Ultrasound Targeting System for Shockwave Lithotripsy

Ultrasound guided shockwave lithotripsy, commonly known as ESWL or extracorporeal shockwave lithotripsy, refers to a system for treating stones or calculi, normally by disintegration for ultimate removal or discharge from the body.

It is particularly desirable to properly focus the shock waves on the stone to avoid damage to healthy tissue about the stone. However, ureteral stones are very difficult, if not impossible, to visualize with ultrasound, and thus accurate focusing of the equipment has been a problem.

One known procedure, in lithotripsy systems, for location of calculi to be disintegrated involves the use of x-ray means and is referred to in U.S. Pat. No. 4,741,008, issued to Kurt Franke on Apr. 26, 1988. This x-ray means normally comprises rather elaborate equipment particularly adpated for use as an adjunct of the lithotripsy equipment to provide a visual representation of a calculi.

The present invention proposes an alternate and substantially improved system for properly focusing or directing the shockwaves when treating ureteral stones with ultrasound guided shockwave lithotripsy. Basically, a target highly visible to ultrasound is positioned immediately adjacent the stone within the ureter with the shockwave focused on the target or in the immediate vicinity thereof. After focusing, the target can be withdrawn.

More specifically, the present invention proposes a catheter target comprising an elongate catheter with an inflatable balloon mounted on the leading end thereof. The balloon defines the actual stone engaging target.

The target to be effective must have good ultrasound visualization, and as such, must comprise a material or be of a nature to provide a significantly different acoustical impedance from the surrounding body tissue. This requirement is uniquely met by air which, when used as the inflation medium for the catheter balloon, provides an inexpensive and highly effective ultrasound target.

In performing a lithotripsy procedure utilizing a target catheter, the target catheter is placed through a cystoscope under fluoroscopy up to and immediately adjacent the distal side of the stone. The cystoscope is then removed and the patient positioned for the shockwave procedure. When ultrasonically focusing the shockwave, the balloon is inflated with air to provide the desired high visualization. As the physician is aware that the stone is just to the proximal side of the balloon, the equipment can now be accurately directed after which the balloon, as desired, may be deflated. The use of an inflatable balloon as the target, particularly with the inflation medium being air, enables a selective deflation and re-inflation of the target balloon should such be necessary to verify location of the target and proximal stone.

It is particularly preferred that the balloon be expandable beyond the leading end of the catheter with no portion of the catheter going through the balloon itself as in the more conventional balloon catheter. This is preferred in that there will be no internal echoes from the balloon, but rather, only a small, cystic-appearing structure on the ultrasound.

Catheters with end-positioned balloons are known and have been used for a variety of purposes. For example, before ESWL procedures, a similar catheter with an inflatable balloon end had been used to propel stones from the ureter back into the kidney. However, with the advent of ESWL, the use of this propelling procedure diminished. There was no suggestion of utilizing such balloon catheters as targets in an ultrasound guided shockwave lithotripsy procedure.

Additional objects and features of the invention will become apparent from the details of the invention as more fully hereinafter described and claimed.

FIG. 1 is a schematic view illustrating introduction of the target catheter into the ureter toward an internal stone or calculi;

FIG. 2 is a schematic view illustrating the target-defining balloon inflated immediately distal of the stone.

The target catheter 10 includes a conventional catheter 12, which may be on the order of 5F (French) by 69 centimeters, with an inflatable latex balloon 14 mounted on the leading end of the catheter. The balloon 14 is to be inflatable to about 18F. The letter F (French) is a conventional size designation with 3F equaling approximately one millimeter.

The drawing schematically illustrate the insertion and location of the target catheter in treating a ureteral stone 16 located within the ureter 18. The primary purpose of the invention is to provide a system whereby a non-invasive lithotriptor or shockwave generator 20 can be accurately focused on the stone or calculi 16 for disintegration of the stone with little or no damage to the healthy surrounding tissue.

The procedure initially involves an insertion of the target catheter 10 to position the target-defining balloon 14. The target catheter will normally be placed through a cystoscope under fluoroscopy as schematically suggested at 22 in FIG. 1. As such, the catheter body is preferably radiopaque for good visibility under fluoroscopy.

The target balloon 18 is preferably placed immediately against the distal side of the stone, after which the cystoscope is removed.

The patient is then taken for ESWL, or extracorporeal shockwave lithotripsy. As an initial step, the balloon is inflated with air. Air is the preferred inflation medium in that the defined air cavity provides a significantly different acoustical impedance from body tissue. This in turn results in good ultrasound visualization. Inflation of the balloon can be conventionally effected utilizing a syringe and approximately 1/2 cc. of air.

By a positioning of the target balloon just to the distal side of the stone, the physician knows the stone is just proximal to the balloon. As such, the lithotriptor or shock wave generator can be accurately focused on the stone, as suggested in FIG. 2. Subsequent to a focusing of the shock wave generator, the balloon can be deflated, if desired, to avoid any potential interference with stone disintegration.

If considered necessary to verify location of the target balloon and stone, the target balloon, through the catheter, can be easily alternatively deflated and inflated in an obvious and simple manner. The target catheter may, of course, be removed as desired either upon a targeting of the shockwaves or a completion of the entire procedure.

As previously noted, the target balloon is provided on the extreme leading end of the catheter to avoid the catheter going through the center portion of the balloon. Thus, there will be no internal echoes from the balloon, but rather, only a small, cystic appearing structure on ultrasound which forms a readily defined target, particularly when the fluid inflation medium is air.

Variations in means and procedures may be suggested to those skilled in the art. It is intended that the scope of the invention be such as to encompass all such variations as may be within the scope of the invention as herein presented and claimed.