Radiologic advances in facial imaging

Key points

• The deleterious effects of ionizing radiation are cumulative, necessitating the judicious use of ionizing radiation.

• Cone beam CT (CBCT) allows for image capture that displays excellent spatial resolution (image detail) of hard tissue at a relatively low dose of ionizing radiation.

• CBCT data sets can be integrated with task specific diagnostic software programs such as virtual surgical planning.

• A radiation reduction approaching 90% can be achieved with CBCT compared with traditional CT.

• With CBCT the patient is either standing upright or seated. This allows for a reproducible head posture to be established and duplicated when sequential scans of the facial complex are indicated.

• Injectable contrast media to highlight vascular tissue, enhance lymph node visibility or outline anatomic boundaries is not clinically feasible with CBCT at this time.

• MRI can distinguish blood vessels and nerves from surrounding soft tissue. This type of anatomical differentiation is far superior to that with other imaging modalities and constitutes the principal benefit of an MR study.

• Bony structures, which contain less water and consequently less available hydrogen protons for imaging, are not welldefined by MR. CT and CBCT remain the state of the art when evaluating these structures.

Introduction

The information gained from an imaging study is called the “diagnostic yield.” The higher the diagnostic yield, the more information the clinician receives about his or her patient. However, the information gained must be of clinical relevance to the surgeon. It must provide answers to diagnostic questions that allow the surgeon to better understand the anatomic relationships under consideration.

The invention of computed tomography (CT) in the 1970s gave birth to a new era in diagnostic imaging. No longer were clinicians restricted to projection radiology (PR), with its distortion, superimposition, and two-dimensional (2D) representation of the patient’s three-dimensional (3D) facial anatomy.

The worldwide acceptance and dependence on CT redefined the state of the art for preoperative diagnostic analysis and image-guided surgery. Ongoing development and refinement of sensors and software drove CT to become the de facto standard of care in maxillofacial imaging.

A decade later magnetic resonance imaging (MRI) supplemented the information gained from a CT examination by providing exceptional visualization of soft tissue. When indicated, the coupling of these two imaging systems provides unprecedented visualization of anatomic structures and pathologic conditions.

The dawn of the twenty-first century saw an additional imaging system, cone beam computed tomography (CBCT), establish its place as a 3D imaging alternative that compliments and, in some respects, surpasses CT.

This chapter outlines the advantages and limitations of CT and CBCT and places MRI in perspective so that the surgeon can appreciate, prescribe, evaluate, and integrate the information gained from an imaging study. Comparison of these advanced imaging modalities in terms of diagnostic yield and radiation burden to the patient are presented so the specialist can optimize every relevant diagnostic tool and achieve the most aesthetically superior surgical outcomes.

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