An amplitude optimized single-shot hybrid QUEST technique

Rapid MR imaging techniques either deposit high amounts of radio frequency power or require powerful gradient systems with high slew rates, which might not be available on conventional scanners. QUEST provides a fast imaging method with scan times of the order of hundreds of milliseconds and avoids these problems at the cost of low signal-to-noise ratios (SNR). In this work, QUEST was optimized with regard to image quality and measuring time. With the use of a Hybrid QUEST technique, that refocuses the image echoes several times, a spatial resolution of 1.9 mm x 1.6 mm x 5 mm was achieved. By acquiring both the necessary correction data and the image information in a single echo train, the Hybrid QUEST technique was implemented as a true single-shot measurement with a total scan time of 190 ms. Optimization of the excitation flip angles and the amplitude and phase correction methods for image reconstruction resulted in an improved SNR of 53.7 in the white matter of the human head for a 10 mm slice thickness at 1.5 T. In contrast to echo planar imaging techniques, no image distortions were observed with Hybrid QUEST in anatomic regions with many tissue interfaces.     

An assessment of the sharpness of carotid artery tissue boundaries with acquisition voxel size and field strength

A measure of the sharpness of vessel wall interfaces in carotid artery MRI may be useful for assessing the conspicuity of the wall's features. An edge detection technique was used to measure the signal intensity gradients in 2D time-of-flight (2D-TOF) and double-inversion recovery black-blood (DIR-BB) carotid artery images of normal subjects that were acquired at 1.5 T with 0.55 x 0.55 x 2.0-mm (0.6 mm3) acquisition voxels and zero filled to reduce the in-plane reconstructed voxel size by one half in each dimension as well as with 0.27 x 0.27 x 2.0-mm (0.15 mm3) acquisition voxels and at 3.0 T with 0.27 x 0.27 x 2.0-mm (0.15 mm3) acquisition voxels using surface coils. The gradient intensities of the lumen-to-background interface varied closely with the contrast-to-noise ratio of the 2D-TOF imaging. For the DIR-BB imaging, in which higher spatial frequency artery structures are visible, the gradient intensities at the interfaces were higher than theoretically predicted at both field strengths with smaller acquisition voxels. The use of acquisition voxels smaller than those previously used at 1.5 T can improve the visualization of carotid artery structures at 1.5 and 3.0 T with surface coil reception.     

Sodium 3-D MRI of the human torso using a volume coil

Sodium MR imaging is considered to provide clinically important information about the human body that is not achievable by hydrogen-based approaches. However, due to the low natural abundance in biological tissues, sodium signals usually lead to low spatial resolution, low SNR, and long acquisition times compared to conventional 1H imaging, even using well-adapted surface coils. For our study, a volume coil was designed with nearly homogeneous excitation/receive characteristics and a suitable geometry fitting the human torso. A sufficient penetration throughout the entire thorax, abdomen, or pelvis is provided allowing for sodium imaging of the kidneys, the liver with gall bladder, or the myocardium. All measurements were performed on a 1.5 T whole body scanner using a spoiled 3-D gradient echo sequence. Imaging parameters TE, TR, and readout bandwidth were optimized for sensitive recording of the sodium component with slow transverse relaxation. Nonselective RF excitation pulses with a duration of 2.5 ms and rectangular shape were applied to avoid SAR problems. Narrow receiver bandwidth and excitation near the Ernst angle provided clinically practicable examinations with measuring times of less than 15 min at a spatial resolution of 8 x 8 x 8 mm3. Under these conditions, SNR of 11 for the kidneys and vertebral disks, 9 for the spinal canal, and 6 for the liver was achieved. A special 3-D spin echo sequence was used to determine T2, times which resulted to 15.3 +/- 1.1 ms for liver, 27.7 +/- 7.2 ms for kidneys, and 24.0 +/- 4.7 ms for the content of the spinal canal.     

