Abstract:
A method for performing Magnetic Resonance Imaging (MRI) guided core biopsies is tendered more accurate and efficient by precisely positioning a disengaged probe assembly with respect to a localization fixture attached to a breast coil platform. The precise position is defined by MRI stereotopic location of suspicious tissue with respect to a fiducial marker on the localization fixture. With the probe inserted, dual lumens in the probe assembly are used for drainage or insertion of fluids as well as inserting diagnostic and therapeutic tools. Core biopsies are performed by engaging a biopsy instrument handle containing a cutter, with the localization fixture providing support and position to the handle. Repeated MRI scans are facilitated by the ability to disengage the handle without risk of displacing the probe assembly from the biopsy site.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application hereby claims the benefit of the provisional patent application of the same title, Ser. No. 60/374,807 filed on Apr. 23, 2002. The present application is related to co-pending and commonly-owned applications filed on even date herewith entitled “LOCALIZATION MECHANISM FOR AN MRI COMPATIBLE BIOPSY DEVICE” to Hibner et al. and “AN MRI COMPATIBLE BIOPSY DEVICE WITH DETACHABLE PROBE” to Hibner et al., the disclosure of both is hereby incorporated by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates, in general to a method of imaging assisted tissue sampling and, more particularly, to an improved method for positioning a biopsy probe with respect to a magnetic resonance imaging (MRI) breast coil for acquiring subcutaneous biopsies and for removing lesions. 
     BACKGROUND OF THE INVENTION 
     The diagnosis and treatment of patients with cancerous tumors, pre-malignant conditions, and other disorders has long been an area of intense investigation. Non-invasive methods for examining tissue are palpation, Thermography, PET, SPECT, Nuclear imaging, X-ray, MRI, CT. and ultrasound imaging. When the physician suspects that tissue may contain cancerous cells, a biopsy may be done either in an open procedure or in a percutaneous procedure. For an open procedure, a scalpel is used by the surgeon to create a large incision in the tissue in order to provide direct viewing and access to the tissue mass of interest. Removal of the entire mass (excisional biopsy) or a part of the mass (incisional biopsy) is done. For a percutaneous biopsy, a needle-like instrument is used through a very small incision to access the tissue mass of interest and to obtain a tissue sample for a later examination and analysis. The advantages of the percutaneous method as compared to the open method are significant: less recovery time for the patient, less pain, less surgical time, lower cost, less risk of injury to adjacent bodily tissues such as nerves, and less disfigurement of the patient&#39;s anatomy. Use of the percutaneous method in combination with artificial imaging devices such as X-ray and ultrasound has resulted in highly reliable diagnoses and treatments. 
     Generally there are two ways to percutaneously obtain a portion of tissue from within the body, by aspiration or by core sampling. Aspiration of the tissue through a fine needle requires the tissue to be fragmented into small enough pieces to be withdrawn in a fluid medium. The method is less intrusive than other known sampling techniques, but one can only examine cells in the liquid (cytology) and not the cells and structure (pathology). In core sampling, a core or fragment of tissue is obtained for histologic examination, genetic tests, which may be done via a frozen or paraffin section. The type of biopsy used depends mainly on various factors present in the patient, and no single procedure is ideal for all cases. However, core biopsies seem to be more widely used by physicians. 
     Recently, core biopsy devices have been combined with imaging technology to better target the lesion. A number of these devices have been commercialized. One such commercially available product is marketed under the trademark name MAMMOTOME™, Ethicon Endo-Surgery, Inc. An embodiment of such a device is described in U.S. Pat. No. 5,526,822 issued to Burbank, et al., on Jun. 18, 1996, and is hereby incorporated herein by reference. 
     As seen from that reference, the instrument is a type of image-guided, percutaneous, coring, breast biopsy instrument. It is vacuum-assisted, and some of the steps for retrieving the tissue samples have been automated. The physician uses this device to capture “actively” (using the vacuum) the tissue prior to severing it from the body. This allows the sampling of tissues of varying hardness. The device can also be used to collect multiple samples in numerous positions about its longitudinal axis, and without removing the device from the body. These features allow for substantial sampling of large lesions and complete removal of small ones. 
     Co-pending application Ser. No. 09/825,899filed on Apr. 2, 1997, which is hereby incorporated herein by reference, described other features and potential improvements to the device including a molded tissue cassette housing permitting the handling and viewing of multiple tissue samples without physical contact by the instrument operator. Another described therein is the interconnection of the housing to the piercing needle using a thumbwheel, to permit the needle to rotate relative to the housing, while preventing the vacuum tube from wrapping about the housing. During use, the thumbwheel is rotated so that the device rotates within the lesion, and samples can be taken at different points within the lesion. 
     In actual clinical use for breast biopsy the instrument (probe and driver assembly) is mounted to the three axis-positioning head of an x-ray imaging machine. The three axis-positioning head is located in the area between the x-ray source and the image plate. The x-ray machines are outfitted with a computerized system which requires two x-ray images of the breast be taken with the x-ray source at two different positions in order for the computer to calculate x, y and z axis location of the suspect abnormality. In order to take the stereo x-ray images the x-ray source must be conveniently movable. The x-ray source therefore is typically mounted to an arm which, at the end opposite the x-ray source, is pivotally mounted to the frame of the machine in the region of the image plate. 
