Equipment Operation and Quality Assurance

Quality Control of Imaging Equipment and Accessories C

1. Beam restriction 2. Recognition and reporting of malfunctions 3. Digital imaging receptor systems 4. Shielding accessories

e. Image Receptors

1. Computed Radiography (CR) 2. Digital Radiography (DR)

A. Imaging Equipment

1. Generator, Transformers and Rectification 2. Components of a Radiographic Unit 3. Components of a Fluoroscopic Unit 4. Accessories

B. Image Processing and Display

1. Raw data (preprocessing) 2. Corrected data for processing 3. Data for display 4. Post-processing 5. Display monitors 6. Imaging informatics

Components

1. Tube support 2. Glass or metal enclosure

External Components

3. Protective Tube Housing

The Image Intensifier

Remnant beam is incident on the input phosphor Input phosphor is made of Cesium Iodide It converts the x-rays to visible light The photo cathode converts the light to electrons The electrons are sped across toward the anode by the voltage potential The electrons maintain the image as they move toward the anode by electrostatic focusing lenses This is called electron optics The anode is doughnut shaped and the electron beam goes through the hole The electrons are incident on the output phosphor which is made of cadmium sulfide The output phosphor converts the electrons to visible light

X-ray Production

Requirements for x-ray production Source of electrons Way to speed them up rapidly Way to focus electrons Way to stop them abruptly Requirements for x-ray production Source of electrons Way to speed them up rapidly Way to focus electrons Way to stop them abrup

Histogram analysis errors

Resulting image is NOT directly related to technique that is used • Exposure field recognition-exposure field is not consistent (i.e. more than one exposure on plate, not having at least 3 collimated margins) • Extraneous exposure information-scatter etc. • Unexpected material • Extreme over or under exposure • Delay in processing • Incorrect algorithm selected

4. Shielding accessories

Testing lead aprons Gloves

Rectified three-phase

Three-phase, 6 pulse 13% Three-phase, 12 pulse 4% Three-phase, high frequency <1%

1. Transformers

Transformer - works only with alternating current Primary function is to adjust voltage Step-up transformer Step-down transformer

1. Raw Data (preprocessing)

a. Analog-to-digital converter (ADC) b. Quantization c. Corrections Rescaling Flat fielding Dead pixel correction d. Histogram

4. Post-processing

a. Brightness b. Contrast c. Region of interest (ROI) d. Electronic cropping and Masking e. Stitching a

2 Digital Radiography: Conversion 2. Digital Radiography: a. Direct and b. Indirect (not on the test)

a. Direct conversion • b. Indirect Conversion • Amorphous silicon (aSi) • Charge coupled device (CCD) • Complementary metal oxide semiconductor (CMOS) • a

2. Corrected Data for Processing

a. Gray scale b. Edge enhancement-makes small details more visible on an image. c. Equalization—unexposed areas are made darker and overexposed areas are made lighter d. Smoothing—suppresses image noise

1. Beam Restriction

a. Light field to radiation field alignment b. Collimator - must be accurate to within + or - 2% of SID c. Central ray alignment--

3. Digital Imaging Receptor Systems

a. Maintenance Routine maintenance Error maintenance b. QC tests Erasure thoroughness Plate uniformity Spatial resolution c. Display monitor quality assurance Grayscale standard display function Luminance

4. Accessories

a. Stationary grids b. Bucky assembly c. Compensating filters

3. Data for Display

a. Values of interest (VOI) • b. LUT is a table of 2 columns of numbers representing input and output values

5. Display Monitors

a. Viewing Conditions Lighting Viewing angles Monitor brightness b. Spatial Resolution - Describes the systems' ability to accurately display objects in two dimensions High Spatial resolution - small objects, close together Low Spatial Resolution - large object, far apart c. Brightness and Contrast The ability to detect and/or display differences in brightness levels

d. Histogram

• Distribution Frequency of digital values • DR- capture pixels • CR- assign pixels • Distribution Frequency of digital values • DR- capture pixels • CR- assign pixels

b. X-ray Tube Construction

• External components • The tube support • The protective housing • The glass or metal enclosure • Internal Components (next slide) • The cathode • The anode

2. Components of a Radiographic Unit

• Generally radiographic equipment may be classified as mobile or fixed (permanently installed). • Mobile equipment, as its name implies, is a unit on wheels and can be taken anywhere • Permanently installed equipment refers to units that are fixed in place in a particular room specifically designed for the purpose and not intended to be mobile. • Generally radiographic equipment may be classified as mobile or fixed (permanently installed). • Mobile equipment, as its name implies, is a unit on wheels and can be taken anywhere • Permanently installed equipment refers to units that are fixed in place in a particular room specifically designed for the purpose and not intended to be mobile.

