1. Field of the Invention (Technical Field)
This invention relates to apparatuses for ultrasonic imaging of angioplasty or atherectomy catheters; and methods for their use.
2. Background Art
Standard percutaneous transluminal angioplasty, atherectomy, dilatation, and stenting techniques of the peripheral vascular system have traditionally required the use of iodinated contrast media and radiographic guidance for the proper positioning of the dilatation balloon across an arterial stenosis. There is a known incidence of allergy to iodinated contrast dye as well as unpredictable reactions to contrast dye, including various degrees of anaphylaxis and renal failure. The ionizing radiation utilized during the procedure is also a hazard to the patient and the medical staff.
Ultrasonographic imaging, on the other hand, presents no known irradiation hazard and requires no use of radiopaque contrast medium, yet provides excellent visualization of the arterial lumen and walls.
The correct placement of the angioplasty balloon during an angioplasty or atherectomy procedure is not only facilitated by the use of radiographic contrast medium to determine the location of the arterial stenosis, but also by radiographic markers, usually small bands of radiopaque material (metal), which mark the proximal and distal limits of the balloon.
The present invention allows for the correct placement of an angioplasty balloon catheter across an arterial stenosis utilizing ultrasonographic imaging alone, for example, B-mode imaging, thereby obviating contrast reactions and ionizing radiation exposure.
The concept of marking catheters with metallic elements is not new. Devices such as that disclosed in U.S. Pat. No. 4,279,252, to Martin, entitled X-Ray Scaling Catheter, utilize metallic foil rings embedded in the walls of an angiography catheter at a set distance apart in order to calculate distances within the heart and correct for errors due to x-ray magnification. These markers are radiopaque and designed for use with radiographically guided cardiac angiography procedures.
The concept of acoustically modifying catheters for enhanced visualization with ultrasound imaging is not per se novel. U.S. Pat. No. 4,401,124, to Guess, et al., entitled Reflection Enhancement of a Biopsy Needle, disclose a diffraction grating comprising parallel grooves etched into the tip of a biopsy needle for enhancing the reflection coefficient when used in conjunction with pulse-echo ultrasound imaging. Similarly, Elkins in U.S. Pat. No. 4,869,259 entitled Echogenically Enhanced Surgical Instrument and Method for Production Thereof discloses an acoustically enhanced surgical needle having a roughened surface with pits and erosions of the order of 50 microns in depth. The resultant roughness increases the density of reflected ultrasound beams to the piezoelectric sensor, resulting in enhanced echogenicity of the treated portion of the needle.
U.S. Pat. No. 4,431,006, to Trimmer, et al., entitled Passive Ultrasound Needle Probe Locator, teaches a sonically conductive needle which conveys ultrasonic energy to an external transducer. Divisional U.S. Pat. Nos. 4,637,401 and 4,674,336, to Johnston, entitled Volumetric Flow Rate Determination in Conduits Not Directly Accessible, both teach ultrasonic energy reflection in combination with a Doppler circuit for measuring blood velocity.
U.S. Pat. No. 4,582,061, to Fry, entitled Needle with Ultrasonically Reflective Displacement Scale, teaches a body puncturing device comprising a plurality of cavities or grooves for trapping gas, thereby improving acoustic reflection. U.S. Pat. No. 4,697,595, to Breyer, et al., entitled Ultrasonically Marked Cardiac Catheters, discloses a plurality of piezoelectric transducers embedded in a catheter to establish catheter location. U.S. Pat. No. 4,571,240, to Samson, et al., entitled Catheter Having Encapsulated Tip Marker, discloses a catheter comprising a broad metallic band at one end thereof for fluoroscopic use. U.S. Pat. No. 4,407,294, to Vilkomersas, entitled Ultrasound Tissue Probe Localization System, teaches an ultrasound imaging system comprising at least three transducers. U.S. Pat. No. 4,577,637, to Mueller, Jr., entitled Flexible Metal Radiopaque Indicator and Plugs for Catheters, discloses a radiopaque coiled metal spring which provides a catheter plug and indicator. U.S. Pat. No. 4,512,762, to Spears, entitled Method of Treatment of Atherosclerosis and a Balloon Catheter for Same, discloses a light-emitting balloon catheter for treatment of atheromatous plaque.
The current invention utilizes the placement of a fine wire monolayer, for example, 5 mm long, proximal and distal, at the limits, or within the angioplasty balloon itself, in order to be detected acoustically by ultrasonographic imaging. The proper detection of the proximal and distal limits of the angioplasty balloon by ultrasonographic imaging results in the ability to correctly position the balloon across an arterial stenosis without the use of radiographic contrast medium or ionizing radiation. Hence, angioplasty can be accomplished by non-radiographic ultrasonic guidance obviating the risks inherent to the traditional use of contrast agents and ionizing radiation.