     Recently, there has been a need for a hand held core sampling biopsy device. This need has been fulfilled by Ethicon-Endo Surgery in U.S. Pat. No. 6,086,544 issued on Jul. 11, 2000, which is hereby incorporated herein by reference. This aforementioned patent discloses a hand-held MAMMOTOME™ that may be held approximately parallel to the chest wall of the patient for obtaining tissue portions close to the chest wall and may be manipulated by the operator&#39;s hand. Thus, the operator may steer the tip of the handpiece on the MAMMOTOME™ with great freedom towards the tissue mass of interest. The surgeon has tactile feedback while doing so and can thus ascertains to a significant degree, the density and hardness of the tissue being encountered. In addition, a hand-held MAMMOTOME™ is desirable because the handpiece on the MAMMOTOME™ may be held approximately parallel to the chest wall of the patient for obtaining tissue portions closer to the chest wall than may be obtained when using an instrument that is mounted to an electromechanical arm. 
     Recently, there has been a desire to use the above described biopsy devices with MRI imaging devices instead of x-ray imaging devices. However, existing medical biopsy sampling devices use small, multi-lumen probes extensively fabricated mostly if not entirely from metal. However, the ability to provide accurate minimally invasive diagnosis of suspicious breast lesions hinges on the size of the sample obtained and accuracy in placement of the sampling device. 
     The metallic nature of these probes has many drawbacks. Typically these metal probes are electrically conductive and often magnetically weak, which interferes with their use under MRI guidance. The electrically conductive and magnetically weak nature of metal probes often work to create field distortions, called artifacts, on the image. The image of the lesion will show the metal probe, and this is problematic because the image of the probe can obscure the image of the lesion. 
     The small sample size of conventional biopsy needles also presents a significant limitation due to the increase in the duration of the procedure. Due to the tendency for contrast agent to “wash out” of suspicious lesions, and the progressive increase in enhancement of surrounding non-malignant breast parenchyma, suspicious lesions may become indistinguishable to the breast parenchyma within a few minutes. This limits the number of samples that can be retrieved using conventional spring-loaded core biopsy needles under direct imaging guidance. 
     A further problem not infrequently encountered during core needle biopsy is the development of a hematoma at the biopsy site during the procedure. An accumulating hematoma can be problematic during MRI-guided biopsy because residual contrast agent circulating in the hematoma can mimic enhancement in a suspicious lesion. In addition, the accumulation of air at the biopsy site can cause susceptibility artifacts that can potentially interfere with the fat-suppression MRI techniques at the biopsy site cavity. 
     These limitations of conventional biopsy needles have led several authors to conclude that lesions should be at least 1 cm in diameter before imaging could confirm that the MRI-guided biopsy device was definitely within (as opposed to adjacent to) the suspicious target. However, the demand for minimally invasive MRI-guided core biopsy is greatest for small lesions because they are more common, more difficult to characterize on MRI grounds alone, and have the best prognosis if they are found to be malignant. 
     Therefore, there has been a desire to have generally non-metallic (especially non-ferromagnetic) biopsy probe of the type described above to eliminate artifacts. These needs have been filled by co-pending and commonly-owned application Ser. No. 10/021,680, “AN MRI COMPATIBLE SURGICAL BIOPSY DEVICE” to Huitema et al filed on Dec. 12, 2001, the disclosure of which is hereby incorporated by reference in its entirety. The lack of undesirable artifacts for the disclosed hand-held biopsy device allows the accurate placement of the probe. Moreover, disclosed vacuum assist allows visualization of the lesion entering a bowl of the probe to confirm accurate placement, as well as avoiding problems associated with a hematoma or an air cavity. Moreover, the volume and ability to rapidly rotate the open cutting bowl of the probe allows for multiple samples in succession without removal of the probe. Thereby, the duration of the procedure is reduced. 
     However, elimination of the artifact created by the metal probe entirely is also problematic because physicians rely extensively on some type of artifact to notify them as to where the tip of the probe is relative to the lesion. These needs have been filled by co-pending and commonly-owned application Ser. No. 10/021,407, entitled “AN MRI COMPATIBLE BIOPSY DEVICE HAVING A TIP WHICH LEAVES AN ARTIFACT” to Rhad et al., filed on Dec. 12, 2001, the disclosure of which is hereby incorporated by reference in their entirety. Having a target in the cutter at the distal end of the probe helps avoid advancing the probe through the chest cavity as well as accurately placing the bowl of the probe adjacent to the suspicious tissue for drawing into the cutting bowl. 
     While the aforementioned hand-held MRI compatible biopsy devices provide many advantages, opportunities exist for improvements and additional clinical functionality. For instance, the hand-held biopsy device presents a long, external handle that is inappropriate for closed magnet MRI machines. Furthermore, while the hand-held biopsy device allows great freedom in lateral and angular orientation, in some instances it is preferable to specifically position the biopsy probe. The MRI machine may provide very accurate stereotactic placement information that is only partially utilized in inserting the probe. In particular, the hand-held biopsy device is inserted through an opening in a compression plate, so some two-dimensional alignment is provided. However, the angle and depth of insertion the probe tends to vary, especially without continual reimaging of the probe during insertion, which is particularly inappropriate for closed MRI magnets. 
     Furthermore, the vacuum assist reduces occurrence of a hematoma and draws in tissue to increase the sample size without repositioning the probe; however, current clinical procedures often require additional invasive procedures to the biopsy site to administer anesthesia or to perform additional diagnostic or treatment procedures. 
     Consequently, a significant need exists for a method of performing MRI-guided biopsy that is applicable to both open and closed MRI machines, especially a method that allows a range of diagnostic and therapeutic operations at the biopsy site with a minimum of invasive procedures. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention overcomes the above-noted and other deficiencies of the prior art by providing a method whereby a core biopsy is accurately and efficiently performed even with only intermittent Magnetic Resonance Imaging (MRI) scans. The stereotopically derived coordinates of the suspicious tissue are used by a surgeon to position alignment positioning guides on a localization mechanism that guide a core biopsy tool. Thereby, even closed MRI machines may be used since constant monitoring of the position of the core biopsy tool during insertion by MRI guidance is not required. 
