Abstract:
An apparatus, system and method for performing a ventriculostomy using an ultrasound probe is disclosed. A head portion of the probe is connected to a handle portion at a proximal end of the head portion. A transducer is mounted in a distal end of the head portion to transmit ultrasound waves into the patient. The head portion includes a conduit portion arranged to accept and to accurately direct a catheter into the body of the patient in a direction parallel to the direction of the ultrasound waves. The head portion is sized to fit into a conventionally-sized craniotomy. An adjustment mechanism connects the head portion to the handle portion for selectively adjusting the angle between the handle portion and the head portion. A sterile sheath having an integral conduit assembly for mounting to the head is optionally provided. An illuminator is optionally provided on the probe.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    The present application claims the benefit of the filing date of U.S. Provisional Patent Application No. 61/224,985, filed on Jul. 13, 2009, under 35 U.S.C. §119(e). U.S. Provisional Patent Application No. 61/224,985, filed on Jul. 13, 2009, is hereby incorporated by reference. 
     
    
     FIELD OF INVENTION 
       [0002]    The present invention relates to an apparatus, system and method for accurately positioning a catheter within a body cavity to be treated. More specifically, the disclosed inventive apparatus, system and method provide for the accurate introduction of a catheter into a targeted ventricular cavity of the brain during a ventriculostomy procedure. 
       BACKGROUND OF THE INVENTION 
       [0003]    A human brain includes four interconnected cavities, the ventricles, which produce and circulate cerebrospinal fluid. A ventriculostomy procedure involves the placement of a catheter into one of the ventricles. The ventriculostomy may be performed for intracranial pressure monitoring, draining or shunting of cerebrospinal fluid and/or the instillation of pharmacological therapeutic agents. A catheter functioning as an external ventricular drain is used to drain cerebrospinal fluid, and is typically done emergently to monitor and treat life-threatening hydrocephalus and/or intracranial hypertension. As a result, quick and accurate placement of the external ventricular drain is necessary. 
         [0004]    The insertion of a catheter during a ventriculostomy was originally done completely by hand by the doctor based on external landmarks on the patient&#39;s body and on the doctor&#39;s knowledge of the internal three-dimensional anatomy of the brain which are used by the doctor to determine the trajectory of the insertion of the catheter into the targeted ventricle. External ventricular drain placement is a highly invasive procedure since the catheter passes through the brain parenchyma before entering the targeted ventricle and can cause iatrogenic hemorrhaging. In the freehand method, often multiple attempts (or passes) are required before the external ventricular drain enters the targeted ventricle, with each subsequent pass likely increasing the risk of iatrogenic hemorrhaging or other problems. For example, some external ventricular drains will inevitably fail to drain for various reasons. Most commonly, the external ventricular drain becomes obstructed by choroid plexus, clotted blood, proteinacious debris, or parenchymal debris. This may be remedied by flushing the catheter, but this can increase the risk of infection. If this and/or other troubleshooting measures fail, the external ventricular drain must be removed and replaced, necessitating an additional invasive procedure. As a result, greater accuracy during the initial placement of the external ventricular drain can decrease the frequency of obstruction by choroid plexus and parenchymal debris and therefore decrease the overall morbidity of an external ventricular drain. Thus, there is a clear need for an improved way to perform a ventriculostomy that provides such greater accuracy. 
         [0005]    Another benefit of accurate placement of the external ventricular drain (i.e., the accurate placement of the catheter tip within the targeted ventricle) is that it broadens therapeutic options. Intraventricular tPA administration for intraventricular clotted blood may hasten patients&#39; recovery from intraventricular hemorrhaging. In order to use intraventricular tPA, all of the eyelets in the catheter tip must be in the ventricle. This treatment is contraindicated when one or more of the eyelets are not in the ventricle but are instead in the parenchyma. Currently, there is no method of determining the location of the eyelets during the placement of an EVD. Although post-procedure head computed tomography (CT) can make such a determination and thus is the only conventional method of determining the viability of tPA therapy via the catheter placed within the ventricle, catheters cannot be repositioned after the procedure is completed and the skin is closed for risk of infection. Any repositioning” requires removal of the initial catheter and replacement by a second catheter and procedure. 
