Intraoperative and interventional MRI: Recommendations for a safe environment

Interventional device tracking under MRI via alternating current controlled inhomogeneities

PURPOSE

To introduce alternating current-controlled, conductive ink-printed marker that could be implemented with both custom and commercial interventional devices for device tracking under MRI using gradient echo, balanced SSFP, and turbo spin-echo sequences.

METHODS

Tracking markers were designed as solenoid coils and printed on heat shrink tubes using conductive ink. These markers were then placed on three MR-compatible test samples that are typically challenging to visualize during MRI scans. MRI visibility of markers was tested by applying alternating and direct current to the markers, and the effects of applied current parameters (amplitude, frequency) on marker artifacts were tested for three sequences (gradient echo, turbo spin echo, and balanced SSFP) in a gel phantom, using 0.55T and 1.5T MRI scanners. Furthermore, an MR-compatible current supply circuit was designed, and the performance of the current-controlled markers was tested in one postmortem animal experiment using the current supply circuit.

RESULTS

Direction and parameters of the applied current were determined to provide the highest conspicuity for all three sequences. Marker artifact size was controlled by adjusting the current amplitude, successfully. Visibility of a custom-designed, 20-gauge nitinol needle was increased in both in vitro and postmortem animal experiments using the current supply circuit.

CONCLUSION

Current-controlled conductive ink-printed markers can be placed on custom or commercial MR-compatible interventional tools and can provide an easy and effective solution to device tracking under MRI for three sequences by adjusting the applied current parameters with respect to pulse sequence parameters using the current supply circuit.

Intraoperative MR Imaging during Glioma Resection

One of the major issues in the surgical treatment of gliomas is the concern about maximizing the extent of resection while minimizing neurological impairment. Thus, surgical planning by carefully observing the relationship between the glioma infiltration area and eloquent area of the connecting fibers is crucial. Neurosurgeons usually detect an eloquent area by functional MRI and identify a connecting fiber by diffusion tensor imaging. However, during surgery, the accuracy of neuronavigation can be decreased due to brain shift, but the positional information may be updated by intraoperative MRI and the next steps can be planned accordingly. In addition, various intraoperative modalities may be used to guide surgery, including neurophysiological monitoring that provides real-time information (e.g., awake surgery, motor-evoked potentials, and sensory evoked potential); photodynamic diagnosis, which can identify high-grade glioma cells; and other imaging techniques that provide anatomical information during the surgery. In this review, we present the historical and current context of the intraoperative MRI and some related approaches for an audience active in the technical, clinical, and research areas of radiology, as well as mention important aspects regarding safety and types of devices.

Real-time device tracking under MRI using an acousto-optic active marker

PURPOSE

This work aims to demonstrate the use of an "active" acousto-optic marker with enhanced visibility and reduced radiofrequency (RF) -induced heating for interventional MRI.

METHODS

The acousto-optic marker was fabricated using bulk piezoelectric crystal and π-phase shifted fiber Bragg grating (FBGs) and coupled to a distal receiver coil on an 8F catheter. The received MR signal is transmitted over an optical fiber to mitigate RF-induced heating. A photodetector converts the optical signal into electrical signal, which is used as the input signal to the MRI receiver plug. Acousto-optic markers were characterized in phantom studies. RF-induced heating risk was evaluated according to ASTM 2182 standard. In vivo real-time tracking capability was tested in an animal model under a 0.55T scanner.

RESULTS

Signal-to-noise ratio (SNR) levels suitable for real-time tracking were obtained by using high sensitivity FBG and piezoelectric transducer with resonance matched to Larmor frequency. Single and multiple marker coils integrated to 8F catheters were readout for position and orientation tracking by a single acousto-optic sensor. RF-induced heating was significantly reduced compared to a coax cable connected reference marker. Real-time distal tip tracking of an active device was demonstrated in an animal model with a standard real-time cardiac MR sequence.

CONCLUSION

Acousto-optic markers provide sufficient SNR with a simple structure for real-time device tracking. RF-induced heating is significantly reduced compared to conventional active markers. Also, multiple RF receiver coils connected on an acousto-optic modulator can be used on a single catheter for determining catheter orientation and shape.

