Spectral photon counting computed tomography imaging for non-calcified coronary plaque characterization

Background Non-calcified plaque (NCP) is an independent predictor of major adverse cardiovascular events (MACE). Yet, the NCP components most prone to destabilization remain uncertain. Spectral imaging by photon-counting computed tomography (PCCT) may enable a more specific characterization of NCP through elemental material decomposition. Purpose of this study was to investigate iodine concentration within NCP compared with the conventional CT density as reference standard. Methods 354 patients referred to PCCT coronary angiography for clinical indications were included. In patients with NCP (<350HU), both iodine concentration (mg/mL) on spectral datasets (VU-map:Res.5, Max.HU 3071, iodine ratio 2.16), and conventional CT-density (HU) were measured on co-axially aligned images. NCP were split into 5 groups (LAP <30HU:lipid-rich; 30-60HU:fibrofatty, 60-90HU:fibrous, 90-150HU:fibrous-dense, 150-350HU:fibrous high-dense). Results A total of 293 lesion sections of 89 coronary NCP were quantified in 54 patients (mean age, 60.02 years ± 7.01 SD). The correlation of intraplaque iodine with plaque CT-density (HU) was r = 0.758 (p<0.001). Iodine concentration increased with CT-density and was different among the 5 plaque types (p<0.001). Iodine concentration was lowest in lipid-rich sections (0.86 ± 0.58 mg/mL). High-density NCP (150-350 HU) showed the highest iodine uptake (4.68 ± 1.57 mg/mL). In lipid-rich/fibrofatty plaque <60 HU, iodine concentration was lower compared to dense NCP>60 HU (1.25±0.86 vs 3.51±1.57 mg/mL, p<0.001). Conclusion Iodine concentration within coronary non-calcified plaque (NCP) assessed by photon-counting CT is elevated in high-density sections, indicative of neovascularization, and lowest within the lipid-rich core. Spectral imaging by PCCT may allow identification of lesions exhibiting neovascularization, suggestive for a more unstable plaque type.