Transcript 20. Medical physics techniques

20. Medical physics techniques
BTEC level 3
Aim
• The aim of this unit is to enable learners to
develop, through a practical vocational skills
approach, an understanding of the important
fundamental physics concepts behind medical
physics techniques such as x-rays, ultrasounds,
diagnostic imaging and magnetic resonance
imaging (MRI) and radiotherapy.
• Learners will also understand the importance of
radiation safety.
• Diagnostic medicine has come a long way since
the time when the best diagnosis occurred
during the postmortem examination. Surgery
today is faster, less invasive and more effective
than ever – thanks in part to improvements in
medical imaging technology. Imaging gives the
doctor a clearer understanding of the patient’s
condition so treatment can be planned more
effectively and therapy delivered more precisely.
• Nuclear medicine is providing hope for the
cure of the most serious diseases,
especially cancer. Radioactive materials
are used in this rapidly developing branch
of medicine. At the cutting edge of
developments in nuclear medicine is the
precise targeting needed to get the
radiation to the exact site of the cancer.
• Future prospects are even more exciting. Medical
imaging is extending human vision into the very nature of
• disease; at the cellular level it will permit diagnosis
before symptoms even appear. Surgery in the future will
be bloodless, painless and non-invasive. It will be
powered by medical imaging systems that focus on the
disease and use energy to destroy the target but
preserve healthy tissue. Researchers are testing the use
of highintensity ultrasound to destroy tumours identified
and targeted while the patient lies in an MRI scanner.
• This unit introduces learners to some of
the established practices in medical
physics imaging. It aims to deliver the
underpinning knowledge of several of the
fundamental techniques and provide a
basic introduction to the more complicated
theory of magnetic resonance imaging.
Learning outcomes
• Know atomic structure and the physical
principles of ionising radiation and ultrasound
• Understand how radiopharmaceuticals are used
in diagnostic imaging
• Know the basic principles of magnetic
resonance imaging
• Understand the importance of radiation safety to
the treatment of malignant disease with
radiotherapy.
1. Know atomic structure and the physical principles of
ionising radiation and ultrasound
• Radioactivity: industrial applications; atomic structure;
characteristics of alpha, beta, and gamma, random
nature of decay, half-life, decay constant, and activity
• X-rays: industrial applications e.g. production of x-rays
from a target; x-ray spectrum and effect of tube voltage,
tube current, target material and filtration; interaction of
x-rays with matter; attenuation, inverse square law,
absorption and scattering, intensity and half value
thickness
• Ultrasound: industrial applications; production of
ultrasound and basic principles of e.g. pulse echo
technique, reflection and refraction, interaction with
tissue, scattering and absorption; intensity measurement
in decibels; specific acoustic impedance; sonar principle
and ultrasonic scanning eg A-scan, B-scan and M-scan;
Doppler effect; measurement of blood flow using Doppler
ultrasound
2. Understand how radiopharmaceuticals
are used in diagnostic imaging
• Radionuclides: industrial applications eg
radionuclides; radionuclide generators and
preparation of radiopharmaceuticals; the
need for quality control, sterility and
apyrogenicity; advantages and
disadvantages of radionuclide imaging
• The gamma camera: operating principles
of main components; function as a
detector
3. Know the basic principles of
magnetic resonance imaging
• Nuclear magnetic resonance: industrial
applications; proton spin, energy levels and
precession; resonance; overview of process,
e.g. block diagram; factors influencing signal
intensity; relaxation, contrast and resolution
• Instrumentation and equipment: magnets,
gradient field coils, radio frequency coils
• MRI applications and safety: abnormal body
water, joints, abdomen, head and spine;
instruments and equipment, implants, patient
tolerance and quenching
4. Understand the importance of radiation safety to the
treatment of malignant disease with radiotherapy
• Effect of x-rays: effect on cells and tissue in relation to
malignant disease; absorbed and effective doses
• Radiotherapy: types eg megavoltage and superficial
therapy; beam characteristics, multiple and rotational
beams, wedges and compensators; linear accelerator;
industrial applications
• Radiation safety: major effects of ionising radiation on
the body; outline of the need for legislative requirements
and dose limits; use of film badges and
thermoluminescent dosimeters; procedures for reducing
radiation hazards
