High-pitch spiral computed tomography: effect on image quality and radiation dose in pediatric chest computed tomography.

Objectives: computed tomography (CT) is considered the method of choice in thoracic imaging for a variety of indications. Sedation is usually necessary to enable CT and to avoid deterioration of image quality because of patient movement in small children. We evaluated a new, subsecond high-pitch scan mode (HPM), which obviates the need of sedation and to hold the breath.

Material And Methods: a total of 60 patients were included in this study. 30 patients (mean age, 14 ± 17 month; range, 0-55 month) were examined with a dual source CT system in an HPM. Scan parameters were as follows: pitch = 3.0, 128 × 0.6 mm slice acquisition, 0.28 seconds gantry rotation time, ref. mAs adapted to the body weight (50-100 mAs) at 80 kV. Images were reconstructed with a slice thickness of 0.75 mm. None of the children was sedated for the CT examination and no breathing instructions were given. Image quality was assessed focusing on motion artifacts and delineation of the vascular structures and lung parenchyma. Thirty patients (mean age, 15 ± 17 month; range, 0-55 month) were examined under sedation on 2 different CT systems (10-slice CT, n = 18; 64-slice CT, n = 13 patients) in conventional pitch mode (CPM). Dose values were calculated from the dose length product provided in the patient protocol/dose reports, Monte Carlo simulations were performed to assess dose distribution for CPM and HPM.

Results: all scans were performed without complications. Image quality was superior with HPM, because of a significant reduction in motion artifacts, as compared to CPM with 10- and 64-slice CT. In the control group, artifacts were encountered at the level of the diaphragm (n = 30; 100%), the borders of the heart (n = 30; 100%), and the ribs (n = 20; 67%) and spine (n = 6; 20%), whereas motion artifacts were detected in the HPM-group only in 6 patients in the lung parenchyma next to the diaphragm or the heart (P < 0,001). Dose values were within the same range in the patient examinations (CPM, 1.9 ± 0.6 mSv; HPM, 1.9 ± 0.5 mSv; P = 0.95), although z-overscanning increased with the increase of detector width and pitch-value.

Conclusion: high-pitch chest CT is a robust method to provide highest image quality making sedation or controlled ventilation for the examination of infants, small or uncooperative children unnecessary, whereas maintaining low radiation dose values.