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Purpose Variable flip angle (VFA) imaging is widely used for whole‐brain T1 quantification. Because of the requirement to acquire at least two sets of MR images at different flip angles, VFA relaxometry is relatively slow. Here, whole‐brain VFA T1 mapping at 1.5 T is accelerated by using efficient spiral non‐Cartesian imaging Methods To quantify T1 in the human brain, radiofrequency spoiled gradient‐echo imaging is performed at two optimized flip angles using an interleaved 2D multislice sequence with high spoiling efficiency. The acquisitions are accelerated by using a spiral trajectory with 10 interleaves combined with a dedicated magnetization preparation to ensure steady‐state conditions in minimal time. Results The investigated MR scan protocol allowed the acquisition of whole‐brain T1 maps at a clinically relevant resolution in only 40 s (0.7 s per slice) with high reproducibility. White and gray matter T1 peaks clearly could be delineated by calculation of whole‐brain T1 histograms, and the delivered T1 values showed good agreement with the reference method in selected regions of interest. Conclusion Due to the use of a fast spiral k‐space trajectory, whole‐brain VFA T1 mapping could be accelerated by an order of magnitude compared to conventional Cartesian sampling.

This study aimed at characterizing the spatio-temporal dynamics of BOLD response at high magnetic field (7T) in the human visual cortex. The spatial pattern of the BOLD response remained approximately stationary across the positive phase of the response. The onset of the response was relatively spatially coherent compared to previous reports from lower magnetic fields. The approximate stationarity of the positive phase of the response validates the usage of analysis methods that assume separability of time and space of the BOLD response.

Echo-planar imaging is the most widely used imaging sequence for functional magnetic resonance imaging (fMRI) due to its fast acquisition. However, it is prone to local distortions, image blurring, and signal voids. As these effects scale with echo train length and field strength, it is essential for high-resolution echo-planar imaging at ultrahigh field to address these problems. Partially parallel acquisition methods can be used to improve the image quality of echo-planar imaging. However, partially parallel acquisition can be affected by aliasing artifacts and noise enhancement. Another way to shorten the echo train length is to reduce the field-of-view (FOV) while maintaining the same spatial resolution. However, to achieve significant acceleration, the resulting FOV becomes very small. Another problem occurs when FOV selection is incomplete such that there is remaining signal aliased from the region outside the reduced FOV. In this article, a novel approach, a combination of reduced FOV imaging with partially parallel acquisition, is presented. This approach can address the problems described above of each individual method, enabling high-quality single-shot echo-planar imaging acquisition, with submillimeter isotropic resolution and good signal-to-noise ratio, for fMRI at ultrahigh field strength. This is demonstrated in fMRI of human brain at 7T with an isotropic resolution of 650 mu m. Magn Reson Med, 2012. (c) 2012 Wiley Periodicals, Inc.

Intracellular targeting with cell penetrating peptides (CPPs) is limited by endocytotic mechanism of uptake. Here, we report that the well known CPP, dTat, chemically coupled with pyrenebutyrate (PB) can efficiently deliver directly into the cytosol. Results indicate that this combination could successfully translocate magnetic resonance imaging (MRI) agents into cytosol.

In this project, a spiral fast imaging sequence was implemented on a Bruker Avance MR system. Acquisition and processing schemes were developed to measure the experimental k-space trajectories. Since errors in k-space are reflected as errors in the corresponding image, we used different strategies to measure and calculate corrections for deviation of the experimental k-space trajectory from the theoretical one. Even if the k-space trajectories deviate from the theoretical ones, an experimentally measured trajectory can be incorporated in the spiral reconstruction and a reduction of image artifacts can be obtained. Trajectories were measured according a method using self-encoding gradients (Takahashi et al., 1995). Necessary corrections were deduced from a quantitative comparison of theoretical and experimental data, which can be used to adjust specific parameters in the MR imaging sequence before spiral image acquisition. The corrections included the assessment of baseline, gradient delay, amplitude and timing mismatch. The influence and extent of different corrections pre- and post-acquistion on the final spiral image quality still remains to be evaluated. KEYWORDS: MRI; fast imaging; Spiral imaging; k-space trajectory

