Real time magneto-optical imaging of vortices in superconductors

We demonstrate here real-time imaging of individual vortices in a NbSe2 single crystal using polarized light microscopy. A new high-sensitivity magneto-optical (MO) imaging system enables observation of the static vortex lattice as well as single vortex motion at low flux densities.Comment: 3 pages, 1 figur

Modeling and suppression of respiration induced B0-fluctuations in non-balanced steady-state free precession sequences at 7 Tesla

OBJECT: To develop and evaluate a model for describing the S1 (S+) and S2 (S-) phase in the presence of off-resonance frequency fluctuations, and to evaluate the performance of a novel interleaved navigator echo scheme. MATERIALS AND METHODS: Using the extended phase graph model, a linear phase term was added to the evolution of transverse states. An approximation for the total S2 phase was derived with one fit parameter τl, which serves as an effective lifetime of the S2 signal. The model was evaluated using synthetic and in vivo phase evolution data. In addition, a novel interleaved phase correction scheme for the nb-SSFP sequence was applied to BOLD-fMRI data, and the number of activated voxels before and after phase correction was determined. RESULTS: The phases of S1 and S2 signals are significantly different from each other. The proposed nb-SSFP phase model provided a good description of the measured phase evolution data, and the approximate model for the S2 phase provided both at good fit to the data, as well as an effective lifetime of the S2 signal. In some subjects the phase contribution from older pathways was underestimated. In the BOLD-fMRI data, a twofold increase of the number of activated voxels for the S2 signal was observed, compared to no correction and a conventional navigator echo method. CONCLUSION: The different phase evolution of S1 and S2 signals can be qualitatively described by the proposed model, and detrimental phase history effects are significant at 7 Tesla when not appropriately corrected

Quantitative comparison of PET performance-Siemens Biograph mCT and mMR

Background: Integrated clinical whole-body PET/MR systems were introduced in2010. In order to bring this technology into clinical usage, it is of great importance to compare the performance with the well-established PET/CT. The aim of this study was to evaluate PET performance, with focus on image quality, on Siemens BiographmMR (PET/MR) and Siemens Biograph mCT (PET/CT).Methods: A direct quantitative comparison of the performance characteristics between the mMR and mCT system was performed according to National ElectricalManufacturers Association (NEMA) NU 2-2007 protocol. Spatial resolution, sensitivity,count rate and image quality were evaluated. The evaluation was supplementedwith additional standardized uptake value (SUV) measurements. Results: The spatial resolution was similar for the two systems. Average sensitivity was higher for the mMR (13.3 kcps/MBq) compared to the mCT system (10.0 kcps/MBq). Peak noise equivalent count rate (NECR) was slightly higher for the mMR(196 kcps @ 24.4 kBq/mL) compared to the mCT (186 kcps @ 30.1 kBq/mL). Scatterfractions in the clinical activity concentration range yielded lower values for the mCT(34.9 %) compared to those for the mMR (37.0 %). Best image quality of the systems resulted in approximately the same mean hot sphere contrast and a difference of 19 percentage points (pp) in mean cold contrast, in favour of the mCT. In general, point spread function (PSF) increased hot contrast and time of flight (TOF) increased both hot and cold contrast. Highest hot contrast for the smallest sphere (10 mm) was achieved with the combination of TOF and PSF on the mCT. Lung residual error was higher for the mMR (22 %) than that for the mCT (17 %), with no effect of PSF. With TOF, lung residual error was reduced to 8 % (mCT). SUV was accurate for both systems, but PSF caused overestimations for the 13-, 17- and 22-mm spheres. Conclusions: Both systems proved good performance characteristics, and the PETimage quality of the mMR was close to that of the mCT. Differences between the systems were mainly due to the TOF possibility on the mCT, which resulted in an overall better image quality, especially for the most challenging settings with higher background activity and small uptake volumes

Effect of task-correlated physiological fluctuations and motion in 2D and 3D echo-planar imaging in a higher cognitive level fMRI paradigm

