Ans. is 'd' i.e., Doppler o Color doppler ultrasonography is the screening method of choice (not simple USG : option a is incorrect),o Carotid angiography is the investigation of choice for diagnosis,o MRI is the investigation of choice for demyelinating disorder, e.g. multiple sclerosis.Investigations in nervous systemo Investigation of choice for white matter disease - MRI (CT is second choice),o Investigation of choice of acoustic neuroma - GD enhanced MRIo Best investigation for all brain tumors - Contrast enhanced MRIo Investigation of choice for meningeal carcinomatosis - Contrast (gadolinium) enhanced MRI.o Investigation of choice for posterior fossa tumor - MRIo Investigation of choice for para meningeal rhabdomyosarcoma - MRIo Investigation of choice for nasopharyngeal angiofibroma - Contrast enhanced CT.o Investigation of choice for hydrocephalus in older patients and for low pressure hydrocephalus - MRI.o Investigation of choice for acute (<48hrs) subarachnoid hemorrhage (SAH) - Non-Contrast CT scan,o Investivation of choice to know the etiology of SAH - Four vessels digital substruction angiography.o Hallmark of SAH - Blood in CSF on lumbar puncture,o Investigation of choice for chronic SAH - MRI.o Primary procedure of choice for evaluating intracranial complications of acute head injury - CT scan,o Best modality for assessing fractures of the skull base, calvarium and facial bone - CT scan,o Investigation of choice for demyelinating disorders MRI.o Investigation of choice for AV malformation and aneurysm - Angiography (MRI angiography or CT angiography),o Investigation of choice for Craniospinal infection - MRIo Investigation of choice for all intrinsic spinal cord lesions; all causes of cord compression - MRI.o Procedure of choice for emergent evaluation of acute intracerebral hemorrhage - CT scan,o Investigation of choice for myelopathy - MRI.o Shape of epidural hematomas on imaging - Biconvex, hyperdense or mixed density.o Shape of acute subdural hematoma on imaging - Crescent-shaped, hyperdense or mixed density ,o Chronic subdural hematoma on imaging - Hypodense.o Most sensitive test for ischaemic stroke - Diffusion weighted (DW) MRI.