Fig. 4

Visual comparison of sensitivity and spatial resolution between magnetic particle imaging (MPI) and magnetic resonance imaging (MRI). The circles represent the sensitivity (vertical axis) and spatial resolution (horizontal axis), which were measured by the same MPI (blue) or the same MRI (orange). Here, the sensitivity is defined as the logarithm of the number of detectable cells. The sensitivity of MPI is within 10,000 cells [20, 30, 33, 66, 69, 70] with the highest sensitivity approximating 69 mesenchymal stem cells [68]. The sensitivities of MPI are higher than those of MRI. However, MPI slightly falls short of MRI in spatial resolution [30, 60, 68]. The metrics of MPI and MRI were measured at the small animal aperture