Evaluation of Enhancement Effects as a Function of the Molarity of Gd-Based Contrast Media at 3.0 and 1.5 T: Based on the T1 Effective Pulse Sequence Parameter

The purpose of this study was to evaluate the alterations of diluted molarity of contrast media to emit the maximum signal intensity by changing the parameters of pulse sequences. The phantom was developed by diluting the magnetic resonance imaging (MRI) T1 contrast medium. The phantom images were obtained by 1.5 and 3.0 T MRI systems. We conducted Pearson’s analysis to reveal the correlation of the signal-to-noise ratio (SNR)_90%, the change of the concentration range of the contrast media which shows over 90% SNR, with changing the parameters of T1 effect pulse sequences in both 1.5 and 3.0 T imaging. As the flip angle increased, the SNR increased for all contrast media in magnetization-prepared rapid gradient echo and two-dimensional fast low angle shot pulse sequences at 1.5 and 3.0 T. Although the SNR increased until 30°, the SNR was almost the same over 30° in volumetric interpolated breath-hold examination at 1.5 and 3.0 T. The minimum contrast molarity of the representing SNR_90% was decreased according to the increasing time to repeat in spin echo. The present study revealed that the high concentration technique of contrast media on three pulse sequences (VIBE, MPRAGE, and 2D FLASH) could be useful to obtain images with better SNR.     

In vivo measurements of multi-component T2 relaxation behaviour in guinea pig brain

Multi-echo Carr-Purcell-Meiboom-Gill (CPMG) imaging sequences were implemented on 1.5 T and 4.0 T imaging systems to test their ability to measure in vivo multi-component T2 relaxation behavior in normal guinea pig brain. The known dependence of accurate T2 measurements on the signal-to-noise ratio (SNR) was explored in vivo by comparing T2 decay data obtained using three methods to increase SNR (improved RF coil design, signal averaging and increased magnetic field strength). Good agreement between T2 values of nickel-doped agarose phantoms was found between imaging and spectroscopic methods. T2 values were determined for gray matter (GM) and white matter (WM) locations from images of guinea pig brain in vivo. T2 measurements of GM were found to be monoexponential at both field strengths. The mean T2 times for GM were 71 ms at 1.5 T, and 53 ms at 4.0T. The highest average SNR was achieved using an improved RF coil at 4.0T. In this case, two peaks were extracted in WM, a "short" T2 peak at approximately 6 ms, and a "medium" T2 peak at approximately 48 ms. T2 values in GM and the major component of WM were significantly decreased at 4.0T compared to 1.5 T. The improved SNR attained with this optimized imaging protocol at 4.0T has allowed for the first time extraction of the myelin-sensitive T2 component of WM in animal brain in vivo.     

Considerations in applying 3D PRESS H-1 brain MRSI with an eight-channel phased-array coil at 3 T

The purpose of this study was to assess the benefits of a 3 T scanner and an eight-channel phased-array head coil for acquiring three-dimensional PRESS (Point REsolved Spectral Selection) proton (H-1) magnetic resonance spectroscopic imaging (MRSI) data from the brains of volunteers and patients with brain tumors relative to previous studies that used a 1.5 T scanner and a quadrature head coil. Issues that were of concern included differences in chemical shift artifacts, line broadening due to increased susceptibility at higher field strengths, changes in relaxation times and the increased complexity of the postprocessing software due to the need for combining signals from the multichannel data. Simulated and phantom spectra showed that very selective suppression pulses with a thickness of 40 mm and an overpress factor of at least 1.2 are needed to reduce chemical shift artifact and lipid contamination at higher field strengths. Spectral data from a phantom and those from six volunteers demonstrated that the signal-to-noise ratio (SNR) in the eight-channel coil was more than 50% higher than that in the quadrature head coil. For healthy volunteers and eight patients with brain tumors, the SNR at 3 T with the eight-channel coil was on average 1.5 times higher relative to the eight-channel coil at 1.5 T in voxels from normal-appearing brains. In combination with the effect of a higher field strength, the use of the eight-channel coil was able to provide an increase in the SNR of more than 2.33 times the corresponding acquisition at 1.5 T with a quadrature head coil. This is expected to be critical for clinical applications of MRSI in patients with brain tumors because it can be used to either decrease acquisition time or improve spatial resolution.     

