Hello,
I am analyzing some subjects from several years ago when we had a protocol that called for slices 1.4x1.4x1.4mm. I am also including in the study more recent scans with a protocol for 1x1x1mm slices. I am using freesurfer 3.0.5. I am wondering if the different slice dimensions will cause differences in the analysis. As I read on a previous post, freesurfer resamples all its input data into 1mm isovolumetric voxels anyways, so I should be ok?
Regards, Jeff Sadino
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Hi Jeff,
are you intending to combine them into a single study? This can be problematic as you'll get differential sensitivity and possibly bias.
cheers, Bruce
On Tue, 17 Mar 2009, Jeff Sadino wrote:
Hello,
I am analyzing some subjects from several years ago when we had a protocol that called for slices 1.4x1.4x1.4mm. I am also including in the study more recent scans with a protocol for 1x1x1mm slices. I am using freesurfer 3.0.5. I am wondering if the different slice dimensions will cause differences in the analysis. As I read on a previous post, freesurfer resamples all its input data into 1mm isovolumetric voxels anyways, so I should be ok?
Regards, Jeff Sadino
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Hi Bruce,
Yes, we are going to combine them into a single study. Is there a place on the wiki I can read about how to error check for these problems?
Thank you, Jeff
Date: Tue, 17 Mar 2009 19:39:34 -0400 From: fischl@nmr.mgh.harvard.edu To: jsadino@hotmail.com CC: freesurfer@nmr.mgh.harvard.edu Subject: Re: [Freesurfer] Changing from 1.4x1.4x1.4 mm slices to 1x1x1
Hi Jeff,
are you intending to combine them into a single study? This can be problematic as you'll get differential sensitivity and possibly bias.
cheers, Bruce
On Tue, 17 Mar 2009, Jeff Sadino wrote:
Hello,
I am analyzing some subjects from several years ago when we had a protocol that called for slices 1.4x1.4x1.4mm. I am also including in the study more recent scans with a protocol for 1x1x1mm slices. I am using freesurfer 3.0.5. I am wondering if the different slice dimensions will cause differences in the analysis. As I read on a previous post, freesurfer resamples all its input data into 1mm isovolumetric voxels anyways, so I should be ok?
Regards, Jeff Sadino
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not really. I would try doing a grooup study of all your 1.4mm subjects compared to your 1mm subjects. If that shows no effect then you are probably ok.
Bruce
On Tue, 17 Mar 2009, Jeff Sadino wrote:
Hi Bruce,
Yes, we are going to combine them into a single study. Is there a place on the wiki I can read about how to error check for these problems?
Thank you, Jeff
Date: Tue, 17 Mar 2009 19:39:34 -0400 From: fischl@nmr.mgh.harvard.edu To: jsadino@hotmail.com CC: freesurfer@nmr.mgh.harvard.edu Subject: Re: [Freesurfer] Changing from 1.4x1.4x1.4 mm slices to 1x1x1
Hi Jeff,
are you intending to combine them into a single study? This can be problematic as you'll get differential sensitivity and possibly bias.
cheers, Bruce
On Tue, 17 Mar 2009, Jeff Sadino wrote:
Hello,
I am analyzing some subjects from several years ago when we had a protocol that called for slices 1.4x1.4x1.4mm. I am also including in the study more recent scans with a protocol for 1x1x1mm slices. I am using freesurfer 3.0.5. I am wondering if the different slice dimensions will cause differences in the analysis. As I read on a previous post, freesurfer resamples all its input data into 1mm isovolumetric voxels anyways, so I should be ok?
Regards, Jeff Sadino
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The recent paper by Wonderlick et al. (Neuroimage 44:1324-1333, 2009) is relevant to your situation. They show that differing voxel geometry can definitely lead to bias in the results (as Bruce noted).
cheers, Mike H.
On Tue, 2009-03-17 at 21:26 -0600, Jeff Sadino wrote:
Hi Bruce,
Yes, we are going to combine them into a single study. Is there a place on the wiki I can read about how to error check for these problems?
Thank you, Jeff
Date: Tue, 17 Mar 2009 19:39:34 -0400 From: fischl@nmr.mgh.harvard.edu To: jsadino@hotmail.com CC: freesurfer@nmr.mgh.harvard.edu Subject: Re: [Freesurfer] Changing from 1.4x1.4x1.4 mm slices to
1x1x1
Hi Jeff,
are you intending to combine them into a single study? This can be problematic as you'll get differential sensitivity and possibly
bias.
cheers, Bruce
On Tue, 17 Mar 2009, Jeff Sadino wrote:
Hello,
I am analyzing some subjects from several years ago when we had a
protocol that called for slices 1.4x1.4x1.4mm. I am also including in the study more recent scans with a protocol for 1x1x1mm slices. I am using freesurfer 3.0.5. I am wondering if the different slice dimensions will cause differences in the analysis. As I read on a previous post, freesurfer resamples all its input data into 1mm isovolumetric voxels anyways, so I should be ok?
Regards, Jeff Sadino
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ocid=TXT_TAGLM_WL_HM_70faster_032009
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Bruce Fischl -
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Michael Harms