[Using 3.0 T MR to dynamically observe ablated lung tumors after percutaneous cryotherapy therapy]

Objective: To initially explore MRI features and its changing trends including of lung tumors after Argon-Helium cryoablation therapy, and enhance the recognition of MR findings of lung tumors postcryoablation. Methods: Twenty-three cases of patients with twenty six nodules of pulmonary malignance who received Argon-Helium cryoablation therapy in Henan Cancer Hospital from July 2014 to January 2016 were enrolled.All patients underwent unenhanced and dynamic contrast-enhanced MRI scans at pre-and 1-day, 1-week, 1-, 3-, 6-, 12-month postcryoablation. Two radiologists independently reviewed MRI images, signal intensity in the ablated zone on T₁WI and T₂WI were assessed by a 5-point scale.The changing trends of size and signal intensity with time were showed by time-maximum diameter and time-score curve.Time-signal intensity curves based on dynamic enhanced sequence were also performed. Results: Typical MRI findings includes: heterogeneous signal intensity on both T₁WI and T₂WI at 1-day postcryoablation(26/26, 100%). Hyper-intense on T₁WI(22/26, 84.6%) and T₂WI(17/26, 65.4%) with a hypo-intense rim at 1-week postcryoablation.Decreasing signal intensity on T₁WI(17/26, 65.4%) and increasing signal intensity on T₂WI(22/26, 84.6%) at 1-month.Signal intensity declined to the level of muscle on both T₁WI(18/26, 69.2%) and T₂WI(19/26, 73.1%) at 3-month, nineteen ablated zone turned into patchy shape(19/26, 73.1%). The maximum diameter was largest at 1-day and gradually shrunk with time. The mean score value toped at 1-week and gradually decreased. A straight line type without definite enhancement was found from 1-day to 1-month postcryoablation, an inflow curve with a mild delayed enhancement was seen from 3- to 12- month. Totally 4 recurrence (4/26, 15.4%) all occurred at 3-month and were lack of a complete hypo-intense rim at 1-week postcryoablation. Conclusion: MRI findings of lung tumors postcryoablation are characteristic, a complete hypo-intense rim at 1-week is helpful to determine further recurrence, 1-week to 3-month is an important period to observe significant change of the ablation zone, MRI is valuable in identifying the ablation zone and can reflect its evolution with time.