[Mristudio-users] Gradient table

Sat Apr 18 14:42:07 EDT 2009

Dear Susumu,

I also have a similar question about gradient tables in Philips scanner.

My data were collected using following protocols:
1) Gradient table: Medium
2) Gradient overplus: no
3) Oblique plane: yes, and different angles between subjects.

Looking through your answer, I know that this set can result in the same
gradient table input into DTIstudio for all subject. However, 1) I am not
sure which coordinates (space) the ultimate gradient table was relative to,
such as frequency- and phase-encoding of image, horizontal and vertical
direction of image, or magnets' x/y/z coordinates. Based on your reply, I
think that it might be the last one.

2) In my *.PAR file, there was last 3 columns representing diffusion
directions but obviously different between subjects. I don't know what
diffusion were recorded in this header file.

Many thanks

Liang

2009/4/16 susumu <susumu at mri.jhu.edu>

>  Hi Eric,
>
>
>
> For Philips scanner there are several types of gradient tables you can
> specify in the scanner. Please check your protocol for the following points;
>
>
>
> 1)       Gradient table: High (32-orientation)/ Medium (15-orientation) /
> Low (6-orientation)
>
> 2)       Overplus (ON / OFF)
>
> 3)       Oblique plane (X/Y/Z angles)
>
>
>
> The first option has 3 choices and the second option has 2 choices.
> Therefore, there are 3 x 2 = 6 gradient tables.
>
> If the second option (Overplus) is NO, the third option has no effect. If
> the second option is YES, the gradient table has to be rotated based on the
> oblique angles.
>
>
>
> To simplify the DTI processing, we recommend Overplus = NO.
>
>
>
> We have the basic 6 tables, which can be used as is if you use Overplus =
> OFF or Oblique angles = 0/0/0 degree.
>
> Please let us know which options you are using.
>
>
>
> Susumu
>
>
>  ------------------------------
>
> *From:* mristudio-users-bounces at mristudio.org [mailto:
> mristudio-users-bounces at mristudio.org] *On Behalf Of *eric Q
> *Sent:* Thursday, April 16, 2009 9:44 PM
> *To:* mristudio-users at mristudio.org
> *Subject:* Re: [Mristudio-users] Gradient table
>
>
>
> Hello Dear DTIstudio users:
>
> I am new to DTIstudio, I was hoping someone could give me some much needed
> advises for beginners.
>
>
> I was trying to obtain the FA values for my brain phantom (PHILIP 3T
> scanner). When I clicked on "DTI mapping", it prompted me to enter the
> "gradient table", how do I calculate the "gradient table"?
>
> Thanks in advanced
>
> Best regards
>
> Eric
>
>
>  ------------------------------
>
> Date: Thu, 9 Apr 2009 11:04:09 -0400
> From: susumu at mri.jhu.edu
> To: mristudio-users at mristudio.org
> Subject: Re: [Mristudio-users] MriView3D application close
>
> Hi Hugh,
>
>
>
> When you got this error, please suspect one of the following two reasons;
>
>
>
> 1) Memory shortage:
>
>
>
> Even if you have many GB of memories, 32-bit Windows system can allocate
> only 1 - 1.5 GB to each program. To check if you have the memory problem,
> please restrict the slices to be calculated. In the initial data parameter
> window, there is a section called "Slices to be processed". Here you can
> specify only a portion of slices to be processed. Please limit the slices
> to, for example, 0-9 and see how it goes. If you can calculate tensors
> without errors, then you have the memory problem. The solution is; a)
> upgrade to the 64-bit system or b) devide the calculation to 2 batches (e.g.
> slice 0-29 for the first batch and 30-59 for the second batch), calculate
> all maps (e.g. FA), and later combine them.
>
>
>
> 2) Mismatch between the gradient table and the number of images:
>
>
>
> For example, if you specify 12-orientation table and 30 volume images, then
> you get the error. After loading the data and before you go to the Dti Map
> tab, make sure that you have 1 b0 + 64 DWIs in the pull-down menu in the
> right column of the Image tab. If you have the correct number of the images,
> then you might have an error in your gradient table. Small mistakes such as
> missing "," are often difficult to detect. The best way is; a) load the data
> using DtiMapping under the "File" button on the top left, b) close the
> window, c) open the image paremater window again by clicking "DtiMapping" in
> the "File" button again, d) the window still remembers the gradient table
> you entered last time. This remembered window tells how DtiStudio
> interpreted your gradient table. If there is any syntax errors, you may find
> them much easier. For example, if you enter, "4: 1 0.5 0", instead of "4: 1,
> 0.5, 0", then you would find, "4: 1, 0, 0".
>
>
>
> If any of these do not solve the issue, please let us know.
>
>
>
> Susumu
>
>
>  ------------------------------
>
> *From:* mristudio-users-bounces at mristudio.org [mailto:
> mristudio-users-bounces at mristudio.org] *On Behalf Of *Hugh Wang
> *Sent:* Wednesday, April 08, 2009 6:30 PM
> *To:* mristudio-users at mristudio.org
> *Subject:* [Mristudio-users] MriView3D application close
>
> Hi,
>
> I was using the dtistudio (ver. 2.4)  to look at the Siemens DICOM
> diffusion images (1baseline,64 gradients). After successfully loading the
> images, I click the "dti map" option at lower right corner. Whatever
> calculation I choose, it always gives me an error:
>
> "MriView3D MFC Application has encountered a problem and needs to close.
> We are sorry for the inconvenience."
>
> I tried several PCs, and the problem keeped the same. I would appreciate
> that if there's anyone having any idea on how to solve it. Thanks.
>
> Best,
> Hugh
>  ------------------------------
>
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-- 
Liang Wang, PhD
Postdoctoral Fellow
Woodward Lab
Department of Psychiatry
University of British Columbia
BC Mental Health & Addiction Services
938 West 28th Avenue
Vancouver BC V5Z 4H4
Telephone: 1-604-875-2000 (ext. 4735)
Fax: 1-604-875-3871
Email: wanglbit at gmail.com
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