Hi, Cinly:

We agree that the relative value is more important than the true counts. However, we think that the signal values reading out from the dicom images by MRIcro or SPM must have been adjusted. When we using the new version of AFNI, after we set the AFNI_DICOM_WINDOW yes, we can read out another "more actual signal values (1000-2000)" which are much higher and seem more reasonable than the 200-700 signal values. Then, which value should we use? In fact, we just want to know whether the adjusting of DICOM signal is same for all voxels in all images. But it seems that different signal values may not be adjusted by the same parameters and this could have effect on the signal changes calculation. Does you or others have experiences on this problem?

Thanks for your and other's comments.

hengyi

>[log in to unmask] wrote:
>
>>Dear all:
>>
>>We are using a 3T Siemens Trio MRI machine to do the fMRI study. Now we are doing some analysis on the ROI fMRI signal changes, but we are confused about the signal intensity we got from the images. All the signal values are between 200-700, which are much lower than the signal values (1000-2000) we got from the images of GE 1.5T scanner. We have used MRIcro and other tools to look the signal values from the DICOM images, but they are the same. It seems that this Trio scanner has done something like automatically scaling on the signal values. Does anyone know how to rule out such scaling and get the raw signal values when export the EPI images? Or does such scaling have effect on the signal changes calculation?
>>
>There might not be any scaling at all. Different scanners yield
>different range of value. Having a larger range does not necessary means
>better resolution, it could mean it is just more sensitive to noise.
>
>Good fMRI program are indifference to scaling: Its not the absolute
>values that counts, but the relative values.
>
>Best regards,
>Cinly