X-ray emission and Image Quality Flashcards
Xray quantity is:
The number of X-rays in the useful beam.
Radiation exposure =
xray intensity = xray quantity.
Radiation exposure, xray intensity and xray quantity are all measured in:
Roentgens (mR)
Roentgen:
a unit of radiation exposure - interaction of X-rays with air.
Factors affecting xray quantity are:
mAs
kVp
Distance
Filtration
The factors that affect X-ray quantity are similar to those affecting:
Optical density
Optical density:
degree of blackness on a film/image.
Optical density is also called:
radiographic density or simply density.
Milliampere (mA)
the unit used to measure the tube current.
Tube current measures:
number of electrons flowing per unit time between cathode and anode.
mA set by radiographer determines:
number of electrons flowing in tube and quantity of X-rays produced.
Higher mA results in:
more electrons that are available in tube current.
The more electrons in tube current:
The more X-rays will be produced.
Quantity of X-rays produced are directly proportional to:
the milliamperage. Therefore, the more mA, the darker the image. Also exposure time.
Longer exposure time results in:
more electrons that move in tube current from cathode to anode.
mA and time are ___________ when maintaining the same mAs.
inversely proportional.
The distance between the source of radiation and the image receptor affects the amount of ______ produced on a radiograph.
density
Xray quantity varies inversely with the
square of the distance from the source.
Inverse square law formula:
I one/I two = D two squared/D one squared.
What is the direct square law used for?
to calculate the new mAs when changing SID in order to maintain the same OD (kVp is constant.)
Direct square law:
When the SID is increased the mAs must be increased by SID squared to maintain constant optical density.
Direct square law formula
I one/ I two = D one squared/D two squared.
When increasing distance, mAs must be ______ to maintain same OD.
increased.
When decreasing distance, mAs must be ______ to maintain same OD.
decreased.
Xray quality indicates:
the penetrating power of the X-ray beam.
Penetrability:
ability of X-ray to pass through tissue and /or the distance the X-ray beam travels in matter.
Xray quality is controlled by:
kVp.
kVp determines the ______ which electrons in the current move.
speed.
As kV increases, the _______ of electrons traveling from cathode to anode _______
speed, increases.
The speed which electrons travel determines
quality or energy of X-rays.
The higher the quality or energy, the greater the
penetrability and the farther they travel.
Lower kV are considered:
soft X-rays and do not travel as far.
Higher kV ______, whereas lower kV ______
penetrates tissure, is more readily absorbed.
Higher kV help make high energy X-ray photons which _______ the X-ray beam
hardens.
kVp has a _____ effect on quantity of X-ray photons produced
small
kVp increases ______ of X-ray production.
efficiency.
kVp has a greater effect on the _______ of the X-ray beam.
quality.
15% rule
A 15% increase in kVp will have the same effect on the OD as doubling the mAs.
A 15% decrease in kVp will have the same effect on the OD as decreasing the mAs by half.
To increase density without increasing mAs:
multiply the kVp by 1.15. This will make the image twice as dark.
To decrease density without changing mAs.
multiply the kVp by .85. This will make your image half as dark.
To maintain density:
increase the kVp by 15% and divide the original mAs by 2, or decrease the kVp by 15% and multiply the mAs by 2.
Quantity is mostly affected by:
mAs
Quality is mostly affected by:
kVp
Density of the image mostly affected by:
mAs
The contrast of the image mostly affected by
kVp
Contrast is:
The degree of difference between light and dark on an image. High contrast has more black and white while low contrast has many shades of greys between the black and white shade.
High contrast = what scale type of contrast?
Short scale. Low kVp (such as 55-60 for a hand exam.)
Low contrast = what scale type of contrast?
Long scale. High kVp (such as 110-125 in a chest exam.)
Filtration affects the _____ of the beam.
Quality
Filter:
any material designed to effectively absorb photons from the x-ray beam.
The primary reason for filtration is to:
eliminate photons that would cause increased radiation dose to pt and not enhance the radiographic image.
Adding filtration to the x-ray beam increases the _____ of the beam. How?
