Diffeomorphic brain mapping based on T1‐weighted images: Improvement of registration accuracy by multichannel mapping

Purpose:

To improve image registration accuracy in neurodegenerative populations.

Materials and Methods:

This study used primary progressive aphasia, aged control, and young control T1‐weighted images. Mapping to a template image was performed using single‐channel Large Deformation Diffeomorphic Metric Mapping (LDDMM), a dual‐channel method with ventricular anatomy in the second channel, and a dual‐channel with appendage method, which utilized a priori knowledge of template ventricular anatomy in the deformable atlas.

Results:

Our results indicated substantial improvement in the registration accuracy over single‐contrast‐based brain mapping, mainly in the lateral ventricles and regions surrounding them. Dual‐channel mapping significantly (P < 0.001) reduced the number of misclassified lateral ventricle voxels (based on a manually defined reference) over single‐channel mapping. The dual‐channel (w/appendage) method further reduced (P < 0.001) misclassification over the dual‐channel method, indicating that the appendage provides more accurate anatomical correspondence for deformation.

Conclusion:

Brain anatomical mapping by shape normalization is widely used for quantitative anatomical analysis. However, in many geriatric and neurodegenerative disorders, severe tissue atrophy poses a unique challenge for accurate mapping of voxels, especially around the lateral ventricles. In this study we demonstrate our ability to improve mapping accuracy by incorporating ventricular anatomy in LDDMM and by utilizing a priori knowledge of ventricular anatomy in the deformable atlas. J. Magn. Reson. Imaging 2013;37:76–84. © 2012 Wiley Periodicals, Inc.     

A novel MRI-compatible brain ventricle phantom for validation of segmentation and volumetry methods

Purpose:

To create a standardized, MRI‐compatible, life‐sized phantom of the brain ventricles to evaluate ventricle segmentation methods using T₁‐weighted MRI. An objective phantom is needed to test the many different segmentation programs currently used to measure ventricle volumes in patients with Alzheimer's disease.

Materials and Methods:

A ventricle model was constructed from polycarbonate using a digital mesh of the ventricles created from the 3 Tesla (T) MRI of a subject with Alzheimer's disease. The ventricle was placed in a brain mold and surrounded with material composed of 2% agar in water, 0.01% NaCl and 0.0375 mM gadopentetate dimeglumine to match the signal intensity properties of brain tissue in 3T T₁‐weighted MRI. The 3T T₁‐weighted images of the phantom were acquired and ventricle segmentation software was used to measure ventricle volume.

Results:

The images acquired of the phantom successfully replicated in vivo signal intensity differences between the ventricle and surrounding tissue in T₁‐weighted images and were robust to segmentation. The ventricle volume was quantified to 99% accuracy at 1‐mm voxel size.

Conclusion:

The phantom represents a simple, realistic and objective method to test the accuracy of lateral ventricle segmentation methods and we project it can be extended to other anatomical structures. J. Magn. Reson. Imaging 2012;36:476–482. © 2012 Wiley Periodicals, Inc.     

A population‐specific symmetric phase model to automatically analyze susceptibility‐weighted imaging (SWI) phase shifts and phase symmetry in the human brain

Purpose:

To create a population‐specific symmetric phase model and to evaluate the susceptibility‐weighted imaging (SWI) phase in terms of phase shift using different segmentation methods (manual and automatic) and phase shift symmetry, which is expected as a marker for lateralized Parkinson's disease (PD) symptoms.

Materials and Methods:

SWI and T₁‐weighted data from 25 PD patients and five healthy controls were acquired on a 3T MRI system. A population‐specific, symmetric phase model was developed. Regions of interest (ROIs) were defined manually on the phase model, manually on each individual data set, and automatically using model‐based segmentation (MBS). Manually‐ and MBS‐defined ROIs were compared using kappa values, and left‐right phase symmetry was evaluated using correlation analysis.

Results:

Independent of the analysis method, a phase increase from the anterior to the posterior putamen, and the average phase value relationship substantia nigra > globus pallidus > red nucleus was found. Phase symmetry analysis shows a difference between lateralized and symmetric PD.

