Digital Radiography
A series of semiconductor capacitors that generate electric charge when stimulated by light is called what?
CCD- charged couple device
What converts light directly into a digital signal?
CMOS- complementary metal oxide semiconductor
Digital Imaging
CR: (cassette) 1. image capture 2. image readout DR: (cassette less) 1. image capture and readout occur at the same time
Detector Element (DEL)
Collects electrons that represent the individual components of the image. Each DEL represents a pixel only the DEL's included in the collimated area send the signal.
CMOS
Complementary Metal Oxide semiconductor used in DR detectors converts light directly into a digital signal high speed readout requires low energy to operate has limited photosensitive area and higher noise than CCD's
What collects electrons that represent the individual components of the image?
DEL
Communication standard for sharing information between PACS and various imaging modalities is known as what?
DICOM 3
DR flowchart
Xray photon patient Flat panel 1. Scintillator (nondirect) -light photons -amorphous silicon 2. Amorphous selenium (direct) Electronic signal ADC computer DAC Monitor
What does a capacitor do?
stores electrical charges -flat panel
what sends electrical charges?
Transistor switch in flat panel
what is an example of a photodetector?
CCD
a-Si
amorphous silicon -a light detector
Charged Couple Device (CCD)
A series of semiconductor capacitors Generates electric charge when stimulated by light. capacitor stores charge each capacitor represents a pixel. Signal sent to TV monitor
Radiographic detectors
A. film screens B. CCD C. flat panel direct D. flat panel nondirect
the photoconductor is made of what?
Amorphous Selenium and is used in nonscintillation
What is an example of a photoconductor?
Amorphous selenium
Amorphous Silicon Vs. Selenium
Amorphous silicon is a flat panel scintillator -2 step -indirect Selenium is a flat panel that is direct -1 step process - electrons to signal
What is an example of a scintillator?
Csi- cesium iodide
Relationships
Decreased DEL size= increased spatial resolution = decreased image blur = increased exposure= increased dose DEL equates to pixels
DICOM (1992)
Digital imaging and communication in medicine enacted standards in 1993 to standardize communication in medical imaging for digital technology communication standard for sharing information between PACS and various imaging modalities all equipment speak the same computer language equipment can either "use" (SCU) or "provide (SCP) a service
Non-scintillation Flat Panel (direct)
Directly converts X-ray photons into an electronic signal amorphous selenium (a-Se)
DAP
Dose area product meter used in DR systems to monitor radiation output and dose to patient (skin dose) combined with collimator housing Dap readout can be a part of the patient's medical record.
Other forms of medical electronic communication
EMR- electronic medical record internet HL-7
Advantages of CCD for medical imaging
High spatial resolution high signal to noise ratio high detective quantum efficiency (DQE) no warm-up required no lag or blooming no spatial distortion no maintenance unlimited life unaffected by magnetic fields linear response lower patient dose
HIS
Hospital Information System register patients, collect and store patient info, patient billing, send orders to RIS.
What is used by PACS for long term storage?
Jukebox
Digital Radiography Advantages
Large dynamic range Increased exposure latitude ability to post process PACS
Flat Panel
Layers: xray converter (diret or indirect) Thin film transistor (TFT) Glass substrate capacitor-stores electrical charges transistor switch sends electrical charges signal gets amplified and then digitized in ADC Electrical charges are read separately from each DEL. Pg 355 adler Pg 299 bushong
Conventional xray disadvantages
Longer processing time decreased exposure latitude, must be spot on with technique.
DR Exposure Indicator
Philips -EI Increased exposure= decreased EI value Indirect relationship between exposure and EI (200-800) - over 800 you are underexposed Siemens- EXI Increased exposure= increased EXI value Direct relationship between exposure and EXI Canon- REX increased exposure = increased REX value (reached exposure value) -Direct relationship between exposure and REX .5mR produces an optimal image -DR has a higher DQE and can reduce patient dose.
Scintillation Flat Panels (Indirect)
Phosphor and photodetector Cesium Iodide (CsI) or GdOs and amorphous silicon (a-Si) CsI and PD (photodiode) CsI and CCD ( charged couple device) CsI and CMOS (complementary metal oxide semiconductor) -similar to CR
Non-scintillation flat panel: Direct conversion
Photoconductor --> TFT--> electrical signals
PACS
Picture Archiving and Communications System Covers three areas: Display Network Storage A computer system that manages images in digital form. digital images created fro multiple modalities computer displays images for quality check before sending to rad workstation or laser printer distributes images within (LAN) and outside (WAN) of network integrates information from HIS and RIS stores and retrieves images
Dead Pixels
Pixels that generate no response to light input. 2 causes: 1. pixel out on LCD monitor or 2. DEL isn't working
What is PACS main storage?
RAID- redundant array of independent discs
PACS storage
RAID- redundant array of independent discs main PACS storage images are stored short term 6-12 months
RIS
Radiology information system schedule appointments, collect and display orders, store and display patient data, track patients, store and distribute radiologist data.
Monitors
Rads station- primary monitor (2048 x 2560) Physician review station Tech QC workstation- secondary monitor (1024x1280)
Direct Digital Radiography (DR) Unit
Same technical factors apply: 1. Correct positioning 2. Careful collimation 3. Use of grids 4. Evaluation of correct exposure index number
Scintillation vs Non-scintillation Flat Panel Detectors
Scintillation: xray photon --> light photon --> Electronic signal Non-scintillation: Xray photon ---> Electronic signal
Scintillation flat panel: Indirect conversion
Scintillator --> photodiode--> TFT --> Electronic signal Scintillator --> charge coupled device array --> electrical signals scitnillator converts X-rays to light photodiode converts light to signal
HL7 (1987)
Standard for exchanging information between medical applications computer integration of health-related information -patient records -labs -billing information -HIS and RIS
Direct Radiography (DR)
Systems have detectors that directly capture and readout an electronic image signal
All flat panels use what to collect and store electrons before sending off to computer?
TFT (thin film transistor)
Teleradiology
Transmits images for off site interpretation and/or consultation extends PACS into radiologists home so that they can read at night or on weekends often used as on-call, emergency basis "night hawking"
Each DEL represents what?
a pixel
What is considered a primary or diagnostic monitor?
a soft copy- monitor
Semiconductor
a substance that conducts electricity
scintillator
a substance that glows when hit by photons
Task Group 116
an effort to standardize the exposure indicators for digital radiography has begun with manufactures, vendors, the international electrotechnical commission and the american association of physicists in medicine. Tasked to develop common exposure indices across detectors and manufacturers -.5 to .5 = target range
Photodetector
any device that converts light into an electronic signal
Cesium Iodide (CsI) or GdOs and Amorphous Silicon (a-Si)
are a photoconductor
Photoconductor
change in electrical conductivity of a substance as a result of absorbing electromagnetic radiation
FPIR
flat panel image receptors
TFT- Thin Film Transistor
it is an electronic readout device A TFT is made up of rows and columns of DEL's All flat panels use TFTs to collect and store electrons before sending off to computer DEL- detector element Also known TFT array
What causes dead pixels?
pixel out on LCD monitor or DEL isn't working.
Advantages of PACS
post process can store images can send images throughout the hospital and globe can conference by viewing images @ multiple sites @ the same time.
TFT is made up of what?
row sand columns of DEL's
Advantages of DR
short processing time- no cassette large dynamic range, greater exposure can reduce exposure factors due to high DQE Better contrast resolution Disadvantage: not compatible with existing X-ray equipment so its expensive
Jukebox
used by PACS for longer term storage 1 year or longer
