Pediatric radiation dose optimization in 16-multislice computed tomography (MSCT) while maintaining image quality

Abstract

Objectives: To determine the methods to reduce the pediatric radiation dose while maintaining image quality based on patient weight and to create new pediatric brain protocol to implement to clinical study. Design: Descriptive cross-sectional. Place: Department of Radiology, King Chulalongkorn Memorial Hospital, Thai Red Cross Society. Samples: 62 children, age ≤12 years, bodyweight from 1 to 40 kilogram of 4 groups of cranial computed tomography. Material and Method: First group of 31 pediatric patients requested for brain CT examination with 16 MSCT were studied. Patient dose is base on CT dose index (CTDIvol), and the dose length product (DLP). Standard deviation (SD) of CT number measured on images, was used to determine the image quality in the terms of image noise. Image noise was measured for head scan with protocol reducing tube current-time appropriate for patient size. Phantom studies were performed using cylindrical water phantom diameters of 9.15, 11.15, 13.15 and 15.8 cm respectively. The tube-current-time reduction of 10, 20, 30 and 40 percent were applied to get 20 percentdose reduction and optimal image quality. The second group of 31 pediatric patients were scanned using reduced mAs technique of special protocol. Two senior pediatric radiologists were assigned to grade the image quality into 5 categories; 1: non-acceptable, 2: poor, 3: acceptable, 4: good, and 5: excellent. Results: The radiation dose in pediatric brain MSCT reduced up to 20% compared to the routine study (manufacturer default technique). Using an adequate MSCT technique in children by adjusting the CT scanning parameters enables a significant reduction of radiation exposure in comparison to standard MSCT protocols for children. The result in this study, before study, the average values of CTDIvol were 22.4-28.2mGy and after study, the were 10.4-23.2 mGy with the acceptable image quality. Conclusion: Dose reduction in pediatric brain CT is possible on our system without a deterioration of diagnostic image quality. This reduced dose technique is especially useful in follow-up case and in those conditions in which CT is used as an ancillary tool. The relationship between AP diameter representing body weight and the appropriate mAs value was determined through a phantom study. For pediatric brain CT, the appropriate mAs values can be objectively determined by a simple measure of AP diameter (skull basal ganglia) in axial plane.