WO2001076453A2

WO2001076453A2 - Mri positioning device

Info

Publication number: WO2001076453A2
Application number: PCT/IL2001/000318
Authority: WO
Inventors: Avinoam Livni; Haim Rotem; Ruth Ben-Kish; Zvi Polunsky; Elyakim Bosak
Original assignee: Odin Medical Technologies Ltd.
Priority date: 2000-04-07
Filing date: 2001-04-05
Publication date: 2001-10-18
Also published as: WO2001076453A3; AU4872501A

Abstract

A pointing device (1) is to be used with a magnetic resonance imaging apparatus. RF coils are provided near each of MR responsive samples. RF coil (5) is located near MR responsive sample (2), RF coil (6) is located near MR responsive sample (3), and RF coil (7) is located near MR responsive sample (4). When the device (1) is introduced into the imaging region of the MR imaging apparatus, the position of the sample may be obtained and marked on the image.

Description

MRI POINTING DEVICE AND METHOD FOR DETERMINING POSITION AND ORIENTATION

FIELD OF THE INVENTION

The present invention relates to magnetic resonance imaging. More particularly it relates to a device and method for determining the position and orientation of a tool using a pointing device for use in a magnetic resonance imaging apparatus.

BACKGROUND OF THE INVENTION

The incorporation of magnetic resonance imaging (MRI) techniques in surgical procedures is known for some years now. Interventional, or inta- operative MRI (iMRI), as it is sometimes called, allows surgeons to obtain a practically on-line image of the patient's body part under surgery, and receive immediate feedback on the outcome of the operation carried out during surgery. Israel Pat. Appl. No. 119558 (Katznelson et al.) filed November 4, 1996, incorporated herein by reference, discloses a compact, transportable, intra operative MRI System, which includes a host computer coupled to a central electronics system which may be coupled to different MRI probes.

Compact MRI systems for performing local imaging of specific body parts or organs may use a hollow tube-like magnet assembly or other assemblies, such as two opposing magnets, such as described in US Patent No. 5,900,793 (Katznelson et al.), filed July 23, 1997 incorporated herein by reference.

US Patent No. 5,735,278 (Hoult et al.), filed March 15, 1996, disclosed an apparatus for use in surgical procedure comprising an operating table for receiving a patient for surgery and an MRI system fσ obtaining images of a part of the patient as a series of time through the surgical procedure for analysis by the surgical team to allow monitoring the progress of the surgery. The high field magnet and the operating table are shaped and arranged for posioning of the part of the patient into the magnetic field while the patient remains in place of the table and the magnet is mounted for movement between a first position spaced from the table and the patient thereon to allow the surgical team to carry outthe surgical procedure and a second position for applying the magnetic field to the part of the patient. The table remains substantially stationary and only the magnet is moved to a position spaced from an adjacent end of the table to allow the surgical team to move around the adjacent end of table and to each side of the table to access the patient.

Usually an intraoperative MRI system (iMRI), such as the ones discussed above, would comprise an MRI system, with a magnet, positioned over an operating table. The magnet assembly is constructed so as to leave open spaces around the patient allowing the medical team to attend the patient. Another solution was the introduction of a magnet probe that can be brought near the patient lying on the operating table to perform the imaging, and then retracted to clear the way for the medical staff to access the patient.

MRI in particularly is appealing for its outstanding ability of obtaining contrast images, differentiating between different tissue types and allowing be visualization and detection of pathologies.

When performing a brain surgery to remove a brain tumor it is not desirable to remove healthy tissue together with the tumoraffected tissue. Any unnecessary removal of brain tissue may result in serious repecussions inflicting substantial neurological damage. For this reason surgeons are usually capable of removing only a large portion of the tumor, leaving some residual malignant tissue. MRI provides the medical staff with good contrast images that allow tte surgeons to locate malignant tissue and evaluate its dimensions.

A major difficulty encountered during a tumor removal procedure is related to the fact that although it is possible to perform known MRI sequences in order to acquire good contrast MRI images thus allowing differentiation between malignant and healthy tissue on the image acquired, it may not be possible to notice the difference on the operated tissue itself. The surgeon can clearly see the tumor and its boundaries on the image, but is unableto distinguish the tumor from its surrounding healthy tissue in the patient. For that reason, to date, only about as much as 70% of a brain tumor is removed in a conventional brain surgery. This may lead to future aggravation in the patient's condition, s the tumor grows back, seriously affecting the patient's quality of life or even endangering his life. For that reason it is sought to provide means for aiding the medical staff in determining the exact location of a medical instrument used in operation vith reference to the image obtained using MRI apparatus. Furthermore it is desirable that such means enable determining the orientation of such instrument.

