Neuroimaging, behavioral, and psychological sequelae of repetitive combined blast/impact mild traumatic brain injury in Iraq and Afghanistan war veterans

Abstract Whether persisting cognitive complaints and postconcussive symptoms (PCS) reported by Iraq and Afghanistan war veterans with blast- and/or combined blast/impact-related mild traumatic brain injuries (mTBIs) are associated with enduring structural and/or functional brain abnormalities versus comorbid depression or posttraumatic stress disorder (PTSD) remains unclear. We sought to characterize relationships among these variables in a convenience sample of Iraq and Afghanistan-deployed veterans with (n=34) and without (n=18) a history of one or more combined blast/impact-related mTBIs. Participants underwent magnetic resonance imaging of fractional anisotropy (FA) and macromolecular proton fraction (MPF) to assess brain white matter (WM) integrity; [(18)F]-fluorodeoxyglucose positron emission tomography imaging of cerebral glucose metabolism (CMRglu); structured clinical assessments of blast exposure, psychiatric diagnoses, and PTSD symptoms; neurologic evaluations; and self-report scales of PCS, combat exposure, depression, sleep quality, and alcohol use. Veterans with versus without blast/impact-mTBIs exhibited reduced FA in the corpus callosum; reduced MPF values in subgyral, longitudinal, and cortical/subcortical WM tracts and gray matter (GM)/WM border regions (with a possible threshold effect beginning at 20 blast-mTBIs); reduced CMRglu in parietal, somatosensory, and visual cortices; and higher scores on measures of PCS, PTSD, combat exposure, depression, sleep disturbance, and alcohol use. Neuroimaging metrics did not differ between participants with versus without PTSD. Iraq and Afghanistan veterans with one or more blast-related mTBIs exhibit abnormalities of brain WM structural integrity and macromolecular organization and CMRglu that are not related to comorbid PTSD. These findings are congruent with recent neuropathological evidence of chronic brain injury in this cohort of veterans.

Magnetic Resonance Imaging Tracking of Graft Survival in the Infarcted Heart: Iron Oxide Particles Versus Ferritin Overexpression Approach

The main objective of cell therapy is the regeneration of damaged tissues. To distinguish graft from host tissue by magnetic resonance imaging (MRI), a paramagnetic label must be introduced to cells prior to transplantation. The paramagnetic label can be either exogenous iron oxide nanoparticles or a genetic overexpression of ferritin, an endogenous iron storage protein. The purpose of this work was to compare the efficacy of these 2 methods for MRI evaluation of engrafted cell survival in the infarcted mouse heart. Mouse skeletal myoblasts were labeled either by cocultivation with iron oxide particles or by engineering them to overexpress ferritin. Along with live cell transplantation, 2 other groups of mice were injected with dead-labeled cells. Both particle-labeled and ferritin-tagged grafts were detected as areas of MRI signal hypointensity in the left ventricle of the mouse heart using T2*-weighted sequences, although the signal attenuation decreased with ferritin tagging. Importantly, live cells could not be distinguished from dead cells when labeled with iron oxide particles, whereas the ferritin tagging was detected only in live grafts, thereby allowing identification of viable grafts using MRI. Thus, iron oxide particles can provide information about initial cell injection success but cannot assess graft viability. On the other hand, genetically based cell tagging, such as ferritin overexpression, despite having lower signal intensity in comparison with iron oxide particles, is able to identify live transplanted cells.

Quantification of MRI signal of transgenic grafts overexpressing ferritin in murine myocardial infarcts

The noninvasive detection of transplanted cells in damaged organs and the longitudinal follow-up of cell fate and graft size are important for the evaluation of cell therapy. We have shown previously that the overexpression of the natural iron storage protein, ferritin, permits the detection of engrafted cells in mouse heart by MRI, but further imaging optimization is required. Here, we report a systematic evaluation of ferritin-based stem cell imaging in infarcted mouse hearts in vivo using three cardiac-gated pulse sequences in a 3-T scanner: black-blood proton-density-weighted turbo spin echo (PD TSE BB), bright-blood T(2) -weighted gradient echo (GRE) and black-blood T(2) -weighted GRE with improved motion-sensitized-driven equilibrium (iMSDE) preparation. Transgenic C2C12 myoblast grafts overexpressing ferritin did not change MRI contrast in the PD TSE BB images, but showed a 20% reduction in signal intensity ratio in black-blood T(2) -weighted iMSDE (p < 0.05) and a 30% reduction in bright-blood T(2) -weighted GRE (p < 0.0001). Graft size measurements by T(2) iMSDE and T(2) GRE were highly correlated with histological assessments (r = 0.79 and r = 0.89, respectively). Unlabeled wild-type C2C12 cells transplanted to mouse heart did not change the MRI signal intensity, although endogenous hemosiderin was seen in some infarcts. These data support the use of ferritin to track the survival, growth and migration of stem cells transplanted into the injured heart.

