Echo-planar Imaging Sequence Research Articles

Comparison of Resting-State Brain Activation Detected by BOLD, Blood Volume and Blood Flow.

Resting-state brain activity has been widely investigated using blood oxygenation level dependent (BOLD) contrast techniques. However, BOLD signal changes reflect a combination of the effects of cerebral blood flow (CBF), cerebral blood volume (CBV), as well as the cerebral metabolic rate of oxygen (CMRO2). In this study, resting-state brain activation was detected and compared using the following techniques: (a) BOLD, using a gradient-echo echo planar imaging (GE-EPI) sequence; (b) CBV-weighted signal, acquired using gradient and spin echo (GRASE) based vascular space occupancy (VASO); and (c) CBF, using pseudo-continuous arterial spin labeling (pCASL). Reliable brain networks were detected using VASO and ASL, including sensorimotor, auditory, primary visual, higher visual, default mode, salience and left/right executive control networks. Differences between the resting-state activation detected with ASL, VASO and BOLD could potentially be due to the different temporal signal-to-noise ratio (tSNR) and the short post-labeling delay (PLD) in ASL, along with differences in the spin-echo readout of VASO. It is also possible that the dynamics of spontaneous fluctuations in BOLD, CBV and CBF could differ due to biological reasons, according to their location within the brain.

High resolution in-vivo DT-CMR using an interleaved variable density spiral STEAM sequence.

Diffusion tensor cardiovascular magnetic resonance (DT-CMR) has a limited spatial resolution. The purpose of this study was to demonstrate high-resolution DT-CMR using a segmented variable density spiral sequence with correction for motion, off-resonance, and T2*-related blurring. A single-shot stimulated echo acquisition mode (STEAM) echo-planar-imaging (EPI) DT-CMR sequence at 2.8 × 2.8 × 8 mm3 and 1.8 × 1.8 × 8 mm3 was compared to a single-shot spiral at 2.8 × 2.8 × 8 mm3 and an interleaved spiral sequence at 1.8 × 1.8 × 8 mm3 resolution in 10 healthy volunteers at peak systole and diastasis. Motion-induced phase was corrected using the densely sampled central k-space data of the spirals. STEAM field maps and T2* measures were obtained using a pair of stimulated echoes each with a double spiral readout, the first used to correct the motion-induced phase of the second. The high-resolution spiral sequence produced similar DT-CMR results and quality measures to the standard-resolution sequence in both cardiac phases. Residual differences in fractional anisotropy and helix angle gradient between the resolutions could be attributed to spatial resolution and/or signal-to-noise ratio. Data quality increased after both motion-induced phase correction and off-resonance correction, and sharpness increased after T2* correction. The high-resolution EPI sequence failed to provide sufficient data quality for DT-CMR reconstruction. In this study, an in vivo DT-CMR acquisition at 1.8 × 1.8 mm2 in-plane resolution was demonstrated using a segmented spiral STEAM sequence. Motion-induced phase and off-resonance corrections are essential for high-resolution spiral DT-CMR. Segmented variable density spiral STEAM was found to be the optimal method for acquiring high-resolution DT-CMR data.

Feasibility of Diffusion Tensor and Morphologic Imaging of Peripheral Nerves at Ultra-High Field Strength.

