NEED TO KNOW
These key terms will help you
understand X-ray technology
mechanically rotating the X-ray tube
and the detector in opposite directions
around the body, thereby producing a
clear image of one section at a time. His
technique, named tomography from the
Greek tomos, ‘to section’, was gradually
improved upon during the middle of the
century but had only limited uses.
Computers have revolutionised many
areas of healthcare, and this is no less true
for X-ray imaging. In 1967 the British
engineer Godfrey Hounsfield invented
‘computed tomography’ (CT or
sometimes CAT) scanning – essentially a
computerised version of Vallebona’s
tomography. CT scanning takes far more
detailed pictures than conventional
X-rays, and these are processed by acomputer before they’re used for
diagnosis. Crucially, the series of
two-dimensional slices that CT scanning
produces can also be digitally stitched
together to create a 3D image.
Hounsfield reportedly got the idea for
CT scanning after realising that you
could find out what was inside an
opaque box by combining a series of
X-rays taken from all angles around it.
He tested his prototype scanner on a
preserved human brain, animal brains
(ferried across London on public
transport) and later himself. In 1971, the
first clinical CT scan of a patient with a
suspected brain tumour took place, and
the scanner was introduced into hospitals
from 1972. A full-body scanner became
available in 1975. Hounsfield, a modest
man, shared the 1979 Nobel prize for
CT scanning with the physicist Allan
Cormack. Unbeknownst to Hounsfield,
Cormack had worked out the
mathematics of the technique.
That 1971 image looks a little pixelated
to modern eyes (it measured just 80
pixels by 80), but it was the first time
science had seen inside the brain in such
a way. Hounsfield’s first scans took fiveminutes per slice, while today’s take less
than a second to produce much higher
resolutions. Today CT scanning is used
to look at particular bone conditions,
but is most useful for its ability to image
soft tissues, detecting cancer or trauma to
internal organs.
Ultimately, Röntgen would produce
only three papers on X-rays, but they
are still known as Röntgen rays in
some countries.
In 2011 a group of researchers
resurrected a set of 1896 X-ray
equipment – including an original
Crookes tube – to see how it compared
with modern-day kit. They found that a
person would receive about 1,500 times
the X-ray dose in 1896 to image a hand
than they do today. They would also
have needed to keep their hand still for
90 minutes, as opposed to 20 milliseconds
today. The X-ray has come a long way,
and despite newer imaging techniques
being developed, it seems there’ll be
a place for successors to the bone portrait
for a while yet.KATHERINE NIGHTINGALE is a science writer with a
degree in molecular biology1
CATHODE RAY /
CROOKES TUBE
A glass tube that has had most of the air
removed. The tube has both a negatively
charged (cathode) and positively charged
electrode (anode). When a voltage is applied,
electrons are released from the cathode, and
X-rays are generated when they hit the anode.
2
COMPUTED TOMOGRAPHY
A computer-based technique in which
images of slices of the body or brain are
captured one at a time and then processed to
produce a clear image. The sections can be
digitally stitched together to produce a three-
dimensional image.
3
FLUOROSCOPY
An imaging technique which uses X-rays
and fluorescence to capture moving images of
the inside of the body in real-time — the video
to standard X-ray imaging’s still photographs.
4
X-RAY
A form of electromagnetic radiation with
a higher energy and shorter wavelength than
visible light. X-rays can pass through materials
that visible light cannot, and so are good for
medical imaging.
Designed by Godfrey Hounsfield, this brain scanner was the first production model and went
into service in 1971. It established computed tomography (CT) as a key imaging technology