In vivo measurement of T1rho dispersion in the human brain at 1.5 tesla

Purpose

To measure T_1ρ relaxation times and T_1ρ dispersion in the human brain in vivo.

Materials and Methods

Magnetic resonance imaging (MRI) was performed on a 1.5‐T GE Signa clinical scanner using the standard GE head coil. A fast spin‐echo (FSE)‐based T_1ρ‐weighted MR pulse sequence was employed to obtain images from five healthy male volunteers. Optimal imaging parameters were determined while considering both the objective of the study and the guarantee that radio‐frequency (RF) power deposition during MR did not exceed Food and Drug Administration (FDA)‐mandated safety levels.

Results

T_1ρ‐weighted MR images showed excellent contrast between different brain tissues. These images were less blurred than corresponding T₂‐weighted images obtained with similar contrast, especially in regions between brain parenchyma and cerebrospinal fluid (CSF). Average T_1ρ values for white matter (WM), gray matter (GM), and CSF were 85 ± 3, 99 ± 1, and 637 ± 78 msec, respectively, at a spin‐locking field of 500 Hz. T_1ρ is 30% higher in the parenchyma and 78% higher in CSF compared to the corresponding T₂ values. T_1ρ dispersion was observed between spin‐locking frequencies 0 and 500 Hz.

Conclusion

T_1ρ‐weighted MRI provides images of the brain with superb contrast and detail. T_1ρ values measured in the different brain tissues will serve as useful baseline values for analysis of T_1ρ changes associated with pathology. J. Magn. Reson. Imaging 2004;19:403–409. © 2004 Wiley‐Liss, Inc.

     

Optimization of high-resolution USPIO magnetic resonance imaging at 4.7 T using novel phantom with minimal structural interference

Purpose:

To characterize the effect of ultrasmall superparamagnetic iron oxides (USPIOs) on magnetic resonance imaging (MRI) signal at 4.7 T, and to find the highest sensitivity pulse sequence for high‐resolution USPIO MRI.

Materials and Methods:

A novel phantom was constructed for optimization of sequence parameters for neuroradiological MR applications, and a wide range of dilutions of the USPIO ferumoxtran‐10 was imaged using T₂/T₁‐, T₁‐, T₂‐, T* ₂‐, and PD‐weighted sequences. The effect of varying sequence parameters was investigated using phantom measurements and simulations.

Results:

The relaxivities r₁, r₂, and r*₂ of ferumoxtran‐10 at 4.7 T (21°C) were 5.1, 82.2, and 148.4 mmol^?1 L s^?1, respectively. Gradient echo sequences produced superior susceptibility artifacts at high concentrations; susceptibility artifacts were seen down to a concentration of 137 nmol Fe/mL. A concentration of 17.5 μmol Fe/mL caused a signal void independently of sequence and parameters, and at concentrations ≤273 nmol Fe/mL no signal void was caused. Signal enhancement on T₁‐weighted imaging was seen only at concentrations 137–547 nmol Fe/mL. For the same effective echo time T₂‐weighted rapid acquisition with relaxation enhancement (RARE) yielded significantly higher contrast‐to‐noise ratio with RARE factor 16 than with RARE factor 8.

Conclusion:

At nanomolar concentrations of USPIO, steady‐state free precession offers an alternative to T₂‐ and T* ₂‐weighted sequences. Optimum parameters depend highly on USPIO concentration. J. Magn. Reson. Imaging 2010;32:1184–1196. © 2010 Wiley‐Liss, Inc.