MR Imaging Safety in the Interventional Environment

Interventional MR imaging procedures are rapidly growing in number owing to the excellent soft tissue resolution of MR imaging, lack of ionizing radiation, hardware and software advancements, and technical developments in MR imaging-compatible robots, lasers, and ultrasound equipment. The safe operation of an interventional MR imaging system is a complex undertaking, which is only possible with multidisciplinary planning, training, operations and oversight. Safety for both patients and operators is essential for successful operations. Herein, we review the safety concerns, solutions and challenges associated with the operation of a modern interventional MR imaging system.

Cardiopulmonary exercise testing - refining the clinical perspective by combining assessments

INTRODUCTION

Cardiorespiratory fitness (CRF) is now established as a vital sign. Cardiopulmonary exercise testing (CPX) is the gold-standard approach to assessing CRF.

AREAS COVERED

A body of literature spanning several decades clearly supports the clinical utility of CPX in those who are apparently health and at risk for chronic disease as well as numerous patient populations. While CPX, in and of itself, is a valid and reliable clinical assessment, combining findings with other available assessments may provide a more comprehensive perspective that enhances clinical decision making and outcomes. The current review will accomplish the following: (1) define key CPX measures based upon current evidence; and (2) describe the current evidence addressing the relationships between CPX and echocardiography, serum biomarkers, and cardiovascular magnetic resonance.

EXPERT OPINION

Cardiopulmonary exercise testing provides prognostic and diagnostic information in apparently healthy individuals, those at risk for one or more chronic conditions, as well as numerous patient populations. Moreover, if the goal of an intervention is to improve one or more systems integral to the physiologic response to exercise, CPX should be considered as a central assessment to gauge therapeutic efficacy. To further refine the information obtained from CPX, combining other assessments has demonstrated promise.

The interventional magnetic resonance imaging suite: Experience in the design, development, and implementation in a pre-existing radiology space and review of concepts

BACKGROUND

Intraoperative magnetic resonance imaging (ioMRI) has led to significant advancements in neurosurgery with improved accuracy, assessment of the extent of resection, less invasive surgical alternatives, and real-time confirmation of targeting as well delivery of therapies. The costs associated with developing ioMRI units in the surgical suite have been obstacles to the expansion of their use. More recently, the development of hybrid interventional MRI (iMRI) units has become a viable alternative. The process of designing, developing, and implementing operations for these units requires the careful integration of environmental, technical, and safety elements of both surgical and MR practices. There is a paucity of published literature providing guidance for institutions looking to develop a hybrid iMRI unit, especially with a limited footprint in the radiology department.

METHODS

The experience of designing, developing, and implementing an iMRI in a preexisting space for neurosurgical procedures at a single institution in light of available options and the literature is described.

RESULTS

The development of the unit was accomplished through the engagement of a multidisciplinary team of stakeholders who utilized existing guidelines and recommendations and their own professional experience to address issues including physical layout, equipment selection, operations planning, infection control, and oversight/review, among others.

CONCLUSION

Successful creation of an iMRI program requires multidisciplinary collaboration in integrating surgical and MR practice. The authors' aim is that the experience described in this article will serve as an example for facilities or neurosurgical departments looking to navigate the same process.

A Novel Expandable Catheter Wireless Amplified NMR Detector for MR Sensitivity Accessing the Kidney in Rodent Model

