Near-infrared light is found between the visible and microwave portions of the electromagnetic spectrum. For instance, when a stove coil is turned on, it will begin to radiate near-IR light just before the coils start to glow red. We can't see near-IR light. Image enhancement techniques are used to amplify the near-infrared light that we can't see with out eyes so that we can observe the image.
Light travels at different speeds through different materials such as tissue. Near-IR light is harmless but is highly sensitive to the presence of blood and water molecules in tissue. The molecules in breast tissue absorb certain frequencies of light and scatter others. Near-IR imaging uses special detectors to pick up the near-IR light that is scattered off of tissue. Doctors have used ultrasound for years to pinpoint the exact location of foreign masses in breast tissue and determine whether they are harmless cysts or solid lesions. But ultrasound cannot determine whether the lesions are benign or malignant, so a biopsy has to be done. Near-IR imaging can determine the type of lesion without a biopsy.
Near-IR light is also useful to monitor the success of chemotherapy, which is often used to shrink tumors before the cancer is removed. Another approach injects a biochemical marker encased in a capsule into the body. The capsule remains sealed until it reaches a cancerous tumor; the tumor's enzymes cause the coating to break down, and the marker emits near-IR light, which can be detected and used to make an image.
The "four vital signs" measure the body's most basic functions. Body temperature can vary, but usually is between 97.8 and 99 degrees Fahrenheit. The pulse rate is a measure of the number of times the heart beats per minute. The respiration rate is the number of breaths a person takes per minute. Blood pressure is the force of the blood pushing against the artery walls.