Whole-Body MRI
Whole body MRI covers the body from the head to the feet, or from the skull base to the mid-thigh, in a single examination of 30 to 60 minutes.
It uses sequences that are fast enough to be stacked from several stations, and it combines anatomical images with diffusion weighted imaging. It has no ionising radiation.
The study uses a 1.5 or 3 tesla scanner with a moving table and a set of surface coils.
The core sequences are coronal T1-weighted and short tau inversion recovery or fat suppressed T2-weighted images, sagittal T1 and T2 images of the spine, and diffusion weighted imaging with a high b value (800 to 1000) in axial slices for each station.
Images are combined into a single data set.
Contrast enhanced sequences, or a dedicated organ study, are added for a particular question. The study can be combined with MR angiography or with a limited set of dedicated sequences for the brain, liver, prostate, breast or joints.
The main clinical uses are staging and response assessment in myeloma, lymphoma and bone metastases, the workup of inflammatory muscle and bone disease in children, and surveillance in inherited cancer syndromes. It is also used for whole body surveillance in private practice, where benefit is not proved.
Myeloma affects about 1 in 10 000 people each year, and bone involvement is the main source of illness.
Whole body MRI detects focal lesions and marrow infiltration in 30 to 50% of patients whose radiographs are normal, with a sensitivity of 90% or more for focal bone lesions, and predicts progression from smouldering to active disease.
In lymphoma and metastatic cancer, diffusion based MRI approaches the accuracy of PET-CT for bone and nodal staging.
Indications.
- Myeloma: staging, smouldering disease, solitary plasmacytoma, and assessment of response.
- Bone metastases from prostate and breast cancer, and response to treatment.
- Lymphoma staging and follow up, especially in children and young adults, where radiation is a concern.
- Inherited cancer predisposition (Li-Fraumeni syndrome, neurofibromatosis, hereditary paraganglioma and multiple endocrine neoplasia): baseline and annual surveillance.
- Chronic non-bacterial osteomyelitis, multifocal bone infection and inflammatory arthritis in children.
- Inflammatory myopathy, muscle dystrophy and fat or muscle replacement (distribution of disease).
- Cancer of unknown primary, when other imaging is not conclusive.
- Systemic sclerosis, vasculitis and large vessel disease (with angiography).
- Fever or pain of unknown origin with suspected multifocal disease.
- Obesity, lipodystrophy and body composition research.
Not for routine screening of well people. Findings are common, mostly benign, and lead to further tests and anxiety.
Contraindications and precautions.
- The usual MRI safety screen. Large metal implants cause local artefact, and some are conditional.
- Claustrophobia and inability to lie still for the duration. Sedation is rarely needed, but younger children may need it.
- Gadolinium (if used): renal precautions apply. A non-contrast study is common.
- Large body size exceeding the bore, or the length of the table, and limits on weight.
- Pregnancy: acceptable without contrast if the clinical need is clear.
- Patients with severe pain at rest may find the long lying time hard.
Preparation and technique.
No fasting is needed. The patient lies supine, feet first or head first, with surface coils over the body, and arms placed at the sides or overhead for lung and arm coverage. A wide bore scanner is useful.
Coronal and sagittal sequences cover the head to the feet in 4 to 6 stations, with overlap. Diffusion images are taken in axial slices with free breathing and fat suppression, and are displayed with inverted grey scale and a calculated high b value. Apparent diffusion coefficient maps provide quantitative values.
Dedicated sequences are added for the brain, spine, liver or other regions of concern. The images are reviewed with maximum intensity projection, multiplanar views and fusion with T1 or T2 images.
