Fluoroscopy Intro to EQUIPMENT RT 244 FALL 2008/9/10 rev Week 1 Mon – day 1 Ref: Fluoroscopy – Bushong’s Ch. 24

Topics for WEEK 1 RT 244 Example of fluoroscopy systems Components of the Imaging Chain Image intensifier, Camera tubes TV & viewing system……..etc Recording systems Digital Fluoroscopy (?) Explanation or/and additional information Instructions for the lecturer/trainer

Fluoro objectives Draw a cross sectional view and identify the components of an image intensifier tube. Describe the operation of an image intensifier tube, including the different image carriers (photons and electrons) that are utilized in the tube. Describe the concepts of brightness gain, minification gain, and flux (electronic) gain as applied to an image intensifier. Show how the total gain is computed from the minification gain and the flux (electronic) gain.

Fluoro objectives Define conversion factor for an image intensifier. A fluoroscopic system is switched to the enlargement mode so that the center 6 inches of the input screen is visualized in place of the entire 9 inch diameter screen. If the brightness of the output screen remains constant, estimate the relative increase in exposure rate that has occurred.

Fluoro objectives Sketch and explain the function of the typical optical beam-splitter used to permit televised fluoroscopy and spot filming or cine-radiography. Describe briefly the video process whereby an image on the output screen of an image intensifier is transferred to the screen of a television monitor. Explain the process of video line interlacing and why it is used.

Fluoro objectives Describe video image fields and frames and the times associated with each. Describe the factors that influence the horizontal detail (blur) and the vertical detail (blur) of a fluoroscopic  image and how you can change detail during a procedure. Describe the principles of operation of an automatic brightness control unit used with fluoroscopy. Describe the principle factor that affects quantum noise in fluoroscopy. Describe the process of evaluating a fluoroscopic system for quantum noise . Explain how the quantum noise level can be changed. State typical and regulatory maximum exposure rates to patients with normal fluoroscopy. Identify the major factor that produces high patient and staff exposures during fluoroscopy. Explain the purpose of the High Level Control (HLC) fluoroscopic mode, when is it used, and potential hazards.  

Fluoro objectives Describe video image fields and frames and the times associated with each. Describe the factors that influence the horizontal detail (blur) and the vertical detail (blur) of a fluoroscopic  image and how you can change detail during a procedure. Describe the principles of operation of an automatic brightness control unit used with fluoroscopy.

Fluoro objectives Describe the principle factor that affects quantum noise in fluoroscopy. Describe the process of evaluating a fluoroscopic system for quantum noise . Explain how the quantum noise level can be changed.

Fluoro & Rad Protection objectives State typical and regulatory maximum exposure rates to patients with normal fluoroscopy. Identify the major factor that produces high patient and staff exposures during fluoroscopy. Explain the purpose of the High Level Control (HLC) fluoroscopic mode, when is it used, and potential hazards.  Review the State Syllabus on Fluoroscopy and Radiation Protection with Title 17

SO, LET’S GET STARTED! Are you ready?

FLUOROSCOPY Primary function – dynamic motion studies Motion of internal structures in real time CONVENTIONAL FLUORO HAS BEEN REPLACED BY IMAGE INTENSIFICAITON Conv Fluoro – Rad directly observing images on a fluoroscopic screen

Basic “Imaging Chain”

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

Basic Componets of “NEW DIGITAL” Fluoro“Imaging Chain” Primary Radiation EXIT Radiation Fluoro TUBE PATIENT Analog to Digital Converter ADC Image Intensifier ABC CCD TV

Fluoroscopy: a “see-through” operation with motion Used to visualize motion of internal fluid, structures Operator controls activation of tube and position over patient Early fluoroscopy gave dim image on fluorescent screen Physician seared in dark room Modern systems include image intensifier with television screen display and choice of recording devices

Fluoroscopy X-ray transmitted trough patient The photographic plate replaced by fluorescent screen Screen fluoresces under irradiation and gives a life picture Older systems direct viewing of screen Nowadays screen part of an Image Intensifier system Coupled to a television camera Radiologist can watch the images “live” on TV-monitor; images can be recorded Fluoroscopy often used to observe digestive tract Upper GI series, Barium Swallow Lower GI series Barium Enema

Early Fluoroscopy

DIRECT FLUOROSCOPY Early fluoroscopy = the image was viewed directly – the xray photons struck the fluoroscopic screen – emitting light. The Higher KVP – brighter the light DISADVANTAGES: ONLY ONE PERSON CAN VIEW IMAGE ROOM NEED COMPLETE DARKNESS PATIENT DOSE (& RADIOLOGIST) WAS VERY HIGH

Main source staff exposure is NOT the patient but direct beam Direct Fluoroscopy: obsolete In older fluoroscopic examinations radiologist stands behind screen and view the picture Radiologist receives high exposure; despite protective glass, lead shielding in stand, apron and perhaps goggles Main source staff exposure is NOT the patient but direct beam

CONVENTIONAL FLUOROSCOPY INVENTED BY THOMAS EDISON

Conventional Fluoroscopic Unit Conventional fluoroscopy User viewed faint image on screen User in direct path of beam Very high dose to user and patient Excellent resolution No longer used

Older Fluoroscopy

Older Fluoroscopic Equipment (still in use in some countries) Staff in DIRECT beam Even no protection

Red goggles for dark adaptation More about the eye and vision later in unit………….

