Transcript Fluoroscopy Review Notes From CDPH RHB Syllabus

Fluoroscopy Review Notes
From CDPH RHB Syllabus
Rad Tech 244 - 2013
Fluoroscopy Notes Ch 1
• Approximately 5% of the US population
has a fluoro procedure each year
• The average number of fluoro exams per
person is 1.3
• The average number of spot films is 4.6
• The MC exam is a GI tract at 53%
• A 2 minute UGI exam can produce an
exposure ranging from 5-15 rads,
comparatively a KUB is between 100-500
mrads.
• Fluoro is defined as a rad exam utilizing
fluorescence for the observation of the
transient image.
• Fluoro was first used as a dynamic
procedure. Second as a means of
positioning for spot films.
• Medical exposure accounts for about 20%
of the total radiation people receive.
• Even though the percentage is small, for
medical exposure, it is the only exposure
that is controllable.
• FLUOROSCOPY TO POSITION
PATIENTS IS PROHIBITED.
Notes Chapter 2
Factors Directly Affect Exposure
•
•
•
•
•
mA
kVp
Collimation
Filtration
Exposure time
– Total fluoro time
• Target to panel distance (TPD)
• Patient to II distance
• Sensitivity of the image receptor
– Essentially speed RSV
The following will reduce exposure
•
•
•
•
•
•
Collimating
Last frame hold
Shortest possible patient to II distance
Highest possible kVp
Pulsed fluoroscopy
Using the largest II mode with collimation
Factors indirectly influencing
exposure
• Room illumination
• Image receptor quality
• Absorption of the table top
mA
• 0.5 – 5 mA
– Usually 1 – 3 mA
• Spot films
– 100 mA or higher
• Output and dose are directly proportional
to mA
kVp
•
•
•
•
Maximum photon energy
Beam quality
Penetrability of the beam
Tube potential
collimation
• Required by law
• Image quality improves as the beam is
collimated
Collimation
Collimate tightly to the
area of interest.
 Reduces the
patient’s total
entrance skin
exposure.
 Improves image
contrast.
 Scatter radiation to
the operator will also
decrease.
Factor affecting staff doses
FIELD SIZE DEPENDENCE
100 kV
1 mA
11x11 cm
17x17 cm
0.8 mGy/h
1.3 mGy/h
0.6 mGy/h
1.1 mGy/h
0.3 mGy/h
0.7 mGy/h
Scattered
dose rate is
higher when
field size
increases
1m patient distance
Patient
thickness 18 cm
12
filtration
• If the tube is operated above 125 kVp, 3
mm Al eq is required.
• Filtration reduces patient dose
Source to table top
target to panel distance
• Cannot be less than 12” and should be 18”
• Mobiles are required to be at least 12”
• Fixed units, 15”
Patient to II distance
• The closer the II, the lower the dose
• This is more pronounced with fixed units.
– Decreases the SID
• Tabletop
– Less than 1 mm Al
eq at 100 kVp
• Exposure switch
– Dead man type
Primary protective barrier
• The II is the primary barrier and must have
2 mm Pb eq for systems operating above
125 kVp
• The II has to be in place for the tube to
energize
Protective Actions
• Bucky Slot Cover
– Automatically covered, 0.25 mm Pb eq
• Protective curtains
– 0.25 mm Pb eq
– Not required on c-arms
– Scatter at 1 foot can reach 500 mrad/hr
• Allowable exposure rates
– Cannot exceed 5 rad/minutes
• Unless, ABC or image recording
• Cumulative timer
– Cannot exceed 5 minutes
• Illumination
II Considerations
• Purpose
– The basic purpose of the II is to make the
fluoro image brighter
– When the image is brighter it is easier to
visualize structures
• Brightness Gain
– Minification gain multiplied by electronic (flux)
gain
II Facts
• Input phosphor, cesium iodide
• Photcathode, danium antimony
• Output phosphor, zinc cadnium sulfide
Image Quality Issues
• Quantum Mottle
– Caused by too few photons
• Contrast
– Subject
– Detector
– Image
• Resolution
Effect of X ray Beam Penetration on Contrast, Body Penetration, and Dose
t
23
Dose vs. Noise
2 µR per frame
15 µR per frame
24
24 µR per frame
• Distortion
– Size, shape, pincushion
• Lag
• Vignetting
– Less bright at the edges than center of image
• Magnification tubes, Multi-mode
– Variable FoV
Closed Circuit TV Systems
• Camera
– MC is the vidicon
• Camera control unit
– Video amplifier
• Monitor
– CRT, etc.
