What is the effect on SNR when slice thickness increases?

When slice thickness increases in imaging techniques such as MRI, the signal-to-noise ratio (SNR) tends to improve. This occurs because a thicker slice encompasses a larger volume of tissue, which captures more of the emitted signals from the protons within that tissue. A greater number of protons contributes more signal to the measured data, which enhances the overall SNR.

In practical terms, when slices are thinner, they may be more sensitive to noise, and because only a smaller volume is sampled, the SNR can suffer. Conversely, with thicker slices, the benefits of averaging over a larger volume help to mitigate the effects of random noise.

The rationale behind the other choices stems from a misunderstanding of how tissue volume and signal accumulation work in relation to noise. As slice thickness increases, noise may remain relatively constant, but by increasing the volume sampled, the signal increases more significantly than the noise, leading to an improved SNR rather than a decrease or no change at all.