Physics of Nuclear Medicine
Yao Wang
Polytechnic Institute of NYU, Brooklyn, NY 11201
Based on J. L. Prince and J. M. Links, Medical Imaging Signals and
Systems, and lecture notes by Prince. Figures are from the textbook.
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Lecture notes on the physics of nuclear medicine. It covers topics such as atomic structure, radioactive decay, decay modes, exponential decay law, statistical properties of decay, and radiotracers. The document also includes examples of PET vs. CT and imaging of functional or metabolic contrasts. The lecture notes are based on the textbook 'Medical Imaging Signals and Systems' by J. L. Prince and J. M. Links, and figures are from the textbook. The course is taught by Yao Wang at Polytechnic Institute of NYU in Brooklyn, NY.
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2021/2022
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Physics of Nuclear Medicine
Yao Wang
Polytechnic Institute of NYU, Brooklyn, NY 11201
Based on J. L. Prince and J. M. Links, Medical Imaging Signals and Systems, and lecture notes by Prince. Figures are from the textbook.
EL5823 Nuclear Physics
Yao Wang, Polytechnic U., Brooklyn
Lecture Outline
Atomic structure
Radioactive Decay
Decay modes
Exponential decay law
Statistical properties of decay
Radiotracers
EL5823 Nuclear Physics
Yao Wang, Polytechnic U., Brooklyn
What is Nuclear Medicine
Also known as nuclide imaging
Steps:
Inject radio tracers into the body
The radio tracers undergo radioactive decay and generate gammy rays
A camera detect gamma rays from the radio tracer after a certain time
Different physiological functions are imaged by using different radiotracers
X-ray projection and tomography:
X-ray transmitted through a body from an outside source to a detector
Nuclear medicine:
Gamma rays emitted from within a body
Emission computed tomography
Two popular method:
Positron Emission Tomography (PET)
Single photon emission computed tomography (SPECT)
EL5823 Nuclear Physics
Yao Wang, Polytechnic U., Brooklyn
Examples: PET vs. CT
X-ray projection andtomography:
X-ray transmitted through abody from a outside source toa detector (transmissionimaging)
Measuring anatomic structure
Nuclear medicine:
Gamma rays emitted fromwithin a body (emissionimaging)
Imaging of functional ormetabolic contrasts (notanatomic)
Brain perfusion, function
Myocardial perfusion
Tumor detection(metastases)
From H. Graber, Lecture Note, F
EL5823 Nuclear Physics
Yao Wang, Polytechnic U., Brooklyn
Stable vs. Unstable Nuclides
Stable nuclides:
neutrons ~= # protons (A ~= 2Z) when Z is small
neutrons > # protons when Z is large
Unstable nuclides (radionuclides, radioactive atoms)
Likely to undergo radioactive decay, which gives off energy andresults in a more stable nucleus
EL5823 Nuclear Physics
Yao Wang, Polytechnic U., Brooklyn
Line of Stability
Stability depends on ratio Z:N
EL5823 Nuclear Physics
Yao Wang, Polytechnic U., Brooklyn
What is Radioactivity?
EL5823 Nuclear Physics
Yao Wang, Polytechnic U., Brooklyn
Decay Modes
EL5823 Nuclear Physics
Yao Wang, Polytechnic U., Brooklyn
Beta Decay
Beta decay occurs when, in a nucleus with too manyprotons or too many neutrons, one of the protons orneutrons is transformed into the other.
Mass number A does not change after decay, protonnumber Z increases or decreases.
Beta minus decay (or simply Beta decay): A neutronchanges into a proton, an electron (beta particle) and aantineutrino
From: http://www.lbl.gov/abc/wallchart/chapters/03/2.html
EL5823 Nuclear Physics
Yao Wang, Polytechnic U., Brooklyn
Positron Decay
Also known as Beta Plus decay
A proton changes to a neutron, a positron (positive electron), and aneutrino
Mass number A does not change, proton number Z reduces
From: http://www.lbl.gov/abc/wallchart/chapters/03/2.html
EL5823 Nuclear Physics
Yao Wang, Polytechnic U., Brooklyn
Gamma Decay (Isometric Transition)
A nucleus (which is unstable) changes from a higher energy state toa lower energy state through the emission of electromagneticradiation (photons) (called gamma rays). The daughter and parentatoms are isomers.
The gamma photon is used in Single photon emission computedtomography (SPECT)
Gamma rays have the same property as X-rays, but are generateddifferent:
X-ray through energetic electron interactions
Gamma-ray through isometric transition in nucleus
From: http://www.lbl.gov/abc/wallchart/chapters/03/3.html
EL5823 Nuclear Physics
Yao Wang, Polytechnic U., Brooklyn
Measurement of Radioactivity
Bq=BequerelCi=Curie:
(orig.: activity of 1 g of 226Ra)
Naturally
occurring radioisotopes discovered 1896 by Becquerel
First
artificial
radioisotopes produced by the Curie 1934 (32P)
The intensity of radiation incident on a detector at range r from a radioactivesource is
A: radioactivity of the material; E: energy of each photon
2
r
AE
I
π
EL5823 Nuclear Physics
Yao Wang, Polytechnic U., Brooklyn
Half-Life
Half-life is the time it takes for the radioactivity todecrease by ½.
EL5823 Nuclear Physics
Yao Wang, Polytechnic U., Brooklyn
Statistics of Decay
The exponential decay law only gives the expected number of atomsat a certain time t.
The number of disintegrated atoms over a short time
t <<T
1/
after
time t=0 with N
0
atoms follows Poisson distribution
t N a t e t
e
N
a
N
t
N
a
e k
a
k
N
t
t
a
k
∆
−
∆
−
−
λ
λ
0
0
0
0