Optics in Medicine
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Optics has, since ancient times, being used as aid for the examination of human patients and in some therapeutic treatments. Many of the optic medical instruments in use today were developed in the nineteenth century and, with the advent of optical fibers and laser light sources in the mid twentieth century, a new generation of medical devices, instruments, and techniques have been developed that have helped modernize medicine and perform task unimaginable only a few decades ago. This chapter illustrates—through several optical instrument and application examples—the uses, benefits, and future prospects that optics brings as an enabling technology to the medicine and the overall healthcare industry.
KeywordsOptical Coherence Tomography Medical Instrument Otitis Externa Direct Illumination Indirect Ophthalmoscope
13.1.1 Why Optics in Medicine?
Unlike the present time, medical practitioners of the ancient world did not have the benefit of sophisticated instrumentation and diagnostic systems, such as X-rays, ultrasound machines, or CT scanners. Visual and manual auscultations were the tools of the day. Hence, since the early days of medicine, optics has been a useful and powerful technology to assist doctors and all forms of healthcare practitioners carry out examination and diagnosis of their patients. This is so because one of the fundamental aspects of medicine is observation and physical examination of the patience’s general appearance. Hence, anything that can help “see” better the condition of a patient will be of aid. As such, optics, as the science that studies the behavior and manipulation of light and images, is an ideal tool to assist doctors gain better visual examination capabilities by providing improved illumination, magnification, access to small or internal body cavities, among others. But it is in reality light and its interaction with living tissues that is at the center of what makes optics in medicine possible. Light possesses energy and is capable of interacting with biological cells, tissues, and organs. Such interaction can be used to probe the state of such living matter for diagnostics and analytical purposes or, it could be used to induce changes on the same living systems and be exploited for therapeutic purposes. The science of light generation, manipulation, transmission, and measurement is known as photonics. The application of photonics technologies and principles to medicine and life sciences is known as biophotonics.
Nowadays, it is not only optics but also photonics that are used extensively in a myriad of medical applications, from diagnostics, to therapeutics, to surgical procedures. Hence, when we use the term medical optics, we are referring to biomedical optics and biophotonics as well. The interrelation between optics and light in medicine is ever present and it could be said that more significant advances in biophotonics are now due to the availability of more powerful, concentrated, and multi-spectral light sources which have been available only in the last 50 years. Historically, ambient light was the illumination source, which precluded performing exams late in the day or during certain hours in the winter time. Oil candles in the ancient world gave way to wax ones and alcohol burning lamps in the fifteenth through the nineteenth centuries until the development of electricity and the introduction of the electric lamp by Edison. Then, in the 1960s, with the development of semiconductor lasers, light emitting diodes (LEDs) and lasers, modern medical optics began to take shape and, coupled with the availability of optical fibers, a new generation of medical instruments and techniques began to be developed.
Fiber optics has been used in the medical industry even before their adoption and subsequent explosion as the technology of choice for long haul data communications . The advantages of optical fibers have been recognized by the medical community long ago. Optical fibers are thin, flexible, dielectric (non-conductive), immune to electromagnetic interference, chemically inert, non-toxic, and of course, small in size. They can also be sterilized using standard medical sterilization techniques. Their major advantage lies in the fact that they are thin and flexible so they can be introduced into the body for both remotely sense, image and treat. Their initial and still most successful biological/biomedical application has been in the field of endoscopic imaging. Prior to the development of such devices, the only method of inspecting the interior of the body was through invasive surgery. Many patients owe their lives today to the existence of fiberoptic endoscopes. Optical fibers are not only useful for endoscopes, but can also be used to transmit light to tissue regions of interest either to illuminate the tissue so that it can be inspected, or if much higher power laser light is used, to directly cut or ablate it. Hence, they are used extensively as laser-delivery probes, as well as imaging conduits in optical coherence tomography (OCT).