Conventional older Fluoroscopy systems 30 min for dark adaptation RODS or CONES VISION?

Light Levels and Fluoroscopy

Early Image Intensified FLUORO

Conventional I I system

Types of Equipment C-arm Under table/over table units

Types of Equipment Raise and lower image receptor for accuracy Can vary beam geometry and image resolution Full beam intercept

The main components of the fluoroscopy imaging chain Image Intensifier Associated image TV system Let’s summarize the main subjects we did cover in this session. (List the main subjects covered and stress again the important features of the session)

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

NEWER SYSTEMS – DIGITAL FLUORO

Basic Componets of “NEW DIGITAL” Fluoro“Imaging Chain” Primary Radiation EXIT Radiation Fluoro TUBE PATIENT Analog to Digital Converter ADC Image Intensifier ABC CCD TV

IMAGE INTENSIFICAITON IMAGES ARE VIEWED ON A TV SCREEN/MONITOR

FLUOROSCOPY IMAGES IN MOTION

Historical maybe– but you have to know this……… THE IMAGING CHAIN Historical maybe– but you have to know this………

Image Intensified Fluoroscopy Electronic conversion of screen image to light image that can be viewed on a monitor  resolution  dose

Photons used: Fluoro vs Radiography

Modern Image Intensifier based fluoroscopy system

Modern Fluoroscopic Unit

Modern fluoroscopic system components

FLUORO TUBES CAN BE LOCATED UNDER OR OVER THE TABLE….. FIRST COVERED – UNDER THE TABLE

Remote – over the table tube

Different fluoroscopy systems Remote control systems Not requiring the presence of medical specialists inside the X Ray room Mobile C-arms Mostly used in surgical theatres.

C-ARM UNIT -STATIONARY

MOBILE C-ARM UNIT

Mini c-arm

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

Fluoroscopy mA Low, continuous exposures .05 – 5 ma (usually ave 1 – 2 ma) Radiographic Exposure (for cassette spot films) mA increased to 100 – 200 mA

I I IMAGE INTENSIFIER

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

Image Intensifier VACUUM TUBE ENCASED IN A LEAD HOUSING = 2MM PB (PRIMARY BARRIER)

Image intensifier systems

Image Intensification Tube Components Input screen and photocathode Electrostatic lenses Magnification tubes

Image Intensification Tube Components Anode and output screen Total brightness gain Minification gain x flux gain

INPUT PHOSPHOR

Functioning of Image Intensifier

IMAGE INTENSIFIER INPUT PHOSPHOR – CESIUM IODIDE PHOTOCATHODE (LIGHT TO E’S) ELECTOSTATIC LENSES – FOCUSES AND ACCELERATES THE E INTENSIFIES LIGHT = BRIGHTNESS GAIN (BG) BG = MG X FG

YOU WILL HAVE TO DRAW THIS

IMAGE INTENSIFIER CESIUM IODIDE – Input Phosphor ZINC CADMIUM SULFIDE – Output phosphor ELECTRON FOCUSING LENS + CURRENT ATTRACTS e TO ANODE 25 – 35 KVP POTIENTIAL ACROSS TUBE Output phosphor contains a thin al plate to prevent light returning to the photocathode

Input Screen and Photocathode 0.1 – 0.2 mm layer of sodium activated CsI Converts intercepted x-ray beam to light Photocathode Emits electrons when struck by light emitted by input screen

Cesium Iodide (CsI) Phosphor on Input Phosphor CsI crystals grown linear and packed closely together The column shaped “pipes” helps to direct the Light with less blurring Converts x-ray photons to visible light SIDE VIEW

II Image Intensifier The input phosphor converts x-ray to light* Light from the input phosphor is sent to the photocathode made of cesium and antimony compounds* Photocathode turns light into electrons (called photoemission)* Now we have electrons that need to get to the anode……….. this is done by the electrostatic lenses 70

Accelerate and focus electron pattern across tube to anode Electrostatic Lenses Accelerate and focus electron pattern across tube to anode Primary source of brightness gain

Image intensifier component Input screen: conversion of incident X Rays into light photons (CsI) 1 X Ray photon creates  3,000 light photons Photocathode: conversion of light photons into electrons only 10 to 20% of light photons are converted into photoelectrons Electrodes (lenses): focalization of electrons onto the output screen electrodes provide the electronic magnification Output screen: conversion of accelerated electrons into light photons

The image intensifier (I.I.) I.I. Input Screen Electrode E1 Electrode E2 Electrode E3 Electrons Path I.I.Output Screen Photocathode +

