Worlds of David Darling > Children's
Encyclopedia of Science > Health Revolution > 1. Looking for Trouble
THE HEALTH REVOLUTION:
Surgery and Medicine in the Twenty-first Century
a book in the Beyond 2000 series by David Darling
1. Looking for Trouble
Sixty years ago the main way to see inside a person's body without cutting
them open involved taking an X-ray photograph. X-rays were discovered in
1895 by a German-born Dutch citizen, William Roentgen. X-rays pass fairly
easily through the soft parts of the human body but are stopped by harder
or more dense parts. So when a beam of X-rays is passed through a person's
body and onto a photographic plate, solid objects such as bone show up in
white on a negative print. This makes X-rays photos ideal for seeing details
of fractures and dislocations without opening the body.
|An X-ray photograph of a human
However, bones are not the only body parts that X-rays can reveal. For example,
if a special dye-like chemical is first introduced into soft tissues, such
as an artery, the intestine, or the stomach, the chemical absorbs the X-rays
and shows more clearly the shapes and positions of the soft structures.
In this way, major blood vessels and organs can be observed to check for
signs of damage or disease. Ordinary X-ray methods, however, are very limited
in what they can show.
CAT's Eye View
In 1967 a British engineer, Geoffrey Hounslow, realized that computers were
the key to providing a much better view of the inside of the human body.
He devised a system called CAT (computerized axial tomography). This systems
works by directing a series of narrow X-ray beams through the patient to
produce detailed cross sections. A computer then combines the cross sections
to build up a three-dimensional picture – a CAT scan – in which
different tissues are distinguished by how well they block X-rays or let
them through. The computer uses a range of colors to show up tissues and
organs according to their density. Then it displays the processed image
on a video monitor.
|A CAT scan in progress, showing
the scanner and patient in the background and the radiographer working
at the scanner's computer terminal in the foreground. An image of
the patient's abdomen appear on the screen.
The earliest CAT scanners were fixed in position and took 30 seconds or
so to produce the image of a single cross section. But as computers became
more and more powerful, the performance of CAT scanners improved dramatically.
The latest devices, which use rotating machinery and scan in a spiral pattern,
can produce an image slice in less then a second. Such sophisticated, high-speed
scanning allows doctors to track the passage of injected substances through
the blood vessels and into organs and tumors.
The main drawback of a CAT scanner is its use of X-rays, which in large
doses can be harmful to the patient. This is particularly true if the patient
is a child. For this reason, although CAT scanners are still widely used
at present and will remain important for studying organs such as the lungs,
stomach, and intestines, they are likely to give way to other scanning methods
in the future.
Scanning Without X-rays
The basic idea of the CAT scanner, to build three-dimensional pictures from
many cross sections with the help of a computer, is now used in several
other types of scanners. The PET (positron emission tomography) scanner,
for instance, is used to identify and monitor problems with the brain. Patients
are injected with a solution of glucose (a type of sugar) and a tiny amount
of radioactive material. As the glucose reaches the brain, different areas
of the brain take up varying amounts of the sugar, depending on the energy
needs of those areas. How much energy a part of the brain needs depends
on its level of activity. The PET scanner detects the radiation coming from
the radioactive glucose and so allows a picture of brain activity to be
built up. This enables doctors to look for the distinctive patterns of activity
associated with specific brain disorders, such as Alzheimer's disease.
An even more advanced method of producing pictures of what is going on inside
the body is MRI (magnetic resonance imaging). This technique is based on
the fact that hydrogen atoms in the body give off radio waves at a special
frequency after having been bombarded with other, high-frequency radio waves
and subjected to a powerful magnetic field.
As does a CAT scanner, the MRI machine enables doctors to view three-dimensional
images of the body on a screen. But MRI can be used when X-rays might be
considered too hazardous to the patient. It is especially useful for monitoring
the progress of diseases such as muscular dystrophy (a muscle-wasting condition)
and of patients who have undergone operations involving organ transplants.
|A patient being prepared for an MRI scan.
The patient's head is surrounded by the coils of the scanner's magnet:
the smaller device above the patient's head is a radio frequency receiver.
MRI has also been applied to the study of muscle injuries. Even when injured
muscles are no longer painful, MRI images show tissue repair continuing
for up to three weeks. This suggests that before resuming heavy training
and competition, athletes with muscle injuries should take a longer period
to recover than previously believed necessary.