     In one aspect of the invention, a method of MRI guided core biopsy of suspicious breast tissue of a patient&#39;s breast includes localizing the patient&#39;s breast in the localization fixture, attaching a probe assembly to the probe assembly guide, positioning the probe assembly guide for a desired spatial coordinate, inserting the probe assembly using the probe assembly guide to a desired biopsy site, and engaging a biopsy instrument handle to the probe assembly. The biopsy instrument handle includes a cutter that translates within the probe assembly to perform the core biopsy. 
     In another aspect of the invention, a method of MRI guided core biopsy of suspicious breast tissue is enhanced with a fiducial marker that is coupled to the localization mechanism. Thereby, stereotopic coordinates for suspicious tissue are readily and accurately made with respect to the localization mechanism. Since the localization mechanism also positions and guides the core biopsy tool, increased accuracy is achievable. 
     In yet another aspect of the invention, a method of diagnostic imaging guided biopsy includes positioning a probe at a specified spatial coordinate on a compression plate of a localization fixture, thereby accurately specifying the insertion point for the probe. Thereafter constraining movement of the probe along an insertion angle for a specified distance to the desired biopsy location. Maintaining the insertion angle avoids the need to active image the probe during insertion to avoid an error due to the angle of insertion of under or over travel during insertion. 
     These and other objects and advantages of the present invention shall be made apparent from the accompanying drawings and the description thereof. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is plan view of the biopsy instrument, mounting fixture, an Magnetic Resonance Imaging (MRI) breast coil fixture, and patient support table in working relationship outside the confines of an MRI machine. 
         FIG. 2  is a plan view of the biopsy instrument, localization fixture, partially cut away MRI breast coil fixture, patient support table, and in working relationship and configured for insertion into a MRI machine. 
         FIG. 3  is a plan view of the localization fixture, partially cut away MRI breast coil fixture, patient support table, and a detached probe assembly of the biopsy instrument mounted to the localization fixture, in working relationship and configured for insertion into the MRI machine. 
         FIG. 4  is an isometric view of the biopsy instrument disassembled into a biopsy instrument handle, probe housing, and probe. 
         FIG. 4A  is a frontal isometric detail view of an alternative needle tip of a biopsy instrument. 
         FIG. 5  is an exploded isometric view of the biopsy instrument handle. 
         FIG. 6  is an exploded isometric view of the probe of the biopsy instrument of  FIG. 4 . 
         FIG. 7  is a transverse cross section of the probe of the biopsy instrument of  FIG. 4  along lines  7 - 7 . 
         FIG. 8  is an enlarged isometric view of the interface between the handle and probe housing illustrating the visual confirmation elements that indicate the position of the distal end of the cutter. 
         FIG. 9  is a fragmentary plan view in partial section of the distal portion of the handle and probe housing and assembly, illustrating the disconnect feature with the cutter retracted. 
         FIG. 10  is a fragmentary plan view in partial section of the distal portion of the handle and probe housing and assembly, illustrating the tolerance take-out feature and the disabled disconnect feature when the cutter is advanced. 
         FIG. 11  is an isometric view of the biopsy instrument with the handle portion disconnected from a tower/bracket localization fixture and probe assembly. 
         FIG. 12  is an isometric view of the biopsy instrument mounted to the tower/bracket localization fixture of  FIG. 11 . 
         FIG. 13  is an exploded isometric view of the tower/bracket localization version of the localization fixture and probe assembly of the biopsy instrument. 
         FIG. 14  is a side elevation view of the biopsy instrument in partial section to illustrate a tower/bracket support for stabilizing the handle and probe assembly of the biopsy instrument. 
         FIG. 15  is a side elevation view of the dual tower support version of the localization fixture positioning a detachable probe assembly with its dual lumens closed by a vacuum conduit and an obturator stylet. 
         FIG. 16  is an isometric view of the biopsy instrument mounted to a dual tower localization fixture. 
         FIG. 17  is an isometric view of the slide plate of a localization fixture guiding a scissors support in a lowered position for vertically orienting a biopsy instrument. 
         FIG. 18  is an isometric view of the slide plate of a localization fixture guiding the scissors support in a raised position for vertically orienting a biopsy instrument. 
         FIG. 19  is a sequence of clinical operations for using the detachable MRI-guided biopsy instrument of  FIG. 1  in both open and closed MRI machines. 
         FIG. 20  is an isometric view of a tip protector mounted onto a needle tip of the detachable probe assembly of  FIG. 11 . 
         FIG. 21  is an isometric detail view of the trip protector of  FIG. 20 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  depicts a core biopsy instrument system  10  that is vacuum assisted, detachable, and compatible with use in a Magnetic Resonance Imaging (MRI) machine, such as the depicted closed MRI machine  12 . In the illustrative embodiment, the core biopsy instrument system  10  includes an MRI-compatible biopsy tool  14  that is selectably attached to a localization mechanism or fixture  16  to accurately and rapidly perform core biopsies of breast tissue with a minimum of insertions of a biopsy probe. A control module (not shown) senses encoder position signal and switch signals from the biopsy tool  14  and provides mechanical and vacuum power to the biopsy tool  14  via power cord  18 . 
     With reference to  FIGS. 1-2 , a patient  20  is lying prone upon a patient support table  22 , depicted in  FIG. 1  as removed from a magnet bore  24  of the MRI machine  12 . The patient&#39;s chest rests upon a top surface  26  of a chest support  28 , the top surface  26  having openings  30 ,  32  for allowing the patient&#39;s breasts to hang downward for imaging and treatment. With particular reference to  FIG. 2 , the right opening  30  is depicted with the localizer fixture  16  laterally positioned to cooperate with a medial compression plate (not shown) to longitudinally fix and compress the patient&#39;s right breast. Antenna elements (not shown) are placed about the opening  30  to detect radio frequency (RF) signals emanated from breast tissue induced by a strong magnetic field from the MRI bore  24 . The chest support  28 , localization fixture  16 , and antennas are, collectively, generally termed a breast coil  34 . 
