1. Fluoroscopic Image Display

2. Television Cameras 3 Methods: Coupling I.I. to TV tube, CCD or APS
Thermionic television camera tube
Solid state charge-coupled device (CCD)
Active pixel sensors (APSs) or (CMOS)
Coupling I.I. to TV tube, CCD or APS
Fiber optics

3. Video Viewing System Closed circuit television Video cameras
Video camera coupled to output screen and monitor
Video cameras
Vidicon or Plumbicon tube
CCD
APS

4. Viewing
The output phosphor of the II is connected by fiber optic cables directly to a TV camera tube when the viewing is done through a television monitor.
The most commonly used camera tube - vidicon
Inside the glass envelope that surrounds the TV camera tube is a cathode, an electron gun, grids and a target.
Past the target is a signal plate that sends the signal from the camera tube to the external video device 4

5. Vidicon (tube) TV Camera

6. Type of TV camera VIDICON TV camera
improvement of contrast
improvement of signal to noise ratio
high image lag
PLUMBICON TV camera (suitable for cardiology)
lower image lag (follow up of organ motions)
higher quantum noise level
CCD TV camera (digital fluoroscopy)
digital fluoroscopy spot films are limited in resolution, since they depend on the TV camera (no better than about 2 lp/mm) for a 1000 line TV system

8. Camera tube have a diameter of approximately 1 inch and a length of 6 inches.

10. Parts of the camera tube
Glass envelope
Electron gun (Cathode)
Control grid
Electrostatic grids
Target

11. Camera Tube steps Light is received by the camera tube.
The light from the II is received at the face plate of the target assembly.
Electrons are formed into an electron beam (by the control grid) at the electron gun.
Electrons are burned off by thermionic emission then focused and accelerated to the target. (made of antimony trisulfide)

12. Vidicon Target Assembly

13. The electrons scan the signal plate similar to reading a page.
Starting in the upper left across to the right, then back to the left to right.
This is called an active trace.
The movement of the electron beam produces a RASTER pattern.
The same pattern occurs in the TV monitor.

14. The signal plate sends the electrical video signal to the control unit which amplifies the signal and synchronizes the pulses between the camera tube and the TV monitor.
TV tube and monitor must be synchronized and duplicated to build a coherent image.

15. Synchronization (Sync Signals)

16. Charge-Coupled Devices (CCDs)
Each electrode is connected to a storage capacitor (TFT)
1980s CCD were developed and replaced TV tubes and miniaturized imaging devices.
Light photons enter the silicon layer, ionization of the light separates the e-. A layer of microscopic electrodes beneath the silicon acts as a ground for the freed electrons. Movement of charges can be measured by a circuit.

17. Video Camera Charged Coupled Devices (CCD)
Operate at lower voltages than video tubes
More durable than video tubes
Semiconducting device
Emits electrons in proportion to amount of light striking photoelectric cathode
Fast discharge eliminates lag

18. CCD’s

19. Advantages of CCDs High spatial resolution High SNR High DQE
No spatial distortion
Unlimited life
Linear response to radiation
Lower patient dose
Wider dynamic range and better contrast resolution than conventional fluoroscopy

20. TV camera and video signal (V)
On most fluoroscopy units, the resolution of the system is governed by the number of lines of the television system. MTF
Thus, it is possible to improve the high contrast resolution by increasing the number of television lines.
Some systems have 1,000 lines and prototype systems with 2,000 lines are being developed.
Color TV requires 3 vidicon tubes for each of the wavelengths (red, green, and blue)

21. TV Monitors

22. Monitors Cathode ray tube (CRT)
Liquid crystal display (LCD) Active matrix liquid crystal display
Emissive displays = produce their own light (diodes)
Not found application for medical imaging so far.
Plasma screen
Light-emitting diode (LED)

23. MONITOR CRT – Cathode Ray Tube
Much larger than camera tube – but similar function
The electrons are synchronized by the control unit – so they are of the same intensity and location as the electrons generated by the pick up (camera) tube.

24. Soft copy viewing digital cathode ray tube (CRT)

25. TV Monitor
The TV monitor contains the picture tube called cathode ray tube (CRT).
It works like the camera tube.
With an electron gun and control grids the electron beam is fired toward the anode.
The TV screen contains small fluorescent crystals

27. Video Field Interlacing

28. Different types of scanning11 1
INTERLACED
SCANNING 13 12 3 2 15 14 5
625 lines in 40 ms
i.e. : 25 frames/s 4 17 16 7 6 19 18 9 8 21 20 10 1 2 3 4 5 6 7
PROGRESSIVE
SCANNING 8 9 10 11 12 13 14 15 16 17 18

29. Two fields = a frame (525 lines)
It take 1/30 of a second.
To prevent flicker, two fields are interlaced to form on television frame.
There are 60 fields and 30 frames per second. Each frame takes 33 ms to form
The eye cannot detect flickering above 20 frames/sec.

