Richard A. Banjavic

Ultrasonic Beam Sensitivity Profile Changes in Mammalian Tissue

When an ultrasonic beam passes through tissue, it undergoes a complex series of interactions with the medium. These serve to attenuate, scatter and oftentimes refract the beam from its initial path. Attenuating regions and scattering sites or interfaces are usually not distributed uniformly throughout the tissue, or for that matter, may not be intercepted to the same degree by all sections of the beam. Scatter of the ultrasonic beam, both diffuse and specular, as well as local nonuniformities in attenuation and refractive index throughout the beam volume could result in an ultrasound beam profile quite different from that predicted using only the frequency, diameter, and focal properties of the transducer itself. The present study was undertaken to investigate changes in such ultrasonic beam sensitivity profiles brought about by transmission and reflection of the beam through normal and abnormal mammalian tissue for a variety of clinically-used transducers.

An automated ultrasound transducer beam profiling system.

An automatic, three-dimensional, ultrasound beam profiling system was developed and incorporated into a radiotherapy planning minicomputer system with few modifications and at minimal cost. This profiler was invaluable in assessing the characteristics of beams emitted by ultrasound transducers.

Imaging Characteristics of Clinical Ultrasonic Transducers in Tissue-Equivalent Material

Our group has been involved in the comparison of ultrasonic pulse-echo transducer characteristics in water versus attenuating and scattering mediums. For this purpose we are using a gelatin- based material with a speed of sound of 1570 m/sec, a variable attenuation coefficient between 0.3 – 1.8 dB/cm/MHz, and a linear dependence of attenuation on frequency over the diagnostic range. Thus we can duplicate under controlled conditions similar interactions that a pulsed ultrasound beam encounters when traversing soft tissue structures. The specific findings regarding clinical pulse-echo equipment and transducers include an increased beam divergence, as seen in tissue samples, in the tissue-equivalent gel as compared to water only. Also, the focal plane and, in fact, the entire focal region whose boundaries are defined by the beam area being twice that of the focal plane are shifted axially closer to the transducer face for the attenuating path. These differences are being studied as a function of transducer frequency, diameter, and focal properties as well as the pulser-receiver combination which is used.

A Projection System for Effective Utilization of Ultrasound Echogram Information in Radiation Therapy

A system employing an opaque projector mounted on a steel-framed cart was constructed to provide full-scale enlargement of ultrasound echograms for use in radiation therapy planning. Anatomical outlines from the enlarged echograms are traced directly into a minicomputer. Life-sized isodose curves for a selected treatment plan are overlayed on the enlarged echogram to produce a permanent record for treatment field adjustments and retrospective analysis.

A Potential Material for Use in Ultrasound Phantoms

An ideal ultrasonic soft tissue equivalent phantom should exhibit the same speed of sound, the same attenuation coefficient, and the same scattering properties as those possessed by soft tissue; these qualities should agree at all frequencies in the clinical ultrasound range (1 to 15 mHz). Our group has made progress developing a material which exhibits speeds of sound in the range 1520–1650 m/s and attenuation coefficients approximating 1 dB/cm/mHz. In pursuing the creation of such a material, we have concentrated our efforts on pharmaceutical gel mixtures with various additives including preservatives and alcohols for varying the speed of sound. The major concern has been the development of control over the attenuation coefficient so that reasonable agreement can be obtained with published values for human tissues.1 This has been accomplished through the introduction of uniform concentrations of graphite powder or tiny plastic spheres. Graphite seems to give the best agreement, and the results using graphite are presented here.

Ultrasonic B-Scanning for radiation therapy planning and follow-up of superficial tumors

Abstract Ultrasonic B -scans are employed for delineating the boundaries of superficial, soft-tissue tumors for radiation therapy treatment planning. Full-scale anatomical information derived from magnified echograms is used for obtaining optimal photon beam dose distributions with the aid of a mini-computer. The feasibility of using ultrasound scans for assisting with electron beam radiation therapy planning is demonstrated. Tumor response following initiation of therapy may be evaluated using echograms for determining overall tumor dimensions or for computing the tumor volume. The use of ultrasonic B -scans for developing a 3-dimensional isometric display of tumor contours is discussed.

Need For Ultrasonic Tissue Equivalent Test Objects For Routine Performance Checks Of Pulse-Echo Equipment

This paper discusses needs for tissue equivalent test objects for use in ultrasound quality control. Currently available test objects are useful for assessing specific aspects of an ultrasound imaging system such as depth calibration and B-scan registration accuracy. A phantom which yields scattered echo signals of a similar magnitude as detected in tissues and producing the same frequency dependent attenuation of the beam would be useful for scan uniformity checks, evaluation of swept gain settings, and possibly for gray scale checks. The phantom material would also be useful for measuring pulse-echo response profiles of ultrasonic transducers.