Abstract:
An MRI apparatus includes a local endovaginal probe ( 30 ) for receiving magnetic resonance in a study of the endopelvic fascia surrounding the female urethra. The probe ( 30 ) includes a shaft portion ( 62 ) an insert portion ( 60 ), the insert portion to be inserted into the vaginal cavity of a female subject. The insert portion ( 60 ), in order to have maximum efficiency in imaging the endopelvic fascia, is designed to specific dimensions to achieve the optimum balance between image quality and patient comfort. In an imaging sequence, a main magnet assembly ( 12 ) produces a main magnetic field through an imaging region ( 14 ). A whole-body RF coil ( 26 ) excites and manipulates magnetic resonance in the vicinity of the vaginal cavity. The probe ( 30 ) detects the magnetic resonance, which is received and demodulated. The received magnetic resonance is then reconstructed into an image representation of the tissue surrounding the vaginal cavity of the subject.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to the diagnostic imaging arts. It has particular application in conjunction with imaging vaginal anatomy and will be described with particular reference thereto. It will be appreciated, however, that the invention is also applicable to the imaging of other portions of the female pelvic region, and is not limited to the aforementioned application.  
           [0002]    Urinary incontinence is a common problem affecting women of all age groups. It is a source of embarrassment and anxiety for many women, especially those of advancing years. As longevity increases, urinary incontinence becomes more of a problem because women can develop this problem with age. As a result, researchers have undertaken the task of investigating the underlying causes of urinary incontinence.  
           [0003]    Magnetic resonance imaging has allowed significant advances in the areas of understanding of urinary incontinence in females, however, there is still much that is unknown.  
           [0004]    Previous methods of investigating urinary stress incontinence have utilized external coils and relate to the description of the pelvic floor muscles, ligaments, and zonal anatomy of the urethra. However, these methods were insufficient for viewing an endopelvic fascia, that is, tissues between the vaginal muscularis and adjacent organs and the pelvic wall.  
           [0005]    Endocavitary coils such as the coils of U.S. Pat. No. 6,051,974 to Reisker, et al. have been utilized. However, this type of coil was designed to be inserted into the anus of male patients to examine the prostate, rather than the area around the vagina in female patients. As a result, tissues around the vagina were distorted and images were not useful in a study of the vagina.  
           [0006]    The present invention provides a new and improved method and apparatus which overcomes the above-referenced problems and others.  
         SUMMARY OF THE INVENTION  
         [0007]    In accordance with one aspect of the present invention, a magnetic resonance apparatus is provided. A main magnet assembly produces a substantially uniform main magnetic field in an imaging region. Magnetic resonance is excited and manipulated in selected dipoles of a subject in the imaging region by an RF coil assembly. An RF vaginal receive coil assembly receives magnetic resonance signals from tissues surrounding the vaginal cavity of the subject. A reconstruction processor reconstructs received magnetic resonance signals into an image representation.  
           [0008]    In accordance with another aspect of the present invention, a magnetic resonance method is provided. A main magnetic field is induced in an imaging region, a subject being located within the imaging region. A vaginal fascia receive coil is inserted into a vaginal cavity of the subject, the coil having an insert portion and a shaft portion. Magnetic resonance is excited and manipulated in selected dipoles adjacent to the vaginal cavity. The resonance signals are received, demodulated, and reconstructed into an image representation.  
           [0009]    In accordance with another aspect of the present invention, a magnetic resonance receive coil assembly is provided. The assembly includes a coil loop, tuning and matching circuitry, and a coil housing for encasing the coil loop and the tuning and matching circuitry.  
           [0010]    One advantage of the present invention is that it presents a reusable MRI endocavitary probe.  
           [0011]    Another advantage resides in high resolution image representations of the endopelvic fascia.  
           [0012]    Another advantage is that it provides images with less distortion of the imaging volume.  
           [0013]    Still further benefits and advantages of the present invention will become apparent to those skilled in the art upon a reading and understanding of the preferred embodiments. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    The invention may take form in various components and arrangements of components, and in various steps and arrangements of steps. The drawings are only for purposes of illustrating preferred embodiments and are not to be construed as limiting the invention.  