Medical industry trends that promote the use of optical fibers
• Drives towards minimally invasive surgery (MIS)→Need for disposable probes and catheters
• Miniaturization, Automation and Robotics→Need for instrumented catheters
• Sensors compatible with MRI, CT, PET equipment as well as thermal ablative treatments involving RF or microwave radiation→Need for fiber sensors
• Increased user of lasers→Need for fiber delivery devices
• Increased use of optical imaging and scanning techniques→Need for fiber OCT probes
Fiber optic and photonic devices are also being exploited as sensing devices for patient monitoring during medical imaging and treatment using radiation devices such as MRI, CT, and PET type scan systems that involve the use of high-intensity electromagnetic fields, radiofrequencies, or microwave signals. Because the patient’s risk of an electric shock conventional electronic monitoring devices and instrumentation cannot be used in these applications. Instead, patient monitoring is performed using optical fiber sensors.
Typical applications of optics in medicine
13.1.2 Global Healthcare Needs and Drivers
Add to this the fact that in certain parts of the world the population is aging, including the USA, Japan, and parts of Europe. Globally, the number of persons aged 65 or older is expected to reach to nearly 1.5 billion by 2050. An aging population puts additional demands on healthcare since older people are more vulnerable to illness and chronic diseases. Furthermore, life expectancy at birth has increased significantly. The UN DESA estimates a 6-year average gain in life expectancy among the poorest countries, from 56 years in 2000–2005 to 62 years in 2010–2015, which is roughly double the increase recorded for the rest of the world. Another key trend and global challenge is the expected shortage of medical doctors and physicians available to meet the healthcare needs of a growing world population.
A large global population requires more doctors, medical devices, medical supplies, clinics, hospitals, and overall healthcare infrastructure to address the needs of people needing immunizations, or getting sick or injured. Hence, there is and will continue to be an overall growth and expansion of the health care industry on a global basis, that continuous to demand more medical instruments and technical innovations that can facilitate and expedite medical examinations, while reducing costs. Historically, optics has been an enabling technology for the design and development of such medical devices and instruments.
Another relevant and converging present trend is how biomedical devices and instruments are so extremely pervasive across the healthcare industry today. We may not realize it, but whenever we get our blood pressure tested, monitor our blood sugar, or when a expectant mother is being monitored by her doctor, an instrument or sensing device is needed which, often times, is based on the use of an optical technique or based on the use of optical components. Couple this with the fact that in many parts of the underdeveloped world there is not enough doctors, hospitals, clinics, and instrumentation available to support local populations. Hence, it becomes critically important to develop simple, practical, effective, and inexpensive medical devices that can be used in rural and remote areas by non-professionals to examine and treat patients.
13.1.3 Historical Uses of Optics in Medicine
Mankind has always been fascinated with light and the miracle of vision, dating back to the first century when the Romans were investigating the use of glass and how viewing objects through it, made the objects appear larger. However, most of the significant developments of optics for medical diagnosis and therapy started occurring in the nineteenth century. Before that, the vast majority of the known published works on optics and medicine dealt mostly with the anatomy and physiology of the human eye. For instance, the Greek anatomist, Claudius Galen (130–201) provided early anatomical descriptions of the structure of the human eye, describing the retina, iris, cornea, tear ducts, and other structures as well as defining for the first time the two eye fluids: the vitreous and aqueous humors. Subsequently, Arab scholars Yaqub ibn Ishaq al-Kindi (801–873) and Abu Zayd Hunayn ibn Ishaq alIbadi (808–873) provided a more comprehensive study of the eye in the ninth century in their Ten Treatises on the Eye and the Book of the Questions of the Eye. In the eleventh century Abu Ali al-Hasan ibn al-Haytham (965–1040)—known as Alhazen—also provided descriptions of the eye’s anatomy in his Book of Optics (Kitab al-Manazir).
It is around this time that the so-called reading stones are being used as magnifying lenses to help read manuscripts. The English philosopher Robert Bacon (1214–1294) described in 1268 in his Opus Majus the mechanics of a glass instrument placed in front of his eyes. Then, in the thirteenth century, Salvino D’Armate from Italy made the first eye glass, providing the wearer with an element of magnification to one eye.
