Medical device review at the Food and Drug Administration: lessons from magnetic resonance spectroscopy and biliary lithotripsy.

Medical devices marketed in the United States must satisfy FDA standards of safety and effectiveness. Many observers have criticized the FDA medical device review process as both time consuming and unpredictable. In this note, Lawrence Makow examines the Agency's treatment of two novel medical technologies, magnetic resonance spectroscopy and biliary extracorporeal shockwave lithotripsy.

Magnetic resonance imaging: a brief review of image contrast.

Because MRI is sensitive to tissue properties that are quite different from those exploited by traditional x-ray technologies, it has provided a highly sensitive new way of looking at the human body. This article summarizes the basic mechanisms of contrast in proton MR images, examining the phenomena responsible and the user's ability to manipulate contrast through system parameters. The intended purpose is to impart a qualitative, intuitive understanding of these mechanisms to the newer user.

Influence of magnetic field strength on image contrast.

In magnetic resonance imaging (MRI) S/N increases with magnetic field strength. The curve, however, flattens out at higher fields, resulting in diminishing gains as the field strength is increased.