Ultra Low Dose CT for CACS and AC of SPECT

CAC and BA limits of agreement between coronary artery calcium score obtained from ultra-low-dose and standard CT. Coronary artery calcium (CAC) is a measure for quantification of coronary artery calcification based on non-contrast enhanced CT, ranging from 0 (no calcifications) to infinite. It is an arbitrary unit. Increasing CAC means higher amounts of coronary artery calcifications and is associated with worse prognosis. Bland-Altman (BA) analysis is a statistical method to compare two modalities or techniques assessing the same measure. Limits of agreement is defined as +/- twice the standard deviation of the differences between the reference method and the new modality/technique. Broader limits of agreement mean less accurate results obtained by the new modality/techniqe, while a 0 BA limit of agreement would theoretically reflect perfect agreement.

For every patient, the CT images from 120 and 70 kVp-CT scans were used to create CTAC maps which were then used to reconstruct SPECT images, displayed as a 17-segment model polar plot with normalized percent tracer uptake given for every segment. Intra-class correlation was then applied to compare segmental relative tracer uptake. Analysis and the resulting correlation coefficient of 0.987 basically demonstrates interchangeability between the two datasets.