Rapid dual‐echo ramped hybrid encoding <scp>MR</scp>‐based attenuation correction (d<scp>RHE‐MRAC</scp>) for <scp>PET/MR</scp>

Jang, Hyungseok; Liu, Fang; Bradshaw, Tyler; McMillan, A.

doi:10.1002/mrm.26953

Cited by 23 publications

(33 citation statements)

References 45 publications

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“…This is crucial in sodium MRI, given its inherently low image quality. Recently, RHE has been applied in whole body MR/PET where volume‐selective SLR pulses were used to mitigate excitation artifacts resulting from outside the field of view . In the current study, we did not observe any unwanted excitation artifacts.…”

Section: Discussionsupporting

confidence: 55%

“…Recently, RHE has been applied in whole body MR/PET where volume-selective SLR pulses were used to mitigate excitation artifacts resulting from outside the field of view. 36 In the current study, we did not observe any unwanted excitation artifacts. Because of the unrealized efficiency, non-selective hard pulses are commonly used in sodium MRI acquisitions.…”

Section: Discussionsupporting

confidence: 47%

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Zero‐gradient‐excitation ramped hybrid encoding (zG_RF‐RHE) sodium MRI

Blunck

Moffat

Kolbe

et al. 2018

Magnetic Resonance in Med

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Purpose Fast bi‐exponential transverse signal decay compounds sodium image quality. This work aims at enhancing image characteristics using a special case of ramped hybrid encoding (RHE). Zero‐gradient‐excitation (zGRF)‐RHE provides (1) gradient‐free excitation for high flip angle, artifact‐free excitation profiles and (2) gradient ramping during dead‐time for the optimization of encoding time (tenc) to reduce T2* signal decay influence during acquisition. Methods Radial zGRF‐RHE and standard radial UTE were investigated over a range of receiver bandwidths in simulations, phantom and in vivo brain experiments. Central k‐space in zGRF‐RHE was acquired through single point measurements at the minimum achievable TE. T2* blurring artifacts and image SNR and CNR were assessed. Results zGRF ‐RHE enabled 90° flip angle artifact‐free excitation, whereas gradient pre‐ramping provided greater tenc efficiency for any readout bandwidths. Experiments confirmed simulation results, revealing sharper edge characteristics particularly at short readout durations (TRO). Significant SNR improvements of up to 4.8% were observed for longer TRO. Conclusion zGRF ‐RHE allows for artifact‐free high flip angle excitation with time‐efficient encoding improving on image characteristics. This hybrid encoding concept with gradient pre‐ramping is trajectory independent and can be introduced in any center‐out UTE trajectory design.

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Section: Discussionsupporting

confidence: 55%

Section: Discussionsupporting

confidence: 47%

Zero‐gradient‐excitation ramped hybrid encoding (zG_RF‐RHE) sodium MRI

Blunck

Moffat

Kolbe

et al. 2018

Magnetic Resonance in Med

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“…Therefore, accelerated imaging is crucial for CSPI to be clinically useful. 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 .…”

Section: Discussionmentioning

confidence: 99%

“…Note that in (B) residual bone marrow distorted the susceptibility, as indicated by the yellow arrow Roux pulse with minimum phase. 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.…”

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

Jang

Carl³

et al. 2018

Magnetic Resonance in Med

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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.

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“…Total variation 58 was used for and the optimization problem was solved using alternating minimization. The regularization parameter was chosen to be 10 -3 of the maximum intensity of the original data, based on the data discrepancy principle 59 61 and an air mask was generated via thresholding with a value determined by evaluating the signal intensity distribution of air 14,32 . For the in vivo studies, an additional air support mask was generated by evaluating the frontal sinus region separately for improved delineation of air, similar to previous study 37 .…”

Section: Image Reconstruction and Lac Map Generationmentioning

confidence: 99%

MR‐based PET attenuation correction using a combined ultrashort echo time/multi‐echo Dixon acquisition

et al. 2020

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†These authors contributed equally to this work. 2 Abstract Purpose: To develop a magnetic resonance (MR)-based method for estimation of continuous linear attenuation coefficients (LAC) in positron emission tomography (PET) using a physical compartmental model and ultrashort echo time (UTE)/multi-echo Dixon (mUTE) acquisitions. Methods:We propose a three-dimensional (3D) mUTE sequence to acquire signals from water, fat, and short-T2 components (e.g., bones) simultaneously in a single acquisition. The proposed mUTE sequence integrates 3D UTE with multi-echo Dixon acquisitions and uses sparse radial trajectories to accelerate imaging speed. Errors in the radial k-space trajectories are measured using a special k-space trajectory mapping sequence and corrected for image reconstruction. A physical compartmental model is used to fit the measured multi-echo MR signals to obtain fractions of water, fat and bone components for each voxel, which are then used to estimate the continuous LAC map for PET attenuation correction. Results:The performance of the proposed method was evaluated via phantom and in vivo human studies, using LACs from Computed Tomography (CT) as reference. Compared to Dixon-and atlas-based MRAC methods, the proposed method yielded PET images with higher correlation and similarity in relation to the reference. The relative absolute errors of PET activity values reconstructed by the proposed method were below 5% in all of the four lobes (frontal, temporal, parietal, occipital), cerebellum, whole white matter and gray matter regions across all subjects (n=6). Conclusions:The proposed mUTE method can generate subject-specific, continuous LAC map for PET attenuation correction in PET/MR.

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

Abstract: Dual-echo ramped hybrid encoding enables rapid and robust imaging for MRAC with a very rapid acquisition. Magn Reson Med 79:2912-2922, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Cited by 23 publications

References 45 publications

Zero‐gradient‐excitation ramped hybrid encoding (zG_RF‐RHE) sodium MRI

Zero‐gradient‐excitation ramped hybrid encoding (zG_RF‐RHE) sodium MRI

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

MR‐based PET attenuation correction using a combined ultrashort echo time/multi‐echo Dixon acquisition

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

Abstract: Dual-echo ramped hybrid encoding enables rapid and robust imaging for MRAC with a very rapid acquisition. Magn Reson Med 79:2912-2922, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Cited by 23 publications

References 45 publications

Zero‐gradient‐excitation ramped hybrid encoding (zGRF‐RHE) sodium MRI

Zero‐gradient‐excitation ramped hybrid encoding (zGRF‐RHE) sodium MRI

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

MR‐based PET attenuation correction using a combined ultrashort echo time/multi‐echo Dixon acquisition

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Product

Resources

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Zero‐gradient‐excitation ramped hybrid encoding (zG_RF‐RHE) sodium MRI

Zero‐gradient‐excitation ramped hybrid encoding (zG_RF‐RHE) sodium MRI