[Indications for chest CT: retrospective study of cases with normal chest CT]

The usefulness of computed tomography (CT) in thoracic radiology is now well appreciated, and the number of chest CTs has greatly increased. There are, however, many chest CT cases that are completely or almost completely normal. Indications for chest CT should be re-evaluated considering the cost and radiation exposure associated with the examination. Reviewing the reports of 4930 chest CT examinations performed in three hospitals during the period of two years, the author found 620 (12.6%) negative CT examinations. In 312 of the 620, the CT was requested because of "abnormal shadow" on chest radiograph. When the same chest radiographs were re-evaluated by two radiologists, no abnormality was noted in 257 cases (82.4%). CT examinations were considered justified in only 55 cases (17.6%). There was a significant difference in the frequency of normal chest CT examinations between the university hospital and two other hospitals. The causes of false positive interpretation of chest radiographs were analyzed, and it was felt that fundamental knowledge necessary to interpret chest radiographs was lacking. The importance of close cooperation between clinicians and radiologists should be emphasized.