Low-dose multislice CT of the thorax in follow-up of malignant lymphoma and extrapulmonary primary tumors

Our objective was to study the impact of low-dose multislice thoracic CT on image quality and lesion conspicuity in follow-up of patients with malignant lymphoma and extrapulmonary primary tumors. Forty consecutive patients with a history of malignant lymphoma or extrapulmonary malignant primaries who had undergone previous standard-dose thoracic spiral CT (120 kVp, 150 mAs, 8 mm) were subjected to low-dose multislice CT (15 mAs/rotation, 120 kVp, pitch 1.5, 4x2-mm collimation reconstructed to contiguous 8-mm slices. Image quality and lesion conspicuity were classified independently by two readers on a four-point ordinal scale (1=poor, 4=excellent). Mean image quality was significantly lower for low-dose CT, 2.35, than for standard-dose CT, 3.25 (p<0.001); however, all low-dose CT examinations were fully readable, none had to be repeated, and no lesions (including 51 lung lesions and 31 soft tissue lesions) remained undetected. Only in the apical lung did the lowered tube current significantly reduce lesion conspicuity. Even in pulmonary lesions smaller than 10 mm (n=21) lesion conspicuity did not significantly differ between standard and low-dose scans. Low-dose thoracic multislice CT based on a 90% reduction in dose compared with standard-dose techniques was not associated with impaired detection of suspicious lesions and may be useful in follow-up of malignant lymphoma and extrapulmonary tumors.