Hi Derin,

you can certainly compute contrast-to-noise. Longer scans have more motion and won't necessarily be better. Are you talking about multiple acquisitions of the same protocol, or changing the acquisition parameters (e.g. TR)? The latter will change the contrast.

cheers, Bruce

On Thu, 14 Dec 2006, Derin Cobia wrote:

Some of the scans I work with are of the same subject, but differ only in the length of time they were in the scanner. Obviously the scans of longer length (everything else being equal) will yield better quality; however, I'm interested in a kind of "bang-for-your-buck" approach. Is there a point where some amount of diminishing returns occurs with respect to FS processing and scan quality? Therefore, my main question:

1. Is there anything in the FS processing stream that would be a

reasonable heuristic for determining if one scan processes better than another (all things being equal beside length of time being scanned)? For example, # of topological defects to correct, length of processing, amount of manual correction, or just visual quality?

I understand some of this is related to what structure(s) I'm interested in measuring, but was wondering about it in a general fashion. This may come in handy down the road for us because many of our subjects are individuals with schizophrenia, and being in an enclosed space (let alone the time it takes to yield a high-quality scan) is traumatic enough for them. Thanks for any input.

-Derin _______________________________________________ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer