"We must not forget that when radium was discovered no one knew that it would prove useful in hospitals." -Marie Curie (1867-1934)
Historically, the inner workings of the human body have been a mystery. Organs and tissues work together, hidden beneath layers of skin and muscle. Doctors today, however, can see and hear beneath the surface of the body, watching the brain function and hearing blood flow through arteries.
Medical technology has combined science and engineering to provide doctors with tools that could not have been imagined a century ago, or, in some cases, 10 years ago. Imaging technologies provide tools to look at specific organs and even trace the activity of individual cells in response to a stimulus or a drug. New surgical techniques send a camera inside a vein so that a surgeon can operate on the heart through a tiny incision in the arm or leg. Some procedures have even been performed by specialists, using robotic tools and an Internet connection, on a patient thousands of miles away.
A large part of the advance in medical technology comes directly from advances in computer technology. As computers become faster and more powerful, they are able to process enormous quantities of data. This allows doctors to obtain images that would otherwise be impossible and to control movements of instruments within a fraction of a millimeter.
How does arthroscopic surgery work?
Severely torn knee ligaments are painful injuries that heal slowly. These tears often afflict athletes, runners, and other active people whose activities are hard on knee joints. Surgery to repair a torn ligament, if the knee is cut open, requires months of recovery and physical therapy. Most ligament repairs today, though, use arthroscopic surgery techniques. Recovery time is normally 4 to 6 weeks. Some athletes are back to their sport in a month. How does arthroscopic surgery work?
To perform arthroscopic knee surgery, the surgeon makes three small incisions, less than V2 inch long, into the knee. An endoscope is inserted into one of the cuts and remote-controlled tools into the others. Images pass through optical fibers and are projected onto a monitor so that the doctor can see exactly what is going on inside the joint.
Definition
An endoscope is a device that uses fiber optics and powerful lenses to view inside the body. It has two fiber-optic systems, one to carry bright light from an outside source to the site and the other the carry images from the tip of the endoscope to a viewing lens or monitor. The endoscope may also have tubes through which small instruments can be manipulated. Endoscopes are used for diagnostic purposes, such as colonos-copy, and as surgical tools.
Miniature tools, including scissors, forceps, suction tubes, and brushes, are guided to the site of the damage from the other incisions. Orthopedic surgeons even employ tiny power tools to grind away excess bone and other hard tissue. Debris is carried away through a suction tube. Because of the magnification and the size of the tools, it is possible to do very precise work at the site of the injury.
Patients recover quickly from arthroscopic knee repair because there is very little damage to muscles, tendons, and other tissues in the joint. This type of surgery is normally performed as an outpatient procedure and the patient can go home the same day. In addition to knee surgery, arthroscopic surgery is used in the shoulder, elbow, wrist, ankle, and hip.
How are materials chosen for replacement body parts?
When a bone is badly broken, it must be held together, sometimes permanently, with metal screws and metal plates to support it during its healing. Damaged valves in the human heart can be replaced by mechanical valves made of steel and plastic. The function of badly worn knee joints can be improved with plastic pads that replace missing cartilage. All of these treatments rely on long-lasting materials that can be used inside the human body. What types of materials can be implanted inside the body?
The human body is not a very friendly place for materials. It is warm, moist, salty, and filled with bacteria as well as cells whose specific function is to destroy anything that doesn’t belong there. Researchers have to carefully investigate the chemical and physical properties of any materials that are to be placed inside the body.
An implant is a medical device that replaces a biological structure. Implants include such things as artificial joints, heart pacemakers, stents that keep arteries open, and even devices that deliver drugs at a controlled rate.
The earliest successful implants were bone plates, first used in the early 1900s to hold bones in place while they healed. These plates used a form of stainless steel made with vanadium, which was specifically designed for use inside the human body. Today, many metal implants are built of titanium, a metal which is strong, lightweight, nonmagnetic, and unreactive.
Implanted materials cannot all be made of metal. For example, in knee replacement, some sort of cushion, usually one or more plastic pads, must be inserted between the metal or bone parts to keep them from rubbing together. The material for these pads must be chosen carefully. If the plastic wears out, forming tiny particles, the body’s immune system can identify the particles as foreign objects. White blood cells are mobilized, causing the surrounding area to become inflamed. This inflammation can lead to autoimmune reactions that destroy bone cells around the implant.
Many implants are now made with ceramic parts that have better wear characteristics than plastic. Ceramics also tend to form bonds with bone, making them much stronger and more durable. Over time, bones grow new tissue that extends into the ceramic material.