Quality. By removing low energy X-rays that cannot get to the image receptor.
Adding filtration to the X-ray beam decreases the ______ of the beam. How?
It removes the lower energy photons. This also results in the beam only having higher energy photons which reach the IR. It “hardens” the beam.
What is the most common filtering material?
Aluminum (Al)
Filtration is expressed in terms of:
thickness of aluminum equivalency (1-3mm Al)
Why is aluminum the most common filtering material?
It is readily available, inexpensive and easily shaped.
Filtration lowers pt dose how?
by reducing low energy X-rays which do not contribute to the image and would be absorbed in superficial tissue of the pt.
Other types of filter material (not common)
Copper, tin, gadolinium. (Higher atomic numbers absorb more penetrating X-rays.)
What are the three types of filtration?
Inherent, added, and compensating.
What is inherent filtration?
Filtration in the path of the X-ray beam (within the tube, such as glass envelope of the tube or the oil surrounding the tube.)
What is added filtration?
Filtration added to the port of the X-ray tube. (Aluminum filter, mirror, plastic collimators, etc)
What is total filtration?
Added filtration and inherent filtration combined.
What is the minimum amount of filtration a tube must have?
2.5mm Al or equivalent.
What is a compensating filter?
Special filters used to image anatomic areas that are non-uniform in makeup (unequal subject densities.)
What do compensating filters do to an image of an anatomic area with non-uniform makeups?
They compensate for the unequal absorption within the subject and create a radiographic image with more even density.
Some types of compensating filters are:
Wedge (for top of foot), trough (for spine), clear leaded plastic (for barium enemas), boomerang (for shoulder) and saline bag (for the top of the foot.)
What is Half Value Layer?
The amount of filtration (thickness of the absorbing material) needed to reduce the intensity of X-ray beam to 1/2 its original value. Measured in mm of aluminum (Al).
HVL (Half Value Layer) testing is recommended as part of quality control. Why?
As the tube ages, the glass envelope gains a coating of vaporized metal which causes an increase in the inherent filtration and reduces the efficiency of the tube.
HVL evaluates:
Tube efficiency.
HVL is affected by
kVp and added filtration.
A diagnostic xray beam usually has a HVL equivalent of
3-5mm Al.
HVL is an indirect measure of
Total filtration of the X-ray beam.
HVL is the most accurate method for specifying
X-ray quality.
Minimum HVL’s for all diagnostic tubes are specified by
the federal government.
What is attenuation?
The reduction in X-ray intensity due to xray absorption and scattering.
Beam attenuation occurs as a result of:
photon interactions with atomic structures. As the primary beam passes through tissue, it loses some energy. This reduction in energy is known as attenuation.
In order to produce an image, X-rays photons must pass through tissue and interact with
the IR.
X-rays (of any given energy) are more penetrating in material of ______ atomic number than ______ atomic number.
Low, high.
Differential absorption:
process whereby some of the X-ray beam is absorbed in the tissue and some passes through anatomy.
The variations in absorption and transmission of the exiting X-ray beam will:
structurally represent the anatomic area of interest.
Scatter:
incoming photons lose energy during interactions with atoms of tissue and change direction. (Increases at higher kV’s)
Backscatter:
occurs when a scattered photon travels bac in the direction of the incident photon or beam.
Transmission:
xray photon passing through anatomic part without any interaction with the atomic structures. Lower kV - less X-ray transmission occurs. Higher kV - more transmission occurs.
A combination of absorption and transmission creates:
the X-ray image.
Exit radiation:
remaining xray beam leaving the pt. Also known as remnant beam. Consists of scattered and transmitted radiation.
Fog
Unwanted density created by scatter radiation. Does not give any useful info, and obscures small details such as kidney stones & calcifications.
Latent image
Exit radiation interacts with IR to create latent or invisible image (film).
Manifest or visible image:
Processed film.
Exit radiation interacts with imaging plate in CR or detectors in DR to create:
A latent image. After being processed through a computer it becomes a visible or manifest image.
Image quality is:
how exact we represent the pt’s anatomy on the image.
