Normal values and reference ranges for quantitative assessment of myocardial first-pass perfusion by spectral computed tomography. From the Cadami-Spectral study
Authors: Herrera C , Sanchez-Puente A , Lopez-Jimenez R , Merchan-Gomez S , Martin-Garcia A , Eiros-Bachiller R , Rodriguez-Nieto J , Maillo-Seco J , Rincon-Diaz L M , Sanchez-Fernandez P L , Perez Del Villar C 
Published: October 2024

Abstract

Background
Spectral computed tomography (SCT) can generate iodine concentration maps according to the tissue iodine uptake, serving as a surrogate marker of organ perfusion. Thus, assessment of the iodine distribution maps derived from SCT allows to detect deviations in normal myocardial perfusion. As of present, reference ranges for the iodine concentration in each myocardial segment of the left ventricle (LV) derived from the first-pass perfusion have not been published.

Purpose
To provide normal values of first pass perfusion in individuals without coronary artery disease (CAD). Additionally, we explored whether these values could vary according to gender, contrast dosing or the cardiac cycle phase assessed.

Methods
From October 2021 to January 2024, we retrospectively identified patients who underwent a CT Cardiac Angiography (CTCA) and had no evidence of CAD or structural heart disease. Subjects were scanned using a dual-layer SCT, following a standard local protocol which included a weight-based contrast medium dosing of 0.8 mL/Kg. Iodine density maps were reconstructed using the MCA filter at a phase of 78%. An additional sample of 18 subjects who received a dosing of contrast of 1 mL/Kg and 16 cases scanned using a systolic acquisition and reconstructed at phase of 35% were also included. Spectral reconstructions were combined with tissue segmentation to obtain the spatial distribution of iodine along the myocardium. Mean, median and standard deviations values of density of iodine (mg/ml) were quantified for each segment following the AHA-17 segment model.

Results
Perfusion data from 80 woman (median age: 60 [IQR: 54-65.6] years) and 47 males (median age: 47 [IQR: 43 – 54] years) were analysed. Despite receiving higher dose of contrast (67.9 vs 59.8 mL; p &lt; 0.05), male subjects exhibited lower iodine density values in the myocardium compared to females (median concentration per segment 1.58 vs 2.01 mg/dL, p&lt;0.001; figure 1). Notably, the volume of the LV myocardium was higher in male than in women (143 mL vs 92 mL, p&lt;0.001). These differences could be partially explained in a mixed model considering the ratio contrast dose/myocardium volume (b = 1.500, p &lt; 0.001). Higher contrast dosing (1 mL/Kg vs 0.8 mL/kg) correlated with higher iodine density values in the myocardium (2.03 vs 1.83 mg/dL, respectively; p = 0.023). No differences were noted when comparing reconstructions at systole vs diastole (1.86 vs 1.80 mg/dL, respectively; p = 0.484). Reference range values of each myocardial segment are listed in table 1.

Conclusions
Significant gender discrepancies are detected in the analysis of first-pass myocardial perfusion. These variations can be partially explained by differences in the LV myocardium volume. Our findings provide applicable reference ranges of the iodine concentration in myocardium at first pass perfusion in controls without coronary or structural heart disease.