Instrumentation Flashcards
_____ produce projection images of the distribution of radioactivity in patients
Scintillation cameras
Scintillation cameras are sometimes called _____
gamma cameras or Anger cameras.
are essential for providing
spatial information in planar NM
imaging
Collimators
____ absorb incident gamma photons and produce many light photons.
Scintillators
Approximately ____ of the absorbed gamma ray energy is converted to light.
10%
Scintillation cameras typically use ___
55 PMTs
___ refers to the registration of a
single gamma ray by the detector, and
~ _____ counts are acquired for a typical scintillation camera image.
Count, 500,000
Scintillation cameras use computers to
________the acquired image data.
store, manipulate, and display
Collimators are typically made of ___ and contain multiple holes. The lead strips between the holes are called
____.
lead, septa
In general, only _____ photons emitted from the radioactive source will be accepted by the collimator and incorporated into the image.
0.01% (i.e., 1 in 10,000)
Types of collimator used in nuclear medicine:
- Pinhole collimator
- Multihole collimator/ Parallel-hole collimator
- Converging multihole collimator
- Diverging collimator
The simplest form collimator
pinhole collimator
It consists of a single, small hole or aperture located a set distance (typically on the order of 20 cm) from the surface of the NaI crystal.
Pinhole collimator
are cone shaped with a single
hole at the apex
Pinhole collimators
Images generated using a pinhole collimator are normally _____
magnified and inverted
can be of significant value when imaging small objects using a camera with a large field of view.
Magnification
Provides substantially better geometric
sensitivity compared to the pinhole
collimator, because the object is viewed
through many small holes rather than through a single hole.
Multihole collimator
The collimator spatial resolution depends on the
diameter
length of the collimator holes
distance from the source collimator
provides both enhanced spatial resolution and improved sensitivity
converging multihole collimator
produce a magnified image, and FOV decreases with distance
Converging collimators
_____ project an image size that is smaller than the object size, and FOV increases with distance.
Diverging collimators
is the fraction of gamma rays reaching it from allBdirections that pass through the holes.
Collimator sensitivity
Collimator sensitivity is low with approximately ____, of
the emitted photons being detected.
10-4, or only 0.01%
have larger holes and lower resolution
High-sensitivity collimators
have smaller holes and lower sensitivity
– High-resolution collimators
is degraded with increasing distance from the collimator.
Resolution
Low-energy collimators used with ____ have thin septa.
99mTc and 201TI
collimators that are most frequently
used
Low-energy high-resolution (LEHR)
– Used with 67Ga and 111In have thicker septa and therefore fewer holes and lower sensitivity.
Medium-energy collimators
– Are required for 131I imaging and have the thickest septa.
High-energy collimators
____ detect gamma rays emerging from patients and are generally rectangular.
NaI scintillators
For gamma ray imaging, NaI scintillators are ____
10 mm thick
• A _____ is when an incident gamma ray is completely absorbed (photoelectric effect).
photopeak
is the percentage of incident gamma rays absorbed in the scintillator.
detection efficiency
Light output from the NaI crystal is detected by
photomultiplier tubes (PMTs)
is measured as the full width half maximum
(FWHM).
Photopeak width
The broadening of the photopeak (FWHM) is termed
energy resolution.
is an electronic device used to determine which portion of the detected spectrum is used to create images.
pulse height analyzer (PHA)
The ___, measured by percent, determines the acceptable range of energies around the peak for
subsequent counting.
window
It consists of a single, small hole or aperture located a set distance (typically on the order of _____) from the surface of the NaI crystal
20 cm
The collimator spatial resolution of the pinhole, RPH, is determined by the diameter or the aperture, d (typically ___ mm) and the distances from both
the object and the NaI crystal to the aperture.
4-6 mm
A typical low-energy, parallel-hole collimator may have hole diameters and lengths of about ___ mm, respectively, and septal thicknesses between holes of about ____.
1 and 20 mm, 0.1 mm
The distance from the collimator to the focal point is typically on the order of ___ and thus far beyond the boundaries of the patient.
50 cm
Increasing the photon energy from 100 to 500 keV reduces detection efficiency from
100% to 6%
A measured width (broadening) of 28 keV for 99mTc (140 keV) corresponds to an energy resolution of ___
20%
% Photons Detected by 10-mm-Thick NaL Crystal with a photon energy of 100 keV
100
% Photons Detected by 10-mm-Thick NaL Crystal with a photon energy of 140 keV
92
% Photons Detected by 10-mm-Thick NaL Crystal with a photon energy of 200 keV
54
% Photons Detected by 10-mm-Thick NaL Crystal with a photon energy of 300 keV
22
% Photons Detected by 10-mm-Thick NaL Crystal with a photon energy of 500 keV
6
