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the breast into a series of slices is growing in Europe. The
evaluationof this technique, currently inprogress in several
Europeancountries, shouldenable its advantages compared
with the traditional planar technique to be determined.
At present, this technique is not recognised in the context
of organised breast cancer screening.
Computed Tomography
ComputedTomography (CT) scanners use a beamof X-rays
emitted by a tubewhichmoves in a spiral around the body
of the patient (spiral or helical CT scanner). Based on a
computerised image acquisition and processing system,
these scanners produce a three-dimensional reconstruction
of the organs with very much better image quality than
that of conventional radiology devices. The number of
rows of detectors (multi-detector-row CT scanner) has
been increased in recent machines, enabling thinner
slices to be produced.
This technique can, like Magnetic Resonance Imaging
(MRI), be associated with functional imaging provided
by nuclear medicine in order to obtain fusion images
combining functional information with structural
information.
Medical imaging: several imaging techniques
can be used for a given organ
Complementary examinations (medical imaging, biological
analysis, samples, etc.) supplement the physician’s
diagnostic approach based on the history of the illness
and the clinical examination of the patient.
There are four broad medical imaging techniques.
They use X-rays (radiology), gamma rays (nuclear medicine),
ultrasounds (ultrasonography) and magnetic fields
(MRI - Magnetic Resonance Imaging). These techniques
enable the morphology of an organ to be analysed or its
function to be studied; the intrinsic qualities and the medical
interpretation of the resulting images are fundamentally
dependent on the physical principle used:
• Radiology reveals differences in density in a tissue
(due to the presence of a tumour, for example) or between
different organs. Radiology, mammography and X-ray
computed tomography are radiological examinations. The
scanner enables an organ to be reconstructed in 3D and slices
of an organ to be created (slice imaging or tomography).
• Nuclear medicine analyses the distribution of a
radiopharmaceutical (drug consisting of a vector marked by
a radioactive isotope or isolated radionuclide) injected into
the human body. This is functional imaging which enables
the physiopathological processes to be studied and provides
important information on the normal or pathological
functioning of a tissue or organ. The radiopharmaceutical is
chosen according to the target and the studied organ.
UNDERSTAND
• Ultrasonography uses ultrasounds: the sudden changes in
acoustic properties of the tissues at the boundaries of the organs
and any other interface produce echoes which are used to
construct images. By combining the Doppler effect with this, it is
also possible to measure the rate of blood flow in the vessels.
• MRI uses the magnetic properties of hydrogen nuclei placed in
a strong and stable magnetic field. The proton (H
+
) is the main
constituent of the molecule of water, an element that is present
to a greater or lesser extent in all the tissues of the human
body. After excitation by radiofrequency waves, the signals
from the protons in the water of the human body are picked up
by dedicated antennas and analysed by computer in order to
reconstruct a slice image.
Radiology and nuclear medicine that use ionising radiation are
regulated by ASN. Ultrasonography and MRI do not use ionising
radiation.
The
Guide to good medical imaging examination practices,
produced by the French Society of Radiology (SFR) and the French
Society of Nuclear Medicine and Molecular Imaging (SFMN),
helps physicians to choose the most appropriate examination
according to the symptomatology, the suggested diagnoses and
the patient’s medical history. It takes into account the proof of the
level of diagnostic performance of the examinations in each of the
situations (analysis of international publications), whether the
examination involves radiation or not, and if so, the corresponding
doses. No technique is universal; a technique that gives good
results for one organ or function of that organ may be less effective
for another organ, and
vice versa
.
The technological developments over the last few years
have made examinations easier and faster to perform,
and led to an increase in exploration possibilities
(example of dynamic volume acquisitions) and in the
indications. On the other hand, these technological
developments have led to an increase in the number
of examinations, resulting in an increase in the doses
delivered to patients and thus reinforcing the need for
strict application of the principles of justification and
optimisation (see chapter 1).
As at 31st December 2015, the French pool of radiological
devices included slightly more than 1,000 computed
tomography facilities covered by an ASN license.
Teleradiology
Teleradiology provides the possibility of guiding the
performance and interpreting the results of radiology
examinations carried out in another location. The
interchanges must be carried out in strict application of
the regulations (relating to radiation protection and the
quality of image production and transfer in particular)
and professional ethics.
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CHAPTER 09:
MEDICAL USES OF IONISING RADIATION
ASN report on the state of nuclear safety and radiation protection in France in 2015