimated line.

Hereby a robust estimation of the centerline is obtained and the orientation of this robust estimated centerline is finally used to rotate the bone to a standardizing orientation.

Cropping of image region

Because unknown intensity values from outside the image area could be rotated into the image area, and as the film corners might not have been exposed, the image is preferably cropped before being analysed.

Unknown intensity values rotated into the image have zero intensity and unexposed film areas have close to maximum intensity. Therefore the image area is narrowed down until the image border intensities are higher than zero and less the 90% of the maximum possible intensity.

Data smoothing

The local cross section model estimation may be made more robust by spatially smoothing the data in the bones longitudinal direction. This smoothing may be implemented as a simple average filtering kernel with a height of 2 mm and a width of 1 pixel as shown in Fig. 6.

Least square estimation step

To simplify a least squares estimate of some of the model parameters the following is defined:

K_S ≡ D_S . H_S ; K_B ≡ (D_B

Formula 8: Introduction of parameters for simplifying full model. Whereby the full model can be simplified to:

K_s - {l + S_s - x)+

Formula 9: Simplified full bone cross section model.

Where:

Formula 10: Simplified outer ellipse height formula.

Formula 11: Simplified inner ellipse height formula.

Given A_B, A_M, C_B and C_M, a least squares estimate of K_s, S_s, K_B, S_B, K_M and S_M with respect to the observed logarithmic transformed cross section intensities can be obtained by solving the following set of linear equations.

/ Log,Observed A 1 -*-l

Log, Observed GO 1 ^Xn

A

Formula 12: Linear equation set for estimating K_s, S_s, K_B, S_B, K_Mand SM

If Formula 12 is expressed as: b - A - x Formula 13: Simple expression of Formula 12

The solution x is obtained by the normal equation:

Formula 14: Normal equation forming the solution ofK_s, S_s K_s, K_B, S_B, K_Mand S_M

Least Squares estimates of K_s, S_s, K_B, S_B, K_M and S_M are obtained and incorporated into an algorithm for estimating A_B, A_M, C_B and C_M.

Rough outer border estimation

A complete search in the four dimensional A_B, A_M, C_B and C_M feature space could be performed. But as each parameter easily could be located anywhere within a range of 500 pixels, such an approach would be prohibitively time consuming.

Instead the estimation of A_B, A_M, C_B and C_M is divided into a initial rough outer border esti- mate, for initializing the algorithm, and a fine border estimate for obtaining close to optimal estimates of the four parameters.

To rough outer border estimation algorithm is in contrast to the fine border estimation based on a simple model including a background area and a bone area intensity as shown sche- matically in Fig. 7.

By iteratively searching through all combination of left and right outer borders an optimal combination, expressed in terms of a minimum sums of squared residuals from the observed data, is found.

By having located the outer left and right border a simple estimate of A_B and C_B can be obtained. This estimate is then used for initializing A_M and C , by:

These initial rough estimates of A_B, AM, C_B and C_M can then be used as starting point to the following fine border estimation.

Fine border estimation

In the present embodiment, the fine border estimation is based on multi scale approach. By multi-scale is understood that the algorithm initiated on a sub-sampled version of the image, and after the processing on that scale the algorithm is re-initiated on a two times resolution version if the image, vide Fig. 8. This process is continued until the algorithm has processed the image in its original resolution. An illustration of the image resolutions included in a multi scale approach is:

The full search performed on a 32 times sub-sampled scale is implemented so that for each possible combination of outer left and inner left ellipse border the parameters A_B, A_M, C_B and

C_M is calculated. These parameters are then used with Formula 12 after which a residual can be calculated. The combination of left outer and inner border providing the minimum residual is then chosen as optimal. After having estimated all model parameters by iteratively modifying the left borders the optimization algorithm is rerun by iteratively modifying the right borders of the ellipses.

The estimated parameters A_B, A_M, C_B and C_M from the full search are then reused on a 2 times finer scale. Again a full search, but this time with a limited parameter range, is performed by first iteratively searching through the allowed range of left borders and then the allowed range of right borders.

The approach described above is continued until sub-pixel accuracy in the optimization is achieved.

An example of the model fitted to a bone cross section is illustrated in Fig. 9, cross section to fit with model, Fig. 10, observed cross section log-transformed intensities, and Fig. 11 , sub- pixel accuracy fit of model to log-transformed intensities.

