Ultrashort echo time (UTE) imaging using gradient pre-equalization and compressed sensing

Abstract

Ultrashort echo time (UTE) imaging is a well-known technique used in medical MRI, however, the implementation of the sequence remains non-trivial. This paper introduces UTE for non-medical applications and outlines a method for the implementation of UTE to enable accurate slice selection and short acquisition times. Slice selection in UTE requires fast, accurate switching of the gradient and r.f. pulses. Here a gradient "pre-equalization" technique is used to optimize the gradient switching and achieve an effective echo time of 10μs. In order to minimize the echo time, k-space is sampled radially. A compressed sensing approach is used to minimize the total acquisition time. Using the corrections for slice selection and acquisition along with novel image reconstruction techniques, UTE is shown to be a viable method to study samples of cork and rubber with a shorter signal lifetime than can typically be measured. Further, the compressed sensing image reconstruction algorithm is shown to provide accurate images of the samples with as little as 12.5% of the full k-space data set, potentially permitting real time imaging of short T2(*) materials.

Accuracy of the Magnetic Field Gradient Waveform Monitor Technique and Consequent Accuracy of Pre‐Equalized Gradient Waveform

“…The impulse response and/or GIRF determined employing these methods would replace the impulse response obtained employing the method summarized in the following subsection and in . The technique employed to calculate the pre‐equalized gradient waveform employing this impulse response or GIRF obtained from a different method would remain unchanged as reported in . Other methods may be employed to measure the resulting waveform accuracy, but this article remains focused quite naturally on MFGM results.…”

Optimized nonlinear conjugate gradient algorithm for MR imaging reconstruction using compressed sensing

“…Hilary T. etc. used compressed sensing for Ultrashort echo time (UTE) by sampling the k-space data radially to minimize the echo time [19]. However, it is typically limited by MR physics including both physical (slew rate and gradient amplitude, etc.)…”

Study of bubble dynamics in gas-solid fluidized beds using ultrashort echo time (UTE) magnetic resonance imaging (MRI)

“…Our previous publication detailed a method for implementation of UTE with gradient pre-equalization and compressed sensing where a UTE image was acquired in 500 ms [17]. This study shows further developments to traditional UTE imaging enabling sequential images to be acquired in 25 ms or 40 frames per second (fps).…”

“…pulse shape [18]. Full details of our implementation of this sequence are given elsewhere [17]. In this work a 10 μs effective echo time (TE) is used to allow for ring down of the hardware, and a single, complex point in k-space is acquired every microsecond.…”

“…UTE is well established in medical MRI for imaging short signal lifetime tissues such as cartilage, cortical bone, and teeth [14][15][16]. We have recently demonstrated the applicability of UTE in materials science and engineering by acquiring an image of cork which has a T2 * of 120 μs [17]. UTE is advantageous for short T2 * materials because the signal is acquired as a free induction decay (FID), rather than an echo.…”