Conclusion:

The symmetric phase model helps to analyze phase data with similar accuracy, but a greatly reduced tracing effort compared to individual tracing and also allows evaluating left‐right phase symmetries. J. Magn. Reson. Imaging 2010;31:215–220. © 2009 Wiley‐Liss, 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.     

Inter- and intraobserver variability in the evaluation of dynamic breast cancer MRI

Purpose

To quantify variations within and between observers ascribable to manual region of interest (ROI) placement in patients with breast cancer undergoing dynamic MRI.

Materials and Methods

Expert and nonexpert observers independently outlined tumor ROIs on 30 dynamic T₁‐weighted (T₁W) MRI scans on five occasions over two months. Lesion size (number of pixels) and kinetic parameter estimates, including the transfer constant (K^trans), were calculated for each ROI placement. Inter‐ and intraobserver variability was assessed with respect to the interval between drawings, lesion morphology, and observer experience.

Results

For the nonexpert, the variability reduced with decreasing time intervals between ROI drawings (the coefficient of variance (wCV) values at two months, two weeks, one day, and same‐day time intervals were respectively 11.6%, 10.7%, 4.8%, and 2.6% for lesion size, and 8.9%, 9.7%, 6.7%, and 3.2% for K^trans). For the expert observer, the variability was smaller overall and more constant, but improved for same‐day ROI placements (region size wCV: 7.5%, 6.2%, 7.1%, and 3.7%; K^trans wCV: 5.4%, 5.3%, 5.6%, and 4.5%).

Conclusion

Significant observer variability in manual ROI placement occurs in dynamic MRI of breast cancer. For serial patient studies, ROI placements should be outlined at the same sitting to minimize observer error. J. Magn. Reson. Imaging 2006. © 2006 Wiley‐Liss, Inc.

     

Improved fat suppression using multipeak reconstruction for IDEAL chemical shift fat‐water separation: Application with fast spin echo imaging

Purpose

To evaluate and quantify improvements in the quality of fat suppression for fast spin‐echo imaging of the knee using multipeak fat spectral modeling and IDEAL fat‐water separation.

Materials and Methods

T₁‐weighted and T₂‐weighted fast spin‐echo sequences with IDEAL fat‐water separation and two frequency‐selective fat‐saturation methods (fat‐selective saturation and fat‐selective partial inversion) were performed on 10 knees of five asymptomatic volunteers. The IDEAL images were reconstructed using a conventional single‐peak method and precalibrated and self‐calibrated multipeak methods that more accurately model the NMR spectrum of fat. The signal‐to‐noise ratio (SNR) was measured in various tissues for all sequences. Student t‐tests were used to compare SNR values.

Results

Precalibrated and self‐calibrated multipeak IDEAL had significantly greater suppression of signal (P < 0.05) within subcutaneous fat and bone marrow than fat‐selective saturation, fat‐selective partial inversion, and single‐peak IDEAL for both T₁‐weighted and T₂‐weighted fast spin‐echo sequences. For T₁‐weighted fast spin‐echo sequences, the improvement in the suppression of signal within subcutaneous fat and bone marrow for multipeak IDEAL ranged between 65% when compared to fat‐selective partial inversion to 86% when compared to fat‐selectivesaturation. For T2‐weighted fast spin‐echo sequences, the improvement for multipeak IDEAL ranged between 21% when compared to fat‐selective partial inversion to 81% when compared to fat‐selective saturation.

Conclusion

Multipeak IDEAL fat‐water separation provides improved fat suppression for T₁‐weighted and T₂‐weighted fast spin‐echo imaging of the knee when compared to single‐peak IDEAL and two widely used frequency‐selected fat‐saturation methods. J. Magn. Reson. Imaging 2009;29:436–442. © 2009 Wiley‐Liss, Inc.     

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.

     

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.     

T2‐weighted 3D fast spin echo imaging with water–fat separation in a single acquisition

Purpose:

To develop a robust 3D fast spin echo (FSE) T₂‐weighted imaging method with uniform water and fat separation in a single acquisition, amenable to high‐quality multiplanar reformations.

