Background
High blood pressure (BP) is a common risk factor for cerebral small vessel disease including white matter hyperintensity (WMH). Whether increased BP exacerbates WMH by impacting cerebral ...vascular morphologies remains poorly studied.
Purpose
To determine the relationships among high BP, cerebrovascular morphologies, and WMH in elderly individuals.
Study Type
Cohort.
Subjects
Eight hundred sixty‐three participants (54.2% female) from the Taizhou Imaging Study without clinical evidence of neurologic disorders were included in the analyses.
Field Strength/Sequence
3.0 T; time‐of‐flight magnetic resonance angiography (TOF MRA); T2 fluid‐attenuated inversion recovery (FLAIR); T1 magnetization‐prepared rapid gradient‐echo; gradient echo T2*‐weighted; diffusion tensor imaging; pulsed arterial spin labeling.
Assessment
Cerebrovascular morphologic measurements were quantified based on the TOF MRA images, including vessel density, radius, tortuosity, and branch number. WMH lesion volumes (WMHV) and WMH lesion counts (WMHC) were calculated automatically based on the T2 FLAIR images.
Statistical Tests
Multivariable linear regression analysis and path analysis with a linear single‐mediator model were employed. A P value <0.05 was considered statistically significant.
Results
Higher BP, especially diastolic BP, was significantly correlated with lower cerebrovascular density (β = −104) and lower branch numbers (β = −0.02). Although decreased tortuosity (β = −1.25) and increased radius (β = 93.8) were correlated with BP, no significant relationship of tortuosity (β = −4.6 × 10−4, P = 0.58) or radius (β = 0.03, P = 0.08) with BP in small vessels was found. The proportion of small vessels decreased as BP increased (SBP: β = −6.6 × 10−4; DBP: β = −9.0 × 10−4). Similarly, increased WMHV and WMHC were associated with decreased vessel density (volumes: β = −24, counts: β = −127), decreased tortuosity (volumes: β = −0.08, counts: β = −0.53), and increased radius (volumes: β = 12.6, counts: β = 86.6). Path analyses suggested an association between high BP and WMHs that were mediated by cerebrovascular morphologic changes.
Data Conclusion
Structural alterations of cerebral vessels induced by high BP are correlated with WMH. This result suggested that elevated BP might be one of the pathophysiological mechanisms involving in the co‐occurrence of cerebrovascular alteration and small vessel disease.
Level of Evidence: 1
Technical Efficacy Stage: 1
Purpose
The phase mismatch between odd and even echoes in EPI causes Nyquist ghost artifacts. Existing ghost correction methods often suffer from severe residual artifacts and are ineffective with ...k‐space undersampling data. This study proposed a deep learning–based method (PEC‐DL) to correct phase errors for DWI at 7 Tesla.
Methods
The acquired k‐space data were divided into 2 independent undersampled datasets according to their readout polarities. Then the proposed PEC‐DL network reconstructed 2 ghost‐free images using the undersampled data without calibration and navigator data. The network was trained with fully sampled images and applied to two‐ and fourfold accelerated data. Healthy volunteers and patients with Moyamoya disease were recruited to validate the efficacy of the PEC‐DL method.
Results
The PEC‐DL method was capable to mitigate the ghost artifacts in DWI in healthy volunteers as well as patients with Moyamoya disease. The fourfold accelerated results showed much less distortion in the lesions of the Moyamoya patient using high b‐value DWI and the corresponding ADC maps. The ghost‐to‐signal ratios were significantly lower in PEC‐DL images compared to conventional linear phase corrections, mini‐entropy, and PEC‐GRAPPA algorithms.
Conclusion
The proposed method can effectively eliminate ghost artifacts for full sampled and up to fourfold accelerated EPI data without calibration and navigator data.
Background
Gamma‐aminobutyric acid (GABA) is an inhibitory neurotransmitter in human brains, playing a role in the pathogenesis of various psychiatric disorders. Current methods have some ...non‐neglectable shortcomings and noninvasive and accurate detection of GABA in human brains is long‐term challenge.
Purpose
To develop a pulse sequence capable of selectively detecting and quantifying the 1H signal of GABA in human brains based on optimal controlled spin singlet order.
Study Type
Prospective.
Subjects/Phantom
A phantom of GABA (pH = 7.3 ± 0.1) and 11 healthy subjects (5 females and 6 males, body mass index: 21 ± 3 kg/m2, age: 25 ± 4 years).
Field Strength/Sequence
7 Tesla, 3 Tesla, GABA‐targeted magnetic resonance spectroscopy (GABA‐MRS‐7 T, GABA‐MRS‐3 T), magnetization prepared two rapid acquisition gradient echoes sequence.
Assessment
By using the developed pulse sequences applied on the phantom and healthy subjects, the signals of GABA were successfully selectively probed. Quantification of the signals yields the concentration of GABA in the dorsal anterior cingulate cortex (dACC) in human brains.
Statistical Tests
Frequency.
Results
The 1H signals of GABA in the phantom and in the human brains of healthy subjects were successfully detected. The concentration of GABA in the dACC of human brains was 3.3 ± 1.5 mM.