Fast macromolecular proton fraction mapping from a single off-resonance magnetization transfer measurement

A new method was developed for fast quantitative mapping of the macromolecular proton fraction defined within the two-pool model of magnetization transfer. The method utilizes a single image with off-resonance saturation, a reference image for data normalization, and T(1), B(0), and B(1) maps with the total acquisition time ~10 min for whole-brain imaging. Macromolecular proton fraction maps are reconstructed by iterative solution of the matrix pulsed magnetization transfer equation with constrained values of other model parameters. Theoretical error model describing the variance due to noise and the bias due to deviations of constrained parameters from their actual values was formulated based on error propagation rules. The method was validated by comparison with the conventional multiparameter multipoint fit of the pulsed magnetization transfer model based on data from two healthy subjects and two multiple sclerosis patients. It was demonstrated theoretically and experimentally that accuracy of the method depends on the offset frequency and flip angle of the saturation pulse, and optimal ranges of these parameters are 4-7 kHz and 600°-900°, respectively. At optimal sampling conditions, the single-point method enables <10% relative macromolecular proton fraction errors. Comparison with the multiparameter fitting method revealed very good agreement with no significant bias and limits of agreement around ± 0.7%.

Simultaneous variable flip angle-actual flip angle imaging method for improved accuracy and precision of three-dimensional T1 and B1 measurements

A new time-efficient and accurate technique for simultaneous mapping of T(1) and B(1) is proposed based on a combination of the actual flip angle (FA) imaging and variable FA methods. Variable FA-actual FA imaging utilizes a single actual FA imaging and one or more spoiled gradient-echo acquisitions with a simultaneous nonlinear fitting procedure to yield accurate T(1)/B(1) maps. The advantage of variable FA-actual FA imaging is high accuracy at either short T(1) times or long repetition times in the actual FA imaging sequence. Simulations show this method is accurate to 0.03% in FA and 0.07% in T(1) for ratios of repetition time to T1 time over the range of 0.01-0.45. We show for the case of brain imaging that it is sufficient to use only one small FA spoiled gradient-echo acquisition, which results in reduced spoiling requirements and a significant scan time reduction compared to the original variable FA method. In vivo validation yielded high-quality 3D T(1) maps and T(1) measurements within 10% of previously published values and within a clinically acceptable scan time. The variable FA-actual FA imaging method will increase the accuracy and clinical feasibility of many quantitative MRI methods requiring T(1)/B(1) mapping such as dynamic contrast enhanced perfusion and quantitative magnetization transfer imaging.

Fast bound pool fraction imaging of the in vivo rat brain: association with myelin content and validation in the C6 glioma model

Cross-relaxation imaging (CRI) is a quantitative magnetic resonance technique that measures the kinetic parameters of magnetization transfer between protons bound to water and protons bound to macromolecules. In this study, in vivo, four-parameter CRI of normal rat brains (N=5) at 3.0 T was first directly compared to histology. The bound pool fraction, f, was strongly associated with myelin density (Pearson's r=0.99, p<0.001). The correlation persisted in separate analyses of gray matter (GM; r=0.89, p=0.046) and white matter (WM; r=0.97, p=0.029). Subsequently, a new time-efficient approach for solely capturing the whole-brain parametric map of f was proposed, validated with histology, and used to estimate myelin density. Since the described approach for the rapid acquisition of f applied constraints to other CRI parameters, a theoretical analysis of error was performed. Estimates of f in normal and pathologic tissue were expected to have <10% error. A comparison of values for f obtained from the traditional four-parameter fit of CRI data versus the proposed rapid acquisition of f was within this expected margin for in vivo rat brain gliomas (N=4; mean±SE; 3.9±0.2% vs. 4.0±0.2%, respectively). In both whole-brain f maps and myelin density maps, replacement of normal GM and WM by proliferating and invading tumor cells could be readily identified. The rapid, whole-brain acquisition of the bound pool fraction may provide a reliable method for detection of glioma invasion in both GM and WM during animal and human imaging.

