Dye for myelography is injected in?

Ans. c (Subarachnoid space). (Ref. Clark, Positioning in Radiography, 10th ed., 588)MYELOGRAPHY# Myelography is the radiographic investigation of the spinal canal for the diagnosis of space occupying & obstructive lesions & requires the contrast agent to be injected into the subarchnoid space (which lies between pia mater & the arachnoid mater) usually following a lumbar puncture.# Either a negative contrast agent like air or oxygen is used or more usually a positive non reactive water-soluble preferably non-ionic, organic iodine compound (Iohexol).# Nonionic iodinated compounds have replaced myodil (iophendylate) due to its advantages like freely miscible with CSF, flows along subarachnoid spaces around the nerve roots & is absorbed from subarachnoid space within 48 hours.# They are isotonic with CSF in concentration usually used for lumbar myelography, made upto a volume of 10 cc.# They also have low viscosity and thus a narrow bone needle can be used.# Reactions like headache, nausea seldom last for more than 24 hours.# Arachnoiditis is severe most complication, however with newer contrast, it is extremely uncommon.- Iohexol (omnipaque) is nonionic contrast commonly used today. Iohexol has more evenly distributed OH groups hence has less subarachnoid toxicity.# MRI has replaced myelography and CT myelography.