Machine-Vision Image-Guided Surgery for Spinal and Cranial Procedures

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Machine-Vision Image-Guided Surgery for Spinal and Cranial Procedures Zahra Faraji-Dana1, Adrian L.D. Mariampillai1, Beau A. Standish1, Victor X.D. Yang2 and Michael K.K. Leung1 1

7D Surgical Inc., North York, ON, Canada Sunnybrook Health Sciences Centre, Toronto, ON, Canada

2

ABSTRACT The 7D Surgical Machine-vision Image-Guided Surgery (IGS) (MvIGS) system provides surgical guidance to spinal and cranial procedures where high navigation accuracy is required. By leveraging machine vision technologies, the 7D Surgical MvIGS System has the advantage of allowing surgeons to quickly achieve image registration and start navigation without the need for intraoperative radiation-emitting devices or laborious traditional point matching techniques. The 7D Surgical MvIGS System uses an all-optical nonionizing structured light to acquire a threedimensional (3D) surface scan of the patient. Advanced machine vision algorithms are then used to register the 3D surface to a preoperative scan of the patient. This approach reduces the need for intraoperative X-rays, significantly reducing the surgeon’s, the staff’s, and the patient’s exposure to radiation. By leveraging the intraoperative highresolution optical surface data acquired from the patient and machine vision algorithms, the 7D Surgical MvIGS System significantly reduces the steps required to set up and operate an IGS system leading to an unprecedentedly fast workflow which we call Flash Registration. Fewer required user interactions with the system also allow for a short learning curve. These innovations have resulted in an IGS system that is more accessible to a broader user base, while providing a radiation-free surgical environment for surgeons, hospital staff, and patients. Handbook of Robotic and Image-Guided Surgery. DOI: https://doi.org/10.1016/B978-0-12-814245-5.00032-3 © 2020 Elsevier Inc. All rights reserved.

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32.1

Overview of image-guided surgery technology

The intraoperative navigational techniques commonly referred to as image-guided surgery (IGS) are a procedure whereby preoperative or intraoperative imaging is used to guide a surgery. They typically involve the use of real-time tracking of surgical instruments, which are shown in multiplanar views, in relation to the patient’s anatomy. IGS can be particularly helpful when the anatomy of interest is unexposed or only partially exposed and allows for the accurate guided positioning of surgical instruments or placement of implants into the patient’s anatomy. IGS technology can improve the accuracy of the surgical procedures, hence improving the surgeons’ assurance and the patients’ safety. Even experienced surgeons who have a thorough knowledge of human anatomy can benefit from the information provided by IGS during surgery [1]. IGS technology should be viewed as complementary to and not a replacement for the surgeon’s experience and judgment. The IGS benefits with respect to the safety and accuracy of a variety of spinal and cranial procedures have been well documented in the medical literature and thus utilization of image guidance continues to grow throughout a broad range of surgical procedures. This chapter provides details about the 7D Surgical Machinevision IGS (MvIGS) system with a focus on spinal and cranial procedures.

32.1.1

Importance of navigation in spinal and cranial procedures

The inclusion of navigation technologies in cranial procedures has become the standard of care as the brain is a very delicate organ and utmost care is required while interacting with this tissue. For example, in a tumor resection procedure, it is important that the tumor is removed as much as possible without damaging the healthy brain tissue. This is a challenging task, especially in cases where areas responsible for critical brain function are adjacent to the tumor. In these cases, IGS allows the surgeon to accurately plan an entry point and trajectory, and to locate the intracranial lesion for resection or biopsy [2]. For spinal procedures, however, use of navigation is not as widespread. Many surgeons still operate freehand or rely on traditional fluoroscopy technologies. As a result, breach of screws outside the intended trajectory occurs in 12% 40% of screw placements (Fig. 32.1) [3 6], potentially causing acute neurovascular injury, and in the longer term, mechanical construct failure, whose complications may require costly revision surgeries [7 9]. IGS allows the surgeon to visualize the unexposed or partially exposed structures such as the pedicle region of a vertebra and avoid potential damage to the sensitive nearby organs such as the spinal cord, nerves, and vascular structures. IGS has improved the accuracy of screw placement in all levels of the spine and has reduced breach rates to under 10% [5,10 14].

32.1.2

Evolution of image-guided surgery system

To guide a surgical procedure, C-arm fluoroscopy can be used to visualize an instrument’s position within an anatomical site, either continuously, or in snapshots. A variety of procedures can be performed using fluoroscopy. The main disadvantage of fluoroscopy, however, is the exposure of ionizing radiation to the patients, the surgeons, and operating room staff, particularly when fluoroscopy is used continuously. Furthermore, a single fluoroscopy image can only acquire one anatomical plane at a time. For other planes, the C-arm must be repositioned. Also, a C-arm machine is quite unwieldy and can constrain access to the surgical field. Lastly, C-arm does not offer navigation in the axial plane which is very beneficial in implant placement during spine surgery. IGS was developed to address the shortcomings of conventional intraoperative navigation and to optimize the accuracy and safety of surgical procedures.

FIGURE 32.1 The importance of navigation for pedicle screw placement. The screws are placed very poorly and have likely caused damage to the nerves and spinal cord and other sensitive organs nearby.

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Early IGS was performed via matching skin surface markers that were placed on a patient during fluoroscopic imaging to that of the skin surface markers as they appear on the patient during the surgical procedure. These markers introduce significant registration inaccuracy, especially when relative movement between the mobile skin and the underlying bony anatomy occurs [15,16]. IGS accuracy was improved when anatomical landmarks were used as registration markers [17 19]. These systems can be categorized into two broad classes: intraoperative and preoperative IGS. These two classes of the IGS systems and their differences are discussed below.

32.1.3

Intraoperative image-guided surgery systems

32.1.3.1 Intraoperative fluoroscopy-based image-guided surgery systems

32.1.3.2 Intraoperative three-dimensional image-guided surgery systems Analogous to the virtual fluoroscopy systems, several manufacturers have taken the approach of combining IGS technologies with 3D intraoperative imaging equipment. A standard setup consists of a computer system, an intraoperative imaging device, several customized surgical instruments that are tracked, a tool tracking system, and a reference array that is attached to the patient. Example devices include the Medtronic O-arm and Ziehm 3D C-arm [25,26]. The 3D intraoperative imaging equipment integrates with the IGS system through a calibration process that either involves touching the imaging device at known locations with a tracked pointer, imaging a calibration device, or by tracking the imaging device itself during 3D imaging. The result of this calibration is the localization of the 3D image volume in the tool tracking system which also tracks the reference array and the customized surgical instruments.

