Lecture 5 - xraykamarul | Just another WordPress.com site •Fluoroscope - an instrument for observing or exhibiting fluorescence. A fluorescent screen for observing the shadows cast

Lecture 5

Prepared by:-

KAMARUL AMIN BIN ABDULLAH @ ABU BAKAR

LESSON OBJECTIVES

At the end of the session, the students should be able to:

• Briefly explain the purpose, construction and principles of fluoroscopy.

• Briefly explain the image intensifier, the principles and its construction.

• List the components in II and explain the function of each components.

• Briefly explain its viewing and recording system.

INTRODUCTION

• Fluoroscope - an instrument for observing or exhibiting fluorescence. A fluorescent screen for observing the shadows cast by objects placed in the path of the x-rays rays.

• Fluoroscopy is an x-ray machine that combines an x-ray source and a fluorescent screen to enable direct observation.

Cont’d..

• Fluoroscopy is a technique for obtaining "live" (30 frames per second) x-ray images of a living patient. The radiologist uses a switch to control an x-ray beam that is transmitted through the patient.

• The x-rays then strike a fluorescent plate that is coupled to an "image intensifier" that is (in turn) coupled to a television camera. The radiologist can then watch the images "live" on a TV monitor.

Cont’d..

• Fluoroscopy is also used during many

diagnostic and therapeutic radiologic

procedures, to observe the action of

instruments being used either to diagnose

or to treat the patient.

DESIGNS

Modes

Dynamic Imaging

• Display for immediate viewing

• Recording of still and motion images (cine)

• Storage of still and motion images

Principles of Fluoroscopy

• Transmitted x-ray beam emerging from the patient is incident on the sensitive input area of an image intensifier area of an image intensifier.

• Instantaneous (dim) image is produced by the phosphor screen.

• Energy from the fluorescence of the phosphor screen is magnified (intensified) by accelerating resultant electrons through a vacuum.

• The output phosphor screen demonstrates a brighter image.

Examples

BARIUM SWALLOW - used to examine the upper GI (gastrointestinal) tract, which includes the esophagus and, to a lesser extent, the upper stomach.

Fluoroscopy

TV Camera/ CCD (Digital)

Image Intensifier

X-ray Tube

Allows dynamic imaging of blood vessels, ducts, or tracts.

Image Intensification (II)

Image Intensifier (Cont’d..)

• Components (5 Elements)

1. Housing

2. Input Screen

3. Vacuum Bottle

4. Electrostatic Lenses

5. Output Screen

1. Housing

• Encased in lead protection in order to minimises x-ray leakage.

2. Input Screen

• Diameter of circular input area ranges from

12 - 40cm.

• Convex front - Maintains a constant

distance between every point on the input

image and the eventual output image.

• It has aluminium substract layer, phosphor

layer, and photocathode layer.

2. Input Screen (Cont’d..)

Aluminium Substrate Layer

• The aluminium substrate ~ 0.5 mm thick.

• To give the support for the CsI (Phosphor Layer).

• It also serves to reflect light back from phosphor towards the photocathode.

2. Input Screen (Cont’d..)

Phosphor Layer

• is made from CsI, doped with Na, which is deposited on an aluminium substrate.

• It has a high x-ray absorption and energy conversion.

• The CsI:Na is grown in a structure of monocrystalline needles, each about 5 μm in diameter and up to 0.5 mm long.

2. Input Screen (Cont’d..)

• Needle structure of the phosphor is used to guide light along one needle (like optical fibre).

• Then, the light provides an image of the x-ray pattern that emerged from the patient which has a substantially greater intensity than when an intensifying screen is used on its own.

2. Input Screen (Cont’d..)

Photocathode

• Photocathode - light-sensitive electron -emitting layer.

• The photocathode typically consists of an alloy of antimony and cesium (SbCs3).

• Emits electrons proportional to intensity of the light energy it receives.

• Potential difference within the II increases energy of the electrons 25-35 kV.

3. Vacuum Bottle

• The vacuum is required so that the electrons can travel unimpeded - as in the case of the x-ray tube.

4. Electrostatic Lenses

• Electrostatic Lenses focus the beam of electrons to converge at the opening of the anode.

• A current of about 10-8 to 10-7 Ampere results, and this is the acceleration and focusing of these electrons in which it gives rise to the image intensification.

5. Output Screen

• It aluminum substrate layer, output phosphor layer, and output window.

Output Phosphor Layer

• The output phosphor is made from ZnCdS: Ag (e.g. a P20 phosphor) deposited on the output window.

• This phosphor emits a green light when it absorbs the accelerated electrons (like a CRT oscilloscope), and is typically about 5μm thick and 25 to 35 mm in diameter.

5. Output Screen (Cont’d..)

Aluminium Substrate Layer

• In addition, a thin aluminium film is placed on the inner surface of the phosphor, which serves both as the anode and to reflect light back towards the output window - so as to increase the output luminance and to prevent these light photons exciting the photocathode.