The aim of this study was to describe the development of morphologic and diffusion tensor imaging sequences of peripheral nerves at 7 T, using carpal tunnel syndrome (CTS) as a model system of focal nerve injury. Morphologic images were acquired at 7 T using a balanced steady-state free precession sequence. Diffusion tensor imaging was performed using single-shot echo-planar imaging and readout-segmented echo-planar imaging sequences. Different acquisition and postprocessing methods were compared to describe the optimal analysis pipeline. Magnetic resonance imaging parameters including cross-sectional areas, signal intensity, fractional anisotropy (FA), as well as mean, axial, and radial diffusivity were compared between patients with CTS (n = 8) and healthy controls (n = 6) using analyses of covariance corrected for age (significance set at P < 0.05). Pearson correlations with Bonferroni correction were used to determine association of magnetic resonance imaging parameters with clinical measures (significance set at P < 0.01). The 7 T acquisitions with high in-plane resolution (0.2 × 0.2mm) afforded detailed morphologic resolution of peripheral nerve fascicles. For diffusion tensor imaging, single-shot echo-planar imaging was more efficient than readout-segmented echo-planar imaging in terms of signal-to-noise ratio per unit scan time. Distortion artifacts were pronounced, but could be corrected during postprocessing. Registration of FA maps to the morphologic images was successful. The developed imaging and analysis pipeline identified lower median nerve FA (pisiform bone, 0.37 [SD 0.10]) and higher radial diffusivity (1.08 [0.20]) in patients with CTS compared with healthy controls (0.53 [0.06] and 0.78 [0.11], respectively, P < 0.047). Fractional anisotropy and radial diffusivity strongly correlated with patients' symptoms (r = -0.866 and 0.866, respectively, P = 0.005). Our data demonstrate the feasibility of morphologic and diffusion peripheral nerve imaging at 7 T. Fractional anisotropy and radial diffusivity were found to be correlates of symptom severity.

Effects of the Phantom Shape on the Gradient Artefact of Electroencephalography (EEG) Data in Simultaneous EEG–fMRI

Electroencephalography (EEG) signals greatly suffer from gradient artefacts (GAs) due to the time-varying field gradients in the magnetic resonance (MR) scanner during the simultaneous acquisition of EEG and functional magnetic resonance imaging (fMRI) data. The GAs are the principal contributors of artefacts while recording EEG inside an MR scanner, and most of them come from the interaction of the EEG cap and the subject’s head. Many researchers have been using a spherical phantom to characterize the GA in EEG data in combined EEG–fMRI studies. In this study, we investigated how the phantom shape could affect the characterization of the GA. EEG data were recorded with a spherical phantom, a head-shaped phantom, and six human subjects, individually, during the execution of customized and standard echo-planar imaging (EPI) sequences. The spatial potential maps of the root-mean-square (RMS) voltage of the GA over EEG channels for the trials with a head-shaped phantom closely mimicked those related to the human head rather than those obtained for the spherical phantom. This was confirmed by measuring the average similarity index (0.85/0.68). Moreover, a paired t-test showed that the head-shaped phantom’s and the spherical phantom’s data were significantly different (p &lt; 0.005) from the subjects’ data, whereas the difference between the head-shaped phantom’s and the spherical phantom’s data was not significant (p = 0.07). The results of this study strongly suggest that a head-shaped phantom should be used for GA characterization studies in concurrent EEG–fMRI.

Detecting perfusion deficit in Alzheimer's disease and mild cognitive impairment patients by resting-state fMRI.

Vascular factors contributing to cerebral hypoperfusion are implicated in the risk of developing Alzheimer's disease (AD). To investigate the time-shift mapping created time-shift value of the brain by resting-state functional magnetic resonance imaging (rs-fMRI), and to determine the differences in time-shift value among AD, mild cognitive impairment (MCI), and normal control (NC) groups to better understand the disease. Prospective. Twenty-four AD, 24 MCI, and 24 age-matched NC participants. T2 *-weighted single-shot echo-planar imaging sequence was performed at 3T. In addition, a T1 -weighted fast spoiled gradient-echo sequence was acquired for coregistration. The brain time-shift value was determined from rs-fMRI-based blood oxygenation level-dependent (BOLD) signal in the three groups by time-shift mapping. The perfusion patterns were also investigated in the NC group. One-way analysis of variance and chi-squared tests were used to compare demographic information. The normalized time-shift maps were analyzed in a second-level test using SPM8. All analyses were evaluated with a significance level of P < 0.05 after false discovery rate (FDR) correction. The time-shift maps obtained from rs-fMRI are consistent with the cerebral blood supply atlas. Compared with NC, both MCI and AD groups had less early perfusion arrival areas among the whole brain. In the delayed time-shift value for the AD group, the areas were located in the bilateral precuneus, the sensory-motor cortex in the left hemisphere, and the bilateral calcarine sulcus, which were different from the MCI group (both P < 0.05, FDR corrected). The time-shift mapping method could detect perfusion deficits in AD and MCI noninvasively. The perfusion deficits detected by rs-fMRI may provide new insight for understanding the mechanism of neurodegeneration. Level of Evidence 2 Technical Efficacy Stage 3 J. Magn. Reson. Imaging 2019;49:1099-1104.

