Ultrasonic Characterization of Human Scalp.

Objective: The ultrasonic properties of scalp may be relevant to a variety of applications including transcranial ultrasound. However, there is no information about the ultrasonic properties of scalp available in the literature. While ultrasonic studies of skin from other anatomic regions have been previously reported, scalp tissue is generally thicker with a higher density of hair follicles, blood vessels and sebaceous glands.

Two-dimensional mapping of the ultrasonic attenuation and speed of sound in brain.

Brain is inhomogeneous due to its composition of different tissue types (gray and white matter), anatomical structures (e.g. thalamus and cerebellum), and cavities in the brain (ventricles).

Thermal property and shear wave speed indicators of phase transitions in a micellar fluid.

High concentration (>100 mM) wormlike micellar (WM) fluids are non-Newtonian with micelle lengths in the tens of nanometers. The viscoelastic properties of the fluid are affected by the structure and entanglement of the micelles and thus structural phase transitions can be indirectly studied using mechanical shear waves. Although these structural phase transitions have been extensively studied as a function of concentration, comparably less work is available on the temperature dependence.

Optimizing MRI sequences and images for MRI-based stereotactic radiosurgery treatment planning.

Aim: Development of MRI sequences and processing methods for the production of images appropriate for direct use in stereotactic radiosurgery (SRS) treatment planning.

Background: MRI is useful in SRS treatment planning, especially for patients with brain lesions or anatomical targets that are poorly distinguished by CT, but its use requires further refinement. This methodology seeks to optimize MRI sequences to generate distortion-free and clinically relevant MR images for MRI-only SRS treatment planning.

Development of a Tissue-Mimicking Phantom of the Brain for Ultrasonic Studies.

Constructing tissue-mimicking phantoms of the brain for ultrasonic studies is complicated by the low backscatter coefficient of brain tissue, causing difficulties in simultaneously matching the backscatter and attenuation properties. In this work, we report on the development of a polyvinyl alcohol-based tissue-mimicking phantom with properties approaching those of human brain tissue. Polyvinyl alcohol was selected as the base material for the phantom as its properties can be varied by freeze-thaw cycling, variations in concentration and the addition of scattering inclusions, allowing some independent control of backscatter and attenuation.

A theoretical study of inertial cavitation from acoustic radiation force impulse imaging and implications for the mechanical index.

The mechanical index (MI) attempts to quantify the likelihood that exposure to diagnostic ultrasound will produce an adverse biological effect by a non-thermal mechanism. The current formulation of the MI implicitly assumes that the acoustic field is generated using the short pulse durations appropriate to B-mode imaging. However, acoustic radiation force impulse (ARFI) imaging employs high-intensity pulses up to several hundred acoustic periods long.

Should the mechanical index be revised for ARFI imaging?

The mechanical index (MI) quantifies the likelihood that exposure to diagnostic ultrasound will produce an adverse biological effect by a nonthermal mechanism. The current formulation of the MI is based on inertial cavitation thresholds in two liquids, water and blood, as calculated by a formalism assuming very short pulse durations. Although tissue contains a high proportion of water, it is not a liquid but a viscoelastic solid.

Augmentation of HIFU-induced heating with fibers embedded in a phantom.

The effect of fibers on the rate of heat deposition in the focal region of high-intensity focused ultrasound (HIFU) beams was investigated. Nylon, stainless steel and copper fibers of diameters 0.23-0.

Biological and environmental factors affecting ultrasound-induced hemolysis in vitro: 5. Temperature.

This research project tested the hypothesis that cold-equilibrated (approximately 0 degrees C) human erythrocytes in vitro in the presence of an ultrasound contrast agent (Albunex) will undergo greater ultrasound-induced hemolysis than physiologically equilibrated (37 degrees C) human erythrocytes in vitro because of a temperature-related transition in membrane fluidity leading to increased fragility. First, it was shown that cold-equilibrated erythrocytes are more susceptible to mechanically induced hemolysis than physiologically equilibrated erythrocytes. Second, when adjustments were made for (1) temperature-dependent efficiencies of a 1-MHz transducer (200 micros pulse length, 20 ms interpulse interval, 30 s exposure duration) such that when cold or physiological temperatures were employed, there were equivalent acoustic outputs in terms of peak negative pressure (MPa P-) and (2) comparable viscosities of the 0 and 37 degrees C blood plasmas, the cold (approximately 0 degrees C) erythrocytes displayed substantially greater amounts of ultrasound-induced hemolysis than the physiological (37 degrees C) erythrocytes.