Assessment and grading
• Snipping tool
Assessment activity 20.1
(P1, M1, D1, P2)
• Scenario: your work as a junior technician
in the radiography section of a large
hospital involves working with other highly
qualified personnel, talking to patients
undergoing therapy and periods of
personal study. You must show that you
have a clear understanding of the terms
used and an understanding of the basic
science principles involved in your
department
For a pass
• Draw sequences which show what
happens to radioactive elements when
they lose: an alpha particles, a beta
particle. What happens to an atom when
gamma rays are emitted? P1
• Draw a fully labelled diagram
demonstrating the principles of: an x-ray
tube; production of ultra-sound. P2
For a merit
• Using graph paper, show a decay curve
and mark on :
– The axis showing the fraction of undecayed
nuclei remaining
– The axis showing time
– Half-life intervals
– Fractions of original number of undecayed
nuclei remaining M1
For a distinction
• Use a suitable diagram to analyse what
happens to an x-ray spectrum when the
tube voltage is changed. Show some
known x-ray peaks in your diagram. What
do these peaks tell you? D1
Grading tips
• Include labels of protons and neutrons in
your answer and at least two element
sequences for each decay to achieve P1
• To achieve M1 you could add a simple
demonstration set of results using dice to
illustrate the random aspect of decay
Assessment activity 20.2
(M2, D2, P3, P4)
• Scenario: As a recent addition to the
technical and nursing staff of a large city
hospital, you must show that you are
familiar with the radiopharmaceuticals
used and the way in which they are
detected within the body of a patient
For a pass
• Make a list of the most common
pharmaceuticals used in medicine,
describe how they are produced and
briefly describe what happens when these
substances enter the body P3
• Explain how the gamma camera works
using a fully labelled diagram P4
For a merit
• Using your list from P3, provide details of
what qualities you are looking for when
choosing a suitable radiopharmaceutical.
Remember that patients have to inhale or
be injected with these substances M2
For a distinction
• Use information in chapter 20.2 (pg 374377) and your own research to evaluate
which radiopharmaceuticals are best for a
given purpose D2
Grading tips
• You should include the formulas for your
radiopharmaceutical in your answer for P3
and what the images received by the
gamma camera tell use for P4. Additional
research is necessary for M2 and D2,
which should provide information on the
choices made by doctors for particular
radiopharmaceutical in specific parts of the
body. Health if the patient is vital and the
image produced is very important
Assessment activity 20.3
(M3, D3, P5)
• Scenario: You are called upon to provide
an explanation of the procedure of an MRI
scan to a patient as part of your duties as
a technician within the radiology
department of a major hospital
For a pass
• Describe how the MRI scanner works in
simple terms and list the main components
with a brief description of each P5
For a merit
• Provide an explanation of the principles of
nuclear magnetic reasonance and how
different factors change the signal intensity
M3
For a distinction
• Use a variety of images of the same body
parts to evaluate the similarities and
differences between x-ray and MR images
D3
Grading tips
• Include some mention of proton spin and
what happens to particles in a magnetic
field in your answer for P5 with a more
detailed explanation for M3. To complete
D3, you will need to put yourself into the
role of an image analyst and become
familiar with the detail of individual images
Assessment activity 20.4
(M4, D4, P6)
• Scenario: working in the x-ray department
of a busy hospital means that you will
need to attend regular specific additional
training sessions for health and safety as
part of your continuing professional
development
For a pass
• Provide a slide demonstration explaining
the way in which x-rays are used to treat
malignant disease. Provide a brief
explanation of equipment which may be
used P6
For a merit
• Explain the physical effects of being
exposed to a lot of radiation M4
For a distinction
• Evaluate the various types of radiotherapy
practices that are currently in use and
explain the function of equipment that
allows these kinds of treatment D4
Grading tips
• List the components of the equipment which
focus x-rays onto the target with a simple
explanation of how they work and highlight what
can happen to cells during radiotherapy for P6
• Link the doses of radiation to the symptoms of
radiation exposure and comment on
preventative measures to achieve M4
• You will need to include specific radiation types
used for particular diseases for D4 and the
equipment used to produce and target the
radiation