digital radiography: best practices Flashcards
when were Digital radiographs first invented
in the late 80’
Characteristics of the first radiographs
V. large
TV not computer
no storage or manipulation of image
cost
when did Digital x-rays become like today
In the 90s
what is a digital image
A representaion of a 2d image as a finite set of digital values called pixels
what do pixels represent
represent gray levels, colors, heights….
is a digital scene actually the real image
No an approximation of a real scene
Benifit of Digital X-ray to standard to patient
reduction compared to F-sped between 0-50 percent (lower dose)
Increase in number of radiographs made
INcrease in ease of remakes
why do digital
Efficient work flow
Image enhancement
Better case acceptance
Co-diagnosis
Digital Imaging chain
Image acquisition
Image processing
Image display
retake rate of digital vs. Film
digital: 20%
FILM: 9%
what is involved in image Acuisition
X-ray tube
Sensor
sensory placement and exposure
How should the X-ray tube act for digital X-rays
timer capable of making reproducible short exposures if image quality is suoptimal (may need to upgrade)
systems for making digital X-rays
CCD
CMOS
Phosphors
what type of digital x-rays are indirect
Phosphors (scanning)
How does CCD digital X ray work
- X-ray hits sensor and produces electrons at the same rate of the x-ray hitting
- One well transfers the electrons to the next
- edge of the CCD provides Electrical signal
How does a CMOS work
each pixel has its own transistor and this is read directly
what happens if too many electrons in a well
spill over and muddy image (over exposure)
which type of sensor has more noise
The CMOS due to the extra transistors
what is a Wireless sensor mades of (PSP)
plastic plate coated with phosphor material sensitive to X-rays
what is a PSP
the plate of a wireless sensor (photostimulable phosphor plate)
how does a PSP work
- Sensor exposed to an x-ray which creates a latent image stored on the plate
- then image digitalized with scanner
what must be done to a PSP after an image is taken
cleared by light exposure for several minutes before next use
steps of a PSP
Exposure
Stimulate with laser
reading due to light emision
Ease with light
what is the weakest part of the sensor
the junction to the computer
what are extraoral digital radigraphs
PAnoramic
Cephalometric
do most current X-ray detectors work well
GEnerally yes, interms of spatial and contrast resoltuions and in terms of exposure latitude
- indepent of modality applied`
Characteristics of digital detector characteristics
Contrast REsolution
Spatial rsolution
Detector Latitude
Detector sensitivity
what is contrast resolution
Dynamic range (ability to distriguish different densities in the image
what affefcts contrast resolution
Attenuation of radiation by tissues
Capacity of receptor
computer display
ability of observer
what does bit mean
it is the power 2 is raised to to determine the amount of gray levels are capable of being made
what is spatial resolution
the capacity to distinuish fine detal
smallest picel size
20 microns (24 lp/mm)
HUman eye can differentiate how many lp/mm without maginification
6-8 (less than the smallest pixel)
what is detector latitude
Ability of receptor to capture a range of exposure
what is detector sensitivity
Ability to respond to small amouts of radiation
standard for detector sensitivity
No classification yet
what is Detector quantum effeciency
Is the measure of noise and contrast expressed as a function of object detail
what does a DQE of 100% mean
A perfect detector, meaning all info that reaches detector is trasferred out of detector
what are qualities of sensors
Spatial resolution
Bit depth
Active area
what should the bit depth be at least for a senosr
at least 12
important things to think about when it comes to sensory
Sensory reliablility (life span) Software integration with practice management software
Roll of image processing
To restore, enhance, or analyze image
aspects of image enhancement
Brightness and contrast
Sharpening and smoothing
color
Digital subtraction
what does a histogram do
Shows certain spectrums of color
what are kinds of analysis tools
Zoom
Measurement
Digital subtraction
what is digital subtraction
- when 2 radiographs are taken with the same exposure geometry over a time interval
- images superimposed
- computer compares and removes whatever is exactly the same giving a clear image of anything that is different
how do changes look in digital subtraction
displayed as a resultant image against a neurtral gray background
how much bone mass can digital subtraction notice
A change as little as 5%
how many practicing dentist have experience problems with digital radiography
about 65%
what is one of the weaker links in the technical chain of digital radiograph
Monitor
room lighting affect on analysis of radiographs
Affects the diagnosistic outcome of low contrast patterns (low light good)
affect of high luminance
results in better image quality, making subtle lesions easier to detect
Luminance of different things
Viewboxes (1000-2000 Cd/ Msequared reg monitors (250-300 medical monitors (1000)
What is luminence
MAx and Min amount of light emitted from display monitor (contrast ratio)
what kind of devices have small picture elemets
High quality photographic and medical display devices
how much does contrast ratio drop at a vewing angle of 85 degrees
10:1
shades of gray in a medical display
4096(12 bit)
- consumer display is 8 bit
important things for image storange
Prevention of permanent deletion or modification
Backup considerations
Size of aradiograph
200 kb to 6MB
what is the standard for for didigtal communcation
Digital imaging and Communication in mediicine stand (DICOM)
benifit of Following DICOM
makes sharing images simpler between providers
where should you test new X-ray machines and why
In your own office so images can be standaradizes and not preselected
also know how to integrate and environement
how long do X-ray ray equipment work
5-7 years
cost of CCD and CMOS
5-8k
cost of PSP plates
30-50
how much ram should you have
4 gigabytes
CPU speed
2 gigahertz
Storage in server
Terabyte
dedicated server need a hardrive of 500GB
USB?
Always good
should you go wireless or nah
Sinve large files, wired is faster and secure