Efficient flow suppressed MRI improves interscan reproducibility of carotid atherosclerosis plaque burden measurements

PURPOSE

To determine if better flow suppression can meaningfully improve the reproducibility of measurements associated with carotid atherosclerotic disease, particularly for lumen and wall areas.

MATERIALS AND METHODS

Eighteen subjects with carotid artery stenosis identified by duplex ultrasound (11 with 16%-49% stenosis; 7 with 50%-79% stenosis) underwent two carotid magnetic resonance imaging (MRI) examinations on a 3T scanner with a 4-channel phased array coil. High-resolution intermediate-weighted TSE (TR/TE = 4000/8.5 msec, 0.55 mm in-plane resolution, 2 mm slice thickness, 16 slices, 3-minute scan time) with two different flow-suppression techniques (multislice double inversion recovery [mDIR] and motion-sensitized driven-equilibrium [MSDE]) were obtained separately. For each subject, bilateral arteries were reviewed. One radiologist blinded to timepoints, flow suppression techniques, and clinical information measured the arterial lumen area, wall area, and total vessel wall area.

RESULTS

Compared to mDIR, the MSDE technique had a smaller interscan standard deviation (SD) in lumen (SD: 3.6 vs. 5.2 mm(2), P = 0.02), wall area measurements (SD: 4.5 vs. 6.4 mm(2), P = 0.02), and a trend towards smaller SD in total vessel area measurement (SD: 4.4 vs. 4.9 mm(2), P = 0.07).

CONCLUSION

The results from this study demonstrate that vessel wall imaging could quantify atherosclerotic plaque measurements more reliably with an improved blood suppression technique. This relationship between flow-suppression efficiency and reproducibility of plaque measurements is important, as more reliable area measurements will be useful in clinical diagnosis and in serial MRI studies that monitor carotid atherosclerotic lesion progression and regression.

Carotid plaque assessment using fast 3D isotropic resolution black-blood MRI

Black-blood MRI is a promising tool for carotid atherosclerotic plaque burden assessment and compositional analysis. However, current sequences are limited by large slice thickness. Accuracy of measurement can be improved by moving to isotropic imaging but can be challenging for patient compliance due to long scan times. We present a fast isotropic high spatial resolution (0.7×0.7×0.7 mm3) three-dimensional black-blood sequence (3D-MERGE) covering the entire cervical carotid arteries within 2 min thus ensuring patient compliance and diagnostic image quality. The sequence is optimized for vessel wall imaging of the carotid bifurcation based on its signal properties. The optimized sequence is validated on patients with significant carotid plaque. Quantitative plaque morphology measurements and signal-to-noise ratio measures show that 3D-MERGE provides good blood suppression and comparable plaque burden measurements to existing MRI protocols. 3D-MERGE is a promising new tool for fast and accurate plaque burden assessment in patients with atherosclerotic plaque.

Enhanced image quality in black-blood MRI using the improved motion-sensitized driven-equilibrium (iMSDE) sequence

PURPOSE

To propose an improved motion-sensitized driven-equilibrium (iMSDE) pulse sequence to enhance the tissue signal-to-noise ratio (SNR) while maintaining the same flow suppression capability in black-blood carotid artery magnetic resonance imaging (MRI).

MATERIALS AND METHODS

Compared to the traditional MSDE sequence, the iMSDE sequence uses an extra refocusing pulse and two extra gradients to achieve SNR improvement. Computer simulation and phantom studies were used to evaluate both eddy currents and local B(1) inhomogeneity effects on SNR behaviors on both MSDE and iMSDE images. To further assess the SNR improvements brought by iMSDE in vivo, five healthy volunteers were also scanned with both sequences. The paired t-test was used for statistical comparison.

RESULTS

Both simulations and phantom studies demonstrated that eddy currents and local B(1) inhomogeneity will cause image SNR reduction in the MSDE sequence, and that these factors can be partially compensated for with the iMSDE sequence. In vivo comparison showed that the iMSDE sequence significantly improved the tissue-lumen contrast-to-noise ratio (CNR) and static tissue SNR (P < 0.001 for both), while maintaining low lumen SNR in carotid MRI.

CONCLUSION

Compared to the traditional MSDE sequence, the iMSDE sequence can achieve improved soft-tissue SNR and CNR in carotid artery MRI without sacrificing flow suppression capability and time efficiency.