In US Patent 5,271 ,400 (Dumoulin et al.), filed Apr. 1 , 1992, there is disclosed a tracking system to monitor the position and orientation of a device using magnetic resonance detection of a sample contained within a device. The detectable device, which can be a guide wire, a catheter, an endoscope, a laparoscope, a biopsy needle or a similar device, cortains an RF (radio frequency) coil and a magnetic resonance responsive sample. When the device is subjected to an RF pulse, generated by an outside RF coil or by the RF coil of the device, the MR responsive sample resonates, and the RF coil of the device, which is a small coil, detects the MR response signal from the MR responsive sample. The coordinates of the MR responsive sample are calculated, and its position is marked on the MRI image, so as to enable the beholder to determine the relative position of the device with respect to the conventional image. It is explained that it is a purpose of that invention to provide a method for tracking a device using MR examination without loss of signal due to lack of MR responsive material in the internal cavities of a subject.

In US Patent 5,318,025 (Dumoulin et al.), filed Apr. 1 , 1992, there is disclosed a tracking system to monitor the position and orientation of a device using magnetic multiplexed resonance detection The detectable device disclosed contains a number of RF coils (instead of just one as described in US Patent 5,271 ,400) The inventors of US Patent 5,318,025 do not explicitly explain the reason for providing at least two RF coils, but it is understood that this allows determining linear orientation (as only one RF coil is provided in the device described in US Patent 5,271 ,400) However the tracking device disclosed in US Patent 5,318,025 (having three aligned and evenly spaced RF coils) does not facilitate obtaining information as to the directionality of the device, and that may be determined only by other independently acquired medical diagnostic devices, as is explained there

US Patent 5,916,162 (Snelten et al ) it is disclosed an invasive device which is intended to cooperate with an MRI appaatus The device is provided with an RF coil situated near the distal part of the invasive device The RF coil is used to visualize the position of a distal end of the invasive device, introduced into an object, in an image of the object In order to counteract the development of heat in the invasive device, the invasive device is provided with a hollow carrier The electric connection extends through said carrier, which is provided with an electrically conductive shield with an additional resistance The mvasive device disclosed in Snelten's patent is in fact a catheter for insertion into a blood vessel of a patient

It is the purpose of the present invention to provide a pointing device aimed to cooperate with an MRI apparatus In a preferred embodiment <6 the present invention it is suggested to provide a magnetic resonance detectable medical instrument to facilitate the use of that instrument during an intraoperative magnetic resonance imaging of the patient's body part or organ which is undergoes surgery

It is another purpose of the present invention to provide such a pointing device that facilitates the determination of the orientation of the pointing device The pointing device may be also incorporated in a medical instrument so as to allow the medical staff to determine via the employment of an intraoperative MRI apparatus the position and orientation of the medical instrument with respect to the patient's part or organ being imaged

BRIEF DESCRIPTION OF THE INVENTION

There is thus provided, in accordance with a preferred embodiment of the present invention, a pointing device to be used in cooperation with a magnetic resonance imaging apparatus, said device comprising a member of a predetermined shape, at least one sample of magnetic resonance responsive material placed within said member in a predetermined position, said sample geometrically arranged to have a distinct directionality, whereby when said device is introduced into said magnetic resonance imaging apparatus image region, the position sample may be obtained and marked on an image of said target

Furthermore, in accordance with a preferred embodiment of the present invention, said member comprises a tube Furthermore, in accordance with a preferred embodiment of the present invention, said sample of magnetic resonance responsive material comprises water or gadolinium or nickel chloride solution provided in void of distinct shape within said member

Furthermore, in accordance with a preferred embodiment of the present invention, said sample of magnetic resonance responsive material is provided in the shape of a cone

Furthermore, in accordance with a preferred embodiment of the present invention, said sample of magnetic resonance responsive material is provided in the shape of a disc Furthermore, in accordance with a preferred embodiment of the present invention, said device comprises a plurality of samples of magnetic resonance responsive material, said plurality of samples of magnetic resonance responsive material geometrically arranged within said member to have a distinct directionality. Furthermore, in accordance with a preferred embodiment of the present invention, said device comprises three samples of magnetic resonance responsive material.

