Nuclear Medicine Instrumentation Vocabulary

Flashcards for Nuclear Medicine Instrumentation Review

Scintillation cameras

Produce projection images of the distribution of radioactivity in patients; sometimes called gamma cameras or Anger cameras.

Photopeak width

is measured as full width half maximum(FWHM)

Energy resolution

The broadening of photopeak (FWHM) is termed

100%

The keV is 100 how many percentage is detected

92%

The keV is 140 how many percentage is detected

54%

The keV is 200 how many percentage is detected

22%

The keV is 300 how many percentage is detected

6%

The keV is 500 how many percentage is detected

10%

When the gamma ray is completely absorbed by the NaI, some of this energy converted into light how many percent?

Photopeak

is when an incident gamma ray is completely absorbed

10mm thick

For gamma ray imaging, NaI scintillators are ~thick

Ga67 and 111IN

Medium-energy collimators

Septa

The lead strips between the holes are called

55 PMTS

Scintillation cameras typically use

Parallel

Scintillation rays emerging from the patient

pass through a lead collimator that only allows photons traveling ____ to the collimator holes to reach the scintillator

4-6mm

Pinhole the typical aperture or diameter

multihole/parallel hole collimator

The workhorse of the collimator

Low energy collimator

used with 99mTc and 201TI have thin septa.

PHA

can be set to allow only selected energies to be counted, and reduce the number of Compton scatter photons in the image

PHA analysis

maximizes the number of photopeak events while minimizing the detected photons that would degrade image quality (i.e., Compton scatter)

NM images

can be viewed in real time on a display monitor during the acquisition

Nm images

can be viewed in real time on a display monitor during the acquisition

3 or 6

Projection images are obtained at selected angles, typically every ____ or ___ degrees

Iterative reconstruction algorithm

New used algorithms

CT SCAN

scan can be a low-dose scan for image coregistration and attenuation correction only

Higher dose CT scan

scans may be acquired for diagnostic imaging

lutetium oxyorthosilicate (LSO) or gadolinium oxyorthosilicate (GSO)

Modern PET scanners use detectors made of

Lutetium yttrium oxyorthosilicate

is also used, which is LSO doped with a small amount of yttrium

BGO AND LSO

have similar gamma ray absorption properties

GSO

is a markedly poorer absorber of 511-keV gamma rays

GSO AND LSO

are inorganic scintillators that emit more light than BGO

improves energy resolution

Increased light output of GSO and LSO

Increased light

output of GSO and LSO improves energy resolution

organic scintillators

emit their light much faster than those of BGO.

Shorter decay times

improve count rate performance (reduced dead time)

thick detectors

To efficiently detect 511-keV annihilation photons, _______are used (i.e., 20–30 mm)

20-30 mm

To efficiently detect 511-keV annihilation photons, thick detectors are used (?mm)

coincidence event

Two interactions occurring within a specified time interval τ (coincidence timing window) are called a

prompt coincidence

• ACD produces an output whenever two events are recorded within a specified coincidence timing window. Generically, any such events are called

extrinsic flood images

are obtained with the collimator in place and will assess the system performance including the collimator

intrinsic floods

are performed without the collimator and assess the performance of NaI crystal and associated light detectors

quadrant bar phantom

Resolution (i.e., the ability to separate two points) is checked using a

four sets of parallel bars

Quadrant bar phantoms have ________, with each rotated through 90 degrees, with dimensions of 3.5, 3.0, 2.5, and 2.0 mm

90

Quadrant bar phantoms have four sets of parallel bars, with each rotated through ___degrees, with dimensions of 3.5, 3.0, 2.5, and 2.0 mm

3.5, 3.0, 2.5, and 2.0 mm

Quadrant bar phantoms have four sets of parallel bars, with each

rotated through 90 degrees, with dimensions of ______

Bar pattern phantom

also check for linearity (i.e., ability to image straight lines)

high energy collimators

Are required for 131I imaging and have the thickest septa

Iodine escape peak

occurs at approximately 30 keV below the photopeak and is the result of characteristic K-shell x-rays from iodine that escape the crystal

