IntroductionChildren with perinatally acquired HIV (CPHIV) are at increased risk of neurodevelopmental difficulties, including hearing-related impairments, despite early initiation of antiretroviral therapy (ART). Previous studies have reported a higher prevalence of hearing loss in CPHIV compared with uninfected children; however, the contribution of the central auditory system to these auditory differences remains unclear. Understanding central auditory processing in CPHIV is important, as even subtle auditory difficulties during childhood can negatively affect speech and language development, academic performance, and quality of life.MethodsFunctional MRI was used to examine neural responses to auditory stimulation in 108 11-year-old children (60 CPHIV and 48 children without HIV). During scanning, participants listened to pure tones at low (500 Hz), middle (1,500 Hz), and high (4,000 Hz) frequencies.ResultsCPHIV demonstrated modestly elevated hearing thresholds (reflecting poorer hearing sensitivity) at several frequencies; however, the prevalence of clinically defined hearing loss did not differ between groups. Across all children, pure-tone stimulation elicited robust bilateral activation of the auditory cortices, with both the spatial extent and magnitude of activation decreasing as tone frequency increased. Relative to controls, CPHIV exhibited significantly reduced bilateral auditory cortex responses across frequencies. These group differences persisted after accounting for sex and handedness and after excluding children with hearing loss. Associations between hearing thresholds and auditory cortex activation were generally weak, except at 4,000 Hz in CPHIV, where poorer hearing was associated with stronger auditory cortex activation, consistent with a compensatory neural response.DiscussionDespite largely normal peripheral hearing, CPHIV receiving ART exhibited reduced bilateral auditory cortex responses during pure-tone processing. These findings suggest that alterations within the central auditory system may contribute to auditory vulnerability in CPHIV.

Abstract Although HIV exposure has previously been found to affect brain white matter (WM) tract integrity and language development in infants and children, the impacts of HIV and antiretroviral therapy (ART) exposure on central auditory tracts remain unclear. Moreover, no research to date has investigated the relationship between auditory WM tract development and language outcomes in infants exposed to HIV but uninfected (iHEU). Brain images were acquired at the age of 0-5 weeks for 31 infants whose mothers began ART pre-conception (iHEU-pre), 29 infants whose mothers began ART post-conception (iHEU-post) and 25 infants who were HIV-unexposed (iHU). Full-probabilistic diffusion tensor imaging (DTI) tractography was used to assess WM integrity in tracts connected to central auditory structures. Language assessments were carried out at 9-14 months using the Griffiths Mental Development Scales (GMDS). Linear regression analysis was used to compare DTI tractography results between iHEU and iHU and to assess the relationship between DTI measures and language. Finally, the impacts of HIV and ART exposure on associations between language and DTI measures were visualised using groupwise language-DTI correlation plots. There were no results after multiple comparison correction. Unadjusted results show recurring patterns of reduced fractional anisotropy (FA), driven by iHEU-post, in auditory tracts of iHEU compared to iHU. Both iHEU-pre and iHEU-post contributed to the patterns of uncorrected elevations in mean diffusivity (MD) observed in the entire iHEU group, with the left medial geniculate nucleus being the auditory structure most frequently observed within the affected tracts. Effect sizes of uncorrected differences, which were small-to-moderate in size, were similar to other infant DTI tractography studies. Groupwise assessment of the data revealed moderately strong correlations between GMDS language scores and DTI measures in some affected tracts, only for iHU. Our findings indicate that HIV/ART exposure may have subtle effects on auditory WM tract development in infants. Delays in auditory tract maturation appear to occur irrespective of ART exposure duration and may be HIV exposure-specific effects. Tracts connected to the left auditory thalamus have notably been implicated in our unadjusted results. HIV and ART exposure may interfere with the way in which auditory WM tracts mature, potentially impacting the role of a small number of these tracts in language processing.

