Chapter 13: Diagnostic tests
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Source: Adapted from Keogh ([114]), Pagana and Pagana ([177]).
Evidence‐based approaches
Rationale
Soft tissue structures (such as the brain, spinal cord, musculoskeletal system, liver and pelvic structures) are particularly well demonstrated using MRI. Although MRI is often targeted to particular areas of the body, it is also possible to scan the whole body with scan times ranging from 20 to 60 minutes. MRI is increasingly being used as a tool in radiotherapy treatment planning (Prestwich et al. [196]) and can be used to guide interventional procedures, for example breast biopsies (O'Flynn et al. [172], Pagana and Pagana [177]). MRI does not use ionizing radiation and can therefore be used for repeated examinations, which is useful for the evaluation of radiotherapy and chemotherapy response during cancer treatments. The magnetic field is always present so strict safety procedures are necessary to protect staff and patients (Pagana and Pagana [177]; Shellock and Spinazzi [227]).
An MRI may be used instead of a computed tomography (CT) scan as the contrast between normal and pathological tissue is better and there are no obscuring bone artefacts. Blood vessels also appear dark from the fast‐moving blood; therefore, this results in a natural contrast between the blood vessels and the surrounding tissues (Pagana and Pagana [177]).
Indications
There are various indications for an MRI, which include:
- scanning of the brain to assess for stroke, tumour or meningeal disease
- evaluation of the central nervous system, neck, back and heart
- evaluation of the back, bones, soft tissues and joints
- spinal pathology, including intervertebral disc pathology, tumour, infarction, spinal dysraphism, infection and degenerative diseases (spinal pathology is particularly well demonstrated)
- differentiation and characterization of benign versus malignant pathology in the liver
- imaging of the breast (MRI is particularly sensitive for this area)
- assessment of pelvic malignancy and pelvic anatomy (MRI is the gold standard for this area) (Keogh [114], Pagana and Pagana [177], Royal College of Radiologists [212]).
MRI scans (Table 13.13) can also be used to identify and quantify various conditions.
Table 13.13 Common MRI scans
| Scan area | Potential findings |
|---|---|
| MRI of brain and meninges |
Benign and malignant neoplasms
Brain oedema
Intracranial haemorrhage |
| Magnetic resonance spectroscopy (MRS) |
Enhanced image of high‐grade malignancy
Chemical abnormalities of the brain related to the human immunodeficiency virus (HIV) |
| Magnetic resonance angiography (MRA) |
Possible arterial blockages
Cardiac abnormalities
Aortic aneurysm |
| MRI of breast |
Localized staging of breast cancer
Surgical staging
Fracture of a breast implant |
| MRI of heart |
Evaluation of pericardial disease
Congenital heart disease |
| Magnetic resonance cholangiopancreatography (MRCP) |
Images of pancreas, pancreatic duct, gall bladder and biliary tree
Pancreatobiliary stones, infection and tumours
Underlying cause of pancreatitis |
| MRI of liver | Liver and biliary tumours |
| Magnetic resonance enterography (MRE) | Inflammatory bowel disease |
| MRI of cervical or lumbar spine | Herniated disc |
Contraindications
Patients with non‐MRI‐compatible implanted devices, such as cardiac pacemakers and cochlear implants, must not be scanned. Other implanted devices, for example stents, must be confirmed as MRI‐safe prior to scanning. Other contraindications are confused or agitated patients and patients weighing more than 140 kg, unless specified by the manufacturer. If a patient is claustrophobic and an enclosed scanner is used, a medical review is required and antianxiety medications may be prescribed (Pagana and Pagana [177]).
Magnetic resonance imaging tends not to be used for acute trauma, for which CT is usually the preferred imaging modality. Nor is it generally used for primary whole‐body staging of malignancies, although a role for whole‐body MRI is increasingly being proposed in some areas for non‐oncological and oncological diagnostic purposes (Lambregts et al. [122], Lin et al. [125]).