PHOTOMULTIPLIER TUBES

Light output from the NaI crystal is detected by

window

measured by percent, determines the acceptable range of energies around the peak for subsequent counting

128×128

A typical NM matrix size is

64 × 64

Cardiac imaging uses matrix size of

1024 × 1024

Whole body imaging uses matrix size

two byte memory

The number of counts in each pixel in a NM

image is stored using a

10-⁴, or only 0.01%

Collimator sensitivity is low with approximately

500,000

The counts in images can vary over a wide

range, with a median value of

Single Photon Emission computed tomography(SPECT)

provides computed tomographic views of the three-dimensional distribution of radioisotopes in the body.

Parallel hole collimator

are commonly used for SPECT imaging

180 and 360

Scintillation cameras rotate ___ or __ degrees around the patient.

Scan projection

were originally used as inputs for filtered-back projection reconstruction algorithms to compute tomographic images

Multiheaded cameras

are used to increase

system sensitivity and reduce scan times

elliptical orbits

(i.e body contouring)for scintillation camera traveling around the patient allows the distance to the patient to be minimized

111In octreotide

for neuroendocrine imaging

111In labeled ProstaScint

for prostate imaging

67Ga

for infections

Bismuth Germanate

Most early-generation PET scanners had detectors made of

Collimators

Essential for providing spatial information in planar NM imaging.

Count

The registration of a single gamma ray by the detector; ~500,000 are acquired for a typical scintillation camera image.

Collimators

Typically made of lead and contain multiple holes; lead strips between holes are called septa.

Pinhole collimator

Simplest form of collimator, consisting of a single, small hole or aperture.

Multihole collimator

Provides substantially better geometric sensitivity compared to the pinhole collimator; consists of a very large number of parallel holes.

Converging multihole collimator

Provides both enhanced spatial resolution and improved sensitivity by focusing the direction of the holes at a point some distance from the collimator surface.

Diverging collimators

Project an image size that is smaller than the object size, and FOV increases with distance.

Collimator sensitivity

The fraction of gamma rays reaching it from all directions that pass through the holes.

NaI Scintillators

Detect gamma rays emerging from patients and are generally rectangular; very fragile and easily damaged.

Detection efficiency

Percentage of incident gamma rays absorbed in the scintillator.

Pulse height analyzer (PHA)

Electronic device used to determine which portion of the detected spectrum is used to create images.

Analog to digital converters

Used to generate the digital information for NM images.

Single photon emission computed tomography (SPECT)

Provides computed tomographic views of the three-dimensional distribution of radioisotopes in the body.

PET camera

Contains rings of detectors (scintillators) surrounding the patient.

Random coincidence (Accidental coincidence)

occur when annihilation photons from two unrelated positron annihilation events are detected in two different detectors, within the coincidence timing window, and recorded as a single coincidence event.

Sinogram

Line of response data are used to create a

filtered back projection

was popular in the early days of PET

but is now rarely used

depth independent

Attenuation in PET is____ and depends only on the total thickness of tissue traveled.

CT images

are used to generate attenuation correction factors for use in PET

ordered-subset expectation maximization

Images are reconstructed using statistically based algorithms such as

Time of flight (TOF) PET

Measuring the difference in arrival times of the two annihilation photons from an annihilation is used

TOF information

can be used in the reconstruction process to improve image quality including improved spatial resolution as well as enhanced lesion contrast

TOF PET

can identify the location of an annihilation event with an uncertainty that corresponds to a Full Width Half Maximum of ~7.5 cm

7.5 cm

TOF PET can identify the location of an annihilation event with an uncertainty that corresponds to a Full Width Half Maximum of

PET images

typically have several million counts

Several million

PET images typically have ______ counts

F18

The most common positron emitter used for PET imaging is

110 minutes

HALF LIFE OF F18

flourodeoxylglucose

18F in the form of ________ is the most commonly used agent