The M0 values are quite specific to the sequence and scanner - 3000 is plausible, but it is hard for me to say if that is right for your setup or not. It is equally hard (and some would argue harder) to get absolute CBF values from DSC-PWI, so that comparison might not be the most helpful one to rely on.
What are your whole brain mean CBF or grey matter CBF values?
Michael
On 15 Jun 2015, at 08:19, Julian Schröder <[log in to unmask]> wrote:
> Dear Michael,
>
> thank you for your answer. We do use TIs (i.e. Bolus duration + PLD) for as_gui. We also have DSC-PWI images corresponding to the asl data and they differ in absolute CBF values. The M0 values calculated by asl_gui are usually around 3000, does that seem plausible?
>
> Julian Schröder
>
>
>> Am 10.06.2015 um 15:54 schrieb Michael Chappell <[log in to unmask]>:
>>
>> Values in grey mater of 100 are not impossible, but I agree that 60-70 in white matter seems rather high. The most likely issues are the M0 value, as you have identified, the default method doesn’t always do a good job of pulling out the pure CSF in the ventricles; or something to do with the setup and the model. Are you calculating the inflow times TIs as the sum of the PLD and the bolus duration? As it stands asl_gui only knows about TIs and not PLDs.
>>
>> Michael
>>
>>
>> On 3 Jun 2015, at 13:00, Julian Schröder <[log in to unmask]> wrote:
>>
>>> Dear ASL experts,
>>>
>>> we are measuring multiple TI pcASL on a Siemens 3T Scanner with currently 10 PLDs (0.3,0.6,0.9 ... 3 s) and use asl_gui to create the perfusion maps. We also aquire M0 calibration data with a TR of 5s (5 volumes). The quantification of absolute perfusion values seems to be inaccurate though. There are values of over 100 ml per 100 g per minute for cortical areas and over 60-70 for white matter, which must certainly be too high. Additionally there are relevant variations in CBF values when measuring the same subject multiple times.
>>>
>>> I have noticed, that the reference tissue CSF mask created automatically by asl_gui, sometimes doesn't fit the respective voxels in the M0 images. Creating a mask manually doesn't improve the results though.
>>>
>>> I hope you can advise me on how to fix these issues.
>>>
>>> with kind regards, Julian Schroeder
>>>
>>> J. Schroeder, M.D.
>>> Department of Neurology
>>> University Medical Center Hamburg-Eppendorf
>
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