Materials and Methods:

The Iterative Decomposition of water and fat with Echo Asymmetry and Least squares estimation (IDEAL) method was integrated with modulated refocusing flip angle 3D‐FSE. Echoes required for IDEAL processing were acquired by shifting the readout gradient with respect to the Carr‐Purcell‐Meiboom‐Gill echo. To reduce the scan time, an alternative data acquisition using two gradient echoes per repetition was implemented. Using the latter approach, a total of four gradient echoes were acquired in two repetitions and used in the modified IDEAL reconstruction.

Results:

3D‐FSE T₂‐weighted images with uniform water–fat separation were successfully acquired in various anatomies including breast, abdomen, knee, and ankle in clinically feasible scan times, ranging from 5:30–8:30 minutes. Using water‐only and fat‐only images, in‐phase and out‐of‐phase images were reconstructed.

Conclusion:

3D‐FSE‐IDEAL provides volumetric T₂‐weighted images with uniform water and fat separation in a single acquisition. High‐resolution images with multiple contrasts can be reformatted to any orientation from a single acquisition. This could potentially replace 2D‐FSE acquisitions with and without fat suppression and in multiple planes, thus improving overall imaging efficiency. J. Magn. Reson. Imaging 2010;32:745–751. © 2010 Wiley‐Liss, Inc.     

Loss of fine structure and edge sharpness in fast-spin-echo carotid wall imaging: measurements and comparison with multiple-spin-echo in normal and atherosclerotic subjects

Purpose:

To test whether the k‐space acquisition strategy used by fast‐spin‐echo (FSE) is a major source of blurring in carotid wall and plaque imaging, and investigate an alternative acquisition approach.

Materials and Methods:

The effect of echo train length (ETL) and T₂ on the amount of blurring was studied in FSE simulations of vessel images. Edge sharpness was measured in black‐blood T₁ and proton‐density weighted (T₁W and PDW) carotid images acquired from 5 normal volunteers and 19 asymptomatic patients using both FSE and multiple‐spin‐echo (Multi‐SE) sequences at 3 Tesla. Plaque images were classified and divided in group α (tissues' average T₂ ～40–70 ms) and group β (plaque components with shorter T₂).

Results:

Simulations predicted 26.9% reduction of vessel edge sharpness from Multi‐SE to FSE images (ETL = 9, T₂ = 60 ms). This agreed with in vivo measurements in normal volunteers (27.4%) and in patient group α (26.2%), while in group β the loss was higher (31.6%).

Conclusion:

FSE significantly reduced vessel edge sharpness along the phase‐encoding direction in T₁W and PDW images. Blurring was stronger in the presence of plaque components with short T₂ times. This study shows a limitation of FSE and the potential of Multi‐SE to improve the quality of carotid imaging. J. Magn. Reson. Imaging 2011;33:1136–1143. © 2011 Wiley‐Liss, Inc.     

Early marker for Alzheimer's disease: Hippocampus T1rho (T1ρ) estimation

Purpose

To evaluate the T1rho (T_1ρ) MRI relaxation time in hippocampus in the brain of Alzheimer's disease (AD), mild cognitive impairment (MCI), and control, and to determine whether the T_1ρ shows any significant difference between these cohorts.

Materials and Methods

With informed consent, AD (n = 49), MCI (n = 48), and age‐matched control (n = 31) underwent T_1ρ MRI on a Siemens 1.5T Scanner. T_1ρ values were automatically calculated from the left and right hippocampus region using in‐house developed software. Bonferroni post‐hoc multiple comparisons was performed to compare the T_1ρ value among the different cohorts.

Results

Significantly higher T_1ρ values were observed both in AD (P = 0.000) and MCI (P = 0.037) cohorts compared to control; also, the T_1ρ in AD was significantly high over (P = 0.032) MCI. Hippocampus T_1ρ was 13% greater in the AD patients than control, while in MCI it was 7% greater than control. Hippocampus T_1ρ in AD patients was 6% greater than MCI.

Conclusion

Higher hippocampus T_1ρ values in the AD patients might be associated with the increased plaques burden. A follow‐up study would help to determine the efficacy of T_1ρ values as a predictor of developing AD in the control and MCI individuals. J. Magn. Reson. Imaging 2009;29:1008–1012. © 2009 Wiley‐Liss, Inc.     