     

Parallel‐transmission‐enabled three‐dimensional T2‐weighted imaging of the human brain at 7 Tesla

Purpose: A promise of ultra high field MRI is to produce images of the human brain with higher spatial resolution due to an increased signal to noise ratio. Yet, the shorter radiofrequency wavelength induces an inhomogeneous distribution of the transmit magnetic field and thus challenges the applicability of MRI sequences which rely on the spin excitation homogeneity. In this work, the ability of parallel‐transmission to obtain high‐quality T₂‐weighted images of the human brain at 7 Tesla, using an original pulse design method is evaluated. Methods: Excitation and refocusing square pulses of a SPACE sequence were replaced with short nonselective transmit‐SENSE pulses individually tailored with the gradient ascent pulse engineering algorithm, adopting a k_T‐point trajectory to simultaneously mitigate B₁⁺ and ΔB₀ nonuniformities. Results: In vivo experiments showed that exploiting parallel‐transmission at 7T with the proposed methodology produces high quality T₂‐weighted whole brain images with uniform signal and contrast. Subsequent white and gray matter segmentation confirmed the expected improvements in image quality. Conclusion: This work demonstrates that the adopted formalism based on optimal control, combined with the k_T‐point method, successfully enables three‐dimensional T₂‐weighted brain imaging at 7T devoid of artifacts resulting from B₁⁺ inhomogeneity. Magn Reson Med 73:2195–2203, 2015. © 2014 Wiley Periodicals, Inc.     

Correspondence of human visual areas identified using functional and anatomical MRI in vivo at 7 T

Purpose:

To study the correspondence of anatomically and functionally defined visual areas (primary visual cortex, V1, and motion selective area V5/human MT+) by using structural magnetic resonance imaging (MRI) and functional MRI (fMRI) in vivo at 7 T.

Materials and Methods:

Four subjects participated in this study. High‐resolution (≈0.4 mm isotropic) anatomical MRI was used to identify cortical regions based on their distinct cortical lamination. The optimal contrast for identifying heavily myelinated layers within gray matter was quantitatively assessed by comparing T₁‐weighted magnetization‐prepared rapid gradient echo (MPRAGE) and T₂*‐weighted, 3D fast‐low angle shot (FLASH) imaging. Retinotopic mapping was performed using GE‐based fMRI at 1.5 mm isotropic resolution to identify functional areas.

Results:

T₂*‐weighted FLASH imaging was found to provide a significantly higher contrast‐to‐noise ratio, allowing visualization of the stria of Gennari in every slice of a volume covering the occipital cortex in each of the four subjects in this study. The independently derived boundary of V1, identified in the same subjects using retinotopic mapping by fMRI, closely matched the border of anatomically defined striate cortex in the human brain. Evidence of banding was also found within the functionally defined V5 area; however, we did not find a good correlation of this area, or the functionally identified subregion (MT), with the banded area.

Conclusion:

High‐resolution T₂*‐weighted images acquired at 7 T can be used to identify myelinated bands within cortical gray matter in reasonable measurement times. Regions where a myelinated band was identified show a high degree of overlap with the functionally defined V1 area. J. Magn. Reson. Imaging 2012;287‐299. © 2011 Wiley Periodicals, Inc.     

Robust tissue–air volume segmentation of MR images based on the statistics of phase and magnitude: Its applications in the display of susceptibility‐weighted imaging of the brain

Purpose

To develop a robust algorithm for tissue–air segmentation in magnetic resonance imaging (MRI) using the statistics of phase and magnitude of the images.

Materials and Methods

A multivariate measure based on the statistics of phase and magnitude was constructed for tissue–air volume segmentation. The standard deviation of first‐order phase difference and the standard deviation of magnitude were calculated in a 3 × 3 × 3 kernel in the image domain. To improve differentiation accuracy, the uniformity of phase distribution in the kernel was also calculated and linear background phase introduced by field inhomogeneity was corrected. The effectiveness of the proposed volume segmentation technique was compared to a conventional approach that uses the magnitude data alone.

Results

The proposed algorithm was shown to be more effective and robust in volume segmentation in both synthetic phantom and susceptibility‐weighted images of human brain. Using our proposed volume segmentation method, veins in the peripheral regions of the brain were well depicted in the minimum‐intensity projection of the susceptibility‐weighted images.

Conclusion

Using the additional statistics of phase, tissue–air volume segmentation can be substantially improved compared to that using the statistics of magnitude data alone. J. Magn. Reson. Imaging 2009;30:722–731. © 2009 Wiley‐Liss, Inc.     

