The Case for Ultrasound

For thousands of years physicians have attempted to "see" disease states in order to better understand and treat them. Initially, only five physical senses were available to guide the treatment process. Available energy sources included visible light and mechanical forces for inspection and pal-pation. More recently, new energy sources have been developed to better "see" disease. These energy sources include: X-ray MRI Nuclear Scan Ultrasound X-ray: X-rays were discovered in 1895 by Wilhelm Konrad Roentgen (1845-1923), and are high energy radiation of short wave length (0.01 to 10 nm). 1 These rays are commonly produced by passing a high voltage current through a special X-ray (vacuum) tube. The X-ray tube (Coolidge tube) consists of a tungsten wire filament cathode that produces a stream of electrons when excited by high voltage electrical current. The electron stream is directed at an anode of solid tungsten within the tube, generating high energy X-rays that are capable of penetrating most human tissue. X-rays also affect photographic film, blackening it upon exposure. This property is used to generate an image of tissue exposed to X-rays. Photographic film is blackened in inverse proportion to the energy lost in passage of X-rays through that tissue. X-ray, one of the earliest alternative energy sources to "see" disease, is very useful for evaluating structures and process within the body. X-rays, however, are powerful sources of potentially dangerous radiation and are not readily utilized by the practicing surgeon-interventionist. High energy X-rays can ionize neutral atoms and cause genetic defects, carcinogenesis, and developmental defects in exposed fetuses. Because they produce ionizing radiation, X-ray machines require special shielding and rooms for their safe use. X-ray devices are relatively bulky, expensive and non-mobile. Special knowledge and training are required to fully exploit their potential. Typically physicians who have specialized in radiology are relied upon to perform the examinations and interpret the images. For these reasons X-ray energy is not readily used by the surgeon-interventionist. Magnetic resonance imaging utilizes signals emitted by a patient's hydrogen atoms when that patient is placed in a strong magnetic field and the magnetic moment of the patient's hydrogen atoms are perturbed by radiofrequency energy. 2 Perturbation of the magnetized hydrogen atoms causes the emission of a radiofrequency signal that is sampled and processed by computers into images. MRI images are produced without the use of ionizing radiation. To perform an MRI examination, the patient is placed into a …