Charles J. Bruce

Intracardiac phased-array imaging: methods and initial clinical experience with high resolution, under blood visualization: initial experience with intracardiac phased-array ultrasound.

OBJECTIVES This study was designed to test the feasibility of high-resolution phased-array intracardiac imaging. BACKGROUND Intracardiac echocardiographic imaging of the heart during interventional electrophysiologic (EP) procedures has been limited by inadequate ultrasound penetration and absence of Doppler hemodynamic and flow information produced by rotating mechanical ultrasound elements. METHODS A 10F (3.2 mm) phased-array, variable 5.5 to 10 MHz frequency imaging catheter with a four-way deflectable tip was applied in 24 patients undergoing EP studies. Sixteen prespecified cardiac targets were imaged from a right heart venue. RESULTS Fifteen patients had no underlying organic heart disease; nine had ischemic, cardiomyopathic, valvular or congenital heart disorders. Longitudinal and short-axis imaging readily disclosed each cardiac valve, support structures and chamber, as well as the pericardium, right and left atrial appendages, the junction of the right atrium and superior vena cava, crista terminalis, tricuspid valve isthmus, coronary sinus orifice, membranous fossa ovalis and pulmonary veins. The average target depth was 8.8+/-1.5 cm (range 0.5 to 15 cm), with adequate penetration at a 7.5 MHz imaging frequency. Color flow and Doppler utilities clearly characterized transaortic and pulmonic valve and pulmonary vein blood flow, including during low output states. CONCLUSIONS These first human studies with this technology demonstrate the methods, feasibility and utility of intracardiac phased-array vector and Doppler imaging for long-axis, apex-to-base global cardiac imaging. High resolution of endocardial structures and catheters suggests additional utility for visualizing interventional procedures from the right heart.

3463 Initial experience with a steerable, phased vector array ultrasound catheter in the gastrointestinal tract.

Endoscopic ultrasound requires significant capital outlay, including dedicated echo endoscopes and processors for both linear and radial scanning. The ability to perform high resolution linear scanning and Doppler interrogation using a catheter that interfaces with a standard ultrasound console could increase the accessibility of EUS to many centers. A 10F steerable catheter with a phased Vector array transducer and Doppler capability has recently been developed for intracardiac use. To date, this technology has not been applied to the gastrointestinal (GI) tract. Aims: To determine the feasibility and imaging characteristics of a new linear-scanning, steerable ultrasound catheter in the GI tract. Methods: Swine under general anesthesia were used. This study utilized a 100cm, 10F, torquable catheter with 4-way tip deflection in excess of 90°. The catheter tip houses a 64-element, linear scanning, transducer with variable frequency (5.5-10MHz) and variable focal distance. It has pulsed/color Doppler capability as well as power- Doppler. The probe was passed through a sigmoidoscope. Scanning was performed from the esophagus and stomach. Acoustic coupling was via a condom filled with water or by gastric water infusion. Needle visualization experiments utilized a second endoscope with a standard EUS-FNA needle. Results: Acoustic coupling was easily achieved. Resolution of the GI wall into characteristic layers (esophagus 5; stomach 7) was demonstrated. At 5.5MHz, tissue resolution was excellent to >10cm from the transducer. An EUS-FNA needle was easily visualized at depth >4cm. Flow in gastric, hepatic and pancreatic parenchymal vessels ~1mm diameter were visualized using power & color Doppler. Measurements of waveform and hemodynamic capabilities were assessed at lower flow rates and greater depth than possible with current EUS instruments. Conclusions: A 10 French, 5.5-10MHz, agile, phased sector array ultrasound catheter with 4 way tip deflection is capable of high resolution 2D imaging of the gut wall as well as high quality Doppler imaging using pulsed and continuous wave, color flow, power, and tissue Doppler. The probe interfaces with a standard cardiac ultrasound console. Needle visualization may allow EUS-FNA procedures without the need for dedicated echoendoscopes. The enhanced Doppler capabilities of this equipment may have new unexplored GI applications eg: blood flow assessment in portal hypertension, malignant and benign processes and peptic ulcer disease.