<p>We present a method to leverage the high fidelity of computed tomography (CT) to quantify regional left ventricular function using topography variation of the endocardium as a surrogate measure of strain. 4DCT images of 10 normal and 10 abnormal subjects, acquired with standard clinical protocols, are used. The topography of the endocardium is characterized by its regional values of fractal dimension (<italic>F</italic><sub>D</sub>), computed using a box-counting algorithm developed in-house. The average <italic>F</italic><sub>D</sub> in each of the 16 American Heart Association segments is calculated for each subject as a function of time over the cardiac cycle. The normal subjects show a peak systolic percentage change in <italic>F</italic><sub>D</sub> of 5.9 % ± 2 % in all free-wall segments, whereas the abnormal cohort experiences a change of 2 % ± 1.2 % (<italic>p</italic> < 0.00001). Septal segments, being smooth, do not undergo large changes in <italic>F</italic><sub>D</sub>. Additionally, a principal component analysis is performed on the temporal profiles of <italic>F</italic><sub>D</sub> to highlight the possibility for unsupervised classification of normal and abnormal function. The method developed is free from manual contouring and does not require any feature tracking or registration algorithms. The <italic>F</italic><sub>D</sub> values in the free-wall segments correlated well with radial strain and with endocardial regional shortening measurements.</p>
Large trials have demonstrated the prognostic value of quantifying left ventricular (LV) twist because of its crucial role in the coupling of systolic and diastolic cardiac function. Current methods for measuring LV twist evaluate rotation in a 2D plane, chosen prospectively, and the data is acquired over multiple heartbeats. In this paper, a new method for assessing 3D endocardial LV twist from single-heartbeat, ECG-gated, 4DCT volumes is proposed. In this study, the ability of the novel LV twist algorithm to accurately measure rotation in a mathematical phantom with known deformation is evaluated. The mathematical phantom was then 3D-printed to determine the accuracy of the rotation measurement from CT images in the presence of varying levels of noise. Lastly, as a proof-of-concept, LV twist was measured in human hearts across the cardiac cycle to determine whether reasonable estimates of endocardial rotation could be obtained from 4DCT studies of standard clinical quality. In both the mathematical and 3D-printed phantoms (for CNR≥9.3), the measured LV twist was highly correlated (r<sup>2</sup>≥ 0.98, p<0.001) with the known ground truth rotation function. In the healthy controls, the mean endocardial LV twist was found to be 25.3° ± 6.5° and occurred within 30-36% of the R-R interval. From these results, it is clear that 3D rotational information and LV twist can be obtained from ECG-gated 4DCT volumes. The accuracy of LV twist in clinical data requires validation via a gold standard, such as MRI-tagging
We present an analytical LV systolic model derived from human CT data to serve as the ground truth for optimization and validation of a previously published CT-derived regional strain metric called SQUEEZ. Physiologically-accurate strains were applied to each vertex of a clinically derived end-diastolic LV mesh to create analytical end-systolic poses exhibiting normal function as well as regional hypokinesia of four sizes (17.5mm, 14mm, 10.5mm, and 7mm in diameter), each with a programmed severe, medium, and subtle dysfunction. Regional strain estimates were obtained by registering the end-diastolic mesh to each end-systolic mesh condition using a non-rigid registration algorithm. Ground-truth models of normal function and of severe hypokinesia were used to identify the optimal parameters in the registration algorithm, and to measure the accuracy of detecting regional dysfunction of varying sizes and severities. We found that for normal LV systolic contraction, SQUEEZ values in all 16 AHA segments of the LV were accurately measured (within ±0.05). For cases with regional dysfunction, the errors in SQUEEZ in the region around the dysfunction increased with decreasing size of regional dysfunction. The mean SQUEEZ values of the 17.5mm and 14mm diameter dysfunctional regions, which we hypothesize are the most clinically relevant, were accurate to within 0.05.