Comparison of visceral adipose tissue quantification on water suppressed and nonwater-suppressed MRI at 3.0 Tesla

Purpose:

To systematically evaluate and compare the performance of water‐saturated and nonwater‐saturated T1‐weighted 3.0 T magnetic resonance imaging (MRI) in the application of visceral adipose tissue (VAT) quantification.

Materials and Methods:

Forty‐five patients underwent abdomen MRI using two different sequences at 3.0 T: 1) a traditional T1‐weighted gradient echo sequence, and 2) the same sequence with water presaturation to enhance fat and nonfat contrast. VAT amounts from both water‐saturated and nonwater‐saturated images were quantified with a manual thresholding technique and an automated segmentation method to study quantification variability and consistency of the two imaging techniques.

Results:

Nonwater‐saturated MRI had significantly larger coefficient of variation than water‐saturated MRI in the imaging reproducibility study based on 112 slices from seven subjects (11.4% vs. 2.5%, P < 0.0001). VAT volumes measured from the nonwater‐saturation MRI sequence had significantly higher variability than those from water‐saturation images even when using a manual quantification method based on images from 38 subjects (1.76% vs. 1.08%, P < 0.001). In addition, the VAT volume amounts from nonwater‐saturation images and water‐saturated images quantified with the automatic and manual quantification methods were statistically consistent.

Conclusion:

Water‐saturated MRI sequences at 3.0 T for VAT quantification improve reproducibility and decrease variability compared with nonwater saturated sequences, especially with the use of automatic quantification methods. J. Magn. Reson. Imaging 2012;35:1445–1452. © 2012 Wiley Periodicals, Inc.     

Angle‐sensitive MRI for quantitative analysis of fiber‐network deformations in compressed cartilage

Purpose

To demonstrate the feasibility of a novel experimental method to quantitatively analyze fiber‐network deformation in compressed cartilage by angle‐sensitive magnetic resonance imaging (MRI) of cartilage.

Methods

Three knee cartilage samples of an adult sheep were imaged in a high‐resolution MRI scanner at 7 T. Main fiber orientation and its “offset” from the direction perpendicular to the bone‐cartilage boundary were derived from MR images taken at different orientations with respect to B₀. Bending of the collagen fibers was determined from weight‐bearing MRI with the load (up to 1.0 MPa) applied over the whole sample surface. A “fascicle” model of the cartilage ultrastructure was assumed to analyze characteristic intensity variations in T₂‐weighted images under load.

Results

T₂‐weighted MR images showed a strong variation of the signal intensities with sample orientation. In the T₂‐weighted weight‐bearing series, regions of high signal intensity underwent shifts from the lateral to the central parts in all three cartilage samples. The bending of the collagen fibers was determined to be 27.2°, 35.4°, and 40.0° per MPa, respectively.

Conclusion

Assuming a “fascicle” model, the presented MRI method provides quantitative measures of structural adjustments in compressed cartilage. Our preliminary analysis suggests that cartilage fiber deformation includes both bending and crimping.     

An MRI study of the differences in the rate of thrombolysis between red blood cell-rich and platelet-rich components of venous thrombi ex vivo

Purpose:

To test whether T₁‐weighted MRI can detect the differences in the rate of thrombolysis induced by recombinant tissue plasminogen activator (rt‐PA) between platelet‐rich regions and red blood cell (RBC)‐rich regions of venous thrombi ex vivo.

Materials and Methods:

Each of 21 venous thrombi ex vivo (8 pulmonary emboli and 13 in situ thrombi) was dissected along the longitudinal axis. Half of it was analyzed for the presence of platelet, fibrin, and RBC components by immunohistochemistry and the other half was imaged serially by high‐resolution T₁‐weighted three‐dimensional MRI to assess the progression of thrombolysis. The MR images were analyzed for proportions of the remaining platelet‐rich and RBC‐rich regions.