Cinefluoroscopy
• Synchronization
– Record with the x-ray pulses
• Framing frequency
– Division of 60
– The higher the rate the higher the dose
• F-number
• Video disk recording (electronic radiography)
– Exposure ends when image is formed
• Basically fluoro phototiming
• 95% dose reduction
• Video tape
– Instant playback and no additional dose
• Spot films
– Conventional cassettes
– Photospot cameras
• ½ to 1/3 dose of convent. Cass.
• Lower image quality
Accessories
• Gonadal shields
– Required when possible
• Grids
– Fluoro uses low ratio grids
• Cassettes
• Cine film
– Per frame basis 10 x the dose than fluoro
Factors affecting an Increase in
Scatter
• High kVp
• Large field size
• Thick body part
Advantages of 3 phase and
medium/high frequency generators
• Relatively high mA
• Higher effective kVp
• Near constant potential
– Less ripple
Notes for Chapter 3
• Fluoro Image Production
• Fluoro units have 2 basic components
– X-ray tube
– Image intensifier
Fluoro X-ray Tube
• Regular rotating anode x-ray tube
• Runs at a lower mA
– Less than 5 mA
– Small focal spot
• Possible because of the low mA
II
• The primary purpose is to increase the
brightness of the fluoro image
• Components
– Glass envelope that provides a vacuum
– Input layer
• Converts x-ray photons to electrons
– Electronic (electostatic) lens
– Output layer
• Input layer
– Converts x-ray photons to light photons
– Light photons then strike the photocathode
and convert into electrons
– Electrons are then accelerated across the II
– Electrons strike the output phosphor and are
converted back into light photons
The image intensifier (I.I.)
I.I. Input Screen
Electrode E1
Electrode E2
Electrode E3
I.I.Output Screen
Photocathode
+
36
Image intensifier component
*
Input screen: conversion of incident X Rays into light
photons (CsI)
*
*
Photocathode: conversion of light photons into electrons
*
*
only 10 to 20% of light photons are converted into
photoelectrons
Electrodes : focalization of electrons onto the output
screen
*
*
1 X Ray photon creates  3,000 light photons
electrodes provide the electronic magnification
Output screen: conversion of accelerated electrons into
light photons
37
Image Intensifier Magnification
Modes
Same area
Output
phosphor
Input
Phosphor
9 inch field
6.5 inch field
IMAGE INTENSIFIER
Active Field-of-View (FOV)
RELATIVE PATIENT ENTRANCE
DOSE RATE
FOR SOME UNITS
12" (32 cm)
100
9" (22 cm)
200
6" (16 cm)
300
4.5" (11 cm)
400
Brightness Gain
• BG is the product of minification gain and
flux(electronic) gain
• Minification Gain
– Input phosphor dia.2/output phosphor dia2
• Making the image smaller will make it
brighter.
– The same number of photons are contained in
a smaller area
• In most IIs the output phosphor is 1 inch.
Flux Gain
• Caused by the conversion efficiency of the
output phosphor and the acceleration of
the electrons across the II
• As the electrons accelerate they gain
kinetic energy
• Flux gain is usually between 50 and 150.
Measuring Brightness Gain
• The actual measurement is done by
calculating the conversion factor
– Intensity of output phosphor (candelas)/mrads/sec
• Brightness gain will deteriorate 10% annually.
– This will ultimately decrease image contrast
Beam Splitter Mirror
• 10% of the output
light goes to the
vidicon (video
camera) the
remainder goes to the
photospot device.
• NOTE: not all units
have a beam splitter
Vignetting and Pincushion
Distortion
• Pincushion
– The loss of shape at the edges of the fluoro
image
• Vignetting
– Loss of brightness at the edge of the image
Veiling Glare
• Occurs when the light from the output
phosphor ‘reflects’ back into the II.
– Remember, the photocathode is stimulated by
light, so light ‘reflecting’ from the output
phosphor would also trigger electron
production.
– Decreased contrast results
Automatic Brightness Stabilization (ABS)
Automatic Brightness Control (ABC)
• Keeps light output of the II constant.
• Brightness of the image varies with
changes to kVp and mA.
