EXAM #5 Flashcards
1
Q
[What is fluoroscopy]
_____ time viewing of anatomical structures
_____ picture x-ray, can stop and take static images,
Most of it IS/IS NOT captured
DOES/DOES NOT have the spatial resolution as normal x-ray (static image)
A
[What is fluoroscopy]
Real time viewing of anatomical structures
Motion picture x-ray, can stop and take static images,
Most of it IS NOT captured
DOES NOT have the spatial resolution as normal x-ray (static image)
2
Q
3 Components of fluoroscopy
A
Image intensifier
TV
CRT tube
3
Q
[Fluoroscopy]
Is flouro dynamic?
A
[Fluoroscopy]
YES
4
Q
[Fluoroscopy]
Discovered in _____ by _____
A
[Fluoroscopy]
Discovered in 1896 by Edison
5
Q
[Fluoroscopy]
Continuous energizing of x-ray tube is needed
A
[Fluoroscopy]
Continuous energizing of x-ray tube is needed
6
Q
[Fluoroscopy]
What is something we can do to reduce heat in fluoroscopy
A
[Fluoroscopy]
Drop mAs
7
Q
[Fluoroscopy]
Low mAs in fluoro = _____ images
A
[Fluoroscopy]
Low mAs in fluoro = noisy images
8
Q
[Fluoroscopy]
DA stands for…
DSA stands for…
A
[Fluoroscopy]
Digital Angiography
Digital Subtraction Angiography (subtracts anatomy we don’t want to look at)
9
Q
[Fluoroscopy]
Where is the tube for fluoroscopy? Except for?
Where should shielding be?
A
[Fluoroscopy]
Tube is in the table (w/ Bucky), except for remote rooms
Shielding should be between the pt and the table
10
Q
[Fluoroscopy]
What exams do not get a curtain
A
[Fluoroscopy]
Anything that is a sterile field does not get the curtain
11
Q
[Fluoroscopy]
What happens when the Bucky slot cover is broken off?
A
[Fluoroscopy]
Leakage from tube
12
Q
[Fluoroscopic Technical Factors ]
Common mAs?
Warning bell purpose?
A
[Fluoroscopic Technical Factors]
1 - 5 mAs
5 minute warning bell to let practitioner know because most cases should be done in less time than that
13
Q
[Fluoroscopic Technical Factors]
Patient dose is considerably high/low
_____, is selected for body type being imaged (chest, belly) and what _____ material we’re using
A
[Fluoroscopic Technical Factors]
Patient dose is considerably high
kVp, is selected for body type being imaged (chest, belly) and what contrast material we’re using
14
Q
[Fluoroscopic Technical Factors]
If we’re using iodine, and I’m looking at vessels or kidneys we want to be around __kVp
If I’m looking at your GI tract, we have to be above kVp
Has to do with z number and k-edge, the average is about 35 and the k-edge is 33
pick ___ to match the contrast
A
[Fluoroscopic Technical Factors]
If we’re using iodine, and I’m looking at vessels or kidneys we want to be around 70KeV
If I’m looking at your GI tract, we have to be above 100KeV
Has to do with z number and k-edge, the average is about 35 and the k-edge is 33
pick kVp to match the contrast
15
Q
[Fluoroscopic Technical Factors]
Image Brightness level is selected, and factors (mAs & kVp) are adjusted automatically to meet the required brightness level know as _____.
The advantage of ABC over AEC?
Disadvantage?
A
[Fluoroscopic Technical Factors]
Image Brightness level is selected, and factors (mAs & kVp) are adjusted automatically to meet the required brightness level know as ABC.
It’s advantage is that it will adjust the KV and the mA (the quality and quantity) while AEC only adjusts mA
It’s disadvantage is that it’s about a second behind (delayed)
16
Q
[How do we provide a moving image? ]
Image intensification is necessary to provide _____ images.
Illumination is measured in _____ (L) and _____ (mL).
A
[How do we provide a moving image?]
Image intensification is necessary to provide quality images.
Illumination is measured in Lambert (L) and mililambers (mL).
17
Q
[How do we provide a moving image?]
An aperture is used to control the _____ between the image intensifier and the television camera tube.
A
[How do we provide a moving image?]
An aperture is used to control the light between the image intensifier and the television camera tube.
18
Q
[How do we provide a moving image?]
Human eyes use _____ and _____ to perceive light levels.
_____ - sensitive to low light 10-6 mL, night or scotopic, not good at seeing detail
_____ sensitive to bright light 10-2 mL, daylight or photopic, better at seeing detail
A
[How do we provide a moving image?]
Human eyes use rods and cones to perceive light levels.
Rod- sensitive to low light 10-6 mL, night or scotopic
Cones sensitive to bright light 10-2 mL, daylight or photopic
19
Q
[How do we provide a moving image?]
With out intensification, _____ vision was used, requiring time to adjust to darkness.
Brightness increase allow for sight with _____ vision, faster and better (higher detail with cone vision).
mAs, kVp, and the anatomy control _____
A
[How do we provide a moving image?]
With out intensification, rod vision was used, requiring time to adjust to darkness.
Brightness increase allow for sight with cone vision, faster and better (higher detail with cone vision).
mAs, kVp, and the anatomy control brightness
20
Q
[Brightness- why is it so important? ]
With out intensification, rod vision was used, requiring time to adjust to darkness.
Brightness increase allow for sight with cone vision, faster and better (higher detail with cone vision).
mAs, kVp, and the anatomy control brightness
A
[Brightness- why is it so important?]
With out intensification, rod vision was used, requiring time to adjust to darkness.
Brightness increase allow for sight with cone vision, faster and better (higher detail with cone vision).
mAs, kVp, and the anatomy control brightness
21
Q
[Image Intensifier ]
Converts image forming x-rays into _____ photons of high _____.
The components to do this are housed in an envelope, creating a _____.
X-rays interact with phosphors (_____) creating light.
SCINTILLATOR the very first layer of this is made of _____ _____
Similar to the process seen with radiographic scintillators, however, CsI phosphors are designed to have little divergence and higher spatial resolution.
A
[Image Intensifier ]
Converts image forming x-rays into light photons of high intensity.
The components to do this are housed in an envelope, creating a vacuum.
X-rays interact with phosphors (CsI) creating light.
SCINTILLATOR the very first layer of this is made of cesium iodine
Similar to the process seen with radiographic scintillators, however, CsI phosphors are designed to have little divergence and higher spatial resolution.
