Use of automatic tube current modulation with a standardized noise index in young children undergoing chest computed tomography scans with 64-slice multidetector computed tomography

Abstract

Background: The automatic tube current modulation (ATCM) technique is available on multidetector computed tomography (MDCT) scanners, and its dose reduction benefits in clinical applications have been documented primarily in adult patients.

Purpose: To evaluate the use of ATCM to reduce radiation dose while maintaining consistent image quality for young children undergoing 64-slice MDCT chest scans.

Material and Methods: Chest scans (120 kV, small-scan field of view, 5-mm image slice thickness) were performed for 50 consecutive young children (0.2–3 years) using 64-slice volume computed tomography (VCT) with ATCM method and a noise index (NI) of either 8 or 9, depending on the patient's age. The scanner automatically selected the actual tube current based on NI values and patient attenuation as determined by scout scans for the study group. Image quality and volume-weighted CT dose index (CTDI_vol) values (measured with small-scan field of view and 16-cm diameter CTDI phantom) were compared with images from a control group of 50 children acquired earlier using a standard protocol with fixed tube current. Two experienced pediatric radiologists assessed image quality, including resolution, noise, and artifacts, on a five-point scale. Scores greater than or equal to 3 were considered to be clinically acceptable.

Results: The mean image quality score and CTDI_vol for the study and control groups were 3.46 and 2.34±0.71 mGy, and 4.65 and 6.68±0.62 mGy, respectively. While there was a statistically significant decrease in image quality in the study group, all studies had acceptable image quality, and CTDI_vol with ATCM was about 65% lower than that with fixed tube current. The average image noise for the control group was 4.78±0.58, versus 7.53±0.42 and 8.28±0.40 for children under and above 1 year of age, respectively, in the study group. Despite a higher average noise level, the study group with ATCM demonstrated a lower standard deviation of image noise.

Conclusion: The z-axis ATCM method produces consistent image quality for young children undergoing 64-slice MDCT chest scans. With noise levels of NI=8 and 9 at 5-mm image slice thickness, one may obtain clinically acceptable images with significantly reduced radiation dose.