Учебники / Computer-Aided Otorhinolaryngology-Head and Neck Surgery Citardi 2002

Eric W. Sargent, M.D., F.A.C.S. Michigan Ear Institute, Farmington Hills,

Michigan

Petra Schmalbrock, Ph.D. Assistant Professor, Department of Radiology, The Ohio State University College of Medicine and Public Health, Columbus, Ohio

Michael J. Sillers, M.D., F.A.C.S. Associate Professor, Division of Otolaryngology/Head and Neck Surgery, Department of Surgery, University of Alabama—Birmingham, Birmingham, Alabama

Marcus K. Simpson Research Assistant, Dartmouth College, Hanover, New

Hampshire

Madeleine A. Spatola, M.A. Thomas Jefferson University Medical School, Philadelphia, Pennsylvania

Don Stredney Director, Interface Laboratory, and Senior Research Scientist, Biomedical Applications, Ohio Supercomputer Center (OSC), Columbus, Ohio

Winston C. Vaughan, M.D. Associate Professor, Stanford Sinus Center, Division of Otolaryngology–Head and Neck Surgery, Stanford University, Stanford, California

Gregory J. Wiet, M.D. Assistant Professor, Division of Pediatric Otolaryngology, Department of Otolaryngology, The Ohio State University College of Medicine and Public Health, and Chief, Department of Otolaryngology, Columbus Children’s Hospital, Columbus, Ohio

Eiji Yanagisawa, M.D., F.A.C.S. Clinical Professor, Section of Otolaryngology, Yale University School of Medicine and Attending Otolaryngologist, Yale–New Haven Hospital and Hospital of St. Raphael, New Haven, Connecticut

Ray Yanagisawa, B.A. Woodbridge, Connecticut

S. James Zinreich, M.D. Associate Professor, Radiology/Otolaryngology– Head and Neck Surgery, Department of Radiology, Johns Hopkins Medical Institutions, Baltimore, Maryland

1.2 PATIENT CARE MODEL

At the most elemental level, surgeons complete distinct, albeit related processes as they care for patients (Figure 1.1):

Data Collection. During the data collection phase, the surgeon performs a variety of maneuvers to collect relevant information. Traditional methods include a detailed history and physical examination. Today, testing methods, such as diagnostic imaging, are also performed.

Diagnosis. Next, the surgeon must review the information and establish a diagnosis. The collective knowledge base of medicine and the surgeon’s clinical intuition guides this process.

Planning. After a diagnosis has been established, the surgeon formulates a plan of treatment. Planning incorporates information from medicine’s knowledge base. In addition, the surgeon’s professional experiences influence planning. Of course, all planning is tailored to the particular patient’s care.

Execution. During the next phase, the surgeon then implements the plan of treatment. For surgeons, this typically involves a surgical procedure that reflects available medical technology.

FIGURE 1.1 The surgical care of patients encompasses four distinct processes. During data collection, the surgeon collects relevant clinical information through routine history and physical examination, diagnostic imaging, and other testing modalities. Next, a formal diagnosis is established, and treatment planning commences. Finally, the treatment is instituted during the remaining phase. Each phase need not be sequential. In fact, data collection leads directly to the diagnosis and planning phases, and the execution phase is monitored via additional data collection. Each phase relies upon the knowledge base of medicine and the surgeon’s clinical intuition.

It is important to realize that these various phases of surgical practice are not necessarily performed sequentially. Commonly, these cognitive processes occur simultaneously. Information acquired during the data collection phase directly influences both the diagnosis and planning phases. Furthermore, the surgeon will continuously reassess new information during the execution phase. In this way, data collection is a continuous process that occurs throughout the delivery of care. In addition, the planning and execution phases are typically simultaneous in a feedback loop that permits modification of the treatment plan in response to new information. Of course, this new data may be specific to a particular patient (i.e., clinical information). Alternatively, the new information that is added to the collective knowledge base of medicine may impact the treatment plan.

Two critical components influence the phases of data collection, diagnosis, planning, and execution. First, the knowledge base of medicine provides the fundamental information about the various disease processes, testing modalities, procedures, etc. The knowledge base has been increasing rapidly; in fact, the explosive growth of the biological sciences and medicine is actually accelerating. Second, the surgeon’s intuition guides him or her through the process of patient care delivery. For each patient encounter, the surgeon relies upon previous personal observations and experiences. In a sense, this ‘‘fuzzy logic’’ combines both deductive and inductive reasoning. By its very nature, it is difficult to characterize, but its impact is undeniable—it supplies the so-called art in the art of medicine.

The surgical care of patients reflects the prevailing technology of the time in which the care is delivered. First, imagine medicine in the preindustrial age. The planning phases consisted mostly of history and physical examination. Modalities such as radiography were unavailable, and the knowledge base was small. Available treatment options were limited. The technology provided by the Industrial Revolution revolutionized this. Diagnostic testing, such as radiography, was introduced, and the information in the knowledge base increased dramatically. Other technological advances, such as the introduction of general anesthesia, greatly increased the treatment options.

