Present Status and Expected Continuing Development of Imaging in Medicine

Introduction

With the predicted decrease in human health and shorter life expectancies that society began to observe within the last century, the world is now is preoccupied with improving overall health of the population and fighting a constant battle against diseases. Breakthroughs in medicine over the years have facilitated this in becoming a waning battle. One such technique employed, which became known in the 1970's as a separate field of study, is Nuclear Medicine. Nuclear medicine involves the use of radioactive isotopes (radioisotopes) to prevent, diagnose, and treat disease. It is unique as it looks at both the physiology and anatomy in imaging the body and establishing a diagnosis. The radioactive substance is given to the patient either intravenously or orally and the image is developed based on the detection of energy emitted from the substance. Radioisotopes are utilized in diagnosis as a standard practice nation-wide, and have been for over 60 years. Positron Emission Tomography scans (PET Scans) use radioactive atoms such as Carbon-11, Flourine-1 or Oxygen-15, produced by bombarding normal atoms with neutrons to create short-lived radioisotopes. Specifically, nuclear medicine can be used to analyze kidney function, image blood flow and function to the heart, locate the presence of tumors and scan the lungs for respiratory and blood flow problems, to name a few. Other examples of these non-invasive methods of disease detection and diagnosis include Single Photon Emission Computed Tomography (SPECT), Cardiovascular Imaging and Bone Scanning. Painful surgeries are thus becoming a part of the past as the human body is now being explored through non-invasive techniques of nuclear medicine.

Positron Emission Tomography

Positron Emission Tomography, also known as PET scans or PET imaging, is most frequently used to determine the presence of cancers, neurological conditions and cardiovascular diseases. Using a radiopharmaceutical such as FDG (flourodeoxyglucose), which consists of both glucose and a radioactive atom, usually marks the substances injected into the body. The radionuclides used in PET are positron emitters, whereas single photon emitters are used in conventional nuclear medicine imaging. When a positron meets an electron, the collision produces two gamma rays that, although they have the same energy, they travel in opposite directions. The gamma rays leave the patient's body and are detected by the PET scanner. The information is then fed into a computer to be converted into a complex picture of the patient's working brain.

The patient is usually administered the radioactive substance either through an existing intravenous line or by inhaling gas (there is a specified waiting period for the substance to become concentrated in the tissue of interest) and lies down on a flat table, that moves through a "dounut" shaped housing. This housing, or PET scanner is made up of an array of circular gamma-ray detectors, which has a series of scintillation crystals that convert the emitted rays into photons of light. Each crystal is connected to a photomultiplier tube, which in turn converts and amplifies the photons to electrical signals, which are then processed