Final Exam Review - Part 2

Front 1

What generator is used in PET imaging?

Back 1

Sr82/Rb82

Front 2

What is the most commonly used generator?

Back 2

Mo99/Tc99m

Front 3

Describe the Mo99 generator's features

Back 3

• Mo99 immobilized on a column of alumina (Al2O3 - aluminum oxide)
• Eluted with 0.9% saline solution to produce sodium pertechnetate
  

Front 4

How is Mo99 produced?

Back 4

• Reactor neutron activation of Mo98
• Fission of U235
  

Front 5

What are the impurities associated with a Mo99/Tc99m generator?

Back 5

• Mo99
• Hydrolyzed-reduced Tc
• Al3
  

Front 6

What are the limits on the impurities associated with a Mo99/Tc99m generator?

Back 6

• <0.15 uCi of Mo99 per mCi of Tc99m at time of administration
• <10 ppm of Al3+ (also expressed is ug/ml)
  

Front 7

What are the radionuclides produced in a cyclotron?

Back 7

• F18
• C11
• N13
  

Front 8

What are the radionuclides produced in a cyclotron used for?

Back 8

PET imaging

Front 9

How does a cyclotron work?

Back 9

• Charged particles are injected into the center of the cyclotron
• They move in a circle parallel to the two magnets
• Accelerated as they travel between the two magnets (dees)
  

Front 10

What radionuclides used in Nuc Med are made in a nuclear reactor?

Back 10

• I131
• Xe133
• Mo99

Front 11

How are the radionuclides produced in a nuclear reactor?

Back 11

• Reactor contains fuel rods that have large, unstable atoms (U235, U238, Pu239)
• Atoms undergo fission
• Neutrons are slowed by a moderator substance like graphite, water, or heavy water
• Cadmium control rods are inserted or withdrawn to control reaction speed

Front 12

How do gas filled detectors operate?

Back 12

• Charge flow
• Charge neutralization (ex: pocket dosimeter)
• Pulse counting (ex: geiger counter)
  

Front 13

What are the five operational modes of gas filled detectors?

Back 13

• Recombination
• Ionization
• Proportional
• Geiger
• Discharge
  

Front 14

Describe the Recombination region of a GFD

Back 14

• Low voltage -> weak field -> ions recombine
• Incomplete charge collection
  

Front 15

Describe the Ionization region of a GFD

Back 15

• Complete primary charge collection
• No multiplication or amplification of charge
  

Front 16

Describe the Proportional region of a GFD

Back 16

• Electron Energy is > ionization energy = charge multiplication (aka secondary charge generation) or electron avalanche
  

Front 17

Describe the Geiger region of a GFD

Back 17

• All gas inside detector is massively involved in multiple, successive ionizations
• Results in secondary avalanches
  

Front 18

Describe the Discharge region of a GFD

Back 18

• Continuous breakdown with or without radiation
• Will damage the counter
  

Front 19

In what region do Ionization Chamber Detectors operate?

Back 19

Ionization Region

Front 20

List three examples of ICDs and pertinent information about them

Back 20

• Dose Calibrator - Current is proportional to the activity of the measured isotope; Only reports activity; Requires a different internal setting for each radionuclide
• Survey Meter - Evaluates exposure; Monitors ambient radiation levels (exposure rates) or counting rates; Subtype called 'cutie pie' used for high fluxes of X and gamma rays; used for measuring thyroid therapy patients; cannot detect contamination
• Pocket Dosimeter - Provides wearer with an immediate reading of x-ray and gamma ray exposure

Front 21

Describe Proportional Counters/Detectors

Back 21

• Similar to ionization chambers with a few exceptions
• Gas amplification of incoming radiation causes a pulse of current that registers as an incoming count
• Operates in proportional region
• Quenching gas is used to stop multiplication
• Can distinguish between types of radiation
• Most commonly used to quantify alpha/beta radiation

Front 22

Describe Geiger Counters

Back 22

• Operates in Geiger-Mueller region
• Impossible for GC to detect type of radiation
• Uses limited to low count rates because of large dead time (interval of insensitivity following a stimulus)
  
• Quenching gas to stop multiplication
• Used for exposure and contamination detection
  

Front 23

What are Photographic and Luminescent Detectors used for? Give two examples.

Back 23

• Measure cumulative exposure to radiation
• Badges and Rings
• Interpreted at a laboratory
  

Front 24

How do solid scintillation detectors operate?

Back 24

Convert energy from ionizing radiation into pulses of light

Front 25

Give three examples of SSDs

Back 25

• Well counter
• Thyroid Probe
• Surgical Probe
  

Front 26

Describe the well counter

Back 26

• Designed for high-sensitivity measurements
• Has high intrinsic and geometric efficiency
  

Front 27

What are the three types of surgical probes and their uses?

Back 27

• Sentinel Node Localization - Staging breast, melanoma, and other cancers. Used to help determine course of treatment
• PET probes - Used by surgeons to localize tumors for excision and evaluation of surgical margins
• Hyperparathyroidism probe - Gamma probe used for small incisions, such as in the neck. Used to localize and remove parathyroid adenomas
  

Front 28

What are the key features of collimators?

Back 28

• Ensures each point on the image corresponds to a unique point on the source
• Thousands of aligned holes
• Designed to allow only photons traveling perpendicular to the crystal's surface to reach the crystal
• Septa of the holes attenuate photons traveling in other directions
  

Front 29

What are the four basic types of collimator?