32. 7D Surgical MvIGS

Fluoroscopy-based IGS systems, also referred to as “virtual fluoroscopy,” combine computer-aided surgical technology with C-arm fluoroscopy [20,21]. There are several manufacturers that provide virtual fluoroscopy systems. Despite the differences in the exact hardware and software among various systems, they generally share the same basic components and functions. They typically include a C-arm fluoroscope situated in the operating room, a calibration target that attaches to the C-arm, a reference array, a tracking system, and various customized surgical instruments such as screwdrivers, awls, probes, and pointers. The reference array and surgical tools are visible to the tracking system and can be tracked in real time. This is made possible either by attaching light-emitting diodes (LEDs), also known as “active arrays,” or reflective spheres, referred to as “passive arrays.” The position and orientation of these arrays in threedimensional (3D) space is measured using a tracking system and transferred to a computer workstation which acts as the primary user interface of the system. The intraoperative fluoroscopic images of the patient are obtained and automatically transferred to the computer for processing. The system automatically calibrates the fluoroscopic images from the spatial information and at least one projection. The calibration process starts by measuring the relative position of the C-arm and the patient by a tracking system that can track the location of the reference array and the calibration target. The computer then links the spatial measurements relative to the obtained fluoroscopic images. The position of the instrument is displayed in reference to acquired fluoroscopic images in different views without any surgeon-derived registration steps. After the registration, the optical tracking system tracks the position of the anatomy via the reference array, and hence maintains the registration accuracy even if the patient or the optical tracking system moves, provided the reference array remains fixed to the anatomy. Thus, it is important that the reference array is firmly attached to the anatomy. Augmenting a traditional C-arm with computer-aided IGS technology strengthens the advantages of fluoroscopy and minimizes its disadvantages. Standard fluoroscopy provides real-time intraoperative visualization of the anatomy. The major disadvantage of the fluoroscopy is the amount of ionizing radiation exposure [22,23] to the patients as well as the surgical staff and surgeons. Moreover, the images can be obtained in only one plane at a time. Virtual fluoroscopy reduces the need for C-arm repositioning because the system can use multiple saved images and effectively acts as a multiplanar imaging unit. Additionally, the surgical team can stand away from the operative field while the fluoroscopic images are acquired, minimizing the occupational ionizing radiation exposure. Although occupational radiation exposure is significantly reduced compared to conventional fluoroscopy, there is still exposure to surgical staff and surgeons. The virtual fluoroscopy system enables two-dimensional navigation in the sagittal and coronal planes yet does not provide navigation in the axial plane. Moreover, poor fluoroscopy image quality, and hence poor navigational accuracy, occurs when imaging patients with high body-mass index, or in the thoracic or thoracic cervical junction due to the decreased ability of X-rays to penetrate through the chest wall and/or shoulders. Image quality is also affected by distortion from image intensifiers. For these reasons, widespread adoption of this IGS approach is limited [24].

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Therefore, the calibration process defines the 3D image volume relative to the reference array and enables the display of customized surgical instruments in relation to the patient’s anatomy. A chief advantage of the 3D IGS systems is navigation in the axial plane which assists the surgeon in visualizing the anatomy immensely. Additionally, compared to the fluoroscopy-based IGS systems, the 3D IGS systems result in a lower radiation dose and faster imaging. Furthermore, the multiplane imaging reduces the need to manually reposition the imaging device at different angles, yielding time savings in the operating room. Another major advantage of intraoperative 3D IGS systems is that the patient’s images at the operative position get transferred automatically to the IGS system and the surgeon can obtain an updated scan whenever needed by rescanning the patient in the operative position. However, the process of initially setting up the 3D intraoperative imaging device is time consuming and takes anywhere between 15 and 30 minutes. Reacquisitions require repositioning of the 3D intraoperative imaging device, which is also a time-consuming process and can interrupt surgical workflow. Additional staff is also required to operate these systems. Despite these benefits, the need for ionizing radiation impacts the patient and the operating room staff. Another disadvantage of the intraoperative IGS systems is the high cost of purchasing a dedicated intraoperative 3D imaging system in addition to an IGS system. Moreover, the long setup time of the system in the operating room (e.g., draping) and ergonomic issues (e.g., size and positioning of the system) can hinder the surgical workflow. More importantly, the intraoperative image is a snapshot in time of the patient relative to a reference array and if, during the operation, the reference array gets accidentally bumped, another scan needs to be acquired to restore the correct correspondence between the patient and the reference array. Similarly, the intervertebral motion over the course of the spine surgery can invalidate the correspondence between the reference array and the vertebrae that is not directly attached to the reference array. Navigation accuracy at these vertebrae tends to worsen with distance away from the reference array. Thus, large motions adversely impact the navigation accuracy, necessitating a new 3D intraoperative scan to be performed.

32.1.4

Preoperative image-guided surgery systems

Alternatively, several manufacturers of the IGS have taken the approach of utilizing preoperative images combined with the same IGS equipment mentioned in Section 32.1.3.1. A scan of the patient’s relevant anatomy is obtained before the surgery. The scan data are transferred to the computer workstation via a network connection or physical data transfer interfaces such as universal serial bus or optical disks. The image data are reformatted by the computer workstation into standard radiological views, such as sagittal, coronal, axial radiological views, providing an opportunity for surgical planning. For example, in spinal procedures, the size of structures such as the width of pedicles can be measured, and a virtual implant of the desired size can be placed along the planned trajectory. This allows the surgeon to confidently direct the screws into this predefined position even in complex surgical procedures. IGS is made possible by registration of the preoperative image to the intraoperative anatomy of the patient. This registration typically involves selecting multiple points ( . 3) that are distinct anatomical landmarks on the preoperative image as well as on the patient’s anatomy. A trackable probe is employed to touch the anatomical points in the surgical field that correspond to those selected on the preoperative images. This method is called paired-point matching. Pairedpoint matching can be augmented with surface matching, a process in which additional points are selected on the patient’s exposed surface anatomy. All preoperative IGS have inaccuracies as a result of the mismatch between the preoperative image and the current state of the surgical anatomy. These errors can arise from the registration process, the quality of the preoperative images, and surgical instrument tracking error. A mean error of less than 2.0 mm is generally considered clinically acceptable for spinal and cranial surgeries. The navigation accuracy must be confirmed before any surgical navigation is attempted. The navigation accuracy can be validated by placing a tracked probe tip on several different exposed anatomical points and observing the virtual probe on the preoperative images. If the locations of the virtual and real probe do not match, then the registration process should be repeated. Once the navigation accuracy is validated, the anatomy previously hidden from direct surgical line of sight can be visualized on the computer monitor. During surgical navigation, a surgical instrument’s tip and trajectory are visualized on the preoperative image of the anatomy in multiple planes such as axial, sagittal, or coronal views (Fig. 32.2). This enables the surgeon to follow the surgical plan by emulating the planned entry point and trajectories or, alternatively, modify the plan as deemed necessary intraoperatively. Every step of the procedure can benefit from the IGS system helping the surgeon eliminate injury to sensitive organs and improve the safety of the patient.

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FIGURE 32.2 Preoperative IGS system for pedicle screw implant trajectory planning. The trajectory of the screw pathway is displayed in axial, sagittal, and coronal views. IGS, Image-guided surgery.

FIGURE 32.3 7D Surgical MvIGS system, including an integrated projection system, stereo machine vision cameras, and infrared tool tracking system integrated into a surgical light. MvIGS, Machinevision Image-Guided Surgery.

