Quantifying B-mode images of in vivo rat mammary tumors by the frequency dependence of backscatter.

OBJECTIVE: To evaluate the frequency dependence of ultrasonic backscatter for its ability to differentiate between neoplastic and healthy tissue. METHODS: Standard B-mode images were created of 5 rats with spontaneous mammary tumors, and regions of interest in the lesion and surrounding tissue were parameterized by the slope of the backscatter amplitude versus frequency. RESULTS: In 4 of the 5 rats, the averaged backscatter slope of the regions of interest in the tumor was significantly (P < .05) different from that of the surrounding tissue, and the fifth case had a moderate difference (P = .20). The consistency of the averaged slope values (1.2-1.8 dB/MHz) across all but 1 of the mammary tumors was encouraging for the prospect of identifying a tissue type by its backscatter slope. CONCLUSIONS: This work suggests that characterization and diagnosis of tissue types may be possible by using ultrasonographic images quantified by the frequency dependence of backscatter.

Anisotropy of ultrasonic propagation and scattering properties in fresh rat skeletal muscle in vitro.

The anisotropy of frequency-dependent backscatter coefficient, attenuation, and speed of sound is assessed in fresh rat skeletal muscle within 5 h post-mortem. Excised rat semimembranosus and soleus muscles are measured in 37 degrees C Tyrode solution, with the muscle fibers at 90 degrees and 45 degrees orientations to the incident sound beam. Reflected and through transmission signals from either a 6- or 10-MHz focused transducer give frequency dependent information in the 4-14 MHz range. The attenuation coefficient in each muscle is consistently a factor of 2.0 +/- 0.4 lower for propagation perpendicular to the fibers than at 45 degrees, whereas speed of sound shows a much milder anisotropy, and is slightly faster for the 90 degrees orientation. The largest anisotropy is seen in the backscatter coefficient, most notably in the semimembranosus where the magnitude at 90 degrees is over an order of magnitude greater than at 45 degrees, with the frequency dependence in both cases giving a power law between 1.5 and 2.0.

Interlaboratory comparison of ultrasonic backscatter, attenuation, and speed measurements.

In a study involving 10 different sites, independent results of measurements of ultrasonic properties on equivalent tissue-mimicking samples are reported and compared. The properties measured were propagation speed, attenuation coefficients, and backscatter coefficients. Reasonably good agreement exists for attenuation coefficients, but less satisfactory results were found for propagation speeds. As anticipated, agreement was not impressive in the case of backscatter coefficients. Results for four sites agreed rather well in both absolute values and frequency dependence, and results from other sites were lower by as much as an order of magnitude. The study is valuable for laboratories doing quantitative studies.

Specific heat and thermal conductivity of solid fullerenes.

Evidence is presented that the lattice vibrations of compacted C(60)/C(70) fullerite microcrystals consist predominantly of localized modes. Vibrational motions of the rigid molecules ("buckyballs") have been identified as well as their internal vibrations. Debye waves play only a relatively minor role, except below approximately 4 kelvin. By comparison with other crystalline materials, for these materials the Einstein model of the specific heat and thermal conductivity of solids, which is based on the assumption of atoms (in this case, buckyballs) vibrating with random phases, is in much better agreement with the measurements than the Debye model, which is based on collective excitations.