FLUOROSCOPY EQUIPMENT

Differentiate between fluoroscopic and radiographic examinations

List the basic components of the fluoroscopic system and identify the function of each component

Describe a typical basic fluoroscopic image IntensifierDescribe advantages of image intensified fluoroscopy

over conventional screen fluoroscopy Identify uses of dynamic and static fluoroscopic

recording systems Discus digital fluoroscopic image acquisition Differentiate between conventional fluoroscopy,

image intensifier

fluoroscopy, and digital fluoroscopy

By the end of this Lecture the student will be able to:

Learning Objectives

• Bushberg, The Essentials of Physics and Medical Imaging, Williams & Wilkins Publisher.

• Positioning in Radiography: By k.C.Clarke.

• Text book of radiographic positioning and related anatomy;bykenneth L.Bontrager,5th edition

Websites

• http://www.e-radiography.net/

References

FLUOROSCOPY

Purpose: To perform dynamic studies. Visualize anatomical structures in real time or motion. View the motion and function of anatomic organs.

Conventional film radiography is restricted to static patient exams. If dynamic events need to e studied such as movement contrast materials through gastrointestinal tract (GIT) the image must be viewed directly using a dynamic method.

HistoryHistory Invented by Thomas A. Edison in 1896

Fluoroscopic systems

Conventional fluoroscopic systems Earliest fluoroscopic systems used phosphor screens where the

transmitted x-ray caused scintillations that were viewed directly.

Fluoroscopic systems

Direct Fluoroscopy

In older fluoroscopic examinations radiologist stands behind screen and view the image.

Fluoroscopic systems

The images of this type were of very poor quality for a number of reasons:- - Poor light output by the

fluorescent screen

- Low efficiency of the light conversion

mechanism

- Poor spatial resolution

for that fluorescent screens are no longer used since they gave high radiation dose to the operator.

Conventional fluoroscopic systems

What is an Image Intensifier ?A complex electronic imaging device that receives the remnant beam and converts it to light and increases the intensity of the light.

The image intensifier tube is contained in a glass envelope in a vacuum and mounted in a metallic container which provides protection for the components.

Fluoroscopic with image intensifiers

Fluoroscopic with image intensifiers

Image Intensifier Schematics

Fluoroscopic with image intensifiers

Input Phosphor

Constructed of cesium iodide.

Responsible for converting the incident photon’s energy to a burst of visible light photon. ◦ Similar to intensifying

screens in cassettes.

Standard size varies from 10 - 35 cm. ◦ Normally used to

identify the II tubes.

Photocathode

Thin metal layer bonded directly to the input phosphor.

Usually made of Cesium and Antimony compounds that respond to light stimulation.

Responsible for Photoemission.

Electron emission after light stimulation

The number of electrons emitted is directly proportional to the intensity of light intensity of the incident x-ray photon.

Electrostatic Focusing Lenses

A series of lenses inside the II tube to maintain proper focus of the photoelectrons emitted from the photocathode.

They contain a positive charge.They are located along the

length of the II tube.The focusing lenses assist in

maintaining the kinetic energy of the photoelectrons to the output phosphor.

Output Phosphor

Usually constructed of zinc cadmium sulfide crystals. Serves to increase illumination of the images by converting photoelectrons to light photons.

Spot Film Device Used to make

permanent images during the radiographic examination.

Film is positioned b/w the patient and the image intensifier.

When the film is needed, the radiologist actuates the control that brings the cassette in position. This changes the tube from fluoroscopic mA to radiographic mA.

During fluoroscopy, the tube is operated at less than 5 mA.

TV MONITORS

This practical and efficient viewing system was employed because of the limitations of the mirror optic viewing system.

TV monitors:

1. Enables viewing by multiple persons.

2. Monitors may be located in remote locations other than the radiographic room.

3. Image brightness and contrast can be manipulated.

4. Images may be stored on different medium for reviewing at a later time.

Fluoroscopy -Modes of operation

Manual Mode◦ Allow the use to select the exact MA and KVp required

AEC Mode◦ Allow the unit to drive the KVp and MA to optimize

dose and image quality Pulsed Digital mode

◦ Modifies the fluoroscopic output by cutting by cutting out exposure between pulses

◦ With the pulsed mode, it can be set to produce less than the conventional 25 or 30 images per second. This reduces the exposure rate.

