Thursday, April 26, 2012

Imaging methods for identifying symptom of sinus infection

Identifying a symptom of sinus infection is the first step in treating it. Different imaging methods are used to diagnose the infection. Some of the images show accurate morphology and location of the ostiomeatal blockage, the main cause of the infection. Correct usage of imaging technology is also necessary for accurate and safe surgery. This article focuses on the main precursors of computed tomography (CT), the most popular imaging method.

Standard roentgenographs or plain films

The plain films have been used since twentieth century to visualize maxillofacial structures. Standard roentgenography is an easy and fast method. Images are taken from four different views viz. submentovertex, lateral, Towne’s and Waters' to evaluate morphology of the region. The combined exposure to radiation of the four views ranges from 40-60 mSv.  The films are still in use. The films offer quite good view of the maxillary sinuses and the lower part of the nasal cavity. The films also display the sphenoid sinus’ view along the mid-sagittal plane and the frontal sinus outline.
However, films are unable to capture a clear view of the posterior and anterior parts of the ethmoid sinus and inferior part of the frontal sinus. Although the films are economical, superpositioning of various facial structures limit their usability.  Plain films do not display required information for an endoscopic surgery.

To get a better radiographic view of delicate bony structures of the paranasal sinus periphery and the ethmoid sinuses, polytomography was developed. Polytomography produces a cross-sectional image.
The exposure to radiation while scanning the sinus along just one plane and using a 5-mm thick image is four times more than that of the plain films taken along the four views. Although imaging along sagittal and coronal planes is possible, phantom artifacts obscure the small bony structures. The artifacts may also indicate a symptom of sinus infection that does not exist. Polytomography can reduce the superpositioning problem of the plain films, but this method requires a lot of time. In fact, now-a-days no one uses polytomography.

The method is based on the ultrasound wave principle: The principle suggest that the waves reflect at the borders of two different media having different acoustic properties. For example, in case of the sinus containing fluid, the sinus’ posterior wall reflects an echo. In case of a normally healthy sinus, the anterior wall of the sinus reflects the sound.
Brightness (B-mode) and amplitude (A-mode) ultrasonography is useful in visualizing paranasal sinuses.  Utlrasonography is mainly used for “accessible” parts of the sinus. The imaging method gives limited access to the maxillary sinus. The ultrasonograhic images of the other sinuses are not useful.

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