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Page 4 of 8 Magaribuchi et al. Mini-invasive Surg 2024;8:6 https://dx.doi.org/10.20517/2574-1225.2023.81

Various methods have been researched to adjust navigation to organ movement and deformation. However,
most reports involving 3D navigation during renal PN use rigid models, which do not accommodate
[14]
deformation. Reports that employ deformable, non-rigid models are rare . Even fifteen years after
[25]
Ukimura et al. reported in 2008 about navigation for renal PN using a 3D model , manual navigation
using a rigid model remains the norm. To achieve more accurate 3D navigation, it is crucial that methods
able to cope with organ deformation and movement become widely available.

Despite most methods reported for actual renal PN using rigid models, a multitude of research has been
done to accommodate organ deformation and movement. From here, we will focus on AR, where the most
significant technological advancements are expected, and introduce its research contents [Figure 2].

Manual registration
The simplest method is manual registration, adopted from early stages due to its low technological
[25]
barrier . There have been reports proving its effectiveness in actual surgery [14,39,40] . Most of these studies
lack a comparative counterpart, but Porpiglia et al. conducted a retrospective study comparing an AR group
[27]
of 48 cases with a control group of 43 cases guided by ultrasound . They demonstrated a significant
reduction in the total arterial clamping rate, a reduction in the urinary tract opening rate, and a similar
complication rate.

Fiducial-based registration
Fiducial markers serve as landmarks for registration, commonly used in 3D navigation in fields such as
otolaryngology. For navigation during renal PN, these markers placed in the kidney can accommodate
organ movement and deformation. Unlike in otolaryngology, kidneys move, so markers need to be placed
in the organ itself rather than fixed landmarks such as the body surface. Animal experiments with pigs have
reported kidney bleeding due to markers embedded directly into the kidneys to prevent movement .
[41]
Conversely, studies reported safe execution of AR navigation using fiducial markers in LPN [28,31] . Adhesive
markers have also been proposed to allow non-invasive fiducial-based registration without inserting
markers into the target organ [42,43] .

Additional methods utilized in actual surgeries
Porpiglia et al. implemented surgical navigation with nonlinear parametric deformation and reported its
effectiveness compared to a group guided only by 2D ultrasound . Nonlinear parametric deformation can
[27]
accommodate complex operations such as bending, stretching, and twisting, allowing for more realistic and
natural movements and shape changes. While registration was performed manually, using this technique in
3D navigation for RAPN significantly improved surgical outcomes compared to the group guided only by
2D ultrasound. Kobayashi et al. reported a method using an infrared reflective marker placed on the camera
and tracked with an optical sensor in 2020 . Initially, the surgical scene was manually registered with the
[44]
3D model, and then the camera movement was tracked to maintain navigation accuracy. This method
reportedly yielded effective treatment results in actual RAPN procedures. Amparore et al. have reported on
effectively using selective clamping of blood vessels by evaluating kidney blood flow using indocyanine
green (ICG) and combining this with AR . Blood flow areas of the 3D kidney model, created from CT, are
[30]
color-coded using a Voronoi diagram, and compared with blood flow areas confirmed intraoperatively with
ICG injection. This method does not directly enhance registration accuracy in response to organ
deformation or movement but successfully improves navigation accuracy by enhancing the precision of
blood flow evaluation.