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.
Description
A monoexponential multi-echo decay becomes linear after taking the natural logarithm of positive signal magnitude.
A monoexponential multi-echo decay becomes linear after taking the natural logarithm of positive signal magnitude. Its slope determines T2* and R2*.
The tool returns r2StarPerSecond (r2 star per second); t2StarMs (t2 star ms); extrapolatedSignalAtZero (extrapolated signal at zero); 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 Iron Deposition R2*
Use Iron Deposition R2* when you already have echoTimesMs, signalMagnitudes and want r2StarPerSecond, t2StarMs, extrapolatedSignalAtZero, logFitRSquared. This is useful for checking a supplied calculation, documenting a measurement convention, or comparing observations prepared on the same basis.
How to use Iron Deposition R2* and understand its results
- Enter echoTimesMs, signalMagnitudes 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 r2StarPerSecond, t2StarMs, extrapolatedSignalAtZero, 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 |
|---|---|---|---|
| echoTimesMs | Echo times ms | list of number | Required |
| signalMagnitudes | Signal magnitudes | list of number | Required |
Fit an intercept to increasing nonnegative echo times and positive signals. Require a negative fitted slope, then report the extrapolated zero-echo signal and log-space R².
ln(signal) ≈ intercept+slope×TEms; T2*ms = −1/slope; R2*s⁻¹ = −1000×slope The symbols refer to the supplied quantities or generated values described above; unit conversions and comparison boundaries follow the stated implementation.
{
"input": {
"echoTimesMs": [
0,
10,
20
],
"signalMagnitudes": [
100,
36.787944117144235,
13.53352832366127
]
},
"output": {
"r2StarPerSecond": 100.00000000000001,
"t2StarMs": 9.999999999999998,
"extrapolatedSignalAtZero": 100.00000000000004,
"logFitRSquared": 1
}
}Limitations and assumptions
No noise-floor correction or nonlinear signal-space fit is applied. R² describes the logarithmic fit.
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
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. Spin Echo Signal Intensity: Evaluate an ideal saturation-recovery spin-echo signal M0(1−e^(−TR/T1))e^(−TE/T2); refocusing imperfections and stimulated echoes are excluded.
Methodological background: Least squares estimation.1
References
-
Least squares estimation — NIST/SEMATECH
Similar or alternative tools
- 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.
- Spin Echo Signal Intensity
Evaluate an ideal saturation-recovery spin-echo signal M0(1−e^(−TR/T1))e^(−TE/T2); refocusing imperfections and stimulated echoes are excluded.