Concepts in Magnetic Resonance Part A最新文献

Arterial Spin Labeling (ASL) is a noninvasive MRI-based method to measure cerebral blood flow (CBF). Recently, the study of ASL as a functional tool has emerged once CBF fluctuation comes from capillaries in brain tissue, giving a more spatially specific response when compared to the standard functional MRI method, based on the blood oxygenation level-dependent (BOLD) contrast. Although the BOLD effect could be desirable to study brain function, if one aims to quantify CBF, such effect is considered contamination that can be more attenuated if short TE value is used in the image acquisition. An approach that provides both CBF and function information in a simultaneous acquisition is the use of a dual-echo ASL (DE-ASL) readout. Our purpose was to evaluate the information provided by DE-ASL regarding CBF quantification and functional connectivity with a motor task. Pseudocontinuous ASL of twenty healthy subjects (age: 32.4 ± 10.2 years, 13 male) was acquired at a 3T scanner. We analyzed the influence of TE on CBF values and brain connectivity provided by CBF and concurrent BOLD (cc-BOLD) time series. Brain networks were obtained by the general linear model and independent component analysis. Connectivity matrices were generated using a bivariate correlation (Fisher Z values). No effect of the sequence readout, but significant effect of the TE value, was observed on gray matter CBF values. Motor networks with reduced extension and more connections with important regions for brain integration were observed for CBF data acquired with short TE, proving its higher spatial specificity. Therefore, it was possible to use a dual-echo readout provided by a standard commercial ASL pulse sequence to obtain reliable quantitative CBF values and functional information simultaneously.

Aim and Background. Inoperable high-grade gliomas (HGGs) comprise a specific group of brain tumors portending a very poor prognosis. In the absence of surgical management, radiation therapy (RT) offers the primary local treatment modality for inoperable HGGs. Optimal target definition for radiation treatment planning (RTP) of HGGs is a difficult task given the diffusely infiltrative nature of the disease. In this context, detailed multimodality imaging information may add to the accuracy of target definition in HGGs. We evaluated the impact of Magnetic Resonance Imaging (MRI) on Gross Tumor Volume (GTV) definition for RTP of inoperable HGGs in this study. Materials and Methods. Twenty-five inoperable patients with a clinical diagnosis of HGG were included in the study. GTV definition was based on Computed Tomography- (CT-) simulation images only or both CT-simulation and MR images, and a comparative assessment was performed to investigate the incorporation of MRI into RTP of HGGs. Results. Median volume of GTV acquired by using CT-simulation images only and by use of CT and MR images was 65.3 (39.6-94.3) cc and 76.1 (46.8-108.9) cc, respectively. Incorporation of MRI into GTV definition has resulted in a median increase of 12.61% (6%-19%) in the volume of GTV defined by using the CT-simulation images only, which was statistically significant (p < 0.05). Conclusion. Incorporation of MRI into RTP of inoperable HGGs may improve GTV definition and may have implications for dose escalation/intensification strategies despite the need for further supporting evidence.

Current methods for estimation of proton density fat fraction (PDFF) of the liver using magnitude magnetic resonance (MR) imaging face the challenge of correctly estimating it when fat is the dominant molecule; i.e., PDFF is more than 50%. Therefore, the accuracy of the methods is limited to half-range operation. We introduce a method based on neural networks for regression capable of estimating over the full range of fat fractions. We built a neural network based on the angles and distances between the data in the discrete MR signal (ADALIFE), using these as features associated with different PDFFs and as input for the network. Tests were performed using ADALIFE and Multi-interference, a state-of-the-art method to estimate PDFFs, with simulated signals at various signal-to-noise (SNR) values. Results were compared in order to verify repeatability and agreement using Bland-Altman and REC curves. Results for Multi-interference were similar to its in vivo literature, showing the relevance of a simulation. ADALIFE was able to correctly estimate fat fractions up to 100%, breaking the current paradigm for full-range estimation using only offline postprocessing. Within half range, our method outperformed Multi-interference in repeatability and agreement, with narrower limits of agreement and lower expected error at any SNR.

Shape analysis provides a unique insight into biological processes. This paper evaluates the properties, performance, and utility of elliptical Fourier (eFourier) analysis to operationalise global shape, focussing on the human corpus callosum. 8000 simulated corpus callosum contours were generated, systematically varying in terms of global shape (midbody arch, splenium size), local complexity (surface smoothness), and nonshape characteristics (e.g., rotation). 2088 real corpus callosum contours were manually traced from the PATH study. Performance of eFourier was benchmarked in terms of its capacity to capture and then reconstruct shape and systematically operationalise that shape via principal components analysis. We also compared the predictive performance of corpus callosum volume, position in Procrustes-aligned Landmark tangent space, and position in eFourier n-dimensional shape space in relation to the Symbol Digit Modalities Test. Jaccard index for original vs. reconstructed from eFourier shapes was excellent (M=0.98). The combination of eFourier and PCA performed particularly well in reconstructing known n-dimensional shape space but was disrupted by the inclusion of local shape manipulations. For the case study, volume, eFourier, and landmark measures were all correlated. Mixed effect model results indicated all methods detected similar features, but eFourier estimates were most predictive, and of the two shape operationalization techniques had the least error and better model fit. Elliptical Fourier analysis, particularly in combination with principal component analysis, is a powerful, assumption-free and intuitive method of quantifying global shape of the corpus callosum and shows great promise for shape analysis in neuroimaging more broadly.

