A new method has been developed for fast image‐based measurements of the transmitted radiofrequency (RF) field. The method employs an actual flip‐angle imaging (AFI) pulse sequence that consists of two identical RF pulses followed by two delays of different duration (TR₁ < TR₂). After each pulse, a gradient‐echo (GRE) signal is acquired. It has been shown theoretically and experimentally that if delays TR₁ and TR₂ are sufficiently short and the transverse magnetization is completely spoiled, the ratio r = S₂/S₁ of signal intensities S₁ and S₂, acquired at the beginning of the time intervals TR₁ and TR₂, depends on the flip angle (FA) of applied pulses as r = (1 + n * cos(FA))/(n + cos(FA)), where n = TR₂/TR₁. The method allows fast 3D implementation and provides accurate B₁ measurements that are highly insensitive to T₁. The unique feature of the AFI method is that it uses a pulsed steady‐state signal acquisition. This overcomes the limitation of previous methods that required long relaxation delays between sequence repetitions. The method has been shown to be useful for time‐efficient whole‐body B₁ mapping and correction of T₁ maps obtained using a variable FA technique in the presence of nonuniform RF excitation. Magn Reson Med 57:192–200, 2007.

Objective— This study evaluates the ability of MRI to quantify all major carotid atherosclerotic plaque components in vivo. Methods and Results— Thirty-one subjects scheduled for carotid endarterectomy were imaged with a 1.5T scanner using time-of-flight–, T1-, proton density–, and T2-weighted images. A total of 214 MR imaging locations were matched to corresponding histology sections. For MRI and histology, area measurements of the major plaque components such as lipid-rich/necrotic core (LR/NC), calcification, loose matrix, and dense (fibrous) tissue were recorded as percentages of the total wall area. Intraclass correlation coefficients (ICCs) were computed to determine intrareader and inter-reader reproducibility. MRI measurements of plaque composition were statistically equivalent to those of histology for the LR/NC (23.7 versus 20.3%; P =0.1), loose matrix (5.1 versus 6.3%; P =0.1), and dense (fibrous) tissue (66.3% versus 64%; P =0.4). Calcification differed significantly when measured as a percentage of wall area (9.4 versus 5%; P <0.001). Intrareader and inter-reader reproducibility was good to excellent for all tissue components, with ICCs ranging from 0.73 to 0.95. Conclusions— MRI-based tissue quantification is accurate and reproducible. This application can be used in therapeutic clinical trials and in prospective longitudinal studies to examine carotid atherosclerotic plaque progression and regression.

Background and Purpose— High-resolution, multicontrast magnetic resonance imaging (MRI) has developed into an effective tool for the identification of carotid atherosclerotic plaque components, such as necrotic core, fibrous matrix, and hemorrhage/thrombus. Factors that may lead to plaque instability are lipid content, thin fibrous cap, and intraplaque hemorrhage. Determining the age of intraplaque hemorrhage can give insight to the history and current condition of the biologically active plaque. The aim of this study was to develop criteria for the identification of the stages of intraplaque hemorrhage using high-resolution MRI. Methods— Twenty-seven patients, scheduled for carotid endarterectomy (CEA), were imaged on a 1.5-T GE SIGNA scanner (sequences: 3-dimensional time of flight, double-inversion recovery, T1-weighted (T1W), PDW and T2W). Two readers, blinded to histology, reviewed MR images and grouped hemorrhage into fresh, recent, and old categories using a modified cerebral hemorrhage criteria. The CEA specimens were serially sectioned and graded as to presence and stage of hemorrhage. Results— Hemorrhage was histologically identified and staged in 145/189 (77%) of carotid artery plaque locations. MRI detected intraplaque hemorrhage with high sensitivity (90%) but moderate specificity (74%). Moderate agreement in classifying stages occurred between MRI and histology (Cohen κ=0.7, 95% CI: 0.5 to 0.8 for reviewer 1 and 0.4, 95% CI: 0.2 to 0.6 for reviewer 2), with moderate agreement between the 2 MRI readers (κ=0.4, 95% CI: 0.3 to 0.6). Conclusion— Multicontrast MRI can detect and classify carotid intraplaque hemorrhage with high sensitivity and moderate specificity.

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. Magn Reson Med 58:973–981, 2007.

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.

At 3.0 T, the magnetization-prepared rapid acquisition gradient-echo MR sequence appears to have higher diagnostic capability for the detection and quantification of relatively large intraplaque hemorrhages compared with the fast spin-echo and time-of-flight sequences. PurposeTo 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 MethodsInstitutional 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 κ values) and agreement between area measurements (Pearson correlation coefficient [r] values) were calculated for each sequence.ResultsWhen all 231 available MR sections were included for analysis, the magnetization-prepared RAGE (κ = 0....