Echo-planar Imaging Sequence Research Articles

Accelerated J-resolved 1 H-MRSI with limited and sparse sampling of ( -space.

To accelerate the acquisition of J-resolved proton magnetic resonance spectroscopic imaging (1 H-MRSI) data for high-resolution mapping of brain metabolites and neurotransmitters. The proposed method used a subspace model to represent multidimensional spatiospectral functions, which significantly reduced the number of parameters to be determined from J-resolved 1 H-MRSI data. A semi-LASER-based (Localization by Adiabatic SElective Refocusing) echo-planar spectroscopic imaging (EPSI) sequence was used for data acquisition. The proposed data acquisition scheme sampled -space in variable density, where t1 and t2 specify the J-coupling and chemical-shift encoding times, respectively. Selection of the J-coupling encoding times (or, echo time values) was based on a Cramer-Rao lower bound analysis, which were optimized for gamma-aminobutyric acid (GABA) detection. In image reconstruction, parameters of the subspace-based spatiospectral model were determined by solving a constrained optimization problem. Feasibility of the proposed method was evaluated using both simulated and experimental data from a spectroscopic phantom. The phantom experimental results showed that the proposed method, with a factor of 12 acceleration in data acquisition, could determine the distribution of J-coupled molecules with expected accuracy. In vivo study with healthy human subjects also showed that 3D maps of brain metabolites and neurotransmitters can be obtained with a nominal spatial resolution of 3.0 × 3.0 × 4.8 mm3 from J-resolved 1 H-MRSI data acquired in 19.4 min. This work demonstrated the feasibility of highly accelerated J-resolved 1 H-MRSI using limited and sparse sampling of -space and subspace modeling. With further development, the proposed method may enable high-resolution mapping of brain metabolites and neurotransmitters in clinical applications.

Altered Whole-Brain Functional Networks in Drug-Naïve, First-Episode Adolescents With Major Depression Disorder.

Neuroimaging studies have demonstrated disrupted brain functional networks in major depression disorder (MDD); however, alterations to whole-brain networks specifically associated with adolescent MDD remain poorly understood. To investigate the topological architecture of intrinsic brain functional networks in drug-naïve, first-episode adolescent MDD patients using graph theoretical analysis. Prospective. In all, 109 adolescent MDD patients and 70 healthy control subjects. 3.0T; gradient-echo echo-planar imaging sequence. After the construction of whole-brain functional networks by thresholding partial correlation matrices of 90 brain regions, we calculated the topological properties (eg, small-world, efficiency, and nodal centrality) using graph theoretical analysis. A chi-squared test was used to compare the gender-ratio difference, and a two-sample t-test was used in the comparison of age. We compared network measures between the two groups using nonparametric permutation tests. Exploratory partial correlation analyses were used to determine the relationships between the topological metrics showing significant between-group differences and the clinical variables for adolescent MDD patients. Small-world architecture in brain functional networks was identified for both the MDD and control groups. However, depressed adolescents exhibited lower characteristic path length, normalized characteristic path length and clustering coefficient, and higher global efficiency than controls (false discovery rate [FDR] q < 0.05). Compared with controls, depressed adolescents exhibited increased nodal centralities in the default mode regions, including the right anterior cingulate and paracingulate gyri, left posterior cingulate gyrus, right superior frontal gyrus (medial part), bilateral hippocampus, and bilateral parahippocampal gyrus, and decreased nodal centralities in the orbitofrontal, temporal, and occipital regions (FDR q < 0.05). This study indicated that drug-naïve, first-episode adolescent MDD patients exhibit disruptions in whole-brain functional networks. 1 TECHNICAL EFFICACY STAGE: 2 J. MAGN. RESON. IMAGING 2020;52:1790-1798.

Dysfunction of cerebellum functional connectivity between default mode network and cerebellar structures in patients with mild traumatic brain injury in acute stage. rsfMRI study

Mild traumatic brain injury (mTBI) is the most common neurological damage in children that's why it is extremely important to identify and analyze biomarkers that can help in predicting patient's treatment and recovery in period of mTBI. Aim of this study is to verify a hypothesis that functional connectivity disturbances between intact cerebellum and DMN nodes are included in symptomatic manifestation of mTBI.Methods. 28 MR negative patients with mTBI were studied in age from 12 to 17 years (mean age – 14.7 years). The control group consisted of 23 healthy children. All MRI studies wereperformed on a Philips AchievadStream 3.0 T scanner equipped with a 32-channelPhilips dStream head coil. A 4 min rsfMRI gradient-echo echo planar imaging (EPI)sequence was acquired (TR = 3000 ms, echo time (TE) = 30 ms, 80 dynamics withdynamic scan time = 3 s). fMRI data were processed using functional connectivitytoolbox CONN.Results. No statistically significant differences in correlation strengths between control group and group of patients were detected as a result of DMN analysis. Intergroup seed-basedcorrelation ROI analysis revealed statistically significant (p &lt; 0.05) differencein links between DMN regions and vermis (cerebellum): positive link in control group and negative link in groupof patients.Conclusions. The revealed changes in DMN neuronal connection and cerebellar regions in acute stage of mTBI patients can be an initial step of damages leading to cognitive deficit which can be developed in future.