The term ophthalmoscope (eye-observer) did not come into common use until later. Helmholtz also invented the ophthalmometer, which was used to measure the curvature of the eye. In addition, Helmholtz studied color blindness and the speed of nervous impulses. He also wrote the classic Handbook of Physiological Optics.
In 1888 Prof. Reuss and Dr. Roth of Vienna used bent solid glass rods to illuminate body cavities for dentistry and surgery. This would be the earliest idea to use a precursor of an optical fiber for medical applications. Decades later, in 1926, J. L. Baird of England and Clarence W. Hansell of the RCA Rocy Point Labs, propose independently of each other fiber optic bundles as imaging devices. A few years later, German medical student Heinrich Lamm assembles the first bundles of transparent optical fibers to carry the image from a filament lamp, but is denied a patent. Then in 1949, Danish researchers Holger M. Hansen and Abraham C. S. van Heel begin investigating image transmission using bundles of parallel glass fibers. Prof. Harold H. Hopkins from Imperial College in London begins work in 1952 to develop an endoscope based on bundles of glass fibers. University of Michigan Medical professor Basil Hirschowitz visits Imperial College in 1954 to discuss with Prof. Hopkins and graduate student, Narinder Kapany, about their ideas for imaging fiber bundles. Hirschowitz hires undergraduate student Larry Curtis to develop a fiber optic endoscope at the University of Michigan. Curtis fabricates the first clad optical fiber from a rod-in-tube glass drawing process. Prof. Hirschowitz tests first prototype fiber optic endoscope using clad fibers in February of 1957, and then introduces it to the American Gastroscopic Society in May of the same year.
The first solid-state laser was built in 1960 by Dr. T. H. Maiman at Hughes Aircraft Company. Within the year, Dr. Leon Goldman, chairman of the Department of Dermatology at the University of Cincinnati, began his research on the use of lasers for medical applications and later established a laser technology laboratory at the school’s Medical Center. Dr. Goldman is known as the “father of laser medicine.” He is also the founder of the American Society for Lasers in Medicine and Surgery . However, the first medical treatment using a laser on a human patient was performed in December 1961 by Dr. Charles J. Campbell of the Institute of Ophthalmology at Columbia–Presbyterian Medical Center, who used a ruby laser that is used to destroy a retinal tumor. Since then, lasers have become an integral part of modern medicine .
During the 1980s and 1990s, extensive research was conducted to develop fiber-optic-based chemical and biological sensors for diverse medical applications .
OCT is a newer optical medical imaging technique, first introduced in the early 1990s, that uses light to capture micrometer resolution, three-dimensional images from within biological tissue based on low-coherence, and optical interferometry . OCT is a technique that makes possible to take sub-surface images of tissues with micrometer resolution. It can be thought of as the optical equivalent of an ultrasound scanning system. This is an active area of medical research at the moment.
13.1.4 Future Trends
Optics and photonics, as mentioned earlier, are powerful, versatile, and enabling technologies for the development of present and future generations of medical devices, instruments, and techniques for diagnostic, therapy, and surgical applications.
Given the present R&D activity worldwide based on optical and photonic techniques it should be no surprise to expect a broader utilization of optically based solutions across the healthcare industry and medical profession. In the future, advances in the development of ever smaller and thinner medical probes and catheters should be expected, as well as broad utilization of OCT devices to become as common as ultrasound scanning devices are in today’s society. There will also be a proliferation of laser-based treatments and therapies. Endoscopy, for its part, will continue to evolve and more sophisticated and smaller devices will be developed that will combine more functions (from the standard illumination and visualization) with direct tissue analysis and laser treatment. Optical imaging techniques will continue to advance along with digital X-rays to make non-invasive examination and diagnosis safe, fast and with greater resolution and pinpoint accuracy.
Other future capabilities brought on by optics will be in the form of the so-called lab-on-a-fiber or LOF for short , where optical fibers are combined with micro- and nano-sized functionalized materials that react to specific physical, chemical, or biological external effects and can thus serve as elements to build multi-function, multi-parameter sensing devices. Light would remotely excite the functionalized materials which are embedded in the fiber’s coating material. These materials in turn will react to specific biological or chemical substances (analytes) and induce an optical signal change proportional to the given analyte concentration.
