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| We feel that this is unlikely to be of much benefit. PACE attempts online correction of subject movement, by tracking the apparent movement of the EPI volumes, and adjusting the gradient angles to try and make the angles of acquisition follow the movement of the EPI. Our worry about this technique is that estimation of movement parameters can be biased by large activations - see CbuImaging:PrinciplesSpatialProcessing. If PACE is disabled, we can look for this problem in the spatial processing phase of the analysis, and try and address it by using different realignment methods, or not doing motion correction. If PACE is enabled, the acquisition itself has changed as a result of the movement parameter estimates, and it is no longer possible to do post-hoc correction. The problem with assessing PACE is that we would expect the problems to depend on the location and size of activation, so a single study will be unable to answer the question as to whether this is worthwhile or not. | We feel that this is unlikely to be of much benefit - see CbuImaging:TipsForDataAcquisition for a discussion. The problem with assessing PACE is that we would expect the problems to depend on the location and size of activation, so a single study will be unable to answer the question as to whether this is worthwhile or not. |
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| We have recently changed the default FMRI slice acquisition from interleaved to sequential. See CbuImaging:TipsForDataAcquisition for discussion. There are theoretical and practical reasons to think that the sequential method is less prone to artefacts, and we think it most unlikely that there would be an easily measurable difference between the techniques in favour of interleaved. | As a result of work by RhodriCusack, we have recently changed the default FMRI slice acquisition from interleaved to sequential. See CbuImaging:TipsForDataAcquisition for discussion. There are theoretical and practical reasons to think that the sequential method is less prone to artefacts, and we think it most unlikely that there would be an easily measurable difference between the techniques in favour of interleaved. |
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| There are well worked out methods of assessing a design for optimum jittering - see [http://www.mrc-cbu.cam.ac.uk/~matthew/abstracts/ER/er_analysis.html my event-related analysis poster and abstract] and CbuImaging:DesignEfficiency and references therein. A rule of thumb is that the effect of jittering is predictable from the design until events come close to 1 second apart, at which point there are significant non-linearities, which will render the standard models of design efficiency invalid. | There are well worked out methods of assessing a design for optimum jittering - see [[http://www.mrc-cbu.cam.ac.uk/~matthew/abstracts/ER/er_analysis.html|my event-related analysis poster and abstract]] and CbuImaging:DesignEfficiency and references therein. A rule of thumb is that the effect of jittering is predictable from the design until events come close to 1 second apart, at which point there are significant non-linearities, which will render the standard models of design efficiency invalid. |
Requests for routine methods studies
Sometimes there will be a genuine empirical question about differences in acquisition or analysis methods that can only be well answered by acquiring data across several subjects and comparing techniques.
As with all studies, this has to be of significant interest and importance to someone, in order justify scanning and analysis time. In practice this means that if we think the parameters under study are likely to have a significant effect on our analysis pipeline, then we will perform the study. Otherwise, we are very happy to support both analysis and acquisition, but will expect the interested researcher to take the lead in analysis.
We will use this page to put up ideas for such studies, and comment on their importance. Please send requests for studies to MatthewBrett, or another member of the AdminGroup for this wiki.
Suggested studies
Comparison of acquisition with Siemens PACE enabled and disabled
We feel that this is unlikely to be of much benefit - see TipsForDataAcquisition for a discussion. The problem with assessing PACE is that we would expect the problems to depend on the location and size of activation, so a single study will be unable to answer the question as to whether this is worthwhile or not.
Comparison of interleaved and sequential slice acquisition in FMRI
As a result of work by RhodriCusack, we have recently changed the default FMRI slice acquisition from interleaved to sequential. See TipsForDataAcquisition for discussion. There are theoretical and practical reasons to think that the sequential method is less prone to artefacts, and we think it most unlikely that there would be an easily measurable difference between the techniques in favour of interleaved.
Optimum jittering for event related design
There are well worked out methods of assessing a design for optimum jittering - see my event-related analysis poster and abstract and DesignEfficiency and references therein. A rule of thumb is that the effect of jittering is predictable from the design until events come close to 1 second apart, at which point there are significant non-linearities, which will render the standard models of design efficiency invalid.