Comparison of image quality and radiation dose of different pulmonary CTA protocols on a 128-slice CT: high-pitch dual source CT, dual energy CT and conventional spiral CT.

OBJECTIVES: To compare image quality and radiation dose of high-pitch dual-source computed tomography (DSCT), dual energy CT (DECT) and conventional single-source spiral CT (SCT) for pulmonary CT angiography (CTA) on a 128-slice CT system.

METHODS: Pulmonary CTA was performed with five protocols: high-pitch DSCT (100 kV), high-pitch DSCT (120 kV), DECT (100/140 kV), SCT (100 kV), and SCT (120 kV). For each protocol, 30 sex, age, and body-mass-index (mean 25.3 kg/m(2)) matched patients were identified. Retrospectively, two observers subjectively assessed image quality, measured CT attenuation (HU±SD) at seven central and peripheral levels, and calculated signal-to-noise-ratio (SNR) and contrast-to-noise-ratio (CNR). Radiation exposure parameters (CTDIvol and DLP) were compared.

RESULTS: Subjective image quality was rated good to excellent in >92% (>138/150) with an interobserver agreement of 91.4%. The five protocols did not significantly differ in image quality, neither by subjective, nor by objective measures (SNR, CNR). By contrast, radiation exposure differed between protocols: significant lower radiation was achieved by using high-pitch DSCT at 100 kV (p < 0.01 in all). Radiation exposure of DECT was in between SCT at 100 kV and 120 kV.

CONCLUSIONS: SCT, high-pitch DSCT, and DECT protocols techniques result in similar subjective and objective image quality, but radiation exposure was significantly lower with high-pitch DSCT at 100 kV.

KEY POINTS: New CT protocols show promising results in pulmonary embolism assessment. High-pitch dual-source CT (DSCT) at 100 kV provides radiation dose savings for pulmonary CTA. High-pitch DSCT at 100 kV maintains diagnostic image quality for pulmonary CTA. Dual energy CT uses more radiation but also provides lung perfusion evaluation. Whether the additional perfusion data is worth the extra radiation remains undetermined.