Biomedical subjects

Douglas N Stephens

Publications and source records attributed to Douglas N Stephens.

3 recordsLinked to original sources

PubMed2005

An integrated semicompliant balloon ultrasound catheter for quantitative feedback and image guidance during stent deployment.

An integrated balloon ultrasound catheter prototype was designed to image from inside the balloon for real-time guidance during stent deployment. It was fabricated using a semicompliant balloon material (polyethylene) and a 20 MHz, 64-element circumferential ultrasound array. A commercial stent, nominally 4.4 mm in diameter and 12 mm in length, was used for a phantom study and placed along the length of the integrated balloon ultrasound catheter. A rubber phantom was created with an elastic modulus of 175 kPa with a 4.36 mm diameter lumen. Real-time balloon pressure measurements were recorded using a digital pressure sensor, and real-time radio-frequency (RF) data were captured as the balloon was inflated. The slope of the area-pressure ratio (APR) was compared to a reference measure of the balloon and stent expanded in water to determine a measure for optimal stent deployment. The results clearly indicate stent deployment at 11.1 atm using this metric. The APR slope could serve as quantitative feedback parameter for guiding stent deployment to reduce arterial injury and subsequent restenosis. After the stent deployment experiment, RF data were captured as the balloon catheter was moved along the length of the stent in pullback mode to confirm successful stent deployment. Ultimately, an integrated balloon ultrasound catheter could serve as a single catheter intervention device by providing real-time intravascular ultrasound (IVUS) imaging and quantitative feedback during stent deployment.

Blood Vessel Prosthesis↗

PubMed2003

Coded excitation with spectrum inversion (CEXSI) for ultrasound array imaging.

In this paper, a scheme called coded excitation with spectrum inversion (CEXSI) is presented. An established optimal binary code whose spectrum has no nulls and possesses the least variation is encoded as a burst for transmission. Using this optimal code, the decoding filter can be derived directly from its inverse spectrum. Various transmission techniques can be used to improve energy coupling within the system pass-band. We demonstrate its potential to achieve excellent decoding with very low (< 80 dB) side-lobes. For a 2.6 micros code, an array element with a center frequency of 10 MHz and fractional bandwidth of 38%, range side-lobes of about 40 dB have been achieved experimentally with little compromise in range resolution. The signal-to-noise ratio (SNR) improvement also has been characterized at about 14 dB. Along with simulations and experimental data, we present a formulation of the scheme, according to which CEXSI can be extended to improve SNR in sparse array imaging in general.

Algorithms↗

PubMed2002

Optimizing the beam pattern of a forward-viewing ring-annular ultrasound array for intravascular imaging.

Intravascular ultrasound (IVUS) imaging systems using circumferential arrays mounted on cardiac catheter tips fire beams orthogonal to the principal axis of the catheter. The system produces high resolution cross-sectional images but must be guided by conventional angioscopy. A real-time forward-viewing array, integrated into the same catheter, could greatly reduce radiation exposure by decreasing angiographic guidance. Unfortunately, the mounting requirement of a catheter guide wire prohibits a full-disk imaging aperture. Given only an annulus of array elements, prior theoretical investigations have only considered a circular ring of point transceivers and focusing strategies using all elements in the highly dense array, both impractical assumptions. In this paper, we consider a practical array geometry and signal processing architecture for a forward-viewing IVUS system. Our specific design uses a total of 210 transceiver firings with synthetic reconstruction for a given 3-D image frame. Simulation results demonstrate this design can achieve side-lobes under -40 dB for on-axis situations and under -30 dB for steering to the edge of a 80 degrees cone.

Blood Vessels↗