What effect does reducing the Phase Matrix have on SNR in an image?

Reducing the Phase Matrix in an MRI image acquisition leads to a corresponding decrease in the signal-to-noise ratio (SNR). The phase matrix is related to the spatial resolution of the image; a lower phase matrix means fewer phase encoding steps and, therefore, reduced data resolution in the phase direction.

When the phase matrix is reduced, the number of excitations or signal acquisitions per image slice decreases. Because SNR is fundamentally dependent on the amount of signal collected relative to the noise present in the image, reducing the data collected inherently results in a less intense signal. Consequently, this leads to a higher relative noise presence in the final image, thus diminishing the SNR.

Hence, the choice stating that reducing the Phase Matrix decreases SNR accurately reflects the impact this adjustment has on the quality of the MRI image.