DE1227504B - Electronic recording process for radiation images of low quantum intensity and device for carrying out the process - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Inta .:

H 04 η

German class: 21 al -32/35

Number: 1227 504

File number: K 50298 VIII a / 21 al

Filing date: July 22, 1963

Opening day: October 27, 1966

The invention relates to an electronic recording method for television and for image converter systems for radiation images of low intensity.

The object of the invention is therefore the contrast resolution to improve and show a way how the principle of the retina of the human eye with its multitude of rods and suppositories can be mimicked.

The disadvantage of the known image recording method by means of a television tube with photocathode is that the per se high resolution radiation-sensitive layers for recording radiation images of low intensity are not very suitable, since the useful or beneficial detail resolution does not affect the Perception required contrast resolution is matched, as this z. B. in the human eye is the case with twilight vision. Since the good resolution of the known methods in The range of low luminance levels and weak contrasts is no longer exhausted are available per picture element there are no longer enough quanta available to generate an image.

It is believed that in order to increase the contrast resolving power, it is necessary first reduce or reduce the resolution of details on the screen of a recording system to reduce and only then to integrate the image information over larger picture elements.

It is now proposed according to the invention in an electronic recording method for television and for image converter systems for radiation images of low intensity to increase the contrast resolution, first reducing the detail resolution on the screen of a recording system and then integrating the image information over larger picture elements, that this detail resolution is reduced to size of the radiation image details to be recorded in each case, that is to say to the necessary resolution. As a result, a selection is made among various possible sizes of the resolution, namely the correct or the so-called beneficial resolution is made usable and the size of the detail resolution is also correctly adapted to the intensity conditions prevailing in the radiation image. In the optical field, the inclusion of very faint images, such as this z. B. is the case for night shots. In the case of X-ray fluoroscopic images, this recording method can also be used for
Low quantum intensity radiation images and
Device for carrying out the method

Applicant:

Jülich nuclear research facility

of the State of North Rhine-Westphalia e. V., Jülich

Named as inventor:
Dr. Manfred Keller, Jülich

drive once the contrast enhancement is significantly increased and thus the clarity of the images is improved, on the other hand, the dose exposure of the patient per image can also be reduced.

In order to explain this in more detail, the relationship between Contrast and detail resolution can be specified.

Since only a limited number N of quanta is available for a picture element of a low-intensity radiation image, the contrast detail resolution and thus the information content is limited by the statistical fluctuation of the radiation.

The number Z of statistically resolvable contrast levels is a suitable measure for the contrast resolution. If an error interval 3 ·] /; v of three times the mean statistical error ] [n is used for the distance between the contrast levels, it follows with

ΔΝ

I) [NKmAN

for the number of statistically resolvable contrast levels

The number of quanta N for a picture element is obtained from the quantum density η (quanta per

609 708/261

1227 5Öt

Area unit) and. the area Δ f of the picture element to N = η · Af.

If you define a - ] / 2i / as blurring of detail or

- = <5 as detail resolution, it follows for the Number of statistically resolvable contrast levels

If one further defines the product of contrast and detail resolution P = ZO = - as

physical contrast detail resolution, it follows

Z-O = - c = -

a 3

The resolution of the X-ray scintillation orthosis, which is described as an embodiment according to, compared with that of an X-ray film recording. ,. , ... - - ^ ...- .; - _f The number of quanta N can be expressed by "the dose. For the relationship between the quantum number N, based on the dose and area at an effective energy of 60 keV, a quantum number of N = 3.03 · 10 ^{5 is obtained} y / mr mm ² .

ίο This value should be used as a basis for the following consideration because the information content, based on the object exposure, between 60 and 80 keV is optimal depending on the object thickness.

The number of X-ray quanta N in an X-ray beam with the surface element Δ f = a ² (mm ² ) and a dose D (mr) is thus given by

N = 3.03-10 ^s -a ² -D,
. .......

so that one for the dissolvable KinträStstüfenzahl

This relationship shows that for a radiation image detail given by η, the product of contrast and detail resolution is constant. In order to increase the contrast resolution in low-contrast images, the detail resolution must accordingly be reduced.

The relationship, resolved according to Z, says: the larger the image element Af = α ^{2 is} selected, the more contrast levels Z can be resolved. In particular, it can be seen that subliminal contrasts can also be resolved for the eye if the resolving power δ - is reduced and thus integrated over a correspondingly larger image element Af . If, on the other hand, the detail resolution δ is increased increasingly, ie the resolution blurring a is reduced, then the contrast resolution Z decreases accordingly and approaches zero. Since then no more contrasts can be resolved, one obtains an »empty« ability to resolve details.

If, in other words, the statistical nature of the radiation images is important, then the detail resolution is important alone not a criterion for the quality of the process. The optimal image information results rather, precisely when the detail resolution corresponds to the size of the radiation image detail to be recorded agrees: This resolving power should be defined as the beneficial resolving power.

