Abstract:
A interventional procedure is performed by advancing a probe into a patient and periodically acquiring magnetic resonance images depicting the probe and adjacent portions of the patient&#39;s body. The patient, or a part of the patient, is reoriented during the procedure to facilitate advancement of the probe as, for example, by changing the position or orientation of internal organs.

Description:
The present application is a continuation-in-part of the aforementioned U.S. patent application Ser. No. 08/975,913 filed Nov. 21, 1997. The present application claims benefit of U.S. Provisional Patent Application 60/066,798, filed Nov. 26, 1997, the disclosure of which is also incorporated by reference herein. The present application incorporates by reference the entire disclosure of co-pending, commonly assigned U.S. patent application Ser. No. 07/993,072 filed Dec. 18, 1992 and incorporates by reference the entire disclosure of co-pending, commonly assigned U.S. patent application Ser. No. 08/975,913 filed Nov. 21, 1997. 
    
    
     BACKGROUND OF THE INVENTION 
     Traditional surgical procedures are conducted by making an incision in the patient&#39;s body to expose those organs which are to be treated. The physician can observe the treatment directly and can guide tools such as surgical instruments to the site requiring treatment by direct visual observation. In typical endoscopic procedures, an elongated probe having a visual observation device such as a lens and fiber optic system or a small television camera is inserted into the patient&#39;s body and guided to the desired treatment location using observation of the visual image acquired by the visual observation device. The observation device can also be used to monitor additional probes such as tools inserted through the bore of a hollow endoscope or separate surgical instruments advanced through the same or other orifices to the treatment location. Endoscopic procedures suffer from various limitations. They require relatively bulky optical elements at the distal end of the endoscope. Moreover, the physician must conduct the procedure based on a limited picture delivered by the optical system. 
     Image-guided interventional procedures have been developed. In image-guided procedures, an imaging device such as an x-ray device is employed to monitor the position of a probe within the body. In the simplest image-guided procedures, a fluoroscope can be used to observe the position of a radioopaque probe while the probe is inserted into the body. Fluoroscopic and other x-ray imaging modalities have serious drawbacks, including exposure of the patient and physician to ionizing radiation and inability or limited ability to image soft tissues. Accordingly, treatment methods relying on x-ray based imaging for guidance of an intrabody probe have been applied only in limited circumstances. 
     Magnetic resonance imaging offers the unique ability to obtain excellent images of all tissues in a patient&#39;s body without the use of ionizing radiation. MRI typically requires the use of a large magnet to apply a strong magnetic field in a patient receiving space, large enough to accommodate that region of the patient&#39;s body which is to be imaged. Some early types of MRI imaging apparatus using superconducting magnets had a patient-receiving space essentially surrounded by components of the apparatus, making it impractical to perform interventional procedures while the patient is being imaged. However, some current MRI apparatus provides an “open” environment so that a patient disposed in the imaging space of the apparatus is accessible to physicians and other medical personnel. For example, magnetic resonance imaging apparatus of the type illustrated in U.S. Pat. No. 5,754,085 provides open access to the patient so that a patient positioned within the magnet is readily accessible to a physician standing outside of the magnet, making it practical to perform MRI-guided interventional procedures. In such procedures, MRI images may be continually acquired while a probe such as a catheter, endoscopic instrument, or other device is advanced into the patient. The MRI images desirably show internal structures of the patient&#39;s body and also depict the probe. 
     The MRI images allow the physician to visualize the disposition of the probe relative to the organs and tissues of the body and allow the physician to maneuver the probe along a desired trajectory within the body. For example, the physician can use MRI images to guide a probe within a tubular or cavernous organ such as within the circulatory tract, digestive tract, respiratory tract or urinary tract. Also, the physician can guide a probe within soft tissue as the probe is advanced through the soft tissue as, for example, through muscle, lung tissue or the like. The MRI images can also be used to monitor the progress of the treatment being performed. For example, if particular tissues such as tumors are being removed, the MRI images can show the tumor in contrast to the surrounding tissue and can show the physician where additional tissue must be removed. 
     Despite all this progress in the art, still further improvements in image-guided interventional procedures would be desirable. 
