Optimization of the scan protocol for the reduction of diaphragmatic motion artifacts depicted on CT angiography: a phantom study simulating pediatric patients with free breathing.
OBJECTIVE
This study was designed to optimize the scan protocol of CT angiography to reduce diaphragmatic motion artifacts in pediatric patients with free-breathing.


METHODS
A phantom with twelve tubes with different diameters was constructed. To simulate free-breathing, the phantom was connected to a motor, and the phantom moved along the axis of scan. Scans were performed under several conditions: different pitch (1, 1.5) and gantry rotation time (0.37 and 0.75 sec), and different movement range (1 cm, 3 cm) and rates (20/min, 40/min). For CT scanning, a 16-channel CT scanner was used and fixed factors of the CT protocol were as follows: 100 effective mAs, 80 kVp, reconstruction with a soft-algorithm, beam collimation 16 x 75 mm, reconstruction thickness of 1 mm, and an interval of 0.5 mm. CT scans were repeated five times. Each tube was evaluated with the use of a grading system (0 for images where tubes were not discriminable and 2 for images where tubes were clearly discriminable).


RESULTS
A higher pitch and shorter gantry rotation time produced images with a higher grade. Average grades for the higher pitch (1.5) and faster gantry rotation time (0.37 sec) for each combination of movement were as follows: 1.94 (range 1 cm and rate 20/min), 1.42 (range 1 cm and rate 40/min), 0.86 (range 3 cm and rate 20/min) and 0.52 (range 3 cm and rate 40/min). Average grades for the lower pitch (1) and slower gantry rotation time (0.75 sec) for each combination of movement were 1.08, 0.56, 0.32 and 0.08, respectively.


CONCLUSIONS
The scanning speed and especially the pitch are important parameters for CT scans to overcome a respiratory motion artifact.
Department of Radiology, Seoul National University College of Medicine, Institute of Radiation Medicine, Seoul National University Medical Research Center, and Clinical Research Institute, Seoul National University Hospital, Jongno-Gu, Seoul, Korea.
Jee Hyun
JH
Baek
Whal
W
Lee
Kee-Hyun
KH
Chang
Jin Wook
JW
Chung
Jae Hyung
JH
Park
D016477:Artifacts; D017023:Coronary Angiography / Q000379:methods*; D003964:Diaphragm; D005240:Feasibility Studies; D010372:Pediatrics / Q000379:methods*; D019047:Phantoms, Imaging; D012119:Respiration; D014057:Tomography, X-Ray Computed / Q000379:methods*