Background:Children who are HIV-exposed but uninfected (CHEU) face elevated risks of hearing loss and language deficits compared to HIV-unexposed peers. The central auditory system (CAS) undergoes substantial maturational changes during adolescence, yet no neuroimaging study has examined its structural or functional integrity in CHEU. Prior work in this cohort identified white matter (WM) alterations in regions adjacent to the CAS at age 7, and reduced auditory working memory in CHEU relative to unexposed children (CHUU). Aim:To characterise WM integrity and functional connectivity (FC) of the CAS and related regions in CHEU at age 11, to investigate structural and functional network topology, and to examine associations between imaging outcomes and neurocognitive function. Methods:Forty-eight children aged 11-12 (20 CHEU, 28 CHUU) from an ongoing longitudinal neurodevelopmental cohort underwent 3T MRI including diffusion tensor imaging (DTI) and resting-state fMRI (RS-fMRI). CAS regions (cochlear nucleus/superior olivary complex, inferior colliculus [IC], medial geniculate nucleus [MGN], and primary auditory cortex [PAC]) were manually segmented and combined with an automated atlas. DTI probabilistic tractography was performed, extracting FA, MD, AD, RD, fractional number of tracts, and tract volume. FC was computed using Pearson correlations between regional time series. Graph theory measures (degree, strength, transitivity, nodal and local efficiency) were derived for structural and functional networks. RS-fMRI group comparisons used Bayesian multilevel modelling (matrix-based and region-based analyses), while DTI comparisons used linear models with FDR correction. Neurocognitive testing employed the KABC-II. Results:No significant group differences in DTI WM metrics (FA, MD, AD, RD) were observed after FDR correction. CHEU demonstrated higher structural nodal strength in the left IC (FDR-significant) and in the bilateral rostral middle frontal cortex (rMFC) and right cuneus. RS-fMRI revealed lower FC between the bilateral IC in CHEU, alongside reduced FC in the left caudate, left hippocampus CA3, left pericalcarine, and left lingual gyrus. CHEU showed higher FC between the left MGN and right precentral, left postcentral, and right rMFC; the right PAC also showed higher FC to the right rMFC and left postcentral gyrus. No significant group differences were observed in functional nodal measures. No significant associations were found between structural or functional imaging outcomes and neurocognitive scores after multiple comparison correction. Discussion:Structural and functional alterations within the CAS were most prominent in the IC, with increased nodal strength in CHEU potentially reflecting compensatory structural connectivity, and reduced interhemispheric FC between the bilateral IC suggesting disrupted auditory integration. Altered FC between the MGN/PAC and cortical regions, including the rMFC and sensorimotor cortices, may reflect differences in top-down auditory processing. The absence of imaging-cognition associations at age 11 suggests that these connectivity differences do not, at this stage, translate into measurable deficits in auditory or language-related neurocognitive performance. Conclusion:This is the first study to examine functional and structural connectivity of the CAS in CHEU children. HIV exposure is associated with subtle but discernible alterations in IC connectivity and in CAS links to cortical regions at age 11, without detectable neurocognitive correlates. Longitudinal follow-up and inclusion of audiological and ART exposure data are needed to clarify the developmental and functional consequences of these findings.

