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Hi Michael,BY the look of your two command lines, you are asking asl_calib to do CSF based calibration - where you use the CSF as reference ‘tissue’ in which a single value of M0 is calculated and ten converted into a single value of M0 of arterial blood that is then applied to the whole image. You are asking oxford_asl to use the voxelwise method, where M0 is calculated in every voxel and there is a voxelwise division at every voxel to arrive at the final absolute perfusion image. These should result in similar perfusion maps (experience thus far bears this out), although there will be some differences. However, it isn’t really feasible to compare the M0 from each approach - since in one you get a single value and in the other a full M0 image - there is no summary measure from the voxelwise M0 image that you can directly compare to the M0 of CSF. You can, however, get oxford_asl to also use the CSF reference method, although that just means that internally it uses the asl_calib command you are using here.
Michael
On 13 Dec 2017, at 10:51, Archana Malagi <[log in to unmask]> wrote:
Hi FSL experts,
I am getting different M0 value from asl_calib i.e.1.243, whereas oxford_asl gives M0 value=1.024. Below are command used for asl_calib:asl_calib -i perfusion -o perf_cal -s structural_brain --mode longtr --tissref csf --te 0.0159 --tr 4.55 --Mo Mo.txt -c calib -t asl2struct.mat
Oxford_asl:oxford_asl -i diffdata --tis 3.2 -o oxford_wp -s structural_brain -t asl2struct.mat --casl --bolus 1.4 --fixbolus --report --te 0.0159 --tr 4.55 --cmethod voxel -c calib --alpha 0.85 -m mask --wp
I want to know why there is differences in M0 values, calculated from asl_calib and oxford_asl and how is csf (reference tissue) used in calibration of perfusion map? Kindly help.
Thank you,--
Archana V. Malagi,PhD Scholar,Centre for Biomedical Engineering,IIT Delhi-110 016
---Michael Chappell MEng DPhilT: +44 1865 617657Associate Professor, Institute of Biomedical Engineering, University of Oxford.Director of Training, EPSRC-MRC CDT in Biomedical ImagingGoverning Body Fellow, Wolfson College, Oxford.