Production: Fluoroscopy

Fluoroscopy

The imaging of the movement of internal structures. Allows continuous and dynamic images

Illumination

The luminous intensity incident on a surface. Measured in lumens or flux

What is the illumination of radiographs?

100-1,000 lux

Image intensifiers

Similar to image receptors, except they convert and amplify low intensity x-rays to visible light

Components of image intensifiers

Housing, input window, input phosphor, photocathode, focusing electrodes, output phosphor, and output window

Input phosphor

Made of cesium iodide; absorbs the exit radiation from the patient and emits light in response

Photocathode

Composed of cesium and is connected to the input phosphor; responds to the stimulation of the input phosphor and induces photoemission

What is unique about the photocathode?

The layers of the photocathode are curved so that all of the electrons travel the same distance to the output phosphor

Photoemission

The emission of electrons in response to light stimulus

Electron optics

Negatively charged plates that repel the electron stream and focuses it toward the output phosphor

Output phosphor

Composed of zinc cadmium sulfide; the electrons arrive at the output phosphor and light is emitted in response. The light is much brighter compared to the input phosphor due to minification gain and flux gain

Flux gain

A measure of the increase of light photons from the input to the output phosphor; it is an increase in light caused by acceleration of the electrons

Flux gain formula

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

Minification gain

The measure of increased light intensities due to the reduced size of the output phosphor compared to the size of the input phosphor

Minification gain formula

Diameter of the input phosphor² / diameter of the output phosphor²

Brightness gain

The ability to increase the illumination level; it is the product of flux gain and minification gain and results in a brighter image on the output phosphor

Brightness gain formula

Minification gain x flux gain

Why is the output phosphor smaller than the input phosphor?

The output phosphor is small because it produces a bright light (minification gain). The light is brighter because the flux gain excites the electrons

What is the appropriate SSD for fixed fluoro and c-arm fluoro?

At least 15” for fixed and 12” for c-arm

How is the field of view affected by the II?

As the II increases with distance, the FOV becomes larger (vice versa)

What is the typical mA range for fluoro?

Operated at less than 5 mA because of long exposure times

What is the purpose of the automatic brightness control (ABC)?

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

Multified mode/magnification mode

A function of the fluoro unit that allows the operator to have a better view of small structures and detail

Advantage of magnification mode

Improved spatial resolution

Disadvantages of magnification mode

Distortion increases, patient dose increases due to mA compensation, FOV is reduced, and vignetting can occur

Vignetting

A loss of brightness around the periphery of the image

Television camera

Used to display the fluoro image. Includes camera tubes and CCDs

Vidicons

Camera tubes that are connected to the output phosphor and converts light into an electronic signal to be sent to the TV screen (monitor)

Charged coupled device (CCD)

A light sensitive semiconducting device that generates an electrical charge when stimulated by light and stores the charge in a capacitor

TV monitor

Cathode ray tube (CRT); controls brightness and contrast

Modulation

The magnitude of the video signal is directly proportional to the light intensity received by the TV camera tube

TV image raster pattern

The movement of the electron beam. The standard frames/second is 30f/s

How are fluoro units designed?

The x-ray tube is located beneath the patient and the intensifier is located above the patient

Pulsed fluoro

A pulsed beam reduces the radiation output necessary for the fluoro image and the patient radiation dose. The unit rapidly turns the x-ray beam on and off during operation

Continuous fluoro

X-ray exposure continues without interruption; patient dose increases

Safety mechanisms

Deadman switch and a 5 minute timer

Why are flat panel detectors advantageous?

They reduce the size, bulk, and weight of the unit, and allows greater flexibility and access to the patient

Why is it important to put the intensifier as close to the patient as possible?

SID decreases, patient dose decreases, and OID decreases

Digital fluoro detector (indirect DR)

Capture element: CSI or gadolinium oxysulfide

Coupling element: amorphous silicon

Collection element: CCD/CMOS or TFT

Advantages of digital fluoro

Minimal distortion, consistent image quality, improved contrast resolution, and high DQE

CFD

Compact fluoroscopy device/detector

Cardinal rules of fluoro safety

Time, distance, and shielding

What is the proper distance that the operator should be during fluoro exams?

6ft from the equipment/patient and standing at a right angle from the source/patient

What is the recommended amount of lead for lead aprons?

0.5mm of lead or equivalent

What is the recommended amount of lead for bucky slot covers?

0.25mm of lead or equivalent

What is the recommended amount of lead for protective curtains?

0.25mm of lead or equivalent

X-ray exit the _____, transmit through the glass envelope, and interact with the _____ phosphor, which is cesium _____

Patient; input; iodide

The _____ phosphor absorbs the x-ray photons and converts them into _____

Input; light

The _____ responds to stimulation of the _____ phosphor by emission of _____

Photocathode; input; photoelectrons

Photoelectrons are accelerated by a _____ and are herded by _____. Photoelectrons arrive at the _____ phosphor and are converted into ______

Voltage; electron optics; output; visible light

In fluoroscopy, a _____ mA is used because of _____ exposure times

Low; long

Generally, _____ kVp and _____ mA are preferred. _____ varies according to patient thickness and the response of the _____ system

High; low; mA; ABC

The image _____ components are all contained within a _____

Intensifier; vaccum

Fluoroscopy is an imaging technique used to obtain _____ or _____ images of the internal structures of a patient through the use of a _____. Spot or _____ images can also be taken, which preserves the image

Dynamic; continuous; fluoroscope; still

The _____ intensifier is located above the _____, while the _____ is located below the patient

Image; patient; x-ray tube

Image _____ are identified by the diameter of the _____ phosphor. A multified image intensification allows us to _____ the _____ on the input phosphor; when we do that, it _____ the image and decreases patient _____

Intensifiers; input; reduce; field of view; magnifies; dose

A disadvantage of a magnified image is a _____ image. To compensate for this, the _____ is increased, which means _____ patient dose.

Dimmer; mA; increased; mA; increased

_____ is a reduction of brightness at the periphery of the image. This is decreased when _____ mode is used since the outside edge of the _____ phosphor is not used

Vignetting; magnification; input

The _____ phosphor is coupled directly to a television camera tube called _____. Its purpose is to convert _____ from the _____ phosphor into an _____ signal to be sent to the _____ screen

Output; vidicon; light; output; electric; TV

Two advantages of television monitoring are: _____ level and _____, which are controlled electronically. The electrical signal _____ the electron beam of the vidicon and transforms it into _____ light at the fluorescent screen. The electrical signal is _____ proportional to the _____ intensity received by the vidicon

Window; width; modulates; visible; directly; signal

_____ gain is a measure of the increase of _____ photons from the input to the _____ phosphor; it is an increase in _____ caused by acceleration of the electrons

Flux; light; output; light

_____ gain is the ability to increase the illumination level; this _____ with tube life, and patient dose _____ to maintain _____ gain

Brightness; reduces; increases; brightness

The _____ gain is the ratio of the square of the diameter of the input phosphor to the square of the diameter of the _____ phosphor. The _____ phosphor is fairly standard at _____ or _____ cm. The _____ of the input phosphor varies from 10 to _____ cm, and is used to identify image _____ tubes

Minification; output; output; 2.5; 10; diameter; 40; intensifier