rad protection unit 3

protective tube housing

lead lined metal that protects personnel and patients from leakage and off focus radiation

cannot exceed 1 mGy per hour at 1m away from housing (Air Kerma of 0.88mGy/hr)

control panel/console

technologist workspace where you can set up the console, technique, and take the exposure

properly shielded barrier

exposure button must be affixed to the console so the exposure cant be taken in an unshielded area

displays when the x-ray tube is energized

kVp (kilovoltage peak)

maximum possible energy of a photon that exits the x-ray tube, unit selected on the operating console

indirectly proportional to patient exposure

mA (milliamperage)

measurement of x-ray tube current or the number of electrons crossing the tube from cathode, unit selected on the operating console

directly proportional to patient exposure

mAs (milliampere seconds)

controls the amount of radiation produced by the x-ray tube

mA X seconds = mAs

directly proportional to patient exposure

AEC (automatic exposure control)

exposure will terminate when a predetermined amount of radiation is reached for the selected body part

can only be used on body parts big enough to cover the cells

back up timer for patient safety

x-ray room design

table must adequately support patient and be uniform density

SID must be accurately measured (digital or tape measure)

beam limiting devices

limits the primary beam to a smaller area

decreases exposure by reducing the amount of tissue that is exposed to radiation, reduces scatter

types of beam limiting devices

• aperture diaphragm

• cones

• collimators

aperture diaphragm

flat lead with a shape and size cut into it that is placed below the window, reduces scatter

• rectangular (most common)

• square

• round

cones

circular metal cylinders connected to the tube housing that limits the size of the beam, can be flared or straight

extensive cylinders - can be telescoped 10-12 inches for smaller exposure area

mostly used in dental radiography but can be used for the heel, skull, and spine imaging

collimators

light-localized variable aperture rectangular collimator

must be bright enough to outline the anatomy to include

most versatile beam restriction - can change sizes

reduces exposure by 20-30%

should not be larger than the size of the image receptor

what are collimators

2 sets of shutters 90 degrees from one another

near (upper) shutters

located close to the window, reduces exposure from off focus radiation

far (lower) shutters

located closer to the light source, confines the beam to the area of interest

skin sparing

minimizes skin exposure by requiring a 15cm distance from the skin to the collimator

can be achieved with spacer bars mounted on the tube

PBL (positive beam limitation) (automatic collimation)

electronic sensors in the bucky that senses the image receptor size that you are suing and opens the light field to that size - can be slits or pegs

reduces user errors by matching the light field to the image receptor size

required to be within 2% accuracy

collimation → scatter/dose

increased collimation → smaller scatter/dose

decreased collimation → larger scatter/dose

filtration

hardens the beam by cleaning up the low energy x-rays

reduces the skin and superficial exposure to the patient - decreases patients absorbed dose because the remaining photons and higher energy

2.5mm Al for units operating above 70kVp

inherent filtration

0.5m Al equivalent

glass envelope, insulating oil, and glass window

added filtration

2.0mm Al equivalent

sheets of Al added outside the glass window above the collimator shutters

accessible by service person, can be changed as the tube ages

mobile & fluoro filtration

2.5mm

NCRP 102

list minimum required filtration for x-ray equipment

diagnostic x-ray beam must always have adequate filtration

intensity decreased

1 HVL - 50%

2 HVL - 25%

3 HVL - 12.5%

4 HVL - 6.25%

HVL

insufficient HVL test could mean improper filtration

must get tested

measures beam quality or effective energy of the beam

measured at least once a year by a physicist or if the tube is replaced or repairs are made

TVL (tenth value layer)

thickness that will decrease the intensity of the beam by 1/10

compensating filters

used when x-raying a part that has varying thickness to reduce dose and provide a uniform density across the image

decreases the entrance skin exposure (ESE)

constructed of aluminum or lead-acrylic that is attached to the bottom of the collimator

types of compensating filters

• wedge filter

• trough filter or bilateral wedge

• ferlic

• boomerage

wedge filter

used for foot and spines

trough filter or bilateral wedge

used on chest x-rays, thicker on both sides and thin in the middle

ferlic filter

used on hips

boomerang filter

used on shoulders

radiation protection - testing on equipment

exposure reproducibility - system must duplicate exposure when taken at the same exposure - variance 5%

exposure linearity - system must consistently produce radiation output when mA and time are changed - variance 10%

radiographic grids

material is parallel radiopaque material of very thin lead, aluminum, or plastic fiber

removes scatter and improves visibility of detail

increases patient dose

when should you use a grid

thickness is over 12cm at 60 kVp or higher

grid ratio

height of lead strip divided by distance between strips

mobile radiography

minimal source to skin distance on a mobile fluoroscopy unit is 12 inches (30cm)

only perform portable x-ray on patients that cannot be transported to the department

digital imaging

utilization of technique charts

grids

has lower doses, immediate images, image manipulation, less maintenance

fluoroscopy

continuous radiation that shows dynamic motion, largest exposure to patients in diagnostic radiology

image intensification

increases brightness on screen

source to skin distance

15 inches (38 cm) for fixed units

12 inches (30 cm) for mobile units

cumulative timing device

audible alarm or interrupt of fluoro every 5 minutes of time

technologist is responsible to record the fluoro time and dose in medical record

federal regulations tabletop exposure - fluoroscopy

88 mGy per minute

ABC/ABC (automatic brightness control/stabilization)