IntroductionChildren living with perinatally acquired HIV (CPHIV) demonstrate hearing impairments and language processing delays even in the presence of combination antiretroviral therapy (cART). Investigations on the effect of HIV on the auditory system have predominantly focused on the peripheral auditory system. Additionally, language processing requires the efficient interaction between central auditory system (CAS) brain regions and non-auditory regions. Investigating the functional connectivity (FC) within the CAS and between the CAS and non-auditory regions may reveal the influence of HIV on regions involved in auditory function.MethodsWithin a Bayesian statistical framework, we used resting-state functional magnetic resonance imaging to map FC in the CAS as well as between CAS regions and non-auditory regions of 11-year-old CPHIV. Graph theory was used to investigate the regional effects of HIV on brain network properties. We explored the relationships between FC and neurocognitive outcomes. We hypothesized that CPHIV would show disruptions in FC between CAS regions as well as between CAS and non-auditory regions. Secondly, we hypothesized that in CPHIV, regional brain network properties would be altered compared to their uninfected peers (CHUU). Finally we hypothesized that FC and functional network regional outcomes would be related to neurocognitive outcomes.ResultsOur investigation revealed lower FC of the primary auditory cortex (PAC) in CPHIV as well as disruptions in FC between CAS regions and non-auditory regions including hippocampal sub-regions, the lingual gyri and basal ganglia. Functional network analysis revealed lower nodal degree and efficiency in CAS regions including the cochlear nucleus/superior olivary complex and the inferior colliculus. We also report associations between the nodal efficiency of middle temporal and superior frontal regions and delayed recall, a neurocognitive marker of working memory, present in CHUU but not in CPHIV.DiscussionOur results demonstrate FC alterations in the PAC and between CAS regions and non-auditory regions involved in limbic, visual and motor processing, as well as disruptions to the regional properties of the CAS regions in the functional brain network. These results provide insight into the state of the CAS FC in the presence of HIV and its possible role in the hearing and language impairments seen in this population.

Children with perinatally acquired HIV (CPHIV) exhibit hearing impairments and language delays despite combination antiretroviral therapy (cART). Efficient sound processing depends on the peripheral and central auditory systems (PAS, CAS), yet studies of HIV's effects have mainly focused on the PAS. Language processing also relies on interactions between CAS and non-auditory brain regions. This study used resting-state fMRI to map functional connectivity (FC) in 11-year-old CPHIV, focusing on CAS and its links to non-auditory regions, within a Bayesian framework. Graph theory analyzed regional network properties, and relationships between FC and neurocognitive outcomes were examined. We hypothesized that CPHIV would show disrupted FC within the CAS and between CAS and non-auditory regions, altered network properties, and links between these changes and neurocognitive outcomes. Findings revealed lower FC in the primary auditory cortex (PAC) of CPHIV, with disrupted connections between CAS regions (including the PAC) and non-auditory regions such as the hippocampus, lingual gyrus, and basal ganglia. Network analysis showed reduced nodal degree and efficiency in CAS regions like the cochlear nucleus/superior olivary complex and inferior colliculus. In CPHIV, associations between middle temporal and superior frontal nodal efficiency and working memory (delayed recall) were absent. These findings highlight CAS FC alterations and network disruptions in CPHIV, linking them to hearing and language impairments. They offer insights into how HIV affects auditory and broader brain function in this population. ### Competing Interest Statement The authors have declared no competing interest.

IntroductionSchool-aged children experience crucial developmental changes in white matter (WM) in adolescence. The human immunodeficiency virus (HIV) affects neurodevelopment. Children living with perinatally acquired HIV (CPHIVs) demonstrate hearing and neurocognitive impairments when compared to their uninfected peers (CHUUs), but investigations into the central auditory system (CAS) WM integrity are lacking. The integration of the CAS and other brain areas is facilitated by WM fibers whose integrity may be affected in the presence of HIV, contributing to neurocognitive impairments.MethodsWe used diffusion tensor imaging (DTI) tractography to map the microstructural integrity of WM between CAS regions, including the lateral lemniscus and acoustic radiation, as well as between CAS regions and non-auditory regions of 11-year-old CPHIVs. We further employed a DTI-based graph theoretical framework to investigate the nodal strength and efficiency of the CAS and other brain regions in the structural brain network of the same population. Finally, we investigated associations between WM microstructural integrity outcomes and neurocognitive outcomes related to auditory and language processing. We hypothesized that compared to the CHUU group, the CPHIV group would have lower microstructural in the CAS and related regions.ResultsOur analyses showed higher mean diffusivity (MD), a marker of axonal maturation, in the lateral lemniscus and acoustic radiations, as well as WM between the CAS and non-auditory regions predominantly in frontotemporal areas. Most affected WM connections also showed higher axial and radial diffusivity (AD and RD, respectively). There were no differences in the nodal properties of the CAS regions between groups. The MD of frontotemporal and subcortical WM-connected CAS regions, including the inferior longitudinal fasciculus, inferior fronto-occipital fasciculus, and internal capsule showed negative associations with sequential processing in the CPHIV group but not in the CHUU group.DiscussionThe current results point to reduced axonal maturation in WM, marked by higher MD, AD, and RD, within and from the CAS. Furthermore, alterations in WM integrity were associated with sequential processing, a neurocognitive marker of auditory working memory. Our results provide insights into the microstructural integrity of the CAS and related WM in the presence of HIV and link these alterations to auditory working memory.

