Transcript ARRT DIGITAL Terms Defined

ARRT & Other
DIGITAL
Terms
Defined
April 2009
Wk 9/10 RT 255
Display Workstations
• Conventional film/screen
radiography uses large multiviewer
lightboxes.
• With early PACS, radiologists
thought that they needed 4-6
monitors.
• Now, the number of monitors has
dropped to an average of 2.
• Development of viewing software
and better hardware.
Name the 3 types of monitors
Name the 3 types of monitors
• Two major types of monitors with a third
type gaining acceptance:
• CRT (?)
• LCD (?)
• Plasma screen
3 types of monitors
• CRT (cathode ray tube)
• LCD (liquid crystal display)
• Plasma screen
Medical Use of Monitors
• Most medical monitors used to
display radiographic images are
monochrome high-resolution
monitors.
• Early displays used were primarily
CRTs, but as the LCD technology has
gotten better, more LCDs are taking
the place of the older CRTs.
ARRT DEFINITIONS
Image Display= MONITORS
• viewing conditions
– (i.e.,luminance,ambient lighting)
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spatial resolution
contrast resolution/dynamic range
DICOM gray scale function
window level and width function
viewing conditions
luminance,ambient lighting
• How does this affect
viewing images
• ? Different monitors
ARRT DEFINITIONS
viewing conditions
luminance,ambient lighting
• How does this affect viewing images?
• Surrounding light impacted what was seen on
image – now :
With different monitors:
• LCD gives more light.
• LCD can be used in areas
with a high amount of ambient light.
“dark rooms” not necessary
Technologist workstation monitors are used
in brightly lighted areas. So monitor
luminance, the brightness of a monitor
display, is an important consideration. Also,
the monitor must allow a technologist to
visualize enough detail to discern motion and
that the recorded lines are sharp and visible.
Monitor Advantages and
Disadvantages
• Most consumers want a monitor that can provide
the highest resolution for the best price.
• Most radiology applications have traditionally
used the CRT because of its superior resolution,
but as the LCD technology has progressed,
more and more departments are buying the
more slim and light weight LCDs to replace the
bulky CRTs.
MONITORS:Display Workstations
• Early PACS reading rooms required
supplemental air-conditioning to offset the
heat from multiple CRTs.
• Resolution and orientation of the monitor
is also a factor in determining which type
of monitor is to be used.
• Most cross-sectional imaging is read on a
1K square monitor.
• Most computed radiography (CR)
and digital radiography (DR)
images are read on at least a
2K portrait monitor
LCD
• 1.3 megapixels
• to 5 megapixels.
• mammography
imaging =
• at least 5 megapixel
resolution is
required.
• The CRT is the most
popular monitor on the
market.
• It consists of a cathode
and anode within a
vacuum tube.
• Cathode boils off a cloud
of electrons, and then a
potential difference is
placed on the tube.
• A stream of electrons is
sent across to the anode,
which in the case of the
monitor is a sheet of
glass coated with a
phosphor layer.
CRT
CRT
• Electrons strike the phosphor on the
glass.
• Impact causes the glass to emit a
color based on the intensity of impact
and area that the electrons strike.
• The electrons interact with a red,
green, or blue dot to form the color
and image that is being sent from the
video card signal.
CRT
• Electron beam starts in the upper left hand
corner and scans across the glass from
side to side and top to bottom.
• Once beam reaches the bottom, it starts
back over at the top left.
• Most monitors have 350 lines to be
scanned.
LCD
• LCD produces images by
shining or reflecting light
through a layer of liquid
crystal and a series of color
filters.
• Monitor is two pieces of
polarized glass with a liquid
crystal material between the
two.
• Light is allowed through the
first layer of glass.
LCD
• When a current is applied to the liquid
crystal, it aligns and allows light in
varying intensities through to the next
layer of glass through color filters.
• Light forms the colors and images
seen on the display.
LCD: Display Workstations
• LCD has dropped in price and has
risen in quality.
• LCD will soon take over PACS display
market because of its size, resolution,
and lack of heat production.
