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Page 150 Kimbowa et al. Art Int Surg 2024;4:149-69 https://dx.doi.org/10.20517/ais.2024.20

INTRODUCTION
Ultrasound guidance lies at the heart of many minimally invasive procedures that require percutaneous
needle insertion. Applications can include minimally invasive localized anesthesia, tissue biopsy, central
venous cannulation, percutaneous drainage, and therapeutic delivery . Guidance ensures that the needle
[1-3]
reaches its intended target without unnecessary pricking of tissue along the way, improving procedure
efficacy and minimizing postoperative complications. Ultrasound is the gold standard for needle
visualization vis-a-vis patient anatomy owing to its safety (it does not use ionizing radiation), real-time
nature and often low cost [2,4,5] .

However, ultrasound needle guidance demands expertise and is challenging, especially for less trained users,
[6]
as in resource-constrained settings such as rural and remote communities . The two major challenges with
ultrasound needle guidance include: (1) aligning the needle with the ultrasound beam, and (2) visualizing
and localizing the needle within the ultrasound image even when properly aligned . Traditionally,
[6]
clinicians employ various handheld techniques to enhance needle visibility, including scanning the
ultrasound probe over the patient’s skin by sliding, rotating, or tilting the transducer to align the needle with
the ultrasound beam signal. The visualization of the needle and its trajectory can also be improved by
moving the entire needle in a short in-and-out or side-to-side motion, or by using hydrolocalization
techniques where a fluid or an ultrasound contrast agent is injected throughout the needle to create a
contrast on the ultrasound image . However, movements of the entire needle could result in unintentional
[6-8]
tissue structural damage if the needle is not visualized, and microbubbles formed during hydrolocalization
can lead to acoustic shadowing and consequently obscure the image of target structures .
[6]

Various approaches have been proposed to address aligning and localizing the needle within the ultrasound
plane, but a review of the broad literature available is necessary to advance research on this topic. Scholten
et al. provided an extensive review on needle tip visualization and localization but focused mainly on
[9]
hardware-based methods . In contrast, Yang et al. gave an extensive review on medical instrument
detection, including needle detection, but only focused on software-based methods with a general outlook
on medical instrument detection, including catheters that have different acoustic properties from
needles . Beigi et al. reviewed both hardware-based and software-based methods but did not discuss the
[10]
underlying challenges with ultrasound needle guidance nor provide a thorough synthesis of the existing
approaches .
[11]

Given the broad range of literature on the topic of needle visualization and localization in ultrasound [9-13] , it
would be helpful to have a compact review of the development of different methods, the motivation behind
them, and the state-of-the-art performance. The main contributions of this review are: (1) we provide a
physics foundation of the exact challenges of needle detection in ultrasound; (2) we provide a concise review
of the existing methods with a focus on learning-based methods; (3) we compare and contrast the
performance of such methods over time; and (4) we highlight promising directions for future research on
needle detection in 2D ultrasound. This review could serve as a reference for further research in a more
focused direction.

NEEDLE APPEARANCE IN ULTRASOUND
An ultrasound transducer consists of an array of piezoelectric elements that generate high-frequency sound
waves, which are then transmitted into the body. For ultrasound transducers used in needle interventions,
these sound waves range from 3 to 15 MHz . Upon hitting tissue boundaries along the line of transmission,
[6]
the sound waves are reflected as echoes, which are received by the piezoelectric elements. The time delay
between transmission of the sound wave and reception of the echo is used to determine the depth of the