Program Information
Evaluation of the Impact of Eddy Current and Excitation Corrections On ADC Map Uniformity
C MacLellan*, J Yung , K Hwang , R Stafford , UT MD Anderson Cancer Center, Houston,
Presentations
TU-AB-601-8 (Tuesday, August 1, 2017) 7:30 AM - 9:30 AM Room: 601
Purpose: To assess the impact of several eddy current corrections and transmit excitation modes on the uniformity of ADC maps.
Methods: Axial ADC maps were acquired in a 19 cm spherical homogenous MR-spectroscopy phantom using a diffusion weighted spin-echo echo planar imaging sequence (b-values: 0, 50, 100, 200, 400, 800, 1000) on 2 General Electric 3 Tesla clinical MRI scanners (60 cm and 70 cm bore size) using a 24 channel receive only head array. Changes in the image uniformity were measured using the NEMA normalized average absolute deviation (NAAD) and ACR uniformity metrics after varying eddy current correction techniques (real-time field correction (RTFA), dual spin echo (DSE), and none) and excitation modes (quadrature, preset, optimized; 70cm only). The changes caused by each variable were assessed using a 3-way analysis of variance (ANOVA) and the magnitude of the differences were quantified using Tukey-Kramer post-hoc multiple comparison test.
Results: All uniformity measurements were in excess of 95% regardless of the selected imaging options. Bore size and eddy current correction method had a significant impact (p<.01) on both uniformity metrics. Specifically, smaller bore size and DSE were associated with a statistically significant increases in mean image uniformity. In both cases (ACR/NAAD) smaller bore size resulted in a larger average increase (+1.64%/+0.69%) than DSE (+0.76%/+0.39%).
Conclusion: Eddy current correction techniques, whose primary purpose is to reduce distortions, can also have a significant impact on the uniformity of ADC maps. The magnitude of this effect can be on the order of the well known bore size dependence. Future work should focus on extending this analysis to larger phantoms and additional scanners and integrating uniformity assessment with more traditional measures of ADC image quality such as image distortion and ADC accuracy.
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