Local 10g SAR

Compute local SAR for caller-supplied spatial 10-gram voxel-fraction regions; does not construct IEC-compliant regions, solve RF fields, or certify scanner safety.

Description

Local SAR averages absorbed power over a defined tissue mass.

Local SAR averages absorbed power over a defined tissue mass. Here each local region is explicitly supplied as voxel fractions that must total ten grams.

The tool returns regionSarWattsPerKg (region sar watts per kg); maximumLocalSarWattsPerKg (maximum local sar watts per kg). Input measurements and model parameters are supplied by the caller; the tool computes the stated summary rather than acquiring those measurements.

When to use Local 10g SAR

Use Local 10g SAR when you already have voxelMassesGrams, voxelAbsorbedPowersWatts, regionVoxelFractions and want regionSarWattsPerKg, maximumLocalSarWattsPerKg. This is useful for checking a supplied calculation, documenting a measurement convention, or comparing observations prepared on the same basis.

How to use Local 10g SAR and understand its results

Enter voxelMassesGrams, voxelAbsorbedPowersWatts, regionVoxelFractions 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 regionSarWattsPerKg, maximumLocalSarWattsPerKg. 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
voxelMassesGrams	Voxel masses grams	list of number	Required
voxelAbsorbedPowersWatts	Voxel absorbed powers watts	list of number	Required
regionVoxelFractions	Region voxel fractions	list of list of number	Required

Use positive masses, nonnegative powers and region fractions in [0,1]. Each region must weigh 10 g within 10⁻⁸ g; return each SAR and the maximum among supplied regions.

region SAR[W/kg] = Σfraction×voxelPower / (Σfraction×voxelMassGrams/1000)

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

json

{
  "input": {
    "voxelMassesGrams": [
      5,
      5,
      5
    ],
    "voxelAbsorbedPowersWatts": [
      0.01,
      0.02,
      0.03
    ],
    "regionVoxelFractions": [
      [
        1,
        1,
        0
      ],
      [
        0,
        1,
        1
      ]
    ]
  },
  "output": {
    "regionSarWattsPerKg": [
      3,
      5
    ],
    "maximumLocalSarWattsPerKg": 5
  }
}

Limitations and assumptions

The tool does not construct spatial regions, solve RF fields or search all possible ten-gram neighborhoods. No safety-limit compliance is established.

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

Specific Absorption Rate SAR: Summarize supplied absorbed RF energy over an explicit time window and mass; a caller comparison level is not a scanner safety certification or regulatory recommendation. Peripheral Nerve Stimulation Threshold: Screen a supplied gradient ramp against an externally calibrated strength-duration model; coil geometry, body coupling and multi-axis effects are not modeled, so this is not a patient safety determination.

Methodological background: Protection of patients and volunteers undergoing MRI procedures.^[1]

References

Protection of patients and volunteers undergoing MRI procedures — UK Health Protection Agency

Similar or alternative tools

Specific Absorption Rate SAR
Summarize supplied absorbed RF energy over an explicit time window and mass; a caller comparison level is not a scanner safety certification or regulatory recommendation.
Peripheral Nerve Stimulation Threshold
Screen a supplied gradient ramp against an externally calibrated strength-duration model; coil geometry, body coupling and multi-axis effects are not modeled, so this is not a patient safety determination.