Furthermore, in accordance with a peferred embodiment of the present invention, said three samples are each provided in a shape of a disc. Furthermore, in accordance with a preferred embodiment of the present invention, the gaps between said three samples are distinctly different whereby this aides in figuring the directionality of said device.

Furthermore, in accordance with a preferred embodiment of the present invention, said device is further provided with an RF coil in the vicinity of said at least one sample of magnetic resonance responsive material, said RF coil adapted to allow it to be electrically connected to said magnetic resonance imaging apparatus.

Furthermore, in accordance with a preferred embodiment of the present invention, said RF coil encircles said at least one sampleof magnetic resonance responsive material.

Furthermore, in accordance with a preferred embodiment of the present invention, said RF coil is engulfed by said at least one sample of magnetic resonance responsive material.

Furthermore, in accordance with a preferred embodiment of the present invention, there is provided a pointing device to be used in cooperation with a magnetic resonance imaging apparatus, said device comprising: a member of a predetermined shape; a plurality of samples of magnetic resonanαe responsive material placed within said member in a predetermined position, said samples geometrically arranged to have a distinct directionality; and RF coil provided in the vicinity of said plurality of samples of magnetic resonance responsive material adapted to allow it to be electrically connected to said magnetic resonance apparatus; whereby when said device is introduced into said magnetic resonance imaging apparatus image region the position of the sample may be obtained and marked on an image of said target. Furthermore, in accordance with a preferred embodiment of the present invention, said plurality of magnetic resonance responsive samples are from the same material but in different densities or concentrations. Furthermore, in accordance with a preferred embodiment of the present invention, said plurality of magnetic resonance responsive samples are provided with different sizes.

Furthermore, in accordance with a preferred embodiment of the present invention, said RF coil is engulfed by said plurality of samples of magnetic resonance responsive material.

Furthermore, in accordance with a preferred embodiment of the present invention, said member comprises a tube.

Furthermore, in accordance with a preferred embodiment of the present invention, said plurality of samples of magnetic resonance responsive material comprises water or gadolinium or nickel chloride solution samples provided in voids of distinct shapes within said member.

Furthermore, in accordance with a preferred embodiment of the pesent invention, said plurality of samples of magnetic resonance responsive material comprise three samples. Furthermore, in accordance with a preferred embodiment of the present invention, said three samples are each provided in a shape of a disc.

Furthermore, in accordance with a preferred embodiment of the present invention, said RF coil comprises a plurality of RF coils, the number of which corresponds to the number of said plurality of samples of magnetic resonance responsive material, said RF coils connected in series, and wherein each of said RF coils encircles one of said plurality of samples of magnetic resonance responsive material

Furthermore, in accordance with a preferred embodiment of the present invention, said RF coil comprises a pluralty of RF coils, the number of which corresponds to the number of said plurality of samples of magnetic resonance responsive material, said RF coils connected in series, and wherein each of said RF coils encircles one of said plurality of samples of magneto resonance responsive material, and is encircled by a ring of magnetic resonance responsive material Furthermore, in accordance with a preferred embodiment of the present invention, the gaps between said three samples are distinctly different whereby this aides in figuring the directionality of said device

Furthermore, in accordance with a preferred embodiment of the present invention, the device is incorporated in a surgeryroom tool Furthermore, in accordance with a preferred embodiment of the preent invention, said surgery-room tool comprises a suction tube

Furthermore, in accordance with a preferred embodiment of the present invention, said plurality of samples of magnetic resonance responsive material are provided in the form of rings encirclng said tube Furthermore, in accordance with a preferred embodiment of the present invention, there is provided a MRI apparatus incorporating a pointing device, said device comprising a member of a predetermined shape, a front end and a back end, the front end comprising a magnetic structure for the provision of a magnetic field, gradient coils, RF transmit coil and RF receive coil, and the back end comprising a central processing unit, at least two gradient amplifiers, RF amplifier, MRI spectrometer, MRI controller and display unit at least one sample of magnetic resonance responsive material placed within said member in a predetermined position, said sample geometrically arranged to have a distinct directionality; whereby when said pointing device is irtroduced into said magnetic resonance imaging apparatus image region, the position of the sample may be obtained and superimposed on an image of said target.

