NALINI SINGHROLL No. 10041

MBT – IBIOPHYSICS

Introduction Radio pharmaceuticals System components of Gamma camera Principle of Gamma camera Types of Gamma camera Applications Advanced techniques Summary References

Gamma camera was invented by H. Anger in the 1960s and is often referred to as the Anger camera.

Why γ rays? Gamma rays are chosen since alpha and beta

particles would be absorbed by tissues and not be detected outside the body, and can easily stopped by lead.

Technitium-99m is most widely used tracer because it has a half-life of 6 hours.

Isotope of molybdenum-99, with a half-life of 66 hours, which progressively decays to technetium-99.

Tracers are generally short-lived isotopes combined with other chemical compounds or pharmaceuticals to form radiopharmaceuticals which permit specific physiological processes to be scrutinized. They can be given by injection, inhalation or orally.

Doctors and chemists have identified a number of chemicals which are absorbed by specific organs.

With this knowledge, radiopharmacists are able to attach various radioisotopes to biologically active substances.

Once a radioactive form of one of these substances enters the body, it is incorporated into the normal biological processes and excreted in the usual ways.

It has a half-life of six hours which is long enough to examine metabolic processes yet short enough to minimize the radiation dose to the patient.

Technetium-99m decays ; which emits gamma rays and low energy electrons. Since there is no high energy beta emission the radiation dose to the patient is low.

The low energy gamma rays it emits easily escape the human body and are accurately detected by a gamma camera. Once again the radiation dose to the patient is minimized.

The chemistry of technetium is so versatile it can form tracers by being incorporated into a range of biologically-active substances to ensure that it concentrates in the tissue or organ of interest.

Collimator

NaI(Tl) crystal

Light Guide (optical coupling)

Photo multiplier-Tube array

Amplifier

Display

The tracer is injected into the patient. The radiation emitted from the patient is detected using a gamma camera.

A typical gamma camera is 40 cm in diameter – large enough to examine body tissues or specific organs. The gamma rays are given off in all directions but only the ones which travel towards the gamma camera will be detected.

A collimator. A detector. Electronic systems.

A gamma camera consists of three main parts:

electronic systems

detector

collimator

The collimator is usually made of lead and it contains thousands of tiny holes.

Only gamma rays which travel through the holes in the collimator will be detected.

Four types of collimators.

The Collimator

The detector is a scintillation crystal and is usually made of Sodium Iodide with traces of Thallium added.

The detector is a scintillation crystal and it converts the gamma rays that reach it into light energy.

The Detector

• The electronic systems detect the light energy received from the detector and converts it into electrical signals.

The Electronic Systems

Principle of PMT

Anger camera can be used for static or dynamic imaging

Stationary cameras are designed to be at a fixed location while mobile camera has wheels.

There is a time delay between injecting the tracer and the build-up of radiation in the organ.

Static studies are performed on the brain, bone or lungs scans.

The amount of radioactive build-up is measured over time.

Dynamic studies are performed on the kidneys and heart.

To assess individual kidney and/or bladder function.

To detect urinary tract infections. To detect and assess obstructed kidney(s). To detect and assess vesico-ureteric reflux. To assess kidney transplant(s).

Renograms are dynamic images of the kidneys and they are performed for the following reasons:

The tracer is injected into the patient. The radioactive material is removed

from the bloodstream by the kidneys. Within a few minutes of the injection,

the radiation is concentrated in the kidneys.

After 10 – 15 minutes, almost all of the radiation should be in the bladder.

The gamma camera takes readings every few seconds for 20 minutes.

The computer adds up the radioactivity in each kidney and the bladder.

This can be shown as a graph of activity versus time – a time-activity curve.

A more recent development is Positron Emission Tomography (PET).

A positron-emitting radionuclide is introduced, usually by injection, and accumulates in the target tissue. As it decays it emits a positron, which promptly combines with a nearby electron resulting in the simultaneous emission of two identifiable gamma rays opposite directions which are detected by a PET camera.

PET's most important clinical role is in oncology, with fluorine-18 as the tracer. It is also well used in cardiac and brain imaging.

PET principle showing annihilation reaction between positron and electron, production of two gamma rays and detection in coincidence detection system.

• Several gamma-detector rings surround the patient.• When one of these detects a photon, a detector

opposite to it, looks for a match.• Time window for the search is few nano secs.• If such a coincidence is detected, a line is drawn

between the detectors.• When done, there will be areas of overlapping lines

indicating regions of radioactivity.

18FDG is probably the most widely used PET tracer.

HIGH FDG pick-up by tumors first reported in 1980.

Can also be used to measure rate of metabolism in the brain.

Diagnostic radiopharmaceuticals can be used to examine blood flow to the brain, functioning of the liver, lungs, heart or kidneys, to assess bone growth, and to confirm other diagnostic procedures. Another important use is to predict the effects of surgery and assess changes since treatment.

Radioactive tracers are used in nuclear medicine because the radiation it emits is easy to detect.

http://www.ejbjs.org/cgi/reprint/65/3/381.pdf http://www.anl.gov/Media_Center/News/

2003/031031gammacam.htm http://en.wikipedia.org/wiki/Nuclear_medicine http://en.wikipedia.org/wiki/Medical_imaging http://www.medicimaging.com/files/Upgrading

%20Gamma%20camera.pdf http://pet.radiology.uiowa.edu/downloads/thomas

%20idstein%20papers/camera%20design%20considerations/scintillation%20crystal%20desi.pdf

http://en.wikipedia.org/wiki/Fludeoxyglucose_(18F)