Whole body magnetic resonance imaging

When Lauterbur and Damadian described the application of magnetic resonance imaging (MRI) as a clinical imaging tool in the early 1970s the popular belief was that the technique would become the ultimate screening tool for the whole body.¹,² However, similar to other modalities limited by cost, acquisition times, availability, and artefact produced by motion, it evolved as a technique to image stationary body parts. Supported by technical developments in the past decade, improved excitatory pulse sequences, and faster methods of localising derived signal, and by increasing awareness of the hazards of radiation imposed by traditional techniques, the ability to use MRI as a rapid imaging tool for the whole body has now been revisited.^3-11 Reduced acquisition times have been mirrored by a logical reduction in acquisition costs, and the recent development of the moving MRI table top has facilitated the clinical introduction of this technique as a practical diagnostic tool.³

Oncological applications

The principal application of whole body MRI is in detecting skeletal metastases as an alternative to skeletal scintigraphy.^3-6 In contrast to scintigraphy, where localisation of tumour deposits is indirect and requires tumour induced activity in osteoblasts, the abundance of protons in the matrix of the tumour allows direct visualisation at MRI. Regional MRI has been shown to be more sensitive than skeletal scintigraphy in the detection of skeletal metastases. More recent studies comparing whole body MRI with scintigraphy have reproduced these results, and again MRI has been found to be at least as effective as scintigraphy (fig 1 and fig 2).^3-5 Whole body MRI tends to better detect lesions in the spine and pelvis. In one study authors evaluating the use of whole body MRI as an alternative to bone scan reported finding metastases in 57 of 175 sites in 25 patients compared with 43 of 175 sites in the same 25 patients at scintigraphy (P < 0.001).⁴ In a more recent study whole body MRI showed 53 of 60 metastases identified at bone scintigraphy. Although lesions in the ribs and skull were missed at magnetic resonance imaging, additional bone metastases were identified when whole body MRI was used in the spine, pelvis, and femur.⁵

Fig 1.

Whole body MRI shows multiple bone infarcts in a patient with sickle cell disease

Fig 2.

Whole body MR images (see bmj.com for full image) show a soft tissue sarcoma over the right shoulder at presentation (left), with axillary node, left neck, and pleural disease at 3 month follow up

In addition to improving detection of skeletal metastases, whole body MRI may allow simultaneous evaluation of soft tissue organs and in so doing facilitate an overview of total tumour burden in an affected patient. In effect, rather than multimodality staging integrating skeletal scintigraphy with computed tomography of the chest, abdomen, and pelvis at the expense of radiation dose, a single whole body MRI scan may facilitate assessment of total tumour burden, particularly in patients whose tumours spread preferentially to brain, bone, and liver, such as breast and lung tumours. In this setting, tumour staging is done without exposing the patient to radiation. In a preliminary study of 17 patients with breast carcinoma, whole body MRI allowed detection of skeletal metastases in 11, liver metastases in five, and intracranial metastases in three patients. Interestingly, contrast enhanced computed tomography identified liver metastases in only three of the 17 patients.⁷

Of the patients who present with skeletal metastatic disease 15% have no known primary tumour.⁸ In these patients, despite an extensive search integrating serological tests, endoscopy, and imaging, a primary tumour is likely to be found in only one in five patients at a mean cost of $16 000 (£7000; €12 000).⁸ As an alternative, total morphological assessment of the body, as afforded by whole body MRI, may allow the detection of a primary tumour as often as the other described, costly approaches. In a preliminary study using whole body MRI in this role, primary tumours were identified in the thyroid, prostate, and lung in patients presenting with skeletal metastases predominantly in the spine.⁸ Similar preliminary studies have proposed a role for positron emission tomography scanning in the same group of patients, to help localise the primary tumour.

In the uncommon event of a neoplasm developing in a pregnant woman, staging information can be gained from a scan obtained by whole body MRI without the ionising risk to the fetus that is incurred by both traditional approaches and positron emission tomography.³

Non-oncological applications

A worldwide fall in autopsies has prompted a search for a minimally invasive alternative. Attempting to provide an acceptable alternative, whole body MRI has been shown to be effective in the gross assessment of the corpse, helping to identify sites suitable for percutaneous biopsy, particularly in immunocompromised hosts.⁹ Whole body MRI has been similarly successful in whole body fat measurements and body composition research, and more recently as a primary diagnostic tool in patients with polymyositis.¹⁰,¹¹ The advent of molecular imaging, fusing the specificity of molecular technology with the spatial resolution of imaging, is likely to herald many new scanning applications for whole body sequences.¹²