Comparison of image quality of abdominal CT examinations and virtual noncontrast images between photon-counting and energy-integrating detector CT

Purpose: To compare image quality of portal venous phase (PVP) abdominal CT examinations and virtual non-contrast (VNC) images between photon-counting CT (PCCT) and energy-integratingDetector CT (EID).

Methods and Materials: In this HIPAA compliant, IRB-approved, retrospective study, multi-phase CT scans from one commercially available PCCT (NAEOTOM Alpha, Siemens Healthineers) and two EID dual-source dual-energy CT systems (SOMATOM Definition Flash and SOMATOM Force, Siemens Healthineers) were retrieved. A total of 45 BMI-matched patients (21 women, 24 men; mean age58.5 ± 15.3 years, range 19-81 years; mean BMI 29.0 ± 6.8 kg/m2, range 13-47 kg/m2) were included: 15 for PCCT and 15 for each EID system. In vivo image quality parameters (MTFf10, noisemagnitude, Fav, Fpeak, NPSf10) were measured and compared between PCCT and EID for standard PVP and VNC images. A subset analysis was also performed in the overweight patient population(BMI>25 kg/m2). CTDIvol values were recorded for the three scanners. Because scanner tube current modulation adapts to patient size, radiation dose was compared among scanners accounting forBMI using a figure of merit: FOM=1/(BMI*lnCTDIvol). A five-point scale (1=best and 5=worst) was used to assess reader perception of noise, visibility of small structures, and overall image quality.

Results: Compared to the two EID systems, PCCT yielded significantly improved resolution and noise magnitude for both PVP (MTFf10 = 0.55 ± 0.08 for PCCT vs. 0.50 ± 0.04 and 0.49 ± 0.03 for Flashand Force, P = 0.02; noise = 9.76 ± 3.10 vs. 15.35 ± 4.14 and 10.70 ± 1.34, P = 0.02) and VNC images (MTFf10 = 0.56 ± 0.01 for PCCT vs. 0.51 ± 0.05 and 0.51 ± 0.03 for Flash and Force, P = 0.02; noise =9.59 ± 2.77 vs. 13.90 ± 3.57 and 10.83 ± 2.83, P = 0.02). A similar statistically significant trend was confirmed in the smaller subset of overweight patients. Our FOM analysis suggests that, for equal radiation exposure levels and comparable patient size, PCCT yields 20% noise reduction compared to the two EID systems, with 18% reduction in overweight patients. Reader’s perceived image noise was significantly lower for PCCT compared to EID for both PVP (1.85 ± 0.88 vs. 2.60 ± 0.88 and 2.70 ± 0.80) and VNC images (1.95 ± 0.83 vs. 3.0 ± 0.97 and 2.90 ±0.85). Of note, overall image quality improved significantly for PCCT compared to EID (1.35 ± 0.67 vs. 2.60 ± 0.82 and 2.45 ± 0.69 for PVP and 1.50 ± 0.67 vs 2.85 ± 0.81 and 2.55 ± 0.60 for VNC).

Conclusions: Compared to conventional EID systems, PCCT yields significantly lower radiation dose along with improved image quality on PVP and VNC images of abdominal CT examinations.

Clinical Relevance/Application: PCCT has a lower radiation dose compared to EID CT, with better image quality parameters and lower noise magnitude.