Minimum SNR and acquisition for bias-free estimation of fractional anisotropy in diffusion tensor imaging - a comparison of two analytical techniques and field strengths

Although it is known that low signal-to-noise ratio (SNR) can affect tensor metrics, few studies reporting disease or treatment effects on fractional anisotropy (FA) report SNR; the implicit assumption is that SNR is adequate. However, the level at which low SNR causes bias in FA may vary with tissue FA, field strength and analytical methodology. We determined the SNR thresholds at 1.5 T vs. 3 T in regions of white matter (WM) with different FA and compared FA derived using manual region-of-interest (ROI) analysis to tract-based spatial statistics (TBSS), an operator-independent whole-brain analysis tool. Using ROI analysis, SNR thresholds on our hardware-software magnetic resonance platforms were 25 at 1.5 T and 20 at 3 T in the callosal genu (CG), 40 at 1.5 and 3 T in the anterior corona radiata (ACR), and 50 at 1.5 T and 70 at 3 T in the putamen (PUT). Using TBSS, SNR thresholds were 20 at 1.5 T and 3 T in the CG, and 35 at 1.5 T and 40 at 3 T in the ACR. Below these thresholds, the mean FA increased logarithmically, and the standard deviations widened. Achieving bias-free SNR in the PUT required at least nine acquisitions at 1.5 T and six acquisitions at 3 T. In the CG and ACR, bias-free SNR was achieved with at least three acquisitions at 1.5 T and one acquisition at 3 T. Using diffusion tensor imaging (DTI) to study regions of low FA, e.g., basal ganglia, cerebral cortex, and WM in the abnormal brain, SNR should be documented. SNR thresholds below which FA is biased varied with the analytical technique, inherent tissue FA and field strength. Studies using DTI to study WM injury should document that bias-free SNR has been achieved in the region of the brain being studied as part of quality control.     

High-resolution 3D MR spectroscopic imaging of the prostate at 3 T with the MLEV-PRESS sequence

A 3 T MLEV-point-resolved spectroscopy (PRESS) sequence employing optimized spectral-spatial and very selective outer-voxel suppression pulses was tested in 25 prostate cancer patients. At an echo time of 85 ms, the MLEV-PRESS sequence resulted in maximally upright inner resonances and minimal outer resonances of the citrate doublet of doublets. Magnetic resonance spectroscopic imaging (MRSI) exams performed at both 3 and 1.5 T for 10 patients demonstrated a 2.08+/-0.36-fold increase in signal-to-noise ratio (SNR) at 3 T as compared with 1.5 T for the center citrate resonances. This permitted the acquisition of MRSI data with a nominal spatial resolution of 0.16 cm3 at 3 T with similar SNR as the 0.34-cm3 data acquired at 1.5 T. Due to the twofold increase in spectral resolution at 3 T and the improved magnetic field homogeneity provided by susceptibility-matched endorectal coils, the choline resonance was better resolved from polyamine and creatine resonances as compared with 1.5 T spectra. In prostate cancer patients, the elevation of choline and the reduction of polyamines were more clearly observed at 3 T, as compared with 1.5 T MRSI. The increased SNR and corresponding spatial resolution obtainable at 3 T reduced partial volume effects and allowed improved detection of the presence and extent of abnormal metabolite levels in prostate cancer patients, as compared with 1.5 T MRSI.     

A hybrid technique for spectroscopic imaging with reduced truncation artifact

Traditionally, Fourier spectroscopic imaging is associated with a small k-space coverage which leads to truncation artifacts such as "bleeding" and ringing in the resultant image. Because substantial truncation artifacts mainly arise from regions having intense signals, such as the subcutaneous lipid in the head, effective reduction of truncation artifacts can be achieved by obtaining an extended k-space coverage for these regions. In this paper, a hybrid technique which employs phase-encoded spectroscopic imaging (SI) to cover the central portion of the k-space and echo-planar spectroscopic imaging (EPSI) to measure the peripheral portion of the k-space is developed. EPSI, despite its inherently low SNR characteristics, provides a sufficient SNR for outer high-spatial frequency components of the aforementioned high signal regions and supplies an extended k-space coverage of these regions for the reduction of truncation artifacts. The data processing includes steps designed to remove inconsistency between the two types of data and a previously described technique for selectively retaining only outer k-space information for the high signal regions during the reconstruction. Experimental studies, in both phantoms and normal volunteers, demonstrate that the hybrid technique provides significant reduction in truncation artifacts.     

Truncation artifact reduction in spectroscopic imaging using a dual-density spiral k-space trajectory

Truncation artifacts arise in magnetic resonance spectroscopic imaging (MRSI) of the human brain due to limited coverage of k-space necessitated by low SNR of metabolite signal and limited scanning time. In proton MRSI of the head, intense extra-cranial lipid signals “bleed” into brain regions, thereby contaminating signals of metabolites therein. This work presents a data acquisition strategy for reducing truncation artifact based on extended k-space coverage achieved with a dual-SNR strategy. Using the fact that the SNR in k-space increases monotonically with sampling density, dual-SNR is achieved in an efficient manner with a dual-density spiral k-space trajectory that permits a smooth transition from high density to low density. The technique is demonstrated to be effective in reducing “bleeding” of extra-cranial lipid signals while preserving the SNR of metabolites in the brain.     

