Nuclear Cardiology: Nuclear Cardiology:

76 Nuclear Cardiology, The BasicsTable 7-2Processing Steps for QuantificationBackground subtractionImage alignmentNormalizing imagesQuantificationNormal databaseArchivingRegion of interest (ROI), 4 pixels from heart,interpolative background algorithm applied.Slight rotation of images to ensure stress and restsegments correspond accurately.Scaling of images so the heart is visualizedoptimally.Plot of image count density.Allows extent and severity of defect to becalculated.Raw and processed data.PROCESSING STEPS FOR QUANTIFICATIONTable 7-2 lists the processing steps for quantification. The followingsubsections contain comments on the individual items.Background SubtractionOn planar myocardial projection images there is substantial foregroundand background activity projected over the images of the heart.Quantification of regional myocardial uptake cannot be performedwithout removal of the extracardiac activity. For this purpose “interpolativebackground correction” was developed (3). A background imageis created on the basis of sampling in multiple areas immediately adjacentto the heart and interpolating this information into a new backgroundimage. This background image is subsequently subtracted fromthe raw projection images. The final result of interpolative backgroundcorrection is a planar image without substantial background that allowsfor quantitative comparison with normal image files and radiotracerwashout. (See Figs. 7-3 and 7-4.)Image AlignmentFor paired quantification of images, it may be necessary to rotate therest or redistribution image slightly in order to match appropriately withthe stress image. Rotation should generally not exceed 20°. (See Fig. 7-5.)Normalizing ImagesRescaling of the images may be necessary when noncardiac activityis more intense than in the left ventricle. (See Fig. 7-6.)