A patient of rheumatoid arthritis presents with progressive quadri-paresis and weakness, Babinsky sign was positive, increased muscle tone of limbs with exaggerated tendon jerks and worsening of gait with no sensory, sphincter involvement. Best initial investigation is-
X-ray of cervical area of neck in flexion and extension
MRI brain
EMG and NCV within 48 hours
Carotid angiography