Although ultrasound-guided percutaneous nephrostomy is relatively safe, a number of factors make it challenging for inexperienced operators. A computerized needle navigation technique using tracked ultrasound snapshots was investigated to determine if performance of percutaneous nephrostomy by inexperienced users could be improved.
Ten operators performed the procedure on a phantom model with alternating needle guidance between conventional ultrasound and tracked ultrasound snapshots. The needle was reinserted until fluid backflow confirmed calyceal access. Needle trajectories were recorded using the real time needle navigation system for offline evaluation of operator performance. Recorded needle trajectories were used to measure needle motion path length inside the phantom tissue, number of reinsertions, total procedure time, and needle insertion time as end-points of this study.
Needle path length measured inside the phantom tissue was significantly lower with ultrasound snapshots guidance (295.0 ± 23.1 mm, average ± SEM) compared to control procedures (977.9 ± 144.4 mm, p < 0.01). This was associated with significantly lower number of needle insertion attempts with ultrasound snapshots (average 1.27 ± 0.10 vs. 2.83 ± 0.31, p < 0.01). The total procedure time and the needle insertion time were also significantly lower with ultrasound snapshots guidance.
Tracked ultrasound snapshots appear to improve the performance of percutaneous nephrostomy in these preliminary investigations, justifying further validation studies. The presented navigation system is reproducible due to commercially available hardware and open-source software components, facilitating its potential role in clinical practice.

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Ungi T, Beiko D, Fuoco M, King F, Holden MS, Fichtinger G, Siemens DR. Tracked ultrasound snapshots enhance needle guidance for percutaneous renal access: A pilot study. Journal of Endourology (In press)