Furthermore, in accordance with a preferred embodiment of the present invention, there is provided a method for the determination of position and orientation of a pointing device relative to a desired target in magnetic resonance imaging, the method comprising the steps of:

1. placing a patient in imaging region of a MRI apparatus;

2. applying predetermined imaging sequence, view gradient strength, oblique axes and bandwidth;

3. processing retrieved MRI data to obtain an image of the patient's imaged part;

4. marking a target on said obtained image;

5. placing a pointing device containing magnetic resonance responsive material in the imaged region;

6. applying a projection sequence having same predetermined view gradient strength, oblique axes and bandwidth;

7. obtaining 3 projections in the predetermined oblique axes of said pointing device;

8. calculating the position of the pointing device; and

9. marking said pointing device position on said obtained image.

Furthermore, in accordance with a preferred embodiment of the present invention, said method further comprises the steps of:

1. determining whether the pointing device ison said target; 2. relocating said pointing device if said pointing device is not on target;

3. applying same predetermined view gradient strength, oblique axes and bandwidth;

4. obtaining 3 projections in the predetermined oblique axes of said pointing device;

5. calculating the position of the pointing device;

6. marking said pointing device position on said obtained image; and

7. repeating steps 2 to 6 if the newly acquired position of the pointing device is still not on the target.

Furthermore, in accordance with a peferred embodiment of the present invention, said magnetic resonance responsive material of said pointing device is geometrically arranged to have a distinct directionality.

BRIEF DESCRIPTION OF THE FIGURES

The invention is described herein, by way of ©cample only, with reference to the accompanying Figures, in which like components are designated by like reference numerals.

Figure 1 illustrates an MRI pointing device in accordance with a preferred embodiment of the present invention, having a plurality of magnetic resonance responsive samples.

Figure 2 illustrates an MRI pointing device in accordance with another preferred embodiment of the present invention, having a magnetic resonance responsive sample having a shape of distinct determinable directionality.

Figure 3 depicts another embodiment of the pointing device of the present invention, having MR responsive samples in different sizes.

Figure 4 illustrates a pointing device in accordance with a preferred embodiment of the present invention incorporated in a suction tube.

Figure 5 is a schematic diagram of a pointing device incorporated with an MRI apparatus, in accordance with a preferred embodiment of the present invention.

Figure 6 shows the procedure steps of applying the method of determiniig the position and orientation of a pointing device in accordance with a preferred embodiment of the present invention.

Figure 7 provides an illustration of an effectively on-line determination of the position and orientation of the pointing device and pacing it on a desired target in accordance to the present invention.

Figure 8 shows an alternative procedure steps of applying the method of determining the position and orientation of a pointing device in accordance with a preferred embodiment of the pesent invention.

DETAILED DESCRIPTION OF THE INVENTION

A main aspect of the present invention is the provision of a pointing device with distinct detectable directionality suitable for use in cooperation with an MRI apparatus. The pointing device is piovided with at least one magnetic resonance responsive sample that can be detected and imaged by the MRI apparatus. The pointing device containing the MR responsive sample is positioned at the patient's imaged region - which may be an open cavity within the patient's body or inside a duct within the body, or over the skin or any other position over the body - and is subjected to a predetermined MRI image acquisition sequence The MRI antenna picks up the induced signal from the MR responsive sample contained within the pointing device and the MRI apparatus displays the pointing device's position on the image of the patient's organ or body part

Figure 1 illustrates an MRI pointing device in accordance with a preferred embodiment of the present invention, ha ing a plurality of magnetic resonance responsive samples The pointing device comprises a tube 1 , or a similar container, in which three samples 2, 3, 4, in the shape of discs, made from an MR responsive material, such as water or gadolinium or nickel chibride (NiCI) solution , are placed, in a distinct directionalitydeterminable arrangement, where the gaps between the MR responsive samples are distinctly different This arrangement allows the determination of the directionality of the pointing device, as the MR responsive samples are prearranged to present a distinct directionality Once an image of the pointing device is obtained its position and orientation is easily determined In case of water serving as the magnetic resonance responsive material, it is provided in voids of predetermined distinct shapes in the tube

Around each sample, an annular void 32 containing water, or other MR responsive material, is provided This is done in order to enhance the signal obtained by the coil, as the coil is sensitive to internal as well as outside Signal responses By engulfing the coil with MR responsive sample, the coil picks up a stronger response

It may be possible to obtain an image of the pointing device, using the MRI apparatus' general antenna as a recever of the induced signal, but it is most likely that such induced signal be too weak to be traceable by an MRI apparatus In order to enhance the receiving of the induced signal from the MR responsive samples of the pointing device, an RF coil is provided in the vicinity of the samples The RF coil serve as a local antenna for the reception of locally induced MR signal (i e the induced signal of the MR responsive sample) In the pointing device depicted in Figure 1 an RF coil is provided near each of the MR responsive samples, i e RF coil 5 is located near MR responsive sample 2, RF coil 6 is located near MR responsive sample 3, and RF coil 7 is located neat MR responsive sample 4 It is recommended to connect RF coils 5, 6 and 7 in series and provide them with two electrical wires (or terminals) 8 to be electrically connected to the MRI apparatus receiver

