MO-G-18C-06: MRI QC: Effects of Multi-Channel Coil Element Failure On Image Quality

Authors


Abstract

Purpose:

To quantitatively evaluate changes in phantom quality control (QC) measurements resulting from malfunctioning channels in multichannel brain coils during routine MRI QC.

Methods:

The large ACR MRI phantom was scanned on a 1.5T GE HDXt scanner using an 8-channel brain array and on a 1.5T Siemens Aera using a 20-channel head-neck array. For the 8-channel array, images were acquired by sequentially turning off an increasing number of adjacent channels. For the 20-channel array, images were acquired with various combinations of active coil elements. Percent integral uniformity (PIU), signal-to-noise ratio (SNR) and ghosting ratio were measured with and without uniformity correction (UC).

Results:

For the 8-channel array, SNR and PIU decreased with the number of inactive coil elements (57% and 34%, respectively). UC increased PIU to >82% and SNR to 80%, but also increased apparent ghosting due to background nonuniformity. For the 20-channel array, the central pair of element groups (H3-H4) closest to the phantom had the greatest impact on image quality. Without UC, PIU and SNR were similar when all groups or both H3-H4 were active. Without UC, PIU decreased by 50% when either H3 or H4 was deactivated. Noise greatly decreased resulting in a ∼500% increase in SNR. Without UC, SNR decreased by 60% and PIU increased when both H3-H4 were deactivated. PIU was most affected by UC (50%–160% increase). For both coils, ghosting ratio generally increased with UC but not above ACR limit (2.5%). With UC applied, PIU failed the ACR limit (87.5%) when 2 elements of the 8-channel array or H3-H4 were inactive.

Conclusion:

Channel failure for the two multichannel arrays tested was reflected in changes in SNR and PIU. For daily MR QC, setting coil-specific SNR, PIU and ghosting QC limits to ensure the detection of malfunctioning elements is necessary due to coil design variations.

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