22
Q
The photocathode is adjacent to the intensifier and made of metal. The light emitted by the _____ (material) causes electrons to be emitted by the photocathode.
The number of electrons emitted is _____ proportional to the intensity of the light (which is proportional to the incident x-ray); however, many light photons are needed to emit one electron.
Starts out dim and spread out, shrunk down and sped up to be focused at anode (made of _____ _____) to be made brighter at the output phosphor
A
The photocathode is adjacent to the intensifier and made of metal. The light emitted by the CsI (material) causes electrons to be emitted by the photocathode.
The number of electrons emitted is directly proportional to the intensity of the light (which is proportional to the incident x-ray); however, many light photons are needed to emit one electron.
Starts out dim and spread out, shrunk down and sped up to be focused at anode (made of zinc cadmium sulfate) to be made brighter
23
Q
A potential of 25 kV is maintained across the vacuum, so the electrons will travel to the opposite end or the anode. This anode has a small hole, where the electrons pass through to the _____ _____.
A
A potential of 25 kV is maintained across the vacuum, so the electrons will travel to the opposite end or the anode. This anode has a small hole, where the electrons pass through to the output phosphor.
24
Q
The output phosphor then converts the electrons back to _____ _____.
A
The output phosphor then converts the electrons back to light photons.
25
Electrostatic focusing lenses are used to _____ the electron beam while maintaining its _____. The electrons have high velocity and are minified at the _____ _____.
Electrostatic focusing lenses are used to focus the electron beam while maintaining its integrity. The electrons have high velocity and are minified at the output phosphor.
26
The intensification is realized at this point where every electron creates __-__ times more light than it took to create it.
The intensification is realized at this point where every electron creates 50-75 times more light than it took to create it.
27
Flux gain is used to describe the ______ _____ at _____ compared to the number of incident x-rays.
Flux gain is used to describe the light photons at output compared to the number of incident x-rays.
28
Brightness gain is used to describe the intensifiers ability to _____ _____. Usually _____-_____.
Brightness gain is used to describe the intensifiers ability to increase illumination. Usually 5,000-30,000.
29
Minification gain is used to describe the _____ in _____ of _____ phosphor verses _____ phosphor.
Minification gain = Big dull image and I squished you down into a small intense image
Minification gain is used to describe the difference in size of output phosphor verses input phosphor.
Minification gain = Big dull image and I squished you down into a small intense image
30
What is convergence factor?
Its usual range?
Convergence factor - ratio of the illumination intensity at output to the radiation incident on input phosphor.
Usually 50-300.
31
Dualfield input phosphor size __ - __
Trifield input phosphor size __ - __ - __
Dualfield input phosphor size 25-17
Trifield input phosphor size 25-17-12
32
_____ and _____ = total brightness gain
FLUX and MINIFICATION = total brightness gain
33
Between _____ and _____ there is a screen (filter) that allows photons go through without coming back
Between ANODE and PHOSPHOR there is a screen (filter) that allows photons go through without coming back
34
Multi-field Image Intensification is also known as...
MAG MODE
35
The electrostatic lenses charge is increased when a SMALLER/LARGER input phosphor is used. Resulting in a SMALLER/LARGER electron beam at the output phosphor. The focal point is also moved CLOSER/FARTHER from the output phosphor.
The electrostatic lenses charge is increased when a SMALLER input phosphor is used. Resulting in a SMALLER electron beam at the output phosphor. The focal point is also moved FARTHER from the output phosphor.
36
If a curved input phosphor wasn't used, the image would be _____
If a curved input phosphor wasn't used, the image would be DISTORTED
37
Electronic collimation = _____ _____, two important things happen
1 - The area irradiated INCREASES/DECREASES, and INCREASES/DECREASES FoV
2 - Focusing lenses need to change their _____ to narrow the beam to not shrink down as much and image appears BIGGER/SMALLER
MORE/LESS technique?
MORE/LESS ESE?
MORE/LESS pt. dose? Why?
Electronic collimation = MAG MODE, two important things happen
1 - The area irradiated DECREASES, and DESCREASES FoV
2 - Focusing lenses need to change their CHARGE to narrow the beam to not shrink down as much and image appears BIGGER
MORE technique
MORE PT ENTRANCE SKIN EXPOSURE
SAME pt. dose because more technique, less FoV
38
The output phosphor must be connected to a viewing devise. Most commonly a _____ _____ _____. _____.
_____ and same size as output phosphor.
The output phosphor must be connected to a viewing devise. Most commonly a TV CAMERA TUBE. VIDICON.
SENSITIVE and same size as output phosphor.
39
The TV camera takes the _____ from output phosphor and converts it to an electrical _____ to be reconstructed as a TV image.
The TV camera takes the light from output phosphor and converts it to an electrical signal to be reconstructed as a TV image.
40
TV monitors can have _____ and _____ adjusters, which is an advantage.
Exams can also be stored _____.
TV monitors can have BRIGHTNESS and CONTRAST adjusters, which is an advantage.
Exams can also be stored electronically.
41
[Vidicon]
Components are housed in an envelope that creates a _____.
Electrons are released from the electron gun and a beam is constructed by the _____/_____ grids.
[Vidicon]
Components are housed in an envelope that creates a vacuum.
Electrons are released from the electron gun and a beam is constructed by the control/acceleration grids.
42
[Vidicon]
External electromagnetic coils _____ and _____ the beam.
At the anode the beam interacts with a _____ layered target.
The signal plate conducts electricity to the _____/_____ layer and produces an image by emitting _____.
[Vidicon]
External electromagnetic coils focus and direct the beam.
At the anode the beam interacts with a three layered target.
The signal plate conducts electricity to the target/photoconductive layer and produces an image by emitting light.
43
[Fiber optics]
Advantage?
Disadvantage?
[Fiber optics]
Advantage small, compact easy to move tower, sturdy
Disadvantage- no additional imaging devices, only spot film can be used.
44
[Lenses]
If _____ or _____ (reel of film) is used lens coupling is required. Careful handling is required.
Object lens converts output phosphor light into two _____ beams. This beam interrupted by beam splitting _____. A portion goes to the spot film and the other to the Vidicon.
[Lenses ]
If spot or cine (reel of film) is used lens coupling is required. Careful handling is required.
Object lens converts output phosphor light into two parallel beams. This beam interrupted by beam splitting mirror. A portion goes to the spot film and the other to the Vidicon.
(Beam splitting mirrors are movable and in place only when needed.)
