MRI Guided Cryoablations of Liver and Kidney Tumors

Cryoablation, also called cryotherapy, is defined as therapeutic tissue destruction by freezing. It is a minimally invasive (percutaneous) thermal ablation technique that can treat kidney, bone, liver, lung, adrenal, and prostate lesions. It is particularly useful in treating tumors near critical structures. The visibility of the iceball intra-procedurally under MRI-guidance is a significant advantage of this technique.

Cryoablation in AMIGO is performed using an argon gas-based system (CryoHit, Galil Medical, Arden Hills, MN). Under MRI-guidance, 17-gauge cryoablation probes are placed by an attending interventional radiologist with the assistance of a clinical fellow-in-training. MRI scans are performed during each of four phases of the procedure: planning, targeting, monitoring, and survey.

MRI Guided Cryoablation Workflow in AMIGO

Planning. An initial planning MRI scan of the tumor is obtained. This scan allows the interventional radiologist to choose how many probes will be used and where to enter.
Planning. The number and positions of the probes are chosen based on the size of the tumor so that the resultant iceball will encompass the tumor plus a minimum 5-10 mm margin all around. Here, you can see different probes and their iceball sizes. No argon leaves the probe; it is confined in the probe and becomes extremely cold so as to generate the iceball.
Targeting. Targeting phase of placing four probes. Freezing begins only after probes are placed in ideal locations using MR guidance.
Targeting. Multiple MRI scans are taken during the targeting phase to assure proper location of the probes in the tumor and with the cryoprobes, ideally, approximately 1.5 cm apart.
Monitoring. In the monitoring phase, cryoablation probes are activated simultaneously. The iceball generated during cryoablation will appear as a signal void (black in color) under MRI-guidance. Monitoring is used to confirm that the iceball has encompassed the tumor plus a margin. If necessary, a lower power can be used to prevent damage to adjacent critical structures.
Monitoring: Iceball formation. The cryoablation protocol consists of a 15-minute freeze (argon gas), followed by a 10-minute thaw (helium gas), followed by a second 15-minute freeze.
Monitoring.
1) Intracellular ice → Cell membrane rupture
2) Extracellular ice → Cellular dehydration (thaw)
3) Vascular stasis → Local tissue ischemia.
Formation. Iceball is monitored by MRI scans. Scans are made every 3 minutes during each freeze to watch the iceball grow and assess nearby critical structures.
Formation. Upon completion of the cryoablation protocol, the probes are removed and a final MRI scan acquired to survey the ablation site for possible complications.

Select Publications

Liu X, Tuncali K, Wells III WM, Zientara GP. Automatic Iceball Segmentation with Adapted Shape Priors for MRI-guided Cryoablation. J Magn Reson Imaging. 2015;41 (2) :517-24.Abstract

PURPOSE: To develop and evaluate an automatic segmentation method that extracts the 3D configuration of the ablation zone, the iceball, from images acquired during the freezing phase of MRI-guided cryoablation. MATERIALS AND METHODS: Intraprocedural images at 63 timepoints from 13 kidney tumor cryoablation procedures were examined retrospectively. The images were obtained using a 3 Tesla wide-bore MRI scanner and axial HASTE sequence. Initialized with semiautomatically localized cryoprobes, the iceball was segmented automatically at each timepoint using the graph cut (GC) technique with adapted shape priors. RESULTS: The average Dice Similarity Coefficients (DSC), compared with manual segmentations, were 0.88, 0.92, 0.92, 0.93, and 0.93 at 3, 6, 9, 12, and 15 min timepoints, respectively, and the average DSC of the total 63 segmentations was 0.92 ± 0.03. The proposed method improved the accuracy significantly compared with the approach without shape prior adaptation (P = 0.026). The number of probes involved in the procedure had no apparent influence on the segmentation results using our technique. The average computation time was 20 s, which was compatible with an intraprocedural setting. CONCLUSION: Our automatic iceball segmentation method demonstrated high accuracy and robustness for practical use in monitoring the progress of MRI-guided cryoablation.

