Ultrasonic Radio-Frequency Spectrum Analysis of Normal Brain Tissue

Abstract 

Acoustic tissue properties can be estimated using texture and/or spectral parameter analysis. Spectral analysis is based on the rf-signals whose frequency-content is commonly neglected in conventional B-mode imaging. Attenuation and backscatter values of normal brain tissue were analyzed. Unprocessed rf-data of 20 patients were sampled intraoperatively after craniotomy using a modified conventional ultrasonic device (Hitachi CS 9600) and analyzed off-line by a custom-made software routine. Before parameter estimation, influences of the diffraction pattern were compensated by means of a correction function obtained using a tissue-mimicking phantom. Attenuation of white matter showed a linear frequency dependence with a slope of 0.94 ± 0.13 dB cm⁻¹ MHz⁻¹. The spectral slope was determined using 10 distinct frequencies between 2.5 and 5.75 MHz. Backscattering properties were analyzed by determining the power spectral density (PSD) and a relative backscatter coefficient (rel BSC) against the values derived from the tissue-mimicking phantom. PSD and rel BSC values were frequency-dependent, with highest PSD values at the probe’s center frequency (−75.69 ± 8.26 dB V² Hz⁻¹). The corresponding rel BSC value at 5 MHz was determined as 15.39 ± 8.26 dB. Finally, backscatter coefficients (BSC) of brain tissue were computed using the known BSC of the phantom. The data provided in this study are meant to serve as a base for intended future characterization of brain tissue that potentially allows intraoperative differentiation between normal and pathologic areas and therefore provides the surgeon with additional information for defining the extent of resection in brain more precisely. (E-mail: martin.strowitzki@uniklinik-saarland.de)

Key Words: Tissue characterization, Ultrasound spectrum analysis, Intraoperative ultrasound, Attenuation, Backscatter, Acoustic parameters