Modeling the entire bone

After having laid out the approach for local cross section modeling, the next step is to apply the model on the entire bone. This is done by modeling a cross section each mm along the bones longitudinal axis, as shown in Fig. 14:

Location of measuring position

To obtain a reproducible measuring position for the later described bone measure, the entire bone is searched in its longitudinal direction. In this search along the bone, the outer ellipse borders and inner ellipse borders are modelled with a 2^nd order polynomial and a 1^st order polynomial, respectively, of cross section measurements within 0.5 mm from the original measuring position, as shown in Fig. 15: In each investigated measuring position along the bone the outer polynomial fitted ellipse width A oiy, β(y) and inner polynomial fitted width A_p0ι_y, _M(y) are calculated, y being the longitudinal position in the image.

The estimates of A_Poι_y, _B(y) and A_p0ι_{yι M}(y) are then used to form the width related measure

W(y):

W{y) = A_{Poly B} (y) + (A_{Poly B} (y) - A_Poly (y))

Formula 15: Width related measure.

The initial starting point on the measuring position is then selected as the position expressing the minimum solution to the equation:

W_μ(y) + W_σ(y) Formula 16: Measure to minimize during initial measuring position location.

Where:

W_μ(y) : Is the average of W(y) measures within 5 mm from y.

W_σ(y) : Is the standard deviation of W(y) measures within 5 mm from y.

After having obtained an initial starting point on the measuring position, the position is modified until a minimum outer ellipse width, expressed in A_Pθι_{yι B}(y), is achieved. As each A_Pθι_y, _B(V) originates from a polynomial fit, it is possible to obtain sub-pixel accuracy in the location of the measuring point.

Calculation of the measure relating to skeletal status

After having located the optimal measuring point, a reproducible measure M related to the bone degradation can be provided. It has been found that an informative measure could be achieved by the formula:

^—

position ))

Formula 17: Measure relating to skeletal status. Accuracy

The accuracy of the measure of the present invention in relation to skeletal status of the indi- vidual may be confirmed by calibrating the measure with other measures of skeletal status.

Using either distal radius, fibula, tibia, ulna, metacarpal, phalanges, or any bone, preferably a tubular bone, in which two-dimensional image data comprising information relating to the cortical structure of the bone can be obtained, and the measure according to the present invention of the skeletal status or bone quality of the vertebrate may be obtained on the ba- sis of a calibration using e.g. human post-mortem bone samples or samples from other vertebrates.

Bone strength may, e.g., be evaluated by directly measuring the elasticity and failure load of a bone in a stress-strain diagram.

As described above, the present method may be used to determine aspects of the skeletal status or bone quality of any vertebrate. Thus, the vertebrate may be a human, a horse, a great ape, a large ape, an anthropoid ape, a pig, a cow, etc, and the actual bone is preferably a tubular bone, such as a bone chosen from the group consisting of radius, ulna, tibia, fibula, metacarpal, phalanges, and femur.

Other information

In addition to the above-mentioned features derivable from the image data, it may be pre- ferred to input into the analysis additional data relating to the vertebrate in question but which may not be derivable from the image data. This type of data may be information relating to the age and/or sex, and/or species, and/or race and/or the specific bone considered in the vertebrate, and/or a estimated Bone Mineral Density, and/or a estimated Bone Mineral Content.

Even though the DXA- or SXA-BMD determined using other equipment may be introduced in the estimation procedure, this measure may also optionally be determined from the image data. BMD is estimated by including data from a reference object in the exposure of the bone to the electromagnetic radiation and on the basis of the absorption of the electromagnetic radiation of the bone and of the reference object. Measure

The measure is preferably compared to at least one norm, namely measures for "young normal adults" in order to have a reference for each individual. It may be preferred also to have an "age-matched" reference.

In a preferred embodiment a standard reference for a measure M relating to skeletal and joint status of an individual is established by the following steps:

In a T-score assessment, the measure of a given individual is compared to young adult nor- mals or peak bone mass, which occurs on average around 30 years of age, under consideration of the biological variation expressed in standard deviations. In a Z-score assessment, the measure is compared to age-matched normals, under consideration of the biological variation of the measurements in such an age group, expressed in standard deviations.