HIV exposed-uninfected (HEU) infants and children are at risk of developmental delays as compared to HIV uninfected unexposed (HUU) populations. The effects of exposure to in utero HIV and ART regimens on the HEU the developing brain are not well understood. In a cohort of 2-week-old newborns, we used diffusion tensor imaging (DTI) tractography and graph theory to examine the influence of HIV and ART exposure in utero on neonate white matter integrity and organisation. The cohort included HEU infants born to mothers who started ART before conception (HEUpre) and after conception (HEUpost), as well as HUU infants from the same community. We investigated HIV exposure and ART duration group differences in DTI metrics (fractional anisotropy (FA) and mean diffusivity (MD)) and graph measures across white matter. We found increased MD in white matter connections involving the thalamus and limbic system in the HEUpre group compared to HUU. We further identified reduced nodal efficiency in the basal ganglia. Within the HEUpost group, we observed reduced FA in cortical-subcortical and cerebellar connections as well as decreased transitivity in the hindbrain area compared to HUU. Overall, our analysis demonstrated distinct alterations in white matter integrity related to the timing of maternal ART initiation that influence regional brain network properties.

Hearing loss places a substantial burden on medical resources across the world and impacts quality of life for those affected. Further, it can occur peripherally and/or centrally. With many possible causes of hearing loss, there is scope for investigating the underlying mechanisms involved. Various signaling pathways connecting gut microbes and the brain (the gut-brain axis) have been identified and well established in a variety of diseases and disorders. However, the role of these pathways in providing links to other parts of the body has not been explored in much depth. Therefore, the aim of this review is to explore potential underlying mechanisms that connect the auditory system to the gut-brain axis. Using select keywords in PubMed, and additional hand-searching in google scholar, relevant studies were identified. In this review we summarize the key players in the auditory-gut-brain axis under four subheadings: anatomical, extracellular, immune and dietary. Firstly, we identify important anatomical structures in the auditory-gut-brain axis, particularly highlighting a direct connection provided by the vagus nerve. Leading on from this we discuss several extracellular signaling pathways which might connect the ear, gut and brain. A link is established between inflammatory responses in the ear and gut microbiome-altering interventions, highlighting a contribution of the immune system. Finally, we discuss the contribution of diet to the auditory-gut-brain axis. Based on the reviewed literature, we propose numerous possible key players connecting the auditory system to the gut-brain axis. In the future, a more thorough investigation of these key players in animal models and human research may provide insight and assist in developing effective interventions for treating hearing loss.