MR carotid plaque imaging and contrast-enhanced MR angiography identifies lesions associated with recent ipsilateral thromboembolic symptoms: an in vivo study at 3T

BACKGROUND AND PURPOSE

Recent research has suggested the importance of plaque composition to identify patients at risk for stroke. This study aims to identify specific plaque features on 3T carotid MR imaging and CE-MRA associated with recent carotid thromboembolic symptoms in patients with mild/moderate versus severe stenosis.

MATERIALS AND METHODS

Ninety-seven consecutive patients (symptomatic, 13; asymptomatic, 84) with 50%-99% stenosis by sonography or CT angiography underwent carotid plaque imaging combined with MRA at 3T. The symptomatic carotid artery or the most stenotic asymptomatic carotid artery was chosen as the index vessel to be analyzed. Plaque features were compared by symptomatic status in patients with mild/moderate (30%-70%) versus severe (70%-99%) stenosis on MRA.

RESULTS

Ninety (92.8%) patients had sufficient image quality for interpretation. In 50 patients with mild/moderate stenosis, there were significant associations between the presence of the following plaque characteristics and symptoms: thin/ruptured fibrous cap (100% versus 36%, P = .006) and lipid-rich necrotic core (100% versus 39%, P = .022), with marginal association with hemorrhage (86% versus 33%, P = .055). In 40 patients with severe stenosis, only the angiographic presence of ulceration (86% versus 36%, P = .039) was associated with symptoms.

CONCLUSIONS

Several plaque components identified on 3T MR imaging are correlated with recent ipsilateral carotid thromboembolic symptoms. These preliminary results also suggest that associations between plaque characteristics and symptom history may vary by degree of stenosis. If confirmed in larger studies, carotid MR imaging may distinguish stable from unstable lesions, particularly in individuals with mild/moderate stenosis in whom the role of surgical intervention is currently unclear.

Arterial remodeling in [corrected] subclinical carotid artery disease

OBJECTIVES

We sought to identify clinical and/or plaque characteristics that affect atherosclerotic disease progression and arterial remodeling in the carotid artery with subclinical stenosis.

BACKGROUND

Increasing severity of stenosis has been associated with a higher risk of stroke. Factors that drive subclinical lesions to become stenotic plaques remain ambiguous. Carotid magnetic resonance imaging (MRI) has been validated with histology to accurately quantify in vivo arterial morphology and plaque composition.

METHODS

A total of 67 asymptomatic participants with 16% to 49% carotid stenosis as demonstrated by duplex ultrasonography were imaged at 1.5-T with a carotid MRI protocol at baseline and at 18-month follow-up. Clinical and/or intra-arterial metrics with a significant association with change in plaque burden during multivariate analysis were evaluated for effects on lumen, wall, and total vessel volume.

RESULTS

From multiple regression analysis, intraplaque hemorrhage (IPH) (p < 0.001) and statin therapy (p = 0.015) were identified as key determinants of change in plaque burden. The group with IPH compared with the group without IPH demonstrated luminal narrowing, with a mean +/- SD decrease in lumen volume (-24.9 +/- 21.1 mm(3)/year vs. -0.5 +/- 26.9 mm(3)/year; p = 0.005), a larger increase in wall volume (44.1 +/- 36.1 mm(3)/year vs. 0.8 +/- 34.5 mm(3)/year; p < 0.001), and no difference in total vessel volume (19.3 +/- 27.4 mm(3)/year vs. 0.4 +/- 42.4 mm(3)/year; p = 0.15). The nonstatin group compared with the statin group demonstrated outward remodeling, with an increase in wall volume (22.4 +/- 35.6 mm(3)/year(3)/year vs. 0.9 +/- 38.0 mm(3)/year; p = 0.026) and total vessel volume (19.2 +/- 36.9 mm(3)/year vs. -4.9 +/- 40.4 mm(3)/year; p = 0.019) and no difference in lumen volume (-5.8 +/- 26.6 mm(3)/year vs. -3.2 +/- 29.5 mm(3)/year; p = 0.72).

CONCLUSIONS

IPH may represent an indication of accelerated plaque growth and impending luminal compromise in the subclinical carotid artery. Statin therapy may stabilize lesions by slowing or halting lesion progression. This phase of plaque stenosis (16% to 49%) may be a critical stage for intrinsic and extrinsic factors to affect the atherosclerotic disease process.