         [0006]    One prior art approach to the need for accurate placement of the catheter tip within the ventricle uses a specially-designed catheter guide to help the doctor insert the catheter into the ventricle. The catheter guide is a tripod device placed on the skull and facilitates the creation of a trajectory for the catheter which is perpendicular to the tangent line of the skull. See, e.g., U.S. Pat. No. 4,613,324 to Ghajar, U.S. Pat. No. 4,821,716 Ghajar et al., U.S. Pat. No. 4,931,056 to Gharjar et al., U.S. Pat. No. 6,206,885 to Ghahremani et al. and U.S. Pat. No. 7,033,367 to Ghahremani et al. for several different catheter guides designed for this purpose. However, this approach is still “blind,” and is dependent on an accurately-positioned burr hole, a normocephalic skull shape and a non-distorted intracranial anatomy. 
         [0007]    Another prior art approach provides an ultrasound probe within the tip of the catheter being inserted into the targeted ventricle. See, U.S. Pat. No. 5,690,117 to Gilbert, U.S. Patent Application Publication No. 2007/0083100 A1 to Schulz-Stubner and U.S. Patent Application Publication No. 2009/0088648 A1 to Jaffe et al. This approach requires a specially-designed and expensive catheter or stylet for performing the ventriculostomy. There are two other disadvantages. One is that the image quality from such a small transducer may be less than optimal. The second is that the perspective is from the tip of the catheter, thus there is no frame of reference provided to determine the depth of the placement. Essentially, this perspective provides “tunnel vision” and the operator would have to watch the target move towards the transducer tip (as opposed to a static image and target with the catheter seen moving into the ventricle). 
         [0008]    Still another prior art approach is to use ultrasound to position a catheter within the targeted ventricle. In the article entitled “Accurate Placement Of Cerebrospinal Fluid Catheters With Real-Time Ultrasound Guidance In Older Children Without Patent Fontanels” by William E. Whitehead, M.D., et al. which appeared in Journal of Neurosurgery:Pediatrics, Volume 107 pp. 406-410 November, 2007 (the “Whitehead Article”) (incorporated herein by reference), the authors describe the use of a conventional ultrasound probe, Aloka Ultrasound Probe Model No. UST-5268P-5 (the “Aloka Probe”), attached to a conventional portable ultrasound machine (e.g., Aloka ProSound Model No. SSD-1700 II) with a conventional ventriculostomy catheter to guide the catheter. However, this probe is designed to fit within the 11 mm diameter spacing provided by a standard-size perforator drill bit, such as the Codman Disposable Perforator Model No. 26-1221, which generates a 14 mm upper diameter and an 11 mm lower diameter aperture through the skull of the patient. In addition, the Aloka Probe includes a shallow groove along one side thereof for use in guiding a needle biopsy probe into the brain. As a result, the method described in this article requires significant enlargement of the standard-sized burr hole to 15 to 20 mm to properly position both the catheter and probe against the dura in the burr hole opening, requiring either additional steps and the resultant extra time to perform the procedure or additional tools (i.e., additional drilling with multiple drill bits), and is not easily performed bedside. Another drawback is that although sterile probe covers are available for the Aloka Probe, these covers obscure the groove on the Aloka Probe and make it difficult to insert the catheter. As a result, it is likely that such covers will not likely be used, necessitating sterilization of the Aloka Probe after every use and a consequent delay in performing a subsequent procedure using the same Aloka Probe of between two to six hours for sterilization. A still further drawback of the use of the Aloka Probe is the need for the doctor to position the catheter within the shallow groove therein and hold it firmly against the Aloka Probe for the entire procedure. This additional effort generates fatigue and tremor in the doctor&#39;s hand and requires additional time for ensuring that the catheter is being properly inserted while performing the procedure. 