– Increase mA increase brightness; direct
relationship
– Increase kVp 10% double brightness
Brightness Sensing
• II photocathode current
• Television camera signal sensing
• Lens coupled phototube sensing
Types of ABS
• Variable mA, preset kVp
– Set the kVp and the unit adjusts mA
• Variable mA with kVp following
– If the mA range is exceeded the unit will
automatically adjust the kVp to compensate
• Variable kVp, preset mA
– Set the mA and the unit adjusts kVp
• Variable kVp, variable mA
Closed Circuit TV Systems
• Camera
• Camera control unit
– Power supply and video amplifier
• Monitor
Cameras
• Vidicon
– MC, inexpensive, lag, 525 raster lines
• Plumbicon
– Cardiac cath labs
– Fixed gain (better contrast) and low lag
– Increased quantum mottle
• Image orthicon
– Not widely used
• CCD
– Solid state semiconductor
– Small, low power consumption, low price, long life
Photoconductive camera tube
Steering coils
Focussing optical lens Photoconductive layer
Deviation coil
Alignement coil
Input plate
Accelarator grids
Control grid
Electron beam
Iris
Video Signal
Signal electrode
Electron gun
Field grid
Electrode
51
Schematic structure of a charged couple device
(CCD)
52
Monitor
• 525 lines 30 times per second
• Combined with the video camera improves
image contrast
TV Image Quality
•
•
•
•
•
Horizontal resolution
Vertical resolution
Contrast
Brightness
Lag
• Horizontal resolution
– Bandwidth or bandpass
– Increase frequency bandwidth increase
horizontal resolution
• Vertical resolution
– Determined by number of scan lines
– Kell factor
• Ratio of vertical resolution and scan lines
• Contrast
• Brightness
– Adjust contrast first and brightness after
• Lag
– Occurs when the II is moved rapidly.
Dynamic Image Recording
• Video Tape
– 2 advantages
• Instant replay
• No additional patient exposure
– Disadvantages
• Poor image quality, fixed frame rate,
• Cinefluoroscopy
– 16 or 35 mm (MC high patient dose, better
image)
• Synchronization
– Camera shutters open at the same rate as x-ray pulses
• Framing rate
• F-number
– The lower the number the more light hitting the camera
the lower the patient dose; however, more distortion at
the edges
• Framing
– Underframing should be
avoided
– Exact framing, diameter of
the II fits in the shortest
dimension of the film
– Overframing, diameter of
the II fits the largest
dimension of the film. Part
of the image is lost
– Total overframing, diameter
of the II is equal to the
diagonal of the film
Static Image Recording
• Video disk
– Last image freeze (hold) (sticky fluoroscopy)
– Electronic radiography, similar to AEC x-ray
only until image is made.
– Decrease dose up to 95%
– 1 to 30 frames per second
• Spot film
• Conventional cassettes
• Spot film
– Photospot
• Image is taken from the II output phosphor
• Dose 20 – 50 X higher per frame than fluoro
because of higher mA
• Currently, 70 mm roll, 105 roll, 100 mm chip
– 105 mm roll ½ the dose of cassette spots
– Cassette spots
• Slower ‘frame’ rate
• Higher dose and better spatial resolution
Digital Fluoroscopy
• Digital image is obtained from the output
phosphor.
– A vidicon then a digital image processor
– Or, digital video camera
• Digital photospot
– Instant playback, possible image enlargement
Pulsed Fluoroscopy
• Variable frame rates are possible with a
corresponding decrease in patient dose
High level (boost) fluoroscopy
• Higher tube currents than normal
– 10-20 mA usual 40 mA potentially
– Increase patient dose 2-10 times reg. Fluoro
– 10-50 rads per minute
– Limited to 20 rad/minute unless recording the
image
• Key points
– Special activation required, audible signal,
dose rate limited to 20 rad.minute
Notes from Chapter 4
Conducting the Fluoro Exam
• Operator dose is directly proportional to
patient dose
• Image brightness is directly proportional to
dose rate at input phosphor
Technical factors which directly
influence dose rate at the table top
•
•
•
•
•
•
mA
kVp
Collimation
Filtration
Exposure time
Target panel distance
Technical factors which indirectly influence
dose by affecting technical factors
• Room lighting
• Image receptor quality
• tabletop
Collimation
• A border needs to be visible when the II is
14 inches above the tabletop and the
collimator is fully opened
• With an automatic collimator, a border
