Week 2: Fluoroscopy Flashcards
Digital Fluoroscopy (DF) - CCD
• Charge coupled device (CCD) –Sensitive component of the CCD is a layer of crystalline silicon. When the silicon is illuminated by the green light from the output phosphor, a charge is generated, which is then sampled, pixel by pixel and manipulated to produce a digital image.
• Coupled to the output phosphor of the II via fiberoptics or lens system.
• CCD is much smaller and rugged than television camera.
Digital Fluoroscopy (DF) – Flat Panel Image Receptor (FPIR)
• FPIR is also referred to as a flat panel detector (FPD).
• FPIRs are indirect detectors (convert x-rays to light via a scintillator).
• Consists of an array of individual detector elements (DELs).
• A cesium iodide (CsI) scintillation layer is coated in amorphous silicon (photodiode), with thin-film transistors (TFTs) capturing the electrons from the photodiode to create an electronic data set.
• FPIR can produce fluoroscopy as high as 30 frames per second (fps).
Advantages of the CCD over the Television Camera
• High spatial resolution
• High SNR
• High DQE
• No warm-up required
• No lag or blooming
• No spatial distortion
• No maintenance
• Unlimited life
• Unaffected by magnetic fields
• Linear response
• Lower patient radiation dose
Advantages of the FPIR over the CCD in DF
• Distortion free images
• Consistent image quality over the entire image
• Improved contrast resolution over the entire image
• Higher DQE
• Rectangular image area coupled to similar image monitor
• Unaffected by external magnetic fields
Tube current (mA) in II non digital fluoro vs DF
• Image intensified fluoroscopy requires: 0.5 – 5.0 mA
• DF with the FPIR requires hundreds of mA
Continuous Fluoroscopy
• Fluoroscopy that is continuously on as long as the fluoro switch is engaged. The x-ray tube is not pulsed, rather is continuously energized. Fluoroscopy is recorded at 30 frames per second onto the image receptor.
• Continuous fluoroscopy provides high diagnostic information with high dose to the patient and fluoroscopist.
• Continuous fluoroscopy places a high heat load on the x-ray tube.
• Low mA is used
Pulsed fluoroscopy
• Pulse width- also called duty cycle; time when the x-ray tube is on; expressed in milli-seconds (ms); 10 ms or less is adequate.
• Pulse height- expressed in mA.
• Interval- time between the pulse width where the x-ray tube is off; expressed in ms.
• Frame rate (frames per second (fps))- aka pulse frequency or pulse rate; refers to quantity of times per second the x-ray tube is energized. Pulsed fluoroscopy at 20 frames per second appears continuous to the human eye.
• Dose rate- shorter the pulse width and lower the frame rate, the lower the patient dose.
• Temporal averaging- individual frames are combined to create an image
Pulse Progressive Fluoroscopy
• Interrogation time- time required for the x-ray tube to be switched/on and reach the selected levels of kVp and mA.
• Duty cycle (pulse width)- fraction of time that the x-ray tube is energized.
• Extinction time- time required for the x-ray tube to be switched off.
FPIR Magnification Mode
• Flat panel image receptors use true electronic magnification to alter the FOV and not image optics like the image intensifier. For this reason, there is no increase in patient dose with the FPIR in magnification mode (unlike the II)
Automatic Brightness Control (ABC)/Automatic Exposure Rate Control (AERC) in DF
• Also referred to as automatic brightness stabilization (ABS), or automatic dose control (ADC).
• Feature of fluoroscopic equipment that maintains proper image brightness automatically by varying the kVp, mA, pulse time, or all three depending upon the patient’s part thickness, position, and/or pathologies present.
• Adjustments are automatically made to technical factors to maintain proper image brightness.
• With DF, no lag with the ABC while scanning a patient fluoroscopically from head to foot.
Fluoroscopy Operation & Manipulation
• Fluoroscopy can be operated and manipulated in many ways.
• Fluoro can be energized on/off at the carriage, at the computer, or by using a foot pedal.
• Manipulation of fluoro can be done at the carriage or at the computer.
• With mobile fluoroscopy, operation and manipulation can be done at the c-arm side panel, work-station, or with hand and/or foot controls.
Detector Element (DEL) Binning
• DELs are combined to form groups of DELs
• The binned DEL dimensions increase.
• The more DELs binned, the smaller the file size.
• The more DELs binned, the less quantum noise.
• The more DELs binned, spatial resolution decreases.
• Binning does NOT impact patient dose.
Fluorography (Recording & Storing Fluoro Images)
• Unsubtracted- Recording dynamic images or digital spot images can be achieved with flash drives, cd’s, DVD’s, or a fluoroscope’s hard drive. Adequate memory is necessary.
• Digital subtraction (DSA)- radiopaque structures such as bones are eliminated (subtracted) digitally from the image, allowing for accurate depiction of blood vessels when IV contrast is introduced. Recording dynamic images or digital spot images can be done similarly to un-subtracted fluoroscopy.
• Cine- Movie camera records the fluoroscopic image while fluoro is on. Recording occurs on 16mm, 35mm, or 70mm film.
Last Image Hold
• Common function on most digital fluoroscopic units (including mobile c-arm equipment) that maintains the last real-time fluoroscopic image until it is replaced by the unit being activated again.
• This allows physicians to continue to work from the most recent image without exposing the patient to additional radiation.
Last Sequence Display
• Function that maintains the last real-time fluoroscopic recorded sequence until it is replaced by the unit being activated again.
• This allows physicians to continue to work from the most recent sequence without exposing the patient to additional radiation.
• Example-a physician records a patient swallowing barium for 5 seconds. This 5 second recording will continue in a loop until fluoro is activated again.
