Three dimensional texture analysis in MRI: a preliminary evaluation in gliomas

The discrimination of tumor boundaries from normal tissue, as well as the evaluation of tissue heterogeneity and tumor grading often continue to pose a challenge in MRI. Although yielding promising results in various fields of medical imaging, two- dimensional (2D) texture analysis in MRI has, until now, demonstrated a lack of specificity in brain tumor classification. A new three-dimensional (3D) approach using Cooccurrence Matrix analysis is proposed to increase the sensitivity and specificity of brain tumor characterization. A preliminary comparative evaluation of 2D and 3D texture analysis was performed on T(1)-weighted MRI of seven gliomas for characterization of solid tumor, necrosis, edema and surrounding white matter. With 3D compared to 2D method, a better discrimination is obtained between necrosis and solid tumor as well as between edema and solid tumor. Using both methods, peritumoral white matter overlaps with edema, but is completely separated from far homo-lateral matter. This latter shows a complete overlapping with contra-lateral matter. The 3D texture analysis approach could provide a new tool for tumor grading and treatment follow-up, as well as for surgery or radiation therapy planning.     

Sodium and proton diffusion MRI as biomarkers for early therapeutic response in subcutaneous tumors

The ability to quantitate early effects of tumor therapeutic response using noninvasive imaging would have a major impact in clinical oncology. One area of active research interest is the ability to use MR techniques to detect subtle changes in tumor cellular density. In this study, sodium and proton diffusion MRI were compared for their ability to detect early cellular changes in tumors treated with a cytotoxic chemotherapy. Subcutaneous 9L gliosarcomas were treated with a single dose of 1,3-bis(2-chloroethyl)-1-nitrosourea. Both sodium and diffusion imaging modalities were able to detect changes in tumor cellularity as early as 2 days after treatment, which continued to evolve as increased signal intensities reached a maximum approximately 8 days posttreatment. Early changes in tumor sodium and apparent diffusion coefficient values were predictive of subsequent tumor shrinkage, which occurred approximately 10 days later. Overall, therapeutical induced changes in sodium and diffusion values were found to have similar dynamic and spatial changes. These findings suggest that these imaging modalities detected similar early cellular changes after treatment. The results of this study support the continued clinical testing of diffusion MRI for evaluation of early tumor treatment response and demonstrate the complementary insights of sodium MRI for oncology applications.     

Cerebral infarction associated with moyamoya disease: histogram-based quantitative analysis of diffusion tensor imaging -- a preliminary study

Moyamoya disease (MMD) is a rare disorder of unknown etiology in which terminal portions of the internal carotid arteries become steno-occlusive, with fine collateral "moyamoya vessels" formed secondarily, resulting in serial ischemic strokes throughout its clinical course. Whole-brain histogram (WBH) of diffusion tensor imaging (WBH-DTI) is an analytical tool whose feasibility has been ascertained in various pathologies. To elucidate whether WBH-DTI could detect any difference between ischemic MMD and normal controls, we examined 27 consecutive MMD patients without hemorrhage and 48 normal controls in this prospective study using a 3.0-T magnetic resonance scanner. WBHs of fractional anisotropy (FA) (WBH-FA) and mean diffusivity (MD) (WBH-MD) were compared among three groups: Group 1, MMD patients with infarct (n=15); Group 2, MMD patients without infarct (n=12); and Group 3, normal controls (n=48). Group 1 showed significantly higher peak height and significantly lower mean value on WBH-FA, as well as significantly lower peak height and significantly higher mean value on WBH-MD, compared with Groups 2 and 3. No significant difference was seen in parameters at either WBH-FA or WBH-MD between Groups 2 and 3. These results might reflect the pathological severity of each group, and WBH-DTI could feasibly detect differences between ischemic MMD with infarction and MMD without infarction and normal controls.     

Motion and diffusion of a passive scalar in a two-dimensional fluid

The motion of a particle in two dimensions in a fluid is considered. The fluid flow is given and time independent. The complex fluid velocity potential can be viewed as a conformal transformation and after rescaling the time, the motion of the particle is uniform and rectilinear in the absence of diffusion. When diffusion of the particle also takes place the same ideas lead to a useful self-consistent approximation based on the average motion of the particle.     

H andH NMR Relaxation in Hydrogen-Bonded Solids Due to a Complex Motion: Classical Jumps over a Barrier and Incoherent Tunneling

Equations for the temperature dependence of proton and deuteron spin–lattice relaxation rates and second moments due to a complex motion consisting of classical jumps over a potential barrier and quantum mechanical tunneling through the barrier have been derived. Asymmetric double and triple potential wells are considered. These equations have been employed to analyze proton spin–lattice relaxation data for solid naphthazarin in the laboratory and rotating frames as a function of temperature. It is shown that tunneling plays an important role in the proton transfer dynamics of this compound.     