     SUMMARY OF THE INVENTION 
     One aspect of the present invention provides methods of conducting image-guided medical procedures. A method according to this aspect of the invention includes the steps of advancing a probe within a patient and, during the probe-advancing step, periodically acquiring information defining an image of the probe and adjacent internal structures of the patient&#39;s body. Most preferably, the step of acquiring the image information is performed by magnetic resonance imaging. A method according to this aspect of the invention further includes the step of changing the orientation of the patient in response to the image information so as to facilitate the probe-advancing step. For example, the step of changing the orientation of the patient may include the step of changing the orientation of the patient so that tissue disposed in front of the probe along a desired probe path is displaced away from the probe path. For example, if an internal organ of the patient is disposed in front of the desired path of advancement of the probe, turning the patient to a new orientation may cause gravity to displace that organ to the surrounding portions of the patient&#39;s body and relative to the probe. Also, where a tubular organ such as a blood vessel is kinked or folded so that a straight or gently curving path along the tubular organ is blocked by the tissue at the kink or fold, the change in patient orientation can remove the kink or fold and thus take the blocking tissue away from the desired path of the probe. Alternatively or additionally, the step of changing the orientation of the patient may include the step of changing the orientation of the patient while the probe is disposed in the patient so as to alter the disposition of the probe. For example, the probe may be flexible and the step of changing the orientation of the patient is performed so that gravitational forces applied to the probe, to the surrounding tissues or both bend the probe to a more favorable configuration. 
     In particularly preferred methods according to this aspect of the invention, the patient&#39;s body is positioned on a support, and the step of changing the orientation of the patient includes the step of tilting the support. For example, the support may be tilted about a tilt axis substantially parallel with the long axis of the patient; around an inclination axis transverse to the long axis of the patient or both. In still further embodiments of the invention, the step of changing the orientation of the patient may include the step of moving one part of the patient&#39;s body relative to another part. For example, where a probe is advanced within the vasculature of a limb, a part of the limb may be moved relative to the torso or relative to another part of the limb so as to reconfigure the vascular system. 
     In the preferred methods according to this aspect of the invention, the orientation of the patient facilitates movement of the probe through the patient&#39;s body to the desired treatment location, with a minimum of damage to surrounding tissues. This benefit is particularly pronounced when the MRI is the imaging modality. The unique ability of MRI to provide details of soft tissue images, coupled with the ability to reposition soft tissues by reorienting the patient provides a particularly valuable combination. 
     These and other objects, features and advantages of the present invention will be more readily apparent from the detailed descriptions set forth below, taken in conjunction with the accompanying drawings. 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagrammatic, sectional elevational view of apparatus utilized in a method according to one embodiment of the invention. 
     FIG. 2 is a diagrammatic, sectional view taken along line  2 — 2  in FIG.  1 . 
     FIGS. 3A-3D are diagrammatic sectional views taken along line  3 — 3  in FIG. 1, depicting elements of the apparatus in moved positions. 
     FIGS. 4 and 5 are diagrammatic depictions of images acquired in the methods of FIGS. 1-2. 
     FIGS. 6 and 7 are diagrammatic depictions of images acquired in a method according to a further embodiment of the invention. 
     FIGS. 8 and 9 are diagrammatic depictions of images acquired in a method according to yet another embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Apparatus utilized in a method according to one embodiment of the invention includes a magnetic resonance imaging instrument incorporating a static field magnet  10 . The particular static field magnet depicted in FIGS. 1 and 2 includes a ferromagnetic frame  12  incorporating top and bottom ferromagnetic pole supports  14  and  16 ; a pair a ferromagnetic poles  18  and  20  projecting downwardly and upwardly from pole supports  14  and  16  respectively and a pair of connecting elements  22  and  24  supporting the upper pole support above the lower pole support. The static field magnet further includes a source of magnetic flux such as a pair of coils  26  and  28  encircling the pole stems  18  and  20 , respectively. The poles  18  and  20  define a patient receiving gap  30  between them. The components of the static field magnet are arranged so that they define a working space  32  extending at least partially around the poles within the magnet structure. Working space  32  is sufficient size to accommodate a physician or other attendant  34  of normal size so that the physician or attendant can be positioned immediately adjacent the patient receiving gap  30  and can attend to a patient  36  disposed within a gap  30 . 