Results:

Laminated platelet‐rich regions, corresponding to Zahn lines, were confirmed immunohistochemically and by MRI in 18/21 venous thrombi. In T₁‐weighted MR images (TE/TR = 10/105 ms) the mean signal intensity of platelet‐rich regions was on average 2.3 higher than that of RBC‐rich regions. The rate of thrombolysis in platelet‐rich regions was on average 30% lower than in RBC‐rich regions. After 120 min of thrombolysis the proportion of lysed platelet‐rich regions was 0.27 ± 0.04 versus 0.40 ± 0.08 in RBC regions, which resulted in 1.4% decrease of lysed thrombus volume per 1% increase of platelet‐rich content.

Conclusion:

Venous thrombi are most often composed of interspersed platelet‐rich and RBC‐rich regions. T₁‐weighted MRI is capable of noninvasive discrimination between those two components of venous thrombi ex vivo which have a different susceptibility to thrombolysis by rt‐PA. J. Magn. Reson. Imaging 2011;. © 2011 Wiley Periodicals, Inc.     

Longitudinal in vivo susceptibility contrast MRI measurements of LS174T colorectal liver metastasis in nude mice

Purpose

To characterize longitudinal tumor progression in a murine orthotopic model of liver metastasis using susceptibility contrast magnetic resonance imaging (MRI).

Materials and Methods

Nude mice were inoculated intrasplenically with LS174T colorectal carcinoma cells 24 hours postadministration of 2.5 mgFe/kg of the ultrasmall superparamagnetic iron oxide particle preparation feruglose. Contiguous T₂ and T₂*‐weighted multislice MR images were acquired 10, 15, 20, 25, 30, and 35 days postinoculation to longitudinally evaluate metastatic progression. Functional tumor vasculature and hypoxia were histologically evaluated at the final timepoint using Hoechst 33342 uptake, pimonidazole and hematoxylin and eosin staining. A parallel cohort of subcutaneous tumors was included for comparison.

Results

All intrasplenically inoculated mice developed liver metastases, evident in both T₂*‐ and T₂‐weighted images as high‐signal deposits, compared to feruglose‐nulled normal liver. Small lesions were detected as early as day 10 and all mice exhibited progressing lesions over 35 days. Liver metastases took longer to establish, but exhibited a similar volume doubling time to the subcutaneously propagated tumors of ≈2–3 days. Different functional tumor vascular architectures between the two growth sites were apparent.

Conclusion

Susceptibility‐contrast MRI using a single dose of feruglose can be used to easily detect and longitudinally monitor orthotopically propagated liver metastases in vivo. J. Magn. Reson. Imaging 2008;9999:1451–1458. © 2008 Wiley‐Liss, Inc.     

Fast T2*-weighted MRI of the prostate at 3 Tesla

Purpose:

To describe a rapid T2*‐weighted (T2*W), three‐dimensional (3D) echo planar imaging (EPI) sequence and its application in mapping local magnetic susceptibility variations in 3 Tesla (T) prostate MRI. To compare the sensitivity of T2*W EPI with routinely used T1‐weighted turbo‐spin echo sequence (T1W TSE) in detecting hemorrhage and the implications on sequences sensitive to field inhomogeneities such as MR spectroscopy (MRS).

Materials and Methods:

B₀ susceptibility weighted mapping was performed using a 3D EPI sequence featuring a 2D spatial excitation pulse with gradients of spiral k‐space trajectory. A series of 11 subjects were imaged using 3T MRI and combination endorectal (ER) and six‐channel phased array cardiac coils. T1W TSE and T2*W EPI sequences were analyzed quantitatively for hemorrhage contrast. Point resolved spectroscopy (PRESS MRS) was performed and data quality was analyzed.

Results:

Two types of susceptibility variation were identified: hemorrhagic and nonhemorrhagic T2*W‐positive areas. Post‐biopsy hemorrhage lesions showed on average five times greater contrast on the T2*W images than T1W TSE images. Six nonhemorrhage regions of severe susceptibility artifact were apparent on the T2*W images that were not seen on standard T1W or T2W images. All nonhemorrhagic susceptibility artifact regions demonstrated compromised spectral quality on 3D MRS.

Conclusion:

The fast T2*W EPI sequence identifies hemorrhagic and nonhemorrhagic areas of susceptibility variation that may be helpful in prostate MRI planning at 3.0T. J. Magn. Reson. Imaging 2011;33:902–907. © 2011 Wiley‐Liss, Inc.     

