Comparative Sectional Anatomy of the Abdominopelvic Cavity

Sonographers should understand other imaging modalities, especially computed tomography (CT) and magnetic resonance imaging (MRI), which most frequently complement sonography. No longer does each of the various imaging modalities operate within a “silo,” independent of each other. Instead, many diagnostic algorithms may require two or more imaging modalities to be employed, and diagnosis requires specific comparisons between them. In this way, ultrasound now interacts extensively with CT and other imaging methods to optimize the workup of a patient. Understanding what each modality offers is of prime importance in crafting the multimodality imaging workup for any particular problem.

Physicians may utilize ultrasound to follow up an abnormality that has been previously diagnosed with CT or MRI. Ultrasound is often the primary imaging tool as it provides rapid access with good soft tissue and vascular analysis. Depending on the clinical problem, it may be preferred over CT, which involves ionizing radiation, or MRI, both time-consuming and costly. To effectively meet the patient’s needs, the sonographer must tailor their exam appropriately to exploit the unique strengths of ultrasound and minimize its limitations. The sonographer must also understand how the ultrasound examination in each setting may be influenced or guided by findings from previous CT, MRI, or other imaging studies.

The various imaging modalities have the ability to ultimately depict and evaluate the same abnormalities, and they are generally equivalent in identifying the physical size and shape of pathologic lesions. However, each modality approaches the problem from a different standpoint, using differing physical properties of the normal tissue and pathologic lesions to derive image contrast and resolve important details. As previously stated, ultrasound and MRI both have a safety advantage in that they do not use ionizing radiation. On the other hand, CT scanning and general diagnostic (radiographic) imaging both image the body using ionizing radiation, often in significant doses. The radiation for both CT and radiography is produced by an external source and tends to produce sharp images with high anatomic detail.

The purpose of this chapter is to introduce the sonographer to sectional anatomy as compared with CT, MRI, and ultrasound images ( Table 5.1 ).