     The magnetic resonance imaging instrument further includes gradient coils  38  and radio frequency antennas  40 , schematically indicated in the drawings, as well as a conventional imaging electronic system  42 . System  42  includes conventional components for driving gradient coils  38  so as to superimpose gradient fields varying in space within gap  30  on the static, substantially constant fields provided by the static field magnet  10 . The imaging electronics system  42  also includes conventional devices for actuating the RF antenna  40  to transmit radio frequency excitation signals in the gap and to receive weak radio frequency signals, commonly referred to as magnetic resonance signals, emitted from materials within the gap. The imaging electronics system  42  further includes a computer for coordinating the operation of these components and reconstructing an image of a patient disposed within the gap from the magnetic resonance signals. These components of the apparatus are well-known in the magnetic resonance art and accordingly are not discussed in detail herein. The imaging electronics system is linked to displays  44  such as cathode ray tubes or other conventional display device. Displays  44  are mounted at locations where they are visible to physicians  34  disposed within the working space  32 . Of course, one display device, or more than one display may be provided. 
     As further described in the aforementioned co-pending, commonly assigned applications, the magnet structure defines portions of a room, with a floor  60  and ceiling  62 . The lower pole  20  projects upwardly from the floor, whereas the upper pole  18  projects downwardly from the ceiling of the room. The working space  32  and patient-receiving gap  30  is disposed within the room. 
     A patient positioning device  600  is used with the magnetic resonance imaging system and magnet to position the patient relative to the poles and magnet gap. Device  600  desirably is formed from non-magnetic materials such as polymers. The positioning device includes a chassis  602  mounted on wheels  604 . A pair of rails  606  extend along the floor  60  of the room and also extend outwardly from the room onto the adjacent floor of the building. Wheels  604  run along these rails so that chassis  602  can be moved along a first horizontal axis, denoted by arrow Z, transverse to the polar axis  19  [mention earlier] of the magnet. As best seen in FIG. 2, chassis  602  includes a pair of vertically-extensive end portions  603  which lie on opposite sides of the lower pole  20  when the chassis is aligned with the polar axis  19  of the magnet. A bridge portion  605  of the chassis extends between the end portions, and overlies pole  20  when the chassis is aligned with the polar axis. Brakes (not shown) on wheels  604 , or other devices for holding chassis  602  in position on the rails may be provided. In addition, the rails or the adjacent portions of the floor may be provided with graduations, and chassis  602  may be provided with a point or other index mark so that the chassis can be brought to a preselected disposition in the first movement or Z direction. Other positioning devices, such as a screw jack, fixed or adjustable stop or optical positioning system may be employed to locate and index the position of the chassis relative to the floor and the magnet frame. 
     An upper member  608  is mounted on chassis  602 . A screw jack  610  (FIG. 1) or other mechanical positioning system such as a hydraulic or pneumatic cylinder, lever system or the like is also provided for moving upper member  608  vertically, in the axial or Y direction, parallel to the polar axis  19  of the magnet. Positioning device  610  may be arranged to displace upper member  608  relative to the remainder of the chassis. Alternatively, upper member  608  may be fixed to the remainder of the chassis and positioning device  610  may be adapted to move the chassis  602  relative to wheels  604 . An elongated, movable support  612  is mounted for pivoting movement relative to the chassis and upper member  608  around a pivot  614  (FIG.  5 A). Pivot  614  is close to the center of the chassis. Thus, when the chassis is positioned in the Z direction so that the center of the chassis is coincident with the polar axis  19 , the pivot  614  is also close to the polar axis. Movable support  612  is also mounted for sliding motion relative to upper member  608  and chassis  602  in a longitudinal direction X, parallel to the long direction of the support itself. Thus, as seen in FIGS. 3A through 3D, the movable support  612  can swing in pivoting motion around pivot  614  so as to orient the longitudinal direction X at any desired angle to the first movement direction Z. Thus, the longitudinal direction X of the movable support can be oriented in any direction relative to the long axis of the rectangular poles  30  and  20 . By moving the movable support relative to the chassis  602  in its longitudinal direction, various locations along the length of the movable support  612  can be aligned with the polar axis  19  of the magnet. 
