Transcript Digital Imaging - Montgomery College

Digital Imaging
CHAPTERS 1, 4-7
CARTER
CHAPTER 1
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Conventional radiography
Film/screen system
Light exposes film
Film processed with chemicals
Film taken to radiologist for
interpretation
Let’s compare rooms for
• Conventional (Film)
• CR
• DR
Let’s compare image
formation/acquisition
• Film
• CR
• DR
Let’s compare image
processing
• Film
• CR
• DR
CR- Chapter 4
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IP layers
Protective
Phosphor/active
Reflective
Conductive
Color
Support
Backing
barcode
• Protects phosphor
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PSP-barium fluorohalide
Sends light forward when
released in the reader
Absorbs/reduces static
electricity
Absorb stimulating light
(laser)/reflects emitted light
Protects the back of cassette
Match image with patient
Reading the IP
• Red laser light scans in a raster
pattern at 2 eV
• Laser scans multiple times as IP
moves through reader =translation
• Light produced –detected by
photomultiplier
DIGITIZING
• PHOSPHOR STORAGE CENTER IS
SCANNED
• RELEASED ELECTRON ENTER
DIGITIZER DIVIDES THE ANALOG
SIGNAL INTO SQUARES (MATRIX).
• EACH SQUARE IS ASSIGNED A
NUMBER BASED ON THE BRIGHTNESS
OF THE SQUARE
• SQUARE IS CALLED A PIXEL
SPATIAL RESOLUTION
• Film screen = 10 line pairs per mm
• CR =2.55 to 5 line pairs per mm
(lp/mm)
• Less detail in CR but more tissue
densities seen given the appearance
of better detail
• Wider dynamic recording range
speed
• Film – determined by size and layers
of crystals and phosphors
• CR – amount of photostimulable
luminescence given off = 100 film
speed screen (approx)
EXPOSURE –CASSETTE
BASED-chapter 5
• What is the relationship between selecting the
correct body part and computer interpretation of
the image?
• Too much kVp (above 120) and too little (below
45) can over excite or produce too little
excitation of the phosphors
• Does the pixel size of a 2000 x 2000 matrix
change when using an 8 X10 vs
a 14 x 17 CRcassette?
• How does the change in pixel size impact
resolution?
MOIRE PATTERN
• Grid lines from a stationary grid can
cause a wavy artifact known as a
moire pattern. The grid lines and the
scanning laser run parallel
Exposure Indicators
• Exposure indicator number
• Fuji, Philips, Konica – S numberindirect relationship
• Kodak –Exposure index (EI)-direct
relationship
• Page 88 tables 5-1 and 5-2
HISTOGRAM
• Graphic representation of the
numerical tone (grays/blacks/whites)
of an x-ray exposure
• Important in CR
• Four modes of date recognition
– Automatic data recognition
– Semiautomatic mode
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Multiple manual selection mode
– Fixed mode
OTHER ARTIFACTS
• Plate artifacts
– Adhesive tape residue
– cracks
• Plate reader artifacts
– Line patterns
– Plate reader loads multiple IP in one cassette
• Image processing artifacts
– Incorrect erasure (ghosting)
– moire
• Printer artifacts
– White lines
CASSETTELESS Chapter 6
• Direct and indirect
• DR plate (amorphous selenium) or(aSe)-converts radiation into an
electrical signal –CCD or silicon
detectors
• Signal stored in a Thin film
transmitter (TFT)
INDIRECT
• Two step process
• X-rays convert to
light
• Light converted to
electrical signal
• Sent to TFT
DIRECT
• X-rays converted
directly to an
electrical signal
• Sent to TFT
DQE
• Detective Quantum Efficiency
• Ability to convert an x-ray signal into
a useful image
• Of the following-which do you think
has the most efficient DQE?
• Film or CR or indirect capture DR or
direct capture DR?
Digital Radiographic
Image Processing and
Manipulation
Chapter 7
CR image *sampling
(*conversion from analog to
digital)
• Histogram
• X axis = amount of
exposure read
• Y axis = number of
pixels for each
exposure
• Low kVp= wider
histogram
• High kVp = narrower
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Histogram is
anatomy specific
NYQUIST THEOREM
• When sampling(converting from analog to
digital) a signal, the sampling frequency
must be greater than the bandwidth of
the input signal
• http://images.google.com/imgres?imgurl=h
ttp://www.cs.cf.ac.uk/Dave/Multimedia/ny
quist.gif&imgrefurl=http://www.cs.cf.ac.uk
/Dave/Multimedia/node149.html&h=420&w
=529&sz=6&hl=en&start=10&um=1&tbnid=z
yDOLJNUH6mM8M:&tbnh=105&tbnw=132
&prev=/images%3Fq%3Dnyquist%
Sample? Try this at home
• http://www.pcguide.com/art/soundSa
mpleRate-c.html
ALIASING
• When the spatial frequency is
greater than the Nyquist frequency
and the sampling occurs less than
twice per cycle, information is lost
causing a moire effect.
Automatic Rescaling
• Fixing the image
• Why is this dangerous?
LUT and Windowing
• Automatic rescaling to achieve
appropriate contrast on an image
• http://www.sprawls.org/resources/D
IGPROCESS/module.htm#13
LATITUDE
• Find the percentage the exposure
can be greater or less than before it
impacts the image in CR
IMAGE
MANIPULATION cont.
• Window- how light or dark an image
should be
• Level-contrast
• Background removal or shuttering
– Removing the unexposed borders or to
blacken the white borders
MTF
• Modular Transfer function
• Reproducing the spatial resolution of
an object as a diagnostic image
• 100% of the spatial resolution of the
object can never be perfectly
reproduced – even with DR and CR –
why? -See Bushong – pgs 451-454
acronyms
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6.
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8.
9.
PSP
CRT
ADC
IP
CR
DR
PACS
SNR
CNR
10.
CCD
11. FOV
12. LUT
13. DICOM
14. RIS
15. HIS
16. TFT
17. DQE
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7.
Photostimulable phosphor-europian activated
barium fluorohalide
Cathode-ray tube or computer monitor
Analog to digital converter
Imaging plate
computed
/digital radiography
Picture archiving communication systems
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SIGNAL TO NOISE RATIO PG 410 –BUSHONG The higher the signal the
9.
CONTRAST TO NOISE RATIO can be manipulated until noise
less the noise.
becomes too apparent-limited by the SNR
10. Charge coupled device- crystal silicon- small, replaces vidicon in
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fluoro, device used in DR
Field of View –how much of the patient is imaged in the matrix
Look up Table – plotting grays on a scale
Digital imaging and communications in medicine -blending PACS
and other imaging modalities
Radiology Information system
Hospital Information system
16. Thin Film Transmitters-
indirect and direct
conversion detector in DR. Stores electronic charge (from
converted light) before computer processes it.
17. Detective Quantum Efficiency converting x-ray
intensities into a radiographic image