This paper demonstrates the enlarged effective range for MRI sensitivity enhancement with a deformable catheter MRI coils integrated with a wirelessly powered amplifier. The expandable balloon wireless amplified nuclear magnetic resonance detector (WAND) is constructed on a copper-clad polyimide film to resonate at the first and second harmonics of the proton Larmor frequency at 7 Tesla. The WAND is then mounted on a balloon catheter system for easy delivery inside confined orifice. Upon reaching the region of interest, it is unfolded out of the sheath tube to increase its effective size. Magnetic resonance (MR) imaging experiments with and without the WAND are performed both in a water phantom and in a live rat to evaluate the WAND's sensitivity advantage. Expanded from a 3 mm diameter in its folded state, this deformable WAND can change its width by >100% in its inflated state to at least 6 mm, leading to a sensitive detection region extending to up to 20 mm in the transverse direction. When the deformable WAND is placed in an artery in the region of the kidney of a live rat, it could achieve at least a 10-fold SNR gain over images acquired by a standard external detector of 22 mm diameter, even though the region of interest is separated from the WAND's surface by a distance larger than the WAND's own width. The proposed expandable catheter WAND could significantly enlarge the effective range for MR sensitivity enhancement in-vivo, enabling versatile applications in interventional MRI.

MRI-guided stereotactic neurosurgical procedures in a diagnostic MRI suite: Background and safe practice recommendations

The development of navigation technology facilitating MRI-guided stereotactic neurosurgery has enabled neurosurgeons to perform a variety of procedures ranging from deep brain stimulation to laser ablation entirely within an intraoperative or diagnostic MRI suite while having real-time visualization of brain anatomy. Prior to this technology, some of these procedures required multisite workflow patterns that presented significant risk to the patient during transport. For those facilities with access to this technology, safe practice guidelines exist only for procedures performed within an intraoperative MRI. There are currently no safe practice guidelines or parameters available for facilities looking to integrate this technology into practice in conventional MRI suites. Performing neurosurgical procedures in a diagnostic MRI suite does require precautionary measures. The relative novelty of technology and workflows for direct MRI-guided procedures requires consideration of safe practice recommendations, including those pertaining to infection control and magnet safety issues. This article proposes a framework of safe practice recommendations designed for assessing readiness and optimization of MRI-guided neurosurgical interventions in the diagnostic MRI suite in an effort to mitigate patient risk. The framework is based on existing clinical evidence, recommendations, and guidelines related to infection control and prevention, health care-associated infections, and magnet safety, as well as the clinical and practical experience of neurosurgeons utilizing this technology.

Neurosurgical laser ablation and MR thermometry: Risks of multisite workflow pattern

Neurosurgical laser ablation is a relatively new but rapidly growing application of stereotactic neurosurgery that allows neurosurgeons to treat many previously untreatable conditions with the added benefit of shorter hospitalizations and recovery times. The vast majority of these procedures, however, are performed using a multisite workflow pattern involving transport of the patient between the operating room (OR), the computed tomography (CT) suite, and the magnetic resonance imaging (MRI) suite, often necessitating patient transfer through public pathways and requiring multiple trips if laser fiber placement is not accurate. There are significant risks posed to the patient with this practice and no existing guidelines addressing it. This article serves to identify those risks and present recommendations for safety optimization and risk reduction for those health care facilities using a multisite workflow pattern.

"Low-field" intraoperative MRI: a new scenario, a new adaptation

AIM

To describe the adaptation of Cruces University Hospital to the use of intraoperative magnetic resonance imaging (ioMRI), and how the acquisition and use of this technology would impact the day-to-day running of the neurosurgical suite.

MATERIALS AND METHODS

With the approval of the ethics committee, an observational, prospective study was performed from June 2012 to April 2014, which included 109 neurosurgical procedures with the assistance of ioMRI. These were performed using the Polestar N-30 system (PSN30; Medtronic Navigation, Louisville, CO), which was integrated into the operating room.

RESULTS

A total of 159 procedures were included: 109 cranial surgeries assisted with ioMRI and 50 control cases (no ioMRI use). There were no statistical significant differences when anaesthetic time (p=0.587) and surgical time (p=0.792) were compared; however, an important difference was shown in duration of patient positioning (p<0.0009) and total duration of the procedure (p<0.0009) between both groups.

CONCLUSIONS

The introduction of ioMRI is necessary for most neurosurgical suites; however, a few things need to be taken into consideration when adapting to it. Increase procedure time, the use of specific MRI-safe devices, as well as a checklist for each patient to minimise risks, should be taken into consideration.

