Hi Martin and Satra, The HCP itself has not extensively evaluated a 1.5 mm multiband DWI acquisition on the Trio platform, so we don't have anything concrete to share at this time. Perhaps we should rephrase that sentence in the Appendix I release guide, but it was included primarily to encourage individuals on other platforms to pilot beyond the "standard" 2 mm resolution.
I'd encourage you to start by piloting ~1.8 mm isotropic on Trio/Verio scanners with a multiband factor of 3-4. cheers, -MH -- Michael Harms, Ph.D. ----------------------------------------------------------- Conte Center for the Neuroscience of Mental Disorders Washington University School of Medicine Department of Psychiatry, Box 8134 660 South Euclid Ave. Tel: 314-747-6173 St. Louis, MO 63110 Email: [email protected] On 7/7/13 10:46 AM, "Reiß-Zimmermann, Martin" <[email protected]> wrote: >Hello Gordon, > >thank you very much for your answers. Due to our resolution limited to 2 >mm isotropic we have a substantial lower TR (3270 vs. HCP 5520 ms) and a >TE of 110.4 ms (HCP 89.50 ms). I wasn't sure if it is the one gradient >direction that needs to be changed (since it always stopped at the same >point) or something else (in this case using a longer TR/TE). >Thanks to your answer, I will now gradually increase TR in a >trial-and-error-fashion. > >Any chance, the mentioned 1.5mm-DTI-TRIO-sequence can be posted here? (I >guess, there are a couple more TRIO users in the mailing list) > >Best regards, >Martin > > >________________________________________ >Von: Xu, Junqian [[email protected]] >Gesendet: Samstag, 6. Juli 2013 16:57 >An: Reiß-Zimmermann, Martin >Cc: [email protected] >Betreff: Re: [HCP-Users] HCP-dMRI gradient table on a TRIO - any >experience? > >Martin, > >Sorry that I misunderstood your problem. However It is still gradient >duty cycle related. The Siemens VB software version doesn't estimate >gradient heating as accurately/conservatively as the Siemens VD software >version. Hence the minimum TE/TR allowed by the sequence can still trip >the gradient duty cycle limit in real time, causing scan crash. > >The solution is to relax the TE/TR little by little with try-and-error >until you find a stable combination that passes your test. > >Gordon > >On Jul 5, 2013, at 9:12 PM, "Xu, Junqian" <[email protected]> wrote: > >> Martin, >> >> The culprit is the gradient power amplifier (GPA) duty cycle too high >>on the Y axis (i.e. the consecutive high value of 0.992 and -0.975). We >>have encountered similar problem in HCP and have implemented a solution >>to solve the gradient duty cycle issue. >> >> You can find the solution to this problem in Sotiropoulos et al. >>NeuroImage special issue >> >> http://www.ncbi.nlm.nih.gov/pubmed/23702418 >> >> Section: Q-space sampling >> >> "However, even when realistic sequences of diffusion gradient >>orientations were used (even with interleaved shells), the gradient duty >>cycle, due to accumulated heating, could still limit the achievable >>minimal TR. The order of the diffusion gradient orientations in the >>final HCP dMRI protocol was therefore optimised by swapping adjacent >>orientations to reduce the auto-correlation (lag = 1) of absolute >>gradient amplitude (~ < 0.5) for each physical gradient axis." >> >> Please let me know if this is clear enough for you to solve your >>specific case. >> >> Regards >> Gordon >> >> On Jul 5, 2013, at 11:06 AM, "Reiß-Zimmermann, Martin" >><[email protected]> wrote: >> >>> Dear all, >>> >>> I tried implementing and converting the HCP dMRI-sequences for our >>>TRIO. I followed the suggestions in the Appendix I and with minor >>>modifications (2 mm isotropic) it works well with MB3 and the >>>MDDW-gradient table (60 directions). >>> >>> However, when I use the HCP gradient table the measurement stops at >>>reproducable stops within the sequence (see following) and always with >>>the same error (hope I can translate that somehow from German into >>>English): >>> Error in gradient amplifier, GPA not ready. duty cycle is to high. >>>Please check sequence parameters. >>> >>> The sequences always stop at these points: >>> >>> 95dir-dMRI: direction number 47 (-1.000 , -0.001 , -0.011) >>> 96dir-dMRI: direction number 75 (-0.094 , 0.992 , -0.082) >>> 97dir-dMRI: direction number 55 (-0.134 , -0.975 , 0.180) >>> >>> The images before look great! >>> >>> I took a look at the page of Emmanuel Caruyer - but if I create a >>>gradient table of 90 dir (the HCP 96dir-table seems to have 6 b0 and >>>the rest b1000-3000, the E.C.-table seems to encode b>0 values, right?) >>>it is totally different from the HCP one. >>> >>> I also read the note in the HCP gradient table that these gradients >>>are customized for the Connectome-Scanner. >>> >>> So my question is: Shall I just use one created on Emmanuel's page or >>>can I (or better: someone else) change the one from HCP? >>> >>> The Appendix I also mentions that the dMRI-sequence has been >>>successfully tested on a TRIO and Verio with 1.5 mm isotropic >>>resolution (and b2000). Is it possible that you could post the protocol >>>(including the gradient table). >>> >>> Thank you very much. Best regards, >>> Martin >>> ____________________________________________________ >>> Dr. med. Martin Reiss-Zimmermann >>> Abteilung für Neuroradiologie >>> Universitätsklinikum Leipzig AöR >>> Liebigstr. 20 >>> 04103 Leipzig >>> >>> Mail: [email protected] >>> Fon: +49 - 341 - 97 17 585 >>> Fax: +49 - 341 - 97 17 490 >>> Net: http://www.neuroradiologie-leipzig.de >>> >>>........................................................................ >>>........................................................................ >>>........................................................ >>> Universitätsklinikum Leipzig - Anstalt öffentlichen Rechts | >>>Aufsichtsratsvorsitzender: Prof. Dr. Wolfram Knapp >>> Medizinischer Vorstand und Sprecher: Prof. Dr. med. Wolfgang E. Fleig >>>| Kaufmännischer Vorstand: Dipl.-Kfm. 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