Fluoroscopy Flashcards
What is fluoroscopy? What is its purpose?
When dynamic/moving images are displayed in real time.
To actively study the motion of organs and the movement of contrast media within anatomic structures in real time
3 main components of a fluoroscope
- X-ray tube and generator
- Image Intensifier
- Video monitoring system
mA range for fluoroscopy
0.5-5mA
What generators are used for fluoroscopy?
High frequency (1%) or three phase (14%)
Purpose of the image intensifier
Electronically brighten the fluoroscopic image by receiving the image-forming x-ray and converting it into a visible light image of high intensity
Primary components of the tube type I.I
- glass envelope
- input phosphor
- photocathode
- electrostatic focusing lenses
- anode
- output phosphor
What is the purpose of the glass envelope?
Allows the free flow of electrons from the photocathode to the anode
What is the input phosphor made of and what does it do?
- glass or thin aluminum base
- cesium iodide (improved spatial resolution)
- absorbs x-rays and coverts their energy into visible light
Purpose of the photocathode
- antimony and cesium compounds
- light photons release electrons from the photocathode through photoemission
- # of electrons directly proportional to intensity of light
Purpose of electrostatic focusing lenses?
- focus electrons towards the output phosphor
- positively charged
What is the output phosphor made of? What is its purpose?
- glass or aluminum with zinc sulphide (2.54cm)
- receives electrons from photocathode and emits 50-75x more light than what was received by the photocathode
How can image brightness be changed by the image intensifier?
- minification gain
- flux gain
Minification gain and its formula
-the image in condensed onto the smaller output phosphor from the larger input phosphor-it appears brighter because it is emitted from a smaller area
-minification gain = d(i)^2 / d(o)^2
(Diameter of input phosphor/diameter of output phosphor)^2
What is flux gain and its formula?
- increased electron kinetic energy from the high voltage accelerating them releases more light from the output phosphor
- flux gain = # of output light photons / # of input x-ray photons
What is brightness gain and its formula?
- how bright an image is with an I.I vs. without and I.I
- brightness gain = (minification gain)(flux gain)
Does brightness gain increase or decrease with tube age? What can be done to compensate?
Decrease, must raise technique
Describe the operation of and I.I
- x-rays pass through patient
- x-rays absorbed by input fluorescent screen
- a light image is produced (direct viewing possible)
- light photons strike photocathode
- photoelectrons are emitted by photocathode (photoemission)
- electrons are attracted to accelerating anode
- electrons focused onto output fluorescent screen
- electrons strike output fluorescent screen
- light photons emitted from output screen
What happens when the electrons cross over at the focal point in the I.I?
The image in inverted
-Right becomes left
-Superior becomes inferior
Image is upside down and reversed
Why do we use magnification mode?
- To enhance the image and increase the capability for a more accurate diagnosis
- moves the focal spot farther from the output phosphor
Advantages/Disadvantages of magnification mode?
- Increased spatial resolution
- Increased contrast resolution
- Increase patient dose
What is the purpose of an I.I coupling device? Two methods of coupling?
Connects the output phosphor to the image monitoring system
(CF= TV camera) (DF= CCD)
-Fiber optics
-Lens coupling
What is fiber optic coupling? Advantages/disadvantages?
A bundle of tiny flexible glass or plastic fibers
- simplest method
- compact
- rugged (can be rough handled)
- inexpensive
- incompatible with auxiliary cameras
What is lens coupling? Advantages/Disadvantages?
Uses a beam splitting mirror to redirect light from the output phosphor to aux devices and a monitoring system
- large
- must be moved gently (misalignment of mirrors causes blurring)
- enables simultaneous viewing of the image while it is being recorded
- enables connection to Cine and spot camera (aux devices)
What is the imaging monitoring system? Two types?
Magnifies the image from the output phosphor of the I.I for easier viewing
- Direct: mirror optics
- Indirect: CCTV, TV cameras, CCDs in DF
How does direct viewing work?
Image from I.I is projected onto a mirror mounted on the side of the I.I tower.
- field of view is small
- low resolution
How does indirect viewing work?
- CCTV (closed-circuit television monitoring) most common
- a tv camera tube is connected to the output phosphor and then connected to a display monitor (tube converts visible light into electronic signal)
- brightness and contrast can be controlled electronically
- dynamic and static images can be recorded
What does a TV camera tube do? Types?
