Needle-related ultrasound artifacts and their importance in anaesthetic practice

Real-time ultrasound guidance for any intervention relies on visualization of needle advancement towards a target. Unfortunately, correct identification of the needle tip is not straightforward, as artifacts always distort the image. The ultrasonic appearance of the needle is often degraded by reverberation, comet tail, side-lobe, beam-width, or bayonet artifacts, which can easily confuse an unprepared operator. Furthermore, the typical needle image, that is, a dot or a straight line (out-of-plane and in-plane approaches, respectively), is also a result of artifacts that hide the real dimensions of the needle. Knowledge and correct interpretation of these artifacts is important for safe practice and is paramount to success when precise needle manipulation is mandatory, for example, when the target is small. In this review, authors discuss the most important needle-related artifacts and provide a physical explanation focusing on implications for everyday practice. Recent advances that allow increased needle visualization and reduction of artifacts are also discussed.