HELICAL COMPUTED-TOMOGRAPHY AT 1.5 1 PITCH RECONSTRUCTED AT 15-MM AND7-MM INTERVALS FOR EXAMINATION OF PATIENTS WITH SUSPECTED METASTATIC DISEASE/

OBJECTIVE: To document the need for overlapped reconstruction when usi ng helical computed tomography (CT) software that reconstructs 10-mm-c ollimation, 1.5:1-pitch images at 15-mm intervals in follow-up examina tion of patients with suspected metastatic disease. PATIENTS AND METHO DS: Forty consecutive patients with known or suspected metastatic dise ase were examined with helical CT at 10-mm collimation and 1.5:1 pitch . The studies were examinations of the chest, abdomen and pelvis; the chest and abdomen; or the abdomen and pelvis. Two image sets, one pros pectively reconstructed at 15-mm intervals and the other retrospective ly reconstructed at 7-mm intervals, were independently reviewed by thr ee radiologists, and the number, size and location of lesions were doc umented. Differences in interpretation were resolved by consensus. The lesions detected on the two sets of images were classified according to lesion size and location, and the results were analysed by multivar iate analysis of variance with repeated measures. RESULTS: Images reco nstructed at 7-mm intervals revealed a total of 436 lesions, 127 (41%) more than were revealed by images reconstructed at 15-mm intervals, T he number of lesions less than 1 cm in diameter that were visible in t he two sets of images was significantly different (p = 0.018). However , there was no significant difference between the two sets of images i n terms of lesion location. CONCLUSION: Metastatic lesions may be miss ed by helical CT at 1.5:1 pitch if overlapped reconstruction is not pe rformed.