Noninvasive imaging of gene expression with magnetic resonance imaging and magnetic resonance spectroscopy

INTRODUCTION Magnetic resonance imaging (MRI) has developed from an intriguing research project initially conceived in 1973 to an essential diagnostic method in the armamentarium of clinical radiologists. An estimated 26.6 million MRI procedures were performed in 2006 in the United States that generated approximately $20 billion in service revenue. The demand for clinical MRI diagnoses is expected to increase by 30% by 2020. This projected growth is due in part to the rising prevalence of age-related pathologies of soft tissues that can be conveniently monitored with MRI, such as the anatomy of pathologies in the cardiopulmonary system (e.g., regions of myocardial infarcts), neurological system (e.g., regions of cerebral infarcts, morphological changes during multiple sclerosis), and musculoskeletal system (e.g., tears in ligaments, tendons, and cartilage). MRI offers advantages relative to optical imaging methods limited to making diagnoses only near tissue surfaces, and relative to PET, SPECT, CT, and X-ray imaging methods that use potentially harmful ionizing radiation. Unlike these other imaging modalities, MRI also provides excellent spatial resolution at or smaller than 1 mm3 for clinical diagnostics and approaching 0.1 mm3 for small-animal research studies. MRI can also assess physiological function, such as the function of the cardiopulmonary system (e.g., MR angiography of vasculature), neurological system (e.g., fMRI of brain activity), renal system (e.g., perfusion imaging of kidney function), musculoskeletal system (e.g., MR elastography of connective tissues), and cancer lesions (e.g., dynamic contrast enhancement MRI of angiogenic tumors).