5. Output Screen (Cont’d..)

Output Window • A number of designs of output window exist and

include:- 1. a glass window (e.g. 15 mm thick) with external

anti-reflection layers, 2. a tinted glass window 3. …a fibre-optic window • The objective of these designs is to minimize

light diffusion and reflections.

LASTLY…

The resulting image is fed to an optical system to be viewed by a cine-camera, photographic

camera, video camera or combinations of these cameras. Orthochromatic film is

needed for the film-based cameras.

Image magnification

• Image magnification can be achieved by varying the voltages on the electrostatic lenses, so that a 38 cm II can also be used to image field sizes of 26 cm and 17 cm, for instance.

• Three discrete field sizes are typical of many systems, although IIs with a continuous zoom feature are also available.

• Image brightness decreases as the field size is reduced when the input exposure rate is maintained constant.

Image Magnification (Cont’d..)

Magnification

• Many fluoroscopy systems have one or several magnification modes

• Magnification is achieved by electronically manipulating a smaller radiation I-I input area over the same I-I output area

Connecting to Viewing System

• The light output from the II needs to directed to a video camera and then to a television screen. There are two ways of coupling the output window to the input of a video camera; - Lens coupling - Fibre optic coupling

Lens coupling:

- uses a pair of optical lens and a “beam splitting mirror” (to enable other accessories like spot film camera or cine camera) and an aperture. Fibre optic coupling: - uses fibre optic cables thus reducing light loss from the II to video camera

VIEWING SYSTEMS

FLUOROSCOPIC DATA AQUSITION-IMAGE INTENSIFIED SYSTEM

1. X-RAY TUBE

2. PATIENT

3. IMAGE INTENSIFIER

4. OUTPUT PHOSPHOR

5. CAMERA (Viewing system)

6. MONITOR

Introduction

• The most commonly used fluoroscopic viewing system is video.

• A system includes

1. Video Camera attached to the II output – Vidicon or Plumbicon or Charge Couple Device (CCD)

2. Display monitor for viewing

Video Camera

• Vidicon and Plumbicon tubes are similar in operation but mainly differ in their target layers.

• Vidicon tubes use antimony trisulfide (Sb2S3) (photo-conductive) while PlumbiconTM use lead oxide (PbO).

1) Plumbicon – has a faster response time. – best for imaging moving organs, i.e., heart

2) Vidicon – best for imaging stationary organs

Video Camera (Cont’d..)

• The tube consists of a cathode with a control grid, a series of electromagnetic focusing and electrostatic deflecting coils, and an anode with face plate, signal plate and target.

i) Cathode • Is an electron gun which

emits electrons by heat (thermionical) and shaped by the grid

• Electron accelerated toward the target

• Focusing coil bring the electron to a point to maintain resolution

• Pair of deflecting coils serve to cause the electron beam to scan the target in a path as a raster pattern

ii) Anode

• The light emitting from II is detected even by fiber optics or optical lens

• Which permits light photon transmitted to the signal plate( thin graphite charge with positive voltage) and thick to conduct electronic signal out of the tube

• This is the portion of the target assembly that send the signals to the TV monitor.

Charged Coupled Devices (CCD)

• Semiconducting device that capable of storing a charge from light photons striking a photosensitive surface.

• CCDs consist of a semiconductor chip which is sensitive to light. The chip contains many thousands of electronic sensors which react to light.

• When lights strikes the photoelectric cathode of the CCD, electrons are released proportionally to the intensity of the incident light.

• Then, it will be stored in the CCD before it releases to produce video signal as pulses into a conductor.

Kamarul Amin (c) 41 1/10/2012

Charged Coupled Devices (CCD)

Advantages

• Extremely fast discharge time, which eliminates

image lag.

• More sensitive than video tubes.

• Operate at lower voltages than video tubes.

• More durable than video tubes.

• Not susceptible to damage from rough handling.

Kamarul Amin (c) 43 1/10/2012

Image Monitor

• The output of a video camera is a video signal which is fed via a coaxial cable to a video / TV monitor.

• The video signal contains voltages representing image brightness as well as timing signals (sync pulses) associated with the raster scanning process.

Video Monitor

• A video monitor is used to display images acquired by the video camera of a fluoroscopy system. - The image is described as a “softcopy” - The video monitor is similar to an oscilloscope, ie, a scanning of the electron beam but in a raster fashion.

Video Monitor

• It is an evacuated glass tube which contains an electron gun, a number of focussing & steering electrodes and a phosphor screen.

• The electron gun forms the cathode and the electrons are accelerated by a high voltage towards the phosphor screen.

• The impact of the electrons on the screen causes it to fluorescent and the resulting light forms the image.

Video Monitor • Video monitors generally have two

viewer adjustable controls; contrast - controlled by the number of electrons in the electron beam brightness - controlled by the acceleration of the electrons in the tube These have a strong influence on the quality of displayed images.