Much of the current research into implant materials focuses on ways to make the material work together with living tissue, and even become part of it. Porous materials can provide surfaces into which tissues can grow and bond with the implant. Another approach that may allow the body to accept materials is coating the material with living cells. If these cell coatings are grown from the patient’s own cells, then the body recognizes the implant as part of the body rather than as an invader.
How do x-rays show a broken bone?
A staple scene in cartoons is a character walking in front of an x-ray machine. You see the character walk past a screen and suddenly you’re viewing his skeleton. Although doctors use a short snapshot instead of continuously watching a screen, that is pretty much what happens when an x-ray image is taken. How do x-rays work?
X-rays are a form of electromagnetic radiation just like visible light, and like visible light, they pass through some materials and are absorbed by others. If you place a strip of black tape on a window, it makes a shadow when sunlight passes through the window. The tape absorbs all of the light while the glass lets it pass through.
When atoms absorb light, the addition of energy causes the electrons to move into a higher energy state. This can only happen when the energy of the light matches the change in energy of the electron. Electrons can only gain specific amounts of energy, and these specific amounts differ for different elements. Light consists of photons, packets of specific amounts of energy. When the energy of a photon exactly matches the amount of energy needed to move an electron to a higher energy level, the atom absorbs the photon.
The discovery of x-rays and their ability to make pictures of bones was an accident. In 1895, Wilhelm Roentgen noticed that a fluorescent screen in his lab began to glow while he was experimenting with electron beams. When he put his hand in front of the screen, he saw an image of his bones.
The atoms that make up your skin and other soft tissues absorb the energy of visible light photons. That is why you cannot see through your hand. The photons of x-rays, however, have much more energy than the photons of light. They pass right through your skin, muscle, and blood without being absorbed. These tissues are transparent to x-rays in the same way that a glass window is transparent to visible light.
Your bones, however, are made of different elements than are your soft tissues. Bones (and teeth) are primarily made up of calcium and phosphorus. Electrons in these elements can gain energy in amounts that match the energy of an x-ray photon, so bones absorb the x-ray photons, just as black tape absorbs photons of visible light.
In an x-ray machine, the radiation comes from exciting atoms with an electric current, similar to the way a light bulb produces radiation in the visible part of the spectrum. The radiation passes through an opening and travels to a piece of film that absorbs x-ray photons. If something that absorbs these photons, such as a bone in your arm, is placed between the source and the film, a shadow of the object appears on the film. This shadow is the familiar x-ray image that your doctor uses to determine whether the bone is damaged.
Some people avoid getting dental x-rays due to fear of harm from the x-rays themselves. While x-rays can cause damage to cells in large amounts, the amount of radiation exposure during a dental x-ray is very small—many times less than annual natural exposure to radiation from space. The risk from undetected dental problems is greater. When x-rays are taken of women who are pregnant, a lead-lined blanket is usually used to avoid exposing her fetus to any radiation. X-rays that strike lead are completely absorbed.
How do CAT scans make images of your body?
An x-ray image is like a shadow of an object placed between the source of the radiation and the film. It is useful for detecting damage on a tooth or showing whether a broken bone has been set straight. But if you need to see the back side of a tooth or an organ that is hidden behind bone, you will need a CAT (or CT) scan, which is spoken as "cat scan." How can a CAT scan provide images of hidden parts of the body?
If you read its name, computerized (axial) tomography (CT or CAT) sounds pretty complicated. However, you already know what computerized means; tomography is an image that is collected in sections, and axial just means all around, or from every direction. And a CAT scan is just what it sounds like: a series of images, taken from different directions, and then combined by a computer.
In a CAT scan, an x-ray beam moves in a full circle around the part of the body to be scanned. It takes hundreds of x-ray images from many different angles. For a full body scan, the scanner moves from head to toe, taking a set of images, each of which is like a single cross-section of the person. Then the computer comes in. It would be impossible for a person to look at all these images and interpret them as a three-dimensional picture. For a computer, though, that sort of thing is a piece of cake. The computer processes the entire sequence of images and builds a composite picture of the patient’s insides.
Although soft tissue, including many organs, does not normally show up in an x-ray image, CAT scans are very important tools for diagnosing problems with organs. Prior to the scan, the patient is given a contrast agent, or contrast dye. This is a soluble material that absorbs x-rays. The dye is designed to concentrate in the organ to be looked at, or to remain in the blood in order to study arteries or veins.
