Coincidence to Image: PET Imaging

Jennifer WhiteMarketing Manager

SNS WorkshopOctober 13, 2003

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Coincidence to Image:

PET ImagingThe PET Mission

“Disease is a biological process and PET is a biological imaging technique that uses molecular probes.”

-Michael Phelps

The CPS mission is to utilize CPS’ unique foundation of knowledge and experience in molecular imaging technology to manage disease better through earlier detection and more complete diagnosis.

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Coincidence to Image:

PET ImagingThe Image

Fused PET CT Image

Brain Imaging

Cardiac Image

PET CT and PET

Dedicated PET

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Coincidence to Image:

PET ImagingPET Principles

18O (p,n) 18F

18-F-FDG most common nuclide

Other PET Radionuclides

11C

13N

15O

82Rb

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Coincidence to Image:

PET ImagingAnnihilation Reaction

e+

e-

Positron emission

Positron scatters in tissue losing

energy

Annihilation511 keV -ray

511 keV -ray

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Coincidence to Image:

PET ImagingPET Principles

Detector Block

LSO

PROCESSING ELECTRONICS

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Coincidence to Image:

PET ImagingPET Principles

Acquisition Disk

Real Time CPU

Ethernet

Optical data link

Workstation

Detector Electronics

GantryController

Serial line

Ethernet

Acquisition MemoryVSB bus

Coincidence Processor

Gantry

Detectors

Singles Events

Formatter & Motion

TranslatorSorter

Rotating Rod

Converter

VME bus

ECAT System Schematic

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Coincidence to Image:

PET ImagingPET Principles

Line of Response is Defined by connecting Pairs in Coincidence

Event

Types of Events Detected

Prompt

True

Random

Scatter

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Coincidence to Image:

PET ImagingEvent Detection

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Coincidence to Image:

PET ImagingEvent Detection

Collection of Events

t = 12ns t = 12ns

DelayConstant

Fraction

Discrim

Detector Detector

t>>12ns

AND

Constant

Fraction

Discrim

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Coincidence to Image:

PET ImagingSinogram Formation

A sinogram is formed by placing the

projection for the angle 0 at the top of a

matrix and the other angles in

ascending order.

EXACT, ART, Accel: 192 x 192 elements.

HR+: 288 x 288 elements

Data is collected as the integral of the

activity along parallel rays for each angle

from 0 to 180 degrees.

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Coincidence to Image:

PET ImagingPET Principles

PROMPT EMISSION SINOGRAM

TRUE EMISSION SINOGRAM

IMAGE

Random Subtraction

acquisition time and decay correction

calibration/branching fraction correction

deadtime correction

detector efficiency normalization

scatter subtraction

ring geometry rebinning

attenuation correction

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Coincidence to Image:

PET ImagingPET Imaging

• Attenuation Corrections– Correction made for number of detection lost

• Scatter (Compton or Rayleigh interactions)• Absorption (photoelectric interaction)

– Significance of Attenuation• The reconstruction algorithms are not valid without AC.• The emitter distribution is distorted.• Quantification is not possible.

Scattered

A

B

Absorbed

Unattenuated

Absorbed

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Coincidence to Image:

PET ImagingPET Principles

Uncorrected Corrected

Image Quality Considerations

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Coincidence to Image:

PET ImagingPET Attenuation Correction

Methods of Attenuation Correction: ROD SOURCE

Measure rod intensity with no object present.

Measure transmission through the object.

Smooth and take the ratio.

Blank/Transmission = ACF

Blank scan Transmission scan Emission scan

Measure emission from object.

Correct the emission data.

Etrue = Emeas x ACF

1 hour 2–4 min 4–8 min

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Coincidence to Image:

PET ImagingPET Attenuation Correction

Methods of Attenuation Correction: CT

soft tissue bone

511 keV

~70 keV

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Coincidence to Image:

PET ImagingCorrected Sinogram to Image

measured N = 1 N = 3

FBP

OSEM

Sinogram

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Coincidence to Image:

PET ImagingPET Images

MI projection Plane 66

Plane 66

Plane 66

FBP

OS-EM 7.1

OS-EM 7.2 (prototype)

Plane 71

Plane 71

Plane 71

Plane 76

Plane 76

Plane 76

Reconstruction Methods vs Image Quality

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Coincidence to Image:

PET ImagingPutting it all together

Transmission scan

Emission scan

Blank scan

Normalization

Attenuationcorrection

-map

Image

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Coincidence to Image:

PET ImagingPET ImageReconstruction: multiple bed positions

25 yr old male, melanoma, 71 kg, 178 cm, 16.9 mCiFDG

Data courtesy of NCPIC, Sacramento, CA

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Coincidence to Image:

PET ImagingCase Study

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Coincidence to Image:

PET ImagingPET Analysis

Measured Activity Weight Volume Injected Activity

SUV =

• Partial volume effect (Resolution dependent)• Size of ROI• Size of lesion• Resolution

• Scanner• Reconstruction parameter• Filter/ Noise

• Glucose concentration before injection• Metabolism

• Pathologic• Stress

• Time after injection• Uptake time• Scan length (to reach ROI)

• Scanner calibration

Weight only used as substitute for blood/ water volume!•Measuring error (esp. when patient estimate)•Tissue/ fat/ bone composition/ distribution

• Measuring error• Cross-calibration

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Coincidence to Image:

PET ImagingAnalysis Packages

Selected Models

• Patlak, Logan plots

• Time-weighted integral method

• Simplified reference model

• Ichise’s reference models

• Logan’s non-invasive model

• Glucose autoradiography

• Fractal analysis

• Fourier analysis

PMOD Technologies

www.pmod.com

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Coincidence to Image:

PET ImagingCase Study

Multi-Planar Fused

Sagittal, Coronal, Transaxial

Coronal Series

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Coincidence to Image:

PET ImagingCase Study

Sub-cm nodes detected with PET localized with CT

Patient with history of Breast Cancer evaluated for treatment follow-up. Small 7 mm nodes detected by examination on PET/CT

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Coincidence to Image:

PET Imaging

Thank youP N + e + + energy+