Purpose. Many patients with metallic implants are aware of the potential dangers in an MRI environment. Some implants cause sensations perceptible by the patient during an MRI scan. We wanted to find out if patients having an implant abort MRI scans more often than patients without implants. Furthermore, we wanted to know if the number of implants of a patient has an influence on the number of aborted MRI scans. As we use 3T MRI scanners from different manufacturers we wanted to see the influence of the “ScanWise” software option where scan parameters are adapted automatically to the maximal allowed limits of implant values. This publication should help to reduce possible anxiety in patients with implants. Materials and Methods. From May 15^th 2017 until July 17^th 2018 the implant type of patients was recorded. We looked how often aborted MRI scans coincided with the occurrence of implants and the MRI scanner type used. Results. 4088 examinations were collected for the analysis. No influence of implants on aborted MRI scans was registered. No influence of the number of implants on aborted MRI scans was registered. No influence of the use of “ScanWise” software on aborted MRI scans was registered when different scanners were compared. Conclusion. “MR Safe” or “MR Conditional” labelled implants did not have an impact on the MRI examinations. “ScanWise” software does not affect how MRI examinations are tolerated.

The present work compares intravenous (IV) and subcutaneous (SC) routes for contrast-enhanced MRI (CE-MRI) in mice. For that purpose, we selected two contrast media used in clinical practice. MRI acquisitions were performed at 1.5 T on five adult mice (Swiss, 41 g +/- 3 g). On each animal, four acquisitions were achieved with IV and SC administration of either Gd-DOTA or MS-325 (1 acquisition per week). For each route, 0.1 mL of NaCl and 0.1 mL of contrast agent were injected. For each acquisition, 200 T1-weighted images were acquired in a 2 h 34 min time lapse. For each route and contrast medium, dynamic contrast enhancement (DCE) curves were obtained. Time-to-peak (TTP), uptake, and washout constant-time values and contrast-to-noise ratio (CNR) were extracted. IV route TTP value was 4.9 min with Gd-DOTA and 5.4 min with MS-325. SC route TTP was 43.3 min with Gd-DOTA and 45.0 min with MS-325. Despite slower uptake constant-time, we show that SC is a potentially valuable alternative to the IV route in mouse preclinical CE-MRI.

In medical magnetic resonance imaging, parallel radio frequency excitation pulses have to respect a large number of specific absorption rate constraints. Geometrically, each of these constraints can be interpreted as a complex, centered ellipsoid. We propose to replace a collection of such constraints by the single constraint which corresponds to the associated maximum volume inscribed ellipsoid and implies all original constraints. We describe how to compute this ellipsoid via convex programming. Examples show that this reduction has very short computation times but cuts away parts of the feasible power domain.

Purpose. To investigate the value of intravoxel incoherent motion (IVIM) magnetic resonance imaging in the evaluation of the osteosarcoma (OS) response to preoperative neoadjuvant chemotherapy (NAC) in teens. Methods. Eighteen consecutive osteosarcoma patients (12 males and 6 females) diagnosed by histopathology were enrolled. All enrolled patients received NAC and underwent MRI examinations before and after 2 cycles of NAC. The volume (V), apparent diffusion coefficient (ADC), (slow) diffusion coefficient (D), pseudo-perfusion (fast) diffusion coefficient (D^⁎or D star), and perfusion fractions (f) of the OS before and after NAC were measured and analysed. The sensitivity and the specificity of the ADC, D, D^⁎ and f values and the correlation between changes in volume (Δ_V) and the IVIM-derived parameters (Δ_ADC, Δ_D, Δ_D⁎ and Δ_f) were also calculated and analysed. Paired Student’s t-tests, receiver operating characteristic (ROC) curves, and Spearman correlation analyses were used. Results. The mean volume of the OS after NAC decreased significantly (61.55±9.3 cm³ vs 40.26±4.1 cm³) (P<0.05). After NAC, the ADC (1.21±0.09 × 10^-3mm²/s vs 1.73±0.11 × 10^-3mm²/s) and D (1.14±0.09 × 10^-3mm²/s vs 1.63±0.1 × 10^-3mm²/s) values increased and f (28.58±1.37% vs 20.93±1.16%) values decreased significantly (P<0.05), while D^⁎ (9.17±0.98 × 10^-3mm²/s vs 8.94±0.13 × 10^-3mm²/s) values changed slightly (P>0.05). The AUC values of ADC (0.938) and D (0.943) were higher than those of D^⁎ (0.574) and f (0.765). The sensitivity and specificity of ADC (0.778, 1) and D (0.944, 0.833) values were superior to those of D^⁎ (0.278, 0.722) and f (0.5, 0.944) values. No significant correlations were found between the Δ_V and Δ_ADC, Δ_D, Δ_D⁎ and Δ_f values (P>0.05). Conclusion. IVIM-derived parameters ADC and D have the potential to be imaging biomarkers for evaluation of the therapeutic response to NAC in OS patients.