• LCD requires less maintenance.
CRT vs LCD
• CRT
• Luminance higher in the
center
• Lower measurable black
levels
• Phosphor granularity
adds to spatial noise
• Viewable area smaller
than stated size
• Better color reproduction
• More responsive on
redraw
• More rugged
• Aspect ratio 4:3
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LCD
Less veiling glare
Consumes less energy
Increased spatial
resolution
Larger viewing area by
described size
Display limited to
designed resolution
Can position screen
Smaller footprint and
lighter
Widescreen aspect ratio
16:9
Monitors – more terms…
• Aspect ratio
• Ratio is the width of the
monitor to the height of the
monitor.
• Most CRT monitors have
an aspect ratio of 4:3, and
LCD monitors have a ratio
of 16:9.
• Viewable area
• The viewable area is
measured from one corner
of the display to the
opposite corner diagonally.
Plasma Display
• Plasma monitors are new to the consumer
market.
• They have been used in government and
military applications since the late 1960s.
• They are made up a many small fluorescent
lights that are illuminated to form the color of the
image.
• Monitor varies the intensities of the various light
combinations to produce a full range of color.
Image Display= MONITORS
• viewing conditions
– (i.e.,luminance,ambient lighting)
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spatial resolution
contrast resolution/dynamic range
DICOM gray scale function
window level and width function
ARRT DEFINITIONS
MONITORS: Spatial Resolution
• Spatial resolution refers to the amount of detail
present in any image.
• Phosphor layer thickness and pixel size
determines resolution in CR.
• The thinner the phosphor layer is, the higher
resolution.
• Film/screen radiography resolution at its best is
limited to 10 line pairs per millimeter (lp/mm).
• CR resolution is 2.55 lp/mm to 5 lp/mm, resulting
in less detail.
MONITOR RESOLUTION
MODULATION TRANSFER FUNCTION - MTF
• A measure of the ability of the imaging system to preserve signal
contrast as a function of the spatial resolution.
• Every image can be described in terms of the amount of energy
for each of its spatial frequency components.
• MTF often is regarded as the ideal expression of the image
quality provided by a detector.
ARRT definitions
digital image characteristics
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spatial resolution
sampling frequency
DEL (detector element size)
receptor size and matrix size
image signal (exposure related)
quantum mottle
SNR (signal to noise ratio) or
CNR (contrast to noise ratio)
Spatial Resolution
• A radiograph typically
does not show soft
tissue structures
• Digital image shows
not only the soft tissue
but also the edge of
the skin.
• Giving the
appearance of more
detail.
MONITORS
contrast resolution
/dynamic range
• Appearance of more detail is due to the
wider dynamic recording range / contrast
resolution
• and does not mean that there is additional
detail
• Because so many more densities are
recorded in CR (wide dynamic range),
images appear more detailed.
contrast resolution
• The contrast resolution of a monitor is the
difference between the maximum and
minimum luminance of the display.
Exposure Latitude
or Dynamic Range
• CR and DR
• Contain a detector that
can respond in a linear
manner
• as compared to S
shape of H&D Curve
• Exposure latitude is
wide, allowing the
single detector to be
sensitive to a wide
range of exposures.
Why do digital systems have
significantly greater latitude?
• Linear response give the imaging plates
greater latitude
• Area recieving little radiation can be
enhanced by the computer
• Higher densities can be separated and
brought down to the visibile density ranges
• (Brightness in DR replaces density)
Monitors - RESOLUTION
• Pixel is a basic picture element on a display.
• A pixel is “any of the small discrete elements that
together constitute an image.”
• Resolution -# of pixels contained on a display
• Relationship:
• More pixels in an image, the higher the
resolution & more information that can be
displayed.
• Resolution also is defined as the process or
capability of distinguishing between individual
parts of an image that are adjacent.
Nyquist frequency
• The highest spatial frequency that can be
recorded by a digital detector.
• is determined by the pixel pitch.
• The Nyquist frequency is half the number
of pixels/mm.