Diffusion tensor imaging of white matter in patients with prediabetes by trace-based spatial statistics.

Prediabetes is an intermediate state in which blood glucose is higher than normal but does not meet the diagnostic criteria for diabetes. Diffusion tensor imaging (DTI) is an MRI method that can sensitively detect microscopic lesions in the white matter of the brain, but most previous DTI studies only focused on patients with diabetes, and little is known about prediabetes. To investigate the changes in the microstructure of brain white matter in prediabetes patients using DTI and trace-based spatial statistics (TBSS). Prospective. Sixty subjects (30 patients with prediabetes and 30 healthy volunteers) were enrolled. 3.0T/DTI-MRI sequence with single-shot echo-planar imaging sequence (SE-EPI). DTI data were collected and analyzed using the TBSS method in the FMRIB software library. DTI using a two-sample t-test. Pearson correlation analysis was performed on DTI values and neuropsychology scale results (mini-mental state examination [MMSE], Montreal cognitive assessment [MoCA], self-rating anxiety scale [SAS], and self-rating depression scale [SDS]) RESULTS: Compared with the control group, the fractional anisotropy (FA) values in the right part of the corpus callosum body (bCC) (P = 0.035), the right superior longitudinal fasciculus (SLF.R) (P = 0.047), and the left superior longitudinal fasciculus (SLF.L) in the prediabetic group were reduced (P = 0.040). DTI as a noninvasive technique can assess early changes in the white matter microarchitecture of patients with prediabetes. 2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;49:1105-1112.

Disrupted functional connectivity and activity in the white matter of the sensorimotor system in patients with pontine strokes.

White matter (WM) blood oxygenation level-dependent (BOLD) signals are reported to be related to neural activity. However, sensitivity of WM BOLD signals to disease remains unclear. To investigate WM BOLD signal changes, directional variations of resting-state correlations in sensorimotor system in patients with pontine strokes, and to determine the relationship between WM BOLD signals and motor deficits. Prospective. Ethical approval was obtained from the local Ethics Committee and each participant gave written informed consent. Sixteen patients with focal pontine lesions and 16 age-matched control subjects were included. 3.0T T1 -weighted anatomic images using a 3D magnetization-prepared rapid gradient-echo sequence. Resting-state fMRI images using gradient-echo echo-planar imaging sequence. Diffusion-weighted images using single-shot spin-echo diffusion echo-planar imaging. Relevant WM tracts in the sensorimotor system by region of interest-wise analysis were identified. Power spectra of BOLD signals and anisotropy of resting-state correlations were measured in sensorimotor system and compared between two groups. Their relationships with clinical scores were analyzed. Two-sample t-test; partial correlation analysis. Power spectra of BOLD signals in nerve tracts on the ipsilesional side were significantly decreased (P < 0.05). Compared with that in healthy subjects, the anisotropy of resting-state correlations along identified WM tracts was decreased in the thalamus-dorsolateral prefrontal cortex bundle on the contralesional side, and all nerve tracts on the ipsilesional side. Partial least squares regression analysis showed the predicted outcome scores correlated significantly with actual Fugl-Meyer scores (R2 = 0.944, P = 0.013). Our findings suggest that disrupted activity and functional connectivity in WM areas of the sensorimotor system can be detected in pontine strokes, and may serve as a biomarker for motor function prediction. 2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;49:478-486.

