CT Number Accuracy and Association With Object Size: A Phantom Study Comparing Energy-Integrating Detector CT and...

Area of Science:

• Medical Imaging
• Radiological Physics
• Detector Technology

Background:

• Energy-integrating detector (EID) CT exhibits variable CT numbers due to beam hardening influenced by patient size.
• Photon-counting detector (PCD) CT provides more accurate effective beam energy determination, enhancing CT number reliability.

Purpose of the Study:

• To compare deep silicon PCD CT with EID CT (single- and dual-energy modes).
• To evaluate the impact of object size on CT numbers.
• To assess the overall accuracy of CT numbers across different detector types.

Main Methods:

• Scanned a phantom with varying polyethylene ring sizes and material inserts using EID CT (SE and DE modes) and PCD CT.
• Measured CT numbers in regions of interest (ROIs) and computed slopes of CT number versus object size.
• Calculated ideal CT numbers using the NIST XCOM database and determined the root mean square error (RMSE) for accuracy assessment.

Main Results:

• PCD CT demonstrated significantly lower CT number variation with object size (slopes closer to zero) compared to both SE and DE EID CT for various materials.
• PCD CT exhibited the smallest RMSE across all tested materials, indicating CT numbers closest to ideal values.
• Specific RMSE values showed PCD CT (17 HU for air, 3 HU for water, 4 HU for polystyrene, 13 HU for iodine, 20 HU for bone) outperformed EID CT (SE: 32, 7, 9, 31, 69 HU; DE: 44, 8, 10, 37, 81 HU).

Conclusions:

• Deep silicon PCD CT offers superior performance over SE and DE EID CT regarding CT number stability with varying object sizes.
• PCD CT provides CT numbers with higher accuracy, closer to ideal values, compared to EID CT methods.
• The enhanced reliability of CT numbers from PCD CT is crucial for diagnostic pathways reliant on quantitative imaging data.