DEVICE FOR INTERFACING MRI WITH OTHER IMAGING MODALITIES

Abstract: A grid system for interfacing MRI with other imaging modalities. The system includes a grid of contrast material which is compatible with MRI and other imaging modalities and a means to reproducibly position the subject in relation to the grid. The grid system is also used to plan radiotherapy and surgical biopsy procedures.

Description: DEVICE FOR INTERFACING MRI WITH OTHER IMAGING MODALITIES TECHNICAL AREA The invention relates to the area of diagnostic imaging and mo specifically to a method and device for interfacing MRI with vario other diagnostic imaging modalities and treatment devices. BACKGROUND OF THE INVENTION Magnetic resonance imaging (MRI) is a recent but extreme powerful noninvasive diagnostic tool. MRI utilizes a combination a powerful static magnetic field and radio frequency pulses whi gather information concerning the location and interrelation of atom nuclei which possess unpaired electron spin within the body. hydrogen is the most prevalent element to possess unpaired spin, M mainly images hydrogen ion concentration. Based upon this inform tion, a computer is able to generate an anatomic image of the subjec For particular studies, MRI has a distinct advantage over comput tomography (CT) scans. For example, it is presently established th MRI is the diagnostic tool of choice in evaluating the posteri fossa, an anatomical location that is poorly visualized by CT. M is also superior to CT in delineating extremity soft-tissue tumors a primary bone malignancies. Whereas CT scans a region of interest one plane, MRI permits imaging in any desired plane, thus more easi permitting multidimensional mapping of tumors. These advantages of MRI make it attractive for use in radiati treatment planning. Over the past several years, CT has been used f this purpose and has revolutionized radiation treatment by maki available more detailed information concerning tumor localization th was ever before possible: (E. Hart, "The Role of the CT Scanner RT Planning" 54(613) Radiotherapy 20, 1988.) Still, as suggest above, certain anatomical studies are better suited to MRI, and thu MRI should potentially complement CT in radiation treatment plannin It has also been suggested that MRI may be synergistic with CT in t definition of tumor volume for a number of disease states. (A. Licht and B. Fraass, "Recent Advances in Radiotherapy Treatment Plannin Oncology, May 1988, p. 43) In order for these expectations to be met, there is a need develop a means to accurately interface MRI with other diagnost imaging modalities such as CT or positron emission tomography (PE and to transfer tumor localization data obtained from MRI and t other imaging modalities to radiation treatment devices. It important to realize that due to spatial and temporal magnetic fie fluctuations within the MRI field, the displayed image is distort to varying degrees in a non-uniform manner. These fluctuations a dependent on multiple factors such as ambient temperature, a extraneous magnetic fields in the immediate scanner vicinity. Imag appearing on the viewing screen (CRT) , and ultimately on the fi hardcopy, are the result of system software manipulations intended f viewer aesthetics. Further, the bony skeleton which is often used a reference in determining tumor location and size with other imagi modalities is not well visualized on MRI. Thus, MRI does not perm direct tumor measurement with the degree of consistency and precisi demanded in a treatment planning setting. SUMMARY OF THE INVENTION The present invention provides an inexpensive but effecti means to interface MRI with other diagnostic imaging modalities a radiation treatment devices in a reproducible manner. The inventi herein described and claimed avoids the interfacing problems with M otherwise caused by distortion and poor visualization of bone employing a grid system. For MRI, the system uses a grid structu of members of contrast material visualized on MRI and a means f reproducibly positioning said grid structure relative to a body pa being imaged. With the grid properly positioned, the image taken wi the MRI will include both data relative to the body part and artifa caused by the contrast agent of the grid. As the true spati relationship of the grid members is known, and the causes distortion affect the grid and the body part similarly, such gr artifact functions as a reference in the same manner that the bo skeleton serves as a reference with other imaging modalities. Thu if a tumor is the structure of interest being imaged, determinatio of location and size of the tumor are made by reference to the kno spatial relationship of the grid. When the subject is studied using other imaging modalitie the system is again employed changing only the contrast material required. Using the positioning means, the subject and the gr structure are aligned in the same manner as when the MRI images we made. With the grid as a reference one can readily and accurate compare MRI images with images made with the other imaging modalitie Thus, by selection of contrast material, and a means to precisely a consistently position the grid and the patient in relation one to t other, the invention functions to reproducibly interface MRI wi other modalities such as CT, PET and radiation treatment device Localization grids have been described for use with CT, PET and M applications: (S. Goerss, et al: A Computerized Tomograph Stereotactic Adaptation System, 10 Neurosurgery 375-379, 198 P.C. Hajek, et. al., Localization Grid for MR-guided Biopsy. 