45
[Lenses]
The parallel light beams are then _____ by lenses from the respective devices, camera or spot film. The lens alignment is critical in point for image quality.
[Lenses]
The parallel light beams are then focused by lenses from the respective devices, camera or spot film. The lens alignment is critical in point for image quality.
46
With photospots, doses are HIGHER/LOWER
LOWER
47
[Television Monitor]
The signal is _____ and transmitted by cable to the monitor, where a visible image is made.
The TV monitor and camera are the two ends of a _____ circuit system
The TV Monitor is essentially a _____ ray tube. It is very similar to the TV camera tube; however, it is larger and its anode is a _____ screen with a graphite lining.
[Television Monitor]
The signal is amplified and transmitted by cable to the monitor, where a visible image is made.
The TV monitor and camera are the two ends of a closed circuit system
The TV Monitor is essentially a cathode ray tube. It is very similar to the TV camera tube; however, it is larger and its anode is a florescent screen with a graphite lining.
48
[Television Monitor]
The input signal can be amplified and is proportional to the light intensity received by the TV camera.
The modulation is controlled by the _____ _____.
This _____ and the _____ _____ focus the electron beam onto the output phosphor, to produce a burst of _____.
[Television Monitor]
The input signal can be amplified and is proportional to the light intensity received by the TV camera.
The modulation is controlled by the control grid.
This grid and the external coil focus the electron beam onto the output phosphor, to produce a burst of light.
49
[The Image]
As the electron beams, TV camera and TV tube, move in synchronous timing to create an image the electromagnetic coil direct its pattern
This pattern is known as a _____ pattern.
This pattern starts at the _____ _____ part of the screen an works in a diagonal fashion down the screen.
[The Image]
As the electron beams, TV camera and TV tube, move in synchronous timing to create an image the electromagnetic coil direct its pattern
This pattern is known as a Raster pattern.
This pattern starts at the upper left part of the screen an works in a diagonal fashion down the screen.
50
[The Image]
Again, the pattern starts at the _____ of the screen and works its way _____, although , the second pattern is worked in _____ the lines of the first.
This is known as _____, two of these fields create one TV _____.
* The _____ lines are one field, the _____ lines are one field, and they make up together an entire _____
[The Image]
Again, the pattern starts at the top of the screen and works its way down, although , the second pattern is worked in between the lines of the first.
This is known as interlacing, two of these fields create one TV frame.
* The odd lines are one field, the even lines are one field, and they make up together an entire frame
51
Fields and frames per second for digital progressive and traditional interlaced?
Digital progressive:
fields = 1/30 sec
frames = 1/30 sec
Traditional interlaced:
fields = 1/60 or 2/30 sec
frames = 1/30 sec
52
As the TV signal is created, it immediately starts to fade, each new TV frame represents __ ms of new information.
___ line systems- ___ lines of active trace per frame ___ are available for hi resolution images
As the TV signal is created, it immediately starts to fade, each new TV frame represents 33 ms of new information.
525 line systems- 525 lines of active trace per frame 1024 are available for hi resolution images
53
What controls quality of the picture?
1 - vertical resolution (how many _____ in system) more _____ = closer together = BETTER/WORSE resolution
2 - horizontal resolution (_____) = how many times can I change the _____ _____ as I'm crossing the field. The more I can change it, the more specific I can be to represent an object
The ideal monitor has _____ vertical and horizontal resolution.
What controls quality of the picture?
1 - vertical resolution (how many lines in system) more lines = closer together = BETTER resolution
2 - horizontal resolution (bandpass) = how many times can I change the electron gun as I'm crossing the field. The more I can change it, the more specific I can be to represent an object
The ideal monitor has equal vertical and horizontal resolution.
54
Monitors display __ lp/mm, intensifiers display __ lp/mm. The monitor is the weakest link in the _____ chain.
Images are taken during Fluoroscopy to take advantage of the intensifiers superior _____.
Monitors display 2 lp/mm, intensifiers display 5 lp/mm. The monitor is the weakest link in the resolution chain.
Images are taken during Fluoroscopy to take advantage of the intensifiers superior resolution.
55
[How do we take images during Fluoroscopy? ]
Spot film cameras- Places receptor between _____ and _____. The receptor is removed from it’s lead housing and exposed using a HIGH/LOW mAs radiographic technique.
These mechanical alterations may take __-__ sec.
[How do we take images during Fluoroscopy?]
Spot film cameras- Places receptor between Patient and intensifier. The receptor is removed from it’s lead housing and exposed using a HIGH mAs radiographic technique.
These mechanical alterations may take 1-2 sec.
56
[How do we take images during Fluoroscopy?]
Several types of film use patterns are available. 1 on 1, 2,3,4, on one.
* Quality images are produced however, dose is LOWER/HIGHER and time is a factor.
[How do we take images during Fluoroscopy?]
Several types of film use patterns are available. 1 on 1, 2,3,4, on one.
* Quality images are produced however, dose is HIGHER and time is a factor.
57
Photospot camera - exposes one frame of film per x-ray exposure.
Image is derived form intensifier, using the beam splitting mirror therefor, less dose is needed. (BETTER/WORSE)
_____ time is required to take image.
70 and 105 mm film are used, _____ film generates better images.
Photospot camera - exposes one frame of film per x-ray exposure.
Image is derived form intensifier, using the beam splitting mirror therefor, less dose is needed. (BETTER)
Minimal time is required to take image.
70 and 105 mm film are used, larger film generates better images.
58
[Digital Fluoroscopy]
* The x-ray tube is _____, so that multiple static images are obtained. 1-__ per second (fields, common 4, 7, 15).
* _____ time is the measure of time it takes the tube to be turned on.
[Digital Fluoroscopy]
* The x-ray tube is pulsed, so that multiple static images are obtained. 1-60 per second (fields, common 4, 7, 15).
* Interrogation time is the measure of time it takes the tube to be turned on.
(we no longer use continuous fluoro, the x-ray tube is going to pulse)
59
[Digital Fluoroscopy]
_____ mode reading of the camera tube is necessary.
One entire field is transmitted in __ms. The signal to noise ratio is also very _____ (___:1) -- providing _____ image quality.
* When do we use it?
[Digital Fluoroscopy]
Progressive mode reading of the camera tube is necessary.
One entire field is transmitted in 33ms. The signal to noise ratio is also very HIGH (1000:1) -- providing HIGH image quality.
* We use progressive mode during digital fluoro.