Fluoroscopy Units

Smaller facilities may use one fluoroscopic system for a wide variety of procedures

Larger facilities have several units dedicated to specific applications, such as:

Gastrointestinal units Remote fluoroscopy rooms Peripheral angiography units Cardiology catheterization units Biplane angiography units Mobile fluoroscopy – C arms units

Fluoroscopy Units 1/An over table model Where the x-ray tube is placed above the table top, and the

image intensifier under the table surface.

2/An under table model Where the x-ray tube is placed under the table surface , and the

image intensifier over the table top.

Fluoroscopy Units

Fluoroscopy Units

An under table model

Fluoroscopy Units

The table have the ability to tilt from horizontal to vertical

Where the x-ray tube and image intensifier are fixed to c-arms.

Mostly used in surgical theatres.

3/Single or bi-planar cine –fluoroscopy model

Fluoroscopy Units

Remote control systems

Fluoroscopy Units

Digital fluoroscopy is currently most commonly configured as a conventional fluoroscopy systemThis method uses digital detector technologies (eg, flat-panel "direct" detection of x rays and charge- coupled device technology) The analog video signal is converted to a digital format with an analog-to-digital converter (ADC).

Digital FluoroscopyDigital Fluoroscopy

General Rule

(ALARA Principle) As Low As Reasonably Achievable

Radiation Protection

Longer usage

more exposure

Radiation Protection

TIME Take foot off fluoro pedal if physician is not viewing the TV monitor

Use last image hold (freeze frame)

Five-minute timer

Use pulsed fluoro instead of continuous fluoro

Pulsed Low-Dose provides further reduction with respect to Normal

Dose continuous mode:

Use record mode only when a permanent record is required

Record beam-on time for review

Radiation Protection

Distance is large factor for reducing exposure.Inverse Square law“ When you double the distance the exposure rate is decreased by 4 times ”

Radiation Protection

DISTANCE- One step back from

tableside: cuts exposure by factor of 4

- Move Image Int. close to patient:

less patient skin exposure less

scatter- Source to Skin Distance

(SSD):

38 cm for stationary fluoroscopes30 cm for mobile fluoroscopes

Radiation Protection

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

The largest amount of scatter radiation is produced where the x-ray beam enters the patient.

By positioning the x-ray tube below the patient, you decrease the amount of scatter radiation that reaches your upper body.

Radiation Protection

ShieldingIncreasing the amount of shielding around a source of radiation will decrease the amount of radiation exposure.

To avoid scatter Be sure to shield all directions.

Shielding

-+

Radiation Protection

SHIELDING- Lead aprons: cut exposure by factor of 20- Proper storage (hanging vs. folding)

Radiation Protection

Protection tools

34

curtain thyroid shieldEye goggles

Lead Apron

Radiation Protection

CollimationCollimate tightly to the area of interest.

Reduces the patient’s total entrance skin exposure. Improves image contrast. Scatter radiation to the operator will also decrease.

Radiation Protection

Radiation Protection

• Familiarity with specific fluoro units

Factors influencing dose:

patient size

kVp, mA and time

tube - patient distance (SSD)

Image Intensifier - patient distance

image magnification vs. patient dose

x-ray field collimation

oblique's vs. perpendicular views

Safety in Fluoroscopy

Radiation Protection

Safety in Fluoroscopy Standard Operating Procedures

- each clinical protocol / procedure

- modes of operation, image recording

- emphasis on minimizing duration

- risk / benefit on a case-by-case basis

Equipment quality control

- periodic PMs

- prompt calibrations

- post radiation output values

- check aprons, shields, gloves annually

Radiation Protection

Final Summary Golden rules” Keep the II close to the patient

Do not overuse magnification modes

Keep the x-ray tube at maximal distance from patient

Use higher kVp where possible

Wear protective aprons and radiation monitors, and know where

scatter is highest

Keep your distance, as far as is practicable