31. RASTER Pattern
The electron beam moves in the same raster pattern as in the camera tube.
The signal consists of many individual pulses corresponding to the individual location on the camera tube target.
The varying voltage pulses are later reassembled into a visible in by the TV monitor.

32. Refresh rate
The refresh rate is the measure of how fast the monitor rewrites the screen or the number of times that the image is redrawn on the display each second. The refresh rate helps to control the flicker seen by the user; the higher the refresh rate, the less flicker.

33. TV RESOLUTION-Vertical
Conventional TV: 525 TV lines to represent entire image. Example: 9” intensifier (9” FOV)
9” = 229 mm
525 TV lines/229 mm = 2.3 lines/mm
Need 2 TV lines per test pattern line-pair
(2.3 lines/mm) /2 lines/line-pair = 1.15 lp/mm
Actual resolution less because test pattern bars don’t line up with TV lines. Effective resolution obtained by applying a Kell Factor of 0.7.
Example: 1.15 x 0.7 Kell Factor = 0.8 lp/mm

34. Kell Factor
The ability to resolve objects spaced apart in a vertical direction.
More dots = more scan lines = more/better resolution
Kell factor for 525 line system is 0.7

35. KELL FACTOR VERTICAL RESOLUTION RATIO OF VERTICAL RESOLUITON
ABILITY TO RESOLVE OBJECTS SPACED APART IN A VERTICAL DIRECTION
MORE DOTS(GLOBULES) = MORE SCAN LINES = MORE/BETTER RESOLUTION
RATIO OF VERTICAL RESOLUITON
# OF SCAN LINES
KELL FACTOR FOR 525 LINE SYSTEM IS

36. Dot pitch
Dot pitch is the measurement of how close the dots are located to one another within a pixel

37. TV RESOLUTION-Horizontal
Along a TV line, resolution is limited by how fast the camera electronic signal and monitor’s electron beam intensity can change from minimum to maximum.
This is bandwidth. For similar horizontal and vertical resolution, need 525 changes (262 full cycles) per line. Example (at 30 frames/second):
262 cycles/line x 525 lines/frame x 30 frames/second
= 4.2 million cycles/second or 4.2 Megahertz (MHz)

38. Bandpass/Horizantal Resolution
Horizontal resolution is determined by the bandpass.
Bandpass is expressed in frequency (Hz) and describes the number of times per second the electron beam can be modulated.
The higher the bandpass, the better the resolution

39. Different types of scanning11 1
INTERLACED
SCANNING 13 12 3 2 15 14 5
625 lines in 40 ms
i.e. : 25 frames/s 4 17 16 7 6 19 18 9 8 21 20 10 1 2 3 4 5 6
PROGRESSIVE
SCANNING
USED IN DIGITAL 7 8 9 10 11 12 13 14 15 16 17 18

40. Digital Uses Progressive Scan
1024 x 1024
Higher spatial resolution
As compared to 525
8 images/sec
(compared to 30 in 525 system)

41. 1080p i

42. Digital Uses Progressive Scan
SNR for TV camera tubes
200:1
SNR necessary for DF
Is 1000:1
Each image takes 33 ms
To display

43. TV SYSTEMS
Images are displayed on the monitor as individual frames – which tricks the eye into thinking the image is in motion (motion integration)
15 f/sec – eye can still see previous image
Weakest Link - 2 lp/mm resolution
Real Time

44. Final Image
The result of hundreds of thousands of tiny dots of varying degrees of brightness.
These dots are arranged in a specific patterns along horizontal scan lines.
Usually 525 scan lines.
The electron gun within the picture tube scans from top to bottom in 1/60 of a second, (262 1/2 lines) called a field.

46. Bandpass/Horizontal Resolution
Horizontal resolution is determined by the bandpass.
Bandpass is expressed in frequency (Hz) and describes the number of times per second the electron beam can be modulated.
The higher the bandpass, the better the resolution

47. TV RESOLUTION-Horizontal
Along a TV line, resolution is limited by how fast the camera electronic signal and monitor’s electron beam intensity can change from minimum to maximum.
This is bandwidth. For similar horiz and vertical resolution, need 525 changes (262 full cycles) per line. Example (at 30 frames/second):
262 cycles/line x 525 lines/frame x 30 frames/second
= 4.2 million cycles/second or 4.2 Megahertz (MHz)

48. active matrix liquid crystal display (AMLCD)
Must have sharper resolution
and high speed, each pixel has
its own TFT

49. Crystals can be aligned by an external electric field

50. Nematic liquid crystals
Light is twisted along with the crystals.
Varying the amount of twisting vs alignment allows
for more or less
light and greys
in between.