should always be visible
• Image is not brighter with a less
collimation (bigger field size)
Filtration
• Total filtration
– 2.5 mm Al eq < 125 kVp
– 3.0 mm Al eq at 125 kVp and above
• Total filtration includes inherent and added
• Exposure rate should be less than 2.2
rads/min at 80 kVp
• HVL
Allowable exposure rates
• Limited to 5 rads per minute
• If the unit has ABC/ABS then 10 rads/minute is
allowed
– However, if the unit has ‘boost’ then the limit is
5rads/minute
• ABC/ABS units have to be checked by a
physicist annually
– Also have to have weekly fluoro checks of mA and
kVp
– No ABS 3 year check by physicist
TPD
• TPD increases from 12 to 18 inches
– Pt. Dose decreases by 30%
• II as close as possible to the patient
Room Lighting
• Affects visual acuity
– Photopic acuity is 10 X better than scotopic
acuity
– Day versus night vision
• Normal viewing distance is 12 – 15 inches
• Image recognition in 0.2 seconds
Gonadal Shields
• 0.5 mm Pb eq
• 97% effective at 100 kVp and 3 mm Al
filtration
Notes from Chapter 5
Basic Operational Procedures
• Minimize exposure time by utilizing short
looks
• Use the cumulative timer
• Use the highest applicable kVp
• Collimate
• Use mag and boost only when necessary
• Use last image hold
•
•
•
•
Use a photospot instead of cassettes
Use video tape
Use II with good contrast
Monitor the TV monitor for brightness and
contrast
• Minimize the pt. II distance
• Position the II prior to exposure
• Prevent pt. Motion with instructions
• Use gonadal shielding when possible
• Use compression devices
Factor affecting staff doses
ANGLE DEPENDENCE
100 kV
1 mA
0.9 mGy/h
0.6 mGy/h
11x11 cm
0.3 mGy/h
1m patient distance
patient thickness 18 cm
Scattered dose
rate is higher
near the area
into which the
X-ray beam
enters the
patient
79
Factor affecting staff doses
DISTANCE VARIATION
mGy/h at 0.5m mGy/h at 1m
100 kV
1 mA
11x11 cm
Scattered
dose rate is
lower when
distance to
the patient
increases
80
Factor affecting staff doses
X-Ray tube
100 kV
1m
mGy/h
2.2 (100%)
2.0 (91%)
20x20 cm
1.3 (59%)
Tube undercouch
position reduces, in
general, high dose rates
to the specialist’s eye
lens
mGy/h
1 Gy/h
(17mGy/min)
1.2 (55%)
1.2 (55%)
1m patient distance
1.2 (55%)
1 Gy/h
(17 mGy/min)
1.3 (59%)
20x20 cm
100 kV
1m
2.2 (100%)
1m patient distance
X-Ray tube
81
Mobile Concerns
•
•
•
•
•
Audible indicator
Cumulative timer visible on the monitor
Video storage
Last frame hold
Longest possible TPD
Notes for Chapter 6
Pediatric Fluoroscopy
• Motion
– Sedation
– Mechanical devices
• Personnel and Parental Protection
– Everyone in the room needs lead
• Gonadal shielding
• Artifacts
• ABS/ABC
– Watch putting the II directly over large
concentrations of contrast
• Distance
• Collimation
• Photospots instead of cassette spots if
possible
Notes for Chapter 7
Mobile Fluoroscopic Equipment
• Primary beam is intercepted by the II
– If the II is used routinely in a single location it
needs to have secondary shielding
• SSD has to be at least 12 inches
• Must have an II
• Collimation has to be used or unit will not
energize
• Unit cannot energize unless the II is in the
primary beam
• Maximum dose rate of 5 rads/minute
• Personnel monitoring in required for all
persons operating fluoro equipment
• Protective aprons are required if exposed
to more than 5mrads/hour
• Boost mode should only be used after
areas of interest have been localized
Notes for Chapter 8
Responsibilities of X-ray Supervisor
• Chief Radiologist or designees are
responsible
• Licentiates who can use and supervise
fluoro
– Radiology supervisor and Operator
– Fluoro supervisor and Operator
• Techs with Fluoro permits can only use
fluoro when supervised by above
Specific requirements
•
•
•
•
•
•
Establish a fluoro procedures manual
Annual review of manual
Assure that techs don’t practice medicine
Observe tech performance
Assure techs are offered training
Assure equipment monitoring is adhered
to
Personnel Protection
• Operator is adequately protected from
scatter
• Individuals in the room need to wear
aprons and film badges
• Use protective devices as applicable
Protection Devices
SCREEN AND
GOGGLES
CURTAIN
THYROID
90
Restrictions
• Techs can only use fluoro equip. under the
supervision of a supervisor operator
• Techs cannot interpret films