In radiology, the details of interest in soft tissue images are in the size of a few millimeters, so that the useful resolution of the recording process should be about 1 mm. When taking pictures at night, it may be necessary to have an even lower resolution of the recording screen from Z. B. to provide only four picture elements.

As already mentioned, the human eye has in twilight vision the ability to integrate over larger areas of the retina. It exists hence the task of specifying a recording system that simulates this visual performance of the eye. To the The eye itself can then create an image with a brightness in the range of clear vision as large as possible Contrast resolution are offered.

In order to clarify the efficiency of the basic idea of the invention, the contrast = 367 x 1 x j / JD

receives.

In practice, the dose behind the patient is the measurable mean image dose

D _m = I (D _min + D _max )

and the contrast ratio V = D _max : D _{min is} specified via the absorption in the object. With

and

-L / max -

1 + V 2D _m V

thus follows for the contrast resolving power

Z =

} fv

The calculation of the number of statistically resolvable contrast levels should be based on a resolving power of a = 1 mm which corresponds to the eye for low contrasts. Although the radiologist can only make out larger areas (3 to 5 mm) in soft tissue x-rays, a resolution of 1 mm should be expected to be on the safe side. The contrast ratio of the dose, which can approximately be detected on an X-ray with visual observation, is V - 5: 1 and the mean image dose is approximately D = 2mr. Under these prerequisites, a contrast deficiency resolution of

Z = 520 - 1/2 = 374
1/5 + 1

reach.

From the blackening characteristic of an X-ray film (Adox, intensifying screen Siemens-Saphir-Universal, 60keV, 4 mm Al filter) you take a

έ 6

Basic blackening of s "= 0.2 at about 0.1 mr. When it is scanned, the surface is covered with mosaic storage electrodes 5 according to "the images are still visually good" evaluable blackening detection. On S ₁ = 1.5 the dose is 4 mm Details ^; is the contrast ter. Way about the photoelectric effect in the semiconductor resolution of the eye, especially in the "5 layer a charge image. The advantage of the less inventive areas, relatively small. As a result of the interpretation, the separate evaluation of a thorax image was found to be a direct integration of the contrast resolution capacity of As _eye = 0.09 of the statistically distributed incident radiation as a guide value for surface elements Δ f. This gives one for which is done with the bare quantum.

Eye resolvable number of contrast levels ro To match the detail resolution to that in the radiation image

adapt to the prevailing intensity conditions,

Δ s _Füm can be the size of the charge image memory

Z = ~ = 15th screen projected image adjusted accordingly

^s ' eye will be. In the optical field, this z. B. by

15 optics with variable focal length

Look at a detail resolution of 1 mm ^2. With fluoroscopic fluoroscopy, the

The proposed method could therefore result in the setting of the desired beneficial resolution

374: 15 = 25 times the number of contrast calls visible ζ. B. by changing the distance between ob-

power will be. Done in one with the eye on the project and charge image storage screen.

Film just resolvable contrast level of so 2. When using the external photo effect, is

1 mm ² details are therefore still another 25 steps possible, the photoemission of the photocathode

adjustable. through an electronic lens system on one

This observation clearly shows that a rough storage screen can be mapped. The construction of one of the

A resolving, contrast-sensitive recording-like system with intermediate image is shown in FIG. 2.

system at low quantum density and weak 25 .mu.m according to the invention a direct area integration

The storage screen 6, the

technology brings with it. usually consists of a glass skin and as

The charge image storage screen serves on the scanning

^{Embodiments serte m} ^ - to provide mosaic storage electrodes.

30 That on the storage screen by the

In order to integrate the photocathode 7 emitted photoelectrons 8 according to the invention

Image information about larger picture elements to be created charge image is on the individual

hold, is in principle between direct and indirect surface elements of the mosaic storage electrodes

ter integration: integrated. This integration of the area becomes

a) With the direct integration of the radiation, the contrast resolution is increased. By forfeiture is the scanning side of the charge image memory - change the size of the image through the elekschirms of the electronic recording system with tronic lens system 9, the detail resolution can be Mosaic of mutually separated electrical capacities adjusted to the required size troden - in the following as a mosaic storage electrical.

denoted - to be provided. 4 ° 3. The following is an exemplary embodiment

b) A possibility of indirect integration of the X-ray scintillation orthicon has been proposed, which exists in the fact that the unpredictable efficiency already recovered in the existing one by scanning Charge image storage screen. The structure of the Röntgen-Orthi video signal is electronically integrated by the cons, consisting of an image converter and each to a picture element of variable size shown in FIG. 3.

listening signal components in a storage system in order to reduce the absorption losses of the radiation in

are summed up and from it to switch off a corresponding glass bulb, is outside of the

larger useful signal component is obtained. Another image converter system 10 of the X-ray orthicon