163( Radiology 825-826, 1987; S. Miura, et. al. Anatomical Adjustments Brain Positron Emission Tomography Using CT Images. 12(2) Journal Computer Assisted Tomography 363-67, 1988; U.S. Patent No. 4,583,538. To varying degrees, these grids are either difficult to use, expensi to manufacture, not conducive to exact repositioning from scan to sca or not readily interchangeable between MRI and the various oth diagnostic modalities. Accordingly, it is an object of this invention to provide method and apparatus which may be used to interface MRI with othe imaging devices as well as with radiotherapy treatment units. Another object of this invention is to provide a method an apparatus to interface MRI with other imaging devices as well as wit surgical intervention techniques. Yet another object of the invention is to satisfy the abov stated objectives in an uncomplicated and inexpensive manner. The novel features which are believed to be characteristic o the invention both as to its organization and method of operation together with further objectives and advantages thereof, will b better understood from the following drawings in which a presentl preferred embodiment of the invention is illustrated by way o example. It is to be expressly understood, however, that the drawing are for the purpose of illustration and description only and are no intended as a definition of the limits of the invention. BRIEF DESCRIPTION OF THE DRAWINGS Figures 1A through 1C: Perspective views of a variety o grid structures. Figure 1A: Perspective view of a grid structure having portion of its side wall cut away to expose tubing embedded in sai wall. Figure 2: Partial perspective view of a grid structur having removable walls. Figure 3: Perspective view of the corner portions of grid structure illustrating the interconnected tubing network embedde within said wall, and specifically showing the beginning and terminu portions which open at the same edge and are able to be capped. Figure 4: Partial perspective view of the corner sectio of the grid structure of Figure ID, illustrating the use of a scre plug at such corner section. Figure 5: Perspective view showing the relation of th patient platform to the patient bed of an imaging unit. Figures 6A and 6B: Two embodiments of a patient platfor with grid structure slidably attached. Figures 7A and 7B: Perspective view illustrating the us of saggital and transverse lasers to align the patient platform an subject. Figures 8A and 8B: Perspective view of the subject on th patient platform with grid structure slidably attached being move into the gantry of an imaging unit. Figure 8B: Perspective view and diagrammatic represen tation of the use of a computer algorithm to correct image distortion. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT While this invention is susceptible of embodiment in man different forms, it is shown in the drawings and will herein b described in detail, preferred embodiments of the invention. I should be understood, however, that the present disclosure is to b considered an exemplification of the principles of the invention an is not intended to limit the invention to the specific embodiment illustrated. The grid system of the preferred embodiment has two basi components. Figure 1A illustrates the first component of the system, the grid structure 11. As illustrated, the grid structure of th preferred embodiment is a rectangular structure having two open ends 12. The walls 13 of the grid structure 11 are made of semi-rigid non¬ magnetic material such as plexiglass. Embedded within the walls are tubes 16, also of a non-magnetic material, containing contrast material. For use with MRI, the preferred contrast material is Gadolinium Chloride. Optimal visualization on both Tl- and T2- weighted spin-echo pulse sequences has been obtained by Hajek, et. al., supra, using 5-mm-diameter tubes filled with 500 mM Gd-DPTA. It is to be understood that other paramagnetic material may be substituted for Gd-DPTA and still come within the scope of the claims. For use with CT radiopaque contrast material such as Barium is desirable. The tubes containing contrast material are regularly spaced and arranged in a mutually orthogonal fashion. Also, one of the tubes embedded in each face of the grid structure is arranged so as to form a diagonal 18. In the presently preferred embodiment, interfacing between diagnostic modalities is accomplished by using identically constructed grid structures having tubes containing contrast material specific for the particular imaging modality being used. Thus, for example, one grid structure having tubes containing Gd-DPTA is used with MRI and an identical structure having tubes containing Barium is used with CT and radiation