32. 7D Surgical MvIGS

32.2

Motivation and benefits of the Machine-vision Image-Guided Surgery system

The 7D Surgical MvIGS system (Fig. 32.3) is the first and only IGS based on machine vision technologies, with the benefits of having a simple and fast workflow, does not require intraoperative radiation, and is cost-effective compared to similar classes of devices. IGS allows surgeons to visualize deeply situated anatomy during surgical procedures, which can reduce procedural complication rates and improve patient care [27]. However, widespread use of IGS has been limited due to several barriers to adoption, including (1) complex workflow and long learning curve, (2) extended surgical time due to workflow disruptions, (3) line-of-sight issue for optical trackers, (4) requiring nonsterile user assistance, (5) needing intraoperative ionizing radiation, and (6) large device footprint. The 7D Surgical MvIGS system,

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approved for spinal and cranial surgical procedures, aims to address these barriers, by employing 3D optical imaging technologies and machine vision algorithms. These barriers and the 7D Surgical MvIGS system’s solutions are discussed in detail below.

32.2.1

Complex workflow and long learning curve

Intraoperative IGS systems require a lengthy setup, which includes maneuvering the imaging device in and out of the desired field of view, adjusting the table height, and steps to maintain sterility of the surgical field. Also, the tool tracking system used for tracking should have line of sight to both the intraoperative scanner and the patient before images can be acquired. Registration is a necessary process to utilize preoperative images for surgical guidance. Traditional paired-point matching registration based on anatomic landmarks has a relatively long learning curve that can result in surgeon frustration and longer operation times, especially for new users. The main difficulty is that it puts the onus on the surgeon to accurately match preselected fiducial points with their respective anatomical location. Often, preselected fiducials might not be reachable during surgery, due to obscured or removed anatomy, or they may be incorrectly selected, due to the lack of distinct features that are recognizable by the surgeon. In these scenarios, a nonsterile user is needed to work with the surgeon intraoperatively to adjust and/or select new fiducials. Complex anatomy can further exacerbate this problem, as a result, add significant time to the registration process and ultimately to the surgical procedure. A significant learning curve thus exists for surgeons to be efficient at this workflow. Instead of requiring the user to accurately pick paired points, the 7D Surgical MvIGS system relaxes this requirement by capturing a high-resolution 3D surface image of the patient. This 3D surface image, in combination with machine vision algorithms, greatly reduces the finesse required in traditional paired-point matching approaches while using thousands of automatically generated points based on the exposed anatomy. The primary benefit is the surgeon only needs to approximately indicate to the system which anatomical location they are interested in (e.g., which spinal level). The workflow to accurately match preselected fiducials is not necessary. The entire registration workflow, which includes optical surface acquisition and patient region identification takes less than 20 seconds. After the registration is complete, the surgeon is asked to verify the registration by touching the anatomy with the tip of the customized trackable surgical instrument and comparing the virtual position of the tool on the system monitor to the location of the tool on the patient’s anatomy. By automating the surface digitization and the registration processes, valuable operating time is saved, and the learning curve is significantly minimized.

32.2.2

Extended surgical time due to workflow disruptions

A common challenge in the intraoperative IGS systems is dealing with variation in the spine alignment as rods and screws are inserted due to the nonrigid anatomy of the spine. The spine level that has the reference array attached to it is always tracked reliably (providing that the reference array is rigidly attached) but the rest of the spine levels can move relative to the reference array, introducing a mismatch between the registered medical image and the patient’s spine. To overcome this, the spine can be imaged again in the new alignment, which involves a lengthy setup process (15 30 minutes) using current intraoperative IGS. In addition, rescanning exposes the patient to additional ionizing radiation. In spinal surgeries involving multiple vertebrae, it is recommended that registration be performed segmentally, to reduce navigation errors associated with intervertebral motions. Here, the benefit of the 7D Surgical MvIGS system is amplified. Traditional preoperative IGS systems deal with this issue by performing multiple consecutive registrations, each requiring movement of the reference array to the spine level that is being operated on. This process is also quite lengthy (5 7 minutes per spine level). The 7D Surgical MvIGS system, however, can perform registrations quickly. Rather than spending 15 30 minutes to acquire new images in case of intraoperative IGS system or 5 7 minutes per registration in the case of current preoperative IGS systems, the surgeon can simply attach the 7D Surgical reference array to the desired spine level, indicate to the system the spine level of interest using a tracked instrument, and engage the system through a foot pedal click to perform a Flash Registration. The system digitizes the surface of the operative anatomy and automatically updates the registration. Since registration can be performed quickly, resistance from the surgeon to perform multiple registrations, one at each spinal level, is reduced. With this technology, the surgeon no longer has to worry about the potential mismatches between the registered medical image and the patient’s spine introduced due to intervertebral motion. Additionally, all IGS systems rely on the use of a reference array that is localized by the tool tracking system. This reference array needs to be fixed to the anatomy of interest and the customized surgical instruments are navigated with

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respect to the reference array. The tool tracking system follows the anatomy via the reference array and hence the registration accuracy is maintained even if the patient or camera moves, as long as the reference array remains fixed to the anatomy. However, unwanted accidental change in the position of the reference array will introduce navigation inaccuracies, which worsens with increased distance from the reference array, disrupting the workflow. This is a wellrecognized limitation of the IGS systems. If the reference array is bumped, a new registration must be performed. In intraoperative IGS systems, this means repositioning the patient to be scanned and/or setting up the intraoperative scanner again and reimaging and reregistering the patient’s anatomy. This process can take 15 30 minutes of valuable operating time and can add to user frustration. In addition, rescanning exposes the patient and surgical team to additional ionizing radiation. In preoperative IGS systems, a new registration involves repicking the point on anatomical landmarks and verifying the quality of the registration. In either case, in order to get back to the state of accurate navigation, significant time costs are incurred. The 7D Surgical MvIGS system and its Flash Fix technology allow for the near instantaneous autocalibration of the patient registration process using machine vision. Rather than spending anywhere between 15 and 30 minutes to fix a registration as you would with existing intraoperative IGS systems, the surgeon simply engages the system through a foot pedal click to enact Flash Fix. The system then digitizes the surface of the operative anatomy and identifies what has spatially changed in the surgical environment since the last registration and updates the patient registration automatically. The surgeon no longer has to wonder if the reference array was bumped or worry about adding extra time to reregister the patient if the reference array is in fact bumped. With the Flash Fix technology, the registration can be updated at any time with minimal impact to the surgical workflow. Lastly, a crucial benefit of both the multilevel Flash Registration and the Flash Fix technology is that the patient and/or operating room staff are not exposed to additional ionizing radiation. These processes take only a few seconds and the IGS navigation can continue seamlessly.

