Real-Time Magnetic Resonance Imaging–Guided Cryoablation of Small Renal Tumors at 1.5 T

Abstract

Objectives-Real-time magnetic resonance imaging (MRI)-guided cryoablation has been investigated in open MRI systems with low magnetic fields (0.2-0.5 T). More advanced imaging techniques and faster imaging rates are possible at higher magnetic fields which often require a closed-bore magnet design. However, there is very little experience with real-time interventions in closed-bore 1.5 T MRI units. Herein, we report our initial experience with real-time MRI-guided cryoablation of small renal tumors using a prototype balanced steady-state free precession (bSSFP) imaging sequence in a closed-bore 1.5-T MRI system. Materials and Methods-FromAugust 2008 to April 2012, 18 patients underwent MRI-guided cryoablation of small renal tumors. A 1.5-T cylindrical MRI scanner with a 125 cm × 70 cm bore and a prototype bSSFP sequence (BEAT IRTTT) were used to guide the placement of 17-gauge cryoprobes in real time. Ice ball formation was monitored every 3 minutes in one or more imaging planes. Each ablation consisted of 2 freeze-thaw cycles. Contrast-enhanced MRI was performed after the second active thaw period. Follow-up consisted of clinical evaluation and renal protocol computed tomography (CT) or MRI performed at 1, 6, 12, 18, and 24 months and annually thereafter.Results-During the study period, we successfully ablated 18 tumors in 18 patients in 18 sessions. The mean tumor size was 2.2 cm (median, 2 cm; range: 1.2-4.4 cm). The number of cryoprobes used per patient was determined based on tumor size. The mean number of cryoprobes used per patient was 3 (median, 3 cryoprobes; range, 2-4 cryoprobes). Fifty-six cryoprobes, 9 biopsy needles, and 2 hydrodissection needles were successfully placed under real time MRI guidance using BEAT IRTTT sequence. Hydrodissection under MRI guidance was successfully performed in 4 patients. In each patient, contrast-enhanced MRI performed after the second active NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript thaw period revealed a sharply defined avascular zone surrounding the targeted tumor, which confirmed complete ablation of the tumor with adequate margins. Although contrast media slowly accumulated in the targeted tumor in 9 patients immediately after the procedure, follow-up imaging studies performed at a mean of 16.7 months revealed no contrast enhancement within the ablation zone in these patients. Disease-specific, metastasis-free, and local recurrence-free survival rates were all 100%.Conclusions-Real-time placement and manipulation of cryoprobes during MRI-guided cryoablation of small renal tumors in a closed-bore, high-magnetic field scanner is feasible.Technical and clinical success rates are similar to those of patients who undergo CT-guided radiofrequency ablation or cryoablation of small renal tumors. Our findings suggest that MRIguided ablation has several advantages over CT-guided ablation, including real-time guidance for probe placement, multiplanar imaging, exquisite soft tissue contrast, and lack of ionizing radiation.

Radiation Exposure From CT-Guided Ablation of Renal Masses: Effects on Life Expectancy

“…If procedural radiation doses were to be curbed by the use of MRI or ultrasound for imaging guidance rather than CT, or if follow-up regimens were altered by the use of dual-energy CT or MRI, then perpatient costs may be substantially impacted [39,41,[48][49][50][51][52]. We elected not to conduct a formal cost-effectiveness analysis because downstream costs associated with radiationinduced cancers, which are expected to occur decades later, would have an associated level of uncertainty that is unreasonably high.…”

Clinical Application and Feasibility of MRI-Guided Breast Biopsy of Breast Minimal Lesions in Chinese Population

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Automated Tumor Volumetry Using Computer-Aided Image Segmentation

“…Although the results presented here focus primarily on brain tumors, the method may be extended to and used for the segmentation of other large solid tumors as well. Likewise, because the algorithm is extremely fast, one could potentially use this methodology for real-time tumor tracking during invasive procedures such as thermal ablation or cryoablation (31). …”