In determining whether to order a particular type of imaging, the clinician first must decide what information is needed and whether diagnostic imaging can provide it. If the answer is yes, the next step is to determine the best imaging technique for the situation. It is possible that several techniques could provide the desired data. For example, an expansile lesion in the mandible may be viewed with panoramic radiography, perhaps supplemented with an occlusal view. However, it could also be visualized with plain-film radiography (at variousangles),
CT, MRI, or a combination of techniques. How much information is necessary? If a lesion is contained and well defined, panoramic radiography alone may be adequate. However, if a lesion is large and poorly defined, the information on lesion extension and effects on adjacent structures may be critical to the management of the patient, and CT may be almost mandatory. On the other hand, if the results of the CT or MRI studies will not affect the diagnosis or management of the case, the procedure could be considered superfluous and a waste of time, money, and radiation risk.All imaging techniques, with the exception of US and perhaps MRI, carry some type of radiobiologic risk. Current practice is to convert the absorbed dose from the radiation to an effective dose, which is a quantity weighted for radiation type and dose and for radiosensitivity of the tissues. This practice allows expression of a dose to a limited portion of the body equivalent, in terms of detriment, to a smaller dose to the entire body, thus allowing comparison between radiographic techniques. Reported average effective doses for several imaging examinations of the head and neck, along with days of equivalent natural exposure, are listed in Table 3-1.
The cost of imaging procedures varies significantly. Intraoral and panoramic radiography is the least expensive; an examination typically costs less than $75.00 (US). Plain films of the skull may be obtained for about $135.00 (US) each in a hospital radiology facility. A typical ultrasound examination of the neck costs about $250.00 (US). CT scans of the maxillofacial region are in the range of $850.00 to $1,000.00 (US) and cost more if there is three-dimensional reconstruction of the image whereas MRI scans usually cost more than $1,200.00 (US). (All stated fees are based on the fees at a Midwestern teaching hospital in the year 2000.) The majority of advanced imaging procedures will be billed to medical insurance rather than to dental insurance. The regulations of the patient’s health care insurer must be followed if payment is not to be denied. For example, in a health maintenance organization (HMO), CT or MRI may need to be ordered by the patient’s primary care physician for payment to be authorized.
A prudent principle to follow when ordering an imaging study is to select the technique that has the lowest cost and radiation dose but that is still capable of providing the needed information. Consultation with an oral and maxillofacial radiologist can help the clinician select the best study for the particular situation.