The “Stealth Protocol” for CT scans is a specific imaging protocol designed to produce CT data compatible with the Medtronic StealthStation, a widely used surgical navigation platform. Rather than a single standardized scan, it refers to a set of acquisition parameters, typically thin-slice helical CT with specific slice thickness, spacing, and field-of-view settings, that allow the resulting images to be imported into the StealthStation software and used for real-time intraoperative guidance. Surgeons and radiology departments sometimes use the term loosely, and the exact parameters vary by institution and surgical application, but the underlying purpose is always the same: to create a three-dimensional map of the patient’s anatomy that the navigation system can use to track instruments during surgery.
How the StealthStation Uses CT Data
The StealthStation is, at its core, a computer that matches a patient’s physical anatomy to a set of preoperative or intraoperative images. CT images acquired under the Stealth Protocol are uploaded to the system, which reconstructs them into a three-dimensional model. During surgery, a handheld probe equipped with infrared-reflective markers is tracked by cameras in the operating room. As the surgeon moves the probe across the patient’s anatomy, the system displays the probe’s position in real time on the uploaded images, essentially turning the CT scan into a live GPS for surgery.1SpringerLink / Annals of Surgical Oncology. Image guidance during abdominal exploration for recurrent colorectal cancer
Before navigation can begin, the system needs to know how the patient’s body in the operating room corresponds to the body in the CT images. This step, called registration, involves matching specific anatomic landmarks or fiducial markers on the patient to the same points in the scan. In some setups, adhesive markers are placed on the skin before the CT is acquired, giving the software precise reference points. In others, the surgeon touches recognizable bony landmarks with the probe, and the system calculates a best fit. Once four or more points are registered, the system computes a global error measurement that tells the surgical team how closely the digital map matches reality.1SpringerLink / Annals of Surgical Oncology. Image guidance during abdominal exploration for recurrent colorectal cancer How those fiducial markers are arranged matters: distributing them widely across the skull or body surface yields better accuracy than clustering them in one area.2Journal of Clinical Neuroscience. Impact of fiducial arrangement and registration sequence on target accuracy using a phantom frameless stereotactic navigation model
What Makes a CT “Stealth-Compatible”
Not every CT scan works well with the StealthStation. The Stealth Protocol specifies parameters that produce images the navigation software can process accurately. The most important requirements are thin slices (often 1 mm or less), no gaps between slices, and a consistent field of view that captures all the anatomy the surgeon needs. The scan is usually acquired helically, meaning the CT table moves continuously while the X-ray tube rotates, producing a smooth volume of data rather than a stack of disconnected images.
Beyond slice thickness, the protocol also specifies details like the tube voltage and current, which affect image quality and radiation dose. If the scan is too noisy or the slices too thick, the three-dimensional reconstruction loses detail and the navigation accuracy suffers. When metallic implants are already present, as in revision spine surgery, the scan may need additional processing to reduce the streaking artifacts that metal creates in CT images. Algorithms that identify and correct corrupted data in the raw scan have been developed specifically for this problem, and testing frameworks now exist to objectively evaluate how well different artifact-reduction methods preserve image quality.3PubMed Central. CT metal artifact reduction algorithms: Toward a framework for objective performance assessment
Surgical Applications
The Stealth Protocol and StealthStation platform are used across a wide range of surgical specialties, though spine surgery and cranial neurosurgery remain the most common. In spine surgery, the system helps guide the placement of pedicle screws, which anchor rods to the vertebral column. The margins for error are small because nerves and blood vessels sit close to the insertion path. One study of cervical spine reconstruction found that over 99% of 121 pedicle screws placed with Stealth Navigation avoided neurovascular injury.4Spine. Safety and Efficacy of Reconstruction of Complex Cervical Spine Pathology Using Pedicle Screws Inserted with Stealth Navigation and 3D Image-Guided (O-Arm) Technology
In sinus and skull-base surgery, the system serves a different purpose: helping the surgeon stay oriented in the tight, complex anatomy of the sinuses and surrounding structures. The localization accuracy has been estimated at about 2 mm, which is sufficient for identifying the boundaries of the frontal recess, the sphenoethmoid region, and the skull base during endoscopic procedures.5PubMed. Image-guided functional endoscopic sinus surgery The system has also been adapted for neurovascular surgery, where CT angiography data are loaded to map the vascular anatomy around aneurysms and other lesions. The three-dimensional reconstructions show the surgeon the relationship between the lesion, surrounding blood vessels, and nearby brain structures before and during surgery.6PubMed. Image-guided microneurosurgical management of vascular lesions using navigated computed tomography angiography. An advanced IGS technology application
Outside the head and spine, the StealthStation has been applied in abdominal surgery, particularly when re-exploring patients with recurrent cancer. In that setting, the CT data help the surgeon identify tumor locations relative to major vessels and organs, even when scar tissue from prior operations has distorted the normal anatomy.1SpringerLink / Annals of Surgical Oncology. Image guidance during abdominal exploration for recurrent colorectal cancer
Preoperative CT Versus Intraoperative CT
One of the ongoing decisions in Stealth-guided surgery is whether to use a preoperative CT scan taken days or weeks before surgery or an intraoperative CT acquired in the operating room, often with a device like the O-arm. The preoperative approach is simpler: the patient gets a standard Stealth Protocol CT beforehand, the images are loaded, and registration happens at the start of surgery. The downside is that the patient’s anatomy in the operating room may not match the preoperative scan exactly. Positioning on the surgical table, tissue swelling, or movement during a long procedure can all shift things enough to degrade accuracy.