MR angiography of the cerebral perforating arteries with magnetization prepared anatomical reference at 7T: Comparison with time‐of‐flight

Purpose

To develop a magnetic resonance imaging (MRI) protocol that visualizes both the perforating arteries and the related anatomy in a single acquisition at 7T.

Material and Methods

T₁‐weighted magnetization prepared imaging (MPRAGE) was empirically modified for use as angiography method at 7T. The resulting sequence depicts the vasculature simultaneously with the surrounding anatomical structures, and is referred to as “magnetization prepared anatomical reference MRA” (MPARE‐MRA). The method was compared to time‐of‐flight (TOF) MRA in seven healthy subjects. The conspicuity of the perforating arteries and the contrast between gray and white matter were evaluated both quantitatively by contrast‐to‐noise (CNR) measurements, and qualitatively by two radiologists who scored the images.

Results

The contrast‐to‐noise ratio (CNR) between blood and background was 28 ± 9 for MPARE‐MRA and 35 ± 16 for TOF‐MRA, indicating good conspicuity of the vessels. CNR values were: internal capsule (IC) vs. caudate head (CH): 4.2 ± 0.7; IC vs. putamen: 3.5 ± 0.6; white matter vs. gray matter: 9.7 ± 2.5.

Conclusion

The benefits of ultra‐high‐field MRI can transform MPRAGE into a new angiography method to image small vessels and associated parenchyma at the same time. This technique can be used to study the correlation between tissue damage and vascular pathology. J. Magn. Reson. Imaging 2008;28:1519–1526. © 2008 Wiley‐Liss, Inc.     

T(2) -weighted STIR imaging of myocardial edema associated with ischemia-reperfusion injury: the influence of proton density effect on image contrast

Purpose

To investigate the contribution of proton density (PD) in T₂‐STIR based edema imaging in the setting of acute myocardial infarction (AMI).

Materials and Methods

Canines (n = 5), subjected to full occlusion of the left anterior descending artery for 3 hours, underwent serial magnetic resonance imaging (MRI) studies 2 hours postreperfusion (day 0) and on day 2. During each study, T₁ and T₂ maps, STIR (TE = 7.1 msec and 64 msec) and late gadolinium enhancement (LGE) images were acquired. Using T₁ and T₂ maps, relaxation and PD contributions to myocardial edema contrast (EC) in STIR images at both TEs were calculated.

Results

Edematous territories showed significant increase in PD (20.3 ± 14.3%, P < 0.05) relative to healthy territories. The contributions of T₁ changes and T₂ or PD changes toward EC were in opposite directions. One‐tailed t‐test confirmed that the mean T₂ and PD‐based EC at both TEs were greater than zero. EC from STIR images at TE = 7.1 msec was dominated by PD than T₂ effects (94.3 ± 11.3% vs. 17.6 ± 2.5%, P < 0.05), while at TE = 64 msec, T₂ effects were significantly greater than PD effects (90.8 ± 20.3% vs. 12.5 ± 11.9%, P < 0.05). The contribution from PD in standard STIR acquisitions (TE = 64 msec) was significantly higher than 0 (P < 0.05).

Conclusion

In addition to T₂‐weighting, edema detection in the setting of AMI with T₂‐weighted STIR imaging has a substantial contribution from PD changes, likely stemming from increased free‐water content within the affected tissue. This suggests that imaging approaches that take advantage of both PD as well as T₂ effects may provide the optimal sensitivity for detecting myocardial edema. J. Magn. Reson. Imaging 2011;33:962–967. © 2011 Wiley‐Liss, Inc.     

T(1) independent, T(2) (*) corrected chemical shift based fat-water separation with multi-peak fat spectral modeling is an accurate and precise measure of hepatic steatosis

Purpose:

To determine the precision and accuracy of hepatic fat‐fraction measured with a chemical shift‐based MRI fat‐water separation method, using single‐voxel MR spectroscopy (MRS) as a reference standard.

