Fluoroscopy
Intro to EQUIPMENT
RT 244
FALL 2008
Week 1
Wed- CONTINUED
Basic Componets of “old” Fluoroscopy “Imaging Chain”
Conventional I I system
IMAGE INTENSIFIER
The anode of the II
Anode and Output Screen
l Anode
l Positively charged
l 25 kVp
l Hole in center allows electrons to pass through to output screen
l OUTPUT SCREEN
l Usually 1 inch in diameter
l Zinc cadnium sulfide coating
l Changes electrons back to LIGHT
Image Intensifier
PROPERTIES
Image Quality
Contrast
Resolution
Distortion
Quantum mottle
Contrast
l Controlled by amplitude of video signal
l Affected by:
l Scattered ionizing radiation
l Penumbral light scatter
Veiling glare
l Scatter in the form of x-rays, light & electrons can
l reduce contrast of an image intensifier tube.
Resolution
l Video viewing
l Limited by 525 line raster pattern of monitor
l Newer digital monitors 1024 - better resolution
l MORE ON THIS LATER IN THE LECTURE
Image distortion
Shape Distortion
l Geometric problems in shape of input screen
l Concave shape helps reduce shape distortion, but does not remove it all
l Vignetting or pin cushion effect
l Vignetting
FALL-OFF OF BRIGHTNESS AT PERIPHERY (EDGES) OF THE IMAGE
VIGNETTING…….
l Darkness on edges (falloff of brightness)
Size Distortion
l Affected by same parameters as static radiography
l Primarily OID
l Can be combated by bringing image intensifier as close to patient as possible
ABC
Basic Componets of “old” Fluoroscopy “Imaging Chain”
Brightness Control
l Automatic brightness stabilization
l Automatic adjustments made to exposure factors by equipment
l Automatic gain control
l Amplifies video signal rather than adjusting exposure factors
BRIGHTNESS CONTROL
l ABC ABS AEC ADC
l MAINTAINS THE BRIGHTNESS OF THE IMAGE – BY AUTOMATICALLY ADJUSTING THE EXPSOURE FACTORS (KVP &/OR MAS) FOR THICKER PARTS
l SLOW RESPONSE TIME - IMAGE LAG
ABC
l Automatic brightness control allows Radiologist to select brightness level on screen by ↑ kVp or ↑ mAs
l Automatic dose control
l Located just beyond the Output Phosphor
l Will adjust according to pt thickness
Automatic Brightness Control
l Monitoring Image Brightness
l Photocell viewing (portion of) output phosphor
l TV signal (voltage proportional to brightness)
l Brightness Control: Generator feedback loop
l kVp variable
l mA variable/kV override
l kV+mA variable
l Pulse width variable (cine and pulsed fluoro)
Quantum Mottle
l Blotchy, grainy appearance
l Caused by too little exposure
l Most commonly remedied by increasing Ma
l Controlled by the ABC
l Affected by too little technique
l size of patient
l distance of II to patient
l size of collimation
Fluoroscopic Noise
(Quantum Mottle)
Fluoroscopic image noise can only be reduced by using more x-ray photons to produce image. Accomplished in 3 ways:
l Increase radiation dose (bad for patient dose)
l Frame-averaging:
l creates image using a longer effective time
l Can cause image lag (but modern methods good)
l Improve Absorption Efficiency of the input phosphor
KEEP I.I. CLOSE TO PATIENT
reduces beam on time
Units of measurement
l INPUT PHOSPHOR – IS MEASURED IN ______
l OUTPUT PHOSPHOR IS MEASURED IN
l ______
Units of measurement
l INPUT PHOSPHOR – IS MEASURED IN
Milliroentgens mR
l OUTPUT PHOSPHOR IS MEASURED IN
CANDELAS (LIGHT)
VIEWBOXES ARE MEASURED IN: lamberts (light)
Fluoroscopic Imaging
Coupling I.I. to TV Monitor
l 2 Methods:
l Fiber optics directly to T.V. camera.
l Lens system which utilizes auxiliary imaging devices.
Directly to T.V.
l Only cassettes can be used.