         [0009]    Similarly, U.S. Patent Application Publication No. 2008/0287916 to Agmon discloses a clip  207  that is used to mate a conventional ultrasound probe  209  with a conventional catheter  205  to ensure that catheter  205  is guided to the targeted ventricle. Because the structures used to mate the catheter  205  to the probe  209  are not integral to the probe  209 , less than optimal results are likely to occur. Furthermore, the use of a standard probe and standard catheter mated together would likely require a hole in the skull that is larger than that provided by the standard perforator drill bit, thereby either requiring a non-standard drill bit or multiple passes for creating the hole through the skull. Additionally, the guiding apparatus is fully enclosed and there is no mention of the guide being calibrated stereotactically towards the target. Finally, the use of a separate clip makes it difficult to employ a sterile sheath over the probe. 
         [0010]    A ventriculostomy procedure is often done bedside in emergent situations, e.g., bedside in an ICU, and there is a need for an apparatus, system and method which ensures that this procedure is done accurately, e.g., without causing tissue damage, quickly, e.g., in a single pass and without requiring multiple pass drilling operations or complex drilling, and inexpensively, e.g., without requiring non-standard drill bits or other parts. 
       SUMMARY OF THE INVENTION 
       [0011]    The present invention is directed to an apparatus, system and method which overcomes the problems in the prior art. In particular, the present invention is an ultrasound probe comprising a handle portion for use in gripping the ultrasound probe and a head portion for directing ultrasound waves emitted from a transducer in a fixed direction into a body of a patient. The head portion is connected to the handle portion at a proximal end of the head portion such that an angle formed between the handle portion and the head portion is less than 150 degrees. The transducer is mounted in a distal end of the head portion. The head portion has a conduit portion on a periphery thereof arranged to accept a catheter therein and to direct the catheter into the body of the patient in a direction parallel to the direction of the ultrasound waves. 
         [0012]    A cross-section of the head portion at the distal end in a direction perpendicular to the direction of the ultrasound waves may have a maximum width of less than 11 mm. The angle formed between the handle portion and the head portion may be approximately 90 degrees in one embodiment. The ultrasound probe may further comprising an adjustment mechanism for connecting the head portion to the handle portion for selectively adjusting the angle formed between the handle portion and the head portion from approximately 90 degrees to about 150 degrees. The conduit portion may be completely enclosed within the head portion or near-completely enclosed within the head portion. In another embodiment, the conduit portion may be attached on a periphery of the head portion adjacent to the proximal end thereof and the head portion may further comprise a channel in the periphery thereof adjacent to the distal end thereof, so that a catheter inserted through the conduit portion is guided to the channel portion and then into the body of the patient in a direction parallel to the direction of the ultrasound waves. 
         [0013]    In a further embodiment, the conduit portion may include a first conduit portion fixedly attached to the head portion and a second conduit portion coupled to the first portion. The second conduit portion may be adapted to rotate into and out of an inner portion of the first conduit portion or may be removable. 
         [0014]    A sterile sheath having an integral conduit assembly may be mounted over the head portion and the handle portion. A member attached as part of the conduit assembly is positioned on the inside of the sterile sheath and fits into a slot on the head portion to secure the conduit assembly against head portion. A conduit portion of the conduit assembly extends on the outside, sterile side, of the sterile sheath to provide a guide for insertion of the catheter. 
         [0015]    In a still further embodiment, the conduit portion may detachable from the head portion via a snap fit female channel in the head portion and a correspond male portion in the conduit portion, or via matching snap fit connections at two edges of the head portion, or a circumferentially mounted snap fit connection. In addition, the conduit portion may be partially enclosed and snap fit stabilizing attachments may be used for securing the catheter within the conduit portion. 
         [0016]    In a yet further embodiment, the ultrasound probe may further comprise an illumination device. 
         [0017]    Furthermore, the present invention is directed to a system for positioning a catheter within a body of a patient, comprising an ultrasound machine and the ultrasound probe discussed above. 
