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Digital Radiography Ch 1-3

Terms in this set (144)

What is conventional radiography
Radiography using film and intensifying screens which must be processed with chemicals and is then read on a lightbox
What is digital imaging
Any imaging acquisition process that produces an electric image that can be viewed and manipulated on a computer
What was one of the first uses of digital imaging
CT
Who introduced the idea of moving images digitally
Albert Jutras
What is teleradiology
moving images via telephone lines to and from remote locations
What is PSP image capture
digital acquisition using phosphor plates to produce projection imaging
What does PSP stand for
photostimulable phosphor
What was PSP previously known as
CR (computed radiography)
Who first introduced PSP imaging in the United States and when
Fuji Medical Systems of Japan, 1983
What is a FPD system
radiography systems that use an x-ray absorber coupled to a TFT or CCD to form the image.
What does FPD stand for
flat panel detector
What two categories can FPD be divided into
indirect capture and direct capture
What is indirect capture digital radiography (IDR)
x-rays are absorbed and converted into light which is then converted into an electrical signal that can be sent to the computer for processing and viewing
What is direct capture digital radiography (DDR)
x-rays are converted directly into an electrical signal which is sent to the computer for processing and viewing
What device is used in both IDR and DDR to convert the analog electrical signal into a digital signal
ADC (analog-to-digital converter)
What advantage do FPD systems have over PSP systems and conventional radiography
the processing is done right at the room's console and the image appears in 3 to 5 seconds so the technologist knows right away if the image needs to be repeated
In which type of radiography is the latent image formed when silver ions are attracted to the sensitivity speck
conventional radiography (film/screen)
In which type of radiography is the latent image formed when photon energy is deposited within phosphor particles
PSP image capture
In which type of radiography is the latent image formed when light is converted to an electrical signal which is sent to a TFT or CCD
IDR
In which type of radiography is the latent image formed when amorphous selenium converts the x-rays to an electrical signal which is sent to a TFT
DDR
How is the exposure latitude of digital radiography different from that of conventional radiography
digital radiography uses a detector which results in a linear exposure latitude. the exposure latitude of conventional radiography is based on the characteristic response of film which is nonlinear.
How is contrast controlled in conventional radiography
kVp
How is contrast controlled in digital radiography
look-up table (LUT)
How is density controlled in conventional radiography
mAs
How is density controlled in digital radiography
look-up table (LUT)
Which type of radiography is more sensitive to scatter radiation
digital
What is PACS
a networked group of computers, servers, and archives that can be used to manage digital images
What image format is used by PACS
DICOM
What does DICOM stand for
digital imaging and communications in medicine
T/F: PACS can only provide image access to one user at a time
false (it can provide image access to multiples users at the same time)
T/F: All PACS systems are huge systems with the same design
false (PACS is often custom designed for each facility)
What made it possible for equipment from different manufacturers to communicate with each on in a PACS system
DICOM
List some commonly used patient demographics
patient name, health care facility, patient ID number, date of birth, exam date
Why should a patient's name always be entered the same way
If their name is entered differently, such as with and without the middle name, it will be saved as more than one patient
T/F: you should only make single exposure images of a body part with digital systems
true
T/F: digitally placed anatomic markers can always be used to determine the correct anatomic side of the patient
false (always place your lead marker correctly)
What are the two types of images in medical imaging
analog and digital
What are analog images
images showing continuously varying levels of brightness and color, such as paintings and printed photographs
What are digital images
images recorded as multiple numeric values divided into an array of small elements
What type of image do you see when you look at a film radiograph
analog
What type of image do you see when you look at a computer screen
digital
What are the critical characteristics of a digital image
spatial resolution, contrast resolution, noise, dose efficiency
What is a pixel
the smallest element in a digital image
How is pixel size related to detail
the smaller the pixel is the greater the detail
When does pixel size change
when the size of the matrix or the FOV changes
What is pixel bit depth
the number of bits within a pixel which determines the number of shades of gray it can produce