Intraoperative CT solves this by scanning the patient after they are positioned for surgery, so the images reflect the anatomy as it actually sits on the table. The O-arm, a mobile CT-like scanner that fits around the patient in the operating room, is commonly paired with the StealthStation for this purpose. The trade-off is additional radiation exposure during the procedure itself. One comparison found that a low-dose intraoperative CT protocol delivered roughly 0.14 mSv per spinal level instrumented, compared to about 0.06 mSv per level with a low-dose preoperative CT. Standard-dose preoperative CT was far higher, at about 1.46 mSv per level. Operative time per level was essentially the same regardless of which approach was used.7PubMed. Radiation exposure in navigated techniques for AIS: is there a difference between pre-operative CT and intraoperative CT?
This comparison highlights something worth knowing: the “standard” dose protocols that many hospitals still use by default deliver far more radiation than necessary for navigation purposes. The low-dose versions produce images that are perfectly adequate for guiding screw placement, at a fraction of the exposure.
Radiation Dose and Low-Dose Protocols
Radiation exposure is a real concern whenever CT is involved, and it becomes especially important in pediatric patients and in surgeries that require multiple scans. The default O-arm protocol, for instance, has been measured at an effective dose of about 4.65 mSv per scan. Switching to an institutional low-dose protocol cut that roughly in half, to about 2.37 mSv. A dedicated pediatric protocol reduced it further to about 0.65 mSv per scan, which is roughly one-seventh of the default. Over an entire surgery requiring multiple scans, the total difference was dramatic: about 1.17 mSv with the pediatric protocol versus nearly 12.8 mSv with the default, a tenfold reduction. Image quality remained satisfactory in all but one case involving a patient over 100 kg with stainless steel implants.8Journal of Pediatric Orthopaedics. Switching to a Pediatric Dose O-Arm Protocol in Spine Surgery Significantly Reduced Patient Radiation Exposure
Researchers have pushed even further, testing “ultra-low-dose” settings on cadavers. By dropping the tube current to about a third of the manufacturer’s lowest recommended setting, they could still identify screw positions adequately on the resulting images.9Spine. Low-Dose Radiation 3D Intraoperative Imaging: How Low Can We Go? An O-Arm, CT Scan, Cadaveric Study The practical message is that many facilities are still using dose settings far higher than what the navigation task actually requires, and the protocols continue to evolve downward.
Why CT Alone Is Sometimes Not Enough
CT excels at showing bone, which is why it dominates in spine and sinus navigation. But for soft-tissue targets like brain tumors, pituitary lesions, or vascular malformations, CT by itself can be limited. MRI does a far better job of delineating soft-tissue boundaries, tumor margins, and the relationship between a lesion and surrounding brain structures. The limitation of MRI for navigation is that it does not show bony landmarks well, which makes it harder to register and harder to use when the surgical approach involves drilling through bone.
Image fusion addresses this by combining CT and MRI datasets into a single navigable volume. The CT provides the sharp bony detail the surgeon needs while approaching the target, and the MRI fills in the soft-tissue information beyond the bone. In pituitary surgery, for example, the bony anatomy of the sphenoid sinus is best seen on CT, but the tumor itself and its relationship to the optic nerves and carotid arteries show up more clearly on MRI. Fusing both into the navigation system gives the surgeon the strengths of each modality simultaneously.10PubMed Central. The use of intraoperative computed tomography navigation in pituitary surgery promises a better intraoperative orientation in special cases Without fusion, a surgeon relying on CT alone may not appreciate the full extent of a soft-tissue lesion beyond the visible margins of the bony opening.
