Essentials of MR Image Interpretation

Abstract

The definition “hybrid imaging” refers to the combination of cross-sectional imaging techniques used in radiology (CT and MRI) with radionuclide imaging used in nuclear medicine. PET/MRI is a rapidly evolving hybrid imaging technique being increasingly used in clinical practice and may represent the most challenging modality for nuclear medicine specialists. In the simplest PET/CT examination, low-dose unenhanced CT images are acquired for both attenuation correction and anatomical localization, with a limited contribution for characterizing lesions detected by tracer uptake in the PET scan. In contrast, even the most generic whole body PET/MRI hybrid imaging, without specific organ-targeted or contrast-enhanced sequences, requires interpretation of multiple images including T1-weighted, T2-weighted, and diffusion-weighted images. In the first part of this chapter, the appearance of various tissue components on pulse sequences commonly used in MR examinations will be described, and the most common imaging patterns of disease – classified on the basis of prevalent tissue composition – will be illustrated. In the second part, imaging findings useful for differentiating pathological processes in various organs will be discussed, with particular emphasis on mass lesions commonly evaluated on MRI.