Radiological investigations in neuroanaesthesia and neurocritical care, part 2: magnetic resonance imaging

Abstract

By reading this article, you should be able to:Describe the basic physical principles behind the formation of a magnetic resonance image. Identify the common contraindications to MRI. Discuss some of the more common clinical indications for MRI. Explain with clinical cases and accompanying images the advantages of MRI over CT.After its advent in the late 1970s, MRI has achieved widespread acceptance as an imaging technique that is an alternative to CT and is free from ionising radiation. MRI has other significant advantages over CT, particularly regarding brain imaging. Because of its greater contrast resolution, MRI depicts anatomy in far greater detail than CT, and the range of imaging sequences available allows for greater sensitivity and specificity in identifying pathology. With the increase in the number of MRI examinations performed and the accessibility of images by clinicians via the picture archive and communication system, images are often reviewed before a formal report is issued by a specialist radiologist. Therefore, a basic understanding of the physics behind the creation of a magnetic resonance (MR) image is required to aid in image interpretation by the general clinician. This article also highlights the main indications and contraindications to MRI in the field of neuroscience, and using cases from our institutions, demonstrates the more common pathologies and associated imaging findings. Physics of MRIThe MRI physics is complex, and an in-depth explanation of the various techniques used to create the wide range of sequences available is beyond the scope of this article.Nick Skipper FRCR EDiNR is a consultant neuroradiologist at Brighton and Sussex University Hospitals NHS Trust. He completed a fellowship in adult and paediatric neuroradiology in Sheffield.Mark Igra FRCR EDiNR is a consultant neuroradiologist at Leeds General Infirmary. He completed his neuroradiology fellowship in Sheffield, and has a subspecialty interest in neuro-oncology and spinal intervention.Andrew Davidson FRCA FFICM is a consultant in neuroanaesthesia and neurointensive care at the Royal Hallamshire Hospital, Sheffield. Key pointsMRI provides greater anatomical detail than CT scanning, and the range of sequences available to the radiologist allows for greater detection of pathology.A basic understanding of the physics behind the creation of a magnetic resonance image is useful in facilitating image interpretation. An understanding of MRI safety issues is essential, because strong magnetic fields, radio-frequency pulses, and i.v. contrast agents are used.