no matter the kVp or mA varying, the brightness of the image remains the same

AERC (automatic exposure rate control)

adjusts exposure factors automatically as the beam moves over varying thicknesses

fluoro exposure switch/dead man switch

foot pedal requires direct pressure to continue fluoro exposure

c-arm fluoroscopy

used in the OR, cardiac cath, and IR

12 inch (30 cm) minimal distance to the patient

should be positioned with the image intensifier on the top - reduces scatter and patient dose

digital fluoroscopy

beam turns off while image is scanned and then turns back on - pulsed

dose area product (DAP)

last image hold

DAP (dose area product)

newer fluoro systems provide the sum of the air kerma (energy) over the exposed area of the patient

last image hold

when the foot comes off the pedal, it holds the last image and displays it on the screen until the foot pedal is activated again

digital subtraction angiography (DSA)

used in interventional and vascular

used to visualize occlusions, stenosis, or aneurysms

uses software to remove the superimposing anatomy so you only see the area of interest

interventional radiology

invasive sterile procedures performed by a physician under fluoro

FDA requires documentation in the chart if skin dose is 1-2 Gy

federal regulations for table-top exposure for high level control fluoro (IR)

176 mGy per minute

equipment safety

• on and off switches

• interlocks - detents & fluoro locks

• visual/audio monitors - control panel, laser light, tae measures

• emergency controls

holistic patient care

treat the patient as a whole person rather than a body part

makes patients feel more respected, comfortable, and more willing to cooperate

patient motion

involuntary & voluntary

involuntary motion

caused by muscles, not controllable

heart & digestion

manifestations that can cause involuntary motion

• chills

• tremors

• spasms

• pain

• active withdrawal

voluntary motion

controlled motion, can be caused by

• patients age

• breathing patterns

• anxiety

• physical or mental discomfort

• fear of exam/prognosis

• mental instability

how is involuntary motion corrected

decreasing exposure time and increasing imaging receptor speed

how is voluntary motion corrected

gaining patient cooperation and use of proper immobilization

immobilization

• piggostat

• papoose/octostop

• sponges and sandbags

• mummy wrap/bunny wrap

---

• tape

• velcro straps

• radiolucent plexiglass

• non-radiology employee helping to hold

sponges

radiolucent

sandbags

radiopaque

what did the AAPM state in April 2019

shielding of patient gonadal or fetal shielding during diagnostic imaging should be discontinued

what committee was created after the statement made by AAPM

the CARES committee (communicating advances in radiation education for shielding)

who supports the statement made by the AAPM

• NCRP

• ACR

• ASRT

• ARRT

radiosensitive organs

• lens of eye

• breasts

• reproductive organs

2 types of shielding

gonadal & specific area

gonadal shielding

could use unless covering the area of interest

shield cannot be in the collimation if AEC is being used

what is the first step for gonadal protection

proper collimation

females receive ___ more exposure than males

3X

flat shields

most effective in the AP or PA recumbent positions

shadow shields

careful to place properly or a repeat image could be caused

not suitable during fluoro

shaped shields

contoured to enclose the male reproductive organs

can be placed by the patient

cannot be used during PA projections

clear shields

transparent lead-plastic material

lap shields (half)

covers only the front or back half of the patient, attached with a velcro strap or on wheels

specific area shields

• eyes

• breast

• thyroid

• gloves

what type of kVp and mAs is best for reducing patient exposure

high kVp, low mAs

high kVp and low mAs

ensures adequate anatomy is penetrated & minimizes dose

technique books

provide an average technique for body part/equipment

AEC needs to be properly functioning

the higher the kVp, the ____ the entrance skin dose

lower

penetrated radiation

radiation that has passed through the body and hit the image receptor

absorbed radiation

radiation that has hit and stopped in the body part

scatter radiation

radiation that has hit the body part, but has scattered outside the body part into the air

exposure index

the number that is found on the image after processing that measures receptor exposure

should be in range for the equipment parameters to be a good diagnostic image

100-300 in the lab

what does under exposure cause

quantum noise (grainy appearance) & should be repeated

what does over exposure cause

will appear as a good image in most cases

in extreme cases, will cause saturation & should be repeated

correct positioning

inadequate processing of image results in repeats

artifacts caused by image receptor, software, or patient related

quality control program

monitors that suboptimal images are not being produced

what are quality control programs looking/watching out for

• repeats

• unnecessary patient dose

• incorrect projections being taken

• machines are working properly - would affect all images taken if not

what is an alternative to using a grid to clean up scatter

air gap technique

air gap technique

patient is placed 4-6 inches (10-15 cm) away from the image receptor with a 10-12 feet (300-366cm) SID

what is a con regarding the air gap technique

there is an increase in magnification and is not useful if the kVp is higher than 90

repeat image

any image that must be done more than once due to human or mechanical errors

patient receives a “double dose”

repeat images are unacceptable if done due to…

carelessness or poor judgment

• positioning

• technique

reasons for unacceptable images

• patient mispositioning

• incorrect centering of the beam

• patient motion during exposure

• incorrect collimation of the beam

• presence of external foreign bodies

• post-processing artifacts

chest x-rays

• pre-admission

• pre employement

• routine health check ups

• screening for TB

lumbar x-rays

pre employment

CT whole body scans

check for disease