# Presentation: 049879

## 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.

## Anatomic vs. Functional Imaging

**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), ...**

## 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 evaluation
- after chemotherapy & operation

## What is PET?

- Isotope production	**CYCLOTRONS**
- Tracer production           	**CHEMISTRY SYSTEMS**
- Imaging                    	**SCANNER**

- Anatomy of PET

## Positron Emitting Isotopes

_**Isotope**__**	**__**Half-Life**__**	**__**Production**_
**Carbon-11****	****20.5 min****	****14****N(p,********)****11****C**
**Nitrogen-13****	****10.0 min****	****16****O(p,********13****N**
**Oxygen-15****	**** 2.1 min****	****14****N(d,n)****15****O**
**Fluorine-18****	****110 min****	****18****O(p,n)****18****F (F****-****)**
**	****	****20****Ne(d,********)****18****F (F****2****)**
**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: ******18******F FDG ( ******18******F labeled fluorodeoxyglucose )***

## Differentiating Tumor Types with PET

- Prolactinoma is often responsive to chemotherapy, avoiding surgery for patient.

## Monitoring Therapy with PET

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

## 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

## 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.

- Basic Principles

## Projection Data Collection

- Basic Principles

## 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**

## Detector Assemblies

**Excellent livetime characteristics, but expensive, and limited in size to smallest available PMT (~1cm****2****).**

**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 PMT’s; measured distribution determines location.**
**Poor livetime, but can have good resolution with enough light output--NaI(Tl).**

## Detector example 

- Detector example
-                     Light sharing  Decoding x = A/(A+B)

## Two Dimensional extension....

## Slide 16

## Detector Materials

**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****	**

**STOP****PHOTONS**

**GROW**
**CRYSTALS**

- Many new crystals from IEEE 2003...

## 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**

##  PET  Image

-  PET  Image

- My Objective  New and better detector design using GEANT4
-                         Better information to Physicians
-                         Better patient care and treatment

## Clinical PET Applications

- Applications

-  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.

## More info on the WEB and others...

- Has a outline of PET applications
- _[http://pet.radiology.](http://pet.radiology.uiowa.edu/)__[uiowa](http://pet.radiology.uiowa.edu/)__[.](http://pet.radiology.uiowa.edu/)__[edu](http://pet.radiology.uiowa.edu/)_
- Lots of pictures, simple explanations of PET
- _[http://faculty.](http://faculty.washington.edu/chudler/introb.html)__[washington](http://faculty.washington.edu/chudler/introb.html)__[.](http://faculty.washington.edu/chudler/introb.html)__[edu](http://faculty.washington.edu/chudler/introb.html)__[/](http://faculty.washington.edu/chudler/introb.html)__[chudler](http://faculty.washington.edu/chudler/introb.html)__[/](http://faculty.washington.edu/chudler/introb.html)__[introb](http://faculty.washington.edu/chudler/introb.html)__[.html](http://faculty.washington.edu/chudler/introb.html)_
- Nice description of brain anatomy, function, methods and disease research
- _[http://www.](http://www.bic.mni.mcgill.ca/)__[bic](http://www.bic.mni.mcgill.ca/)__[.](http://www.bic.mni.mcgill.ca/)__[mni](http://www.bic.mni.mcgill.ca/)__[.](http://www.bic.mni.mcgill.ca/)__[mcgill](http://www.bic.mni.mcgill.ca/)__[.ca](http://www.bic.mni.mcgill.ca/)_
- Many examples and animations
- Megazines : Medical Imaging, Radiology today, Diagnostics Imaging

## Intra-pulmonary lesion

- PET-CT fusion localizes

- PET-CT

## PET reimbursement 

- CAG-00065 HCFA report (80pp)
- www.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

- 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

## 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 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