Abstract:
An ultrasound probe assembly adapted for bio-imaging. The assembly comprises a catheter, an electrical assembly, including a set of linear conductors, at least partially housed within said catheter. An ultrasound transceiving unit is electrically connected to said electrical assembly and can be placed in both an undeployed state in which the transceiving unit is oriented coincidentally to said catheter and a deployed state in which it is directed to provide imaging signals over a volume of interest.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention is an apparatus and method for introducing an ultrasound transceiver into a body cavity such as the right atrium of the heart in order to image a portion of the body, such as the left ventricle of the heart.  
           [0002]    The mammalian heart typically has four chambers: Two ventricles for pumping the blood and two atria, each for collecting the blood from the vein leading to it and delivering that blood to the corresponding ventricle when it is not pumping. The left ventricle pumps blood to the vast bulk of the mammalian body. As a result, problems with the left ventricle or with the mitral valve, which leads from the left atrium into the left ventricle, can cause serious health problems for an affected individual. When it appears that a patient has inadequate blood circulation in a portion of his or her body, the left ventricle and the mitral valve are naturally suspect. Specifically diagnosing the problem to these structures, however, and more specifically to a particular problem with the left ventricle or mitral valve is not an easy proposition. In fact unnecessary surgeries are sometimes performed due to the difficulty of forming a certain diagnosis.  
           [0003]    More generally, heart disease, including ischemic, valvular and arrhythmias, represents one of the most common debilitating disease complexes in the elderly of the US, and is a common cause of death. A number of therapies have been created for treating cardiac conditions by way of the introduction of a laser or other device into a chamber of the heart by way of a catheter. One of the most active areas, in need of the most sophisticated approach to ultrasound intracardiac imaging, involves the transcatheter attempts to produce linear and continuous electrophysiologic lesions on the atrial wall for treatment of chronic atrial fibrillation in elderly adults. 2.2 million people in the U.S.A. have this condition, and it is increasing in frequency as our population ages. In the Maze procedure, a grid of linear interruptions is produced on the atrial wall to treat this condition—most commonly in the right atrium and less commonly the left atrium. Unfortunately, the limitations of currently available cardiac imaging techniques result in these therapies being performed with a great shortage of desirable information.  
           [0004]    Accordingly, there are many important purposes for creating images of the heart, including in particular the left ventricle and the mitral valve. Among these purposes is the assessment of the need for corrective cardiac surgery and the informing and guiding of cardiac therapeutic procedures by way of imaging performed during such procedures. Unfortunately, currently available methods for imaging the heart and specifically the left ventricle and the mitral valve leave much to be desired. One method, termed transthoracic imaging, typically requires the placement of an ultrasound transceiver against the chest of the patient and the use of this transceiver to image the heart. Unfortunately, the bones and the other tissue types that are interposed between the ultrasound transceiver and the heart during this procedure prevent the formation of a sufficiently detailed image of the heart. Another cardiac imaging method, trans-esophageal imaging, involves the insertion of an ultrasound transceiver into the esophagus of the patient. Although trans-esophageal imaging places the ultrasound transceiver closer to the heart, the patient must be rendered unconscious by way of a general anesthetic for this method to be employed. As a result, the patient&#39;s cooperation is surrendered. In cardiac imaging it is very valuable to have a cooperative patient who can change position upon request in order to facilitate the imaging of different views of the heart under various operating conditions.  
           [0005]    Other body cavities could host the distal end of an ultrasound probe, if it were possible to introduce the probe into the body cavity in a form that could be passed through a relatively narrow passageway leading to the cavity. Unfortunately, currently available ultrasound probes are not constructed to have an undeployed state in which the probe is very narrow and amenable to this method of introduction into a body cavity.  
         SUMMARY  
         [0006]    In a first separate aspect, the present invention is method for imaging at least a portion of a mammalian heart, having a right atrium and residing in a mammal having veins leading to the right atrium. As a preliminary step, an ultrasound probe assembly is provided. This assembly has a proximal end and a distal end and can be placed into both a deployed state and an undeployed state. In the undeployed state the probe assembly can be inserted into a vein leading to the right atrium and thereby into the right atrium. When placed in the deployed state the probe assembly is positioned into an advantageous imaging orientation. The distal end is capable of transmitting and receiving ultrasound signals, converting the received signals into electrical signals and transmitting the received signals to a receiving apparatus. In the next steps, the assembly is placed into its undeployed state and the distal end of the probe assembly is introduced into the right atrium by way of a vein leading to the right atrium. Next the assembly is placed into its deployed state and used to image at least a portion of the heart.  
           [0007]    In a second separate aspect, the present invention is an ultrasound probe assembly adapted for bio-imaging. The assembly comprises a catheter, an electrical assembly, including a set of linear conductors, at least partially housed within said catheter. An ultrasound transceiving unit is electrically connected to said electrical assembly and can be placed in both an undeployed state in which the transceiving unit is oriented coincidentally to said catheter and a deployed state in which it is directed to provide imaging signals over a volume of interest.  
           [0008]    The foregoing and other objectives, features and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention, taken in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 shows a perspective view of preferred embodiment of the ultrasound probe assembly of the present invention, in the right atrium of a human heart.  
