The MRI scan is very noisy, the length of the scan will vary depending on the area of the body to be examined; times can range from 20 minutes to two hours. You will be asked to lie on a couch and keep as still as possible; you will be given earplugs and headphones to protect your hearing. Radiographers will communicate with you over a two-way intercom in between scan sequences. An emergency call button will also be provided.  
During an MRI scan it is sometimes necessary to give you an injection gadolinium-based contrast (a type of dye that highlights structures in the body) to provide more detail and information for your referring clinician. This contrast injection will be administered by a radiographer through a small plastic tube , usually placed in a vein in your arm.
Sources of information:
https://www.nhs.uk/
https://www.uclh.nhs.uk/
https://www.uclh.nhs.uk/our-services/find-service/neurology-and-neurosurgery/neuroradiology/magnetic-resonance-imaging-mri
Secure Scanners Limited is working with over 200 hospitals and over 100 community based medical centers, GP surgeries and health clinics, providing fast access to a wide range of diagnostic and healthcare services for patients across the UK.