Spatial-temporal perfusion patterns of the human liver assessed by pseudo-continuous arterial spin labeling MRI

PurposeTo investigate the capabilities of a modern pseudo-continuous arterial spin labeling (PCASL) technique for non-invasive assessment of the temporal and spatial distribution of the liver perfusion in healthy volunteers on a clinical MR system at 3T. Materials and methodsA 2D-PCASL multi-slice echo planar imaging sequence was adapted to the specific conditions in liver: a) labeling by PCASL was optimized to the flow characteristics in the portal vein, b) background suppression was applied for reduction of motion related artifacts, c) post labeling delays (PLDs) were varied over a large range (0.7–3.5s) in order to get better insight in the temporal and spatial distribution of tagged blood in the liver, and d) a special timed-breathing protocol was used allowing for recording of 16 to 18 label-control image pairs and a reference M0 image for each of 4 to 6 slices within approx. 5min for one PLD. ResultsMeasurements with multiple PLDs showed dominating perfusion signal in macroscopic blood vessels for PLDs up to 1.5 s, whereas pure liver parenchyma revealed maximum perfusion signal for a PLD of approx. 2 s, and detectable signal up to PLDs of 3.5 s. Data fitting to a perfusion model for liver provided a mean global perfusion of 153±15ml/100g/min and a mean transit time of 1938±332ms in liver parenchyma. Measurements with a single PLD of 2 s demonstrated that portal-venous and arterial perfusion components can be measured separately by two measurements with two different positions of the labeling plane (one for labeling of the global hepatopetal blood flow and one for selective labeling of the portal blood flow only). Relative contribution of blood from the hepatic artery to the global liver perfusion, the hepatic perfusion index (HPI), amounted to approx. 23%. ConclusionModern and adapted protocols for assessment of liver perfusion by PCASL have the potential to provide perfusion and blood transit time maps in reasonable acquisition time.

A thermometry software tool for monitoring laser-induced interstitial thermotherapy.

The purpose of this study was to develop a thermometry software tool for temperature monitoring during laser-induced interstitial thermotherapy (LITT). C++ programming language and several libraries including DICOM Toolkit, Grassroots DICOM library, Insight Segmentation and Registration Toolkit, Visualization Toolkit and Quasar Toolkit were used. The software's graphical user interface creates windows displaying the temperature map and the coagulation extent in the tissue, determined by the magnetic resonance imaging (MRI) thermometry with the echo planar imaging sequence and a numerical simulation based on the radiation and heat transfer in biological tissues, respectively. The software was evaluated applying the MRI-guided LITT to ex vivo pig liver and simultaneously measuring the temperature through a fiber-optic thermometer as reference. Using the software, the temperature distribution determined by the MRI method was compared with the coagulation extent simulation. An agreement was shown between the MRI temperature map and the simulated coagulation extent. Furthermore, the MRI-based and simulated temperatures agreed with the measured one - a correlation coefficient of 0.9993 and 0.9996 was obtained, respectively. The precision of the MRI temperature amounted to 2.4°C. In conclusion, the software tool developed in the present study can be applied for monitoring and controlling the LITT procedure in ex vivo tissues.

Accelerated silent echo-planar imaging

PurposeThe standard approach to Echo-Planar Imaging (EPI) is to use trapezoidal readout (RO) gradients with blipped phase-encoding (PE) gradients. Sinusoidal RO gradients with constant PE gradients can reduce acoustic noise. However, this sequence, originally introduced by Mansfield et al., constitutes major challenges for Cartesian parallel imaging techniques. In this study two alternatives to reconstruct a non-blipped EPI are proposed and evaluated. Theory and methodsThe first method separates the acquired k-space data into odd and even echoes and applies Cartesian GRAPPA separately to each partial data set. Afterwards, the resulting reconstructed data sets for each echo are summed in image space. In the second method, an iterative parallel-imaging algorithm is used to reconstruct images from the highly non-Cartesian data samples. ResultsCompared to blipped-EPI, the first method reduces image SNR depending on the acceleration factor between 11% and 60%. For an acceleration factor of 3 folding artefacts appear. The second method produces slight fold-over artefacts although image SNR is on the same level as the blipped approach. ConclusionIn this study, we have introduced two new approaches to EPI that allow the use of Cartesian parallel imaging in conjunction with continuous data sampling. In addition to providing a reduction in acoustic noise compared to the standard blipped PE EPI sequence, the proposed techniques improve sampling efficiency, resulting in a reduction of the echo-spacing. Of the two methods, the second approach, based on an iterative image reconstruction, provides higher SNR, but requires a longer reconstruction time.