Tuncali K, Liu X, Wells III WM, Silverman SG, Zientara GP. Real‐time Quantitative Monitoring of Percutaneous MRI‐guided Cryoablation of Renal Cancer, in International Society for Magnetic Resonance in Medicine. Vol 22. ; 2014.Abstract
The safety and effectiveness of percutaneous image‐guided ablations can be improved if the procedure could be assessed quantitatively and in real time. Using MRI’s ability to depict both the tumor and the iceball during cryoablations, we developed a novel computerized tool that utilizes fast automatic segmentation methods to compute ablation metrics and tested its accuracy in MRI guided cryoablations of renal cancer.
Fairchild AH, Tatli S, Dunne RM, Shyn PB, Tuncali K, Silverman SG. Percutaneous Cryoablation of Hepatic Tumors Adjacent to the Gallbladder: Assessment of Safety and Effectiveness. J Vasc Interv Radiol. 2014;25 (9) :1449-55.Abstract
PURPOSE: To assess safety and effectiveness of percutaneous image-guided cryoablation of hepatic tumors adjacent to the gallbladder. MATERIALS AND METHODS: Twenty-one cryoablation procedures were performed to treat 19 hepatic tumors (mean size, 2.7 cm; range, 1.0-5.0 cm) adjacent to the gallbladder in 17 patients (11 male; mean age, 59.2 y; range, 40-82 y) under computed tomography (n = 15) or magnetic resonance imaging (n = 6) guidance in a retrospective study. All tumors (mean size, 2.67 cm; range, 1.0-5.0 cm) were within 1 cm (mean, 0.4 cm) of the gallbladder; seven (33%) were contiguous with the gallbladder. Primary outcomes included complication rate and severity and postprocedure gallbladder imaging findings. Secondary outcomes included technical success and technique effectiveness at 6 months. RESULTS: Complications occurred in six of 21 procedures (29%); one (5%) was severe. Ice balls extended into the gallbladder lumen in 20 of 21 procedures (95%); no gallbladder-related complications occurred. The most common gallbladder imaging finding was mild, asymptomatic focal wall thickening after nine of 21 procedures (42%), which resolved on follow-up. Technical success was achieved in 19 of 21 sessions (90%). Six-month follow-up was available for 16 tumors; of these, all but two (87%) had no imaging evidence of local tumor progression. CONCLUSIONS: Percutaneous cryoablation of hepatic tumors adjacent to the gallbladder can be performed safely and successfully. Although postprocedural gallbladder changes are common, they are self-limited and clinically inconsequential, even when the ice ball extends into the gallbladder lumen.
Dunne RM, Shyn PB, Sung JC, Tatli S, Morrison PR, Catalano PJ, Silverman SG. Percutaneous Treatment of Hepatocellular Carcinoma in Patients with Cirrhosis: A Comparison of the Safety of Cryoablation and Radiofrequency Ablation. Eur J Radiol. 2014;83 (4) :632-8.Abstract
PURPOSE: To compare the safety of image-guided percutaneous cryoablation and radiofrequency ablation in the treatment of hepatocellular carcinoma in patients with cirrhosis. MATERIALS AND METHODS: This retrospective HIPAA-compliant study received institutional review board approval. Forty-two adult patients with cirrhosis underwent image-guided percutaneous ablation of hepatocellular carcinoma from 2003 to 2011. Twenty-five patients underwent 33 cryoablation procedures to treat 39 tumors, and 22 underwent 30 radiofrequency ablation procedures to treat 39 tumors. Five patients underwent both cryoablation and radiofrequency ablation procedures. Complication rates and severity per procedure were compared between the ablation groups. Potential confounding patient, procedure, and tumor-related variables were also compared. Statistical analyses included Kruskal-Wallis, Wilcoxon rank sum, and Fisher's exact tests. Two-sided P-values <0.05 were considered significant. RESULTS: The overall complication rates, 13 (39.4%) of 33 cryoablation procedures versus eight (26.7%) of 30 radiofrequency ablation procedures and severe/fatal complication rates, two (6.1%) of 33 cryoablation procedures versus one (3.3%) of 30 radiofrequency ablation procedures, were not significantly different between the ablation groups (both P=0.26). Severe complications included pneumothoraces requiring chest tube insertion during two cryoablation procedures. One death occurred within 90 days of a radiofrequency ablation procedure; all other complications were managed successfully. CONCLUSION: No significant difference was seen in the overall safety of image-guided percutaneous cryoablation and radiofrequency ablation in the treatment of hepatocellular carcinoma in patients with cirrhosis.
Aghayev A, Tatli S. The use of Cryoablation in Treating Liver Tumors. Expert Rev Med Devices. 2014;11 (1) :41-52.Abstract
Percutaneous image-guided tumor ablation techniques have been used as an alternative method for patients with unresectable liver tumors. Although all techniques avoid morbidity and mortality of major surgery and have advantage of preserving non-tumoral liver parenchyma, cryoablation currently is the only percutaneous ablation technique allowing intraprocedural monitoring because of visibility of its ablation effect with computed tomography and MRI. Cryoablation uses extremely low temperatures to induce local tissue necrosis to treat both primary and metastatic liver tumors. This article discusses the principles of liver tumor percutaneous cryoablation, including mechanisms of tissue injury, technique, equipment, image-guidance used, patient selection criteria, clinical outcome and complications as well as current trends and future goals.
Oguro S, Tuncali K, Elhawary H, Morrison PR, Hata N, Silverman SG. Image registration of pre-procedural MRI and intra-procedural CT images to aid CT-guided percutaneous cryoablation of renal tumors. Int J Comput Assist Radiol Surg. 2011;6 (1) :111-7.Abstract
PURPOSE: To determine whether a non-rigid registration (NRR) technique was more accurate than a rigid registration (RR) technique when fusing pre-procedural contrast-enhanced MR images to unenhanced CT images during CT-guided percutaneous cryoablation of renal tumors. METHODS: Both RR and NRR were applied retrospectively to 11 CT-guided percutaneous cryoablation procedures performed to treat renal tumors (mean diameter; 23 mm). Pre-procedural contrast-enhanced MR images of the upper abdomen were registered to unenhanced intra-procedural CT images obtained just prior to the ablation. RRs were performed manually, and NRRs were performed using an intensity-based approach with affine and Basis-Spline techniques used for modeling displacement. Registration accuracy for each technique was assessed using the 95% Hausdorff distance (HD), Fiducial Registration Error (FRE) and the Dice Similarity Coefficient (DSC). Statistical differences were analyzed using a two-sided Student's t-test. Time for each registration technique was recorded. RESULTS: Mean 95% HD (1.7 mm), FRE (1.7 mm) and DSC (0.96) using the NRR technique were significantly better than mean 95% HD (6.4 mm), FRE (5.0 mm) and DSC (0.88) using the RR technique (P < 0.05 for each analysis). Mean registration times of NRR and RR techniques were 15.2 and 5.7 min, respectively. CONCLUSIONS: The non-rigid registration technique was more accurate than the rigid registration technique when fusing pre-procedural MR images to intra-procedural unenhanced CT images. The non-rigid registration technique can be used to improve visualization of renal tumors during CT-guided cryoablation procedures.