MR monitoring of tumour thermal therapy

Abstract

Thermal therapy of tumour including hyperthermia and thermal ablation by heat or cold delivery requires on line monitoring. Due to its temperature sensitivity, Magnetic Resonance Imaging (MRI) allows thermal mapping at the time of the treatment. The different techniques of MR temperature monitoring based on water proton resonance frequency (PRF), longitudinal relaxation time T1, diffusion coefficient and MR Spectroscopic Imaging (MRSI) are reviewed and debated. The PRF method appears the most widely used and the most efficient at high magnetic field in spite of important drawbacks. The T1 method is the easiest method of visualisation of qualitative temperature distribution and quantitative measurement seems possible in the tissue surrounding the tumour up to a temperature of 45-65 degrees C. Despite its high temperature sensitivity, application of the diffusion method in vivo is restricted due to its high motion sensitivity. The recent MRSI technique seems very promising provided acquisition times can be reduced. Results from the literature indicate that MR temperature monitoring in vivo can be achieved in vivo with a precision of about 3 degrees C in 13 s for a voxel of 16 mm3 (1.5 x 1.5 x 7 mm) in 1.5 T scanners.

Measurement of regional brain temperature using proton spectroscopic imaging: validation and application to acute ischemic stroke

“…A reference value of CS NA = 2.035 ppm was determined from occipital voxels in a group of 20 healthy control subjects (age, 46F10 years) with an assumed brain temperature of 378C. The constant of proportionality (1008C/ppm or, equivalently, 0.01 ppm/8C) was taken from the literature [11]. Eq.…”

“…Methods based on water PRF, which has a temperature dependence of approximately 0.01 ppm/8C [11], are the most popular. In bphase-shiftQ PRF techniques, the pixel-by-pixel phase change between successive gradient-echo images is used to monitor thermal interventions such as forced heating [11,12]. Although rapid and yielding spatial resolutions of imaging, these techniques are restricted to monitoring temperature changes and, thus, are not suitable for observational studies.…”

“…Clearly, a reliable noninvasive method is highly desirable and could have many clinical uses. Several magnetic resonance parameters can be used for the noninvasive measurement of regional temperatures [11], including the diffusion coefficient, the longitudinal relaxation time constant (T 1 ) and the proton resonance frequency (PRF). Methods based on water PRF, which has a temperature dependence of approximately 0.01 ppm/8C [11], are the most popular.…”

“…Several magnetic resonance parameters can be used for the noninvasive measurement of regional temperatures [11], including the diffusion coefficient, the longitudinal relaxation time constant (T 1 ) and the proton resonance frequency (PRF). Methods based on water PRF, which has a temperature dependence of approximately 0.01 ppm/8C [11], are the most popular. In bphase-shiftQ PRF techniques, the pixel-by-pixel phase change between successive gradient-echo images is used to monitor thermal interventions such as forced heating [11,12].…”

MR imaging-guided laser ablation of osteoid osteomas with use of optical instrument guidance at 0.23�T

“…The unique ability of the MRI is the capability of monitoring thermal changes in tissue. This is not possible to the same extent with CT or ultrasound, as only MRI can provide quantitative information about thermal changes in tissue [35,36,37,38,39]. Generally, high-field devices are more suitable for thermal monitoring because of better signalto-noise ratio; however, the high-field devices lack the patient access that open scanners possess.…”