     The biopsy tool  14  includes a biopsy handle  36  that is attachable to a probe assembly  38 . The localization fixture  16  accurately positions the probe assembly  38  for stereotactic mammography biopsy procedures for a specific biopsy site location for a distal tip  40  of the probe assembly  38 . This location is identified by an X-axis coordinate that is horizontal and longitudinal with respect to the patient (up and down in  FIGS. 2 and 3 ). A Z-axis is defined as the vertical height, with the X and Z axis orthogonally defined on a lateral compression plate  42  of the localization fixture  16 , the lateral compression plate  42  cooperating with the medial compression plate (not shown) to fix and compress the patient&#39;s breast. This location is also defined in terms of depth of insertion, or Y-axis, which is horizontal and transverse with respect to the patient (right to left in  FIGS. 2 and 3 ). A probe assembly mounting device  150  connects to a probe housing  46  of the biopsy tool  14 . 
     The mounting device  150  includes alignment positioning guides (described in more detail below) to orient the probe housing  46 , and hence the probe assembly  38 , to the desired X-Y-Z coordinate. For instance, a depth slide  48  allows mounting of the probe assembly  38  with the distal tip  40  extending outside of the opening  30  and lateral compression plate  42 . Thereafter, the probe assembly  38  is guided along the Y-axis by the depth slide  48  while maintaining the selected X-Z-axes coordinates. In addition, the mounting device  150  advantageously supports the biopsy handle  36  when attached to the probe assembly  38  as depicted in  FIG. 2  to maintain the angle of insertion of the probe assembly  38 . The probe housing  46  provides access to the interior of the probe assembly  38  via a vacuum lumen access conduit  50  for draining fluids, inserting fluids such as anesthetics. 
       FIG. 3  depicts the core biopsy instrument system  10  with the biopsy handle  36  removed and the depth slide  48  moved inward to allow insertion of the patient support table  22  into the narrow confines of the MRI magnet bore  24 . Moreover, the surgeon may take full advantage of the stereotactic coordinates provided by the MRI machine  12 , even if using a closed magnetic bore  24 . In particular, the stereotactic derived coordinates may be used even if not actively imaging the probe assembly  38  during insertion. The localization fixture  16  enables the surgeon to manually insert the probe assembly  38  in depth with an indication of current depth. The surgeon is given tactile feedback while doing so and can thus ascertain to a significant degree the density and hardness of tissue being encountered. In addition, with the probe assembly  38  maintained in the correct location after insertion, the probe assembly  38  provides access for other diagnostic and therapeutic tools and fluid treatments. 
     Alternatively or in addition, a depth adjustment mechanism may be incorporated into the localization fixture  16  to provide mechanical advantage, thereby achieving a controlled and deliberate insertion of the probe assembly  38 . Moreover, the depth adjustment mechanism may incorporate a frictional, ratcheting or locking feature to prevent inadvertent movement of the probe assembly  38  after placement at the desired biopsy location. Examples of such depth adjustment include but are not limited to a thumb wheel in geared communication between the probe assembly mounting device  150  and the localizer support frame  126 . 
       FIG. 4  depicts the biopsy tool  14  with the biopsy handle  36  depicted as readily attached to the probe housing  46 , which in turn is readily attached to the probe assembly  38 . The probe assembly  38  includes a male cylindrical mating portion  52  presenting a central cutter opening  54  on a proximal end that is aligned with the longitudinal length of a cutter lumen  56  of an elongated needle  58 . The cutter lumen  56  communicates with a sample port  60  laterally presented near a needle tip  62  at the distal end of the needle  58 . The needle tip  62  is for penetrating the soft tissue of a surgical patient. The needle tip  62  is sharpened and is preferably made from an MRI compatible resin such as ULTEM or VECTRA. In the illustrative embodiment, the needle tip  62  is a three-sided pyramidal shaped point, although the needle tip  62  configuration may also have other shapes and/or inserts. In addition, as in the aforementioned application Ser. No. 10/021,407, entitled “AN MRI COMPATIBLE BIOPSY DEVICE HAVING A TIP WHICH LEAVES AN ARTIFACT”, the illustrative embodiment advantageously includes a material that leaves a small, but not troublesome artifact on an MRI scan. 
     Referring back to  FIG. 4 , it will be appreciated that a cutter element or an obturator stylet is advanced inside the cutter lumen  56  to block the sample port  60  during insertion. Once the needle  58  is positioned, the sample port  60  is exposed to allow tissue to enter. In particular, a vacuum may be presented to a “sample bowl” inside the cutter lumen  56  near the sample port  60  by applying vacuum power through a vacuum chamber lumen  64  that communicates along the longitudinal length of the needle  58  to the male cylindrical mating portion  52 . In particular, a series of small holes allow gas and fluid to enter the vacuum chamber lumen  64  from the sample port  60  but prevent tissue samples from entering. 
     Annular rings  66  about the cylindrical mating portion  52  grip and seal to an interior of a female cylindrical mating portion  68  on the probe housing  46 . Between annular rings  66 , a proximal vacuum port (not shown in  FIG. 4 ) communicates with a vacuum passage (not shown) in the probe housing  46 . The engagement between the mating portions  52 ,  68  advantageously allows rotation of the needle  58  with a thumb wheel  70  annularly presented near the proximal end of the needle  58 . The radial opening presented by the annular rings  66  maintains communication between the vacuum passage in the probe housing  46  and the vacuum chamber lumen  64  regardless of radial orientation of the needle  58 . Thereby, the sample port  60  may be presented to tissue at any and all radial positions about the distal end of the needle  58 . With the assistance of vacuum, a large volume of tissue may be selectably drawn into the sample bowl for biopsy sampling. 