It may be optionally suitable to provide a longer single coil which encircles all of MR responsive samples, but for efficient design reasons it is recommended to arrange the pointing device of the present invention with a coil near each MR responsive sample In effect RF coils 5, 6 and 7 act as a single coil when connected in series

Another optional embodiment is to use three different MR responsive samples, i e made from different materials or same material but with different densities or concentrations , so as to allow distinction between the samples It is noted that it may be possible to provide a pointing device with more than three MR responsive samples and in different configuration as long as the arrangement of the MR responsive sample within the device has a distinct MR! detectable directionality Any such device would still be covered by the scope of the present invention and the accompanying Qaims Figure 2 illustrates an MRI pointing device in accordance with another preferred embodiment of the present invention, having a magnetic resonance responsive sample having a shape of distinct determinable directionality

Here the MR responsive sample 12 is located inside a tube 1 1 , having the shape of a cone, with a broad base at one end and a tipped point at the other end The MR responsive sample 12 is encircled by an RF coil 13, which is provided with electrical wiring 15 for connection to an MRI apparatus receiver

The pointing device of the present invention may be incorporated in other tools, such as at the distal end of a suction tube used in surgery to evacuate blood or other fluids from the surgery site, etc Figure 3 illustrates another preferred embodiment of the present invention, where the pointing device comprises three MR responsive samples having different sizes. The pointing device 110 comprises a body in the form of a tube 114 having three voids, 116, 118 and 120 containing MR respons/e sample (like water). The voids differ in their sizes, in a predetermined manner so as to allow determining the directionality of the pointing device by viewing the MR image in which it is shown. The viewer may determine the directionality by spotting Hie differences in sizes on the MR samples as they appear on the image. Note that in this embodiment the coils 122 are immersed in the MR responsive sample. Again this is done in order to enhance the appearance of the MR responsive samples on the image acquired. The coils are connected in series and are provided with wiring 124 that may be connected to the electronic circuit of the MRI apparatus.

Figure 4 illustrates a pointing device in accordance with a preferred embodiment of the present invention incorpσated in a suction tube.

The suction tube 21 is primarily a fluid evacuation device aimed at evacuating blood or other fluids from the surgery site within the patient. The suction tube's proximal end is connected to a suction pump 29 which pumps the fluids away from the surgery site. The tube's distal end is placed by a member of the surgical team adjacent the fluids to be evacuated and the fluid is then pumped away into the tube's conduit 21. At the distal end of the suction tube 21 three MR responsive samples are provided arranged in rings 22, 23, 24, unevenly spaced so that the distance between the ring 22 nearest to the edge of the tube and the middle ring 23, is notably different from the distance between the middle ring 23 and the third ring 24. In thecase of the embodiment shown in Figure 3 the distance between the first two rings is smaller than the distance between the middle and the last ring, but an opposite arrangement would still be covered by the scope of the present invention.

The pointing device of the present invention allows the surgical team to determine with high accuracy the location and orientation of the pointer and thus facilitates marking specific targets during the surgery for operation. The ability to determine the directionality of the pointing device brings about the ability to pinpoint a target, be it a tumor to be removed in a brain surgery, or a blood vessel etc., minimizing the risk for inadvertent or accidental damage being inflicted during surgery.

Furthermore, as is further explained, the pointing device of the present invention can be used to aid the surgical team in determining the precise direction they should choose to make an incision in order to get to the target to be operated.