Highly undersampled supraaortic MRA at 3.0 T: initial results with parallel imaging in two directions using a 16-channel neurovascular coil and parallel imaging factors up to 16

PurposeTo present the feasibility of highly undersampled contrast-enhanced MRA (CE-MRA) of the supraaortic arteries with a 16-channel neurovascular coil at 3.0 T using parallel imaging in two directions with parallel imaging factors (PIF) up to 16.Materials and MethodsInstitutional review board approval and informed consent were obtained. In a prospective study, MRA protocols including PIF of 1, 2, 4, 9 and 16 yielding a spatial resolution from 0.81×0.81×1.0 mm³ to 0.46×.46×0.98 mm³ were acquired. In 32 examinations, image quality and vascular segments were rated independently by two radiologists. SNR estimations were performed for all MRA protocols.ResultsThe use of high PIF allowed to shorten acquisition time from 2:09 min down to 1:13 min and to increase the anatomic coverage while maintaining or even increasing spatial resolution down to 0.46×0.46×0.98 mm³. The larger anatomic coverage that was achieved with the use of high PIF allowed for visualization of vascular structures that were not covered by the standard protocols. Despite the resulting lower SNR using high PIF, image quality was constantly rated to be adequate for diagnosis or better in all cases.ConclusionThe use of high PIF yielded diagnostic image quality and allowed to increase the anatomic coverage while maintaining or even improving spatial resolution and shortening the acquisition time.     

Parallel imaging with 3D TPI trajectory: SNR and acceleration benefits

Three-dimensional (3D) twisted projection imaging (TPI) trajectory has a unique advantage in sodium (²³Na) imaging on clinical MRI scanners at 1.5 or 3 T, generating a high signal-to-noise ratio (SNR) with a short acquisition time (∼10 min). Parallel imaging with an array of coil elements transits SNR benefits from small coil elements to acquisition efficiency by sampling partial k-space. This study investigates the feasibility of parallel sodium imaging with emphases on SNR and acceleration benefits provided by the 3D TPI trajectory. Computer simulations were used to find available acceleration factors and noise amplification. Human head studies were performed on clinical 1.5/3-T scanners with four-element coil arrays to verify simulation outcomes. In in vivo studies, proton (¹H) data, however, were acquired for concept–proof purpose. The sensitivity encoding (SENSE) method with the conjugate gradient algorithm was used to reconstruct images from accelerated TPI-SENSE data sets. Self-calibration was employed to estimate coil sensitivities. Noise amplification in TPI-SENSE was evaluated using multiple noise trials. It was found that the acceleration factor was as high as 5.53 (corresponding to acceleration number 2×3, ring-by-rotation), with a small image error of 6.9% when TPI projections were reduced in both polar (ring) and azimuthal (rotation) directions. The average noise amplification was as low as 98.7%, or 27% lower than Cartesian SENSE at that acceleration factor. The 3D nature of both TPI trajectory and coil sensitivities might be responsible for the high acceleration and low noise amplification. Consequently, TPI-SENSE may have potential advantages for parallel sodium imaging.     

In vivo 31P echo-planar spectroscopic imaging of human calf muscle

Localized phosphorus-31 NMR spectra of human calf muscle in vivo were obtained by means of echo-planar spectroscopic imaging (EPSI) with a 1.5-T whole-body scanner. The technique permits the measurement of two-dimensional 31P SI data at a minimum acquisition time of 2.4 s (8x8 voxels, TR=300 ms). With 9.4 min measurement time (TR=1100 ms, 64 averages) and 25x25x40 mm spatial resolution in vivo the 31P NMR signal-to-noise ratio (S/N) of the phosphocreatine (PCr) resonance was about 45; the multiplets of nucleoside 5'-triphosphates were resolved. Spectral quality permits quantitative assessment of the PCr signal in a measurement time that is shorter by a factor of 2 or more than the minimum measurement time feasible with chemical-shift imaging. In a functional EPSI study with a time resolution of 20.5 s on the calf muscle of volunteers, spectra showed a 40% decrease of the PCr signal intensity (at rest: S/N congruent with12) upon exertion of the muscle.     