60
1) The TV camera tube transmits the analog signal to the _____ to _____ Converter, where it is put in digital form. _____ then transfers information to memory for storage.
2) A CCD (charged coupled device) can be connected via _____, acquires the image and sends to the computer as a digital signal.
3) A FPIR (flat panel image receptor) can be used with out an _____.
1) The TV camera tube transmits the analog signal to the Analog to Digital Converter, where it is put in digital form. ADC then transfers information to memory for storage.
2) A CCD can be connected via optics, acquires the image and sends to the computer as a digital signal.
3) A FPIR (flat panel image receptor) can be used with out an II.
61
Image subtraction accomplished with digital images.
An _____ beam is needed for subtraction imaging
Two types are available:
• _____ subtraction
• _____ subtraction
Image subtraction accomplished with digital images.
An area beam is needed for subtraction imaging
Two types are available:
• Temporal subtraction
• Energy subtraction
62
1) Temporal subtraction
an image obtained at the _____ is subtracted from further images.
* Mask mode- mask is taken _____ to injection, this image is subtracted from all subsequent images.
* Time interval difference mode- each subtracted image is made with a different mask. Often set __-__ frames apart.
_____ is possible with each of these modes
2) Energy subtraction
two energy x-ray beams are used at pulsating _____. Different energies can be created or a metal filter can be used to accomplish.
1) Temporal subtraction
an image obtained at the start is subtracted from further images.
* Mask mode- mask is taken prior to injection, this image is subtracted from all subsequent images.
* Time interval difference mode- each subtracted image is made with a different mask. Often set 2-4 frames apart.
Misregistration is possible with each of these modes
2) Energy subtraction
two energy x-ray beams are used at pulsating times. Different energies can be created or a metal filter can be used to accomplish.
63
ABC = ABS
ABC = ABS
64
AGC
Electronic _____ of _____, not the amount of _____ going into the system
Noisy = not enough _____
AGC = Automatic Gain Control
Electronic amplification of signal, not the amount of radiation going into the system
Noisy = not enough signal
EXAMPLE: heavy person, upped to the max kV and mAs, ABC still doesn't get what it wants so AGC amplifies it
65
What is pixel shift?
pixel shift = shifting mask over by pixels in temporal subtraction
66
Advantage of PACS?
everyone can read an image at the same time
67
[PACS]
A networked group of computers, servers, and archives that can be used to manage digital images.
A PACS serves as _____ room, _____ room, _____ and _____.
All images must be in _____ format, for communication among computers and storage.
[PACS]
A networked group of computers, servers, and archives that can be used to manage digital images.
A PACS serves as file room, reading room, duplicator and courier.
All images must be in DICOM format, for communication among computers and storage. (all of the image information, RAW data which can communicate between different branded units) kV, mA, and time (exposure index, REX) header (info) and image are separate
68
[HL-7]
This standard oversees what?
Used to communicate between _____ _____ _____ (HIS) and _____ _____ _____ (RIS) and EMR.
HL-7 interfaces with DICOM for error free data flow.
[HL-7]
Standard oversees most clinical and administrative data such a demographics, reports, claims and orders.
Used to communicate between Hospital Information system (HIS) and Radiology Information System (RIS) and EMR (Electronic Medical Record).
HL-7 interfaces with DICOM for error free data flow.
69
[The Computer]
Basically there are _____, _____ and _____ devices.
Information is a series of __s and __s known as binary code.
Bit, a __ or a __, indicates flow of _____
* Byte- is __ bits strung together
One byte usually represents an _____ character.
1 million bytes are a _____
1 billion bytes are a _____
[The Computer]
Basically there are input, output and processing devices.
Information is a series of 0s and 1s known as binary code.
Bit, a 1 or a 0, indicates flow of current
* Byte- is 8 bits strung together
One byte usually represents an alphanumeric character.
1 million bytes are a Megabyte (MB)
1 billion bytes are a Gigabyte (GB)
70
Motherboard - where all components are _____
Central Processing Unit (CPU) - where all calculations happen (controls _____)
Other three components?
Motherboard - where all components are CONNECTED
Central Processing Unit (CPU) - where all calculations happen (controls SPEED)
OTher three components:
• Bus
• Ports
• CMOS (Complimentary Metal Oxide Semiconductor)
71
[Central Processing Unit]
Is a small computer chip on the motherboard.
The CPU function?
Two main manufacturers, _____ and _____
Discussion generally is about speed, modern CPUs are at ___ - ___ (unit?).
[Central Processing Unit]
Is a small computer chip on the motherboard.
The CPU functions to read data from storage, manipulate or process data, and then move it to storage or send for printing or to external devices.
Two main manufacturers, Intel and AMD
Discussion generally is about speed, modern CPUs are at 3.2 -3.8 GHz.
72
array and micro processors
microprocessor = _____ system, one _____ of information calculated and sent out (pipeline system)
array = _____ problems at the same _____, fast
array and micro processors
microprocessor = bus system, one packet of information calculated and sent out (pipeline system)
array = multiple problems at the same time, fast
73
[BIOS]
Function of the BIOS?
Intermediates what two things together?
[BIOS]
Simple set of instructions for the computer
Used during boot up, ensures all peripheral devices are working properly
Intermediary Operating system and hardware
74
[BUS]
A series of _____, _____, and chips that create the information highway of the computer.
There are several highways within one computer
Allows connection for _____ _____, most common is the _____ _____ _____ or _____
[BUS]
A series of connections, controllers, and chips that create the information highway of the computer.
There are several highways within one computer
Allows connection for data exchange, most common is the universal serial bus or USB
75
[CMOS]
What does it stand for?
Small chips powered by batteries that maintain some _____ while computer is turned off. (time and date)
[CMOS]
Complimentary metal oxide semiconductor
Small chips powered by batteries that maintain some memory while computer is turned off. (time and date)
76
[Network Card]
Allows one PC to connect to a _____ for communication with other computers.
[Network Card]
Allows one PC to connect to a network for communication with other computers.
77
[Hard drive]
Main storage for programs and files on a PC
Composed of many hard, thin, magnetic platters that are stacked with only enough room between for a read/write head to perform tasks
Modern computers can hold ~___GB of information and access it at rates of ~__msec
[Hard drive]
Main storage for programs and files on a PC
Composed of many hard, thin, magnetic platters that are stacked with only enough room between for a read/write head to perform tasks
Modern computers can hold ~100GB of information and access it at rates of ~9msec
78
[CD/DVD NOT GOOD FOR LONG TIME STORAGE]
Both of these can be read only memory (ROM), write once read many (R), or read and write many (WR).
