Contrast enhancement in medical imaging: At the crossroads of techniques and contrast agents – Improvements over the last decade

Abstract

Early detection and diagnosis of pathologies is an essential part of clinical practice. This continually drives improvements in imaging modalities and contrast agents. The challenge is always to obtain the most accurate images possible of lesions, but also to detect tissue microstructures or metabolic events. This means combining resolution and sensitivity with deep-tissue imaging. Here, we review examples of contrast agents used in the various biomedical imaging modalities currently in use (CT, US, MRI, SPECT, PET, Fluorescence). We will then take a closer look at photoacoustic imaging (PAI), because of its intrinsic resolution and sensitivity. The review is structured as follows: first, the principle of each technique is discussed, followed by a description of the characteristics that the dedicated contrast agents must meet. Third, recent examples of molecular and nanoparticulate contrast agents will be described. Finally, a special section will be devoted to bimodal contrast agents combining MRI and PAI imaging, showing that it is a very promising tandem.