J. Louis Hinshaw MD, Presenter: Research grant, Endocare, Inc

Fred T. Lee MD, Abstract Co-Author: Stockholder, NeuWave Medical Inc, Madison, WI Patent holder, Covidien AG, Boulder, CO

Nathan A. Durick MD, Abstract Co-Author: Nothing to Disclose

Lisa Ann Sampson, Abstract Co-Author: Research Consultant, NeuWave Medical Inc

Winifred Leung MD, Abstract Co-Author: Nothing to Disclose

Christopher L. Brace PhD, Abstract Co-Author: Shareholder, NeuWave Medical Inc, Madison, WI Consultant, NeuWave Medical Inc, Madison, WI

Pulmonary cryoablation is being utilized clinically, but the relationship between the imaging findings and the zone of necrosis is unknown. The purpose of this study was to define this relationship in a porcine model.

Percutaneous cryoablation (n=9) was performed in normal lung parenchyma under CT fluoroscopic guidance. A 10-5-10 minute freeze-thaw protocol was performed and non-contrast CT scans were performed 3, 6, 10, 16, 20, and 25 minutes into the ablation. The diameter, area, and circularity of final ablation zones were measured on pathology and imaging. A regression analysis was performed to identify the correlation between the imaging findings and the pathology.

The imaging findings identified on CT followed a consistent and predictable pattern and ultimately evolved into a “bulls-eye” appearance during the second freeze with a central zone of high attenuation (Zone 1) surrounded by a halo of decreased attenuation (Zone 2), a second zone of denser high attenuation (Zone 3) and a variable halo of ground glass opacity (Zone 4). Pathology revealed that Zone 1 represented confluent coagulative necrosis, Zone 2 was a combination of confluent coagulative necrosis and coalesced airspaces, Zone 3 was a second zone of confluent coagulative necrosis centrally, but there was a transition more peripherally to a region with viable cells, followed by Zone 4, which represented primarily pulmonary hemorrhage. Zones 1 and 2 identified on CT correlated precisely with cellular necrosis identified at pathology (diameter, R2 = 0.88, p = 0.002; area, R2 = 0.73, p = 0.03). Ablation zones were also characterized by a high circularity (0.96 ± 0.03)

The precise correlation between the imaging findings identified at CT and the resulting zone of necrosis should allow excellent monitoring of the ablation zone during pulmonary cryoablation. Since Zones 1 and 2 along with the central portion of zone 3 represent confluent necrosis, a targeted tumor and an adequate margin should be encompassed within these zones in order to ensure complete treatment.

This study establishes the relationship between the imaging changes identified at CT and the resulting zone of necrosis, which is critical for monitoring the ablation and ensuring complete treatment.

Hinshaw, J, Lee, F, Durick, N, Sampson, L, Leung, W, Brace, C, Computed Tomography Findings during Percutaneous Pulmonary Cryoablation Predict the Zone of Necrosis.  Radiological Society of North America 2008 Scientific Assembly and Annual Meeting, February 18 - February 20, 2008 ,Chicago IL. http://archive.rsna.org/2008/7121877.html