Functional MR imaging in monkeys promises a bridge between brain research in humans and the large body of systems neuroscience work in animals. Prerequisite for successful interspecies-comparisons, however, is a profound understanding of the neural events underlying the hemodynamic responses. Combined physiology and neuroimaging experiments made the first step in this direction by examining directly the relationship of cell activity to the BOLD signal [1]. The tight coupling between regional neural activity and blood flow, however, suggests that perfusion-based MRI may improve even further the electrophysiological investigations of the neurovascular coupling, as perfusion imaging measures cerebral blood flow (CBF) directly at the capillary level. Moreover, CBF changes and interleaved-acquired BOLD data can be combined to compute changes in oxygen consumption rate. Obtaining functional CBF maps with high spatial resolution is challenging, because the CBF signal is intrinsically low and the signal-to-noise ratio is critical. Here we report the first high-resolution CBF maps that were obtained with voxel sizes as small as 0.5 x 0.5 x 3 mm3 in the Macaca mulatta. High sensitivity was achieved by using a high magnetic field scanner and custom-made RF combination-coil designs. CBF maps and functional CBF data were acquired and compared with BOLD data in the macaque primary visual cortex.

1H NMR spectroscopy provides a quantitative chemical analysis of brain metabolites. Thus it is a useful, non-invasive method to follow in vivo both the regular metabolism in the brain and the pathological changes. LCModel is a commonly used program to quantify in vivo spectroscopic data of brain metabolites in the frequency domain. The program LCModel uses prior knowledge in the form of sets of basis spectra to decompose the measured spectra by means of a linear combination from the single spectra of the expected metabolites. The task of the internship was to use the specialized software package NMR-Sim (Analytic Suite, Bruker) and to simulate such basis sets for different magnetic field strengths based on published literature values. As a result, it is now possible to analyze and quantify the measured in vivo spectroscopic data automatically and to compare the appearance of the single magnetic resonance spectra at different field strengths.

In functional magnetic resonance imaging, it is known that physiological influences such as cardiac pulsation, respiration or brain motion can induce signal intensity and phase fluctuations. Some of the mechanisms potentially involved in those phenomena are expected to be amplified at higher magnetic fields. This study specifically addresses the issue of B0 fluctuations induced by susceptibility changes during respiration attributed to movements of chest and diaphragm and variations in the oxygen concentration. It is demonstrated that respiration induced resonance offsets (RIRO) at 7 T are significant and were found in data acquired with a RF pulse without gradients, multi-slice echo-planar imaging (EPI), and dynamic 3D-FLASH imaging. The experimental findings can be summarized with three main observations. First, in FIDs measured after a single RF pulse, a RIRO with large amplitude was consistently detected although the average amplitude varied from subject to subject, ranging from 1.45Hz to 4Hz. Second, in transverse EPI images obtained in the occipital lobe, the RIRO amplitude showed a monotonic increase along Z axis toward the lungs. Third, a more detailed spatial analysis with 3D FLASH phase maps revealed that a previously published analytical model can describe the spatial distribution of RIRO accurately. Subsequent apparent motions in the EPI series as well as implication of slice orientation on correction strategies are discussed.

MR Spectroscopy at large diffusion weighting can specifically look at intracellular components of tissue that are characterized by restricted diffusion and a small apparent diffusion coefficient. Beyond water, 1H MRS of metabolites at large diffusion weighting proved to be very useful to separate extra- and intracellular contributions of metabolites in the brain. Further application of diffusion-weighted MRS with other nuclei than 1H, e.g., 31P, 19F, 7Li, 13C, can be utilized to answer specific questions tied to various animal models of disease like ischemia, excitotoxicity, tumor or hydrocephalus (1). Such diffusion-weighted spectroscopy is a powerful tool, using information tied to different compartments, different metabolites, and different tracers.