Purpose: To compare 2D and 3D echo-planar imaging (EPI) in a higher cognitive level fMRI paradigm. In particular, to study the link between the presence of task-correlated physiological fluctuations and motion and the fMRI contrast estimates from either 2D EPI or 3D EPI datasets, with and without adding nuisance regressors to the model. A signal model in the presence of partly task-correlated fluctuations is derived, and predictions for contrast estimates with and without nuisance regressors are made. Materials and Methods: Thirty-one healthy volunteers were scanned using 2D EPI and 3D EPI during a virtual environmental learning paradigm. In a subgroup of 7 subjects, heart rate and respiration were logged, and the correlation with the paradigm was evaluated. FMRI analysis was performed using models with and without nuisance regressors. Differences in the mean contrast estimates were investigated by analysis-of-variance using Subject, Sequence, Day, and Run as factors. The distributions of group level contrast estimates were compared. Results: Partially task-correlated fluctuations in respiration, heart rate and motion were observed. Statistically significant differences were found in the mean contrast estimates between the 2D EPI and 3D EPI when using a model without nuisance regressors. The inclusion of nuisance regressors for cardiorespiratory effects and motion reduced the difference to a statistically non-significant level. Furthermore, the contrast estimate values shifted more when including nuisance regressors for 3D EPI compared to 2D EPI. Conclusion: The results are consistent with 3D EPI having a higher sensitivity to fluctuations compared to 2D EPI. In the presence partially task-correlated physiological fluctuations or motion, proper correction is necessary to get expectation correct contrast estimates when using 3D EPI. As such task-correlated physiological fluctuations or motion is difficult to avoid in paradigms exploring higher cognitive functions, 2D EPI seems to be the preferred choice for higher cognitive level fMRI paradigms

Single-shot echo-planar imaging with Nyquist ghost compensation:interleaved dual echo with acceleration (IDEA) echo-planar imaging (EPI)

Echo planar imaging is most commonly used for BOLD fMRI, owing to its sensitivity and acquisition speed. A major problem with EPI is Nyquist (N/2) ghosting, most notably at high field. EPI data are acquired under an oscillating readout gradient and hence vulnerable to gradient imperfections such as eddy current delays and off-resonance effects, as these cause inconsistencies between odd and even k-space lines after time reversal. We propose a straightforward and pragmatic method herein termed Interleaved Dual Echo with Acceleration (IDEA) EPI: Two k-spaces (echoes) are acquired under the positive and negative readout lobes, respectively, by performing phase blips only before alternate readout gradients. From these two k-spaces, two almost entirely ghost free images per shot can be constructed, without need for phase correction. The doubled echo train length can be compensated by parallel imaging and/or partial Fourier acquisition. The two k-spaces can either be complex-averaged during reconstruction, which results in near-perfect cancellation of residual phase errors, or reconstructed into separate images. We demonstrate the efficacy of IDEA EPI and show phantom and in vivo images at both 3 and 7 Tesla

Accuracy of breast cancer lesion classification using intravoxel incoherent motion diffusion-weighted imaging is improved by the inclusion of global or local prior knowledge with bayesian methods