S151. HIPPOCAMPAL CONNECTIVITY AND VOLUME AS PREDICTORS OF TREATMENT RESPONSE – A REPLICATION STUDY IN TWO PSYCHOSIS COHORTS

BackgroundApproximately 30% of patients with schizophrenia do not improve with antipsychotic drug (APD) treatment and 60% show sub-optimal response. Converging lines of evidence point to hippocampal dysfunction in schizophrenia. It is thought that hippocampal dysfunction spreads across hippocampal subfields and to cortical regions by way of long-range efferent projections. Our prior studies have shown altered hippocampal regional cerebral blood flow in unmedicated patients and normalization after APD treatment. Meta-analyses show reduced hippocampal volume in first episode psychosis (FEP) patients. We evaluated resting state hippocampal functional connectivity (hFC) as well as hippocampal and hippocampal subfield volumes as predictors of treatment response (TR) in two cohorts of patients with a psychosis spectrum disorder. All patients were subsequently treated with an APD for 6 weeks.MethodsCohort 1 consisted of 55 medication-naïve first episode psychosis (FEP) subjects (36 male; mean age 24.18 years). Cohort 2 consisted of 42 unmedicated patients with schizophrenia (SZ) (31 male; mean age 27.9 years).FEP were scanned on a Siemens MAGNETOM Prisma MRI scanner using a 20 channel head coil. Anatomical scans were acquired via T1-weighted and T2-weighted images. Two 6-minute resting state scans were acquired in opposing phase encoding directions (A > P and P > A).SZ were scanned on a Siemens MAGNETOM Allegra MRI scanner with a circularly polarized transmit/receive head coil. Anatomical scans were acquired via a T1-weighted sequence. Resting state scans were acquired with a single 5-minute gradient recalled echo-planar imaging sequence.For both datasets, resting state data were preprocessed in the CONN toolbox (version 18a). We used the left hippocampus as a seed region to create whole brain seed-to-voxel correlation maps for each subject. Regression analyses were then performed to assess the relationship between resting state connectivity and TR (% change in BPRS positive score from (A) baseline to (B) after 6 weeks of APD: (((B-A)/A)*-100). Analyses were corrected using voxel (p < 0.05, uncorrected) and cluster level correction (p < 0.05, FDR corrected). Age, sex, and framewise displacement were used as covariates of no interest.T1 and T2 weighted images were preprocessed using FreeSurfer 6.0. Freesurfer’s hippocampus subfield segmentation module was used to calculate left and right subfield volumes. SPSS 25 was used to regress hippocampal subfield volumes on TR. Age and estimated total intracranial volume (eTIV) were included as covariates of no interest.ResultsIn both cohorts greater hFC to the cuneus and precuneus was predictive of better TR, as was greater hFC to the fusiform gyrus, medial prefrontal cortex (PFC) and anterior cingulate cortex in cohort 2. Reduced hFC connectivity to the angular gyrus in supramarginal gyrus and temporal pole in cohort 1 as well as the orbitofrontal cortex and dorsolateral PFC in cohort 2 were also predictive of better TR. Results from the stepwise regression showed that neither right nor left whole hippocampal volume, or subfield volumes, significantly predict TR for either cohort.DiscussionIn two patient cohorts, we observed a similar pattern where increased hFC to the cuneus and precuneus was predictive of better response to APD. Furthermore, the lack of a significant predictive value of hippocampal volumes in predicting TR was replicated in each cohort. The replicability of these findings, particularly in a cohort of medication-naïve FEP provides potential biological patterns useful in determining initial response to APD medication in patients with a psychosis spectrum disorder.

3D isotropic resolution diffusion-prepared magnitude-stabilized bSSFP imaging with high geometric fidelity at 1.5 Tesla.

