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This study was aimed at improving the conspicuity of titanium high-dose rate (HDR) brachytherapy needles under B-mode ultrasound imaging by applying a commercially available echogenic surface coating (Sono-Coat™, Encapson, Netherlands).  The echogenic coating was intended to improve needle visualization within regions of signal degradation that can occur during prostate or gynecological HDR brachytherapy. Sono-Coat™ is a commercial product designed to improve ultrasound visibility, particularly when imaging objects which are nonparallel to the ultrasound transducer.

17-gauge, 25 cm titanium HDR brachytherapy needles (Varian Medical Systems, USA) were coated with Sono-Coat™, a coating composed of acoustically reflective microspheres, over a 2 cm region starting from the needle tip. Three coatings of variable thickness: M2 (25 um thickness), M3 (40 um), and M5 (64 um) were compared against an uncoated control needle. The coated and uncoated needles were imaged using B-mode ultrasound in a CIRS tissue equivalent prostate phantom (CIRS Inc., USA) with a bk3000 (BK Medical, USA) unit and E14CL4b transrectal probe. Needle conspicuity was assessed under three conditions: a single needle implant, an implant with multiple needles between the probe and the needle of interest, and an implant with simulated rectal gas. The simulated rectal gas was introduced into images through taping medical gauze to the ultrasound probe surface then wrapping the probe with a condom. All images were assessed qualitatively for needle visibility and the presence of artifacts.

Under ideal geometry, where the needle is implanted parallel to the transrectal probe, the control needle and microsphere coated needle were equally visible (Figure 1, top panels). The microsphere coated needles produced noticeably less reverberation artifact and appeared as a contiguous object, whereas the control needle imaged as a bifurcated object along the body of the needle. When the angle of incidence between the needle and probe was increased, the visibility of the microsphere-coated needle was noticeably better than the control needle (Figure 1, bottom panels). In the rectal gas simulation (Figure 2), the microsphere coating improved visibility into a region of signal degradation, an effect that may be attributed to the redirection of ultrasound waves by the microspheres from non-void regions towards the probe.

An echogenic surface coating reduced reverberation artifacts and improved needle visibility when brachytherapy needles were implanted at an angle to the ultrasound probe or in the presence of B-mode signal degradation. The results are consistent with the hypothesis that a microsphere coating can redirect ultrasound waves to improve needle visibility when the signal-generating ultrasound waves impinge nonparallel to the transducer. Testing is ongoing within a cadaverous male pelvis.