Materials and Methods:

In 42 patients, two repeated measurements were made using a T₁‐independent, T‐corrected chemical shift‐based fat‐water separation method with multi‐peak spectral modeling of fat, and T₂‐corrected single voxel MR spectroscopy. Precision was assessed through calculation of Bland‐Altman plots and concordance correlation intervals. Accuracy was assessed through linear regression between MRI and MRS. Sensitivity and specificity of MRI fat‐fractions for diagnosis of steatosis using MRS as a reference standard were also calculated.

Results:

Statistical analysis demonstrated excellent precision of MRI and MRS fat‐fractions, indicated by 95% confidence intervals (units of absolute percent) of [?2.66%,2.64%] for single MRI ROI measurements, [?0.81%,0.80%] for averaged MRI ROI, and [?2.70%,2.87%] for single‐voxel MRS. Linear regression between MRI and MRS indicated that the MRI method is highly accurate. Sensitivity and specificity for detection of steatosis using averaged MRI ROI were 100% and 94%, respectively. The relationship between hepatic fat‐fraction and body mass index was examined.

Conclusion:

Fat‐fraction measured with T₁‐independent T‐corrected MRI and multi‐peak spectral modeling of fat is a highly precise and accurate method of quantifying hepatic steatosis. J. Magn. Reson. Imaging 2011;33:873–881. © 2011 Wiley‐Liss, Inc.

     

Feasibility study of exploring a T₁-weighted dynamic contrast-enhanced MR approach for brain perfusion imaging

Purpose:

To investigate the feasibility of T₁‐weighted dynamic contrast‐enhanced (DCE) MRI for the measurement of brain perfusion.

Materials and Methods:

Dynamic imaging was performed on a 3.0 Tesla (T) MR scanner by using a rapid spoiled‐GRE protocol. T₁ measurement with driven equilibrium single pulse observation of T₁ (DESPOT1) was used to convert the MR signal to tracer concentration. Cerebral perfusion maps were obtained by using an improved gamma‐variate model in 10 subjects and compared with those with arterial spin label (ASL) approach.

Results:

The cerebral blood volume (CBV) values were calculated as 4.74 ± 1.09 and 2.29 ± 0.58 mL/100 g in gray matter (GM) and whiter matter (WM), respectively. Mean transit time (MTT) values were 6.15 ± 0.59 s in GM and 6.96 ± 0.79 s in WM. The DCE values for GM/WM cerebral blood flow (CBF) were measured as 53.41 ± 9.23 / 25.78 ± 8.91 mL/100 g/min, versus ASL values of 49.05 ± 10.81 / 23.00 ± 5.89 mL/100 g/min for GW/WM. Bland‐Altman plot revealed a small difference of CBF between two approaches (mean bias = 3.83 mL/100 g/min, SD = 11.29). There were 6 pairs of samples (5%, 6/120) beyond the 95% limits of agreement. The correlation plots showed that the slop of Y (CBF__DCE) versus X intercept (CBF__ASL) is 0.95 with the intercept of 4.53 mL/100 g/min (r = 0.74; P < 0.05).

Conclusion:

It is feasible to evaluate the cerebral perfusion by using T₁‐weighted DCE‐MRI with the improved kinetic model. J. Magn. Reson. Imaging 2012;35:1322–1331. © 2012 Wiley Periodicals, Inc.     

MR‐diffusion weighted imaging of healthy liver parenchyma: Repeatability and reproducibility of apparent diffusion coefficient measurement

Purpose:

To compare repeatability and reproducibility of four different methods of apparent diffusion coefficient (ADC) evaluation of liver parenchyma. In fact, repeatability and reproducibility assessment is mandatory in quantitative evaluations, however, these have not been accurately investigated in liver MR‐diffusion‐weighted studies.

Materials and Methods:

Diffusion‐weighted sequences, b‐value = 0–1000 s/mm², were acquired on 30 healthy volunteers by a 1.5T scanner whose reliability has been validated by a phantom study. Four sampling methods, evaluating various parenchyma percentages by different‐sized region‐of‐interests (ROIs), were compared by two observers: 70% and 30% of the volume, 4%‐one‐ROI‐per‐segment, and 4%‐one‐ROI‐per‐slice in the right‐lobe. Ninety‐five percent limits of agreement and intraclass correlation coefficient (ICC) were calculated.

