1.
Dostopno za:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
2.
Opportunities in Interventional and Diagnostic Imaging by Using High-Performance Low-Field-Strength MRI
Campbell-Washburn, Adrienne E; Ramasawmy, Rajiv; Restivo, Matthew C ...
Radiology,
11/2019, Letnik:
293, Številka:
2
Journal Article
Background Commercial low-field-strength MRI systems are generally not equipped with state-of-the-art MRI hardware, and are not suitable for demanding imaging techniques. An MRI system was developed ...
that combines low field strength (0.55 T) with high-performance imaging technology. Purpose To evaluate applications of a high-performance low-field-strength MRI system, specifically MRI-guided cardiovascular catheterizations with metallic devices, diagnostic imaging in high-susceptibility regions, and efficient image acquisition strategies. Materials and Methods A commercial 1.5-T MRI system was modified to operate at 0.55 T while maintaining high-performance hardware, shielded gradients (45 mT/m; 200 T/m/sec), and advanced imaging methods. MRI was performed between January 2018 and April 2019. T1, T2, and T2* were measured at 0.55 T; relaxivity of exogenous contrast agents was measured; and clinical applications advantageous at low field were evaluated. Results There were 83 0.55-T MRI examinations performed in study participants (45 women; mean age, 34 years ± 13). On average, T1 was 32% shorter, T2 was 26% longer, and T2* was 40% longer at 0.55 T compared with 1.5 T. Nine metallic interventional devices were found to be intrinsically safe at 0.55 T (<1°C heating) and MRI-guided right heart catheterization was performed in seven study participants with commercial metallic guidewires. Compared with 1.5 T, reduced image distortion was shown in lungs, upper airway, cranial sinuses, and intestines because of improved field homogeneity. Oxygen inhalation generated lung signal enhancement of 19% ± 11 (standard deviation) at 0.55 T compared with 7.6% ± 6.3 at 1.5 T (
= .02; five participants) because of the increased T1 relaxivity of oxygen (4.7e-4 mmHg
sec
). Efficient spiral image acquisitions were amenable to low field strength and generated increased signal-to-noise ratio compared with Cartesian acquisitions (
< .02). Representative imaging of the brain, spine, abdomen, and heart generated good image quality with this system. Conclusion This initial study suggests that high-performance low-field-strength MRI offers advantages for MRI-guided catheterizations with metal devices, MRI in high-susceptibility regions, and efficient imaging. © RSNA, 2019
See also the editorial by Grist in this issue.
več
Dostopno za:
NUK, UL, UM, UPUK
3.
The Human Connectome Project and beyond: Initial applications of 300mT/m gradients
McNab, Jennifer A.; Edlow, Brian L.; Witzel, Thomas ...
NeuroImage (Orlando, Fla.),
10/2013, Letnik:
80
Journal Article
The engineering of a 3T human MRI scanner equipped with 300mT/m gradients – the strongest gradients ever built for an in vivo human MRI scanner – was a major component of the NIH Blueprint Human ...
Connectome Project (HCP). This effort was motivated by the HCP's goal of mapping, as completely as possible, the macroscopic structural connections of the in vivo healthy, adult human brain using diffusion tractography. Yet, the 300mT/m gradient system is well suited to many additional types of diffusion measurements. Here, we present three initial applications of the 300mT/m gradients that fall outside the immediate scope of the HCP. These include: 1) diffusion tractography to study the anatomy of consciousness and the mechanisms of brain recovery following traumatic coma; 2) q-space measurements of axon diameter distributions in the in vivo human brain and 3) postmortem diffusion tractography as an adjunct to standard histopathological analysis. We show that the improved sensitivity and diffusion-resolution provided by the gradients are rapidly enabling human applications of techniques that were previously possible only for in vitro and animal models on small-bore scanners, thereby creating novel opportunities to map the microstructure of the human brain in health and disease.
•Diffusion spectrum imaging to study traumatic coma recovery•In vivo human axon diameter measurements using 300mT/m gradients•High-resolution (0.6mm isotropic) diffusion imaging in whole, fixed human brain
več
Dostopno za:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
4.
Reducing sensitivity losses due to respiration and motion in accelerated echo planar imaging by reordering the autocalibration data acquisition
Polimeni, Jonathan R.; Bhat, Himanshu; Witzel, Thomas ...
Magnetic resonance in medicine,
February 2016, Letnik:
75, Številka:
2
Journal Article
Purpose
To reduce the sensitivity of echo‐planar imaging (EPI) auto‐calibration signal (ACS) data to patient respiration and motion to improve the image quality and temporal signal‐to‐noise ratio ...
(tSNR) of accelerated EPI time‐series data.
Methods
ACS data for accelerated EPI are generally acquired using segmented, multishot EPI to distortion‐match the ACS and time‐series data. The ACS data are, therefore, typically collected over multiple TR periods, leading to increased vulnerability to motion and dynamic B0 changes. The fast low‐angle excitation echo‐planar technique (FLEET) is adopted to reorder the ACS segments so that segments within any given slice are acquired consecutively in time, thereby acquiring ACS data for each slice as rapidly as possible.