A great deal of research and development is going on to improve MRI technology,
and it is likely that this method of scanning will become increasingly important
in the future. MRI scanners will become less expensive, and as a result
more hospitals will be able to afford them. At the same time, the equipment
will become smaller and capable of producing higher-quality images. This
will lead to the technique's being applied in new ways, such as the imaging
of blood vessels and very small tumors.
Medicine by Numbers
Today, doctors are making more and more use of digital images – pictures
built up from numbers that have been processed by a computer. Digital X-rays
and pictures produced by various types of scanning machines will eventually
make conventional X-ray film obsolete.
|A three-dimensional reconstruction of a child's
face obtained using CAT scan data, showing the skin surface on the
left and the underlying skull on the right
Much more can be done with picture information stored in a computer than
with simple X-ray photographs. A doctor can create a three-dimensional model
of the a patient's organs, soft tissues, or bones and then rotate or slice
through this model in various ways at a computer workstation. Output from
the computer can be used to manufacture accurately shaped artificial body
parts. Using the computer, surgeons can practice a new or difficult type
of operation before carrying out the procedure on a patient. Medical students
can study the layout of the body and the appearance of various diseases
in a totally new way.
Another great benefit of digital images over conventional X-rays is that
digital images can be produced using a much lower dose of radiation. This
reduces the chance of any harmful side effects to the patient. Also, information
in digital form can be sent easily from one computer to another. For example,
detailed pictures of a patient in one location can be studied by a surgeon
at a computer linked to the Internet in another city or country.
In the future, images produced by a variety of different devices, such as
CAT and MRI scanners, will be combined to reveal even more details of the
body's internal structure. This process will be extended to control the
delivery of treatment. At a computer workstation, doctors will merge all
the image information about a patient's condition with the most appropriate
surgical procedure, including details of the instruments and techniques
to be used. The computer will then generate all the information needed to
direct needles, lasers, and even robotic surgical tools under the remote
guidance of the surgeon.
An unborn baby, or fetus, in its mother's womb resembles a submerged submarine
– a similarity that triggered an idea by a Scottish medical professor,
Ian Donald, in the 1950s. To study the fetus, Donald and his colleagues
borrowed a technique called sonar, developed by French, British, and American
scientists during World War II to detect enemy vessels and other objects
underwater. The medical professors realized that, when adapted, sonar could
be used to check the progress of a fetus during pregnancy.
|An ultrasound picture of a seven-month-old
fetus in its mother's womb, showing the face and shoulders in profile
Sonar is based on the fact that very high pitched sound waves, known as
ultrasound, travel particularly well through water and similar liquids and
send back clear echoes from any solid object they meet. The echoes can be
converted into a picture of the object and displayed on a screen.
Great advances have been made in ultrasound methods over the pat 50 years,
to the extent that roughly a quarter of all medical imaging carried out
in hospitals now involves this technique. Because experience has shown that
ultrasound is less harmful than X-rays and other types of radiation, it
is used routinely to check on the health of fetuses. But it is also applied
in many other ways. Ultrasound devices have been made in hundreds of specialized
forms. Some scan organs from outside the body, and others are inserted through
holes in the body to scan blood vessels and organs such as the heart, the
stomach, and the intestines.
An adaptation of the ultrasound method, called Doppler scanning, can be
used to measure how fast blood is slowing through a patient's arteries and
veins and so help to detect any blockages in blood vessels.
With further progress in the miniaturization of equipment, the ultrasound
technique will be applied in even more varied ways. As the scanning method
of first choice when infants and young children are involved, it will be
used increasingly in procedures such as heart and brain surgery in newborn
babies. It will also be employed more and more frequently to monitor in
adults those parts of the body, for example, the prostate gland, that are
particularly sensitive to exposure to X-rays and other radiation.
The fact that muscles make low-frequency sounds when they contract
has been known for over three centuries, but until recently nothing
useful had come of this knowledge. Within the past decade or so, researchers
have begun to exploit the medical potential of muscle sounds. When
an electronic stethoscope is attached to a body area such as the arm,
the sound produced by contracting muscles is fed to an amplifier and
a special computer. This computer separates the various components
of the sounds and produces a visible record of its findings. Doctors
can then study the results to look for telltale sounds made by torn
or strained muscles. The same technique may eventually be used to
detect abnormalities of the heart – the most important muscle-containing
structure in the body.