Reflective terahertz imaging of porcine skin burns

A reflective pulsed terahertz imaging system based on direct detection was developed and used to obtain high-resolution images of a porcine skin specimen with superficial partial-thickness (second-degree) burns. Images were also obtained of the sample through ten layers of dry medical (cotton) gauze with minimal image degradation. The burned and unburned regions of skin had large differences in terahertz reflectivity, displaying clear delineation [20 dB signal-to-noise ratio (SNR) difference signal] between both regions in the images. The terahertz images also exhibited a "halo" surrounding the burn areas that may correlate to the extent of burn injury. The system operated at a center frequency of 500 GHz with 125 GHz of 3 dB bandwidth and used whiskbroom scanning to generate images with a spatial resolution of 1.5 mm. Each pixel was acquired with a 16 ms integration time, resulting in a 40 dB postdetection SNR. The simplicity and high SNR of the reflective terahertz system are promising steps toward real-time terahertz medical imaging.     

Evaluation of the inner ear by 3D fast asymmetric spin echo (FASE) MR imaging: phantom and volunteer studies

The 3D fast asymmetric spin echo (FASE) method combines the half-Fourier technique and 3D fast spin echo (FSE) sequence. The advantage of this method is that it maintains the same spatial resolution as FSE while markedly reducing the imaging time. The purpose of the present study was to evaluate the usefulness of the 3D FASE technique in displaying the inner ear structure using phantom and volunteer studies. 3D FSE sequence images were obtained for comparison, and the optimum 3D FASE sequence was investigated on a 1.5T MR scanner. The results of phantom experiments showed increased signal-to-noise ratio (SNR) with prolonging repetition time (TR) on both 3D FASE and 3D FSE sequences. Although the SNR of 3D FASE images was 20-25% lower than that of 3D FSE images with the same TR, the SNR per minute with 3D FASE was about twice that with 3D FSE. On 3D FASE images, a higher spatial resolution was obtained with 2- or 4-shot images than with single-shot images. However, no significant difference was observed between 2-shot and 4-shot images. In the volunteer study, 3D FASE images using a TR of 5000 ms and an effective echo time (TEeff) of 250 ms showed a high SNR and spatial resolution and provided excellent contrast between cerebrospinal fluid and nerves in the internal auditory canal. The highest contrast was achieved in the 2-shot/2 number of excitations sequence. 3D FASE provides the same image quality as 3D FSE with a significant reducing in imaging time, and gives strong T2-weighted images. This method enables detailed visualization of the tiny structures of the inner ear.     

Fast 3D echo planar SSFP-based 1H spectroscopic imaging: demonstration on the rat brain in vivo

A fast proton spectroscopic imaging pulse sequence based on the condition of steady-state free precession is presented. High 3D spatial and temporal resolution is achieved using simultaneous detection of both one spatial and one spectral dimension, with a time-dependent gradient cycle known from echo planar imaging. Additionally, in order to increase the spectral width of the measurement, an interleaved acquisition scheme is shown either for systems with limited gradient switching capabilities or applications with a wide chemical shift range. The pulse sequence is implemented on a standard 4.7-T nuclear magnetic resonance animal imaging system. Measurements with a total measurement time of less than 2.5 min and a nominal voxel size of 6.75 microl using a total of 64 x 32 x 16 voxels are performed on phantoms and healthy rat brain in vivo allowing the rapid detection of signals from both uncoupled and J-coupled spin systems with high signal-to-noise ratio.     

High-speed spectroscopic imaging for cancellous bone marrow R(2)* mapping and lipid quantification