Converts visible light into electronic signals for television monitoring
- Orthicon
- Plumbicon
- Vidicon
- CCD (only in DF)
CF television monitors
convenience of viewing the image on a TV screen/monitor decreases the quality of the image
- decreases spatial resolution
- requires recording of the image on an alternate device to capture the high resolution from the I.I
Types of static recording systems?
- Cassette spot filming
- Photospot camera
Cassette spot filming characteristics
- only capable with lens coupling
- located between patient and I.I
- uses fluoro x-ray tube to create image, not I.I
- slight pre-exposure delay to change to high mA setting
- has multiple modes to display numerous images on one film
- appears as radiograph
Characteristics of photospot camera
- only capable with lens coupling
- exposes one frame at a time (up to 12 frames/sec)
- receives image from the output phosphor of the I.I
- less patient dose compared to cassette spot film
- no exposure delay
- appears as live fluoro image
Dynamic recording systems
-Cinefluoroscopy
Characteristics of cinefluoroscopy
- only capable with les coupling
- similar to photospot (uses videotape to monitor and record images from I.I)
- no exposure delay
- high speed motion picture capture (up to 120frames/sec)
- ideal for cardiac, minimizes image motion, increased patient dose
What do all digital fluoroscopy systems have the capability to do?
Pulse fluoroscopy
2 methods of DF?
- I.I tube DF systems
- Flat-panel DF systems
Components of DF
- Tube and generator: High frequency
- Image receptors: I.I or flat-panel
- Coupling devices: lens/fiber optic
- CCD
- ADC
- multiple viewing monitors (flat screen)
- operating console: for post-processing
What is the difference between CF I.I systems and DF I.I systems?
The I.I connects to a CCD (DF) instead of a vidicon (CF)
Flat-panel IR systems (FPIR) characteristics
- replace the I.I and vidicon components
- acts like an radiography IR
- smaller, lighter, easier to move
- unaffected by external magnetic fields
- pulsed mode capabilities where exposure time can be continuously varies, reducing dose to patient
What is interrogation time, extinction time, and duty cycle?
Interrogation time: time required for x-ray tube to be switched on and reach the selected kVp and mA
Extinction time: time required for the x-ray tube to be switched off
Duty cycle: period of time when the x-ray tube is energized
Advantages of Pulsed fluoroscopy
- decreased quantum mottle
- increased resolution
- increased SNR
- decrease probability of image flicker
How does OID affect things in pulsed fluoroscopy?
Decreased OID =
- increased resolution
- decreased dose
- decreased penumbra
DF coupling devices purpose and types
- fiber optic
- lens
Connects the I.I to the CCD
Purpose of the CCD and advantages.
Converts light to electrical charge
- small
- more sensitive to light (increased DQE)
- crystalline silicon (active component)
- increased contrast resolution
- linear response
- no lag, no warm up period
- ABC
- wide dynamic range
Advantages of CCD over vidicon
- increased contrast resolution
- increase spatial resolution
- increased SNR
- no maintenance or warm up
- unlimited lifetime and fast response time (high DQE)
- linear response, no lag time or blooming
- decreased patient dose
- no image distortion or lag
- enables use of an automatic brightness control
What is automatic brightness control?
Controls and maintains the brightness of an image by automatically adjusting the exposure factors to adapt to the thickness of the body part
Another name for ABC
Automatic brightness stabilization (ABS)
2 ways to control the image brightness with automatic brightness control?
- Monitor the current flow between the photocathode & anode: chamber is positioned in front of the output screen
- Monitor the intensity of light at the output phosphor: chamber is places after the output screen
ADC
Analog to digital converter
- located between CCD and array computer
- converts electrical signal from CCD to digital signal for computer
Why do we use an acquisition computer instead of a microprocessor?
- primary memory of an array processor is faster
- capable of processing thousands of functions at the same time
- applies algorithms to the incoming digital signal
DF television monitors compared to CF
- Higher SNR
- display incoming data in progressive mode (sharper image, less flicker)
- Flat panel high definition displays (LCD can replace CRTs)
What is the primary limitation of spatial resolution?
