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

[Lucas Lessa]

Good Morning Malek,
I'm using a 128x128 matrix, no ASSET, minimum TE and the  standard excitation with FatSat is turned off too.I tried to cover the entire brain, using multiple directions (33) and 2 NEX. The sequence takes about 10 min and the noise is quite significant.Thank you.

--- Em sex, 24/9/10, Makki Malek <Malek.Makki at kispi.uzh.ch> escreveu:

De: Makki Malek <Malek.Makki at kispi.uzh.ch>
Assunto: Re: [Mristudio-users] What is the difference between a TR 7500 and a TR 17000?
Para: "DTI Studio, ROI Editor,DiffeoMap Questions/Support" <mristudio-users at mristudio.org>
Data: Sexta-feira, 24 de Setembro de 2010, 3:27




 
 

 

 
 

 







 



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 

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

   

   

   









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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