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)

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.

• 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

– physician– physicist– chemist, pharmacologist– computer specialist– engineer

Topics

• 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

• 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

Mother nuclide Daughter nuclide+ particles+ energy (e.g.photon)

Type of decay

Half life

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.

Alpha decaye.g. 224Ra

A

Z XA-4

Z-2 Y + alpha + E4

2

Beta decaye.g. 14C, 99Mo

X Y + e + Ev + EßAZ

AZ+1

0-1

Positron decaye.g. 11C, 18F X Y + e + Ev + Eß+

AZ

AZ-1 +1

0

Electron capturee.g. 111In, 125I

X + e- Y* Y + gammaA A AZ Z-1 Z-1

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

excitation

ionization

close approach

Interaction of Beta Particles

• Bremsstrahlung (breaking radiation)• Cerenkov radiation• Positron annihilation

Positron annihilation

Interactions of photons• 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, pulse-

height 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)

• 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)

• 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)