Variation correction algorithm: analysis of phase suppression and thermal profile fidelity for proton resonance frequency magnetic resonance thermometry at 0.2 T.
OBJECTIVE
To develop and analyze the performance of the variation correction algorithm (VCA), a phase correction technique that mitigates the contribution of background phase variations by combining accurate alignment of echoes, K-space-based phase correction (as opposed to spatial polynomials), and extraction of alias-free phase difference images.


METHODS
A series of echo-shifted gradient-recalled echo (GRE) images was processed with K-space alignment and phase corrected with increasing sizes of M x M masks of central K-space coefficients. The extent of background phase variation suppression due to magnet field drift was assessed. Further, a simulated thermal profile was superimposed on the same data in a related experiment. Residual errors in reconstructed simulated thermal profiles were quantitatively characterized to estimate algorithm performance.


RESULTS
Using a 3 x 3 K-space mask, the VCA was able to 1) maintain the typical mean background error in a 35 x 35 pixel region of interest (ROI) at -0.1 degrees C; and 2) reconstruct, relative to the applied thermal profile, a phase-corrected profile that typically contains a 1.7 degrees C underestimation of peak temperature difference and a mean error along the 60 degrees C line of -0.8 degrees C.


CONCLUSIONS
The results suggest that thermal profiles can be accurately reconstructed at 0.2 T using the VCA, even in the presence of over 1 ppm spatially and temporally dependent field drift over a 1-hour time frame.
Barkauskas
Kestutis J
KJ
Department of Radiology, University Hospitals of Cleveland and Case Western Reserve University, 11100 Euclid Avenue, Cleveland, OH 44106, USA.
Lewin
Jonathan S
JS
Duerk
Jeffrey L
JL
D000465:Algorithms; D006801:Humans; D008279:Magnetic Resonance Imaging; D011522:Protons; D013821:Thermometers
D011522:Protons