• A digital system with a pixel density of 10
pixels/mm would have a Nyquist frequency
of 5 line pair/mm.
10 PIXEL DENSITY
WHAT IS THE
NYQUIST FREQUENCY= ?
ARRT definitions
sampling frequency
• The frequency that a data sample is acquired
from the exposed detector.
• It is expressed in pixel pitch and pixels per mm.
• Sampling frequency may be determined by
receptor size depending on the vendor.
• KODAK 8x10 better detail than 14x17
• Use of the smallest imaging plate possible for
each exam results in the highest sampling rate.
•
When the smallest possible imaging plate is selected, a corresponding matrix is used
by the computer algorithm to process the image
.
Pixel “picture element,”
• the smallest area represented in a digital
image.
• A digital radiography image consists of a
matrix of pixels which is typically several
thousand pixels in each direction.
• Pixel density – A term that describes the
number of pixels/mm in an image. Pixel
density is determined by the pixel pitch.
DEL (detector element size)
receptor size and matrix size
• a pixel or picture element.
• The typical number of pixels in a matrix
range from about 512 × 512 to 1024 ×
1024 and can be as large as 2500 × 2500.
• The more pixels there are, the greater the
image resolution.
• The image is digitized by position (spatial
location) and by intensity (gray level).
DELs – detector elements
• DELs collect electrons
that are extracted from
the detector assembly
and converted into a
digital value by an ADC.
That process creates the
image that displays on
our monitor.
• DEL size controls the
recorded detail, or spatial
resolution, for the flatpanel device. The
technologist can’t change
the size of the DEL,
which is fixed for that
piece of equipment.
• .
Detective Quantum Efficiency
• Known as the fill factor, the larger the area
of the TFT photodiodes, the more radiation
can be detected and the greater amount of
signal generated.
• Consequently, the greater the area of the
TFT array, the higher the DQE.
• Over 1 million pixels are read & converted
FILL FACTOR
• A field-effect transistor (FET) or silicon TFT
• Isolates each pixel element
• Reacts like a switch to send the electrical charges to
the image processor
Detective Quantum Efficiency
• How efficiently a system converts the x-ray input
signal into a useful output image is known as
detective quantum efficiency, or DQE.
• DQE is a measurement of the percentage of xrays that are absorbed when they hit the
detector.
Detective Quantum Efficiency
• In other words, CR records all of the phosphor
output. Systems with higher quantum efficiency
can produce higher-quality images at a lower
dose.
• Indirect and direct DR capture technology has
increased DQE over CR.
• However, DR direct capture technology, because
it does not have the light conversion step and
consequently no light spread, increases DQE
the most.
ARRT definitions
SNR (signal to noise ratio) or
CNR (contrast to noise ratio)
• SNR (signal to noise ratio): there is always a
very small electric current flowing in any circuit is called background electronic noise.
• It is similar to the fog on a radiograph in that it
conveys no information and serves only to
obscure the electronic signal.
• CNR (contrast to noise ratio): measure for
assessing the ability of imaging an procedure to
generate clinically useful image contrast.
• gives an objective measure of useful contrast.
Image Display
• spatial resolution
contrast resolution/dynamic range
• What is a 3-D array of Pixels ?
• A voxel (a volumetric pixel) is a volume
element, representing a 3-D value space.
A pixel which represents 2D image data.
Pixel Pitch
• The space from the
center of a pixel to the
center of the adjacent
pixel. It is measured in
microns (μm).
• Pixel pitch is determined
by sampling frequency for
cassette-based PSP
systems and by DEL
spacing for TFT flat
panel.
The Nyquist Theorem
• Theorem states that when sampling a signal, the
sampling frequency must be greater than twice
the bandwidth of the input signal so that the
reconstruction of the original image will be
nearly perfect.
• At least twice the number of pixels needed to
form the image must be sampled.
• If too few pixels are sampled, the result is a lack
of resolution.
Monitors: Display Workstations
• Pixels are arranged in a matrix.
