Indications for performing spiral CT angiography:
(1) nondiagnostic ventilation-perfusion scan (not normal and not high probability)
(2) high clinical suspicion for PE and ventilation-perfusion scan normal or near normal
(3) abnormalities are present on chest radiograph or in clinical history that indicate a high probability that the ventilation-perfusion scan will be nondiagnostic
(4) suspect that the scan may positively identify an alternative diagnosis to explain all of the clinical findings
Conditions having a high risk for nondiagnostic ventilation-perfusion scan:
(1) COPD
(2) any significant cardiopulmonary disease
Spiral CT angiography would not be indicated for a patient with a ventilation-perfusion scan that is highly probable for PE.
Limitations of spiral CT angiography:
• The scan may be insensitive (fail to detect) peripheral emboli in subsegmental blood vessels.
• A negative study currently is insufficient to exclude the diagnosis of pulmonary embolism although this may change as the technology evolves.