Beam splitting mirror
Basic Componets of “old” Fluoroscopy “Imaging Chain”
Beam splitting mirror
l Often a beam splitting mirror is interposed between the two lenses.
l The purpose of this mirror is to reflect part of the light produced by the image intensifier onto a 100 mm camera or cine camera.
l Typically, the mirror will reflect 90% of the incident light to other RECORDING DEVICES
l and transmit 10% onto the television camera*.
l *TV MONITOR is the weakest link (low resolution)
Viewing Fluoroscopic Images
Lenses / Mirrors
l Used to direct image to recording devices
l Several mirrors in a series and angled - the last mirror is outside the II for the operator to view
l Image decreases as it is projected from 1 mirror to the next
l Only 1 person can view image
RECORDING THE IMAGE
STATIC IMAGES
DYNAMIC IMAGES
Basic Componets of “old” Fluoroscopy “Imaging Chain”
Recording the Fluoroscopic Image
l STATIC IMAGES
l Cassettes
l 105 mm chip film = 12 frames per second
l Digital fluoroscopy
l DYNAMIC VIEWING:
l Cine film
l Videotape
Recording Fluoroscopic Images
IMAGE RECORDING
l OLD II - ONLY FIBER OPTICS –NO LENS SPLITTER TO OTHER RECORDING DEVICES
l ONLY RECORED IMAGE ON SPOT CASSETTES (9X9 ONLY)
l NEWER - TAKES CASSETTES or uses /105 PHOTOSPOT / VIDEO/ CINE
l NEWEST = USES DIGITAL !!!!!!!!!
l (but the tests* still have all of it!)
Basic Componets of “old” Fluoroscopy “Imaging Chain”
Fluoroscopy mA
l Low, continuous exposures .05 – 5 ma
(usually ave 1 – 2 ma)
l Radiographic Exposure
for cassette spot films
l mA increased to 100 – 200 mA
RECORDING IMAGES
l OLD (Smaller) II with fiber optic
l ONLY RECORDING WAS CASSETTE
l CASSETTE “SPOT” IMAGES
l TAKEN DURING FLUORO PROCEDURE
l VERY OLD 9X9 inch cassettes
l Later could take up to 14 x 14 inches
Cassettes
l Standard size - 9” x 9” (old)
l NOW CAN TAKE UP TO 14X14
l Stored in lead-lined compartment until ready for exposure
l When exposure is made, mA is raised to radiographic level
l Multiple image formats
Image recording
Basic Componets of “old” Fluoroscopy “Imaging Chain”
70 & 105 PHOTOSPOT (CAMERA)
l Photo spot camera will take the image right off the output phosphor
l This requires less patient dose
l 70 & 105 mm roll film
CASSETTE SPOT FILMING
vs PHOTOSPOT FILMING
l First type of recording used
l 9x9 cassettes then later up to 14x 14
l 9 on 1, 4 on 1, 2 on 1
l Delay while filming (anatomy still moving)
l Radiographic mA - must boost up to
l 100 – 200 mA for filming
l And moving cassettes around inside tower
l Higher patient dose
l Replaced by Photospot (f/sec) filming
CASSETTE SPOT FILMING
vs PHOTOSPOT FILMING
l Photospot (f/sec) filming –
l Set at control panel from 1 f/sec – 12 f/sec
l Used for rapid sequence:
l Upper Esophogram
l Voiding Cystourethrograms (Peds)
l Lower patient dose
Recording the Fluoroscopic Image
l Dynamic systems
l Cine film systems
l Videotape recording
l Static spot filming systems
TV camera and video signal
& Recording the image
Cine Film Systems
l Movie camera intercepts image
l 16 mm and 35 mm formats
l Record series of static exposures at high speed
l 30 – 60 frames per second
l Offer increased resolution
l At the cost of increased patient dose
Cinefluorgraphy aka CINE
l 35 or 16 mm roll film (movie film)
l 35 mm ↑ patient dose / 16 mm –
l higher quality images produced
l 30 f/sec in US – (60 frames / sec)
l THIS MODALITY = HIGHEST PATIENT DOSE (10X greater than fluoro)
l (VS SINGLE EX DOSE IS ↓)
Cine
l Cinefluorography is used most often in cardiology and neuroradiology.
l The procedure uses a movie camera to record the image from the image intensifier.
l These units cause the greatest patient doses of all diagnostic radiographic procedures, although they provide very high image quality.
l The high patient dose results from the length of the procedure and relatively high inherent dose rate.
l For this reason special care must be taken to ensure that patients are exposed at minimum acceptable levels.
l 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.
l CINE - 2mR per frame (60f/sec)
l 400 mr per “look”
More on Cine
l Synchronization
l Framing frequency
l F-number of the optical system
l Framing and patient dose
Synchronization
l Camera shutters and x-ray pulsed fluoro happen at the same time
l Only exposes pt when shutter is open to record image
l Patient radiation dose ↑ as #/f/sec ↑
l (filming a TV show – pattern seen)
F-number of the optical system
l Speed of any given camera system
l The amount of light made available to the lens
Framing and patient dose
syll = Pg 31
l The use of the available film area to control the image as seen from the output phosphor.
l Underframing
l Exact Framing, (58 % lost film surface)
l Overframing,(part of image is lost)
l Total overframing
OVERFRAMING vs Exact Framing
Framing frequency
l Number of frames per second
l Cine – division of 60 (7.5, 15,30,90,120)
l Organ if interest determines f/s rate
l Patient exposu
More on Safety later….
