| Popis: |
The detection of coronary calcifications with CT is generally accepted as a useful method for predicting early onset of coronary artery disease. Film-screen X-ray and fluoroscopy have also been shown to have high predictive value for coronary disease diagnosis, but have minimal sensitivity. Recently, flat-panel detectors capable of dual-energy techniques have enabled the separation of soft-tissue and bone from images. Clinical studies report substantially improved sensitivity for the detection of coronary calcifications using these techniques. However, heart motion causes minor artefacts from misregistration of both calcified and soft-tissue structures, resulting in inconsistent detection of calcifications. This research examines whether cardiac gating improves the reliability of calcification detection. Single-energy, gated, and non-gated dual-energy imaging techniques are examined in a dynamic phantom model. A gating system was developed to synchronize two dual-energy exposures to a specified phase of the cardiac cycle. The performance and repeatability of the gating system was validated with the use of a cyclical phantom. An anthropomorphic phantom was developed to simulate both cardiac and soft-tissue motion, and generate ECG-like output signals. The anthropomorphic phantom and motion artefact accuracy was verified by comparison with clinical images of patients with calcifications. The ability of observers to detect calcifications in non-gated, and gated techniques was compared through the use of an ROC experiment. Gating visibly reduces the effect of motion artifacts in the dual-energy images. Without gating, motion artefacts cause greater variability in calcification detection. Comparison of the average area-under-the-curve of the ROC curves show that gating significantly increases the accuracy of calcification detection. The effects of motion and gating on DE cardiac calcification detection have been demonstrated and characterized in a phantom model that mimics the clinical scenario for dual-energy examinations. There exists significant potential for reliable cardiac calcification detection with gated dual-energy radiography. |