     The probe housing  46  includes laterally presented attachment prongs  72  for mounting to the localization fixture  16 . In addition, the probe housing  46  presents a proximally directed cuboidal engagement member  74  with longitudinally aligned vertical and horizontal grooves  76  for flanges  78  from the biopsy handle  36 . Referring to  FIGS. 9 and 10 , the probe housing  46  also receives hooked locking tabs  80 ,  82  on the distal engaging end of the biopsy handle  36  for selective locking and unlocking under the influence of a pair of opposing depression grips  84 ,  86  attached to respective tabs  80 ,  82 . The biopsy handle  36  includes a sample window  88  for extracting any tissue sample withdrawn from the cutter lumen  52  under the influence of a vacuum passing through the cutter, as described in more detail below. 
       FIG. 5  depicts a disassembled biopsy handle  36  that contains the means for translating and rotating a cutter  90  within the cutter lumen  56 . It will be appreciated that two rotating mechanical power sources are presented to the proximal end of the biopsy handle  36  through the power cord  18  to provide the independent translation and rotation motions. These two rotating mechanical power sources enter through a cord opening  92  defined between a removable shell  94  and a bottom shell  96 , the two held together by screws. The removable shell  94  is removed when assembling a power cord  18  to the handle  36 . A lower gear housing  98  is supported upon the bottom shell  96  and cooperates with a top shell  100  to constrain movement of an elongate drive screw  102 , an elongate axial screw  104  and cutter carriage  106 . In particular, both screws  102 ,  104  are allowed to rotate, positioned parallel to one another and the longitudinal axis of the cutter lumen  56 . Each screw  102 ,  104  is driven by a respective power source from the power cord  18 . The drive screw  102  passes through the carriage  106  and interacts with corresponding ridges therein to impart a longitudinal translation corresponding to the direction and rate of rotation of the drive screw  102 . 
     In some applications, a single rotary power source may be used as an alternative to two independent rotating mechanical power sources. A transmission mechanism at the biopsy handle  36  may convert the single rotary power source into the two motions, translation and rotation. As yet another alternative, the single rotary power source may directly supply both a translation and rotary motion. Such a translating and rotating power cable would be coupled to the cutter  90  to directly control its movement. 
     The cutter  90  is an elongate tube with a sharpened distal end for cutting tissue presented within the distal end of the cutter lumen  56 . The proximal end of the cutter  90  includes a cutter gear  108  that is exposed through a gear window  110  of the carriage  106  to mesh with the axial screw  104  for axial rotation of the cutter  90 . A tissue remover  111  is a tube that is fixedly aligned with the longitudinal axis to enter the proximal end of the cutter  90 . The tissue remover  111  extends up to the sample window  88  and has a vacuum selectably applied to it by the control module. Thus, when the cutter  90  is retracted, vacuum from the tissue remover  111  draws the sample to the distal end of the cutter  90  for retraction to the sample window  88 , whereupon the sample encounters the tissue remover  111  and is dislodged for exiting the biopsy tool  14 . 
     The carriage  106  includes distally projected guides  112 ,  114  that advantageously take-out slack between biopsy handle  36  and the probe housing  46 , as well as providing indicia to the surgeon as to the depth of translation of the cutter  90 . Taking out slack between the assembled parts of the handle  36  and housing  46  advantageously minimizes the deadzone length of the distal end of the needle  58 . The cutter  90  should completely translate past the sample port  60  in order to reliably cut a sample. To ensure a full cut, the cutter  90  should translate the maximum distance expected for the assembly. If variation exists in manufacturing tolerances between the engagement components, then a further distance has to be included in the cutter lumen  56  distal to the sample port  60  to accommodate the over-travel. Thereby, the needle tip  62  must be advanced farther than desirable in some instances, preventing placement of the sample port  60  near critical body tissues. At or near full travel, the guides  112 ,  114  contact the probe housing  46 , causing movement of the housing  46  to its maximum, distal position. Thus, critical dimensioning to minimize tolerance build-up is simplified. 
       FIG. 5  also depicts a brace  116  and brace arm  118  that are employed in one version of the localization fixture  16  to support the weight and maintain the alignment of the handle  36 . Thereby, flexure of the assembly is avoided that may place a load on the probe assembly  38 , and thus unwanted movement of the needle  58  from the desired biopsy site location. 
       FIGS. 6-7  depict the needle  58  of  FIG. 4  and described more fully in the aforementioned application Ser. No. 10/021,680, entitled “AN MRI COMPATIBLE SURGICAL BIOPSY DEVICE”. In particular, elongated needle  58  is formed from a left body member  120  and a right body member  121  on either side of the longitudinal axis. The edges of the halves  120  and  121  are gated for easy part filling, and the edges are stepped with ridges that allow the two halves  120  and  121  to attach together with ease. The two halves  120 ,  121  are adhesively attached to one another. A cutter tube liner  122  is inserted between the two halves  120 ,  121  to provide a smooth surface for the cutter  90 , especially by preventing adhesive from entering the cutter lumen  56  during assembly. 
       FIG. 8  shows an enlarged view of the engagement of the handle  36  to the probe housing  46 , with the advanced cutter  90  evident through the window  88 . In addition, the guides  112 ,  114  are advanced almost into contact with the probe housing  46 , indicating that the distal end of the cutter  90  is approaching its furthest translation. The guides  112 ,  114  contact the probe housing  46  when at or near this extreme to take-out any tolerance. Indicia on the side of the guides  112 ,  114  may be referenced by the surgeon to determine the position of the cutter. Also shown in more detail is hooked locking tabs  80 ,  82  entering the probe housing  46 , the thumb wheel  70  used to rotate the needle  58 , and the vacuum lumen access conduit  50  used to evacuate or otherwise access the vacuum lumen  64 . 