Back 29

• Parallel Hole (standard)
• Diverging
• Converging
• Pinhole
  

Front 30

Describe Low Energy All Purpose or General All Purpose collimators

Back 30

• Relatively large holes
• High sensitivity, low resolution
• Best for low energy photons and dynamic imaging
• Typically used with Tc99m and Tl201
  

Front 31

Describe Low Energy High Resolution collimators

Back 31

• High resolution, low sensitivity
• Larger number of holes with smaller diameter and longer length
• Typically used with Tc99m and Tl201
  

Front 32

Describe Medium Energy collimators

Back 32

• Thicker septa than LE collimators
• Lower sensitivity than LE, higher sensitivity than HE
• Best for use with photons like In111 and Ga67
  

Front 33

Describe High Energy collimators

Back 33

• Best for use with high energy nuclides like I131
• Thickest septa, smallest holes
• Lowest sensitivity
  

Front 34

Name and briefly describe the four common types of non-parallel hole collimators

Back 34

• Slant Hole - Holes are angled or slanted to provide oblique views when perpendicular to the patient
• Converging - Holes are angled inward, towards the organ (think \/) to magnify it
• Diverging - Holes are angled away from organ (think /\) to minimize the organ's size
• Pinhole - Single hole, 2-4mm in diameter, generates magnified image.
  

Front 35

How does an image appear when a pinhole collimator is used?

Back 35

Image is upside down and reversed right to left (software usually corrects automatically)

Front 36

What is the ideal scenario for photon behavior in imaging?

Back 36

Photons leave source/patient and travel perpendicular to detector head, pass through collimator, and strike crystal.

Front 37

How do scattered photons occur and what results?

Back 37

• Radiation is emitted in an isomeric fashion
• Some photons traveling in a non-perpendicular fashion can make it through the collimator
• This gives false positional information as the camera cannot distinguish the direction
  

Front 38

How does compton scatter affect images?

Back 38

• Gamma photons scatter within the body, changing trajectory on their way out
• May wind up passing through collimator and striking crystal, giving false positional info
• Additionally, compton scatter may result in energy loss that puts the photon outside the energy window

Front 39

What happens if photons don't strike the crystal? (I know, I know... this is super obvious)

Back 39

No scintillation event, no count recorded, no contribution to image

Front 40

Describe how PMTs convert light to electrical impulse

Back 40

• Scintillation light is absorbed by all PMTs
• Amount of light is an indication of distance from PMT (important later)
• Light strikes photocathode of the PMT, causing it to emit photoelectrons
• Electrons are multiplied by passing through dynodes en route to the anode
  

Front 41

Describe what takes place when photons strike the scintillation crystal

Back 41

• Photons interact with crystal via Compton and photoelectric effect
• NaI atoms are excited and return to ground state, which emits light
• Brightness is proportional to the energy of the incident photon
• Each keV of energy absorbed by the crystal results in the emission of about 40 light photons
  

Front 42

What does the analog to digital converter (ADC) do?

Back 42

Converts the pulse of energy to an electrical pulse

Front 43

How does the positioning algorithm generate its results?

Back 43

• Combines digital signals from adjacent PMTs after they've gone through the ADC
• Uses the signal strength to localize count
  

Front 44

Where is a preamplifier in relation to a PMT and what does it do?

Back 44

• Close to the PMT on the anode side
• Increases the charge sufficiently to allow transmission to the main amplifier
  

Front 45

What does the main amplifier do?

Back 45

Increases electrical pulse a thousandfold

Front 46

Is the end result of amplification proportional to the original energy absorbed by the crystal?

Back 46

Yes

Front 47

What is the Z pulse and how is it generated?

Back 47

• Z pulse is a representation of the energy of the gamma ray that struck the crystal
• Sum Circuits gather and total the output signals of PMTs to create the Z pulse
  

Front 48

How is the Z pulse used?

Back 48

Z pulse allows us to set an energy window and discriminate incoming counts that are above or below a certain keV as well as acquire photons of differing energy peaks

Front 49

What are the components of the energy spectrum graph?

Back 49

• Photopeak - the peak that corresponds to principal energies of the gamma rays
• Compton continuum/edge/valley/plateau - Occurs over a large range of energies
• Iodine escape peak - results from photoelectric effect, produces a 28 keV xray
• Coincidence peak - A spike in the spectrum caused by two photons striking the detector at the same time (shows as twice the energy of one of the photons)
  
• Backscatter peak - Photons deflected from the lead and not previously counted
• Characteristic x-ray peak - 72 keV x-ray, produced by photoelectric interaction with lead shielding
  

Front 50

What are the 3 output signals produced by a scintillation event?

Back 50

• X position
• Y position
• Z pulse
  

Front 51

What is the formula for calculating pixel size in a given matrix?

Back 51

Pixel Size (mm) = FOV (mm)/matrix dimension

Front 52

What is the formula for calculating pixel size with a zoom factor applied?

Back 52

Pixel size (mm) = FOV (mm)/matrix dimension x zoom factor

Front 53

Name the four types of image acquisition and briefly describe each

Back 53

• Static - set for a pre-determined number of counts or time
• Gated - data is synchronized with patient's EKG signals to create images at the desired rate and sequence
• Dynamic - used when RP distribution changes rapidly
• SPECT - for RP distribution in coronal, sagittal, and transverse planes