The authors present and evaluate concepts for image reconstruction in dual source CT (DSCT). They describe both standard spiral (helical) DSCT image reconstruction and electrocardiogram (ECG)-synchronized image reconstruction. For a compact mechanical design of the DSCT, one detector (A) can cover the full scan field of view, while the other detector (B) has to be restricted to a smaller, central field of view. The authors develop an algorithm for scan data completion, extrapolating truncated data of detector (B) by using data of detector (A). They propose a unified framework for convolution and simultaneous 3D backprojection of both (A) and (B) data, with similar treatment of standard spiral, ECG-gated spiral, and sequential (axial) scan data. In ECG-synchronized image reconstruction, a flexible scan data range per measurement system can be used to trade off temporal resolution for reduced imagenoise. Both data extrapolation and image reconstruction are evaluated by means of computer simulated data of anthropomorphic phantoms, by phantom measurements and patient studies. The authors show that a consistent filter direction along the spiral tangent on both detectors is essential to reduce cone-beam artifacts, requiring truncation of the extrapolated (B) data after convolution in standard spiral scans. Reconstructions of an anthropomorphic thorax phantom demonstrate good image quality and dose accumulation as theoretically expected for simultaneous 3D backprojection of the filtered (A) data and the truncated filtered (B) data into the same 3D image volume. In ECG-gated spiral modes, spiral slice sensitivity profiles (SSPs) show only minor dependence on the patient’s heart rate if the spiral pitch is properly adapted. Measurements with a thin gold plate phantom result in effective slice widths (full width at half maximum of the SSP) of for the nominal slice and for the nominal slice. The visually determined through-plane ( axis) spatial resolution in a bar pattern phantom is for the nominal slice and for the nominal slice, again almost independent of the patient’s heart rate. The authors verify the theoretically expected temporal resolution of at gantry rotation time by blur free images of a moving coronary artery phantom with rest phase and demonstrate imagenoise reduction as predicted for increased reconstruction data ranges per measurement system. Finally, they show that the smoothness of the transition between image stacks acquired in different cardiac cycles can be efficiently controlled with the proposed approach for ECG-synchronized image reconstruction.
II. MATERIALS AND METHODS
II.A. Image reconstruction for dual source CT
II.A.1. System geometry
II.A.2. Extrapolation of truncated spiral (helical) data
II.A.3. Spiral (helical) image reconstruction
II.A.4. ECG-gated spiral (helical) image reconstruction
II.A.5. ECG-triggered axial image reconstruction
II.B. Evaluation of the image reconstruction
II.B.1. Evaluation of data extrapolation and combined 3D backprojection both for standard and ECG-gated spiral (helical) image reconstruction
II.B.2. Evaluation of through-plane (z-axis) spatial resolution for ECG-gated spiral image reconstruction as a function of heart rate and pitch
II.B.3. Evaluation of temporal resolution versus dose accumulation for ECG-gated spiral image reconstruction using a moving coronary artery phantom
II.B.4. Evaluation of the influence of the reconstruction parameter on the transition between image stacks in cardiacCT
III.A. Image quality with data extrapolation and combined 3D backprojection
III.B. Through-plane (-axis) spatial resolution for ECG-gated spiral image reconstruction
III.C. Temporal resolution versus dose accumulation for ECG-gated spiral image reconstruction
III.D. Influence of the reconstruction parameter on the transition between image stacks in cardiacCT
IV. Discussion and Conclusion
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