Optimized energy of spectral CT for infarct imaging: Experimental validation with human validation

Abstract

Objectives Late contrast enhancement visualizes myocardial infarction, but the contrast to noise ratio (CNR) is low using conventional CT. The aim of this study was to determine if spectral CT can improve imaging of myocardial infarction. Materials and Methods A canine model of myocardial infarction was produced in 8 animals (90-minute occlusion, reperfusion). Later, imaging was performed after contrast injection using CT at 90kVp/150kVpSn. The following reconstructions were evaluated: Single energy 90 kVp, mixed, iodine map, multiple monoenergetic conventional and monoenergetic noise optimized reconstructions. Regions of interest were measured in infarct and remote regions to calculate contrast to noise ratio (CNR) and Bhattacharya distance (a metric of the differentiation between regions). Blinded assessment of image quality was performed. The same reconstruction methods were applied to CT scans of four patients with known infarcts. Results For animal studies, the highest CNR for infarct vs. myocardium was achieved in the lowest keV (40 keV) VMo images (CNR 4.42, IQR 3.64–5.53), which was superior to 90 kVp, mixed and iodine map (p=0.008, p=0.002, p<0.001, respectively). Compared to 90 kVp and iodine map, the 40 keV VMo reconstructions showed significantly higher histogram separation (p=0.042 and p<0.0001, respectively). The VMo reconstructions showed the highest rate of excellent quality scores. A similar pattern was seen in human studies, with CNRs for infarct maximized at the lowest keV optimized reconstruction (CNR 4.44, IQR 2.86–5.94). Conclusions Dual energy in conjunction with noise-optimized monoenergetic post-processing improves CNR of myocardial infarct delineation by approximately 20 – 25%.

Myocardial Delayed Enhancement CT for the Evaluation of Heart Failure: Comparison to MRI

“…Dual-energy CT can be used to derive virtual monochromatic (VM) images, effective atomic number images, and material density images by using the two-material decomposition method (10,11). Dual-energy CT has been used in several preliminary studies to characterize MDE of the myocardium by using image-based approaches in patients with myocardial infarction or cardiomyopathy (7,12,13).…”

Highlights of the Twelfth Annual Scientific Meeting of the Society of Cardiovascular Computed Tomography

“…He discussed how such an approach markedly increased the contrast to noise ratio of infarct imagingcurrently challenging in the clinical realm. 25 The utility of this was further reported by Dr Yasutoshi Ohta in the scientific abstract sessions where, using single-source dual-energy CT, iodine mapping and virtual monochromatic images were far superior to standard imaging for scar detection in patients with heart failure, with area under the receiver operating curve (AUC) of 0.97 and 0.95 achieved as compared with late gadolinium enhancement sequences on MRI. 4 Dr Suhny Abbara illuminated the audience on spectral CT whereby the energies of the arriving photons can be extracted by the detector allowing quantification of the photoelectric and Compton effect interactions, thus allowing tissue finger printing using CT (see Fig.…”

Automatic high-resolution infarct detection using volumetric multiphase dual-energy CT

“…Due to higher signal of gadolinium contrast and lower noise levels automatic segmentation of infarcts was shown to be feasible in delayed enhancement MRI 18, 19 although visual assessment is frequently used. Using improved image reconstructions and dual energy CT, the signal to noise ratio can be increased 5, 20-22 but infarct imaging using CT remains technically challenging. Using dual energy CT, Wichmann et al 5 report CNR between myocardium and infarct of (74.6/26.7 = ∼3) but the CNR between infarct and blood pool even with optimized dual energy CT was only about (33.2/29.6 = 1.2).…”

“…Using dual energy CT, Wichmann et al 5 report CNR between myocardium and infarct of (74.6/26.7 = ∼3) but the CNR between infarct and blood pool even with optimized dual energy CT was only about (33.2/29.6 = 1.2). We recently showed that advanced post-processing can further improve CNR of infarct vs. normal myocardium to ∼ 4.2, 22 but the issue of limited separation between infarct and blood pool remains problematic. Thus, spectral CT by itself is unlikely to be sufficient for CT identification of infarct and thus late contrast enhancement CT scans requires new solutions for automatic segmentation.…”

“…Compared with single-energy CT, dual-energy CT can improve CNR to some extent. 5, 6 To maximize infarct conspicuity, late contrast enhancement CT is performed after intravenous administration of 40-50 g iodine. High iodine loads improve the contrast to noise ratio of the enhancing infarct compared to normal myocardium.…”