MRI has been increasingly used in radiation therapy to facilitate tumor and organ delineation and assess treatment response. Diffusion MRI can provide cellularity information and may enable functional-based treatment planning and adaptation. However, strong distortion associated with the conventional diffusion-weighted single-shot echo-planar imaging (DW-ssEPI) sequence is problematic for accurate target delineation. The goal of this work is to propose a 3D diffusion sequence with minimal distortion for radiation therapy applications. A 3D diffusion-prepared magnitude-stabilized balanced steady-state free precession sequence (DP-MS-bSSFP) was developed. A 2D navigator was acquired during the linear catalyzation stage of the bSSFP readout to estimate the phase, which was then used in a plane-by-plane low-rank constrained reconstruction to correct the shot-to-shot k-space inconsistency. A diffusion phantom was scanned to evaluate and compare the geometric reliability and apparent diffusion coefficient (ADC) accuracy with the conventional DW-ssEPI. Eight landmarks were selected on each slice of the images to calculate the target registration error (TRE), which was used as a surrogate for geometric fidelity. The phantom was scanned under both 0℃ and room temperature. Brain scans were performed on five healthy volunteers. In the first volunteer, protocols of 1, 2, and 4 shots per Kz plane were compared. In vivo geometric fidelity and ADC accuracy were evaluated on the remaining four volunteers using the protocol of four shots per Kz plane. In the geometric fidelity study, 8-10 landmarks were picked on each slice to calculate the TRE. Regions of interest were placed on the white matter, the cerebellum, and the cerebrospinal fluid region to evaluate the ADC agreement between DW-ssEPI and DP-MS using the Bland-Altman plot. All scans were performed at 1.5mm isotropic resolution to meet the high-resolution requirement of many radiotherapy applications. The DP-MS had drastically improved geometric accuracy compared with DW-ssEPI on the phantom. The mean TRE decreased from 2.09mm to 0.70mm. The percentage difference of the ADC values between the two diffusion sequences were less than 5.5% and 7% for the 0℃ and room temperature study, respectively. The DW-ssEPI had strong distortion and susceptibility-related artifacts at tissue air boundary, whereas distortion was minimal in DP-MS images. Overall, the mean/max TRE was over 2mm/7mm in the volunteers for DW-ssEPI, whereas less than 0.8mm/2mm for DP-MS. Good ADC agreement was observed for the white matter, the cerebellum, and the CSF based on the Bland-Altman plots. A 3D diffusion sequence was developed and validated. It provided high-resolution diffusion imaging with mean distortion less than 1mm at 1.5T, and is a promising imaging technique for treatment planning and adaptive radiotherapy.

Evaluation of microstructural changes in spinal cord of patients with degenerative cervical myelopathy by diffusion kurtosis imaging and investigate the correlation with JOA score

BackgroundTo explore the feasibility of the metrics of diffusion kurtosis imaging (DKI) for investigations of the microstructural changes of spinal cord injury in patients with degenerative cervical myelopathy (DCM) and the correlation between Japan Orthopaedic Association (JOA) scores and DKI metrics.MethodsFifty-seven patients with DCM and 38 healthy volunteers underwent 3.0 T magnetic resonance (MR) imaging with routine MRI sequences and DKI from echo-planar imaging sequence. Based on the JOA score, DCM patients were divided into four subgroups. DKI metrics of the DCM group and control group were obtained and compared, separately for the white matter (WM) and the gray matter (GM).ResultsThe FA values in WM were significantly lower (P = 0.020) in the DCM group than in the control group. The MK values in GM were lower (P = 0.011) in the DCM group than in the control group. The MD values in WM were significantly higher (P = 0.010) in the DCM group than in the control group. In GM, the JOA score was positively correlated with the MK values (r = 0.768, P < 0.05). In the WM, the JOA score was positively correlated with the FA values (r = 0.612, P < 0.05).ConclusionDKI provides quantitive evaluation to the characters of microstructure of the spinal cord damage in patients with DCM compared to conventional MR. MK values can reflect microstructural abnormalities of gray matter of the cervical spinal cord and provide more information beyond that obtained with routine diffusion metrics. In addition, MK values of GM and FA values of WM may as a be highly sensitive biomarker for the degree of cervical spinal cord damage.

Concurrent Imaging of Markers of Current Flow and Neurophysiological Changes During tDCS.

Despite being a popular neuromodulation technique, clinical translation of transcranial direct current stimulation (tDCS) is hampered by variable responses observed within treatment cohorts. Addressing this challenge has been difficult due to the lack of an effective means of mapping the neuromodulatory electromagnetic fields together with the brain’s response. In this study, we present a novel imaging technique that provides the capability of concurrently mapping markers of tDCS currents, as well as the brain’s response to tDCS. A dual-echo echo-planar imaging (DE-EPI) sequence is used, wherein the phase of the acquired MRI-signal encodes the tDCS current induced magnetic field, while the magnitude encodes the blood oxygenation level dependent (BOLD) contrast. The proposed technique was first validated in a custom designed phantom. Subsequent test–retest experiments in human participants showed that tDCS-induced magnetic fields can be detected reliably in vivo. The concurrently acquired BOLD data revealed large-scale networks characteristic of a brain in resting-state as well as a ‘cathodal’ and an ‘anodal’ resting-state component under each electrode. Moreover, ‘cathodal’s BOLD-signal was observed to significantly decrease with the applied current at the group level in all datasets. With its ability to image markers of electromagnetic cause as well as neurophysiological changes, the proposed technique may provide an effective means to visualize neural engagement in tDCS at the group level. Our technique also contributes to addressing confounding factors in applying BOLD fMRI concurrently with tDCS.

Diffusion Tensor Imaging for Diagnosing Root Avulsions in Traumatic Adult Brachial Plexus Injuries: A Proof-of-Concept Study.

