Lancet 1997; 350: 280-85.
Departments of Radiology, University of
British Columbia and Vancouver Hospital and Health Sciences Center, Vancouver,
Canada V57 1M9 (Prof B Lentle MD, J Aldrich PhD).
Correspondence to: Prof Brian
Lentle.
Outline
Graphics
Abstract^
Few observations can have been as rapidly and widely disseminated in medicine as the diagnostic X-ray (radiograph). The first few decades after Rontgen's discovery saw technical developments that made radiography more practical, quicker, safer for both imager and patient, and able to achieve greater contrast. This article reviews the history of imaging but it also looks to the future and begins to open up some of the issues that radiology faces in the 21st century-issues that the next six articles in this Lancet series will enlarge upon. The conventional radiograph remains the most common medical image but a host of new techniques have come along. Are they research tools, clinical methods, or both-and how, in an age of sensitivity about the costs of health care, do they stand up?
Wilhelm Rontgen was a professor of physics at the University of Wurzburg, Germany, when he discovered X-rays on Nov 8, 1895. This finding and that of Henri Becquerel, who discovered radioactivity in early 1896 changed the practice of medicine. [1-7] Both were chance discoveries. Rontgen was experimenting with a cathoderay tube when he noticed fluorescence at a distance. This could only have come from a much more penetrating radiation than cathode rays. Becquerel had put pitchblende on wrapped photographic film to examine the effect of sunlight on the mineral. He noticed that there was as much film blackening on an overcast day as in sunlight and deduced that the radiation came from the ore itself. Subsequently several investigators in Europe and North America realised that they might have discovered X-rays before Rontgen did-inexplicably fogged photographic film, sometimes with "shadows" of overlying materials visible, betrayed the existence of penetrating rays-but the connection was not made. [1,3,5]
As Pascal observed, "chance favours the prepared mind". Rontgen was a careful experimentalist, and his first paper, Eine neue Art von Strahlen, described much of what we know about X-rays even today, including their use to explore human anatomy (Figure 1). [8,9] Rontgen refused to profit from his discovery, for which he was awarded the first Nobel prize for physics in 1901. [10] Rontgen's paper was circulated in Europe and the copy sent to Vienna was discussed at a dinner party in the presence of a young physicist whose father edited the daily Die Presse. By that route, and by personal communication, the news rapidly spread around the world. Reaction varied: The Lancet, the first English-language medical journal to report the discovery, "was initially sceptical, then factual and by the end of January [1896] enthusiastic". [4,11]
Figure 1. First human radiograph (of Frau Rontgen's hand).
Because many scientists, some amateur, had apparatus similar to that used by Rontgen, they were immediately able to repeat his observations. Equally quickly many of these scientists made their equipment available to clinicians. In Britain A C Swinton, an electrical engineer, "showed the ghastly pictures of his hands to his friends" on the evening of Jan 7, 1896 [11] and published a hand radiograph in the BMJ later that month. [4,11] Rontgen's own radiographs were shown to the Manchester Literary and Philosophical Society, also on Jan 7, by C E Lees on behalf of Arthur Schuster, a recipient of one of Rontgen's reprints. [11]
At Dartmouth College, New Hampshire, Edwin Frost, a professor of astronomy, was asked by Gilman Frost, his physician-brother to radiograph a patient. The resulting image of the left forearm, exposure time 20 min, was made on Feb 3, 1896, and this was the first radiograph in North America. [1,3,5] In Montreal, Canada, a young man had been shot in the leg on Dec 24, 1895. Several explorations had failed to locate the bullet so his surgeon, hearing about the new ray, took him to John Cox, the professor of physics at McGill University on Feb 7, 1896. Cox's exposure, lasting 45 min, [12,13] revealed the bullet lodged between tibia and fibula, and it was removed. The film was used in court, probably the first use of radiography in jurisprudence. [14]
Thus within a couple of months, radiography was being used in many places in the English-speaking world, although a translation of Rontgen's paper had only appeared in Nature on Jan 16, 1896. [4] Few discoveries have been adopted into medicine so quickly, or now will be.
