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Questions and Answers
The number of photons directly represent the intensity level in a ______ pixel.
The number of photons directly represent the intensity level in a ______ pixel.
single
Sectra Microdose Mammography (MDM) is based on ______ detectors.
Sectra Microdose Mammography (MDM) is based on ______ detectors.
Si
CCD systems use a ______ like gadolinium disulphide to convert x-rays to visible light.
CCD systems use a ______ like gadolinium disulphide to convert x-rays to visible light.
scintillator
A-Se is an example of ______ detection.
A-Se is an example of ______ detection.
Continuous fluoroscopy displays at ______ frames/sec.
Continuous fluoroscopy displays at ______ frames/sec.
Pulsed fluoro reduces blurring from patient motion by using a series of short x-ray ______.
Pulsed fluoro reduces blurring from patient motion by using a series of short x-ray ______.
The purpose of the automatic brightness control (ABC) is to keep the brightness of the image constant at the ______.
The purpose of the automatic brightness control (ABC) is to keep the brightness of the image constant at the ______.
The last-frame-hold feature is useful at ______ institutions.
The last-frame-hold feature is useful at ______ institutions.
Road mapping is a software-enhanced variant of the ______ feature.
Road mapping is a software-enhanced variant of the ______ feature.
Using 7.5 frames/sec instead of 30 frames/sec in pulsed fluoroscopy results in a dose savings of ______ %.
Using 7.5 frames/sec instead of 30 frames/sec in pulsed fluoroscopy results in a dose savings of ______ %.
In Indirect detection systems, the X-rays are absorbed in a ______ layer and produce light photons.
In Indirect detection systems, the X-rays are absorbed in a ______ layer and produce light photons.
The ______ detector converts X-ray photons directly into charges (electron-hole pairs).
The ______ detector converts X-ray photons directly into charges (electron-hole pairs).
In digital fluoroscopy, the image is captured using a ______ sensor.
In digital fluoroscopy, the image is captured using a ______ sensor.
The Fill Factor is calculated by dividing the sensitive area by ______ x ______.
The Fill Factor is calculated by dividing the sensitive area by ______ x ______.
The ______ detection systems use Imaging Plates based on photostimulable phosphors.
The ______ detection systems use Imaging Plates based on photostimulable phosphors.
In Direct photon counting systems, ______ photons are counted.
In Direct photon counting systems, ______ photons are counted.
Flat Panel Digital Fluoroscopy is a type of ______ radiography.
Flat Panel Digital Fluoroscopy is a type of ______ radiography.
The ______ screen is used in analogue fluoroscopy.
The ______ screen is used in analogue fluoroscopy.
Flat panel devices are thin film transistor (TFT) arrays that are rectangular in format and are used as ______ detectors
Flat panel devices are thin film transistor (TFT) arrays that are rectangular in format and are used as ______ detectors
CsI, a ______ is used to convert the incident x-ray beam into light
CsI, a ______ is used to convert the incident x-ray beam into light
TFT systems have a ______ at each detector element which converts light energy to an electronic signal
TFT systems have a ______ at each detector element which converts light energy to an electronic signal
Flat panel detectors would replace the image ______, video camera, and other peripheral devices
Flat panel detectors would replace the image ______, video camera, and other peripheral devices
Digital fluoroscopy uses ______ panel detectors to convert x-ray energy into an electronic signal
Digital fluoroscopy uses ______ panel detectors to convert x-ray energy into an electronic signal
The ______ of digital fluoroscopy allows for real-time image acquisition and display
The ______ of digital fluoroscopy allows for real-time image acquisition and display
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Study Notes
Image Detection Systems
- Indirect image detection: x-rays are converted to visible light, then to electric charges, and finally to an electric signal
- Examples: CCD systems, a-Si indirect detectors, and CsI-scintillator with a-Si switching diodes or TFT-readout
CCD Systems
- Use a scintillator like gadolinium disulphide to convert x-rays to visible light
- Light is collected by optics to demagnify the 35x45cm2 film to 2-4 cm2 CCD
- Visible light is converted into charge that is amplified and readout
a-Si Indirect Detectors
- CsI-scintillator with a-Si switching diodes or TFT-readout
- 100 m pixel size, giving ~5 lp/mm
Direct Detection
- Also called flat panel detectors (FPD)
- Charge proportional to the x-rays received is stored on a capacitor
- The charges are conducted out by transistors one row at a time and subsequently amplified, multiplexed, and digitized
- The readout is very fast
a-Se Direct Detection
- Direct image detection
- X-ray photoconductor layer (usually amorphous selenium) converts x-rays to charge
- An applied electric field directs the charges to the charge collection electrodes
Spot-Film Devices and Cine-Radiography Cameras
- Attach to the front of the II and produce conventional radiographic screen-film images
- Better resolution than images produced by II
- Cine-radiography cameras attach to a port and can record a very rapid sequence of images on 35-mm film
Fluoroscopy Modes of Operation
- Continuous fluoroscopy: continuously on x-ray beam, 0.5 – 4 mA or higher, display at 30 frames/sec, 33 msec/frame acquisition time
- High dose rate fluoroscopy: specially activated fluoroscopy, 20 R/min is the maximum legal limit, audible signal required to sound
- Pulsed fluoro: series of short x-ray pulses, 30 pulses at ~10 msec per pulse, exposure time is shorter, reduces blurring from patient motion
- Last-frame hold: when the fluoroscopist takes their foot off the fluoroscopy pedal, the last live image is shown continuously
- Road mapping: software-enhanced variant of the last-frame-hold feature, useful for advancing catheters through tortuous vessels
Digital Image Quality
- Gray levels at a constant 512 x 512 matrix size
- The purpose of the automatic brightness control (ABC) is to keep the brightness of the image constant at the monitor
Flat Panel Digital Fluoroscopy
- Replace image intensifier
- Flat panel devices are thin film transistor (TFT) arrays that are rectangular in format and are used as x-ray detectors
- CsI, a scintillator, is used to convert the incident x-ray beam into light
- TFT systems have a photodiode at each detector element which converts light energy to an electronic signal
Type of Detector
- Indirect detection systems: the X-rays are absorbed in a phosphor layer and produce light photons which convert into electric charges in a photo detector and then to an electric signal
- Direct detection systems: the X-ray photons directly convert into charges (electron-hole pairs) and thus to an electric signal in a photoconductor
- Direct photon counting systems: single photons are counted, i.e.
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