Accelerated 4D quantitative single point EPR imaging using model‐based reconstruction

Liu

Bradshaw

et al. 2017

Self Cite

{normalT}_{2}^{*}

of bone by additional SPI oversampling to secure a wider range of TEs, which could be used to assign continuous HU values based on the

{normalT}_{2}^{*}

of bone or contrast of PDW UTE image . In this study, we have shown the efficacy of using multiple UTE images to improve air and bone detection.…”

Section: Discussionmentioning

confidence: 86%

Rapid dual‐echo ramped hybrid encoding MR‐based attenuation correction (dRHE‐MRAC) for PET/MR

Liu

Bradshaw

et al. 2017

Self Cite

“…Restricting the effective FOV would be a simple strategy to accelerate CSPI, for instance, by using coils with small volume and sensitivity (e.g., surface coils) or applying slab selection, for example, by using a half pulse or Shinnar–Le Roux pulse with minimum phase . Furthermore, a 3D non‐Cartesian sampling pattern with variable density can be used to produce noise‐like aliasing patterns that can be removed by postprocessing, such as denoising or compressed sensing techniques . With any of the above strategies for accelerating CSPI, the key advantageous feature of CSPI, true phase imaging, will be still preserved.…”

Section: Discussionmentioning

confidence: 99%

“…31,32 Furthermore, a 3D non-Cartesian sampling pattern with variable density can be used to produce noise-like aliasing patterns that can be removed by postprocessing, such as denoising or compressed sensing techniques. 33,34 With any of the above strategies for accelerating CSPI, the key advantageous feature of CSPI, true phase imaging, will be still preserved. In future studies, we will explore the aforementioned strategies more rigorously to evaluate CSPI in clinical applications, including patients with metallic implants or hemophilia.…”

Section: F I G U R E 3 Reconstructed Images For Iron Phantom Qsm (A)mentioning

confidence: 99%

True phase quantitative susceptibility mapping using continuous single‐point imaging: a feasibility study

Carl³

et al. 2018

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Purpose In this study, we explore the feasibility of a new imaging scheme for quantitative susceptibility mapping (QSM): continuous single‐point imaging (CSPI), which uses a pure phase encoding strategy to achieve true phase imaging and improve QSM accuracy. Methods The proposed CSPI is a modification of conventional SPI to allow acquisition of multiple echoes in a single scan. Immediately following a phase encoding gradient, the free induction decay is continuously sampled with extremely high temporal resolution to obtain k‐space data at a fixed spatial frequency (i.e., at a fixed k‐space coordinate). By having near‐0 readout duration, CSPI results in a true snapshot of the transverse magnetization at each TE. Additionally, parallel imaging with autocalibration is utilized to reduce scan time, and an optional temporal averaging strategy is presented to improve signal‐to‐noise ratio for objects with low proton density or short T2* decay. The reconstructed CSPI images were input to a QSM framework based on morphology enabled dipole inversion. Result In an experiment performed using iron phantoms, susceptibility estimated using CSPI showed high linearity (R2 = 0.9948) with iron concentration. Additionally, reconstructed CSPI phase images showed much reduced ringing artifact compared with phase images obtained using a frequency encoding strategy. In an ex vivo experiment performed using human tibia samples, estimated susceptibilities ranged from –1.6 to –2.1 ppm, in agreement with values reported in the literature (ranging from –1.2 to –2.2 ppm). Conclusion We have demonstrated the feasibility of using CSPI to obtain true phase images for QSM.

“…Moreover, hybrid encoding schemes with an oversampled SPI encoded region may allow reconstruction of images at multiple TEs in early encoding times, which can be used to estimate short T 2 * parameters with a single experiment (e.g., using k‐space extrapolation methods as recently proposed in single point electron paramagnetic resonance imaging) . The additional scanning time imposed by oversampling SPI encoded region can be reduced by using variable density sampling pattern and appropriate reconstruction method such as compressed sensing using k‐space domain data or model‐based reconstruction using k‐space domain data and free induction decay data (parameter domain) simultaneously .…”

Section: Discussionmentioning

confidence: 99%

Ramped hybrid encoding for improved ultrashort echo time imaging

Wiens

McMillan

2015

Self Cite

Purpose We propose a new acquisition to minimize the per-excitation encoding duration and improve the imaging capability for short T2* species. Method In the proposed ramped hybrid encoding (RHE) technique, gradients are applied before the RF pulse as in pointwise encoding time reduction with radial acquisition (PETRA) and Zero TE (ZTE) imaging. However, in RHE, gradients are rapidly ramped after RF excitation to the maximum amplitude to minimize encoding duration. To acquire central k-space data not measured during RF deadtime, RHE utilizes a hybrid encoding scheme similar to PETRA. A new gradient calibration method based on single-point imaging was developed to estimate the k-space trajectory and enable robust and high quality reconstruction. Result RHE enables a shorter per-excitation encoding time and provides the highest spatial resolution among ultrashort T2* imaging methods. In phantom and in vivo experiments, RHE exhibited robust imaging with negligible chemical shift or blurriness caused by T2* decay and unwanted slice selection. Conclusion RHE allows the shortest per-excitation encoding time for ultrashort T2* imaging, which alleviates the impact of fast T2* decay occurring during encoding, and enables improved spatial resolution.