IMAGE QUALITY Flashcards
What improves spatial resolution?
Spatial resolution improves as screen blur, motion blur, and geometric blur decrease.
It is the exactness of representation of the patient’s anatomy on an image.
image quality
Name the three major categories of radiographic quality.
Film Factors, Geometric Factors, and Subject Factors
A radiograph that faithfully reproduces structures and tissues with good spatial resolution, contrast resolution, low noise, and minimal artifacts.
high quality radiograph
The ability to image small objects with high subject contrast, such as bone-soft tissue interfaces.
spatial resolution
What does contrast resolution measure?
The ability to distinguish anatomical structures of similar subject contrast, such as liver-spleen differentiation.
Define detail in radiographic terms.
Detail refers to the degree of sharpness of structural lines on a radiograph.
What is visibility of detail?
The ability to visualize recorded detail when image contrast and optical density are optimized.
The random fluctuation in the optical density (OD) of the image, often appearing as graininess.
radiographic noise
What are the components of radiographic noise?
Film graininess, structure mottle, quantum mottle, and scatter radiation.
The distribution in size and space of silver halide grains in the emulsion, contributing minimally to radiographic noise.
film graininess
The principal contributor to radiographic noise, caused by the random nature of x-ray interactions with the image receptor.
quantum mottle
How can quantum mottle be reduced?
By using high-mAs, low-kVp settings, and slower image receptors.
refers to the sensitivity of x-rays to film, which influences both resolution and noise.
speed
What factors influence radiographic quality?
Film Factors, Geometric Factors, and Subject Factors.
To study the relationship between film exposure intensity and resulting blackness after processing.
sensitometry
What does the characteristic curve represent?
The relationship between optical density (OD) and radiation exposure.
Name the sections of the characteristic curve.
Toe, shoulder, and straight-line portions.
What tool is used to create a characteristic curve?
A sensitometer (optical step wedge) and a densitometer.
a logarithmic function representing the darkness of a radiograph.
optical density
What is base density?
The optical density inherent in the film base, generally around 0.1.
What causes fog density?
Caused by inadvertent exposure during storage, chemical contamination, or improper processing.
Describe reciprocity law.
States that OD on a radiograph is proportional only to the total energy imparted to the film.
How does film contrast relate to the characteristic curve?
Film contrast is related to the slope of the straight-line portion of the characteristic curve.
product of image receptor contrast and subject contrast.
radiographic contrast
What factors influence image receptor contrast?
The range of ODs and film processing technique.
Determined by the size, shape, and x-ray attenuating characteristics of the anatomy, as well as the kVp of the x-ray beam.
subject contrast
Define speed in terms of image receptor sensitivity.
Speed = 1 / Exposure in roentgens needed to produce an OD of 1.0 above base and fog.
The range of exposure over which the image receptor responds with ODs in the diagnostically useful range.
latitude
How does development time and temperature affect radiographic contrast?
Increased time and temperature increase speed and fog, which can decrease image receptor contrast.
Name the three principal geometric factors affecting radiographic quality.
Magnification, Distortion, and Focal-spot Blur.
What is magnification in radiography?
Condition where the image on the radiograph is larger than the object it represents.
How can magnification be minimized?
By using a large SID and a small OID.
Define magnification factor.
MF = SID / SOD (Source-to-Image Distance divided by Source-to-Object Distance).
Unequal magnification of different parts of an object, often due to shape, position, or thickness.
distortion
How does object thickness affect distortion?
Thicker objects result in greater distortion due to unequal magnification.
occurs when an object is inclined and not parallel to the image receptor.
foreshortening
Caused by an inclined object that is not located on the central x-ray beam.
elongation
Misrepresentation of spatial relationships among objects due to different distances from the image receptor.
spatial distortion
A blurred region on the radiograph, influenced by the effective size of the focal spot.
focal-spot blur
Where is focal-spot blur smaller on the radiograph?
Smaller on the anode side and larger on the cathode side.
What factors reduce focal-spot blur?
Use of a small focal spot size and a small OID.
The phenomenon where the image toward the cathode side has higher blur and poorer resolution than the anode side.
heel effect
List the main subject factors in radiographic quality.
Subject contrast, patient thickness, tissue mass density, effective atomic number, object shape, and kilovolt peak.
How does patient thickness affect subject contrast?
Thicker body sections attenuate more x-rays, impacting the contrast between sections.
A factor affecting subject contrast; denser tissues attenuate more x-rays.
tissue mass density
How do photoelectric interactions vary with atomic number?
They vary in proportion to the cube of the atomic number (Z³), affecting subject contrast.
A reduction in spatial and contrast resolution due to characteristics of the subject.
absorption blue
How does kVp influence subject contrast?
Lower kVp results in higher subject contrast with a short gray scale, while higher kVp results in lower contrast with a long gray scale.
Name two disadvantages of low-kVp technique.
Higher patient dose and less penetration of the x-ray beam.
