Cone-beam technique for 64-MDCT of lung: image quality comparison with stepwise (step-and-shoot) technique

The purpose of this study was to use phantom and patient data acquired with 64-MDCT to compare the image quality and characteristics of helical high-resolution CT images obtained with cone-beam reconstruction with those of stepwise high-resolution CT images obtained with fan-beam reconstruction.

We reconstructed helical high-resolution CT images with cone-beam technique and stepwise high-resolution CT images with fan-beam technique. In the phantom study, we measured high-contrast spatial resolution and image noise using a phantom. Streak artifact was evaluated by five radiologists using the phantom. In the clinical phase of the study, two radiologists independently evaluated high-resolution helical and stepwise CT images of the lung fields of 30 patients with diffuse lung disease. Using a 3-point ordinal scale, the radiologists assessed the sharpness of peripheral vessels and interlobular fissures, artifacts, and graininess in the lung fields; overall image quality; and the sharpness of the contour of the left ventricle.

In high-contrast spatial resolution, the contrast curves in each spatial frequency were similar on the helical and stepwise images. In the clinical study, there was no statistically significant difference between helical and stepwise images with respect to sharpness of the contour of the left ventricle, peripheral vessels, or interlobular fissures (p>0.05). With respect to streak artifacts and graininess in the lung fields, helical images received a significantly higher quality grade than did stepwise images (p<0.05).

Our phantom and clinical evaluation showed that the quality of high-resolution CT images of the lung obtained with helical scanning was comparable with the quality of stepwise scans.