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Background: Venous blood oxygenation (Yv), which can be derived from venous blood T2 (T2b), combined with oxygen‐extraction fraction (OEF) and cerebral metabolic rate of oxygen, is considered indicative for tissue viability and brain functioning and frequently assessed in patients with sickle cell disease. Recently, T2‐Prepared‐Blood‐Relaxation‐Imaging‐with‐Inversion‐Recovery (T2‐TRIR) was introduced allowing for simultaneous measurements of blood T2 and T1 (T1b), potentially improving Yv estimation by overcoming the need to estimate hematocrit. Purpose: To optimize and compare T2‐TRIR with T2‐relaxation‐under‐spin‐tagging (TRUST) sequence. Study Type: Prospective. Population: A total of 12 healthy volunteers (six female, 27 ± 3 years old) and 7 patients with sickle cell disease (five female, 32 ± 12 years old). Field Strength/Sequence: 3 T; turbo field echo planar imaging (TFEPI), echo planar imaging (EPI), and fast field echo (FFE). Assessment: T2b, Yv, and OEF from TRUST and T2‐TRIR were compared and T2‐TRIR‐derived T1b was assessed. Within‐ and between‐session repeatability was quantified in the controls, whereas sensitivity to hemodynamic changes after acetazolamide (ACZ) administration was assessed in the patients. Statistical Tests: Shapiro–Wilk, one‐sample and paired‐sample t‐test, repeated measures ANOVA, mixed linear model, Bland–Altman analysis and correlation analysis. Sidak multiple‐comparison correction was performed. Significance level was 0.05. Results: In controls, T2b from T2‐TRIR (70 ± 11 msec) was higher compared to TRUST (60 ± 8 msec). In patients, T2b values were lower pre‐ compared to post‐ACZ administration (TRUST: 80 ± 15 msec and 106 ± 23 msec and T2‐TRIR: 95 ± 21 msec and 125 ± 36 msec). Consequently, Yv and OEF were lower and higher pre‐ compared to post‐ACZ administration (TRUST Yv: 68% ± 7% and 77% ± 8%, T2‐TRIR Yv: 74% ± 8% and 80% ± 6%, TRUST OEF: 30% ± 7% and 21% ± 8%, and T2‐TRIR OEF: 25% ± 8% and 18% ± 6%). Data Conclusion: TRUST and T2‐TRIR are reproducible, but T2‐TRIR‐derived T2b values are significantly higher compared to TRUST, resulting in higher Yv and lower OEF estimates. This bias might be considered when evaluating cerebral oxygen homeostasis. Evidence Level: 2 Technical Efficacy: Stage 2 [ABSTRACT FROM AUTHOR]

Purpose: To compare cerebral blood flow (CBF) and cerebrovascular reserve (CVR) quantification from Turbo‐QUASAR (quantitative signal targeting with alternating radiofrequency labeling of arterial regions) arterial spin labeling (ASL) and single post‐labeling delay pseudo‐continuous ASL (PCASL). Methods: A model‐based method was developed to quantify CBF and arterial transit time (ATT) from Turbo‐QUASAR, including a correction for magnetization transfer effects caused by the repeated labeling pulses. Simulations were performed to assess the accuracy of the model‐based method. Data from an in vivo experiment conducted on a healthy cohort were retrospectively analyzed to compare the CBF and CVR (induced by acetazolamide) measurement from Turbo‐QUASAR and PCASL on the basis of global and regional differences. The quality of the two ASL data sets was examined using the coefficient of variation (CoV). Results: The model‐based method for Turbo‐QUASAR was accurate for CBF estimation (relative error was 8% for signal‐to‐noise ratio = 5) in simulations if the bolus duration was known. In the in vivo experiment, the mean global CVR estimated by Turbo‐QUASAR and PCASL was between 63% and 64% and not significantly different. Although global CBF values of the two ASL techniques were not significantly different, regional CBF differences were found in deep gray matter in both pre‐ and postacetazolamide conditions. The CoV of Turbo‐QUASAR data was significantly higher than PCASL. Conclusion: Both ASL techniques were effective for quantifying CBF and CVR, despite the regional differences observed. Although CBF estimated from Turbo‐QUASAR demonstrated a higher variability than PCASL, Turbo‐QUASAR offers the advantage of being able to measure and control for variation in ATT. [ABSTRACT FROM AUTHOR]

