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How to acquire good diffusion images for DSI or GQI

The major limiting factor in DSI is the scanning time. DSI usually takes a very lengthy scan to achieve good quality, and the most of the principles aim at reducing the scanning time and improve the image quality. Here are some rules I concluded from my personal experiences, and it may change case by case, especially a difference pulse sequence is used to acquire DSI.

General rules:

1. Use shortest possible FOV, TE, and TR

    Shorter TE has less distortion, less scanning time, and less T2-shine through. Shorter TR also reduces scanning time. A small FOV may also improves a bit in getting shortest scanning time.

2. Isotropic resolution, i.e. in-plane resolution = through plane resolution

    This aims at getting a good result in fiber tracking. Diffusion fiber tracking is non-isotropic resolution is problematic, and not recommended.  

3. Acquire at least 100 diffusion weighted images

    My personal experience. Acquiring less than 100 directions may not be able to achieve enough angular resolution.

4. Use grid sampling scheme. 

5. Consider ignoring cerebellum

Example:



Description

High angular resolution diffusion MRI sequence for GQI analysis

Acquisition time

14min 21s

Type

2D

Slices

55

Slice gap

none

Slice thickness

2.5 mm

Slice order

Interleaved

FOV

240mm x 240mm

Matrix

96 x 96

Resolution

2.5 mm x 2.5 mm

TR

8200 ms

TE

69 ms

Diff directions

101, b-tableb_table for SIEMENS

Diff weightings

multiple

max b-value

4000 s/mm2

flip angle

90 deg

Bandwidth

2004 Hz/Px

Parallel imaging

GRAPPA 
Acceleration factor PE: 3 
Reference lines PE: 40


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