Axial or Helical? CT imaging of the thorax for dyspnoea patients with free-breathing using 16 cm wide-detector CT.

AIM To compare image quality and radiation dose between fast-helical mode (FHM) and two-axial mode (TAM) in chest computed tomography (CT) with 16 cm wide-detector for emergency patients with dyspnoea. MATERIALS AND METHODS Ninety-six emergency chest CT patients who cannot comply with breathing instructions were prospectively divided randomly into two groups: the FHM group (n=48, helical scan with 80 mm collimation and pitch 0.992:1), the TAM group (n=48, two axial scans with 160 mm collimation). Both groups used 0.28 seconds rotation speed and automatic tube current modulation. All scans were performed in free breathing. CT value, image noise, and signal-to-noise ratio (SNR) were measured on the descending thoracic aorta, lung parenchyma, and paraspinal muscle at the carina level. Two radiologists assessed images for subjective image quality, motion artefacts and diagnostic confidence. The volume CT dose index and dose–length product (DLP) were evaluated and effective dose (ED) was calculated. RESULTS The TAM group required less exposure time than the FHM group (0.56 versus 1.14 seconds, p 0.05). CONCLUSIONS TAM with 16 cm detector coverage further reduces the exposure time in chest CT for dyspnoea patients and ensures good image quality with 24% radiation dose reduction, compared with fast-helical chest CT with 80 mm collimation.