Photon-counting computed tomography for tissue characterization in patients with left ventricular hypertrophy

Background Photon-counting computed tomography (PCCT) has emerged as a promising modality for cardiac imaging. In patients with left ventricular hypertrophy (LVH), PCCT may offer an alternative to cardiac magnetic resonance (CMR), which is contraindicated or unavailable in some individuals. Methods We prospectively evaluated 79 patients presenting with LVH. Each underwent a PCCT scan, with measurements including LV mass index (LVMI), maximal LV wall thickness, ejection fraction (EF), late iodine enhancement (LIE) extent, iodine density, and extracellular volume (ECV). Patients were classified into three groups: hypertrophic cardiomyopathy (HCM, n=30), amyloid transthyretin cardiomyopathy (ATTR-CM, n=27), and secondary LV hypertrophy (LVH, n=24). A subset (43%) underwent a clinically indicated CMR scan within three months of PCCT. Results We evaluated 30 patients with HCM, 27 with ATTR-CM, and 24 with secondary LVH. Significant differences between groups emerged in patient age (66 years [55-73] vs. 80 [74-83] vs. 74 [66-81], respectively; p<0.001) and male sex (64% vs. 89% vs. 58%, respectively; p=0.036). All patients underwent a photon-counting CT scan. Thirty-four patients (43%) underwent a CMR scan (median time interval from the CT scan, -14 days; interquartile range, -111 days to +7 days). As compared to patients with HCM, those with ATTR-CM had lower LVEF, more often LIE, as well as higher LIE extent, ECV and iodine density. Furthermore, the ATTR-CM group had a much higher proportion of patients with LIE and much higher LIE extent, ECV and iodine density than patients with secondary LVH. Conversely, LVMI did not differ significantly between HCM and ATTR-CM or between HCM and secondary LVH, and was only higher in patients with ATTR-CM than those with secondary LVH (Figure 1). When comparing different CT metrics, similar findings were observed in the three categories, with the main exception of a lack of correlation between ECV and iodine density in ATTR-CM and secondary LVH, as opposite to a modest correlation in HCM (Figure 2). CT and CMR display an almost perfect agreement in terms of LVMI, maximal LV wall thickness and LVEF in patients with HCM, ATTR-CM or secondary LVH. Conversely, no significant correlations were found between ECV values from CT and CMR. Among the other comparisons, a difference between HCM and ATTR-CM emerged in the relationship between iodine density and ECV: no correlation was found in HCM (p=0.645), while a significant correlation was found in ATTR-CM (p=0.023, beta=0.875) (Figure 2). Conclusions PCCT accurately characterizes key structural and functional parameters and discriminates among different etiologies, notably detecting diffuse disease in amyloidosis. While ECV quantification by PCCT remains challenging, late iodine enhancement evaluation is feasible and may contribute to risk stratification.