       FIGS. 8-10  show that each grip  84 ,  86  includes a respective inwardly projecting member  124 ,  125  that contact the guides  112 ,  114  when the cutter  90  is distally advanced, thereby preventing removal of the handle  36 . In  FIG. 9 , the cutter  90  is retracted, allowed the depression of the grips  84 ,  86 , unlocking the hooked locking tabs  80 ,  82  from the probe housing  46 . In  FIG. 10 , cutter carriage  106  is advanced, the guides  112 ,  114  are contacting the probe housing  46 , thereby removing any longitudinal gap between the hooked locking tabs  80 ,  86  and the probe housing  46 . 
       FIGS. 11-14  depicts a localization fixture  16  that includes means for accurately positioning the probe assembly  38  and supporting the biopsy handle  36 . In particular, a localizer support frame  126  is formed from the compression plate  42  in a hinged, orthogonal relation to a horizontal slide plate  128 , both laterally attached to one another by gussets  130 ,  132 . Rods  134 ,  136  horizontally pass through the compression plate to adjustably attach to the medial compression plate (not shown) for compressing the patient&#39;s breast. Apertures, depicted as parallel rows of slots  138 , in the compression plate  42  are provided to obtain access to a desired biopsy site location while providing enough remaining structure in the compression plate  42  for adequate contact with the patient&#39;s breast. Alternatively, the apertures may be a series of holes aligned both vertically and horizontally, parallel columns of slots, or a large opening of other shapes. As yet a further alternative, portions of the compression plate  42  may be permeable to allow an aperture to be formed as needed. 
     The desired biopsy site location is stereotopically determined during an MRI scan with reference to a fiducial marker  140  that presents a small artifact. The fiducial marker  140  is contained within a fiducial marker holder  142  that may be placed at a convenient location on the compression plate  42 , accurately placed with reference to indents spaced along the slots  138 . Alternatively, the fiducial marker may be embedded or affixed to the compression plate  42 . 
     The localizer support frame  126  defines and provides the guide for positioning the probe assembly  38 . The X-Y-Z axes are defined with regard to the slots  138  and compression plate  42 . In particular, the vertical dimension, or Z-axis, and horizontal dimension, or X-axis, are defined by the surface of the compression plate  42 . The depth dimension, or Y-axis, is defined as distance away from the plane of the compression plate  42 . The horizontal slide plate  128  includes laterally aligned front and back rails  144 ,  146  for setting the X-axis coordinate. Horizontal indicia  148  along the front rail  144  give the surgeon an accurate measurement of the position of a probe assembly mounting device  150 . 
     A first version of the mounting device  150  is depicted that uses a single vertical pedestal  152  to position and support the probe assembly  38 . In addition, the biopsy handle  36  is supported by a brace  116 , which is connected to the proximal underside of the handle  36  and to a handle support rod  156  that is slid through a rod hole  158  at the corresponding side of the vertical pedestal  152 . The appropriate height for the brace  116  is determined by selecting one of a range of slots arrayed along the underside of the handle, thereby pivoting the brace  116  about a brace arm  118  whose first end slidably pivots within a slot  162  in the middle of the brace  116  and second end attaches to the distal end of the handle  36 . 
     With the handle  36  detached from the probe assembly  38  as depicted in  FIG. 11 , an obturator stylet  164  is slid into the cutter lumen  56  to close the cutter port  88 . The stylet  164  may have radially-oriented through holes near its distal end to maintain fluid communication between the vacuum lumen chamber  64  and cutter lumen  56 . Alternatively, the stylet  164  may be partially withdrawn, allowing the cutter port  88  to be in fluid communication with the conduit  50 . 
     A slide  166  includes a grooved underside to horizontally slide on rails  144 ,  146  of the slide plate  128 . The slide  166  also includes a central channel  168  oriented in the Y-axis depth dimension to guide the pedestal  152  as it slides in the Y-axis direction. Sufficient range of motion in depth is achieved with a pivoting depth slide  170 , aligned and pivotally attached to the slide  166 . With the pivoting depth slide  170  in its lowest, horizontal position, the pedestal  152  may be slid outward sufficiently for the probe assembly  38  to be out of the compression plate  42 . With the pedestal  152  distally slid onto the slide  166 , the pivoting depth slide  170  may be pivoted upward or otherwise removed. Depth indicia  172  along the central channel  168  give the surgeon an indication of the insertion depth of the probe assembly  38 . 
     A vertical slide  174  slides on the pedestal  152  for vertical positioning along the Z-axis, with a measurement provided by vertical indicia  176  on the pedestal  152 . Holes  178  on each lateral side of the vertical slide  174  allow mounting of the probe housing  46  on either side by insertion of attachment probes  72 . 
       FIGS. 15-16  depict a second version of the mounting device  150  that uses a second vertical pedestal  180  in lieu of a brace assembly to support the handle  36 . The probe housing  46  is also depicted as attached to the opposite side of the first vertical pedestal  152 . A second vertical slide  181  of the second vertical pedestal  180  contacts the first vertical slide  174 , as shown in  FIG. 16 , so that setting the vertical height for both is accomplished in one step. Each vertical slide  174 ,  181  moves in a ratchet fashion against its respective vertical pedestal  152 ,  180 , and thus remains in position after being separated from one another as shown in  FIG. 15 . Moreover, the close nesting of the two vertical pedestals  152 ,  180  enhances the ability to minimize the proximal displacement of the localization fixture  16  when used within the close confines of a closed MRI magnetic bore  24 . It will be further appreciated that the second vertical slide  181  includes a shaped area that engages the underside of the handle  36  in such a way as to correctly align the handle  36  at the same X-axis horizontal dimension as the probe assembly  38 . 