Another possibility for indirect integration of the image-rasterized scintillation screen 11 is attached. This

information about larger picture elements is obtained, 5 ° screen is made up of a large number of rod-shaped

by cutting the cross-section of the scanning beam through scintillation rods, which are light-wise from each other

change of the focusing of the beam generator system are separated by a reflective coating 12,

honeycomb-like structure adjusted to the desired resolution. The chopsticks are in hers

will. Length to be dimensioned so that the luminous efficacy,

The following exemplary embodiments relate to the X-ray quantum absorption, opti-

Systems with direct integration. times is. At 60 keV, the length of the rods is included

1. In the simplest way, the recording system has about 5 mm.

If there is no electron-optical intermediate image, then the cross-section of the rods and thus the

the radiation-sensitive recording screen can lock the screen depends on the

even from individual, mutually separate image 60 respective resolution requirements. As already mentioned,

elements are built. is this size in soft tissue exposures

As an example, Fig. 1 shows a, with a mosaic of a few millimeters, which is also about Storage electrodes provided photo semiconductor La resolving power of the eye with a low condensation image storage screen. The photo semiconductor grid in the area of clear vision corresponds to Layer 1 is on a for the incident 65 Instead of an orthicon system, a Radiation 2 transparent carrier electrode 3. Step on the iconoscope system.

other side of the photo semiconductor layer, which the screened scintillation screen is now in front of

by an electrode beam 4 in a known manner the glass bulb of the image converter system of the X-ray

gene orthicons brought into optical contact. About a diffusion of the light through the glass bulb and thus to prevent deterioration of the resolving power, can in the glass envelope In addition, a light screen grid for light guidance can be melted. Such a grid can can be omitted if the mutual light shielding of the scintillation sticks is used as a support structure is designed for the glass bulb, since its thickness can then be selected to be small.

From the photocathode 7 of the image converter part 10 there is a photoelectronic one in a known manner Emission instead. The emitted photoelectrons are imaged as an intermediate image on the storage screen 6. A suitable electronic lens system 9 can change the size of the image will. According to the invention, the mosaic storage electrodes 5 are located on the storage screen 6. The charge image stored on the storage screen is generated in a known manner with slow electrons 14, e.g. B. according to the orthicon principle, scanned. The further processes of signal generation should be assumed to be known.

The advantage of the X-ray orthicon with a screened scintillation screen is that the quantum yield of the radiation image is almost 100%. Such a quantum yield is cannot be achieved with the known recording process, since neither fluorescent screens nor photographic layers can be made so thick. to achieve 100% quantum absorption. At z. B. 50% absorption in the glass flask and 20% useful absorption in the fluorescent screen of a X-ray image converter results in an overall efficiency of only 10%. On the other hand, it takes place on the Mosaic storage electrodes improve the contrast resolution by reducing the resolution. Since, as shown, the relatively mean statistical error is proportional - == - r

is, with increasing pick t Δ f from the statistical error and the stored charge amount such that the proportion of the quantum noise in the image signal is reduced accordingly. Is the natural resolution of the unprepared image storage screen z. B. 10 μ and if the detail resolution is set to 1 mm by the application of mosaic storage electrodes, the relatively mean error is reduced by a factor of 100. This means that 100 times more contrast levels can be resolved, and the contrast sensitivity has been increased by a factor of 100 as a result of this measure.

Claims (3)

Patent claims: 1. Electronic recording process for television and for image converter systems for radiation images low intensity to increase the contrast resolution, with initially the detail resolution on the screen of a recording system is reduced and then the image information is integrated over larger picture elements, characterized in that, that this detail resolution is dependent on the size of the radiation image detail to be recorded, d. H. on the beneficial Resolving power, is adjusted. 2. The method according to claim 1 for the indirect integration of the image information over larger ones Surface elements, characterized in that either the one obtained by the scanning Video signal is electronically integrated by the signal components belonging to a picture element are summed up in a memory system pixel by pixel, or that the cross-section of the Scanning beam by changing the focus of the beam generator system to the desired one Resolving power is adjusted. 3. Apparatus for carrying out the method according to claim 1 or 2 for changing the integration the image information, in particular to improve the contrast detail resolution, characterized in that a variable magnification imaging system is present, by which the size of the charge generated on the charge image storage screen • the training picture is changeable. '4. Device according to one of Claims 1 to 3, in particular for X-ray images, characterized in that a latched, a plurality of mutually light-shielded Scintillation screen (12) having scintillation sticks onto the photocathode from the outside an image converter or television pickup tube (10) is attached. Considered publications:
German Auslegeschriften No. -4-θ92-63? Τ
1035197, 1033 248, 1014154;
U.S. Patent No. 2,900,445. 1 sheet of drawings 609 708/261 10.66 © Bundesdruckerei Berlin