         [0015]    [0015]FIG. 1 is a diagrammatic illustration of a magnetic resonance apparatus including a reusable vaginal cavity probe in accordance with the present invention;  
         [0016]    [0016]FIG. 2 is a perspective view of the vaginal cavity probe, in accordance with the present invention;  
         [0017]    [0017]FIG. 3A is a top view of the vaginal cavity probe in partial section;  
         [0018]    [0018]FIG. 3B is a side expanded view of the vaginal cavity probe;  
         [0019]    [0019]FIG. 4 is a side view of a notched embodiment;  
         [0020]    [0020]FIG. 5 is an alternate embodiment utilizing two loop coils. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0021]    With reference to FIG. 1, a main magnetic field control  10  controls superconducting or resistive magnets  12  such that a substantially uniform, temporally constant main magnetic field is created along a z axis through an examination region  14 . A magnetic resonance generation and manipulation system applies a series of radio frequency (RF) and magnetic field gradient pulses to invert or excite magnetic spins, induce magnetic resonance, refocus magnetic resonance, manipulate magnetic resonance, spatially and otherwise encode the magnetic resonance, to saturate spin, and the like to generate magnetic resonance imaging and spectroscopy sequences. More specifically, gradient pulse amplifiers  20  apply current pulses to selected ones or pairs of whole-body gradient coils  22  to create magnetic field gradients along x, y and z-axes of the examination region  14 . A digital radio frequency transmitter  24  transmits radio frequency pulses or pulse packets to a whole-body RF coil  26  to transmit RF pulses into the examination region. A typical radio frequency pulse is composed of a packet of immediately contiguous pulse segments of short duration which taken together with each other and any applied gradients achieve a selected magnetic resonance manipulation. The RF pulses are used to saturate, excite resonance, invert magnetization, refocus resonance, or manipulate resonance in selected portions of the examination region. For whole-body applications, the resonance signals are commonly picked up by the whole-body RF coil  26 .  
         [0022]    For generating images of limited regions of the subject, local coils are commonly placed contiguous to the selected region. A receive-only local endovaginal radio frequency coil probe  30  receives resonance signals introduced by body-coil RF transmissions. The resultant radio frequency signals are picked up by the endovaginal probe  30 , the whole-body RF coil  26 , or other specialized RF coils and demodulated by a receiver  32 , preferably including a preamplifier (not illustrated).  
         [0023]    A sequence control circuit  40  controls the gradient pulse amplifiers  20  and the transmitter  24  to generate any of a plurality of multiple echo sequences such as echo planar imaging, echo volume imaging, gradient and spin echo imaging, fast spin echo imaging, and the like. For the selected sequence, the receiver  32 , preferably a digital receiver, generates a plurality of digital data lines in rapid succession following each RF excitation pulse. optionally an analog-to-digital converter  42  converts the demodulated data to form the digital data lines. The digital data lines are reconstructed into an image representation by a reconstruction processor  50  which applies a Fourier transform or other appropriate reconstruction algorithm. The image may represent a planar slice through the patient, an array of parallel planar slices, a three-dimensional volume, or the like. The image is then stored in an image memory  52  where it may be accessed by a video processor  54  that converts slices, projections, or other portions of the image representation into appropriate format for a display, such as a video monitor  56  which provides a human-readable display of the resultant image.  
         [0024]    Although a bore type magnet is illustrated, it is to be appreciated that open or vertical field magnets are equally applicable.  
         [0025]    With reference to FIG. 2, the endovaginal probe  30  includes an insert portion  60  and a shaft portion  62  which are inserted into a vaginal cavity of a subject being examined contiguous to the endopelvic fascia. The proximity of the coil to the region of interest provides for a relatively high signal-to-noise ratio. Both the insert portion  60  and the shaft portion  62  are preferably constructed seamlessly of a medical grade plastic, such as Delrin™, or epoxy. Eliminating seams eliminates shelter for microorganisms, making sterilization a more facile task. The Delrin™ is appropriately flame retardant and is specifically intended for limited exposure to mucus membrane or blood barrier contact. The shaft portion  62  is telescopically connected to an enlarged portion  64  of the shaft portion  62 . The enlarged portion  64  grants extra support for an interface of the shaft portion  62  with an over-molded form  66 .  
         [0026]    The over-molded form  66  seals an open proximate end of the shaft  62 . Preferably, the over-molded form  66  is constructed of PVC plastic. An RF cable  68  extends from outside the RF coil assembly through the over-molded form  66 . A portion of the over-molded form  66  is embedded in circumferential grooves and flats formed on the outer surface of an enlarged portion  64  of the shaft  62  to provide, a tight mechanical seal which is appropriately resistant to the ingress of fluid. The interface between the over-molded form  66  and RF cable  68  is appropriately resistant to the ingress of fluid due to a chemical PVC-to-PVC or other fluid-tight seal provided therebetween.  
