One of the many ailments of mankind is the formation of calculi, that is stones or concrements, within the body. More common places for the development of such concrements are in the renal system and the gallbladder. Some of these stones pass through the renal system without causing any adverse affects noticed by the person having the stones. Other stones lodge within the kidney, the bladders or passageways between kidney, the bladder and the exterior of the body causing pain or impairing the operation of organs; then the removal of the calculi becomes imperative.
Originally the only way of removing these stones was through invasive surgery. With the advent of improved imaging techniques it became possible to utilize percutaneous techniques for the removal of many of the calculi. The percutaneous techniques are also invasive and require the insertion of means such as a nephrotomy catheter to accomplish the stone removal. The catheters are equipped with devices to grasp the calculi or ultrasonic generators for fragmenting the calculi by vibrating while contigious thereto.
More recently, extra corporeal shock wave lithotripsy has been applied to fragment and thereby eliminate renal calculi.
A lithotripsy system now being used has a pair of substantially orthogonally positioned X-ray generators designed to exactly locate the stone to be eliminated. The patient is moved three-dimensionally in a bath until cross-hairs on each of two images displayed by the system are juxtaposed to the stone. The cross-hairs are each at a line projection of the focal point of the shock wave generator. The patient is manipulated until the cross-hairs in each of the images are superimposed on the image of the stone; at that time the shock wave generator is triggered and the shock waves focused to shatter the stone down to sizes where the fragments will be washed out of the body through normal body functions.
The imaging systems used presently for the calculi locating function leave room for improvement. Among other things it is desirable to reduce the exposure of the patient to X-rays. The patient presently is exposed to X-rays, originally to ascertain that stones are indeed causing problems and that they can be eliminated by lithotripsy.
X-rays are used to align the stone with the focal point of the shock wave generator and X-rays are used subsequent to the application of the shock waves to assure that the stones have been shattered into fragments which can be disposed of by normal functions of the body. Thus, the procedure requires a relatively large accumulated dose of X-rays. It would be advantageous to lower the amount of X-ray radiation required in the lithotripsy process. To this end ultrasound has been tried in the past. Additionally ultrasound radiation is more capable of imaging gallbladder stones than X-ray radiation. However, the prior art attempts at imaging with ultrasound for locating calculi to be fragmented by shock waves have encountered difficulties.
In the prior attempts at using ultrasound as the medium for locating the calculi, different acoustic windows were used by the ultrasound transducers and by the shock wave generator. The prior systems also failed to make any effective correction for the distortions of the ultrasound signals and the shock waves due to refraction caused by the differences of the transmission velocities of the ultrasound signals and the shock waves in the different media.
In addition in the past no provisions were made for enabling a single ultrasound transducer to image a plurality of planes for assuring accurate location of the calculi.
Similarly, no provisions were made for varying the field of view of the individual transducers to provide for the different views required when searching for calculi and when centering the discovered calculi at the cross-hairs.
Accordingly it is an object of the present invention to overcome the shortcomings of the prior art ultrasound imaging systems used in calculi location and to thereby improve on the presently available calculi locating imaging systems used in cooperation with extra corporeal shock wave lithotripsy.