Correlation of DNA ploidy and cell cycle analysis with diffusion tensor and dynamic susceptibility contrast MRI metrics in meningiomas

Purpose: To investigate the relationship between diffusion tensor imaging and dynamic susceptibility perfusion MRI metrics with cell cycle analysis findings in meningiomas. Material and Methods: Fourteen patients (4 men, 10 women, aged 30-76 years; median 58 years) with meningiomas were included in the study. There were 9 grade I and 5 grade II meningiomas. The MRI protocol consisted of T2-weighted turbo spin echo, unenhanced and contrast enhanced T1-weighted 3D spoiled gradient echo sequences. Diffusion tensor imaging (DTI) metrics, such as apparent diffusion coefficient (ADC) and fractional anisotropy (FA), were assessed with a single shot, multi-slice, spin-echo planar sequence (max b-value: 700 sec/mm²) and dynamic susceptibility perfusion imaging (DSC) metrics, such as the relative cerebral blood volume (rCBV), with a T2* gradient-echo, multishot echo planar imaging sequence. DNA ploidy and cell cycle analysis was analysed by flow cytometry. Results: There was a significant negative correlation between rCBV and G0/G1 phase fraction ( r =−0.791, p =0.004) and a positive correlation with G2/M phase fraction ( r =0.621, p =0.04). A significant correlation was also observed between FA ratio and G0/G1 phase fraction ( r =0.721, p =0.018). No significant correlation was found between G0/G1, S-phase, G2/M and ADC values. Conclusions: DSC MRI and DTI metrics are correlated to meningioma aggressiveness as assessed by cell cycle analysis.

Development of a Symmetric Echo-Planar Spectroscopy Imaging Framework for Hyperpolarized 13C Imaging in a Clinical PET/MR Scanner.

Here, we developed a symmetric echo-planar spectroscopic imaging (EPSI) sequence for hyperpolarized 13C imaging on a clinical hybrid positron emission tomography/magnetic resonance imaging system. The pulse sequence uses parallel reconstruction pipelines to separately reconstruct data from odd-and-even gradient echoes to reduce artifacts from gradient imbalances. The ramp-sampled data in the spatiotemporal frequency space are regridded to compensate for the chemical-shift displacements. Unaliasing of nonoverlapping peaks outside of the sampled spectral width was performed to double the effective spectral width. The sequence was compared with conventional phase-encoded chemical-shift imaging (CSI) in phantoms, and it was evaluated in a canine cancer patient with ameloblastoma after injection of hyperpolarized [1-13C]pyruvate. The relative signal-to-noise ratio of EPSI with respect to CSI was 0.88, which is consistent with the decrease in sampling efficiency due to ramp sampling. Data regridding in the spatiotemporal frequency space significantly reduced spatial blurring compared with direct fast Fourier transform. EPSI captured the spatial distributions of both metabolites and their temporal dynamics in vivo with an in-plane spatial resolution of 5 × 9 mm2 and a temporal resolution of 3 seconds. Significantly higher spatial and temporal resolution for delineating anatomical structures in vivo was achieved for EPSI metabolic maps than for CSI maps, which suffered spatiotemporal blurring. The EPSI sequence showed promising results in terms of short acquisition time and sufficient spectral bandwidth of 500 Hz, allowing to adjust the trade-off between signal-to-noise ratio and encoding speed.

Simultaneous multislice acquisition with multi-contrast segmented EPI for separation of signal contributions in dynamic contrast-enhanced imaging.

We present a method to efficiently separate signal in magnetic resonance imaging (MRI) into a base signal S0, representing the mainly T1-weighted component without T2*-relaxation, and its T2*-weighted counterpart by the rapid acquisition of multiple contrasts for advanced pharmacokinetic modelling. This is achieved by incorporating simultaneous multislice (SMS) imaging into a multi-contrast, segmented echo planar imaging (EPI) sequence to allow extended spatial coverage, which covers larger body regions without time penalty. Simultaneous acquisition of four slices was combined with segmented EPI for fast imaging with three gradient echo times in a preclinical perfusion study. Six female domestic pigs, German-landrace or hybrid-form, were scanned for 11 minutes respectively during administration of gadolinium-based contrast agent. Influences of reconstruction methods and training data were investigated. The separation into T1- and T2*-dependent signal contributions was achieved by fitting a standard analytical model to the acquired multi-echo data. The application of SMS yielded sufficient temporal resolution for the detection of the arterial input function in major vessels, while anatomical coverage allowed perfusion analysis of muscle tissue. The separation of the MR signal into T1- and T2*-dependent components allowed the correction of susceptibility related changes. We demonstrate a novel sequence for dynamic contrast-enhanced MRI that meets the requirements of temporal resolution (Δt < 1.5 s) and image quality. The incorporation of SMS into multi-contrast, segmented EPI can overcome existing limitations of dynamic contrast enhancement and dynamic susceptibility contrast methods, when applied separately. The new approach allows both techniques to be combined in a single acquisition with a large spatial coverage.

