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137 Cards in this Set
- Front
- Back
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Spatial resolution of CR is _______________ (less than/more than) film screen radiography
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Less than
CR is 3-5 lp/mm Film screen 10-15 lp/mm |
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When were flat panel detectors first used?
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1995
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What's the photoconductor of flat panel?
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Selenium
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How does a flat panel detector work?
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Positive charge is placed on drum; x-rays change charge distribution in selenium to produce an electrostatic image stored on drum; probe scans electrostatic image & creates a voltage that's sent to ADC, then sends digital data to PC
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What are the flat panel detector components?
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Detector, host computer, image display device, network communications, & image storage device
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What's contained in the detector in a flat panel?
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Pre-amplifiers, switching control, central logic circuits, ADCs, & internal memory
X-ray detection & digitization of signal both occur in detector (don't need special reader) |
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What's the purpose of a host computer in a flat panel detector?
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- acts as an interface between the flat panel detector & the x-ray machine
- plays an important role in controlling x-ray production & signal readout - applies appropriate image processing |
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Indirect Flat Panel Detector
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- uses phosphor
- 2 types --> CCD & TFT (main difference = technical component used to convert light to electrical signals) |
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Charged Coupled Device (CCD) - Indirect
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- not a true flat-panel digital detector
- uses CCD chip to convert light to electrical signal |
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What are the components of a CCD?
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X-ray absorber, light optics, CCD sensor for capturing light, electrical charge readout device
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Thin Film Transistor (TFT) - Indirect - Components
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X-ray scintillator, amorphous silicon photodiode flat panel layer (a-Si), TFT array for readout, capacitors
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TFT X-ray Scintillator - Cesium Iodide (CsI)
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- crystals are deposited in a "needle-like" fashion & lay parallel to the x-ray beam
- ex. structured scintillator |
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TFT X-ray Scintillator - Gadolinium Oxysulfide (Gd2O2S)
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- crystals deposited as powder particles (turbid phosphor)
- produces lateral light spread which diminishes spatial resolution - ex. unstructured scintillator |
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What's the purpose of the amorphous silicon photodiode flat panel layer?
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To convert light from x-ray detection scintillator into electrical charges
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What's the purpose of a capacitor in a TFT?
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To collect & store electrical charge produced by the a-Si photodiode array
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Direct Flat Panel Detector
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- uses a photoconductor (usually amorphous selenium [a-Se])
- a-Se displays superb x-ray detection & high spatial resolution properties |
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What are the components of a digital flat panel detector?
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Source of high voltage, top electrode, dielectric layer, collection electrode, TFT, storage capacitor, glass substrate
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Design characteristics of Direct Flat Panel Detectors
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1) Designed as a matrix of detector elements, each which can be regarded as a pixel ("large area integrated unit")
2) There are other electrical components that are included in the flat-panel detector gateline or dataline |
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Active Matrix Array
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- consists of rows & columns that play a role in addressing the readout of the signal from each pixel in the direct flat panel detector
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What does each pixel in a direct flat panel detector consist of?
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TFT (switch), storage capacitor, sensing area
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What does the sensing area of a flat panel detector sense?
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Indirect --> CsI scintillator light
Direct --> X-ray photons passing through the patient |
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Gateline / Dataline
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- switching electronics to activate each row of pixels
- electronic amplifiers for signal readout from each column - signal sent to ADC for digitization |
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What are some normal sizes of direct flat panel detectors?
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17" x 17" (43x43cm)
12" x 15" (30x40cm) 7" x 7" (18x18cm) |
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What are the average sizes of the pixels in a direct flat panel detector?
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139 µm - 200 µm
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What determines spatial resolution in a direct flat panel detector?
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Pixel size & pixel pitch
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Pixel Pitch
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Distance from midpoint of 1 pixel to the midpoint of the adjacent pixel
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How can pixel size be calculated?
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- with given physical dimension size of the detector & known matrix size for that detector
ex. 43x43cm detector has a matrix of 2688x2688 pixels so: 43 cm / 2688 pixels = 0.01599 cm or 160 µm |
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How can the number of pixels be determined?
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By multiplying the dimensions of the matrix size
Ex. 2688x2688 = 7,225,344 pixels |
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Fill Factor of Pixels
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Ratio of sensing area of the pixel to the area of the pixel itself
FF = Sensing Area of Pixel / Total Area of Pixel |
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What 3 components does a pixel contain?
