Pediatric cardiovascular CT angiography: Radiation dose reduction using automatic anatomic tube current modulation

OBJECTIVE. The purpose of this study was to assess the effect of weight-based scanning protocols and automatic tube current modulation on the tube current - time product and image quality at pediatric cardiovascular 64-MDCT angiography. MATERIALS AND METHODS. Our pediatric cardiovascular 64-MDCT protocols use a weight-based algorithm to determine nominal tube voltage settings with 80, 100, and 120 kV. Automatic tube current modulation was used for each case. The mAs, volume CT dose index (CTDIvol), and dose - length product (DLP) values were recorded and the effective dose calculated. On the basis of the selected nominal tube current, the dose values that would have been delivered without tube current modulation were also calculated. Scans were compared with 16-MDCT using 120 kVp and 120 mAs. Two radiologists independently rated image quality on a 5-point scale. Image noise was objectively measured within four different regions of interest. Findings at CT were clinically correlated with results of cardiac sonography, angiography, or surgery. RESULTS. Thirty-eight 64-MDCT and 30 16-MDCT scans were evaluated. Mean diagnostic quality for 64-MDCT was rated at 3.6 +/- 0.4 and mean image noise was 8.9 +/- 4.5 H. Results with 16-MDCT were not significantly different: diagnostic quality ( 3.6 +/- 0.4; p = 0.97) and image noise ( 9.1 +/- 2.8 H; p = 0.31). Scanning with automatic tube current modulation significantly ( p < 0.05) reduced the tube current time - product compared with scanning without automatic tube current modulation (-57.8% / 54.1 / 128 mAs) or with 16-MDCT (-47.9% / 54.1 / 104.37 mAs), respectively. The mAs values were significantly ( p < 0.05) lower for 80 kVp than for 100 or 120 kVp scans, but image quality and image noise were not significantly (p = 0.24) different. Agreement between MDCT and clinical findings was excellent. CONCLUSION. Under simulated conditions, automatic tube current modulation combined with low tube voltage settings significantly reduced radiation exposure and thus appears preferable in pediatric cardiovascular 64-MDCT.