Hi Anastasia and freesurfers, I have more questions regarding SNR on DTI data.
I masked the low-b images by the white matter label (aseg), then calculated the SNR ( mean / standard deviation within the label). The mean values ranged for 250-350 across subjects, and the sd ranged for 60-140 across subjects. As a result, I got the SNR ranged for 2.5-4.0 ish. When I compared these values with the ones reported in other studies, I realized that my values are much smaller. http://www.ncbi.nlm.nih.gov/pubmed/21591016 http://www.scirp.org/journal/PaperInformation.aspx?paperID=370#.U0JSS8dLFAI They reported SNR to be around 20-50. It looks like they used different calculations, so probably I should not make direct comparisons, but still the difference worries me. My questions are: (1) Do our values look valid to you? (2) Are there any article that reported SNR as mean low-b / sd in the white matter aseg mask? Thank you in advance! Yuko Yotsumoto Mar 18, 2014 1:26 PM、Anastasia Yendiki <ayend...@nmr.mgh.harvard.edu> のメール： > > Signal-to-noise ratio = mean / standard deviation > > On Tue, 18 Mar 2014, Yuko Yotsumoto wrote: > >> Anastasia, >> >> Thank you so much for your reply. >> >> So I should calculate the mean and s.d. of the values of the low-b within >> the white matter region for each subject, and compare those numbers between >> groups. >> Is it correct to say that the higher mean values indicate larger SNR? >> >> Yuko >> >> On Mar 18, 2014, at 12:53 AM, Anastasia Yendiki wrote: >> >>> >>> Hi Yuko - You can use the low-b images and compute the SNR of those images >>> inside a mask of the white matter. Because dt_recon computes a registration >>> from the diffusion to the structural data, you can use that registration to >>> map the white matter label from the freesurfer segmentation (aseg) to the >>> diffusion data. Then calculate the mean and standard deviation of the >>> values of the low-b images inside that white matter mask. >>> >>> Hope this helps, >>> a.y >>> >>> On Mon, 17 Mar 2014, Yuko Yotsumoto wrote: >>> >>>> Hello Freesurfers, >>>> I have DTI data for two groups of subjects, and were asked SNR for each >>>> group. >>>> I did ROI analysis on FA values, therefore, I do not have the averaged DTI >>>> data. >>>> I am wondering if there is any way to compute SNR from dt_recon output. It >>>> doesn't have to be the ROI specific SNR values, I just need SNR for the >>>> whole DTI data for each group. >>>> Any suggestions will be appreciated! >>>> Yuko Yotsumoto >>>> --- >>>> ------------------------------------------------------------- >>>> Yuko Yotsumoto, Ph. D. >>>> Associate Professor >>>> The University of Tokyo, Department of Life Sciences >>>> Bldg #2, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902 Japan >>>> phone : (+81)-3-5454-4332 >>>> E-mail: cy...@mail.ecc.u-tokyo.ac.jp >>> _______________________________________________ >>> Freesurfer mailing list >>> Freesurfer@nmr.mgh.harvard.edu >>> https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer >>> >>> >>> The information in this e-mail is intended only for the person to whom it is >>> addressed. If you believe this e-mail was sent to you in error and the >>> e-mail >>> contains patient information, please contact the Partners Compliance >>> HelpLine at >>> http://www.partners.org/complianceline . If the e-mail was sent to you in >>> error >>> but does not contain patient information, please contact the sender and >>> properly >>> dispose of the e-mail. >> >> >> >> _______________________________________________ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer
