FLUOROSCOPY Ch25

What is conventional Fluoroscopy?

is a technique that allows still or moving image of internal structures and fluid on monitor or TV screen

When can conventional Fluoroscopy be used?

can be used in:

• G.I. studies

• Urology studies

• Surgery

• Cardiovascular exams

R/F Room

additional “features” in exam room

Fluoroscopic Imaging Chain

• Monitor

• Video Camera

• Optical Coupling

• Image Intensifier

• Grid

• Patient

• Table

• Filtration

• Collimator

• X-ray tube

• X-ray Generator

What are the two basic components of Fluoroscopy

1. X-ray table

2. Image intensifier (conventional)

   OR

   FPIR used - newer technology (DR)

How are Fluoro and X-ray tube design different?

• Fluoro time - smaller focal spot and operate on lower mA with longer exposure times, tube current: .5 to 5 mA

• X-ray tubes - usually 1 to 3 mA (most common) - higher mA with shorter exposure time

I.I. Gride Purpose

• Increase image quality

• Decrease scatter radiation

• Conventional Fluoroscopy → Linear grid

• Lower grid ratios used

I.I. Tube Purpose

Evacuated glass envelope capable of converting x-ray photons into visible light and intensifies light (brightness)

by moving the I.I closer to the patient during fluoro, what is the result/reason:

1. decrease SID

2. decrease patient dose

3. improves image quality

Components of the I.I. Tube

• Input phosphor

• Photocathode

• Electrostatic Focusing Lenses

• Accelerating anode

• Output phosphor (screen)

What does the input phosphor do?

Absorbs x-rays and converts their energy into light (like intensifying screen)

What is the input phosphor made of?

Cesium Iodide (thin coating)

How big and what shape is the inout phosphor?

4 to 16 inches in diameter, slightly convex shape

Where is the photocathode?

attached to the input phosphor by adhesive layer

Photocathode, what are the thing layers?

Cesium Iodide and Antimony

What does the Photocathode do?

Converts light from input phosphor to electrons by photoemission

How are both Input screen and photocathode shaped? & why?

Both slightly curves so each electron travels same distance (preventing distortion)

What do Electro Static Focus lenses do?

Accelerated and focuses electrons stream onto putput phosphor

Where is the electrostatic focusing lense located?

located along length of image intensifier tube

How do electrostatic focusing lenses change modification of image?

By changing the focusing point of electrons

What is the accelerating anode?

Circular plate with a hole in the middle to allow electrons through to the output phosphor

Where do the electrons speed up?

Accelerating anode

What is the output screen phosphor?

Convert high energy Photo electrons to light photons

What is the output green phosphatase made of?

Made of zinc cadmium sulfide

How much brighter does the output phosphatase make the image?

The image from the output phosphor is over 5000 times brighter than the image at the input Phosphor

What is the image intensifier process?

• output Phosphor

• Accelerating anode

• Electrostatic focusing lenses

• Photo cathode

• Input phosphor

Output phosphor

Convert photoelectrons to light photos

Accelerating anode

Speed up electrons photo electrons

Electrostatic focusing lenses

Focuses electrons

Photo cathode

Convert light protons to electrons

Input phosphatase

X-ray, converting to light photos

What is automatic brightness control ABC?

Keep brightness of image contrast at monitor

What is automatic brightness control A.k.a.

Automatic brightness stabilization ABS or automatic exposure rate control AERC

When can you adjust ABC?

Can adjust for part thickness and contrast medias

What does ABC prevent?

Prevents fluctuation and image brightness and signal to noise ratio by adjusting kVp and mA

How must the part be position for ABC?

Part must be centered properly

What happens once ABC hits maximum levels of technical factors?

The AGC kicks in and adjust the brightness by amplifying the electronic signal. It is adjusted within the viewing system and does NOT affect patient dose.

What does AGC stand for?

Automatic gain control

What is brightness Gain ?

Ability of imaging intensifier to increase brightness levels of image

What does total brightness gain equal?

Total brightness gain = minification gain x Flux gain

What is the brightness gain of most images?

The brightness gain of most image intensifiers is 5000 to 30,000 (Will decrease with tube age and use)

What is minification gain?

