When evaluating possible cases of pulmonary embolism, we can no longer carry out a simply probabilistic analysis as indicated by the different stages of the research work known as PIOPED (Prospective Investigation of Pulmonary Embolism) where the final report was based on different probability levels of PE (Thrombotic Pulmonary Embolism). Thanks to the techniques of SPECT and SPECT/CT of pulmonary ventilation and perfusion together with the mathematical analyzes of these volumetric images, a quantitative value of the extension and severity of the PE can be given, which allows reporting in a trinary way as positive, negative or inconclusive.