       FIGS. 17-18  depict a third version of the mounting device  150  wherein the slide  166  and pedestal  152  are replaced with a scissors table assembly  182  that includes a first slide  184  for horizontal movement on a slide plate  128  and a second slide  186  for vertical movement relative to the slide plate  128 . Similar to the slide  166  of  FIGS. 11 and 13  having the central channel  168 , the second slide  186  of  FIGS. 17-18  has a top channel  188 . With particular reference to  FIG. 18 , a pair of scissors braces  190  are extended when drawn together with a screw  192 , thereby elevating the second slide  186  with respect to the first slide  184 . It will be appreciated that the third version of the mounting device  150  advantageously provides a level support for both the detachable probe assembly  38  as well as the biopsy handle  36  without having to perform two vertical adjustments, as well as not having to perform two separate attachments for each of the handle  36  and probe assembly  38 . 
       FIG. 19  depicts a sequence of operations, or method  200 , for performing an MRI-guided breast core biopsy that accurately and quickly performs a core biopsy even in a closed MRI. Moreover, the method takes full advantage of the stereotopic location information rendered from the MRI scan to position an MRI compatible core biopsy probe without the necessity of continuous imaging of the distal tip of the biopsy probe. 
     Prior to performing a clinical breast biopsy, the equipment is initialized to ensure proper function. Thus, in block  202 , the probe that comprises a needle, thumb wheel and housing is assembled with the handle. The assembled biopsy tool is connected via a power cord to a control module and the system is powered up, initiating power up logic in the control module (block  204 ). Parameters for rotation speed and translation distances are loaded. If the control module determines that the system has not been powered up recently, such as 60 minutes, then initialization logic is performed. Thus, translational drivetrain initialization is performed (block  206 ); rotational drivetrain initialization is performed (block  208 ); and vacuum system initialization is performed (block  210 ). If initialization is not required, then blocks  206 - 210  are bypassed. 
     Then, the patient&#39;s breast is immobilized in the localization mechanism (block  212 ) and the patient is moved into the MRI magnet bore (block  214 ). An MRI scan is performed to stereotopically locate suspicious tissue with reference to a movable fiducial marker on the localization mechanism (block  216 ). For a closed MRI magnet bore, the patient is then removed (block  218 ), which is not necessary for an open bore. Anesthesia is administered prior to the minimally invasive vacuum assisted core biopsy procedure (block  220 ). Using the X-Y-Z positioning capabilities of the localization mechanism, the positioning guides on the localization mechanism are positioned for insertion to the predetermined biopsy site (block  222 ). 
     Optionally, insertion may be enhanced by use of an insertion tool installed through the probe assembly  38  (block  224 ). For instance, an ultrasonic cutting tip, extender, and outer tube assembly may be inserted through the probe assembly  38  through a slot in the needle tip  62 , or exiting from the sample port  60  to be snapped onto the needle tip  62 . This could be accomplished with a housing on the ultrasonic device that is configured to snap onto the needle  58 , similarly to how a trocar obturator snaps onto the trocar cannula. Then, the ultrasonic tip is energized prior to insertion into the patient. 
     The probe assembly is mounted on the localization mechanism (block  226 ) at the designated X-Z coordinate and with the mounting device withdrawn along the depth axis. The cutter lumen is sealed with an obturator stylet (block  228 ), if not otherwise sealed by a tool in block  224 . The vacuum lumen may be similarly sealed (e.g., stopcock attached to vacuum lumen access conduit  50 ) or be used to aspirate fluid and tissue during insertion. Then the probe is advanced along the Y-axis, guided by the localization mechanism to avoid misalignment (block  230 ). Once in place, if an insertion enhancement tool was installed in block  224 , then this tool is withdrawn through the cutter lumen of the probe assembly (block  232 ). 
     With the probe in place, various fluid transfers may advantageously take place through the probe assembly (block  234 ). For example, vacuum may be applied through the vacuum lumen with the sample port exposed to drain any hematoma or air bubble formed at the biopsy site. Treatment fluids may be inserted directly to the biopsy site, such as anesthesia or MRI contrast agent. If the patient is to be scanned in a closed magnet bore, then the patient is moved back into the bore for scanning (block  236 ). In addition, vacuum may optionally be applied to the biopsy site to draw in suspicious tissue into the bowl of the sample port for confirmation prior to cutting the sample (block  238 ). Then, the MRI scan is performed to confirm placement of tissue in the bowl of the probe assembly, and adjustment of the probe assembly placement and re-scans are performed as required (block  240 ). 
     Sample mode is selected through the control module to perform the sequence of steps to translate and rotate the cutter according to predetermined settings, with vacuum assist to draw in the sample and to retract the sample along with the cutter to the sample window (block  244 ). If more samples at this biopsy site are required for diagnostic or for treatment purposes (block  246 ), then the thumb wheel is rotated to reorient the sample port to another angle (block  248 ), and sample mode is performed again by returning to block  244 . 
