The schematic diagram of the in vitro experiment. (A) The picture on the left displays a side view of a double-sided cut spherical acrylic container with fabricated wells filled with extracellular media and cell pellets. As depicted in the top-view picture on the right, fourteen wells (matrix = 2 × 7) were created on the acrylic container, allowing each of the seven samples with six different K+ concentrations ([K+] = 0.2–80 mM) and one Ba2+ concentration ([Ba2+] = 10 mM) to be doubled in the same column for improved signal-to-noise ratio (SNR) in MR signal acquisition. (B) The image illustrates the configuration after loading cells into the wells and pelleting them at the bottom of the wells. (C) Representative one-dimensional T2-weighted MR signals with different echo times.

MR parameters and membrane potential (Vm) of SH-SY5Y cells versus extracellular K+ concentrations ([K+]). Changes in (A) T2, (B) PSR, and (C) kmf are displayed with blue bars (n = 15). Membrane potentials are plotted with red triangles (n = 3). The abscissa is in logarithmic scale. Error bars denote standard deviation. Statistical significance of changes in MR parameters is marked with asterisks (ns: p > 0.05, *: p < 0.05, **: p < 0.01, ***: p < 0.001).

Changes in (A) T2, (B) PSR, and (C) kmf of SH-SY5Y cells across experimental conditions: [K+] = 0.2–80 mM (blue cross) and [Ba2+] = 10 mM (green triangle), compared to the control condition (black cross). Data from fifteen experiments (n = 15) are displayed. Linear regression lines for [K+] data (blue solid line) and [Ba2+] data (green solid line) are drawn along with dotted lines representing 95% confidence intervals. Error bars denote standard deviation. Statistical significance of changes in MR parameters with [Ba2+] = 10 mM is marked with asterisks (ns: p > 0.05, *: p < 0.05, **: p < 0.01, ***: p < 0.001).

Changes in (A) T2, (B) PSR, and (C) kmf of Jurkat cells across experimental conditions: [K+] = 0.2–80 mM (blue bar) and [Ba2+] = 10 mM (green bar), compared to the control condition of [K+] = 4.2 mM (n = 5). Error bars denote standard deviation. Statistical significance of changes in MR parameters is marked with asterisks (ns: p > 0.05, *: p < 0.05, **: p < 0.01, ***: p < 0.001).

Experimental setup for in vivo manipulation of membrane potential. (A) A schematic diagram of the rat head post-craniotomy, showing the burr hole centered at 2.5 mm anterior and 2.0 mm lateral to the lambda. (B) Photograph of the rat head with a cylindrical chamber fixed over the burr hole, filled with artificial cerebrospinal fluid. (C) A representative series of T2-weighted MR images for T2 mapping. The chamber was connected to inlet and outlet perfusion tubes. (D) The experimental paradigm of the in vivo rat MR imaging. Four conditions were sequentially applied: control, depolarization, further depolarization, and recovery. Each condition lasted 12 minutes during which T2 mapping were conducted.

Results of the in vivo experiment results in rat models. (A) A representative T2 map from a single rat with an enlarged image depicting the ROI for estimating average T2 in the exposed cortical area, marked by a white rectangle (width = 1.8 mm, depth = 0.6 mm). (B) The changes in T2 values within the ROI is plotted against elapsed time from the initial conditions. [K+] in the perfused artificial cerebrospinal fluid are indicated on the bottom abscissa. Results from the [K+]-modulation experiments are shown with blue bars, and those from the control experiments are shown with green bars. Statistical significance of the T2 changes are marked with asterisks (ns: p > 0.05, *: p < 0.05, **: p < 0.01).