Differential regional lung uptake analysis of the lung scan as an adjunct to interpretation of pulmonary embolism

OBJECTIVE: Differential regional lung uptake (DRLU) analysis of a lung perfusion scan is used to provide information on diversion of the radiotracer from areas supplied by obstructed pulmonary artery branches to areas with patent vessels, which could assist in the diagnosis of pulmonary embolism (PE), especially the intermediate-probability studies. METHODS: Lung perfusion scans performed over 3 years (n=121) were analyzed using a computer overlay of six regions of interest per lung on the posterior view. DRLU was defined for neighboring region pairs as the ratio of the difference in the average count rate to the sum of the count rate in the region pair for a total of 18 region pairs per study. RESULTS: Comparison of the DRLU for high-probability studies (n=30) with normal scans (n=40) showed significant deviation in a least three region pairs per study. For low-probability scans (n=30), there was no significant deviation from the normal. For the intermediate category (n=21), a subgroup (n=7) showed significant deviation in at least three region pairs, which also had a positive computed tomography pulmonary angiography for PE, and another subgroup (n=14) had deviation in two or fewer region pairs with a negative computed tomography pulmonary angiography. CONCLUSION: Using DRLU analysis, intermediate scans for PE could be redefined as low or high probability, on the basis of the number of region pairs showing deviation of DRLU. This could lead to improved diagnostic performance of the study without recourse to additional maneuvers or specialized equipment and would obviate the need for more tests on the patient.