32.2.3

Line-of-sight issues for optical trackers

32.2.4

Requiring nonsterile user assistance

Almost all IGS systems require a clinical specialist in practice to help with the hardware setup and the operation of the IGS system throughout the clinical workflow. This not only adds cost to the operation but can also create frustration for the surgeons, while adding additional time to the surgery, especially when the surgeon needs to deviate from the preplanned workflow. For example, as mentioned in Section 32.2.2, when the reference array is bumped, significant effort and time are required to restore navigation accuracy. On the contrary, the 7D Surgical MvIGS system gives surgeons full control over the workflow as well as the system hardware while the surgeon remains sterile. The surgeon can individually progress through the entire workflow to navigation by interacting with a foot pedal. Additionally, in the case of a reference array bump, Flash Fix quickly restores navigational accuracy. Additionally, as explained in Section 32.2.3, the surgeon can control the placement of the onboard surgical light and optical tracking cameras through a sterile handle. On the other hand, if intraoperative IGS or traditional fluoroscopy is used, a technician needs to be present to operate the radiation machine. The 7D Surgical MvIGS system operates based

32. 7D Surgical MvIGS

Instruments can be guided with electromagnetic (EM) tracking systems. These systems localize small EM field sensors in an EM field of known geometry, allowing tracking the position and orientation of an instrument. However, they are susceptible to distortions from nearby metal sources and have limited accuracy compared to the optical tracking systems [28]. Due to limitations of EM tracking systems, nowadays optical tracking systems are widely adopted in IGS systems. These systems rely on arrangements of optical tracking cameras (usually two cameras) positioned away from the surgical table and looking at the operation field. Although they offer accurate navigation, their line-of-sight issues have plagued IGS systems. If at any time the cameras cannot see the arrays on the customized surgical instruments due to their line of sight being blocked, the tracking is interrupted, which can cause disturbance of the navigation and frustration for surgeons. In addition, the surgeon does not have direct control over these cameras as they are not sterile. Therefore, they must remotely provide instructions to operating room staff to adjust the cameras to improve line of sight to the tracked instruments. To overcome this, the 7D Surgical MvIGS system has embedded the optical tracking system in an onboard overhead surgical light, which can be adjusted via a sterile light handle. Surgeons are used to pointing the light source toward the site of operation. This means that as the embedded surgical light is adjusted, the surgeon is in effect also updating the position of the cameras. This greatly improves the trackability of the surgical instruments. The 7D Surgical tools are designed to leverage this optimization by having their planar tracking array facing upwards, while preserving the surgeon’s line of sight down to the surgical field (see Fig. 32.4).

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FIGURE 32.4 Examples of 7D Surgical’s trackable surgical tools: (A) spine reference array, (B) awl, (C) pedicle probe, (D) cranial reference array, and (E) pointer.

on preoperative medical images and hence does not require additional personnel to operate the ionizing radiation device, yielding additional time and cost savings.

32.2.5

Exposure to intraoperative ionizing radiation

When traditional intraoperative IGS is used, the patient, surgical staff, and surgeon are exposed to ionizing radiation. To minimize the occupational radiation, the staff and surgeons must wear lead aprons. However, wearing the heavyweight aprons over prolonged periods of time has been shown to cause orthopedic and ergonomic problems, particularly those related to the spine [29,30]. In addition, lead aprons do not allow for full coverage of the person’s body, nor do they fully block the radiation. In fact, the standard 0.5 mm lead aprons block just over one-third of the scattered radiation [31]. Therefore, the surgeons and staff receive a significant dosage of ionizing radiation despite wearing the heavy lead aprons. The staff are used to simply leaving the operating room during a scan. As these ionizing emitting devices have been used consistently for spine procedures over the last 20 30 years, the operating room staff members have experienced significant deleterious effects including an increased chance of developing several types of cancers. Mastrangelo et al. found a statistically significant increase in solid malignant tumors among orthopedic surgeons compared to other healthcare workers in the same facility [32]. Also, there has been an increase in the incidence of radiation-induced cataracts among the surgical staff and surgeons and hence many surgeons have started wearing surgical shielding goggles to decrease this risk [33]. These factors strongly indicate that radiation dosage for spinal surgeons should be reduced through the utilization of radiation-free technologies. The 7D Surgical MvIGS system removes the need to use radiation for navigation in the operating room. Instead, the patient’s preoperative image is loaded to the system and the operative anatomy of the patient is digitized using nonionizing visible light. The two surfaces are then automatically registered, enabling the surgeon to accurately navigate on the preoperative images of the spine, while providing a radiation-free surgical environment for surgeons, staff, and patients. Finally, by having the patient imaged in the controlled setting of the radiology department, further radiation exposure can be reduced for the patient through the use of size and weight-specific imaging protocols, with better image quality [34]. These individualized scans are difficult to achieve using intraoperative CT or 3D fluoroscopy technologies.

32.2.6

Large device footprint

The traditional fluoroscopy or intraoperative IGS machines are very unwieldy and handling these machines in small operating rooms and narrow hallways of hospitals is cumbersome. Also, additional personnel are required for operating the machines during the surgery, further cluttering the small operating rooms. The 7D Surgical MvIGS system can be easily wheeled through the hospital and it is designed to roll through standard entrance doors without the need for further floor support or retrofitting as required by some of the larger intraoperative imaging technologies. As the 7D Surgical MvIGS system is controlled by the surgeon or operating room staff, additional personnel such as clinical specialists are not required, reducing the number of people in the operating room.

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FIGURE 32.5 Hardware overview of the 7D Surgical MvIGS system. MvIGS, Machine-vision Image-Guided Surgery.

32.3 32.3.1

Technical aspects of the 7D Surgical Machine-vision Image-Guided Surgery system Hardware components

32.3.2

The Machine-vision Image-Guided Surgery system workflow

The 7D Surgical MvIGS system is designed to provide an easy and fast workflow for surgeons. The system has five key steps: (1) load data, (2) adjust 3D model, (3) select anatomy of interest, (4) register, and (5) navigate. Initially, the patient’s preoperative CT or magnetic resonance (MR) image is loaded into the system. A 3D model of the preoperative image is then created based on a threshold value applied to the intensity of the image volume

32. 7D Surgical MvIGS

The 7D Surgical MvIGS system is designed and manufactured in Ontario, Canada. Fig. 32.5 shows the main components of the 7D Surgical MvIGS system: (1) surgical arm with extension arm, (2) yoke, (3) system head, (4) surgeon monitor, (5) operator monitor, (6) workstation (includes computer, keyboard, computer mouse, software), (7) system cart, (8) castor locking pedal, (9) foot pedal, and (10) connector for removable sterile light handle. The surgical arm and yoke allow the surgeon to aim the system head toward the desired volume to utilize the builtin surgical lights and to direct the optical cameras for tool tracking and 3D surface scan. Joints allow both the surgeon and operator monitors to be adjusted to user preferences. These components also allow the cart components to be folded into a more compact configuration for transport and storage. The system head consists of a camera gantry integrated with a surgical-grade LED light source. The camera gantry is composed of a proprietary machine-vision camera system and projector, aiming lasers, and an infrared (IR) optical tracking system. The 7D Surgical MvIGS system utilizes the Polaris Vicra (Northern Digital, Ontario, and Canada), which consists of two cameras with IR filters, surrounded by IR LEDs that illuminate the tracking volume [35]. The projector device and the machine-vision camera system are employed to digitize the operative surface intraoperatively. The aiming lasers are used for positioning the system head at the correct working distance and orientation. The surgeon monitor and the operator monitor are mirrored. Having the same content on both displays helps coordinate the surgeon and the staff during the surgery. The system cart includes four castors for mobility. The castor locking pedal at the front of the cart can be used to lock, unlock, or set the directional lock for the castors. The directional lock confines the cart to move in a forward direction to facilitate transport (e.g., in long corridors), whereas unlocked castors allow movement in all directions. The foot pedal and the sterile light handle allow the surgeon to interact with the 7D Surgical MvIGS system while remaining sterile. The foot pedal has three buttons and their functions are context-sensitive.

