Medicine Light

Why are optics at the front of emerging new medical technology? Because optical techniques foster minimally-invasive health care.

Minimally-invasive optical procedures started in the first half of the nineteenth century with the endoscope. The endoscope provides physicians with diagnostic information, usually by snaking an optical scope and light through a natural cavity. If you've turned 50, you've likely had the pleasure of a colonoscopy, an endoscopic procedure that checks for signs of colon cancer.

In 1929 Heinz Kalk performed liver biopsies using a device he invented, a device that inspired the modern laparoscope. Kalk performed these "laparoscopies" using only local anesthesia and without mortality. Laparoscopes have evolved into a minimally invasive surgical tool for many kinds of abdominal surgery.

By 1944, Raoul Palmer had started filling the pelvis with air during laparoscopic gynecological exams. Then, in 1960, Kurst Semm invented the automatic insufflator. It sounds like a device to make perfect souffles, but it's really a device that safely pumps gas into the abdomen during a laparoscopy. In the 1970s and 1980s, the use of laparoscopy for gynecological procedures grew rapidly, especially with the introduction of integrated video technology in 1982.



A laparoscopic procedure such as a tubal ligation (see diagram above) can be performed in 10-20 minutes with small incisions under the navel through which the entire surgery takes place. Laparoscopy has had many benefits: less expensive and faster surgery with quicker recovery and lower mortality. Since 1990, doctors have adopted this minimally-invasive surgical technology to many other procedures like gallbladder removal, or cholecystectomy, and achieved the same benefits.

Another branch of minimally-invasive surgery uses catheters to perform procedures through small paths like arteries and urinary tracts. While not strictly optical devices, catheters are used for angiography. Experiments with catheters started on animals in the nineteenth century. Werner Forssmann won a Nobel prize for his pioneering catheter experiments in the 1929, in which he took an X-ray of a cathether in his heart. By 1997, Andreas Gruentzig performed the first angioplasty on a human. In this procedure, Gruentzig fashioned a balloon on the end of a Dotter catheter, which was used to position the balloon in a blocked artery. When the balloon inflated, it reduced the blockage.

In angiography, a catheter introduces a radio-opaque dye into the arteries of interest. Usually, the arteries of interest are in the heart or the brain. An X-ray clearly shows the arteries full of dye, and any blockage or bleeding. The angiogram below is of an arteriovenous malformation (AVM) which Senator Tim Johnson (D-SD) has made famous recently. If it's any consolation to Senator Johnson, my mother has recovered nearly completely from her AVM surgery.



Advances in computers and signal processing in the 1970s laid the groundwork for non-invasive imaging technology that has replaced most X-ray and angiography imaging. In 1972, Sir Godfrey Hounsfield invented the CT (Computer Tomography) scan, also known as the CAT (Computer Axial Tomography) scan. To make a CT scan, highly collimated X-rays beams are sent through the body axially. A computer processes the signals received from all beams and calculates a slice of the body. CT scans give significantly more information that X-rays and use less radiation. A CT scan shows the relative density of materials in the slice. CT scanning revolutionized the radiological diagnosis.

In 1980, Raymond Damadian made the first commercial MRI (Magnetic Resonance Imaging) device, which was orginally known as an NMR (Nuclear Magnetic Resonance) device until the marketing people decided the word "nuclear" might lead patients to think the thing was radioactive. The MRI scanner produces images by turning a magnetic field on and off, measuring the radio waves produced by atomic nuclei when the magnetic field is turned off, and computing a slice of the body. The calculations are very different than those for a CT scan, and the MRI scan shows concentrations of molecules rather than relative density. One advantage of MRI over CT is its ability to measure metabolism. I worked with a Ph.D. candidate who was measuring the metabolism of anesthetics in the brain in 1985.

The PET (Positron Emission Tomography) scan is a new twist on original CT scan.

Positron emission tomography, also called PET imaging or a PET scan, is a diagnostic examination that involves the acquisition of physiologic images based on the detection of radiation from the emission of positrons. Positrons are tiny particles emitted from a radioactive substance administered to the patient. The subsequent images of the human body developed with this technique are used to evaluate a variety of diseases. -- from RadiologyInfo

You don't want to know the physics behind PET scans. What's important is that PET scans have many applications including management of cancer treatment, detection of scarred heart muscle, and tumor detection.

Laser surgery is another innovation area in optical medicine. Most Americans have heard of Lasik (Laser-Assisted In Situ Keratomileusis) eye surgery, a quick procedure to improve eye sight. Lasers are popular for dermatology, too, especially removal of dialated superficial blood vessels. Less well known may be endoscopic use of lasers to remove tumors and for microsurgery applications, especially in neurosurgery. Fiber-optically delivered laser is used to vaporize and reduce discs in patients with herniated discs.

What are the emerging ideas in optics and medicine?

These days, researchers are experimenting with ideas like integrating MEMS and GRIN lenses to create non-linear medical optic systems (pdf). These systems may allow doctors to look at tissue in vivo microscopically, which would provide minimally-invasive diagnosis of disease without biopsies.

Fiber optic systems also could be designed to detect certain chemicals in the body, such as by-products from cancer or naturally occurring chemical reactions. If you put materials on the end of a fiber-optic line that react with chemicals you want to detect, you can measure changes in the reflection of a light off the end of the fiber optic to determine how much of the chemical is present.

Another area of minimally-invasive medicine revolves around photodynamic therapy. Photodynamic therapy may provide treatments for a range of diseases, from acne to cancer. For cancer, one idea is to introduce a photosensitive chemical that cancer cells absorb and that, when irradiated with otherwise benign light (or other electromagnetic radiation), kill the cancer cells.

In the catheter world, the FDA has recently cleared a device that removes blood clots from stroke patients. After an angiogram to locate the clot, a balloon is moved into place to block blood flow. Then a retriever (see below) captures the clot and the doctor pulls it out. As optics and nanotechnology provide smaller innovations, expect to see more surgical procedures delivered via catheter.



How all these emerging technologies make it into the medical market may be the largest problem of all. But that's for another post.