Robotic-assisted thermal ablation of liver tumours

OBJECTIVE

This study aimed to assess the technical success, radiation dose, safety and performance level of liver thermal ablation using a computed tomography (CT)-guided robotic positioning system.

METHODS

Radiofrequency and microwave ablation of liver tumours were performed on 20 patients (40 lesions) with the assistance of a CT-guided robotic positioning system. The accuracy of probe placement, number of readjustments and total radiation dose to each patient were recorded. The performance level was evaluated on a five-point scale (5-1: excellent-poor). The radiation doses were compared against 30 patients with 48 lesions (control) treated without robotic assistance.

RESULTS

Thermal ablation was successfully completed in 20 patients with 40 lesions and confirmed on multiphasic contrast-enhanced CT. No procedure related complications were noted in this study. The average number of needle readjustment was 0.8 ± 0.8. The total CT dose (DLP) for the entire robotic assisted thermal ablation was 1382 ± 536 mGy.cm, while the CT fluoroscopic dose (DLP) per lesion was 352 ± 228 mGy.cm. There was no statistically significant (p > 0.05) dose reduction found between the robotic-assisted versus the conventional method.

CONCLUSION

This study revealed that robotic-assisted planning and needle placement appears to be safe, with high accuracy and a comparable radiation dose to patients.

KEY POINTS

• Clinical experience on liver thermal ablation using CT-guided robotic system is reported. • The technical success, radiation dose, safety and performance level were assessed. • Thermal ablations were successfully performed, with an average performance score of 4.4/5.0. • Robotic-assisted ablation can potentially increase capabilities of less skilled interventional radiologists. • Cost-effectiveness needs to be proven in further studies.

Advances in Haptics, Tactile Sensing, and Manipulation for Robot-Assisted Minimally Invasive Surgery, Noninvasive Surgery, and Diagnosis

The developments of medical practices and medical technologies have always progressed concurrently. The relatively recent developments in endoscopic technologies have allowed the realization of the “minimally invasive” form of surgeries. The advancements in robotics facilitate precise surgeries that are often integrated with medical image guidance capability. This in turn has driven the further development of technology to compensate for the unique complexities engendered by this new format and to improve the performance and broaden the scope of the procedures that can be performed. Medical robotics has been a central component of this development due to the highly suitable characteristics that a robotic system can purport, including highly optimizable mechanical conformation and the ability to program assistive functions in medical robots for surgeons to perform safe and accurate minimally invasive surgeries. In addition, combining the robot-assisted interventions with touch-sensing and medical imaging technologies can greatly improve the available information and thus help to ensure that minimally invasive surgeries continue to gain popularity and stay at the focus of modern medical technology development. This paper presents a state-of-the-art review of robotic systems for minimally invasive and noninvasive surgeries, precise surgeries, diagnoses, and their corresponding technologies.

Multimodality intraoperative MRI for brain tumor surgery

Intraoperative MRI has already fundamentally changed the way current brain tumor surgery is performed. The ability to integrate high-field MRI into the operating room has allowed intraoperative MRI to emerge as an important adjunct to CNS tumor treatment. Furthermore, the ability of MRI to successfully couple with molecular imaging (PET and/or optical imaging), neuroendoscopy and therapeutic devices, such as focused ultrasound, will allow it to emerge as an important image-guidance modality for improving brain tumor therapy and outcomes.

[Principles of MR-guided interventions, surgery, navigation, and robotics]

The application of magnetic resonance imaging (MRI) as an imaging technique in interventional and surgical techniques provides a new dimension of soft tissue-oriented precise procedures without exposure to ionizing radiation and nephrotoxic allergenic, iodine-containing contrast agents. The technical capabilities of MRI in combination with interventional devices and systems, navigation, and robotics are discussed.

Origins of intraoperative MRI

Neurosurgical diagnosis and intervention has evolved through improved neuroimaging, allowing better visualization of anatomy and pathology. This article discusses the various systems that have been designed over the last decade to meet the requirements of neurosurgical patients and opines on the potential future developments in the technology and application of intraoperative MRI. Because the greatest amount of experience with intraoperative MRI comes from its use in brain tumor resection, this article focuses on the origins of intraoperative MRI in relation to this field.

