Accurate blood peak velocity estimation using spectral models and vector doppler.

Ultrasound blood peak velocity estimates are routinely used for diagnostics, such as the grading of a stenosis. The peak velocity is typically assessed from the Doppler spectrum by locating the highest frequency detectable from noise. The selected frequency is then converted to velocity by the Doppler equation.

Finding the peak velocity in a flow from its Doppler spectrum.

The signal backscattered by blood cells crossing a sample volume produces a Doppler power spectrum determined by the scatterers¿ velocity distribution. Because of intrinsic spectral broadening, the peak Doppler frequency observed does not correspond to the peak velocity in the flow. Several methods have been proposed for estimating the maximum velocity component--an important clinical parameter--but these methods are approximate, based on heuristic thresholds that can be inaccurate and strongly affected by noise.

Development of a flexible implantable sensor for postoperative monitoring of blood flow.

We have developed a blood flow measurement system using Doppler ultrasound flow sensors fabricated of thin and flexible piezoelectric-polymer films. These flow sensors can be wrapped around a blood vessel and accurately measure flow. The innovation that makes this flow sensor possible is the diffraction-grating transducer.

A trial of detecting impending access-graft failure by simplified weekly flow monitoring.

Access graft failure is a major problem in hemodialysis. Monitoring the flow through the access so that impending failure can be detected and prevented seems reasonable, but recent clinical trials have failed to show any benefit of such monitoring. Described here are plans for a clinical trial of a new flow monitoring procedure that measures access flow weekly instead of monthly and, being performed before dialysis, avoids the dialysis-induced changes in graft flow that may have affected earlier trials.

Non-specialist ultrasound measuring of access flow: new technology.

A new ultrasound instrument has been developed, using vector Doppler and embedded machine intelligence, to enable measurement of access flow rates by non-specialists. Ultrasound measurement of access flow can be performed with the patient off the dialysis machine, avoiding the hemodynamic changes that may affect indicator-dilution methods. A research version of the instrument was tested on flow phantoms simulating graft flow, and showed accuracy better than 5%.

Echocardiographic transponder-guided catheter ablation feasibility and accuracy.

Background: The utility of echocardiography for catheter guidance during percutaneous endocardial ablation is increasingly apparent. However, the technique is currently imperfect due to limitations in discerning the ablation electrode from other parts of the catheter shaft.

Purpose: To examine the feasibility and accuracy of echocardiography-guided ablation using commercial ablation catheters fitted with a transponder to improve localization of the ablation electrode.

Localization of needle tip with color doppler during pericardiocentesis: In vitro validation and initial clinical application.

This study evaluates a new device that uses color Doppler ultrasonography to enable real-time image guidance of the aspirating needle, which has not been possible until now. The ColorMark device (EchoCath Inc, Princeton, NJ) induces high-frequency, low-amplitude vibrations in the needle to enable localization with color Doppler. We studied this technique in 25 consecutive patients undergoing pericardiocentesis, and in vitro, in a urethane phantom with which the accuracy of color Doppler localization of the needle tip was compared with that obtained by direct measurement.

Angioplasty of lower limb arterial stenoses under ultrasound guidance: single-center experience.

Purpose: To examine the feasibility and utility of ultrasound-guided angioplasty for treating lower limb stenoses.

Methods: Duplex ultrasonography was employed to guide 55 balloon dilation procedures (27 iliac, 26 superficial femoral, 1 profunda, and 1 vein graft) with the help of a special ultrasound catheter (EchoMark). Ultrasound was used to determine balloon size, monitor guidewire passage, direct the dilation, and judge procedural success.

New, angle-independent, low cost Doppler system to measure blood flow.

Background: A new Doppler flowmeter using a special transducer forming two ultrasound beams to insonate vessels was developed. This low-cost flowmeter allows the flow to be measured independently of the angle of insonation.

Methods: Sixty-five flow determinations were made in the carotid arteries of five pigs.

A system for ultrasonic beacon-guidance of catheters and other minimally-invasive medical devices.

Catheters and other interventional medical devices are presently guided by X-ray imaging, despite the advantages of ultrasound imaging over X-ray imaging in cost, safety, and availability. X-ray imaging is used because ultrasound reflects specularly from catheters and similar devices; their visibility is highly angle-dependent. With an omni-directional receiver mounted on a device, the receiver's location in the ultrasound image can be deduced from knowing which acoustic ray struck the receiver and the time from transmission of the imaging pulse to its reception by the receiver.