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1) TFT
2) Capacitor (storage area) 3) Sensing area |
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What does the fill factor of pixels affect?
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Both spatial resolution (detail) & contrast resolution (signal to noise ratio)
Proportional relationship |
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What does PACS stand for?
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Picture Archiving Communication Systems
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What are the definition points of a PACS?
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Network of computers, electronically stores & displays images, provides archives for storage, integrates info w/ patient database info, allow for viewing of images in remote locations
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Who introduced the term "digital radiology" in 1970?
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Dr. Paul Capp
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When did PACS go "mainstream"?
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Early 2000s
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Home Grown PACS
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PACS developed by radiology department & hospital using technical components from various manufacturers
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Two-Team Effort PACS
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Based on collaboration of individuals from both outside & inside the hospital who address PACS specifications
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Turn-Key PACS
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PACS developed completely by manufacturer who sells it as a single unit to a hospital
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Partnership PACS
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Manufacturer & hospital work together to ensure the optimum performance & integrity of system via training from personnel, upgrading, & general system maitenance
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Application Service Provider (ASP) PACS
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A system integrator provides all PACS related services to a client, no IT requirements needed by client
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What were early PACS based off of?
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UNIX Operating Systems
- not intuitive, lack of integration w/ HIS & RIS |
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Image Acquisition Modalities
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- must be digital in nature
- ex. CR, DR, CT, MRI, digital mammo, etc - 2 types: inherently digital & frame grabbing |
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Inherently Digital
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- image data is obtained from scanners at the full spatial resolution & bit depth
- ex. CT & MRI |
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Frame Grabbing
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- digitize analog signals obtained from the IR, images are sent to image display device
- ex. digital fluoro |
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LAN
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- local area network
- ex. computers connected by a short distance |
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Topologies - Bus
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Computers (nodes) are connected via single cable
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Topologies - Star
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All computers are connected to a central host computer, called a "hub"
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Topologies - Ring
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Computer is connected to 2 adjacent computers, all connections collectively form a ring
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WAN
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- Wide Area Network
- ex. computers connected by large distances |
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Bandwidth
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Data transfer rate of info on a WAN
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Network Protocol
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Language used to send info on WAN (Control Protocol/ Internet Protocol)
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Intranet
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Isolated network (ex. one used by a hospital)
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Internet
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Network of networks, all interconnected
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Teleradiology
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- concept of using wired or wireless internet to send images to distant site to be interpreted, that info is then shipped back
- some hospitals use this during third shift so no radiologist has to be on call - network security is very important |
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PACS Main Computer
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- high performance PC
- PACS controller, database server, image server - images & patient data are sent from acquisition gateway computer via HIS to PACS controller - lots of internal memory |
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Types of Image Storage Devices
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Solid state memory magnetic data carriers (expensive, limited storage capacity); optical disks & magnetic tape storage (cheap, large storage capacity)
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RAID
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Redundant Array of Independent Disks
- may contain several magnetic or optical disks, operates as single large storage device - used for short term storage |
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DLT
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Digital Linear Tape
- usually 0.5" long - intended for long term storage |
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Location of Storage Devices - Offline
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- must be retrieved by an individual & loaded into a drive for access
- most economical, provides largest storage capacity |
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Location of Storage Devices - Nearline
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- removable (RAID)
- longer image retrieval time |
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Location of Storage Devices - Online
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- cannot be removed
- provides image access to images within seconds - ex. RAM |
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What's the purpose of image compression?
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Speed up the transmission of info & to reduce storage requirements
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Lossless Compression
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REVERSIBLE
No info is lost |
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Lossy Compression
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IRREVERSIBLE
Some info is lost in compression process |
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JPEG
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Joint Photographic Expert Group
- image compression that features both kinds - present compression method for DICOM medical images |
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What does JPEG 2000 use?
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Wavelets to decrease the compressed image size while enhancing image quality
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What does the compression ratio influence?
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Size of the compressed image
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Small compression ratios are used with ____________ (lossless/lossy)
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Lossless (2:1 or 3:1)
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Large compression ratios are used with _____________ (lossless/lossy)
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Lossy (10:1 or 50:1)
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What's the current standard for the utilization of lossless or lossy?
