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Biomedical subjects

D Vilkomerson

Publications and source records attributed to D Vilkomerson.

11 recordsLinked to original sources
PubMed2005

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. The planned trial is to be carried out in two stages, the first to establish the sensitivity and specificity of the new method, and the second (if the results of the first stage warrant it) a controlled trial comparing access-costs and hospitalization days between a monitored group and a matched standard care control group. It is hoped that this trial of the new method will establish it as an effective means of extending access-graft life.

Arteriovenous Shunt, Surgical↗
PubMed2001

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. METHODS: Fifteen healthy pigs and five pigs with chronic anterior myocardial infarction were studied. In healthy animals, echocardiographically distinct endocardial sites in right and left cardiac chambers were targeted for ablation. In infarcted animals, the left ventricular infarction border zone was targeted. Both intracardiac (ICE; 12.5 megahertz and 5 megahertz) and transesophageal echocardiographic (TEE) techniques were utilized. RESULTS: In healthy animals, transponder-guided ablation was feasible with each of the echocardiographic techniques. Accuracy was 82 % (45 of 55 lesions) with ICE-12.5 MHz, 87 % (27 of 31 lesions) with ICE-5 MHz, and 81 % (22 of 27 lesions) with TEE. In infarcted animals, the accuracy was 38 % (3 of 8 lesions) for ICE-5 MHz and 38 % (3 of 8 lesions) for TEE. Errant lesions in healthy animals were observed in earlier experiments, due to operator misinterpretation of the plane of imaging. Errant lesions in infarcted animals were observed throughout the experimental series, and may have been due to a variable relationship between echocardiographic and histologic infarction border zones. CONCLUSIONS: Echocardiographic transponder-guided catheter ablation is feasible. Accuracy for normal endocardial targets was excellent, less so for chronic infarction border.

Animals↗
PubMed2001

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. Tip localization was excellent in vitro; errors axial to the ultrasound beam (velocity Doppler -0.13 +/- 0.90 mm, power Doppler -0.05 +/- 1.7 mm) were less than lateral errors (velocity -0.36 +/- 1.8 mm, power -0.02 +/- 2.8 mm). In 18 of 25 patients, the needle was identified and guided into the pericardial space with the ColorMark technique, and it allowed successful, uncomplicated drainage of fluid. Initial failures were the result of incorrect settings on the echocardiographic machine and inappropriate combinations of the needle puncture site and imaging window. This study demonstrates a novel color Doppler technique that is highly accurate at localizing a needle tip. The technique is feasible for guiding pericardiocentesis. Further clinical validation of this technique is required.

Echocardiography↗
PubMed1999

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. Angiography was performed prior to the procedure to confirm preprocedural ultrasound findings and afterward to compare with duplex visual and hemodynamic parameters of success (peak systolic velocity ratio < 2.0). RESULTS: The balloon size determined from duplex measurements correlated in all cases with sizes selected based on the angiographic image. Guidewire visualization was possible in 95% of the cases. Angioplasty using ultrasound alone was feasible in 84%; inability to obtain a satisfactory image owing to vessel tortuosity, calcification, and bowel gas accounted for the failures. Against the duplex success criterion, initial completion angiograms had an accuracy of 76%, sensitivity of 76%, and specificity of 100%. The additional time for ultrasound guidance averaged 42 +/- 12 minutes for all cases. CONCLUSIONS: Our results show that ultrasound guidance is feasible in routine clinical practice. In this series of well-selected cases of arterial stenoses, angioplasty was performed safely using ultrasound guidance alone in over 80% of the cases. Fluoroscopic monitoring is needed when ultrasound visualization is suboptimal.

Aged↗
PubMed1998

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. The flowmeter measured the flow in an artery bled into a calibrated vessel. Results were compared with the true volume of the blood captured. RESULTS: On average, 13 measurements per animal were made at different flow rates (80 to 600 mL/min). The flowmeter measured flow-volume rates in mL/min were found to be within +/- 15% of the cylinder captured volume. CONCLUSIONS: The accuracy of the angle-independent flowmeter is comparable with that of flowmeters currently used clinically. The small size and portability, low operator dependency, and low cost suggest potential for continuous acute and chronic-flow monitoring and a potential for an implantable flow-monitoring device.

Animals↗
PubMed1996

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. This allows accurate catheter guidance using ultrasound. This paper describes the principles of ultrasound guidance of catheters and the initial clinical experience using this new catheter system (Echomark) in carrying out peripheral transluminal angioplasty.

Angioplasty↗
PubMed1993

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. METHODS: The new catheter is integrated externally into a standard duplex scanner. A spherical brass bead positioned on the catheter shaft in the middle of the balloon is covered with a piezoelectric material. This omnidirectional receiver is connected through a wire to a catheter interface system, which allows the exact position of the balloon to be represented on the screen of a duplex unit. The catheter is advanced under visual control with use of the scanner. RESULTS: The system has been used to perform balloon angioplasty on 21 lesions (16 superficial femoral, 3 iliac, 2 popliteal arteries) in 17 patients. Procedures in 16 patients were performed percutaneously; in an additional patient bilateral angioplasties were performed during operation. The balloon was successfully positioned in each case with use of ultrasonography alone; each procedure was confirmed by use of angiography. Angioplasty was accomplished in 16 (76%) of 21 with the ultrasound-guided catheter alone. Supplemental use of a high-pressure balloon or atherectomy device was necessary in five patients. CONCLUSIONS: This technique records physiologic and anatomic data in real time so that the progress of the angioplasty can be monitored. In three patients the inadequacy of the initial angioplasty was recognized by a persistent velocity increase but not by angiography. As a result corrective measures were taken. This new procedure allows vascular surgeons to use equipment with which they are familiar, reduces the risk of ionizing radiation and contrast nephropathy, and permits the monitoring of the angioplasty with hemodynamic parameters.

Angioplasty, Balloon↗
PubMed1991

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. This catheter was tested successfully in 10 dogs with bilateral femoral arteriovenous fistulas. With the use of duplex guidance, eight arterial and three venous stenoses were dilated and two stents were placed. Catheter placements and therapeutic outcomes predicted by ultrasound correlated with arteriographic findings. Ultrasound guidance has several advantages. It eliminates the risks associated with radiographic imaging. It also reduces patient costs and discomfort. Furthermore, procedures can be monitored continuously in real time with the collection of anatomic and physiologic data.

Angiography↗
PubMed1983

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. This has two advantages. One, it is easier to align the transducer with the reflected beam. Two, the diffuse reflection is similar to the scattering from tissue, and the system gain need not be turned abnormally low. Diverging wires improve the accuracy and convenience of the measurement. Rather than many pairs of parallel wires, a single pair of wires which diverge from an apex is used. By scanning across this pair until the wires are just resolved, the resolution can be easily calculated.

Ultrasonics↗
PubMed1976

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 3.0 MHz we employed. The apparatus, measurement method, results, and the possible causes of the differences in attenuation are presented.

Breast Diseases↗