Intrastriatal injection of quinolinic acid (QA) provides an animal model of Huntington disease. In vivo (1)H NMR spectroscopy was used to measure the neurochemical profile non-invasively in seven animals 5 days after unilateral injection of 150 nmol of QA. Concentration changes of 16 metabolites were measured from 22 microl volume at 9.4 T. The increase of glutamine ((+25 +/- 14), mean +/- SD, n = 7) and decrease of glutamate (-12 +/- 5), N-acetylaspartate (-17 +/- 6), taurine (-14 +/- 6) and total creatine (-9 +/- 3) were discernible in each individual animal (P < 0.005, paired t-test). Metabolite concentrations in control striata were in excellent agreement with biochemical literature. The change in glutamate plus glutamine was not significant, implying a shift in the glutamate-glutamine interconversion, consistent with a metabolic defect at the level of neuronal-glial metabolic trafficking. The most significant indicator of the lesion, however, were the changes in glutathione ((-19 +/- 9), P < 0.002)), consistent with oxidative stress. From a comparison with biochemical literature we conclude that high-resolution in vivo (1)H NMR spectroscopy accurately reflects the neurochemical changes induced by a relatively modest dose of QA, which permits one to longitudinally follow mitochondrial function, oxidative stress and glial-neuronal metabolic trafficking as well as the effects of treatment in this model of Huntington disease.

Localized in vivo H-1 NMR spectroscopy was performed with 2-ms echo time in the rat brain at 9.4 T, Frequency domain analysis with LCModel showed that the in vivo spectra can be explained by 18 metabolite model solution spectra and a highly structured background, which was attributed to resonances with fivefold shorter in vivo T-1 than metabolites. The high spectral resolution (full width at half maximum approximately 0.025 ppm) and sensitivity (signal-to-noise ratio approximately 45 from a 63-mu L volume, 512 scans) was used for the simultaneous measurement of the concentrations of metabolites previously difficult to quantify in H-1 spectra. The strongly represented signals of N-acetylaspartate, glutamate, taurine, myo-inositol, creatine, phosphocreatine, glutamine, and lactate were quantified with Cramer-Rao lower bounds below 4%. Choline groups, phosphorylethanolamine, glucose, glutathione, gamma-aminobutyric acid, N-acetylaspartylglutamate, and alanine were below 13%, whereas aspartate and scyllo-inositol were below 22%. Intra-assay variation was assessed from a time series of 3-min spectra, and the coefficient of variation was similar to the calculated Cramer-Rao lower bounds. Interassay variation was determined from 31 pooled spectra, and the coefficient of variation for total creatine was 7%. Tissue concentrations were found to be in very good agreement with neurochemical data from the literature.

To determine the distribution of cerebral glucose and lactate between the intracellular and the extracellular space of the rat brain in vivo, the diffusion characteristic of glucose and lactate was compared with that of metabolites known to be mainly intracellular (N-acetylaspartate, choline, creatine, glutamate, myo-inositol, and taurine) using a pulsed-field-gradient 1H nuclear magnetic resonance technique. The detection of a glucose signal at large diffusion weighting provided direct experimental evidence of intracellular glucose in the rat brain. At large diffusion weighting, the apparent diffusion coefficient (ADC) of glucose and lactate was similar to that of the intracellular metabolites such as N-acetylaspartate, creatine, and glutamate. At small diffusion weighting, the ADC of glucose and lactate was increased, which was explained by a decreased relative contribution of intracellular glucose to the total signal. The calculated extracellular volume fraction of glucose (0.19 ± 0.05) and lactate (0.17 ± 0.06) was consistent with a substantial fraction of glucose and lactate signals being intracellular. The findings were direct in vivo evidence that the largest concentration gradient of glucose is at the blood-brain barrier and that glucose is evenly distributed in the brain in vivo between the intracellular and extracellular space.