Diffusion tensor imaging of forearm nerves in humans

Purpose:

To implement a diffusion tensor imaging (DTI) protocol for visualization of peripheral nerves in human forearm.

Materials and Methods:

This Health Insurance Portability and Accountability Act (HIPAA)‐compliant study was approved by our Institutional Review Board and written informed consent was obtained from 10 healthy participants. T₁‐ and T₂‐weighted turbo spin echo with fat saturation, short tau inversion recovery (STIR), and DTI sequences with 21 diffusion‐encoding directions were implemented to acquire images of the forearm nerves with an 8 channel knee coil on a 3T MRI scanner. Identification of the nerves was based on T₁‐weighted, T₂‐weighted, STIR, and DTI‐derived fractional anisotropy (FA) images. Maps of the DTI‐derived indices, FA, mean diffusivity (MD), longitudinal diffusivity (λ_//), and radial diffusivity (λ_?) along the length of the nerves were generated.

Results:

DTI‐derived maps delineated the forearm nerves more clearly than images acquired with other sequences. Only ulnar and median nerves were clearly visualized on the DTI‐derived FA maps. No significant differences were observed between the left and right forearms in any of the DTI‐derived measures. Significant variation in the DTI measures was observed along the length of the nerve. Significant differences in the DTI measures were also observed between the median and ulnar nerves.

Conclusion:

DTI is superior in visualizing the median and ulnar nerves in the human forearm. The normative data could potentially help distinguish normal from diseased nerves. J. Magn. Reson. Imaging 2012;36:920–927. © 2012 Wiley Periodicals, Inc.

     

Evaluation of pressure‐driven brain infusions in nonhuman primates by intra‐operative 7 tesla MRI

Purpose:

To characterize the effects of pressure‐driven brain infusions using high field intra‐operative MRI. Understanding these effects is critical for upcoming neurodegeneration and oncology trials using convection‐enhanced delivery (CED) to achieve large drug distributions with minimal off‐target exposure.

Materials and Methods:

High‐resolution T2‐weighted and diffusion‐tensor images were acquired serially on a 7 Tesla MRI scanner during six CED infusions in nonhuman primates. The images were used to evaluate the size, distribution, diffusivity, and temporal dynamics of the infusions.

Results:

The infusion distribution had high contrast in the T2‐weighted images. Diffusion tensor images showed the infusion increased diffusivity, reduced tortuosity, and reduced anisotropy. These results suggested CED caused an increase in the extracellular space.

Conclusion:

High‐field intra‐operative MRI can be used to monitor the distribution of infusate and changes in the geometry of the brain's porous matrix. These techniques could be used to optimize the effectiveness of pressure‐driven drug delivery to the brain. J. Magn. Reson. Imaging 2012; 36:1339–1346. © 2012 Wiley Periodicals, Inc.     

Fluid and white matter suppression with the MP2RAGE sequence

Purpose:

To develop a magnetic resonance imaging (MRI) sequence (fluid and white matter suppression, FLAWS) for generating two sets of images from a single acquisition: one with contrast similar to a T1‐weighted magnetization‐prepared rapid gradient‐echo sequence (MPRAGE) for structural definition; the other with nulled white matter (WM) signal intensity, similar to the fast gray matter T1 inversion recovery (FGATIR) sequence, for improved delineation of subcortical brain structures.

Materials and Methods:

The recently proposed MP2RAGE, which is a modification of the MPRAGE and generates two image sets at different inversion times, was employed to generate the FGATIR‐like contrast (FLAWS1) and MPRAGE‐like contrast (FLAWS2). Five healthy volunteers were scanned at 3T and brain tissue contrast and contrast‐to‐noise were compared.

Results:

FLAWS1 and FLAWS2 exhibited similar tissue contrast and contrast‐to‐noise as the “reference” sequences, FGATIR and MPRAGE, respectively. Synthetic minimum value images generated from FLAWS1 and FLAWS2 provided a gray matter‐dominant image.

