Stereotaxy is a surgical technique that establishes a Cartesian coordinate system, known as stereotactic space, anchored to the organ of interest, in order to reach specific anatomical targets with precision in minimally invasive neurosurgical procedures. The conventional frame-based approach relies on a localizer, used to define the stereotactic space during Computed Tomography (CT) acquisition, and on a stereotactic frame which, set to the coordinates of the surgical plan, guides the surgical instrument to the planned target. Preoperative CT and Magnetic Resonance Imaging (MRI) scans are ac-quired in the days before surgery, but on the day of the procedure a new CT scan is re-quired, with the localizer fixed to the patient’s skull, in order to define the stereotactic space and register these images to it; only then is the localizer replaced by the frame so that the procedure can be performed. This workflow has several limitations. Commercial frames can reach only one target at a time, making bilateral and multi-target procedures, such as stereoelectroencephalog-raphy (sEEG) and Deep Brain Stimulation (DBS), lengthy. Intraoperative CT exposes the patient to ionizing radiation and requires transfer to the CT suite, prolonging surgical time. Swapping the localizer for the frame can introduce repositioning errors. Finally, no system exists to quantitatively verify the frame’s final targeting error, leaving the pro-cedure exposed to human setting errors and mechanical inaccuracies. We therefore propose an optimized approach based on radiation-free 3D structured-light scanning (3DSS) of the patient’s face, which reconstructs the stereotactic space without intraoperative CT. In addition, a purpose-built stereotactic frame, the Navinetics E1, also serves as the localizer: scanned together with the patient’s face in the operating room, it defines the stereotactic space by itself, eliminating both the local-izer-to-frame exchange, with its associated error, and the transfer to the CT suite. The frame also has two pointing units: in the conventional Single Arm configuration they are joined into a single rigid structure and reach one target at a time, whereas in Double Arm mode they operate independently, one per hemisphere, allowing simultaneous bi-lateral targeting. Finally, the same structured-light imaging technique underlies a con-trol system that determines the coordinates of the target actually reached, detecting and compensating for both setting errors and mechanical inaccuracies. In Single Arm mode, the E1 frame prototype achieved a mechanical accuracy of 0.78 ± 0.38 mm, comparable to that of conventional frames. In Double Arm mode, accuracy was 1.23 ± 0.36 mm for the right hemisphere and 1.65 ± 0.47 mm for the left: values close to the 2 mm clinical acceptability threshold, yet promising for a prototype. The 3DSS-based approach, evaluated in 22 patients undergoing DBS, produced surgical plans that deviat-ed from CT-based ones by 0.80 ± 0.32 mm, well within this threshold. Finally, with the control system, a deliberate frame setting error of 7.07 mm was detected as 8.03 mm and reduced to 0.85 mm after correction; with the frame correctly set, a detected error of 1.73 mm fell to 0.60 mm. Although preliminary, these results suggest that the frame configuration can be verified and corrected before surgery. Overall, the system outlines a new paradigm for frame-based stereotaxy: faster, free of intraoperative radiation, suited to bilateral and multi-target procedures, and equipped with quantitative error verification, which allows even a 3D-printed prototype frame to approach the reliability of far more expensive systems.
La stereotassi è una tecnica chirurgica che stabilisce un sistema di coordinate cartesiane, detto spazio stereotassico, solidale con l’organo di interesse, per raggiungere con precisione specifici bersagli anatomici (target) nelle procedure neurochirurgiche mininvasive. L’approccio convenzionale, detto frame-based, si fonda su un localizer, usato per definire lo spazio stereotassico durante una tomografia computerizzata (TC), e su un frame stereotassico che, impostato sulle coordinate del piano chirurgico, guida lo strumento fino al target pianificato. Le immagini preoperatorie di TC e risonanza magnetica (RM) vengono acquisite nei giorni precedenti l’intervento, ma il giorno stesso è necessaria una nuova TC con il localizer fissato al cranio, per definire lo spazio stereotassico e allinearvi tali immagini; solo allora il localizer viene sostituito dal frame per svolgere l’intervento. Questo flusso presenta diversi limiti. I frame commerciali raggiungono un solo target alla volta, rendendo lunghe le procedure bilaterali e multi-target, come la stereoelettroencefalografia (sEEG) e la stimolazione cerebrale profonda (DBS). La TC intraoperatoria espone il paziente a radiazioni ionizzanti e ne impone il trasferimento in sala TC allungando i tempi chirurgici. La sostituzione del localizer con il frame può introdurre errori di riposizionamento. Infine non esiste alcun sistema di verifica quantitativa dell’errore finale commesso col frame, lasciando esposti a possibili errori umani di impostazione e ad imprecisioni meccaniche. Proponiamo dunque un approccio ottimizzato basato sulla scansione tridimensionale a luce strutturata (3DSS) del volto del paziente, priva di radiazioni, che ricostruisce lo spazio stereotassico senza TC intraoperatoria. Inoltre, un nuovo frame stereotassico apposta sviluppato, il Navinetics E1, svolge anche la funzione di localizer: scansionato in sala operatoria insieme al volto, definisce da solo lo spazio stereotassico, eliminando sia il passaggio di sostituzione e relativo errore sia il trasferimento in sala TC. Esso ha inoltre due unità