RECORDING DEVICES
RESOLUTION P 542 (3rd ed)
OPTICAL MIRROR – BEST BUT NOT PERMANENT RECORDING MEDIUM
l SPOT FILM CASSETTES 6LP/MM
l PHOTO SPOT 105 / 70
l CINE 35 MM / 16 MM
l DIGITAL (?) (VS FILM)
l VIDEO – VIEWING REALTIME
l VIDEO TAPE - PLAYBACK
Line pair gauges
Line pair gauges
Video disc
l This technique is referred to as electronic radiography.
l Fluoroscopic radiation continues only long enough to build up a useful image on the display monitor.
l The image is stored as a single television frame on the video disc recorder.
l There is about a 95% reduction in patient dose.
Video tape
l Utilizes VHS or high-resolution tapes.
l Patient’s exposure to radiation is not increased.
l Used for barium swallows.
Image Quality - Review
l Terms that are necessary to know:
l Vignetting is the loss of brightness at the periphery of the II due to the concave surface
l Pincushion effect is the drop off at the edges of the II due to the curved surface
l Quantum mottle is the grainy appearance on the image due to statistical fluctuations
l The center of the II will always have the best resolution.
l Lag is the blurry image from moving the II too fast
OVERFRAMING vs Exact Framing
Monitoring
VIDEO/CAMERA TUBE
l PLUMICON, VIDICON, ORTHOCON
l VIDICON MOST COMMOM
l ORTHOCON – VERY $$$$
l PLUMICON – BETTER RESOLUTION
l TRANSFERS IMAGE FROM OUTPUT PHOSPHOR TO TV MONITOR
l CONNECTED BY FIBER OPTICS
VIDEO/CAMERA TUBE
PLUMICON, VIDICON, ORTHOCON, CCD’s
l TRANSFERS IMAGE FROM OUTPUT PHOSPHOR TO TV MONITOR
l CONNECTED BY FIBER OPTICS or Optical Lens
l VIDICON- MOST COMMOM
l PLUMICON – BETTER RESOLUTION
l CCD – Charged Coupling Devices
l ORTHOCON – VERY $$$$
VIDEO/CAMERA TUBE
l VIDICON MOST COMMOM
l – good resolution with moderate lag – ok for organs
l Uses ANTIMONY TRISULFATE
l PLUMICON (a modification of Vidicon)
l – BETTER RESOLUTION / (↓ dose)
l Better for moving part like the heart –faster response time
l High performance, lag may improve, but ↑quantum mottle
l Uses LEAD OZIDE
l ORTHOCON – VERY $$$$ - Larger (Not used) BEST RESOLUTION WITH NO LAG
l Functions as both II and pick up tube
l CCD – smaller & longer life, very little image lag
Type of TV camera
F VIDICON TV camera
F improvement of contrast
F improvement of signal to noise ratio
F high image lag
F PLUMBICON TV camera (suitable for cardiology)
F lower image lag (follow up of organ motions)
F higher quantum noise level
F CCD TV camera (digital fluoroscopy)
F 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
TV camera and video signal (II)
Vidicon (tube) TV Camera
camera tube have a diameter of approximately
1 inch and a length of 6 inches.
Parts of the camera tube
l Glass envelope
l Electron gun (Cathode)
l Control grid
l Electrostatic grids
l Target
Camera Tube steps
l Light is received by the camera tube.
l The light from the II is received at the face plate of the target assembly.
l Electrons are formed into an electron beam (by the control grid) at the electron gun.
l Electrons are burned off by thermionic emission then focused and accelerated to the target. (made of antimony trisulfide)
Target of the Camera Tube
l The electrons scan the signal plate similar to reading a page.
l Starting in the upper left across to the right, then back to the left to right.
l This is called an active trace.
l The movement of the electron beam produces a RASTER pattern.
l The same pattern occurs in the TV monitor.
l 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.
l This synchronization
Vidicon Target Assembly
Viewing Systems
l Video camera charge-coupled device (CCD)
l Video monitor
l Digital
Video Viewing System
l Closed circuit television
l Video camera coupled to output screen and monitor
l Video cameras
l Vidicon or Plumbicon tube
l CCD
Synchronization (Sync Signals)
TV camera and video signal (V)
TV Monitor
TV MONITOR
l CRT – Cathode Ray Tube
l Much larger than camera tube – but similar function
l 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.
TV Monitor
l The TV monitor contains the picture tube called cathode ray tube (CRT).
l It works like the camera tube.
l With an electron gun and control grids the electron beam is fired toward the anode.