as part of their initial workup. These tests help with screening for bleeding or hypercoagulable conditions. Other lab tests, such as a full hypercoagulable state workup or serum drug screening, should be considered based on the clinical situation and factors, such as age of the patient and family history. A fasting lipid panel is also appropriate to thoroughly evaluate the patient's risk for atherosclerotic disease and ischemic events in the future. Other lab tests may be indicated based on the history and presentation; such as obtaining inflammatory markers (erythrocyte sedimentation rate and C-reactive protein) to evaluate for giant cell arteritis (which can mimic a TIA) in those presenting with headaches and monocular blindness. Cardiac rhythm monitoring An electrocardiogram is necessary to rule out abnormal heart rhythms, such as atrial fibrillation, that can predispose patients to clot formation and embolic events. Hospitalized patients should be placed on heart rhythm telemetry, which is a continuous form of monitoring that can detect abnormal heart rhythms. Prolonged heart rhythm monitoring (such as with a Holter monitor or implantable heart monitoring) can be considered to rule out arrhythmias like paroxysmal atrial fibrillation that may lead to clot formation and TIAs, however this should be considered if other causes of TIA have not been found. Imaging According to guidelines from the American Heart Association and American Stroke Association Stroke Council, patients with TIA should have head imaging "within 24 hours of symptom onset, preferably with magnetic resonance imaging, including diffusion sequences". MRI is a better imaging modality for TIA than computed tomography (CT), as it is better able to pick up both new and old ischemic lesions than CT. CT, however, is more widely available and can be used particularly to rule out intracranial hemorrhage. Diffusion sequences can help further localize the area of ischemia and can serve as prognostic indicators. Presence of ischemic lesions on diffusion weighted imaging has been correlated with a higher risk of stroke after a TIA. Vessels in the head and neck may also be evaluated to look for atherosclerotic lesions that may benefit from interventions, such as carotid endarterectomy. The vasculature can be evaluated through the following imaging modalities: magnetic resonance angiography (MRA), CT angiography (CTA), and carotid ultrasonography/transcranial doppler ultrasonography. Carotid ultrasonography is often used to screen for carotid artery stenosis, as it is more readily available, is noninvasive, and does not expose the person being evaluated to radiation.