Chapter 7 - Radiography Flashcards
A procedure where X-ray shadows project the patient’s anatomy onto the detector
Projection radiography
An exposed film that has not been chemically developed which contains a pattern of invisible silver halide grains with latent image centers
Latent image
Slight differences in film density depending on the exposure rate
Reciprocity law failure
Aqueous chemical bath containing a reducing agent
Developer
Bath of an aqueous oxidizing solution
Fixer
- dissolves the remaining (inactivated) silver halide from the emulsion layer areas that were not exposed (or were underexposed) to light.
Plot of the log of the relative exposure on the X axis and the optical density (OD) of the processed film on the y-axis
H and D curve (Hurter and Driffield)
Defined as the negative of the base-10 logarithm of the transmittance (T) of the film
Optical density
Refers to a photostimulable phosphor detector (PSP) systems
Computed radiography
PHOSTIMULABLE PHOSPHOR DETECTOR (PSP) screens
Storage phosphors
Activation procedure that creates defects in the BaFBr crystals that allow electrons to be trapped more efficiently
Doping
Defects in the crystalline lattice caused by the europium dopant
F-centers
Refers to the stage where the number of quanta is the lowest and therefore where the statistical integrity of the signal is worst
Quantum sink
The quantum sink should be at the stage where the X-ray photons are absorbed in the converter (scintillator or solid state detector)
X-Ray quantum limited detector
Detectors that make use of technology similar to that used inflation panel displays….
Flat panel thin-film-transistor(TFT) array detectors
Uses a scintillator to convert X-rays to light with optical coupling of the scintillator to the active matrix
Indirect X-Ray conversion TFT(thin-film-transistor) arrays
An electronic switch that is comprised of three connections: gate, source, and drain
Thin-Film-Transistor (TFT)
Refers to the percent of the area of each Dexel that is photosensitive
Fill factor
Use a semiconductor material that produces electron-hole pairs in proportion to the incident X-ray intensity
Direct X-ray conversion TFT arrays
Lower kVs emphasize _______due to the photoelectric effect in the patient
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Contrast
At the same kV and distance, the X-ray fluence is ______ proportional to the mAs– double the mAs and the X-ray fluence _____.
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Linearly; doubles
Used to describe how well X-ray detectors captures the incident X-ray photon beam
Quantum detection efficiency
Most X-ray detectors are?
A. Energy integrators
B. Photon counters
A. Energy integrators
Include X-ray to light photon Energy transfer in scintillators, etc.
Conversion efficiency (CE)
Increasing the speed of the detector by increasing the CONVERSION EFFICIENCY _______ image noise.
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Increases
Increasing ABSORPTION EFFICIENCY can ____ dose but has ______ on quantum noise in the image
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Reduce; no detrimental effect
A phenomenon where technologists tend to use unnecessarily high exposures(most likely occurs in exams such as portable radiography)
Dose creep
Indicates the amount of radiation reaching the detector and is not an indicator of dose to the patient
Exposure index
Feedback to the user on whether an appropriate exposure has been achieved is given by the_____.
Deviation index (DI)
DI=0 ; intended exposure to the detector is achieved
DI>0 ; overexposed
DI<0 ; underexposed
Higher atomic number materials (i.e.bone,with effective Z = 13,or Iodine, with Z=53) have _______ photoelectric absorption levels than lower atomic materials such as soft tissue (effective Z=7.6)
HIGHER
Characterizes the amount of scatter detected in an image
Scatter-to-primary ratio (SPR) OR the Scatter Fraction
Most widely used technology for reducing scatter in radiography,fluoroscopy and mammography
Anti-scatter grid (aka scatter grid)
The ratio of the height of the interspace material to its width; most fundamental descriptor of the grid’s construction
Grid ratio
The number of grid septa per centimeter
Grid frequency
Occurs if the X-ray tube is accidentally located at a different distance from the grid
Grid cut-off
A grid that moves with a reciprocating motion during the X-ray exposure,causing the grid bars to be blurred by this motion and not visible in the image. The motion is PERPENDICULAR to the long axis of the linear septa in the grid
Bucky grid
Essentially describes the radiation dose penalty of using the grid
Bucky factor
Fraction of primary photons that are transmitted through the grid
Primary transmission factor
Fraction of scattered radiation that penetrates the grid
Scatter transmission factor
Refers to the reduction in contrast due to scattered radiation
Contrast Degradation Factor
By moving the patient away from the detector, less of the scatter that is emitted from the patient will strike the detector; concept is similar to INVERSE SQUARE LAW (radiation intensity decreases as the square of the distance from the source)
Air gap principle
Gold standard in scatter reduction methods
Scan-slot radiography
Rare earth scintillator (3)
Gd2O2S, LaOBr and YTaO4
Silver halide film composition…
95% AgBr and 15% AgI
(Film) _____ introduces defects in the ionic crystal structures
AgS