Cross-sectional MRI has modest diagnostic accuracy for diagnosing traumatic brachial plexus root avulsions. Consequently, patients either undergo major exploratory surgery or months of surveillance to determine if and what nerve reconstruction is needed. This study aimed to develop a diffusion tensor imaging (DTI) protocol at 3 Tesla to visualize normal roots and identify traumatic root avulsions of the brachial plexus. Seven healthy adults and 12 adults with known (operatively explored) unilateral traumatic brachial plexus root avulsions were scanned. DTI was acquired using a single-shot echo-planar imaging sequence at 3 Tesla. The brachial plexus was visualized by deterministic tractography. Fractional anisotropy (FA) and mean diffusivity (MD) were calculated for injured and avulsed roots in the lateral recesses of the vertebral foramen. Compared to healthy nerves roots, the FA of avulsed nerve roots was lower (mean difference 0.1 [95% CI 0.07, 0.13]; p < 0.001) and the MD was greater (mean difference 0.32 × 10−3 mm2/s [95% CI 0.11, 0.53]; p < 0.001). Deterministic tractography reconstructed both normal roots and root avulsions of the brachial plexus; the negative-predictive value for at least one root avulsion was 100% (95% CI 78, 100). Therefore, DTI might help visualize both normal and injured roots of the brachial plexus aided by tractography. The precision of this technique and how it relates to neural microstructure will be further investigated in a prospective diagnostic accuracy study of patients with acute brachial plexus injuries.

MR-guided focused ultrasound application for moving target tumor ablation in abdominal area: coil selection.

Magnetic Resonance Imaging (MRI)-guided Focused Ultrasound Surgery (MRgFUS) is a non-invasive thermal ablation method utilizing high-intensity focused ultrasound (HI-FU) energy for tissue ablation under MRI with real-time thermal mapping. Ablating to a dynamic target as in the liver is very challenging, requiring approval. A novel quality-assured liver tumor ablation system has been proposed for clinics. The paper reports the evaluation of conventional and new MR-receiving coils. To evaluate the suitability of MR coils as part of the MRgFUS treatment system for liver, while simulating breathing motion in pre-clinical settings. The novel software communicates with the MR scanner and the transducer. To monitor the temperature via proton resonance frequency (PRF) methodology echo planar imaging (EPI) sequence was used while the algorithms of static, static and dynamic tracking were tested with sonications of 100 W for 30 s on tissue-mimicking phantoms. Different coil sets were used to assess the performance of the system for fitness for dynamic thermometry. Finally, in vivo experiments were performed over a porcine model. Single-loop four-channel Duoflex and Gem coils provided adequate signal-to-noise ratio and contrast with consistent thermal readings. Body array coils showed severe loss of signal in dynamic cases since the integration of tracking algorithm causes low efficiency. Body array coils are unsuitable for MRgFUS of the liver due to signal loss. The dedicated coil set with a single loop around the FUS transducer combined with four-channel arrays might be the best option for liver treatment using dynamic MRgFUS applications.

Role of diffusion-weighted imaging in differentiation between posterior fossa brain tumors

BackgroundDiffusion-weighted imaging (DWI) is an imaging modality using multi-section single-shot spin echo planar imaging (EPI) sequence which is extremely sensitive for detection of water motion within intra, extra, and transcellular regions. This character is important to differentiate between brain tumors either low (benign) or highly (malignant) cellular tumors.ObjectiveTo evaluate the role of DWI and apparent diffusion coefficient (ADC) in evaluation and differentiation between different brain posterior fossa tumors in children and adults.Patients and methodsThe study included 34 patients with different brain posterior fossa tumors for evaluation by conventional MRI (using 1.5 T MRI PHILIPS Achieva 2.1 Best Netherland) and DWI.ResultsOur study showed that mean ADC values were significantly different between the four groups of posterior fossa tumors in children: juvenile pilocytic astrocytoma (JPA), medulloblastoma, ependymoma, and brain stem glioma while mean ADC values were not significantly different between posterior fossa tumors in the adult group. Regions of interest were manually positioned, and all values were automatically calculated and expressed in 10−3 mm2/s.ConclusionDWI is an ideal additional imaging technique, which is a rapid, easy, non-invasive imaging modality, with no contrast injection needed. It has been widely applied in the differentiation between posterior fossa brain tumors and in the diagnosis of various intracranial diseases.

Neuroprotective Effect of Low-Intensity Transcranial Ultrasound Stimulation in Moderate Traumatic Brain Injury Rats.

Traumatic brain injury (TBI) is a kind of severe brain injury characterized with a high incidence rate and a high disability rate. Low-intensity transcranial ultrasound stimulation (LITUS) is a promising neuroprotective method for improving the functional prognosis of TBI. The fractional anisotropy (FA) value and mean diffusivity (MD) value can be sensitive to abnormal brain structure and function and can thus be used to evaluate the effect of LITUS on TBI. Our purpose was to evaluate the therapeutic effect of LITUS in a moderate TBI rat model with FA and MD values. For our method, we used 45 male Sprague Dawley rats (15 sham normal, 15 TBI, and 15 LITUS treatment rats). We used single-shot spin echo echo-planar imaging sequences at 3.0T to obtain the DTI parameters. Parameters of FA and MD on the treated side of the injury cortex were measured to evaluate the therapeutic effect of LITUS in a TBI rat model. For FA and MD values, groups were compared by using a two-way analysis of variance for repeated measures, and this was followed by Tukey’s post hoc test. Differences were considered significant at P < 0.05. The results were that the FA value in the LITUS treatment group at 1 day after TBI was significantly higher than that in the control group (adjusted P = 0.0422) and significantly lower than that in the TBI group at 14, 21, and 35 days after TBI (adjusted P = 0.0015, 0.0064, and 0.0173, respectively). At the end of the scan time point, the differences between the two groups were not significant (adjusted P = 0.3242). The MD values in the LITUS treatment group were significantly higher in the early stage than that in the TBI group (adjusted P = 0.0167) and significantly lower at the following time points than in the TBI group. In conclusion, daily treatment with LITUS for 10 min effectively improved the brain damage in the Controlled Cortical Impact (CCI)-caused TBI model. FA and MD values can serve as evaluation indicators for the neuro-protective effect of LITUS.

