Scintillation Camera

Nuclear imaging

produces images of radionuclide distribution in the body.

Imaging photons

include gamma rays, characteristic x-rays, and annihilation photons.

To form a projection image, an imaging system must determine not only the photon flux density (number of x-or gamma rays per unit area) at each point in the image plane but also

the directions of the detected photons.

Photon emission

radionuclides emit photons isotropically in all directions.

Projection imaging

requires photon flux density and direction information.

Collimator function

allows photons from specific directions to reach the detector.

Collimator limitation

wastes over 99.9% of emitted photons.

Positron imaging advantage

can determine photon direction without collimation.

Rectilinear scanner

early device using a single moving detector which dominated nuclear imaging from the early 1950s through the late 1960s

Rectilinear scanner

used a single moving radiation detector to sample the photon fluence at a small region of the image plane at a time.

large area position-sensitive detector

Scintillation Camera is improved by the use of _____ to sample simultaneously the photon fluence over the entire image plane

large area position-sensitive detector

a detector indicating the location of each interaction

positron-sensitive detector system

permits more rapid image acquisition and has replaced single scanning detector systems

Anger scintillation camera

most widely used nuclear imaging device.

Radiopharmaceutical role

determines lesion detectability and image quality.

dosimetric properties of a radiopharmaceutical

determine the maximal activity that can be administered to a patient

Radiopharmaceutical dose

affects the amount of statistical noise (quantum mottle) in the image and the spatial resolution.

 Tc-99m labeled radiopharmaceuticals

ideally suited radiopharmaceuticals for Anger gamma scintillation camera

Scintillation camera advantage

allows faster image acquisition and dynamic studies.

70keV (TI-201) to 364 keV (I-131) or even 511 keV (F-18

Although it can produce satisfactory images using x-or gamma rays ranging in energy from about

the scintillation camera is best suited for imaging photons with energies in the range of

100 to 200 keV

70keV

TI-201

364 keV

I-131

511 keV

F-18

thallium- activated sodium iodide (NaI: TI) crystal

A scintillation camera, contains a disk-shaped or rectangular a what crystal?

typically 0.95cm (1/2 inch)

How thick is thallium- activated sodium iodide (NaI: TI) crystal in a scintilation camera?

Photomultiplier tubes (PMTs)

convert light from crystal into electrical signals.

Preamplifier (preamps)

amplifies signals from PMTs.

Gamma camera

The device that is optically coupled to Photomultiplier tubes (PMTs) is?

typically 37 to 91

How many PMT is coupled to a Gamma camera?

5.1 to 7.6-cm (2-to3-inch) diameter

How thick is a PMTs?

Lucite light-pipe

Some camera designs incorporate a ___ between the glass cover of the crystal and PMTs

does not generate meaningful images

a scintillation camera without a collimator

septa

The lead walls, called___  between the holes in the collimator

lead walls

between the holes in the collimator absorb most photons approaching the collimator from directions that are not aligned with the holes

perpendicular

Most photons approaching the collimator from a nearly __ in direction

visible and ultraviolet light

many of photons are absorbed in the sodium iodide crystal, causing the emission of what?

proportional to the amount of light it received from an x- or gamma- ray interaction in the crystal.

The amplitude of the pulse produced by each PMT

forms a two-dimensional projection of the three-dimensional activity distribution in the patient.

Because the collimator septa intercept most photons approaching the camera from non-perpendicular directionsthe pattern of photon interactions in the crystal

hexagonal holes

most state-of-the-art collimators have _______ and are usually made from lead foil, although some are cast.

its spatial resolution degrades rapidly

what happens to Spatial Resolution when increasing collimator-to-object distance

pinhole collimator

commonly used to produce magnified views of small objects, such as thyroid or hip joint.

small (typically 3- to 5-mm diameter) hole in a piece of lead or tungsten mounted at the apex of a leaded cone.

A pinhole collimator is consist of

converging collimator

has many holes, all aimed at a focal point in front of the camera.

converging collimator

This type of collimator magnifies the image (The magnification increases as the object is moved away from the collimator.)

diverging collimator

has many holes aimed at a focal point behind the camera.

diverging collimator

This type of collimator minifies the image (minification increases as the object is moved away from the camera.)

fan-beam collimator

A hybrid of the parallel-hole and converging collimator, used in single photon emission computed tomography (SPECT) to take advantage of the favourable imaging properties of the converging collimator.

emission imaging

another term of Image formation

pulse height analyzers

function of the camera’s energy discrimination circuit is known as

function of the camera’s energy discrimination circuits

is to reduce this loss in resolution and contrast by rejecting photons that scatter in the patient or result in coincident interactions.

system or extrinsic measurements

Measures of the performance of a scintillation camera with the collimator attached

intrinsic measurements.

Measures of camera performance with the collimator removed

System measurements

What measurements gives the best indication of clinical performance?

comparing the performance of different cameras

intrinsic measurements are often more useful for _____ because they isolate camera performance from collimator performance.

Uniformity

is a measure of the camera's response to uniform irradiation of the detector surface

Spatial Resolution

is a measure of the camera's ability to accurately portray spatial variations in activity concentration and to distinguish as separate radioactive objects in close proximity.

Spatial Linearity (lack of spatial distortion)

is a measure of the camera's ability to portray shapes of objects accurately. It is determined from the images of a bar phantom, line source, or other phantom by assessing the straightness of the lines in the image.

System efficiency (sensitivity) of a scintillation camera

is the fraction of the x- or gamma rays emitted by a source that produces counts in the image

quantum mottle (graininess)

system efficiency is important because it, in conjunction with the imaging time, determined what in the image?

Collimator efficiency

is the fraction of photons emitted by a source that penetrate the collimator holes. In general, it is a function of the distance between the source and the collimator and the design collimator

Energy resolution of a scintillation camera

is a measure of its ability to distinguish between interactions depositing different energies in its crystal.

reject larger fractions of photons that have scattered in the patient and coincident interactions

A camera with superior energy resolution is able to?? That produces image with better contrast