Figure 5 is a schematic diagram of a pointing device incorporated with an MRI apparatus, in accordance with a preferred embodiment of the present invention. A magnetic resonance imaging apparatus 50 comprises a front end and a back end, the front end comprising a magnetic structure 51 for the provision of a magnetic field, at least two gradient coils, RF transmit coil 52 and RF receive coil 53, and the back end comprising a central processing unit 60(usually a host computer), gradient amplifiers 54, RF amplifier 55, MRI spectrometer 56, MRI controller 57 and display unit 58. The RF coil, or coils, of the pointing device 59 of the present invention is electrically connected to the RF amplifier 55, which transmits an amplified response signal to the central processing unit 60 for processing of the signal to obtain an image which is displayed on the display unit. As can be appreciated from this figure, a member of the medical staff 62 (usually a surgeon) holds the pointing device 59 and introduces it to the organ of the patient 61 that is imaged. The CPU is programmed to compute the position of the pointing device and superpose it on the retrieved image of the patient's organ under examination in the manner explained hereafter. The method of determining the position and orientation of the pointing device according to the present invention preferably involves two alternative procedures:

A first suggested procedure (see Figure 6) comprises the following steps: 1. placing a patient in imaging region of a MRI apparatus; 2. applying predetermined imaging sequence view gradient strength, oblique axes and bandwidth;

4. marking a target on said obtained image; 5. placing a pointing device containing magnetic resonance responsive material in the imaged region;

8. calculating the position of the pointing device and

9. marking said pointing device position on said obtained image.

It is suggested to use the following parameters of the predetermined imaging sequence for the derivation of the location of the MR responsive sample of the pointing device: view gradient strength, bandwidth, and oblique angles. Projected Fids are collected along each of the three oblique axes, with the view gradient in the same polarity and in reversed polarity. From the above six (2 polarities X 3 axes) projections one can derive the positon of the pointing device either in the "true" coordinates (i.e. the relative position with respect to the MRI magnets) or in the image coordinates (which may itself be distorted due to magnetic field imperfections). The reason for performing each view gadient twice (in reversed polarities) is in order to cancel effects of local distortions caused by flaws in the magnetic field, as in the case of image elements that are not found in the same position, their true position may determined by calculating the true position to be exactly in the middle between the position of the element when applying the first view gradient and the position of the same element when applying the same view gradient with reversed polarity.

The inventors suggest that the latter be preferred for several reasons: a. The pointing device of the present invention is primarily intended to be used as a pointing tool, to help the surgical team locate their target and direct their incision tool or any other device to a desired location; b. It is stipulated that a surgical team would not be really interested in the real coordinates of the pointing device but rather in the relative position of the pointing device with respect to the patient's organ image. The surgical team would track the position of a pointing device on the monitor relative to the image of the organ under examination, and would try to make sense of that relative position in determining where to place a surgery tool, or where to perform an incision etc. c. Superimposing the pointing device position on the original image using the image coordinates as reference eliminates the possible error, and therefore would account for a precise superposition of the pointing device image on the previously retrieved image.

To the inventors' best knowledge, prior art positioning methods use the real coordinates of the superimposed pointing device as their reference, whereas the method of the present invention uses the image coordinates as the reference coordinates.

It is noted that the imaging sequence used for the acquisition of the organ image can be either a 2-dimensional multi slice sequence or a 3-dimensional sequence.

The significantly shortened acquisition time of the pointing device position allows a fast sequential acquisition of a series of images of the pointing device (see Figure 7), during which the pointing device is relocated in the imaged region until the surgeon (or the surgical personnel operating the device) verifies that the pointing device is positioned where was desired. The surgeon first marks the predetermined target on the image. He then places the pointing device in the presumed target location and a superimposed position of the pointing device on the organ image is acquired. If the pointing device is found not to be an the target the surgeon relocates the pointing device to another location and another superimposed image is acquired. If the pointing device is still off the target the surgeon determines whether the pointing device is closer to the target than it was before and consequently may determine in which direction the pointing device ought to be moved in order to coincide with the target.

The method then comprises the following additional steps: 1. determining whether the pointing device is on said target;

2. relocating said pointing device if said pointing device is not on target;

3. applying same predetermined view gradient strength, oblique axes and bandwidth; 4. obtaining 3 projections in the predetermined oblique axes of said pointing device;

5. calculating the position of the pointing device;

6. marking said pointing device position on said obtained image; and 7. repeating steps 2 to 6 if the newly acquired position of the pointing device is still not on the target. Again it is noted that due to the genuine difficulty to distingjish in-vivo healthy tissue from malignant tissue, the introduction of the pointing device of the present invention provides the surgical team with a reliable way to determine the location of a target (such as a malignant tissue) on the acquired image, and allows the precise positioning of a surgical tool on the target.

