Tube current modulation feature improves quality at price of higher radiation dose

X-ray tube current modulation, a popular feature available on newer multislice CT scanners, improves image quality but may result in a higher radiation dose, according to a report at the Stanford MDCT meeting on Wednesday.

Tube current modulation, also called automatic exposure control, is an optional or standard feature that adjusts the mAs depending on the part of the body being imaged and the size of the patient. With this feature, highly attenuating anatomic parts and larger patients receive a higher dose. Conversely, smaller patients such as children get a smaller dose.

Use of tube current modulation was analyzed in a study of 55 consecutive oncology patients. The patients had undergone contrast-enhanced MSCT with the tube current modulation feature on the z-axis, said presenter Dr. Vassilios Raptopoulos, a professor of radiology at Harvard Medical School.

The researchers assessed dose and quality or signal-to-noise ratio in the celiac trunk, left renal vein, iliac crest, and acetabulum roof. They found that image quality/SNR was much improved over a fixed level dose. Use of the feature also resulted, however, in a significantly higher radiation dose, Raptopoulos said.

The results suggest that other factors need to be considered with respect to tube current modulation. If an operator reduces the noise level to improve image quality, the modulation feature automatically increases the current (within operator-selected limits) to allow for improvement in noise. But as tube current rises, so does radiation dose.

Adjustment of noise levels is currently not standardized, and this study indicates further research is necessary.