Intra-patient comparison of portal-venous CT attenuation on virtual monoenergetic reconstructions: Spectral EID versus photon-counting detector CT with 30% contrast media dose reduction.

INTRODUCTION

Reducing iodinated contrast media (CM) dosage in CT is desirable to minimize the risk of contrast-associated renal injury in patients. Photon-counting detector (PCD) CT has been promoted as enabling CM reduction compared to energy-integrating detector (EID) CT. However, whether PCD offers superior iodine enhancement compared to spectral EID at identical virtual monoenergetic (VME) levels remains unclear. This study compared intra-patient portal-venous chest-abdomen-pelvis (CAP) CT scans, looking at the objective enhancement between spectral EID (sEID) and PCD with 30% CM reduction.

METHODS

Ninety-three patients undergoing CAP CT on both dual-source sEID (0.46 gI/kg) and PCD (0.32 gI/kg) scanners within six months were retrospectively analysed. Attenuation measurements were obtained in contrast-enhancing tissues (aorta, renal cortex, portal vein, liver) and non-enhancing tissues (psoas muscle, subcutaneous fat) at 60, 65, and 70 keV VME. Liver iodine enhancement ratio (IER) was calculated to assess enhancement relative to iodine dose.

RESULTS

PCD attenuation was significantly lower than sEID for all contrast-enhancing tissues (p <0.001), with reductions of 21-23% (aorta), 19-20% (renal cortex), 17% (portal vein), and 13-17% (liver). Non-enhancing tissues showed no significant differences. Critically, IER values were equivalent between scanners at all VME levels (p >0.39), indicating identical enhancement per gram of iodine.

CONCLUSIONS

When looking at objective image quality, a 30% contrast media reduction in PCD relative to sEID CAP scans is not feasible unless different absolute enhancement is acceptable. Our results point to VME reconstruction algorithms, rather than intrinsic detector differences, determine iodine enhancement. For consistent parenchymal enhancement, identical iodine doses should be applied to both PCD and sEID spectral CT.

IMPLICATIONS FOR PRACTICE: There is minimal potential for CM dose reduction when reproducible parenchymal enhancement between sEID and PCD CAP-CT is required.