For surgeons, the technological impact of the past 150 years is perhaps best seen in diagnostic imaging. Without even plain radiography, physicians could only infer the status of internal body parts. In the late nineteenth century, the discovery of x-rays and their application to medicine began to give physicians the ability to assess issues in vivo that they could not directly observe. The significance of this change cannot be underestimated. Strategies that extended the usefulness of radiography were developed. For instance, the administration of contrast for barium enemas or upper gastrointestinal (GI) series permitted the observation of soft-tissue pathology that standard plain films do not. Similarly, arteriography provided detailed vascular anatomy that would otherwise be unknown (unless a formal surgical exploration was performed). Later, diagnostic radiography technology was adapted for therapeutic interventions (such as trans-

arterial embolization). Finally, in the last third of the twentieth century, computed tomography (CT) and magnetic resonance (MR) were introduced; these diagnostic imaging modalities provide information that plain x-ray films simply cannot. As CT and MR became widely available and as physicians became familiar with them, they dramatically altered the delivery of care to patients.

The technological advances in diagnostic imaging have dramatically altered the data collection, diagnosis, planning, and execution phases of surgical care. CT and MR (and even advanced plain film radiography) provide better information for diagnosis; this information was heretofore unavailable. Furthermore, this information facilitates the creation of a more realistic surgical plan.

All of theses advances provide the surgeon with additional information, which the surgeon must then assemble for diagnosis and treatment. Better images only provide better information; the understanding of their significance requires a difficult cognitive process. After creation of the treatment plan, the surgeon must then implement this plan. This requires further extrapolation from the original data. Each step in this process introduces potential sources of error and may overlook critical information that may not be readily apparent.

As the available information for patient evaluation has grown, the complexity of treatment methods has also grown dramatically. Techniques such as minimally invasive procedures demand exquisite technical expertise.

It is for these numerous reasons, that the surgeon needs better tools for the management of this information. Computer-aided surgery (CAS) answers this need.

1.3 TERMINOLOGY

The term computer-aided surgery first appeared in the German scientific literature in 1986 [1]. Over the subsequent 15 years, a variety of other terms have appeared. Some authors have referred to computer-assisted surgery, and in the United States and Japan, the phrase image-guided surgery has been applied to surgical navigation in endoscopic sinus surgery. This abundance of terminology has led to some fragmentation of the field; however, computer-aided surgery (CAS) has emerged as the preferred term.

The problem with terminology was readily apparent in the early and mid1990s. At that time, interest in the area was beginning to grow significantly. It was in this context that the International Society for Computer-Aided Surgery (ISCAS, www.iscas.org or http://igs.slu.edu) was established in 1996. The society created an organized forum for the exchange of ideas and the support of technological and clinical development. By its choice of name, ISCAS also promoted a term for the various manifestations of the underlying technologies.

ISCAS has proposed a rather broad definition for CAS [2]: ‘‘The scope of Computer-Aided Surgery encompasses all fields within surgery, as well as

biomedical imaging and instrumentation, and digital technology employed as an adjunct to imaging in diagnosis, therapeutics, and surgery. Topics featured include frameless as well as conventional stereotactic procedures, surgery guided by ultrasound, image-guided focal irradiation, robotic surgery, and other therapeutic interventions that are performed with the use of digital imaging technology.’’ The unifying theme in each of these applications of CAS is that they are all semiconductor-based. The basic advances in semiconductor technology— which are driving the transition to the Digital Age—underlie CAS in all its specific applications. The increasing prevalence of computers and communications in the nonmedical world is reflected in the medical world.

The other terms, such as computer-assisted surgery, or image-guided surgery, are probably best used to describe specific areas within CAS. For instance, computer-assisted surgery encompasses surgical robotics, which is only a small part of the entire discipline of CAS. Similarly, image-guided surgery refers to intraoperative surgical navigation, but not to areas such as telesurgery. CAS includes both computer-assisted surgery and image-guided surgery. The converse statements that computer-assisted surgery includes CAS and that image-guided surgery includes CAS are simply inaccurate.

1.4 SCOPE OF CAS

Admittedly, the scope of CAS is quite broad. Today, many surgeons would state that intraoperative surgical navigation is CAS. Such conclusions overlook other important technologies, including, but not limited to robotics, telesurgery, virtual reality, computer-based simulations/modeling, and internet-based applications.

CAS has huge implications for the processes that constitute contemporary surgical care. Information management—which is obviously facilitated by com- puters—occurs throughout the various phases of surgical care. Surgeons must manipulate information from two sources. First, the knowledge base of medicine is continuously expanding. Second, patient information that is specific to a particular patient must be systematically organized and critical reviewed. Computers, which after all are simply complex information appliances, contribute to all aspects of this information management. Desktop and laptop computers, personal digital assistants, and network appliances are just some of the devices that are impacting this area. The Internet, which provides a decentralized but easily accessible store of vast quantities of information, has also emerged as important information management tool.

Furthermore, these technologies provide organization for the vast quantities of information. Without such organization, the information may become meaningless; with such information, the hidden patterns (that would otherwise go unnoticed) may become apparent. In this way, the structure provided by these various information management technologies may positively influence patient care.

