Description: Purpose Magnetic resonance (MR) guidance for biopsy procedures requires high intrinsic soft-tissue contrast. However, artifacts induced by the metallic needle can reduce its localization and require low-susceptibility needle materials with poorer cutting performance. In a proof of concept, we demonstrate the feasibility of 2D multispectral imaging (2DMSI) for both needle tracking and for needle artifact reduction for more precise needle localization and to enable the usage of needle materials with higher susceptibility. Method We applied 2DMSI for imaging of MR-compatible biopsy needles, conventional stainless-steel needles, and mixed-material needles and compared it to conventional techniques. In addition, we exploited intrinsic off-resonance information for passive needle tracking. Results 2DMSI achieved a stronger reduction of the needle artifact compared to conventional techniques. For the mixed-material needles, the artifact was reduced to a level below that for MR-compatible needles with conventional imaging. The passive tracking also improved the ability to pinpoint the needle. Conclusion 2DMSI is promising for both needle tracking and artifact-reduced imaging of biopsy needles for a more precise needle localization. 2DMSI may be particularly promising for needles inducing large distortions or for targeting of small lesions. In addition, it may enable the use of needle materials with higher susceptibility and potentially better sampling performance. Magn Reson Med, 2017. © 2017 International Society for Magnetic Resonance in Medicine.

Description: Purpose This study investigates metabolite concentrations using metabolite-cycled 1 H free induction decay (FID) magnetic resonance spectroscopic imaging (MRSI) at ultra-high fields. Methods A non-lipid-suppressed and slice-selective ultra-short echo time (TE) 1 H FID MRSI sequence was combined with a low-specific absorption rate (SAR) asymmetric inversion adiabatic pulse to enable non-water-suppressed metabolite mapping using metabolite-cycling at 9.4T. The results were compared to a water-suppressed FID MRSI sequence, and the same study was performed at 3T for comparison. The scan times for performing single-slice metabolite mapping with a nominal voxel size of 0.4 mL were 14 and 17.5 min on 3T and 9.4T, respectively. Results The low-SAR asymmetric inversion adiabatic pulse enabled reliable non-water-suppressed metabolite mapping using metabolite cycling at both 3T and 9.4T. The spectra and maps showed good agreement with the water-suppressed FID MRSI ones at both field strengths. A quantitative analysis of metabolite ratios with respect to N-acetyl aspartate (NAA) was performed. The difference in Cre/NAA was statistically significant, ∼0.1 higher for the non-water-suppressed case than for water suppression (from 0.73 to 0.64 at 3T and from 0.69 to 0.59 at 9.4T). The difference is likely because of chemical exchange effects of the water suppression pulses. Small differences in mI/NAA were also statistically significant, however, are they are less reliable because the metabolite peaks are close to the water peak that may be affected by the water suppression pulses or metabolite-cycling inversion pulse. Conclusion We showed the first implementation of non-water-suppressed metabolite-cycled 1 H FID MRSI at ultra-high fields. An increase in Cre/NAA was seen for the metabolite-cycled case. The same methodology was further applied at 3T and similar results were observed. Magn Reson Med, 2017. © 2017 International Society for Magnetic Resonance in Medicine.

Description: Purpose Neuroimaging research relies on the skills of increasingly multidisciplinary individuals and often requires the installation and use of additional home-built or third-party equipment. The purpose of the present work was the safe, ergonomic, durable, and aesthetically pleasing installation of magnetic field monitoring equipment into a scanner, while keeping the setup compatible with standard operating procedures. Methods An extensive set of steps was required to design a 3D printed solution to install a magnetic field camera into the eight-channel head coil of a 3T MRI scanner. First, the outer surface of the plastic coil housing was recreated into a 3D model, and the installation of the magnetic field sensors around this 3D model was performed in a virtual environment. The 3D printed solution was then assembled and tested for safety, reproducible performance, and image quality. Results The 3D printed solution holds the probes in stable positions and guides the necessary cables in an organized fashion and away from the volunteer. Assembly is easy and the solution is ergonomic, durable, and safe. We did not find excessive heating in the 3D printed parts, nor in the electronics, that they help to incorporate. The material used interferes minimally with transmit field. Conclusion The design met all of the boundary conditions for a durable, safe, cost-effective, attractive, and functional installation. This work will provide the basis for installing the magnetic field sensors into other available head coils, and for designing the experimental setup for projects with varying experimental requirements. Magn Reson Med, 2017. © 2017 International Society for Magnetic Resonance in Medicine.

