Chang-Sheng Mei PhD, Presenter: Nothing to Disclose

Renxin Chu PhD, Abstract Co-Author: Nothing to Disclose

W. Scott Hoge PhD, Abstract Co-Author: Nothing to Disclose

Lawrence P. Panych PhD, Abstract Co-Author: Nothing to Disclose

Bruno Madore PhD, Abstract Co-Author: Research Consultant, Millikelvin Technology LLC

The present study aimed at developing an MRI-based temperature monitoring strategy capable of providing accurate temperature measurements even in the presence of field inhomogeneities. Such inhomogeneities commonly occur near air-tissue transitions, for example, around the sphenoid sinuses, and can significantly degrade the accuracy of temperature measurements.

The use of a multi-pathway steady-state sequence is proposed here to help detect and correct for susceptibility-induced temperature measurement errors. The two different signal pathways sampled by the sequence lead to temperature errors of different polarity, ΔT and -ΔT, making it possible to detect and correct for such errors. These two pathways correspond to the so-called ‘fast imaging with steady-state precession’ (FISP) signal and the inverse-FISP (PSIF) signal. The heating curve from both signal pathways can be measured, on a pixel-by-pixel basis, and a single-variable equation can be solved to evaluate the temperature errors, allowing them to be corrected for. The method was tested in gel phantoms and in a rabbit model.  

Measurement errors of several °C were observed and corrected for in controlled phantom experiments where known field inhomogeneities were intentionally introduced by de-adjusting high-order shim settings. Temperature errors were also observed and corrected for in a rabbit model, where field inhomogeneities were unavoidably present despite shimming, due to nearby air-tissue interfaces. After the proposed correction scheme was applied on a pixel-by-pixel basis, agreement was obtained between both FISP and PSIF measurements. Errors by up to about 20% in temperature elevation (overestimation by 5 °C on a 25 °C peak temperature elevation) have been observed and avoided.  

We have demonstrated a method for detecting and correcting for susceptibility-induced temperature measurement errors. The method allows accurate temperature measurements to be performed even near air-tissue interfaces, with potential benefits in prostate, uterus, and brain MR-guidance applications.

The proposed thermometry method allows susceptibility-induced temperature errors to be detected and corrected for. As a result, improved MR guidance may be achieved, during thermal therapies.

Mei, C, Chu, R, Hoge, W, Panych, L, Madore, B, Accurate Temperature Measurements in the Presence of Field Inhomogeneities for MR Guided Thermal Therapies.  Radiological Society of North America 2013 Scientific Assembly and Annual Meeting, December 1 - December 6, 2013 ,Chicago IL. http://archive.rsna.org/2013/13025788.html