Description
Subtract a supplied additive water-reference HU offset, without inferring tissue type or calibrating a full attenuation scale.
An image grid has array indices as well as physical spacing, timing, and signal conventions. A calculation on supplied metadata describes one part of that grid or signal; it does not inspect an image, validate a complete file, or interpret anatomy.
Subtract a supplied additive water-reference HU offset, without inferring tissue type or calibrating a full attenuation scale.
When to use this tool
Use it for ct number water reference gap when the required inputs and conventions are already available.
How to use the tool and how it works
- Enter measuredHu, observedWaterHu, expectedWaterHu. Use the stated units and boundary conventions.
- Run the calculation. Correct any input error before interpreting a result.
- Read waterOffset, correctedHu. Inspect any known, defined, inclusion, or boundary flags before interpreting numeric values.
Return waterOffset=observedWaterHu-expectedWaterHu and correctedHu=measuredHu-observedWaterHu+expectedWaterHu using supplied values in Hounsfield units.1
| Input field | Meaning and units | Accepted input |
|---|---|---|
| measuredHu | Measured Hu | Required. Finite number. |
| observedWaterHu | Observed Water Hu | Required. Finite number. |
| expectedWaterHu | Expected Water Hu | Required. Finite number. |
| Output field | Interpretation | Returned shape |
|---|---|---|
| waterOffset | Water Offset | Required. Finite number. |
| correctedHu | Corrected Hu | Required. Finite number. |
{
"input": {
"measuredHu": 40,
"observedWaterHu": 5,
"expectedWaterHu": 0
},
"output": {
"waterOffset": 5,
"correctedHu": 35
}
}Limitations and assumptions
- This is a supplied additive water-reference adjustment, not a full scanner calibration or a tissue classification. It does not establish whether the reference measurement is valid.
- The field tables describe structural bounds; the mechanics also state cross-field requirements. Malformed input shapes, disallowed keys, and invalid domains cause input errors. Results must remain finite and within the declared output contract. A successful false flag or zero placeholder is distinct from an error.
- Numeric arithmetic uses binary floating point. Exact comparisons have no hidden tolerance or decimal rounding; negative zero is exported as zero. Decimal-text integer operations retain the exactness specifically stated above.
Alternative or Complementary methods
For ct number water reference gap, check the source records and the supplied rule before comparing the result with another method. Use a full image reader and geometry or signal analysis when the task requires interpreting image data.
References
Similar or alternative tools
- Acquisition Time Offset Precision Flag
Preserve a truncated timestamp quantum and offset-known flag; unknown UTC values use flagged zero placeholders.
- DICOM Frame Increment Time Index Term
Constant Frame Time coordinate for one zero-based frame index; not a variable Frame Time Vector or acquisition datetime parser.