         [0027]    The RF cable  68  connects the output of tuning and matching circuitry to the MRI system preamplifier. Preferably, the cable  68  has been constructed from a non-magnetic version of a standard RG174 cable. Over the outer cable insulation, a non-toxic PVC outer jacket has been molded. The PVC jacket provides an appropriate non-toxic contact with a patient and also provides an electrical field insulating distance between the patient and the outer electrical shield of the cable thereby preventing the risk of RF burn.  
         [0028]    In the preferred embodiment, a printed circuit board  70  including the tuning circuitry is disposed adjacent a distal end of the insert portion  60 . The circuit board  70  is disposed below the surface of the Delrin™ plastic such that it is not exposed to the patient or to sterilants. Similarly, a second printed circuit board  72  carrying a matching circuit, and detuning circuitry for protection during RF excitation and, preferably a preamplifier, is disposed adjacent a proximal end of the insert portion  60  adjacent a juncture of the shaft portion  62  and the insert portion  60 . The second circuit board  72  is also preferably imbedded below the plastic surface.  
         [0029]    In order to create an accurate frame of reference for imaging, the vaginal fascia probe  30  is held stationary relative to the imaged tissue during the imaging sequence. Preferably, the probe  30  is secured by a clamp  74 , which grips the over-molded form  66 . Preferably, the probe is clamped into its stationary position after it has been inserted into the vaginal cavity of the patient, to accommodate the comfort of the patient as much as possible.  
         [0030]    With reference to FIGS. 3A and 3B, with continuing reference to FIG. 2, the insert portion  60  of the RF coil assembly preferably has a coil loop  80  embedded in the probe. The RF coil loop  80  senses resonance signals of relaxing dipoles during an imaging sequence. The coil loop  80  is connected at the distal end with the tuning circuit  70  and at the proximal end with the matching circuit  72 . The lead  68  is connected to the coil loop via the matching circuit  72 . In one embodiment, the coil loop  80 , the tuning circuit  70 , and the matching circuit are molded into a unitary medical grade plastic insert and shaft unit.  
         [0031]    In the embodiment of FIG. 4, a groove  82  is cut or otherwise formed into a periphery of the insert  60  to receive the coil loop  80 . A recess or notch  84  receives the tuning circuit and another recess or pocket  86  receives the matching circuit A medical grade epoxy is applied to the whole of the insert portion  60  and preferably, to the shaft portion  62  at least back to the over-molded form  66 . The application of the epoxy insures that the RF coil loop  80  is secured within the groove  82 . Additionally, the epoxy provides an easily sterilizable, smooth surface to facilitate multiple uses of the coil assembly.  
         [0032]    The preferred usage of the coil assembly is to examine the anatomical vicinity of the female urethra. Preferably, as is illustrated in FIGS. 3A and 3B, the insert portion  60  has a length parallel to the shaft portion  62  of nominally 80 mm and preferably not less than 60 mm. If the coil  80  is too short in this dimension, it will not receive resonance signals from the entire area of interest. Also, this dimension is preferably no greater than 100 mm. As the length of the coil  82  increases, the signal to noise ratio decreases, and as a result image quality degrades.  
         [0033]    A width  92 , perpendicular to the length  90 , is preferably 35 mm. If the width  92  is too short, the whole anatomy of interest is not imaged. Preferably, the width  92  is no less than 25 mm. The width  92  is limited by physical restraints of the vaginal cavity. As the width increases, so does patient discomfort and tissue compression. This, of course, varies from patient to patient, but in order to accommodate most patients, the width  92  is preferably no greater than 42 mm.  
         [0034]    A height  94  is preferably 10 mm. Any added height stretches the vaginal cavity in an unwanted direction, distorting the tissues of interest, providing degraded image quality. On the other hand, any less height, and the insert portion  60  becomes more knife-like. Narrow or sharp edges increase patient discomfort and risk patient injury. Moreover, the insert portion  60  is thick enough to remain rigid under stresses that result from being inserted into the vaginal cavity. The more stationary the coil, the more assurance will be had that the region of interest remains still during imaging.  
         [0035]    With reference to FIG. 5, in an alternate embodiment, multiple coil loops are utilized instead of a single coil loop. For example, instead of a single coil with a length of 80 mm in length, two coils  80   1  and  80   2  measuring just over 40 mm in length are utilized. Beneficially, the signal to noise ratio of each individual coil is increased, at the cost of extra tuning and matching circuitry. Other coil array patterns including quadrature coil arrays are also contemplated.  
         [0036]    The invention has been described with reference to the preferred embodiment. Modifications and alterations will occur to others upon a reading and understanding of the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.