Upload
others
View
2
Download
0
Embed Size (px)
Citation preview
Basics of NuclearMedicine
Principles of Medical Imaging
Prof. Dr. Philippe Cattin
MIAC, University of Basel
Oct 24th, 2016
Oct 24th, 2016Principles of Medical Imaging
1 of 29 26.09.2016 08:36
Contents
2
4
5
6
8
9
10
11
12
13
14
15
16
17
18
19
20
22
23
24
25
26
27
29
30
31
32
Prof. Dr. Philippe Cattin: Basics of Nuclear Medicine
Contents
Abstract
1 Introduction
Transmission versus Emission Imaging
Transmission versus Emission Imaging (2)
Transmission versus Emission Imaging (3)
2 Nuclear Parameters and Decay Schemes
Nuclear Structure
Isotopes, Isotones and Isobars
Nuclear Decay Rate
Nuclear Decay Rate (2)
Measurement
Modes of Decay
Alpha Decay
Beta Minus Decay
Positive Beta Decay
Spectrum of Beta Decay
Gamma Decay
Gamma Decay (2)
Radiation Properties
3 Radionuclide Production
Radionuclide Production
Cyclotron Production
Cyclotron Production (2)
Reactor Production
Generator Production
Common Radioisotopes
4 The Gamma Camera
Gamma Camera
Gamma Camera (2)
Positional and Pulse Height Analysis
Animated Schematic of the Gamma Camera
Oct 24th, 2016Principles of Medical Imaging
2 of 29 26.09.2016 08:36
Oct 24th, 2016Principles of Medical Imaging
(2)
Prof. Dr. Philippe Cattin: Basics of Nuclear Medicine
Abstract
In this chapter...
3 of 29 26.09.2016 08:36
Introduction
Oct 24th, 2016Principles of Medical Imaging
(4)Transmission versus EmissionImaging
Transmission Imaging: planar X-ray, Fluoroscope, CT
Radiation position and strength (spectrum, energy) is known
(6.1)
with known, we measure and infer the tissue absorption factor .
Fig. 6.1: Principle of X-ray transmission imaging
4 of 29 26.09.2016 08:36
Oct 24th, 2016Principles of Medical Imaging
Introduction
(5)
Prof. Dr. Philippe Cattin: Basics of Nuclear Medicine
Transmission versus EmissionImaging (2)
Position of the radiation source and its strength is unknown
Energy is known (mono-energetic)
Fig. 6.2: Principle of nuclear medicine
5 of 29 26.09.2016 08:36
Oct 24th, 2016Principles of Medical Imaging
Introduction
(6)
Prof. Dr. Philippe Cattin: Basics of Nuclear Medicine
Transmission versus EmissionImaging (3)
Transmission Imaging (X-ray based methods)
We measure tissue dependent attenuation coefficients
→ anatomical information
Emission Imaging (Scintigraphy, SPECT, PET)
We measure concentrations of injected radio-
pharmaceutics → corresponds to ???
Hundreds of different radio-pharmaceutics have beendesigned to visualise various physiological e.g.functional processes → Functional imaging
Fig. 6.3:
Fig. 6.4: Typical PET
acquisition of a brain
6 of 29 26.09.2016 08:36
Nuclear Parameters andDecay Schemes
Oct 24th, 2016Principles of Medical Imaging
(8)Nuclear Structure
A nucleus of any atom consists of a mixture of protonsand neutrons. A simple nuclear model therefore consistsof
protons
neutrons
making a total of nucleons. Each element can thus bewritten in terms of these three components
(6.2)
where is the atomic number, the number ofneutrons and the atomic mass ( ).
The atomic number is redundant, as the element name defines the value of , the mass number can thus beused as the single identifier, e.g.
(6.3)
Fig. 6.5: Nucleus with three
electrons (green) neutrons,
(red) protons, (blue) electrons
7 of 29 26.09.2016 08:36
Oct 24th, 2016Principles of Medical Imaging
Nuclear Parameters and Decay Schemes
(9)
Prof. Dr. Philippe Cattin: Basics of Nuclear Medicine
Isotopes, Isotones and Isobars
Nuclides with a constant proton number
but with a varying neutron number
are called Isotopes.
Nuclides with a constant neutron
number but with a varying proton
number are call Isotones.
Nuclides having a constant mass but
varying and are called Isobars.
Not all isotopes are stable. forexample has a half-life of .
