Abstract
Ultrashort echo time (UTE) imaging is commonly used in medical MRI to image ‘solid’ types of tissue; to date it has not been widely used in engineering or materials science, in part due to the relatively long imaging times required. Here we show how the acquisition time for UTE can be reduced to enable a preliminary study of a fluidized bed, a type of reactor commonly used throughout industry containing short T2∗ material and requiring fast imaging. We demonstrate UTE imaging of particles with a T2∗ of only 185μs, and an image acquisition time of only 25ms. The images are obtained using compressed sensing (CS) and by exploiting the Hermitian symmetry of k-space, to increase the resolution beyond that predicted by the Nyquist theorem. The technique is demonstrated by obtaining one- and two-dimensional images of bubbles rising in a model fluidized bed reactor.
Highlights
Magnetic resonance (MR) is a powerful tool for studying optically opaque systems in medicine as well as engineering and materials science
A rapid imaging technique has been developed based on the ultrashort echo time (UTE) pulse sequence originally developed for use in medical MRI
Spin echo images of a static sample are used as a reference to show that UTE can be used to acquire accurate images of a sample of Nicotiana seeds with a T2⁄ of 185 ls
Summary
Magnetic resonance (MR) is a powerful tool for studying optically opaque systems in medicine as well as engineering and materials science. FLASH uses a small tip angle and is heavily T2⁄ weighted which limits the signal to noise ratio (SNR), and resolution, when imaging samples with very short T2⁄ times These studies were able to show bubbles, the low spatial resolution, both in-plane and through plane, limited the conclusions that could be drawn. Whilst three-dimensional images would provide further information about bubble motion in a sample, at present the acquisition time is too long to acquire 3D images of bubbles rising in a fluidized bed. In this paper we will describe a volume selective onedimensional technique derived from UTE and ZTE, which enables the acquisition of one-dimensional images to characterize a dynamic system, for calculating the average bubble rise velocity in a fluidized bed. Preliminary experiments will show the potential for using UTE to image a fluidized bed, which is a heterogeneous, dynamic system, at higher spatial resolution than previously attainable without decreasing the temporal resolution
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