A system for ultrasonic beacon-guidance of catheters and other minimally-invasive medical devices.

Catheters and other interventional medical devices are presently guided by X-ray imaging, despite the advantages of ultrasound imaging over X-ray imaging in cost, safety, and availability. X-ray imaging is used because ultrasound reflects specularly from catheters and similar devices; their visibility is highly angle-dependent. With an omni-directional receiver mounted on a device, the receiver's location in the ultrasound image can be deduced from knowing which acoustic ray struck the receiver and the time from transmission of the imaging pulse to its reception by the receiver.

Principles of angioplasty guidance using ultrasound.

Marker bands that cast dense shadow on X-ray are placed at crucial points on a catheter (for example on a peripheral angioplasty catheter on either side of the balloon) so that those parts of the catheter can be guided inside the body by X-ray. For catheter guidance by ultrasound, an ultrasound sensor in the mid-balloon region of an angioplasty catheter is integrated to the scanhead of an ultrasound scanner, via a catheter system interface (CSI). When the sensor in the catheter is imaged by the ultrasound scanner, the CSI injects a bright arrow corresponding to its position.

Ultrasound Guided Balloon Angioplasty: What is its Role?

A modified angioplasty catheter has been developed which can be guided-into position with duplex ultrasound. This reduces the risks of ionizing radiation and contrast agents and uses a modality familiar to the vascular surgeon. This catheter was tested successfully in a canine model for safety, accuracy and therapeutic efficacy.

Transcutaneous ultrasonography can be used to guide and monitor balloon angioplasty.

Purpose: Percutaneous balloon angioplasty is an accepted technique for the treatment of short segmental stenoses of the iliac and superficial femoral arteries. Some surgeons have not embraced this technique because of lack of training, unfamiliarity with radiologic equipment, or poor-quality fluoroscopy equipment in the operating room. A new technique, ultrasound-directed balloon angioplasty, enables the vascular surgeon to guide the catheter and evaluate the progress of the procedure without the use of radiographic imaging.

Ultrasound-guided balloon angioplasty is a new technique for vascular surgeons.

A new catheter has been developed that can be accurately and precisely positioned using duplex ultrasonography alone. A piezoelectric transducer that functions as a passive, omnidirectional receiver is attached to the mid-balloon region of an angioplasty catheter. Integration to a standard duplex imaging system allows visualization of this receiver in all planes, with the location of the receiver represented by a flashing bright arrow superimposed on the ultrasound B-mode image.

A new wire phantom for accurate measurement of acoustical resolution.

This article describes a phantom which is easier to use and gives more accurate results than a phantom made from several pairs of solid wires. This phantom employs two concepts: spatially modulated wires and diverging wires. Spatially modulated wires, such as helically twisted wires, reflect the sound into a broad range of angles.

New technique for ultrasound imaging.

A new system of ultrasonic imaging has been developed which utilizes optical interferometry. This system has a broad frequency range, wide angular response, and good resolution. Operation of the system and the results of experimental imaging are described.

Differences in the attenuation of ultrasound by normal, benign, and malignant breast tissue.

In quantitative measurements of the attenuation of ultrasound in 18 samples of variously normal, benign, and malignant breast tissue, we found significantly different ranges of attenuation. As observed in previous in vivo studies, with the exception of medullary carcinoma, malignant tissue produces the most attentuation of ultrasound in the frequency range of 1.5 to 3.

Ultrasonic waves: their interferometric measurement and display.

A system for the measurement and visualization of small displacements has been developed that features high sensitivity and acoustic-wavelength-limited resolution over apertures as large as 15 cm at frequencies up to 10 MH(z). Acoustic-wave displacement amplitudes as small as 0.07 A are measured by interferometrically detecting the motion of a thin, acoustically transparent, metallized pellicle as the ultrasonic wave passes through it.

Measurements of the noise spectral power density of photosensitive materials at high spatial frequencies.

A new method of measuring the scattered light to determine the noise spectral power density is described The technique is shown to be useful at the high spatial frequencies used in holography, beyond the range of the former methods of noise power measurement. Measurements of the grain noise of several photographic emulsions used for holography are presented; they are consistent with a model of emulsions characterized by a transmission correlation length. The measured correlation length of several of the emulsions fit experimentally observed spatial frequency responses.