Prediction of cell necrosis with sequential temperature mapping after radiofrequency ablation

Abstract

Purpose:To assess the feasibility of magnetic resonance (MR) thermometry after thermoablative therapy and to quantitatively evaluate the ability of two sequence types to predict cell necrosis. Methods:Twenty patients with hepatic tumors were treated by MR-guided radiofrequency ablation. For each 10 patients, postinterventionally performed gradient echo and segmented echo planar imaging sequences were used to calculate temperature maps based on the proton resonance frequency shift method. Contrast-enhanced images acquired 1 month after therapy were registered on the temperature maps and the necrotic, nonenhanced area was segmented and compared to the area with a displayed temperature above 60°C. Sensitivity and positive predictive value of the temperature map was calculated, using the follow-up imaging as the gold standard. Results:Temperature mapping reached acceptable image quality in 45/47 cases. Sensitivity, ie, the rate of correctly detected coagulated tissue was 0.82 Ϯ 0.08 for the gradient echo imaging (GRE) sequence and 0.81 Ϯ 0.14 for the echo planar imaging (EPI) sequence. Positive predictive value, ie, the rate of voxel in the temperature map over 60°C that actually developed necrosis, was 0.90 Ϯ 0.07 for the GRE sequence and 0.84 Ϯ 0.11 for the EPI sequence. Conclusion:Sequential MR temperature mapping allows for the prediction of the coagulation zone with an acceptable sensitivity and positive predictive value using EPI and GRE sequences. 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 (2-5), 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 (11-14), 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.Due to technical and medical challenges linked to this approach, the majority of the literature up to now concerns preclinical questions. In case of RF ablation, the simultaneous use of an RF generator with frequencies between 300 and 500 kHz during imaging decreases image quality (6,18). To date, only noncommercial filters were used to overcome this problem (4,18) or generators with an adapted frequency were employed in animal studies (3,19). Therefore, we performed temperature measurement with a sequential approach: The sedated pat...

Threshold-based prediction of the coagulation zone in sequential temperature mapping in MR-guided radiofrequency ablation of liver tumours

“…The examination included standard MR sequences [14,17,18], including a T2-weighted coronal HASTE sequence, a T2-weighted transversal turbo spin-echo sequence, a diffusion-weighted transversal echo planar imaging sequence and a nonenhanced T1-weighted transversal fast low angle shot gradient echo (FLASH) sequence. A 3D-encoded FLASH sequence was part of the protocol for a contrast-enhanced dynamic liver study after intravenous injection of macrocyclic gadobutrol (Gadovist, Bayer Healthcare, Leverkusen, Germany; dose: body weight/10 mL of gadobutrol, corresponding to 0.1 mmol/kg at an injection rate of 2 mL/s followed by 20 mL of normal saline solution) with the parameters: TR=3.19 msec, TE=1.49 msec, slice thickness = 2 mm, resolution 256 × 200, bandwidth = 560 Hz/pixel, flip angle=10°, number of slabs=2, number of slices per slab=88; the number of slices per slab were adapted to the individual patient.…”

“…Thermal dose mapping based on a continuous acquisition of temperature data during energy application is the most elaborated technique for therapy monitoring and offers the almost immediate visualisation of the temperature of each voxel [12,13]. Sequential temperature mapping is the acquisition of singular, and if necessary, repeated temperature maps subsequent to energy application side-stepping the necessity of filtering the RF which otherwise interferes with the measurements [14]. The direct benefit of the temperature maps is the potential for the protection of sensitive anatomical structures adjacent to the target lesion and the visualisation of a possible heatsink effect caused by vessels crossing the tumour.…”

“…The direct benefit of the temperature maps is the potential for the protection of sensitive anatomical structures adjacent to the target lesion and the visualisation of a possible heatsink effect caused by vessels crossing the tumour. Furthermore, temperature maps can be used to estimate the size and location of the developing coagulation zone [14]. The objective of this work was to compare the temperature maps generated at the end of thermal therapy using the proton resonance frequency shift method (PRF) with the coagulation zones and to evaluate different cutoff temperature values with regard to their ability to correctly predict the ablation zone.…”

Residual tumor after laser ablation of human non-small-cell lung cancer demonstrated by ex vivo staining: correlation with invasive temperature measurements

“…The next step would therefore be to combine the IHLP with MR thermometry, which is possible with some specific modifications, i.e., with an MR-compliant respirator and perfusion pump. With MR thermometry the acquired temperature data can be directly, topographically mapped to the whole target area [43,45,46]. The polygon representing the mean zone of coagulation of our experiments resembles the thermal maps acquired from MR thermometry during thermal ablation, which also show a region of damaged tissue that is irregular in shape [47].…”

Therapy Monitoring of Magnetic Resonance–Guided Radiofrequency Ablation Using T1- and T2-Weighted Sequences at 1.5 T

“…However, they require a high technical standard and clinical validation is not yet completed. 10,11 A specific problem of temperature-sensitive measurements has been identified in white cavitation gas bubbles leading to erroneous temperature values. 12 Standard T1-weighted (T1W) and T2-weighted (T2W) images visualize areas with contrast changes due to the developing ablation zone without applying contrast agents and can be repeatedly acquired.…”