Altered static and dynamic voxel-mirrored homotopic connectivity in subacute stroke patients: a resting-state fMRI study.

Sixty-four subacute stroke patients and 55 age-matched healthy controls (HCs) underwent a resting-state functional magnetic resonance imaging scan using an echo-planar imaging sequence and high-resolution sagittal T1-weighted images using a three-dimensional magnetization-prepared rapid gradient echo sequence. Static and dynamic voxel-mirrored homotopic connectivity (VMHC) was computed, respectively. The relationships between the clinical measures, including National Institutes of Health Stroke Scale (NIHSS), illness duration, Fugl-Meyer assessment for upper and lower extremities (FMA-total) and size of lesion volume, and the static/ dynamic VMHC variability alterations in stroke patients were calculated. The stroke patients showed significantly increased static VMHC in the corpus callosum, middle occipital gyrus and inferior parietal gyrus, and decreased static VMHC in the inferior temporal gyrus and precentral gyrus (PreCG) compared with those of HCs. For dynamic VMHC variability, increased dynamic VMHC variability in the inferior temporal gyrus and PreCG was detected in stroke patients relative to that in HCs. Correlation analysis exhibited that significant negative correlations were shown between the FMA scores and dynamic VMHC variability in PreCG. The present study suggests that combined static and dynamic VMHC could be helpful to evaluate the motor function of stroke patients and understand the intrinsic differences of inter-hemispheric coordination after stroke.

Iron Sucrose as MRI Contrast Agent in Ischemic Stroke Model

Despite the growing concern about the safety of gadolinium-based contrast agents (GBCAs), they are still the most commonly used. Ferumoxytol, as an off-label alternative MRI contrast agent, cannot be administered by a rapid bolus for dynamic susceptibility contrast perfusion-weighted imaging (DSC-PWI). To assess the feasibility of iron sucrose (IS) as a contrast agent for MR angiography (MRA) and DSC-PWI. Prospective animal model. Thirty-six normal rats (16 for MRA, 20 for biocompability tests) and 36 occlusion of the middle cerebral artery (MCAO) model rats. 3.0T; head and neck angiography, using a fast spoiled gradient-recalled-echo (FSPGR) sequence and DSC-MRI using echo planar imaging(EPI) sequence. MRA was performed on normal rats to examine the signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of different doses of IS. DSC-PWI was performed on MCAO rats at 0, 24, 48, and 72 hours postreperfusion to investigate the lesion detectability of IS. Arterial spin labeling (ASL) and DSC-PWI enhanced by GBCAs were conducted on MCAO rats as controls. Kruskal-Wallis test was used to compare qualitative assessment. One-way analysis of variance (ANOVA) was used to compare the parametric data. Pearson's r values were evaluated between relative cerebral blood flow(rCBF)-ASL, rCBF-DSCIS , and rCBF obtained from DSC-PWI enhanced by GBCA. The mean SNR and CNR of the common carotid artery at doses of 10 mg Fe/kg of IS were comparable with the standard dose of GBCAs (SNR: 68.04 ± 12.55 vs. 67.72 ± 14.66; CNR: 23.78 ± 7.21vs. 21.63 ± 6.83). In MCAO rat models, rCBF and relative cerebral blood volume (rCBV) of ipsilateral striatum declined (0.72 ± 0.14, 0.86 ± 0.11) with prolonged relative mean transit time (rMTT) and relative time-to-peak (rTTP) (1.27 ± 0.24, 1.07 ± 0.03) following occlusion. Hyperperfusion was observed in all rats at 48 and 72 hours postreperfusion, in 4/6 rats at 24 hours postreperfusion for IS-mediated DSC-PWI. IS may be an effective contrast agent for both MRA and DSC-PWI in ischemic stroke models. 1 TECHNICAL EFFICACY STAGE: 1 J. Magn. Reson. Imaging 2020;52:836-849.

Looping Star fMRI in Cognitive Tasks and Resting State.

