Comments on: Diffusion Tensor Imaging Cheat Sheet

By: Dave Higgins

Dave Higgins — Mon, 11 Jan 2010 10:57:05 +0000

@kostas
An image with b=0 has no diffusion weighting, so it is no more “diffusion weighted” than a normal MR image. Whether it’s T2 weighted or not depends on the echo time. (DWI images are often T2 weighted because the diffusion gradients are large and a longer TE is required to fit them in).

By: kostas

kostas — Sun, 10 Jan 2010 16:33:55 +0000

Is an image with b=0 DWI? or is it just a T2-W?

thanks

By: Missy

Missy — Fri, 03 Jul 2009 01:35:53 +0000

Trying to figure out DTI measurement/coefficient rationale… when would you want to use mean diffusivity (MD) or ADC over or in conjunction with FA? And can you speak more about what axial and radial diffusivity tell us (about white matter degradation?) Thanks!!

By: rezap

rezap — Thu, 23 Apr 2009 18:24:31 +0000

Thanks a bunch

By: rezap

rezap — Thu, 23 Apr 2009 18:23:39 +0000

Thank you

By: Fox

Fox — Fri, 03 Apr 2009 16:22:37 +0000

I am curious about why DTI is used so infrquently by clinicians. I have been told that it is fairly difficult to analyze DTI image sets (comparitivly to regular MRI image sets). Is this true?

By: najaru

najaru — Wed, 04 Mar 2009 11:48:20 +0000

the eadc can be used in all districts body? or is mainly specific for the brain?

Thank

By: Dave Higgins

Dave Higgins — Mon, 12 Jan 2009 11:47:28 +0000

Hi Jan,
The ADC and eADC are different calculations. Both remove T2 shine-through, which is where T2 or T2* contrast gets into the DW image because the TE is too long. The T2 shine-through can invert the diffusion contrast (bad!). The problem can be that large diffusion gradients push out the TE.
The ADC map uses an image (S) with large diffusion-weighting and another image (S0) with zero (or close to zero) diffusion weighting. Then using S=S0.e^(-bD) an average ADC can be calculated for each pixel. Alternatively multiple b-values can be used, to acquire multiple images, and a linear regression is used to extract D from S=S0.e^(-bD). (Slight modifications can be made to this method if anisotropy is suspected.)
For the eADC, the ratio of the S image (with the diffusion gradient) and the S0 image (without a diffusion gradient) is calculated. This gives an image which is weighted by e^(-bD). In this way T2 effects are removed without explicity calculating the ADC.
Dave