Is tissue harmonic ultrasound imaging (THI) of the prostatic urethra and rectum superior to brightness (B) mode imaging? An observer study.

Quality ultrasound images are an essential part of prostate brachytherapy procedure. The authors have previously reported that tissue harmonic ultrasound images (THI) are superior to brightness (B) mode for the prostate. The objective of the current study was to compare both imaging modes for visualization of the prostatic urethra and rectum. B and THI mode transrectal ultrasound images were acquired for ten patients. The prostatic urethra and rectal wall were contoured by a radiation oncologist (RO) and five observers on randomly presented images. The contours on one patient were repeated four additional times by four observers. All the images were qualitatively scored using a five-level Likert scale. The values of the Pearson product-moment correlation coefficients showed that the observers were in close agreement with the RO. Two sample paired student t-test showed that the rectum volumes with THI were significantly smaller than B-mode, but no significant difference for urethra. Two-factor analysis of variances showed significant observer variability in defining the rectum and urethra in both imaging modes. Observer consistency of the rectum volumes, estimated by standard deviations as percentages of means was significantly improved for THI. The Likert scale based qualitative assessment supported quantitative observations. The significant improvement in image quality of the prostate (reported previously) and rectum with THI may offer better-quality treatment plans for prostate brachytherapy and potential improvement in local control.