Final answer:
The first step imaging for suspected stroke is usually Computed tomography (CT) scan. Magnetic resonance imaging (MRI) is also commonly used in stroke diagnosis, but it is not the first step.
Step-by-step explanation:
The first step imaging for suspected stroke is usually Computed tomography (CT) scan. This technique uses x-rays to produce detailed images of the brain. CT scans are effective in identifying bleeding or blood clots in the brain, which can help in diagnosing a stroke.
Magnetic resonance imaging (MRI) is also commonly used in stroke diagnosis, but it is not the first step. Positron emission tomography (PET) scan and ultrasound are not typically used as first-line imaging modalities for suspected stroke.