Data Conclusion
The developed pulse sequences can be used to selectively probe the 1H MR signals of GABA in human brains in vivo.
Evidence Level
1
Technical Efficacy Stage
1
Quantitative in-situ pH mapping of gliomas is important for therapeutic interventions, given its significant association with tumor progression, invasion, and metastasis. Although chemical exchange ...saturation transfer (CEST) offers a noninvasive way for pH imaging based on the pH-dependent exchange rate (k
), the reliable quantification of k
in glioma remains constrained due to technical challenges.
To quantify the pH of gliomas by measuring the proton exchange rate through optimized omega plot analysis.
Prospective.
Creatine and murine brain lysates phantoms, six rats with glioma xenograft model, and three patients with World Health Organization grade 2-4 gliomas.
11.7 T, 7.0 T, CEST imaging, T
-weighted (T
W) imaging, and T
-mapping.
Omega plot analysis, quasi-steady-state (QUASS) analysis, multi-pool Lorentzian fitting, amine and amide concentration-independent detection, pH enhanced method with the combination of amide and guanidyl (pH
), and magnetization transfer ratio (MTR) were utilized for pH metric quantification. The clinical outcomes were determined through radiologic follow-up and histopathological analysis.
Mann-Whitney U test was performed to compare glioma with normal tissue, and Pearson's correlation analysis was used to assess the relationship between k
and other parameters.
In vitro experiments reveal that the determined k
at 2 ppm increases exponentially with pH (creatine phantoms: k
= 106 + 0.147 × 10
; lysates: k
= 185.1 + 0.101 × 10
). Omega plot analysis exhibits a linear correlation between 1/MTR
and 1/ω
in the glioma xenografts (R
> 0.98) and glioma patients (R
> 0.99). The exchange rate in the rat glioma decreases compared to the contralateral normal tissue (349.46 ± 30.40 s
vs. 403.54 ± 51.01 s
, P = 0.025), while keeping independence from changes in concentration (r = 0.5037, P = 0.095). Similar pattern was observed in human data.
Utilizing QUASS-based, spillover-, and MT-corrected omega plot analysis for the measurement of exchange rates, offers a feasible method for quantifying pH within glioma.
NA TECHNICAL EFFICACY: Stage 1.
Purpose
The purpose of this study is to introduce a novel design method of a shim coil array specifically optimized for whole brain shimming and to compare the performance of the resulting coils to ...conventional spherical harmonic shimming.
Methods
The proposed design approach is based on the stream function method and singular value decomposition. Eighty‐four field maps from 12 volunteers measured in seven different head positions were used during the design process. The cross validation technique was applied to find an optimal number of coil elements in the array. Additional 42 field maps from 6 further volunteers were used for an independent validation. A bootstrapping technique was used to estimate the required population size to achieve a stable coil design.
Results
Shimming using 12 and 24 coil elements outperforms fourth‐ and fifth‐order spherical harmonic shimming for all measured field maps, respectively. Coil elements show novel coil layouts compared to the conventional spherical harmonic coils and existing multi‐coils. Both leave‐one‐out and independent validation demonstrate the generalization ability of the designed arrays. The bootstrapping analysis predicts that field maps from approximately 140 subjects need to be acquired to arrive at a stable design.
Conclusions
The results demonstrate the validity of the proposed method to design a shim coil array matched to the human brain anatomy, which naturally satisfies the laws of electrodynamics. The design method may also be applied to develop new shim coil arrays matched to other human organs.
Electroencephalography (EEG) concurrently collected with functional magnetic resonance imaging (fMRI) is heavily distorted by the repetitive gradient coil switching during the fMRI acquisition. The ...performance of the typical template-based gradient artifact suppression method can be suboptimal because the artifact changes over time. Gradient artifact residuals also impede the subsequent suppression of ballistocardiography artifacts.
Here we propose recording continuous EEG with temporally sparse fast fMRI (fast fMRI-EEG) to minimize the EEG artifacts caused by MRI gradient coil switching without significantly compromising the field-of-view and spatiotemporal resolution of fMRI. Using simultaneous multi-slice inverse imaging to achieve whole-brain fMRI with isotropic 5-mm resolution in 0.1 s, and performing these acquisitions once every 2 s, we have 95% of the duty cycle available to record EEG with substantially less gradient artifact. We found that the standard deviation of EEG signals over the entire acquisition period in fast fMRI-EEG was reduced to 54% of that in conventional concurrent echo-planar imaging (EPI) and EEG recordings (EPI-EEG) across participants. When measuring 15-Hz steady-state visual evoked potentials (SSVEPs), the baseline-normalized oscillatory neural response in fast fMRI-EEG was 2.5-fold of that in EPI-EEG. The functional MRI responses associated with the SSVEP delineated by EPI and fast fMRI were similar in the spatial distribution, the elicited waveform, and detection power. Sparsely interleaved fast fMRI-EEG provides high-quality EEG without substantially compromising the quality of fMRI in evoked response measurements, and has the potential utility for applications where the onset of the target stimulus cannot be precisely determined, such as epilepsy.