Fig. 6.6: Example isotopes, isotone and
isobars for three atoms
8 of 29 26.09.2016 08:36
Oct 24th, 2016Principles of Medical Imaging
Nuclear Parameters and Decay Schemes
(10)
Prof. Dr. Philippe Cattin: Basics of Nuclear Medicine
Nuclear Decay Rate
Decay of an unstable nuclide is a statistical process mathematically expressed, asthe rate of transformation of nuclei changing per unit time , yielding
(6.4)
where is the decay constant. The negative sign indicates that the number ofnuclei decreases with each event. The solution of this differential equation is
(6.5)
where is the number of nuclei at time and is the radionuclide'sparticular decay rate.
9 of 29 26.09.2016 08:36
Oct 24th, 2016Principles of Medical Imaging
Nuclear Parameters and Decay Schemes
(11)
Prof. Dr. Philippe Cattin: Basics of Nuclear Medicine
Nuclear Decay Rate (2)
A more commonly used parameter as thedecay constant is the half-life . Given a
sample of a particular radionuclide, thehalf-life is the time taken for half theradionuclide's atoms to decay. The half-life isrelated to the decay constant as follows
(6.6)
Together with Eq 6.5 this yields
(6.7)
Isotope Half-life Clinical use
Vascular imaging
Lung ventilation
Cardiac imaging
Universal imaging
Imaging sepsis
In vitro analysis
Marker source
Tab. 6.1: Physical half-lifes of common
clinical nuclides
10 of 29 26.09.2016 08:36
Oct 24th, 2016Principles of Medical Imaging
Nuclear Parameters and Decay Schemes
(12)
Prof. Dr. Philippe Cattin: Basics of Nuclear Medicine
Measurement
Radioactivity is equal to the
number of disintegrations per second.
(6.8)
where is measured in → Bequerel[http://en.wikipedia.org/wiki/Bequerel] with
(6.9)
The intensity of radiation incident on adetector at range from a radioactivesource is
(6.10)
where is the energy of each photon.
11 of 29 26.09.2016 08:36
Oct 24th, 2016Principles of Medical Imaging
Nuclear Parameters and Decay Schemes
(13)
Prof. Dr. Philippe Cattin: Basics of Nuclear Medicine
Modes of Decay
There are three basic → modes of decay [http://en.wikipedia.org
/wiki/Nuclear_decay#Decay_modes_in_table_form]
→ Alpha decay [http://en.wikipedia.org/wiki/Alpha_decay] ( )
→ Beta decay [http://en.wikipedia.org/wiki/Beta_decay] ( and )
→ Gamma decay [http://en.wikipedia.org/wiki/Gamma_ray] ( )
Other more complex modes of decay exist but are not covered in this lecture.
12 of 29 26.09.2016 08:36
Oct 24th, 2016Principles of Medical Imaging
Nuclear Parameters and Decay Schemes
(14)
Prof. Dr. Philippe Cattin: Basics of Nuclear Medicine
Alpha Decay
Principle:
The alpha decay involves an alpha particle (Heliumnucleus) and causes the greatest loss of energy froman unstable nucleus, since it looses two neutrons andtwo protons.
(6.11)
Clinical value:
Alpha decay is rarely used in clinical work.Fig. 6.7: Alpha decay
13 of 29 26.09.2016 08:36
Oct 24th, 2016Principles of Medical Imaging
Nuclear Parameters and Decay Schemes
(15)
Prof. Dr. Philippe Cattin: Basics of Nuclear Medicine
Beta Minus Decay
For those unstable nuclei with an excess ofneutrons a negative particle (electron) isproduced by neutron decay forming a proton
(6.12)
Since the mass number does not change theparent and daughter nuclei are isobars, but asthe proton number increases the elementchanges from to .
The emitted photon has an energy of .
Clinical Value:
Very few emitters are used as they cause ahigh patient radiation dose.
Fig. 6.8: Beta minus decay
14 of 29 26.09.2016 08:36
Oct 24th, 2016Principles of Medical Imaging
Nuclear Parameters and Decay Schemes
(16)
Prof. Dr. Philippe Cattin: Basics of Nuclear Medicine
Positive Beta Decay
A positive beta particle (Positron) is producedby proton decay in the nucleus
(6.13)
Since the mass number does not change theparent and daughter nuclei are isobars, but asthe proton number decreases the elementchanges from to .
The positron (anti-matter) undergoes mutualannihilation with a nearby electron thatresults in two opposed photons with each.
Clinical Value:
Positron emission tomography (PET) imagingrelies on the decay which produces opposedphotons ( -radiation).
