Faster MRI Near Metal Using Subsampling
Hexagonal or Checkerboard Undersampling of 3D images of distorted slices leads to replication, but since it does not interfere with the desired information, this can reduce scan times by up to 50%
Faster MRI near metal is enabled by subsampling and tightening the field of view to fit the shape of distorted slices. MR imaging close to metallic implants is challenging because the metal affects the magnetic field, resulting in distortions or "curving" of the acquired slices. This can be corrected by "mapping" the curvature of each slice using 3D volume scans, but this results in longer scan times. In this work, we note that the slices will only be distorted close to the implant. This means that much of the 3D volume will contain a normal, "flat" slice, leaving much of the volume unused. This allows for undersampling the data using a "checkerboard" pattern. From the principles of sampling theory, this leads to some replication of image information. However, the "checkerboard" pattern results in the replicated data only appearing in the unused volume regions. Therefore, the desired slice information is not corrupted and the scan time can be reduced by up to 50%.
Sveinsson B, Worters PW, Gold GE, Hargreaves BA. Hexagonal undersampling for faster MRI near metallic implants. Magn Reson Med. 2015 Feb;73(2):662-8.
Examples of full and reduced sampling, and resulting images in a subject with a total hip replacement. The images look identical, in spite of a 50% scan time reduction.
Bragi Sveinsson and Pauline Worters are alumni of the BMR group