Pioneers^
Much early radiography was done by physicists and even
photographers. [4,6,15] In Baddeck, Nova Scotia,
Alexander Graham Bell made many experiments with X-rays. He even attempted
telephone transmission of X-ray signals. This may not have been the birth of
teleradiology (a development to be reviewed in this Lancet series by Giles
Stevenson) but it was arguably the conception. Bell was the first to suggest
the use of radium to treat cancer. [16,17] Sir
William Osler was prompted to use X-rays experimentally in 1896. He embedded
gallstones in a beefsteak to see if they could be detected. The result was
negative, and we now know that only a small proportion of gallstones are
radio-opaque. [18]
In early radiographs bone and foreign bodies provided tissue contrast. Soon an orally administered contrast agent (bismuth nitrate, replaced a decade later by barium sulphate) was given to study the alimentary tract, [19] and later on an intravenous contrast agent was developed and marketed in 1927 (Uroselectan, Schering) for urinary tract radiography. [20]
The early development of X-ray technology was determined by technical feasibility. [21] Important advances included the Coolidge tube (1913), permitting very much more reliable and shorter exposures; Bucky grids and Potter's moving grids; tomography by Ziedes de Plantes (1921) among many others; and cerebral angiography by Moniz (1927). Forssmann was the first to place a catheter in the heart (his own) (1929). [3,5] Hevesy's description of the tracer principle, stemming from his collaboration with Rutherford beginning in 1912, was also to be important in physiological imaging. [20]
We should not forget that the X-ray pioneers paid a price for their inventiveness, most strikingly recorded in the memorial to the X-ray martyrs in Hamburg. [1,3-5,14]
X-rays as metaphor^
Rontgen's work had ramifications beyond the obvious.
[14,23] Frau Rontgen saw in the radiograph her
husband made of her hand (Figure 1) an intimation
of mortality. Public interest in X-rays was huge, and to understand this
interest we must reflect on the society into which X-rays were launched. Radio
was soon to be invented by Marconi (1901) and, with other inventions, suggested
boundless technological promise.
In Britain, Queen Victoria was in the last years of her reign (1837-1901). The peculiar mixture of sexual repression, perversion, and commercialisation that we associate with the "Victorian era" was a worldwide phenomenon. [24] Scientifically, the world seemed a tidy place in the early 1890s. Atoms were perceived as tiny, indestructible spheres; the era of modern physics only began with the discovery of X-rays. A professor of physics at that time is even reputed to have told his students not to become physicists since physics was "over". That scientific sense of an imposed order, unrelated to reality, perhaps matched the moral environment.
The public immediately recognised that X-rays might change the practice of medicine and accepted them as another example of technological mastery that was expected to relieve the human condition. At the same time there was a prurient interest in the fact that these new rays might be used to see through materials, particularly clothing. Victorian society, certainly among its upper classes, set great store by propriety. X-rays as a means of invading privacy were the subject of cartoons (Figure 2) [25] and much comment in the popular press. [14,23,26] The magazine Photography published some doggerel shortly after the discovery which read in part: "Thro' cloak and gown-and even stays, Those naughty, naughty Roentgen rays". According to Harvey Graham, "A London firm rose to the occasion, and made a small fortune from the sale of [X-]ray proof underwear", and in New York there was an attempt to legislate against the use of X-rays in opera glasses. [27]
Figure 2. Advertisement from Toronto Globe, Feb 27, 1896.
Technological explosion^
While the history of radiology is rooted in Rontgen's
discovery, subsequently most if not all of the known physical energies have
been explored for potential use in diagnosis and treatment (panel 1) (Figure 7). However, the evolution of the
radiological sciences has led to more profound changes than a simple
multiplication of tools.
Figure 7. Panel 1: Penetrating radiation and imaging and treating
disease.
Early radiology was rooted in morphology, chiefly skeletal morphology. Beginning with nuclear medicine powerful methods have been developed to examine bodily function. With this transformation has developed a capacity not merely to display the epiphenomena of disease (eg, tumour masses and sinus tracks) but also to reveal mechanisms of disease and treatment, even in the brain.
From a passive role in supporting medical diagnosis radiology has also returned to the bedside with interventional techniques that allow image-guided biopsy, drainage, and treatments such as catheter-based cerebral aneurysm ablation (Figure 3) and radionuclide therapy. Thus while the creation or use of images of internal structures plays a part in radiological practice, images are neither a necessary nor sufficient part of radiology to define its practice.
Figure 3. Selected views from right internal carotid rotational
angiogram Left: first coil passing from microcatheter into posterior
communicating artery aneurysm. Middle and right: subtracted right internal
carotid injection 6 months later revealing stability of aneurysm closure.
(Images courtesy of Dr Thomas Marotta, University of British Columbia [UBC] and
Vancouver Hospital and Health Sciences Centre [VHHSC]; reprinted from Ann Roy
Coll Physns Surg Canada 1995; 28: 470-76, with permission.).
