Measurement of the ultrasound backscatter signal from three seed types as a function of incidence angle: Application to permanent prostate brachytherapy

Purpose: To measure the relative ultrasound backscatter of different seed types as a function of seed orientation and to evaluate the corresponding images of these seeds. Methods and Materials: Three seed types were evaluated: OncoSeed (standard), EchoSeed (corrugated), and RAPID Strand(RS). Ultrasound images for angles of incidence varying from 90° (perpendicular) to 20° at 5MHz and 7.5MHz were produced by raster scanning the seeds in a degassed water bath. Seed images were visually inspected and analyzed using the integrated-optical-density (IOD) method. Results: Corrugated seeds appear as contiguous objects over the range of frequencies and orientations examined, whereas standard seeds appear as contiguous objects from 90° to 80° only. The ranges and means of the backscattered IOD ratio of the seeds from 85° to 20° were: (corrugated vs. standard) 1.48 to 3.72 (2.32 ± 0.62) for 5 MHz and 1.26 to 3.77 (2.19 ± 0.84) for 7.5 MHz and (corrugated vs. RS) 1.21 to 9.53 (2.98 ± 2.48) for 5 MHz and 1.008 to 10.86 (2.79 ± 3.08) for 7.5 MHz. Backscattered signal increase ranged from 1.66 dB to 20.7 dB for the corrugated seed as compared to the other seeds. Conclusions: Corrugated seeds produce greater backscatter signal and a more readily identifiable seed image over a large range of seed orientation as compared with standard brachytherapy seeds.