Description: Purpose To demonstrate simultaneous editing of the two most commonly edited and overlapping signals, γ-aminobutyric acid (GABA), and glutathione (GSH), with Hadamard encoding and reconstruction of MEGA-edited spectroscopy (HERMES) using sLASER localization at 7T. Methods Density matrix simulations of HERMES at 7T were carried out and compared with phantom experiments. Additional phantom experiments were performed to characterize the echo time (TE) -dependent modulation of GABA- and GSH-edited HERMES spectra at TE of 80–160 ms. In vivo experiments were performed in 10 healthy volunteers, comparing HERMES (11 min) to sequentially acquired MEGA-sLASER detection of GABA and GSH (2 × 11 min). Results Simulations of HERMES show GABA- and GSH-edited spectra with negligible levels of crosstalk, and give modest agreement with phantom spectra. The TE series of GABA- and GSH-edited HERMES spectra modulate as a result of T 2 relaxation and coupling evolution, with GABA showing a stronger TE-dependence. In vivo HERMES experiments show well-edited GABA and GSH signals. Measured concentrations are not statistically different between HERMES and MEGA-sLASER for GABA (1. 051 ± 0.254 i.u. and 1.053 ± 0.248 i.u; P  〉 0.985) or GSH (0.300 ± 0.091 i.u. and 0.302 ± 0.093 i.u; P  〉 0.940). Conclusion Simulated, phantom and in vivo measurements of HERMES show excellent segregation of GABA- and GSH-edited signals, and excellent agreement with separately acquired MEGA-sLASER data. HERMES allows two-fold acceleration of editing while maintaining spectral quality compared with sequentially acquired MEGA-sLASER measurements. Magn Reson Med, 2017. © 2017 International Society for Magnetic Resonance in Medicine.

Description: Purpose To investigate the correlation between renal ischemia and 13 C-urea T 2 relaxation rate in an acute kidney injury (AKI) rat model. Methods Six rats subjected to unilateral renal ischemia were investigated. Creatinine clearance, urine output, plasma creatinine as well as blood-urea nitrogen (BUN) values were acquired before and after the procedure. 1 H mapping was acquired using blood oxygenation level dependent (BOLD) MRI and hyperpolarized 13 C-urea T 2 mapping was acquired using a 2D golden-angle radial approach. Kidney perfusion was estimated using noncontrast flow alternating inversion recovery arterial spin labeling. Results All rats showed clinical signs of AKI with increased plasma creatinine and increased BUN. Whole kidney 13 C-urea T 2 significantly decreased 26% ( P  = 0.001) 24 h after reperfusion. A significantly different (3.7 times steeper; P  = 0.008) osmolality gradient was observed in the contralateral kidney ( P  = 0.008; R 2  = 0.86) compared with the postischemic kidney ( P  = 0.0004, R 2 =0.97). Whole kidney signal ( P  = 0.14) and gradient ( P  = 0.26) was similar between the two kidneys. Oxygen availability dependency on 13 C-urea T 2 was investigated by means of the correlation between the BOLD and T 2 signals; a statistically significant difference ( P  = 0.03) was found in the contralateral kidney ( P  = 0.0001; R 2  = 0.95), but not in the postischemic kidney ( P  = 0.31; R 2  = 0.25). Conclusion We demonstrate that hyperpolarized [ 13 C, 15 N 2 ]urea T 2 relaxation correlates with renal oxygen tension ( ) in the healthy contralateral kidney, but not in the postischemic kidney. The whole kidney T 2 relaxation difference between the postischemic and contralateral kidney may originate from altered blood volume in the postischemic kidney. Magn Reson Med, 2017. © 2017 International Society for Magnetic Resonance in Medicine.