Occurs as a result of same number of electrons produced at large input Phosphor being compressed into area of small output Phosphor

What is the equation for minification gain?

MG = (Input screen diameter)* Squared / (output screen diameter)* Squared

Most imaging intensifier are constructed with how big output phosphorus

1 inch

What is flux gain?

Measurement of increase in light photons due to conversion efficiency of output phosphatase

What does flex deal only with?

Deals only with the gain accomplished by the electrons to light conversion at the output Phosphor

Where does the electron energy come from?

Electron energy comes from accelerating voltage from between Photo cathode and anode

Flux gain equals?

Flex gain = Number of output light photons / Number of input x-ray photon

Two types of light receptors

1. Rod

2. Cones

What are both rod and cones responsible for?

Both are responsible for human vision

Both are found in retina and detected light

What is the function of rods?

Function in light or scotopic vision; Perceived grays (Colorblind)

Where are rods located?

On the peripheral of the retina

What is the function of cone?

Function in daylight or photopic vision; perceive color and brightness levels.

Perceive small objects better than rods

Where are the cones located?

In center of retina

What is the cornea?

Clear part of eye covering the iris and pupil, let’s light into the eye allowing site

What is the pupil?

Round, dark center of eye, which opens and closes to regulate amount of light the retina receives

What is the iris?

Colored part of the eye surrounding the pupil. It acts like a diaphragm to widen or narrow the pupil, controlling the amount of light that enters the eye.

What is the retina?

Sensory membrane that line the eye; It receives image formed by the lens and converts them into signal that reaches the brain by way of optic nerve

What is a lens?

Spherical body in eye located behind cornea, that focuses light raise onto retina

What is the vision process?

• Light passes through cornea, through the lens, where light is focused on retina

• Between cornea and lens is Iris (Which constricts and dilate amount of light entering the eye)

• When light enters retina detected by rods and cones

Low light equals

Iris dilates (opens up) Allowing more light in

Bright light equals

Iris constricts (closes) Not allowing as much light in

What is Visual Acuity?

Ability to perceive find detail

What is the normal viewing distance of an image?

12 to 15 inches

What is the time required by the eye for recognition of an image?

Integration time is about .2 seconds

How is an image magnified?

Occurs when useful area of input phosphorus, decreased while output phosphatase remains the same

How is the image intensifier designed to magnify?

Electronically by changing voltage on electrostatic lenses

A magnified image results in =

Small diameter = Fewer photo electrons from the image = Dimmer image = Tube mA Increase to compensate or maintain brightness (ABC) = HIGHER PATIENT DOSE

Magnification mode =

INCREASED PATIENT DOSE

Magnification Ex:

Smaller FOV = Spatial resolution is increased, and patient dose is increased

Image intensifier number refers to diameter of

Input phosphor

Normal mode equals

4 LP/MM

Mag mode =

6 LP/MM

What is resolution?

Detail; Ability of imaging system to differentiate small objects as separate images as they are position close together

Resolution relationship is

Between object, size and line pairs per millimeter is inversely related

Smaller object size =

Better resolution

How big is the resolution of cesium iodide in I.I.?

4 plus/mm

Magnification mode results in

1. Better spatial resolution

2. Better contrast resolution

3. Higher patient dose

What are image quality issues with imaging intensifier?

• Vignetting

• Pincushion effect

• S shape distortion

• Blooming

• Vail glare

• Lag

• Noise

What is Vignetting?

Decrease brightness on peripheral of image; Reduces contrast and detail

What causes Vignetting?

1. Curved input phosphor

2. Increase OID

What is pincushion effect?

Caused by curved input phosphatase to a flat output phosphor

Form of spatial distortion

What is S shape distortion?

Same idea as pincushion effect, more of S shaped distortion

When is blooming?

High energy photons hit input Phosphor = Results in loss of acuity

Shows up on image as white streaks

What is Vail glare?

Type of blooming

Loss of visual sharpness, hazy

What is lag?

Delay in response of image intensify due to change in beam intensity

What is noise?

Quantum mottle

Not enough mAs

Impacts image clarity