• Common screen resolutions found on today’s
monitors are the following:
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1280 × 1024 (1K)
1600 × 1200 (2K)
2048 × 1536 (3K)
2048 × 2560 (5K)
Monitors – DOT PITCH
• Dot pitch is the measurement of how close the
dots are located to one another within a pixel.
• The smaller the dot pitch of a display, the finer the
resolution.
• Dot pitch may be expressed as aperture grille pitch or
slot pitch.
Monitors – REFRESH RATE
• Refresh rate or vertical scanning rate
• Refresh rate is a measure of how fast the monitor
rewrites the screen or the number of times that the
image is redrawn on the display each second.
• Refresh rate helps to control the flicker seen by the
user.
• The higher the refresh rate, the less flicker will be seen.
• Most refresh rates on today’s computer are set
between 60 and 75 Hz; the image is redrawn 60 to 75
timers per second.
Image Display= MONITORS
• viewing conditions
– (i.e.,luminance,ambient lighting)
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spatial resolution
contrast resolution/dynamic range
DICOM gray scale function
window level and width function
MONITOR RESOLUTION
DICOM gray scale function – calibration of
monitors to the same standard &
communication of images
•Window level affects brightness (density) - B
•Window width function affects contrast/gray scale - A
“windowing and level”
MONITOR Image Manipulation and
Enhancement Functions
• Window/level
• This is a default function of the left mouse button.
• By depressing and holding down the mouse button
and moving the mouse up and down and left and
right, the window and level can be adjusted.
• Window (width) represents the range of gray values.
• Level represents the center value of the range.
• A change in the window and level appears to change
the brightness and contrast of the image.
Image Manipulation
and Enhancement Functions
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Other Tools: Annotations
Annotations are NOT to be used
to label left or right to indicate the patient’s side.
Annotations are used to indicate prone or
supine, 30 minutes, upright or flat.
• Any other image information is appropriate.
• Radiologist will place arrows or circles around
pathologic or questionable areas.
MONITOR Image Manipulation
and Enhancement Functions
• Pan, zoom, and magnify
• Tools are used primarily by the
radiologist to increase the size of an area on the image.
• Magnify usually magnifies a square area of the image
• Pan and zoom functions are usually used together.
• Image is first zoomed up to the desired magnification
level then Pan icon is activated.
• Zoomed image can be moved around to view the
different areas of the image.
Image Manipulation
and Enhancement Functions
• Measurements
• Size of a pixel is a known
so the software
has the ability to measure
structures on the image
based on this.
• Angle measurement.
– Can give an angle measurement between two
structures
– Commonly used when reading spine studies
Image Manipulation
and Enhancement Functions
• Measurements
– Region of interest
– Measurement tool determines the pixel intensity of a
certain area.
– Each type of tissue or fluid has a different intensity of
reading.
– Radiologist can make a determination whether
something is solid or fluid.
– Each pixel can have a gray
level between 0 (20) and 4096 (212).
The gray level will be a factor
in determining the quality of the image
DR
Monitor :Navigation Functions
• Hanging protocols
Can be viewed:
1:1 4:1 etc
• Protocol can also be specified to show the
previous exam on one monitor and the
current exam on the other
• Once set, the most efficient study navigation
is determined.
Image Management
Functions
• Patient demographics
• Patient demographics
• must be correct.
– If demographics are not correct at the archive level,
the images could be lost.
• Changes should only be made when the
information is absolutely known to be wrong.
• Many hospitals allow only certain persons the
access to change demographics just to keep the
errors to a minimum.
Image Management Functions
• Query/retrieve icon
• Used to retrieve on demand
any studies from the archive
• Allows user to query a study
on multiple fields
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Patient’s name or identification
Date of service
Modality
Diagnosis code or comment
field
WINDOW LEVEL / WIDTH
Which one controls
Denisty (brightness) ?
Contrast
What else control these in DIGITAL IMAGING?
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The ability to window is a valuable
feature of all digital images.
