Getting Technical
a strong magnetic field. The magnetic field
extends beyond the machine and exerts very
powerful forces on objects of iron, magnetic
steels, and other magnetisable objects. In
one instance it has been reported as ‘strong
enough to fling a wheelchair across the
room’! Patients must notify their physicians
of any form of medical or other implants
prior to undergoing an MRI scan.
X-rays carry enough energy to ionise
atoms and disrupt molecular bonds. This
makes it a type of ionising radiation which
is potentially harmful to living tissue. High
radiation doses over a short period of time
can cause radiation sickness, while lower
doses can increase risks of radiation-induced
cancer. In medical imaging this increased
cancer risk is generally greatly outweighed
by the benefits of the examination. Also,
the ionising capability of X-rays can be
beneficially utilised in cancer treatment to kill
malignant cells using radiation therapy.
X-rays carry enough
energy to ionise
atoms and disrupt
molecular bonds.
One of the continually growing areas of
X-ray technology, Phase-contrast X-ray
imaging, refers to a variety of techniques
that use phase information of an X-ray
beam to image soft tissues. It has become
an important method for visualising organic
structures over a wide range of biological
and medical studies. These methods provide
higher contrasts making it possible to see
smaller details. However, a disadvantage
is that these methods require more
sophisticated equipment such as high-
resolution X-ray detectors.
In addition to medical uses, both
MRI and X-rays are widely used across
commercial, industrial and manufacturing
processes to image the inside of visually
opaque objects. The most often seen
applications are airport security scanners,
www.hvacronline.co.za
but many similar scanners have become
important particularly for quality control
on highly automated production lines.
Compared to X-ray radiation, MRI is still
a relatively new technology but is finding
increasing uses for routine analysis of
chemicals, measuring the ratio between
water and fat in foods, monitoring flows
of corrosive fluids in pipes and studying
complex molecular structures such as
catalysts.
A larger range and number of technical
methods have been developed for X-ray
radiation mainly due X-ray applications
starting almost half a century before MRI.
Examples are X-ray crystallography in which
the pattern produced by diffraction of X-rays
through a closely spaced lattice of atoms
in a crystal is recorded and then analysed
to reveal the nature of the lattice. Fibre
diffraction; a technique which was used by
Rosalind Franklin to discover the double
helical structure of DNA. X-ray fluorescence,
a technique in which X-rays are generated
within a sample and detected and outgoing
energies of the X-rays can be used to identify
the composition of the sample. Industrial
radiography in which X-rays are increasingly
used for inspection of industrial parts,
particularly welds.
X-ray technology is regarded as
relatively mature while cryogenic
cooling needed for newer technologies
including MRI is still proceeding through
developmental stages. Only nine countries
in the world in addition to the US produce
the core product for cryogenics, liquid
helium. However, according to a recent
Reuters report in The Star newspaper
another country plans to bring liquid
helium production on-line by 2021; South
Africa, where deposits of liquid natural
gas (LNG) containing sufficient helium
have been found in the Virginia region of
the Free State province. According to the
report, the Virginia Gas Project is planned
for daily production of 654.3tons of LNG
and 350kg of helium making South Africa
the only African country to have these
facilities. RACA
RACA Journal I March 2020
59