Finals Flashcards
One of the two photographic properties that comprise visibility of detail; degree of overall blackening of the film
Density/image receptor (IR) exposure
The image is visible to the human eye only because sufficient IR exposure/density and contrast exists to permit the structural details to be percieved
Visibility of detail
Monitor control function that can change the lightness and darkness of the image on a display monitor but is not related to IR exposure; luminous intensity (measured in candelas) of the display monitor’s light emission
Brightness
Digital post-processing that produces changes in density/brightness
Window level
Range of densities of human visibility
OD 0.25-2.50
What is the controlling factor of density/IR exposure (principal method for adjusting for insufficient or excessive exposure)?
Milliamperage-seconds (mAs)
Film density should remain unchanged as long as the intensity and duration of the x-ray exposure (controlled by mAs) remains unchanged; fails for extremely short (less than 0.01 second) or long (more than a few seconds) exposure times
Reciprocity law
Minimum change necessary to cause visible shift in film density
30% of mAs or any other influencing factors that would equal this change
Acceptance limit for density/IR exposure that requires repeating exposure
30% over- or underexposed
General rule of thumb for mAs changes
Make adjustments in increments of doubles or halves
9 influencing factors affecting density/IR exposure
Kilovoltage (kV) Focal spot size Anode heel effect Distance (SID and OID) Filtration Beam restriction Anatomical part Grid construction Image receptors
3 ways kV alters the intensity of the beam reaching the IR
Controls the energy and therefore the strength of the electrons striking the target of the x-ray tube for any given mAs
Controls the average energy of the x-ray photons produced at the anode target therefore a change in kV alters the intensity of the beam when the mAs and other factors remain the same
Affects the production of scatter
Used as a guide to maintain the same IR exposure/density when kV changes
A 15% increase in kV causes a doubling of exposure to the IR; a 15% decrease in kV causes a halving or exposure to the IR
15% rule
Range of kVp the 15% rule is accurate in
60-100 kVp
Large focal spots tend to do this more at higher mA’s (because the incident electron beam is not as easily focused by the focusing cup) and may occasionally reach a point where they alter the IR exposure; rare for this to cause a visible density/IR exposure difference
Blooming
Due to the geometry of the angled anode target, the radiation intensity is greater on the cathode side
Depending on the angle of the anode, this can cause an IR/exposure variation of up to 45%
More pronounced when the collimator is open wide than when it is closed because a greater portion of the peripheral beam and therefore a greater portion of the intensity difference, reaches the IR when the collimator is wide open
More significant when using extremely small angle anodes (12º or less)
Anode heel effect
At what end of the tube is IR exposure always greater?
Cathode
How can the anode heel effect be minimized?
By collimating the beam and eliminating as much of the intensity difference at the periphery as possible; if a given film size is required collimation may be achieved by using a greater SID
The intensity (exposure) varies inversely with the square of the distance
Inverse square law
What formula represents the inverse square law?
I1/I2 = D2^2/D1^2
Direct square law that states mAs must increase when distance increases, and vice versa, in order to maintain IR exposure
To maintain IR exposure, mAs (or an influencer) must be changed to compensate for the exposure change
Only accurate within a moderate acceptance range; the nonlinearity of some components in the imaging system makes it impossible to exactly quantify the relationship between radiation beam intensity and IR exposure
Exposure maintenance formula
What is the exposure maintenance formula?
mAs1/mAs2 = D1^2/D2^2
OID has an effect on density/IR exposure
Uses and increases OID to prevent scatter (which would normally cause a visible increase in density/IR exposure when radiographing large patients) from reaching the IR
By increasing OID, scatter that would normally strike the IR will miss it, causing a decrease in density/IR exposure
However in most instances OID variations are insufficient to cause visible density/IR exposure changes
Air-gap technique
Density/IR exposure _______ when filtration is increased
Decreases
4 circumstances technical factor compensation for changes in density/IR exposure is required
Large anatomical part
High kV
Low grid efficiency
Non-grid examinations
2 factors that affect the tissue type
Average atomic number
Density (quantity of matter per unit volume) of the tissue
Compensation for varying grid ratios is generally accomplished by increasing mAs; the amount of mass required can be calculated using these
Grid conversion factors
Changing between grids (most common clinical problem) is accomplished by using what formula?
