How Easy is it to Identify the Cricothyroid Membrane in Children? Can Ultrasound Imagine be Used to Aid Identification?

The Investigators aim to determine how easy it is for anaesthetists to identify the Cricothyroid membrane (CTM) in children and infants and whether ultrasound maybe useful in addition. The investigators aim to conduct a randomised single blinded trial to compare methods to detect the CTM. The first group of patients will be randomised to palpation of anatomical landmarks group. Prior to commencing the MRI scan the anaesthetist is timed to identify the CTM and then the trachea using a felt tip pen. A ficidual marker will be placed on the 2 marked areas. The second group of patients will be randomised to receive ultrasound. Prior to commencing the MRI scan the sonographer is timed to identify the CTM and then the trachea using a felt tip pen. A ficidual marker will be placed on the two marked areas.