RECORDING SYSTEMS

Introduction

• Several methods are available for recording images during fluoroscopy.

1. Spot film devices

2. Automatic film changers

3. Photofluorography

4. Digital fluorography

5. Cine fluorography

6. Videotape recording

Spot Film Devices Fluoroscopic systems designed for gastrointestinal imaging are generally equipped with a spot film device.

The spot film device allows exposure of a conventional screen-film cassette in conjunction with fluoroscopic viewing.

Cassettes may be loaded from the front or rear depending on the design of the system.

The screen-film cassette is parked out of the x-ray field until the spot film trigger is pressed, causing both the cassette and the formatting mask to move into position.

One of the major shortcomings of conventional spot film devices is the delay involved in moving the cassette into position for exposure.

Automatic film changers The automatic film changers used in vascular imaging are also screen-film systems.

The system consists of a supply magazine for holding unexposed film, a receiving magazine, a pair of radiographic screens, and a mechanism for transferring the film. When an exposure is required, the screens are mechanically separated, the film is pulled into place between them, and they are closed.

After the film is exposed, the screens separate again. The film is moved to the receiver, and another film is pulled into place for the next exposure. The number of films and filming rates must be preprogrammed for proper operation.

Approximately 20 films are held in the supply magazine. During exposure, a film is advanced between the high-speed screens, exposed, and removed to the receiving magazine.

Photofluorography More rapid filming than that provided by film changers can be achieved by using a photospot (photofluorographic) camera. Photospot cameras can expose as many as 200 films before reloading at rates as high as 12 per second. The camera is mounted on the optical coupling system behind the image intensifier. Because direct viewing of the fluoroscopic image is almost always reserved for the television (TV) camera, the photo-spot camera is usually side mounted. The image of the output phosphor is collimated by a lens and reflected by a partially silvered mirror. An iris or diaphragm, placed in front of the camera lens, is used to adjust the amount of light reaching the camera for an optimal trade-off of image noise with patient dose. The camera may have additional mirrors to direct the image onto the film plane (Fig 3). Typically, 105-mm-wide film is used in roll film cameras. Some cameras hold 100-mm-square cut film instead.

Digital fluorography

• Many radiology facilities are replacing conventional image recording systems with digital technology.

• Digital charge-coupled device (CCD) TV cameras are rapidly replacing conventional TV cameras in fluoroscopic systems.

• There are several other advantages to digital photospot images.

1. Mechanical devices are not needed for film transport. 2. Film processing is not required. 3. Images can be viewed immediately. 4. The linear response of the digital system makes it very

forgiving of under- or overexposure.

Cine fluorography

• Cine fluorography is the standard for imaging the movement of a contrast agent through vessels.

• The mechanism of a cine camera differs somewhat from that of a roll film photospot camera.

• The major differences are that the film is smaller (35 mm wide) and longer (400 ft [120 m] on a roll) and that the camera is capable of operating at up to 90 images (ie, frames) per second.

• The higher frame rates are usually used in cardiography, particularly for pediatric imaging.

Videotape recording

• Videotape recorders used in fluoroscopy are only slightly more sophisticated than those used for home video.

• They use Super-VHS (or S-video) technology, which is now also available on better home TV systems.

• Super-VHS recorders sold for medical imaging have an electronic band-pass matched to, or better than, that of the TV so that there is essentially no loss of resolution due to the recorder for conventional 525-line TV.

• As a replacement for cine fluorography, 1,023-line TV (or 1,024 × 1,024 digital CCD TV) cameras are used.

• High-resolution TV recording is a compromise offering about half the resolution of cine fluorography but reduce about four times the dose of conventional TV.

• One advantage of using a CCD camera for this purpose is that the images are recorded digitally, rather than on tape.

DIGITAL FLUOROSCOPY

Digital (Computerized) Fluoroscopy

• Developed in late 70’s • Images are taken directly from output

phosphor • A video camera and digital image processor

are used to obtain images • The image is converted from analog to digital • A dynamic recording can be made • Image can be manipulated in many ways • Less radiation is used

Digital Fluoroscopy Chain of Events

CCD SYSTEM ADVANTAGE OVER CAMERA SYSTEM

• LOW LEVEL OF ELECTRONIC NOISE

• HIGH SPATIAL RESOLUTION

• NO LAG OR BLOOMING

• NO MAINTENANCE

• UNLIMITED LIFE

• UNAFFECTED BY MAGNETIC FIELD

• LINEAR RESPONSE

• LOWER DOSE

Radiation Protection In FLUOROSCOPY

• Collimate tightly to region of interest.

• Reduce directing the beam through the patient at an oblique angle.

• Position the X-ray tube under the patient not above the patient.

• Use lead apron, neck collar, goggle and other PPE.

• Reduce exposure time and time of screening.

THANK YOU