Medical Imaging
Magnetic Resonance Imaging (MRI) and other imaging techniques have opened windows on our bodies and brains. Today MRC scientists are pioneering new imaging techniques that allow scrutiny of the tiniest structures to illuminate the origins of health and disease and help the development of new treatments. Sir Keith Peters, President of the Academy of Medical Sciences, has called medical imaging “the most important advance in diagnostics in the twentieth century”.
Until 30 years ago, doctors had to rely on X-rays for showing bones and dense clumps of cells like tumours inside our bodies. Then scientists started using MRI – which makes use of the magnetic properties of cells – to create images of the body. The field took a huge leap forward in 1973 when MRC-funded scientist Sir Peter Mansfield used MRI to produce exquisitely detailed images of soft tissues1. He won the 2003 Nobel Prize in Physiology or Medicine for this work.
The technique enabled doctors for the first time to peer deep inside the body, allowing them to diagnose disease without exposing patients to the trauma of exploratory surgery.
Advances in high speed computing and superconducting magnets have since allowed researchers to build ever more powerful MRI scanners, capable of producing stunningly clear images, making it possible to detect early cancers and subtle damage to tissues including delicate nerve fibres.
The brain in action
MRI’s offspring, functional magnetic resonance imaging (fMRI), which also builds on techniques conceived by Sir Peter, is helping scientists to gain the first real understanding of how the brain functions by enabling them to view the working brain.
Today MRI is used in research centres and hospitals worldwide to diagnose disease and monitor treatment. All major hospitals are equipped with MRI whole-body scanners and more than 22,000 systems in use across the world perform at least 60 million investigations every year. In 2005, MRC-funded researchers at the Institute of Cancer Research showed that MRI can improve breast screening for younger women. Their study revealed that MRI was twice as sensitive as X-ray mammography at detecting breast cancer among under-50s who were at high genetic risk of breast cancer2. MRI is also safer than traditional mammography as it does not use X-rays.
X-ray images with depth
MRC research also played a role in the origin of computed tomography (CT) imaging, also known as ‘CAT scanning’ (computed axial tomography), an ingenious way of using X-rays to take images of parts of the body.
CT scanning builds up three-dimensional images from large numbers of low-dose X-rays transmitted across the body. In a traditional X-ray film, there is no dimension of depth.
The principle of this method stemmed from research by Sir Aaron Klug at the MRC Laboratory of Molecular Biology, who put together ‘slices’ – layered electron microscopy images – to form a detailed picture with depth. Sir Aaron combined conventional electron microscopy with the use of X-rays to enhance the resolution of images of proteins.
Sir Godfrey Hounsfield, an engineer at EMI Central Research Laboratories in Middlesex, and Professor Allan Cormack, a South African born physicist, developed the technology of CT scanning. CT head and body scanners were tested separately in the early 1970s, work which the MRC supported.
Sir Godfrey and Professor Cormack shared the Nobel Prize in Physiology or Medicine in 1979. Then in 1982, Sir Aaron won the Nobel Prize in Chemistry. The development of the CT scanner has had an explosive impact on diagnostic radiology and its principles have been applied to other areas including ultrasound imaging.
Positron imaging
Positron emission tomography, also called PET imaging or a PET scan, is a highly sophisticated scanning technology used to create images of molecular events inside the body. As one of the most important tools in hospital diagnosis, research and drug discovery around the world, it has increased understanding of disease processes and treatment in areas such as movement disorders, stroke, dementia and coronary heart disease.
PET involves the collection of images based on the detection of radiation from the emission of positrons – particles emitted from a short-lived radioactive substance given to a patient by injection or inhalation. The MRC initiated the development of PET 50 years ago by installing the world’s first medical cyclotron, which produces artificially radioactive substances, at Hammersmith Hospital in London.
In 2001, a public-private partnership between the MRC and Amersham BioSciences (now GE Healthcare) established a new company, Hammersmith Imanet, with substantial new funding including money for a new cyclotron. Now, over 1,000 PET scans a year are run there for research purposes. Throughout the rest of the UK there are 10 cyclotrons used in medical projects, with many hundreds around the world producing materials for diagnostic scans and medically-related research. In pre-clinical research, such as that carried out at the MRC Centre for Behavioural and Clinical Neuroscience in Cambridge, PET imaging is used to determine where in the human brain various cognitive operations are carried out. It can also establish how drugs work to produce changes in brain chemistry, and how these affect behaviour.
As a convenient non-invasive technique, PET imaging is increasingly used in MRC phase II clinical trials to assess changes in the body. For example, a scan can reveal how active a patient’s tumour is or track diabetes by measuring the quantity of insulin-producing cells in the pancreas.
References
1. First Specialized Colloque Ampère in Krakow, Poland, September 1973.
2. MARIBS study group (2005). Screening with magnetic resonance imaging and mammography of a UK population at high familial risk of breast cancer: a prospective multicentre cohort study (MARIBS). The Lancet, 365, 1769.
MRC, July 2006