The preliminary study of white matter integrity in patients with olfactory dysfunction

Objective: To investigate the white matter integrity in patients with olfactory dysfunction using diffusion tensor imaging (DTI). Methods: Twenty-one patients with olfactory dysfunction and sixteen age, sex and level of education matched normal subjects were recruited in this study. Sniffin' Sticks olfactory test was performed to evaluate the olfactory function of all subjects. We acquired diffusion tensor images with a echo planar imaging (EPI) sequence from all subjects on a 3T scanner. The fractional anisotropy (FA) images were performed using DTI-studio, and bilateral piriform cortex, orbitofrontal cortex, hippocampus and insula cortex adjacent white matter as well as capsula interna were delineated from the FA images as the region of interest associated with olfactory (ROI(awo)) manually. Independent sample t test analysis was used to compare the FA value of all ROI(awo) between the controls and patients. Results: In olfactory dysfunction group, the FA value of adjacent white matter of right piriform cortex and orbitofrontal cortex were significantly lower than those of control group (0.42±0.05 (x±s) vs 0.45±0.05, 0.43±0.06 vs 0.49±0.07, t value was 2.32, 2.79, respectively, all P<0.05). The FA value of adjacent white matter of left piriform cortex and orbitofrontal cortex had no significant difference compared with those of control group (0.43±0.05 vs 0.45±0.04, 0.44±0.04 vs 0.47±0.06, t value was 1.65, 1.37, respectively, all P>0.05). The FA value of the adjacent white matter of bilateral hippocampus, insula cortex and capsula interna had no significant difference compared with those of control group, neither (0.45±0.08 vs 0.44±0.08, 0.45±0.09 vs 0.44±0.10, 0.41±0.08 vs 0.39±0.07, 0.41±0.07 vs 0.38±0.05, 0.64±0.08 vs 0.63±0.08, 0.64±0.07 vs 0.63±0.07, t value was 0.30, 0.15, 0.88, 1.34, 0.14, 0.35, respectively, all P>0.05). Conclusions: The patients with olfactory dysfunction showed abnormal white matter connection in the major primary and secondary olfactory cortex. The reduced white matter integrity in ROI(awo) might contribute to the pathogenesis of olfactory dysfunction.

Altered Spontaneous Regional Brain Activity in the Insula and Visual Areas of Professional Traditional Chinese Pingju Opera Actors.

Recent resting-state fMRI studies have revealed neuroplastic alterations after long-term training. However, the neuroplastic changes that occur in professional traditional Chinese Pingju opera actors remain unclear. Twenty professional traditional Chinese Pingju opera actors and 20 age-, sex-, and handedness-matched laymen were recruited. Resting-state fMRI was obtained by using an echo-planar imaging sequence, and two metrics, amplitude of low frequency fluctuation (ALFF) and regional homogeneity (ReHo), were utilized to assess spontaneous neural activity during resting state. Our results demonstrated that compared with laymen, professional traditional Chinese Pingju actors exhibited significantly decreased ALFF in the bilateral calcarine gyrus and cuneus; decreased ReHo in the bilateral superior occipital and calcarine gyri, cuneus, and right middle occipital gyrus; and increased ReHo in the left anterior insula. In addition, no significant association was found between spontaneous neural activity and Pingju opera training duration. Overall, the changes observed in spontaneous brain activity in professional traditional Chinese Pingju opera actors may indicate their superior performance of multidimensional professional skills, such as music and face perception, dancing, and emotional representation.

