Which test would be considered safest for a patient suspected of having a stroke whose tPA eligibility is uncertain?

The CT scan is the safest test for a patient suspected of having a stroke when the eligibility for tPA (tissue Plasminogen Activator) is uncertain primarily because it is rapid, widely available, and effective at ruling out intracranial hemorrhage, which is a critical consideration before administering tPA.

In the acute setting of a stroke, time is of the essence, and a CT scan can quickly provide crucial information about the patient's condition. It can differentiate between ischemic strokes, where tPA might be indicated, and hemorrhagic strokes, where such treatment would be contraindicated.

Other options, while they may have specific advantages, present greater risks or require more time. MR diffusion-weighted imaging, although sensitive for detecting ischemic stroke, involves longer acquisition times and the presence of a magnetic field, which can be problematic in emergencies. Ultrasound is useful for assessing carotid arteries but does not provide detailed intracranial information necessary for tPA decision-making. A cerebral angiogram, while helpful in evaluating blood vessels in cases of stroke, is an invasive procedure that carries risks like vessel injury or allergic reactions, making it less suitable in situations where quick and safe assessment is essential.