Imaging
High-tech diagnostic imaging techniques that have allowed physicians to explore bodily structures and functions with a minimum of invasion to the patient have been exploited for other uses. Forensic investigations have been one of the beneficiaries.
A forensic investigator may be faced with a body that displays no outward signs of trauma. Learning the cause of death may involve delving inside the body. Imaging techniques allow a detailed examination without the immediate need of a destructive autopsy.
The use of imaging techniques in forensics has followed the development of the techniques for other purposes. During the 1970s, advances in computer technologies, in particular the development of algorithms powerful enough to allow difficult equations to be solved quickly enough to be of real-time use in the clinical diagnostic setting and to eliminate "noise" from sensitive measurements, allowed the development of accurate, accessible, and relatively inexpensive (when compared to surgical explorations) non-invasive technologies. Although relying on different physical principles (i.e., electromagnetism vs. sound waves), all of the high-tech methods relied on computers to construct visual images from a set of indirect measurements. The development of high-tech diagnostic tools was the direct result of the clinical application of developments in physics and mathematics. These technological advances allowed the creation of a number of tools that made diagnosis more accurate, less invasive, and more economical.
The use of non-invasive imaging traces it roots to the tremendous advances in the understanding of electromagnetism during the nineteenth century. By 1900, physicist Wilhelm Konrad Roentgen's (1845–1923) discovery of high-energy electromagnetic radiation in the form of x rays were used in medical diagnosis.
The development of powerful high-tech diagnostic tools in the later half of the 20th century was initially the result of fundamental advances in the study of the reactions that take place in excited atomic nuclei. Applications of what were termed nuclear spectroscopic principles became directly linked to the development of non-invasive diagnostic tools used by physicians.
In particular, Nuclear Magnetic Resonance (NMR) was one such form of nuclear spectroscopy that eventually found widespread use in the clinical laboratory and medical imaging. NMR is based on the observation that a proton in a magnetic field has two quantized spin states. Accordingly, NMR allowed the determination of the structure of organic molecules and, although there are complications due to interactions between atoms, in simple terms NMR allowed physicians to see pictures representing the larger structures of molecules and compounds (i.e., bones, tissues, and organs) obtained as a result of measuring differences between the expected and actual numbers of photons absorbed by a target tissue.
Groups of nuclei brought into resonance, that is, nuclei absorbing and emitting photons of similar electromagnetic radiation (e.g., radio waves) make subtle yet distinguishable changes when the resonance is forced to change by altering the energy of impacting photons. The speed and extent of the resonance changes permits a non-destructive (because of the use of low energy photons) determination of anatomical structures. This form of NMR is used by physicians as the physical and chemical basis of a powerful diagnostic technique termed Magnetic Resonance Imaging (MRI).
MRI scanners rely on the principles of atomic nuclear-spin resonance. Using strong magnetic fields and radio waves, MRI collects and correlates deflections caused by atoms into images of amazing detail. The resolution of the MRI scanner is so high that they can be used to observe the individual plaques in multiple sclerosis.
Principles of SONAR technology (originally developed for military use) found clinical diagnostic application with the 1960s development of ultrasound. A sonic production device termed a transducer was placed against the skin of a patient to produce high frequency sound waves that were able to penetrate the skin and reflect off internal target structures. Modern ultrasound techniques using monitors allow physicians real-time diagnostic capabilities. By the 1980s, ultrasound examinations became commonplace in the examination of fetal development.
The advent of other imaging to supplant x rays provided for less potentially damaging forms of diagnosis. High photon energies found in x rays are ionizing and are thus capable of destroying chemical and molecular bonds in cells. In contrast, ultrasound relies not on electromagnetic radiation but rather on pressure waves that are non-ionizing.
Microscopes using ultrasound can be utilized to study cell structures without subjecting them to lethal staining procedures that can also impede diagnosis through the production of artifacts (extraneous bits of highlighted material). Ultrasonic microscopes differentiate structures based on underlying differences in pathology. Ultrasonic imaging devices are also among the least expensive of the latest high-tech innovations in diagnostic imaging.
During the early 1970s, enhanced digital capabilities spurred the development of Computed Tomography (derived from the Greek Tomos, meaning slice) imaging, also called CT, Computed Axial Tomography or CAT scans, invented by English physician Godfrey Hounsfield. CT scans use advanced computer-based mathematical algorithms to combine different readings or views of a patient into a coherent picture usable for diagnosis. Hounsfield's innovative use of high energy electromagnetic beams, a sensitive detector mounted on a rotating frame, and digital computing to create detailed images earned him the Nobel Prize. As with x rays, CT scan technology progressed to allow the use of less energetic beams and vastly decreased exposure times. CT scans increased the scope and safety of imaging procedures that allowed physicians to view the arrangement and functioning of the body's internal structures on a small scale.
American chemist Peter Alfred Wolf's (1923–1998) work with positron emission tomography (PET) led to the clinical diagnostic use of the PET scan, allowing physicians to measure cell activity in organs. PET scans use rings of detectors that surround the patient to track the movements and concentrations of radioactive tracers. The detectors measure gamma radiation produced when positrons emitted by tracers are annihilated during collisions with electrons. PET scans have attracted the interest of psychiatrists for their potential to study the underlying metabolic changes associated with mental diseases such as schizophrenia and depression. During the 1990s, PET scans found clinical usage in the diagnosis and characterizations of certain cancers and heart disease, as well as clinical studies of the brain.
MRI and PET scans, both examples of functional imaging (in addition to detailing structures they provide a view of dynamic functions), are the subject of increased research and clinical application. MRI and PET scans are used to measure reactions of the brain when challenged with sensory input (e.g., hearing, sight, smell), activities associated with processing information (e.g., learning functions), physiological reactions to addiction, metabolic processes associated with osteoporosis and atherosclerosis, and to shed light on pathological conditions such as Parkinson's and Alzheimer's disease.
During the 1990s, the explosive development of information technologies and the Internet allowed imaging data to be shared globally, both in real-time and by mining databases.