Task-Based Evaluation of Low-Contrast Detectability In Deep Silicon-Based Pcct(dSi-PCCT) Using AUC and d′ Metrics
Abstract
Purpose
To quantify low-contrast detectability (LCD) of deep silicon-based PCCT (dSi-PCCT) compared to energy-integrated detector (EID) CT using task-based image quality metrics—Receiver Operating Characteristic (ROC) area under the curve (AUC) and detectability index (d′)—matched radiation dose, in-plane and cross-plane spatial resolution
Methods
MITA‑FDA Low Contrast Head (CCT191) and Body (CCT189 with oval annulus) phantoms were scanned on dSi‑PCCT (65 keV) and EID CT (120 kVp) at matched CTDIvol (Head: 5.0 mGy; Body: 4.1 mGy). Each phantom was scanned 30 times. A soft‑tissue kernel was tuned so that in‑plane and cross‑plane MTF (50% and 10%) matched between systems for 1.25‑mm slices with DL‑M denoising. Images were reconstructed with the matched kernel, 1.25‑mm thickness, 512 matrix, and DL‑M. Four low‑contrast objects per phantom with varying sizes and contrasts were evaluated using a Channelized Hotelling Observer (CHO) with dense DoG channels. ROI pairs (720 per object/system) were randomized into 240 training and 480 testing samples. For the location‑known detection task, CHO test statistics from the testing set yielded ROC AUC and detectability index d′. AUC uncertainty was estimated using the one‑shot method.
Results
Across all object sizes and contrasts, dSi-PCCT demonstrated similar or superior LCD to EID-CT. AUC value improvement of dSi-PCCT from EID CT baseline ranges from -2% to 14%. Detectability index analysis showed dSi-PCCT performance similar or better compared to EID CT for both head and body modes, with differences ranging from −7% to +56% across objects, indicating comparable or improved detectability at the same dose.
Conclusion
Task-based metrics (AUC and d′) confirm that dSi-PCCT maintains or improves low-contrast detectability relative to EID CT at matched clinically relevant doses for both head and body sizes. Enhanced LCD supports greater diagnostic confidence for subtle lesion detection without requiring increased radiation dose.