CD
• A plastic disk, with bumps molded in to it representing __s or __s of data.
• Can hold upwards of ___MB of data, or ~75 minutes of music
DVD
Capacity is __ times that of CD, ~__/__ GB, single or double sided.
[CD/DVD NOT GOOD FOR LONG TIME STORAGE]
Both of these can be read only memory (ROM), write once read many (R), or read and write many (WR).
CD
A plastic disk, with bumps molded in to it representing 0s or 1s of data.
Can hold upwards of 650MB of data, or ~75 minutes of music
DVD
Capacity is 7 times that of CD, ~10/20 GB, single or double sided.
79
Which of the following encompasses image data?
DICOM
80
[Operating Systems]
Software that controls hardware, acts as a bridge between _____ and _____.
Three major vendors in modern computers, which is best?
[Operating Systems]
Software that controls hardware, acts as a bridge between applications and hardware.
Three major vendors in modern computers:
* Widows
* Macintosh
* UNIX/Linux- best available, least likely to incur problems
81
_____ _____ _____- LAN
Small area networked through _____, _____, cover small area, allow many users to share data.
Several LANs can be networked to form a _____
Local Area Network- LAN
Small area networked through cable, faster, cover small area, allow many users to share data.
Several LANs can be networked to form a WAN
82
_____ _____ _____ –WAN
Large area networked, often through _____, _____ due to area. Allows the most number of users access.
_____ is generally part of a WAN.
Wide Area Network –WAN
Large area networked, often through wireless, slower due to area. Allows the most number of users access.
PACS is generally part of a WAN.
83
What is teleradiology/telemedicine?
Teleradiology/telemedicine = doing stuff over a distance (Radiologists at home through VPN)
84
[Server]
Manages _____ of other computers, servers are networked devices
House _____, provide _____, has _____ tasks
Generally the most _____ computer in network
Thin Client- ?
Thick Client- ?
[Server]
Manages resources of other computers, servers are networked devices
House programs, provide storage, has limited tasks
Generally the most robust computer in network
Thin Client- requests services from server (PC)
Thick Client- capable of managing its own data and processing it, on network to share security and use peripherals, like printers. (3D workstation in CT)
85
Bus
• All computers are attached by _____ _____. _____ point of failure.
Star
• All devices are connected to a central _____. All data passes through _____. _____ used.
• May be slow due to data _____ at one point
Mesh
• Multiple pathways _____ PCs and networks- the internet!
Bus
• All computers are attached by single wire. Single point of failure.
Star
• All devices are connected to a central hub. All data passes through hub. Commonly used
• May be slow due to data congestion at one point
Mesh
• Multiple pathways interconnecting PCs and networks- the internet!
86
What are the three components to PACS and what do they do?
Image Acquisition
• CT,MR, CR or Digital Room
Display Workstation
• Technologist workstation
• Radiologist reading station
Archive Servers
• File room of PACS
• Database server, short term and long term storage, workflow manager computer.
87
[Client/Server Based PACS System]
Images are sent to archive server after _____
Pulling up images from a list is actually asking the server to send a copy of the images to the _____, the _____.
Once images are no longer needed they are _____ from the _____ memory
[Client/Server Based PACS System]
Images are sent to archive server after acquisition
Pulling up images from a list is actually asking the server to send a copy of the images to the client, the PC.
Once images are no longer needed they are deleted from the PCs memory
88
[Client/Server Based PACS System]
Advantages?
Disadvantages?
[Client/Server Based PACS System]
Advantages:
• Exam available thru PACS
• Only one person can read it
• Old/new studies are available
Disadvantages:
• Single point of failure- archive server
• Network dependent- can slow speed
• Archive dependent- can slow speed
89
[Distributed PACS System]
Images are sent to _____ _____
Images may be sent to _____ also, system dependent
Once read they are sent for _____ storage
All images stay on PC hard drive, until _____
[Distributed PACS System]
Images are sent to read/viewing station
Images may be sent to archive also, system dependent
Once read they are sent for permanent storage
All images stay on PC hard drive, until deleted
90
[Distributed PACS System]
Advantages?
Disadvantages?
[Distributed System]
Advantages:
• Not archive dependent
• Multiple data copies- less loss
• Not Network dependent- increase speed
Disadvantages:
• Incorrect distribution – no old exam
• Work list is PC limited- can slow reading speed
• Non scheduled exams- might not have data
91
[Web Based System]
Same data flow as _____ server.
Both images and display software are held at _____.
[Web Based System]
Same data flow as Client server.
Both images and display software are held at server.
92
[Web Based System]
Advantages?
Disadvantages?
[Web Based System]
Advantages:
• Flexibility in hardware
• Software can be used by all
Disadvantages:
• Not all hardware is at diagnostic quality
• Large software may limit of slow system
• Network dependent
93
[Archiving Components ]
The archive is a complex arrangement of _____ and _____ space.
This consists of hardware and software
• Image _____/_____
• Image _____ /_____
Archives store all image data often on magnetic tape or optical disks.
[Archiving Components]
The archive is a complex arrangement of computers and storage space.
This consists of hardware and software
• Image managers/controllers
• Image storage /servers
Archives store all image data often on magnetic tape or optical disks.
94
[Archiving Components]
Image Mangers:
Master database of _____ in archive.
Controls _____, _____ and _____ of _____
Database contains only the _____ information, no _____ data.
This component is mirrored for seamless processing, if one fails, _____ kicks in
Manager communicates with _____ and _____
[Archiving Components]
Image Mangers:
Master database of everything in archive.
Controls receipt, retrieval and distribution of images
Database contains only the header information, no image data.
This component is mirrored for seamless processing, if one fails, backup kicks in
Manager communicates with RIS and HIS
95
[Archive server]
This is the physical _____ area, consists of layers
Short term:
_____, magnetic disks or hard drives in an array
200Gb to 1 Tb
As data enters the _____, it is broken into packets and stored separately.
Some redundancy, good for _____ prevention
Also FASTER/SLOWER for retrieval
[Archive server]
This is the physical storage area, consists of layers
Short term:
RAID, magnetic disks or hard drives in an array
200Gb to 1 Tb
As data enters the RAID, it is broken into packets and stored separately.