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FIGURE 32.6 7D Surgical’s Flash Registration: proprietary 3D imaging method and software algorithms automate the registration process. (Right image) 3D intraoperatively digitized surface of the spine, (left image) 3D rendering of the preoperative CT. The yellow highlighted region on the left defines the target anatomy. Shown in this figure is a lumbar spine model covered with red Play-Doh which mimics the presence of soft tissue. 3D, Three-dimensional.

pixels or voxels. This 3D model represents the anatomical site that the 7D Surgical MvIGS system will register to. Optionally, cropping tools are available to remove undesired regions. The surgeon then selects a minimum of three regions on the 3D model to demarcate the anatomy of interest. For example, in spinal surgeries, the anatomy of interest could be a vertebral level. In cranial surgeries, this could be the face of the patient (skin) or the cranium (bone). During registration, the system digitizes the patient using visible light. This is performed using the technique of structured light [36], which we referred to as a Flash of light, and is an integral part of the registration process. To perform Flash Registration, the system head is aimed directly at the target patient’s anatomy that is to be registered to. The aiming laser system embedded in the system head assists with the aiming. 3D surface acquisition follows, leading to the measurement of hundreds of thousands of points that accurately represents the visible surface anatomy. Using a tracked tool, the surgeon selects the corresponding regions from the preoperative 3D model. Alternatively, they can be acquired using a mouse by clicking on corresponding regions from the acquired structured light point cloud of the surface, also referred to as the digitized surface. The availability of the digitized surface thus gives the user an option to proceed with a completely patient contactless registration workflow. Additionally, existing technologies require corresponding points to be picked accurate to a few millimeters, whereas 7D Surgical’s approach only requires approximate identification, made possible by leveraging machine vision technology. The system then automatically registers the digitized surface to the preoperative dataset of the patient. This overall process is referred to as Flash Registration and reduces the length of existing workflows to seconds. Fig. 32.6 shows an example visualization of Flash Registration that digitizes a human lumbar spine phantom and automatically aligns its current spatial position to a preoperative dataset (e.g., CT). Once the preoperative image and the intraoperative digitized surface are registered, the surgeon then validates the registration accuracy using a tracked pointed tool, by touching known anatomical landmarks and sliding the tip of the pointed tool along the surface of the patient and verifying that they are seeing the expected anatomy on the IGS navigation monitor. In the navigation stage, the surgical tools are visualized in relation to the patient’s anatomy such that they are presented with various radiological (e.g., sagittal, axial, coronal, inline) and 3D views. These visualizations of the patient’s anatomy in relation to the surgeon’s tools are what is used during the procedure to guide tissue resection or implant insertion. A photograph of the 7D Surgical MvIGS system being used by the surgeon to navigate the patient’s anatomy is shown in Fig. 32.7. In addition to standard navigation views, the 7D Surgical cranial software enables simultaneous registration of multiple modalities, such as MR and CT. The workflow consists of independently registering multiple preoperative datasets. Once completed, the registrations can be linked during navigation. No preoperative image fusion is required. An example usage of multimodal navigation for cranial surgeries is shown in Fig. 32.8.

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FIGURE 32.7 The Machine-vision IGS system registers the spatial position of the patient in the operating room, while also tracking the movement of surgical tools as they relate to the patient’s anatomy in a spinal procedure. IGS, Image-guided surgery.

FIGURE 32.8 Screenshot from the cranial software of the 7D Surgical MvIGS system during navigation, linking the registration information performed separately to the CT and MR dataset. MR, Magnetic resonance; MvIGS, Machine-vision Image-Guided Surgery.

Flash Registration

At any time during the procedure, the surgeon can use the foot pedal to initiate a Flash Registration, which acquires an intraoperative 3D digitized surface of the patient’s anatomy based on structured light imaging, followed by registration. The registration process is based on the iterative closest point algorithm [37], which iteratively computes a transformation by reducing a distance metric between the intraoperative 3D digitized surface scan and the preoperative 3D model. In a cranial procedure, the surgeon may Flash to the patient’s face to plan their skin flap, and Flash again directly to the skull to confirm the location of the bone flap. Due to the density and accuracy of the 3D patient surface points collected by 7D Surgical Machine-vision cameras, registering directly to any cranial anatomy is fast, efficient, and accurate. In spinal procedures, if the reference array gets accidentally bumped, Flash Registration can be performed without the need to repick points. This is done by comparing the 3D surface scan at the time when the registration was first performed and the current scan which has the reference array in a different orientation. This process completes in a matter of seconds to restore navigation accuracy. We refer to this feature as Flash Fix.

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32.4

Clinical case studies with 7D Surgical Machine-vision Image-Guided Surgery system

The 7D Surgical MvIGS system has been used in a wide range of clinical cases by numerous surgeons. Here we present a few spinal and cranial clinical case studies that have employed the 7D Surgical MvIGS system.

32.4.1

Revision instrumented posterior lumbar fusion L3 L5

In this example, the patient is a 60-year-old female who had previously undergone a lumbar laminectomy for symptomatic lumbar stenosis. Significant improvement in her symptoms were observed postoperatively. Unfortunately, she presented again with a history of worsening lower back pain radiating into the bilateral buttocks and thighs. Her symptoms were exacerbated by walking and relieved by sitting. Imaging disclosed significant scar tissue in the region of her previous laminectomy, and recurrent lumbar stenosis (Fig. 32.9). A large mass of scar tissue from the previous laminectomy was spared during the initial approach. The surgical site was digitized intraoperatively in 230 ms using 7D Surgical’s Flash Registration technology (Fig. 32.10). The surgeon identified the anatomical areas to be used for registration (Fig. 32.11) by selecting preplanned level definition points with the 7D Surgical awl and foot pedal. This anatomical information was then automatically registered to the preoperative CT via 7D Surgical’s proprietary machine-vision algorithms. The segmental regions used for registration included the spinous process and lamina of L5 along with transverse processes of L4. Shown in Fig. 32.12, each green point represents an individual digital fiducial (1430 in total) that the technology identifies automatically to make a successful match to the patient. A total of three vertebral levels were navigated and six screws were instrumented during this case. This patient has done extremely well in the postoperative period. She has had complete resolution of her preoperative symptoms and was back to her normal level of function within 6 weeks of surgery. Compared to manipulating the C-arm in and out of the field for anterior posterior and lateral imaging during cases without the 7D Surgical MvIGS system, significant surgical time was saved during the procedure. Maintaining sterility in the field requires extensive clinical experience as the C-arm is maneuvered in and out of the field as the table height is adjusted to accommodate the positioning of the C-arm. The 7D Surgical MvIGS system eliminates the need for any of these maneuvers. Additionally, it provides the surgeon with optimal overhead lighting to perform the procedure. Lastly, due to the patient’s small pedicles and the previous laminectomy, proper and accurate placement of the six pedicle screws would have been challenging without the use of the 7D Surgical MvIGS system (Fig. 32.13). The surgeon of this case commented that “The process of intraoperative registration is quick, user-friendly, and accurate. The entire registration process can be done by the operating surgeon within a few seconds. Preoperative

FIGURE 32.9 A 3D volumetric view of the preoperative CT of a 60-year-old female showing the previous laminectomy. 3D, Three-dimensional.