How does an MRI scanner make an image?
Images obtained from x-rays and CAT scans provide a lot of information about bones and other hard parts of the body. With a contrast dye, CAT scans can also show doctors what is going on in internal organs. However, for a detailed picture of the soft tissues and organs of the body, an MRI scan produces pictures that are far better than scans based on x-rays. How do MRI scanners produce images of soft tissue?
Compared to x-ray technology, magnetic resonance imaging (MRI) is a fairly new way to see inside your body. It is a noninvasive technique that does not expose the patient to any potentially harmful radiation and does not require any probes inside the body. By adjusting the position of the patient and the settings of the instrument, doctors can obtain a detailed picture of internal organs, blood vessels, bones, and other tissues.
An MRI machine uses a combination of powerful magnetic fields and radio waves to produce its images. When a hydrogen atom is near a strong magnet, its nucleus lines up with the magnetic field. Most molecules in the human body contain hydrogen atoms, so they are sensitive to MRI. The atoms on different molecules respond slightly differently from one another, increasing the ability to tune, or focus, the instrument.
The MRI machine has a giant magnet that creates a very strong magnetic field that runs the length of a large tube. As the patient lies inside the tube, all of the hydrogen atoms align themselves with the field. When energy is added in the form of radio waves, some of the atoms absorb energy and move out of alignment with the field. When the radio-wave source is turned off, these atoms move back into place and release energy as radio waves. This energy is detected and a computer converts the data into a digital signal that can be converted into a picture. By properly tuning the instrument, the doctor can look at very small locations in a particular organ or tissue.
MRI demonstrates how quickly technology can advance when the basic science is well known and understood. The first MRI exam of a human occurred in 1977 taking almost five hours to complete. Due to advances in computer technology, magnet technology, and electronics, today’s MRI scanners obtain much more information in a few seconds.
Unlike x-rays and CAT scans, MRI does not require ingestion of a contrast agent to make an image of an organ, such as the liver or a blood vessel. Tuning magnets in the instrument allow it to look at specific places. Also, soft tissues generally contain a lot of water. Two of the three atoms in a water molecule are hydrogen, so MRI images are especially sensitive to water. Diseases such as cancer and inflammation, which cause fluid to accumulate, are particularly easy to study by MRI compared to other techniques.
MRI is a safe and noninvasive way to look into the body, although some people become claustrophobic when they are inside the tube. The greatest risk of MRI comes from the effects of its very strong magnetic field on metal objects. MRI technicians must be certain that neither they nor the patient bring objects such as keys, stethoscopes, or paperclips into the area. These normally harmless items can become deadly projectiles when they are close to the powerful MRI magnet. Buckets, oxygen tanks, and even a police officer’s sidearm have been known to fly across a room magnetized by a MRI magnet.
How does a PET scan differ from other imaging techniques?
One of the main goals of imaging technology is to learn what is happening inside a person’s body without needing to cut into the body. While MRI and ultrasound look into the body, and x-rays and CAT scans look through the body, nuclear imaging uses information that starts inside. Positron emission tomography (PET) is one example of a nuclear imaging technique. How does a PET scanner make an image of an internal organ?
PET produces images by looking at radiation given off by radioactive atoms. Radioactive atoms of many elements can be made in large particle accelerators, which cause atoms to smash together at nearly the speed of light. When these radioactive atoms break apart, they emit radiation that can be easily detected.
For PET scans, radioactive carbon, fluorine, oxygen, or nitrogen atoms are used to make compounds that are injected into the patient. The patient is placed in a tubular scanner that converts the radiation that is emitted into electronic signals. The scanner moves back and forth around the area of interest and then a computer assembles the data into a three-dimensional image. The image shows where the radioactive material has accumulated.
PET scans are often used to detect cancer. The radioactive atoms are used to make sugar molecules that are injected into the body. The radiation will be higher in regions of the body that metabolize the sugar faster. Metabolic rates are higher in cancer cells than in the normal cells around them, so tumors show up very well in PET scans.
Other uses of PET include tracing the flow of blood through the circulatory system to detect areas of impaired flow and detected areas of the brain that are not functioning properly. PET is also used in research studies of the normal function of the brain. The scan shows which parts of the brain are most active as the research subject performs a particular task.