         [0018]    Finally, the present invention is directed to a method of inserting a catheter into a body of a patient using the ultrasound probe discussed above coupled to an ultrasound machine. The method comprises preparing an entry point for the catheter adjacent to a surface of a body of a patient, positioning the ultrasound probe against the entry point, inserting a catheter into the conduit portion of the ultrasound probe, guiding the catheter through the conduit portion into the body of the patient, and using a display coupled to the ultrasound machine to guide the continued insertion of the catheter to a targeted internal portion of the body. In particular, the method of the present invention includes a preparing step which comprises performing a craniotomy at a predetermined position on the patient and in which the entry point is a surface of the brain, the catheter is a ventriculostomy catheter and the targeted internal portion of the body is a ventricle within the brain. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The following detailed description, given by way of example and not intended to limit the present invention solely thereto, will best be understood in conjunction with the accompanying drawings in which: 
           [0020]      FIG. 1  is a cross-sectional top view of the head of the ultrasound transducer probe of the present invention inserted within a conventional burr hole formed in a patient; 
           [0021]      FIG. 2A  is a side view of the ultrasound transducer probe of the present invention set to a first position, and  FIG. 2B  is a side view of the ultrasound transducer probe of the present invention set to a second position; 
           [0022]      FIG. 3A  is a perspective view of an embodiment of the head and integral conduit of the ultrasound transducer probe of the present invention,  FIG. 3B  is a perspective view of a further embodiment of the head and integral conduit of the ultrasound transducer probe of the present invention, and  FIG. 3C  is a perspective view of a still further embodiment of the head and integral conduit of the ultrasound transducer probe of the present invention; 
           [0023]      FIGS. 4A ,  4 B and  4 C show an embodiment of the head and partially rotatable conduit of the ultrasound transducer probe of the present invention; 
           [0024]      FIGS. 5A ,  5 B and  5 C show an embodiment of the head and partially removable conduit of the ultrasound transducer probe; 
           [0025]      FIG. 6A  is a perspective view of an embodiment of the head and snap fit conduit of the ultrasound transducer probe,  FIG. 6B  is a perspective view of a further embodiment of the head and snap fit conduit of the ultrasound transducer probe,  FIG. 6C  is a perspective view of a still further embodiment of a conduit assembly mounted within a slot in the head of the ultrasound transducer probe, and  FIG. 6D  is a perspective view of a yet still further embodiment of a conduit assembly of the ultrasound transducer probe showing snap fit attachments used to hold the catheter within the conduit; 
           [0026]      FIG. 7A  shows a sterile sheath assembly according to the invention having an integral conduit assembly for connection to the head portion of the ultrasound transducer probe, and  FIG. 7B  shows the sterile sheath assembly mounted on an ultrasound transducer probe; and 
           [0027]      FIG. 8  is a side view of an ultrasound transducer probe of the present invention including an illumination device. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0028]    Referring now to the drawings and in particular  FIG. 1 , an ultrasound transducer probe  10  for use in guiding the placement of a ventriculostomy catheter via an aperture  20  in a stereotactic conduit  30  mounted on a side of probe  10 . Transducer probe  10  is dimensioned to fit within an 11 mm diameter “burr hole” (craniotomy)  15  without requiring an additional step of increasing the diameter of the craniotomy. As discussed above, 11 mm is the current standard size inner cusp diameter craniotomy for ventriculostomies, and 14 mm is the current standard size outer cusp diameter  18 . Transducer probe  10  is connected to a conventional portable ultrasound machine (not shown). Conduit  30  serves as a self-contained guide-port for probe  10  for insertion of a standard ventriculostomy catheter (not shown) via a cable  33  ( FIG. 2 ). When the head of probe  10  is placed within the craniotomy and against the exposed surface of the brain (i.e., the dura), the alignment of the phased-array ultrasound waves emitted from a transducer  55  (see also  FIGS. 3A to 3C ) in the distal end of probe  10  and the guide-port are such that the area of the brain constituting the desired trajectory of the ventriculostomy catheter to the targeted ventricle may be seen on a monitor (not shown) of the portable ultrasound machine. In particular, the doctor inserting the ventriculostomy catheter may view the ventriculostomy catheter on the monitor as it is inserted, allowing a quicker and more accurate insertion of the catheter into the targeted ventricle. 
