From the discovery of X-rays back in 1895, the wonder of seeing inside the human body without a scalpel has pushed scientists to develop better methods of getting under your skin. Here are the basic methods.
The old-school standard broken-leg-detector uses a machine to shoot rays against the area in question with film set behind it. Still in wide use, but as with the advent of digital cameras, actual film is used less and less. The mammogram machine is just a specialized x-ray machine.
Kind of like sonar, this machine reads sound waves that bounce off of solid things in your innards. Of course the most beloved application is to view a fetus inside a mother's womb, and advances in resolution have allowed a lot of diagnostic work to be done prior to birth. But it's also used for other things, like to check the health of the gallbladder or even to detect breast cancer.
The Magnetic Resonance Imaging machine uses magnetic and radio waves to make its pictures. This machine is used to see soft tissue, so it's used to figure out knee injuries to athletes and, in some cases, to diagnose breast cancer. MRIs have become more widespread; even some rural hospitals have them now.
Formerly known as the CAT scanner, this is essentially a really big X-ray machine. Instead of taking one picture, however, it takes a series of photos -- in slices. Then the computer puts the big picture together for a detailed look at a patient's anatomy. It wasn't long ago, however, that there weren't many computers big enough to process the image. Only five years ago, in fact, Inland Imaging would overnight their CT scan files to a supercomputer lab in Torrance, Calif., receiving the results a day later. CT scanners are fairly common today, and powerful new computers allow the scan to go faster and come out at a higher resolution.
This scanner has been the big innovation over the last 10 years, culminating in the hybrid PET/CT scanner. The Positron Emission Tomography machine reads radioactive molecules that have been injected into a patient and have migrated to a problem area. This machine does not read anatomy -- it only shows a vague outline of the body -- but it does reveal any tumor or infection. PET scanners are also used to determine whether a course of treatment has been effective -- if a patient is "cancer-free." For now, insurance covers some applications of the PET machine, but doctors believe it has many more uses; for example, it is approved by insurance for use in detecting liver cancer, but not cervical cancer.