X-Ray Imaging System

Operating Console aka Control Panel kVp selection mAs selection High Voltage Generator Step-up Transformer Rectification X-ray Tube Step-down transformer Filament Circuit

1. Transformers

Primary function is to adjust voltage Incoming voltage is 220V: works only with AC Most high-voltage, step-up transformers The high-voltage transformer (E) and the step-down transformer for the filament circuit (K) are housed in the same box filled with insulating oil

3. Components of Fluoroscopic Unit

Provides real-time dynamic viewing of anatomic structures Integrated with a radiography room (R/F rooms) The fluoroscopic tube is under the table The image intensifier is over the table Provides real-time dynamic viewing of anatomic structures Integrated with a radiography room (R/F rooms) The fluoroscopic tube is under the table The imag

6. Imaging Informatics a. Information systems (HIS, RIS, EMR or EHR) b. Networking 1. PACS 2. DICOM

Radiology information system RIS Hospital information system HIS Electronic medical record or electronic health record EMR or EHR Digital imaging and communication in medicine. Standardize digital devices in a PACS system. DICOM Receives images from CR, DR, CT, etc. Stores in jukeboxes or discs.

Basic X-Ray Machine Circuit

Consists of three general sections: 1. The control console circuit 2. The high-voltage section 3. The x-ray tube filament circuit

1.Generator

Consists of: Step up transformer The rectifiers; convert AC to pulsating DC Filament transformer; designed to increase current

Rectification System

Converts AC to DC

X-ray Production

Current applied to the filament Electrons are boiled off and form a cloud around the filament Space Charge A high voltage potential is applied across the tube. The anode is made positive, the cathode is made negative + - The projectile electrons smash into the target. As the electrons slow, their kinetic energy is converted to heat and x-ray

1. Computed Radiography (not on the test)

Advantages Post-processing benefits Wider dynamic range Reduce repeats for technical factors Improved image accessibility Disadvantages Inefficient Lower detection deficiency Plates damage easily Readers may produce artifacts

a. Operating Console

Allows radiographer to control the x-ray tube current and voltage so that the useful beam is of proper quantity and quality selects • Quantity-mGya or • mGya/mAs • Quality-kVp or HVL • These features allow the radiographer to modify exposure parameters to best image the area of interest

1.High-Frequency Generators

Alter the waveform of the incoming electricity before it reaches the step-up transformer Full wave rectified power is converted to a higher frequency Use almost ½ technique compared to 3-phase equipment - kVp is often set 8-10 less than for 3-phase units Average kV is nearly equal (considered equal) to the set kVp Voltage ripple is less than 1%

Internal Components

Anode The positive side of the tube Two types Stationary Rotating Three main purposes Conduct electricity Support for the target Dissipate heat Made of copper, molybdenum, or graphite Target made of tungsten with rhenium Filtration

Internal Components

Cathode The negative side of the x-ray tube (diode) Houses of the filament (electron source) Focusing cup (negative charge) Cathode The negative side of the x-ray tube (diode) Houses of the filament (electron source) Focusing cup (negative cha

a. Plate

Image recorded on a thin sheet of plastic known as the imaging plate Plate consists of several layers PSP-Photostimulable Storage Phosphor

a. Image receptors 1. Image Intensification

Input phosphor Made of cesium iodide (CsI) Receives radiation exiting patient Emits light photons Photo cathode Responds to light exiting input phosphor Emits electrons Electrostatic lenses Focus electrons Output phosphor Made of zinc cadmium sulfide Receives electrons from photocathode Emits 50-75 × more light than received by photocathode

b. Plate Reader

Data extraction • Plate scanned with laser • Release of electrons from the high energy traps • Light emitted • Light "samples" collected • Sampling Frequency • Light converted to electric charge • ADC converts analog charge to digital signal •

Tube Current c. Automatic Exposure Control

Measures quantity of radiation Two types Phototimers Ionization Chambers Radiation Detectors

c. Automatic Exposure Controls

Minimum response time Back-up time/mAs Density Adjustment -2, -1, +1, and +2 Patient centering

Single-phase

Half-wave: 100% Full-wave: 100

1. Transformers

High Voltage transformer - step-up Filament transformer - step-down Autotransformer can act as either

e. Magnification Mode

Higher patient radiation dose Better contrast resolution Better spatial resolution

Histogram

Histogram analysisgraphic display of the distribution of pixel values Histogram analysisgraphic display of the distribution of pixel values