A 75-year-old right handed lady presents having woken at 7am with new onset speech disturbance and right-sided weakness. She was last seen well before going to bed at 10pm the night before. She has a past medical history of hypertension and hypothyroidism. You complete an ABCDE assessment and an ECG shows an irregularly irregular rhythm at a rate of 75bpm. On examination, right upper and lower limb power is 3/5 and she is unable to name objects. The rest of the examination is unremarkable. Following your assessment, which initial investigation should be carried out?