# Calculate FA map using multishell data

**URL:** https://community.mrtrix.org/t/calculate-fa-map-using-multishell-data/6814
**Category:** Uncategorized
**Tags:** preprocessing
**Created:** [July 19, 2023, 9:35am UTC](https://community.mrtrix.org/t/calculate-fa-map-using-multishell-data/6814 "2023-07-19T09:35:58Z")
**Posts on this page:** 2
**Page:** 1

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### Author: ![CarlisleYun79](https://community.mrtrix.org/user_avatar/community.mrtrix.org/carlisleyun79/32/3410_2.png) [@CarlisleYun79](https://community.mrtrix.org/u/CarlisleYun79)
#### Post date: [July 19, 2023, 9:35am UTC](https://community.mrtrix.org/t/calculate-fa-map-using-multishell-data/6814/1 "2023-07-19T09:35:58Z")

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Hi, MRtrix3 experts.

I obtained b-800 and 2800 multi-shell data from Siemens Skyra equipment.

I calculate the diffusion map (e.g., FA, AD, RD, ADC) using mrtrix3.

dwi2mask A\_preproc\_end.mif A\_preproc\_mask.mif  
dwi2tensor A\_preproc\_end.mif -mask A\_preproc\_mask.mif dt.mif  
tensor2metric dt.mif -fa fa.mif

according like this,

I just wonder that mrtrix3 calculate the FA map automatically using low b-value? (in my data, b-800)

or

It calculates the FA map using two b-value? (bi-exponential data)  
As follow my FA map result, It looks quite well… but I’m not sure about, which protocol has been used to calculate the FA map.

 ![Screenshot 2023-07-19 at 6.29.19 PM](https://community.mrtrix.org/uploads/default/original/2X/8/87eb79bbd7cacacf1d0207f34a302fb59c96614b.jpeg)

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### Author: ![StarVolcano](https://community.mrtrix.org/letter_avatar_proxy/v4/letter/s/e0b2c6/32.png) [@StarVolcano](https://community.mrtrix.org/u/StarVolcano)
#### Post date: [August 2, 2023, 6:00am UTC](https://community.mrtrix.org/t/calculate-fa-map-using-multishell-data/6814/2 "2023-08-02T06:00:27Z")

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Hi Yun,

I think you should check the document of command [dwi2tensor](https://mrtrix.readthedocs.io/en/latest/reference/commands/dwi2tensor.html) and [tensor2metric](https://mrtrix.readthedocs.io/en/latest/reference/commands/tensor2metric.html).

Hope it helps.

Best,  
Volcano