Radiographic quality is affected by:
Film factors
Geometric factors
Subject factors
The four characteristics of image quality are:
Spatial resolution
contrast resolution
Noise
Artifacts
Resolution is:
the ability to image two separate objects and visually distinguish one form the other.
Spatial resolution refers to:
the ability to image small objects that have high subject contrast (such as coccyx gone in soft tissue, breast calcification, calcified lung nodule.).
Contrast resolution is:
the ability to distinguish anatomic structures of similar subject contrast (such as liver-spleen, kidneys, and psoas muscle.). CT and MRI show excellent contrast resolution.
Optical density is:
the degree of blackness on a radiograph. OD is dependent on mAs and the time of exposure.
The most useful range of OD is highly dependent on:
view box (light box) illumination and the viewing conditions.
Reciprocity law:
the OD on a radiograph is proportional only to the total energy imparted to the radiographic film and independent of the time of exposure.
Any combination of mA and time will yield:
the exact amount of optical density.
The density produced by a radiograph is equal (for any combination of mA and time) as long as:
the product of mAs is equal.
The reciprocity law sometimes fails (the OD is somewhat less) when?
At short or long exposure times.
For angiointerventional or mammography where procedures require very short or very long exposure times:
the mAs setting may need to be increased if AEC does not compensate for reciprocity law failure.
The reciprocity law is used to:
control motion
change focal spot
utilize breathing technique.
Noise:
the grainy or uneven appearance of an image caused by an insufficient number of primary xrays.
Four components that contribute to noise:
Film graininess
structure mottle
quantum mottle
scatter radiation
Film graininess refers to:
the distribution in size and space of the silver halide grains in the emulsion.
Structure mottle is:
similar to film graininess but refers to the phosphor of the radiographic intensifying screen.
Film graininess and structure mottle are ______ in the IR - they are ___ _____ _____ of the RT.
Inherent, not under control.
Quantum mottle is somewhat under control of the RT and is ______ to radiographic noise.
a principal contributor
Quantum mottle is:
the random nature in which xrays interact with the IR.
Quantum mottle is a result of:
Non-uniform intensity over the cross section of an xray beam as it leaves the tube port.
How does quantum mottle appear on an image?
blotchy or mottled.
If an image is produced with just a few xrays, the quantum mottle will be ____ than if the image is formed from a large number of xrays.
higher
Quantum mottle decreases:
recorded detail.
Speed is:
the sensitivity of the image receptor to xrays and is interrelated with noise and resolution.
Speed cannot be seen on an image but:
it does affect the resolution and noise. A fast imaging system results in decreased resolution.
____ image receptors have high noise with low spatial and low contrast resolution.
Fast
____ image receptors have lower noise with higher spatial and higher contrast resolution.
slow
Which speed image receptor gives a lower dose? Fast or slow?
Fast.
The higher the speed, the (more or fewer?) xrays needed to produce an image of optical density.
fewer
Radiographic image receptors are identified as either ___ or ___ according to their sensitivity to xray exposure
fast/slow
An IR speed higher than 100 refers to
high speed IRs
An IR speed below 100 refers to:
slow speed IRs
When image receptors are replaced, a change in mAs may be necessary to maintain the same OD. What is the mAs conversion formula used to achieve this?
mAs2 IR speed1
mAs and speed are _______ proportional.
inversely. The slower the speed, the more mAs.
Latitude refers to:
the range of exposures over which the IR responds with ODs in the diagnostically useful range. (Think the margin of error in technical factors)
The amount of kV and the amount of latitude are related how?
Directly. The higher the kV, the more latitude. (Changes in kV are more apparent when using a small amount than when using a large amount.)
Latitude and contrast are related how?
Inversely proportional. With a wider latitude, the mAs can vary more and still result in a diagnostic image.
Image receptors with wide latitude are said to have _______ gray scale.
Long. (Low contrast)
Image receptors with narrow latitude are said to have ______ gray scale.
Short. (High contrast.)
Digital IR are more responsive to the wide range of X-ray intensities exiting the anatomic part and retain more information than film. This information (received from the digital IR and processed in the computer) is called
Dynamic Range.
