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Image reconstruction and image quality evaluation for a dual source CT scanner
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10.1118/1.3020756
/content/aapm/journal/medphys/35/12/10.1118/1.3020756
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/35/12/10.1118/1.3020756

Figures

Image of FIG. 1.
FIG. 1.

Technical realization of a DSCT system (SOMATOM Definition, Siemens Healthcare, Forchheim, Germany). One detector (A) covers the entire scan field of view with a diameter of , while the other detector (B) is restricted to a smaller, central field of view.

Image of FIG. 2.
FIG. 2.

System geometry of a DSCT system. The axis points into the paper plane and from the patient table into the gantry.

Image of FIG. 3.
FIG. 3.

Data completion of truncated (B) data in parallel geometry. The -axis corresponds to the patient axis. A slice on detector (B) is indicated. (A) data measured at the same view angle are used to extrapolate the (B) projections in the direction. If no (A) data from the current half turn of the spiral are available, as in this case, (A) data from the adjacent half turn are used.

Image of FIG. 4.
FIG. 4.

Schematic illustration of data segments in parallel geometry used for ECG-synchronized DSCT image reconstruction. Due to the mechanical assembly, the minimum data interval per measurement system is in parallel geometry (indicated by dashed lines). The data interval for each measurement system can be increased (indicated by solid lines) to trade-off temporal resolution for dose accumulation in order to reduce the image noise for obese patients.

Image of FIG. 5.
FIG. 5.

Angular weighting functions for both measurement systems (A) and (B) to ensure correct normalization and smooth data transition for ECG-synchronized DSCT image reconstruction. Left: Minimum data interval per measurement system to optimize temporal resolution. Right: Larger data interval per measurement system to accumulate dose and trade-off temporal resolution for reduced image noise.

Image of FIG. 6.
FIG. 6.

Computer-controlled robot arm moving a tube filled with contrast agent (“coronary artery”) in a water tank. The motion amplitudes and velocities of the robot arm can be adjusted to provide a realistic motion pattern of the tube.

Image of FIG. 7.
FIG. 7.

Spiral reconstructions of the anthropomorphic thorax phantom at pitch (left) and (right), . (a) Reconstruction using (A) data only. (b) Simultaneous 3D backprojection of (A) and (B) data without extrapolation of the truncated (B) data. Note the severe truncation artifacts at the boundary of the small SFOV. (c) Simultaneous 3D backprojection of (A) and (B) data with extrapolation of the truncated (B) data, but without truncation of the extrapolated (B) data after convolution. Cone-beam artifacts (arrows) are a result of the inconsistent filter direction of the (B) data. (d) Simultaneous 3D backprojection of (A) and (B) data with extrapolation of the truncated (B) data and truncation of the extrapolated (B) data after convolution. Cone-beam artifacts are significantly reduced. The ROIs 1, 2, and 3 were used to measure image noise.

Image of FIG. 8.
FIG. 8.

Spiral reconstructions of the anthropomorphic thorax phantom at pitch (left) and (right), detail. For (a), (b), (c), and (d) see Fig. 7.

Image of FIG. 9.
FIG. 9.

Relative image noise reduction in a water phantom obtained by simultaneously backprojecting both the (A) data and the truncated (B) data. Ratio of the standard deviation of the image noise using (A) and (B) data with truncation of the extrapolated (B) data after convolution, and using (A) data only as a function of the distance from the isocenter. The solid line represents the theoretically expected value for .

Image of FIG. 10.
FIG. 10.

ECG-gated spiral (helical) reconstructions of the stationary anthropomorphic thorax phantom at pitch , assuming an artificial ECG at , for , , and . Cone-beam artifacts decrease with increasing , but temporal resolution is then compromised.

Image of FIG. 11.
FIG. 11.

Measured SSPs (at the isocenter) of the nominal slice as a function of the heart rate of an artificial ECG at 60, 70, 80, 90, and 100 bpm with the correspondingly adapted pitch values , 0.32, 0.37, 0.43, and 0.46, respectively, using dual source acquisition and ECG-gated spiral (helical) image reconstruction. The indicated slice widths are the FWHMs of the SSPs.

Image of FIG. 12.
FIG. 12.

Measured SSPs (at the isocenter) of the nominal slice as a function of the heart rate of an artificial ECG at 60, 70, 80, 90, and with the correspondingly adapted pitch values , 0.32, 0.37, 0.43, and 0.46, respectively, using dual source acquisition and ECG-gated spiral (helical) image reconstruction. The indicated slice widths are the FWHMs of the SSPs.

Image of FIG. 13.
FIG. 13.

Fourier transforms of the measured SSPs of the nominal slice (see Fig. 11) at various heart rates. The SSPs were obtained by using dual source acquisition and ECG-gated spiral (helical) image reconstruction. The Fourier transforms are the MTFs in the direction.

Image of FIG. 14.
FIG. 14.

Fourier transforms of the measured SSPs of the nominal slice (see Fig. 12) at various heart rates. The SSPs were obtained by using dual source acquisition and ECG-gated spiral (helical) image reconstruction. The Fourier transforms are the MTFs in the direction.

Image of FIG. 15.
FIG. 15.

MPRs of the -resolution phantom at nominal reconstruction slice width, as a function of the heart rate of an artificial ECG at 60, 70, 80, 90, and with the correspondingly adapted pitch values , 0.32, 0.37, 0.43, and 0.46, respectively. Independent of the heart rate, the bar patterns with are visible, which corresponds to object size. This result is in good agreement with the evaluation of the -MTFs, see Fig. 13.

Image of FIG. 16.
FIG. 16.

MPRs of the -resolution phantom at nominal reconstruction slice width. Independent of the heart rate, the bar patterns with are visible, corresponding to about true resolution due to the 30° angle of the bar-patterns. Hence, objects of about in size can be differentiated. This result is in good agreement with the evaluation of the -MTFs, see Fig. 14.

Image of FIG. 17.
FIG. 17.

Axial images and MPRs of the moving coronary artery phantom for various choices of the reconstruction data interval per measurement system. With increasing , image noise is reduced, but at the expense of temporal resolution. ROI 1 was used for image noise measurements.

Image of FIG. 18.
FIG. 18.

MPR of a DSCT coronary angiographic patient examination for various values of the smoothing parameter , which controls the smoothness of the transition between image stacks acquired in different cardiac cycles, see the arrows. As approaches 0, the transition is more pronounced (image courtesy of Dr. J. Hausleiter, German Heart Center, Munich).

Tables

Generic image for table
TABLE I.

Temporal resolution, measured and theoretically expected relative noise values for ECG-gated spiral (helical) DSCT image reconstruction, as a function of .

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/content/aapm/journal/medphys/35/12/10.1118/1.3020756
2008-11-24
2014-04-24
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Image reconstruction and image quality evaluation for a dual source CT scanner
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/35/12/10.1118/1.3020756
10.1118/1.3020756
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