Fluoroscopy Review NotesFrom 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 2Factors 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

CollimationCollimate 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.

12

Scattered dose rate is higher when

field size increases

0.3 mGy/h

0.6 mGy/h

0.8 mGy/h100 kV

1m patient distancePatient

thickness 18 cm

0.7 mGy/h

1.1 mGy/h

1.3 mGy/h

17x17 cm11x11 cm 17x17 cm

1 mA

FIELD SIZE DEPENDENCE

Factor affecting staff doses

filtration

• If the tube is operated above 125 kVp, 3 mm Al eq is required.

• Filtration reduces patient dose

Source to table toptarget 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

t 23Effect of X ray Beam Penetration on Contrast, Body Penetration, and Dose

24

2 µR per frame 15 µR per frame 24 µR per frame

Dose vs. Noise

• 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

36

The image intensifier (I.I.)

+

I.I. Input Screen

I.I.Output Screen

Photocathode

Electrode E1

Electrode E3

Electrode E2

Electrons Path

37

Image intensifier component

Input screen: conversion of incident X Rays into light photons (CsI)

1 X Ray photon creates 3,000 light photons

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

electrodes provide the electronic magnification

Output screen: conversion of accelerated electrons into light photons

Image Intensifier Magnification Modes

9 inch field 6.5 inch field

Same area

Output phosphor

Input Phosphor

IMAGE INTENSIFIER Active Field-of-View (FOV)

RELATIVE PATIENT ENTRANCE DOSE RATEFOR 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

51

Photoconductive camera tube

Focussing optical lens

Input plate

Steering coils Deviation coilAlignement coil

Accelarator grids

Control grid

Electron beam

Video Signal

Signal electrode Field grid ElectrodeElectron gun

Iris

Photoconductive layer

52

Schematic structure of a charged couple device (CCD)

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 4Conducting 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 5Basic 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

79

Factor affecting staff doses

Scattered dose rate is higher near the area into which the

X-ray beam enters the

patient

0.3 mGy/h

0.6 mGy/h

0.9 mGy/h100 kV

11x11 cm

1m patient distancepatient thickness 18 cm

1 mA

ANGLE DEPENDENCE

80

Scattered dose rate is lower when distance to the patient increases

100 kV

11x11 cm

1 mA

mGy/h at 1mmGy/h at 0.5m

DISTANCE VARIATION

Factor affecting staff doses

81

Tube undercouch position reduces, in

general, high dose rates to the specialist’s eye

lens1.3 (59%)

2.0 (91%)

2.2 (100%)100 kV

20x20 cm

1m patient distance

1 m

1 Gy/h

(17mGy/min)

mGy/h

1.2 (55%)

X-Ray tube

1.3 (59%)

1.2 (55%)

1.2 (55%)

100 kV

20x20 cm

1m patient distance1 m

1 Gy/h(17 mGy/min)

mGy/h

2.2 (100%)

X-Ray tube

Factor affecting staff doses

Mobile Concerns

• Audible indicator

• Cumulative timer visible on the monitor

• Video storage

• Last frame hold

• Longest possible TPD

Notes for Chapter 6Pediatric 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 7Mobile 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 8Responsibilities 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

90

CURTAINTHYROID

SCREEN AND GOGGLES

Protection Devices

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 9Supervision 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 10Health 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 11Biological Effects and Significance of Dose

• Effects appear to follow a linear non-threshold 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

ThresholdNon-linear

Non-thresholdlinear

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 12Personnel 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 13Personnel 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 DoseFor 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

General public Limited to 0.1 rem/year (Addition to the background radiation)0.002 Rem (2 mrem) per hour

Whole Body – 5rem/yearExtremities – 50rem/yearEye – 15rem/yearPregnant workers – 0.5rem/gestation period

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

0

1000

2000

3000

4000

5000

mre

m/y

r

MPD Cardio. Pain Mgnt.

X-Ray Tech

Typical Exposures