Nuclear Medicine Imaging (SPECT and PET) Techniques Nuclear ...
Nuclear Medicine Imaging (SPECT and PET) TechniquesNuclear Medicine Imaging (SPECT and PET) Techniques
and Applicationsand Applications
Youngho Seo, PhD
Center for Molecular and Functional Imaging
UCSF Department of Radiology
Outline of This LectureOutline of This Lecture
Types of decay
Gamma radiation, source of signals for Nuclear Medicine
Transmission vs. emission
What is emission?
Study of function and physiology
Production of radiotracers
How data are acquired
Scintillators, photodetectors (e.g., photomultiplier tubes)
Gamma camera, SPECT, PET
Collimation, scatter, attenuation
Positron-electron annihilation, coincidence logic
Applications (Cancer and Musculoskeletal)
Four Forces (Interactions) and Their MediatorsFour Forces (Interactions) and Their Mediators
Okay. Then, electromagnetic force is carried by “photons”. In other words,
photons == electromagnetic radiation that involves interactions of leptons
(electrons and positrons in most cases). – This is what we are interested in
the most for Nuclear Medicine.
Figure from The Particle Adventure (particleadventure.org)
Radioactive DecaysRadioactive Decays
Little importance in nuclear medicine
Alpha (α) Decay
Little importance in nuclear medicine
Beta (β) Decay
β- (electron) emission
β+ (positron) emission
β- (electron) capture
Gamma (γ) Decay: γ (gamma-ray) radiation
BetaBeta++ (Positron) Emission(Positron) Emission
These mostly proton-rich (except 124I) radionuclides are used in positron
imaging (a.k..a. Positron Emission Tomography or PET, in short).
Gamma EmissionGamma Emission -- Isomeric Transition (IT)Isomeric Transition (IT)
Isomer: Nucleus with different arrangements
Ground states: The most stable energy states
Excited states: Arrangements are so unstable that there is only a short
transient time (less than 10-12 sec) becoming ground states.
Metastable states: Arrangements are unstable, but relatively long-lived
(sometimes up to several hours) before becoming ground states.
Tc-99m (6 h half-life)
AlternativeAlternative -- Internal Conversion (IC)Internal Conversion (IC)
Internal Conversion (IC): Energy from excited nucleus is transferred
directly to an orbital electron.
When the electron is ejected, the vacancy is filled by an electron from an
outer shell followed by characteristic x-ray.
Radioactive decay is a random process (Poisson
Mother radionuclide -> Daughter (radio)nuclide
NdtdN λ=− /
N: The number of radioactive atoms at
λλλλ: Decay constant, Radionuclide-specific
A: Activity = λλλλN
Time required to reduce its initial activity (A0) to a half (1/2*A0)
= − 2/1
Imaging Radioactive EmissionImaging Radioactive Emission
Nuclear Medicine (e.g., SPECT) is based on emission data from radioactive materials
injected in the body.
Nuclear signals penetrated through the body are detected and reconstructed to form
To Data Acquisition Electronics
Patient with Radioactivity
Nuclear Medicine ImagingNuclear Medicine Imaging
Study of Function and PhysiologyStudy of Function and Physiology
Common radiologic imaging (x-ray, ultrasonography, CT, or MRI)
Basically transmission imaging
Morphological, structural information
The images in anatomical imaging consist of true physical parameters (e.g., CT
number in CT is directly proportional to photon attenuation coefficient in the
Nuclear Medicine Imaging (scintigraphy, SPECT, or PET)
Basically emission imaging
Physiologic, metabolic, biochemical information
Use of pharmaceutical (physiology or function) chemically labeled with
radioactive elements: radiopharmaceutical (or radiotracer)
Production of Radiopharmaceuticals (aka (Production of Radiopharmaceuticals (aka (Radio)tracersRadio)tracers))
Radioactive elements (radionuclides) are produced by:
Natural occurrence, but rarely
Nuclear reactors (bombarding neutron beams to stable nuclides)
Nuclear fission (as a product)
Cyclotron (bombarding accelerated charged particles to stable nuclides)
A radioactive compound used for the diagnosis and therapeutic treatment
of human diseases.
Radiopharmaceutical = Radionuclide + Pharmaceutical
99mTc-MDP = 99mTc (radionuclide) + MDP (methylene diphosphonate)
Used in skeletal scintigraphy primarily for detection of neoplasm, infection, or
18F-FDG = 18F (radionuclide) + FDG (fluorodeoxyglucose)
Used in positron emission tomography primarily to diagnose many brain
diseases, measure regional brain function, measure myocardial viability, and
diagnose or stage a variety of cancers.
