Real time monitoring of radiofrequency ablation based on MR thermometry and thermal dose in the pig liver in vivo

Abstract

Real time monitoring of radiofrequency ablation based on MR thermometry and thermal dose in the pig liver in vivo Abstract To evaluate the feasibility and accuracy of MR thermometry based on the thermal dose (TD) concept for monitoring radiofrequency (RF) ablations, 13 RF ablations in pig livers were performed under continuous MR thermometry at 1.5 T with a filtered clinical RF device. Respiratory gated fast gradient echo images were acquired simultaneously to RF deposition for providing MR temperature maps with the proton resonant frequency technique. Residual motion, signal to noise ratio (SNR) and standard deviation (SD) of MR temperature images were quantitatively analyzed to detect and reject artifacted images in the time series. SD of temperature measurement remained under 2°C. Macroscopic analysis of liver ablations showed a white zone (Wz) surrounded by a red zone (Rz). A detailed histological analysis confirmed the ongoing nature of the coagulation necrosis in both Wz and Rz. Average differences (±SD) between macroscopic size measurements of Wz and Rz and TD predictions of ablation zones were 4.1 (±1.93) mm and −0.71 (±2.47) mm, respectively. Correlation values between TD and Wz and TD and Rz were 0.97 and 0.99, respectively. MR thermometry monitoring based on TD is an accurate method to delineate the size of the ablation zone during the RF procedure and provides a clinical endpoint.

Automatic temperature control for MR-guided interstitial ultrasound ablation in liver using a percutaneous applicator: Ex vivo and in vivo initial studies

“…Such conditions are critical with respect to MR thermometry in liver, when intrascan ghosting artifacts and interscan misregistration must be avoided under regular breathing. In the current study, the SD of MR thermometry within the target region ranged between 1.0 and 1.9 C. Our voxel volume in vivo was 33% smaller as compared to previously reported studies of MR-monitored thermal ablation in pig liver (33), where the SD of thermometry ranged between 1.1 and 2.44 C after additional image postprocessing performed off line. Note that retrospective (i.e., off line) postprocessing is not compatible with real-time active control of temperature.…”

“…To our best knowledge, while quantitative MR thermometry for thermal ablation in the pig liver with RF (32,33) and MR-based active temperature control of US ablation in the canine prostate have been previously reported, in vivo interstitial US ablation in pig liver operating under MR-based active temperature control has not yet been reported. The purpose of this study was (1) to develop an MR-compatible percutaneous US applicator with a dedicated positioning system, (2) to design ex vivo and in vivo studies for evaluating the feasibility of automatic temperature control based on real-time MR thermometry, and (3) to provide ablative liver lesions in pig under general anesthesia and forced breathing.…”

Hyperthermia classic commentary: ‘Arrhenius relationships from the molecule and cell to the clinic’ by William Dewey,Int. J. Hyperthermia, 10:457–483, 1994

“…Some examples include lethal thermal dose thresholds of CEM 43 4210 min for 100% necrosis of breast tumors, 180-240 CEM 43 for prostate [23][24][25][26], 240 CEM 43 for liver during RF ablation [27], and 240 CEM 43 threshold for general soft tissue destruction and treatment of uterine fibroids with MR guided ultrasound [28,29]. The thermal isoeffect dose concept has also been extended to describe regions of thermal fixation produced during ablation, as demonstrated for kidney [30] with temperatures of $65 C; the thermal isoeffect dose that was dependent on the time of damage assay after treatment was associated with activation energies of 61-95 kcal mole…”

Prediction of cell necrosis with sequential temperature mapping after radiofrequency ablation

“…REAL-TIME TEMPERATURE MAPPING of magnetic resonance (MR)-guided minimally invasive radiofrequency (RF) ablation has been shown to be feasible both ex vivo (1) and in vivo (2)(3)(4)(5), and has the potential of becoming the gold standard for therapy monitoring of thermoablative therapies. Different MR techniques have been proposed for temperature measurement (6 -10); the most frequently used is the proton resonance frequency shift (PRF) method (11)(12)(13)(14), which is based on a temperature-dependent phase shift allowing for the measurement of temperature changes relative to a baseline image.…”

“…Different MR techniques have been proposed for temperature measurement (6 -10); the most frequently used is the proton resonance frequency shift (PRF) method (11)(12)(13)(14), which is based on a temperature-dependent phase shift allowing for the measurement of temperature changes relative to a baseline image. With frequent repetitive measurements during thermoablative therapy, this approach allows a precise estimation of the lethal thermal dose (15) based on the Arrhenius model (16,17) and could be used to predict the size and position of the coagulation zone in animal studies (3,5). Furthermore, real-time temperature monitoring could allow for visualizing a vessel-related cooling effect and thus prevent a survival of cancer cells due to an undetected heat-sink effect.…”