Download Introduction to Nuclear Medicine

Introduction to Nuclear Medicine Physics
Jerry Allison, Ph.D.
Department of Radiology
Medical College of Georgia
Augusta University
Augusta, GA
Welcome to new residents 2016
GRU Medical Physics Resource
• Medical Physics Course
 Calendar
 Handouts
•
http://www.gru.edu/mcg/radiology/residency/resphysicscourse.php
What to learn?
•
AAPM Diagnostic Radiology Residents Physics Curriculum
 Module 17: Nuclear Medicine
•
•
http://www.aapm.org/education/documents/Curriculum.pdf
ABR Core Exam Study Guide
 Physics Section: Part 17) Nuclear Medicine and Instrumentation
 Radioisotope Safety Examination (RISE) Section
•
http://www.theabr.org/sites/all/themes/abrmedia/pdf/CORE_Exam_Study_Guide_FINAL%28V10
%29.pdf
Wonderful new books (FREE)!
Nuclear Medicine Physics : A Handbook for Teachers and Students
Diagnostic Radiology Physics: A Handbook for Teachers and Students
International Atomic Energy Agency, 2014
http://www-pub.iaea.org/books/IAEABooks/Subject_Areas/0103/Medical-physicsincluding-dosimetry-
A note of thanks to
Sameer Tipnis, Ph.D.
G. Donald Frey, Ph.D.
Medical University of South Carolina
And
Z. J. Cao, Ph.D.
for
Sharing nuclear medicine presentation content
Outline for Today
I.
II.
III.
IV.
V.
Radioactivity
Gamma Camera
SPECT
PET
Hybrids
I.
II.
III.
SPECT/CT
PET/CT
PET/MR
Radioactivity
Atoms
• Neutrons and
Protons (+)
 In Nucleus
• Electrons (-)
Line of Stability
• Naturally occurring
(stabile) nuclides
• These nuclei have a
stable configuration of
protons and neutrons in
the nucleus
Radionuclides
• Many nuclei are not
stable (radioactive)
• Radionuclides close to
line of stability
 Return by beta decay
and electron capture
 Radionuclides below the
line b- (e.g. I-131)
 Radionuclides above the
line b+ (e.g. F-18) and
EC (e.g. Tl-201)
https://commons.wikimedia.org/wiki/File%3ATable_isotopes_en.svg
Radioactive Decay
A = lN
A(t) = A0e-lt
•
•
•
•
N = number of radioactive nuclei
A = radioactivity (decays per second)
A(t) = radioactivity (disintegrations per second) at time t
l = decay constant (fraction of N that decays per unit time)
Radioactivity
• unit in SI: 1 Bq = 1 dps
(Becquerel)
• unit in traditional: 1 Ci = 3.7×1010 dps
• (1g of Ra-226, extracted first by Mme. Curie)
• 1 mCi = 37 MBq
• NM imaging: ~ 1 to 30 mCi (30 – 1100 MBq)
Half-Life
(Physical Half-Life)
• The physical half life T1/2 is the time it
takes for 50% of the radioactive nuclei
to decay
T1/2 = 0.693/l
 T1/2 for Tc-99m is 6 hours
 l for Tc-99m is 0.1155/hr
Biologic Half-life (Tb)
Tb = Time taken to reduce the amount of
radiopharmaceutical in the body by one half
due to functional clearance
2015
Nuclear Medicine Physics for Radiology Residents
Sameer Tipnis, PhD, DABR
Effective Half-Life
Te = Time to reduce radiopharmaceutical in
the body by one half due to functional
clearance and radioactive decay
if Tp >> Tb, Te ≈ Tb
if Tp << Tb, Te ≈ Tp
Radionuclides used in nuclear
medicine
Less than 20 radionuclides but hundreds
of labeled compounds
© Physics in Nuclear Medicine: Cherry, Sorenson and Phelps, 4th edition, 2012 17
Most radionuclides used in nuclear medicine are
produced
Radionuclide Production
Radionuclide
Production Method
P-32
I-125
I-131
F-18
Ga-67
In-111
I-123
Tl-201
Neutron Activation (Reactor)
Neutron Activation (Reactor)
Neutron Activation (Reactor)
Cyclotron
Cyclotron
Cyclotron
Cyclotron
Cyclotron
Rb-82
Sr82/Rb82 Radionuclide Generator
Tc-99m
Mo99/Tc99m Radionuclide Generator
99mTc
– a workhorse in NM!
• T1/2 = 6 hr – ideally suited to study metabolic
processes in patients
• 140 keV emission - low patient dose & ideal for
gamma cameras
• No high-energy b- radiation – low pt. dose
• Versatile chemistry - can form tracers by being
incorporated into a range of biologically-active
substances to target tissue or organ of interest
2015
Nuclear Medicine Physics for Radiology Residents
Sameer Tipnis, PhD, DABR
Dose Definition
• Effective dose E (Sv): measure of absorbed
dose to whole body, the product of
equivalent dose and organ specific
weighting factors
 Whole body dose equivalent to the nonuniform
dose delivered
20
Effective dose of NM
procedures
21
Nuclear Medicine
Gamma Camera
• The dual head is the most
common design
• Most cameras use
rectangular heads
• Most cameras are
designed to do SPECT
imaging
How to obtain a NM image?