Fig. 6.9: Beta plus decay
15 of 29 26.09.2016 08:36
Oct 24th, 2016Principles of Medical Imaging
Nuclear Parameters and Decay Schemes
(17)
Prof. Dr. Philippe Cattin: Basics of Nuclear Medicine
Spectrum of Beta Decay
The random nature of the energy loss throughthe neutrino and anti-neutrino makes theenergy spectrum of -decay continuous, Fig6.10.
Fig. 6.10: Kinetic energy spectrum of
beta decay ranges from 0 to maximum
energy (in the range of ) that
depends on the nuclear states of the
participating nuclei
16 of 29 26.09.2016 08:36
Oct 24th, 2016Principles of Medical Imaging
Nuclear Parameters and Decay Schemes
(18)
Prof. Dr. Philippe Cattin: Basics of Nuclear Medicine
Gamma Decay
Gamma radiation in the range of is ideal forimaging, since lower energies undergo tissue absorptionand higher energies are not seen (absorbed) by thedetector material in the gamma camera.
The photon emitted in the previously shown decayschemes came from short lived (pico-seconds) excitednuclear states, others can last for relatively long periods(up to hours) and are called metastable states.
(6.14)
As no other decay process ( is involved they impart a
low radiation dose to the patient.
Clinical Value:
Gamma radiation in the range of is optimalas it has low tissue absorption and can be well detectedby the gamma camera.
Fig. 6.11: Gamma decay
17 of 29 26.09.2016 08:36
Oct 24th, 2016Principles of Medical Imaging
Nuclear Parameters and Decay Schemes
(19)
Prof. Dr. Philippe Cattin: Basics of Nuclear Medicine
Gamma Decay (2)
Molybdenum-99 ( ) has a long half-life and can be easily transported over longdistances to hospitals, where its decay product Technetium-99m ( ) with ashort half-life is → extracted [http://en.wikipedia.org/wiki/Technetium-99m_generator] and usedin a variety of nuclear medicine diagnostic procedures.
Fig. 6.12: Molybdenum decays to a
metastable state that then decays with a pure
gamma photon to a stable state.
Fig. 6.13: Atom model
18 of 29 26.09.2016 08:36
Oct 24th, 2016Principles of Medical Imaging
Nuclear Parameters and Decay Schemes
(20)
Prof. Dr. Philippe Cattin: Basics of Nuclear Medicine
Radiation Properties
Property Alpha Beta Gamma
Type High speed electrons Electromagnetic
Range in air
Range in tissue
19 of 29 26.09.2016 08:36
Radionuclide Production
Oct 24th, 2016Principles of Medical Imaging
(22)Radionuclide Production
Three methods exist for producing nuclear medicine radionuclides
Bombardment of stable elements with charged beams (cyclotron) → requires a
considerable amount of electrical power and is thus costly
1.
Irradiation of stable elements with neutrons (in a nuclear reactor) → cheaper2.
Generator production3.
Both charged beams and nuclear reactors can provide parent isotopes that decayto give short half-life daughters which may be removed or eluted from time totime.
20 of 29 26.09.2016 08:36
Oct 24th, 2016Principles of Medical Imaging
Radionuclide Production
(23)
Prof. Dr. Philippe Cattin: Basics of Nuclear Medicine
Cyclotron Production
Short explanation of the → Cyclotron Principle[http://en.wikipedia.org/wiki/Cyclotron]
The charged particles are injected near the
centre of the magnetic field
Electron gun similar to the design in an
X-ray cathode tube
Light gases (hydrogen, deuterium or
helium) that were ionised an electron
beam or radio-frequency field
1.
The particles accelerate only when passing
through the gap between the electrodes
2.
The perpendicular magnetic field, combined
with the increasing energy of the particles,
forces the particles onto a spiral path
3.
Charged particles, extracted from the Cyclotron,can be accelerated to sufficiently high energiesso that when they collide with target materialsnuclear reactions are induced.
Fig. 6.14: Design of a clinical cyclotron
Fig. 6.15: An electron beam in a
perpendicular magnetic field ionises a
gas and makes it glow
21 of 29 26.09.2016 08:36
Oct 24th, 2016Principles of Medical Imaging
Radionuclide Production
(24)
Prof. Dr. Philippe Cattin: Basics of Nuclear Medicine
Cyclotron Production (2)
The small cyclotrons available at hospitalscommonly use negative ion acceleration ().
The stripping foil removes the electrons
leaving a proton beam ( ) that hits thetarget material.
Depending on the target material differentradionuclides can be produced.
In particular can be produced whenhitting a target. is a positron emitteroften used in PET imaging.
Since the target and the producedradionuclei are mostly different elementsthey can be separated chemically.