51. Active matrix liquid crystal displays are superior to cathode ray tube displays.
AMLCD design – gives out more light,
reduces ambient light interference
Better contrast resolution
Less noise
Less maintenance

52. Luminance Rate of light emitted from a source. Measured in lumen (Lm)
Luminous flux – light as perceived by the human eye.

53. CRT vs. AMLCD Lightweight Portable Less expensive More sizes
Smaller profile
Less heat
Longer life
Do not produce veiling glare (light leaking)

54. LCDs VS CRTs Geometric corrections needed
Perfect geometry
Uniform sharpness & brightness
Low surface reflectance (glare)
No image flicker
No veiling glare
Geometric corrections needed
Uneven sharpness & brightness
Image flicker
Veiling glare

55. LCDs 3 substantial disadvantages
Off-angle viewing degrades rapidly, brightness is less.
Have 1/5 less light intensity of a viewbox. Reducing the contrast and apparent spatial resolution.
Can not transmit true black density.
Requires 30 minutes to warm up and sensitive to extreme tempertures.

56. When a digital display device is viewed from the side, illumination and image contrast are reduced.

57. Spatial Resolution
improves with the use of higher-megapixel digital display devices
A 1-megapixel display will have a 1000×1000-pixel arrangement. A high-resolution monitor will have a 5-megapixel display, or a 2000×2500-pixel arrangement

58. Image Display Resolution
Minimum display resolution of 2.5 LP/mm
LCDs resolution is consistent and always uniform.
CRTs must be frequently checked for deterioration.

59. Contrast Resolution
Dynamic range – the number of different gray levels or brightness levels that can be represented in the displayed digital image. (gray scale)
Display monitor is the weakest link in the imaging chain, dynamic range compression.
Bit Depth?

60. Pixels

61. Digital Images – Bit Depth
Pixel values can be any bit depth (values from 0 to 1023)
Bit depth = # or gray shades available for image display
Image contrast can be manipulated to stretched or contracted to alter the displayed contrast.
Typically use “window width” and “window level” to alter displayed contrast and brightness

62. Digital - Grayscale Bit depth. Number of gray shades 8 bit 256
available for display
8 bit 256
10 bit 1024
12 bit 4096
4 bit 16384

63. Display Bit Depth 1 bit 6 bit 8 bit
2 shades shades shades

64. DICOM Gray Scale Standard Display Function
EHR

65. DICOM Function
Image exchange for both senders and receivers, support for connecting to a database and retrieving image information. Enabling another device to which images have been locally for retrieval Other dimensions deal with image management, patient scheduling information, image quality, media storage, security,

66. Image Quality
Problem how to achieve consistency in the image presentation on different monitors, as well as on film, independent of the make or type of characteristics of the media?
Solution: DICOM Grayscale Standard Display Function.

67. DICOM Gray Scale Standard Display Function
It specifies exactly what luminance or density level should be produced for a certain input value, based on the Barten curve, which maps the values into a range that is perceptually linear. This means that input values are mapped into a space that is perceived as linear by a human observer.

68. Inconsistent image display. The lump visible on the left is almost
invisible on the right

69. Viewable area
The viewable area is measured diagonally from one corner of the display to the opposite corner.

70. Window Level & Width Function

71. STATIC IMAGES DYNAMIC IMAGES
RECORDING THE IMAGE
STATIC IMAGES
DYNAMIC IMAGES

72. Basic Componets of “old” Fluoroscopy “Imaging Chain”
Primary
Radiation
EXIT Radiation
Fluoro TUBE
PATIENT
105 Photospot
Fiber Optics OR
Image Intensifier
ABC
LENS
SPLIT
Image Recording Devices
CINE
CONTROL
UNIT
VIDICON
Camera Tube TV

73. Recording the Fluoroscopic Image
STATIC IMAGES
DYNAMIC VIEWING:
Cassettes
Cine film
105 mm chip film = 12 frames per sec.
Videotape
DSA
Digital fluoroscopy/spot

74. Conventional Spot film
Changes the operation of the tube from low fluoroscopic mA to high radiographic mA. 05 – 5 ma (usually ave 1 – 2 ma)
Exposure delayed
Masking capabilities

75. Fluoroscopy mA vs spot exposure
Radiographic Exposure
for cassette spot films
mA increased to 100 – 200 mA
ESE 200 mR = 1 image

76. Photons used: Fluoro vs Radiography

77. Image recording Cassette loaded spot film Where is the tube?
How should you put the IR into the II slot?
You can format the image,
2 on 1, 4 on 1 or 1 on 1
Cassette loaded spot film increases patient dose 77

78. CASSETTE SPOT FILMING vs PHOTOSPOT FILMING
First type of recording used
9x9 cassettes then later up to 14x 14
9 on 1, 4 on 1, 2 on 1
Delay while exposing (anatomy still moving)
Radiographic mA - must boost up to
100 – 200 mA for filming
And moving cassettes around inside tower
Higher patient dose
Replaced by Photospot (f/sec) filming

79. 70 & 105 PHOTOSPOT (CAMERA)
Similar to a movie camera, only one frame exposed when activated.