     Additionally, the litter or actual patient-carrying device  80  is mounted to the movable support  612  for pivoting movement around a tilt axis  616  parallel to the longitudinal or X direction of the movable support. Thus, as seen in FIG. 4, the tilt axis  616  extends into and out of the plane of the drawing. A tilt actuation device  618 , such as a pneumatic bladder or pneumatic cylinder, screw jack, or wedge jack, is provided for tilting the litter through a range of tilt angles A (FIG.  1 ). The patient support is also pivotable relative to the movable support about an inclination axis  617  transverse to the lengthwise direction of the support and transverse to the tilt axis. An inclination actuator (not shown) similar to the tilt actuator is provided for pivoting the support about the inclination axis through a range of inclination angles B (FIG. 2) . This allows positioning of the patient in a Trendlenbug position as indicated in broken lines in FIG. 2, wherein the patient&#39;s thorax is lowered relative to the abdomen or in a counter-Trendlenburg position, wherein the thorax is elevated relative to the abdomen. Thus, the patient positioner  600  provides litter or support  80  with movement in six degrees of freedom: translation in a first lateral direction Z transverse to the polar axis; translation in the X or longitudinal direction of the movable support  612 , also transverse to polar axis  19  and at an arbitrary angle to the first or Z direction; rotation in a horizontal plane transverse to the polar axis so as to orient the longitudinal direction X at any angle B relative to the long axes of the poles; elevation or axial movement Y (FIG. 4) parallel to the polar axis; tilt to any desired angle A to the horizontal plane; and inclination B so as to raise either end of the support. This provides extraordinary versatility in positioning of the patient relative to the magnet. For example, as seen in solid lines in FIG.  2 , the head and neck of the patient is substantially aligned with the polar axis. Translation in the longitudinal direction allows positioning of the feet adjacent the polar axis, as seen in broken lines in FIG.  2 . Other arbitrary positions of the patient relative to the polar axis and relative to the remainder of the magnet are also shown in FIGS. 3A through 3D. As described in greater detail in the copending, commonly assigned applications, the magnet of the MRI apparatus provides a large clearance between the poles. Desirably, the vertical dimension of the gap, measured between the poles, at least about 17.5 inches and more desirably about 36 inches. The large clearance within the magnet provided by the ferromagnetic frame contributes to the positioning versatility and facilitates the methods discussed below. Thus, the large vertical dimension of the gap provides enough room to tilt the patient/s body through substantial angles A and B. Because the connecting elements are spaced at a radial distance R from the polar axis of about seven feet or more, longitudinal movement of the patient relative to the frame can be accommodated over a range sufficient to position essentially any part of the patient&#39;s body at the polar axis. 
     In a method according to one embodiment of the invention, a patient  36  is disposed by the patient support  80  and maintained within the gap  30  of the magnetic resonance imaging apparatus. A physician  34  standing adjacent to patient and adjacent gap  30  inserts a probe  700  into the patient&#39;s body. Patient support  80  is initially at a flat position indicated in broken lines at  80 ′ in FIG.  1 . As the physician inserts the probe, the magnetic resonance imaging apparatus operates to acquire an image of the patient and the probe. Probe  700  is desirably formed from a non-ferromagnetic material having MRI response different from the MRI response of the body tissues in the region to be imaged. Many MRI images are based on the response of hydrogen nuclei (protons). If probe  700  is formed in whole or in part from a hydrogen-free material such as a non-ferromagnetic metal, the probe will show zero response, where the surrounding tissues will show some response. The image depicted on screen  44  is a map of MRI response versus location, with response shown as color and/or brightness at each location on the screen, the probe will appear as a contrasting object superposed on the patient&#39;s tissues. For example, one form of MRI image is the so-called “proton density” image, in which the brightness or color of each spot on the image represents the amount of hydrogen present at the corresponding location in the patient&#39;s body. A probe formed from a hydrogen-free material such as a metal will show as a region of zero proton density, whereas the surrounding tissues typically have substantial hydrogen content. Other forms of MRI images include so-called T 1  and T 2  relaxation time images. In these images, the brightness or color of each spot on the displayed image represents a property of hydrogen nucleii at the corresponding location in the body referred to as T 1  relaxation time or T 2  relaxation time. These properties, in turn, vary with the nature of the chemical compounds containing the hydrogen nucleii. If probe  700  is formed from synthetic polymers, the relaxation times of the hydrogen nucleii constituting the probe will be markedly different from the relaxation times of the hydrogen nucleii in compounds such as water constituting the bodily tissues. Here again, the depiction  700 ′ of probe  700  can be readily differentiated from the depictions of bodily tissues. The image of the patient also shows internal organs such as bony structures  702  and soft tissues  704 . 
