CH 13 - Instrumentation

Gamma Camera: Basic Principles

radionuclide imaging

what is the most important application of radioactivity in nuclear medicine

distribution of a radioactively labeled substance within the body after administration

the purpose of radionuclide imaging is to obtain a picture of the:

by recording the emissions from the radioactivity with external radiation detectors placed at different locations outside the patient

how is obtaining an image of the distribution of radioactivity with the body accomplished

50-500 keV

what is the preferred energy range of radiation for a gamma camera?

they are ideal to penetrate the body but not powerful enough to pass through the scintillator material

why is 50-500 keV the preferred range of radionuclide energy?

detection effiency

imaging system detectors must have good _____ for gamma ray

energy discrimination

an installed system should also have _____, so that gamma rays that have lost positional information (energy) by compton scattering within the body can be rejected based on their reduced energy

NaI(Tl)

what kind of detector provides both good detection efficiency and energy discrimination for gamma cameras?

8-300 keV

what is the range of gamma ray energies typically detected by NaI(Tl) detectors.

low penetrating power

why are alpha and beta particles of little use to imaging?

late 1940s

first attempts of radionuclide imaging occurred when?

an array of detectors around the head

how was early imaging performed in the 1940s

the incredible mathematical load

why was advancements of nuclear medicine a slow process?

rectilinear scanner

what did Benedict Cassen invent

Benedict Cassen

who invented the rectilinear scanner

1950s

when was the rectilinear scanner invented

raster like pattern

with the rectilinear scanner, the detector was scanned mechanically in a ________ over the area of interest

rectilinear scanner

the image was a pattern of dots imprinted on a sheet of paper by a mechanical printer that followed the scanning motion of the detector was the process of what instrument?

real time

in a rectilinear scanner, dots were added to the image in ______ as the gamma rays were detected

long imaging time due to needing several measurements at different angles around the organ of interest

the primary disadvantage of a rectilinear scanner

Hal Anger

who invented the first gamma ray camera

1953

when was the first gamma ray camera invented?

gamma ray camera

what did Hal Anger invent?

gamma ray camera

this instrument was capable of recording at all points of the images

pinhole aperture embedded in a sheet of lead

what allowed Hal Anger’s gamma camera to record at all points on the image

collimator

Hal Anger’s pinhole aperture in a sheet of lead is essentially a modern day ______

crystals

Hal Angers lead sheet was later changed to _____ to allow for faster imaging times as well as lower the administered doses

Anger scintillation/gamma camera

the introduction of crystal instead of lead in Anger’s gamma camera lead to the development of

light

radiation interacts with the NaI(Tl) scintillator and releases _____

electrical current

light released by the scintillation crystal is then converted and recorded as ____

titanium oxide (TiO2)

the NaI(Tl) crystal is surrounded by reflective material such as _____

maximize light output

titanium oxide is used to:

hermetically

how is the TiO2 sealed inside of a thin aluminum casing?

vacuum sealed or air tight

what does hermetically mean?

moisture

the aluminum casing and hermetic seal protects the crystal from:

silicone based adhesive or grease

an array of PM tubes is coupled optically to the back face of the crystal with a:

plastic light guides or guides grafted directly onto the crystal

what is used in a PM tube to help shuttle light into the PM tube

coordinates

once counts are sent to the circuits, data is assigned _____ in a graph

uses simple energy discrimination for falling into the energy window

describe this approach

photopeak positions and discriminator levels are set and stored in the computer. it has to be an exact match to known values saved or it is ignored from processing

describe this approach

9-10% at 140 keV

a modern gamma camera has a energy resolution of about

14% or 20 keV

the energy window on a modern gamma camera is normally set to ____ around 140 keV

pinhole

what kind of collimator is this

parallel hole

what kind of collimator is this

converging

what kind of collimator is this

diverging

what kind of collimator is this

no

can gamma cameras have normal lens to focus the radiation?

absorptive collimation

gamma cameras utilize what type of collimation for image formation

absorptive collimation

this projects an image of the source distributions to travel through to the detector only from the desired plane to the projector and blocks unwanted radiation from other angles.

they are absorbed by the collimator

what happens to projections that are not traveling in the proper direction?

valid event

a gamma ray is emitted parallel to the collimator, depositing all of its radiation at a single location

detector scatter event

a gamma ray is emitted parallel to the collimator holes, passing through and causing compton scattering in the NaI(Tl) crystals. this causes the scatter to either interact with the crystal or keep scattering.

object scatter event

the gamma ray is not emitted toward the collimator, instead it scatters through the body until it is emitted toward the detector

septal penetration

this occurs if the gamma ray is emitted toward the detector, but not straight on and it contains enough energy to move through the lead collimation

I-131 energy

what kind of energy can cause septal penetration for the camera?

valid event

A

detector scatter event

B

object scatter event

C

septal penetration

D