Biomedical subjects

Albert Goldstein

Publications and source records attributed to Albert Goldstein.

4 recordsLinked to original sources

PubMed2006

Steady state spherically focused, circular aperture beam patterns.

This review was written to aid ultrasonic investigators using spherically focused transducers. It introduces a new direct method for computing steady state focused beam patterns on personal computers in nonattenuating and attenuating fluids and tissues. The method results in single integral expressions for uniform transducer excitation that can easily be altered for nonuniform surface excitation (apodization) or focused ring transducers. Procedures for verifying the accuracy of the derived equations are demonstrated. It is shown that beam diffraction errors are larger the higher the fluid or tissue attenuation. An experimental procedure is presented for measuring the effective focal length and effective aperture size of a spherically focused transducer with a single experimental measurement in a fluid with known acoustic velocity. Procedures are suggested for reducing the errors caused by beam diffraction in fluid attenuation measurements, avoiding them entirely or estimating their magnitude when they cannot be avoided.

Body Fluids↗

PubMed2004

Beam width measurements in low acoustic velocity phantoms.

Analysis of focused ultrasound (US) beams in low acoustic velocity phantoms demonstrates that beam width measurements yield results much larger than comparable measurements in phantoms with the correct acoustic velocity, 1540 m/s. These erroneous beam width measurements are shown to be due to two factors: a refocusing of the beam due to the low acoustic velocity (as compared with the design focus at 1540 m/s) and the necessary repositioning of the wire targets in these phantoms to simulate target depths in US phantoms with the proper acoustic velocity.

Acoustics↗

PubMed2004

Steady state unfocused circular aperture beam patterns in nonattenuating and attenuating fluids.

Single integral approximate formulas have been derived for the axial and lateral pressure magnitudes in the beam pattern of steady state unfocused circular flat piston sources radiating into nonattenuating and attenuating fluids. The nonattenuating formulas are shown to be highly accurate at shallow beam depths if a normalized form of the beam pattern is utilized. The axial depth of the beginning of the nonattenuated beam pattern far field is found to be at 6.41Y0. It is demonstrated that the nonattenuated lateral beam profile is represented at this and deeper depths by a Jinc function directivity term. Values of alpha and z are found that permit the attenuated axial pressure to be represented by a plane wave multiplicative attenuation factor. This knowledge should aid in the experimental design of high accuracy attenuation measurements. The shifts in depth of the principal axial pressure maxima and minima due to fluid attenuation are derived. Single integral approximate equations for the attenuated full beam pattern pressure are presented using complex Bessel functions.

Journal Article↗

PubMed2002

Design of quality assurance for sonographic prostate brachytherapy needle guides.

OBJECTIVE: Needles are guided to their proper anatomic locations in sonographically guided percutaneous prostate brachytherapy by a mechanical system (template). A quality assurance procedure has been designed to test this template's alignment with the needle position overlay grid displayed in the sonographic image. METHODS: A mechanical arrangement was designed to position the needles properly with respect to the prostate probe's transducer in a liquid-filled test tank. Two liquids were tested: tap water and an ethylene glycol mixture with an acoustic velocity of 1540 m/s. Needle images with the superposed grid were analyzed for needle placement accuracy. RESULTS: The tap water produced misregistration of the needle images. The ethylene glycol mixture yielded images of vertical and horizontal needle positions accurate to 0.3 and 1 mm, respectively. Also, the importance of selecting the lowest possible equipment echo amplitude dynamic range in these tests was shown. CONCLUSIONS: This quality assurance test with the ethylene glycol mixture will permit accurate alignment of the brachytherapy needle position overlay grid for each separate transrectal probe used.

Brachytherapy↗