Conventional T2 *-weighted functional magnetic resonance imaging (fMRI) is performed with echo-planar imaging (EPI) sequences that create substantial acoustic noise. The loud acoustic noise not only affects the activation of the auditory cortex, but may also interfere with resting state and task fMRI experiments. To demonstrate the feasibility of a novel, quiet, T2 *, whole-brain blood oxygenation level-dependent (BOLD)-fMRI method, termed Looping Star, compared to conventional multislice gradient-echo EPI. Prospective. Glover stability QA phantom; 10 healthy volunteers. 3.0T: gradient echo (GE)-EPI and T2 * Looping Star fMRI. Looping Star fMRI was presented and compared to GE-EPI with a working memory (WM) task and resting state (RS) experiments. Temporal stability and acoustic measurements were obtained for both methods. Functional maps and activation accuracy were compared to evaluate the performance of the novel sequence. Mean and standard deviation values were analyzed for temporal stability and acoustic noise tests. Activation maps were assessed with one-sample t-tests and contrast estimates (CE). Paired t-tests and receiver operator characteristic (ROC) were used to compare fMRI sensitivity and performance. Looping Star presented a 98% reduction in sound pressure compared with GE-EPI, with stable temporal stability (0.09% percent fluctuation), but reduced temporal signal-to-noise ratio (tSNR) (mean difference = 15.9%). The novel method yielded consistent activations for RS and WM (83.4% and 69.5% relative BOLD sensitivity), which increased with task difficulty (mean CE 2-back = 0.56 vs. 0-back = 0.08, P < 0.05). A few differences in spatial activations were found between sequences, leading to a 4-8% lower activation accuracy with Looping Star. Looping Star provides a suitable approach for whole-brain coverage with sufficient spatiotemporal resolution and BOLD sensitivity, with only 0.5 dB above ambient noise. From the comparison with GE-EPI, further developments of Looping Star fMRI should target increased sensitivity and spatial specificity for both RS and task experiments. 2. 1 J. Magn. Reson. Imaging 2020;52:739-751.

Utility of Diffusion‐Weighted Imaging for Guiding Clinical Management of Patients With Kidney Transplant: A Prospective Study

Although biopsy is essential for the diagnosis and management of kidney transplant recipients, it is invasive. Intravoxel incoherent motion diffusion-weighted imaging (IVIM-DWI) is a noninvasive technique that can assess both capillary perfusion and tissue diffusion. To evaluate the capability of IVIM-DWI as a differentiation of kidney transplant patients who need clinical intervention from those who need not. Prospective. In all, 33 kidney transplant patients who needed clinical intervention and 19 who need not. 3.0T; IVIM-DWI with a single-shot echo planar imaging sequence. All patients underwent kidney transplant biopsy and IVIM-DWI scans. Patients were dichotomized into those who needed clinical intervention (CHANGE group) and those who need not (Non-CHANGE group) based on biopsy results. The values of total apparent diffusion coefficient (ADCT ), diffusion coefficient (D), and perfusion fraction (f) were acquired from renal cortex and medulla, respectively. The area under the curve (AUC) was calculated and compared. Independent Student's t-test, receiver-operating characteristic curve, and Spearman correlation analysis. All the cortical and medullary DWI parameters in the CHANGE group were significantly lower than those in the Non-CHANGE group (all P ≤ 0.012). Except for medullary fp, all DWI parameters in both the cortex and the medulla were inversely correlated with both the chronic (ρ ranging from -0.33 to -0.54, all P ≤ 0.02) and acute (ρ ranging from -0.35 to -0.60, all P ≤ 0.01) composite scores. Cortical ADCT and D had the largest AUC and specificity of 0.84 and 75.8%, respectively. Combined use of cortical D and medullary fp at each optimal cutoff point yielded a specificity of 90.9%. DWI demonstrated potential as a noninvasive biomarker to allow the stratification of patients into categories in which kidney allograft biopsy results are or are not likely to change clinical management. 1 TECHNICAL EFFICACY STAGE: 5 J. Magn. Reson. Imaging 2020;52:565-574.

Abstract TP479: Early Effect of Human Immunodeficiency Virus on Cerebral Blood Flow and Autoregulation

Introduction: Human immunodeficiency virus (HIV)-infected individuals are at high risk for ischemic stroke. We measured cerebral blood flow (CBF), oxygen extraction fraction (OEF), and autoregulation in HIV infected subjects and controls. Methods: In treatment-naive HIV infected subjects and age-, gender-, and race-matched controls, OEF was measured by using MRI T2*-weighted echo-planar imaging sequences and CBF was measured by MRI pulsed arterial spin labeling (PASL) approach. Static cerebral autoregulation was determined by measuring changes in CBF and OEF, in response to ≈10% reductions in MAP induced by using IV Nicardipine infusion. All images were acquired using a Siemens 3T MR scanner (Treo, Siemens Medical Systems Inc). Cerebral autoregulation was measured globally and regionally in gray matter (GM), white matter (WM) and subcortical GM. Autoregulatory Index (AI) was computed using the equation AI = %CBF change/% MAP change supplemented by CBF associated OEF changes. Nominal p-values are uncorrected for multiple comparisons. Results: Forty-one treatment naive HIV-infected subjects and 47 age-, gender-, race-matched controls participated. HIV-infected subjects had higher CBF in cortical GM compared to the controls (76.8± 12 mL/100 g/min versus 71.6 ± 11 mL/100 g/min; p= 0.04), but not in white matter (30.9± 8 mL/100 g/min versus 30.0 ± 8 mL/100 g/min; p = 0.60) or subcortical GM (62.8± 13 mL/100 g/min versus 61.3 ± 13 mL/100 g/min; p = 0.57). Whole brain (WB), GM, WM, and subcortical GM, OEF were similar between the groups (p &gt; .05). The median AI were similar between cases and controls in WB (0.40 vs 0.18, p=0.86), GM (0.10 vs. 0.16, p=0.87), WM (0.80 vs. 0.87, p=0.31), and subcortical GM (1.65 vs. 1.77, p=0.26). A 12-month follow-up (N=30) in HIV-subjects on antiretroviral therapy did not produce a significant change in CBF or OEF in the WB, GM, WM, or subcortical GM (Paired sample t test p&gt;0.05). Similarly, no changes were noted on the AI (Wilcoxon Match Rank test p&gt;0.05). Conclusions: AI was similar between HIV cases and control and remained so after 12-months of antiretroviral therapy. We found no evidence of a defect in autoregulation to explain the high-risk of ischemic stroke documented in other studies.

