View source for MUX EPI

=Simultaneous Multi-Slice EPI at CNI=

NOTE: This page is a stub. Please help us flesh it out!

==Overview==
The CNI, in collaboration with GE, has implemented [http://www.sciencedirect.com/science/article/pii/S1090780713000311 simultaneous multi-slice EPI] (also known as multiband EPI, multiplexed EPI, or, as we like to call it, "mux EPI"). We have functioning sequences for both gradient-echo (GRE) and spin-echo (SE) EPI. GRE-EPI is useful for BOLD imaging and SE-EPI is useful for diffusion imaging and other quantitative anatomical methods.

==General Issues==

===Useful Parameters===
* number of simultaneously-acquired bands (mux factor): How many slices to acquire simultaneously.
* inplane acceleration (arc factor): Determines the ky undersampling. Currently limited to an integer. E.g., 2 will acquire every other ky line. 
* slice separation (mm): For a contiguous set of slices, this must equal (slice_thickness + gap) * num_slices.
* CAIPI z-blip flag: enables CAIPIRHINIA z-blips (see [http://www.ncbi.nlm.nih.gov/pubmed/21858868 Setsompop et. al. 2012])

===Reference Images===
The first few acquired images are fully-sampled and used as reference images for the reconstruction. It is critical the the subject not move during this calibration phase, or the whole dataset may be impossible to reconstruct without significant artifacts (if at all). The number of reference images depends on the mux and arc factors as well as a non-exposed CV that controls the number of reference scan repetitions (stop_mux_cycling_rf1). The number of TRs needed for the reference images is: arc * mux * num_mux_cycle. (num_mux_cycle default is 2).

===Reconstruction===
Describe Kangrong's recon:
* reference images
* virtual coils
* GRAPPA vs. SENSE

===Slice acquisition order===
The multiband sequences acquire slices in ascending interleaved order (as with other EPI sequences at the CNI). But note that for the mux>1, multiple slices are acquired simultaneously. 

E.g., for a mux 3 scan with 14 muxed slices (that will result in 14*3=42 unmuxed slices), the acq. order is [1,3,5,7,9,11,13,2,4,6,8,10,12,14]. And mux slice 1 will get reconstructed as unmuxed slices [1,15,29], which are all acquired simultaneously. Likewise, mux slice 2 will get deconvolved into unmuxed slices [2,16,30]. And so on.

==SMS-GRE-EPI (muxepi)==

(more here)

==SMS-SE-EPI (muxepi2)==

(more here)