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Hi

We have combined repeated high-resolution anatomical scans using the attached procedures.

"combinerepeatssimilar" uses SPM realign functions, with a couple of parameters tweaked to reduce smoothing ("sep" and "fwhm" are reduced - see code). This function assumes the scans are repeated within one subject, collected in the same in-plane resolution, and have the same slice thickness. We have found this to work very well. We have been collecting high-res T1-weighted scans (MPRAGE, < 1 x 1 x 1 mm3) with a relatively short scan time of ~5 min. Each individual scan is noisy, but if we collect three scans, we are usually get two with no motion. Combining two scans gives us good quality images. This approach is helpful in the case where subject motion is a problem, as in the child population we study.

We have also combined scans of differing resolution using the attached "combinerepeats," which first combines any similar scans then performs an affine normalization of the differing scans (with a couple of parameters changed from the defaults).

Cheers,
Paul Macey
UCLA Dept. Neurobiology



Robert Welsh wrote:
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In principal combining the 3 T1's would provide for a better image.

HOWEVER, you have introduced an "effective" motion between scans which
with co-registration will result in a certain amount of added variance.
That is the person got up and back into the scanner. Yes, you could
attempt to prescribe exactly the same slices from day to day, but that
is limited by the graphical prescriber (unless you made some sort of
allowance for this at the beginning with very precise landmarks).

If you have acquired just a longer MPRAGE at the first session with
higher through plane resolution (1.5 mm instead of 5mm for example) you
would have been better off from the start.

You should remember that your resolution is limited by the resolution of
your T2* image (the fMRI data) and not really your T1.

Operationally, to do the coreg, you just need to pick one as the target
and the other as the object. Do this for image pairs 1-2 and 1-3. Of
course this does produce a bias towards image 1.



-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Robert C. Welsh, PhD
Research Investigator
Department of Radiology
University of Michigan
(734) - 764 - 2412 (fax)
[log in to unmask]


  
"Charisma D. Edwards" <[log in to unmask]> 02/13/05 8:48 PM >>>
        
Hi,

We've collected low resolution T1 images on the same person during 3
consecutive days (MPRAGE 1x1x5).  We are interested in combining our
three T1
images collected on 3 consective days into one single T1 image. It is
our
understanding that combining 3 T1's will lead to a 'better' image
compare to
our single T1.  Our goal is to overlay functional maps on the combined
T1.  Has
anyone combined/coregistered multiple anatomical/high resolution images
in order
to get a more clear high(er) resolution image? If so can you please
provide
details on how this is performed.

Thank you,
Charisma D. Edwards
Research Specialist
Emory University
Rehabilitation Medicine
phone: 404.712.5324 fax: 404.712.1630
e-mail: [log in to unmask]



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