[Chest examination protocol with a reduced dose using a multi-slice spiral CT]

Comparison of multi-slice computed tomography (MSCT) for examination of the chest using two protocols differing in tube voltage (kV) and effective tube current (mAs), as to image quality, diagnostic quality and radiation dose.

Re-staging examinations of 20 patients with bronchial carcinoma on a MSCT (Somatom Volume Zoom, Siemens AG, Forchheim) with 140 kV/100 mAseff and again after an average interval of 4.5 months, a second examination using 120 kV/80 mAseff, employing identical detector width (4 x 2.5 mm), slice, pitch, increment, kernel and selecting the same use or non-use of contrast medium. Image quality, delineation of mediastinal and pulmonary anatomy and pathology, and frequency of artifacts were evaluated by two radiologists and the effective radiation doses were calculated.

Subjective image quality was good to very good for both protocols, and no significant differences were found for visualizing anatomic and pathologic structures in mediastinum and lung. Only the region surrounded by the shoulder girdle showed significantly more artifacts with 120 kV/80 mAsff, but without loss of diagnostic quality. The effective doses were 8 mSv (women) and 6 mSv (men) for 140 kV/100 mAseff versus 4.3 mSv and 3.3 mSv for 120 kV/80 mAseff.

In view of the equal diagnostic quality of both images, CT of the chest should be obtained with 120 kV and 80 mAseff rather than with 140 kV/100 mAseff, regardless of the slightly lower aesthetic quality of the former. This will keep the radiation dose as low as possible. Follow-up examinations should be obtained with even further dose reduction (low dose CT).