Carotid intraplaque hemorrhage imaging at 3.0-T MR imaging: comparison of the diagnostic performance of three T1-weighted sequences

PURPOSE

To compare the diagnostic performances of three T1-weighted 3.0-T magnetic resonance (MR) sequences at carotid intraplaque hemorrhage (IPH) imaging, with histo logic analysis as the reference standard.

MATERIALS AND METHODS

Institutional review board approval and informed consent were obtained for this HIPAA-compliant study. Twenty patients scheduled for carotid endarterectomy underwent 3.0-T carotid MR imaging, including two-dimensional fast spin-echo, three-dimensional time-of-flight (TOF), and three-dimensional magnetization-prepared rapid acquisition gradient-echo (RAGE) sequences. Two reviewers blinded to the histologic findings assessed the presence, area, and signal intensity of IPH with each sequence. Detection statistics (sensitivity, specificity, and Cohen kappa values) and agreement between area measurements (Pearson correlation coefficient [r] values) were calculated for each sequence.

RESULTS

When all 231 available MR sections were included for analysis, the magnetization-prepared RAGE (kappa = 0.53) and fast spin-echo (kappa = 0.42) sequences yielded moderate agreement between MR and histologic measurements, while the TOF sequence yielded fair agreement (k = 0.33). However, when 47 sections with either small IPHs or heavily calcified IPHs were excluded, sensitivity, specificity, and kappa values, respectively, were 80%, 97%, and 0.80 for magnetization-prepared RAGE imaging; 70%, 92%, and 0.63 for fast spin-echo imaging; and 56%, 96%, and 0.57 for TOF imaging. MR imaging-histologic analysis correlation for IPH area was highest with magnetization-prepared RAGE imaging (r = 0.813), followed by TOF (r = 0.745) and fast spin-echo (r = 0.497) imaging. The capability of these three sequences for IPH detection appeared to be in good agreement with the quantitative contrast of IPH versus background plaque tissue.

CONCLUSION

The magnetization-prepared RAGE sequence, as compared with the fast spin-echo and TOF sequences, demonstrated higher diagnostic capability for the detection and quantification of IPH. Potential limitations of 3.0-T IPH MR imaging are related to hemorrhage size and coexisting calcification.

Improvements in carotid plaque imaging using a new eight-element phased array coil at 3T

PURPOSE

To design and compare an eight-channel phased array (PA) coil for carotid imaging to an established four-channel PA design at 3T.

MATERIALS AND METHODS

An eight-channel PA (8PA) coil was designed specifically for imaging the carotid bifurcation and compared with the existing four-channel (4PA) design using a phantom and by in vivo black-blood magnetic resonance imaging (MRI). The 8PA and 4PA were compared in terms of coverage, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR).

RESULTS

The 8PA showed up to 1.7-fold improvement in SNR at a depth of 3.5 cm and greater longitudinal coverage at a given SNR on a phantom. The 8PA showed improved vessel wall SNR for high spatial resolution (0.63 mm(2)) PD, T1, and T2 (1.7, 1.7, 1.6 times, respectively; P <or= 0.002) and improved CNR (1.7, 1.6, 1.5 times, respectively; P <or= 0.002). Ultrahigh-resolution (0.27 mm(2)) T1-weighted images showed better SNR and CNR (1.4 times, P <or= 0.0001) on 8PA compared to 4PA.

CONCLUSION

Carotid imaging studies may benefit from the improved SNR and larger coverage provided by use of the 8PA.

Predictors of surface disruption with MR imaging in asymptomatic carotid artery stenosis

BACKGROUND AND PURPOSE

Surface disruption, either ulceration or fibrous cap rupture, has been identified as a key feature of the unstable atherosclerotic plaque. In this prospective observational study, we sought to determine the characteristics of the carotid lesion that predict the development of new surface disruption.

MATERIALS AND METHODS

One hundred eight asymptomatic individuals with 50%-79% carotid stenosis underwent carotid MR imaging at baseline and at 3 years. Multicontrast imaging criteria were used to determine the presence or absence of calcification, LRNC, intraplaque hemorrhage, and surface disruption. Volume measurements of plaque morphology and the LRNC and calcification, when present, were collected.

RESULTS

At baseline, 21.3% (23/108) of participants were identified with a surface disruption. After 3 years, 9 (10.6%) of the remaining 85 individuals without disruption at baseline developed a new surface disruption during follow-up. Among all baseline variables associated with new surface disruption during regression analysis, the proportion of wall volume occupied by the LRNC (percentage LRNC volume; OR per 5% increase, 2.6; 95% CI, 1.5-4.6) was the strongest classifier (AUC = 0.95) during ROC analysis. New surface disruption was associated with a significant increase in percentage LRNC volume (1.7 +/- 2.0% per year, P = .035).