Evaluating the Therapeutic Effect of Low-Intensity Transcranial Ultrasound on Traumatic Brain Injury With Diffusion Kurtosis Imaging.

Low-intensity transcranial ultrasound (LITUS) has a therapeutic effect on traumatic brain injury (TBI). Diffusion kurtosis imaging (DKI) might be able to evaluate the effect changes of injured brain microstructure. To evaluate the therapeutic effect of LITUS in a moderate TBI rat model with DKI parameters. Prospective case-control animal study. Forty-five rats were randomly divided into sham control, TBI, and LITUS treatment groups (n = 15). Single-shot spin echo echo-planar imaging and fast T2 WI sequences at 3.0T. DKI parameters were obtained on days 1, 7, 14, 21, 28, 35, and 42 after TBI. For the mean kurtosis (MK), axial kurtosis (Ka), and radial kurtosis (Kr) values, groups were compared using a two-way analysis of variance (ANOVA). LITUS inhibited TBI and caused MK values to increase significantly during the early stage (LITUS vs. TBI, day 7, adjusted P < 0.0001) and decrease during the late stage (LITUS vs. TBI, day 42, adjusted P = 0.0156) in the damaged cortex. In the thalamus, the MK value of the TBI group began to rise on day 7, with no change observed in the LITUS group. TBI increases Ka value during the early stage in the cortex and decreases during the late stage in the cortex and thalamus. LITUS inhibited these Ka changes (LITUS vs. TBI, day 7, adjusted P = 0.0014; LITUS vs. TBI, day 42, adjusted P = 0.0026 and 0.0478, respectively, for cortex and thalamus). The Kr value increased slightly during the early stage in the cortex (TBI vs. Sham, day 1, adjusted P = 0.0016). The DKI parameter, particularly the MK value, evaluates primary cortical injury as well as the secondary brain injury that could not be detected by conventional T2 WI. 1 Technical Efficacy Stage: 4 J. Magn. Reson. Imaging 2020;52:520-531.

Blood Oxygen Level-Dependent MRI of the Myocardium with Multiecho Gradient-Echo Spin-Echo Imaging.

Background Myocardial oxygenation imaging could help determine the presence of microvascular dysfunction associated with increased cardiovascular risk. However, it is challenging to depict the potentially small oxygenation alterations with current noninvasive cardiac MRI blood oxygen level-dependent (BOLD) techniques. Purpose To demonstrate the cardiac application of a gradient-echo spin-echo (GESE) echo-planar imaging sequence for dynamic and quantitative heartbeat-to-heartbeat BOLD MRI and evaluate the sequence in populations both healthy and with hypertension in combination with a breath hold-induced CO2 intervention. Materials and Methods GESE echo-planar imaging sequence was performed in 18 healthy participants and in eight prospectively recruited participants with hypertension on a 3.0-T MRI system. T2 and T2* maps were calculated per heartbeat with a four-parameter fitting technique. Septal regions of interests were used to determine T2 and T2* values per heartbeat and examined over the course of a breath hold to determine BOLD changes. T2 and T2* changes of healthy participants and participants with hypertension were compared by using a nonparametric Mann-Whitney test. Results GESE echo-planar imaging approach gave spatially stable T2 and T2* maps per heartbeat for healthy participants and participants with hypertension, with mean T2 values of 43 msec ± 5 (standard deviation) and 46 msec ± 9, respectively, and mean T2* values of 28 msec ± 5 and 22 msec ± 5, respectively. The healthy participants exhibited increasing T2 and T2* values over the course of a breath hold with a mean positive slope of 0.2 msec per heartbeat ± 0.1 for T2 and 0.2 msec per heartbeat ± 0.1 for T2*, whereas for participants with hypertension these dynamic T2 and T2* values had a mean negative slope of -0.2 msec per heartbeat ± 0.2 for T2 and -0.1 msec per heartbeat ± 0.2 for T2*. The difference in these mean slopes between healthy participants and participants with hypertension was significant for both T2 (P < .001) and T2* (P < .001). Conclusion Gradient-echo spin-echo echo-planar imaging sequence provided quantitative T2 and T2* maps per heartbeat and enabled dynamic heartbeat-to-heartbeat blood oxygen level-dependent (BOLD)-response imaging by analyzing changes in T2 and T2* over the time of a breath-hold intervention. This approach could identify differences in the BOLD response between healthy participants and participants with hypertension. © RSNA, 2020 Online supplemental material is available for this article. See also the editorial by Friedrich in this issue.

