A new temperature measurement procedure using phase mapping was developed that makes use of the temperature dependence of the water proton chemical shift. Highly accurate and fast measurements were obtained during phantom and in vivo experiments. In the pure water phantom experiments, an accuracy of more than +/- 0.5 degrees C was obtained within a few seconds/slice using a field echo pulse sequence (TR/TE = 115/13 ms, matrix = 128 x 128, number of slices = 5). The temperature dependence of the water proton chemical shift was found to be almost the same for different materials with a chemical composition similar to living tissues (water, glucide, protein). Using this method, the temperature change inside a cat's brain was obtained with an accuracy of more than +/- 1 degree C and an in-plane resolution of 0.6 x 0.6 mm. The temperature measurement error was affected by several factors in the living system (B0 shifts caused by position shifts of the sample, blood flow, etc.), the position shift effect being the most serious.

A precise and fast temperature mapping using water proton chemical shift.

The noninvasive thermometry method is based on the temperature dependence of the proton resonance frequency (PRF). High-quality temperature images can be obtained from phase information of standard gradient-echo sequences with an accuracy of 0.2 degrees C in phantoms. This work was focused on the in vivo capabilities of this method. An experimental setup was designed that allows a qualitative in vivo verification. The lower-leg muscles of a volunteer were cooled and afterwards reheated with an external water bolus. The temperature of the bolus water varied between 17 degrees C and 37 degrees C. The in vivo temperature images can be used to extract the temperature in muscle tissue. The data in the fat tissue are difficult to interpret because of the predominance of susceptibility effects. The results confirm the method's potential for hyperthermia control.

Noninvasive MRI thermometry with the proton resonance frequency (PRF) method: in vivo results in human muscle.

The proton resonance frequency (PRF) shift provides a means of measuring temperature changes during minimally invasive thermotherapy. However, conventional PRF thermometry relies on the subtraction of baseline images, which makes it sensitive to tissue motion and frequency drift during the course of treatment. In this study, a new method is presented that eliminates these problems by estimating the background phase from each acquired image phase. In this referenceless method, a polynomial is fit to the background phase outside the heated region in a weighted least-squares fit. Extrapolation of the polynomial to the heated region serves as the background phase estimate, which is then subtracted from the actual phase. The referenceless method is demonstrated on a phantom during laser heating, 0° temperature rise images of in vivo human liver, interstitial laser ablation of porcine liver, and transurethral ultrasound ablation of canine prostate. A good correlation between temperature maps reconstructed with the referenceless and subtraction methods was found. Magn Reson Med 51:1223–1231, 2004. © 2004 Wiley-Liss, Inc.

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Referenceless PRF shift thermometry.

The temperature dependence of proton resonance frequency (PRF) is related to the temperature dependence of the screening constant and of the volume susceptibility constant. To evaluate the relative importance, an experimental setup was designed allowing quantification of both effects in different tissues, notably pure water in a gel structure, and porcine muscle and fat tissue. The temperature varied from 28 to 44 degrees C, a range significant for hyperthermia applications. Good agreement with results from the literature was obtained for water. Porcine muscle tissue behaves like water. Its screening constant varies linearly at a rate of 0.97 10(-8) (degree C)-1 and the effects of temperature-induced changes of the susceptibility constant are negligible for muscle thermometry applications. The PRF-temperature relation in fat tissue, however, is almost completely determined by susceptibility effects.

Noninvasive MRI thermometry with the proton resonance frequency method: Study of susceptibility effects

PURPOSE: To differentiate between benign and malignant cartilaginous tumors with fast contrast material–enhanced magnetic resonance (MR) imaging. MATERIALS AND METHODS: In 37 patients, fast contrast-enhanced MR images were obtained in eight enchondromas, 11 osteochondromas, and 18 chondrosarcomas. Start of enhancement—early, within 10 seconds after arterial enhancement; delayed, between 10 seconds and 2 minutes; late, after 5 minutes on spin-echo images—and progression of enhancement were represented with three types of time–signal intensity curves. Findings were correlated with the surgical specimen in 27 cases, curettage material in three cases, and biopsy combined with long-term follow-up findings in seven cases. RESULTS: Start of enhancement and the combination of start and progression of enhancement correlated significantly (P < .001) with benign and malignant tumors. Early enhancement was seen in chondrosarcoma, not seen in enchondroma, and seen in osteochondroma only when growth plates were unfused...

Cartilaginous tumors: fast contrast-enhanced MR imaging.

The Proton-Resonance-Frequency-Shift Method Compared with Molecular Diffusion for Quantitative Measurement of Two-Dimensional Time-Dependent Temperature Distribution in a Phantom

J. Depoorter

Papers

The Proton-Resonance-Frequency-Shift Method Compared with Molecular Diffusion for Quantitative Measurement of Two-Dimensional Time-Dependent Temperature Distribution in a Phantom

Dynamic contrast enhanced magnetic resonance imaging (MRI) of musculoske-letal neoplasms: different types and slopes of time-intensity curves