Ultrasound Assessment of Ice-Ball Formation by Cryoneurolysis Device in an Ex Vivo Model

Background and Objectives Real-time ice-ball formation during cryoneurolysis has sparsely been assessed with ultrasound (US). Cryoneurolysis in lower back pain syndrome represents a validated management option in cases of facet joint syndrome. Ultrasound may be a useful tool to perform facet joint cryodenervation. The objective of this study was to assess, ex vivo, the ability of US to assess the ice-ball formation of a cryoneurolysis device. Methods Ultrasound assessment of the ice-ball depiction was done using chicken muscle at 22°C in which several freezing cycles were performed with both 2.1- and 1.3-mm cryoprobes. For each freezing cycle, static images and dynamic videos were generated for both needle insertion and ice-ball formation with 18-, 11-, and 6-MHz transducers. The following data were assessed in each combination of cryoprobe and transducers: quality of needle tip visualization, quality of the ice-ball formation depiction, size of the ice ball, presence of a shadow cone, and usefulness of power Doppler mode to assess ice-ball formation. Results The 18- and 11-MHz linear transducers allowed to directly depict the formation of the ice ball. Visualization of the cone shadowing allowed indirect visualization of the ice ball with both 18- and 11-MHz transducers. However, the ice ball was not depicted (directly or indirectly) with the convex 6-MHz transducer, and power Doppler was the only way to indirectly monitor the ice ball during the freezing cycles. Conclusions Ultrasound is a useful tool to monitor the formation of ice ball during a cryoneurolysis freezing cycle. Power Doppler appears as the only option to monitor the ice ball with low-frequency transducers. This novel finding may be useful in cases of lumbar medial branch cryoneurolysis, an application we plan to assess in a future pilot prospective study. Accepted for publication January 15, 2018. Address correspondence to: Adrian Kastler, MD, PhD, Neuroradiology Unit, Centre Hospitalier Universitaire Grenoble Alpes, Bvd de la Chantourne CS 10217, 38043 Grenoble CEDEX 9, France (e-mail: kastler.radio@gmail.com). Attribution: This work should be attributed to the Radiology Unit of the Medical University of Innsbruck, Innsbruck, Austria. No financial sources have supported this work. The authors declare no conflict of interest. Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal's Web site (www.rapm.org). Copyright © 2018 by American Society of Regional Anesthesia and Pain Medicine.

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