The invention also relates to a method for screening skeletal and joint status of an individual comprising

subjecting the individual to a method as described above, and analysing the image detected obtaining a measure M for said individual, and then comparing the obtained measure M with a standard reference. The image detected is preferably analysed by the method as described above.

The method is preferably implying the standard reference obtained in accordance with the present invention.

The difference between the determined measure and that of a healthy young adult is referred to as a standard deviation (SD). Scores below the "norm" are indicated in negative numbers. For Hip DXA-BMD, a score from -1 to -2.5 SD below the norm indicates low measure, or osteopenia, and a score of more than -2.5 SD below the norm is considered a diag- nosis of osteoporosis, according to the WHO. For most tests, -1 SD equals a 10-12 percent decrease in bone density.

Application

The present system and method should be used as a screening tool for screening ideally the whole population, and in particular postmenopausal women and the elderly male population, or at least individuals at risk for suffering from osteoporosis, such as those being genetically predisposed for osteoporosis.

In particular the following individuals should be screened:

Those with one or more additional risk factors for osteoporotic fracture (including menopause)

Those who have had a fracture (broken bone) to determine if osteoporosis is the underlying cause

Those who are ages 55 and older, regardless of other risk factors

Those who are considering therapy for osteoporosis, and

Those who have been on hormone replacement therapy for prolonged periods.

The individuals identified to have a measure relating to skeletal status indicating that the individual is at risk of having low bone mass or bone density, should then be examined by means of for example a DXA-BMD measurement, in order to establish a full skeletal diagnosis. Accordingly, the present invention provides a measure for discriminating between individuals having a normal hip BMD and a low hip BMD. Thereby the present invention is a pre- screening tool for allocating individuals to hip BMD measurements.

Furthermore, the method may be used for monitoring treatment of skeletal diseases, such as osteoporosis, wherein changes in the measure obtained may be indicators of the effect of the treatment.

In the following a preferred method of determining a measure relating to skeletal status is described. Example

Image of third proximal phalanges of a female

The images of 3^rd proximal phalangeal bone of the non-dominant hand of 36 women in the age of from 20 to 80 years were acquired by a system as shown in Fig. 15. For 36 women in the age of from 20 to 80 years the images were acquired and analysed. The X-ray apparatus used was a Heliodent DS, see Fig. 16.

The x-ray images were scanned and the digitized image was transferred to a computer for analysis as described above for obtaining a measure relating to the skeletal status for the female in question.

The result of the analysis is shown in Fig. 17 wherein two areas, one corresponding to young adults, and the other to elder women, are shown in a plot of the measure M as a function of age.

Claims

1. A method for establishing a measure relating to skeletal and joint status of an individual comprising

establishing a radiation source having a tube head capable of rotating in any angle, meaning that the tube head has at least one degree of freedom in relation to the detector, and a radiation detector for acquisition of an image,

arranging the tube head in a predetermined distance from the radiation detector, so that the distance between the tube head and the radiation detector is a constant distance independent of the size of the limb, and/or arranging the tube head in a predetermined angle from the radiation detector, so that the radiation path from the tube head is substantially orthogonal to the detector,

capturing an image of the limb in the radiation detector,

analysing the image detected thereby establishing the measure relating to skeletal and/or joint status of the individual.

2. The method according to claim 1 , wherein the tube head is a dental X-ray tubehead.

3. The method according to claim 1 , or 2, wherein the radiation detector is a dental X-ray film, such as a dental intra-oral X-ray film.

4. The method according to claim 1 , or 2, wherein the radiation detector is a digital detector.

5. The method according to claim 4, wherein the limb is in a constant distance from the detector.

6. The method according to any of the preceding claims, wherein the limb is a finger or a hand.

7. The method according to any of the preceding claims, wherein the tube head is positioned in a predetermined distance from the radiation detector by means of a distance piece, and the limb is positioned in a predetermine distance from the detector by means of the same said distance piece.

8. The method according to claim 7, wherein the distance piece is arranged on a surface, said surface further comprising the radiation detector.

9. The method according to any of the preceding claims, wherein the measure relating to skeletal and joint status of an individual is a measure relating to the thickness of the cortical layer of the bone.