Some redundancy, good for loss prevention
Also faster for retrieval
96
[Long term]
_____ _____ _____ (ASP)-
• _____ of archiving and management functions on a pay per click or pay per month charge.
• _____ recovery or _____ _____ data storage, as in another state. Would update every night at 12 act, so it would not be fully complete, but very close.
[Long term]
Application Service Providers (ASP)-
• Outsourcing of archiving and management functions on a pay per click or pay per month charge.
• Disaster recovery or off site data storage, as in another state. Would update every night at 12 act, so it would not be fully complete, but very close.
97
[Long term]
_____-_____ _____-MOD- similar to a DVD or CD, but disk is housed in a plastic cassette, they withstand reading very well over time, holds __ Gb
DVD- least expensive form of storage, holds __Gb
[Long term]
Magnetic-optical disk-MOD- similar to a DVD or CD, but disk is housed in a plastic cassette, they withstand reading very well over time, holds 9.1 Gb
DVD- least expensive form of storage, holds 17Gb
98
[Long term]
Tape- able to archive the most data, hundreds of Tb:
Tapes are housed in a jukebox for playing
Tapes can wear and break, a disadvantage
___ Gb/tape linear open tape
___ Gb/tape Digital linear tape
___Gb-___ TB/ tape Advanced intelligence tape
[Long term]
Tape- able to archive the most data, hundreds of Tb
Tapes are housed in a jukebox for playing
Tapes can wear and break, a disadvantage
400 Gb/tape linear open tape
300 Gb/tape Digital linear tape
200Gb-2 TB/ tape Advanced intelligence tape
99
[Display Stations]
_____, 2 _____, _____ and _____
Monitors can be a _____ or _____
LCD are most common:
INCREASED/DECREASED resolution
Lack of _____/_____ production
INCREASED/DECREASED maintenance
Can be used with _____ ambient light
[Display Stations]
PC, 2 monitors, mouse and keyboard
Monitors can be a CRT or LCD
LCD are most common:
Increased resolution
Lack of heat/x-ray production
Decreased maintenance
Can be used with moderate ambient light
100
[Display resolution]
CT and MR
Require a __ K square monitor, or a ___ X ___
Radiology
Require a __ K square monitor, or a ___ X ___
Mammography
Require a __ K square monitor, or a ___ X ___
[Display resolution]
CT and MR
Require a 1 K square monitor, or a 1280 X 1024
Radiology
Require a 2 K square monitor, or a 1600 X 1200
Mammography
Require a 5 K square monitor, or a 2048 X 2056
101
[Workstations]
Reading:
Must be of _____ quality
Access to ___, ___ and _____ are needed.
[Workstations]
Reading:
Must be of highest quality
Access to RIS, HIS and dictation are needed.
102
[Workstations]
Viewing:
Step _____ model of reading station.
Reports are available with images for referring physicians, _____ manipulation of image
[Workstations]
Viewing:
Step down model of reading station.
Reports are available with images for referring physicians, limited manipulation of image
103
[Workstations]
Technologist QC:
_____ quality, can access old exams when needed.
[Workstations]
Technologist QC:
Lowest quality, can access old exams when needed.
104
PIXEL SIZE = _____ / _____
PIXEL SIZE = FoV / MATRIX
105
What is grayscale?
More grayscale = MORE/LESS shades of gray
the amount of grays that can be displayed
More grayscale = MORE shades of gray
106
Which modality creates the most data?
CT and MR
107
[Image Characteristics]
Matrix- combination of _____ and _____. Each cell represents a _____ for that location.
Pixel- each cell in an image, AKA _____ _____. The value of this cell determines _____ and is related to _____ of tissue imaged. In CT it is a Houndsfield Unit. _____ can never be better than size of pixel.
[Image Characteristics]
Matrix- combination of rows and columns. Each cell represents a brightness for that location.
Pixel- each cell in an image, AKA picture element. The value of this cell determines brightness and is related to attenuation of tissue imaged. In CT it is a Houndsfield Unit. RESOLUTION can never be better than size of pixel.
108
In CR, we are always going to choose the BIGGEST/SMALLEST IR that will fit the part
Why?
In CR, we are always going to choose the smallest IR that will fit the part
Because it’s going to give us the smallest pixel and best spatial resolution
109
[Image Characteristics]
FOV- field of view, area for display of image, _____ X _____ for diagnostics, _____ x _____ for mammography (size of IR)
Pixel size equation?
[Image Characteristics]
FOV- field of view, area for display of image, 2000 X 2000 for diagnostics, 4000 x 3000 for mammography (size of IR)
Pixel size = FOV/matrix
110
What is dynamic range?
Eyes perceive __ shades of gray(2^5), 65536 (2^16) can be displayed; however we cannot appreciate them.
Dynamic range is the numerical range of each pixel, what it can show
Eyes perceive 32 shades of gray(25), 65536 (216) can be displayed; however we cannot appreciate them.
111
[Dynamic Range]
Windowing- post processing done to limit range of gray scale visualized.
* Level- selected as midpoint of image, selected to show tissue being imaged. Controls _____
* Width- range around level that is included in image. Controls _____
The wider the width, the LARGER/SMALLER the exposure latitude, the grayer the image
[Dynamic Range]
Windowing- post processing done to limit range of gray scale visualized.
* Level- selected as midpoint of image, selected to show tissue being imaged. Controls BRIGHTNESS
* Width- range around level that is included in image. Controls CONTRAST
The wider the width, the LARGER the exposure latitude, the grayer the image
112
WIDE/NARROW window width to see soft tissues
NARROW window width to see soft tissues
113
With increased subject contrast, WIDE/NARROW window width
With decreased subject contrast, WIDE/NARROW window width
With increased subject contrast, WIDE window width
With decreased subject contrast, NARROW window width
114
[Computed Radiography]
uses cassettes filed with a _____ _____-stimulable phosphor plate
[Computed Radiography]
uses cassettes filed with a reusable photo-stimulable phosphor plate
115
What is hanging protocol?
The order in which images are taken and displayed to the radiologist
116
CR cassettes are highly sensitive to _____ and _____; therefore, they must be processed _____ a day to prevent excessive fog
CR cassettes are highly sensitive to scatter and fog; therefore, they must be processed once a day to prevent excessive fog
117
Latent images will degrade over time, ~ __% in __ hr.
Latent images will degrade over time, ~ 25% in 8 hr.
118
[Bonus Q?] CRs are made of...
Barium fluorohalide bromides BaFBr:Eu or BaFI:Eu and iodide
119
Which phosphor is better?
