If you do not have any calibration then you should treat the values as relative CBF - so you can compare regions to each other but not say anything about the absolute scale. Depending upon what you want to do with the data you could try normalising to a reference, such as mean grey matter perfusion. If you have the raw data (before tag control subtraction) and happen to not be using background suppression then it is possible to extract calibration information from the control images (since these are generally of the form of a proton density weighted image).
Michael
On 4 Apr 2014, at 13:07, R. Duke <[log in to unmask]> wrote:
> Michael & Experts,
>
> I have followed the BASIL tutorial for my ASL data (see parameters below) and have a perfusion image (in the native space directory) and was wondering about the values in each voxel. The tutorial states that these values are in the same (arbitrary) units as the original data. Unfortunately we do not have a calibration image to convert to physiological units. The range for these values is 0 to 30. Since I do not have a calibration image how do you recommend I present these values? Do I need to take it a step further?
>
> Bolus duration (--bolus) would be 0.7
> Inversion time (--tis) would probably be 2.5
> BAT = 1.3
>
> Cheers,
>
> R
>
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