Magnetic resonance electrical impedance tomography (MREIT) aims at producing high-resolution cross-sectional conductivity images of an electrically conducting object such as the human body. Following numerous phantom imaging experiments, the most recent study demonstrated successful conductivity image reconstructions of postmortem canine brains using a 3 T MREIT system with 40 mA imaging currents. Here, we report the results of in vivo animal imaging experiments using 5 mA imaging currents. To investigate any change of electrical conductivity due to brain ischemia, canine brains having a regional ischemic model were scanned along with separate scans of canine brains having no disease model. Reconstructed multi-slice conductivity images of in vivo canine brains with a pixel size of 1.4 mm showed a clear contrast between white and gray matter and also between normal and ischemic regions. We found that the conductivity value of an ischemic region decreased by about 10-14%. In a postmortem brain, conductivity values of white and gray matter decreased by about 4-8% compared to those in a live brain. Accumulating more experience of in vivo animal imaging experiments, we plan to move to human experiments. One of the important goals of our future work is the reduction of the imaging current to a level that a human subject can tolerate. The ability to acquire high-resolution conductivity images will find numerous clinical applications not supported by other medical imaging modalities. Potential applications in biology, chemistry and material science are also expected.

Magnetic resonance electrical impedance tomography (MREIT) has the potential to provide conductivity images with high spatial resolution and accuracy. Recent studies using various conductivity phantoms showed that the spatial resolution could be similar to that of conventional MR images as long as enough current is injected. Before we try in vivo animal imaging studies using a small injection current of less than 5 mA, we have performed MREIT conductivity imaging of postmortem canine brains using 40 mA injection currents. The primary goals were to produce high-resolution conductivity images of white and gray matter in situ and to accumulate experimental techniques to undertake in vivo animal imaging studies in the near future. Reconstructed conductivity images of two canine brains with a pixel size of 1.4 x 1.4 mm(2) showed a clear conductivity contrast between gray and white matter. Considering the anisotropic conductivity of white matter, we interpreted reconstructed conductivity images as equivalent isotropic conductivity images. Estimated conductivity ratios of white to gray matter were between 1.13 and 1.20 depending on the choice of a region of interest in reconstructed images. A higher conductivity value of white matter compared with that of gray matter stems from the fact that the reconstructed equivalent isotropic conductivity value of white matter reflects a high conductivity of white matter in the direction parallel to its fibers. We expect that this kind of postmortem animal imaging can provide conductivity information on tissues in situ to be utilized in numerous modeling studies.

The purpose of this study was to describe relevant canine brain structures as seen on T2-weighted images following magnetic resonance (MR) imaging at 7 T and to compare the results with imaging at 1.5 T. Imaging was performed on five healthy laboratory beagle dogs using 1.5 and 7 T clinical scanners. At 1.5 T, spin echo images were acquired, while gradient echo images were acquired at 3 T. Image quality and conspicuity of anatomic structures were evaluated qualitatively by direct comparison of the images obtained from the two different magnetic fields. The signal-to-nose ratio (SNR) and contrast-to-noise ratio (CNR) were calculated and compared between 1.5 and 7 T. The T2-weighted images at 7 T provided good spatial and contrast resolution for the identification of clinically relevant brain anatomy; these images provided better delineation and conspicuity of the brain stem and cerebellar structures, which were difficult to unequivocally identify at 1.5 T. However, frontal and parietal lobe and the trigeminal nerve were difficult to identify at 7 T due to susceptibility artifact. The SNR and CNR of the images at 7 T were significantly increased up to 318% and 715% compared with the 1.5 T images. If some disadvantages of 7 T imaging, such as susceptibility artifacts, technical difficulties, and high cost, can be improved, 7 T clinical MR imaging could provide a good experimental and diagnostic tool for the evaluation of canine brain disorders.

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Magnetic resonance electrical impedance tomography (MREIT) is a new bio-imaging modality providing cross-sectional conductivity images from measurements of internal magnetic flux densities produced by externally injected currents. Recent experimental results of postmortem and in vivo imaging of the canine brain demonstrated its feasibility by showing conductivity images with meaningful contrast among different brain tissues. MREIT image reconstructions involve a series of data processing steps such as k-space data handling, phase unwrapping, image segmentation, meshing, modelling, finite element computation, denoising and so on. To facilitate experimental studies, we need a software tool that automates these data processing steps. In this paper, we summarize such an MREIT software package called CoReHA (conductivity reconstructor using harmonic algorithms). Performing imaging experiments of the postmortem canine abdomen, we demonstrate how CoReHA can be utilized in MREIT. The abdomen with a relatively large field of view and various organs imposes new technical challenges when it is chosen as an imaging domain. Summarizing a few improvements in the experimental MREIT technique, we report our first conductivity images of the postmortem canine abdomen. Illustrating reconstructed conductivity images, we discuss how they discern different organs including the kidney, spleen, stomach and small intestine. We elaborate, as an example, that conductivity images of the kidney show clear contrast among cortex, internal medulla, renal pelvis and urethra. We end this paper with a brief discussion on future work using different animal models.