Session Item

Ultrasound-guided brachytherapy requires conspicuous applicators for proper applicator placement and accurate digital reconstruction. The conspicuity of brachytherapy applicators during ultrasound (US) prostate brachytherapy may be reduced by the presence of artifacts and tissue interfaces, unintentionally resulting in geometrically inaccurate treatment plans. The US visibility of HDR brachytherapy needles may be improved by including color-Doppler (CD) alongside standard B-mode imaging.  This work describes the development of, and initial results for, a prototype vibrational device that produces a strong and reliable mechanical CD signal that consistently enhances applicator conspicuity.

A device was designed and constructed to introduce vibrations at 300 Hz, <1mm amplitude, in applicators using two different approaches: 1) a stylet attachment, which induces vibration from within the needle, or 2) a click-fit attachment, which induces vibrations from the proximal end of the needle. The device was tested with both attachments using 17gauge titanium HDR brachytherapy needles implanted into a CIRS tissue-equivalent prostate phantom. Images were acquired with a bk3000 US unit with a E14CL4b transrectal probe under B-mode and CD US mode. Needle conspicuity between the two attachments was assessed for various US machine settings. A comparison between mechanical CD signals and the CD twinkling artifact produced by laser-etched patterned needles was performed using a time-averaged absolute velocity spectrum.

The prototype vibrational device consistently produced a strong CD signal that highlighted the implanted brachytherapy needle (Figure 1). The vibration power and US unit gain were optimized to minimize undesirable CD signal produced in regions adjacent to the needle in the phantom.  The mechanical CD signal was robust to artifacts that reduced B-mode visibility regions, up to the point where the B-mode signal was obscured. The stylet attachment was preferred over the click-fit because it generated a more uniform signal throughout the needle body. The mechanical CD signal best demarcated the needle with reduced CD gain, using a needle locked into an implant template with a collet, and with C-mode ROI constrained to the immediate vicinity of the needle. The time-averaged velocity spectrum of the vibrationally-induced CD signal yielded harmonics distinct from the CD twinkling artifacts (Figure 2).

A prototype device was developed to enhance brachytherapy applicator visibility during US-guided procedures.  The device produces a strong, consistent color-Doppler signal by mechanically inducing vibrations in the applicator. In-phantom results were used to demonstrate proof-of-principle and optimize the US imaging parameters to generate a consistent, uniform CD signal that demarcated the needle tip and body, and cadaver testing is ongoing. This device has the potential to assist with applicator placement and digitization in US guided prostate brachytherapy.