Quantitative assessment of microvasculopathy in arcAβ mice with USPIO-enhanced gradient echo MRI.
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ABSTRACT:
SUBMITTER: Klohs J
PROVIDER: S-EPMC5010097 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:PURPOSE:To evaluate the technical feasibility of high-resolution USPIO-enhanced magnetic resonance imaging of pelvic lymph nodes (LNs) at ultrahigh magnetic field strength. MATERIALS AND METHODS:The ethics review board approved this study and written informed consent was obtained from all patients. Three patients with rectal cancer and three selected patients with (recurrent) prostate cancer were examined at 7-T 24-36 h after intravenous ferumoxtran-10 administration; rectal cancer patients also received a 3-T MRI. Pelvic LN imaging was performed using the TIAMO technique in combination with water-selective multi-GRE imaging and lipid-selective GRE imaging with a spatial resolution of 0.66?×?0.66?×?0.66mm3. T2*-weighted images of the water-selective imaging were computed from the multi-GRE images at TE?=?0, 8, and 14 ms and used for the assessment of USPIO uptake. RESULTS:High-resolution 7-T MR gradient-echo imaging was obtained robustly in all patients without suffering from RF-related signal voids. USPIO signal decay in LNs was visualized using computed TE imaging at TE?=?8 ms and an R2* map derived from water-selective imaging. Anatomically, LNs were identified on a combined reading of computed TE?=?0 ms images from water-selective scans and images from lipid-selective scans. A range of 3-48 LNs without USPIO signal decay was found per patient. These LNs showed high signal intensity on computed TE?=?8 and 14 ms imaging and low R2* (corresponding to high T2*) values on the R2* map. CONCLUSION:USPIO-enhanced MRI of the pelvis at 7-T is technically feasible and offers opportunities for detecting USPIO uptake in normal-sized LNs, due to its high intrinsic signal-to-noise ratio and spatial resolution. KEY POINTS:• USPIO-enhanced MRI at 7-T can indicate USPIO uptake in lymph nodes based on computed TE images. • Our method promises a high spatial resolution for pelvic lymph node imaging.
| S-EPMC6828641 | biostudies-literature
Project description:PurposeTo develop a method to reconstruct quantitative susceptibility mapping (QSM) from multi-echo, multi-flip angle data collected using strategically acquired gradient echo (STAGE) imaging.MethodsThe proposed QSM reconstruction algorithm, referred to as "structurally constrained Susceptibility Weighted Imaging and Mapping" scSWIM, performs an ℓ 1 and ℓ 2 regularization-based reconstruction in a single step. The unique contrast of the T1 weighted enhanced (T1WE) image derived from STAGE imaging was used to extract reliable geometry constraints to protect the basal ganglia from over-smoothing. The multi-echo multi-flip angle data were used for improving the contrast-to-noise ratio in QSM through a weighted averaging scheme. The measured susceptibility values from scSWIM for both simulated and in vivo data were compared to the: original susceptibility model (for simulated data only), the multi orientation COSMOS (for in vivo data only), truncated k-space division (TKD), iterative susceptibility weighted imaging and mapping (iSWIM), and morphology enabled dipole inversion (MEDI) algorithms. Goodness of fit was quantified by measuring the root mean squared error (RMSE) and structural similarity index (SSIM). Additionally, scSWIM was assessed in ten healthy subjects.ResultsThe unique contrast and tissue boundaries from T1WE and iSWIM enable the accurate definition of edges of high susceptibility regions. For the simulated brain model without the addition of microbleeds and calcium, the RMSE was best at 5.21ppb for scSWIM and 8.74ppb for MEDI thanks to the reduced streaking artifacts. However, by adding the microbleeds and calcium, MEDI's performance dropped to 47.53ppb while scSWIM performance remained the same. The SSIM was highest for scSWIM (0.90) and then MEDI (0.80). The deviation from the expected susceptibility in deep gray matter structures for simulated data relative to the model (and for the in vivo data relative to COSMOS) as measured by the slope was lowest for scSWIM + 1%(-1%); MEDI + 2%(-11%) and then iSWIM -5%(-10%). Finally, scSWIM measurements in the basal ganglia of healthy subjects were in agreement with literature.ConclusionThis study shows that using a data fidelity term and structural constraints results in reduced noise and streaking artifacts while preserving structural details. Furthermore, the use of STAGE imaging with multi-echo and multi-flip data helps to improve the signal-to-noise ratio in QSM data and yields less artifacts.