mAs1/mAs2 = GCF1/GCF2
One of the two properties that comprise visibility of detail; the difference between adjacent densities/IR exposures
Can be mathematically evaluated as the percentage or ratio of the differences between densities/IR exposure
Contrast
Describes the concept of contrast as it is displayed on a soft-copy monitor for digital images; proper term for the range of brightness of the display monitor light emission
Dynamic range
Digital processing that produces changes in the range of density/brightness, which can be used to control contrast
Window width
Grayscale bit depth (z axis)
Contrast/dynamic range/window width
Differences between adjacent densities that comprise contrast are great
Fewer discernible shades of gray
Low kVp
Short scale
Directly related to the number of photoelectric effect interactions that occur in the subject
High contrast
Differences between adjacent densities that comprise contrast are minimal
More discernible shades of gray
High kVp
Long scale
Directly related to the amount of Compton scatter that occurs in the subject
Low contrast
The number of useful visible densities or shades of gray
Scale of contrast
Total range of density/IR exposure values recorded by the IR
Physical contrast
Total range of density/IR exposure values that can be perceived by the human eye in a single image
Visible contrast
Total amount of contrast acquired from both the IR and anatomical part
Image contrast
4 factors that film contrast depends on
Intensifying screens
Film density
D log E curve
Processing
The number of shades of gray in a radiographic image
Grayscale
The result of differences in transmission of the beam as it passes through the patient resulting in signal differences to the digital detector
Differential attentuation
Range of differences in the intensity of the x-ray beam after it has been attenuated by the subject
Result of the differential attenuation by the tissues in the body
Subject contrast
2 factors subject contrast is dependant on
kV
Amount and type of irradiated material
What is the controlling factor of subject contrast?
kVp
A visible change in contrast will not be perceived until kVp is changed by what percent depending on the kVp range?
1-12%
There is no reason to repeat an exposure for contrast reasons unless at least what percent change is made, although higher kVps require even greater changed?
4-5%
kVp levels should not exceed what for any non-grid radiography?
80 kVp
2 properties that comprise visibility of detail
Density/image receptor (IR) exposure
Contrast
10 influencing factors of contrast
mAs Focal spot size Anode heel effect Distance Filtration Beam restriction Anatomical part Grids Film/screen combinations Processing
What is the contrast improvement factors of most girds?
1.5-3.5
One of the two geometric properties of image quality; the degree of geometric sharpness or accuracy of structural lines actually recorded in the image
Detail Recorded detail Definition Sharpness Spatial resolution
Recorded detail of the radiographic image
Detail
Quantified discussions of recorded detail; the ability of an imaging system to accurately display objects in two dimensions
Spatial resolution
Primary film/screen unit of resolution
Line pairs per millimeter (lp/mm)
What range is most human visual acuity limited to?
5 lp/mm
3 factors that determine digital imaging recorded detail
Matrix size
Pixel size
Grayscale bit depth
A shorter-wavelength signal with higher frequency represents pairs of lines that can be visualized very close together
High resolution
Low-frequency frequency spatial resolution has a longer wavelength and lower frequency representing pairs of lines that are further apart
Low resolution
4 units spatial resolution is measured in
Point spread function (PSF)
Line spread function (LSF)
Modulation transfer function (MTF)
System noise
Lack of sharp definition of fine detail caused by unacceptable levels of penumbra as compared to the umbral shadows that are expected from the part
Unsharpness
Measures penumbra and is used to quantify digital system spatial resolution
Point spread function (PSF)
Measures the accuracy of an image compared to the original object on a scale of 0 to 1/fidelity/trueness of the image
Mathematically measures the percentage of object contrast that is recorded
Modulation transfer function (MTF)
Background information that the IR receives
Imaging noise
Lack of sufficient incoming data for processing
Insufficient number of incoming x-ray photons reaching the IR which results in blotchy or mottled image
Quantum noise
Sampling of the spatial resolution frequency signal twice from each cycle in digital systems
Processing algorithm that averages the incoming analog data by using the distance between the imaging detector elements (to ensure the data is not missed or double sampled)
Nyquist criterion
Occurs when spatial frequency exceeds the Nyquist frequency and the incoming data are sampled less than twice per cycle; look like a moire pattern
Aliasing
One of the two geometric properties affecting radiographic image quality; misrepresentation of the size or shape of the structures being examined
Distortion
2 types of distortion
Shape
Size
What is the only possible size distortion in radiography?
Magnification
What is the magnification factor calculated by?