         [0029]    As shown in  FIG. 2A , transducer probe  10  preferably includes a handle  40  and a head  50  shown oriented at an angle of approximately 90 degrees to handle  40 . Preferably, probe  10  includes an adjustment mechanism  45  so that this angle is adjustable to provide an angle from about 90 degrees to about 150 degrees, with the initial setting preset to an angle of 135 degrees ( FIG. 2B ). As one of ordinary skill in the art will readily recognize, the present invention is not limited to the use of an adjustment mechanism  45  and the angle between probe handle  40  and head  50  may be alternatively be preset to any angle between about 90 degrees and about 150 degrees. This configuration provides a much more ergonomic design than the design of the prior art Aloka Probe which has a bayoneted transducer in which the handle and probe head are oriented at an angle of approximately 180 degrees to each other (and the probe head bayoneted from the handle). This handle configuration allows the doctor to hold the probe  10  like a magnifying glass or joystick. The inventors have found that the configuration of the ultrasound probe  10  shown in  FIG. 2  allows the doctor to stabilize his or her palm on the patient&#39;s head, thereby reducing fatigue and tremor while performing the ventriculostomy procedure and thereby providing better results. 
         [0030]    As shown in  FIGS. 3A ,  3 B and  3 C, conduit  30  on probe head  50  is positioned and sized to ensure that a ventriculostomy catheter (not shown) is accurately inserted parallel and stereotactically aligned to the direction of the ultrasound waves so that any operator error with regards to trajectory variability of the catheter is minimized. In one embodiment shown in  FIG. 3A , conduit  30  is completely enclosed within the probe head  50 . In another embodiment shown in  FIG. 3B , conduit  30  is near-completely enclosed within the probe head  50 . In the embodiments shown in  FIGS. 3A and 3B , the conduit  30  runs for the entire length of the probe head  50 . In a still further embodiment shown in  FIG. 3C , conduit  30  is completely enclosed and is attached perpendicularly to an end of probe head  50  adjacent to handle  40  and guides a ventriculostomy catheter (not shown) into a channel  60  on the probe head  50  to stabilize and maintain the catheter in proper alignment to stereotactic precision during insertion. Transducer  55  is coupled to the ultrasound machine via a cable  33  ( FIGS. 2A and 2B ). 
         [0031]    By providing an enclosed or nearly-enclosed conduit  30  on probe  10 , the effort required by the doctor in inserting the ventriculostomy catheter is significant reduced as opposed to performing the same procedure using the Aloka Probe discussed above and in the Whitehead Article. This result is obtained because the shallow groove on the Aloka Probe will contact less than about 25% of the circumference of the catheter and therefore requires the doctor to continuously and manually force and hold the catheter in place against the Aloka Probe during the insertion process. This makes the ventriculostomy procedure using the Aloka Probe prone to human error in alignment of the catheter trajectory to the targeted ventricle, creating a potential for failure of the procedure (necessitating an additional attempt or pass) and increasing the potential for harm to the patient. In the present invention, since conduit  30  is either completely or near-completely enclosed, the catheter is stabilized and maintained in alignment to stereotactic precision during insertion which greatly reduces human error and increases accuracy of the desired catheter trajectory because of the true stereotactic alignment of the conduit and the ultrasound waves. 
         [0032]    The head  50  of ultrasound transducer probe  10  is shown in  FIG. 2  with a nearly square cross-sectional head and in  FIGS. 3A to 3C  with a round cross-sectional head. The actual shape is arbitrary and may be selected for convenience of manufacture, with the only requirement being that head  50  and conduit  30  both fit into the inner-most area of a craniotomy created by a standard-size perforator drill bit, i.e., having a maximum outer diameter which allows the head to seat within the inner diameter (11 mm) of the craniotomy, is flush to the dura matter, and no part of the head  50  or conduit  30  are obstructed by the surrounding bone of the skull. 
         [0033]    Although the conduit  30  may be either completely enclosed ( FIG. 3A ) or near-completely enclosed ( FIG. 3B ), in both cases a doctor must be able to remove probe  10  without disrupting the ventriculostomy catheter after insertion thereof into the targeted ventricle. As a result, when conduit  30  is completely enclosed as in  FIG. 3A , probe  10  can only be removed by sliding it distally to the open (non-inserted) end of the ventriculostomy catheter. This may be impractical in certain situations because, e.g., cerebral spinal fluid could potentially leak onto the patient, doctor or the general area surrounding the patient; the newly-placed catheter could become dislodged; the movement of probe  10  could prove to be physically awkward; and the catheter could move into a non-sterile area or touch a non-sterile object while removing the probe  10 . As one of ordinary skill in the art will readily recognize, when conduit  20  is partially enclosed as shown in  FIG. 3B , the ventriculostomy catheter can be compressed along its central axis to slide it out of conduit  30  on probe  10 . As a result, in this embodiment, there is no need to slide probe  10  distally along the ventriculostomy catheter. 
