[Mristudio-users] What is the difference between a TR 7500 and a TR 17000?

[Makki Malek]

I agree with Susumo however there are some differences between vendors

 

We have similar GE system and I am sure that TR=17s is quite long for 33
directions and 50 slices.

 

Are you using 128x128 matrix? Asset On? optimal TE?

 

These systems do not allow to go below 2.5mm slice thickness with
spectral slice excitation. Are you using standard excitation with FatSat
which may increase SAR and thus increase the TR to compensate with

 

Con you provide further information about your protocol to figure it out

 

Regards

 

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Malek I. Makki, PhD

Diagnostic Imaging Department

MRI Center

Kinderspital Zurich

 

Phone. +41(0)44 266 3130

Fax:      +41(0)44 266 7153

malek.makki at kispi.uzh.ch <mailto:malek.makki at kispi.uzh.ch> 

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 

 

 

________________________________

From: mristudio-users-bounces at mristudio.org
[mailto:mristudio-users-bounces at mristudio.org] On Behalf Of susumu mori
Sent: Thursday, September 23, 2010 11:28 PM
To: DTI Studio, ROI Editor, DiffeoMap Questions/Support
Subject: Re: [Mristudio-users] What is the difference between a TR 7500
and a TR 17000?

 

Usually, one-slice single-shot imaging takes less than 150ms, I believe.
50 slices thus should take about 50 x 150ms = 7.5 s.

This is the repetition time; within this time you are done with one 3D
volume. With 33 directions and 3 b0s, for example, you spend 7.5s x 36
images = 4.5 min.

 

If you use repetition time of 17s, your total imaging time will be 17s x
36 = 10 min.

 

So, I would say, 17s is a bit too long and I recommend you to use the
shortest TR, if possible.

I noticed that some older GE scanners do not allow to use the minimum TR
such as 7.5s probably due to gradient heating. So, if the 17s is the
shortest you can do, then, that is your only option. 

 

Other than that, 2.2 mm isotropic could be a bit too small for 1.5T with
33 DWIs. The SNR may be a noisy side depending on your coil performance.
We do 2.5 mm for 1.5T

On Thu, Sep 23, 2010 at 11:51 AM, Lucas Lessa <lucas_lessa at yahoo.com.br>
wrote:

Dear friends,

I made a new protocol for a GE 1,5T HDX, using 33 directions and 50
slices with 2.2 mm thickness.
I did this because the vendor programmed a sequence that uses only 12
directions, 20 slices with 5 mm tichness and 1 NEX.
I tried to obtain an isotropic image with more signal.
But to to this I've changed the TR to 17000 (the maximum).
Is there any problem?
And, if is possible, can anyone explain for me the significance of this?
Thank you very much.

Lucas Lessa.


 
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