Children with perinatally acquired HIV (CPHIV) have poor cognitive outcomes despite early combination antiretroviral therapy (cART). While CPHIV-related brain alterations can be investigated separately using proton magnetic resonance spectroscopy (H-1-MRS), structural magnetic resonance imaging (sMRI), diffusion tensor imaging (DTI), and functional MRI (fMRI), a set of multimodal MRI measures characteristic of children on cART has not been previously identified. We used the embedded feature selection of a logistic elastic-net (EN) regularization to select neuroimaging measures that distinguish CPHIV from controls and measured their classification performance via the area under the receiver operating characteristic curve (AUC) using repeated cross validation. We also wished to establish whether combining MRI modalities improved the models. In single modality analysis, sMRI volumes performed best followed by DTI, whereas individual EN models on spectroscopic, gyrification, and cortical thickness measures showed no class discrimination capability. Adding DTI and H-1-MRS in basal measures to sMRI volumes produced the highest classification performance ovalidation accuracy = 85%, AUC = 0.80). The best multimodal MRI set consisted of 22 DTI and sMRI volume features, which included reduced volumes of the bilateral globus pallidus and amygdala, as well as increased mean diffusivity (MD) and radial diffusivity (RD) in the right corticospinal tract in cART-treated CPHIV. Consistent with previous studies of CPHIV, select subcortical volumes obtained from sMRI provide reasonable discrimination between CPHIV and controls. This may give insight into neuroimaging measures that are relevant in understanding the effects of HIV on the brain, thereby providing a starting point for evaluating their link with cognitive performance in CPHIV.

PurposeAlthough 3D EPI is more susceptible to motion artifacts than 2D EPI, it presents some benefits for functional MRI, including the absence of spin‐history artifacts, greater potential for parallel imaging acceleration, and better functional sensitivity in high‐resolution imaging. Here we present a self‐navigated 3D‐EPI sequence suitable for prospective motion‐corrected functional MRI without additional hardware or pulses.MethodsFor each volume acquisition, the first 24 of the 52 partitions being acquired are accumulated to a new feedback block that was added to the image reconstruction pipeline. After zero‐filling the remaining partitions, the feedback block constructs a volumetric self‐navigator (vSNav), co‐registers it to the reference vSNav acquired during the first volume acquisition, and sends motion estimates to the sequence. The sequence then updates its FOV and acquires subsequent partitions with the adjusted FOV, until the next update is received. The sequence was validated without and with intentional motion in phantom and in vivo on a 3T Skyra.ResultsFor phantom scans, the FOV was updated 0.704 s after acquisition of the vSNav partitions, and for in vivo scans after 0.768 s. Both phantom and in vivo data demonstrated stable motion estimates in the absence of motion. For in vivo acquisitions, prospective head‐pose estimates using the vSNav's and retrospective estimates with FLIRT (FMRIB's Linear Image Registration Tool) agreed to within 0.23 mm (< 10% of the slice thickness) and 0.14° in all directions.ConclusionDepending when motion occurs during a volume acquisition, the proposed method fully corrects the FOV and recovers image quality within one volume acquisition.

Introduction: Even with the increased access and early initiation of combination antiretroviral therapy, children with perinatally acquired human immunodeficiency virus (CPHIV) continue to demonstrate white matter alterations. Children perinatally HIV-exposed, but uninfected (CHEU) alike show differences in white matter integrity compared with children who are HIV-unexposed and uninfected (CHUU).Objectives: Mapping white matter connections that link gray matter regions that form resting-state (RS) functional networks may demonstrate whether structural and functional connectivity alterations in HIV infection and exposure may be related. We hypothesized reduced structural connectivity in CPHIV within the default mode network (DMN), visual, ventral DMN (vDMN), somatosensory, salience, auditory, motor, executive, basal ganglia, and posterior DMN (pDMN). We also hypothesized that CHEU will have increased structural connectivity compared with CHUU in the vDMN, somatosensory, pDMN, dorsal attention, salience, auditory, motor and basal ganglia.Methods: Study participants were 61 seven-year-old CPHIV and 46 age-matched children who are HIV uninfected (CHU) (19 CHEU). We used diffusion tensor imaging-based tractography to investigate white matter connections that link gray matter regions within RS functional networks.Results: We found altered white matter integrity in the somatosensory, salience, default mode, and motor networks of CPHIV compared with CHU. The superior temporal cortex, superior frontal cortex, and putamen were affected in all four networks and have also been reported to demonstrate morphological alterations in the same cohort. In CHEU, white matter integrity was higher in the visual network, pDMN, and motor network compared with CHUU.Conclusion: Our results suggest that altered white matter integrity may influence gray matter morphology and functional network alterations. Impact statementThe long-term effects of human immunodeficiency virus (HIV) and exposure on the developing brain in the combination antiretroviral therapy era are still not well known. We use diffusion tensor imaging-based tractography to explore these effects on white matter connections that link gray matter regions within functional networks. Our findings provide a context for HIV-associated white matter and connectivity abnormalities.