Ionic diffusion in dynamically-disordered materials: Motion on a renewing, percolative lattice

Diffusion in concentrated ionic solutions involves ionic motion subject both to interionic Coulomb forces and to the fluctuating potentials arising from solvent motion. To study how these reflect themselves in the ion transport, we examine a problem in which Coulomb particles hop on a lattice that is percolative (some jumps are forbidden) and renewing (the forbidden jumps evolve in time). Diffusivity and tracer correlation are both effected by both renewal and Coulomb interaction. Coulomb effects can destroy the validity of the dynamic percolation result that the diffusivity is proportional to the renewal rate; non-exponential decay of the energy fluctuation correlation function is observed.     

Dynamic contrast-enhanced MRI of Implanted VX2 tumors in rabbit muscle: comparison of Gd-DTPA and NMS60

We studied the dynamics of injected contrast enhancement in implanted VX2 tumors in rabbit thigh muscle. We compared two contrast agents Gd-DTPA and NMS60, a novel gadolinium containing trimer of molecular weight 2.1 kd. T1-weighted spin echo images were acquired preinjection and at 5-60 min after i.v. injection of 0.1 mmol/kg of agent. Dynamic T1-weighted SPGR images (1.9 s/image) were acquired during the bolus injection. Male NZW rabbits (n = 13) were implanted with approximately 2 x 10(6) VX2 tumor cells and grew tumors of 28+/-27 mL over 12 to 21 days. NMS60 showed significantly greater peak enhancement in muscle, tumor rim, and core compared to DTPA in both T1-weighted and SPGR images. NMS60 also showed delayed peak enhancement in the dynamic scans (compared to Gd-DTPA) and significantly reduced leakage rate constant into the extravascular space for tumor rim (K21 = 5.1 min(-1) vs. 11.5 min(-1) based on a 2 compartment kinetic model). The intermediate weight contrast agent NMS60 offers greater tumor enhancement than Gd-DTPA and may offer improved regional differentiation on the basis of vascular permeability in tumors.     

Reproducibility and biases in high field brain diffusion MRI: An evaluation of acquisition and analysis variables

Diffusion tensor imaging (DTI) of in-vivo human brain provides insights into white matter anatomical connectivity, but little is known about measurement difference biases and reliability of data obtained with last generation high field scanners (> 3 T) as function of MRI acquisition and analyses variables. Here we assess the impact of acquisition (voxel size: 1.8 × 1.8 × 1.8, 2 × 2 × 2 and 2.5 × 2.5 × 2.5 mm³, b-value: 700, 1000 and 1300 s/mm²) and analysis variables (within-session averaging and co-registration methods) on biases and test-retest reproducibility of some common tensor derived quantities like fractional anisotropy (FA), mean diffusivity (MD), axial and radial diffusivity in a group of healthy subjects at 4 T in three regions: arcuate fasciculus, corpus callosum and cingulum. Averaging effects are also evaluated on a full-brain voxel based approach. The main results are: i) group FA and MD reproducibility errors across scan sessions are on average double of those found in within-session repetitions (≈ 1.3 %), regardless of acquisition protocol and region; ii) within-session averaging of two DTI acquisitions does not improve reproducibility of any of the quantities across sessions at the group level, regardless of acquisition protocol; iii) increasing voxel size biased MD, axial and radial diffusivities to higher values and FA to lower values; iv) increasing b-value biased all quantities to lower values, axial diffusivity showing the strongest effects; v) the two co-registration methods evaluated gave similar bias and reproducibility results. Altogether these results show that reproducibility of FA and MD is comparable to that found at lower fields, not significantly dependent on pre-processing and acquisition protocol manipulations, but that the specific choice of acquisition parameters can significantly bias the group measures of FA, MD, axial and radial diffusivities.     

Influence of age and osteoporosis on calcaneus trabecular bone structure: a preliminary in vivo MRI study by quantitative texture analysis

Recent developments in high-resolution MR imaging techniques have opened up new perspectives for structural characterization of trabecular bone by non-invasive methods. In this study, 3-D MR imaging was performed on 17 healthy volunteers and 6 osteoporotic patients. Two different MR sequences were used to evaluate the impact on MR acquisition on texture analysis results. Images were analyzed with four automated methods of texture analysis (grey level histogram, cooccurrence, runlength and gradient matrices) enabling quantitative analysis of grey level intensity and distribution within three different regions of interest (ROI). Texture analysis is not very frequently used since the interpretation of the large number of calculated parameters is difficult. We applied multiparametric data analyses such as principal component analysis (CFA) and hierarchical ascending classification (HAC) to determine the relevant parameters to differentiate between three sets of images (healthy young volunteers, healthy postmenopaused and osteoporotic patients). The results suggest that relevant texture information (depending on the ROI localization in the calcaneus) can be extracted from calcaneus MR images to evaluate osteoporosis and age effects on trabecular bone structure if strictly the same acquisition sequences are used for all patients' examination.     

