Slice Gap

Audit adjacent slice edge gaps and overlaps along a common slice-normal axis; centers and physical slice thicknesses share millimetre units.

Description

Slice center spacing and thickness jointly determine whether adjacent ideal slab edges have a gap or overlap.

Slice center spacing and thickness jointly determine whether adjacent ideal slab edges have a gap or overlap. Negative edge gaps indicate overlap.

The tool returns edgeGapsMm (edge gaps mm); overlapPairIndexes (overlap pair indexes). Input measurements and model parameters are supplied by the caller; the tool computes the stated summary rather than acquiring those measurements.

When to use Slice Gap

Use Slice Gap when you already have sliceCentersMm, sliceThicknessesMm and want edgeGapsMm, overlapPairIndexes. This is useful for checking a supplied calculation, documenting a measurement convention, or comparing observations prepared on the same basis.

How to use Slice Gap and understand its results

Enter sliceCentersMm, sliceThicknessesMm using the field table below. Match the units, ordering and data boundaries described in the calculation.
Run the tool after checking the stated bounds and matching paired observations or categories. A malformed request gives a tool error rather than a usable measurement.
Read edgeGapsMm, overlapPairIndexes. Use the calculation and interpretation below to distinguish amounts, ratios, signs and decision flags where applicable.
Review the supplied parameters and assumptions before using the result in a report or comparing it with another observation.

Input field	Meaning	Value type and bounds	Requirement
sliceCentersMm	Slice centers mm	list of number	Required
sliceThicknessesMm	Slice thicknesses mm	list of number	Required

Use increasing centers and aligned positive thicknesses. Return each signed gap and the zero-based index of the earlier slice in overlapping pairs.

gap[i] = center[i+1]−center[i]−(thickness[i]+thickness[i+1])/2

The symbols refer to the supplied quantities or generated values described above; unit conversions and comparison boundaries follow the stated implementation.

json

{
  "input": {
    "sliceCentersMm": [
      0,
      6,
      12
    ],
    "sliceThicknessesMm": [
      5,
      5,
      7
    ]
  },
  "output": {
    "edgeGapsMm": [
      1,
      0
    ],
    "overlapPairIndexes": []
  }
}

Limitations and assumptions

Zero means touching ideal edges. Actual RF slice profiles, cross-talk and three-dimensional orientation are not modelled.

Numerical inputs must be finite. The tool checks its declared input shape and calculation constraints; those checks do not verify the quality, calibration or representativeness of the supplied observations.

Alternative or Complementary methods

Slice Thickness: Compute nominal slice thickness from RF bandwidth and slice-select gradient in explicit Hz/T and mT/m units; RF profile and off-resonance effects are not modeled. SMS Multiband Factor: Plan spatially interleaved simultaneous-slice groups and retain smaller tail groups; CAIPI shifts, RF peak power and sequence timing are external.

Methodological background: RAD229: MRI signal and sequence lecture notes.^[1]

References

RAD229: MRI signal and sequence lecture notes — Brian Hargreaves and colleagues, Stanford University

Similar or alternative tools

Slice Thickness
Compute nominal slice thickness from RF bandwidth and slice-select gradient in explicit Hz/T and mT/m units; RF profile and off-resonance effects are not modeled.
SMS Multiband Factor
Plan spatially interleaved simultaneous-slice groups and retain smaller tail groups; CAIPI shifts, RF peak power and sequence timing are external.