Results
Subject breathhold and motion phantom experiments demonstrate that artifacts in the ACS data reduce tSNR and produce tSNR discontinuities across slices in the accelerated EPI time‐series data. Accelerated EPI data reconstructed using FLEET‐ACS exhibit improved tSNR and increased tSNR continuity across slices. Additionally, image quality is improved dramatically when bulk motion occurs during the ACS acquisition.
Conclusion
FLEET‐ACS provides reduced respiration and motion sensitivity in accelerated EPI, which yields higher tSNR and image quality. Benefits are demonstrated in both conventional‐resolution 3T and high‐resolution 7T EPI time‐series data. Magn Reson Med 75:665–679, 2016. © 2015 Wiley Periodicals, Inc.
več
Dostopno za:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
5.
Wave‐CAIPI for highly accelerated MP‐RAGE imaging
Polak, Daniel; Setsompop, Kawin; Cauley, Stephen F. ...
Magnetic resonance in medicine,
January 2018, Letnik:
79, Številka:
1
Journal Article
Purpose
To introduce a highly accelerated T1‐weighted magnetization‐prepared rapid gradient echo (MP‐RAGE) acquisition that uses wave‐controlled aliasing in parallel imaging (wave‐CAIPI) encoding to ...
retain high image quality.
Methods
Significant acceleration of the MP‐RAGE sequence is demonstrated using the wave‐CAIPI technique. Here, sinusoidal waveforms are used to spread aliasing in all three directions to improve the g‐factor. Combined with a rapid (2 s) coil sensitivity acquisition and data‐driven trajectory calibration, we propose an online integrated acquisition‐reconstruction pipeline for highly efficient MP‐RAGE imaging.
Results
The 9‐fold accelerated MP‐RAGE acquisition can be performed in 71 s, with a maximum and average g‐factor of gmax = 1.27 and gavg = 1.06 at 3T. Compared with the state‐of‐the‐art method controlled aliasing in parallel imaging results in higher acceleration (2D‐CAIPIRINHA), this is a factor of 4.6/1.4 improvement in gmax/gavg. In addition, we demonstrate a 57 s acquisition at 7T with 12‐fold acceleration. This acquisition has a g‐factor performance of gmax = 1.15 and gavg = 1.04.
Conclusion
Wave encoding overcomes the g‐factor noise amplification penalty and allows for an order of magnitude acceleration of MP‐RAGE acquisitions. Magn Reson Med 79:401–406, 2018. © 2017 International Society for Magnetic Resonance in Medicine.
več
Dostopno za:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
6.
Interslice leakage artifact reduction technique for simultaneous multislice acquisitions
Cauley, Stephen F.; Polimeni, Jonathan R.; Bhat, Himanshu ...
Magnetic resonance in medicine,
July 2014, 2014-Jul, 20140701, Letnik:
72, Številka:
1
Journal Article
Purpose
Controlled aliasing techniques for simultaneously acquired echo‐planar imaging slices have been shown to significantly increase the temporal efficiency for both diffusion‐weighted imaging and ...
functional magnetic resonance imaging studies. The “slice‐GRAPPA” (SG) method has been widely used to reconstruct such data. We investigate robust optimization techniques for SG to ensure image reconstruction accuracy through a reduction of leakage artifacts.
Methods
Split SG is proposed as an alternative kernel optimization method. The performance of Split SG is compared to standard SG using data collected on a spherical phantom and in vivo on two subjects at 3 T. Slice‐accelerated and nonaccelerated data were collected for a spin‐echo diffusion‐weighted acquisition. Signal leakage metrics and time‐series SNR were used to quantify the performance of the kernel fitting approaches.
Results
The Split SG optimization strategy significantly reduces leakage artifacts for both phantom and in vivo acquisitions. In addition, a significant boost in time‐series SNR for in vivo diffusion‐weighted acquisitions with in‐plane
2× and slice
3× accelerations was observed with the Split SG approach.
Conclusion
By minimizing the influence of leakage artifacts during the training of SG kernels, we have significantly improved reconstruction accuracy. Our robust kernel fitting strategy should enable better reconstruction accuracy and higher slice‐acceleration across many applications. Magn Reson Med 72:93–102, 2014. © 2013 Wiley Periodicals, Inc.
več
Dostopno za:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
7.
Quantitative oxygenation venography from MRI phase
Fan, Audrey P.; Bilgic, Berkin; Gagnon, Louis ...
Magnetic resonance in medicine,
July 2014, Letnik:
72, Številka:
1
Journal Article
Purpose
To demonstrate acquisition and processing methods for quantitative oxygenation venograms that map in vivo oxygen saturation (SvO2) along cerebral venous vasculature.
