Measuring local RF heating in MRI: Simulating perfusion in a perfusionless phantom

Purpose: To overcome conflicting methods of local RF heating measurements by proposing a simple technique for predicting in vivo temperature rise by using a gel phantom experiment. Materials and Methods: In vivo temperature measurements are difficult to conduct reproducibly; fluid phantoms introduce convection, and gel phantom lacks perfusion. In the proposed method the local temperature rise is measured in a gel phantom at a timepoint that the phantom temperature would be equal to the perfused body steady-state temperature value. The idea comes from the fact that the steady-state temperature rise in a perfused body is smaller than the steady-state temperature increase in a perfusionless phantom. Therefore, when measuring the temperature on a phantom there will be the timepoint that corresponds to the perfusion time constant of the body part. Results: The proposed method was tested with several phantom and in vivo experiments. Instead, an overall average of 30.8% error can be given as the amount of underestimation with the proposed method. This error is within the variability of in vivo experiments (45%). Conclusion: With the aid of this reliable temperature rise prediction the amount of power delivered by the scanner can be controlled, enabling safe MRI examinations of patients with implants. © 2007 Wiley-Liss, Inc

MRI‐Related Heating of Implants and Devices: A Review

During an MRI scan, the radiofrequency field from the scanner's transmit coil, but also the switched gradient fields, induce currents in any conductive object in the bore. This makes any metallic medical implant an additional risk for an MRI patient, because those currents can heat up the surrounding tissues to dangerous levels. This is one of the reasons why implants are, until today, considered a contraindication for MRI; for example, by scanner manufacturers. Due to the increasing prevalence of medical implants in our aging societies, such general exclusion is no longer acceptable. Also, it should be no longer needed, because of a much-improved safety-assessment methodology, in particular in the field of numerical simulations. The present article reviews existing literature on implant-related heating effects in MRI. Concepts for risk assessment and quantification are presented and also some first attempts towards an active safety management and risk mitigation.Level of Evidence 5Technical Efficacy Stage

Thermal-mechanical detector array with integrated diffraction grating

An uncooled thermal detector array with low NETD is designed and fabricated using MEMS bimaterial structures. A diffraction grating is embedded on the pixel membrane for sensing sub-nm mechanical deflections. The first order reflected light was focused on a CCD camera to monitor the entire array. Results show that it is possible to achieve <50mK NETD using a 12 bit CCD camera

A Laser-Machined Stainless-Steel Micro-Scanner for Confocal Microscopy

A stainless-steel based micro-scanner with magnetic actuation is fabricated via laser-cutting technology targeted for confocal microscopy. Laser cutting offers low-cost and high speed fabrication of such scanners. The device is designed to establish a 2D Lissajous pattern. For a coil drive of 180 mA, fabricated scanner is able to deliver 4 degrees of optical scan angle for both slow scan and fast scan axes at 663 Hz and 2211 Hz, respectively. Fabricated mirror is integrated into a confocal microscopy setup and tested with the United States Air Force target accomplishing a 200 μm × 200 μm field of view and sub 10 μm resolution. With further improvement, our scanner will contribute to manufacturing of low-cost and compact scanning microscopy technologies