Nuclear Cardiology: Nuclear Cardiology:

Chapter 17 / Quality Assurance 257Fig. 17-3. Daily floods of a triple-head camera. The center field of view (CFOV)is marked by the red-lined rectangle in the center of the useable field of view(UFOV). The small circles and squares indicate pixels used for uniformitycalculations. Head 1 has marked nonuniformity. Head 2 has minor nonuniformity.Head 3 shows good uniformity. For Head 1 integral uniformity of theUFOV is 13.3% and that of the CFOV is 9.7%. Both should be less than 5%. Thevendor of this camera recommends that the calculation of the integral uniformityis used rather than of differential uniformity. For Head 2 UFOV and CFOVuniformity is marginal at 5.53% and 5.37%. The area of nonuniformity canclearly be appreciated in the upper middle-half of the UFOV. Gamma cameraservice should be called to correct the problem before a patient can be imagedwith this camera.tions. A high-count uniformity flood should be done for each type ofcollimator used and for each isotope commonly used in the laboratory.However, it should be noted that on some older systems (over 10 yr old),only one high-count uniformity flood is capable of being stored. In thesecases, by necessity, only one uniformity flood is applied to the differentisotopes acquired. While this is not ideal, storing one uniformity floodis an inherent limitation of the older imaging systems. Cameras under10 yr of age usually require a separate high-count uniformity flood foreach isotope. Check with the manufacturer for details.High-count uniformity floods can be done extrinsically or intrinsicallysimilar to the daily floods. It is usually recommended acquiringextrinsic floods in order to correct for irregularities of the collimator.