Helical computed tomography at 1.5:1 pitch reconstructed at 15-mm and 7-mm intervals for examination of patients with suspected metastatic disease.
OBJECTIVE
To document the need for overlapped reconstruction when using helical computed tomography (CT) software that reconstructs 10-mm-collimation, 1.5:1-pitch images at 15-mm intervals in follow-up examination of patients with suspected metastatic disease.


METHODS
Forty consecutive patients with known or suspected metastatic disease 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 prospectively reconstructed at 15-mm intervals and the other retrospectively reconstructed at 7-mm intervals, were independently reviewed by three radiologists, and the number, size and location of lesions were documented. 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 multivariate analysis of variance with repeated measures.


RESULTS
Images reconstructed at 7-mm intervals revealed a total of 436 lesions, 127 (41%) more than were revealed by images reconstructed at 15-mm intervals. The number of lesions less than 1 cm in diameter that were visible in the two sets of images was significantly different (p = 0.018). However, there was no significant difference between the two sets of images in terms of lesion location.


CONCLUSIONS
Metastatic lesions may be missed by helical CT at 1.5:1 pitch if overlapped reconstruction is not performed.
Department of Radiology, Loyola University Medical Center, Maywood, Ill 60153, USA.
M C
MC
Olson
H V
HV
Posniak
T C
TC
Demos
K L
KL
Pierce
T L
TL
Lawson
D000008:Abdominal Neoplasms / Q000000981:diagnostic imaging / Q000556:secondary; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001943:Breast Neoplasms / Q000473:pathology; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008113:Liver Neoplasms / Q000000981:diagnostic imaging / Q000556:secondary; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D009362:Neoplasm Metastasis / Q000000981:diagnostic imaging*; D010386:Pelvic Neoplasms / Q000000981:diagnostic imaging / Q000556:secondary; D011446:Prospective Studies; D011856:Radiographic Image Enhancement / Q000379:methods*; D013736:Testicular Neoplasms / Q000473:pathology; D013899:Thoracic Neoplasms / Q000000981:diagnostic imaging / Q000556:secondary; D014057:Tomography, X-Ray Computed / Q000379:methods*