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. He concludes that the outcomes of these cases exemplify the mismatch between clinical utility and FDA approval status that has prompted concerns about lack of predictability. Mr. Makow asserts that this mismatch results from the FDA's implementation of the medical device statute rather than from the statute itself. He proposes an asymmetric standard for evaluating the safety and efficacy of new medical devices. While the safety showing would always require a high burden of proof, the efficacy standard would vary depending on the relationship between the device's safety and efficacy. Under this asymmetric standard, the FDA could better manage its workload and achieve more predictable results without sacrificing the public interest in avoiding injury from unproven medical devices.

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.