PET uses radioactive atoms that decay very quickly to minimize the patient’s exposure to radiation. However, this does limit the capabilities of the technique. Because the radioactive material must be used within a few days, or sometimes a few hours, from the time they are made, most PET facilities are located near a particle accelerator.
"Science can never be a closed book. It is like a tree, ever growing, ever reaching new heights. Occasionally, the lower branches, no longer giving nourishment to the tree, slough off. We should not be ashamed to change our methods; rather, we should be ashamed not to do so."
How do defibrillators save a person having a heart attack?
On just about every episode of a television hospital drama, someone goes into cardiac arrest. A team rushes in with a cart full of electronic equipment, places paddles on the patient’s chest, cries "Clear," and administers a shock that restarts the heart. How can an electric shock cause a heart to start beating?
A heart attack occurs when blood flow to the heart, or to a section of it, becomes blocked. There are two severe problems linked to a heart attack that can be treated by defibrillation, or administering an electric shock to the chest. Heart failure occurs when the heart cannot pump enough blood and, sometimes, completely stops beating. Arrhythmia, or irregular heartbeat, is any change from the normal pumping sequence of the heart.
One particular type of arrhythmia, ventricular tachycardia, occurs when the ventricles (lower chambers) of the heart beat very rapidly. When this occurs, the heart can start to quiver without actually pumping blood. Tissues throughout the body die within a few minutes if blood flow stops, so quick action is necessary to start the blood pumping. In many cases, an electric shock can start the flow again.
When the heart is functioning normally, cells in the heart, called pacemaker cells, send chemical signals that are converted to an electrical impulse. This electrical impulse is carried to the heart muscle by nerves, signaling the heart to contract and pump blood. When these signals become uncontrolled, the heart does not beat with its normal rhythm.
A defibrillator is a device that delivers electrical energy near the heart. A sudden jolt of electricity causes all the heart muscles to contract at once. This frequently ends the arrhythmia and the heart resumes its normal pace. If the heart has stopped beating, this sudden contraction can push it back into motion.
The paddles used in hospitals, and prominent on television shows, represent only one type of defibrillator. Many people have implanted artificial pacemakers. These battery-operated defibrillators administer a shock to the heart at each beat, taking over for the natural pacemaker cells.
If you know about defibrillators only from television, you may assume that they always restart the heart. Unfortunately, this is not the case. A study at hundreds of hospitals found that, if the shock was administered within two minutes of the time that the heart stopped beating, a patient had a 39 percent chance of survival. After five minutes, the survival rate dropped to 15 percent. Still, these numbers are better than the 0 percent rate without treatment. If a heart attack is recognized and treatment is started before the heart stops beating, survival is much more likely.
In the past decade, the technology of defibrillation has advanced significantly. Defibrillators have been part of normal ambulance equipment for a long time. Trained operators have saved many lives with them. Recent defibrillators, however, have dispensed with the trained operator. They have a computer that is programmed to analyze the heartbeat and determine whether a shock is needed. This capability means that they can be used by someone with little or no training since they will not send a shock if the heartbeat is normal. These defibrillators have now shown up in airplanes, police cars, and at senior centers as essential equipment.
How does a sonogram make a picture of a fetus?
When was your baby’s first picture taken? Fifty years ago, it might have been a photograph taken in the hospital shortly after birth. Today, that first "picture" might occur seven months earlier. Ultrasound technology has allowed obstetricians to make images during the early stage of pregnancy to monitor development and detect or avoid problems during the pregnancy. How can an image be made with sound?
A sonogram is an image formed by bouncing sound waves off an organ or tissue and recording its echo.
A sonogram uses ultrasound—very high frequency sound waves that cannot be detected by the human ear. Images are formed by recording echoes of the sound waves from an object, such as an organ or fetus, inside a person’s body. This technique is similar to sonar detection used by submarines to safely navigate around obstructions deep underwater. Every second, millions of pulses of sound enter the body. When the sound waves strike a boundary between two different tissues, an echo returns to the detector. A computer calculates the distance the sound has traveled and uses that information to make an image.
Sonograms are widely used in obstetrics because they do not use any ionizing radiation, which could be harmful to the rapidly growing fetus. They provide information with sufficient detail to determine sex and facial features very early in the pregnancy. Because ultrasound images are available in real time, they are also useful for guiding other, more invasive procedures.
A fairly recent use of ultrasound in medicine uses the Doppler effect, a change in frequency due to the motion of the reflecting object relative to the source of the sound. Doppler ultrasound can be used to measure the flow of blood through the heart and inside arteries.
