Low-dose spiral CT: applicability to paediatric chest imaging

Spiral CT of the chest is an imaging technique with unequivocal indications and proven higher sensitivity and specificity than conventional chest X-rays. However, particularly in children, attempts should be made to reduce radiation exposure to a minimum. OBJECTIVE. To evaluate whether a low-dose technique in spiral CT scanning results in adequate diagnostic information.

In a prospective study, 27 children (range 3 weeks to 14 years, mean 7 years) underwent a low-dose CT examination of the chest for various indications. The tube energy was 12.5 mAs (n = 5), 25 mAs (n = 17), 50 mAs (n = 3), or 75 mAs (n = 2) per slice. Two radiologists evaluated, in consensus, the CT scans with respect to their diagnostic value and comparison was made with 20 standard-dose chest CT examinations of adults (175 mAs per slice, mean age 56 years) with respect to technical image quality (noise and artefacts). In a second part of the study, dose measurements were carried out by means of exposing thermoluminescent dosimeters attached to a water/air phantom simulating a child's chest.

All low-dose CT scans were of diagnostic image quality and no additional studies were necessary. The average image noise was significantly higher than in standard-dose CT examinations (SD 39.5 compared with 12.5 for unenhanced soft tissue, P < 0.01), but did not hinder accurate diagnosis. Artefacts were exclusively due to patient motion. Radiation exposure per slice was approx. 4 mGy at 25 mAs and 34 mGy at 250 mAs, regardless of slice thickness.

For all indications in paediatric CT scanning of the chest, low-dose technique provides adequate image quality without loss of diagnostic information. The radiation exposure is approximately 5-20 % of a standard-dose CT.