Simulation of the stripe sign in a scintigraphic model of the lungs.

Using a virtual model of the lungs, we investigated the nature of the 'stripe sign' which is sometimes encountered in pulmonary scintigraphy. A model of the segmental anatomy of the lungs was developed from a number of sources and counts generated within the phantom by Monte-Carlo simulation of photon emission. Multiple segmental and subsegmental defects were created in both lungs and submitted for blinded reporting of the 'stripe sign'. Images were resubmitted for reporting with the contralateral lung removed. The stripe sign was reported in 32 of the 117 studies performed. Nearly half of these were present in defects involving approximately 25% of a segment and the sign was most commonly seen in the lateral projection. Removal of activity from the contralateral lung abolished the sign in only 2 of 32 cases. We conclude that shine through of activity from the contralateral lung is a mechanism rarely responsible for the stripe sign. Most occurrences of the sign are due to interposition of activity from unaffected areas of the same lung between the defect and the periphery of the lung. Orientation of the segments, particularly in the lung bases, accounts for the lateral projection being the most common view in which the sign is present.