Windowing is the process of
selecting some segment of the
total pixel value range (the wide
dynamic range of the receptors)
and then displaying the pixel
values within that segment over
the full brightness (shades of gray)
range from white to black.
Important point...Contrast will be
visible only for the pixel values
that are within the selected
window. All pixel values that are
either below or above the window
will be all white or all black and
display no contrast.
The person controlling the display
can adjust both the center and the
width of the window. The
combination of these two
parameters determine the range
of pixel values that will be
displayed with contrast in the
image.
Enhanced Visualization
Image Processing
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Takes image diagnostic quality to a new level
Increases latitude while preserving contrast
Process decreases windowing and leveling
Virtually eliminates detail loss in dense tissues
Contrast / Denisty (Brightness)
• CR and DR
• Kilovoltage peak still influences subject
contrast, but radiographic contrast is primarily
controlled by an image processing look-up
table. LUT
• Milliampere-second setting has more control
over image noise, whereas density is
controlled by image-processing algorithms.
End of 1 hr lecture
Monday Make-up
Nyquist frequency Review
• The highest spatial frequency that can be
recorded by a digital detector.
• is determined by the ________________
• The Nyquist frequency is half the number
of pixels/mm.
10 PIXEL DENSITY
WHAT IS THE
NYQUIST FREQUENCY= ?
A digital system with a pixel density of 10
pixels/mm would have a Nyquist frequency
of 5 line pair/mm.
10 PIXEL DENSITY
WHAT IS THE
NYQUIST FREQUENCY= ?
Sampling Frequency ?
Define ……
Sampling Frequency
• The sampling frequency is the rate at
• which the laser extracts the image data
• from the plate.
• What other term does this relate to?
Nyquist Frequency
• The Nyquist Frequency will be ½ of the
sampling frequency.
• A plate that is scanned using a sampling
frequency of 10 pixels per millimeter would not
be able to demonstrate more than 5 line pairs
per millimeter based upon the Nyquist
Frequency.
• The Nyquist Frequency allows the
• determination of the spatial resolution for
• a given sampling frequency.
LUT
• In the typical digital
radiographic system, a
variety of LUTs are
installed.
• The appropriate LUT is
then automatically
selected to give the
desired contrast
characteristics to match
the type of procedure
(chest, extremity, etc) that
is designated by the
operator.
a histogram of the luminance values derived during image acquisition
used as a reference to evaluate the raw information and correct the
luminance values.
a mapping function in which all pixels are changed to a new gray value.
LOOK UP TABLE (LUT)
Linear LUT
Black
Saturation
White
Saturation
Black Shirt
Facial Tones
* No Detail in Black Areas
* High Contrast
* Only Detail in White
Areas can be seen
* No Detail in White Areas
* Low Contrast
* Only Detail in Black
Areas can be seen
Physician Review Stations Monitors
• Step-down model of the radiologist’s reading
station (lower res)
• Some functions reduced
• One of the most important features
• is ability to view current and previous reports
with images.
• Many vendors are integrating
• the RIS functions
• with PACS software.
Technologist QC Stations
• review images after acquisition
but before sending them to the
radiologist
• May be used to improve or
adjust image-quality
characteristics
• May be used to verify patient
demographic information
• Placed between the CR and DR
acquisition modalities as a passthrough to ensure that the
images have met the
departmental quality standard
Technologist QC Station
• Generally has a 1K monitor
• Does not have the resolution capabilities of the
radiologist’s reading station
• Care required of technologist when manipulating
images not to change the appearance too much
from original acquired image
The File Room Workstation
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Workstation may be used to
look up exams for a physician
or to print copies of images
for the patient to take to an
outside physician.
Many hospitals are moving away from
printing films because of the cost.
• Hospitals are moving toward burning
compact disks (CDs) with the patient’s
images.
ARRT definitions
Image Receptors
digital image characteristics
– spatial resolution
– sampling frequency
– DEL (detector element size)
– receptor size and matrix size
– image signal (exposure related)
– quantum mottle
– SNR (signal to noise ratio) or
– CNR (contrast to noise ratio)
image signal (exposure related)
Exposure Indicators
• The amount of light given off by the imaging
plate is a result of the radiation exposure that the
plate has received.