Participation in ultra-endurance events has increased in recent years and requires extreme levels of moderate to vigorous physical activity (MVPA). Moderate levels of MVPA have been associated with increased brain volume but the effects of extreme levels of MVPA on brain volume is unknown. As a result, we sought to compare the brains of those who engage in extremely high levels of MVPA with those who are sedentary using magnetic resonance imaging. We performed whole brain volumetric analyses and voxel-based morphometry on 12 ultra-endurance athletes (1078.75 ± 407.86 min of MVPA/week) and 9 sedentary persons (18.0 ± 56.9 min of MVPA/week). Whole-brain analyses revealed that those who participate in ultra-endurance training have increased grey (p< 0.0001), white (p = 0.031), and total matter volume (p < 0.0001), while regional analyses revealed that ultra-endurance athletes have smaller regional grey matter volume in the right primary sensory and motor cortex, inferior and middle frontal gyrus, and left thalamus. Future research is warranted to determine why ultra-endurance athletes have lower regional volumes in these areas despite having overall increased grey and white matter volumes.

Background: Due to changes in guidelines and access to treatment, more children start combination antiretroviral therapy (ART) in infancy. With few studies examining the long-term effects of perinatal HIV infection and early ART on neurodevelopment, much is still unknown about brain maturation in the presence of HIV and ART. Follow-up studies of HIV infected (HIV+) children are important for monitoring brain development in the presence of HIV infection and ART. Methods: We use diffusion tensor imaging (DTI) to examine white matter (WM) in 65 HIV+ and 46 control (HIV exposed uninfected (HEU) and HIV unexposed uninfected (HU)) 7-year-old children. This is a follow up of a cohort studied at 5 years, where we previously reported lower fractional anisotropy (FA) in corticospinal tract (CST) and mean diffusivity (MD) increases in inferior/superior longitudinal fasciculi (ILF/SLF), inferior fronto-occipital fasciculus (IFOF) and uncinate fasciculus (UF) in HIV+ children compared to uninfected controls. In addition, we also found a difference in FA related to age at which ART was initiated. Results: At 7 years, we found two regions in the left IFOF and left ILF with lower FA in HIV+ children compared to controls. Higher MD was observed in a similar region in the IFOF, albeit bilaterally, as well as multiple clusters bilaterally in the superior corona radiata (SCR), the anterior thalamic radiation (ATR) and the right forceps minor. Unlike at 5 years, we found no impact on WM of ART initiation. In HEU children, we found a cluster in the right posterior corona radiata with higher FA compared to HU children, while bilateral regions in the CST demonstrated reduced MD. Conclusions: At age 7, despite early ART and viral load (VL) suppression, we continue to observe differences in WM integrity. WM damage observed at age 5 years persists, and new damage is evident. The continued observation of regions with lower FA and higher MD in HIV+ children point to disruptions in ongoing white matter development regardless of early ART. Lastly, in HEU children we find higher FA and lower MD in clusters in the CST tract suggesting that perinatal HIV/ART exposure has a long-term impact on WM development.

