ABSTRACT
Magnetic resonance imaging (MRI) is the leading noninvasive for diagnostics in medicine. Among other clinical imaging techniques (i.e., x-ray, computed x-ray tomography, positron emission tomography, and ultrasound), MRI is able to image and provide anatomical information for both hard and so¹ tissues (Na et al. 2009). Since MRI displays qualitative information, it must produce well-de™ned images, accounting for diŸerences among all types of tissues. Failure to do so may result in images that cause physicians to misinterpret or misdiagnose diseases. High spatial and contrast resolution are needed to distinguish the location and the nature of tissues in a quality MRI image. Clinical MRI scanners with 1.5 or 3 T magnets provide su±cient signal-to-noise ratio (SNR) to produce images up to micron-scaled spatial resolution (25-100 μm) (Massoud and Gambhir 2003). Since heterogeneous tissues have unique proton densities and relaxation times that generate diŸerent magnetic resonance (MR) signals, image contrast is achieved (Na et al. 2009). Detecting small diŸerences in signal intensity, however, is limited by the strength of the scanner magnet and timing parameters set in pulse sequences, resulting in low contrast in MRI images (Massoud and Gambhir 2003). One inexpensive approach to acquire high MRI contrast is to use magnetic agents that can increase the local MR signal from selective tissues. Contrast agents (CAs) selectively shorten proton relaxations of tissues to enhance MR signal diŸerences, improving image contrast. However, since problems with MR signal enhancement exist in current CAs, there is a need to improve the design of MRI CAs.