Description: Purpose Depressed coronary endothelial function (CEF) is a marker for atherosclerotic disease, an independent predictor of cardiovascular events, and can be quantified non-invasively with ECG-triggered spiral cine MRI combined with isometric handgrip exercise (IHE). However, MRI-CEF measures can be hindered by faulty ECG-triggering, leading to prolonged breath-holds and degraded image quality. Here, a self-gated golden angle spiral method (SG-GA) is proposed to eliminate the need for ECG during cine MRI. Methods SG-GA was tested against retrospectively ECG-gated golden angle spiral MRI (ECG-GA) and gold-standard ECG-triggered spiral cine MRI (ECG-STD) in 10 healthy volunteers. CEF data were obtained from cross-sectional images of the proximal right and left coronary arteries in a 3T scanner. Self-gating heart rates were compared to those from simultaneous ECG-gating. Coronary vessel sharpness and cross-sectional area (CSA) change with IHE were compared among the 3 methods. Results Self-gating precision, accuracy, and correlation-coefficient were 7.7 ± 0.5 ms, 9.1 ± 0.7 ms, and 0.93 ± 0.01, respectively (mean ± standard error). Vessel sharpness by SG-GA was equal or higher than ECG-STD (rest: 63.0 ± 1.7% vs. 61.3 ± 1.3%; exercise: 62.6 ± 1.3% vs. 56.7 ± 1.6%, P  〈 0.05). CSA changes were in agreement among the 3 methods (ECG-STD = 8.7 ± 4.0%, ECG-GA = 9.6 ± 3.1%, SG-GA = 9.1 ± 3.5%, P  = not significant). Conclusion CEF measures can be obtained with the proposed self-gated high-quality cine MRI method even when ECG is faulty or not available. Magn Reson Med, 2017. © 2017 International Society for Magnetic Resonance in Medicine.

Description: Purpose UTE sequences with a minimal nominal TE of 8 µs have shown promise for direct imaging of myelin protons (T 2 , 〈 1 ms). However, there is still debate about the efficiency of 2D slice-selective UTE sequences in exciting myelin protons because the half excitation pulses used in these sequences have a relatively long duration (e.g., 0.3–0.6 ms). Here, we compared UTE and inversion-recovery (IR) UTE sequences used with either hard or half excitation pulses (durations 32 µs or 472 µs, respectively) for imaging myelin in native and deuterated ovine brain at 3T. Methods Freshly frozen ovine brains were dissected into ∼2 mm-thick pure white matter and ∼3 to 8 mm-thick cerebral hemisphere specimens, which were imaged before and/or after different immersion time in deuterium oxide. Results Bicomponent analysis of UTE signals obtained with hard excitation pulses detected an ultrashort T 2 component (STC) fraction ( f S ) of 0% to 10% in native specimens, and up to ∼86% in heavily deuterated specimens. f S values were significantly affected by the TIs used in IR-UTE sequences with either hard or half excitation pulses in native specimens but not in heavily deuterated specimens. The STC was in the range of 150 to 400 µs in all UTE and IR-UTE measurements obtained with either hard or half excitation pulses. Conclusion Our results further support myelin protons as the major source of the ultrashort signals seen on IR-UTE images and demonstrate the potential of IR-UTE sequences with half excitation pulses for directly imaging myelin using clinical scanners. Magn Reson Med, 2017. © 2017 International Society for Magnetic Resonance in Medicine.