The separate acquisition of the pointing device image and consequent provision of a superimposed image is a fast method, which in effect allows the surgical team to obtain an almost on-line image of the pointing device. On the other hand, it is important to make sure that the patient remains still throughout the entire positioning procedure, for if the patient resumes a different position the superimposed image of the pointing device on the anginal image would not reflect the actual relative position of the pointing device with respect to the patient's organ. It may be necessary, in lengthier operations, that a full image be reacquired every time the patient moves or is shifted, and the posibnmg procedure repeated as explained herein On the other hand, if the MRI imager is registered in an additional tracking system that can detect the position and location of the patient than reacquisition of images may prove unnecessary Figure 8 shows alternative procedure steps of applying the method of determining the position and orientation of a pointing device in accordance with a preferred embodiment of the present invention An alternative procedure of determining the position and orientation ofthe pointing device according to the present invention comprises a simultaneous imaging of the patient's organ with the pointing device (see Figure 5) It involves the following steps

1 Placing the patient in the imaging region of the MRI apparatus

2 Placing the pointing device of the present invention in the imaged region

3 Applying a predetermined imaging sequence 4 Acquiring the MR data with the RF viewing (receiving) coils and the viewing receiving coil of the pointing device, in an array coil configuration, to obtain the desired superimposed image The latter procedure, although insensitive to the patient's movement, is significantly more cumbersome a method, as the acquisition time of a superimposed image increases greatly to the order of about a minute, and therefore cannot provide the surgical team with an "online" means for determining the target position and orientation and is therefore less appealing as a position determining method for an on-going surgery

When derivation of the coordinates of the pointing device are desired, one must keep track on the Larmor (central) frequency In order to achieve that, the pointing device may be placed in a predetermined location, preferably out of the field of view of the MRI apparatus Before acquiring an imagethe MRI apparatus can be made to automatically detect the Larmor frequency at that location and register it Later, when it is desired to use the pointing device, the pointing device is again placed in the same predetermined location in order to detect clanges in the Larmor frequency from the time an image was acquired updating the MRI apparatus with the same change in frequency.

The pointing device of the present invention makes it simpler and easier for the surgeon to determine the position of the targetand optimal position of the surgery tool to be used. However as the pointing device is a physical item of finite dimensions, it may be positioned only as close to the target as the distance of the target from the upper surface of the imaged region, such a? in the case of a malignant tumor, which is found inside the head of a patient, before the opening of the skull in surgery. From knowing the actual dimensions of the pointing device, and in particular the distance of the MR active sample edge from the pointing device tip, it can be taken into consideration in a program calculating the position of the pointing device and adjustment can be made to mark the tip of the pointing device on the superposed image.

It may be needed to determine the direction of the target relative to a position further away, such as a location on the patient's skin over the target.

It is therefore suggested in another embodiment of the present invention to optionally add on the image a virtual straight line, or any predetermined cure, extending coaxially beyond the pointing device tip, which will allow the surgeon to determine the direction of the target relative to a certain reference point. The pointing device may than be positioned on a predetermined reference point and the surgeon may twist and reorientate the pointing device until the virtual line provided on the superimposed image coincide with the target, thus helping the surgeon to determine the direction in which he must work his way towards the target. It should be clear that the description of the embodiments and attached

Figures set forth in this specification serves only for a better understanding of the invention, without limiting its scope as covered by the following Claims.

It should also be clear that a person skilled in the art, after reading the present specification could make adjustments or amendments to the attached Figures and above described embodiments that would still be covered by the following Claims.

Claims

C L A I M S

1 A pointing device to be used in cooperation with a magnetic resonance imaging apparatus, said device comprising a member of a predetermined shape, at least one sample of magnetic resonance responsive material placed within said member in a predetermined position, said sample geometrically arranged to have a distinct directionality, whereby when said device is introduced into said magnetic resonance imaging apparatus image region, the position of the sample may be obtained and superimposed on an image of said target

2 The device as claimed in Claim 1 , wherein said member comprises a tube

3 The device as claimed in Claim 1 , wherein said sample of magnetic resonance responsive material comprises water or gadolinium or nickel chloride solution provided in void of distinct shape within said member

4 The device as claimed in Claim 1 , wherein said sample of magnetic resonance responsive material is provided in the shape of a cone

5 The device as claimed in Claim 1 , wherein said sample of magnetic resonance responsive material is provided in the shape of adisc

6 The device as claimed in Claim 1 , wherein it comprises a plurality of samples of magnetic resonance responsive material, said plurality of samples of magnetic resonance responsive material geometrically arranged within said member to have a distinctdirectionality

7 The device as claimed in Claim 6, wherein it comprises three samples of magnetic resonance responsive material

8 The device as claimed in Claim 7 wherein said three samples are each provided in a shape of a disc

9. The device as claimed in Claim 6, wherein the gaps between said three samples are distinctly different whereby this aides in figuring the directionality of said device.

