Chandarana H, Godoy MCB, Vlahos I, et al. MPI cell tracking: what can we learn from MRI? Imaging 2011 7965: 79650Z–79650Z-4. Barrett T, Brechbiel M, Bernardo M, Choyke PL. Coronary computed tomography angiography with a consistent dose below 1 mSv using prospectively electrocardiogram-triggered high-pitch spiral acquisition. Where S max=20 T/s is the maximum slew rate as described above and μ 0 G ab is the partial derivative of the magnetic field in the a direction with respect to b. As we determine below, the slew rate causes the slow shift fields to become binding constraints on imaging time in addition to the drive field. The ICNIRP define a maximal magnetic field slew rate of 20 T/s for pulse durations longer than a couple of milliseconds. Slow shift fields also limit the acquisition time for an MPI system owing to magnetostimulation limits. In a system with slow shift magnets, the space covered solely by the drive field (with the slow shift field disabled) is termed a “partial FOV” (pFOV) or “imaging station” with multistation reconstruction.
These slow shift magnets slowly raster the mean position of the FFP or FFL (see Figure 8), expanding the FOV beyond what is covered by the drive field alone. To address the limited FOV coverage of the drive subsystem, slow shift magnets or focus field magnets are used. With a G=10 T/m gradient strength, which will produce 1 mm native (i.e., no deconvolution) resolution with Resovist, the FOV can be calculated as FOV=2 B th/ G=1.4 mm. Between 5 and 50 kHz, the magnetostimulation threshold in the human torso is extrapolated as approximately B th=7 mT. The drive field in MPI is typically a ~25 kHz frequency sinusoidal field. For human-sized MPI scanners, magnetostimulation will restrict the amplitude of both the excitation (drive) field and the slow shift (focus) fields. Owing to the frequency range in which MPI operates, magnetostimulation (and not SAR) is the dominant limitation for scanning speed in MPI. We can calculate the optimum imaging time based on specific absorption rate (SAR) and magnetostimulation (d B/d t) limits, the two primary safety concerns when imaging human subjects using time-varying magnetic fields. Appendix 2 MPI acquisition time calculation
Depends on the shape of the filter G( k).
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