Another such smartphone innovation is the so-called CellScope developed by researchers at the University of California at Berkeley . The CellScope is a microscope that attaches to a camera-equipped cell phone and produces two kinds of microscopy imaging: brightfield and fluorescence. The idea is that such device can then be used in the field (on remote locations or those where little medical infrastructure is available) and take snap magnified pictures of disease samples and transmit them to medical labs via mobile communication networks, and screen for hematologic and infectious diseases in areas that lack access to advanced analytical equipment.
13.2 Early and Traditional Medical Optical Instruments
As discussed earlier, optics has been used throughout the centuries as a technology to assist medical doctors perform examinations of patients. Many of the medical instruments in use today rely on optics and optical components to perform their intended function. In particular, there a set of very basic but very popular and common medical instruments that were developed in the nineteenth century and continue to be used in the medical profession of today. Among these optical instruments we have the otoscope, the ophthalmoscope, retinoscope, laryngoscope, and even basic devices such as the head mirror.
In the sections to follow, we shall describe the basic optical operating principles and uses of such devices. Our discussion of these devices is by no means exhaustive, but is intended to provide the reader with an overall idea on the utilization of optics in medicine and brief introduction on the subject of medical optical instruments .
13.2.1 Head Mirror
In use, the patient sits and faces the physician. A bright lamp is positioned adjacent to the patient’s head, pointing towards the physician’s face and hence towards the head mirror. The lamp’s light gets concentrated by the curvature of the mirror and reflected off it towards the area of examination, and along the line of sight of the doctor, thus providing shadow-free illumination. When used properly, the head mirror thus provides excellent shadow-free illumination.
A French obstetrician named Levert, who was fascinated with the intricacies of the larynx and dabbled with mirrors, is credited with conceiving the idea for the head mirror back in 1743. Today’s head mirror has withstood the test of time and is still routinely used by ophthalmologists and otolaryngologists, particularly for examination and procedures involving the oral cavity.
An otoscope is a hand-held optical instrument with a small light and a funnel-shaped attachment called an ear speculum, which is used to examine the ear canal and eardrum (tympanic membrane). It is also called auriscope. The otoscope is one of the medical instruments most frequently used by primary care physicians . Health care providers use otoscopes to screen for illness during regular check-ups and also to investigate ear symptoms. Ear specialists—such as otolaryngologists and otologists—use otoscopes to diagnose infections of the middle and outer ear (otitis media and otitis externa).
The most commonly used otoscopes in emergency rooms and doctors’ offices are monocular devices. They provide only a two-dimensional view of the ear canal. Another method of performing otoscopy (visualization of the ear) is use of a binocular microscope, in conjunction with a larger metal ear speculum, with the patient supine and the head tilted, which provides a much larger field of view and depth perception, thus affording a three-dimensional perception of the ear canal. The microscope has up to 40× power magnification, which allows for more detailed viewing of the entire ear canal and eardrum.
The otoscope is a valuable tool beyond its primary role as an examination tool for detecting ear problems. It can also be used for transillumination, dermatologic inspection, examination of the eye, nose, and throat and as an overall handy light source.
18.104.22.168 History of the Otoscope
Von Troltsch is generally credited with popularizing the use of a mirror in otoscopy after he showed it in 1855 at a meeting of the Union of German Physicians in Paris. He ultimately fastened the mirror to his forehead as is still currently practiced by some doctors. The size and focal length of the mirror was not standardized for some time. In an attempt to catch more light, used huge mirrors and only gradually was a diameter of 6–7 cm eventually adopted. A further improvement to Von Troltsch’s early auriscope is Brunton’s device which was first described in an 1865 Lancet article. This auriscope combined mirror and speculum into a single instrument and worked on the principle of a periscope: light from a candle or lamp was concentrated by a funnel and then reflected by a plane mirror set at an angle of 45° into the ear canal. The mirror had a central perforation through which the doctor could view the ear. Brunton’s auriscope was fitted with a magnifying lens for the observer and could also be sealed with plain glass at the illuminating end. These were the first otoscopes to be electrically illuminated.