What is the maximum pixel bit depth
2^16 or 65,536 shades of gray
What is a matrix
a grid of pixels arranged in columns and rows, with each pixel corresponding to a specific location in the image and the pixel value corresponding to the shade of gray of the patient's tissue at that location
What is the relationship between matrix, pixel, and resolution
a larger matrix with smaller pixels gives better spatial resolution
If you have 2 CR cassettes, a 10x12 and a 14x17, and both have a 512x512 matrix, which cassette will capture a more detailed image
10x12 (since the 14x17 has the same size matrix it must have larger pixels which results in less detail)
What is FOV (field of view)
the amount of the body part or patient included in the image
What 2 things can be changed to cause a change in pixel size
matrix size and/or FOV
What is the exposure index
the amount of exposure received by the image receptor (not by the patient)
What is air kerma
the measurement of radiation energy absorbed in a unit of air
What does kerma stand for
kinetic energy released per unit mass of air
What units are used to express air kerma
J/kg or Gy
What is standardized radiation exposure (Kstd)
a standard exposure typical of that imaging receptor system
What is indicated equivalent air kerma (K ind)
the amount of exposure on the IR
What is target equivalent air kerma value (Ktgt)
a set of values that represents an optimal exposure for each specific body part and view
What is deviation index (DI)
the difference between the actual exposure (K ind) and the target exposure (Ktgt) expressed in a logarithmic fashion
What is the purpose of the deviation index
to help the technologist determine whether the image has been underexposed or overexposed
What DI value indicates a perfect image
0.0
How does DI indicate underexposed images
with a negative value
How does DI indicate overexposed images
with a positive value
How would you change your technique to raise the DI +1
increase technique 20%
How would you change your technique to decrease the DI -1
decrease technique 25%
What are some issues that could cause the DI to be incorrect
a prostheses, shielding, failure to recognize the collimated border, unexpected body part
What should the technologist use as the true determining factor of image acceptance
image noise
What is brightness
level of intensity of a digital image on a display monitor
What can affect image appearance on a monitor
the amount of light transmitted by the monitor and light reflected off the monitor
T/F: a monochromatic monitor is susceptible to drift
true
How is glare reduced on cathode ray tube (CRT) monitors
the glass is tinted
What technique can technologists use to adjust the brightness of the image while they are viewing it on the monitor
window level
What is contrast resolution
ability of the system to display subtle changes in the shade of gray
Higher contrast resolution means
more shades of gray can be shown so it is easier to see small differences in densities
What is the determining factor for contrast resolution in digital imaging
bit depth of the pixels
What can be used to allow higher kVp values without compromising contrast resolution
tight collimation and the correct grid
Sufficient kVp for appropriate _____ of the tissues is still required with digital systems
penetration
What technique can be used to control screen resolution while the image is being viewed on the monitor
window width
What is spatial resolution
the ability of the imaging system to demonstrate small details
What is the resolution in digital receptors
2.55 line pairs/mm to 10 line pairs/mm
What one factor affects spatial resolution
pixel size (small pixels=higher spatial resolution)
What is modulation transfer function (MTF)
the ability of a system to record available spatial frequencies
Since MTF is a ratio of image to object, a perfect system would have an MTF of ?
1 or 100%
What is noise
anything that interferes with the formation of the image
What is anatomic noise
superimposition of body parts
What is equipment noise
noise in the detector elements and non-uniform detector responses
What is the noise power spectrum (NPS)
the spatial frequency content as well as spatial characteristics of the noise (higher NPS = higher noise for a specific detector)
What is SNR
signal-to-noise ratio
What is a good SNR
1000:1
As SNR increases noise decreases, but with what negative consequence
higher exposure to patient
What is exposure latitude
the range of exposure diagnostic image values the image detector is able to produce
What is detective quantum efficiency (DQE)
how efficiently a system converts the x-ray signal into a useful image expressed as a measurement of the percentage of x-rays that are absorbed when they hit the detector
T/F: systems with lower quantum efficiency can produce higher quality images at lower doses
false (systems with HIGHER quantum efficiency can produce higher quality images at lower doses)
Which detectors have the highest DQE
amorphous selenium
Why do amorphous selenium detectors have the highest DQE
they do not have the light conversion step
The DQE of detectors changes with?