treatment devices. Alternatively, interfacing may be accomplished using a grid structure, as illustrated in Figure 2, wherein the walls 22 of said structure may be removed and replaced with identically constructed walls with tubes containing a different contrast material. Thus, one would have a set of grid structure walls containing contrast material specific for MRI, a set of walls containing contrast material spec fic for PET, and yet another set of walls specific for CT a radiation treatment devices. Said grid structure walls would be he in place by conventional framing means manufactured of non-magnet material 23. An example of suitable material would be semi-rig nylon or plastic. Alternatively, the walls themselves could ha interlocking means at their edges such as a mitered joint type assembly so as not to require an external frame to hold the walls place. Interfacing between MRI, CT and radiotherapy treatme devices is also made possible using a grid structure with tub containing both paramagnetic and radiopaque contrast material. example would be a grid structure with tubes containing a soluti with sufficient amounts of both Gd-DPTA and Barium sulfate. An alternative to using separate grid structures removable grid structure walls is a means to empty and refill t tubing of the wall of contrast material. Figure 3 illustrates su an embodiment. In this embodiment, the tubes of a wall form interconnected network, the beginning and terminal portions (26, 2 of which fit flush with the edge of the wall. These and portions op to the outside are fitted with a capping means such as a simple pl or screw cap 24. Thus, to empty the tubing network of contra material one removes the cap from the beginning and terminus end the tubing and tips the wall to let the material drain. To refil one tips the wall up and fills at the beginning until the soluti runs out the terminal end. Once refilled, the ends are recapped. The ability to empty and refill the tubes of the gr structure is particularly useful when using the grid structure interface with PET. Imaging with PET is dependent on the emission positrons. The materials which are generally used as positr emitters have only a short half life and are thus prepared short before use. Figure ID illustrates yet another embodiment of the gr structure of the invention. In this embodiment the grid structure is an assembly of hollow tubes 31 joined in a generally rectangul shape with additional hollow tubes as diagonals 32 across four of t faces of said rectangle. The hollow tubes of this embodiment a formed of a non-magnetic material such as a rigid plastic and fill with a solution of contrast material. As indicated above, t contrast material would be selected with regard to the particula imaging modality being used. Further, as illustrated in Figure 3, th corners of the grid structure of the embodiment of Figure ID contai a screwable plug 33 which allows emptying and refilling the hollo tubes (31, 32) such that solutions containing other preferred type of contrast material are readily substituted as the need arises. Figures IB and 1C illustrate other suitable configuration of the grid structure. As will be appreciated, the exac configuration of a grid structure is not important to the essence o the invention. In the same manner, the invention may also be carrie out by using contrast material in solid rather than liquid form. Fo example, contrast material in a defined pattern could be embedded i a matrix of nonmagnetic material or embedded within solid rods or bar that are arranged so as to form a grid. Although the exact configuration of the grid structure i unimportant, as illustrated in Figure 5 the grid structure 11 must b of a size sufficient to fit about the body of the subject 29 bein imaged but within the gantry 27 of the diagnostic imaging machine 2 being used. The second component of the grid system is a means fo reproducibly positioning the grid system relative to the body par being imaged. In the preferred embodiment, this is accomplished b using a grid locating means and a crossed laser system. A illustrated in Figures 6A and 6B, the grid locating means of th preferred embodiment is a patient platform 41 to which the grid 11 i slidably attached such that it may be moved horizontally along th length of said platform and positioned at the appropriate place abou the subject being imaged. Located on the top surface of the platfor and at either side of the grid is a scale in the form of regularl spaced and numbered demarcations. Slidable attachment means attaching the grid structure t the platform may be accomplished by a tongue and groove mechanism, roller and track mechanism or other conventional means. In the presently preferred embodiment Fig. 6A, the platfor consists of an upper member 43 and a lower member 44. The uppe member is sufficiently narrow to pass between the side walls of th grid structure, but sufficiently wide so as not to allow latera movement of the grid structure. As can be seen in Figure 6A, at eac end the members are joined to a spacer 46 such that the upper membe is separated from the lower member by a space sufficient t accommodate the