An ophthalmoscope is an optical instrument for examining the interior of the eyeball and its back structures (called the fundus) through the pupil by injecting a light beam into the eye and looking at its back-reflection. An ophthalmoscope is also referred to as a funduscope. The fundus consists of blood vessels, the optic nerve, and a lining of nerve cells (the retina) which detects images transmitted through the cornea, a clear lens-like layer covering of the eye. Ophthalmoscopes are used by doctors to exam the interior of eyes and help diagnose any possible conditions or detect any problems or diseases of the retina and vitreous humor. For instance, a doctor would look for changes in the color the fundus, the size, and shape of retinal blood vessels, or any abnormalities in the macula lutea (the portion of the retina that receives and analyzes light only from the very center of the visual field). Typically, special eyedrops are used to dilate the pupils and allow a wider field of view inside the eyeball.
An indirect ophthalmoscope produces an inverted (reversed) image with a 2–5× magnification and formed. A small hand-held lens and either a slit lamp microscope or a light attached to a headband are used to form an image of the back of the eye in space, at approximately arm’s length from the doctor. An indirect ophthalmoscope provides a stronger light source, a specially designed objective lens, and opportunity for stereoscopic inspection of the interior of the eyeball. It is invaluable for diagnosis and treatment of retinal tears, holes, and detachments.
To determine the corrective refractive lens power needed, lenses of increasing refractive power are placed in front of the eye and the change in the direction and pattern of the reflex is observed. The optometrist keeps changing the lenses until reaching a lens power that provides adequate focusing on the retina, which manifests as alignment of the reflex with the streak light image outside of the pupil.
A phoropter is an ophthalmic binocular refracting testing device, also called a refractor. It is commonly used by ophthalmologists, optometrists, and eye care professionals during an eye examination to determine the corrective power needed for prescription glasses. It is commonly used in combination with a retinoscope.
The blades in a laryngoscope help provide leverage to open wide the mouth and throat, as well as to keep the tongue in place and avoid a gag reflex. There are two basic styles of laryngoscope blades most commonly used: curved and straight. The Macintosh blade is the most widely used of the curved laryngoscope blades, while the Miller blade is the most popular style of straight blade. Blades come in different sizes, to accommodate different patients.
An indirect laryngoscope consists of a combination of a small mirror mounted at an angle on a long stem and a light source. The mirror is usually circular in form and made in various sizes, but is small enough to be placed in the throat behind the back of the tongue. The source of light is either a small bright lamp worn on the forehead of the observer, or a concave mirror, also worn on the forehead, for the purpose of concentrating light from some other source. Light is reflected to the back of the throat by the mirror and directed to illuminate up the interior of the larynx. The mirror also serves to reflect back to the doctor an image of the throat, to appreciate the structure of the glottis and vocal cords.
All previous observations of the glottis and larynx had been performed under indirect vision (using mirrors) until 1895, when Alfred Kirstein (1863–1922) of Germany performed the first direct laryngoscopy in Berlin, using an esophagoscope he had modified for this purpose, calling device an autoscope, and the modern, direct laryngoscope was born .
13.3 Fiber Optic Medical Devices and Applications
The field of fiber optics has undergone a tremendous growth and advancement over the last 50 years. Initially conceived as a medium to carry light and images for medical endoscopic applications, optical fibers were later proposed in the mid-1960s as an adequate information-carrying medium for telecommunication applications. Ever since, optical fiber technology has been the subject of considerable research and development to the point that today light wave communication systems have become the preferred method to transmit vast amounts of data and information from one point to another.
Given their EM immunity, intrinsic safety, small size and weight, autoclave compatibility and capability to perform multi-point and multi-parameter sensing remotely, optical fibers and fiberoptic-based devices are seeing increased acceptance and new uses for a variety of biomedical applications—from diverse endoscopes, to laser-delivery systems, to disposable blood gas sensors, and to intra-aortic probes. This section illustrates—through several application and product examples—some of the benefits and uses of biomedical fiber sensors, and what makes them such an attractive, flexible, reliable, and unique technology.
