MRI Math
Stephen J. Powers B.S.R.T. (R), (CT), (MR) · 2021
The most important number we need to know in MRI is the gyromagnetic ratio of hydrogen. It is a constant, which means it never, ever, changes. It is used in the Larmor equation. A voxel is a pixel with a slice thickness, the third dimension. To find a voxel-s volume, we must multiply height by width by thickness. The Dixon technique is a way to get fat-sat-like images at low fields. It is not a true fat-sat, it just provides fat-sat-like images. This is done mathematically by adding or subtracting the echoes. Signal-to-noise ratio (SNR) in a 3D increases with the number of locations or partitions. We may have noticed that the SNR in a 3D goes up as we add slices-or another slab. Scan time goes up at the expense of coverage. The net gain or loss of SNR is the square root of the number of partitions.