RT 209 Image Intensified Fluoroscopy (copy)

RT 209 Image Intensified Fluoroscopy PREI by YJV

Fluoroscopy

• To aid the radiologist in dynamic studies of the human body

• “Real time” imaging

• Images are moving

Thomas Edison

Invented fluoroscope (calcium tungsten) in 1896

William Chamberlain

Studies the poor illumination from the fluoroscopic screen in 1941

1950’s

development of the image intensifier

Illumination

measure in units of Lamberts (L) and millilamberts (mL)

Lumens and Millilumens

Now/Current measuring units of Illumination

10 to 1000 mL (millilamberts)

Radiographs are viewed under illumination level of ______

Rods (scotopic)

night vision; located at the periphery of the eye

Cones (photopic)

daylight vision; located at the fovea of the retina of the eyes.

Scotopic

refers to the eye’s ability to see in low-light or dim conditions; it is mediated by the rods in the eyes.

Photopic

refers to the eye’s ability to see in well-lit conditions, such as daylights; it is mediated by the cones in the eyes.

Visual Acuity

refers to how sharp or clear your vision is.

Image Intensifiers

Recording system

Viewing System

Fluoroscopic Chain

Image Intensifiers

• Electronic vacuum tube that converts beam to light then to electrons, then back to light, increasing the light intensity in the process.

• Complex electronic device that receives the remnant x-ray beams, converts it into light, and increases the light intensity.

• It brightened the image significantly

• Allows for a means to indirectly viewing the fluoroscopic image.

• Input Phosphor

• Photocathode

• Accelerating Anode

• Output Phosphor

• Electrostatic Focusing Lenses

Basic Parts of an Image Intensifier

Input Phosphor

• Cesium Iodide (CsI)

• energy to visible light

• Csl crystals are tightly packed as 100 to 200 micrometer layer

100 to 200 micrometer layer

CsI crystals are tightly packed as _________

Photocathode

• Cesium and antimony compounds

• Emit electrons when stimulated by light (photoemission)

Accelerating Anode

Maintains constant potential of 25 kV

Output Phosphors

• Electrons interact to produce light

• silver activated zinc cadmium sulfide

Electron Optics

Engineering aspects of maintaining proper electron travel.

Electrostatic Focusing Lens

Located along the length of image intensifier tube.

Not really lenses, but are negatively charged plates along the length of the image intensifiers

Image Intensifier Tube

• Approximately 50 cm in length and 15 to 58 cm in diameter.

• High energy electrons that interacts with the output phosphor each result in substantially more light photons than was necessary to cause their release at the photocathode

Flux Gain

• The ratio of the number of light photons at the output phosphor to the number of x-rays at the input phosphor.

• tube’s conversion efficiency

• Number of output light photons/number of input x-ray photons

Minification Gain

• An expression of the degree to which the image is minified from the input phosphor to output phosphor

• The ratio of the square of the diameter of the input phosphor to the square of the diameter of the output phosphor.

• This characteristic makes the image brighter because the same number of electrons is being concentrated on a smaller surface area.

2.5 to 5 cm

In Minification Gain, Output phosphor size is fairly standard at ______

10 to 25 cm

In Minification Gain, Input Phosphor size varies from _______

input phosphor diamter2 /output phosphor diameter2

Minification Gain

5000 to 20000

Brightness gain of most image intensifiers is ______

Brightness Gain

• an expression of the ability of an image intensifier tube to convert x-ray energy into light energy and increase the brightness if the image in the process

• ability of the image intensifier to increase illumination level of the image.

minification gain x flux gain

Brightness gain

Conversion Factor

Is an expression of the luminance at the output phosphor divided by the input exposure rate.

Recommended by the IRCU to quantify the increase in brightness by image intensifiers

increase: maintain brightness

As an image intensifier ages, the exposure rate to the patient ______: to ______

Automatic Brightness Control (ABC)

A function of the fluoroscopic unit that maintains the overall appearance of the fluoroscopic image by automatically adjusting the kVp or mA or both.

Magnification Mode or Multi Field Mode

• The voltage to the electrostatic focusing lenses is increased.

• The increase tighten the diameter of the electron stream and the focal point is shifted farther from the output phosphor.

• The degree of magnification (MF) may be found by dividing the full-size input diameter by the selected input diameter.

