[Mristudio-users] Is better to do 3 DTI series or just one well done?

[Lucas Lessa]

Dr. Susumu Mori you helped me a lot.
I'm using 3 repetions of a 33 dir DTI in a Philips 1.5T (the voxel is about 2.2mm.) when I want to do an exam for a research, for the real life I use just one repetion.
Indeed the SNR is much better with 3 repetions, but just in DTI Studio, because Philip's software don't handle the 3 series like one.
What do you think in increase my resolution to 256x256 in this scanner?
Will the exam take so long? Can I use just 2 repetitions?
Thank you.
 
Lucas Lessa.
 


--- Em qui, 10/12/09, susumu mori <susumu at mri.jhu.edu> escreveu:


De: susumu mori <susumu at mri.jhu.edu>
Assunto: Re: [Mristudio-users] Is better to do 3 DTI series or just one well done?
Para: "DTI Studio, ROI Editor, Landmarker Questions/Support" <mristudio-users at mristudio.org>
Data: Quinta-feira, 10 de Dezembro de 2009, 15:22


If you are using a 1.5 T scanner, I think 2.5 mm isotropic resolution is a good compromise between scanning time and SNR. With a 30-orientation scheme, you may want to do at least two repetition (total 60 DWIs) to get a decent SNR. If you want to increase the resolution, you need more dwis and a longer scanning time.

What is important is the total number of images, in this case 60. So, if you are using a 15-orientation scheme, you need 4 repetitions. A 30-orientation scheme should take about 4-5min in Siemens and Philips. GE may take 7-8 min in some versions because of gradient overheating precaution (TR can't be too short). So, two repetitions (total 60 dwis) should take 8-10 min in Siemens/Philips. This is certainly a long scan, especially for clinical. If time is important, you can do one repetition (total 30 dwis), scarifying the SNR. In this case, you definitely don't want to increase the resolution, which would make the SNR worse.

For 3T, 30 dwis can give you a decent SNR with 2.5mm resolution. Or if you stick with a 60 dwis protocol, you can use 2.2 mm resolution. I have seen nice 2.0 mm resolution with the latest head coils. For 2.2 mm, you need to use 112x112 matrix. Please note that larger matrix leads to more distortion. Because 3T has larger distortion than 1.5 T, using a larger matrix in 3T is not a good idea in general. 

Hope it helps.

Susumu


On Thu, Dec 10, 2009 at 9:47 AM, Lucas Lessa <lucas_lessa at yahoo.com.br> wrote:





Good morning,

As I said in aonther post, I'm in the middle of a DTI study that, obsviously, uses DTI studio to process the data.
The other researcher brought (a think from John Hopkins) a model that uses 3 DTI series, just to increase the ratio between sign/noise.
The exams are taking so long and I would like to increase the resolution from 112x110 to 256x256, and maybe, 512x512.
Is this a good idea? Or it's better to continue making the exams with the 3 DTI series?
And wich is the bennefit of doing 3 DTI series (the vendor software only uses one at a time)?
One more time thank you.

Lucas Lessa
São Paulo/Brazil




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