Computer-enabled therapeutics fuses computer-based technologies into treatment modalities. A variety of telesurgery platforms have been proposed over the years. The early systems showed considerable promise; however, their expense was considerable and their use was extremely cumbersome. Newer applications, which rely upon digital imaging and communications (i.e., the Internet) show considerable promise. Robotic-assisted surgery devices are now under development; such devices will likely enhance surgical precision. Such robotics also may permit procedures that would otherwise be impossible. Virtual reality display systems may present imaging data to surgeons in ways that facilitate minimally invasive procedures with lower morbidity and higher success rates. Computer-based models depict three-dimensional anatomy and pathology. The quality of the resultant images has improved dramatically over the recent years. Now such models are beginning to be used for surgical simulations.

Intraoperative surgical navigation is probably the most widely utilized CAS therapeutic application. Through surgical navigation, the operating surgeon can directly relate preoperative imaging data (namely CT or MR) with intraoperative anatomy. This remarkable technology relies upon technology that permits tracking of surgical instruments with millimetric or even submillimetric accuracy.

These surgical navigation systems share a number of common components (Figure 1.2):

Computer workstation. Early CAS systems relied upon relatively complex computer workstations that were optimized for image processing; however, more recently, PC-based computers have been used. Most CAS systems rely upon the UNIX operating system, although Windows 98, Windows NT, and Windows 2000 are increasingly common. Obviously, the computer workstation is the central component of CAS surgical navigation.

Display systems. Current CAS navigation systems utilize a standard computer monitor; other display options, including head-mounted displays or other techniques, are under active development (Figure 1.3).

Tracking system. Surgical navigation must include specific hardware for the tracking of surgical instruments. In the late 1980s and early 1990s, instrument tracking via an electromechanical arm was popular; such systems were quite accurate, but they were also cumbersome. More recent systems rely upon optical tracking or electromagnetic tracking. Of course, each particular technology has its own relative advantages and disadvantages. All of these technologies accomplish the same result; that is, they permit the precise localization of instruments in the operative field.

Specific surgical instrumentation. Initially, CAS surgical navigation systems provided pointers that could be used for identification of relevant

FIGURE 1.3 The CAS surgical navigation system monitor depicts localization data by displaying crosshairs on the preoperative CT images. In this example (LandmarX 3.0, Medtronic Xomed, Jacksonville, FL), the main part of the display is divided into four quadrants, which show the planar CT data (axial, coronal and sagittal planes) in the three orthogonal planes through the calculated location as well as a video input that displays to the location of the pointer tip. The display can be customized for the specific application; surgical planning modes can be shown in the place of the fourth quadrant. The CAS surgical navigation system can be controlled via a variety of menus shown on the right side of the image. Although this display arrangement is probably the most common, other options are also possible.

structures. Today, a variety of standard instruments (such as forceps) have been adapted so that their positions can also be tracked. Even the positions of surgical drills and microdebriders can be monitored through surgical navigation. The use of standard surgical tools has greatly expanded the role of surgical navigation during surgical procedures.

Data transfer hardware. Preoperative imaging data (i.e., the CT or MR) must be transferred to the computer workstation. Such data transfers may

be accomplished through computer networks that link the scanner and the CAS workstation. Alternatively, the data sets can be transferred on portable digital media, such as DAT tape or CD-ROM.

Software. Finally, software unifies the various hardware components into a functional system. Through software interfaces, surgeons have access to the imaging data and the entire CAS system.

Surgical navigation systems all rely upon two processes that much be successfully executed prior to actual intraoperative use:

Calibration. The desired surgical instrument must be calibrated. Calibration verifies that the anticipate instrument tip position and the actual instrument tip position are identical. Calibration failure will produce significant localization errors.

Registration. All surgical navigation systems require a registration step. Through registration, the software maps points in the preoperative imaging data set volume to the corresponding points in the operative field volume. All further localizations are actually positions that are determined relative to these points. Registration is maintained by keeping a tracking device in the identical position relative to the operative field throughout the entire surgical procedure. In principle, registration is a simple concept; however, in practice registration is challenging, since registration must be accurate, but not intrusive. Multiple registration strategies have been devised. Each of these strategies has been optimized for a specific surgical application.

Although CAS surgical navigation systems are surprisingly simple to use, surgeons must be cognizant of potential errors. Registration errors can produce significant localization inaccuracies. Furthermore, all systems are prone to drift from a variety of causes. For this reason, CAS navigation systems include localization accuracy mechanisms so that the localization accuracy can be monitored (Figure 1.4).

Finally, CAS surgical navigation systems usually include software tools that permit image review, modeling, and surgical planning (Figure 1.5). Because of the importance of surgical navigation, surgeons tend to overlook these other features; however, these tools can be useful in specific circumstances. Using the tools, the surgeon can develop a better understanding of specific three-dimen- sional anatomical relationships (Figure 1.6). It should be emphasized that the tools can often be adapted for situations for which they were not designed. When surgeons pursue these novel applications, the utility of the CAS system is naturally extended.