Hi,
thanks for the quick response.
So if I turned off the interpolation and just acquired DTI imaging at 0.87 x 0.87 x 3 with 32 directions and 1 average, would this take too long to scan? Wouldn't this resolution work for tractography as well? Is 2.5 x 2.5 in plane resolution suggested to cut down on the scan time? wouldn't higher resolution scans avoid partial volume effects and EPI-related distortions.
also, what program do you use to average separate 4D DTI volumes?
Thanks so much for your helpful comments,
AJ
--- On Thu, 3/4/10, Matt Glasser <[log in to unmask]> wrote:
> From: Matt Glasser <[log in to unmask]>
> Subject: Re: [FSL] DTI question
> To: [log in to unmask]
> Date: Thursday, March 4, 2010, 9:32 PM
> If you are wanting to do tractography
> I would think you would want at least
> 30 directions and 2.5x2.5x2.5mm resolution. 2x2x2mm
> resolution would be
> better, but perhaps harder to get at 1.5T with reasonable
> SNR and a
> reasonable amount of averages (i.e. scan time). You
> should acquire your
> diffusion averages separately (not average on the scanner),
> and you should
> not have any interpolation turned on.
>
> How much scan time you have will determine how many
> averages and how many
> directions you can get, but it is better to acquire more
> unique directions
> rather than more averages (i.e. one average of 60
> directions is better for
> tractography than 2 averages of 30 directions).
>
> At 3T, it is definitely worth correcting your data for EPI
> distortion with a
> field map, however perhaps this is somewhat less important
> at 1.5T as the
> distortion is less.
>
> Peace,
>
> Matt.
>
> -----Original Message-----
> From: FSL - FMRIB's Software Library [mailto:[log in to unmask]]
> On Behalf
> Of Adil Javed
> Sent: Thursday, March 04, 2010 9:23 PM
> To: [log in to unmask]
> Subject: [FSL] DTI question
>
> Hi,
> I am acquiring DTI images on our Phillips 1.5 T. I
> need to overlay T2 scans
> on DTI to get lesion and non-lesion MD/FA/tractography
> info. My questions
> are:
> 1-I am acquiring DTI images in 32 directions, b=1000, only
> 1 4D volume,
> acquired in plane resolution of 0.87 x 0.87 with 3 mm slice
> thickness. The
> reconstructed dimensions are 2.5mm x 2.5mm x 3mm.
> Reconstructed Voxel
> resolution 256 x 256 x 60. Does this sound
> reasonable? I have seen other
> publications acquire DTI at 2-to-3 x 2-to-3 x 5-to-6mm?
> with voxel
> resolution of 90-128 x 90-128? Not sure if this too low of
> a resolution.
> can anyone comment on this? What are advantages or
> disadvantages of lower vs
> higher acquired resolutions? Also, some use an
> average of 3-9 images per
> slice. Any advantage of this, b/c the scan time would
> be huge.
>
> many thanks in advance,
> aj
>
>
>
|