80. 70 & 105 PHOTOSPOT (CAMERA)
Photo spot camera will take the image right off the output phosphor
This requires less patient dose
70 & 105 mm roll film
General rule, larger film format = better image quality but at increased patient dose.

82. CASSETTE SPOT FILMING vs PHOTOSPOT FILMING
Photospot (f/sec) filming –
Set at control panel from 1 f/sec – 12 f/sec
Used for rapid sequence:
Upper Esophogram
Voiding Cystourethrograms (Peds)
Lower patient dose

83. Photospot filming
100 mR
Frame rate
12/s

84. Recording the Fluoroscopic Image
Dynamic systems
Cine film systems
Videotape recording
Static digital spot filming systems

85. Cine Film Systems Movie camera intercepts image
16 mm and 35 mm formats
Record series of static exposures at high speed
30 – 60 frames per second
Offer increased resolution
At the cost of increased patient dose

86. Cinefluorgraphy aka CINE
35 or 16 mm roll film (movie film)
35 mm ↑ patient dose / 16 mm –
higher quality images produced
30 f/sec in US – (60 frames / sec)
THIS DYNAMIC IMAGE CAPTURE = HIGHEST PATIENT DOSE (10X greater than fluoro)
(VS SINGLE EX DOSE IS ↓)

87. Cine
Cinefluorography is used most often in cardiology and neuroradiology.
The procedure uses a movie camera to record the image from the image intensifier.
These units cause the greatest patient doses of all diagnostic radiographic procedures, although they provide very high image quality.
The high patient dose results from the length of the procedure and relatively high inherent dose rate.
For this reason special care must be taken to ensure that patients are exposed at minimum acceptable levels.
Patient exposure can be minimized in a number of ways. The most obvious means of limiting exposure is to limit the time the beam is on.
CINE - 2mR per frame (60f/sec)
400 mr per “look”

88. Synchronization
Camera shutters and x-ray pulsed fluoro happen at the same time
Only exposes pt when shutter is open to record image
Patient radiation dose ↑ as #/f/sec ↑
(filming a TV show – pattern seen)

89. Framing frequency Number of frames per second
Cine – division of 60 (7.5, 15,30,90,120)
Organ if interest determines f/s rate
Patient exposure?

90. Video disc Referred to as electronic radiography.
Fluoroscopic radiation continues only long enough to build up a useful image on the display monitor.
The image is stored as a single television frame on the video disc recorder.
There is about a 95% reduction in patient dose.

91. Video tape Utilizes VHS or high-resolution tapes.
Patient’s exposure to radiation is not increased.
Used for barium swallows.

92. Fluoroscopy & Digital Photospot
Real-time fluoroscopy operates at 30 f/sec the human eye can perceive 3-5 frames of image information.
Last image will appear very noisy.
Digital spot images are acquired through the II display system (TV tube or CCD)

93. Fluoroscopy & Digital Photospot
Real-time fluoroscopy operates at 30 f/sec the human eye can perceive 3-5 frames of image information during that second.
Last image hold will appear very noisy.
Digital spot images are acquired through the II TV tube to ADC or CCD.

94. Digital Spot Imaging
Half the image resolution of photospot images, 2.4 lp/mm
Digital spots are acquired with a much higher mA (radiographic mode). 50 – 100 x one frame of fluoroscopy
Digital images can be windowed/leveled, smoothing algorithms can reduce noise and enhance edges of images.

95. 1 frame of fluoro digital spot

96. Digital Subtraction Angiography
Computer controlled image matrix size, dynamic range and image acquisition rate.
Matrix size requirement will determine imaging rate capability. 512 x 512 = 30 images per sec x 1024 only 8 image per second can be acquired.
Limitation is enormous quantities of data transfer.

97. Postprocessing image subtraction - DSA
Temporal subtraction
Dual Energy subtraction
Hybrid subtraction
Using both
subtraction techniques

98. Temporal Subtraction Time
Exposures made over time will be subtracted from each other.
Ex: scout, during, post
Automatic injector and x-ray generator work in tandem.

99. Dual energy subtraction
2 images acquired at very different kVp.
Each pixel value can be compared to determine how much change occurred.
Tissues are identified. Specific ranges of value can be subtracted from the image.

100. Questions?