CH.42 Flashcards
The rate of exposure is directly proportional to what?
The time exposed
Inverse Square Law does not apply to what?
Fluoroscopy
SCatter exposure at 1 meter from the patient is how much exposure to the tech?
1/1000th the patients beam exposure
Standing 1 meter away and wearing a lead apron will give how much exposure to the tech?
1/10,000th
This curve indicates that the least exposure to personnel is to the side of the table.
Iso-Exposure Curve
Radiation exposure to personnel is always the least at what angle to the central ray of the x-ray beam?
right angles
Which type of scatter is more intense, Backscatter or forward scatter?
Backscatter
This is the amount of radiation a person can receive with no significant somatic or genetic harm, it is for occupational dose only.
Dose Limit
95% of the radiographers occupational dose comes from what 2 areas?
Fluoroscopy and portables
This is defined as the summed total of the entrance exposure representative of the radiographic procedure.
Distributed Skin Exposure
This is the effective occupational dose limit.
Annual-50mSv
Cumulative- 10mSv * age
This is the equivalent annual dose for occupational workers lens of the eye dose limit.
150 mSv
This is the equivalent annual dose for occupational workers thyroid, skin, hands and feet dose limit.
500mSv
This is the effective dose frequent exposure limit for the public annually.
1 mSv
This is the equivalent dose limit of the publics lens of the eye.
15 mSv
This is the equivalent dose limit of the public skin, hands and feet.
50mSv
What is the annual effective dose for education and training exposures annually?
1mSv
What is the equivalent dose for education and training exposures to the tissues and organs?
lens of the eye- 15mSv
skin, hands, feet- 50mSv
Same as public exposures
What is the total equivalent dose limit for the embyro?
5mSv
What is the total equivalent dose for a fetus in 1 month?
.5mSv
What is the negligible individual dose limit annually?
.01mSv
For there to be fetal responses to irradiation there must be a very high dose of radiation greater than what?
25rad
Leakage radiation from the tube housing must be less than what?
100mR/hr at 1 meter
SID, Collimation and PBL must be accurate to what percent?
2% of SID (FFD)
What is the total filtration for tubes operated at over 70kvp, 50-70kvp, 50kvp?
over 70- 2.5mm
50-70- 1.5mm
below 50- .5
What are the 3 exceptions to the “dead mans” switch?
- portables
- FLuoro
- C-arm
The source to table top distance for fixed fluoroscopic units should not be less than what? for mobile units?
Fixed- 38cm or 15in
Mobile- 30cm or 12in
There is a 2mm lead equivalent barrier on the fluoro machine. at 100 kVp scatter from the patient is what at 1ft, 2ft, 3ft?
1ft- 500mR/hr
2ft- 100mR/hr
3ft- 50mR/hr
Lead aprons must be worn by anyone whose exposure may exceed what?
5mR/hr
What is the lead thickness required if a machine is routinely operated above 100kVp?
.5mm
What is the average ESE of most conventional fluoroscopes?
5R/min
What is the limit of ESE for conventional fluoroscopy?
10mA and 10R/min
How many frames per second are sent to the TV monitor in pulsed mode fluoroscope?
30 frames per second
What are spectral filters made of?
Copper or Copper/Aluminum
What is pulsed width?
Exposure time for each pulse
The fluoro procedure dose is affected by what 6 things?
- Mode used input phosphor diameter
- Selected mA
- OPeration in continuous vs pulsed
- Actual source skin distance
- Cumulative beam on time
- Number of “spots” taken
All fluoroscopy examinations should be performed with the x-ray tube where?
Under the exam table
What is the c-arm scatter radiation to the technologists eye/thyroid if the tube is under the table vs tube over the table?
12mR under table
60mR over table
What is the c-arm scatter radiation to the technologist gonads if the tube is under the table vs over the table?
27mR under table
25mR over table
Higher kVp increase the percentage of forward or backward scatter?
forward scatter
Why does keeping the II as close to the patients surface as possible reduce pt and operator exposures?
The II will intercept the primary beam earlier and allow less scatter to the operator.
What is the purpose of plastic “cones” on the collimator?
Prevents the x-ray tube from being brought closer than 12” to the pt
What are the 3 high-risk procedures identified by the FDA which present the “possibility of exceeding 100 minutes fluoro time at 2-5R/min using 5” or 7” mode”
- PTCA- Percutaneous Transhepatic Cholangiography
- RFAB- Radio Frequency Ablation
- STEN- Stent Placement
What is the most effective means the radiographer can use to limit radiation exposure to the patients?
Proper Collimation
Which grid ratio should be used that will provide sufficient clean up of scatter?
the minimum grid ratio able
Which speed class should be used to decrease exposure?
The highest speed class which does not present an unacceptable level of mottle.
Patients gonads must be shielded anytime they lay how close to the edge of a collimated beam provided diagnosis is not compromised?
5cm (2’)
What are the 4 types of shielding?
- Flat contact shields
- Shaped contact shields
- Shadow shields
- Contact lens and eye shields
What is the difference between lead aprons and gonadal shields?
lead aprons are used to shield from scatter radiation and has a lower lead equivalency, they are also secondary barriers.