Characterization of serial hyperpolarized 13C metabolic imaging in patients with glioma

BackgroundHyperpolarized carbon-13 (HP-13C) MRI is a non-invasive imaging technique for probing brain metabolism, which may improve clinical cancer surveillance. This work aimed to characterize the consistency of serial HP-13C imaging in patients undergoing treatment for brain tumors and determine whether there is evidence of aberrant metabolism in the tumor lesion compared to normal-appearing tissue. MethodsSerial dynamic HP [1-13C]pyruvate MRI was performed on 3 healthy volunteers (6 total examinations) and 5 patients (21 total examinations) with diffuse infiltrating glioma during their course of treatment, using a frequency-selective echo-planar imaging (EPI) sequence. HP-13C imaging at routine clinical timepoints overlapped treatment, including radiotherapy (RT), temozolomide (TMZ) chemotherapy, and anti-angiogenic/investigational agents. Apparent rate constants for [1-13C]pyruvate conversion to [1-13C]lactate (kPL) and [13C]bicarbonate (kPB) were simultaneously quantified based on an inputless kinetic model within normal-appearing white matter (NAWM) and anatomic lesions defined from 1H MRI. The inter/intra-subject consistency of kPL-NAWM and kPB-NAWM was measured in terms of the coefficient of variation (CV). ResultsWhen excluding scans following anti-angiogenic therapy, patient values of kPL-NAWM and kPB-NAWM were 0.020 s−1 ± 23.8% and 0.0058 s−1 ± 27.7% (mean ± CV) across 17 HP-13C MRIs, with intra-patient serial kPL-NAWM/kPB-NAWM CVs ranging 6.8–16.6%/10.6–40.7%. In 4/5 patients, these values (0.018 s−1 ± 13.4% and 0.0058 s−1 ± 24.4%; n = 13) were more similar to those from healthy volunteers (0.018 s−1 ± 5.0% and 0.0043 s−1 ± 12.6%; n = 6) (mean ± CV). The anti-angiogenic agent bevacizumab was associated with global elevations in apparent rate constants, with maximum kPL-NAWM in 2 patients reaching 0.047 ± 0.001 and 0.047 ± 0.003 s−1 (±model error). In 3 patients with progressive disease, anatomic lesions showed elevated kPL relative to kPL-NAWM of 0.024 ± 0.001 s−1 (±model error) in the absence of gadolinium enhancement, and 0.032 ± 0.008, 0.040 ± 0.003 and 0.041 ± 0.009 s−1 with gadolinium enhancement. The lesion kPB in patients was reduced to unquantifiable values compared to kPB-NAWM. ConclusionSerial measures of HP [1-13C]pyruvate metabolism displayed consistency in the NAWM of healthy volunteers and patients. Both kPL and kPB were globally elevated following bevacizumab treatment, while progressive disease demonstrated elevated kPL in gadolinium-enhancing and non-enhancing lesions. Larger prospective studies with homogeneous patient populations are planned to evaluate metabolic changes following treatment.

Ensemble Learning for Early‐Response Prediction of Antidepressant Treatment in Major Depressive Disorder

In order to reduce unsuccessful treatment trials for depression, neuroimaging and genetic information can be considered as biomarkers. Together with machine-learning methods, prediction models have proved to be valuable for baseline prediction. To propose an ensemble learning modeling framework that integrates imaging and genetic information for individualized baseline prediction of early-stage treatment response of antidepressants in major depressive disorder (MDD). Prospective. In all, 98 inpatients with MDD. 3.0T MRI and gradient-echo echo-planar imaging sequence. Participants were divided into responders and nonresponders based on reducing rates of HDRS-6 after early-stage treatment of 2 weeks. Fourteen brain regions of interest were selected according to previous studies. An ensemble learning modeling framework was used to integrate imaging data and genetic data. Support vector machine (SVM) with linear kernel was utilized to integrate multimode information and then to construct the prediction model. Leave-one-out cross-validation (LOOCV) was used to evaluate the performance. The position characteristics obtained through SVM-RFE (recursive feature elimination) algorithm and LOOCV was considered to compare each feature's relative importance for the prediction model. Compared with the single-level prediction model, the ensemble learning prediction model showed improvement in prediction performance (accuracy from 0.61 to 0.86 with imaging data and genetic data). Integrated with 14 priori brain regions, the region of interest (ROI) map ensemble learning prediction model can achieve a performance that is analogous with the model with information from whole-brain regions (both with accuracy of 0.81). The integration of genetic features further improved the sensitivity of prediction (sensitivity from 0.78 to 0.87 under the ensemble learning framework). Our ensemble learning prediction model demonstrated significant advantages in interpretability and information integration. The findings may provide more assistance for clinical treatment selection in MDD at the individual level. 1 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2020;52:161-171.