In this work an interleaved multiple-gradient-echo chemical shift imaging (IMGE-CSI) technique was designed, implemented and evaluated at 1.5 and 4T for high-resolution lipid quantification and R(2)* measurement in-vivo. The method is analogous to echo planar CSI but utilizes conventional gradient echoes, exploiting the principle of spectroscopic bandwidth extension by interleaving temporally offset gradient-echo trains. It is shown that IMGE-CSI is able to measure true fat volume fraction in oil/water mixtures with high accuracy, not possible with Dixon-type methods which approximate the spectrum as consisting of only two spectral components. Correlation of the CSI- derived volume fractions with volumetry afforded r(2) > 0.99 with a slope of 0.98. The method is shown to be able to quantify regional variations in bone marrow composition in vivo with a spatial resolution of 2.5 x 2.5 x 5 mm(3.) R(2)* was obtained by multi-line spectral curve fitting. For the measurement of R(2)* in cancellous bone marrow the method is shown to agree well with time-domain fitting techniques but is superior in instances where the marrow has both hematopoietic and fatty constituents. Finally, excellent inter-scan reproducibility (1% coefficient of variation for global means and medians) was achieved, yielding r(2) = 0.98 of the test-retest correlation for three scans in four test subjects. In conclusion, IMGE-CSI is found to enable highly accurate lipid quantification and measurement of cancellous bone marrow R(2)* at spatial resolutions and scan times typical of standard clinical protocols.     

Signal-to-noise ratio comparison of phased-array vs. implantable coil for rat spinal cord MRI

The signal-to-noise ratio (SNR) performance and practicality issues of a four-element phased-array coil and an implantable coil system were compared for rat spinal cord magnetic resonance imaging (MRI) at 7 T. MRI scans of the rat spinal cord at T10 were acquired from eight rats over a 3 week period using both coil systems, with and without laminectomy. The results demonstrate that both the phased array and the implantable coil systems are feasible options for rat spinal cord imaging at 7 T, with both systems providing adequate SNR for 100-mum spatial resolution at reasonable imaging times. The implantable coils provided significantly higher SNR, as compared to the phased array (average SNR gain of 5.3x between the laminectomy groups and 2.5x between the nonlaminectomy groups). The implantable coil system should be used if maximal SNR is critical, whereas the phased array is a good choice for its ease of use and lesser invasiveness.     

An optimized solenoidal head radiofrequency coil for low-field magnetic resonance imaging

Applications of low-field magnetic resonance imaging (MRI) systems (<0.3 T) are limited due to the signal-to-noise ratio (SNR) being lower than that provided by systems based on superconductive magnets (≥1.5 T). Therefore, the design of radiofrequency (RF) coils for low-field MRI requires careful consideration as significant gains in SNR can be achieved with the proper design of the RF coil. This article describes an analytical method for the optimization of solenoidal coils. Coil and sample losses are analyzed to provide maximum SNR and optimum B₁ field homogeneity. The calculations are performed for solenoidal coils optimized for the human head at 0.2 T, but the method could also be applied to any solenoidal coil for imaging other anatomical regions at low field. Several coils were constructed to compare experimental and theoretical results. A head magnetic resonance image obtained at 0.2 T with the optimum design is presented.     

Development and initial evaluation of 7-T q-ball imaging of the human brain

Diffusion tensor imaging (DTI) noninvasively depicts white matter connectivity in regions where the Gaussian model of diffusion is valid but yields inaccurate results in those where diffusion has a more complex distribution, such as fiber crossings. q-ball imaging (QBI) overcomes this limitation of DTI by more fully characterizing the angular dependence of intravoxel diffusion with larger numbers of diffusion-encoding directional measurements at higher diffusion-weighting factors (b values). However, the former technique results in longer acquisition times and the latter technique results in a lower signal-to-noise ratio (SNR). In this project, we developed specialized 7-T acquisition methods utilizing novel radiofrequency pulses, eight-channel parallel imaging EPI and high-order shimming with a phase-sensitive multichannel B0 field map reconstruction. These methods were applied in initial healthy adult volunteer studies, which demonstrated the feasibility of performing 7-T QBI. Preliminary comparisons of 3 T with 7 T within supratentorial crossing white matter tracts documented a 79.5% SNR increase for b=3000 s/mm2 (P=.0001) and a 38.6% SNR increase for b=6000 s/mm2 (P=.015). With spherical harmonic reconstruction of the q-ball orientation distribution function at b=3000 s/mm2, 7-T QBI allowed for accurate visualization of crossing fiber tracts with fewer diffusion-encoding acquisitions as compared with 3-T QBI. The improvement of 7-T QBI at b factors as high as 6000 s/mm2 resulted in better angular resolution as compared with 3-T QBI for depicting fibers crossing at shallow angles. Although the increased susceptibility effects at 7 T caused problematic distortions near brain-air interfaces at the skull base and posterior fossa, these initial 7-T QBI studies demonstrated excellent quality in much of the supratentorial brain, with significant improvements as compared with 3-T acquisitions in the same individuals.