Imaging in percutaneous nephrolithotomy

Image guidance is a critical factor for the performance of urologic interventions. Percutaneous minimally invasive procedures have been developed and are being used with constantly increasing frequency. Procedures such as percutaneous nephrolithotomy (PCNL) are not performed without any image guidance. Recent developments in medical imaging, such as three-dimensional radiographic fluoroscopy, CT, and magnetic resonance (MR) fluoroscopy, four-dimensional ultrasonography, and image fusion techniques, propose a new generation of image-guidance tools that promise to improve patient care. These developments have been used or have the potential to be used in PCNL and other urologic interventional procedures. Moreover, advanced needles and needle guidance systems provide a new perspective for the nephrolithotomy suite of the future. The current review presents existing imaging technology in PCNL and interventional urology as well as advanced imaging techniques that are being or are expected to be evaluated in PCNL practice.

Origins of intraoperative MRI

Neurosurgical diagnosis and intervention has evolved through improved neuroimaging, allowing better visualization of anatomy and pathology. This article discusses the various systems that have been designed over the last decade to meet the requirements of neurosurgical patients and opines on the potential future developments in the technology and application of intraoperative MRI. Because the greatest amount of experience with intraoperative MRI comes from its use in brain tumor resection, this article focuses on the origins of intraoperative MRI in relation to this field.

Physiological recordings: basic concepts and implementation during functional magnetic resonance imaging

Combining human functional neuroimaging with other forms of psychophysiological measurement, including autonomic monitoring, provides an empirical basis for understanding brain-body interactions. This approach can be applied to characterize unwanted physiological noise, examine the neural control and representation of bodily processes relevant to health and morbidity, and index covert expression of affective and cognitive processes to enhance the interpretation of task-evoked regional brain activity. In recent years, human neuroimaging has been dominated by functional magnetic resonance imaging (fMRI) studies. The spatiotemporal information of fMRI regarding central neural activity is valuably complemented by parallel physiological monitoring, yet such studies still remain in the minority. This review article highlights fMRI studies that employed cardiac, vascular, respiratory, electrodermal, gastrointestinal and pupillary psychophysiological indices to address specific questions regarding interaction between brain and bodily state in the context of experience, cognition, emotion and behaviour. Physiological monitoring within the fMRI environment presents specific technical issues, most importantly related to safety. Mechanical and electrical hazards may present dangers to scanned subjects, operator and/or equipment. Furthermore, physiological monitoring may interfere with the quality of neuroimaging data, or itself be compromised by artefacts induced by the operation of the scanner. We review the sources of these potential problems and the current approaches and advice to enable the combination of fMRI and physiological monitoring in a safe and effective manner.

MR‐guided percutaneous ethanol ablation of hepatocellular carcinomas before liver transplantation

It was the objective of this study to evaluate MR-guided, percutaneous ethanol injection of hepatocellular carcinoma in ten patients scheduled for liver transplantation. Using a 0.2 T open MR scanner (Magnetom Open, Siemens Medical Systems, Erlangen, Germany) and percutaneous instillation of ethanol, 12 liver tumors (median tumor volume, 6.3; range, 0.6-43.2 ccm) were treated. Coagulation necrosis, morbidity, and post-transplant histology were assessed. No major complications were observed. A mean of 16.4+/-11.4 ml ethanol was injected for each tumor. The median volume of the ablation necrosis was 12.3 (range, 0.3-48.3) ccm. Three tumors were retreated and complete radiological necrosis before liver transplantation was found in eight of 12 tumors (67%). One patient developed multifocal disease and was excluded from transplantation; thus nine of ten patients underwent liver transplantation within 3.9+/-3.1 months. In the explants, satellite nodules (n = 2), new liver tumors (n = 2) and a complete necrosis were found in five of 12 treated tumors (42%). During follow-up (median 41.3; range, 0.4-86.1 months), three patients died, but no tumor-seeding or post-transplantation recurrence occurred. MR-guided ethanol injection is feasible, and may delay tumor progression. However, the local recurrence rate is high, and the spatial resolution of a low-field MR scanner limits the detection of small tumors.