A scintillator is a device or substance that absorbs high energy (ionizing)
electromagnetic or charged particle radiation then, in response, fluoresces
photons at a characteristic Stokes-shifted (longer) wavelength, releasing the
previously absorbed energy.
Most scintillators are inorganic crystals.
Examples are: NaI(Tl) (commonly used in gamma cameras), BaF2, CsI, BGO
(bismuth germanate, commonly used in PET), LaBr3, LuI3, etc.
Incident nergetic particles
(photons or charged particles)
Scintillation Photon DetectionScintillation Photon Detection
Scintillation photons are detected by photon detectors such as
photomultiplier tubes (PMTs).
Emission TomographyEmission Tomography
Tomography: [Gk tomos section, cut; Gk graphikos, to write] Process of
imaging the structures along a plane through the body.
Single Photon Emission (Computed) Tomography (SPECT or SPET)
Positron Emission Tomography (PET)
Rotational SPECTRotational SPECT
(Projection) Projection Data
Coincidence Logic (Electronic Collimation)Coincidence Logic (Electronic Collimation)
BGO or LSO Crystal
Photons (511 keV)
And Coincidence Timing
TomographicTomographic (SPECT and PET) Image Reconstruction(SPECT and PET) Image Reconstruction
Tomographic images are generated from projection data using
Analytic method: Filtered backprojection
Statistical method: Iterative Maximum Likelihood Expectation Maximization
(MLEM) or Ordered Subsets Expectation Maximization (OSEM)
Filter projections removes
blurring of backprojection
projections prior to
FilteredFiltered BackprojectionBackprojection (FBP)(FBP)
Iterative Reconstruction Algorithm (MLEM or OSEM)Iterative Reconstruction Algorithm (MLEM or OSEM)
The tomogram is a
sentation of the radio-
within the patient
Some of Tumor Specific RadiopharmaceuticalsSome of Tumor Specific Radiopharmaceuticals
99mTc-methylene diphosphonate (MDP)
123I-vasoactive intestinal peptide
glioma, lymphoma, lung
lung, stomach, pancreas, colon
CO2 + H20
“FDG, glucose analogue… …FDG-6-phosphate does not undergo glycolysis, and does not enter the fructose-pentose shunt or
glycogen synthesis pathway… …cellular FDG uptake reflects the overall rate of transmembranous exchange of glucose…”
(Medcyclopaedia provided by Amersham Health)
F]fluorodeoxyglucose (FDG) metabolismF]fluorodeoxyglucose (FDG) metabolism
FF--FDGFDG--PET ScanPET Scan
*Data courtesy of Tom Lewellen, Ph.D., University of Washington
FF--FLT (FLT (fluorothymidinefluorothymidine) PET) PET
FLT is a cell proliferation marker. The figures show tumor uptake in patient’s tongue.
TcTc--MDP Bone ScanMDP Bone Scan
Normal Metastatic Prostate Cancer
Bone scintigraphy reveals changes in bone metabolism (bone turnover or
blood flow) rather than changes in bone structure.
Structural information is not present. So, bone scintigraphy cannot replace any
other structural imaging (x-ray radiography, CT, or MRI).
Very sensitive (because it reveals the metabolism of the bone), but usually
specificity is very low.
Can be used (and is primarily useful) for:
Stress fractures (the result of repeated low-level impact) when radiography is
Confirmation of fracture when radiography is normal.
Infection (osteomyelitis) when combined with gallium scan or radiolabeled
white blood cell (WBC) scan.
TcTc--MDP or 18FMDP or 18F--Fluoride in Musculoskeletal ApplicationsFluoride in Musculoskeletal Applications
99mTc99mTc--MDP to Image Stress FractureMDP to Image Stress Fracture
Pain in the right foot for three weeks caused by stress fracture.
Skeletal muscle activity
measurements by 18F-FDG PET
(glucose metabolism) in runners.
Useful imaging technique for:
Sports science and rehabilitation
Index for proper training of a
particular muscle group
201Tl-SPECT can be used for a
similar application. However,
201Tl, a Potassium analog, is
directly proportional to blood flow.
It has been reported that blow flow
in the leg during strenuous
exercise increases corresponding
to an increase of cardiac output.
Tashiro M, et al. J Nucl Med. 1999;40:70-76.
Direct Musculoskeletal Measurements byDirect Musculoskeletal Measurements by 1818
FF--FDG PETFDG PET