Hippocampal structural and functional integrity in multiple sclerosis patients with or without memory impairment: a multimodal neuroimaging study.

The increasing evidence for a pure amnestic-like profile in multiple sclerosis (MS) introduces the role of hippocampal formation in MS episodic memory function. The aim of the present study was to investigate structural and functional hippocampal changes in mildly-disabled MS patients with and without memory impairment. Thirty-one MS patients with or without memory impairment and 16 healthy controls (HC) underwent MRI in a 3.0T MRI scanner. Patients were categorized as memory preserved (MP) and memory impaired (MI) based on verbal and visual memory scores extracted from the Brief Repeatable Neuropsychological Battery. The acquisition protocol included high-resolution 3D-T1-weighted, diffusion weighted imaging and echo-planar imaging sequences for the analysis of hippocampal gray matter (GM) density, perforant pathway area (PPA) tractography, and hippocampal functional connectivity (FC), respectively. Compared to HC, we found decreased left and bilateral hippocampal GM density in MP and MI patients, respectively, decreased fractional anisotropy and increased radial diffusivity on left PPA in MI patients, and reduced FC in MI between left hippocampus and left superior frontal gyrus, precuneus/posterior cingulated cortex and lateral occipital gyrus/angular gyrus. The only differences between MP and MI were found in FC. Specifically, MP patients showed FC changes between left hippocampus and right temporo-occipital fusiform/lingual gyrus (increased FC) as well as supramarginal gyrus (decreased FC). In conclusion, we highlight the early detection of structural hippocampal changes in MS without neuropsychologically-detected memory deficits and decreased hippocampal FC in MS patients with impaired memory performance, when both GM density and PPA integrity are affected.

Diffusion-weighted imaging in acute pulmonary embolism: a feasibility study.

BackgroundMagnetic resonance imaging (MRI) can be an alternative method to computed tomography angiography (CTA) for pulmonary embolism.PurposeTo evaluate the feasibility of diffusion-weighted imaging (DWI) detecting acute pulmonary embolism (PE) in free-breathing humans.Material and MethodsTwenty patients with PE verified by CTA and 20 controls were investigated with MRI (1.5 Aera, Siemens Healthcare). All sequences were performed in the transversal plane using free-breathing without gating. The protocol consisted of a two-dimensional steady-state free precession (SSFP) and a single-shot DWI echo-planar imaging sequence with a voxel resolution of 2 × 2 × 5 mm. Three b values were used: 50, 400, and 800 s/mm2. Images were analyzed in two orders: an open source analysis (OSA); and a blinded only DWI analysis (BDA) simulating clinical work.ResultsOSA of corresponding images showed 370 findings on CTA (i.e. one elongated emboli could be represented in multiple images). SSFP identified 237 of those (64%). DWI with b values of 50, 400, and 800 identified 327 (88%), 245 (66%), and 138 (37%), respectively. In BDA we found 160 true emboli (according to CTA) on b50, 78 on b400, and 54 on b800. Fifty-two of these findings at the subsegmental level could be correlated to PE on CTA but were not visible on SSFP.ConclusionsDWI has a high sensitivity for detecting PE but suffers from poor specificity. It could potentially be used as an eye catcher, i.e. where to look for PE in other MRI sequences.

Diffusion-weighted MRI in the evaluation of the thyroid nodule: Comparison between integrated-shimming EPI and conventional 3D-shimming EPI techniques.

