Erratum: Scanning parameters of RS-fMRI for 3T SIEMENS

Submitted by ZangYF on Sat, 03/28/2009 - 10:21

I am sorry that in the following parameters, I made a type error. The thickness/gap should be 3.5/0.7 mm. If you have used 3.5/0.6, it OK.
Please note that an FOV of 200*200 is sometimes small.

The following parameters are what we are using on a SIEMENS 3T trio scanner. 33 axial slices, thickness/gap = 3.5/0.6 mm, in-plane resolution = 64 × 64, TR = 2000 ms, TE = 30 ms, flip angle = 90, FOV = 200 × 200 mm, volumes = 240 (480 s). I strongly recommend that the RS-fMRI session is placed before the task sessions.

Submitted by hawkmu on Tue, 04/14/2009 - 22:36

Dear Dr. Zang,

I found there are two other parameters in the SIEMENS 3t scanner.
1, iPAT , some body set  " Integral parallel acquisition technique (iPAT) was used with an accelerate factor of 2 ". Do you think iPAT is really useful?
2, Matrix Coil Mode, there are 3 kinds of modes: 4-channel CP Mode；8-channel Dual Mode；12-channel Triple Mode. Does this paremeters have impact on other parameters?

Thanks,

Submitted by ZangYF on Wed, 04/15/2009 - 14:10

I am sorry that I know little about them. Is there any expert who will help answer this question? If no in the forum, I will ask MRI-physician.
Yufeng

Submitted by rh on Wed, 04/15/2009 - 22:29

Let me try to answer these two questions.

A1. Usually, DTI study need use more directions and repeat few times. The purpose is to increase the angular resolution and increase the SNR (signal-to-noise ratio). Thus, it is very necessary to make the DTI data acquisition time reasonable> For example, the DTI scanning should be finished in half hour or one hour if you put the volunteers inside the scanner.

The normal head coil (volume coil) is widely used in fMRI study. But we cannot use the volume coil to accelerate the data acquisition speed. 

In 1997-1999, two parallel acquisition techniques (SENSE and SMASH) appeared. With phased-array coil (in Siemens system, it is called iPAT coil) and using SENSE (see Phillips scanner) or SMASH (in Siemens scanner, it is called GRAPPA), the data acquisition time can be shorten to half---quarter of the normal scanning time in principle. 

For DTI study, it is necessary to use iPAT coil and choose ‘accelerator factor 2’ to run ‘ep2d_diff’ sequence if directions >30 and repetition = 2-4.  
In DTI study, there are some advantages  of using iPAT coil  and select GRAPPA scheme:  reduce the distortion caused by the susceptivity and choose small TE (compare to the volume head coil)  for gaining SNR.

A2. TIM technique has been used in the Siemens 3T Trio scanner to reconstruct images. (TIM= total image matrix). When you use iPAT coil, you can select three modes: CP Mode, Dual Mode, and Triple Mode. In DTI scanning, you need to choose ‘Triple Mode’.

Hope it helps

rh
++

Submitted by hawkmu on Wed, 04/15/2009 - 23:31

Thanks dear all.
So, if use iPAT, could we using th following parameters ( edit from non parallel mode):
FOV= 240×240mm, Slice thickness= 3mm, Slice number=45, Gap=0mm, Acquisition  Matrix=128×128,  Reconstruction Matrix=256×256, NEX=2, TR=6046ms, TE=93 , Diffusion directiuon =30, b=1000, b0=0.   iPAT=GRAPPA, Matrix Coil Mode= Triple.

Best,

tang

Submitted by wdh on Mon, 08/31/2009 - 15:57

Hi,

1. If the SNR is good enough, then iPAT would be a good choice. As  mentioned by rh, iPAT help to minmize the distortion caused by susceptibility, in addition, reduce the scanning time.
2. The Matrix mode has no effect on other parameters if you don't use iPAT, if iPAT is used, the Triple mode is highly recommended.