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The unreliability of CT numbers as absolute values
AJR. American Journal of Roentgenology
|September 1, 1982
Summary
CT scanner performance significantly impacts CT numbers, leading to wide variations for the same tissue. These machine-related differences must be understood for accurate CT number diagnosis.
Area of Science:
- Medical Imaging
- Radiology
- Diagnostic Imaging
Background:
- Computed Tomography (CT) is a vital diagnostic tool.
- CT numbers (Hounsfield units) quantify tissue density.
- Standardization of CT numbers is crucial for accurate diagnosis.
Purpose of the Study:
- To evaluate the consistency of CT numbers across different CT scanners.
- To identify sources of variability in absolute CT number measurements.
- To assess the impact of scanner performance on CT number accuracy.
Main Methods:
- A standard phantom was scanned on five CT scanners.
- Scans were performed under conditions simulating routine body CT.
- Variations in CT numbers were analyzed based on scanner, location, and physical factors.
Main Results:
- Significant differences in absolute CT numbers were observed between most scanners.
- Variability existed even between scanners of the same model.
- CT numbers varied within a single scan based on location and scanner type.
- Physical factors like kilovoltage and phantom orientation influenced CT numbers.
Conclusions:
- Scanner performance alone introduces substantial variability in CT numbers.
- Absolute CT numbers are not consistently comparable across different CT systems.
- Users must account for machine-related variations before using CT numbers for diagnosis.