Conclusion:

FLAWS provides two coregistered 3D volumes, one with nulled WM signal intensity and another with nulled cerebrospinal fluid. The coregistered nature of the two datasets allows for generating images that might be helpful in segmentation algorithms and clinical diagnosis. J. Magn. Reson. Imaging 2012;35:1063‐1070. © 2011 Wiley Periodicals, Inc.     

Reproducibility and correlation between quantitative and semiquantitative dynamic and intrinsic susceptibility‐weighted MRI parameters in the benign and malignant human prostate

Purpose:

To assess the reproducibility of relaxivity‐ and susceptibility‐based dynamic contrast‐enhanced magnetic resonance imaging (MRI) in the benign and malignant prostate gland and to correlate the kinetic parameters obtained.

Materials and Methods:

Twenty patients with prostate cancer underwent paired scans before and after androgen deprivation therapy. Quantitative parametric maps for T₁‐ and T₂*‐weighted parameters were calculated (K^trans, k_ep,v_e, IAUC₆₀, rBV, rBF, and R₂*). The reproducibility of and correlation between each parameter were determined using standard methods at both timepoints.

Results:

T₁‐derived parameters are more reproducible than T₂*‐weighted measures, both becoming more variable following androgen deprivation (variance coefficients for prostate K^trans and rBF increased from 13.9%–15.8% and 42.5%–90.8%, respectively). Tumor R₂* reproducibility improved after androgen ablation (23.3%–11.8%). IAUC₆₀ correlated strongly with K^trans, v_e, and k_ep (all P < 0.001). R₂* did not correlate with other parameters.

Conclusion:

This study is the first to document the variability and repeatability of T₁‐ and T₂*‐weighted dynamic MRI and intrinsic susceptibility‐weighted MRI for the various regions of the human prostate gland before and after androgen deprivation. These data provide a valuable source of reference for groups that plan to use dynamic contrast‐enhanced MRI or intrinsic susceptibility‐weighted MRI for the assessment of treatment response in the benign or malignant prostate. J. Magn. Reson. Imaging 2010;32:155–164. © 2010 Wiley‐Liss, Inc.     

Evaluation of flow measurement from the first pass bolus T1 weighted images using inversion recovery sequence

Objective

Previous studies have shown that the organ blood flows (OBFs) calculated using the T₁ weighted MRI technique were lower than the expected values. The aim of this study was a flow measurement comparison between the theoretical and experimental flows based on the technique before and after corrections (coil non-uniformity and inflow) using a flow phantom at two different concentrations (0.8 and 1.2 mmol l^–1).

Methods

A flow phantom was designed to produce three different flow rates at the same time. Theoretical flow was calculated by measuring the volumes of the phantom and dividing them by the time taken to fill these volumes. T₁ weighted turbo fast low-angle shot images were used to measure signal intensity (SI) change during the first bolus passage of the contrast medium through the phantom using linear phase-encoding acquisition.

Results

The corrected experimental flow based on the technique shows a good agreement with the theoretical flow, where the flow rate is low at the two concentrations.