Conventional powder PSP or Needle PSP?
Needle PSP (CsI)
120
[Workstation and Monitors]
When reading a plate the Technologist must load demographic information, such as _____, _____ & _____
This is often done with a _____ code/_____ from the _____ that will automatically load data.
[Workstation and Monitors]
When reading a plate the Technologist must load demographic information, such as name, DOB & X-ray #
This is often done with a bar code/worklist from the RIS that will automatically load data.
121
[Workstation and Monitors]
The technologist must also select the _____ and _____ to be processed for each plate.
Selecting the _____ will select the _____, Look Up Table and algorithm for processing the plate.
[Workstation and Monitors]
The technologist must also select the exam and view to be processed for each plate.
Selecting the view will select the histogram, Look Up Table and algorithm for processing the plate.
122
[Workstation and Monitors]
The histogram is specific to the _____, if the selected _____ and that which is run differ, the image will be of poor quality.
Generally CR has a linear __ & __ curve this can be “tweaked” for optimal viewing of data and technical flexibility (LUT)
[Workstation and Monitors]
The histogram is specific to the part, if the selected part and that which is run differ, the image will be of poor quality.
Generally CR has a linear H & D curve this can be “tweaked” for optimal viewing of data and technical flexibility (LUT)
123
What is VoI in regards to histograms?
VoI = values of interest
I don’t care about part that was collimated, it’s not an area of interest
I don’t care about the raw radiation either
124
[Algorithms]
High frequency algorithm = ?
Edge enhancing algorithm = ?
Low frequency algorithm = ?
[Algorithms]
High frequency algorithm = small objects/detail
Edge enhancing algorithm = increases edge of bone
Low frequency algorithm = decreases noise and improves contrast
125
Which algorithm would be used for lungs?
high frequency algorithm to improve detail of soft tissue
126
What does a lookup table do?
Lookup table takes very gray image and adjusts brightness and contrast
127
Due to the linear nature of the H & D curve the system can compensate for overexposure of __% and underexposures of __%
Due to the linear nature of the H & D curve the system can compensate for overexposure of 80% and underexposures of 20%
128
Over exposures result in loss of contrast, due to detector _____.
Over exposures result in loss of contrast, due to detector saturation.
129
Underexposure results in excessive _____.
Underexposure results in excessive noise .
130
* The image that appears on the workstation is for initial viewing only, do not change Window or use edge enhancement if sending to PACS- image maybe locked and the Radiologist will not be able to _____ _____!!
The image that appears on the workstation is for initial viewing only, do not change Window or use edge enhancement if sending to PACS- image maybe locked and the Radiologist will not be able to post process!!
131
Dia positive- Fuji, Cronex:
Overexposure appears BLACK/WHITE
Underexposure appears BLACK/WHITE
Take only one projection per cassette- reader covers whole plate at one time
Dia positive- Fuji, Cronex:
Overexposure appears white/bright
Underexposure appears black/dark
Take only one projection per cassette- reader covers whole plate at one time
132
Positive- Kodak, Agfa:
Similar to film screen, white is _____ and black is _____ exposed
More than one projection per cassette is possible, not recommended- reader covers plate in areas or blocks
Positive- Kodak, Agfa:
Similar to film screen, white is under and black is over exposed
More than one projection per cassette is possible, not recommended- reader covers plate in areas or blocks
133
Fuji systems’ method of locating the raw data
• Automatic:
Adjusts the _____ and _____ for the image
Used when collimation is parallel/equidistant and the central ray and part are centered
• Semiautomatic:
Adjusts the _____, but not the _____
Can be used when collimation is not parallel/equidistant
• Fixed- film like:
Does not adjust _____ or _____
Requires use of proper technical factors
Fuji systems’ method of locating the raw data
• Automatic:
Adjusts the latitude and sensitivity for the image
Used when collimation is parallel/equidistant and the central ray and part are centered
• Semiautomatic:
Adjusts the sensitivity, but not the latitude
Can be used when collimation is not parallel/equidistant
• Fixed- film like:
Does not adjust sensitivity or latitude
Requires use of proper technical factors
134
* In CR/DR do we have lower patient doses OVERALL?
yes, because less repeats only
135
[Collimation]
Must be _____ on both sides
_____ is imperative
Must go back to proper positioning protocols (must use lead markers)
No more _____ of exams
Always use the _____ cassette possible
[Collimation]
Must be even on both sides
Centering is imperative
Must go back to proper positioning protocols (must use lead markers)
No more combining of exams
Always use the smallest cassette possible
136
[*] ___ of exposure = good amount for any system
[*] 1mR of exposure = good amount for any system
137
Sensitivity numbers in a Dia-positive- Fuji system range ___-___
_____ related to amount of exposure received
S number ___ ~ __ mR exposure
S number ___ ~ __ mR exposure
* As S# goes up, exposure goes down
* As S# goes down, exposure goes up
* When S# doubles, the exposure changes by ____
Sensitivity numbers in a Dia-positive- Fuji system range 50-200 (can be stretched to 200-400)
Inversely related to amount of exposure received
S number 200 ~ 1mR exposure
S number 20 ~ 10 mR exposure
* As S# goes up, exposure goes down
* As S# goes down, exposure goes up
* When S# doubles, the exposure changes by decreasing one half
(fig. 32-2, 32-3, 32-4)
138
[Grids]
Should be used on _____ projections
Must be ___ lp/mm, buckys are only ___, not enough
All portable must be done with ___, what kind?
When using AEC, __% increase in exposure is needed
[Grids]
Should be used on most projections
Must be 156 lp/mm, buckys are only 108, not enough
All portable must be done with grids, linear non focused
When using AEC, 15% increase in exposure is needed
139
[*] Exposure index in a Positive- Kodak system range ___-___
_____ related to amount of exposure received
Exposure Index of ___ ~ ___ exposure
Exposure Index of ___ ~ ___ exposure
• Doubling of exposure = ___ = ___ exposure
• Halving the exposure = ___ = ___ exposure
+/- ___
Exposure index in a Positive- Kodak system range 1000-2000
Directly related to amount of exposure received
Exposure Index of 2000 ~ 1mR exposure
Exposure Index of 3000 ~ 10mR exposure
• Doubling of exposure = 2300 = 2mR
• Halving the exposure = 1700 = 0.5mR
+/- 300
140
[Technical Factors]
Optimal keV of ___-___, for highest DQE
Should not exceed kVp of ___-___, due to scatter and decreased DQE
Changes of ___ keV can affect image quality and exposure
Due to linear H & D curve, one can increase ___ to increase exposure and INCREASES/DECREASES dose without negative impact on contrast
[Technical Factors]
Optimal keV of 35-50, for highest DQE
Should not exceed kVp of 80-100, due to scatter and decreased DQE
Changes of 2 keV can affect image quality and exposure
Due to linear H & D curve, one can increase ___ to increase exposure and DECREASES dose without negative impact on contrast
141
Is Agfa positive or diapositive?
