Comparison of four magnetic resonance methods for mapping small temperature changes

Abstract

Non-invasive detection of small temperature changes (< 1 degree C) is pivotal to the further advance of regional hyperthermia as a treatment modality for deep-seated tumours. Magnetic resonance (MR) thermography methods are considered to be a promising approach. Four methods exploiting temperature-dependent parameters were evaluated in phantom experiments. The investigated temperature indicators were spin-lattice relaxation time T1, diffusion coefficient D, shift of water proton resonance frequency (water PRF) and resonance frequency shift of the methoxy group of the praseodymium complex (Pr probe). The respective pulse sequences employed to detect temperature-dependent signal changes were the multiple readout single inversion recovery (T One by Multiple Read Out Pulses; TOMROP), the pulsed gradient spin echo (PGSE), the fast low-angle shot (FLASH) with phase difference reconstruction, and the classical chemical shift imaging (CSI). Applying these sequences, experiments were performed in two separate and consecutive steps. In the first step, calibration curves were recorded for all four methods. In the second step, applying these calibration data, maps of temperature changes were generated and verified. With the equal total acquisition time of approximately 4 min for all four methods, the uncertainties of temperature changes derived from the calibration curves were less than 1 degree C (Pr probe 0.11 degrees C, water PRF 0.22 degrees C, D 0.48 degrees C and T1 0.93 degrees C). The corresponding maps of temperature changes exhibited slightly higher errors but still in the range or less than 1 degree C (0.97 degrees C, 0.41 degrees C, 0.70 degrees C, 1.06 degrees C respectively). The calibration results indicate the Pr probe method to be most sensitive and accurate. However, this advantage could only be partially transferred to the thermographic maps because of the coarse 16 x 16 matrix of the classical CSI sequence. Therefore, at present the water PRF method appears to be most suitable for MR monitoring of small temperature changes during hyperthermia treatment.

MR thermometry

“…And although the proportionality constant of PRF with temperature appears low compared to T 1 and D, PRF-based methods have resulted in higher precision (103), suggesting that temperature monitoring with the PRF is the most sensitive among endogenous MRI parameters in detecting small temperature changes (104). When field inhomogeneity is poor, eg, due to an inserted needle or applicator, the PRF method may not be as accurate as diffusion or T 1 relaxation which can be acquired with spin echo methods.…”

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

“…Direct monitoring of temperature throughout the targeted zone should improve the effectiveness of ablation. MR thermometry, which provides near-real-time temperature maps (9)(10)(11) and enables thermal dose calculation (8) in a noninvasive manner, is considered a very promising tool for this purpose. Despite the difficulties of temperature mapping in the liver, mostly due to low T 2 * values and motion-related artifacts, PRFS-based fast temperature mapping has been shown feasible and stable in vivo, in a range of 1.6-3 C temperature uncertainty, with a temporal resolution of a few seconds and a spatial resolution of 2-3 mm (12)(13)(14).…”

Postmortem Magnetic Resonance Imaging Dealing with Low Temperature Objects

“…30 The body temperature of a refrigerated cadaver reaches near 09 C. MR imaging machines are sensitive to temperature and can be used to measure temperature precisely to over a 19 C diŠer-ence. 31 Thus, PMMRI is considered to depict many characteristic changes in SI dependent upon temperature. The correlation time (t c ) varies inversely with the temperature, according to the following equation: t c ＝t 0 ･exp (-E/kT), where t 0 is the correlation time at an inˆnite temperature, E is the activation energy for rotational motion, k is the Boltzmann constant, and T is the absolute temperature in degrees Kelvin.…”