Importance of the choice of the collimator for the detection ofsmall lesions in scintimammography: a phantom study

Abstract

99mTc methoxyisobutylisonitrile planar scintimammography (SMM) is mostly performedusing low-energy high-resolution (LEHR) parallel collimators. We studiedwhether using a different collimator could improve the detection of small(<1.5 cm) lesions for which SMM sensitivity is poor. Thirty fourbreast phantom configurations were considered, either with hot spheressimulating lesions or without any spheres. For each configuration, fourplanar acquisitions were performed using LEHR, low-energy ultrahigh-resolution (LEUHR), high-resolution fan-beam (HRFB) and ultrahigh-resolution fan-beam (UHRFB) collimators. Images corresponding to the20% and 10% energy windows and to the Jaszczak subtraction werecalculated. A database including 156 borderline images was derived. Aftertraining, 10 observers scored the images for the presence of a sphere. Theperformances in sphere detection were studied using receiver operatingcharacteristic (ROC) analysis. For all types of image, the area under theROC curve was highest with the UHRFB collimator and lowest with either theLEUHR or the HRFB collimator. For the 10% energy window imagesconventionally used in SMM, the detection sensitivities averaged 91%,73%, 60% and 55% for the UHRFB, LEHR, HRFB and LEUHR collimatorsrespectively, for the same specificity of 64%. We conclude that detectionof small tumours in planar SMM might be significantly improved by using aUHRFB collimator instead of an LEHR collimator.