This study aimed to evaluate whether a prototype echo planar imaging sequence with integrated-shimming (iShim-EPI) can improve image quality in the thyroid gland in comparison to 3D-volume shimming echo planar imaging (3D-Shim-EPI), and to compare ADC values derived from iShim-EPI with those of 3D-Shim-EPI. Twenty-one patients with thyroid disease were enrolled and underwent axial DWIs with iShim-EPI and 3D-Shim-EPI using a 3 Tesla magnetic resonance scanner in this prospective study. Both sets of DWI images were evaluated by two independent observers who identified susceptibility and ghost artifacts and evaluated the images' capacity to detect thyroid nodules using quantitative scores. The ADC values of the thyroid nodules and the normal thyroid gland were measured two times within a 4-week period. The reproducibility was evaluated using the intraclass correlation coefficient (ICC) and Bland-Altman plots. There were significant differences in the image quality scores for susceptibility (2.81 ± 0.37 vs. 1.93 ± 0.29, p < 0.001), ghost artifacts (2.95 ± 0.15 vs. 1.93 ± 0.29, p < 0.001) and the detectability of thyroid nodules (3.00 ± 0.00 vs. 2.55 ± 0.75, p = 0.008) between the iShim-EPI and 3D-Shim-EPI techniques, except for the ADC values of the thyroid nodules (1.607 ± 0.466×10−3 mm2/s vs. 1.561 ± 0.483 × 10−3 mm2/s, p = 0.184) and contralateral normal thyroid gland (1.295 ± 0.340 × 10−3 mm2/s vs.1.279 ± 0.411 × 10−3 mm2/s, p = 0.777). Both techniques demonstrated excellent agreement between the ADC values using the ICC (range, 0.963 to 0.999) and Bland-Altman plots. The iShim-EPI technique demonstrated significantly higher image quality compared with the conventional 3D-Shim-EPI technique, with no significant differences in the ADC values.

Altered gray matter volume and disrupted functional connectivity of dorsolateral prefrontal cortex in men with heroin dependence.

Chronic heroin use can cause various neuropathological characteristics that may compromise brain function. The present study evaluated the alteration of gray matter volume (GMV) and its resting-state functional connectivity (rsFC) over the dorsolateral prefrontal cortex (DLPFC) among male heroin users. Thirty heroin-dependent men undergoing methadone maintenance therapy and 30 educational-level- and age-matched male controls were recruited for this study. To assess their GMV and rsFC, the participants were evaluated using spoiled gradient echo and gradient-recalled echo planar imaging sequences with a 3-Tesla General Electric MR scanner under resting state. The heroin-dependent men showed lower GMV over the right DLPFC in comparison with the controls. Further evaluation of the rsFC of the right DLPFC revealed a marked decrease in interhemispheric DLPFC connectivity among those with heroin dependence under control of head movement and GMV of the right DLPFC. Although the mechanism remains unclear, the present study shows that chronic heroin use is associated with alteration of morphology as well as rsFC over the right DLPFC. As the DLPFC plays an imperative role in various domains of cognitive function, service providers for heroin users should consider the impacts of possible DLPFC-related cognitive deficits on treatment effectiveness.

MR-compatibility assessment of MADPET4: a study of interferences between an SiPM-based PET insert and a 7 T MRI system

Compromises in the design of a positron emission tomography (PET) insert for a magnetic resonance imaging (MRI) system should minimize the deterioration of image quality in both modalities, particularly when simultaneous demanding acquisitions are performed. In this work, the advantages of using individually read-out crystals with high-gain silicon photomultipliers (SiPMs) were studied with a small animal PET insert for a 7 T MRI system, in which the SiPM charge was transferred to outside the MRI scanner using coaxial cables. The interferences between the two systems were studied with three radio-frequency (RF) coil configurations. The effects of PET on the static magnetic field, flip angle distribution, RF noise, and image quality of various MRI sequences (gradient echo, spin echo, and echo planar imaging (EPI) at 1H frequency, and chemical shift imaging at 13C frequency) were investigated. The effects of fast-switching gradient fields and RF pulses on PET count rate were studied, while the PET insert and the readout electronics were not shielded. Operating the insert inside a 1H volume coil, used for RF transmission and reception, limited the MRI to T1-weighted imaging, due to coil detuning and RF attenuation, and resulted in significant PET count loss. Using a surface receive coil allowed all tested MR sequences to be used with the insert, with 45–59% signal-to-noise ratio (SNR) degradation, compared to without PET. With a 1H/13C volume coil inside the insert and shielded by a copper tube, the SNR degradation was limited to 23–30% with all tested sequences. The insert did not introduce any discernible distortions into images of two tested EPI sequences. Use of truncated sinc shaped RF excitation pulses and gradient field switching had negligible effects on PET count rate. However, PET count rate was substantially affected by high-power RF block pulses and temperature variations due to high gradient duty cycles.