Blurring caused by patient or x-ray tube movement during exposure.
motion blur
How is voluntary motion controlled in radiography?
By immobilization or instructing the patient to remain still.
How is involuntary motion controlled?
By using a short exposure time.
What factors help reduce motion blur?
Short exposure time, large SID, small OID, and patient instructions or restraints.
List tools that improve radiographic quality
Proper patient positioning, selecting the right imaging devices, and using proper technique.
How should a structure be positioned in relation to the IR?
As close to the IR as possible and parallel to the plane of the IR.
What is the role of a central ray in radiographic quality?
The central ray should be incident on the center of the structure to ensure accurate imaging.
Why is patient immobilization important?
To minimize motion blur during imaging.
How do intensifying screens affect patient dose?
They reduce patient dose by a factor of approximately 20.
What are the effects of increased image receptor speed?
Increases radiographic noise and decreases spatial resolution.
How does low contrast imaging affect radiographic latitude?
provides a wider latitude or margin of error in exposure factors.
What is the primary control of radiographic contrast?
Kilovoltage peak (kVp).
What happens to subject contrast as kVp increases?
Subject contrast decreases due to increased Compton interactions and reduced differential absorption.
What is the principal advantage of using high kVp?
Reduced patient dose and wider exposure latitude.
What is the principal disadvantage of high kVp?
Loss of contrast in the radiographic image.
Define milliampere-second (mAs) in radiography.
mAs is the primary control of optical density (OD) in a radiograph.
What effect does increasing mAs have on patient dose?
It increases patient dose by raising the radiation quantity.
How does filtration affect the x-ray beam?
Filtration reduces beam intensity and enhances beam quality.
Filtration reduces beam intensity and enhances beam quality.
Increased SID decreases optical density but does not change contrast.
Name factors that increase patient dose.
Increased film speed, screen speed, grid ratio, patient thickness, and field size.
What effect does grid ratio have on contrast?
Higher grid ratios improve contrast by reducing scatter radiation.
What factors affect film contrast?
Processing time, temperature, patient thickness, and field size.
What is the impact of field size on contrast?
Larger field sizes decrease contrast by increasing scatter radiation.
Substances used to enhance contrast of specific body areas, commonly affecting image contrast positively.
contrast media
How does focal-spot size affect radiographic image quality?
Larger focal-spot size increases focal-spot blur, reducing image sharpness.
What happens when SID is increased?
Magnification decreases, spatial resolution improves, and patient dose reduces.
Define OID in radiography.
Object-to-Image Distance - the distance between the object being imaged and the image receptor.
How does increasing OID affect the radiographic image?
Increased OID leads to more magnification, greater focal-spot blur, and reduced spatial resolution.
Describe screen-film contact.
The closeness between the intensifying screen and the film, which affects image sharpness.
How does mAs influence noise in radiography?
Higher mAs reduces radiographic noise, while too low mAs increases it.
What is the purpose of voltage ripple in x-ray imaging?
Reduces the amount of radiation fluctuation, affecting contrast and noise.
How does increased filtration affect contrast?
It generally reduces contrast by removing low-energy x-rays that contribute to image contrast.
What is film speed?
The sensitivity of film to x-ray exposure, influencing both contrast and optical density.
The speed at which the intensifying screen responds to x-ray exposure.
screen speed
How does development temperature influence radiographic contrast?
Higher temperature increases fog, which can decrease contrast.
Describe the toe region of the characteristic curve.
The low-exposure area where large changes in exposure result in only small changes in optical density.
What does the shoulder region of the characteristic curve represent?
High exposure where large exposure changes result in minimal optical density changes.
An instrument that exposes film to known light levels to measure film sensitivity and contrast.
sensitometer
Measures the optical density of exposed film by assessing light transmission through the film.
densitometer
What is the average gradient of a film?
A measure of the slope of the characteristic curve, representing image receptor contrast.
Define average gradient in terms of optical density and exposure.
Average Gradient = (OD2 - OD1) / (LRE2 - LRE1) over the useful range of optical density.
How does latitude relate to contrast?
Latitude and contrast are inversely proportional; wider latitude corresponds to lower contrast.
Latitude and contrast are inversely proportional; wider latitude corresponds to lower contrast.
Contrast inherent to the screen-film combination, influenced by film processing and optical density range.
What is subject contrast influenced by?
Anatomy size and shape, atomic number of tissues, and energy of the x-ray beam.
Explain the impact of low ripple power on radiographic image quality.
Reduces the likelihood of motion blur and improves image stability.
What happens to OD with increased mAs?
Optical Density (OD) increases with higher mAs.
How does screen-film contact affect image detail?
Poor screen-film contact leads to loss of detail and image blurring.
An alternative to the sensitometer, used for evaluating image contrast by measuring exposure levels.
penetrometer
Define high-speed IR in terms of sensitivity.
image receptors with speed ratings over 100, used for fast imaging but with more noise.
Why is optical density important in radiography?
Determines the visual quality of the image, with optimal range enhancing detail and contrast.