• Techs cannot use a title implying the right
to practice medicine
Notification Requirements
• Immediate notification (prompt phone call and
timely letter)
– Total dose 25 rems
– Eye dose 75 rems
– Skin or extremity dose of 250 rems
• 24 hour notification ( call within 24 hours and a
letter follow-up)
– Total dose 5 rems
– Eye dose 15 rems
– Skin or extremity 50 rems
Notes on Chapter 9
Supervision of Techs w/Fluoro permits
•
•
•
•
•
•
Clear the room of unnecessary personnel
Collimate
Use shields
Use correct technical factors
Position the patient correctly
Avoid patient motion
• Direct supervision
– Use equipment only as trained
• Indirect supervision
– Spot filming and video taping
Notes on Chapter 10
Health Effects of Low Level Radiation dose
• Somatic dose indicators
– Injuries to superficial tissue
– Induction of cancer
– Cataracts, fertility issues, life-span shortening
– Injuries to developing fetus
• Based on dose at specific locations or
points
• High marrow dose exams
– BE, UGI, abdominal angio
• Genetic dose indicators
– 50 rads temp male sterility
– 30 rads temp female sterility
• Genetically significiant dose
– Number of future kids
– X-ray exam rate
– Mean gonadal dose/exam
Notes on Chapter 11
Biological Effects and Significance of Dose
• Effects appear to follow a linear nonthreshold dose curve
– Dose rate to tissue
– Total dose
– Type of cell exposed
Radiobiological injury
• Cellular amplification
• Gross cellular effects
– MC effect is the cessation of cell division
• Latent Period
– Short term, weeks or less
• Immediate or early effects
– Long term, years or longer
• Delayed or late effects
Dose relationship curves
Threshold
Non-linear
Non-threshold
linear
Regulations are based on non-threshold linear curves
Variations in Cell Sensitivity
• Bergonie and Tribondeau
– Number of undifferentiated cells
– Degree of mitotic activity
– Duration of active proliferation
• Radiation induced mitotic delay is usually
reversable
Cell Sensitivity
•
•
•
•
•
•
•
•
•
Lymphocytes or white blood cells
RBCs
Epithelial
Endothelial
Connective tissue cells
Bone
Nerve
Brain
Muscle
Short Term Effects
• 25 rads or less demonstrate no effects
Long Term Effects
• No specific effect associated with radiation
exposure
• Somatic damage
– Increased incidence of cancer
– Embryological effects
– Cataracts
– Life span shortening
• Genetic mutations
Carcinogenic Effects
• Human evidence
– Early radiologists and dentists
– Radium dial painters
– Uranium miners
– Survivors of Hiroshima and Nagasaki
Radiation Induced Cancers
•
•
•
•
•
•
Female breast
Thyroid
Hemopoitic tissue
Lungs
GI tract
Bones
Embryological Effects
• As little as 10 rads demonstrates effects in
animal models
• 50 rads can cause spontaneous abortion
Notes on Chapter 12
Personnel Radiation Protection
• ALARA
• Basis for radiation protection requirements
– Stochastic effects
• Probability of an event occurring, ie cancer
– Non-stochastic effects (deterministic)
• Severity of the effects varies with exposure
Operator Exposure
• Distance
• Apparel
– Aprons, 0.25 mm Pb 97% effective
• 0.5 mm Pb, 99.9 % effective
• Should be placed on hangers when not in use
• Aprons cover 80% of the bone marrow
Notes on Chapter 13
Personnel Monitoring
•
•
•
•
Record exposure
Measure accumulated exposure
Indicate type of exposure
Provide a record of exposure
Types
• Film badge
– 10 mrad to 700 rads
– +/- 25% accuracy
• TLD
– Lithium fluoride
– +/- 9%, cannot be reread
• Others
– Pocket dosimeter
– Audible device
Maximum Permissible Dose
For adults over 18 y/o
• Whole body - head, trunk, arms above the
elbow, and legs above the knee
– 5 Rem
• Skin and extremities
– 50 rem
• Lens
– 15 Rem
• Occupational dose for people under 18 y/o
10% of adult dose
Occupational Exposure Limit
Whole Body – 5rem/year
Extremities – 50rem/year
Eye – 15rem/year
Pregnant workers – 0.5rem/gestation period
General public
Limited to 0.1 rem/year (Addition to the background radiation)
0.002 Rem (2 mrem) per hour
Who must be monitored?
• Persons in high radiation area
– 0.1 Rem per hour at 30 cm
– Fluoro rooms
• Persons operating mobile x-ray equipment
• Radiation Area
– 0.005 Rem per hour at 30 cm
Typical Exposures
mrem/yr
5000
4000
3000
2000
1000
0
MPD
Cardio.
Pain
Mgnt.
X-Ray
Tech