Dynamic Range refers to
the shades of gray (range of densities) that are displayed within the digital image.
The greater the number of shades of gray available to create an image, the _____ the dynamic range of the imaging system.
Wider
Digital has the ability to visually display a ______ range of densities than film.
wider.
Xray intensities must fall within a smaller range to display radiographic densities that can be visible. Digital offers a ____ range of densities available for display within the digital image.
greater.
The ability of the digital IR to respond to a ______ range of X-ray intensities and visually display a ______ range of densities is a significant advantage of digital imaging.
wider/greater
The advantage of digital is that the wide dynamic range that digital offers allows for some ______ ______ or simply a _____ margin of error.
exposure error/ wider.
The diametric properties of a film-screen or digital image refer to:
the sharpness of structural lines recorded in the radiographic image.
Optimal geometric quality is achieved by:
Maximizing the amount of recorded detail.
minimizing the amount of image distortion.
Recorded detail refers to
the distinctness of sharpness of the structural lines that make up the recorded image.
If an image can demonstrate sharp lines then that image has:
good recorded detail.
the amount of recorded detail is controlled by:
minimizing geometric unsharpness and by eliminating motion unsharpness.
Three geometric factors factors that produce high-quality radiographs:
magnification
distortion
focal-spot blur
Magnification:
All images on the radiograph are larger than the object they represent.
What two distances play in important role in minimizing the amount of size distortion of the radiographic image?
SID and OID.
Magnification factor is defined as:
image size/object size.
As OID increases, magnification:
increases
AS SID increases, magnification:
decreases.
What distance has the greatest effect on size distortion?
OID
It is not always possible to reduce OID. In this situation the radiographer should__________ to reduce magnification.
increase their SID
The magnification factor indicates:
how much size distortion or magnification is demonstrated on a radiograph. SID/SOD
Magnification factor formula
SID/SOD
If the SOD is not available it can be determined by:
subtracting the OID from the SID. (SOD + OID = SID)
To minimize magnification:
Use a large SID and/or a small OID.
Object size can be detrained by:
dividing the image size by the magnification factor.
Percent magnification:
Image size - object size divided by object size x 100. (I-O)/O
Shape distortion:
is the unequal magnification of different portions of the same object.
Shape distortion appears in two ways:
Elongation and foreshortening.
Elongation refers to:
the image of an object that appears longer than the actual object.
Elongation occurs when:
the object is straight and parallel with the IR but the tube is angled. Also when the tube and part are straight but the IR is misaligned or angled.
Foreshortening refers to:
an image of an object that appears shorter than the object itself.
Foreshortening occurs:
When the object or anatomical part is angled.
The amount of foreshortening increases as:
the angle of inclination increases.
Shape distortion occurs when any one of the following three things are not aligned:
xray tube
anatomic part
image receptor
Distortion: If the object plane and the image plane are parallel, then:
the image is not distorted. It may be magnified, but not distorted.
If the CR is not directed to enter or exit the anatomy as required for the particular projection or position then:
shape distortion will occur (off centering).
Any structure that is not positioned at the CR will be distorted because of
the divergence of the beam.
The farther from the CR, the ______ the distortion.
greater.
Shape distortion is sometimes used to an advantage, such as to:
elongate a particular part in order to better visualize it (lateral elbow).
CR angulation is sometimes required to eliminate superimposition of objects that normally would:
obstruct the area of interest.
Spatial distortion is:
the misrepresentation in the image of the actual spatial relationships among objects.
As an object position is shifted laterally from the central axis:
spatial distortion can become more significant.
A single image is not enough to define the three-dimensional configuration of a complex object because of:
Spatial distortion.
Most xray exams are made with at least two different projections. And they would be:
AP/PA and lateral.
The ___ will change considerably across a thicker object compared to a thinner one.
OID. Therefore a thicker object will become more distorted as it moves laterally in the beam.
Focal spot blur is also referred to as:
Penumbra or edge gradient.
Focal spot blur is:
the imperfect, unsharp shadow surrounding the umbra.
