Evaluation of diagnostic imaging tests: diagnostic probability estimation.

In the evaluation of a diagnostic imaging test for the diagnosis of a particular illness in a particular category of patients, the test should be construed as leading to a test result in the sense of a set of descriptive readings from the image(s), not interpretation of these; and in the evaluation of the test, therefore, the first challenge is the translation of each test result (set of readings) into the corresponding probability that the illness is present. This interpretive translation should not be subjective, nor should it be based on an objective algorithm founded on clinical judgments. Instead, a suitable diagnostic probability function (of the elements in the test result) should be derived empirically by logistic regression analysis of suitable data. We illustrate this alternative outlook by reanalysis of the data from the Prospective Investigation of Pulmonary Embolism Diagnosis.