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Technological advancements in medical imaging have significantly benefited research studies and the field of medical diagnostics and therapy. From 1985, Wilhelm Roentgen discovered x-rays, the humble beginnings of medical imaging where ionized radiation absorbs through various tissues and leaves an impression on film. X-ray technology is an excellent utility for detecting fractures to pneumonia, but in 1970's computed tomography (CT) scanning technology revolutionized the x-ray and medical imaging industry. By recording numerous x-rays from a rotating source and detector around the specimen, the CT computer constructs detailed three-dimensional images of the body with good spatial resolution. Instead of operating on radiation, magnetic resonance imaging (MRI) more safely uses the body's inherent magnetic properties, however, with several caveats – prominently its relatively low speed and high equipment costs. The latest contender, positron emission tomography (PET), is a radiation based scan with thus far limited standalone applications based on the altered metabolism rates and locales of certain compounds, for instance, in the brain to detect regional/anatomic metabolic (de)activation – functional characteristics. Each modern medical imaging/scanning modality has its sets of drawbacks and limitations: clinical efficacy, organ-disease specific diagnostic potential, and economic practicality. In particularly, clinical CT applications are escalating along with technological developments in resolution and visualization, while MRI and PET remain expensive, currently confined, yet promising technologies.

X-rays remains widely used in clinical practice, for instance, for orthopedic fractures, breaks, and misalignments and pneumonia. However, x-ray films can only differentiate tissue density, where more dense tissues appear white and less dense black. The latter generations CTs generate detailed images of the chest, nervous system, and abdomen. Multiple detectors rotate the body's axis and continuously records x-ray images. The computer uses the images to reconstructs the body and outputs a remarkable three-dimensional visualization for effective diagnostics. CT is especially used in cancer diagnostics and not only reveals the presence of a tumor, but the size, spatial location, and extent of tumor metastasis. Given its short scan times, CT is used for virtually all anatomic areas and is the primary modality for areas of the body vulnerable to movement, including the lungs and abdomen. Its robust utility is explicated by its use in colongraphy (virtual versus optical colonscopy). In less than 30 seconds, the procedure allows a complete examination of the colon and surrounding organs without invasive or penetrative measures (Burling, Taylor, & Halligan, 2004).

MRI and PET scans offer selective applications. MRIs create a magnetic field and submit a pulse of radiowaves that excite the spin of hydrogen – an element abundant in the human body. Due to the relaxation of the spin to the normal state, the hydrogen atoms emit a pulse of radiowaves that are recorded and quantified. Successive and alternating pulses are used to develop a detailed image of the specimen. MRIs have relatively long imaging times (30 minutes or more), cannot be performed on patients with metal in their bodies or suffer from claustrophobia, and are expensive. MRIs are generally not recommended for trauma diagnostics, for CT scans offer quick and good quality imaging. PET scans use radiolabeled molecular probes to study metabolic events. These chemicals emit radiation (positrons) that is registered by the PET detector. Therefore, such scans can offer valuable functional (and anatomical) information based on the metabolism of labeled compounds. It is useful for detecting and monitoring certain cancers, neurophysiology studies, and, importantly, drug development. Labeled pharmaceuticals can be monitored by PET scans to pin point sites of delivery, metabolism, and action. As a novel clinical nuclear imaging utility, PET scanning is very expensive and limited in availability.

No single medical imaging modality offers the best spatial resolution, contrast, economic outlook, and diagnostic applicability. Perhaps a fusion of technologies, especially coupling a standard anatomical modality (CT or MRI) with PET functional imaging, can best identify and localize functional abnormalities. For example, PET/CT offers individual patient image guided cancer therapy and the ability to define and monitor the response of radiation and/or chemotherapy therapies (Schillaci & Simonetti, 2004). Each imaging methodology and new fusion technologies that promise integration of greater information must be further evaluated before widespread use in the clinical setting.

References

Burling, D., Taylor, S., & Halligan, S. (2004). Computerized tomography colonography. Expert Review of Anticancer Therapy, 4(4), 615 625. Retrieved from PubMed database (15270665).

Schillaci, O., & Simonetti, G. (2004, February). Fusion imaging in nuclear medicine applications of dual modality systems in oncology. Cancer Biotherapy & Radiopharmaceuticals, 19(1), 1 10. Retrieved from PubMed database (15068606).

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