| S-EPMC7645168 | biostudies-literature
Project description:PurposeConventional MRI using contrast agents is semiquantitative because it is inherently sensitive to extravoxular susceptibility artifacts, field inhomogeneity, partial voluming, perivascular effects, and motion/flow artifacts. Herein we demonstrate a quantitative contrast-enhanced MRI technique using ultrashort time-to-echo pulse sequences for measuring clinically relevant concentrations of ferumoxytol, a superparamagnetic iron oxide nanoparticle contrast agent with high sensitivity and precision in vitro and in vivo.MethodsThe method achieves robust, reproducible results by using rapid signal acquisition at ultrashort time-to-echo (UTE) to produce positive contrast images with pure T1 weighting and little T2* decay. The spoiled gradient echo equation is used to transform UTE intensities directly into concentration using experimentally determined relaxivity constants and image acquisition parameters.ResultsA multiparametric optimization of acquisition parameters revealed an optimal zone capable of producing high-fidelity measurements. Clinically relevant intravascular concentrations of ferumoxytol were measured longitudinally in mice with high sensitivity and precision (∼7.1% error). MRI measurements were independently validated by elemental iron analysis of sequential blood draws. Automated segmentation of ferumoxytol concentration yielded high quality three-dimensional images for visualization of perfusion.ConclusionsThis ability to longitudinally quantify blood pool CA concentration is unique to quantitative UTE contrast-enhanced (QUTE-CE) MRI and makes QUTE-CE MRI competitive with nuclear imaging.
| S-EPMC6691359 | biostudies-literature
Project description:A protocol for evaluating ultrasmall superparamagnetic particles of iron oxide (USPIO) uptake and elimination in cerebral small vessel disease patients was developed and piloted. B?-insensitive R? measurement was evaluated in vitro. Twelve participants with history of minor stroke were scanned at 3-T MRI including structural imaging, and R? and R?* mapping. Participants were scanned (i) before and (ii) after USPIO (ferumoxytol) infusion, and again at (iii) 24?30 h and (iv) one month. Absolute and blood-normalised changes in R? and R?* were measured in white matter (WM), deep grey matter (GM), white matter hyperintensity (WMH) and stroke lesion regions. R? measurements were accurate across a wide range of values. R? (p < 0.05) and R?* (p < 0.01) mapping detected increases in relaxation rate in all tissues immediately post-USPIO and at 24?30 h. R?* returned to baseline at one month. Blood-normalised R? and R?* changes post-infusion and at 24?30 h were similar, and were greater in GM versus WM (p < 0.001). Narrower distributions were seen with R?* than for R? mapping. R? and R?* changes were correlated at 24?30 h (p < 0.01). MRI relaxometry permits quantitative evaluation of USPIO uptake; R?* appears to be more sensitive to USPIO than R?. Our data are explained by intravascular uptake alone, yielding estimates of cerebral blood volume, and did not support parenchymal uptake. Ferumoxytol appears to be eliminated at 1 month. The approach should be valuable in future studies to quantify both blood-pool USPIO and parenchymal uptake associated with inflammatory cells or blood-brain barrier leak.
| S-EPMC6387454 | biostudies-literature
Project description:Recent studies have shown that there is a direct link between the orientation of the nerve fibers in white matter (WM) and the contrast observed in magnitude and phase images acquired using gradient echo MRI. Understanding the origin of this link is of great interest because it could offer access to a new diagnostic tool for investigating tissue microstructure. Since it has been suggested that myelin is the dominant source of this contrast, creating an accurate model for characterizing the effect of the myelin sheath on the evolution of the NMR signal is an essential step toward fully understanding WM contrast. In this study, we show by comparison of the results of simulations and experiments carried out on human subjects at 7T, that the magnitude and phase of signals acquired from WM in vivo can be accurately characterized by (i) modeling the myelin sheath as a hollow cylinder composed of material having an anisotropic magnetic susceptibility that is described by a tensor with a radially oriented principal axis, and (ii) adopting a two-pool model in which the water in the sheath has a reduced T(2) relaxation time and spin density relative to its surroundings, and also undergoes exchange. The accuracy and intrinsic simplicity of the hollow cylinder model provides a versatile framework for future exploitation of the effect of WM microstructure on gradient echo contrast in clinical MRI.
| S-EPMC3494918 | biostudies-literature
Project description:PurposeA method named DECOMPOSE-QSM is developed to decompose bulk susceptibility measured with QSM into sub-voxel paramagnetic and diamagnetic components based on a three-pool complex signal model.MethodsMulti-echo gradient echo signal is modeled as a summation of three weighted exponentials corresponding to three types of susceptibility sources: reference susceptibility, diamagnetic and paramagnetic susceptibility relative to the reference. Paramagnetic component susceptibility (PCS) and diamagnetic component susceptibility (DCS) maps are constructed to represent the sub-voxel compartments by solving for linear and nonlinear parameters in the model.ResultsNumerical forward simulation and phantom validation confirmed the ability of DECOMPOSE-QSM to separate the mixture of paramagnetic and diamagnetic components. The PCS obtained from temperature-variant brainstem imaging follows the Curie's Law, which further validated the model and the solver. Initial in vivo investigation of human brain images showed the ability to extract sub-voxel PCS and DCS sources that produce visually enhanced contrast between brain structures comparing to threshold QSM.
