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Page 154 Kimbowa et al. Art Int Surg 2024;4:149-69 https://dx.doi.org/10.20517/ais.2024.20

Therefore, there remains a need for a better system for needle tip localization that does not involve the
excess costs associated with modifying all new needles.

Needle tracking
Needle tip tracking can be accomplished optically by tracking markers on the needle shaft. Briefly, an
optical camera is affixed to the ultrasound transducer and tracks the markers as the needle penetrates the
skin and deeper tissue. Simultaneously, a tracking algorithm predicts the trajectory of the needle tip by
calculating the relative position of the needle to the transducer [37,38] . In a pediatric central venous catheter
placement feasibility study, two stereo cameras fixed to the transducer predicted the catheter trajectory and
led to a 90% successful central vein cannulation on the first pass. However, no statistical results on whether
[39]
this method improved catheter placement were assessed in the study . The main drawback of an optical
tracking approach is that the system assumes that the needle tip does not bend during surgery. Acoustic
sensors, such as fiber-optic piezoelectric hydrophones, have been developed to facilitate physicians to
localize the needle within the ultrasound image [40-42] . These sensors are integrated into an intraoperative
needle to measure the time difference between sound emission by the ultrasound transducer and reception
[40]
at the needle tip . In bovine phantoms, the accuracy of fiber optic hydrophones was found to be within
1 mm between tracked and labeled positions, and its tracking performance was independent of needle
insertion angle . In a porcine phantom, anesthesiologists found that using acoustic sensors reduced the
[41]
[42]
procedure time and the number of hand movements in out‐of‐plane peripheral nerve block procedures .
A similar approach to hydrophones is using a photoacoustic emitter at the needle tip. A pulse laser is
transmitted through an optical fiber onto a photoacoustic material which transforms light into acoustic
sound waves at the needle tip. The produced sound waves are then detected by the ultrasound transducer
[43]
and the needle tip can be localized in real time . In a phantom simulation study, anesthesiologists,
residents, and medical students watched videos of needle tip placements: two successful and one failed, with
and without the photoacoustic emissions. Failure of needle placement was identified with 100% across all
participants for both in-plane and out-of-plane approaches . However, the efficacy of photoacoustics in
[44]
clinical practice remains to be determined.

Another approach that can help the localization of the needle in an ultrasound image is to use a filament
sensor embedded in the needle. Briefly, the sensor induces a small current which can be detected by an
electromagnetic measuring device [45,46] . The needle tip position is then triangulated and projected onto the
ultrasound image. In a clinical study, electromagnetic needle tracking was shown to reduce the number of
[47]
needle reinsertion and shorten block performance time in out-of-plane approaches . Moreover, in
percutaneous liver biopsies, the spatial accuracy of the needle tip displayed electronically was within 2 mm
[48]
from the real position seen on the ultrasound image . However, the magnetic interference caused by
surrounding magnetic tools and the required proximity of the field generator to the procedure are
limitations for such a system. Although prototypes have been developed to integrate magnetic sensors into
the transducer to reduce the additional equipment needed [49,50] , such solutions still require magnetizing the
needles instead of using standard operative needles.

Software based methods
Software-based methods for needle visualization and localization can be categorized into three: (1) image
acquisition methods; (2) classical image processing methods; and (3) learning-based methods. In this
section, we briefly describe these methods.

Image acquisition
Currently, the image acquisition method used to improve needle visualization is beam steering, in which the