DTI Quality Control - Part 1: Acquisition

Tuesday, March 04, 2014 Do Tromp 0 Comments

A major issue in DTI image analysis is quality control. Effective quality control for diffusion images relies both on pre tensor fitting (the diffusion weighted images; DWI), and post tensor fitting (the  diffusion tensor images; DTI) checks.

First you will have to check if all volumes were acquired correctly; using fslinfo is one method:

This way you can check if each image has the correct number of volumes and the correct pixel dimensions. Something else you should really pay attention to is the quality of each raw DWI image. If you visually scroll through all the different directions you might come across this:

This does not necessarily have to be a problem if it happens occasionally, but I can become a problem for the tensor calculation if it occurs more frequently (depending on how many directions you acquired).

Next, check the amount of distortion in your image; echo planar imaging (EPI), which is used for diffusion images - are particularly sensitive to stretching in the prefrontal and ventral temporal parts of the brain (depending on the direction of acquisition). For example:
This can be fixed by acquiring a fieldmap that measures the amount of distortion. Read more about this here and here. Or by acquiring data in two opposite directions and then calculating the average. FSL's TOPUP can help out here. 

Some other more serious error images that have no fix: