Rationale and Objectives
To evaluate the potential of high-pitch, dual-source computed tomography (DSCT) for compensation of motion artifacts.
Materials and Methods
Motion artifacts were created using a moving chest/cardiac phantom with integrated stents at different velocities (from 0 to 4-6 cm/s) parallel (z direction), transverse (x direction), and diagonal (x and z direction combined) to the scanning direction using standard-pitch (SP) (pitch = 1) and high-pitch (HP) (pitch = 3.2) 128-detector DSCT (Siemens, Healthcare, Forchheim, Germany). The scanning parameters were (SP/HP): tube voltage, 120 kV/120 kV; effective tube current time product, 300 mAs/500 mAs; and a pitch of 1/3.2. Motion artifacts were analyzed in terms of subjective image quality and object distortion. Image quality was rated by two blinded, independent observers using a 4-point scoring system (1, excellent; 2, good with minor object distortion or blurring; 3, diagnostically partially not acceptable; and 4, diagnostically not acceptable image quality). Object distortion was assessed by the measured changes of the object’s outer diameter (x) and length (z) and a corresponding calculated distortion vector (d) (d = √(x 2 + z 2 )).
Results
The interobserver agreement was excellent ( k = 0.91). Image quality using SP was diagnostically not acceptable with any motion in x direction (scores 3 and 4), in contrast to HP DSCT where it remained diagnostic up to 2 cm/s (scores 1 and 2). For motion in the z direction only, image quality remained diagnostic for SP and HP DSCT (scores 1 and 2). Changes of the object’s diameter (x), length (z), and distortion vectors (d) were significantly greater with SP (overall: x = 1.9 cm ± 1.7 cm, z = 0.6 cm ± 0.8 cm, and d = 1.4 cm ± 1.5 cm) compared to HP DSCT (overall: x = 0.1 cm ± 0.1 cm, z = 0.0 cm ± 0.1 cm, and d = 0.1 cm ± 0.1 cm; each P < .05).
Conclusion
High-pitch DSCT significantly decreases motion artifacts in various directions and improves image quality.
Computed tomography (CT) is increasingly used for the diagnostic workup of patients. Its speed and accuracy is, particularly in the emergency medicine setting , of utmost importance. Motion artifacts decrease the image quality, resulting in blurring, shading, or streaking of the image and decreasing the accuracy of the diagnosis . Avoidance of motion artifacts would be the most reasonable option. However, patients’ involuntary motions are often unavoidable, particularly in the emergency setting when they are in pain, have orthopnea, decreased consciousness or are small children.
Several technical options have been introduced to reduce the severity of motion artifacts, including 1) prospective and/or retrospective electrocardiogram (ECG) gating to decrease cardiac motion artifacts, 2) over- and underscan modes, and 3) postprocessing methods and software correction algorithms . Decreasing the scan time can further reduce motion artifact. The recently introduced second-generation dual-source CT (DSCT) systems allows to scan at very high-pitch (HP) values, up to 3.2 by using two tube detector systems simultaneously to achieve gapless projection data and increase the temporal resolution (up to 75 ms) . This allows a chest CT to be performed in less than 1 second . This rapid data acquisition may render the HP mode less prone to motion artifacts compared to standard-pitch (SP) acquisitions. In addition, the new 128-slice DSCT permits prospective ECG-synchronized high-pitch acquisitions, resulting in the ability to scan the entire heart within one cardiac cycle . This allows achieving similar image quality with significant decreased radiation doses compared to a retrospective, ECG-gated, low-pitch spiral acquisition mode .
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Materials and methods
Phantom Information
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CT Scanner Information and Scanning Parameters
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Scanning Modes: Motion Artifacts Created with Different Velocities and Directions
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Image Quality Evaluation
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Object Distortion Evaluation
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Statistical Analysis
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Results
Subjective Image Quality
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Table 1
Noise as SD of HU Expressed as the Mean of Three Measurements in the Phantom and Subjective Image Quality for Motion in X Direction, Z Direction, and in X and Z Direction Combined Using SP and HP Acquisitions
Subjective Image Quality Noise (HU) (Mean ± SD) SP HP SP HP_P_ Value R1 R2 R1 R2 Overall 21.2 ± 3.8 21.0 ± 1.1 .8 x = 1; z = 0 17.4 21.5 3 3 1 1 x = 2; z = 0 20.3 19.1 4 4 1 1 x = 3; z = 0 23.9 20.0 4 4 3 3 x = 4; z = 0 27.5 20.6 4 4 3 3 x = 6; z = 0 25.4 22.5 4 4 4 4 Total in the x direction 22.9 ± 4.0 20.8 ± 1.3 .29 x = 0; z = 1 18.3 21.1 1 1 1 1 x = 0; z = 2 20.1 19.4 1 1 1 1 x = 0; z = 3 18.0 18.7 2 2 1 1 x = 0; z = 4 20.5 22.0 2 2 1 1 x = 0; z = 5 30.7 22.2 2 2 2 2 x = 0; z = −1 18.6 22.8 1 1 1 1 x = 0; z = −2 16.7 20.3 1 1 1 1 x = 0; z = −3 20.6 21.0 2 2 1 1 x = 0; z = −4 22.6 18.4 2 2 1 1 Total in the z direction 20.7 ± 4.2 21.1 ± 0.6 .78 x = 1; z = 1 17.9 20.6 3 3 1 1 x = 2; z = 2 22.7 20.6 4 4 2 2 x = 3; z = 3 18.3 21.8 4 4 2 3 x = 4; z = 4 22.5 21.4 4 4 3 3 Total in the x and z directions combined 20.4 ± 2.5 21.1 ± 0.6 ∗
HP, high pitch; HU, Hounsfield units; R1, reader 1; R2, reader 2; SD, standard deviation; SP, standard pitch.
Subjective image quality was evaluated using a 4-point scoring system (1, excellent image quality without visible object distortion or image blurring; 2, good image quality with minor object distortion or blurring; 3, diagnostically partially not acceptable image quality or intermediate blurring; and 4, diagnostically not acceptable image quality with severe object distortion or blurring).
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Object Distortion
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Table 2
Object Diameter Change, Object Length Change, and the Calculated Distortion Vectors (d = √(x 2 + z 2 )) for SP and HP modes
SP HP_P_ Value Object diameter change Overall (cm) 1.9 ± 1.7 0.1 ± 0.1 <.05 x direction (cm) 2.2 ± 2.1 0.1 ± 0.1 <.05 z direction (cm) 0 0 x and z direction (cm) 0.9 ± 0.9 0.1 ± 0.1 ∗ Object length change Overall (cm) 0.6 ± 0.8 0.0 ± 0.1 <.05 x direction (cm) 0 0 z direction (cm) 0.7 ± 0.9 0.1 ± 0.1 <.05 x and z direction (cm) 0.2 ± 0.2 0 ∗ Distortion vector Overall (cm) 1.4 ± 1.5 0.1 ± 0.1 <.05 x direction (cm) 2.2 ± 2.2 0.1 ± 0.1 <.05 z direction (cm) 0.7 ± 0.9 0.1 ± 0.1 <.05 x and z direction (cm) 0.9 ± 0.9 0.1 ± 0.1 ∗
HP, high-pitch; SP, standard-pitch.
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Image Noise
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Discussion
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Uncited figure
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