Fluoroscopy Ch 36

List Fluoroscopic Protective Features

1. Source to skin distance

2. primary protective barrier

3. filtration

4. collimation

5. exposure control

6. Bucky slot cover

7. lear apron/apparel

8. protective curtain

9. Cumulative time

10. Last image hold

What is Source to Skin distance requirment?

federal requirement

SSD stationary unit

not less than 38 cm (15 inches)

SSD mobile unit

not less than 12in (30cm)

Primary Protective Barrier is?

Barrier of attenuation materials used to reduce radiation exposure

What does Primary Protective Barrier protect from

protects from useful beam

Ex of Primary protective barrier?

wall, floors, ceiling

Filtration

functions to abdorb low energy photons (soft x-ray)

Total filtration

must be at least 2.5mm Al equivalent

What does filtration do?

reduces patient dose

What are x-rays make it through filtration?

high energy (hard x-rays)

Collimation

beam restricting device

How should the boarders be for collimation?

unexposed boarder must be visible at 35cm above tabletop with collimator fully open

Exposure Switch

Dead man type - terminated exposure when pressure is released

How long should the exposure switch be?

cord must be at least 6 feet long

Bucky Slot Cover during fluoro exam

Tray must be moved to the end of the table

What is the minimum lead for Bucky Slot Cover

should be 0.25 mm of lead

Lead Apparel

Should be worn during all fluoro procedures

Protective Curtain should be positioned where?

Should be positioned between the fluoroscopist and patient

Minimum lead for Protective Curtain

should be at least 0.25 mm of lead

Primary purpose for Protective Curtain

reduces scatter from patient

When should the protective curtain be removed?

during a sterile procedure

Cumulative Timer produces?

Produces an audible signal when fluoro time exceeds 5 min

Last Image Hold (LIH)

Displays last fluoro image shown after beam has been shut off

T/F LIH reduces patient dose

True

What is mandated to have on modern equip?

LIH

When is LIH used?

used in OR and pediatric studies mostly

Types of Radiation

1. Primary - useful beam

2. Secondary

• Leakage Radiation

• Scatter radiation

Leakage Radiation

Emitted from tube housing isotropically

What is the limit for leakage radiation?

not to exceed 100mR/hr at 1 meter

who is the main source of Scatter Radiation ?

patient is main source of occupation exposure during fluoroscopy

How is scatter radiation produced?

primarily by compton interaction

What helps to minimize radiation exposure

under table tubes

What are increasing factors that affect scatter?

• high kVp

• large field size 

• thick body part

Primary Barriers

a barrier to attenuate the useful beam

What is most often used with Primary Barriers?

Lead bonded to sheet rock or wood paneling most often used

Primary Barrier: what can be used as alternate to lead

Concrete or steel can be used as alternatives to lead for primary barriers.

height required for primary barrier

must be at least 7 feet tall; rule of thumb - 4in of masonry = 1/16in of lead

Secondary Barrier

A barrier to attenuate leakage and scatter radiation

How much less is Secondary than Primary Barrier?

less thick than primary barriers (1/32in)

What is not required in Secondary barrier?

Lead not required, usually gypsum board, glass or lead acrylic is used

What does Protective Barrier Thickness depend on

Depends on distance (distance adjacent to occupied area, not inside of walls of x-ray room)

Areas in department

1. Controlled Area

2. Uncontrolled Area

Controlled Area 

Occupied by x-ray personnel and patients

What are controlled areas limits based on?

based on proportionate weekly exposure (radiology personnel and patient

What is the exposure rate for controlled area?

exposed rate must be less than 100mrem (1sV/wk)

Uncontrolled Area

Can be occupied by anyone

What are uncontrolled areas limits based on?

can be occupied by anyone (hallway, hospital staff other than radiology)

What is the exposure rate for uncontrolled area?

Exposure rate must be less than 2mrem/wk

What is Workload?

greater number of exams done each week = the thicker the shielding required

use factor (u) = ?

percentage of the x-ray beam is on and directed toward a particular wall

kVp (penetrability) depends on

kVp used in exam room

NCRP recommends

¼ use factor - wall

1 use factor - floor

Personnel monitoring devices

1. Thermoluminescence dosimetry monitor radiation exposure

What is dosimeter made of?

crystals are made up of lithium fluoride

What is the process of personnel monitoring dosimeter?

Once exposed to ionizing radiation and then heated, these crystals five off light depending on amount of radiation received. 

NCRP #1 16 recommends (re:dose)

a max annual effective dose limit of 50 mSv recommended to provide for annual exposure

What does OSL stand for?

Optically Stimulated Luminescence dosimetry

Steps for OSL

1. Exposed to ionizing radiation

2. laser illumination

3. measurement of the intensity of the stimulated light emission

What does OSL use?

Uses aluminum oxide as the radiation detector material

What is a pocket dosimeter aka

Pocket ionization chamber

Describe what a pocket dosimeter

Small pocket sized instrument thst discharged a capacitor by ionization of air with in the presence of ionizing radiation.

When is pocket dosimeter used?

used primarily when working with large amounts of radiation; gives a daily readingof ionizing radiation exposure.

What is pulsed fluoroscopy?

Uses short pulses of x-ray (5 msec or less) instead of constant output

T/F does Pulsed Fluoroscopy reduce patient dose?

TRUE; Reduces patient dose and occupational exposure

General Fluoro

30 pulse/sec

Pulsed Fluoro

15 pulses/sec

High Level (boost) fluoroscopy tube current?

Significantly higher tube current (10 to 40mA)

Where is high level fluoro used?

Used with Angiography and Cardiac studies

What is the max table top dose for High-level fluoro?

Max tabletop dose rate is 10 mrads/min unless recording devices are used

What alerts staff?

Audible alarm

What should always be documented?

Dose or time 

What is DSA?

Digital Subtraction Angiography

What is DSA used for?

Interventional study used to clearly visualize blood vessels in a bony or dense soft tissue environment

What is temporal Averaging Fluoroscopy?

Reduces signal to noise in a image by averaging current frames with one or more previous frames.

(if some body part is images for several seconds, all the frames will be averaged and the results is noise reduction)

What is pincusion?

caused by a curved input phosphor to a fla output phosphor

What is lag?

quality of vidicon tube (monitor) occurs because it takes a certain amount of time for image to build up and decay on vidicon target. This results in image blurring when camera is moved rapidly during fluoro

What us Quantum Mottle?

Grainy appearance

aka Noise

more apparent in high resolution systems

happens when not enough x-rays

Can noise be removed post processing?

no