Purpose: For rapid spatial mapping of gamma‐aminobutyric acid (GABA) at the increased sensitivity and spectral separation for ultra‐high magnetic field strength (7 tesla [T]), an accelerated edited magnetic resonance spectroscopic imaging technique was developed and optimized for the human brain at 7 T. Methods: A MEGA‐sLASER sequence was used for GABA editing and volume selection to maximize editing efficiency and minimize chemical shift displacement errors. To accommodate the high bandwidth requirements at 7 T, a single‐shot echo planar readout was used for rapid simultaneous encoding of the temporal dimension and 1 spatial. B0 and B1 field aspects specific for 7 T were studied together with correction procedures, and feasibility of the EPSI MEGA‐sLASER technique was tested in vivo in 5 healthy subjects. Results: Localized edited spectra could be measured in all subjects giving spatial GABA signal distributions over a central brain region, having 45‐ to 50‐Hz spatial intervoxel B0 field variations and up to 30% B1 field deviations. MEGA editing was found unaffected by the B0 inhomogeneities for the optimized sequence. The correction procedures reduced effects of intervoxel B0 inhomogeneities, corrected for spatial editing efficiency variations, and compensated for GABA resonance phase and frequency shifts from subtle motion and acquisition instabilities. The optimized oscillating echo‐planar gradient scheme permitted full spectral acquisition at 7 T and exhibited minimal spectral‐spatial ghosting effects for the selected brain region. Conclusion: The EPSI MEGA‐sLASER technique was shown to provide time‐efficient mapping of regional variations in cerebral GABA in a central volume of interest with spatial B1 and B0 field variations typical for 7 T. [ABSTRACT FROM AUTHOR]

Object: Cerebrospinal fluid (CSF) T2 mapping can potentially be used to investigate CSF composition. A previously proposed CSF T2-mapping method reported a T2 difference between peripheral and ventricular CSF, and suggested that this reflected different CSF compositions. We studied the performance of this method at 7 T and evaluated the influence of partial volume and B1 and B0 inhomogeneity.Materials and methods: T2-preparation-based CSF T2-mapping was performed in seven healthy volunteers at 7 and 3 T, and was compared with a single echo spin-echo sequence with various echo times. The influence of partial volume was assessed by our analyzing the longest echo times only. B1 and B0 maps were acquired. B1 and B0 dependency of the sequences was tested with a phantom.Results: T2,CSF was shorter at 7 T compared with 3 T. At 3 T, but not at 7 T, peripheral T2,CSF was significantly shorter than ventricular T2,CSF. Partial volume contributed to this T2 difference, but could not fully explain it. B1 and B0 inhomogeneity had only a very limited effect. T2,CSF did not depend on the voxel size, probably because of the used method to select of the regions of interest.Conclusion: CSF T2 mapping is feasible at 7 T. The shorter peripheral T2,CSF is likely a combined effect of partial volume and CSF composition. [ABSTRACT FROM AUTHOR]

Objective: In previous work we have developed a fast sequence that focusses on cerebrospinal fluid (CSF) based on the long T2 of CSF. By processing the data obtained with this CSF MRI sequence, brain parenchymal volume (BPV) and intracranial volume (ICV) can be automatically obtained. The aim of this study was to assess the precision of the BPV and ICV measurements of the CSF MRI sequence and to validate the CSF MRI sequence by comparison with 3D T1-based brain segmentation methods. Materials and methods: Ten healthy volunteers (2 females; median age 28 years) were scanned (3T MRI) twice with repositioning in between. The scan protocol consisted of a low resolution (LR) CSF sequence (0:57min), a high resolution (HR) CSF sequence (3:21min) and a 3D T1-weighted sequence (6:47min). Data of the HR 3D-T1-weighted images were downsampled to obtain LR T1-weighted images (reconstructed imaging time: 1:59 min). Data of the CSF MRI sequences was automatically segmented using in-house software. The 3D T1-weighted images were segmented using FSL (5.0), SPM12 and FreeSurfer (5.3.0). Results: The mean absolute differences for BPV and ICV between the first and second scan for CSF LR (BPV/ICV: 12±9/7±4cc) and CSF HR (5±5/4±2cc) were comparable to FSL HR (9±11/19±23cc), FSL LR (7±4, 6±5cc), FreeSurfer HR (5±3/14±8cc), FreeSurfer LR (9±8, 12±10cc), and SPM HR (5±3/4±7cc), and SPM LR (5±4, 5±3cc). The correlation between the measured volumes of the CSF sequences and that measured by FSL, FreeSurfer and SPM HR and LR was very good (all Pearson’s correlation coefficients >0.83, R2 .67–.97). The results from the downsampled data and the high-resolution data were similar. Conclusion: Both CSF MRI sequences have a precision comparable to, and a very good correlation with established 3D T1-based automated segmentations methods for the segmentation of BPV and ICV. However, the short imaging time of the fast CSF MRI sequence is superior to the 3D T1 sequence on which segmentation with established methods is performed. [ABSTRACT FROM AUTHOR]