         [0010]    [0010]FIG. 2 a  shows perspective view of the ultrasound transceiver of the ultrasound probe of FIG. 1.  
         [0011]    [0011]FIG. 2 b  shows a partial side view of ultrasound transceiver of FIG. 2 a.    
         [0012]    [0012]FIG. 3 a  shows a side view of the distal portion of the ultrasound probe assembly of FIG. 1.  
         [0013]    [0013]FIG. 3 b  shows a perspective view of the distal portion of FIG. 3 a.    
         [0014]    [0014]FIG. 4 a  shows a side view of the distal end of an ultrasound probe assembly that represents an alternative preferred embodiment of the present invention.  
         [0015]    [0015]FIG. 4 b  shows a top view of the distal end of the present invention.  
         [0016]    [0016]FIG. 4 c  shows a perspective view of the distal end of the present invention.  
         [0017]    [0017]FIG. 5 is a perspective view of an alternative preferred embodiment of an intracardiac imaging device according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0018]    In one preferred embodiment the invention is an ultrasound probe assembly  10  that includes a catheter  12  (in one preferred embodiment a No. 14 French catheter is used) that houses an conductor bearing structure  14  in the form of a stiffened ribbon cable and terminating in an ultrasound transceiver  16  that is a linear array of 128 piezoelectric (preferably ceramic) elements  17  supported by a polymer backing layer  19  that is in turn supported by a substrate of shape memory material  18 . An acoustic lens  20 , preferably constructed of silicone shapes the ultrasound beam created by elements  17 . A polymeric matching layer  22  is interposed between element  17  and the lens  20 . In its undeployed state the transceiver  16  is straight, enabling it to fit conveniently within the catheter  12 , for introduction into a body cavity, such as the right atrium. To place assembly  10  into its deployed state, however, a human operator pushing on the proximal end of structure  14  pushes the transceiver  16  outwardly from the end of the catheter  12 . The warmth of the human body then warms the shape memory material of substrate  18  to the point that it assumes its memorized shape, which is in the form of a hook, as shown. Extending and retracting catheter  12  relative to transceiver  16  steers transceiver  16  in the plane of the paper in FIG. 3 a , permitting various views of portions of the heart.  
         [0019]    The array of elements  17  may be constructed to operate a center frequency of 9 MHz, with a Doppler range of 6 MHz. The effective aperture length may be 18 mm with an aperture width of 3 mm and a radius of curvature of 20 mm, to produce an effective field of view of 45 to 50 degrees. Lens  20  may have a transverse radius of 10 mm. Elements  17  may be divided into two subdivisions and positioned with a pitch of 0.07 mm.  
         [0020]    An alternative preferred embodiment  50  is shown in FIGS. 4 a - 4   c . (In these Figs., structures that are identical with structures already introduced are labeled with the previously introduced reference numbers and structures that are analogous with previously introduced structures are designated by the previously introduced reference number primed. In this embodiment a collection of shape memory strands  52  fans out into a rigid web when warmed to body temperature. Strands  52  bear a collection of piezoelectric elements that can be coordinated together into a large aperture electrically steerable array, thereby collecting data sufficient to permit three-dimensional imaging.  
         [0021]    In yet another embodiment a set of strands form the volumetric outline of a bulb when the memorized shape is assumed.  
         [0022]    Assembly  10 , or assembly  50 , is introduced into the right atrium by placing assembly  10  into its undeployed state and introducing it into the jugular vein at the patient&#39;s neck. The patient may remain conscious during this procedure, with a local anesthetic being applied to permit the device insertion. The distal end of the assembly is then introduced into the right atrium, where it assumes its deployed state and is used for imaging. The total in vivo travel distance of the assembly  10  is on the order of six to nine inches. Because the patient remains conscious during the procedure, he or she may aid in the imaging process by shifting position during the imaging procedure. To remove, ultrasound transceiver  16  is pulled back into catheter  12 , which constrains transceiver  16  to the general shape of catheter  12 , permitting the removal of assembly  10  by a simple pulling motion.  
         [0023]    Referring to FIG. 5, in an additional preferred embodiment, an imaging probe  110 , includes a piezoelectric array  116 , which may be very similar to array  16  (FIG. 2 b ). Assembly  110 , however, is placed into a deployed state (as shown by dashed line portion of figure), by pulling on one or the other of a pair of tension lines  120  and  122 . Line  120  pulls array  116  downwardly, whereas line  122  pulls array  116  upwardly in the plane of FIG. 5. A spring  124  urges array  116  into a position that is straight with respect to catheter  130 . Catheter  130  includes one hundred and twenty-eight coaxial cables (not shown), one for each piezoelectric element. These coaxial cables are typically bound together inside the catheter  130 . At the interior of spring  124 , however, the signal paths take the form of traces in a flex circuit  126 , which may be flexed up or down as shown in FIG. 5. A fixture  132  and a knob  134 , attached to tension lines  122  and  124 , is provided to aid a doctor in manipulating array  116 .  
         [0024]    The terms and expressions which have been employed in the foregoing specification are used as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding equivalents of the features shown and described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims which follow.