•We propose recording continuous EEG with temporally sparse fast fMRI.•Fast MRI can achieve whole-brain sampling with isotropic 5-mm resolution in 0.1 s.•Using fast MRI once every 2 s substantially reduces the EEG gradient artifact.•The 15-Hz SSVEP in fast fMRI-EEG was 2.5-fold of that in EPI-EEG.•The fMRI responses for 15-Hz SSVEP were similar in EPI and fast fMRI.
Introduction
Chronic cerebral hypoperfusion has been considered the etiology for sporadic Alzheimer's disease (AD). However, no valid clinical evidence exists due to the similar risk factors between ...cerebrovascular disease and AD.
Methods
We used moyamoya disease (MMD) as a model of chronic hypoperfusion and cognitive impairment, without other etiology interference.
Results
Based on the previous reports and preliminary findings, we hypothesized that chronic cerebral hypoperfusion could be an independent upstream crucial variable, resulting in AD, and induce pathological hallmarks such as amyloid beta peptide and hyperphosphorylated tau accumulation.
Discussion
Timely intervention with revascularisation would help reverse the brain damage with AD hallmarks and lead to cognitive improvement.
Field probes are miniature receiver coils with localized NMR-active samples inside. They are useful in monitoring magnetic field. This information can be used to improve magnetic resonance image ...quality. While field probes are coupled to each other marginally in most applications, this coupling can cause incorrect resonance frequency estimates and image reconstruction errors. Here, we propose a method to reduce the coupling between field probes in order to improve the accuracy of magnetic field estimation. An asymmetric sensitivity matrix describing the coupling between channels of field probes and NMR active droplets within field probes was empirically measured. Localized signal originating from each probe was derived from the product of the inverse of the sensitivity matrix and the coupled probe measurements. This method was used to estimate maps of dynamic magnetic fields in diffusion weighted MRI. The estimated fields using decoupled probe measurement led to images more robust to eddy currents caused by diffusion sensitivity gradients along different directions.
Noninvasive prediction of isocitrate dehydrogenase (IDH) mutation status in glioma guides surgical strategies and individualized management. We explored the capability on preoperatively identifying ...IDH status of combining a convolutional neural network (CNN) and a novel imaging modality, ultra-high field 7.0 Tesla (T) chemical exchange saturation transfer (CEST) imaging.
We enrolled 84 glioma patients of different tumor grades in this retrospective study. Amide proton transfer CEST and structural Magnetic Resonance (MR) imaging at 7T were performed preoperatively, and the tumor regions are manually segmented, leading to the "annotation" maps that offers the location and shape information of the tumors. The tumor region slices in CEST and T1 images were further cropped out as samples and combined with the annotation maps, which were inputted to a 2D CNN model for generating IDH predictions. Further comparison analysis to radiomics-based prediction methods was performed to demonstrate the crucial role of CNN for predicting IDH based on CEST and T1 images.
A fivefold cross-validation was performed on the 84 patients and 4090 slices. We observed a model based on only CEST achieved accuracy of 74.01% ± 1.15%, and the area under the curve (AUC) of 0.8022 ± 0.0147. When using T1 image only, the prediction performances dropped to accuracy of 72.52% ± 1.12% and AUC of 0.7904 ± 0.0214, which indicates no superiority of CEST over T1. However, when we combined CEST and T1 together with the annotation maps, the performances of the CNN model were further boosted to accuracy of 82.94% ± 1.23% and AUC of 0.8868 ± 0.0055, suggesting the importance of a joint analysis of CEST and T1. Finally, using the same inputs, the CNN-based predictions achieved significantly improved performances above those from radiomics-based predictions (logistic regression and support vector machine) by 10% to 20% in all metrics.
7T CEST and structural MRI jointly offer improved sensitivity and specificity of preoperative non-invasive imaging for the diagnosis of IDH mutation status. As the first study of CNN model on imaging acquired at ultra-high field MR, our results could demonstrate the potential of combining ultra-high-field CEST and CNN for facilitating decision-making in clinical practice. However, due to the limited cases and B1 inhomogeneities, the accuracy of this model will be improved in our further study.
Granger causality analysis has been suggested as a method of estimating causal modulation without specifying the direction of information flow a priori. Using BOLD-contrast functional MRI (fMRI) ...data, such analysis has been typically implemented in the time domain. In this study, we used magnetic resonance inverse imaging, a method of fast fMRI enabled by massively parallel detection allowing up to 10 Hz sampling rate, to investigate the causal modulation at different frequencies up to 5 Hz. Using a visuomotor two-choice reaction-time task, both the spectral decomposition of Granger causality and isolated effective coherence revealed that the BOLD signal at frequency up to 3 Hz can still be used to estimate significant dominant directions of information flow consistent with results from the time-domain Granger causality analysis. We showed the specificity of estimated dominant directions of information flow at high frequencies by contrasting causality estimates using data collected during the visuomotor task and resting state. Our data suggest that hemodynamic responses carry physiological information related to inter-regional modulation at frequency higher than what has been commonly considered.
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