Author: Afrouz Ataei, Xinhui Duan, Mi-Ae Park, Liqiang Ren 👨🔬
Affiliation: Department of Radiology, UT Southwestern Medical Center, UT Southwestern Medical Center, Rush University 🌍
Purpose:
Photon-counting CT (PCCT) has become commercially available recently, offering significant potential to enhance patient care. However, it also introduces unique challenges. One such challenge is that it does not generate conventional CT images as energy-integrating detector CT (EID-CT) scanners, so the common task of comparing CT numbers with other scanners, e.g., monitoring calcium scores, becomes difficult. The purpose of this work is to find monoenergetic levels from the PCCT with matching CT numbers with the EID-CT of different kVp levels for various materials in a phantom study, so these matched monoenergetic images can be used for comparison.
Methods:
An elliptical solid phantom (in-plane 40x30 cm, depth 16.5 cm) made of water equivalent material was used in the study, which hosted 16 solid inserts with variety of compositions to mimic human tissues, including 4 non-fatty soft tissues, 2 fatty tissues, bones and calcifications, iodine and gadolinium in tissues and blood. The phantom was scanned using a PCCT (SOMATOM Alpha, Siemens) and an EID-CT (SOMATOM Force, Siemens) with similar protocols. The matched monoenergetic level was determined by identifying the closest CT numbers between the EID-CT scanned at 100-150 kVp (10 kV interval) and the PCCT images at 40-190 keV (1 keV interval).
Results:
Linear regression showed each insert had a unique relationship between the matched monoenergetic levels from the PCCT and the kVp levels from the EID-CT. or non-fatty soft tissues, the matched monoenergetic levels were 62, 65, 69, 72, 75 and 79 keV, and for bony and iodine inserts, they were 70, 74, 77, 80, 84 and 87 keV, for 100-150 kVp (10 kV interval) of the EID-CT, respectively.
Conclusion:
The monoenergetic levels determined in this phantom study may alleviate the challenges of comparing PCCT results with other scanners. However, their practical utility warrants further validation in clinical settings.