Introduction Although previous MRI studies have consistently shown immunodeficiency-related white matter (WM) alterations in humans and animal models, investigations of early development in childhood have typically included wide age ranges during which both WM volume and fractional anistropy (FA) increase significantly as part of normal development. Here, we use diffusion tensor imaging (DTI) to examine WM alterations in HIV infected children at age 7 years and compare those who initiated Antiretroviral therapy (ART) before and after 12 weeks of age. Methods POPULATION: MRI scanning was performed on 121 Xhosa and Cape Coloured 7 year old children as part of the longitudinal, neurodevelopmental Children with HIV Early Antiretroviral Therapy (CHER) trial in Cape Town, South Africa. The group included HIV-infected children who were stable on ART, and age-matched controls from the same community as part of a parallel vaccine study. After exclusion of subjects (due to motion, artifacts, etc.), we examined data from 64 HIV-infected (HIV) children and 46 uninfected controls (CTRL). SCANNING PROCEDURE: Children in the study were scanned on a 3T Siemens Allegra (Erlangen, Germany) with a single channel head coil. Children were scanned with structural T 1 imaging (MEMPRAGE) followed by 2 DTI acquisitions with opposite phase encoding (AP-PA) directions using a prospectively motion-corrected navigated twice-refocused spin echo sequence with 5 reacquisitions. Acquisition parameters for diffusion were: TR/TE = 10100/86 ms, 72 slices, voxel = 2 × 2 × 2 mm3, FOV = 224 mm, 30 non-collinear diffusion directions with b = 1000 s/mm2, and four non-diffusion-weighted (b0) acquisitions. Results Comparing the HIV group to CTRL, two regions in the left inferior fronto-occipital fasciculus and left inferior longitudinal fasciculus showed lower FA, and 7 bilateral regions throughout the superior longitudinal fasciculus, superior and inferior fronto-occipital fasciculi, and left corticospinal tract showed higher MD. Conclusion Lower FA and higher MD in HIV-infected children were largely attributable to higher radial diffusivity, indicative of poorer myelination in the affected regions. Some regions with increased MD also showed increased axial diffusivity. Both axial and radial diffusivity have been shown to decrease from neonates to 1-year olds and throughout childhood. The higher levels in HIV-infected children seen here could be indicative of altered developmental trajectories.

Purpose: To reconstruct accurate single- and multichannel Bloch-Siegert transmit radiofrequency (|B-1(+)|) field maps from highly accelerated data.Theory and Methods: The approach is based on the fact that the |B-1(+)|-to-phase encoding pulse for each transmit coil and off-resonance frequency applies a unique phase shift to the same underlying image. This enables joint reconstruction of all images in a Bloch-Siegert acquisition from an augmented set of virtual receive coils, using any autocalibrated parallel imaging reconstruction method.Results: Simulations with an eight channel transmit/receive array head coil at 7T show that accurate |B-1(+)| maps can be produced at acceleration factors of 16x and 6x for Cartesian and spiral sampling, respectively. A phantom experiment with a six channel transverse electromagnetic (TEM) transceive array coil allowed accurate reconstruction at 16x acceleration. 7T in vivo experiments performed using 32 channel receive and two-channel transmit coils further demonstrate the proposed method's ability to produce high-quality |B-1(+)| maps at accelerations of 32x and 8x for Cartesian and spiral trajectories, respectively. Reconstruction accuracy is improved using disjoint k-space sampling patterns between acquisitions.Conclusion: The proposed approach allows high acceleration factors in Bloch-Siegert |B-1(+)| mapping and can significantly reduce the scan time requirements for mapping the |B-1(+)| fields of transmit arrays. (c) 2013 Wiley Periodicals, Inc.

A new family of optimized encoding pulses for Bloch–Siegert (BS) |B1+| mapping is introduced, as well as an algorithm to design them. The pulses are designed by numerical maximization of BS sequence sensitivity, subject to constraints that ensure low on-resonance excitation. The pulses are in all cases characterized by a constant envelope and U-shaped frequency sweep. They are validated in simulations, 7T in vivo experiments, and an experiment to measure their on-resonance excitation, and are compared to a Fermi pulse conventionally used in the BS method. The pulses are shown to produce larger phase shifts in a shorter time and with lower on-resonance excitation than the Fermi pulse, which results in lower SAR and improved |B1+| accuracy in areas of the body with large main field inhomogeneities.