         [0034]    In one alternative embodiment shown in  FIGS. 4A to 4C , conduit  30  on head  50  may be temporarily enclosed by configuring the outer half  35  of conduit  30  to roll (or rotate) into (and out of) the inner half  25  of conduit  30  to form, when closed, an aperture  20  for the catheter to move through. Thus the outer half is solid and the inner half is hollow and completely accepts the outer portion within it. As shown in  FIG. 4A , conduit  30  may be constructed from two outer half portions  35  and  36  which each roll into (and out of) inner half  25 . Alternatively, a single outer half  35  extending the length of inner half  25  may be provided or one of the outer half portions  35  and  36  (e.g., outer half portion  36 ) may be omitted.  FIGS. 4B and 4C  show the outer half  35  in the closed and open position, respectively. 
         [0035]    After the ventriculostomy is completed and the catheter is inserted into the targeted ventricle, the outer half  35  of conduit  30  may be rotated into inner half  25  to enable easy removal of probe  10  without the drawbacks associated with removable by sliding probe  10  distally along the catheter. 
         [0036]    In another alternative embodiment shown in  FIGS. 5A ,  5 B and  5 C, conduit  30  on head  50  may be formed from a first part  70  forming a partial tube which is permanently affixed to head  50  and a second flexible part  80  which either slides or snaps onto part  70  to form fully-enclosed conduit  30  with an aperture  20  ( FIG. 5C ) for the catheter to move through. Flexible part  80  is made of a material (e.g., plastic) that is flexible enough to snap on and off (as shown in  FIG. 5A ), but rigid and attached firmly enough so that the set alignment of the system is maintained ( FIG. 5B ). 
         [0037]    As with the prior embodiment, after the ventriculostomy is completed and the catheter is inserted into the targeted ventricle, the outer portion  80  of conduit  30  may be detached to enable easy removal of probe  10  without the drawbacks associated with removable by sliding probe  10  distally along the catheter. 
         [0038]    In a still further variation shown in  FIGS. 6A to 6B , conduit  30  itself attaches in a “snap fit” (or sliding) manner to head  50 . In  FIG. 6A , conduit  30  is shown separated from head  50  and includes a male member  90  which fits into a female channel  100  on the head  50  to hold conduit  30  securely against head  50 . In  FIG. 6B , conduit  30  is shown mounted to head  50 , with member  90  within channel  100 . 
         [0039]    In  FIG. 6C , conduit  30  includes a flat member  210  which slides into slot  200 . Conduit  30  is secured to head  50  in a conventional manner, e.g., with tie-wraps  120  which fit through a slot (not shown) on conduit  30 .  FIG. 6D  shows snap fit attachments  120  for holding catheter  125  within a partially-enclosed conduit  30  (which itself may be attached to head  50  in any way discussed herein). Snap fit attachments  120  may be easily removed after placement of the catheter  125  to facilitate removal of the head  50  from the installed catheter  125 . 
         [0040]    Although there are commercially available sterile sheaths for use with the Aloka Probe so that it can be used repetitively on consecutive patients without the need for sterilization between each consecutive use, these sheaths take up more space in the operative field and obscure the groove in the side of the Aloka Probe. The ultrasound transducer probe  10  of the present invention allows a customized sterile sheath to be used with certain embodiments without any detrimental effect in the catheter insertion process, thereby negating any need for sterilization of the probe  10  between each procedure. For example, the embodiment shown in  FIG. 6C  designed such that a sterile sheath having an integral conduit  30  may be attached to head  50 . 