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FIGURE 32.10 Surgical incision showing scar tissue from previous laminectomy.

loading of the CT scan can be done at any point before the surgical procedure. Additionally, reregistration is a simple, straightforward process, should it be necessary during the procedure. From a surgical perspective, the pedicle screw placement workflow is not altered by use of the 7D Surgical MvIGS system, while the total surgical time is reduced due to the reduction of time spent placing and adjusting the C-arm for fluoroscopic imaging.”

32.4.2

Revision instrumented posterior lumbar fusion L4 S1

A 60-year-old male presented with a history of posterior L4 S1 decompression and fusion 1 year prior. Pseudarthrosis at L5 S1 then occurred postprocedure. Posterior reexploration along with placement of S2 pedicle screws (due to a left

32. 7D Surgical MvIGS

FIGURE 32.11 Regions corresponding to the anatomy of interest (in yellow) are selected in the preoperative image for registration.

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FIGURE 32.12 Points acquired using 7D Surgical’s Flash imaging technology are automatically selected for registration (in green). Scar tissues (in gray) are not used.

FIGURE 32.13 The axial and sagittal views shown during navigation on the 7D Surgical MvIGS system that are used to guide the trajectory of pedicle screws. Measurement tools enable live implant sizing. MvIGS, Machine-vision Image-Guided Surgery.

S1 screw fracture) was planned along with an anterior lumbar interbody fusion at L5 S1. Bony union was confirmed on CT at L4 5. The patient suffered from refractory back pain and bilateral leg numbness and tingling, but no radiating pain; he failed many months of conservative therapy for his symptomatic nonunion before considering repeat surgery. The patient’s preoperative CT contained heavy image artifacts due to existing pedicle screws at L4 S1. Registration was performed on the remaining spinous processes of those levels, where the scan was free of artifacts, and the anatomy free of scar tissue. The surgeon was able to sterilely position the 7D Surgical Machine-vision cameras in an intuitive fashion, similar to how he would be aiming the built-in surgical lighting, and perform the Flash Registration process via the system’s foot pedal. The 7D Surgical MvIGS system was able to digitize the patient, and used 1558 points for registration, in a total workflow time of 32 seconds (Figs. 32.14 32.15). Accuracy was maintained throughout the procedure, allowing for cannulation and placement of three new pedicle screws at S1 and S2. The pedicle screw on L5 was placed adjacent to an existing screw (Fig. 32.16). The patient had an uncomplicated hospital course but was readmitted for 24 hours for nausea and emesis on postoperative day 4; no specific source was found. At 2 weeks, he had decreased his narcotic requirement by half, and at 2 months, his back pain was significantly reduced (although not resolved completely) as he began formal lumbar stretching and core strengthening.

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FIGURE 32.14 A 3D model of a tracked tool is overlaid on top of the 3D surface point cloud of the patient’s anatomy during registration, enabled by the 7D Surgical MvIGS system which fuses information from the 3D surface imaging system and the tool tracker. This assists the surgeons with identifying anatomical targets during the registration process. 3D, Three-dimensional; MvIGS, Machine-vision Image-Guided Surgery.

32. 7D Surgical MvIGS FIGURE 32.15 The 1558 points (shown in green) were used to register the 3D surface point cloud of the patient to the preoperative CT. Points not used for registration, potentially due to the presence of soft tissue on the bone, are shown in gray. Beige regions show the anatomical registration target. 3D, Three-dimensional.

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FIGURE 32.16 Navigation views as displayed on the 7D Surgical MvIGS system. In this surgical case, the system has enabled the accurate placement of a new pedicle screw adjacent to an existing screw. MvIGS, Machine-vision Image-Guided Surgery.

32.4.3

Cervical fusion with radiofrequency ablation and vertebroplasty

A 54-year-old male with a history of esophageal cancer presented with a burst fracture in his C7 vertebral body along with posterior projection to the spinal canal. He experienced significant mechanical cervical spinal pain that worsened with movement in addition to radiculopathy involving both arms. The decision was made to perform a posteriorapproach fusion of C5 T2 with bilateral C7 transpedicular radiofrequency (RF) tumor ablation and vertebroplasty. Prior to the procedure, the patient’s preoperative CT was reviewed. The surgeon exposed the patient’s C5 T2, sterilely positioned the cameras, and initiated the Flash Registration process via the foot pedal. Using the 7D Surgical awl, he then collected points on the patient’s anatomy similar to those defined on the preoperative CT (Fig. 32.17). The system performed Flash Registration to C6 in less than a second, while colocalizing 1123 points between the digitized surface and preoperative CT scan (Fig. 32.18). For this registration, the surgeon had a total workflow time of 68 seconds. Soon after instrumenting C5 using the previous registration, the reference array was accidentally hit. The 7D Surgical Flash Fix was used to simultaneously digitize the patient and correct the registration instantly to allow the surgeon to continue operating. This entire registration correction took 4 seconds without the need for any intraoperative ionizing radiation. To maintain accuracy throughout the construct, T1 T2 was reregistered in only 47 seconds, and the pedicles were cannulated using a drill with a tracked guide. One last registration was performed on the highly mobile C7 vertebra. To stabilize the fracture, the C7 registration was performed to create bilateral pilot holes for the insertion of RF ablation (RFA) and vertebroplasty needles. The remaining steps of the RFA and vertebroplasty were performed under fluoroscopic guidance as per standard of care. The cannulation of the pedicles allowed for easy placement of eight screws and was greatly assisted by the 7D Surgical MvIGS system, while minimizing operating time and radiation (Figs. 32.19 and 32.20). The patient has done very well postoperatively and was ready for discharge on postoperative day 1, with Eastern Cooperative Oncology Group score 1, which indicated that the patient was able to carry out work of a light or sedentary nature [38]. Additionally, the patient’s spinal cord American Spinal Injury Association impairment score was E which indicates normal sensory and motor functions [39].