     After the core biopsy is performed, the probe assembly provides an excellent opportunity for other minimally invasive diagnostic procedures and treatments without the necessity for another insertion. If the biopsy handle is installed, such as in an open MRI magnet bore, the handle is removed so that the detachable probe assembly may be accessed (block  250 ). Examples of tools that may be inserted through the probe assembly include: (1) gamma detectors; (2) energized tunneling tips to reduce tunneling forces; (3) inserts to aid in reconstruction of removed tissue (e.g., one or two sided shaver inserts); (4) spectroscopy imaging devices; (5) general tissue characterization sensors {e.g., (a) mammography; (b) ultrasound, sonography, contrast agents, power Doppler; (c) PET and FDG ([Flourine-18]-2-deoxy-2-fluoro-glucose); (d) MRI or NMR, breast coil; (e) mechanical impedance or elastic modulus; (f) electrical impedance; (g) optical spectroscopy, raman spectroscopy, phase, polarization, wavelength/frequency, reflectance; (h) laser-induced fluorescence or auto-fluorescence; (i) radiation emission/detection, radioactive seed implantation; (j) flow cytometry; (k) genomics, PCR (polymerase chain reaction)-brca1, brca2; (l) proteomics, protein pathway}; (6) tissue marker sensing device; (7) inserts or devices for MRI enhancement; (8) biochips on-a-stick; (9) endoscope; (10) diagnostic pharmaceutical agents delivery devices; (11) therapeutic anti-cancer pharmaceutical agents delivery devices; (12) radiation therapy delivery devices, radiation seeds; (13) anti-seeding agents for therapeutic biopsies to block the release of growth factors and/or cytokines (e.g., chlorpheniramine (CPA) is a protein that has been found to reduce proliferation of seeded cancer sells by 75% in cell cultures.); (14) fluorescent tagged antibodies, and a couple fiber optics to stimulate fluorescence from a laser source and to detect fluorescence signals for detecting remaining cancer cells; (15) positive pressure source to supply fluid to the cavity to aid with ultrasound visualization or to inflate the cavity to under the shape or to reduce bleeding; (16) biological tagging delivery devices (e.g., (a) functional imaging of cellular proliferation, neovacularity, mitochondrial density, glucose metabolism; (b) immunohistochemistry of estrogen receptor, her2neu; (c) genomics, PCR (polymerase chain reaction)-brca1, brca2; (d) proteomics, protein pathway); and (17) marking clips. 
     Then, a tissue marker is inserted through the probe assembly so that subsequent ultrasonic, X-ray, or MRI scans will identify the location of the previous biopsy (block  252 ) and the probe is removed (block  254 ). 
       FIGS. 20-21  depict a tip protector  260  that advantageously protects the needle tip  62  of the probe assembly  38  prior to insertion into tissue and simplifies localization of the probe assembly  38  in some instances. Furthermore, the tip protector  260  does not interfere with pre-clinical setup procedures (e.g., testing for vacuum leaks). In particular, the tip protector  260  includes an attachment member  262  with clips onto the needle  58  without obstructing the sample port  60 . A distal portion of the tip protector completely encompasses the needle tip  62  with a protection member, depicted as a hemispheric disk  264 , that may be placed in contact with a patient&#39;s breast without discomfort. In addition, in some applications the hemispheric disk  264  may be comprised of or include an MRI artifact producing material, such as those described above. Since the hemispheric disk  264  is MRI scanned outside of the patient&#39;s breast, a stronger artifact may be presented to aid in quickly locating the artifact without obscuring the suspected lesion. 
     With a novel fiducial marker integrated into the tip protector  260 , there is potentially one less step in the localization process for operators that prefer to position fiducial marker at the closest insertion point to a suspected lesion prior to insertion. Procedurally, with the tip protector  260  in place, the operator would attach the probe assembly  38  onto the pedestal  152  and move the probe assembly  38  up against the breast tissue in the vicinity of where they believe the suspicious tissue to be, based on an earlier diagnostic image. Next, when the distance from this fiducial marker to the lesion is calculated, the “delta” distances are based on where the probe is currently positioned. There is a fixed offset along the Y axis to account for the distance from the fiducial to the middle of the bowl. The attachment member  262  accurately locates the hemispheric disk  264  so that this Y-axis offset is predictable. This would be more intuitive because the delta positions are from where the probe is currently located. 
     While the present invention has been illustrated by description of several embodiments and while the illustrative embodiments have been described in considerable detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications may readily appear to those skilled in the art. For example, although the detachable probe assembly provided numerous benefits, it will be appreciated aspects of the present invention may be directed to a single piece biopsy tool. For example, access to the cutter lumen for diagnostic and therapeutic tools may be incorporated through the cutter or similar openings. 
     For another example, although a localization mechanism  16  is depicted that laterally compresses a downward hanging patient&#39;s breast, aspects of the present invention are applicable to other orientations of localization and imaging. 
     As an additional example, although MRI is discussed herein as the imaging modality for stereotopically guiding the core biopsy, aspects of the present invention apply to other imaging modalities. 
     As yet a further example, although a Cartesian X-Y-Z positioning approach is disclosed herein, it will be appreciated that a polar or spherical positioning approach may be implemented in whole or in part so that the detachable probe assembly enters at a predefined angle. 
     As yet an additional example, although a prone breast compression device is depicted, application of the present invention may be used in medical compression devices oriented in other manners, to include standing, lying on one side, or supine. In addition, aspects of the present invention may be applicable to positioning a biopsy probe through a medial compression plate, or a top and bottom compression plate pair, instead of a lateral compression plate. Furthermore, aspects of the present invention are applicable to other diagnostic imaging modalities currently used or that become available in the future. In addition, aspects of the present invention would have application to diagnostic guided biopsy procedures on other portions of the body, as well as to positioning a probe for utilizing other diagnostic and treatment devices in a minimally invasive manner. 
     As yet a further example, an elongate needle may be formed without a structural, longitudinal barrier between the vacuum chamber lumen and the cutter lumen. Instead, the advancing cutter  90  may define a cutter lumen having a circular cross section within a noncircular cross section (e.g., oval) of the internal cavity of the elongate needle. Moreover, a noncircular liner may be used to prevent adhesive entering the undifferentiated internal cavity.