         [0041]    As shown in  FIG. 7A , a sterile sheath  300  has a conduit assembly mounted therein having a conduit portion  30  on the outer, sterile side of sheath  300  and having a member  210  mounted on the inner, non-sterile side of sheath  300 . Member  210  is adapted to fit into a corresponding slot  200  on head  50  as the sterile sheath  300  is placed over head  50 , thereby securing the conduit assembly against head  50  and properly aligning conduit portion  30  for placement of the catheter. The sterile sheath  300  is shown mounted over the head  50 , handle  40  and part of the cable  33  of ultrasound transducer probe in  FIG. 7B . Member  210  is shown as an inverted-T structure which fits into a slot  200  on head  50 , but any type of corresponding mating structures may be used, e.g., the snap fit connection shown in  FIGS. 6A and 6B . 
         [0042]    By employing a sterile sheath  300  having an integral conduit assembly, repeated sterilizations of the ultrasound transducer probe from procedure to procedure are not necessary, as only the removable sterile sheath  300  need to be replaced for each subsequent procedure. Furthermore, since all of the parts, i.e., the parts within the sheath that directly contact probe head  50  (and are within the non-sterile areas) and the parts outside the sheath that fall within the sterile areas are rigidly affixed to each other, the alignment of conduit  30  is maintained in stereotactic alignment with the phased-array ultrasound waves emitted from the head  50 . 
         [0043]    As discussed above in the Background of the Invention section, the Aloka Probe is too large to fit within the 11 mm diameter craniotomy hole created by the standard-sized perforator drill bit together with a ventriculostomy catheter and to resolve this problem, the authors of the Whitehead Article resorted to a 15 to 20 mm diameter craniotomy. By using the transducer head  10  shown in  FIGS. 1 to 6 , a doctor may perform a ventriculostomy using a standard-sized perforator drill bit (11 mm inner diameter/14 mm outer diameter) without the need for increasing the size of the craniotomy (as in the Whitehead Article). 
         [0044]    As shown in  FIG. 7 , an illuminator  130  may preferably be added to probe  10  which allows additional light to be provided on the surface of the patient to aid the doctor in placement of the probe  10  and catheter  125 . Illuminator  130  preferably includes a light source  140  coupled to a light tube  150  and is mounted integrally within probe  10  as shown in  FIG. 7  or is attached to the periphery of probe  10  in a manner similar to conduit  30  as shown in  FIGS. 6A to 6C . Illuminator  130  may include an on/off switch  160  mounted on the surface of probe  10  in a position easily accessed by the doctor performing the procedure. As one of ordinary skill in the art will readily recognize, light tube  150  may be mounted in a manner in which light is projected from the distal end of head  50  or in a manner in which light is projected from a point spaced away from the distal end of head  50  to assist in illuminating the area around the craniotomy when the probe  10  is placed against the surface of the patient. Illuminator  130  may also include a focusing lens  170  for directing the light in a predetermined pattern on the patient to additionally aid the doctor in the placement of the probe  10  and catheter  125 . Also, the light tube  150  may be partially transparent and run along the surface of head  50  to further assist in lighting the area around probe  10 . 
         [0045]    The present invention provides a doctor with the ability to quickly and accurately insert a ventriculostomy catheter. The doctor first performs a craniotomy in the patient at the appropriate spot using the conventional burr-hole drill bit. Then the doctor positions probe  10  against the exposed dura in the 11 mm diameter hole created by the craniotomy. Probe  10  is coupled to an ultrasound machine to provide an ultrasound view of the brain. The doctor slides a conventional ventriculostomy catheter through the conduit  30  in probe  10 . Conduit  30  accurately guides the ventriculostomy catheter in a direction parallel to the direction in which ultrasound waves are emitted from probe  10 . As the ventriculostomy catheter enters the brain, the doctor is able to follow its progress on a display of the ultrasound machine. Probe  10  of the present invention is configured in an ergonomical manner so that the doctor can grip the handle  40  with one hand while guiding the ventriculostomy catheter with the other hand, thereby ensuring more accurate movement of the catheter towards the targeted ventricle. 
         [0046]    While the present invention has been particularly shown and described with reference to the preferred embodiments and various aspects thereof, it will be appreciated by those of ordinary skill in the art that various changes and modifications may be made without departing from the spirit and scope of the invention. It is intended that the appended claims be interpreted as including the embodiments described herein, the alternatives mentioned above, and all equivalents thereto.