Murat Acar BMBCH, Presenter: Nothing to Disclose

Servet Tatli MD, Abstract Co-Author: Nothing to Disclose

Kemal Tuncali MD, Abstract Co-Author: Nothing to Disclose

Cheryl A. Sadow MD, Abstract Co-Author: Nothing to Disclose

Paul Richard Morrison MS, Abstract Co-Author: Nothing to Disclose

Stuart George Silverman MD, Abstract Co-Author: Consultant, Galil Medical Ltd, Yokneam, Israel Consultant, Siemens AG

To evaluate the value of subtraction MRI in the detection of residual tumor following percutaneous liver ablation.

Thirty-five liver tumors in 21 consecutive patients were treated with MRI-guided cryoablation (n=21) or CT-guided RF ablation (n= 14). Two blinded abdominal radiologists independently reviewed three-month follow-up MRI for tumoral enhancement (considered residual tumor) and rated their confidence level on a scale of 1 to 5. ROI were placed on residual tumor, ablation zone, and normal liver parenchyma. After 1 year, the same analysis was repeated on subtraction images. Presence or absence of recurrent tumor was determined with follow-up MRI, CT, or PET/CT (mean 21 months, range: 5-42 months) and when available biopsy or surgery. Accuracy of the detection of residual tumor, and contrast-to-noise ratios (CNR) for enhancing lesion-to-liver, enhancing lesion-to-ablation zone, and ablation zone-to-liver were calculated for analyses with and without subtraction images and compared using Wilcoxon signed ranks test. Interobserver variability was calculated using Kappa (κ) statistics.

Accuracy of detecting residual tumor (reader 1: 94% vs. 79%; reader 2: 94% vs. 88%), and interobserver agreement (κ=0.72, good vs. κ=0.57: moderate) improved significantly when subtraction images were used. Subtraction images yielded significantly higher mean CNR for enhancing lesion-to-liver (0.2±5 vs. 11.6±14.4, p=0.03), enhancing lesion-to-ablation zone (10.1±12.5 vs. 34.4±29.4, p=0.02) and ablation zone-to-liver (11.8±13.3 vs. 102.5±238.4, p=0.03).

Subtraction images help identify residual tumor by improving radiologists’ ability to detect enhancement. The benefit of subtraction images is likely explained by a significantly higher CNR in the regions critical to the assessment of liver ablation.

Subtraction images help radiologists use MRI to detect residual tumor after liver ablation. Earlier detection of residual tumor may allow tumors to be treated earlier, and therefore more successfully.

Acar, M, Tatli, S, Tuncali, K, Sadow, C, Morrison, P, Silverman, S, Assessment of Percutaneous Liver Ablation with MRI: Value of Subtraction Images.  Radiological Society of North America 2008 Scientific Assembly and Annual Meeting, February 18 - February 20, 2008 ,Chicago IL. http://archive.rsna.org/2008/6010763.html