Conclusion

The T₁ weighted MRI technique after the two correction factors can be used to measure the absolute flow where the flow rate is low, such as in the capillaries. For measuring high flow rate (e.g. artery), additional correction factors should be considered.Several methods have been used for determining the haemodynamic parameters of the brain, including transcranial Doppler ultrasonography (TCD), dynamic or xenon-enhanced CT (Xe-CT), single photon emission CT (SPECT), positron emission tomography (PET) CT and MRI [1-5]. There are two main approaches to quantify the flow from contrast-enhanced data obtained using MRI, and these are the non-deconvolution or summary parameters methods and the deconvolution methods [6]. Moody et al [7] have applied a T₁ weighted MRI technique based on the microsphere technique [8] to calculate tissue blood flow to MR cerebral perfusion scanning. Organ blood flow can be calculated by measuring the gradients of the tissue signal intensity curve as a bolus of contrast agent passes through it and then dividing that value by the peak value of the arterial input function (AIF) based on the T₁ weighted MRI technique (T₁ technique).Moody et al state that measurement of the asymptomatic middle cerebral artery (MCA) territory grey matter (GM) gave an average CBF of 42.6 ml 100 g^–1/min. This value was slightly lower than the other quantitative techniques such as SPECT, PET or Xe-CT.Absolute renal blood flow measurement was reported by Vallee et al [9]. They used the T₁ weighted technique to obtain the flow from MRI. They reported the values of the cortical and the medullary perfusion, which were lower than the expected values from CT and PET.In addition, Montet et al [10] used the T₁ technique to calculate absolute renal perfusion in the rabbits in 2003. The MRI-derived perfusion was systematically lower than the expected values.Until now, all perfusion measurements from the T₁ weighted MRI technique are lower than the expected values.Therefore, some corrections should be applied on the equations, which were used for measuring absolute organ blood flow from the T₁ technique.Two common acquisition strategies in MRI are linear phase encoding and centre out phase encoding [11]. This study is based on linear phase-encoding acquisition by use of T₁ weighted turbo fast low-angle shot (turbo fast low angle shot, TurboFLASH) images with application of the non-uniformity of the coil and the inflow effect corrections to evaluate the T₁ technique.     

Simultaneous bilateral magnetic resonance imaging of the femoral arteries in peripheral arterial disease patients

Purpose:

To image the femoral arteries in peripheral arterial disease (PAD) patients using a bilateral receive coil.

Materials and Methods:

An eight‐channel surface coil array for bilateral MRI of the femoral arteries at 3T was constructed and evaluated.

Results:

The bilateral array enabled imaging of a 25‐cm segment of the superficial femoral arteries (SFA) from the profunda to the popliteal. The array provided improved the signal‐to‐noise ratio (SNR) at the periphery and similar SNR in the middle of a phantom compared to three other commercially available coils (4‐channel torso, quadrature head, whole body). Multicontrast bilateral images of the in vivo SFA with 1 mm in‐plane resolution made it possible to directly compare lesions in the index SFA to the corresponding anatomical site in the contralateral vessel without repositioning the patient or coil. A set of bilateral time‐of‐flight, T1‐weighted, T2‐weighted, and proton density‐weighted images was acquired in a clinically acceptable exam time of ≈45 minutes.

Conclusion:

The developed bilateral coil is well suited for monitoring dimensional changes in atherosclerotic lesions of the SFA. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.     

Diffusion-tensor MRI reveals the complex muscle architecture of the human forearm

Purpose:

To design a time‐efficient patient‐friendly clinical diffusion tensor MRI protocol and postprocessing tool to study the complex muscle architecture of the human forearm.

Materials and Methods:

The 15‐minute examination was done using a 3 T system and consisted of: T₁‐weighted imaging, dual echo gradient echo imaging, single‐shot spin‐echo echo‐planar imaging (EPI) diffusion tensor MRI. Postprocessing comprised of signal‐to‐noise improvement by a Rician noise suppression algorithm, image registration to correct for motion and eddy currents, and correction of susceptibility‐induced deformations using magnetic field inhomogeneity maps. Per muscle one to five regions of interest were used for fiber tractography seeding. To validate our approach, the reconstructions of individual muscles from the in vivo scans were compared to photographs of those dissected from a human cadaver forearm.

Results:

Postprocessing proved essential to allow muscle segmentation based on combined T₁‐weighted and diffusion tensor data. The protocol can be applied more generally to study human muscle architecture in other parts of the body.

Conclusion:

The proposed protocol was able to visualize the muscle architecture of the human forearm in great detail and showed excellent agreement with the dissected cadaver muscles. J. Magn. Reson. Imaging 2012;36:237–248. © 2012 Wiley Periodicals, Inc.     

Comparative study of standard space and real space analysis of quantitative MR brain data

Purpose:

To compare the robustness of region of interest (ROI) analysis of magnetic resonance imaging (MRI) brain data in real space with analysis in standard space and to test the hypothesis that standard space image analysis introduces more partial volume effect errors compared to analysis of the same dataset in real space.

