You are answering a USMLE-style medical question. Question: A 75-year-old woman presents to the emergency department with 30 minutes of slurred speech and arm weakness. On the drive over to the hospital, her symptoms have resolved completely. The patient has a past medical history of hypertension, atrial fibrillation, diabetes, morbid obesity, gout, and vascular claudication. Her temperature is 99.0°F (37.2°C), blood pressure is 184/111 mmHg, pulse is 88/min, respirations are 15/min, and oxygen saturation is 98% on room air. Physical exam reveals cranial nerves II-XII as grossly intact with normal strength and sensation in the patient's upper and lower extremities. The patient's memory is intact and her speech seems normal and fluent. Her gait is stable with no ataxia. An initial head CT demonstrates diffuse atrophy which is consistent with previous head CT scans. Which of the following is the best next step in management? Options: A) CT angiogram B) Echocardiogram C) Heparin D) MRI Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.