• The light is converted into a signal that is used to
calculate the exposure indicator number, which
is a different number from one vendor to
another.
Digital artifacts
• Grid Lines: Appear as grid cutoff.
• Moire (Aliasing)
– wavy artifact occurs because the grid lines and the
scanning laser are parallel.
– When the spatial frequency is greater than the
Nyquist frequency
• Maintenance (e.g., detector fog): When errors
occur in equipment performance, corrective
action must occur. These corrections will
generally be done by service personnel
employed by the vendor.
• non-uniformity, erasure - blub problems
How else can Morie OCCUR?
ARRT definitions
quantum mottle
failure of an imaging system to record
densities usually caused by a lack of xray photons.
“PHOTON STARVED”
KVP & MAS HOW IS THIS AFFECTED
IN DR / CR?
PREPROCESSING ARTIFACTS
-
dead detector elements
dead columns or rows
nonuniform response
heel effect (fixed systems)
light guide variations
ghosting
ARRT definitions
Image Receptors
digital image characteristics
– spatial resolution
– sampling frequency
– DEL (detector element size)
– receptor size and matrix size
– image signal (exposure related)
– quantum mottle
– SNR (signal to noise ratio) or
– CNR (contrast to noise ratio)
Image Acquisition and Readout
• PSP (photo-stimulable phosphor)
• flat panel detectors
– (direct and indirect)
CR Imaging Plate
• Construction
• Image recorded on a thin sheet of plastic known
as the imaging plate - PSP
• Consists of several layers:
• Phosphor?
Imaging Plate
• Phosphor?
• BARIUM FLUORO
• HALIDE WITH
• A EUROPIUM BASE
Digital Radiography
• Two types of digital radiography
• Indirect capture DR
• Machine absorbs x-rays and converts
them to light.
• CCD or thin-film transistor (TFT)
converts light to electric signals.
• Computer processes electric signals.
• Images are viewed on computer
monitor.
Digital Radiography
• Direct capture DR
• Photoconductor
absorbs x-rays.
• TFT collects signal.
• Electrical signal is
sent to computer for
processing.
• Image is viewed on
computer screen.
Image Acquisition and Readout
flat panel detectors
Phosphors?
– direct = Am SELENIUM
– indirect = Am SILICON
• CR
• Indirect
array
• Direct
array
• CCD/CMOS
CCD/CMOS
PSL
light guide
PMT/PD
CsI/GOS contact layer PD/TFT
a-Se
none
Cs/GOS
lens/fiber
TFT
CMOS ?
CMOS ?
• Complimentary metal-oxide semiconductor (CMOS) – A photographic
detector.
• CCD and CMOS
systems – both use a
scintillator. These
systems are cameralike,
• they both use lenses
to focus the light onto
a detector.
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Digital Systems
electronic collimation
grayscale rendition or look-up table (LUT)
edge enhancement/
– noise suppression
• contrast enhancement
• system malfunctions (e.g., ghost image,
banding, erasure, dead pixels, readout
problems, printer distortion)
Image Data Recognition
and Preprocessing shutter
• Agfa uses the term collimation, Kodak uses the
term segmentation, and Fuji uses the phrase
“exposure data recognition.”
• All systems use a region of interest to define the
area where the part to be examined is
recognized and the exposure outside the region
of interest is subtracted.
•So in essence, rescaling provided an acceptable image, despite
an excess level of exposure to the receptor.
What about the dose to the patient?
•
Excessive exposure to
receptor without rescaling.
•
Excessive exposure to
receptor with rescaling.
Rescaling
• image pixel values to appear appropriate,
display properly, can lead to overexposing a
patient.
• The visual cue to the technologist that
overexposure has occurred isn’t present.
• With an analog system, a technologist would
have seen the image on the left as it came out of
the processor and used the excessive density of
the image as a visual cue to repeat the image.