Image Intensifier Tube Vacuum diode tube 1. Input phosphor (CsI) X-rays  light 2. Photocathode Photoemission Light  electron beam 3. Electrostatic lenses Maintain & minify e- 4. Anode Attracts e- in beam 5. Output phosphor (ZnS-CdS) e-  light 5 4 3 1 2

Magnification Input screen diameter Diameter used during exam

Multi-field II Units II that allows selection of input phosphor size 25 cm vs. 17 cm II that allows selection of input phosphor size 2 or 3 size selections 25/17 cm 25/17/12 or 23/15/10 Smaller input magnifies output by moving focal point away from output Requires more x-rays to maintain brightness

STOPPING PLACE FOR DAY 1 - 2010

Magnification Tubes Greater voltage to electrostatic lenses Dual focus Increases acceleration of electrons Shifts focal point away from anode Dual focus 23/15 cm 9/6 inches Tri focus 12/9/6 inches

Intensifier Format and Modes Note focal point moves farther from output in mag mode

MAG MODE VS PT DOSE MAG USED TO ENLARGE SMALL STRUCTURE OR TO PENETRATE THROUGH LARGER PARTS FORMULA: PATIENT DOSE IS INCREASED IN THE MAG MODE – DEPENDANT ON SIZE OF INPUT PHOSPHOR

MAG MODE FORMULA IP OLD SIZE IP NEW SIZE = %mag

PT dose in MAG MODE IP OLD SIZE 2 IP NEW SIZE 2 = ↑ pt dose

Fluoroscopic Dose Rates may show as “boost” button

Intensifier Format and Mag Modes

Image Intensifier Performance Conversion factor is the ratio of output phosphor image luminance (candelas/m2) to x-ray exposure rate entering the image intensifier (mR/second). Very difficult to measure: no access to output phosphor No absolute performance criteria Bushong pg 362 – 0.01 x brigtness gain Usually 50-300 (BG= 5000 to 30000

BG = MG X FG Brightness gain BG = MINIFICATION GAIN X FLUX GAIN Brightness gain is a measure of the conversion factor that is the ratio of the intensity of the output phosphor to the input phosphor conversion factor = intensity of OP Ø mR/sec

BRIGHTNESS GAIN can be expressed as: conversion factor = intensity of OP Ø mR/sec conversion factor = Output phosphor illumination (candelas/m2 ) Input exposure rate (mR/sec)

BG = MG X FG Brightness gain The II makes the image brighter because it minified it and more light photons. Multiply the flux gain times the minification gain. BG = MG X FG 89

Intensifier Brightness Gain (BG) BG = MG x FG Minification Gain x Flux Gain Minification gain (MG): The ratio of the squares of the input and output phosphor diameters. This corresponds to “concentrating” the light into a smaller area, thus increasing brightness MG = (Input Diameter )2 (Output Diameter)2

Minification (↑ BRIGHTNESS OF LIGHT) Electrons had to be focused down to fit through the hole at the anode Input phosphor is much bigger than the anode opening Input phosphors are 10-35 cm in diameter* (6, 9 , 12 inches) Output phosphors are 2.5 to 5 cm (1 in) in diameter* Most fluoro tubes have the ability to operate in 2 sizes (just like small and large focal spot sizes) Bi focus - M=Newer units - tri focus 91

Minification gain - again BG = MINIFICATION GAIN X FLUX GAIN MINIFICATION GAIN – same # e at input condensed to output phosphor – ratio of surface area on input screen over surface area of output screen IP SIZE 2 OP SIZE 2

Flux gain The ratio of the number of light photons striking the output screen to the ratio of the number of x-ray photons striking the input screen is called fluxgain

Intensifier Flux Gain

1000 light photons at the photocathode from 1 x-ray photon FLUX GAIN 1000 light photons at the photocathode from 1 x-ray photon photocathode decreased the # of ë’s so that they could fit through the anode Output phosphor = 3000 light photons (3 X more than at the input phosphor!) This increase is called the flux gain

BG = MG X FG FLUX GAIN – increase of light brightness due to the conversion efficiency of the output screen 1 electron = 50 light photons is 50 FG Can decrease as II ages Output phosphor almost always 1 inch Zinc cadnium phosphot Flux gain is almost always 50

Intensifier Brightness Gain Flux Gain (FG): Produced by accelerating the photoelectrons across a high voltage (>20 keV), thus allowing each electron to produce many more light photons in the output phosphor than was required to eject them from the photcathode. Summary: Combining minification and flux gains:

Intensifier Brightness Gain Example: Input Phosphor Diameter = 9” Output Phosphor Diameter = 1” Flux Gain = 75 (usually 50) BG = FG x MG = 75 x (9/1)2 = 6075 Typical values: a few thousand to >10,000 for modern image intensifiers

Image Intensifier FORMULAS Brightness Gain Ability of II to increase illumination Minification Gain Flux Gain (usually stated rather than calculated) MAGNIFICATION?????

MAG MODE FORMULA IP OLD SIZE IP NEW SIZE = %mag

PT dose in MAG MODE IP OLD SIZE 2 IP NEW SIZE 2 = ↑ pt dose