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- there's isn't one
- almost all radiologists concerned about litigation potential of an incorrect diagnosis based on irreversibly compressed images |
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Types of PACS Displays - High Resolution
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- 2.5k x 2.5k
- used by radiologists for primary diagnoses - most expensive type |
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Types of PACS Displays - Medium Resolution
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- 1.5k x 1.0k
- used for secondary diagnoses - review function often performed by radiologists |
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Types of PACS Displays - Desktop
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- for techs & physicians other than radiologists
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Types of PACS Displays - Hardcopy
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- used for image printing
- may eventually become obsolete |
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What kind of printer is still commonplace among PACS?
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Dry printers
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RIS/PACS Broker
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- acts as intermediary device to help the 2 systems communicate w/ each other
- helps ensure all the chart info is with the right image info |
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DICOM
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Digital Imaging & Communication in Medicine
- addresses communication of images |
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HL-7
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Health Level 7
- address communication of textual info such as patient info, radiology reports, etc. |
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Classification System - By Size: Single Digital Modality
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- termed a "mini-PACS"
- a single LAN is a central feature |
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Classification System - By Size: All Modalities
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- link to HIS/RIS using either extended LAN or a WAN
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What's the major role of IHE (Integrating the Healthcare Enterprise)?
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Facilitate communications between various computer based HIS & PACS vendors through the integrated use of DICOM & HL7
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Components of IHE - Data Model
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Should communicate using DICOM & HL-7
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Components of IHE - Actors
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- items that use those data models
- ex. patient registration, image manager, master patient index |
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Components of IHE - Integration Profiles
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- function: outline roles of actors in DICOM/HL-7 environment
- ex. scheduled workflow profile ensures effective communication from RIS to imaging modality |
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The RT as Informaticist
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- rapid evolution & growth of info systems & technology in healthcare has large impact on future of RT
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Definition of Info Technology
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“The acquisition, processing, storage, and transmission of vocal, pictorial, textual, and numeric information by microelectronics, computers, and telecommunications” – Library of Congress
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PARCA
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PACS Administrators Registry & Certification Association
- aimed at developing set of skills for PACS administrators |
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RCSA
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Radiation Control & Safety Act of 1968
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CPRHSA
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Consumer-Patient Radiation Health & Safety Act of 1981
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SMDA
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Safe Medical Devices Act of 1990
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MQSA
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Mammography Quality Standards Act of 1992
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Which 2 pieces of legislature have the most impact on radiologic tech's today?
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SMDA & MQSA
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What is quality assurance?
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Activities that provide adequate confidence that a radiology service will render consistently high-quality images & services
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What are some evaluating activities quality assurance consists of?
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Intepretation of exams, maintenance of equipment, performance of procedures, filing systems, staff development, scheduling, supply lines
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How does quality assurance work?
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By identifying problems, monitoring problems, & addressing/fixing it
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What's quality control?
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Monitors technical equipment to maintain quality standards
Important for this to be seen as a method for controlling radiographic images from start to finish |
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How do you successfully order & purchase equipment?
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Identify imaging requirements; develop equipment specifications; bids for equipment compared to budget; installation & acceptance testing for equipment
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Who's responsibility is it to do continuing education on the machines?
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The Vendor
- more complex equipment should be demonstrated & explained by vendor to at least 2 people as part of purchase contract |
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Processor Sensitometry measures what?
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Speed & contrast of film
Should be performed regularly |
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Film Processing Systems - Monitoring Equipment Performance
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- encompasses the digital environment, electronics maintenance, algorithm checking
- processor monitoring - dark room fog test (safelight test) - processor sensitometry |
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Processor Monitoring - Whose responsibility?
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Radiography Tech/Radiographer
- anyone can perform tests - only qualified radiographers or maintenance should make corrective changes |
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External Beam Evaluation
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- someone w/ physical knowledge of equipment should perform this exam
- tools: wire mesh, collimator accuracy, pinhole focal spot camera, digital dosimeter, spinning top & pentrometer |
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Where should a log of external beam evaluation be kept?
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In each room to record test results, maintenance logs for each machine, etc.
