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

Sat Sep 25 13:07:27 EDT 2010

 If you are using 2 Nex and no ASSET, than it is normal to take 10 min. It is like acquiring 65 directions + 1 T2w. But I don't understnad the reason of the noise. With standard excitation I expect chemical shift artefact.

I recommend ASSET which will reduce the distortion and improve acquistion time. Any reason for not selecting it?

Regards

________________________________

From: mristudio-users-bounces at mristudio.org on behalf of Lucas Lessa
Sent: Sat 9/25/2010 3:14 PM
To: ROI Editor DiffeoMap Questions/SupportDTI Studio
Subject: Re: [Mristudio-users] What is the difference between a TR 7500 and a TR 17000?

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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