ABSTRACT

Keywords: diagnostic imaging, multi-modality, contrast, nanoparticles, positron emission tomography, magnetic resonance imaging, ultrasound, computed tomography, single photon emission computed tomography

(CT), positron emission tomography (PET), single photon emission computed tomography (SPECT), and ultrasound imaging (US). There are strengths and limitations associated with each imaging modality and each is used to capitalize on its characteristic capabilities. No single modality is perfect, and they differ in detection sensitivity, limits of spatial resolution, and depth of penetration or range of image generation. PET and SPECT are highly sensitive to functional information, and can detect biological activity generated by a small number of cells or molecules, but lack the ability to detect structural details. MRI and CT boast high spatial resolution and provide superb detail of biological structures. US images have relatively high sensitivity, but poorer resolution, often with inferior image quality; however, the devices are inexpensive, portable, and convenient to use while still providing valuable real-time functional information [1, 2].All currently approved imaging modalities in use clinically are generally regarded as safe, although several carry the risk of exposure to ionizing radiation. Specifically, CT exposes the patient to external X-rays, while PET and SPECT rely on internally administered radioisotopes that necessarily result in exposure to ionizing radiation. The strength of a radioactive source is defined according to units of becquerels (Bq) or curies (Ci), which measures the rate of emission. A becquerel is a very small unit of measure, while a curie is a very large unit of measure, so multiples are typically used. Common multiples typically used for Bq are kilobecquerel (kBq = 1000 Bq) and megabecquerel (MBq = 1000 kBq); common multiples used for Ci are millicurie (1000 mCi = 1 Ci) and microcurie (1000 μCi = 1 mCi).