image production - Equipment Operation (Pt. 2)

What is Computed Radiography?

Cassette-based digital imaging
using phosphor to store X-rays

What are the layers of the CR IR?

• Protective

• PSP, Active Layer

• Conductive

• Support

• Light Shield

• Backing

What is the Photostimulable Phosphor Layer?

Active Layer; absorbs light generated from X-rays as latent image

What is Photostimulated Luminescence (PSL) Process?

• Crystals are energized (Metastable) by X-rays
• Latent image is laser read by IRD

How do the Phosphor crystals form store an image?

Amount of energy trapped in each area of the IP reflects the subject contrast of the body part imaged

What is the PSP layer made of?

• Barium Fluorohalide
• Cesium Bromide

Which type of material provides better resolution for PSP Layer?

Cesium Bromide; columnar shape reduces light divergence

What is the purpose of the conductive Layer?

absorbs and reduces static electricity

What is the purpose of the light shielding layer?

prevents light from erasing data or striking through the backing layer

Which layers are structural for the CR?

• Protective
• Support
• Backing

What is the Image Reader Device?

Digitizer, lasers and receives latent image data from IR and sends it to the computer for processing

What is the IRD Process?

• Rollers extract PSP Layer
• Helium Neon lasers layer
• Photoemission
• Photosensors (PMT)
• Light is sent to ADC
• Fluorescent light erases IR

What is a Photo-multiplier Tube (PMT)?

Collects and amplifies the releaased light photons

What is Digital Radiography (DR)?

Computer captures directly or indirectly on flat panel detector

What are the types of DR?

• Indirect Conversion
• Direct Conversion

What is Indirect DR?

A type of digital X-ray that turns X-rays into light first, then changes that light into a digital image

What are the two types of Indirect DR?

CCD and TFT

List the Layers for Indirect DR (TFT)

• Scintillation
• Photodiode
• TFT

What does 'scintillating' mean?

sparkling or shining brightly; process of photoemission

What is the Scintillation Layer?

Incoming Photons interact with the layer and create light

What is the scintillation layer made of?

• Cesium iodide
• Gadolinium oxysulfide

What is a photodiode?

A semiconductor device that converts light into an electrical current

What is the photodiode made of?

Amorphous silicon

What is the Thin Flat Panel Transistor (TFT)?

DEL matrix/array, storage capacitor for the converted electrical charge before sent to ADC

List the Layers for Indirect DR (CCD)?

• Scintillation Layer
• Seonsor Chip

What is a CCD (charge-coupled device)?

Converts Light photons to an electrical signal and sends it to the computer as a digital signal

What is Direct DR?

Converts X-rays directly into a digital image (skips the light step).

What are the Layers of Direct DR?

-Semiconductor (Capture and Conversion)
-TFT

What is the Semiconductor Layer in DDR?

ionization of the layer results in the atom's of the material freeing electrons

What is the Semiconductor Layer of DDR made of?

Amorphous Selenium

What is Fluoroscopy?

Creation of dynamic/real-time images used to visualize the dynamics of internal structures and fluids

How can the Fluoroscopy Tube be Configured?

• Tube Below Patient
• Tube Above Patient

Which configuration of the Fluoroscopy Tube is safer for the operator?

Tube below the patient allows backstatter to be limited to the patient's unprotected lower half (Legs & Feet)

What are the types of Fluoroscopy Detectors?

• Tube-Type
• Flat Panel

How does the Fluoroscopic Flat Panel Detector Work?

Sameas Indirect DR

What are the Layers of the Tube Type?

• Glass Envelope
• Input Phosphor
• Photocathode
• Electrostatic Lenses
• Anode
• Output Phosphor
• Video Capture Device

What is the Glass Envelope in Fluoro?

Vacuum created to allow for the free movement of electrons across the tube

What does the input phosphor do?

converts x-rays to light

What is the input phosphor made of?

Glass coated with Cesium iodide

What does the photocathode do?

Photoemission; Converts visible light into electrons

What is the photocathode made of?

photoemissive metal ( cesium & antimony compound)

What does the electrostatic lenses do?

Negatively charged it accelerates and focuses the electrons across the tube to the anode

What does the Anode do?

Positively charged, electrons accelerate toward the output due to the applied potential difference

What does the output phosphor do?

converts photoelectrons to light photons

What is the output phosphor made of?

Glass coated with zinc cadmium sulfide

What is the Video Capture Device?

Captures released Light

What are the types of Video Capture Devices?

• Tube Systems: Vidicom or Plumbicom
• Solid-State CCD

What are the disadvantages of Tube Type Detectors?

• Lag
• Blooming
• Veiling Glare
• Distortion

What is veiling glare?

When internal scatter radiation or light results in reduced contrast of the image intensifier

What kind of distortion appears on Tube Type detectors?

• Pincushion (narrowed center)
• Barrel (dilated center)
• S-Shape (wavy image)

What type of grids are used in Fluoroscopy?

• Stationary
• Focused
• 4.5:1-10:1

What are some common features used with Fluoroscopy?

• Magnification
• Intensifier
• Spot
• Pulsed Fluoroscopy
• AERC, ABS, ABC
• Last Image Hold

What is Image Intensification?

a method to electronically brighten fluoroscopic images

What is Brightness Gain?

= minification gain x flux gain

What is minification gain?

Brightness increase resulting from a reduction in image size from the input phosphor to the output phosphor

What is the minification gain formula?

= diameter input^2 / diameter output^2

What is Flux Gain

brightness gained because of the potential difference on tube. Acceleration of photon electrons to a higher energy, generates more fluorescent photons

How is flux gain calculated?

= kV x 2

What are the factors affecting brightness?

• mA
• kVp
• Part Thickness & Denisty
• AERC, ABS, ABC

What is Automatic Exposure Rate Control?

technique changes automatically according to body part size in order to maintain brightness level

Automatic Exposure Rate Control is also known as ______

• Automatic Brightness Stabilization (ABS)
• Automatic Brightness Control (ABC)

Maximum Entrance exposure rate is limited to ______ for units with AERC

100 mGya/min

Maximum Entrance exposure rate is limited to ______ for units without AERC

50 mGya/min

What is magnification mode?

mode that increases the magnification of the image at
the output phosphor

Why should magnification mode be limited?

Mode requires increased mAs to compensate to maintain brightness

What is magnification gain?

Diameter of largest^2 input phosphor / diameter of selected ^2 input phosphor size

What is Spot Fluoroscopy?

Static Image; regular radiograph using convential mA

What is Pulsed Fluoroscopy?

Computer Controlled generator that limits FPS to 15-30; reduces patient dose up to 90%

What is the last image hold?

Displays the last fluoro frame

What are grids used for?

Limiting the amount of scatter radiation that reaches the image receptor improves the quality of the radiograph

When are grids used?

10cm Part thickness
70 kVp

What are some types of grids?

• Stationary
• Moving

What is a moving grid?

A grid that moves during exposure to blur grid lines.

What are some types of Moving Grids?

• Single stroke - moved once spring activated,
• Reciprocating - moving back and forth by a solenoid
• Recipromatic - moving back and forth by an electric motor

What is a Potter-Bucky Diaphragm?

A device that holds the IR and sets the grid in motion so that grid lines cannot be seen on the finished radiograph

What are Compensating Filters?

Filters used on exams where there are significant variations in tissue density