Nuclear Medicine Physics
University of Szeged
Department of Nuclear Medicine
History 1.
1896 Henri Becquerel - mysterious rays (Uranium)
1897 Marie and Pierre Curie - radioactivity
1901-1914 Therapy with radium
1924-1935 Georg de Hevesy - radiotracer studies in
animals (bone mineral, 32P)
• 1938 Glenn Seaborg - 131I, 99mTc
• 1946 Allen Reid, Albert Keston - 125I, RIA (insulin) (1959)
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History 2.
• 1957 Benedict Cassen, David Kuhl - rectilinear
scanner (Picker 1959)
• 1958 Hal Anger - gamma camera (Nuclear
Chicago 1962)
• 1962 David Kuhl - emission tomography
(SPECT, PET)
• 1964 commercial 99mTc-generator
History 3.
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1971 nuclear medicine - medical speciality US
1976 John Keyes, Ronald Jaszczak - SPECT
1983 Henry Wagner- neuroreceptor PET
1990 Computer network for nuclear medicine
1995 Coincidence SPECT (SPECT/PET)
1999 PET/CT
Nuclear Medicine
• Diagnostics
– in vivo
– in vitro
• Therapy
• multidisciplinary approach
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physician
physicist
chemist, pharmacologist
computer specialist
engineer
Topics
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Basic physics
Instrumentation, measurement systems
Radiochemistry, radiopharmacology
In vitro diagnostics
In vivo diagnostics (organ systems)
Therapy
Radiation safety
Radio-nuclides in NM
• Penetration of the radiation
• No penetration
• Half-life T 1/2
• Atomic number
Atomic physics
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Nucleus and electron shell
Electron (e) shell (10-10 m) K, L, M etc.
Nucleus (10-15 m) proton (p)(Z), neutron (n)(N)
Mass number A=Z+N
• Isotopes z X, isobars AX
• Nuclide card (Karlsruher Nuklidkarte)
Energy level diagram for 99mTc
Decay of radionuclides
Type of decay
Mother nuclide
Daughter nuclide
Half life
+ particles
+ energy (e.g.photon)
Activity
• The activity of a radioactive sample is the
number of atoms undergoing transformation per
unit time
• 1 bequerel (Bq): one disintegration per second
(dps)
• 1 curie (Ci): 3.7x1010 dps (1g 226Ra)
Decay processes 1.
A
X
Alpha decay
e.g. 224Ra
Z
Beta decay
e.g. 14C, 99Mo
A
Z
Positron decay
e.g. 11C, 18F
A
Z
X
Electron capture
e.g. 111In, 125I
A
Z
X+
X
A-4
Z-2
4
Y + 2 alpha + E
A
Y
Z+1
0
+ -1e
+ Ev + Eß
A
0
Z-1Y ++1e + Ev + Eß+
A
A
e- Z-1Y* Z-1Y + gamma
Decay scheme of 14C
Principal decay scheme of 99Mo
Decay scheme of 18F
Decay processes 2.
• Isomeric transition (e.g. 99mTc)
• Internal conversion (therapy)
• Nuclear fission (reactor)
Interaction of radiation with matter
• Radiation detection, biologic effect
• Ionization, excitation
• Ionization: ion pair (negative electron,
positively charged nucleus)
• Excitation: light, heat, chemical reaction
Interaction of charged particles
(Alfa, beta etc.)
• Elastic collisions with atomic nuclei
(Bremsstrahlung)
• Excitation of electrons (X-rays, Auger
electrons)
• Ionisation (ion pairs)
• Catastrophic collision
Path of heavy charged particle in
matter
close approach
ionization
excitation
Interaction of Beta Particles
• Bremsstrahlung (breaking radiation)
• Cerenkov radiation
• Positron annihilation
Positron annihilation
Interactions of photons
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Photoelectric absorption
Compton scatter
Pair production
(Rayleigh scattering (coherent scattering) (CT))
(Photonuclear reaction)
Measure of photon absorption
( linear attenuation coeff. [cm-1 ])
Principal photon interactions in
matter
Radiation detector systems
University of Szeged
Department of Nuclear Medicine
Classification of detectors
• Medium in which the interaction takes place
(liquid, solid, gas)
• Nature of the physical phenomenon produced
(excitation, ionisation, chemical change)
• Type of electronic pulse generated
Gas-filled detectors
• Ionisation chambers (personal dosimeters, dose
calibrators)
• Proportional counters (gas chromatography,
alfa beta particles directly, survey dosimeters)
• Geiger-Müller tubes (survey instruments, low
level radiation)
Gas-filled detector
Characteristic pulse-height curves
Scintillation detectors
• Higher counting rates (fast resolving times)
• Gamma radiation (proportionality)
• Sodium iodine crystals (Tl activated) (well counters,
Gamma camera, SPECT)
• BGO, LSO (PET)
• Semiconductors (dosimeter, camera?)
Scintillation detector system
Principles of a single-channel PHA
Gamma camera
• Scintillation crystal (NaI)
• PM tubes
• Electronics (high-voltage supply, amplifiers, pulseheight analyser)
• Collimators
• Computer
• Quality assurance (sensitivity, uniformity, linearity)
Block diagram of the Anger
scintillation camera
Collimation
Parallel-hole collimator
Converging collimator
Diverging collimator
Pinhole collimator
Position-determining circuitry
Single photon emission computed
tomography (SPECT)
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Dedicated SPECT
Gamma camera based SPECT (single head, multiple head)
Detector
Gantry
Computer
Quality assurance (uniformity, linearity, geom. resolution,
COR, 3D phantoms)
Positron emission tomography
(PET)
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Dedicated PET (Brain)
Whole body PET
Animal PET
Detectors BGO, LSO (coincidence detection)
Gantry, bed
Computer
Quality assurance (uniformity, linearity, geom. resolution,
COR, transmission source)