Umbra:
the distinctly sharp area of a shadow or the region of complete shadow.
In actuality, the X-ray does not come from on point but rather:
a rectangular source varying in size from .1 - 1.5mm.
As the X-rays are formed over the area on the focal spot, they spread as they pass ________. This produces a blurred margin on the image with the width of the blur being proportional to:
the edge of the object toward the IR/the effective focal spot size.
The smaller the effective focal spot, the ______ the focal spot blur.
smaller.
The smaller the focal spot, the _____ the edge gradient and the _______ the recorded detail.
smaller/better
Penumbra is also affected by:
SID and OID
The geometric relationships that govern magnification also influence:
focal spot blur.
As the geometry of the source, object and image is altered to produce greater magnification, _________ focal spot blur is produced.
increased
Formula for finding the region of focal spot blur?
Effective focal spot (OID) / SOD
The focal spot blur is _____ when the OID is smaller, and as SID _______, the focal spot blur decreases due to less divergence of beam after passing the object.
smaller/decreases
The RT has no control over this blurred region on the radiograph, however, selecting a ______ ______ _______ will cut down on this blur.
smaller focal spot.
When a small focal spot is used, the heat created during the X-ray exposure:
is concentrated in a smaller area and could cause tube damage.
Repeated exposures make just under the limit over a long period can:
still do damage to the tube.
The focal spot size is a major controller of image resolution because
it controls penumbra.
As focal spot size increases, unsharpness:
increases and recorded detail decreases.
As focal spot size decreases, unsharpness:
decreases and recorded detail increases.
Most xray tubes are equipped with two focal-spot sizes:
Usually identified as small and large. .5mm/1.0mm .6mm/1.2mm 1.0mm/2.0mm For magnification radiography (mammo) a .3mm/1.0mm focal spot size is used.
A large focal spot is used for what types of body parts?
Thick and/or dense (chest and abdomen).
A large focal spot provides for what kind of exposure time?
A shorter exposure time.
Focal spot blur is smaller on the anode side than the cathode side because of:
The anode heel effect.
Subject factors (dealing with subject contrast) that deal more with the patient than with the positioning of the patient are:
Pt thickness tissue mass density effective atomic number object shape kVp
Subject contrast is:
the result of the absorption characteristics of the anatomic tissue radiographed and the kVp used.
How Pt thickness effects subject contrast:
a thick body section attenuates more X-rays than a thin body section.
Tissue Mass Density:
even though two body parts are the same thickness, they can have different mass densities.
How does Effective atomic number affect subject contrast?
when the effective atomic number of adjacent tissues is very much different, then subject contrast is very high.
Higher atomic number materials attenuate a (greater or smaller) percentage of the beam than lower atomic numbers.
greater
Subject contrast can be greatly enhanced by the use of
contrast media.
How does object shape effect subject contrast?
the shape of the anatomic structure influences its contribution to subject contrast due to the change in thickness of the part as it meets the X-ray beam.
A shape having a form that coincides with the X-ray beam has _______ (maximum or minimum) subject contrast.
maximum
kVp’s affect on subject contrast:
Subject contrast is greatly controlled by kVp.
Low kVp results in _____ subject contrast
high
High kVp results in _____ subject contrast
low
Disadvantage of low kVP:
the X-ray beam is less penetrating requiring higher mAs setting which results in higher pt dose.
With a low kVp, there is less margin for error due to:
narrow latitude.
Motion has the most ________ effect on the recorded detail of the radiographic image.
detrimental
Motion blue can be caused by:
motion of the tube, patient, part, or IR.
Most common cause of motion blur is
Motion of the patient.
Voluntary motion of limb and muscle is controlled by
immobilization.
Involuntary motion (of heart and lungs) is controlled by:
short exposure time
Another way to reduce motion blur is by
carefully instructing the pt.
Geometric factors that affect image quality are the same for digital as they are for film, with the following added for digital:
Size of detector elements matrix size pixel size bit depth phosphor size, layer thickness & concentration of the photostimulable phosphor (CR plates)