• MF = 30 ÷ 15 = 2 x magnification

• Improve the fluoroscopist’s ability to see small structures (spatial resolution) but at the price of increasing patient dose.

4 to 6 Lp/mm

Fluoroscopic systems

Distortion

Is a result of inaccurate control or focusing of the electrons released at the periphery of the photocathode.

pincushion appearance

combined result in unequal magnification

Vignetting

Reduction of brightness at the periphery

Image Noise

• Results when insufficient information is present to create the image.

• Insufficient quantity of x-rays

• “grainy” or “noisy” image

• More likely caused by insufficient mAs

Camera Tube

Charged - coupled Device

Fluoroscopic Image Monitoring

television camera tube

In camera tube, this converts light image into electrical signal

vidicon and plumbicon

are most often used television camera tube in fluoroscopy

Electron Gun

Control grid

Cathode of the Tube

Electron Gun

provides continuous stream of electrons

Control grid

forms the electron streams into a “beam”.

Deflection Coils

Focusing Coils

Alignment Coils

ELECTROMAGNETIC COILS types:

Electromagnetic Coils

• Act to accelerate and precisely control the electron beam.

• Through this action, the beam sweeps the anode back and forth from top to bottom in a sequence known as raster pattern.

raster pattern

• Through this action, the beam sweeps the anode back and forth from top to bottom in a sequence known as ________

Charged-Coupled Device

Light-sensitive semiconducting device that generates an electrical charge when stimulated by light and stores this charge in a capacitor

is a series of metal oxide semiconductor capacitors, with each capacitor representing a pixel.

The charged is proportional to the light intensity and is stored in rows and pixels.

Fiber-optics bundle

Lens-coupling

Coupling the Television Camera

Fiber Optics Bundle

• Simply a bundle of very thin optical glass filaments

• Very durable and simple design but does not allow for spot filming.

Optical Lens System

Series of optical lenses that focus the image from the output phosphor on the camera tube.

Susceptible to rough handling, which may cause maladjustment of the mirrors and lenses and result in a blurred image.

Beam-splitting mirror enables spot filming

Television picture table (cathode ray tube)

• heart of the television monitor

• Convert the electronic signal from the camera tube or CCD back into a visible image

• 1 to 2 Lp/mm

TRUE

TRUE OR FALSE: The camera tube and CCD are devices that couple the image intensifier to the television monitor to convert the image from the output phosphor to an electronic signal that can be reconstructed on the television monitor.

Cassette spot film

Film Cameras

Video Recorders

RECORDING SYSTEMS

Cassette Spot Film

• Static imaging process in which a standard radiographic cassette is used to obtain an image

• The unit shifts to radiographic mode and the radiation does to a patient is much higher than in fluoroscopic mode.

Film Cameras

photo-spot cameras

Commonly used 105-mm chip film or 70-mm roll film

Static imaging that is used with an optical lenses system

Incorporating a beam-splitting mirror

Video Recorders

• Used when dynamic imaging is desired.

• Useful in functional studies of the esophagus or placement catheters or medical devices, for example. DIGITAL

Digital Fluoroscopy

• Used analog-to-digital converter (ADC).

• Computer between the camera tube and the monitor

Analog To Digital Converter

• A device that takes the video (analog) signal and divides it into a number of bits (1’s and 0’s) that the computer “understands”.

• The number of bits that the signal is divided into determines the contrast resolution of the system.

Charged Coupled Device

• Eliminated some of the problems associated with the camera tubes.

• More light-sensitive (higher DQE) and exhibits less noise and no spatial distortion.

• Higher spatial resolution and less radiation.

Detective Quantum Efficiency (DQE)

measures how efficient an imaging detector converts x-ray incident photons into a useful image.

Cesium iodide amorphous silicone

indirect capture detector

Amorphous selenium

direct capture director

• Reduction in size, bulk and weight of the fluoroscopic tower, allowing for easier manipulation, greater access to patient during examination

• Replace spot filming and other recording devices

• Can be readily archived with the patient record in PACS.

• Does not degrade with age.

• More durable and better contrast resolution

• Higher DQE

• Wider dynamic range or post-processing options

• Do not exhibit most image artifacts such as glare and peripheral distortion

• Lower patient dose.

ADVANTAGE OF DIGITAL FLUOROSCOPIC SYSTEMS COMPARED TO IMAGE INTENSIFIERS