medical imaging devices
Medical imaging has come a long way since Roentgen first stumbled across X-rays at the end of the 19th century. Roentgen’s first published X-ray image, a photographic plate showing the bone structure of his wife’s hand, looks little different from what a patient might receive after a visit to hospital today.
Advances in technology, however, have given health professionals a much wider array of diagnostic tools with which to delve beneath the skin of the human body.
Roentgen would be amazed at how X-rays have been harnessed in computed tomography (CT) devices. Here, an X-ray source and detector spin around the patient to yield three-dimensional images of the body. It has proved spectacularly successful in studying the brain and in assessing injuries to internal organs such as the spleen and liver and to the spine.
Medical imaging has long been a favourite of the committees of the wise and good that decide the annual Nobel prizes. Just over a hundred years after Roentgen received the Nobel Prize for Physics for his discovery of X-rays, medical imaging is again winning plaudits. In the early 1970s, work by Paul Lauterbur and Peter Mansfield led to the development of magnetic resonance imaging (MRI) for medical purposes and this was recognised with the award of the 2003 prize for Physiology or Medicine. Rather than using X-rays to investigate the human body, MRI uses high-powered magnets to deliver radio frequency pulses to hydrogen atoms in body tissue, increasing their energy. When the pulse ends, radio waves are emitted by these atoms. Crucially, different types of tissue react in different ways to these pulses and this can be used to create diagnostic images. In the first years of MRI in the early 1980s, just over 22,000 scans were performed. Today, more than 60 million are carried out worldwide every year, particularly for looking at soft tissue, such as the brain, nerves, muscles, ligaments and tendons.
Equally clever is the science that allows positron emission tomography (PET) scanning. Here, patients are administered a radioactively-labelled substance, often modified glucose. When the substance is used in a metabolic process in the body, it emits a particle known as the positron. When this antimatter particle meets its everyday counterpart, the electron, a pair of gamma rays are created and these can be detected with complex crystals such as bismuth germanium oxide and lutetium oxyorthosilicate.
PET’s key strength is its ability to investigate the body’s internal chemistry rather than its anatomy. This has led to its key role in oncology, where PET scans can successfully distinguish between normal and cancerous tissue in many cases.
CT, MRI and PET are now well established in the health professional’s armoury but some of the most interesting developments in the field are happening where the techniques are used together.
Scanners that combine PET and CT scanning technology are now a commercial reality and finding applications in oncology in particular, where it is valuable for early diagnosis, accurate tumour detection and better assessment of response to chemotherapy or radiotherapy treatment. In neurology, the technique is useful in assessing Alzheimer’s disease while it also has applications in cardiology.
Recently, researchers at John Hopkins Hospital in Baltimore in the US have found that combining PET and CT has helped in detecting the spread of ovarian cancer. Dr Elliot K. Fishman, professor of radiology and oncology and director of diagnostic imaging and body CT at the hospital’s Kimmel Cancer Center says: "The CT portion of combined PET-CT scanners is very helpful at locating disease, but it could miss some lesions that can be found with contrast-enhanced CT." Integrating the techniques in a single scanner has also shown improvements over visual comparison of the individual scans. Studies by researchers at the Klinik und Poliklinik für Nuklearmedizin in Zurich found that integrated CT/PET discovered additional information in 41 per cent of patients with proven or suspected lung cancer compared to visual correlation of the two scans.
It isn’t just CT and PET that are being combined to achieve better results. German researchers in Aachen have combined two different forms of MRI – diffusion weighted MRI and functional MRI to analyse lesions in functionally important regions of the brain. The research should help brain surgeons reduce the number of patients who die during surgery.
Researchers at John Hopkins Hospital in Baltimore in the US have looked at combining various types of MRI in studies of breast cancer. T1-weighted MRI is good for imaging fatty tissues, while T2-weighted MRI shows fluids, such as those found inside cysts, well. Three-dimensional MRI helps define the size and shape of tumours. “Each individual imaging modality has its advantages," says Dr Michael Jacobs, the lead researcher for the study at the Hopkins Department of Radiology. "When all these techniques are combined into one data set, you can achieve an approach that shows the characteristics of a lesion not normally available using just one imaging technique."
In the US, the Brookhaven National Laboratory is looking at how PET and MRI scans can be used together to investigate how therapeutic drugs and drugs of abuse are transferred between mother and baby during pregnancy. Researchers in Switzerland and Germany have found that combined MRI/PET scanning is useful in finding recurrent cancers.
Medical imaging technologies are also being combined with other diagnostic techniques to good effect. Electroencephalography (EEG), which is used to study electrical activity in the brain, is being combined with functional MRI scans. This research has great potential in the area of epilepsy.
Using such complex medical devices together, particularly when they generate high powered magnetic fields or are strong sources of ionising radiation, means that international standards for their testing and use will become increasingly important in the years to come.
It is fitting that just as this co-operation between differing technologies has become important in the field of medical imaging, co-operation between international organisations involved in their standardization has also moved to a new level. This February’s High-Level Workshop on International Standards for Medical Technologies brought together the IEC, the International Organization for Standardization and the International Telecommunications Union under the auspices of the World Health Organization. New medical imaging technologies will doubtless arise and such collaboration will prove invaluable in helping health professionals give patients the best possible diagnoses.