10. The method according to any of the preceding claims, wherein the skeletal and joint status provides information relating to osteoporosis and/or related bone disorders.

11. A system for establishing a measure relating to skeletal and joint status of an individual, comprising

a radiation source having a tube head capable of rotating in any angle,

a radiation detector for acquisition of an image, and

a distance piece for determining a constant predetermined distance between the tube head and the radiation detector.

12. The system according to claim 11, wherein the tube head is a dental X-ray tubehead.

13. The system according to claim 11, or 12, wherein the radiation detector is a dental X-ray film, such as a dental intra-oral X-ray film.

14. The system according to claim 11, or 12, wherein the radiation detector is a digital de- tector.

15. The system according to claim 14, wherein the digital detector is a CCD.

16. The system according to any of claims 11-15, comprising positioning means for posi- tioning a limb between the tube head and the radiation detector.

17. The system according to claim 16, wherein the limb is a finger or a hand.

18. The system according to claim 16 or 17, wherein the distance piece also functions as positioning means.

19. The system according to any of the claims 11-18, wherein the distance piece is arranged on a surface, said surface also comprising the radiation detector.

20. A method for establishing a measure relating to skeletal status of an individual, comprising

establishing an image of a tubular bone having an outer projected width D, and inner projected width d and a cortical layer there-between,

establishing a plurality of starting points on the image of the tubular bone, and for each starting point calculating at least the outer projected width D, and inner projected width d,

establishing the measure.

21. The method according to claim 20, wherein the bone is selected from phalangeal bones, metacarpeal bones, radius and ulna.

22. The method according to claim 20 or 21, wherein the landmark is the part of the tubular bone having the smallest outer projected width D.

23. The method according to any of claims 20-22, wherein the outer projected width D and the inner projected width d is determined by means of determining the dimensions and affine transformation of an inner and an outer ellipse corresponding to the tubular bone and a background level corresponding to the surrounding soft tissues, for which the absorption characteristics would be as close as possible to the observed density profile in the image.

24. The method according to any of claims 20-23, wherein the measure is the thickness of the cortical layer of the tubular bone.

25. The method according to any of claims 20-24, further comprising estimating the porosity of the cortical layer of the tubular bone.

26. The method according to claim 25, wherein the measure includes the thickness of the cortical layer of the tubular bone and the porosity of the cortical layer of the tubular bone.

27. The method according to any of the claims 20-26, wherein the image is detected as de- fined in claim 1.

28. A method for establishing a measure relating to skeletal and joint status of an individual comprising

capturing an image of the limb in the radiation detector,

29. The method according to claim 28, wherein the tube head is a dental X-ray tubehead.

30. The method according to claim 28 or 29, wherein the radiation detector is a dental X-ray film, such as a dental intra-oral X-ray film.

31. The method according to claim 28 or 29, wherein the radiation detector is a digital detector.

32. The method according to claim 28, wherein the limb is in a constant distance from the detector.

33. The method according to any of the preceding claims 28-32, wherein the limb is a finger or a hand.

34. The method according to any of the preceding claims 28-33, wherein the tube head is positioned in a predetermined distance from the radiation detector by means of a distance piece, and the limb is positioned in a predetermine distance from the detector by means of the same said distance piece.

35. The method according to claim 34, wherein the distance piece is arranged on a surface, said surface further comprising the radiation detector.

36. The method according to any of the preceding claims 28-35, wherein the measure relat- ing to skeletal and joint status of an individual is a measure relating to the thickness of the cortical layer of the bone.

37. The method according to any of the preceding claims 28-36, wherein the skeletal and joint status provides information relating to osteoporosis and/or related bone disorders.

38. A method for establishing a standard reference for a measure M relating to skeletal and joint status of an individual comprising

obtaining the measure M relating to skeletal and joint status for each individual by a method as defined by any of the claims 1-10 and 20-37,

39. A method for screening skeletal and joint status of an individual comprising

subjecting the individual to a method as described in any of claims 1-10 or 28-37, and analysing the image detected obtaining a measure M for said individual,

comparing the obtained measure M with a standard reference.

40. The method according to claim 38, wherein the image detected is analysed by the method as described in any of claims 20-27.

41. The method according to claim 38, wherein the standard reference is obtained as described in claim 37.