Biopsy needles and devices: assessment of ferromagnetism and artifacts during exposure to a 1.5-T MR system.

Forty-eight biopsy devices (needles, stylets, guide wires, biopsy guns, etc) were evaluated for ferromagnetism (n = 48) and artifacts (n = 43) in a 1.5-T magnetic resonance (MR) system, with previously described techniques. Forty-five of the 48 devices were found to be ferromagnetic. Artifacts varied, depending on the type and size of the component material(s) of the device. Most of the commercially available biopsy devices are not useful for MR imaging-guided biopsy procedures because of the presence of ferromagnetism and associated artifacts.

Ex vivo evaluation of ferromagnetism, heating, and artifacts produced by heart valve prostheses exposed to a 1.5-T MR system.

Ex vivo testing techniques were used to determine the ferromagnetic qualities of, presence of heating in, and artifacts produced by 13 different heart valve prostheses exposed to a 1.5-T (64-MHz) magnetic resonance (MR) system. None of the heart valve prostheses showed a measurable deflection in the 1.5-T static magnetic field. Only minimal artifacts were produced during MR imaging with a fast spoiled GRASS (gradient-recalled acquisition in the steady state) pulse sequence. The largest temperature changes measured during a "worst case" MR imaging sequence (estimated average specific absorption rate, 2.5 W/kg; estimated spatial peak specific absorption rate, 7.6 W/kg) were +0.2 degree C with the implant imaged "in air" and +0.3 degrees C with the implant imaged in normal saline. Therefore, MR procedures performed with a 1.5-T (64-MHz) MR system may be performed safely in patients with any of the 13 different heart valve prostheses evaluated in this study.

Measurement of acoustic noise during MR imaging: evaluation of six "worst-case" pulse sequences.

PURPOSE: To assess acoustic noise levels for ambient noise and magnetic resonance (MR) imaging at 1.5 T during use of six "worst-case" pulse sequences. MATERIALS AND METHODS: Acoustic noise measurements were obtained at the entrance, center, and exit of the magnet bore of the MR system by means of a specially modified device that is unaffected by electromagnetic radiation. RESULTS: The highest ambient noise level was 73 dB at both the entrance and exit of the magnet bore (A-weighted scale). The highest noise levels during MR imaging occurred during use of a gradient-echo (GRE) pulse sequence and was 102 dB at the entrance and exit of the magnet bore and 103 dB at the center (A-weighted scale). CONCLUSIONS: MR imaging performed with the worst-case pulse sequences did not produce noise levels that exceeded federal guidelines. Noise levels were, however, high enough to impair oral communication and annoy patients. Thus, techniques to attenuate acoustic noise and allow improved operator-patient communication should be used during MR imaging, especially during use of GRE pulse sequences.

Ex vivo evaluation of ferromagnetism and artifacts of cardiac occluders exposed to a 1.5-T MR system.

Magnetic resonance (MR) procedures are contraindicated for patients with certain ferromagnetic biomedical implants, primarily owing to the risk of movement or dislodgment of the implants by the static magnetic field. An additional concern is the amount of artifact that the implant produces, which can affect image quality and interpretation of the examination. Therefore, an ex vivo assessment of ferromagnetism and artifact was conducted for 12 different occluders used to treat patients with patent ductus arteriosus, atrial septal defects, and ventricular septal defects, in a 1.5-T MR system. Seven of the occluders, made of 304 stainless steel, were ferromagnetic and displayed deflection forces of 248-299 dynes. Five of the implants, made of MP35n, were nonferromagnetic. Artifacts were variable and depended primarily on the type and amount of metal used to construct the implant. The authors conclude that patients with ferromagnetic cardiac occluders may undergo MR procedures approximately 6 weeks after placement of these devices, to allow tissue growth to provide additional retentive force. After this time, it is highly unlikely that the magnetic fields associated with a 1.5-T MR system are capable of moving or dislodging any of these cardiac occluders.