kVp
The larger the area of the TFT photodiodes, the ____ radiation can be detected
more
The greater the area of the TFT array, the ___ the DQE
higher
What is preprocessing
computer processing using the the look-up table and histogram resulting in the manifest image
What is postprocessing
processing done by the technologist after the manifest image is created
What is a histogram
a graph showing the densities (shades of gray) detected in the collimated area and the number of pixels having each shade
Which side of a histogram represents white
extreme right
Which side of a histogram represents black
extreme left
What 2 errors can cause a PSP reader to create an image that is too bright or too dark
failure to find the collimation edges and failure to center the anatomy to the center of the imaging plate
____ kVp gives a wider histogram
low
___ kVp gives a narrower histogram
high
What is the Nyquist Theorem
the sampling frequency must be greater than twice the frequency of the input signal
In digital imaging how many pixels must be sampled
at least twice the number of pixels needed to form the image
What is the result if too few pixels are sampled
lack of resolution
Why should PSP plates be read as soon as possible
more information is lost the longer the image is stored because the electrons trapped in the meta stable F centers lose energy over time and if they lose enough may not react correctly when stimulated by the laser
What is aliasing
loss of digital information due to a fluctuating signal
What are some other names for aliasing
foldover, biasing, wraparound
What is critical frequency
the frequency of a signal that exactly matches the Nyquist frequency and results in a zero amplitude signal caused by phase shifts
What is automatic rescaling
when the computer tries to "fix" exposure errors due to an exposure being greater or less than optimal to produce a diagnostic image
What is the result of automatic rescaling when too little exposure is used
quantum mottle
What is dose creep
an increase in patient dose over time due to technologists increasing the technical factors in an attempt to avoid exposure errors
What is a look-up table (LUT)
a histogram used as a reference to evaluate the raw information and correct values so the final image will have appropriate brightness and contrast
How many look-up tables are there
there is a LUT for every anatomic part
What is contrast manipulation
conversion of the digital image using contrast enhancement parameters
What is spatial frequency resolution
detail or sharpness
Why do many health care facilities not wan the technologists to manipulate images before they are sent to PACS
their changes reduce the amount of manipulation the radiologist can do
T/F: all post processing results in a loss of information from the original image
true
What is edge enhancement
when fewer pixels in the neighborhood are included in the signal average
What is high-pass filtering
technique for enhancing the contrast and edge that amplifies the frequencies of the areas of interest that are known and suppresses frequencies outside the area of interest
What is masking
suppressing frequencies
What is smoothing
averaging each pixel's frequency with surrounding pixel values to remove high-frequency noise
What is another name for smoothing
low-pass filtering
What is the result of smoothing
a reduction of noise and contrast
What is smoothing useful for
viewing small structures such as fine bone tissues
What is window level
changes screen image brightness
What is window width
changes screen image contrast
What is veil glare
excess light that enters the eye due to unexposed borders around the collimation which causes temporary white light blindness
What is shuttering
a viewing technique used to blacken out the white collimation borders and eliminate veil glare
What should shuttering not be used for
to hide poor collimation practices
What is another method to eliminate veil glare
background removal (removal of white unexposed borders)
What is image orientation
the way the anatomy is oriented on the imaging plate
What is image stitching
"stitching"multiple images together using special software to create a larger image
What is image annotation
addition of information to an image during post processing, such as ERECT, SUPINE, or general notes such as the time and technique
What are the two types of magnification techniques standard with digital systems
magnifying glass to only magnify the area under the cursor, and zoom which magnifies the entire image
What are patient demographics
information about the patient, such as age, ID number, ordering physician, etc.
What patient demographics are commonly used to link an image to a patient
name, health care facility, patient ID, date of birth, and exam date
What is manual send
a function that allows the QC technologist to send images to one or more local computers
What is archive query
a request for specific images from the PACS system based on patient demographics or other parameters, such as type of exam
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