The not measured distance between the slices. For some sequences there is a slightest space of e.g. 10-20% necessary. A lower spacing can introduce more noise into adjoining slices.
Echospacing is the distance in time between the echoes in multiple echosequences like, e.g. echo planar imaging, fast spin echo. A short echo space produces compact sequence timing and less image artifacts.
The shorter the rise time, the faster the gradients and therefore the echospacing. Gradients with a shorter echospacing will have a better resolution and more slices per TR.
Crosstalk is an artifact introduced into images by interferencebetween adjacent slices of a scan, caused by a slice profile that is not ideal due to the constraints of the measurement technology. If the slice distances are too small, there is cross talk between the slices, which can affect T1 contrast.
Image Guidance
This artifact can be eliminated by limiting the minimum spacing (for the most sequences a minimum gap 10% and for IR sequences 20%) between the slices. Crosstalk can also be reduced by selection of interleaved slices (so a slice gap will not be necessary), but interleaved data acquisition can produce large mean intensity differences between adjacent slices.
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