mriconvert: lcni-users: FSL/Nifti output and Minnesota multiband -- IMPORTANT!!

[Andreas Bartsch]

Hi,

yes ­ the latter would be good to know. I always assumed that there is no
loss involved.
Hope all is well,
best regrads-
Andreas

Von:  "jolinda at uoregon.edu" <jolinda at uoregon.edu>
Antworten an:  MRIConvert user's list <mriconvert at lists.uoregon.edu>
Datum:  Dienstag, 24. Februar 2015 12:11
An:  MRIConvert user's list <mriconvert at lists.uoregon.edu>,
"lcni-users at lists.uoregon.edu" <lcni-users at lists.uoregon.edu>
Betreff:  Re: mriconvert: lcni-users: FSL/Nifti output and Minnesota
multiband -- IMPORTANT!!

Largest image pixel value does not include intercept and slope. The issue
does not necessarily involve rescaling, but that does add another wrinkle.
Thanks for bringing it up. I'll need to refresh my memory regarding whether
mriconvert changes the output data type when "apply rescale slope and
intercept" is selected. It clearly should to avoid loss of data, but I don't
remember if it does.

Sent from my HTC

----- Reply message -----
From: "Roman Fleysher" <roman.fleysher at einstein.yu.edu>
To: "MRIConvert user's list" <mriconvert at lists.uoregon.edu>,
"lcni-users at lists.uoregon.edu" <lcni-users at lists.uoregon.edu>
Subject: mriconvert: lcni-users: FSL/Nifti output and Minnesota multiband --
IMPORTANT!!
Date: Mon, Feb 23, 2015 6:34 PM

Dear Jolinda,

Does LargestImagePixelValue include intercept and scale? Is the issue
related to the original pixel values (before scaling) or after?

Thank you,

Roman

________________________________________
From: mriconvert-bounces at lists.uoregon.edu
[mriconvert-bounces at lists.uoregon.edu] on behalf of Jolinda Smith
[jolinda at uoregon.edu]
Sent: Monday, February 23, 2015 12:12 PM
To: lcni-users at lists.uoregon.edu; mriconvert at lists.uoregon.edu
Subject: Re: mriconvert: lcni-users: FSL/Nifti output and Minnesota
multiband -- IMPORTANT!!

Local users: there is now a tool on bordeaux called max_pixel_check that
recursively checks all dicom files in a directory and returns the names of
any with maximum pixel values > 32767. To use, just type "max_pixel_check
[directory name]". If the maximum pixel value for all files is < 32767, you
can use MRIConvert with these files with no changes to your processing
stream. If you have any with pixel values in the 60,000 range let me know,
we need to adjust the sequence (I've seen this in a phantom but not in
vivo).

Non-local users: you can check your own dicoms by looking at the tag
"Largest image pixel value" (0028,0107). If you have dcmtk installed, you
can use this command to output this value for all files in a directory:

dcmdump +sd +r +P LargestImagePixelValue +F [directory_name]

Jolinda

On Fri, 20 Feb 2015 11:36:36 -0800, Jolinda Smith <jolinda at uoregon.edu>
wrote:

> Hi everyone,
>
> A quick but important note regarding the FSL/Nifti output of MRIConvert and
the multiband epi from Minnesota. First a review: MRIConvert has two options for
nifti output: regular and FSL/nifti. This was necessary in the early days of
nifti, until FSL fully supported the format. One important difference between
the two is that "regular" nifti keeps the data in the same representation as the
original dicom (typically unsigned 16 bits for MR). FSL did not support unsigned
16 bit data, but did support signed 16 bit data. Since MR images typically only
use the first 12 bits, MRIConvert calls it signed 16 bits for the FSL/nifti
version.
>
> HOWEVER, the multiband sequence from Minnesota uses the full 16 bit dynamic
range, so this conversion is no longer safe. I'm waiting to hear back from the
FSL mailing list regarding whether FSL now supports unsigned 16 bit data. If it
does, we will eliminate the FSL nifti variant, as it's no longer necessary. If
it doesn't, we'll convert data that uses all 16 bits to float.
>
> Until that happens, you have two choices if you are using FSL & the Minnesota
multiband sequence:
>
> 1. Use fsl/nifti output, and check the range of your data. You can do this
with fslstats filename -R. If your minimum value is 0 or higher, and your
maximum is less than 32768 (and it will be if you are using fsl/nifti output),
you are safe to continue as before. You'll need to do this for every file.
>
> 2. Use nifti output, and change the datatype to float: fslmaths input_file
output_file -odt float.
>
> I will keep everyone posted on further developments.
>
> Jolinda
>
>


--
Jolinda Smith, Ph.D.
MR Physicist
Lewis Center for Neuroimaging
University of Oregon
Eugene, OR USA
_______________________________________________
mriconvert mailing list
mriconvert at lists.uoregon.edu
https://lists-prod.uoregon.edu/mailman/listinfo/mriconvert

_______________________________________________
mriconvert mailing list
mriconvert at lists.uoregon.edu
https://lists-prod.uoregon.edu/mailman/listinfo/mriconvert
_______________________________________________ mriconvert mailing list
mriconvert at lists.uoregon.edu
https://lists-prod.uoregon.edu/mailman/listinfo/mriconvert

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists-prod.uoregon.edu/pipermail/mriconvert/attachments/20150224/36fe85bf/attachment-0001.html>