Background Diffusion‐weighted MRI (DWI) has potential to noninvasively characterize breast cancer lesions; models such as intravoxel incoherent motion (IVIM) provide pseudodiffusion parameters that reflect tissue perfusion, but are dependent on the details of acquisition and analysis strategy. Purpose To examine the effect of fitting algorithms, including conventional least‐squares (LSQ) and segmented (SEG) methods as well as Bayesian methods with global shrinkage (BSP) and local spatial (FBM) priors, on the power of IVIM parameters to differentiate benign and malignant breast lesions. Study Type Prospective patient study. Subjects 61 patients with confirmed breast lesions. Field Strength/Sequence DWI (bipolar SE‐EPI, 13 b values) was included in a clinical MR protocol including T2‐weighted and dynamic contrast‐enhanced MRI on a 3T scanner. Assessment The IVIM model was fitted voxelwise in lesion regions of interest (ROIs), and derived parameters were compared across methods within benign and malignant subgroups (correlation, coefficients of variation). Area under receiver operator characteristic curves (ROC AUCs) were calculated to determine discriminatory power of parameter combinations from all fitting methods. Statistical Tests Kruskal–Wallis, Mann–Whitney, Pearson correlation. Results All methods provided useful IVIM parameters; D was well‐correlated across all methods (r> 0.8), with a wider range for f and D* (0.3–0.7). Fitting methods gave detectable differences in parameters, but all showed increased f and decreased D in malign lesions. D was the most discriminatory single parameter, with LSQ performing least well (AUC 0.83). In general, ROC AUCs were maximized by the inclusion of pseudodiffusion parameters, and by the use of Bayesian methods incorporating prior information (maximum AUC of 0.92 for BSP). Data Conclusion DWI performs well at classifying breast lesions, but careful consideration of analysis procedure can improve performance. D is the most discriminatory single parameter, but including pseudodiffusion parameters (f and D*) increases ROC AUC. Bayesian methods outperformed conventional least‐squares and segmented fitting methods for breast lesion classification. Level of Evidence: 3 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019

Exploring the diagnostic potential of adding T2 dependence in diffusion-weighted MR imaging of the prostate.

BackgroundMagnetic resonance imaging (MRI) is essential in the detection and staging of prostate cancer. However, improved tools to distinguish between low-risk and high-risk cancer are needed in order to select the appropriate treatment.PurposeTo investigate the diagnostic potential of signal fractions estimated from a two-component model using combined T2- and diffusion-weighted imaging (T2-DWI).Material and methods62 patients with prostate cancer and 14 patients with benign prostatic hyperplasia (BPH) underwent combined T2-DWI (TE = 55 and 73 ms, b-values = 50 and 700 s/mm2) following clinical suspicion of cancer, providing a set of 4 measurements per voxel. Cancer was confirmed in post-MRI biopsy, and regions of interest (ROIs) were delineated based on radiology reporting. Signal fractions of the slow component (SFslow) of the proposed two-component model were calculated from a model fit with 2 free parameters, and compared to conventional bi- and mono-exponential apparent diffusion coefficient (ADC) models.ResultsAll three models showed a significant difference (pConclusionSignal fraction estimates from a two-component model based on combined T2-DWI can differentiate between tumor and normal prostate tissue and show potential for prostate cancer diagnosis. The model performed similarly to conventional diffusion models

Structural connectivity-based segmentation of the human entorhinal cortex

The medial (MEC) and lateral entorhinal cortex (LEC), widely studied in rodents, are well defined and characterized. In humans, however, the exact locations of their homologues remain uncertain. Previous functional magnetic resonance imaging (fMRI) studies have subdivided the human EC into posteromedial (pmEC) and anterolateral (alEC) parts, but uncertainty remains about the choice of imaging modality and seed regions, in particular in light of a substantial revision of the classical model of EC connectivity based on novel insights from rodent anatomy. Here, we used structural, not functional imaging, namely diffusion tensor imaging (DTI) and probabilistic tractography to segment the human EC based on differential connectivity to other brain regions known to project selectively to MEC or LEC. We defined MEC as more strongly connected with presubiculum and retrosplenial cortex (RSC), and LEC as more strongly connected with distal CA1 and proximal subiculum (dCA1pSub) and lateral orbitofrontal cortex (OFC). Although our DTI segmentation had a larger medial-lateral component than in the previous fMRI studies, our results show that the human MEC and LEC homologues have a border oriented both towards the posterior-anterior and medial-lateral axes, supporting the differentiation between pmEC and alEC

Stromal collagen content in breast tumors correlates with in vivo diffusion-weighted imaging: A comparison of multi b-value DWI with histologic specimen from benign and malignant breast lesions

