Post on 20-Jan-2016
Positron Emission Tomography Oct. 28, 2003
Chang Kim, GE Medical Systems
1. Anatomic vs. Functional Imaging2. Anatomy of PET
• What is PET? • Isotopes and Detector
3. Basic physics and Principles4. Detector example
* Most of Presentations are from GE internal contributions.
Anatomic vs. Functional ImagingAnatomic vs. Functional Imaging
Anatomic ImagingAnatomic Imaging– Physical Structures, Bulk Properties of PatientPhysical Structures, Bulk Properties of Patient
– Generally Very High Resolution Images (~1mm or less)Generally Very High Resolution Images (~1mm or less)
– X-Ray/CT, MRI, UltrasoundX-Ray/CT, MRI, Ultrasound
Functional ImagingFunctional Imaging– Biochemical ProcessesBiochemical Processes Ongoing in Patient Ongoing in Patient
– Generally Poorer Resolution (~4-5mm or more)Generally Poorer Resolution (~4-5mm or more)
– Radioisotope Techniques: NM /SPECT, PETRadioisotope Techniques: NM /SPECT, PET
– Other Techniques: MR (MRS, fMRI), MEG (MSI), ...Other Techniques: MR (MRS, fMRI), MEG (MSI), ...
MR Scan (or CT)MR Scan (or CT)
Anatomic imaging
Functional imaging
Glucose + Isotope (e+)
Injection(~2-5mCi)
Scan (15-30 minutes)
Tools for • Initial diagnosis • Progress or success evaluationafter chemotherapy & operation
What is PET?What is PET?
• Isotope production CYCLOTRONS
• Tracer production CHEMISTRY SYSTEMS
• Imaging SCANNER
Anatomy of PET
Positron Emitting IsotopesPositron Emitting IsotopesIsotope Half-Life Production
Carbon-11 20.5 min 14N(p,)11C
Nitrogen-13 10.0 min 16O(p,13N
Oxygen-15 2.1 min 14N(d,n)15O
Fluorine-18 110 min 18O(p,n)18F (F-)
20Ne(d,)18F (F2)
Gallium-68 68 min Daughter of Ge-68 (271days)
Rubidium-82 1.27 min Daughter of Sr-82 (25days)
• Small elements (C,N,O,F) allow “real” biochemistry
• Short half-lives make tracer production an integral part of PET
Tracer ex: 18F FDG ( 18F labeled fluorodeoxyglucose )
Tracer binds to Tracer binds to receptors expressed on receptors expressed on one tumor type, not one tumor type, not the other.the other.
Prolactinoma is often Prolactinoma is often responsive to responsive to chemotherapy, chemotherapy, avoiding surgery for avoiding surgery for patient.patient.
Differentiating Tumor Types with PETDifferentiating Tumor Types with PET
Effects of therapy on tumor metabolism seen in hours.Effects of therapy on tumor metabolism seen in hours. Anatomic change (size reduction) will take weeks.Anatomic change (size reduction) will take weeks.
Monitoring Therapy with PETMonitoring Therapy with PET
Basic Physics
~1-3mm511KeV
511KeV
• Positron travels 1-3 mm before annihilation (depending on energy)
• Energy and Momentum conservation- 511 keV Photons and back-to-back
• Simultaneous detection of two 511KeV photons - event along line between detectors
Coincidence DetectionCoincidence Detection
DET 1 DET 2
Pulse Processing
AND
Pulse Processing
• Events occurring anywhere on line between detectors Events occurring anywhere on line between detectors contribute coincidence counts to detector pair.contribute coincidence counts to detector pair.
• Recorded counts are proportional to line integral of Recorded counts are proportional to line integral of activity between the detectors.activity between the detectors.
Basic Principles
Projection Data CollectionProjection Data Collection
PMT
PMT
COINCIDENCE PROCESSING
DETECTOR RING
ProcessingElectronics
ProcessingElectronics
CoincidenceProcessor
Data Sorting,Histogram
Image ReconComputer Images
Basic Principles
Coincidence EventsCoincidence Events
1
1. Detected True Coincidence Event
2
2. True Event Lost to Sensitivity or Deadtime
3
3. True Event Lost to Photon Attenuation
4
4. Scattered Coincidence Event
5a 5b
5a,b. Random Coincidence Event
1-to-1 CouplingExcellent livetime characteristics, but expensive, and limited in size to smallest available PMT (~1cm2).
Block DetectorIndividual crystals “pipe” light to detectors.
More complex, but required with low light output--BGO.
Anger CameraLight from scintillator is distributed among several PMT’s; measured distribution determines location.
Poor livetime, but can have good resolution with enough light output--NaI(Tl).
Detector AssembliesDetector Assemblies
PMT
A B
No Optical grease
(a) (b)
(c) (d) Alignment
Detector example Light sharing Decoding x = A/(A+B)
Two Dimensional extension….