di puntamento: nella configurazione convenzionale Single Arm sono unite in un’unica struttura rigida e raggiungono un target alla volta, ma in modalità Double Arm esse operano in modo indipendente, una per emisfero, consentendo il puntamento bilaterale simultaneo. Infine, la stessa tecnica di imaging è alla base di un sistema di controllo che determina le coordinate del target effettivamente raggiunto, rilevando e compensando sia gli errori di impostazione sia le imprecisioni meccaniche. In modalità Single Arm il prototipo del frame E1 ha raggiunto un’accuratezza meccanica di 0,78 ± 0,38 mm, paragonabile a quella dei frame convenzionali. In modalità Double Arm l’accuratezza è stata di 1,23 ± 0,36 mm per l’emisfero destro e di 1,65 ± 0,47 mm per il sinistro: valori prossimi alla soglia di accettabilità clinica di 2 mm ma promettenti, trattandosi solo di un frame prototipale. L’approccio 3DSS, valutato su 22 pazienti sottoposti a DBS, ha prodotto piani chirurgici che si discostano da quelli basati su TC di 0,80 ± 0,32 mm, ben entro tale soglia. Infine, col sistema di controllo, un errore di impostazione deliberato di 7,07 mm è stato rilevato come 8,03 mm e ridotto a 0,85 mm dopo la correzione; con il frame correttamente impostato, l’errore rilevato di 1,73 mm è sceso a 0,60 mm. Pur preliminari, questi risultati suggeriscono che la configurazione del frame possa essere verificata e corretta prima dell’intervento. Nel complesso, il sistema delinea un nuovo paradigma per la stereotassi frame-based: più rapido, privo di radiazioni intraoperatorie, adatto alle procedure bilaterali e multi-target e dotato di verifica quantitativa dell’errore, che consente a un frame prototipale stampato in 3D di avvicinarsi all’affidabilità di sistemi ben più costosi.
A Novel Structured-Light-Based Stereotactic Imaging Technique Integrated with a Simultaneous Bilateral Targeting Frame for Surgical Guidance and Feedback
ALFONSI, ADRIANO
2025/2026
Abstract
Stereotaxy is a surgical technique that establishes a Cartesian coordinate system, known as stereotactic space, anchored to the organ of interest, in order to reach specific anatomical targets with precision in minimally invasive neurosurgical procedures. The conventional frame-based approach relies on a localizer, used to define the stereotactic space during Computed Tomography (CT) acquisition, and on a stereotactic frame which, set to the coordinates of the surgical plan, guides the surgical instrument to the planned target. Preoperative CT and Magnetic Resonance Imaging (MRI) scans are ac-quired in the days before surgery, but on the day of the procedure a new CT scan is re-quired, with the localizer fixed to the patient’s skull, in order to define the stereotactic space and register these images to it; only then is the localizer replaced by the frame so that the procedure can be performed. This workflow has several limitations. Commercial frames can reach only one target at a time, making bilateral and multi-target procedures, such as stereoelectroencephalog-raphy (sEEG) and Deep Brain Stimulation (DBS), lengthy. Intraoperative CT exposes the patient to ionizing radiation and requires transfer to the CT suite, prolonging surgical time. Swapping the localizer for the frame can introduce repositioning errors. Finally, no system exists to quantitatively verify the frame’s final targeting error, leaving the pro-cedure exposed to human setting errors and mechanical inaccuracies. We therefore propose an optimized approach based on radiation-free 3D structured-light scanning (3DSS) of the patient’s face, which reconstructs the stereotactic space without intraoperative CT. In addition, a purpose-built stereotactic frame, the Navinetics E1, also serves as the localizer: scanned together with the patient’s face in the operating room, it defines the stereotactic space by itself, eliminating both the local-izer-to-frame exchange, with its associated error, and the transfer to the CT suite. The frame also has two pointing units: in the conventional Single Arm configuration they are joined into a single rigid structure and reach one target at a time, whereas in Double Arm mode they operate independently, one per hemisphere, allowing simultaneous bi-lateral targeting. Finally, the same structured-light imaging technique underlies a con-trol system that determines the coordinates of the target actually reached, detecting and compensating for both setting errors and mechanical inaccuracies. In Single Arm mode, the E1 frame prototype achieved a mechanical accuracy of 0.78 ± 0.38 mm, comparable to that of conventional frames. In Double Arm mode, accuracy was 1.23 ± 0.36 mm for the right hemisphere and 1.65 ± 0.47 mm for the left: values close to the 2 mm clinical acceptability threshold, yet promising for a prototype. The 3DSS-based approach, evaluated in 22 patients undergoing DBS, produced surgical plans that deviat-ed from CT-based ones by 0.80 ± 0.32 mm, well within this threshold. Finally, with the control system, a deliberate frame setting error of 7.07 mm was detected as 8.03 mm and reduced to 0.85 mm after correction; with the frame correctly set, a detected error of 1.73 mm fell to 0.60 mm. Although preliminary, these results suggest that the frame configuration can be verified and corrected before surgery. Overall, the system outlines a new paradigm for frame-based stereotaxy: faster, free of intraoperative radiation, suited to bilateral and multi-target procedures, and equipped with quantitative error verification, which allows even a 3D-printed prototype frame to approach the reliability of far more expensive systems.| File | Dimensione | Formato | |
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https://hdl.handle.net/20.500.12075/29245