The field of medical imaging is advancing at a rapid pace. Imaging modalities like x-ray radiography, x-ray computed tomography (CT), ultrasound, nuclear imaging, magnetic resonance imaging (MRI), and optical imaging have been used in biology and medicine to visualize anatomical structures as large as the lung and liver and as small as molecules. Ultrasound is considered the most cost-effective among them. It is used routinely in hospitals and clinics for diagnosing a variety of diseases. It is the tool of choice in obstetrics and cardiology because it is safe and capable of providing images in real time. New applications in small-animal imaging and cellular imaging are being explored