Results:

Complete measurements on the left lobe could be obtained in less than half of patients. The 4%‐one‐ROI‐per‐slice and 4%‐one‐ROI‐per‐segment yielded lower mean values compared with 30–70% volume methods (1343–1373 versus 1463–1560·10^?6 mm²/s, respectively). Repeatability was acceptable (ICCs ～ 0.80) whereas reproducibility was low (ICCs ≤ 0.45) for all methods. Averaging at least 3 measurements in middle‐lower sections of the right lobe improved both repeatability (ICCs to ≥0.87) and reproducibility (ICCs to 0.82) for 30–70% V methods.

Conclusion:

ADC measurements were repeatable but not reproducible in our study. Reproducibility could be improved by taking averages on the right lobe with large ROI methods. Studies on procedures that standardize ADC measurements using more than two observers are needed. J. Magn. Reson. Imaging 2010;31:912–920. ©2010 Wiley‐Liss, 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.     

In vivo assessment of age-related brain iron differences by magnetic field correlation imaging

Purpose:

To assess a recently developed magnetic resonance imaging (MRI) technique called magnetic field correlation (MFC) imaging along with a conventional imaging method, the transverse relaxation rate (R2), for estimating age‐related brain iron concentration in adolescents and adults. Brain region measures were compared with nonheme iron concentrations (C_PM) based on a prior postmortem study.

Materials and Methods:

Asymmetric spin echo (ASE) images were acquired at 3T from 26 healthy individuals (16 adolescents, 10 adults). Regions of interest (ROIs) were placed in areas in which age‐related iron content was estimated postmortem: globus pallidus (GP), putamen (PUT), caudate nucleus (CN), thalamus (THL), and frontal white matter (FWM). Regression and group analyses were conducted on ROI means.

Results:

MFC and R2 displayed significant linear relationships to C_PM when all regions were combined. Whereas MFC was significantly correlated with C_PM for every individual region except FWM and detected significantly lower means in adolescents than adults for each region, R2 detected significant correlation and lower means for only PUT and CN.

Conclusion:

Our results support the hypothesis that MFC is sensitive to brain iron in GM regions and detects age‐related iron increases known to occur from adolescence to adulthood. MFC may be more sensitive than R2 to iron‐related changes occurring within specific brain regions. J. Magn. Reson. Imaging 2012;36:322–331. © 2012 Wiley Periodicals, Inc.     

MRI of late microstructural and metabolic alterations in radiation‐induced brain injuries

Purpose

To evaluate the late effects of radiation‐induced damages in the rat brain by means of in vivo multiparametric MRI.

Materials and Methods

The right hemibrains of seven Sprague‐Dawley rats were irradiated with a highly collimated 6 MV photon beam at a single dose of approximately 28 Gy. Diffusion tensor imaging (DTI), proton MR spectroscopy (¹H‐MRS), T2‐weighted imaging, and T1‐weighted imaging were performed to the same animals 12 months after radiation treatment.

Results

Compared with the contralateral side, a significantly higher percentage decrease in fractional anisotropy was observed in the ipsilateral fimbria of hippocampus (29%) than the external capsule (8%) in DTI, indicating the selective vulnerability of fimbria to radiation treatment. Furthermore, in ¹H‐MRS, significantly higher choline, glutamate, lactate, and taurine peaks by 24%, 25%, 87%, and 58%, respectively, were observed relative to creatine in the ipsilateral brain. Postmortem histology confirmed these white matter degradations as well as glial fibrillary acidic protein and glutamine synthetase immunoreactivity increase in the ipsilateral brain.

Conclusion

The microstructural and metabolic changes in late radiation‐induced brain injuries were documented in vivo. These multiparametric MRI measurements may help understand the white matter changes and neurotoxicity upon radiation treatment in a single setting. J. Magn. Reson. Imaging 2009;29:1013–1020. © 2009 Wiley‐Liss, Inc.     

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.