Spiral (also termed helical) CT angiography is indicated in a patient being evaluated for pulmonary embolus (PE) when certain conditions are present.


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.


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