Materials and Methods:

Twenty healthy adults with no history or evidence of neurological diseases were recruited; high‐resolution T₁‐weighted, quantitative T₁, and B₀ field‐map measurements were collected. Algorithms were implemented to perform analysis in real and standard space and used to apply a simple standard ROI template to quantitative T₁ datasets. Regional relaxation values and histograms for both gray and white matter tissues classes were then extracted and compared.

Results:

Regional mean T₁ values for both gray and white matter were significantly lower using real space compared to standard space analysis. Additionally, regional T₁ histograms were more compact in real space, with smaller right‐sided tails indicating lower partial volume errors compared to standard space analysis.

Conclusion:

Standard space analysis of quantitative MRI brain data introduces more partial volume effect errors biasing the analysis of quantitative data compared to analysis of the same dataset in real space. J. Magn. Reson. Imaging 2011;33:1503–1509. © 2011 Wiley‐Liss, Inc.     

T1 independent,T2* corrected MRI with accurate spectral modeling for quantification of fat: Validation in a fat‐water‐SPIO phantom

Purpose:

To validate a T₁‐independent, T₂*‐corrected fat quantification technique that uses accurate spectral modeling of fat using a homogeneous fat‐water‐SPIO phantom over physiologically expected ranges of fat percentage and T₂* decay in the presence of iron overload.

Materials and Methods:

A homogeneous gel phantom consisting of vials with known fat‐fractions and iron concentrations is described. Fat‐fraction imaging was performed using a multiecho chemical shift‐based fat‐water separation method (IDEAL), and various reconstructions were performed to determine the impact of T₂* correction and accurate spectral modeling. Conventional two‐point Dixon (in‐phase/out‐of‐phase) imaging and MR spectroscopy were performed for comparison with known fat‐fractions.

Results:

The best agreement with known fat‐fractions over the full range of iron concentrations was found when T₂* correction and accurate spectral modeling were used. Conventional two‐point Dixon imaging grossly underestimated fat‐fraction for all T₂* values, but particularly at higher iron concentrations.

Conclusion:

This work demonstrates the necessity of T₂* correction and accurate spectral modeling of fat to accurately quantify fat using MRI. J. Magn. Reson. Imaging 2009;30:1215–1222. © 2009 Wiley‐Liss, Inc.     

Gadoxetic acid-enhanced MRI findings of early hepatocellular carcinoma as defined by new histologic criteria

Purpose:

To describe the imaging features of early hepatocellular carcinoma (HCC) on gadoxetic acid‐enhanced MRI (Gd‐EOB‐MRI) in comparison with multidetector computed tomography (MDCT) examinations.

Materials and Methods:

We analyzed imaging findings of 19 pathologically proven early HCC lesions in 15 patients who underwent both MDCT and Gd‐EOB‐MRI at 3.0 Tesla (T) units before surgery. MRI included in‐phase and out‐of‐phase T1‐weighted dual‐echo gradient‐recalled‐echo sequences, dynamic T1‐weighted images before and after bolus injection of gadoxetic acid disodium, fat‐saturated T2‐weighted fast spin‐echo sequences, and T1‐weighted hepatobiliary phase images 20 min after contrast injection. Two radiologists retrospectively evaluated the signal intensities and enhancement features on MRI and MDCT.

Results:

None of the lesions displayed arterial enhancement and washout on MDCT. On Gd‐EOB‐MRI, six (32%) lesions showed T2‐hyperintensity, five (26%) lesions showed signal drop on opposed‐phase. Three lesions (16%) showed arterial enhancement and washout. Twelve (63%), 13 (68%), and 15 (79%) lesions were hypointense on hepatic venous, equilibrium, and hepatobiliary phase, respectively.

Conclusion:

Most early HCCs did not show arterial enhancement and washout pattern on both MDCT and Gd‐EOB‐MRI. Gd‐EOB‐MRI may provide several ancillary findings for diagnosis of early HCC such as decreased hepatobiliary uptake, T2 hyperintensity and signal drop in opposed phase. J. Magn. Reson. Imaging 2012;393‐398. © 2011 Wiley Periodicals, Inc.