Positron%20Emission%20Tomography

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Positron Emission Tomography
Oct. 28, 2003 Chang Kim, GE Medical
Systems

• Anatomic vs. Functional Imaging
• Anatomy of PET
• What is PET?
• Isotopes and Detector
• Basic physics and Principles
• Detector example

Most of Presentations are from GE internal
contributions.
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Anatomic vs. Functional Imaging

• Anatomic Imaging
• Physical Structures, Bulk Properties of Patient
• Generally Very High Resolution Images (1mm or
  less)
• X-Ray/CT, MRI, Ultrasound
• Functional Imaging
• Biochemical Processes Ongoing in Patient
• Generally Poorer Resolution (4-5mm or more)
• Radioisotope Techniques NM /SPECT, PET
• Other Techniques MR (MRS, fMRI), MEG (MSI), ...

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Anatomic imaging
MR Scan (or CT)
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Functional imaging
Glucose Isotope (e)
Injection(2-5mCi)
Scan (15-30 minutes)

• Tools for
• Initial diagnosis
• Progress or success evaluation
• after chemotherapy operation

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Anatomy of PET
What is PET?

• Isotope production CYCLOTRONS
• Tracer production CHEMISTRY SYSTEMS
• Imaging SCANNER

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Positron Emitting Isotopes

• Isotope Half-Life Production
• Carbon-11 20.5 min 14N(p,a)11C
• Nitrogen-13 10.0 min 16O(p,a)13N
• Oxygen-15 2.1 min 14N(d,n)15O
• Fluorine-18 110 min 18O(p,n)18F (F-)
• 20Ne(d,a)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 )

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Differentiating Tumor Types with PET

• Tracer binds to receptors expressed on one tumor
  type, not the other.
• Prolactinoma is often responsive to chemotherapy,
  avoiding surgery for patient.

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Monitoring Therapy with PET

• Effects of therapy on tumor metabolism seen in
  hours.
• Anatomic change (size reduction) will take weeks.

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Basic Physics

• 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

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Basic Principles
Coincidence Detection

• Events occurring anywhere on line between
  detectors contribute coincidence counts to
  detector pair.
• Recorded counts are proportional to line integral
  of activity between the detectors.

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Basic Principles
Projection Data Collection
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Coincidence Events
1. Detected True Coincidence Event
2. True Event Lost to Sensitivity or Deadtime
3. True Event Lost to Photon Attenuation
4. Scattered Coincidence Event
5a,b. Random Coincidence Event
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Detector Assemblies
1-to-1 Coupling Excellent livetime
characteristics, but expensive, and limited in
size to smallest available PMT (1cm2).
Block Detector Individual crystals pipe light
to detectors. More complex, but required with low
light output--BGO.
Anger Camera Light from scintillator is
distributed among several PMTs measured
distribution determines location. Poor livetime,
but can have good resolution with enough light
output--NaI(Tl).
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Detector example Light
sharing ? Decoding x A/(AB)
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Two Dimensional extension.
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(No Transcript)
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Detector Materials
BGO NaI(Tl) GSO LSO
m(cm-1) 0.95 0.37 0.67 0.89 Photofraction 40 15
35 30
STOPPHOTONS
Light Output 20-25 100 35 75 Decay Constant
300 230 65 50
PRODUCE LIGHT
Radioactive NO NO NO YES Melting
Point 1050 - gt2000 gt2000 Furnace Platinum Iridiu
m Iridium Cost 10/cc 5/cc 20/cc gt25/cc
GROW CRYSTALS
Many new crystals from IEEE 2003
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Detector 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
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PET Image
My Objective ? New and better detector design
using GEANT4 ? Better
information to Physicians
? Better patient care and treatment
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Applications
Clinical PET Applications

• Cardiology
• Cardiomyopathy or disease of the myocardium,
  etc.
• Flow tracer NH3, Metabolic tracer FDG
• Neurology
• Alzheimers, Parkinsons
• Tumor recurrence and viability vs.
  post-surgical,
• post-chemo, post-radiotherapy changes of
  tissue
• necrosis
• Oncology
• Melanoma, Lymphoma, etc.

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More info on the WEB and others

• http//www.indyrad.iupui.edu/IUPET/
• Has a outline of PET applications
• http//pet.radiology.uiowa.edu
• Lots of pictures, simple explanations of PET
• http//faculty.washington.edu/chudler/introb.html
• Nice description of brain anatomy, function,
  methods and disease research
• http//www.bic.mni.mcgill.ca
• Many examples and animations
• Megazines Medical Imaging, Radiology today,
  Diagnostics Imaging

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PET-CT
PET-CT fusion localizes
Intra-pulmonary lesion
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PET reimbursement

• 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 nonsmall cell lung cardinoma

• July 1999 (3)
• colorectal cancer with rising carcinoembryonic
  antigen (CEA)
• Detection of recurrent melanoma
• staging and restaging of Hodgkins and
  non-Hodgkins lymphoma
• July 1, 2001 (8)
• nonsmall cell lung cancer
• esophageal cancer
• colorectal cancer
• Lymphoma
• Melanoma
• head and neck cancers, excluding central nervous
  system and thyroid cancers
• Myocardial Viability
• Refractory Seizures

April 2001 JNM, 11N-12N (2pp) CAG-00065 HCFA
report (80pp) www.hcfa.gov/pubforms/06_cim/ci50.ht
m
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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

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depending on Cancer Type
Glucose Methionine for Characterization
Structure
Lesion which requires clarification in MR...
Energy Metabolism
Still not clear when looking with FDG... (due
to brain metabolic activity)
Growth Activity
Actively growing without a doubt when tracked
with methionine...