In the past decade, magnetic resonance imaging (MRI) research has been focused on the acquisition of physiological and biochemical information noninvasively. Probably the most notable accomplishment in this general effort has been the introduction of the MR approaches to map brain function. This capability, often referred to as functional magnetic resonance imaging. orfMRI, is based on the sensitivity of MR signals to secondary metabolic and hemodynamic responses tliaî accompany increased neuronal activity. Despite this indirect link to neurotransmission, recent studies demonstrate that under appropriate conditions, these jMRl maps have accuracy at the scale of submillimeter neuronal organizations such as the orientation columns of the visual cortex, and are directly proportional in magnitude to electrical signals generated by the neurons. High magnetic fields have been critical in achieving such specificity in functional maps because they provide advantages through increased signal-to-noise ratio, diminishing blood-related contributions to mapping signals, and enhanced sensitivity to microvasculature. Equally important is MR spectroscopy studies, which, at high magnetic fields, provide for the first time the opportunity to measure local metabolic correlates of human brain function and neurotransmission rates. Together, these MR methods provide a complementary set of approaches for probing important aspects of the nervous system. © 2001 IEEE. Publisher Item Identifier S 0018-9219(01)07636-8.

Intrastriatal injection of quinolinic acid (QA) provides an animal model of Huntington disease. In vivo 1H NMR spectroscopy was used to measure the neurochemical profile non-invasively in seven animals 5 days after unilateral injection of 150 nmol of QA. Concentration changes of 16 metabolites were measured from 22 μl volume at 9.4 T. The increase of glutamine ((+25 ± 14)%, mean ± SD, n = 7) and decrease of glutamate (-12 ± 5)%, N-acetylaspartate (-17 ± 6)%, taurine (-14 ± 6)% and total creatine (-9 ± 3%) were discernible in each individual animal (P < 0.005, paired t-test). Metabolite concentrations in control striata were in excellent agreement with biochemical literature. The change in glutamate plus glutamine was not significant, implying a shift in the glutamate-glutamine interconversion, consistent with a metabolic defect at the level of neuronal-glial metabolic trafficking. The most significant indicator of the lesion, however, were the changes in glutathione ((-19 ± 9)%, P < 0.002)), consistent with oxidative stress. From a comparison with biochemical literature we conclude that high-resolution in vivo 1H NMR spectroscopy accurately reflects the neurochemical changes induced by a relatively modest dose of QA, which permits one to longitudinally follow mitochondrial function, oxidative stress and glial-neuronal metabolic trafficking as well as the effects of treatment in this model of Huntington disease. © 2001 Wiley-Liss, Inc.

BACKGROUND: Presbycusis is the hearing loss (HL) determined by aging mechanisms affecting the inner ear. Auditory cortical hypoperfusion has been shown in the early phases of presbycusis, suggesting a regionally selective metabolic vulnerability secondary to peripheral loss of function. In this study, HL patients were stratified according to the audiogram profiles to possibly enable a finer regional characterization of cortical perfusion changes within the primary auditory cortex. METHODS: Sixty-two HL patients (age range: 47-78 years, PTA

Age-related hearing loss (HL) can be related to brain dysfunction or structural damage and may result in cerebral metabolic/perfusion abnormalities. Arterial spin labeling (ASL) magnetic resonance imaging (MRI) allows investigating noninvasively brain perfusion changes. Pseudocontinuous ASL and T1-weighted MRI (at 3 T) and neuropsychological testing (Montreal Cognitive Assessment) were performed in 31 HL (age range = 47–77 years, mean age ± SD = 63.4 ± 8.4 years, pure-tone average [PTA] HL > 50 dB) and 28 normal hearing (NH; age range = 48–78 years, mean age ± SD = 59.7 ± 7.4 years) subjects. Cerebral blood flow (CBF) and gray matter volume (GMV) were analyzed in the cortical volume to assess perfusion and structural group differences. Two HL subjects showing cognitive impairment were excluded from group comparisons. No significant differences in either global or local atrophy were detected between groups but the HL group exhibited significant regional effects of reduced perfusion within the bilateral primary auditory cortex, with maximal CBF difference (−17.2%) in the right lateral Heschl's gyrus. For the whole sample of HL and NH subjects (n = 59 = 31 HL + 28 NH), the regional CBF was correlated positively to the regional GMV (p = 0.020). In HL subjects (n = 31), the regional CBF was correlated negatively to the audiogram steepness (frequency range: 2–4 kHz, right ear: p = 0.022, left ear: p = 0.015). The observed cortical pattern of perfusion reduction suggests that neuronal metabolism can be related to HL before the recognition of brain structural damage. This also illustrates the potential of ASL-MRI to contribute early functional markers of reduced central processing associated with HL.