Blood speed imaging with an intraluminal array.

In applications in which Doppler processing is not possible, such as side-looking intravascular imaging systems, decorrelation methods can be used to estimate blood speed. Here, a method is presented measuring relative blood speed using an FIR filter bank to estimate temporal decorrelation rates. It can be implemented in a modern commercially available ultrasound imaging system with no additional hardware. Both simulations and experiments using an intraluminal scanner appropriate for coronary artery applications have tested the system. In this study, the FIR filter bank is contrasted with previous methods, and its utility is further demonstrated with real-time color flow images from a pig model.

The latest in electronic imaging.

Development of new transducer and system technologies has led to major advances in image quality for electronic imaging catheters. New, 64-element arrays have increased sensitivity and optimized image resolution. System technology has advanced to include high speed reconstruction using 'complete data sets' of information. The incorporation of personal computer technology has enabled new user interfaces and digital image archiving. New, combined imaging and therapy catheters allow for efficient usage of devices. The debut of intravascular colour flow imaging technology promises a new dimension in the treatment of coronary artery disease.

Strain imaging of coronary arteries with intraluminal ultrasound: experiments on an inhomogeneous phantom.

In coronary arteries, knowing the relative stiffness of atherosclerotic lesions can help physicians select the most appropriate therapeutic modality. Because soft material supports larger strains than hard, measurements of this quantity can distinguish tissue of differing stiffness. In a previous paper, we described techniques for computing displacements and strains in coronary arteries using an integrated angioplasty and imaging catheter. Here, we demonstrate that hard and soft materials in a tissue-mimicking phantom can be differentiated with this device. Because tissue motion cannot be distinguished from catheter motion a priori, we perform all computations in the coordinate system centered at the balloon's geometric center. This reference frame depends only on balloon shape and is independent of catheter motion. A specialized correlation-based, phase-sensitive speckle tracking algorithm has been developed to compute strain. Maximum phantom displacement was about 25 microns, and the maximum radial, normal strain was about 1.5 percent.

Experimental studies on an efficient catheter array imaging system.

A new synthetic aperture system for intraluminal imaging has been tested using a 32 element, 20 MHz circular array wrapped around the surface of a catheter appropriate for coronary artery applications. This system is based on an optimal reconstruction method that has been extended to reduce grating lobes using a slight modification to classic synthetic aperture data acquisition. Optimal reconstruction filters have been derived for two different operating modes based on this new data acquisition strategy. Imaging results on a wire target phantom show that spatial resolution is a simple linear function of depth, reaching a minimum 6 dB beam width of approximately 2.2 wavelengths. Sidelobe levels are inherently high for this system because of the small number of firings used to synthesize an aperture. Optimal reconstruction filters, however, can reduce these sidelobes to at least -20 dB in all cases. Finally, images of an excised segment of porcine femoral artery demonstrate the overall performance of the system as an intraluminal imager.

Clinical percutaneous imaging of coronary anatomy using an over-the-wire ultrasound catheter system.

This manuscript describes initial applications of a unique new intravascular ultrasound imaging catheter. This 5.5F catheter uses an over-the-wire design and incorporates a phased array transducer at its tip. There are no moving parts. A 360 degree image is produced perpendicular to the catheter axis using a 20 MHz center frequency. A dedicated minicomputer is used for initial image processing, as well as enhancement and analysis. Initial studies using phantoms demonstrated excellent accuracy for linear dimensions (r = 0.99, range 3.0 to 7.6 mm, image = 1.0 phantom + 0.1). Serial imaging of the same arterial segment in vitro showed good reproducibility (coefficients of variance 2.5-5.2%). Likewise, intra- and inter-observer variability in image analysis was minimal (r = 0.92-0.99). Initial in vivo studies were performed in dogs. The catheter was easily passed over a wire into mesenteric, cerebral and coronary vessels without evidence of significant vessel trauma. Subsequently, 20 patients had percutaneous coronary imaging performed during cardiac catheterization. Cardiac motion was rarely a problem and acceptable images were obtained in all but two patients. Areas of calcification, mild stenoses, branching vessels and graft atherosclerosis could be identified. We conclude that intracoronary ultrasound imaging will be useful for assessing vascular pathology, for studying both rapid change in vessel size as well as chronic progression or regression of atherosclerosis, and for assisting with new therapeutic interventions.