Ultrasound guidance can improve accuracy for needle biopsies, vascular access, nerve blocks, administering anaesthetic, or steroid or medicine delivery for musculoskeletal (MSK) and podiatry applications. Through visualisation of surrounding structures, it can also improve procedure safety.
However, it is a difficult skill to master, and requires a lot of practice. To aid with this, manufacturers of higher end systems offer needle guidance software on their machines – for example, on the Apogee 1000 Lite. As well as optimising machine controls (turning on spatial compound imaging and often turning off tissue harmonic imaging), this algorithm electronically steers the ultrasound beam to make it as close to perpendicular to the needle as possible (Cheung & Rohling, 2004).
Above left: Before needle enhancement is active. Above right: After activating needle enhancement on the Siui Apogee 1000 Lite.
Performing ultrasound-guided needle procedures
The needle can be advanced in plane or out of plane. Either approach is equally valid. The in-plane approach results in the needle being seen advancing across the imaging plane, as you might expect. This is more difficult than it sounds because the beam width is very narrow. Visibility can be improved by approaching at a shallower angle (with the needle at 90° to the beam being optimal), in order to maximise the amount of reflected energy that returns to the probe. This is because the needle is a smooth, specular reflector – think of it like a mirror. With the needle at 180° to the beam, there is no surface for the ultrasound to reflect off. At close to 180°, any reflections will be directed out of plane, and will not return to the transducer. Where deeper nerves are being targeted and an angle close to 180° is inavoidable, the operator can press one side of the transducer deeper into the skin to help to adjust the angle.
If you do not have needle enhancement on your scanner, the following will improve visibility:
- Turn spatial compounding on (if you have it). This allows the ultrasound machine to acquire multiple images of the same region from slightly different angles, and sum them together. This eliminates artefacts as they won’t be present from one angle to the next (they’re not “real”), but strengthens the signal of genuine reflectors, like your needle.
- Turn tissue harmonic imaging off. THI has been shown to worsen needle visibility (Chin et al., 2008), possibly because of the fact that it narrows an already very thin beam even further (Reusz et al., 2014).
- Use echogenic needles. It is possible to obtain needles designed specifically for visualisation on ultrasound. They are made with rough surfaces (on the scale of a wavelength) so that they scatter ultrasound energy in all directions, increasing the amount of energy that returns back to the transducer, regardless of angle of incidence.
The out-of-plane approach involves positioning the transducer over the target region, entering the skin to the side of this area and looking for the needle tip as it enters the imaging plane (and therefore the target). There is some evidence to suggest that this approach is easier for beginners, but the downside is that you do not see the whole needle at once. If you are not confidence in fanning your probe, you may find it difficult to identify the tip of the needle, as it will not look any different from this projection to the shaft.
If you are considering purchasing an affordable MSK ultrasound machine, please get in touch. We are approved NHS suppliers, and have extensive experience supplying hospitals, universities and research teams in both human and veterinary medicine.
Cheung, S., Rohling, R. (2004). Enhancement of needle visibility in ultrasound-guided percutaneous procedures. Ultrasound Med Biol. 30(5):617-24.
Chin, K. Perlas, A., Chan, V., Brull, R. (2008). Needle Visualization in Ultrasound-Guided Regional Anesthesia: Challenges and Solutions. Regional Anesthesia and Pain Medicine, Vol 33, No 6: pp 532–544.
Reusz, G., Sarkany, P., Gal, J., Csomos, A. (2014) Needle-related ultrasound artifacts and their importance in anaesthetic practice. BJA: British Journal of Anaesthesia, Volume 112, Issue 5, Pages 794–802.