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

Abstract

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.
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.
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).
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.