CONCLUSIONS

This prospective investigation of asymptomatic individuals with 50%-79% stenosis provides compelling evidence that LRNC size may govern the risk of future surface disruption. Identification of carotid plaques in danger of developing new surface disruption may prove clinically valuable for preventing the transition from stable to unstable atherosclerotic disease.

Direct quantitative comparison between cross-relaxation imaging and diffusion tensor imaging of the human brain at 3.0 T

Cross-relaxation imaging (CRI) describes the magnetization transfer within tissues between mobile water protons and macromolecular protons. Whole-brain parametric maps of the principle kinetic components of magnetization transfer, the fraction of macromolecular protons (f) and the rate constant (k), revealed detailed anatomy of white matter (WM) fiber tracts at 1.5 T. In this study, CRI was first adapted to 3.0 T, and constraints for transverse relaxation times of water and macromolecular protons were identified to enable unbiased f and k estimation. Subsequently, whole-brain CRI and diffusion tensor imaging (DTI) were performed in five healthy subjects. The parameters f and k were compared to DTI indices (fractional anisotropy (FA), apparent diffusion coefficient (ADC), radial diffusivity (RD), and axial diffusivity (AD)) across a range of anatomic regions. In WM, neither f nor k was significantly correlated to FA, RD, and AD. In contrast, both f (r=0.90 and r=-0.80) and k (r=0.92 and r=-0.89) in gray matter (GM) were strongly correlated to FA and RD, respectively. A moderate correlation between ADC and k (r=0.48) was identified in WM, while an inverse correlation was identified in GM (r=-0.72). The lack of association between CRI and FA in WM is consistent with differences in the underlying physical principles between techniques - fiber density vs. directionality, respectively. The association in GM may be attributable to variable axonal density unique to each structure. Our findings suggest that whole-brain CRI provides distinct quantitative information compared to DTI, and CRI parameters may prove constructive as biomarkers in neurological diseases.

Comparison between 2D and 3D high-resolution black-blood techniques for carotid artery wall imaging in clinically significant atherosclerosis

PURPOSE

To compare two- (2D) and three-dimensional (3D) black-blood imaging methods for morphological measurements of the carotid artery wall and atherosclerotic plaque.

MATERIALS AND METHODS

A total of 18 subjects with 50% to 79% carotid stenosis were scanned with 2D (2-mm slice thickness) and 3D (1-mm/0.5-mm actual/interpolated slice thickness) T1-weighted fast spin-echo (FSE) black-blood imaging sequences with double inversion-recovery (DIR) blood suppression. Morphological measurements (lumen area, wall area, vessel area, mean wall thickness, and maximal wall thickness), signal-to-noise ratio (SNR) in the wall and lumen, and wall-lumen contrast-to-noise ratio (CNR) were compared between 2D and 3D images. The effect of improved slice resolution in 3D imaging was evaluated for visualization of small plaque components.

RESULTS

Lumen SNR (P = 0.16), wall SNR (P = 0.65), and CNR (P = 0.94) were comparable between 2D/3D. There was no difference in average lumen area (P = 0.16), average wall area (P = 0.99), average vessel area (P = 0.0.58), mean wall thickness (P = 0.09), and maximum wall thickness (P = 0.06) between 2D/3D. Distributions of small plaque components such as calcification were better characterized by the 3D acquisition. There was a higher sensitivity to motion artifacts with 3D imaging, resulting in three examinations with low image quality.

CONCLUSION

2D and 3D protocols provided comparable morphometric measurements of the carotid artery. The major advantage of 3D imaging is improved small plaque component visualization, while the 2D technique provides higher reliability for image quality.

Carotid plaque morphology and composition: initial comparison between 1.5- and 3.0-T magnetic field strengths

PURPOSE

To prospectively compare the interpretation and quantification of carotid vessel wall morphology and plaque composition at 1.5-T with those at 3.0-T magnetic resonance (MR) imaging.