Fig. 6.16: Particle path through a cyclotron
22 of 29 26.09.2016 08:36
Oct 24th, 2016Principles of Medical Imaging
Radionuclide Production
(25)
Prof. Dr. Philippe Cattin: Basics of Nuclear Medicine
Reactor Production
Neutron bombardment of stable elements in a nuclear reactor produceradionuclides by two different reactions
Neutron capture: the nucleus accepts an additional neutron. The
nucleus then has an excess of neutrons and decays as
Fission: the nucleus accepts an additional neutron, becomes unstable
and splits into two smaller nuclei
A complex fission sequence yields for example that can bechemically separated and is a very common generator for (99-Technetium).
Canadian → nuclear reactor shutdown [http://en.wikinews.org
/wiki/Canadian_nuclear_reactor_shutdown_causes_worldwide_medical_isotope_shortage]
(heavy water leak) causes worldwide medical isotope shortage.The reactor produces of the international supply of medicalisotopes.
Fig. 6.17:
Simplified
design of a
small nuclear
reactor used
for
radionuclides
production.
The enriched
fuel
is held in
graphite
blocks which
act as
moderator to
slow down
the neutrons
to allow
neutron
capture. The
carmium
control rods
regulate the
reaction
23 of 29 26.09.2016 08:36
Oct 24th, 2016Principles of Medical Imaging
Radionuclide Production
(26)
Prof. Dr. Philippe Cattin: Basics of Nuclear Medicine
Generator Production
Cyclotrons and nuclear reactors can produce long-lived (days) parent isotopes, e.g.( ) shown in Fig 6.12, that can be easily shipped. As the parent decays, theactivity of the daughter rises ( ).
Fig. 6.18: The parent isotopes slowly decays. From time to time the clinically useful daughter
element can be chemically separated (eluted)
24 of 29 26.09.2016 08:36
Oct 24th, 2016Principles of Medical Imaging
Radionuclide Production
(27)
Prof. Dr. Philippe Cattin: Basics of Nuclear Medicine
Common Radioisotopes
Radioisotope Half-life EnergyPhoton Energy
SPECT
PET
25 of 29 26.09.2016 08:36
The Gamma Camera
Oct 24th, 2016Principles of Medical Imaging
(29)Gamma Camera
The first → Gamma Camera[http://en.wikipedia.org/wiki/Gamma_camera]
was developed by → Hal Anger[http://en.wikipedia.org/wiki/Hal_Anger] in1957 and is thus often referred to asan Anger Camera.
Gamma radiation is absorbed by
the sodium iodide scintillator
and converted into ultraviolet
photons
The closely attached
photomultiplier tubes amplify
the incident photons
Fig. 6.19: Basic design of the gamma camera
26 of 29 26.09.2016 08:36
Oct 24th, 2016Principles of Medical Imaging
The Gamma Camera
(30)
Prof. Dr. Philippe Cattin: Basics of Nuclear Medicine
Gamma Camera (2)
Mature technology (desiged
by → Hal Anger in 1957
[http://en.wikipedia.org
/wiki/Hal_Anger])
The Photo-Multiplier Tubes
(PMT) are directly coupled
with the continuous NaI(TI)
crystal
Spatial resolution
at FWHM
Energy resolution at
FWHM
Large area is
typical
Simple and cost-effectiveFig. 6.20: Image of a gamma camera (Anger camera)
27 of 29 26.09.2016 08:36
Oct 24th, 2016Principles of Medical Imaging
The Gamma Camera
(31)
Prof. Dr. Philippe Cattin: Basics of Nuclear Medicine
Positional and Pulse Height Analysis
Position Extraction:
When gamma photon ( -photon) hitsthe scintillator crystal a flash of lightwith multiple ultraviolate photons isproduced.
The → Photomultiplier tubes[http://en.wikipedia.org/wiki/Photomultiplier]
(PMT) then amplify these photons.
As the photons are spread overmultiple PMTs their relativestrengths can be used for a moreaccurate estimation of incident
location on the scintillator crystal.
Pulse Height:
The cumulative PMT strength isused to estimate and differentiatethe energy of the incident -photon.
Fig. 6.21:
Fig. 6.22: Photomultiplier design
28 of 29 26.09.2016 08:36
Oct 24th, 2016Principles of Medical Imaging
The Gamma Camera
(32)
Prof. Dr. Philippe Cattin: Basics of Nuclear Medicine
Animated Schematic of the GammaCamera
Fig. 6.23: Animated schematic of the gamma-camera physics and its main constituents.
29 of 29 26.09.2016 08:36