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.

Ga-67 scintigraphic imaging: role of combined optimized energy photopeaks and scatter correction in improving lesion detectability.

BACKGROUND: The detection of lymphoma in gallium imaging is largely affected by image quality as Ga-67 emits three different energies with the highest contributing to septal penetration and image noise. Therefore, determining an optimal imaging protocol is crucial in the diagnosis and staging of lymphoma. The aim of this study was to further investigate the effect of using two energy windows rather than three (in improving signal-to-noise ratio, contrast, and resolution). In addition, application of the triple-energy-window (TEW) scatter correction method and its influence on lesion detectability have also been studied with emphasis placed on minimum detectable lesion and contrast. METHODS: An anthropomorphic torso phantom with chest lesion of different sizes and locations was used. Static planar and single-photon emission computed tomographic images for various lesion sizes and contrasts were acquired using the two different acquisition protocols. Contrast, resolution, and image noise were determined by the lesion-to-background ratio, full width at half maximum, and uniformity measurements, respectively. The TEW scatter compensation method was applied on two peaks-acquired images using two subwindows. RESULTS: Significant improvement (32%) in contrast was found in images acquired with two photopeaks in both planar and single-photon emission computed tomography (P<0.05). Observers' performance was significantly in favor of two photopeaks (P=0.003). The minimum detectable lesion was found to be 7 mm with an object ratio of 5 : 1 in two peaks images. This lesion, however, was not detectable in three photopeaks. Lesion detectability was significantly improved with the TEW scatter compensation method (P<0.01). CONCLUSION: Images acquired using two peaks were found to be superior to those normally used in clinical practice (i.e. three energies). The TEW scatter compensation method was found to be useful in improving Ga-67 image quality and lesion detectability. Thus, it is advised to reconsider using two photopeaks in gallium imaging with TEW scatter correction.