Methods
Regularized ...
quantitative susceptibility mapping (QSM) is used to reconstruct susceptibility values and estimate SvO2 in veins. QSM with ℓ1 and ℓ2 regularization are compared in numerical simulations of vessel structures with known magnetic susceptibility. Dual‐echo, flow‐compensated phase images are collected in three healthy volunteers to create QSM images. Bright veins in the susceptibility maps are vectorized and used to form a three‐dimensional vascular mesh, or venogram, along which to display SvO2 values from QSM.
Results
Quantitative oxygenation venograms that map SvO2 along brain vessels of arbitrary orientation and geometry are shown in vivo. SvO2 values in major cerebral veins lie within the normal physiological range reported by 15O positron emission tomography. SvO2 from QSM is consistent with previous MR susceptometry methods for vessel segments oriented parallel to the main magnetic field. In vessel simulations, ℓ1 regularization results in less than 10% SvO2 absolute error across all vessel tilt orientations and provides more accurate SvO2 estimation than ℓ2 regularization.
Conclusion
The proposed analysis of susceptibility images enables reliable mapping of quantitative SvO2 along venograms and may facilitate clinical use of venous oxygenation imaging. Magn Reson Med 72:149–159, 2014. © 2013 Wiley Periodicals, Inc.
več
Dostopno za:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
8.
Dostopno za:
DOBA, GEOZS, IJS, IMTLJ, IZUM, KILJ, KISLJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, UILJ, UKNU, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
9.
Diffusion MRI in the heart
Mekkaoui, Choukri; Reese, Timothy G.; Jackowski, Marcel P. ...
NMR in biomedicine,
March 2017, Letnik:
30, Številka:
3
Journal Article
Diffusion MRI provides unique information on the structure, organization, and integrity of the myocardium without the need for exogenous contrast agents. Diffusion MRI in the heart, however, has ...
proven technically challenging because of the intrinsic non‐rigid deformation during the cardiac cycle, displacement of the myocardium due to respiratory motion, signal inhomogeneity within the thorax, and short transverse relaxation times. Recently developed accelerated diffusion‐weighted MR acquisition sequences combined with advanced post‐processing techniques have improved the accuracy and efficiency of diffusion MRI in the myocardium. In this review, we describe the solutions and approaches that have been developed to enable diffusion MRI of the heart in vivo, including a dual‐gated stimulated echo approach, a velocity‐ (M1) or an acceleration‐ (M2) compensated pulsed gradient spin echo approach, and the use of principal component analysis filtering. The structure of the myocardium and the application of these techniques in ischemic heart disease are also briefly reviewed. The advent of clinical MR systems with stronger gradients will likely facilitate the translation of cardiac diffusion MRI into clinical use. The addition of diffusion MRI to the well‐established set of cardiovascular imaging techniques should lead to new and complementary approaches for the diagnosis and evaluation of patients with heart disease. © 2015 The Authors. NMR in Biomedicine published by John Wiley & Sons Ltd.
Diffusion MRI provides unique information on the integrity of the myocardium without the need for exogenous contrast agents. However, diffusion MRI in the heart has proven technically challenging. In this review, we describe approaches that have been developed to overcome these challenges, and briefly examine the application of diffusion MRI in ischemic heart disease. The use of diffusion MRI as a clinical tool may lead to new and complementary approaches to diagnose and treat patients with heart disease.
več
Dostopno za:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
10.
Autocalibrated wave‐CAIPI reconstruction; Joint optimization of k‐space trajectory and parallel imaging reconstruction
Cauley, Stephen F.; Setsompop, Kawin; Bilgic, Berkin ...
Magnetic resonance in medicine,
September 2017, 2017-09-00, 20170901, Letnik:
78, Številka:
3
Journal Article
Purpose
Fast MRI acquisitions often rely on efficient traversal of k‐space and hardware limitations, or other physical effects can cause the k‐space trajectory to deviate from a theoretical path in a ...
manner dependent on the image prescription and protocol parameters. Additional measurements or generalized calibrations are typically needed to characterize the discrepancies. We propose an autocalibrated technique to determine these discrepancies.
Methods
A joint optimization is used to estimate the trajectory simultaneously with the parallel imaging reconstruction, without the need for additional measurements. Model reduction is introduced to make this optimization computationally efficient, and to ensure final image quality.
Results
We demonstrate our approach for the wave‐CAIPI fast acquisition method that uses a corkscrew k‐space path to efficiently encode k‐space and spread the voxel aliasing. Model reduction allows for the 3D trajectory to be automatically calculated in fewer than 30 s on standard vendor hardware. The method achieves equivalent accuracy to full‐gradient calibration scans.
Conclusions
The proposed method allows for high‐quality wave‐CAIPI reconstruction across wide ranges of protocol parameters, such as field of view (FOV) location/orientation, bandwidth, echo time (TE), resolution, and sinusoidal amplitude/frequency. Our framework should allow for the autocalibration of gradient trajectories from many other fast MRI techniques in clinically relevant time. Magn Reson Med 78:1093–1099, 2017. © 2016 International Society for Magnetic Resonance in Medicine
več
Dostopno za:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
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