bottom wall 48 of the grid structure. The fit of th bottom wall in this space should be such that sliding of the gri back and forth is accomplished without difficulty but it should no be so great as to allow vertical movement of the grid structure. I is desirable to have sufficient horizontal movement of the gri structure such that it can be moved the entire length of an averag sized subject centered on the platform. Using the above describe construction, the horizontal movement of the grid structure i dictated by the strength and rigidity of the upper member. It i desirable that the upper member support the subject withou deformation so that the grid structure is not pinched and prevente from horizontal movement. Thus, the stronger and more rigid th upper member, the greater the span between the supporting spacers 46 and the greater the horizontal movement of the grid structure. A with the grid structure 11, the platform must be manufactured o nonmagnetic material. Figure 5 illustrates the relationship of the platform 41 t the patient bed 30 of an imaging unit 28. As illustrated in Figure 5 the patient platform 41 approximates the dimensions of the patient be 30 in terms of length and width and rests on top of said patient bed The patient bed for the conventional MRI unit as well as for th conventional CT unit has a generally convex surface 36. The provisio of a patient platform as illustrated in Figure 5 transforms th generally convex surface of the patient bed to a flat surface. Mean may be provided to conform the bottom surface of the patient platfor 41 to the concavity 36 of the patient bed so as to prevent sai patient platform from moving about while it rests on the surface o the patient bed. Commercial patient platforms are available from suc manufacturers as Victoreen Corporation and General Electric Medica Systems. Said commercial patient platforms can be adapted to recei the grid structure as illustrated in Figure 5 and would fall with the scope of the claims of this invention. Figures 7A and 7B illustrate the crossed laser syst which, together with the grid locating means, is used to reproducib position the subject in relation to the grid. As illustrated Figures 7A and 7B, the saggital laser 51 aligns the platform a subject in the X and Z coordinates whereas the transverse laser aligns the subject and platform in the Y and Z coordinates. Cross laser systems are available commercially and can be readily adapt to the use described herein. An example of a commercially availab system is the Patient Positioning Systems from Gammex Inc. METHOD OF USE In Fig. 7A, the patient platform 41 with grid structure is mounted on the patient bed of the imaging unit 28. The patie platform is then aligned via the crossed laser system utilizin sagittal 51 and transverse 52 lasers. The use of a crossed lase technique to align structures in three dimensional space is known i the art. In relation to the present invention, the sagittal an transverse lasers are fixed and define a point in X, Y and coordinates to which the patient platform is related. The sagitta laser defines the X and Z coordinates of the patient platform 41 i relation to the imaging unit table 30, while the transverse lase allows for adjustments in the Y and Z coordinates. By recording th X, Y and Z coordinates of the imaging unit table with respect to som initial point of laser intersection on the table, the location of th patient platform 41 is reproducible from room to room, or from imagin device to imaging device. With the subject 29 for imaging stationed on the patien platform 41, standard body immobilization techniques such as bod casting or pleximolds can be employed. As illustrated in Fig. 7B, th sagittal and transverse lasers are then used to position the subjec with relation to the table and the desired X, Y and Z coordinates Positioning of the subject 29 is accomplished by employing marks o ink tattoos 44 on either the subject or immobilization devices. The grid structure 11 is then positioned so as to flank th region of interest of the subject 29 which is to be imaged. In th preferred embodiment, the location of the grid structure, onc positioned, is indicated by the numbered demarcations 42 provided o each side of the platform. These numbered demarcations are recorded and the table with the grid structure platform and subject is the passed into the gantry 27 of the imaging device 28 and the region o interest is scanned as illustrated in Figures 8A and 8B. When the subject is studied with imaging modalities othe than MRI the appropriate contrast material is selected and the abov described procedure is repeated. For example, if the subject is als to be studied using CT, a grid structure and patient platfor identical but for the contrast material contained within the tubes i mounted on the CT patient bed. In the case of CT, barium or othe radiopaque contrast material is used. The platform is aligned usin the cross laser system as described above; the subject is statione on the platform; the subject is laser aligned and the grid structur is then positioned over the region of interest using the numbere demarcations. Using the above