Acquisition Order

The Acquisition Order variable allows you to choose the desired method for acquiring slices.

• Enter an Acquisition Order to acquire multiple groups in an interleaved slice or sequential format.
• Dark banding artifacts, commonly known as cross-talk, and low SNR tissue contrast changes are likely to occur when MSMA slices intersect. Use care to avoid overlapping groups on top of the anatomy of interest.

Table 1. Multi-slice Multi-angle image legend

Number	Description
1	Slices 1 to 5
2	Slices 6-10
3	Cross-talk where slices intersect at slices 4-7

• When prescribing MSMA or MSMG acquisitions, the group with the largest number of slices controls the frequency and phase direction. For example, if you are prescribing axial slices through the disc spaces on a Lumbar (L) spine examination, you may prescribe three slices through L3-4 and L4-5 that have a small angle. Then, you may prescribe five very steep, angled slices through the L5-S1 disc space. The steep angle, passing 45°, makes the slices an oblique coronal, and the frequency direction changes to S/I.
• When using MSMA acquisitions, if two slices or groups of slices are 90° to each other, one of the groups of the resulting images will be rotated. The R/L, A/P, and S/I annotations on the images are correct.
• Interleaved slice acquisition (0) order (MSMG) results in the image data for 10 slices being gathered as follows: 1/3/5/7/9 followed by the second acquisition acquiring slices 2/4/6/8/10. Collecting the data in an MSMG order means there is a time interval of one TR period from the end of one group acquisition to the start of the next group. This interval allows spins to return to a state of equilibrium, reducing the possibility of cross-talk.
• Collecting the data in a Sequential (1) order (MSMA) results in images in the first acquisition being acquired in slice order of 1/2/3/4/5 and the second acquisition slice order of 6/7/8/9/10.