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. Ekkehard Zimmer > Sitz: Liebigstraße 18, 04103 Leipzig | Telefon +49-341-971709 | St.Nr.: > 23114904074 | IK: 261401052 > Bankverbindung: Deutsche Bank | BLZ: 86070000 | Kto.: 1247998 | Swift-Code: > DEUTDE8L | IBAN: DE27860700000124799800 > Internet: www.uniklinikum-leipzig.de > > Universität Leipzig | Ritterstr. 26, 04109 Leipzig | Körperschaft des > Öffentlichen Rechts | Vertreten durch die Rektorin Prof. Dr. Beate Schücking > Zuständige Aufsichtsbehörde: SMWK, Wigardstr. 17, 01097 Dresden, www.smwk.de > Umsatzsteuer-Identifikationsnummer gemäß §27a Umsatzsteuergesetz DE 141510383 > > Diese E-Mail enthält vertrauliche und/oder rechtlich geschützte > Informationen. Sollten Sie nicht der richtige Empfänger sein oder Sie haben > diese E-Mail irrtümlich erhalten, informieren Sie uns bitte sofort und > vernichten diese E-Mail. Das unerlaubte Kopieren sowie die unbefugte > Weitergabe dieser E-Mail und der darin enthaltenen Informationen ist nicht > gestattet. > > _______________________________________________ > HCP-Users mailing list > [email protected] > http://lists.humanconnectome.org/mailman/listinfo/hcp-users _______________________________________________ HCP-Users mailing list [email protected] http://lists.humanconnectome.org/mailman/listinfo/hcp-users
