gamma camera

GAMMA CAMERA

GAMMA CAMERA

a

• Gamma radiation is one of the three types of natural

radioactivity discovered by Becquerel in 1896. Gamma rays were first observed in 1900 by the French chemist Paul

Villard when he was

investigating radiation from radium

GAMMA CAMERA

in 1957



Developed by Hal Anger at Berkeley therefore also called Anger camera



An electronic device that detects gamma rays

emitted by radio pharmaceautical (e.g technetium

99m (Tc-99m) that have been introduced into the

body as tracers. The position of the source of the

radioactivity can be plotted and displayed on a TV

monitor or photographic film.

• Gamma camera detects radioactive energy that is emitted from the patient's body and converts it into an image.

• The gamma camera does not emit any radiation.

• The gamma camera is composed of radiation detectors, called

gamma camera heads, which are encased in metal and plastic and most often shaped like a box, attached to a round circular donut shaped gantry.

• The patient lies on the examination table which slides in between the parallel gamma camera heads which are suspended over the examination table and located beneath the examination table.

• Sometimes, the gamma camera heads are oriented at a 90 degree angle and placed over the patient's body.

GAMMA CAMERA

WORKING PRINCIPLE

Note: the gamma camera emitted in all

direction 

COMPONENTS OF GAMMA CAMERA

 Collimator

 NaI(Tl) crystal.

 Photomultiplier Tubes(PMT)

 Pre-amplifier

 Position logic circuits

 Amplifier

 Pulse height analyzer

 Data Analysis Computer

 Display (Cathode Ray Tube etc).

 Gantry

THE MAIN COMPONENTS

FLOW DIAGRAM OF

GAMMA CAMERA

C OLLIMATOR

 Collimator is made from lead.

 Maintains the quality of image

 Spaces between holes known as septa

 Collimator consisting of a series of holes in a lead plate can be used to select the direction of the rays falling on the crystal. There are 4 types of collimator.

◦ Parallel-hole collimator

◦ Pin-hole collimator

◦ Diverging

◦ Converging

 Most collimators in use are parallel hole collimators. A parallel hole collimator is shown schematically in Figure.

C OLLIMATOR(CONT)

SCINTILLATOR (C RYSTAL)



Sodium iodide with thallium NaI( Tl )



The main function of crystal is convert gamma ray to photons of visible light process called scintillation.



Amount of light proportional to deposited energy.

CRYSTAL (CONT)

P HOTOMULTIPLIER TUBE(PMT)

•

The photomultiplier tube (PMT) is an

instrument that converts light to electrical signals.

•

Gamma Camera contains 37 -91 PMT.

•

It detects and amplifies the electrons that are produced by the photocathode. The

photocathode, when stimulated by light

photons, ejects electrons. The PMT is attached

to the back of the crystal.

PHOTOMULTIPLIER TUBE(PMT)

Only a very small amount of light is given off from the scintillation detector. Only one electron is generated for every 7 to 10 photons incident on the photocathode.This

is

focused on a it

and re- emits

dynode

that many more

electron absorbs

electrons (usually 6 to 10).These new electrons are focused on the next dynode and the process is repeated over and over in an array of dynodes.

At the base of the PMT is an anode that attracts the final large cluster of electrons and converts them into an electrical pulse.

PRE AMPLIFIER AND AMPLIFIER

 Preamps attach above the PMT.

 The amount of charge given by PMT is very small. Even though we have used a sophisticated photodetector like a PMT we still end up with quite a small

electrical signal.

 A very sensitive amplifier is

therefore needed to amplify this signal. This type of amplifier is generally called a pre-amplifier.

 Afte that use amlifier to amlify the signal as need.



Position circuitary receive the electrical impulses from the tubes in the summing matrix circuit (SMC).



This allows the position circuits to determine where each scintillation event occurred in the detector crystal



The amplitude of each electrical pulse from the amplifiers is measured in the electrical circuits of the pulse-height analyzer



Peak height analyzer and a computer convert the light into a useful anatomical image

P OSITIO CIRCUITARY &

P ULSE HEIGHT ANALYSER

• A pulse-height analyzer (PHA) is an instrument that accepts electronic pulses of varying heights from particle and event detectors, digitizes the pulse heights, and

saves the number of pulses of each height in registers or channels, thus recording a pulse-height spectrum or

pulse-height distribution used for later pulse-height analysis. PHAs are used in nuclear- and elementary- particle physics research. A PHA is a specific

modification to multichannel analyzers.

• A pulse-height analyzer is also integrated into  particle counters or used as a discrete module to calibrate particle counters.

PHA

DATA ANALYSIS COMPUTER



Finally, a processing computer is used to deal

with the incoming projection data and processes it into a readable image of the 3D spatial

distribution of activity within the patient.



The computer may use various methods

to reconstruct an image, such as filtered

back projection or iterative reconstruction .

GANTR



A gamma camera system attached with Y

gantry.



All circuits and motors related to movement ( longitudnal,rotational,up & down)of

gamma camera placed in gantry.

gantry

GAMMA CAMERA

The scan of whole body. SCAN

APPLICATION OF GAMMA CAMERA

 GAMMA CAMERA used to locate cancerous tumours,minor bone fractures,abnormal functioning of organs and other medical problems .

 Iodine-131 is used to detect thyroid (a gland that absorbs Iodine) problems.

 Technetium-99 is used to find tumours in the body.

 Gamma camera give structural and functional image of body organs.



Bone scan.



Myocardial Perfusion



Lungs scan.



Kidney function.



Thyroid uptake



Whole body scan.

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