Radiographic Exposures Final Flashcards
While DICOM is concerned primarily with images from the digital image acquisition modalities, HL-7 is concerned mainly with textual information from the __ and __.
HIS and RIS
Since PACS contains confidential patient data and information, it is essential that they be secured; hence,___ is of central importance in a digital hospital as well as in a PACS environment.
data security
Direct conversion digital radiography systems use detectors that convert x-Rays directly into___________ ___________.
electric signals
The conversion of analog signals into digital data is the function of the_____.
ADC Analog-to-digital-converter
What class of digital image processing allows measurements and statistics to be performed, as well as image segmentation, feature extraction and classification of objects?
Image analysis
Define voxel:
(volume element) the information contained in a volume of tissue that is converted into numerical values and expressed in pixels.
What does the width of a histogram imply regarding image contrast?
Wide-more contrast
Narrow-less contrast
When the PSP IP is erased by exposing it to a high intensity light beam to get rid of any residual latent image? (At what point in the digital image processing cycle?)
After laser scanning
What is likely to occur if there is substantial extraneous exposure on the plate?
histogram analysis error
Which exposure causes the system to rescale the image as if the plate is actually underexposed? (high-intensity, low-intensity?)
low-intensity exposure
In digital imaging what has more of an effect on image contrast than the kVp?
processing algorithm
Because of increased sensitivity to scatter radiation? The kVp should not exceed__for any nongrid radiography, including chest.
80
Acquiring one image on the smallest plate available avoids which recognition error?
exposure field recognition error
___occurs when a large number of pixels will be at the maximum digital value (black) so that there is no signal difference in the very high exposure areas, resulting in a loss of anatomical structures in that region.
Saturation
What is the standard expression for the receptor’s contribution to recorded detail?
Spatial resolution
What is the name of the structure that will detect the light from the CsI scintillator I the indirect flat-panel TFT detector?
sensing area
What indirect flat-panel TFT digital detectors, what is used to first convert X-Ray photons into the light photons?
Scintillator layer (CsI)
Which concept examines the response of the latent image receptor (screen-film detector or digital detector) to the radiation falling upon it?
exposure latitude
Which type of image is obtained initially from the detector and contains artifacts due to bad detector elements?
flat-field image
Too much edge enhancement produces image noise and creates ________.
“halo” effect
Define spatial resolution:
sharpness of an image
Define/describe the purpose of: modulation transfer function.
(MTF) mathematical function that measures the ability of a detector to transfer it’s spatial resolution characteristics to the image.
An MTF of ___ represents a perfect transfer of spatial and contrast information.
1
Which performance characteristic deals with the efficiency of a detector to convert the x-radiation signal at its entrance window into a useful image signal?
DQE
In imaging applications, because contrast resolution (the ability to resolve small differences in tissue contrast) is mandatory for diagnostic interpretation,___ is important.
it; high signal to noise ratio
Define HL-7:
Communication for patient data: demographics, administration, discharge/transfer, radiology reports, image exam type
What are image data sets? How are they described?
Matrix size, overall image quality, number of OD slices, study size, inherent spatial resolution, bit depth
What is the data transfer rate network called?
bandwidth
What is an HIS used for?
Not only patient information, but acts related to hospital administration, billing, accounting, stats, personnel, budgets, material management
In a simple DICOM configuration, a CR unit sends images to a PACS for___.
Storage
Distinguish between input and output. What does each use?
data entry using hardware devices (keyboard, mouse, etc.)-input
computer processing can be displayed on monitors for viewing by a human observer-output
What does informatics refer to?
The process of changing data into information, and therefore computers and communications technologies are central elements to the process.
According to Chapter 9, what is PACS and what is it used for?
More recently, the use of picture archiving and communications systems; (PACS) has become a common place in digital imaging.
What is order entry and what is it known as?
Requested radiology examinations ordered by physicians are entered into the system.
What is EHR as defined in the text?
electronic health record
What is another name for the flowchart of the steps involved in performing a DR exam?
processing map
What is metadata?
demographic and exam data accompanying the DR image in an electronic file header
The DICOM modality worklist (MWL) is a feature designed specifically to take advantage of information that already exists in___.
RIS-Radiology Information System
Which type of imagining system makes use of photo stimulate or storage phosphors to produce digital images using existing X-ray equipment?
Computed Radiography
Define scattering. What interaction with matter causes it?
Incoming photons that aren’t absorbed, instead lose energy during atom interactions composing the tissue.
For every 4-5 cm of tissue, the x-Ray beam quantity is reduced by:
50%
How does tissue density affect attenuation?
muscle tissue has atomic particles that are more dense or compact and therefore attenuate the x-Ray beam more
How do tissues with higher atomic numbers appear on a digital image?
demonstrate light areas or greater brightness
Rank the four types of body tissue from greatest to least attenuation ability.
bone
muscle
fat
air
How does the energy (quality) of the beam affect attenuation?
it decreases with a high-energy x-ray beam;
increased with a low-energy x-ray beam
Visibility of the recorded detail is accomplished by balancing_______and_______
differences between adjacent densities (contrast)
Define contrast:
The degree of difference or ratio between adjacent structures.
