Noninvasive MRI Thermometry with the Proton Resonance Frequency (PRF) Method: In Vivo Results in Human Muscle

Purpose: To investigate Gd-DTPA kinetics as predictors of histopathological changes following focused ultrasound (FUS) thermal ablation for improved planning and assessment. Materials and Methods:Twenty-nine FUS lesions were created in the thigh muscle of eight rabbits under MRguidance at 1.5 Tesla. Three rabbits were killed at four hours; and 11 lesions were analyzed with histopathology. Temperature-sensitive MRI using proton-resonant frequency-shift was used for time-dependent temperature measurements. Analysis of the uptake kinetics of Gd-DTPA was performed after Gd-DTPA injection, within 20 minutes after heating and again at two hours after heating. The resulting kinetic maps, permeability (K trans ) and leakage space (v e ), were correlated to peak temperatures, T 2 -weighted MR, and histopathology.Results: Images of K trans and v e reveal regions of histopathological change not visible on conventional posttherapy MR. At early times after heating, v e predicts the area of injury more accurately than T 2 (7 Ϯ 2% vs. 25 Ϯ 6% underestimation). A circular region of extensive structural/ vascular disruption is indicated only on K trans maps. The sharp decrease in K trans at the boundary of this region occurs at 47.5 Ϯ 0.5°C, and may be a better estimate of cell death than the conventional method of temperature threshold (55°C for coagulation) used in therapy planning. Conclusion:Our results suggest Gd-DTPA kinetics can predict different histopathological changes following FUS ablation and may be valuable for early prediction.

Section: Temperature Monitoring During Therapymentioning

confidence: 99%

Prediction of subtle thermal histopathological change using a novel analysis of Gd‐DTPA kinetics

Cheng

Purcell

Bilbao

et al. 2003

“…Using a radio frequency (RF)-spoiled gradient-echo sequence, the change in temperature ⌬T (°C) can be determined from the difference in phase of the MR signal ⌬ between the current image and a reference (baseline) image (5,13):…”

mentioning

confidence: 99%

Simultaneous temperature and magnetization transfer (MT) monitoring during high‐intensity focused ultrasound (HIFU) treatment: Preliminary investigation on ex vivo porcine muscle

Peng

Huang

Tseng

et al. 2009

Purpose:To measure temperature change and magnetization transfer ratio (MTR) simultaneously during high-intensity focused ultrasound (HIFU) treatment. Materials and Methods:This study proposed an interleaved dual gradient-echo technique to monitor the heat and tissue damage brought to the heated tissue. The technique was applied to tissue samples to test its efficacy. Results:Ex vivo experiments on the porcine muscle demonstrated that both temperature changes and MTR exhibited high consistency in localizing the heated regions. As the heat dissipated after the treatment, the temperature of the heated regions decreased rapidly but MTR continued to be elevated. Moreover, thermal dose (TD) maps derived from the temperature curves demonstrated a sharp margin in the heated regions, but MTR maps may show a spatial gradient of tissue damage, suggesting complimentary information provided by these two measures.Conclusion:In a protocol of spot-by-spot heating over a large volume of tissue, MTR provides additional values to mark the locations of previously heated regions. By continuously recording the locations of heated spots, MTR maps could help plan the next target spots appropriately, potentially improving the efficiency of HIFU treatment and reducing undesirable damage to the normal tissue. RECENT DEVELOPMENT OF HIGH-INTENSITY FO-CUSED ULTRASOUND (HIFU) technology has offered a potentially new approach to the local ablation of malignant or benign tumors (1,2). By focusing an ultrasound beam at the target tissue, HIFU maximizes the heating damage to the targeted tissue while preserving the surrounding normal tissue. To improve treatment efficiency and ensure patient safety, it is crucial to perform continuous and real-time monitoring of local heat deposition during HIFU treatment. Owing to satisfactory spatial and temporal resolution, high tissue contrast, and no ionizing radiation, MRI is advantageous over other imaging modalities in guiding, monitoring, and controlling the HIFU treatment, and has therefore been used for preheating localization of the targets or postheating evaluation of the treatment effect (3). Several MR parameters, such as the equilibrium magnetization (M 0 ), T1, T2, and the diffusion coefficient of water molecules, are known to exhibit temperature dependence (4 -10). The temperature sensitivity of these parameters, however, is tissue-dependent, nonlinear, or varies with tissue conditions such as thermal coagulation or denaturation (5,11,12). Currently, the MR parameter that is sensitive to temperature and stable under various tissue conditions is the water proton resonant frequency (PRF) shift (5). The method of PRF shift deter-

“…Typically, for treatment of one tumor with a 30-mm diameter, three ablations were carried out at two different points along with one needle path and four punctures (three for the periphery and one for the center) were repeated. In the later cases, relative temperature changes were calculated by the proton resonance frequency method (11), using an SPGR with 50 msec TR, 12 msec TE, 7-mm slice thickness, 250 ϫ 250 mm 2 FOV, 256 ϫ 128 resolution and 6.4 second acquisition time. Temperature in each pixel was calculated using a Real Time Image Processing (RTIP) application in the SIGNA SP System, which was modified to display temperature increase values.…”

Section: Methodsmentioning

confidence: 99%

MR‐guided microwave thermocoagulation therapy of liver tumors: Initial clinical experiences using a 0.5 T open MR system

Morikawa¹,

Inubushi²,

Kurumi

et al. 2002

Purpose: To utilize a microwave coagulator for MR-guided interstitial thermal therapy of liver tumors as a clinically feasible heating device. Materials and Methods:MR-guided microwave thermocoagulation therapy was carried out 34 times in 30 patients with liver tumors (eight hepatocellular carcinoma, 22 metastatic tumors) using a 0.5 T open configuration MR system.Results: Percutaneous puncture could be accomplished both accurately and safely while monitoring real-time magnetic resonance imaging (MRI). Using a notch filter, MR images could be observed without electromagnetic interference even during microwave ablation. Temperature monitoring during ablation was possible using the proton resonance frequency method. All procedures could be successfully carried out without any complications, and the therapeutic effects were deemed satisfactory. Conclusion:MR-guided microwave thermocoagulation therapy could be one promising procedure of minimally invasive treatment for liver tumors.