PARENT SESSION
1:30 PM to 3:30 PM
Saturday, April 20, 2002
Poster Session 1 Noninvasive Treatment Monitoring and Treatment Planning
Room: Nevada 1-2

(MP01-2) Correction of drift and motion artifacts in magnetic resonance thermal imaging.

Das, Shiva^*,1, Craciunescu, Oana¹, McCauley, Robert¹, Samulski, Thaddeus¹, ¹ Dept. of Radiation Oncology, Durham, NC

ABSTRACT-
The use of Magnetic Resonance Imaging (MRI) in real time monitoring of hyperthermia temperature distributions is becoming increasingly popular. Its appeal comes from the noninvasive nature of the monitoring, and the ability to view the temperature in three dimensions, in contrast to one-dimensional temperatures along catheter tracks obtained from invasive temperature probes. The MRI thermal measurement techniques most commonly used are the Proton Resonance Frequency Shift (PRFS) method and the Apparent Diffusion Coefficient (ADC) method. Both methods, however, suffer some drawbacks. The PRFS technique is highly susceptible to magnetic drift of the applied fields and motion, leading to image deterioration over time (drift induced) or large artifacts (motion induced). ADC, on the other hand, suffers from low signal to noise ratio, necessitating the use of lower resolution to obtain meaningful images. We herein propose a method to combine the high resolution of PRFS with the relative stability of the lower resolution ADC to generate stable, high-resolution images. The heated object is simultaneously imaged with PRFS and ADC. We propose using a set of weighted correction patterns to be added to the original PRFS images consisting, among others, of gradients, uniform shift, and circularly symmetric patterns. The weights assigned to these correction patterns are determined by minimizing the least squares error between the corrected PRFS images and the corresponding ADC images, summed over all the (low resolution) pixels of the ADC images. Application of this technique is demonstrated using PRFS and ADC images obtained in an experiment, wherein a gel phantom is heated in a mini-annular radiofrequency phased array. Drift and motion artifacts of the PRFS method are substantially eliminated by applying the correction technique; comparison to invasive probe measurements confirm the correction. We are currently in the process of applying this technique to recently acquired thermal images from a human patient treatment.

KEYWORDS: mri, artifact, correction, temperature