MR systems for MRI-guided interventions

The field of MR imaging has grown from diagnosis via morphologic imaging to more sophisticated diagnosis via both physiologic and morphologic imaging and finally to the guidance and control of interventions. A wide variety of interventional procedures from open brain surgeries to noninvasive focused ultrasound ablations have been guided with MR and the differences between diagnostic and interventional MR imaging systems have motivated the creation of a new field within MR. This review discusses the various systems that research groups and vendors have designed to meet the requirements of interventional MR and suggest possible solutions to those requirements that have not yet been met. The common requirements created by MR imaging guidance of interventional procedures are reviewed and different imaging system designs will be independently considered. The motivation and history of the different designs are discussed and the ability of the designs to satisfy the requirements is analyzed.

Cardiac function and myocardial perfusion immediately following maximal treadmill exercise inside the MRI room

Treadmill exercise stress testing is an essential tool in the prevention, detection, and treatment of a broad spectrum of cardiovascular disease. After maximal exercise, cardiac images at peak stress are typically acquired using nuclear scintigraphy or echocardiography, both of which have inherent limitations. Although CMR offers superior image quality, the lack of MRI-compatible exercise and monitoring equipment has prevented the realization of treadmill exercise CMR. It is critical to commence imaging as quickly as possible after exercise to capture exercise-induced cardiac wall motion abnormalities. We modified a commercial treadmill such that it could be safely positioned inside the MRI room to minimize the distance between the treadmill and the scan table. We optimized the treadmill exercise CMR protocol in 20 healthy volunteers and successfully imaged cardiac function and myocardial perfusion at peak stress, followed by viability imaging at rest. Imaging commenced an average of 30 seconds after maximal exercise. Real-time cine of seven slices with no breath-hold and no ECG-gating was completed within 45 seconds of exercise, immediately followed by stress perfusion imaging of three short-axis slices which showed an average time to peak enhancement within 57 seconds of exercise. We observed a 3.1-fold increase in cardiac output and a myocardial perfusion reserve index of 1.9, which agree with reported values for healthy subjects at peak stress. This study successfully demonstrates in-room treadmill exercise CMR in healthy volunteers, but confirmation of feasibility in patients with heart disease is still needed.

COMBINED X-RAY AND MAGNETIC RESONANCE IMAGING FACILITY

OBJECTIVE

To assess the feasibility of a hybrid imaging setup combining x-ray and magnetic resonance imaging (MRI) in the setting of both stereotactic and functional neurosurgery.

METHODS

A combined x-ray and MRI scanning facility with a trolley system for a fast patient transfer between both modalities was installed in a neurosurgical setting. A registration algorithm for fusion of MRI scans and x-ray images was derived for augmentation of fluoroscopic x-ray projection images with MRI scan data, such as anatomic structures and planned probe trajectories. Phantom measurements were obtained between both modalities for estimation of registration accuracy. Practical application of our system in stereotactic and functional neurosurgery was tested in brachytherapy, deep brain stimulation, and motor cortex stimulation.

RESULTS

Phantom measurements yielded a mean spatial deviation of 0.7 +/- 0.3 mm with a maximum deviation of 1.1 mm for MRI scans versus x-rays. Augmentation of x-ray images with MRI scan data allowed intraoperative verification of the planned trajectory and target in three types of neurosurgical procedures: positioning iodine seeds in brachytherapy in one case with cerebellar metastasis, placement of electrodes for deep brain stimulation in two cases of advanced Parkinson's disease, and placement of an epidural grid for motor cortex stimulation in two cases of intractable pain.

CONCLUSION

Combined x-ray and MRI-guided stereotactic and functional neurosurgery is feasible. Augmentation of x-ray projection images with MRI scan data, such as planned probe trajectories and MRI scan segmented anatomic structures may be beneficial for probe guidance in stereotactic and functional neurosurgery.