Acoustical properties of the human skull

Abstract

The acoustical properties insertion loss, reflection loss, and sound speed were measured on a series of fresh and subsequently formalin immersed human skulls. Measurements were made in the frequency range from 0.25 to 6 MHz. Most studies were restricted to an upper frequency limit of 2.2 MHz. An axisymmetric focused beam configuration was used as the sound source for the measurements and the receivers were small disk-type (3-mm-diam) piezoelectric ceramics. The geometric and temporal character of the focused beam was studied as a consequence of passage through the skull sections. Some skulls were sectioned so that their individual layer components could be studied. A simple three-layer analytical model seems to explain the major aspects of insertion and reflection loss. The dominant feature in determining human adult skull losses is the middle layer (diploe) of cancellous bone. This study corroborates previous work on insertion loss as a function of frequency for composite skull. The study provides new quantitative information on the acoustic scattering properties of diploe, sound velocity, and dispersion in composite skull and its components, attenuation coefficients in skull components and sound-beam distortion and shifts after transmission through composite skull. We conclude that with selection of appropriate frequencies (0.5-1.0 MHz) and beam configuration it will be possible to perform clinically significant transkull diagnostic imaging and interrogation in the adult human brain.

Characterization of Ultrasound Propagation Through Ex-vivo Human Temporal Bone

“…The speed of sound in the outer table was from 2940 to 2960 m/s. The range for the speed of sound in the entire temporal bone was also reported to be from 2570 to 3030 m/s by Fry and Barger (1978). Goldman and Hueter (1955) and Goss et al (1978) reported a speed of sound in skull of 3360 m/s at 0.8 MHz.…”

“…Intracranial -3 dB beam widths were very similar to those in the free field at all three frequencies. Beam dimensions of a 0.5-MHz transducer were quantified intracranially by Fry and Barger (1978), who similarly noted negligible reduction in the -6 dB beam width (not more than 0.4 mm). Fry and Barger (1978) determined the attenuation coefficients of a single human temporal bone both experimentally and numerically for a range of frequencies from 0.25 to 2.00 MHz.…”

“…This important property of the human skull was measured by Fry and Barger (1978). They identified a large range for the speed of sound (2570 to 3030 m/s) in the temporal bone.…”

Tissue Pulsatility Imaging of Cerebral Vasoreactivity During Hyperventilation

“…Compared to other locations in the body, the SNR from the brain can be particularly poor given the significant attenuation of US by the skull (Fry and Barger 1978). As SNR decreases, the variance in the pulse amplitude estimate increases.…”

“…The advantage of TPI over TCD for assessing CVR is the use of tissue rather than blood as the signal source. US backscatter from tissue is significantly stronger than that from blood which is particularly important when imaging the brain given the significant attenuation of US by the skull (Fry and Barger 1978). Because of this, TCD is generally limited to imaging blood flow in the major cerebral blood vessels that supply large portions of the brain.…”