channel implementations of amplitude and phase modulated pulses. Each pixel corresponds to a mean percent error calculated for the central axial slice of a single/dual B1 + map of the same human head phantom. For the dual channel simulations two classes of pulses were generated. The first class utilized maximal available RF amplitude on both channels; the second class utilized half of the available amplitude. Notice that performance similar to the singlechannel implementation can be achieved for the second class of pulses but in half the time. Grey dots mark a 1 ms pulse duration. Fig.1: Schematic of the optimization space S for a dualtransmit channel system. The amplitude and phase modulated waveforms RF1(t) and RF2(t) act on spins in different spaces [S1 S3] and [S2 S3], correspondingly. Their combined performance in the final space S is the results of interaction of these two waveforms at each point in time during their execution. Multi-channel Implementation of Semi-Adiabatic Excitation Pulses Marcin Jankiewicz and Jay Moore MRC/UCT Medical Imaging Research Unit, Department of Human Biology, University of Cape Town, Observatory, Western Cape, South Africa, Department of Radiology and Radiological Sciences, Vanderbilt University, Nashville, TN, United States

Quantitative magnetization transfer (qMT) imaging yields indices describing the interactions between free water protons and immobile macromolecular protons. These indices include the macromolecular to free pool size ratio (PSR), which has been shown to be correlated with myelin content in white matter. Because of the long scan times required for whole-brain imaging (≈20–30min), qMT studies of the human brain have not found widespread application. Herein, we investigated whether the increased signal-to-noise ratio available at 7.0T could be used to reduce qMT scan times. More specifically, we developed a selective inversion recovery (SIR) qMT imaging protocol with a i) novel transmit radiofrequency (B1+) and static field (B0) insensitive inversion pulse, ii) turbo field-echo readout, and iii) reduced TR. In vivo qMT data were obtained in the brains of healthy volunteers at 7.0T using the resulting protocol (scan time≈40s/slice, resolution=2×2×3mm3). Reliability was also assessed in repeated acquisitions. The results of this study demonstrate that SIR qMT imaging can be reliably performed within the radiofrequency power restrictions present at 7.0T, even in the presence of large B1+ and B0 inhomogeneities. Consistent with qMT studies at lower field strengths, the observed PSR values were higher in white matter (mean±SD=17.6±1.3%) relative to gray matter (10.3±1.6%) at 7.0T. In addition, regional variations in PSR were observed in white matter. Together, these results suggest that qMT measurements are feasible at 7.0T and may eventually allow for the high-resolution assessment of changes in composition throughout the normal and diseased human brain in vivo.

Spatially selective excitation pulses have been designed to produce uniform flip angles in the presence of the RF and static field inhomogeneities typically encountered in MRI studies of the human brain at 7 T. Pulse designs are based upon non-selective, composite pulses numerically optimized for the desired performance over prescribed ranges of field inhomogeneities. The non-selective pulses are subsequently transformed into spatially selective pulses with the same field-insensitive properties through modification of the spectral composition of the individual sub-pulses which are then executed in conjunction with an oscillating gradient waveform. An in-depth analysis of the performance of these RF pulses is presented in terms of total pulse durations, slice profiles, linearity of in-slice magnetization phase, sensitivity to RF and static field variations, and signal loss due to T(2) effects. Both simulations and measurements in phantoms and in the human brain are used to evaluate pulses with nominal flip angles of 45° and 90°. Target slice thickness in all cases is 2mm. Results indicate that the described class of field-insensitive RF pulses is capable of improving flip-angle uniformity in 7 T human brain imaging. There appears to be a subset of pulses with durations ≲10 ms for which non-linearities in the magnetization phase are minimal and signal loss due to T(2) decay is not prohibitive. Such pulses represent practical solutions for achieving uniform flip angles in the presence of the large field inhomogeneities common to high-field human imaging and help to better establish the performance limits of high-field imaging systems with single-channel transmission.