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Semi-Annual Exams - Focal Spot Size Estimation
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- needs to be kept within limits to maintain image detail
- Types: line pair resolution tool, star test pattern, pinhole camera |
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Line Pair Resolution Tool & Star Test Pattern
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Works by imaging a resolution pattern on film
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Pinhole Camera
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Permits measurement of focal spot by creating an image of the effective focal spot size on film
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Semi-Annual Exams - Half Value Layer
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- radiation protection is validated by eliminating the low energy photons
- measured w/ dosimetry equipment to detect quality of aluminum filtration which reduces beam intensity to half the original value |
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Semi-Annual Exams - Collimator Test Tool
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- lead marker for each corner of light beam, plus crosshairs or lead marker placed several cm above cassette surface
- 2% SID error is allowed - centering should be +/- 1% of light field CR |
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Semi-Annual Exams - Positive Beam Limitation (PBL)
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- mechanism shouldn't permit the primary beam to be larger than the cassette in the bucky tray
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Semi-Annual Exams -Distance & Centering Indicator Accuracy
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- inverse square law is used
- distance indicators should be measured w/ tape measurer; should be +/- 10% - centering indicators should be +/- 2% |
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Semi-Annual Exams - Angulator/Protractor Accuracy
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- can be evaluated w/ large protractor for angle measurements, & a level to verify locks, stops, detents, etc
- angles should be +/- 1% |
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Semi-Annual Exams - kV Accuracy
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- kV drifts over time as a result of tube aging
- computerized dosimeters provide digital readouts of average & single-pulse kVp (if settings drift +/- 5% generator must be recalibrated) |
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Semi-Annual Exams - Timer Accuracy
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- computerized dosimeters may be used or a spinning top may be used to measure single-phase generators
- a motorized synchronous top may be used for 3-phase units - should be +/- 5% |
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Semi-Annual Exams - mR/mAs & mA Linearity
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- cannot be measured w/ noninvasive methods
- inferred by comparing mR/mAs measurements after both time & kVp accuracy are verified - should be +/- 10% |
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Semi-Annual Exams - Exposure Reproducibility
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Must be reproducible +/- 5%
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Semi-Annual Exams - Display Monitors
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- spatial resolution is evaluated through display of a standardized image, SMPTE test pattern, & grayscale tool
- all 3 display axes must be evaluated |
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How are the X & Y Axes measured?
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Measures matrix & pixel size accuracy
Imaging spatial resolution test tools to evaluate point spread function, line spread function, & modulation transfer function |
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How is the Z axis measured?
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Measure gray scale bit depth
Imaging gray scale performance memory of monitor itself |
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What's the function of digital detectors?
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Like screen-film receptors, digital detectors are designed to capture the beam exiting the patient
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Cassette-Based Digital Detector
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- look similar to s/f receptors
- contains PSP, TFT, or a PSP w/ CCD |
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Cassette-Less Digital Detector
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- incorporated as part of imaging equipment
- flat panel detector/TFT - CCD - PSP plate w/ CCD |
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Detector Element (DEL)
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Term for each individual square in a TFT array
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What's the purpose of the image gently campaign?
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Education, awareness, & advocacy
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What's the purpose of the image gently campaign in peds?
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Improve radiation protection for children nationally & internationally
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Alliance for Radiation Safety in Pediatric Imaging
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- more than 70 healthcare orgs have joined
- represents more than 800k health care professional worldwide - Goal = change current practice to improve care provided to children |
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Are anatomically programmed radiography machines always appropriate for children?
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No because the size of a normal anatomical part is different in children who are still growing
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Dynamic Range of Detector Response
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Range of exposures to which the detector can respond
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Digital Response Regions
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- represented by "E" w/ subscripts of "-", "o", or "+"
"-" = underexposure "o" = optimal exposure "+" = overexposure |
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The dynamic range of a detector ___________ (should/should not) be equated w/ a wide rage of exposures for obtaining an image
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Should not
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Exposure Indicator - Fuji
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S-number or sensitivity
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Exposure Indicator - Kodak
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Exposure Index
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Exposure Indicator - Agfa
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IgM
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Who published an exposure terminology standard in 2008? (Hint: IEC)
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International Electrotechnical Commission
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What 3 terms does the IEC standard use that are important?
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1) Exposure Index (indicates the detector exposure)
2) Target Exposure Index (IR has to be properly exposed) 3) Deviation Index (provides immediate feedback of exposure; measures how far EI deviates from normal) |
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What is DI (Deviation Index) useful for?
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Helps lower dose by optimizing radiographic studies
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Exposure Creep
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Gradual increase over time of RT's selected exposures; leads to excessive dose for peds
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What does BASICS stand for in regard to image analysis?
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Beam / Artifacts / Shielding / Indicators & Immobilization / Collimator / Structures
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