Monitors
What is image lag?
Persistence of luminescence of the screen after the x-ray stimulation has been terminated
Can occur with rapid movement causing blurred or ghost images on the monitor
Automatic gain control
- brightness of the image can be controlled by varying the sensitivity on the monitor
- exposure factors are not affected
- only video signal is adjusted
2 methods to control brightness of the displayed image
- ABS: adjusts exposure factors
- AGC: adjusts video/digital signal, 1st choice better for patient
Benefits of DF
- Last image hold: last frame remains on monitor when x-ray beam is shut off
- Image grab/snapshot mode: frame can be saved on static monitor from the live monitor
- both result in reduced dose
Components of conventional Fluoro
- tube and generator
- image intensifier
- image distributor (lens coupling)
- aux cameras
- vidicon
- array computer
- console
- table side monitor
Components of convention/digital conversion fluoro
- tube and generator
- image intensifier
- image distributor (lens coupling)
- aux cameras
- vidicon
- ADC
- array computer
- console
- table side monitor
Components of digital fluoro with I.I and CCD
- tube and generator
- image intensifier
- fiber optics
- CCD
- ADC
- array computer
- console
- table side monitor
Components of Digital Flat panel fluoro
- Tube and generator
- direct/indirect detector with CCD
- ADC
- array computer
- console
- table side monitor
Digestive system examination
Esophagus: esophogram
Stomach and duodenum: upper gastrointestinal series, UGI, OS&D, barium meal/swallow, modified barium swallow
Small bowel: small bowel follow through, enteroclysis
Large Bowel: single or double contrast enema
How is the esophagus positioned in the body?
Anterior to the vertebra, posterior to the trachea and heart
Passes through the diaphragm at T10
Esophagram contraindications and exam prep
Contraindications:
-sensitivity to contrast media used
-change of perforated bowel (mixture might escape into peritoneal cavity)
Exam Prep:
-no prep
-when imaging more than esophagus-nothing by mouth after midnight
What kind of contrast is used for an esophagram?
Thick barium: paste or thick powder mixture
Projections and positions of the esophagus? Centering for each
- AP or PA: 1” inferior to sternal angle (T5-T6 @MSP)
- Lateral: T5-T6 @MCP
- RAO or LPO (RAO preferred): T5-T6 10-15cm inferior to jugular notch, 5cm lateral to MSP on elevated side
- Optional swimmer’s lateral (to see esophagus without superimposition)
Which position best demonstrates a barium filled esophagus between the shadows of the heart and vertebral column?
RAO 40 deg
What is the most anterior and posterior portion of the stomach?
Fundus
Air-Barium distribution in the stomach for each position
Supine: fundus and duodenal bulb barium filled, pylorus air filled
Prone: fundus and duodenal bulb air filled, pylorus barium filled
Erect: fundus is air filled, pylorus is barium filled
Stomach and duodenum contraindications and exam prep
- sensitivity to contrast media
- change of perforated bowel (could possibly use a water soluble contrast agent)
- NPO from midnight the night before
- no smoking or chewing gum (increase gastric secretions)
Other names for exam of esophagus, stomach, and duodenum?
- Upper GI
- UGI (series)
- OS&D
- Barium swallow
- Barium meal
Projections and positions for an upper GI
- RAO
- PA
- Rt Lateral
- LPO
- AP
What kind of contrast is used for an upper GI exam?
Usually 2 kinds (positive and negative)
How do we coat the walls of the stomach with contrast?
Patient does a 360 deg log roll
Upper GI centering for each body habitus
Sthenic: CR at L1 above L3 and midway between spine and upside lateral border of abdomen
Asthenic: CR 5cm below the level of L1
Hypersthenic: CR 5cm above L1 and nearer midline
Which is the best image of the pyloric canal and duodenal bulb in profile?
RAO
Obliques for body habitus and positions of upper GI
RAO: Sthenic: 45-55 deg Asthenic: 40 deg Hypersthenic: 70deg LPO: Sthenic:45 deg Asthenic: 30deg Hypersthenic: 60deg
Why do we do a modified barium swallow?
- Performed to assess the patient’s ability to swallow
- Patient observed while swallowing foods of various consistencies from thick fluids to thick paste barium
- Patient history usually queries aspiration