Advancing intraoperative magnetic tracing using 3D freehand magnetic particle imaging

Abstract

Purpose Sentinel lymph node biopsy is a routine procedure for nodal staging in penile cancer. Most commonly, this procedure is guided by radioactive tracers, providing various forms of preoperative and intraoperative guidance. This is further extended with fluorescence imaging using hybrid radioactive–fluorescence tracers. Alternatively, a magnetic-based approach has become available using superparamagnetic iron-oxide nanoparticles (SPIONs). This study investigates a novel freehand magnetic particle imaging and navigation modality (fhMPI) for intraoperative localization, along with a hybrid approach, combining magnetic and fluorescence guidance. Materials and methods The fhMPI set-up was built with a surgical navigation device, optical tracking system and magnetometer probe. A dedicated reconstruction software based on a look-up-table method was used to reconstruct a superficial 3D volume of the SPION distribution in tissue. For fluorescence guidance, indocyanine green (ICG) was added to the SPIONs. The fhMPI modality was characterized in phantoms, ex vivo human skin and in vivo porcine surgery. Results Phantom and human skin explants illustrated that the current fhMPI modality had a sensitivity of 2.2 × 10–2 mg/mL SPIONs, a resolving power of at least 7 mm and a depth penetration up to 1.5 cm. Evaluation during porcine surgery showed that fhMPI allowed for an augmented reality image overlay of the tracer distribution in tissue, as well as 3D virtual navigation. Besides, using the hybrid approach, fluorescence imaging provided a visual confirmation of localized nodes. Conclusion fhMPI is feasible in vivo, providing 3D imaging and navigation for magnetic nanoparticles in the operating room, expanding the guidance possibilities during magnetic sentinel lymph node procedures. Furthermore, the integration of ICG provides the ability to visually refine and confirm correct localization. Further clinical evaluation should verify these findings in human patients as well.

The current status and future prospects for molecular imaging-guided precision surgery

“…Alternative to registration of preoperative images to the patient, intraoperative tracking and interventional modalities using exogenous fiducials, can help register the output of an imaging modality to a specific anatomical location in the patient; a concept used to generate so-called freehand scans. Freehand options have been reported for US [ 169 ], beta particles [ 170 ], gamma-ray [ 171 ], fluorescence [ 172 ], and magnetic signals [ 173 ], and have been utilized in both open and laparoscopic/robotic surgery [ 174 ]. Unique for open surgery applications is that larger detectors can be used (e.g., hand-held gamma cameras [ 175 ]) and that the rotational movement in general allows for better coverage.…”

Preclinical feasibility of robot‐assisted sentinel lymph node biopsy using multi‐modality magnetic and fluorescence guidance in the head and neck

“…The result of premixing ICG with the commercially available magnetic tracer “Magtrace” (Endomag, Cambridge, UK) has been briefly described elsewhere 30 . In this instance, premixing created a non‐covalent binding of ICG to the carboxydextran coating of Magtrace nanoparticles, resulting in a concurrence between fluorescent and magnetic signals 30 .…”

Radioisotope-Guided Sentinel Lymph Node Biopsy in Penile Cancer: A Long-Term Follow-Up Study

“…Moreover, initial results indicated that magnetometer-guided DSNB using superparamagnetic iron oxide nanoparticles was a feasible, radiation-free technique for the identification of SLNs in penile cancer ( 57 , 58 ). Another recent study investigated the use of intraoperative freehand magnetic particle imaging together with a hybrid indocyanine green–superparamagnetic iron oxide nanoparticle tracer for intraoperative SLN detection ( 59 ). The feasibility of this method was confirmed in ex vivo human skin transplants and in a porcine model, but the results need to be verified in human patients.…”