32.4.4

Cervical fusion

A patient who required cervical fusion was identified. The cervical levels to be instrumented were exposed, and an intraoperative CT was acquired. The CT dataset was loaded into the 7D Surgical MvIGS system. The surgeon aimed the stereo machine vision cameras at the anatomy of interest using the sterile light handle and attached the 7D Surgical Reference Array to C6. Flash Registration was initiated using the foot pedal, instantly digitizing the patient’s exposed anatomy (Fig. 32.21). The surgeon then identified three regions on C6 using the 7D Surgical awl, and with one additional foot pedal press, 622 unique points were registered in 1.5 seconds (Fig. 32.22). From initiating the Flash to the completed registration, the complete 7D Surgical workflow took the surgeon 21 seconds. This registration was used to instrument C5 and C6. Following a second registration to C3 and C4, the surgeon cannulated the lateral masses of these levels. The navigation screenshots are shown in Fig. 32.23. When the surgeon moved on to C2, he determined that the spine had changed position since the initial CT scan due to movement during instrumentation of the previous vertebral levels. Using 7D Surgical’s

FIGURE 32.17 A 3D model of a tracked tool is overlaid on top of the 3D surface point cloud of the patient’s anatomy during registration. 3D, Three-dimensional.

FIGURE 32.19 The axial and sagittal views during navigation in the thoracic region as displayed on the 7D Surgical MvIGS system. MvIGS, Machine-vision Image-Guided Surgery.

32. 7D Surgical MvIGS

FIGURE 32.18 The 1123 points selected for registration are shown in green.

FIGURE 32.20 Postoperative CT showing successful screw placement in C5 C6 and T1 T2.

FIGURE 32.21 A 3D surface point cloud inside an incision in the cervical region acquired using the 7D Surgical Machine-vision cameras. 3D, Three-dimensional.

FIGURE 32.22 The 622 points selected for registration are shown in green.

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FIGURE 32.23 The axial and sagittal views during navigation of C4 as displayed on the 7D Surgical MvIGS system. MvIGS, Machine-vision Image-Guided Surgery.

machine-vision-powered Flash Registration, the surgeon was able to reregister to C2 using the original CT scan without the need for any further radiation in under 1 minute. C2 was then instrumented with the 7D Surgical awl, pedicle probe, and a hand-held drill. Overall, the 7D Surgical MvIGS system demonstrated its ability to support a multilevel cervical procedure while maintaining excellent navigational accuracy and keeping registration time at a minimum (Fig. 32.24). In this case, the average registration workflow time was 48 seconds and an average of 608 points were used for each registration. The total radiation exposure was significantly reduced and the estimated time saving in this case was about 20 minutes by eliminating the need for additional intraoperative CT scans.

32.4.5

Left temporal open biopsy

Prior to the procedure, the patient’s preoperative CT and MR images were loaded into the 7D Surgical MvIGS system. To build the 3D model, a threshold was applied to the MR data such that the skin surface was visible, and a different threshold was applied to the CT data to create the skull surface. The patient was positioned in the skull clamp in an extreme lateral position for access to the region of interest. The 7D Surgical cranial reference array was rigidly attached to the skull clamp using the starburst connector. The 7D Surgical MvIGS system head was aimed at the patient’s face and the site was instantly digitized (Fig. 32.25). Four

32. 7D Surgical MvIGS

FIGURE 32.24 Postoperative CT showing eight bilateral screws placed in C2, C4, C5, and C6.

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FIGURE 32.25 Corresponding regions identified on the MR image and intraoperative digitized patient surface. MR, Magnetic resonance.

FIGURE 32.26 Green dots represent registered points between preoperative MR images and intraoperative digitized patient surface. MR, Magnetic resonance.

FIGURE 32.27 Corresponding regions identified on patient CT (left) and intraoperative digitized patient surface point cloud (middle); the region in green is points which have been selected for registration, whereas the points in orange are not. The beige region belongs to the preoperative CT image (right).

regions were picked virtually on the MR and on the digitized patient surface without the need to contact the patient using the 7D Surgical MvIGS system user console. The 7D Surgical MvIGS system then registered thousands of points in under 2 seconds using the patient’s anatomy, shown below in green (Fig. 32.26). After the patient was draped, the surgeon used this registration to plan the appropriate location for the skin flap. In order to minimize the craniotomy size, the surgeon chose to perform a second registration by aiming the system to Flash directly at the exposed bone (Fig. 32.27). Virtual regions were picked on the CT and on the intraoperative digitized surface, as shown in blue. Of the 300,000 points collected instantly using Flash, the 7D Surgical MvIGS system was able to detect which points to use for registration. Using the Linked Registration feature of the 7D Surgical cranial software, the registered CT and MR datasets were shown simultaneously on the monitor, overlaid on each other. No preoperative image fusion was required. Using both

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FIGURE 32.28 Navigation of 7D Surgical pointer which is used to plan biopsy trajectory.

registered modalities, the surgeon was able to plan the craniotomy location and biopsy approach using the 7D Surgical Probe intraoperatively (Fig. 32.28).

32.5

Future of 7D Surgical Machine-vision Image-Guided Surgery system

7D Surgical’s powerful suite of optical imaging capability and machine-vision algorithms provide the groundwork for solutions to many critical spinal and cranial IGS navigation problems. Below we present one challenge and how 7D Surgical’s technology can potentially improve the current standards of care. It is important to note that at the time of writing this chapter, the following application of the 7D Surgical MvIGS system has not achieved any jurisdictional regulatory approval and is in the research and development phase.

Multilevel registration for spine deformity procedures

A common challenge in spinal surgery is progressively measuring the shape of the spine intraoperatively as rods and screws are inserted and the spine alignment changes. This capability is especially valuable for spine deformity surgeries where considerable change in spinal anatomy may be needed to improve the patient’s morbidity. For example, to correct for a deformity such as scoliosis, it may be desirable to reduce the angle between adjacent vertebrae to within a threshold range [40]. Current technologies require ionization radiation to provide feedback to the surgeon on whether they have achieved an ideal spinal alignment, but even then, the feedback in most cases is qualitative. Fluoroscopy images can only provide 2D planar views, which can obscure certain anatomies. Some intraoperative X-ray imaging devices can provide 3D information, however, their lengthy setup time and workflow mean they are not commonly used to incrementally measure the alignment of the spine. Scanners that do not include a mechanized scan table are also limited to approximately four vertebral levels, and complicated deformity cases often involve many more. In addition, using intraoperative X-ray imaging devices exposes harmful radiation to patients and surgical staff. There exists a need to provide surgeons with fast and accurate intraoperative feedback for complex multilevel spinal deformity cases. By leveraging data from an intraoperative 3D digitized surface, the 7D Surgical’s Flash Align technology can independently register multiple vertebrae at once. After registration, each vertebra can be tracked independently in three dimensions, enabling the measurement of the shape of the surgically exposed spine as it appears on the surgical table. A 3D model of the spine can also be reconstructed, as shown in Fig. 32.29. This simultaneous segmental registration approach overcomes one of the challenges with preoperative IGS systems that is associated with the discrepancy between the shape of the spine in the preoperative image and the patient position on the surgical table. This discrepancy arises due to differences in the patient’s orientation between a preoperative scan (usually performed supine) and when