BGO NaI(Tl) GSO LSO
PRODUCE
LIGHT
(cm-1) 0.95 0.37 0.67 0.89
Photofraction ~40% ~15% ~35% ~30%
Light Output 20-25 100 35 75
Decay Constant 300 230 65 50
Radioactive NO NO NO YES
Melting Point 1050 - >2000 >2000
Furnace Platinum Iridium Iridium
Cost $10/cc $5/cc $20/cc >$25/cc
Detector MaterialsDetector Materials
STOP
PHOTONS
GROW
CRYSTALS
Many new crystals from IEEE 2003…
Detector RequirementsDetector Requirements
Goal Requirement
High Spatial Resolution Small Detector Elements High Photofraction
High Sensitivity High Stopping Power
Low Scatter Fraction Good Energy Resolution
Low Randoms Good Timing Resolution
Low Deadtime Fast Event Handling (High Livetime) Small Channel Size Limited Multiplexing
Low Cost None of the Above
PET Image
My Objective New and better detector design using GEANT4 Better information to Physicians Better patient care and treatment
Clinical PET ApplicationsClinical PET ApplicationsApplications
• Cardiology Cardiomyopathy or disease of the myocardium, etc. Flow tracer: NH3, Metabolic tracer: FDG
• Neurology Alzheimer’s, Parkinson’s Tumor recurrence and viability vs. post-surgical, post-chemo, post-radiotherapy changes of tissue necrosis
• Oncology• Melanoma, Lymphoma, etc.
http://www.indyrad.iupui.edu/IUPET/• Has a outline of PET applicationsHas a outline of PET applications
http://pet.radiology.uiowa.edu• Lots of pictures, simple explanations of PETLots of pictures, simple explanations of PET
http://faculty.washington.edu/chudler/introb.html• Nice description of brain anatomy, function, methods Nice description of brain anatomy, function, methods
and disease researchand disease research http://www.bic.mni.mcgill.ca
• Many examples and animationsMany examples and animations
Megazines : Medical Imaging, Radiology today, Megazines : Medical Imaging, Radiology today, Diagnostics ImagingDiagnostics Imaging
http://www.indyrad.iupui.edu/IUPET/• Has a outline of PET applicationsHas a outline of PET applications
http://pet.radiology.uiowa.edu• Lots of pictures, simple explanations of PETLots of pictures, simple explanations of PET
http://faculty.washington.edu/chudler/introb.html• Nice description of brain anatomy, function, methods Nice description of brain anatomy, function, methods
and disease researchand disease research http://www.bic.mni.mcgill.ca
• Many examples and animationsMany examples and animations
Megazines : Medical Imaging, Radiology today, Megazines : Medical Imaging, Radiology today, Diagnostics ImagingDiagnostics Imaging
More info on the WEB and others…More info on the WEB and others…
Intra-pulmonary lesionPET-CT fusion localizes
PET-CT
April 2001 JNM, 11N-12N (2pp)April 2001 JNM, 11N-12N (2pp)CAG-00065 HCFA report (80pp)CAG-00065 HCFA report (80pp)www.hcfa.gov/pubforms/06_cim/ci50.htmwww.hcfa.gov/pubforms/06_cim/ci50.htm
April 2001 JNM, 11N-12N (2pp)April 2001 JNM, 11N-12N (2pp)CAG-00065 HCFA report (80pp)CAG-00065 HCFA report (80pp)www.hcfa.gov/pubforms/06_cim/ci50.htmwww.hcfa.gov/pubforms/06_cim/ci50.htm
1994– FDA approves FDG for abnormal
glucose metabolism for foci of epileptic seizures
1995 (1)– Rb82 chloride myocardial perfusion with
inconclusive SPECT or w/o SPECT 1997
– FDA Modernization and Accountability Act (FDAMA)
– Congress mandated FDA to provide a mechanism for PET approval of PET radiopharmaceuticals
January 1998 (2)– FDA approval for FDG– indeterminate solitary pulmonary nodule– initial staging of non–small cell lung
cardinoma
1994– FDA approves FDG for abnormal
glucose metabolism for foci of epileptic seizures
1995 (1)– Rb82 chloride myocardial perfusion with
inconclusive SPECT or w/o SPECT 1997
– FDA Modernization and Accountability Act (FDAMA)
– Congress mandated FDA to provide a mechanism for PET approval of PET radiopharmaceuticals
January 1998 (2)– FDA approval for FDG– indeterminate solitary pulmonary nodule– initial staging of non–small cell lung
cardinoma
July 1999 (3)– colorectal cancer with rising
carcinoembryonic antigen (CEA)– Detection of recurrent melanoma– staging and restaging of Hodgkin’s and
non-Hodgkin’s lymphoma July 1, 2001 (8)
– non–small cell lung cancer– esophageal cancer– colorectal cancer– Lymphoma– Melanoma– head and neck cancers, excluding
central nervous system and thyroid cancers
– Myocardial Viability– Refractory Seizures
July 1999 (3)– colorectal cancer with rising
carcinoembryonic antigen (CEA)– Detection of recurrent melanoma– staging and restaging of Hodgkin’s and
non-Hodgkin’s lymphoma July 1, 2001 (8)
– non–small cell lung cancer– esophageal cancer– colorectal cancer– Lymphoma– Melanoma– head and neck cancers, excluding
central nervous system and thyroid cancers
– Myocardial Viability– Refractory Seizures
PET reimbursement PET reimbursement
Reimbursement and Regulatory issues..Reimbursement and Regulatory issues.. Dec 1, 2001 (Medicare): 82Rb scan : $953
FDG scan : $1375 ( $2331 for 2000)
But, • for gamma camera with at least one inch thick crystal or FDA 510(k) clearance ( ongoing issues )• Not for screening• Diagnosis : to avoid an invasive diagnostic procedure
or to determine the optimal anatomical location for an invasive diagnostic procedure
• Staging and Restaging : the stage of the cancer remains in doubt after standard diagnostic workup; Restaging after treatment ( expect to replace one or more conventional imaging studies )
• Not for monitoring during the planned course of therapy
Glucose & Methionine for CharacterizationGlucose & Methionine for Characterization
Lesion which requires clarification in MR...
Still not clear when looking with FDG... (due to brain metabolic activity)
Actively growing without a doubt when tracked with methionine...
Structure
Energy Metabolism
Growth Activity
… depending on Cancer Type