The motivation to reproject gated blood pool SPECT data as planar data

In the current issue of the Journal, Wells et al, describe the results of deriving left ventricular (LV) ejection fraction (EF) values from planar radionuclide ventriculography (RNV) images that are not conventionally obtained via best septal view planar imaging, but rather by reprojecting gated blood pool SPECT data as planar RNV images. 1 This is a topic of relevance for laboratories having SPECT-only cameras which are requested to perform gated blood pool scans. The most common reason for requesting RNV studies is to monitor possible cardiotoxicity caused by chemotherapeutic agents, such as the use of anthracycline-based chemotherapy to treat breast carcinoma in adults 2 and to treat Hodgkin disease (HD) in children. 3 Serial RNV studies of EF during therapy provide a sufficient means of avoiding drug-induced congestive heart failure. 4 Some published guidelines for evaluating anthracycline cardiotoxicity in children advocate using both echocardiography and planar RNV studies. 5 However, as treatment protocols can extend over several weeks or months, serial evaluations of EF are required, so that in general serial measurement of EF for children is performed by echocardiography, 5 but for adults is performed by planar RNV as it has been considered the best non-invasive EF method. 6 Subjects can be followed for 10 years or more because features of abnormal cardiac function will sometimes appear only many years later after completion of treatment. 7,8 Reproducibility is therefore critical for serial studies of patients undergoing chemotherapy. Changes in EF as small as 10% may be interpreted as clinically significant. These changes are not accompanied by corroborative symptoms and decisions to initiate or withhold potentially life-saving therapy may be based solely on the EF values. So, what is one to do now, in 2013, in a laboratory without a planar gamma camera, but with a solid state detector that can only perform SPECT, not planar, imaging? How does one relate an EF value obtained by this newer technology to serial EF values obtained by the older planar RNV studies acquired with Anger cameras? Planar EFs have long been the desired means of evaluating EFs because of the simplicity of the imaging conditions. Planar RNV imaging also provides diastolic filling parameters, which progressively deteriorate with anthracycline therapy, along with phase histograms and fairly robust visual images that can be used for quality control and to corroborate significant changes in the value of EF. In terms of acquiring images, it is relatively undemanding to identify the angle for the best planar septal LAO view. In terms of processing acquired data,