positive
142
Is Philips positive or diapositive?
diapositive
143
(DI) deviation index
number of ___ = where you should be
numbers go up = exposures go ___
numbers go negative = exposures go ___
(32-4)
(DI) deviation index
number of 0 = where you should be
numbers go up = exposures go up
numbers go negative = exposures go down
(32-4)
144
[Scanned Projected Radiography- SPR]
developed by GE Medical Systems, used for __
Tube is set _____ a row of detectors. X-ray beam is collimated into a _____ for little _____. The patient is moved through the beam and an image is formed.
Resolution is BETTER/LESS than conventional, but contrast is BETTER/LESS.
Detectors can be ____ ____ ____ ____ or ____ ____ ____ (____ ____)
[Scanned Projected Radiography- SPR]
developed by GE Medical Systems, used for CT (to reference
Tube is set opposite a row of detectors. X-ray beam is collimated into a fan beam for little divergence. The patient is moved through the beam and an image is formed.
Resolution is less than conventional, but contrast is better (due to wide beam).
Detectors can be gas filled ionization chambers or solid state photodiodes (scintillation crystals)
145
InDirect-Capture Radiology (steps to get to DR)
Utilize a flat panel image receptor the size of a regular cassette. An _____ _____ _____ (_____) is used.
_____/_____ is coated over a matrix of a-Si photo diodes.
• X-ray -- _____/_____ produces light--
_____ produces signal -- _____ stores
signal held until readout one pixel
at a time.
_____ for extremities
_____ for chest and everything else
a-Si = _____ _____, represents _____, pixel sizes _____ change unlike in CR
Better DQE but w/ split pixels
InDirect-Capture Radiology (steps to get to DR)
Utilize a flat panel image receptor the size of a regular cassette. An active array matrix (TFT) is used.
```
CsI/GdOS is coated over a matrix of a-Si photo diodes.
• X-ray -- CsI/GdOS produces light--
a-Si produces signal -- TFT stores
signal held until readout one pixel
at a time.
```
CsI for extremities
GdOS for chest and everything else
a-Si = amorphous silicon, represents pixels, pixel sizes never change unlike in CR
Better DQE but w/ split pixels
146
What is fill factor?
The gray part is the active part, a certain portion of each pixel is called active space
Part of that pixel, the white boxes in the corners are the electronics that are required (dead-space)
The a-SI is the only part that can take in info, a high active area, and little dead space, what that means is in a certain area, if 90% can take in info and 10% is dead, that’s good. Iff a diff arrangement, 30% info and 70% dead, not good. Fill factor
147
less fill factor = MORE/LESS technique
more fill factor = MORE/LESS technique
less fill factor = MORE technique (more noise)
more fill factor = LESS technique
148
[In Direct-Capture Radiology]
Charged Coupled Devices (CCD)
_____ typically used with a screen _____
Requires _____ _____ by _____ or _____ _____
CCD captures light emitted by Scintillator (CsI/GdOS) and stores it as an _____ signal
Signal is read out in a _____ pattern
_____ signal from CCD sent to _____
[In Direct-Capture Radiology]
Charged Coupled Devices (CCD)
Photodetector typically used with a screen Scintillator
Requires optical coupling by lenses or fiber optics
CCD captures light emitted by Scintillator (CsI/GdOS) and stores it as an electrical signal
Signal is read out in a linear pattern
Electric signal from CCD sent to computer
149
What are CCDs?
light sensitive chips
take in light and send out electronic signal that can be digitized for the computer
150
If indirect, we has a phosphor, crystal, or light that is then digitized
disadvantage of indirect capture radiography?
If indirect, we has a phosphor, crystal, or light that is then digitized
disadvantage is some loss of info
151
[Direct-Capture Radiology]
a-Se is directly interacted with by x-ray
x-ray -> a-Se produces electron hole pairs --
this signals TFT-- signal stored
until readout --one pixel at a time
advantage is no light diversion as
seen in CsI/GdOS coated a-Si
each TFT represents one pixel
in our image
MORE/LESS steps = MORE/LESS loss = MORE/LESS light = MORE/LESS divergence
```
TFT = ?
Septa = ?
```
Disadvantage?
Usually found in which modality?
2 reasons why?
[Direct-Capture Radiology]
a-Se is directly interacted with by x-ray
x-ray-> a-Se produces electron hole pairs --
this signals TFT-- signal stored
until readout --one pixel at a time
advantage is no light diversion as
seen in CsI/GdOS coated a-Si
each TFT represents one pixel
in our image
LESS steps = LESS loss = LESS light = LESS divergence
```
TFT = dead spot
Septa = lines between capture elements
```
Disadvantage = higher pt. dose, doesn't absorb higher energy x-ray
Usually in found in mammo
1. low kVs
2. most narrow line spread function (better spatial resolution)
152
a-Se = used in _____-capture radiography
a-Si = used in _____-capture radiography
a-Se = used in direct-capture radiography
a-Si = used in indirect-capture radiography
153
[Digital preprocessing]
Largely _____
Designed to produce _____ _____ digital images
What is pixel interpolation?
[Digital preprocessing]
Largely automatic
Designed to produce artifact free digital images
Pixel interpolation- if there is a dead pixel, those around it are averaged to create pixel data.
154
[Digital preprocessing]
Lag correction- seen after a _____ _____ exam when switching to a _____ _____ exam, and offset _____ is used to prevent _____.
Noise Correction- caused by _____ _____ along electrical connections, _____ _____ is applied.
Offset images happen daily, Gain images occur monthly. Provide uniform IR response.
[Digital preprocessing]
Lag correction- seen after a high dose exam when switching to a low dose exam, and offset voltage is used to prevent artifact. (some info was left on TFTs and gets subtracted out)
Noise Correction- caused by voltage variations along electrical connections, voltage correction is applied.
Offset images happen daily, Gain images occur monthly. Provide uniform IR response. (take image with a filter over it to calibrate it)