There has been, in the past three decades, a rapid growth in the capacity of physicians to "image" disease. This has led to a bewildering number of acronyms (panel 2) (Figure 8) This "medical-scientific phase" of radiology [19] began with Hounsfield and Cormack's invention of CT. Thus also began the transition from analogue to digital imaging. The modern tomographic methods all provide sectional images in one or more planes, avoiding the superimposition of structures that still characterise a chest radiograph. Some techniques also use computer image processing but do not yield sectional data (eg, digital subtraction angiography [Figure 3] and magnetic resonance angiography). It is important, nevertheless, to note that the chest radiograph is still the most common radiological procedure.
Figure 8. Panel 2: Imaging acronyms.
These new technologies depend on high-capacity microcomputers to reconstruct images from complex data sets. The computational tasks involved in image reconstruction would not be possible with a sliderule, at least on a time scale relevant to disease.
CT^
In today's (third and fourth generation) CT machines a
fan beam of X-radiation sweeps through 360[degree sign] while, on the opposite
side of the patient, detectors provide a digital read-out of the amount of
radiation and hence the degree to which it has been attenuated. From the linear
attenuation in multiple projections, it is possible to reconstruct a sectional
display of body structure in terms of electron density.
PET^
Radionuclides that decay by beta+ emission emit
positrons (beta+ particles or positively charged electrons) which collide with
an electron, resulting in a mutual annihilation and the transformation of their
rest mass into two gamma rays emitted at 180[degree sign] to each other. The
detection of these rays permits reconstruction of the tissue distribution of
the parent radionuclide slice by slice through an organ or in the body (Figure 4). Radionuclides that decay in this way
include isotopes of the biologically important elements carbon, nitrogen, and
oxygen (11) C,13 N,15 O), and PET has been
described as providing "autoradiographs in life". This technology, requiring
both a detector as well as cyclotron to produce the radionuclides, has yet to
become widely available.
Figure 4. Transverse PET images of brain Upper:18
F-fluorodopa and (11) C-raclopride scans in patient with idiopathic
Parkinson's disease. (18) F-fluorodopa scan shows clear evidence of
damage to presynaptic neurons;11 C-raclopridescan (sensitive to
D2 postsynaptic receptor concentration) shows compensatory
up-regulation. Lower: serial (baseline, 6 and 12 months) scans
with18 F-fluorodopa in Parkinson's disease patient who had undergone
fetal cell transplant. Changes matched by some clinical improvement. (Images
courtesy of Dr Tom Ruth, UBC and VHHSC.).
SPECT^
This technique uses the single gamma-rays emitted by
other radionuclides used in nuclear medicine such as99m
Tc,123 I, and (111) In. One or more gamma camera heads,
mounted on a rotating gantry, circles the patient, and, by computer methods
similar to those used in CT or PET, an image of tracer distribution in multiple
organ sections is obtained (Figure 5).
Figure 5. Combined use of SPECT and CT in patient with right apical lung
mass Upper: SPECT demonstrating hypermetabolism of18
F-fluorodeoxyglucose. Middle: transverse CT scan at same sight revealing 3 cm
diameter mass. Lower: composite anatomical and functional images of mass which
subsequently proved to be large-cell lung carcinoma. (Images courtesy of Dr D
Worsley, UBC and VHHSC.).
US^
The idea that high-frequency soundwaves could be
applied to medicine came from the sonar detection of submarines. Today's
ultrasound machines provide images in real time in which the signal strength is
proportional to reflection from tissue interfaces. Doppler shift
analysis-drawing on the physical principle that the perceived pitch of a
soundwave varies with the velocity of its source-permits recognition of the
velocity and direction of blood flow. Ultrasound is widely used in pregnancy
for both mother-to-be and fetus since no exposure to ionising radiation is
involved. As Sam Mindel will show in a later article in this Lancet series,
ultrasound is often the only technique available in the developing world.
MRI^
Nuclear magnetic resonance analysis has a long pedigree
in physics, chemistry, and biochemistry laboratories. Its use in life to obtain
images of organ structure stemmed from the realisation that the use of gradient
magnetic fields in intersecting coordinates will provide information about both
the molecular environment of atoms and their spatial location. Thus images (so
far, of protons [(1) H] and23 Ha) have been created by
algorithms similar to those used in CT. Some see the future of MRI as being in
proton imaging (already shown to be superior to CT in many contexts). Others
are optimistic about the future clinical applications of other nuclides
(13) C,19 F,23 Na) or of obtaining spectra
(MRS) revealing, for example, concentrations of phosphorus (31) P)
metabolites in particular regions of organs such as the brain as well as other
functional data (Figure 6). MRI can be enhanced
by agents analogous to the iodine-containing contrast agents used in
radiography.
