Aliasing Artifact Checker

Map one-dimensional phase positions into the centered half-open FOV and flag geometric wraps; coil sensitivity and suppression can change observed aliasing.

Description

Phase-direction coordinates alias periodically into the imaged field of view.

Phase-direction coordinates alias periodically into the imaged field of view. A centered half-open interval resolves the endpoint convention.

The tool returns wrappedPositionsMm (wrapped positions mm); wrappedObjectIndexes (wrapped object 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 Aliasing Artifact Checker

Use Aliasing Artifact Checker when you already have objectPositionsMm, phaseFovMm and want wrappedPositionsMm, wrappedObjectIndexes. This is useful for checking a supplied calculation, documenting a measurement convention, or comparing observations prepared on the same basis.

How to use Aliasing Artifact Checker and understand its results

Enter objectPositionsMm, phaseFovMm 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 wrappedPositionsMm, wrappedObjectIndexes. 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
objectPositionsMm	Object positions mm	list of number	Required
phaseFovMm	Phase fov mm	number	Required

Use a nonempty coordinate list and positive FOV. Flag original positions outside [−FOV/2,FOV/2); the positive endpoint wraps to the negative endpoint.

wrapped = mod(position+FOV/2,FOV)−FOV/2

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

json

{
  "input": {
    "objectPositionsMm": [
      -150,
      0,
      150
    ],
    "phaseFovMm": 200
  },
  "output": {
    "wrappedPositionsMm": [
      50,
      0,
      -50
    ],
    "wrappedObjectIndexes": [
      0,
      2
    ]
  }
}

Limitations and assumptions

This wraps one-dimensional positions, not image intensities, and does not correct aliasing artifacts.

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

Phase Matrix Size: Plan the smallest phase matrix meeting a maximum nominal pixel size and caller hardware multiple; this does not estimate true reconstructed spatial resolution. Susceptibility Artifact Shift: Estimate EPI phase-direction displacement from a measured off-resonance map and effective reconstructed phase bandwidth; susceptibility source fields and nonlinear pile-up are not solved.

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

Phase Matrix Size
Plan the smallest phase matrix meeting a maximum nominal pixel size and caller hardware multiple; this does not estimate true reconstructed spatial resolution.
Susceptibility Artifact Shift
Estimate EPI phase-direction displacement from a measured off-resonance map and effective reconstructed phase bandwidth; susceptibility source fields and nonlinear pile-up are not solved.