M = SID/SOD
Misrepresentation by unequal magnification of the actual shape of the structure being examined; displaces the projected image of an object from its actual position
Occurs because of the divergence of the x-ray beam
The projected length varies, depending on the angle between the object of the diverging beam
Shape distortion
2 types of shape distortion
Elongation
Foreshortening
Projects the object so it appears to be longer than it really is; occurs when the tube or the IR is improperly aligned or changes in the tube angle
Elongation
Projects the object so it appears to be shorter than it really is; occurs only when the part is improperly aligned
Foreshortening
Theoretical photon that exits from the exact center of the focal spot
Central ray
Safeguards patient security and confidentiality and simplifies standards by encouraging electronic transactions
Health Insurance Portability and Accountability Act (HIPAA)
4 things HIPAA established national standards
Electronic record security
Standardized electronic formats for record keeping
Standardized electronic identifiers and codes for institutions, personnel, diagnoses and treatments
Requirements for confidentiality and privacy rules
Mandates that any serious injury or death due to a medical device be reported
Safe Medical Devices Act (SMDA)
Largest hospital accreditation agency
Joint Commission on the Accreditation of Healthcare Organizations (JCAHO)
Establish quality standards, assess them and provide certification that individual institutions have met the agency’s standards
Accreditation agencies
Consists of a coherent system designed to monitor equipment performance through a variety of quality assurance and quality control standards or benchmarks
Quality management
Consists of activities that provide adequate confidence that a radiology service will render consistently high-quality images and services
Assesses everything that affects patient care and may be medically, technically or managerially oriented
Includes evaluating activities such as interpretation of examinations, maintenance of equipment, performance of procedures, filing systems, staff development, scheduling of examinations and supply lines
Operates by identifying problems or potential problem areas, monitoring the problem and then resolving it
Monitoring problems involves several steps, including establishing criteria, performing monitoring and collecting,analyzing and evaluating data
Quality assurance
Aspect of quality assurance that monitors technical equipment to maintain superior standards
Quality control
3 types of focal spot test tools
Line pair resolution tools
Star test patterns
Pinhole cameras
2 focal spot test tools that function by imaging a resolution pattern on a film; the image can then be analyzed to estimate the focal spot size
Line pair resolution tools
Star test patterns
Permits measurement of the focal spot by creating an image of the effective focal spot on a film
Pinhole camera
When the focal spot is smaller than 0.8 mm may be what percent larger than the stated nominal size?
50%
When the focal spot is between 0.8-1.5 mm may be what percent larger than the stated nominal size?
40%
When the focal spot is larger than 1.5 may be what percent larger than the stated nominal size?
30%
Measured by using dosimetry equipment to detect the quality of aluminum filtration that will reduce the beam intensity to half the original value
Half-value layer
What percent SID error is allowed between the primary beam image and the light field size?
2%
The centering mark should be within what percent of the light field central ray?
1%
Distancing and centering indicators should be accurate within what percent?
± 10%
± 2%
Angles should be accurate within what percent?
± 1%
kVp settings should not drift beyond what of the labeled setting?
± 5 kVp
Exposure time settings should be maintained within what percent of the label?
± 5%
mA stations should be maintained within what percent of each other?
± 10%
Reproducibility should be maintained within what percent?
± 5%
6 tests for AECs
Exposure reproducibility Ion chamber sensitivity IR exposure variation control accuracy Response capability Backup timer verification Digital radiography detectors
Densitometer readings of images produced with the AEC should be within what OD range in the same areas?
OD ± 0.1
Ion chambers should all respond within what percent?
± 10%
AECs should produce exposures within what percent mR/mAs of one another until a time below the minimum exposure time is used?
± 10%
Measures the ratio of the transfer efficiency of the detector as the signal-to-noise ratio squared going into the system compared to that coming out
Detective quantum efficiency (DQE)
What is the range of DQE values
0-1 with 1 representing a perfect system
A figure that is calculated as a percentage of the total number of images produced during the period of study
Total repeat rate
Radiographer repeat rate should be within what percent?
3-10%
Device used to measure part thickness
Caliper
2 exposure systems
Fixed kVp
Variable kVp
7 advantages of fixed kVp systems
Decrease patient dose Provide more information on the image Increase the consistency of IR exposure Lengthen exposure latitude Reduce x-ray tube wear Decrease time settings and therefore patient motion Easier to remember
What is a disadvantage of fixed kVp systems?
Produce more scatter which tends to provide a lower contrast image
Maximum kVp level that will produce images with appropriate contrast that are consistently within acceptable limits; must ensure sufficient penetration of the subject as well as provide acceptable image contrast
Optimal kVp
2 advantages of variable kVp systems
Permit small incremental changes in exposure to compensate for variation in body part thickness
Produce higher-contrast images which enhance the visibility of fine detail and increase the perception of resolution
What is a disadvantage of variable kVp systems?
Increasing kV reduces image contrast which can reduce the radiologist’s ability to see fine detail in the image
Serve to measure the exposure to the receptor
Ionization chambers
Signals from the cells are sent to a special operational amplifier which sums the voltages received from each cell and divides by the number of cells that have been activated
Averaging
Length of time necessary for the AEC to respond to the ionization and send a signal to terminate the exposure
Minimum response time
What is the minimum response time of modern AECs?
0.001 second
Establishes the maximum exposure time for the system in order to prevent overexposure
Backup time
At what percent should the backup time be set to of the anticipated manual exposure time
150%
Combine an AEC system with an exposure system that is computerized to correspond to anatomical procedures
Anatomically programmed radiography (APR) units