• Administer radiopharmaceutical (a
radionuclide labeled to a pharmaceutical)
• The radiopharmaceutical is concentrated in
the desired locations.
• Nucleus of the radionuclide decays to emit
g photons
• Detect the g photons using a “gamma
camera”
Gamma Camera Basics
Pulse Height
Analysis
position
analysis
X
Y
Z
c o m p ut e r
amplify & sum
p r e - a m p
P M T
d et e ct or
displa y
c o lli m a t o r
p a t ie n t
Why collimator? – image formation
w/o collimator
with collimator
images
image
detector
collimator
sources
Image of a point source is the whole
detector.
Image of a point source is a point.
Why collimator? – image formation
• to establish geometric
relationship between the
source and image
• The collimator has a major
affect on gamma camera
count rate and spatial
resolution
parallel-hole collimator
Modern Camera Design
© GE: Discovery
© Siemens: Symbia
© Philips: Brightview
SPECT
(Single Photon Emission Computed Tomography)
• We can produce tomographic images by
acquiring conventional gamma camera
projection data at several angles around the
patient
 Similar to CT
Sinogram
© Physics in Nuclear Medicine: Cherry, Sorenson and Phelps
© Physics in Nuclear Medicine: Cherry, Sorenson and Phelps
Filtered Back Projection
• Attenuates streaks by filtering the projections
© Physics in Nuclear Medicine: Cherry, Sorenson and Phelps
Iterative Reconstruction
• Quantitatively more accurate
 Can model various corrections
•
•
•
•
Collimator
Scatter
System geometry
Detector resolution
Attenuation Correction
• Like all radionuclide imaging there is
a problem due to attenuation.
• Correction can be important for
quantiifying the activity of lesions
 Modeling attenuation (Chang)
 Measuring attenuation with
transmission sources
Attenuation correction:
Transmission measurements
• Radionuclide source (e.g. Gd-153)
• X-ray source (SPECT/CT)
SPECT/CT
PET (Positron Emission Tomography)
The Positron
 Positron is an elementary particle
 Has same mass as electron
 The charge is equal but opposite to
electron
+
-
Positron
Electron
Positron is an Anti-particle
• When a particle and and
antiparticle interact they
annihilate
 Both particles are
destroyed
 Two photons(Gammarays) are created
 Two photons are emitted
in ~opposite directions (±
0.25 degrees for F-18)
Gamma 1
+
-
Gamma 2
Photon Energy
• For positron-electron annihilation
 511 keV (for each gamma-ray)
• This is much higher than the 140 keV of
Tc-99m
Where was the event?
?
Coincidence
Where was the event?
Annihilation Detection
In coincidence counting an event is ONLY registered
if a signal is received from two detectors within a
narrow window of time.
A few nanoseconds is usually used.
Coincidence
Time-of-Flight PET
In “Time-of-Flight” pet, use of a very small time window
(<100 picoseconds) can localize an annihilation event to
within a few cm along the line of coincidence.
Time-of-Flight PET can improve SNR.
Coincidence
PET/CT
Events in PET Scanners
Trues
Scatter
RRnd = CTW Rtrue Rtrue
Random
CTW = timing window
Attenuation Correction
• Like all radionuclide imaging
there is a problem due to
attenuation.
• It is much less for PET than for
Tc-99m imaging
• Correction can be important for
quantifying the metabolic
activity of lesions
Attenuation Correction
• Radioactive rod sources
 Ge -68 or Cs-137
• CT data reconstructed to
make a attenuation map
of the body
 Attenuation map
information is used in
image reconstruction
Positron Emitting
Radionuclides
•
•
•
•
Usually cyclotron produced
Most are very short lived
F-18 (110 min) can be shipped
Sr-82 (25 day)/Rb-82 (1.2min) is a
generator system
• Others have very short half-lives
PET Radionuclides
Radionuclide
Half-life
Positron
Energy
Production
C-11
N-13
O-15
F-18
Rb-82
20.5 min
10.0 min
2.0 min
110 min
1.2 min
960 keV
1198 keV
1732 keV
634 keV
3356 keV
Cyclotron
Cyclotron
Cyclotron
Cyclotron
Sr-82/Rb-82
Hybrids: Incorporation of CT (& MRI)
SPECT/CT
PET/CT
• CT images can be used for
• Attenuation Correction
• Scatter correction
• Diagnosis (# CT slices varies widely)
• Fusion of physiological map on anatomical map
PET/CT
SPECT/CT
•Enables SPECT and PET images having spatially
registered/fused CT images
•Spatial resolutions
•SPECT ~10mm
•PET ~5mm
•CT ~1mm
PET
Registration
and Fusion
CT
PET + CT
PET/MRI
MRI improves soft tissue contrast
More complex to integrate with PET
MRI has some inherent spatial distortion
More expensive
Difficult if PET PMTs are involved
Primary Reference
• Physics in Nuclear Medicine: Simon Cherry, James Sorenson
and Michael Phelps, 4th Edition, Elsevier, 2012