MATERIALS AND METHODS

Twenty participants (mean age, 69.8 years [standard deviation] +/- 10.5; 75% men) with 16%-79% carotid stenosis at duplex ultrasonography were imaged with 1.5-T and 3.0-T MR imaging units with bilateral four-element phased-array surface coils. This HIPAA-compliant study was approved by the institutional review board, and all participants gave written informed consent. Protocols designed for similar signal-to-noise ratios across platforms were implemented to acquire axial T1-weighted, T2-weighted, intermediate-weighted, time-of-flight, and contrast material-enhanced T1-weighted images. Lumen area, wall area, total vessel area, wall thickness, and presence or absence and area of plaque components were documented. Continuous variables from different field strengths were compared by using the intraclass correlation coefficient (ICC) and repeated measures analysis. The Cohen kappa was used to evaluate agreement between 1.5 T and 3.0 T on compositional dichotomous variables.

RESULTS

There was a strong level of agreement between field strengths for all morphologic variables, with ICCs ranging from 0.88 to 0.96. Agreement in the identification of presence or absence of plaque components was very good for calcification (kappa = 0.72), lipid-rich necrotic core (kappa = 0.73), and hemorrhage (kappa = 0.66). However, the visualization of hemorrhage was greater at 1.5 T than at 3.0 T (14.7% vs 7.8%, P < .001). Calcifications measured significantly (P = .03) larger at 3.0 T, while lipid-rich necrotic cores without hemorrhage were similar between field strengths (P = .9).

CONCLUSION

At higher field strengths, the increased susceptibility of calcification and paramagnetic ferric iron in hemorrhage may alter quantification and/or detection. Nevertheless, imaging criteria at 1.5 T for carotid vessel wall interpretation are applicable at 3.0 T.

Micro magnetic resonance angiography of the finger in systemic sclerosis

OBJECTIVE

To characterize vascular lesions in SSc disease with high-resolution magnetic resonance angiography (Micro-MRA) of the finger.

METHODS

Eight SSc subjects and eight age- and sex-matched healthy controls were recruited for this study. Among the SSc subjects, the mean +/- s.d. age was 54.5 +/- 4.9 yrs, and the mean +/- s.d. duration of disease was 8.3 +/- 8.4 yrs. The numbers of SSc subjects that had telangiectasia, calcinosis and impaired finger flexion were 3, 2 and 3, respectively. The 2D time-of-flight micro-MRA was performed on a 3T clinical MRI scanner using a custom-designed finger coil with an in-plane resolution of 0.16 x 0.21 mm(2) and slice thickness of 1.2 mm. The data for the proper palmar digital artery lumen area, the number of visible dorsal digital veins and a semi-quantitative vascular score, which evaluates the overall integrity of digital vessels, were independently evaluated by two experienced reviewers who were blinded to the status of the subject.

RESULTS

Micro-MRA detected significant differences in the digital vasculature between SSc subjects and healthy volunteers. The SSc subjects had a significantly decreased digital artery lumen area (0.13 +/- 0.06 vs 0.53 +/- 0.26 mm(2), P < 0.001), a reduced number of digital veins (0.63 +/- 1.06 vs 3.13 +/- 0.99, P = 0.001) and a lowered overall vascular score (1.75 +/- 1.04 vs 3.5 +/- 0.53, P = 0.001). The study also found that both the digital artery lumen area (Pearson's; r = -0.72, P = 0.044) and vascular scores (Spearman's; rho = -0.75, P = 0.047) of the SSc subjects were inversely correlated with the duration of the disease.

CONCLUSIONS

Micro-MRA can be used to identify and quantitatively characterize the vascular disease in SSc fingers. The parameters derived from micro-MRA could potentially be used as prospective biomarkers for clinical evaluation.

Differences in carotid arterial morphology and composition between individuals with and without obstructive coronary artery disease: a cardiovascular magnetic resonance study

OBJECTIVE

We sought to determine differences with cardiovascular magnetic resonance (CMR) in the morphology and composition of the carotid arteries between individuals with angiographically-defined obstructive coronary artery disease (CAD, > or = 50% stenosis, cases) and those with angiographically normal coronaries (no lumen irregularities, controls).