method, the region of interest as studie with MRI is defined in terms of the grid. As the grid pattern and th position of the subject relative to the grid is identical in the C studies as with the MRI studies direct comparison between the studie of the two different modalities can be made in spite of the distortio obtained with MRI. As should be appreciated, the above-described grid syste and procedure can be used to interface MRI with any other imagin modality including PET and Digital Subtraction Angiography. The grid system and procedure also provides a means to mor accurately follow the course of a disease state and to judge th effectiveness of a treatment plan on that disease state. For example if one is treating a tumor with radiotherapy, it is desirable t periodically repeat MRI and CT scans of the tumor in order to monito the treatment. Because of the distortion obtained with MRI, it i difficult to assess minute changes in tumor location and size. Usi the grid system and procedure described above, one avoids the inhere distortion obtained with MRI. Because the system and procedure perm exact repositioning of the subject relative to the grid structu during repeated scans and because the tumor is defined in terms of t grid, small changes in tumor size or location can be monitored. For radiotherapy purposes, using the methods and apparat of the present invention, a tumor defined by MRI (including coron and sagittal sections) may thus be more accurately translated to images (which are by necessity transverse) , with a resulta improvement in target volume determination. In the case of comput enhanced dosimetry, CT imaging cannot be bypassed as it provid important electron density information. In the case of coplan radiation, a tumor may be defined in X, Y and Z coordinates, and simpler connect-the-dot method of target volume determination employed. The accuracy of this can be easily checked at a thera simulator or treatment machine using an array of lead wires inste of the gadolinium chloride or barium sulfate which are well visualiz via MRI and CT respectively. The invention is also adaptable to MR guided needle biopsy, or PET-guided biopsy. METHOD OF USING THE GRID SYSTEM TO CORRECT MRI DISTORTION Although the invention herein described can be used inspi of the distortion caused by magnetic field fluctuations in MRI, it m also be used as a means to correct such distortion. As befo mentioned, the magnetic field fluctuations distort the image of t grid artifact in the same manner as such magnetic field fluctuatio distort the image of the subject. The grid artifacts which can directly related to the known spatial relationship of the grid th act as indices of the degree of distortion present in a particul image. By manipulating the image so as to bring the grid artifac into proper relation to one another, the image distortion of t subject would be simultaneously corrected. Such manipulation can done using conventional mathematical computations which are known the art. As illustrated in Figure 8B, the above described method can b accomplished by using a computer algorithm which applies the require mathematical procedures to remove image distortion. In this manner the computer algorithm means can be incorporated with the software o the MRI to recognize the misalignment of grid artifact 54, manipulat the uncorrected image to bring the grid artifact into proper alignmen and thus produce a corrected image.

Claims: CLAIMS What I claim is: 1. A grid structure for use in making an image of a body pa with MRI and other imaging means, comprising: regularly spaced members containing contrast material; means for fixedly holding said regularly spaced members. 2. A grid structure as claimed in claim 1, wherein sa members comprise hollow tubes. 3. A grid structure as claimed in claim 2, further comprisi a means for emptying and refilling said hollow tubes of contra material. 4. A grid structure as claimed ih claim 1, wherein said gr structure is rectangular in shape and sufficiently large to fit abo said body part being imaged but sufficiently small so as to fit with the gantry of said MRI or said other imaging means. 5. A grid structure as claimed in claim 1, wherein sa contrast material comprises a combination of Gd-DPTA or simil paramagnetic material and barium or similar radiodense material. 6. A grid structure as claimed in claim 5, wherein sa paramagnetic material and said radiodense material is in sufficie amount to cause visualization of said contrast material with X-ra computed tomography and magnetic resonance imaging systems. 7. A grid system for use in making an image of a body pa with MRI and other imaging means, comprising: a means for forming a grid of contrast material; a means for reproducibly positioning said grid means relative said body part such that artifact relative to said contrast materi is produced on said image of said body part by said MRI and said oth imaging means. 8. A grid system as claimed in claim 7, wherein said gri means comprises a grid structure of regularly spaced member containing contrast material and means for fixedly holding sai regularly spaced members. 