Description: Purpose To develop a non–contrast-agent MRI technique to quantify cerebral venous T 2 in mice. Methods We implemented and optimized a T 2 -relaxation-under-spin-tagging (TRUST) sequence on an 11.7 Tesla animal imaging system. A flow-sensitive-alternating-inversion-recovery (FAIR) module was used to generate control and label images, pair-wise subtraction of which yielded blood signals. Then, a T 2 -preparation module was applied to produce T 2 -weighted images, from which blood T 2 was quantified. We conducted a series of technical studies to optimize the imaging slice position, inversion slab thickness, post-labeling delay (PLD), and repetition time. We also performed three physiological studies to examine the venous T 2 dependence on hyperoxia ( N  = 4), anesthesia ( N  = 3), and brain aging ( N  = 5). Results Our technical studies suggested that, for efficient data acquisition with minimal bias in estimated T 2 , a preferred TRUST protocol was to place the imaging slice at the confluence of sagittal sinuses with an inversion-slab thickness of 2.5-mm, a PLD of 1000 ms and a repetition time of 3.5 s. Venous T 2 values under normoxia and hyperoxia (inhaling pure oxygen) were 26.9 ± 1.7 and 32.3 ± 2.2 ms, respectively. Moreover, standard isoflurane anesthesia resulted in a higher venous T 2 compared with dexmedetomidine anesthesia ( N  = 3; P  = 0.01) which is more commonly used in animal functional MRI studies to preserve brain function. Venous T 2 exhibited a decrease with age ( N  = 5; P  〈 0.001). Conclusion We have developed and optimized a noninvasive method to quantify cerebral venous blood T 2 in mouse at 11.7 T. This method may prove useful in studies of brain physiology and pathophysiology in animal models. Magn Reson Med, 2017. © 2017 International Society for Magnetic Resonance in Medicine.

Description: Purpose To demonstrate the feasibility of the so-called quadrupolar jump-and-return (QJR) pulse sequence by assessing its performance on the contrast modification to knee cartilage and quality of fluid suppression in the knee joint in vivo at 7T. Methods The right knee joints of five healthy volunteers (3 males: mean age = 32.4 ± 1.3 years; 2 females: mean age = 27.9 ± 1.0 years; mean age = 30.6 ± 2.7 years) were scanned on a 7T scanner with variation of the delay in the QJR sequence from 1 ms to 5 ms. For one healthy volunteer, the QJR scan with the delay of 3 ms and the inversion-recovery (IR) scan were performed. Numerical simulations were conducted to evaluate the effects of B 0 - and B 1 -field inhomogeneities and residual quadrupolar couplings on fluid suppression and tissue contrast, respectively. Results The QJR sequence suppressed the fluid signal from the artery and produced the contrast of knee cartilage in vivo. Its performance was comparable to that of the conventional IR sequence. Numerical simulations suggested that the fluid suppression may not be affected much by field inhomogeneities but that a distribution of residual quadrupolar couplings and weak RF pulses may interfere with the clear interpretation of cartilage contrast. Conclusion This preliminary work demonstrated that the QJR pulse sequence produces contrast for knee cartilage while suppressing the fluid signal from the artery. The knee cartilage contrast and quality of fluid suppression obtained from the QJR sequence were comparable to those of the IR sequence. Magn Reson Med, 2017. © 2017 International Society for Magnetic Resonance in Medicine.

Description: Purpose The purpose of this study is to develop double diffusion encoding (DDE) MRI methods for clinical use. Microscopic diffusion anisotropy measurements from DDE promise greater specificity to changes in tissue microstructure compared with conventional diffusion tensor imaging, but implementation of DDE sequences on whole-body MRI scanners is challenging because of the limited gradient strengths and lengthy acquisition times. Methods A custom single-refocused DDE sequence was implemented on a 3T whole-body scanner. The DDE gradient orientation scheme and sequence parameters were optimized based on a Gaussian diffusion assumption. Using an optimized 5-min DDE acquisition, microscopic fractional anisotropy (μFA) maps were acquired for the first time in multiple sclerosis patients. Results Based on simulations and in vivo human measurements, six parallel and six orthogonal diffusion gradient pairs were found to be the minimum number of diffusion gradient pairs necessary to produce a rotationally invariant measurement of μFA. Simulations showed that optimal precision and accuracy of μFA measurements were obtained using b-values between 1500 and 3000 s/mm 2 . The μFA maps showed improved delineation of multiple sclerosis lesions compared with conventional fractional anisotropy and distinct contrast from T 2 -weighted fluid attenuated inversion recovery and T 1 -weighted imaging. Conclusion The μFA maps can be measured using DDE in a clinical setting and may provide new opportunities for characterizing multiple sclerosis lesions and other types of tissue degeneration. Magn Reson Med, 2017. © 2017 International Society for Magnetic Resonance in Medicine.