• Rescaling forces a technologist to look
elsewhere for signs that a proper exposure was
used to produce an image.
Dose creep
• refers to the potential
to gradually increase
patient exposure over
time.
• However, a
technologist lacks
visual feedback that
additional radiation is
being used to
produce the images
DAP
• The dose area product
(DAP) meter is a device
that may be interlinked
with the x-ray unit to
determine the actual
patient entrance skin
exposure dose with
accurately calibrated
equipment. Currently, no
standards are established
for using a dose area
product meter
These two radiographs
show the difference in
entrance skin exposure
measured by the DAP
meter. The area with a
smaller exposure field size
carries a lower exposure
without reducing image
quality
Exposure Latitude
• The analog receptor exposure latitude
ranges from approximately
• 30% underexposed
• to 50% overexposed relative to
• the “ideal” exposure level.
Exposure Latitude
The digital image receptor
• exposure latitude ranges from
• approximately
• 50% underexposed
• to 100% over exposure
• relative to the “ideal” exposure level.
Note
It is important to note that just because a
• digital imaging system has the capacity to
• produce an image from gross underexposure
• or gross overexposure it does not equate to
• greater exposure latitude.
• The reason the system is capable of producing
an image when significant exposure errors occur
is through a process called automatic rescaling.
• In a digital system, underexposure of
• 50% or greater will result in a mottled
• image.
• 􀂡 In a digital system, overexposure
• greater than 200% of the ideal will result
• in loss of image contrast.
Image Evaluation:
Brightness and Contrast in Images
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Exposure Field Recognition Error
Gross Overexposure
Excessive Scatter Striking the Receptor
Excessive Fog on the Receptor
Grid Cutoff
Intra-Field or Off-Focus Radiation
Wrong Menu Selection
EDR
• Exposure Data Recognition
• When laser scans it is looking for area of
plate that has exposure
• Some read from center out and look for
two sides of collimation
• Works best when image centered
S# 8,357
S# 12,361 lat CXR
Exposure Numbers
• The exposure numbers can only be used if
all other parameters are correct
– Centering to plate
– Collimation
• Position over AEC, look at mAs readout to
determine if poor positioning caused light
or dark image
Same technique, different centering
and collimation
S# 592
S# 664
ARRT SPECS - DIGITAL
• PACS
• HIS (hospital information system) - work
list
• RIS (radiology information system)
• DICOM
• Workflow (inappropriate documentation,
lost images, mismatched images, corrupt
data)
PACS
• Image is stored on a computer: retrieval and
viewing system for digital imaging examinations.
• The PACS software provides “tools” that enable
a PACS operator to manipulate images.
• The basic image manipulations possible are:
magnification and minification of an image;
altering image brightness and contrast; and
annotating the image using text, symbols, lines
and arrows.
Picture Archival and
Communication Systems
• Networked group of computers,
servers, and archives to store
digital images
• Can accept any image that is in
DICOM format
• Serves as the file room, reading
room, duplicator, and courier
• Provides image access to multiple
users at the same time, ondemand images, electronic
annotations of images, and
specialty image processing
HIS – RIS INTERFACE
RIS Data Storage
• Less ERRORS
• A radiology information system, or RIS, is a data system for
patient-related functions in the radiology department.
Examples of functionality a RIS provides within a radiology
department include (but are not limited to):
• scheduling
• appointments;
• collecting and displaying orders for radiologic examinations;
• storing and displaying patient data;
• tracking patients
• providing patient and order data to a PACS; storing and
distributing radiology reports; providing billing services;
and providing a database to track and project trends.
HIS
• A hospital information
system, or HIS, is a
paper and/or data
system that manages
the administrative,
financial and clinical
information necessary
to operate a hospital
or health care system
Health Level 7 (HL7)
• HL7 are the software standards
established for exchanging electronic
information in health care. PACS is mainly
concerned with images and data
associated with images, whereas HL7 sets
standards for transmitting text-based
information throughout a medical center.
Cassette-based
systems
PSP plates
• Turbid phosphors ?