METHODS AND RESULTS

191 participants (50.3% female; 50.8% CAD cases) were imaged with a multi-sequence, carotid CMR protocol at 1.5T. For each segment of the carotid, lumen area, wall area, total vessel area (lumen area + wall area), mean wall thickness and the presence or absence of calcification and lipid-rich necrotic core were recorded bilaterally. In male CAD cases compared to male controls, the distal bulb had a significantly smaller lumen area (60.0 +/- 3.1 vs. 79.7 +/- 3.2 mm2, p < 0.001) and total vessel area (99.6 +/- 4.0 vs. 119.8 +/- 4.1 mm2; p < 0.001), and larger mean wall thickness (1.25 +/- 0.03 vs. 1.11 +/- 0.03 mm; p = 0.002). Similarly, the internal carotid had a smaller lumen area (37.5 +/- 1.8 vs. 44.6 +/- 1.8 mm2; p = 0.006) and smaller total vessel area (64.0 +/- 2.3 vs. 70.9 +/- 2.4 mm2; p = 0.04). These metrics were not significantly different between female groups in the distal bulb and internal carotid or for either gender in the common carotid. Male CAD cases had an increased prevalence of lipid-rich necrotic core (49.0% vs. 19.6%; p = 0.003), while calcification was more prevalent in both male (46.9% vs. 17.4%; p = 0.002) and female (33.3% vs. 14.6%; p = 0.031) CAD cases compared to controls.

CONCLUSION

Males with obstructive CAD compared to male controls had carotid bulbs and internal carotid arteries with smaller total vessel and lumen areas, and an increased prevalence of lipid-rich necrotic core. Carotid calcification was related to CAD status in both males and females. Carotid CMR identifies distinct morphological and compositional differences in the carotid arteries between individuals with and without angiographically-defined obstructive CAD.

Improved suppression of plaque-mimicking artifacts in black-blood carotid atherosclerosis imaging using a multislice motion-sensitized driven-equilibrium (MSDE) turbo spin-echo (TSE) sequence

In this study, a turbo spin-echo (TSE) based motion-sensitized driven-equilibrium (MSDE) sequence was used as an alternative black-blood (BB) carotid MRI imaging scheme. The MSDE sequence was first optimized for more efficient residual blood signal suppression in the carotid bulb of healthy volunteers. Effective contrast-to-noise ratio (CNR(eff)) and residual signal-to-noise ratio (SNR) in the lumen measured from MSDE images were then compared to those measured from inflow saturation (IS) and double inversion-recovery (DIR) images. Statistically significant higher CNR(eff) and lower lumen SNR were obtained from MSDE images. To assess MSDE sequence in a clinical carotid protocol, 42 locations from six subjects with 50% to 79% carotid stenosis by duplex ultrasound were scanned with both MSDE and multislice DIR. The comparison showed that MSDE images present significantly higher CNR and lower lumen SNR compared to corresponding multislice DIR images. The vessel wall area and mean wall thickness measurements in MSDE images were slightly but significantly lower than those obtained with other blood suppression techniques. In conclusion, in vivo comparisons demonstrated that MSDE sequence can achieve better blood suppression and provide a more accurate depiction of the lumen boundaries by eliminating plaque mimicking artifacts in carotid artery (CA) imaging.

Reader and platform reproducibility for quantitative assessment of carotid atherosclerotic plaque using 1.5T Siemens, Philips, and General Electric scanners

PURPOSE

To evaluate the platform and reader reproducibility of quantitative carotid plaque measurements.

MATERIALS AND METHODS

A total of 32 individuals with >or=15% carotid stenosis by duplex ultrasound were each imaged once by a 1.5T General Electric (GE) whole body scanner and twice by either a 1.5T Philips scanner or a 1.5T Siemens scanner. A standardized multisequence protocol and identical phased-array carotid coils were used. Expert readers, blinded to subject information, scanner type, and time point, measured the lumen, wall, and total vessel areas and determined the modified American Heart Association lesion type (AHA-LT) on the cross-sectional images.

RESULTS

AHA-LT was consistently identified across the same (kappa = 0.75) and different scan platforms (kappa = 0.75). Furthermore, scan-rescan coefficients of variation (CV) of wall area measurements on Siemens and Philips scanners ranged from 6.3% to 7.5%. However, wall area measurements differed between Philips and GE (P = 0.003) and between Siemens and GE (P = 0.05). In general, intrareader reproducibility was higher than interreader reproducibility for AHA-LT identification as well as for quantitative measurements.

CONCLUSION

All three scanners produced images that allowed AHA-LT to be consistently identified. Reproducibility of quantitative measurements by Siemens and Philips scanners were comparable to previous studies using 1.5T GE scanners. However, bias was introduced with each scanner and the use of different readers substantially increased variability. We therefore recommend using the same platform and the same reader for scans of individual subjects undergoing serial assessment of carotid atherosclerosis.