• Object ID: 00000018WIA306DE870GYZ
  • Topic ID: id_40024353 Version: 1.6
  • Date: Aug 16, 2022 6:08:24 PM

Slice Spacing

Select the Spacing between the slices for your prescription, except 2D and 3D vascular prescriptions.

Choosing spacing allows you to increase the scan range or image coverage with larger interscan spacing to ensure complete coverage. Insert small gaps (spacing) between slices, to reduce crosstalk. Crosstalk or overlap is caused by partial excitation of adjacent slices during RF excitation and refocusing by a 180° pulse. This results in a reduction of image contrast and SNR, as the expected TR and the effective TR may differ.

Figure 1. The slices numbers (1 to 10) are at the top of the illustration and the time of excitation (0 to 0.9 TR) is at the bottom of the illustration. In this example, the excitation of slice #5 is 0.2 TR resulting in partial excitation of slices #4 and #6, which are excited at time t = 0.6 and t = 0.7 TR

This difference in TR alters the CNR and SNR. The effects on short TR/TE sequences may be lower SNR and possibly, greater T1 contrast, similar to decreasing TR. The overall effect may be decreased CNR. Decreased SNR tends to offset the increase in contrast. This usually means that the scan’s CNR has been decreased, although the cross talk effect may not be the same for all slices.

  • For 2D scans, select a slice spacing that reduces cross-talk.
    • Typically 20% of the actual slice thickness for a SE sequence.
    • Typically 10 to 20% of the actual slice thickness for a FSE family pulse sequence.
    • Typically 0 to 20% of the actual slice thickness for GRE/SPGR sequences.
  • To reduce the effects of interslice cross-talk use interleave (doubles the scan time), a larger interscan spacing, a 3D technique, or the Sequential Imaging Option.
  • A zero spacing can be used when acquiring images in a sequential fashion.
  • For 2D CSI # CSI Slices = 1. For 3D CSI spectroscopy, (Slices per Slab) × (CSI Slice Thickness) = CSI volume depth. Typical value of # CSI Slices = 8.
  • For localizer acquisitions, unique spacing can be entered for each scan plane.