Background:Increased deposition and reorientation of stromal collagenfibers are associated with breast cancer progres-sion and invasiveness. Diffusion-weighted imaging (DWI) may be sensitive to the collagenfiber organization in the stromaand could provide important biomarkers for breast cancer characterization.Purpose:To understand how collagenfibers influence water diffusion in vivo and evaluate the relationship between colla-gen content and the apparent diffusion coefficient (ADC) and the signal fractions of the biexponential model using a highb-value scheme.Study Type:Prospective.Subjects/Specimens:Forty-five patients with benign (n= 8), malignant (n= 36), and ductal carcinoma in situ (n= 1) breasttumors. Lesions and normalfibroglandular tissue (n= 9) were analyzed using sections of formalin-fixed, paraffin-embeddedtissue stained with hematoxylin, erythrosine, and saffron.Field Strength/Sequence:MRI (3T) protocols:Protocol I:Twice-refocused spin-echo echo-planar imaging with: echo time(TE) 85 msec; repetition time (TR) 9300/11600 msec; matrix 90×90×60; voxel size 2×2×2.5 mm3;b-values: 0 and700 s/mm2.Protocol II:Stejskal–Tanner spin-echo echo-planar imaging with: TE: 88 msec; TR: 10600/11800 msec, matrix90×90×60; voxel size 2×2×2.5 mm3;b-values [0, 200, 600, 1200, 1800, 2400, 3000] s/mm2.Assessment:Area fractions of cellular and collagen content in histologic sections were quantified using whole-slide imageanalysis and compared with the corresponding DWI parameters.Statistical Tests:Correlations were assessed using Pearson’sr. Univariate analysis of group median values was done usingthe Mann–WhitneyU-test.Results:Collagen content correlated with the fast signal fraction (r= 0.67,P< 0.001) and ADC (r= 0.58,P< 0.001) andwas lower (P< 0.05) in malignant lesions than benign and normal tissues. Cellular content correlated inversely with the fastsignal fraction (r=–0.67,P< 0.001) and ADC (r=–0.61,P< 0.001) and was different (P< 0.05) between malignant,benign, and normal tissues.Data Conclusion:Ourfindings suggest stromal collagen content increases diffusivity observed by MRI and is associatedwith higher ADC and fast signal fraction of the biexponential mode

Favorable effects on arterial stiffness after renal sympathetic denervation for the treatment of resistant hypertension: a cardiovascular magnetic resonance study

Aims: Renal sympathetic denervation (RDN) has recently been suggested to be a novel treatment strategy for patients with treatment-resistant hypertension. However, the latest randomized studies have provided conflicting results and the influence of RDN on arterial stiffness remains unclear. Therefore, this study aimed to detect the effects of RDN on arterial stiffness as measured with aortic pulse wave velocity (PWV) and distensibility in addition to cardiac function and T1 mapping at baseline and at 6-month follow-up. Methods: RDN was performed in a total of 16 patients with treatment-resistant hypertension, and the procedures were conducted at two university hospitals using two different RDN devices. All patients and age-matched controls underwent a comprehensive clinical examination and cardiac magnetic resonance protocols both at baseline and at a 6-month follow-up. Results: In the treatment group, the systolic blood pressure (SBP) was found to be decreased at the follow-up visit (office SBP; 173±24 compared to 164±25 mmHg [P= 0.033]), the 24-hour ambulatory SBP had decreased (163±25 compared to 153±20 mmHg [P=0.057]), the aortic PWV had decreased from 8.24±3.34 to 6.54±1.31 m/s (P=0.053), and the aortic distensibility had increased from 2.33±1.34 to 3.96±3.05 10−3 mmHg−1 (P=0.013). The changes in aortic PWV and distensibility were independent of the observed reductions in SBP. Conclusion: The arterial stiffness, as assessed with aortic PWV, and distensibility were improved at 6 months after RDN. This improvement was independent of the reduction in SBP