13.3.1 Optical Fiber Fundamentals
13.3.2 Coherent and Incoherent Optical Fiber Bundles
In medicine, optical fibers have been considered for illuminating and imaging applications since the 1920s. Typically, a single glass optical fiber has a diameter ranging from 1 mm down to ~8 μm. However, a single optical fiber cannot transmit an image—only a bright light spot would be observed at its end. Hence, in order to carry a reasonable amount of light for illumination purposes, or to transmit and image, hundreds to thousands of optical fibers need to be assembled into bundles. Bundles of multiple single optical fibers of small diameter solid glass rods can thus be used to guide light or transmit images around bends and curved trajectories.
In the particular case of leached fiber bundles, each bundle end is properly secured and the entire bundle is soaked in an acid solution which will dissolve the leachable glass, allowing the fibers to move freely between the bundle ends.
Wound imaging bundles are made by winding a multi-fiber array as a single layer on a drum, and then stacking the desired number of layers manually in a laminating operation.
13.3.3 Illuminating Guides
13.3.4 Fiberscopes and Endoscopes
13.3.5 Fused Fiber Faceplates and Tapers for Digital X-rays
Optically, an FOFP behaves as zero-thickness optical window transferring an image, fiber by fiber, from one face of the plate to the other. Image magnification or reduction can be achieved by tapering the cross section of the bulk plate during the manufacturing process. In this case, the boule is drawn down and a neck region is formed with an hour-glass shape piece. The piece is cut into two pieces, machined and the ends polished resulting in a fused fiber optic taper.
Faceplates and tapers also function as dielectric barrier and mechanical interface and are optically used as a two-dimensional image conduit for energy conversion, field-flattening, distortion correction, and contrast enhancement. They are typically used for imaging applications bonded to cathode ray tubes (CRT) and LCD displays, image intensifiers, charged coupled device (CCD) or complementary metal-oxide semiconductor (CMOS) detectors, image plane transfer devices, X-ray digital detectors, among others.
In the medical area, fiber optic tapers and faceplates have found widespread use for both dental and medical digital radiography (such as mammography, fluoroscopy, intra-oral, panoramic, or cephalometric) where instead of using conventional film to obtain the X-ray images, an electronic photosensitive device such as a CCD or CMOS detector chip is used to convert the X-ray energy into electronic pixel signals via the use of an intermediate faceplate. Digital radiography offers high-resolution images while greatly reducing patient and sensor exposure to harmful X-rays by using low-dose X-ray sources. In addition, digital X-ray imaging speeds the availability of images for diagnostic, while also making the viewing, sharing, transmitting, and storing of X-ray patient data so much easy and compatible with modern electronic record systems. Furthermore, faceplates also provide a critical X-ray absorbing barrier between the X-ray emitter and the semiconductor detector device, prolonging their service life and reducing background noise.
As discussed in this section, optics is a useful, practical, versatile, and powerful technology that, throughout history, has helped human kind perform visual examination, diagnostics, and therapeutics on both the sick and healthy. Optics technology and optical components are at the core in a variety of modern-day optical devices and instruments such as endoscopes, patient monitoring probes, and sensors, as well as in advanced robotic assisted surgery systems.
The harnessing power of light, and its interaction with living matter, is extremely useful and beneficial for a variety of medical purposes and treatments ranging from laser procedures for tattoo removal, to eye surgery to vessel and tissue ablation and coagulation, up to modern photodynamic therapy treatments. We have seen how the field of optics is in itself a subset of a more complex and interdisciplinary area of research known as Biophotonics.
New advancements in optics and photonics are driving the development of a new generation of imaging tools—such as optical coherence and photo-acoustic tomography—that can readily provide two and three-dimensional images of diverse human body tissues and organs.
Optics has, and will continue to be, an enabling technology for the advancement of medicine promoting unimaginable new devices, techniques, and applications to happen in the not too distant future.
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