First clinical experiences in Europe’s first intraoperative magnetic resonance imaging unit with a ceiling mounted moveable high-field magnet are presented
Constantin Roder MD
Sotirios Bisdas MD PhD
Marcos Tatagiba MD PhD
Department of Neurosurgery and, Department of Radiology, Eberhard Karls University, Tübingen, Germany
Intraoperative magnetic resonance imaging (iMRI) has been used since the late 1990s in an aim to improve neurosurgical procedures by providing the possibility to update high-resolution MR imaging intraoperatively in order to evaluate anatomical and pathological structures and to overcome inaccuracies due to brain shift by updating neuronavigational data.(1-4) The main indications for using iMRI are the resection of gliomas and pituitary gland tumours; however, surgery of vascular malformations, metastases, large skull base tumours or epileptic foci can be supported greatly by this technique.(5) Low-field magnets with 0.12–0.5 Tesla (T) and high-field magnets with 1.5–3T are, generally speaking, the two main concepts in iMR imaging.(4)
Whereas high-field systems are superior in terms of image quality and the possibilities of functional imaging, low-field magnets are more time- and cost effective at sufficient imaging quality with lower resolution, for example, to detect contrast-enhancing residual tumours. However, high-field systems are capable of providing the surgeon and neuroradiologist with high resolution images at a quality similar to diagnostic scanners, including the entire spectrum of advanced functional imaging, such as fiber tracking and MR perfusion imaging or spectroscopy, among others.(4) Surgical theatres with high-field MR scanners consist of either a stationary magnet, to which the patient has to be brought, or a mobile magnet that can be moved along ceiling-mounted rails from its parking bay either to the patient or to a diagnostic MR room. Here we report our initial experience of more than 100 cases with Europe’s first ceiling-mounted moveable 1.5T iMRI, the VISIUS surgical theatre (IMRIS Visius Surgical Theatre, IMRIS Inc, Winnipeg, Canada).
Surgical setup and workflow
The suite consists of an operating room (OR) of approximately 60m2 and the magnet’s parking bay (approximately 15m2), which can be closed by shielded doors. When the scanner is in its parking position, the magnetic field in the entire OR is outside the 5-Gauss (5-G) line, enabling the use of standard neurosurgical instruments including a conventional operating microscope (Pentero, Karl-Zeiss, Oberkochen, Germany or Leica M720 OH5, Leica Microsystems, Wetzlar, Germany) and conventional neuronavigation (CBYON, Med-Surgical Inc, Sunnydale, CA, USA).
Few MR-compatible devices are needed as they remain with the patient during iMRI: skull clamp (MR-compatible DORO® skull clamp with disposable cranial pins, ProMed Instruments GmbH, Freiburg, Germany); vital parameter transmitters (Invivo Precess, Invivo Corporation, Orlando, FL, USA); anaesthesia machine (Aestiva/5 MRI, Datex-Ohmeda, Helsinki, Finland); and infusion pumps (MRidium, IRadimed, Winter Park, FL, USA). Patient positioning is possible in the supine, prone and lateral positions under respect of fitting the patient into the scanner’s 70cm bore and being at the magnet’s iso-centre. All cables and lines need to be padded to prevent possible burning if in direct contact with the patient’s skin.
Surgery can be performed as usual with standard instruments. After deciding to perform an intraoperative resection control scan, all ferromagnetic instruments will be removed and the patient is draped carefully in sterile sheets. Once the room has been prepared for iMRI, any tables and ferromagnetic instruments should be positioned outside the 5G line. After all safety checklists are confirmed, the scanner can be moved along the ceiling rails to its positing at the operating table. The acquisition of images can be controlled from the control room directly adjacent to the OR and usually takes 15–30 minutes, depending on the number of different MR sequences.
Analysis of these data is performed by an experienced neuroradiologist who discusses a possible continuation of the resection with the neurosurgeon. After the scanner is back in its parking bay, the sterile operating field is re-opened and sterile ferromagnetic instruments, which were placed outside the 5G line, can be used to continue the surgery. All media devices in the theatre are connected with a video system (Black Diamond Video, Point Richmond, CA, USA) enabling real-time use, as well as the recording, of all imaging data including MR data, microscopic, endoscopic, neuronavigation, ultrasound and IOM on any of the seven installed HD screens in the OR. No adverse events that would compromise the safety of the patient (such as ferromagnetic accidents, anaesthesia complications or procedure-related infections) or the OR staff, were noted in any of the cases. Total additional time needed to prepare and perform iMRI-guided surgery is about two hours per case.
Main indications and improvement of surgical results
iMRI can be used for the surgery of vascular malformations, metastases, large skull base tumours or epileptic foci, yet its main indications are the resection of gliomas and pituitary adenomas. Retrospective analysis of patients after iMRI-guided resection of pituitary adenomas showed that the resection is improved in approximately 30% of the cases.(6,7)
The resection of tumour masses invading the cavernous sinus were not increased substantially, but preservation of a normal pituitary stalk and gland could be achieved safely by iMRI guidance. Postoperative pituitary function was preserved or improved – possibly due to a more exact iMRI-assisted tumour removal.(7) Our experience with 16 difficult pituitary adenomas showed that the resection of adenomas was continued in up to 63% of the cases.
The primary indication for iMRI-guided surgery is gliomas, which account for more than two-thirds of all iMRI procedures at our department. Recently published data for a randomised controlled trial proved that iMRI-guided surgery significantly increases the number of total resections (96% in the iMRI group versus 68% in the control group; p=0.023) at comparable new postoperative neurological deficits.(8) It is well known that a safe total resection of high-grade gliomas is one of the most important prognostic factors and expands the time of progression-free survival and overall survival in combination with adjuvant chemoradiation significantly.(9)
Analysis at our institution revealed that the extent of resection (EOR), as well as the number of total resections, of glioblastomas was improved significantly (p<0.05) by iMRI-guided surgery compared with conventional surgery at similar peri- and postoperative morbidities. Special accentuation should be put on the increase of the total resection of contrast enhancing tissue, which was 21% in the intraoperative scan and 70% after continuing iMRI-guided resection. Most of the tumour remnants were small fragments (volume <2cm3) that could be identified and removed safely with the newly acquired high-field iMRI and updated neuronavigation. If not removed, such small remnants are known to be the starting point of relapse tumours in 80% of cases.(10)
Conclusions
Intraoperative MR imaging is a powerful tool to enable neurosurgeons to perform more radical resection of various brain pathologies without increasing the patients’ risk of new neurological deficits. The VISIUS surgical theatre, with its moveable 1.5-T MR scanner and its fully integrated media system, provides an outstanding working environment for the entire OR staff. Neurosurgeons receive all the additional imaging data needed to improve surgeries in real-time without any drawbacks in their routines, because standard instruments and setups can be used. Maximum safety is provided as the patient remains in the standard positioning without being moved during the entire procedure.
The high-field magnet enables high-resolution imaging at diagnostic quality, including the possibility of advanced functional MRI. Drawbacks are high acquisition costs and extended surgery times, which might be problematic in smaller low-volume centres, but which are well compensable in large high-volume clinics. Recent literature shows the significant benefit of iMRI-guided surgery to patients, but it is our opinion that much more proof has to, and will, follow throughout the next years, in order to justify these procedures against health economic aspects.
References
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