V. Abraham

Temperature elevation in the rat fetus due to ultrasound exposure.

The temperature elevation resulting from sonically generated heat in rat fetuses was measured for various intensity levels. The temperature elevation produced inside the fetus was higher than that on the outside surface. In live fetuses, a portion of the heat generated was carried off by the circulating blood. The temperature elevation curves were used to estimate the absorption coefficient of rat fetuses. Absorption coefficient values range from 0.065 to 0.086 Np/cm at 1 MHz. The present results are consistent with a theoretical model of temperature elevation in a heated sphere.

Effect of scan format on refraction artifacts

Refraction artifacts occur when the ultrasound beam is bent from its original direction as it passes through a boundary between tissues having different sound speeds. Refraction artifacts result in both the improper positioning and the improper brightness of echoes displayed in clinical sonograms. The effect of scan format on the sonographic appearance of several refraction artifacts due to a circular object possessing a sonic speed differing from its surrounding tissue was studied using a mathematical model and computer generated images. A quantitative index of artifact prominence was developed to compare the differences between the rectilinear and the sector scan formats. Theoretically predicted results were compared with actual sonograms of a specially designed phantom. Results included the finding that the retrolenticular afterglow was more prominent in the sector scan format, and that differences were most prominent when the refracting object was close to the transducer.

Effect of ultrasound on regional cerebral blood flow in neonatal rats

By employing a laser-Doppler flowmeter, an investigation was performed to determine whether ultrasound causes a change in regional cerebral blood flow (rCBF). rCBF in neonatal rats (age: 2-6 days postgestation) was measured before, during, and after exposure of both cerebral hemispheres to continuous-wave ultrasound (1.0 MHz) at an intensity of 2.0 W/cm2 (SATA) for a period of 5 min. After 3 min of ultrasound treatment, there was a statistically significant augmentation in rCBF (p less than 0.05) with rCBF increasing by a factor of 2.7 +/- 0.4 (mean +/- SEM) after 5 min of ultrasound. This response was demonstrated to be a transient effect, because rCBF returned to its original value 4-6 min after termination of the ultrasound treatment.

The Effect Of Ultrasound On Neonatal Cerebral Blood Perfusion

Using a laser Doppler flowmeter, cerebral blood flow (CBF) measurements were performed on neonatal rats before and after exposing both hemispheres of the cerebrum to 5 minutes of continuous wave ultrasound (2.25 MHz). Ultrasonic intensities were varied from 0.5 W/cm* to 2.5 W/cm* (SPTA) in order to reveal how significantly ultrasound affects blood perfusion in the cerebral microvasculature. These results were compared with theoretical calculations based on mathematical models of the microcirculation and ultrasonic heating. It was demonstrated that ultrasound can affect the magnitude of perfusion in the brain of neonatal rats.

Biochemical Effects Of Ultrasound On The Developing Rat Central Nervous System

The uterine horns of rats at the tenth gestational day were exposed to continous wave ultrasound, ISATA of 2.5 W/cm2 at 1 MHz for 5 min. The temperature at the surface of the embryos was monitored before and after exposure. The activities of biochemical markers AchE and CNP, as well as weight and protein content of the brains of the fetuses were measured at different stages during development of the fetus. There were no differences in body weight or in gross anatomy between exposed and control fetuses. There was a transient decrease in CNP and AchE activity of the insonated fetal brains that may be associated with the hyperthermia produced by ultrasound. 1 MHz. The activities of biochemical markers were measured to study the effect of the ultrasound in the development of neurons and oligodendrocytes on gd 14,17,21 and 26. AchE was measured as a marker for cholinergic neurons and CNP was measured for oligodendrocytes and myelination of the central nervous system [7,8,9]. The weight of the brain and the protein content were also measured. The rectal temperature of the pregnant rat and the temperature at the surface of the embryo were monitored before and after exposure. We limited our study to one ultrasound intensity level at lMHz, 2.5 W/cm2/ based on preliminary studies in our laboratory which showed that lower intensities did not cause any effect while higher intensities were shown to be embryotoxic.

Temperature Elevation Measurements In Rat Fetuses During Ultrasound Exposure

Temperature elevation measurements in rat fetuses exposed to ultrasound (1 MHz) were carried out at various intensity levels ranging from 0.5 to 5 W/cm2. The artifacts exhibited by various thermocouples employed for the measurement are discussed in detail. Experimental results were in agreement with the values suggested by a theoretical model of tissue heating.