Objectif
To assess the potential of virtual monoenergetic images on a photon-counting CT (PCCT) device for reducing the amount of iodine injected compared to an energy-integrating CT (EICT) device
Patients et Méthodes
A multi-energy CT phantom was scanned with PCCT at the standard dose (11mGy) for abdomen-pelvis examinations and two lower doses (6 and 1.8 mGy). It was also scanned with an energy-integrating dual-source CT (EICT) at standard dose level. Virtual monoenergetic images (VMIs) were generated at low energy levels (40, 50, 60 and 70 keV) for PCCT acquisitions and at reference energy level (60 keV) for EICT. For all VMIs, the root-mean-square deviation (RMSDHU) and the monochromatic bias (MB) were assessed for 6 iodine concentrations (0.5, 1, 2, 5, 10 and 15 mg/mL). Noise was assessed on a water insert and the contrast-to-noise ratio (CNR) was calculated for all iodine concentrations. The potential for reducing the amount of contrast media with PCCT compared to EICT was calculated.
Résultats
A similar noise level was found for PCCT at 1.8 mGy to EICT at 11 mGy, with energy levels of 60 keV (p=0.055,) and 70 keV (p=0.164). The CNR values for concentrations above 2 mg/mL were significantly higher with PCCT at 60 keV for 11 mGy and 6 mGy (45.94±0.66%; p<0.001 and 24.13±17.41%; p<0.001 respectively) but similar at 1.8 mGy. Similar results were found for 2 mg/mL except at 1.8 mGy where a lower CNR was observed with PCCT. For 1 mg/mL and 0.5 mg/mL, the CNR was similar at 11 mGy (p=0.237 and p>0.1) and lower for 6 mGy and 1.8 mGy. For lower energy levels, higher CNR values were found with PCCT for all dose levels and concentrations above 1 mg/mL, except for 2 mg/mL at 50 keV and 1.8 mGy. A potential for reducing the amount of iodine was found with PCCT at all energy levels (-28.00 ± 4.11 %). This increased as the energy decreased but decreased as the dose level decreased.
Conclusion
For abdomen-pelvis examinations, using VMIs with the PCCT scanner can reduce the amount of contrast medium, even at low dose levels, without affecting image quality except for lesions with an iodine concentration below 1 mg/mL.