2. Non-vis rates……….
Myths
Sonosite machines have higher non-vis rates than GE machines
• The non-vis rates are very similar
• The sonosite has less functionality
• One of the reasons for it being chosen
• Newer machines do have better imaging at depth but not sufficient to
warrant new machines as yet
Areas with high non-vis rates have higher levels of obese patients
• All screening programmes have mixed degrees of socio-economic and
ethnic backgrounds
• Very similar across the country
• No obesity epidemic within Oxfordshire
Part time staff have higher non-vis rates than full time staff
• Very similar rates across the programmes
• May take longer time to stabilise once training has been completed
3. • High non vis rates are usually down to technician
confidence at measuring the aorta at depth
• National average is 1.43%
• Achievable standard is 3.0%
• NAAASP are looking at reducing the threshold for non-
visualisation
5. How to improve the images…..
• What’s the point?
• Hopefully reduce the non-vis rates
• Provides a better service to the subjects being screened
• Improves performance and cost effectiveness of the programme
• Ensures that the screening programmes and technicians are
providing a quality service to the community based on quality
standards that can be measured
• May seem like a blunt tool
• Every image should be optimised before taking a measurement
• The images on obese patients will never be as good as those on
slimmer patients
• Use the non-vis guidance
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6. • Increase depth
• Sounds counter intuitive
• Sonosite machines have the focal zone in the middle of the screen
• Decrease the dynamic range
• Reduces the number of shades of grey and therefore should help
highlight the vessel walls
• Can be reduced to -3 in obese patients on sonosite
• Alter as much as required on the other machines
• Reduce the frequency of the
probe/ultrasound
• Reducing the frequency of the probe will increase the wavelength
• Improves penetration
• Reduces image quality
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7. • Remove harmonic imaging
• Improves the frame rate
• US machine has to wait less time before acquiring the
image
• Can make image worse
• Remove compound imaging
• Improves frame rate
• Can make image worse
• Always adjust the gain when taking this on or off
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8. • Press harder
• Brings aorta nearer to the probe
• Mindful of patient comfort level
• Image in transverse
• Easier to image in transverse
• Think of transverse as your friend
• If you get stuck rotate probe
• Don’t get obsessed with anterior vessels or
IVC
• Might not see them in obese patients
• 50% visualisation rate
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9. • Use two hands to press the probe down
• Mindful of MSK injury
• Get colleague to freeze
• Get patient to breath in and hold breath
• Relaxes the diaphragm
• Push probe down when breathing in
• Stop the scan
• Get colleague to have a look
• 2 mins away can give you different perspective
• Know your limitations
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10. Hints and tips
Increase depth
Decrease dynamic range
Reduce frequency of the probe
Remove harmonic imaging
Remove compound imaging
Press harder
Transverse imaging
Anterior vessels
Use two hands
Get patient to breath in, hold it and then breath out
Ask colleague to look/take a break/know when to stop
Tell patient to wait outside