| S-EPMC8720043 | biostudies-literature
Project description: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.
| S-EPMC7053244 | biostudies-literature
Project description:In this paper we demonstrate that gradient echo MRI with hyperpolarized (3)He gas can be used for simultaneously extracting in vivo information about lung ventilation properties, alveolar geometrical parameters, and blood vessel network structure. This new approach is based on multi-gradient-echo experimental measurements of hyperpolarized (3)He gas MRI signal from human lungs and a proposed theoretical model of this signal. Based on computer simulations of (3)He atoms diffusing in the acinar airway tree in the presence of an inhomogeneous magnetic field induced by the susceptibility differences between lung tissue (alveolar septa, blood vessels) and lung airspaces, we derive analytical expressions relating the time-dependent MR signal to the geometrical parameters of acinar airways and the blood vessel network. Data obtained on eight healthy volunteers are in good agreement with literature values. This information is complementary to the information obtained by means of the in vivo lung morphometry technique with hyperpolarized 3He diffusion MRI previously developed by our group, and opens new opportunities to study lung microstructure in health and disease.
| S-EPMC4232999 | biostudies-other
Project description:Objects making up complex porous systems in Nature usually span a range of sizes. These size distributions play fundamental roles in defining the physicochemical, biophysical and physiological properties of a wide variety of systems - ranging from advanced catalytic materials to Central Nervous System diseases. Accurate and noninvasive measurements of size distributions in opaque, three-dimensional objects, have thus remained long-standing and important challenges. Herein we describe how a recently introduced diffusion-based magnetic resonance methodology, Non-Uniform-Oscillating-Gradient-Spin-Echo (NOGSE), can determine such distributions noninvasively. The method relies on its ability to probe confining lengths with a (length)6 parametric sensitivity, in a constant-time, constant-number-of-gradients fashion; combined, these attributes provide sufficient sensitivity for characterizing the underlying distributions in ?m-scaled cellular systems. Theoretical derivations and simulations are presented to verify NOGSE's ability to faithfully reconstruct size distributions through suitable modeling of their distribution parameters. Experiments in yeast cell suspensions - where the ground truth can be determined from ancillary microscopy - corroborate these trends experimentally. Finally, by appending to the NOGSE protocol an imaging acquisition, novel MRI maps of cellular size distributions were collected from a mouse brain. The ensuing micro-architectural contrasts successfully delineated distinctive hallmark anatomical sub-structures, in both white matter and gray matter tissues, in a non-invasive manner. Such findings highlight NOGSE's potential for characterizing aberrations in cellular size distributions upon disease, or during normal processes such as development.
| S-EPMC4509907 | biostudies-literature
Project description:PurposeSensitivity and specificity of blood oxygenation level-dependent (BOLD) functional MRI (fMRI) is sensitive to magnetic field strength and acquisition methods. We have investigated gradient-echo (GE)- and spin-echo (SE)-BOLD fMRI at ultrahigh fields of 9.4 and 15.2 Tesla.MethodsBOLD fMRI experiments responding to forepaw stimulation were performed with 3 echo times (TE) at each echo type and B0 in α-chloralose-anesthetized rats. The contralateral forelimb somatosensory region was selected for quantitative analyses.ResultsAt 9.4 T and 15.2 T, average baseline T2 * (n = 9) was 26.6 and 17.1 msec, whereas baseline T2 value (n = 9) was 35.7 and 24.5 msec, respectively. Averaged stimulation-induced ΔR2 * was -1.72 s-1 at 9.4 T and -3.09 s-1 at 15.2 T, whereas ΔR2 was -1.19 s-1 at 9.4 T and -1.97 s-1 at 15.2 T. At the optimal TE of tissue T2 * or T2 , BOLD percent changes were slightly higher at 15.2 T than at 9.4 T (GE: 7.4% versus 6.4% and SE: 5.7% versus 5.4%). The ΔR2 * and ΔR2 ratio of 15.2 T to 9.4 T was 1.8 and 1.66, respectively. The ratio of the macrovessel-containing superficial to microvessel-dominant parenchymal BOLD signal was 1.73 to 1.76 for GE-BOLD versus 1.13 to 1.19 for SE-BOLD, indicating that the SE-BOLD contrast is less sensitive to macrovessels than GE-BOLD.ConclusionSE-BOLD fMRI improves spatial specificity to microvessels compared to GE-BOLD at both fields. BOLD sensitivity is similar at the both fields and can be improved at ultrahigh fields only for thermal-noise-dominant ultrahigh-resolution fMRI.
| S-EPMC6585650 | biostudies-literature