32. 7D Surgical MvIGS

32.5.1

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FIGURE 32.29 Segmented virtual vertebrae models as displayed on the 7D Surgical MvIGS system software. In this example, a curved spine phantom where a preoperative image has been acquired is straightened. The preoperative image is shown in opaque gray, and the updated intraoperative position of the spine is shown in the segmented colored models. MvIGS, Machine-vision Image-Guided Surgery.

they are on the surgical table (usually in the prone position), and also due to forces and corrections applied during surgery. With existing IGS systems, a common practice is that the surgeon would register multiple spinal levels at once for a multilevel surgery. In essence, they are assuming the intervertebral motion between adjacent spinal levels is minimal and are willing to trade navigation accuracy for a shorter registration workflow. The 7D Surgical MvIGS system can perform multilevel segmental registration with negligible workflow impediment, enabling accurate navigation using the preoperative image despite changes in the shape of the spine during surgery. At any time during the procedure, the surgeon can simply press the foot pedal to initiate Flash Align, involving the intraoperative structured light acquisition of the surgical area. Without additional user actions, the system then proceeds to identify and register all vertebrae, based on the acquired structured light image, and see the updated position of all vertebra. Knowing the individual position of each vertebra can enable the 7D Surgical MvIGS system to generate metrics that can help the surgeon decide whether additional correction of the spine is required. These metrics include the Cobb angles, derotation angles, and sagittal balance [41,42]. The 7D Surgical’s Flash Align has the potential to improve surgical outcomes by providing feedback of the correction to surgeons intraoperatively, thereby reducing the need for revision surgeries, which can be between 3.9% and 12.9% [43,44]. It also has the potential to mitigate radiation exposure for navigation by eliminating the need for intraoperative CT and fluoroscopy to provide intraoperative spine alignment updates. This radiation reduction is especially important as many spinal deformity patients are young girls, and a link between early radiation exposure in adolescent women and an increased risk of breast cancer has been demonstrated [45]. Furthermore, this capability could reduce procedural time by instantly updating the virtual vertebral models to reflect the patient’s anatomical position during the procedure rather than having to rescan, a lengthy process using existing intraoperative imaging systems. This can in turn reduce the patient’s anesthesia time. Additionally, consistent live feedback improves the surgeon’s confidence in meeting the preoperative plans.

32.6

Conclusion

Using advanced optical surface digitization technologies, robust image registration, and cutting-edge machine-vision algorithms, the 7D Surgical MvIGS system performs registration of intraoperative anatomy to preoperative MR or CT images considerably faster than current IGS navigation systems. This is achieved without the need to be dependent on intraoperative ionizing imaging technologies, which greatly reduces radiation to the patient, surgeon, and operating room staff. Integration of the tool tracking system into the overhead surgical lighting unit provides improved instrument tracking and alleviates line-of-sight issues. We believe these innovations eliminate many of the restrictions that have traditionally led some surgeons to forgo navigation in favor of freehand or fluoroscopy-based approaches. A significant number of clinical cases, involving surgeons at major research centers, teaching hospitals, and private practice clinics have demonstrated the short learning curve and the evolution of a novice user to become a skilled operator after only a couple of cases. Additionally, high-accuracy navigation, enormous operating room time savings, and

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elimination of ionizing radiation exposure to the patient and surgical staff are the salient advantages of the 7D Surgical innovative technology.

References

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[29] lexandre D, Prieto M, Beaumont F, Taiar R, Polidori G. Wearing lead aprons in surgical operating rooms: ergonomic injuries evidenced by infrared thermography. J Surg Res 2017;209:227 33. [30] Goldstein J, Balter S, Cowley M, Hodgson J, Klein L. Occupational hazards of interventional cardiologists: prevalence of orthopedic health problems in contemporary practice. Catheter Cardiovasc Interv 2004;63(4):407 11. [31] Hyun S, Kim K, Jahng T, Kim H. Efficiency of lead aprons in blocking radiation 2 how protective are they? Heliyon 2016;2(5). Available from: https://doi.org/10.1016/j.heliyon.2016.e00117. [32] Mastrangelo G, Fedeli U, Fadda E, Giovanazzi A, Scoizzato L, Saia B. Increased cancer risk among surgeons in an orthopaedic hospital. Occup Med 2005;55(6):498 500. [33] Harstall R, Heini PF, Mini RL, Orler R. Radiation exposure to the surgeon during fluoroscopically assisted percutaneous vertebroplasty. Spine 2005;30(16):1893 8. [34] Donnelly LF, Emery KH, Brody AS, Laor T, Gylys-Morin VM, Anton CG, et al. Minimizing radiation dose for pediatric body applications of single-detector helical CT strategies at a large children’s hospital. AJR Am J Roentgenol 2001;176(2):303 6. [35] Frantz DD, Leis SE, Kirsch S, Schilling C. System for determining spatial position and/or orientation of one or more objects. U.S. patent 6, 288, 785; 1999. [36] Geng J. Structured-light 3D surface imaging: a tutorial. Adv Opt Photonics 2011;3(2):128 60. [37] Besl P, McKay N. A method for registration of 3-D shapes. IEEE Trans Pattern Anal Mach Intell 1992;14(2):239 56. [38] Oken MM, Creech RH, Tormey DC, Horton J, Davis TE, McFadden ET, et al. Toxicity and response criteria of the Eastern Cooperative Oncology Group. Am J Clin Oncol 1982;5:649 55. [39] Roberts TT, Leonard GR, Cepela DJ. Classifications in brief: American Spinal Injury Association (ASIA) impairment scale. Clin Orthop Relat Res 2017;475(5):1499 504. [40] Majdouline Y, Aubin C-E, Robitaille M, Sarwark JF, Labelle H. Scoliosis correction objectives in adolescent idiopathic scoliosis. J Pediatr Orthop 2007;27(7):775 81. [41] Ames CP, Smith JS, Scheer JK, Bess S, Bederman SS, Deviren V, et al. Impact of spinopelvic alignment on decision making in deformity surgery in adults. J Neurosurg 2012;16(6):547 64. Available from: https://doi.org/10.3171/2012.2.SPINE11320. [42] Berthonnaud E, Dimnet J, Roussouly P, Labelle H. Analysis of the sagittal balance of the spine and pelvis using shape and orientation parameters. J Spinal Disord Tech 2005;18(1):40 7. [43] Luhmann S, Lenke L, Bridwell K, Schootman M. Revision surgery after primary spine fusion for idiopathic scoliosis. Spine 2009;34 (20):2191 7. [44] Richards B, Hasley B, Casey V. Repeat surgical interventions following “definitive” instrumentation and fusion for idiopathic scoliosis. Spine 2006;31:3018 26. [45] Hoffman D, Lonstein J, Morin M, Visscher W, Harris B, Boice J. Breast cancer in women with scoliosis exposed to multiple diagnostic X rays. J Natl Cancer Inst 1989;81(17):1307 12.