Define scale of contrast:
The range of densities visible on a radiographic image.
Define high contrast. Is it long-scale or short scale? How many shades of gray (densities) are associated with high contrast (few or many)? Are they very different from one another or similar to each other?
A radiograph with few densities, but great differences between them, short-scale contrast.
Define low contrast. Is it long-scale or short scale? How many shades of gray (densities) are associated with low contrast (few or many)? Are they very different from one another or similar to each other?
A radiograph with a large number of densities but little differences among the long-scale contrast
How does kVp level affect x-ray beam transmission?
Low quality photons in the beam, high kVp higher quality in kVp decrease wavelength.
How does kVp affect x-ray beam quality?
higher energy photons
Define resolution:
The ability of the imaging system to resolve or distinguish between two adjacent structures
What type of relationship does mAs have with the quantity of x-rays produced?
directly proportional
With digital imaging, if the mAs is too high, how will the image appear?
brightness-appropriate
With digital imaging, if the image receptor is not exposed to enough radiation (mAs), how will the image appear?
brightness-appropriate
How does increasing kVp affect the energy, quantity, and penetrating power of x-ray production?
everything is increased
How does kVp that is too low affect digital image brightness?
brightness-appropriate
The relationship between kVp and quantity of remnant radiation is known as the:
15% rule
Low kVp produces_____radiographic contrast and high kVp produces_____radiographic contrast.
high;low
Focal spot size affects only: (which geometric property?)
recorded detail
The inverse square law describes the relationship between____and____.
distance and x-ray beam intensity
State the inverse square law formula:
I1 over I2 =D2 squared over D1 squared
State the formula for (density maintenance)
mAs1 over mAs2 =D1 squared over D2 squared
How does SID affect magnification/size distortion?
X-Ray intensity spreads over a large area decreasing the beam reaching the IR
When OID cannot be reduced, in what way is SID adjusted in order to compensate?
increase SID
State the magnification factor formula:
MF=SID over SOD
How should radiographic technique be adjusted when performing pediatric chest imaging? (mA,time,high or low, long or short?)
kVp lower
mAs lower
short exposure time
The variable kVp-fixed mAs technique chart adjusts___as part thickness changes and the ___remains constant.
kVp;mAs
For radiographic procedures, scatter radiation is primarily the result of what type of interaction with matter?
Compton Interaction
How does restriction of the primary beam (collimation) to the anatomy of interest of affect patient dose and scatter production?
It is used to limit scatter radiation and patient dose.
What is most easily adjusted radiographic beam-restricting device?
collimator
Define grid frequency:
expresses the number of lead lines per unit of length in inches, centimeters, or both
State the formula for calculating grid ratio:
Grid Ratio=h/D
What is focused grid? How are the lead strips arranged?
Has lead lines that are arranged, or canted, to approximately match the angle of divergence of the primary beam.
Define focal range. What is its importance with the use of focused grids?
The recommended range of source-to-image receptor distance measurements that can be used with a focused grid.
State the formula used when changing from one grid ration to another.
GCF=mAs with the grid over mAs without the grid
Define grid cutoff.
A decrease in the number of transmitted photons that can reach the IR because of some misalignment of the grid.
What factors should be considered when determining the grid to be used for a specific examination?
increase kVp, over 60 use grid
What is the air gap technique? How is it used to reduce scatter radiation to the IR? Why does it work?
Based on the simple concept that much scatter will miss the IR if there is increased distance between the patient and IR increased object-to-image distance (OID). The greater the gap the greater scatter reduction. Because less scatter reaches the IR, mAs is changed to compensation.
AEC controls the amount of radiation reaching the IR by controlling which prim factors?
exposure factor
How many AEC detectors are typically used in the Automatic Exposure Control units? How are they configured (how are they arranged?)
3; two top cells one bottom
Once the electric charge from an AEC detector reaches a present point, what happens to the exposure?
terminated
Define maximum response time.
The shortest exposure time that the system can produce.
The maximum length of time that an exposure lasts when using AEC is called____.
back up
How does using a lower mA station during an AEC examination affect exposure time?
longer exposure, increases exposure time
How does back-up time affect patient exposure and X-ray tube heat?
Protects the patient from unnecessary exposure and X-ray tube from exceeding its heat-loading capacity.
If the back-up time is set by the equipment, the exposure time should end when the mAs reaches____mAs.
600
When the radiographer has the opportunity to set the back-up time, it should be approximately___of the expected exposure time.
150%
Which is the most critical aspect of successfully performing an examination using AEC?
detector selection
