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Register a new userIn vivo three-dimensional brain and extremity MRI at 50 mT using a permanent magnet Halbach array
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Purpose: To design a low-cost, portable permanent magnet-based MRI system capable of obtaining in vivo MR images within a reasonable scan time. Methods: A discretized Halbach permanent magnet array with a clear bore diameter of 27 cm was designed for operation at 50 mT. Custom built gradient coils, radiofrequency coil, gradient amplifiers and radiofrequency amplifier were integrated and tested on both phantoms and in vivo. Results: Phantom results showed that the gradient non-linearity in the y- and z-directions was less than 5% over a 15 cm field-of-view and did not need correcting. For the x-direction, it was significantly greater, but could be partially corrected in post-processing. Three dimensional In vivo scans of the brain of a healthy volunteer using a turbo-spin echo sequence were acquired at a spatial resolution of 4x4x4 mm in a time of ~2 mins. T1-weighted and T2-weighted scans showed a good degree of tissue contrast. In addition, in vivo scans of the knee of a healthy volunteer were acquired at a spatial resolution of ~3x2x2 mm within a twelve minutes to show the applicability of the system to extremity imaging. Conclusion: This work has shown that it is possible to construct a low-field MRI unit with hardware components costing less than 10000 euros, which is able to acquire human images in vivo within a reasonable data acquisition time. The system has a high degree of portability with magnet weight ~75 kg, gradient and RF amplifiers each 15 kg, gradient coils 10 kg and spectrometer 5 kg.
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Optical pumping of He-3 produces large (hyper) nuclear-spin polarizations independent of the magnetic resonance imaging (MRI) field strength. This allows lung MRI to be performed at reduced fields with many associated benefits, such as lower tissue susceptibility gradients and decreased power absorption rates. Here we present results of 2D imaging as well as accurate 1D gas diffusion mapping of the human lung using He-3 at very low field (3 mT). Furthermore, measurements of transverse relaxation in zero applied gradient are shown to accurately track pulmonary oxygen partial pressure, opening the way for novel imaging sequences.
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