ADC Calculation
Fit apparent diffusion coefficient from all supplied b-value/log-signal observations; rising signals yield a preserved negative ADC estimate rather than a fabricated nonnegative diffusivity.
Description
A monoexponential diffusion signal becomes linear in log signal versus b value.
A monoexponential diffusion signal becomes linear in log signal versus b value. The negative fitted slope is an apparent diffusion coefficient.
The tool returns adcSquareMmPerSecond (adc square mm per second); extrapolatedS0 (extrapolated s0); logFitRSquared (log fit r squared). Input measurements and model parameters are supplied by the caller; the tool computes the stated summary rather than acquiring those measurements.
When to use ADC Calculation
Use ADC Calculation when you already have bValuesSecondsPerSquareMm, diffusionSignals and want adcSquareMmPerSecond, extrapolatedS0, logFitRSquared. This is useful for checking a supplied calculation, documenting a measurement convention, or comparing observations prepared on the same basis.
How to use ADC Calculation and understand its results
- Enter bValuesSecondsPerSquareMm, diffusionSignals 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 adcSquareMmPerSecond, extrapolatedS0, logFitRSquared. 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 |
|---|---|---|---|
| bValuesSecondsPerSquareMm | B values seconds per square mm | list of number | Required |
| diffusionSignals | Diffusion signals | list of number | Required |
Use increasing nonnegative b values in s/mm² and aligned positive signals. Fit an intercept, return extrapolated S0 and log-space R².
ln(signal) = intercept−ADC×b; ADC[mm²/s] = −slope The symbols refer to the supplied quantities or generated values described above; unit conversions and comparison boundaries follow the stated implementation.
{
"input": {
"bValuesSecondsPerSquareMm": [
0,
500,
1000
],
"diffusionSignals": [
100,
60.653065971263345,
36.787944117144235
]
},
"output": {
"adcSquareMmPerSecond": 0.0010000000000000005,
"extrapolatedS0": 100.00000000000004,
"logFitRSquared": 1
}
}Limitations and assumptions
Nondecaying data may yield zero or negative ADC and are retained. Multi-compartment effects and noise-floor bias 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
Diffusion B-Value: Compute the Stejskal–Tanner b value for ideal rectangular PGSE pulses in s/mm² with γ supplied in Hz/T; waveform cross-terms and imaging gradients are excluded. Iron Deposition R2*: Fit monoexponential multi-echo magnitude decay in log space and derive R2*; no conversion to iron concentration is inferred and magnitude noise can bias the fit.
Methodological background: Spin Diffusion Measurements: Spin Echoes in the Presence of a Time-Dependent Field Gradient.1
References
-
Spin Diffusion Measurements: Spin Echoes in the Presence of a Time-Dependent Field Gradient — Stejskal and Tanner; Journal of Chemical Physics
Similar or alternative tools
- Diffusion B-Value
Compute the Stejskal–Tanner b value for ideal rectangular PGSE pulses in s/mm² with γ supplied in Hz/T; waveform cross-terms and imaging gradients are excluded.
- Iron Deposition R2*
Fit monoexponential multi-echo magnitude decay in log space and derive R2*; no conversion to iron concentration is inferred and magnitude noise can bias the fit.