9. A grid system as claimed in claim 8, wherein said member are hollow tubes. 10. A grid system as claimed in claim 9, further comprising means for emptying and filling said hollow tubes of contrast material 11. A grid system as claimed in claim 10, wherein said gri structure is rectangular in shape and sufficiently large to fit abou said body part being imaged but sufficiently small so as to fit withi the gantry of said MRI or said other imaging means. 12. A grid system as claimed in claim 7, wherein said contras material comprises a combination of Gd-DPTA or similar paramagneti material and barium or similar radiodense material. 13. A grid system as claimed in claim 12, wherein sai paramagnetic material and said radiodense material is in sufficien amount to cause visualization of said contrast material with X-ray computed tomography and magnetic resonance imaging systems. 14. A grid system as claimed in claim 7, wherein sai positioning means comprises: a crossed laser means for reproducibly positioning said bod part; means for locating said grid means about said body part. 15. A grid system as claimed in claim 14, wherein said locatin means comprises: a patient platform; means for slidably attaching said grid means to said patient platform such that when slidably attached to said patient platfor said grid means can be moved horizontally along the length of sai patient platform; means for determining the position of said grid means along t length of said patient platform. 16. A grid system for correcting distortion which occurs whe an image of a body part is produced with a magnetic resonance imagin means, comprising: a means for forming of contrast material a grid of predetermine shape; a means for reproducibly positioning said grid relative to sai body part such that artifact relative to said contrast material i produced on said image of said body part by said imaging means. a means for conforming said artifact essentially to sai predetermined shape of said grid thereby conforming said image of sai body part to the shape of said body part. 17. A method for correcting distortion which occurs when a image of a body part is produced with a magnetic resonance imagin means, comprising: forming a grid structure of predetermined shape from contras material; reproducibly positioning said grid structure relative to sai body part and said imaging means such that artifact relative to sai contrast material is produced on said image of said body part by sai imaging means. conforming said artifact to essentially said predetermined shap of said grid structure thereby conforming said image of said body par to the shape of said body part. 18. A method as claimed in claim 17, wherein said conformin means comprises a computer algorithm. 19. A method for interfacing the image of a body part made wit MRI with the image of said body part made with other imaging means, comprising: forming a grid of contrast material; reproducibly positioning said grid relative to said body part such that artifact relative to said grid is produced on said image of said body part made with MRI; positioning said grid in said reproducible position relative to said body part such that artifact relative to said grid is produced on said image of said body part made with said other imaging means. 20. A method as claimed in claim 19, wherein said grid comprises a grid structure of regularly spaced members containing contrast material and means for fixedly holding said regularly spaced members. 21. A method as claimed in claim 20, wherein said members are hollow tubes. 22. A method as claimed in claim 21, further comprising a means for emptying and filling said hollow tubes of contrast material. 23. A method as claimed in claim 22, wherein said grid structure is rectangular in shape and sufficiently large to fit about said body part being imaged but sufficiently small so as to fit within the gantry of said MRI or said other imaging means. 24. A method as claimed in claim 23, wherein said contrast material comprises a combination of Gd-DPTA or similar paramagnetic material and barium or similar radiodense material. 25. A method as claimed in claim 24, wherein said paramagnetic material and said radiodense material is in sufficient amount to cause visualization of said contrast material with X-ray, computed tomography and magnetic resonance imaging systems. 26. A method as claimed in claim 25, wherein said positionin means comprises: a crossed laser means for reproducibly positioning said bo part; means for locating said grid structure about said body part. 27. A method as claimed in claim 26, wherein said locati means comprises: a patient platform; means for slidably attaching said grid structure to said patie platform such that when slidably attached to said patient platfo said grid structure can be moved horizontally along the length of sa patient platform; means for determining the position of said grid structure alo the length of said patient platform.

Inventors: GIESE WILLIAM L, GIESE, WILLIAM, L.
Applicants: GIESE WILLIAM L, GIESE, WILLIAM, L.
Application year: 1989
Main classification: G01R33
IPC codes: A61B5, A61B6, A61B19, A61N5, G01R33, H05G1