     In the particular procedure illustrated, the physician is seeking to advance the probe to a lesion  706  along a trajectory  708 . Organ  704  extends across the trajectory. As the physician is advancing the probe, he or she can see that organ  704  is blocking the desired path or trajectory  708  of the probe. While the system continues to acquire images of the patient, the physician actuates the patient positioning system  600  to tilt the patient support  80  about the tilt axis  616 , thereby tilting the entire body of the patient about the patient&#39;s longitudinal axis  710 . The image acquired when the patient is in this moved position is depicted schematically in FIG.  5 . In this moved position, organ  704  has moved, under the influence of gravity, out of path  708 , so that the position can advance the probe along path  708  to lesion  706 . Because the physician can continually observe the internal structures of the patient, including the soft tissues, using the MRI apparatus and can continually readjust the position of the patient to move internal structures, the physician can advance probe  700  to the desired location with a minimum of tissue damage. 
     The method may include numerous repositionings of the patient so as to place the organs in the desired position at each stage of the treatment. For example, the tip of a probe may be threaded past an organ and the patient may then be turned once again so as to move another organ out of the way of the probe tip. As shown schematically in FIGS. 6 and 7, movement of the patient may also be used to deform the probe. Thus, in FIG. 6 the flexible probe  713  such as a flexible catheter or endoscope is being threaded within a cavernous organ such as the bronchial tract. The physician notes that the probe is bent toward an undesired branch  714  of the bronchial tract rather than into the desired branch  716 . By tilting the patient about longitudinal axis  710 , the patient tilts the desired branch  716  downwardly. The tilting motion is also applied to the flexible probe  713 . Thus, the tip of probe  713  bends toward the downwardly tilted side and thus aligns itself with the desired passage  716 . The same principles can be applied using tilting movements about other axes as, for example, about the inclination axis  617 . 
     It is not necessary to tilt the entirety of the patient&#39;s body. For example, where a limb or other portion of the patient&#39;s body is being treated, that portion alone may be tilted. As depicted in FIGS. 8 and 9, a probe  720  is being advanced through a tubular organ such as a blood vessel  722  extending through a first portion  724  and a second portion  726  of a limb such as an arm or leg. In the position indicated in FIG. 8, the joint of the limb is bent so that the tubular blood vessel  722  is also bent. Thus, tissues such as the blood vessel wall lie in the path of advancement of probe  720 . Using the guidance provided by MRI imaging, the physician can manipulate the limb to the position indicated in FIG. 9, in which the tubular blood vessel is aligned with the path of the probe  720 . The simplified, schematic views shown in the drawings do not fully show all of the complexities encountered in anatomical structures. However, the ability of MRI imaging to provide full depictions of soft tissues and other tissues within the body are coupled with the ability to reorient body structures during the procedure, allows the physician to accommodate the wide range of anatomical complexities. 
     Methods according to this aspect of the present invention can be practiced utilizing other magnetic resonance imaging instruments. Desirably, the magnetic resonance imaging instrument provides a large patient-receiving gap and good access to the patient while the patient is exposed in the gap. For example, as described in the preferred embodiments of the aforementioned U.S. Pat. No. 5,754,085, may be employed. Also, the invention can be practiced using more than one probe simultaneously. The probe may be essentially any instrument to be inserted into the patient&#39;s body as, for example, catheters, endoscopic instruments, trocars, needles and conventional surgical instruments. 
     In the embodiments discussed above, the image of the probe is acquired by the MRI system itself during the same imaging sequences used to create the images of the patient. However, this is not essential. A wide variety of systems are known for tracking the locations of instruments in a known frame of reference as, for example, in the frame of reference of the magnetic resonance imaging instrument. Systems of this nature can use magnetic, radiofrequency, ultrasonic or other signals transmitted to or from a device mounted on the probe to determine the location and/or orientation of the probe in the fixed frame of reference. The position and orientation of the probe can be determined using these systems, and a representation of the probe can be superposed on an MRI image of the patient based upon the position and/or orientation acquired in this fashion and data defining the configuration of the probe. 
     According to the broadest compass of the invention, imaging other than magnetic resonance imaging, such as X-ray, CAT, ultrasound or other imaging modalities may be employed, however, such other imaging modalities are distinctly less preferred, as they lack the capabilities of MRI imaging discussed above. 
     As these and other variations and combinations of the features discussed above can be utilized without departing from the present invention as defined by the claims, the foregoing description of the preferred embodiment should be taken by way of illustration rather than by way of limitation of the invention as defined in the claims.