Figure 6. Eunctional data (in yellow) in orthogonal planes from single
shot gradient-echo echoplanar internal speech experiment superimposed on T
(1) -weighted MRI images Yellow pixels reflect significant
(p<0[center dot]05) signal increases in inferior frontal region of dominant
hemisphere in this left-handed patient, who had been asked to think (but not
speak aloud) of as many words as possible, starting with given letter of
alphabet. (Images courtesy of Dr Bruce Forster, UBC and VHHSC.).
Clinical or research tools?^
It is important to distinguish between tools to study
mechanisms of disease and their use in the clinic to diagnose and follow up an
individual patient. It is sometimes argued that certain imaging methods (eg,
PET and SPECT) might serve only for research but it is more likely that all of
them will have some clinical role, the extent of dissemination outside academic
institutions varying for each. Our view is that MRI and US (with image-guided
interventions, discussed by K R Thomson in this series) will be the defining
radiological technologies of the 21st century.
Resolution^
The resolution achievable by an imaging method can be
classified as spatial, contrast, or temporal. Spatial resolution is the ability
of a system to resolve anatomical detail; contrast is the ability to
distinguish one tissue from another or diseased from normal tissue; temporal is
the system's ability to reflect changing physiological events (eg, cardiac
motion) or disease remission or progression as a function of time. High spatial
and temporal resolution are strong features of radiography, CT, MRI, and US;
for high-contrast resolution PET, SPECT, MRI, and US perform best; and MRI is
probably the most powerful single tool in all three contexts. However, there is
no prospect of MRI supplanting PET for example, in displaying cell-surface
receptors in the human brain using a probe such as18
F-fluorodopamine (Figure 4).
Future technical developments^
The next two decades will see less radical change and
instead the wider application and better understanding of the roles of the
technologies described. However, other developments are taking place in
radiology.
Magnetic source imaging
(magnetoencephalography)^
Magnetometers are used to detect the tiny magnetic
fields produced by electrical activity in the brain and image the resulting
dipoles. This technique is used in patients with surgically treatable epilepsy
(particularly partial complex seizures) and cardiac arrhythmias as well as in
planning brain surgery to avoid damaging critical areas of the cerebral
cortex.
ESR diagnosis^
This method, which also requires high field magnets, is
less eloquent than NMR in the laboratory. Some doubt that the technique is
possible in life, but research is going on and if the history of radiology
teaches one anything it is that what is preposterous today is often in clinical
use tomorrow.
Digital radiography^
Techniques have now been developed for digital rather
than photographic recording of conventional X-ray images.
[21,28] The investment may be offset in part by
savings in film purchase and storage but more importantly by efficiencies in
film retrieval by other clinicians. Digital images will provide more latitude
in exposure and some potential for image processing (eg, edge enhancement).
Information systems^
Hospitals have in general been slow to adopt modern
information technology. This is particularly damaging in radiology departments
which generate about 80% of the data bits produced in a typical hospital. This
is now changing and as fluid systems for image management and transfer result,
there will be fewer radiographs lost and shorter waits at film loan
libraries.
Digital radiography and information systems come together in the handling and transmission of images both locally and by telemetry, while computer-assisted film interpretation and decision support are on the horizon.
Industrial connection^
The manufacturers of machines and contrast agents
clearly have a close relationship with the practice of radiology. The history
and sociology of radiological technology has been examined by Blume
[29] who argues that radiologists and industry
have conspired in deciding which technologies survive. However, that view must
be set against the biological and physical limitations which determine what is
and is not possible in imaging and treating disease.
Education^
Radiological methods are an obvious resource for the
teaching of anatomy, physiology, and gross pathology. Some university
departments of anatomy are now coming to depend very heavily on radiological
teachers, and not just for sectional structure. However, medical schools in
general have been slow to respond to the rapid evolution of radiology, even
though Barjon wrote before 1918 that "If the radiologist ought to be a
physician, it would be well also for the physician to be, in a less degree, a
radiologist." [30]
Radiology and health-care policy^
Issues of health-care policy are central to the future
of the radiological sciences. New technologies must be rigorously assessed
while avoiding technological nihilism. Unnecessary examinations need to be
eliminated, and the evidentiary basis of radiological practice will be covered
by Adrian Dixon in this Lancet series. Yet radiology does have the potential to
help solve some of the issues in patient care and education which face medicine
in the future, notably in information management and in providing low-cost and
patient-friendly diagnostic and treatment procedures. Image-guided surgical
methods are likely to contribute positively to our ability to provide care
using a realistic fraction of society's wealth. So funding radiological methods
may come to be seen less as a resource-intensive burden and more as a strategic
solution to delivering cost-effective care.
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