Contribution of photon counting CT to the detectability of lung nodules using ultra-low dose CT protocols: a phantom...

To compare the image quality obtained with an energy-integrating detector CT (EID-CT) and a photon-counting CT (PCCT) in ultra-low dose (ULD) chest CT protocols for three patient morphology configurations.

ULD-CT acquisitions were performed at Sn100 kV on PCCT and EID-CT using an image quality phantom. Different phantom sections were used to simulate standard, overweight and obese patients and the ULD levels were adapted to each section: 0.4, 0.8 and 1.6 mGy, respectively. Noise power spectrum (NPS) and task-based transfer function (TTF) were computed to assess noise magnitude, noise texture and spatial resolution, respectively. Detectability indexes (d') were computed to model the detection of a high-contrast solid nodule (HCN).

At all dose levels, noise magnitude values were significantly lower with PCCT than with EID-CT (-8.9 ± 0.4 %; p < 0.05). Values of average NPS spatial frequencies were significantly higher (p < 0.05) with PCCT (0.446 ± 0.010 mm^-1) than with EID-CT mode (0.323 ± 0.011 mm^-1). For the air insert, TTF values at 50 % were significantly lower for PCCT (0.719 ± 0.045 mm^-1) than with EID-CT (0.916 ± 0.030 mm^-1) at 1.6 mGy but similar for other dose levels (p < 0.05). For the simulated chest lesion, d' values were significantly higher (p < 0.05) with PCCT than with EID-CT. The improvements in d' values was 23.6 ± 5.5 % for HCN.

Compared with EID-CT, using PCCT makes it possible to reduce noise, improve noise texture and, above all, improve the detection of simulated high-contrast thoracic lesion in ULD CT protocols.