10. The device claimed in Claim 1 , further provided with an RF coil in the vicinity of said at least one sample of magnetic resonance responsive material, said RF coil adapted to allow it to be electrically connected to said magnetic resonance imaging apparatus.

1 1. The device as claimed in Claim 10, wherein said RF coil encircles said at least one sample of magnetic resonanoe responsive material.

12. The device as claimed in Claim 10, wherein said RF coil is engulfed by said at least one sample of magnetic resonance responsive material.

13. A pointing device to be used in cooperation with a magnetic resonance imaging apparatus, said device comprising: a member of a predetermined shape; a plurality of samples of magnetic resonance responsive material placed within said member in a predetermined position, said samples geometrically arranged to have a distinct directionality; and RF coil provided in the vicinity of said plurality of samples of magnetic resonance responsive material adapted to allow it to be electrically connected to said magnetic resonance apparatus; whereby when said device is introduced into said magnetic resonance imaging apparatus image region the position of the sample may be obtained and superimposed on an image of said target.

14. The device as claimed in Claim 13, wherein said plurality of magnetic resonance responsive samples are from the same material but in different densities or concentrations.

15. The device as claimed in Claim 13, wherein said plurality of magnetic resonance responsive samples are provided with different sizes.

16. The device as claimed in Claim 13, wherein said RF coil is engulfed by said plurality of samples of magnetic resonance responsive material.

17. The device as claimed in Claim 13, wherein said member comprises a tube.

18. The device as claimed in Claim 13, wherein said plurality of samples of magnetic resonance responsive material comprises water or gadolinium or nickel chloride solution samples provided in voids of distinct shapes within said member.

19. The device as claimed in Claim 13, wherein said plurality of samples of magnetic resonance responsive material comprise three samples.

20. The device as claimed in Claim 19, wherein said three samples are each provided in a shape of a disc.

21. The device as claimed in claim 13, wherein said RF coil comprises a plurality of RF coils, the number of which corresponds to the number of said plurality of samples of magnetic resonance responsive material, said RF coils connected in series, and wherein each of said RF coils encircles one of said plurality of samples of magnetic resonance responsive material.

22. The device as claimed in claim 13, wherein said RF coil comprisesa plurality of RF coils, the number of which corresponds to the number of said plurality of samples of magnetic resonance responsive material, said RF coils connected in series, and wherein each of said RF coils encircles one of said plurality of samples cf magnetic resonance responsive material, and is encircled by a ring of magnetic resonance responsive material.

23. The device as claimed in Claim 13, wherein the gaps between said three samples are distinctly different whereby this aides in figuring the directionality of said device.

24. The device as claimed in Claim 13, wherein it is incorporated in a surgery-room tool.

25. The device as Claimed in Claim 24, wherein said surgeryroom tool comprises a suction tube.

26. The device as claimed in Claim 24, wherein said pluality of samples of magnetic resonance responsive material are provided in the form of rings encircling said tube.

27. A MRI apparatus incorporating a pointing device, said device comprising: a member of a predetermined shape; a front end and a back end, the font end comprising a magnetic structure for the provision of a magnetic field, gradient coils, RF transmit coil and RF receive coil, and the back end comprising a central processing unit, at least two gradient amplifiers, RF amplifier, MRI spectrometer, MRI controller and display unit at least one sample of magnetic resonance responsive material placed within said member in a predetermined position, said sample geometrically arranged to have a distinct directionality; whereby when said pointing device is htroduced into said magnetic resonance imaging apparatus image region, the position of the sample may be obtained and superimposed on an image of said target.

28. A method for the determination of position and orientation of a pointing device relative to a desired target in magnetic resonance imaging, the method comprising the steps of:

1. placing a patient in imaging region of a MRI apparatus; 2. applying predetermined imaging sequence, view gradient strength, oblique axes and bandwidth;

3. processing retrieved MR data to obtain an image of the patient's imaged part;

8. calculating the position of the pointing device; and

9. marking said pointing device position on said obtained image.

29. The method claimed in Claim 28, further comprising the steps of:

1. determining whether the pointing device is on said target;

2. relocating said pointing device if said pointing device is not on target;

5. calculating the position of the pointing device;

6. marking said pointing device position on said obtained image; and

30. The method claimed in Claim 27, wherein said magnetic resonance responsive material of said pointing device is geometrically arranged to have a distinct directionality.