QA and Safety Flashcards
Where do QA guidelines come from? (3 marks)
BMUS, IPEM, NEMA, IEC.
What basic QA tests are there? What is the wire test for? What is a hydrophone used for? (5 marks)
Basic QA = lateral and axial res, slice thickness, caliper accuracy, penetration, CNR.
Wire tool test is to test for element drop out and is performed simply by running a wire along parallel to the elements along the face of the transducer. There should be reverberation patterns if the elements are working correctly and nothing detected if they are not.
Hydrophone is used to show the field characterisation, spatial and time intensity.
Where do the safety indices come from? (2 marks)
From ODS from NEMA. The output display standard.
Explain what is meant by the TI and what limits are there on this? How does the time taken for adverse effects to occur vary with temperature? (9 marks)
TI = delta W / delta W_0 (power in over the power required to get a 1C temp rise.
It is an indication on the likely worst case temperature rise, not the actual temp rise.
There are limits on the value from the FDA of 6C for general applications and 1C for opthalmology.
There are three different types of TI:
- TIC for cranial.
- TIB for bone or 2nd/3rd trimester.
- TIS for soft tissue and first trimester.
The graph for time taken for adverse effects from increases in temp is linear between 37 and 43 degrees with an equation of t=4^(43-T).
Above 43 deg there is a break-point where the time decreases dramatically, t = 2^(43 -T).
Explain the MI and what are the limits on the MI values from the FDA? (9 marks)
MI = p_- / f^0.5
p_ is the peak rarefractional pressure derated at 0.3 dB/MHz/cm
f is the centre frequency in MHz
MI is an indication of potential damage from microbubles and cavitiation effects. It is more likely when contrast agents are used as they consist of micro-bubbles.
Limits from the FDA are 0.23 for opthalmology or 1.9 for general.
What are the temperature rise limits from the IEC? (3 marks)
In air the transducer temp cannot go above 50 deg, or 43 deg in tissue, internal or externally.
How can ALARA be applied? (4 marks)
Use freeze mode. Turn power settings down from presents if they are too high. Be careful when using doppler mode. Minimise TI and MI. If temp rise kept below 39 deg and 38.5 deg (fetal) then should be safe.
