Positron Emission Positron Emission Tomography (PET)Tomography (PET)

HistoryHistory

1975 the first commercial PET scanner was introduced

70s and 80s PET was mainly used for research

1990s being used in clinics regularly

PET vs. CT & MRIPET vs. CT & MRIPET CT and MRI

Shows the extent of the disease

Detects changes in body sturcture

Can help in monitoring treatment and shows it’s effectiveness

Simply confirms the presence of a mass

Reveals disease earlier, can diagnose faster

Can detect whether a mass is benign of malignant

Can detect abnomalities before there is an anatomical change

What Can PET Detect?What Can PET Detect?

Coronary Artery DiseasePET imaging is unique in its ability to determine whether a patient's heart muscle will benefit from coronary artery bypass surgery.

The first heart has a mycardial infarction. The arrows point to damaged areas (‘dead’ tissue).Therefore it is assumed that the patient will not benefit from heart surgery.

The second heart is normal

Example: Myocardial Viability

                                                                    

TumorsPET imaging is very accurate in differentiating malignant from benign growths, as well as showing the spread of malignant tumors. PET imaging can help detect recurrent brain tumors and tumors of the lung, colon, breast, lymph nodes, skin, and other organs. Information from PET imaging can be used to determine what combination of treatment is most likely to be successful in managing a patient's tumor.

The fist picture shows a malignant breast mass not shown in the conventional imaging techniques. (CT, MRI, mammogram)

Second picture is that of the same patient with enlarged left axillary lymph nodes. Through a biopsy they were found to be metastatic.

Example: Breast Cancer

                                                                            

Diseases of the BrainPET imaging can provide information to pinpoint and evaluate diseases of the brain. PET imaging can show the region of the brain that is causing a patient's seizures and is useful in evaluating degenerative brain diseases such as Alzheimer's, Huntington's, and Parkinson's. Within the first few hours of a stroke, PET imaging may be useful in determining treatment therapies.

First picture is that of a normal brain. The image of a 9 year old, female patient

with a history of poorly controlled seizures. The arrow points to the area that is responsible for the seizures. Through surgical removal the seizures subsequently stop.

Example: Seizures

                                                                              

Overview of MethodologyOverview of Methodology

production of positron emitting isotope in a cyclotron chemistry of labeling compound with positron emitter and

preparing compound in a form suitable for administration in humans

transport of labeled compound from chemistry group to camera group

administration (injection) of tracer compound & data acquisition with PET camera

processing of data from PET camera to extract information related to the tracer's kinetics in the body

interpretation of result

PositronsPositrons

When a positron meets an electron the collision creates two gamma rays that have the same energy but go in opposite directions. PET detects the gamma rays as they leave the patients body. The information is fed to a computer and makes a picture.

Positrons Continued…Positrons Continued…

http://www.austin.unimelb.edu.au/dept/nmpet/pet/detail/principle.html

Short clip to further illustrate the function of positrons.

                                                  

TracersTracers

Depending on the type of tracer, different gamma rays are given off and detected. In this way multiple things can be evaluated.

Examples:

Fluorodeoxyglucose [18F]-labeled 2-deoxyglucose (FDG) is used in neurology, cardiology and oncology to study glucose metabolism. FDG is potentially useful in differentiating benign from malignant forms of stimulated osteoblastic activity because of the high metabolic activity of many types of aggressive tumors.

Oxygen[15O]-labeled water and oxygen are being evaluated for the quantification of myocardial oxygen consumption and oxygen extraction fraction. [15O]-labeled oxygen can also be used to measure tumor necrosis.

Ammonia[13N]-labeled ammonia can be used to measure blood flow.

Leucine[11C]-labeled methionine and leucine can be used to evaluate amino acid uptake and protein synthesis, providing an indicator of tumor viability.

Fluorine IonRadiolabeled fluorine ion [18F-] was once a standard agent for clinical bone scanning.

Camera DesignCamera Design

Many detectors are connnected to a photomultiplier tube and arranged in circular, hexagonal, or orthoganal rings.

The field of view is defined by the width of the array of detectors.

The smaller the size of detectors the better the spatial resolution of the PET system.

Interpretation of PETInterpretation of PET

Examples: case studies

Case StudyCase Study

A 71 year-old male with metastatic melanoma on the left shoulder, discovered 12/94.

Original Diagnosis A CT performed on 7/10/95

demonstrated a tumor of the distal femur and adjacent soft tissue with negative findings in the abdomen.  A bone scan from 7/13/95 showed on abnormal femur and four spine lesions.

PET Findings History A whole-body FDG PET scan

demonstrated numerous lesions throughout the body.

Change in Treatment The patient was scheduled for an

amputation based on CT and bone scan results.  After the PET scan found multiple lesions, surgery was cancelled, avoiding both the cost and the trauma of an operation that would not have been effective.

Case Study 2Case Study 2

History A 64 year-old male who was found to

have serum CEA elevation for 16 months after resection of colon carcinoma.

Original Diagnosis Endoscopy with biopsy demonstrated

recurrence at the site of anastamosis at the hepatic flexure.  CT of the abdomen and pelvis showed no abnormality.

PET Findings Preoperative PET scan showed a new

abnormal focus in the mediastinum and two on the lumbar spine (left image), and a focus in left lobe of the liver and two in the left chest wall (right image).

Change in Treatment The findings indicate local recurrence

and metastatic disease to the liver, mediastinum, and skeleton.  This patient will have to be placed in chemotherapy in addition to any surgery planned.

Case Study 3Case Study 3

History A 63 year-old male with lung cancer.  A

tumor was removed from the right upper lobe.

Original Diagnosis Several months later a CT scan showed a

new lesion in the left lung. PET Findings A whole-body FDG PET scan found focal

FDG accumulation in the left lung lesion, as shown in figure 1.  In addition, several other lesions unsuspected by CT were seen in the right lung and mediastinal lymph nodes.

Change in Treatment The conventional treatment plan based on

CT results would have been a thoracotomy to resect the lesion in the left lung.  After the PET scan found other areas of focal FDG uptake, the treatment was switched to chemotherapy.  The lesions could still be seen on a follow-up CT scan after chemotherapy, but a second PET study showed the FDG uptake had returned to normal, avoiding a possible resection.

Factors Affecting PETFactors Affecting PET

Attenuation Random Coincidences Scatter Coincidences Spatial Resolution Sensitivity

Quality Control TestsQuality Control Tests

Daily Tests Uniformity of the image is checked daily using a

elictical filled with a positron emitter Weekly Tests Spatial Resolution is checked for by service

personnel by periodically using the line spread functions

Center of Rotation is checked so that there are no deviations from the proper alignment.

Future StudiesFuture Studies

In 2000 CTI Molecular Imaging Inc. was the first to market the combination PET/CT scanner; provides the most complete and accurate picture

PET/CT scanning allows for instantaneous results for both anatomy and function, taking the guess work out of comparison with separate images.

                                                                           

For More InformationFor More Information

www.petscaninfo.com www.petnetpharmaceutical.com www.nucmed.buffalo.edu www.crump.ucla.edu