• Structured
phosphors ?
• Turbid Phosphor – A phosphor layer with a
random distribution of phosphor crystals
within the active layer.
• Structured (needle) phosphor – A
phosphor layer with columnar phosphor
crystals within the active layer. Resembles
needles lined up on end and packed
together.
Exposure index
• Cassette based– represents exposure level to plate
• a. Vendor specific values
• 1). Sensitivity “S” (Fuji, Philips, Konica) inversely related
to exposure- 200 S# =1mR to the plate – optimal range
250-300 for trunk, 75-125 for extremities
• 2). Exposure Index (EI)- (Kodak) – directly related to
exposure has a logarithmic component (change of 300 in
EI = factor of 2; i.e. 1800 is exposed twice as much as
1500) optimal range 1800-1900.
• 3). Log Mean (LgM) - (Agfa) – directly related to
exposure has a logarithmic component (change of 0.3 in
LgM = factor of 2, ie 2.3 is exposed twice as much as
2.0) optimal range 1.9-2.1.
• MTF ?
MODULATION TRANSFER FUNCTION - MTF
• A measure of the ability of the imaging system to preserve signal
contrast as a function of the spatial resolution.
• Every image can be described in terms of the amount of energy
for each of its spatial frequency components.
• MTF often is regarded as the ideal expression of the image
quality provided by a detector.
Exposure myths associated with digital
systems
1. mAs – myth: digital is mAs driven.
Truth: digital is exposure driven. The digital
detector is unable to discriminate whether the
exposure change was mAs or kVp. The
only thing that matters is exposure to pixels.
2. kVp – myth: digital is kVp driven.
Truth: see above
3. Collimation – myth: you cannot collimate.
Truth: you can and should collimate.
Inappropriate collimation will cause a histogram
analysis error.
Exposure myths associated with
digital systems
4. Grid – myth: cannot use grids and don’t need
them.
Truth: digital systems are sensitive to scatter just
like film; in fact they are more sensitive.
Appropriate grid useis even more important. A
grid should be used when the remnant beam is
more than 50% scatter, chest larger than 24cm
and anything else larger than 12cm.
5. SID – myth: magnification doesn’t occur with
digital so SID is unimportant.
Truth:Geometric rules of recorded detail and
distortion are unchanged from film to digital.
Exposure myths associated with
digital systems
7. Fog – myth: digital systems can’t be
fogged by scatter or background radiation.
Truth:digital systems are more sensitive to
both.
8. Myth: fluorescent lights fog PSP plates.
Truth: that is not true.
Exposure myths associated with
digital systems
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
1. mAs – myth: digital is mAs driven. Truth: digital is exposure driven. The digital
detector is unable to discriminate whether the exposure change was mAs or kVp. The
only thing that matters is exposure to pixels.
2. kVp – myth: digital is kVp driven. Truth: see above
3. Collimation – myth: you cannot collimate. Truth: you can and should collimate.
Inappropriate collimation will cause a histogram analysis error.
4. Grid – myth: cannot use grids and don’t need them. Truth: digital systems are
sensitive to scatter just like film; in fact they are more sensitive. Appropriate grid use
is even more important. A grid should be used when the remnant beam is more than
50% scatter, chest larger than 24cm and anything else larger than 12cm.
5. SID – myth: magnification doesn’t occur with digital so SID is unimportant. Truth:
Geometric rules of recorded detail and distortion are unchanged from film to digital.
6. Speed class – myth: it is a 200 speed class, you need to double your mAs and increase
your kVp by 10. Truth: this technique adjustment would be like changing to a 100
speed class from a 400 speed class. Also your digital system will operate at whatever
speed class you choose.
7. Fog – myth: digital systems can’t be fogged by scatter or background radiation. Truth:
digital systems are more sensitive to both. Myth: fluorescent lights fog PSP plates.
Truth: that is not true.
Next
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ODIA - Register
Review Modules 5 & 6 (& 11 ??)
Do study test at end of modules ?Print out certificate of completion