What Can Go Wrong With Navigation Accuracy
Image-guided navigation is accurate, but it is not infallible. Several technical factors can degrade the system’s reliability during a case. The most common culprits include the distance between the vertebra being treated and the reference frame clamp (the metal frame attached to the patient that the cameras track), line-of-sight obstruction between the infrared cameras and the instruments, calibration drift over the course of a long procedure, and accidental bumps to the reference frame that shift its position without the surgeon realizing it.11PubMed Central. Surgical Navigation Technology Based on Augmented Reality and Integrated 3D Intraoperative Imaging A Spine Cadaveric Feasibility and Accuracy Study
In practice, experienced surgical teams learn to check the system’s accuracy repeatedly during a case by touching a known landmark with the probe and confirming that the system places it correctly on the images. If the registration has drifted, they re-register before proceeding. The navigation system is treated as a tool that supplements the surgeon’s anatomical knowledge, not one that replaces it. A screw trajectory that looks correct on the screen but contradicts what the surgeon sees and feels is a red flag, not a reassurance.
The Financial Case for Navigation
Stealth navigation systems are expensive to purchase and maintain, which raises a legitimate question about whether the investment pays for itself. The economic argument largely rests on avoiding the cost of revision surgery. When a pedicle screw is misplaced and causes nerve injury or instability, the revision operation can cost anywhere from roughly $17,650 to nearly $40,000, with an average around $27,000. Across the literature, screw misplacement rates using image-guided systems range from about 1% to 15%, and reoperation rates from 0% to about 7.4%.12PubMed Central. Economics of image guidance and navigation in spine surgery
That wide range in misplacement rates reflects differences in how “misplacement” is defined across studies, the complexity of the cases being studied, and the experience of the surgical teams. Still, even modest reductions in revision rates can offset the capital cost of the navigation equipment over time, especially in high-volume spine surgery programs. Institutions also weigh indirect savings: shorter operative times when navigation reduces the need for repeated fluoroscopic checks, and reduced staff radiation exposure from fewer intraoperative X-rays.
How Stealth Protocols Relate to Older Stereotactic Techniques
The concept of using coordinates and imaging to guide surgical instruments to precise targets is not new. Stereotactic surgery dates to the mid-twentieth century, when rigid metal frames were bolted to the patient’s skull and used to define a coordinate system for targeting deep brain structures. The Swedish neurosurgeon Lars Leksell developed a pivotal arc-radius stereotactic apparatus in the 1950s that enabled targeting of structures like the Gasserian ganglion with submillimeter precision.13PubMed Central. History and Development of Clinical Use of Functional Stereotaxy for Radiation Oncologists: From Its Origins to Its Current State
The StealthStation and its Stealth Protocol represent the frameless evolution of that idea. Instead of physically bolting a frame to the patient, the system uses fiducial markers or anatomic surface matching, combined with real-time infrared tracking, to achieve a similar coordinate-based guidance without the invasiveness of a rigid frame. The accuracy is generally considered sufficient for the vast majority of spine, sinus, and cranial procedures, though frame-based systems still have a role in applications that demand the tightest possible targeting, such as certain deep brain stimulation implantations. For the typical spine or skull-base case, frameless navigation has become the standard, and the Stealth Protocol CT scan is the imaging foundation it rests on.
What to Expect if Your Surgeon Orders a Stealth Protocol CT
If you are scheduled for a surgery that will use StealthStation navigation and your surgeon orders a Stealth Protocol CT, the scan itself feels like any other CT. You lie on a table, hold still, and the scan takes a few minutes. The main differences are behind the scenes: the technologist selects specific acquisition parameters to ensure the images will import cleanly into the navigation system. Depending on the surgical plan, small adhesive markers may be placed on your skin or scalp before scanning, and you will be asked not to remove them before surgery.
In some cases, the navigation scan is done weeks before the operation and loaded into the system ahead of time. In others, an intraoperative scanner acquires the images after you are positioned and anesthetized. The choice between these approaches depends on the type of surgery, the surgeon’s preference, the available equipment, and how much the anatomy is expected to shift between scanning and the actual procedure. For spine surgery, intraoperative scanning has become increasingly popular because it eliminates any mismatch between the scan and the patient’s surgical position. For sinus and skull-base cases, a preoperative scan often suffices because the bony anatomy is rigid and does not shift much with positioning.
If your surgical team mentions the O-arm in addition to the Stealth Protocol, they are referring to the intraoperative scanner rather than the navigation software itself. The two systems are designed to work together but serve different roles: the O-arm acquires the images, and the StealthStation uses them for guidance. Asking your surgeon which approach they plan to use, preoperative CT or intraoperative O-arm, is a reasonable question, and understanding that low-dose protocols exist gives you a basis for asking about radiation exposure if that is a concern.