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Instrumentation NMTCB Practice Questions and Answers 100% Solved
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Instrumentation NMTCB Practice
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Instrumentation NMTCB PracticeWhat is a gamma camera crystal made of? - answer Sodium iodide activated with
thallium
What is the purpose of the crystal in a gamma camera? - answer To absorb gamma (γ)
rays and convert them into visible-light photons
What is the mechanism by which gamma (γ) rays interact with a gamma camera
crystal? - answer Photoelectric effect or Compton scattering.
What is the relationship between the energy of an absorbed gamma (γ) ray and the
amount of light produced by a gamma camera crystal? - answer The amount of light
produced is directly *proportional* to the amount of energy lost by the absorbed gamma
(γ) ray.
What is the purpose of the photomultiplier tube (PMT) array? - answerTo detect the
photons produced in the crystal and produce a proportional pulse
How does increasing crystal thickness influence camera sensitivity and resolution? -
answerThick crystals have higher sensitivity but lower resolution
(i.e., thicker than 0.5 inch or 1 cm)
What is the output of a single PMT? - answerA pulse (very small signal) that represents
amplification of the light detected.
The PMTs are __________ to the crystal by optical grease or a light pipe. -
answeroptically coupled
What is the output of the PMT array decoder circuit? - answerSpatial coordinates (x+ ,
x- , y+ , y- ) of the scintillation event.
How does increasing the number of PMTs affect the resolution? - answerIt improves the
resolution.
How many PMTs are in a modern gamma camera? - answer75 or 91 per head
The electronic component in a gamma camera that is used to disregard unwanted
photons is called __________. - answera pulse height analyzer
Why do scattered photons from within the patient cause major imaging difficulties? -
answerThe scattered photons lead to incorrectly positioned radioactive events.
, What is the "window" in a pulse height analyzer (PHA)? - answerThe range of
acceptable energies around a photopeak.
What are the energy limits of a 20% window centered at 140 keV? - answer126 to 154
keV
********
140kev(0.20) = 28
28/2 = 14
140 +14 = 154 kev
140 -14 = 126kev
Why do some gamma cameras have multiple PHAs? - answerTo acquire several peaks
simultaneously (e.g., 67Ga).
What is a gamma camera collimator made of? - answerlead or tungsten
What is the purpose of a gamma camera collimator? - answerProject an image of the
source distribution directly onto the crystal
What does the term "collimator sensitivity" mean? - answerThe ratio of gamma (γ) rays
that pass through the collimator to those incident upon it.
When is it appropriate to use a pinhole collimator? - answerWhen imaging small organs
that lie close to the skin (e.g., thyroid gland)
. What are the principal *disadvantages* of a pinhole collimator? - answerImage
distortion and poor sensitivity
Walls within the collimator that separate adjacent holes are called _________ -
answercollimator septa
What is the purpose of collimator septa? - answerTo block gamma (γ) rays traveling
obliquely toward the crystal.
The presence of a starburst-type appearance when imaging a hot object with a parallel-
hole collimator is due to __________. - answerseptal penetration
What defines the energy range of a collimator? - answerThe composition, thickness,
and length of the septa.
How does increasing the septal *length* affect collimator resolution and sensitivity? -
answerIt improves the resolution and lowers sensitivity
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