Imaging Perfusion Deficits in Ischemic Heart Disease with Susceptibility-Enhanced T2-Weighted MRI: Preliminary Human Studies

Aim: This feasibility study explores relative myocardial perfusion characterization with an investigational T₂/T₂1 contrast agent. Methods: Dysprosium-DTPA bis (methylamide) was administered peripherally in six patients with thallium defects. Rest and stress multi-section, gated, T₂-weighted images were acquired with a 1.5 T echo-planar imager. Change in transverse relaxation rate was calculated in four segments for each subject. Results: Magnetic resonance (MR) identified five of five instances of ischemia or infarction, at a dose of agent (0.25 mmol/kg) that was comparable to that currently used with clinically approved gadolinium agents. Injection at twice this dose resulted in saturation of the signal change, and the one ischemic segment corresponding to the higher dose was not identified by MR. MR was negative in two segments which, on final diagnosis, were determined to manifest thallium attenuation artifact. Conclusion: MR perfusion imaging with high susceptibility agents has the potential to characterize myocardial perfusion deficits.     

Atypical X-linked adrenoleukodystrophy: new MRI observations with FLAIR,magnetization transfer contrast,diffusion MRI,and proton spectroscopy

An 11-year-old boy with an atypical form of X-linked adrenoleukodystrophy is reported predominantly involving the frontal lobes, and later spreading to temporal lobes. Magnetization transfer contrast T1-weighted, and FLAIR images without intravenous paramagnetic contrast medium, clearly identified the leading edge of a central necrotic zone, as well as a splenial lesion. Zonal differences were identified on ADC maps of an echo-planar diffusion MRI sequence that the ADC value of central zone (2.06 x 10(-3) mm(2)/sec) was higher than that of the peripheral zone (1.67 x 10(-3) mm(2)/sec). On proton spectroscopy, besides changes in the peaks of NAA, choline, and myoinositol, prominent peaks between 0.9 and 1.4 ppm were shown belonging to macromolecules, probably to very long chain fatty acids, a diagnostic feature of adrenoleukodystrophy. In addition, a distinct and prominent glycine peak was observed at 3.50 ppm, reflecting excitotoxic brain damage.     

Assessment of hepatocellular carcinoma using apparent diffusion coefficient and diffusion kurtosis indices: preliminary experience in fresh liver explants

Objectives

The objective was to perform ex vivo evaluation of non-Gaussian diffusion kurtosis imaging (DKI) for assessment of hepatocellular carcinoma (HCC), including presence of treatment-related necrosis, using fresh liver explants.

Methods

Twelve liver explants underwent 1.5-T magnetic resonance imaging using a DKI sequence with maximal b-value of 2000 s/mm². A standard monoexponential fit was used to calculate apparent diffusion coefficient (ADC), and a non-Gaussian kurtosis fit was used to calculate K, a measure of excess kurtosis of diffusion, and D, a corrected diffusion coefficient accounting for this non-Gaussian behavior. The mean value of these parameters was measured for 16 HCCs based upon histologic findings. For each metric, HCC-to-liver contrast was calculated, and coefficient of variation (CV) was computed for voxels within the lesion as an indicator of heterogeneity. A single hepatopathologist determined HCC necrosis and cellularity.

Results

The 16 HCCs demonstrated intermediate-to-substantial excess diffusional kurtosis, and mean corrected diffusion coefficient D was 23% greater than mean ADC (P=.002). HCC-to-liver contrast and CV of HCC were greater for K than ADC or D, although these differences were significant only for CV of HCCs (P≤.046). ADC, D and K all showed significant differences between non-, partially and completely necrotic HCCs (P≤.004). Among seven nonnecrotic HCCs, cellularity showed a strong inverse correlation with ADC (r=−0.80), a weaker inverse correlation with D (− 0.24) and a direct correlation with K (r= 0.48).

Conclusions

We observed non-Gaussian diffusion behavior for HCCs ex vivo; this DKI model may have added value in HCC characterization in comparison with a standard monoexponential model of diffusion-weighted imaging.     

Spontaneous emission in Ĉerenkov FEL devices: a preliminary theoretical analysis

Summary The main features of the spectral characteristics of the spontaneously emitted Ĉerenkov light in circular and rectangular wave guides filled with dielectric are discussed. The characteristics of the radiation emitted by an electron beam moving near and parallel to the surface of a dielectric slab are also analysed. Finally, the relevance of these results to a possible FEL-Ĉerenkov operation is briefly discussed.

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Riassunto In questo lavoro si discutono le caratteristiche dello spettro della radiazione Ĉerenkov, emessa in guide d'onde circolari e rettangolari riempite con dielettrico. Si analizzano inoltre le proprietà della radiazione emessa da un fascio di elettroni in moto in prossimità e parallelamente alla superficie di una ?slab? di dielettrico. Si discute, infine, brevemente, l'importanza di questi risultati per la realizzazione di un possibile FEL-Ĉerenkov.

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Резюме Обсуждаются основиые особенности спектральных характеристик спонтанного черенковского излучения в круговых и прямоугольных волноводах, заполненных диэлектриком. Также анализируются характеристики излучения, испущенного электронным пучком, движущимся вблизи и пораллелйно поверхности диэлектрической пластинки. В заключение, вкратце обсуждется применимость полученных результатов в возможных FEL-черенковских приборах.

     

Mass-spectrometric analysis of diffusion and solubility of helium in cerium-gadolinium ceramics with a submicrocrystalline structure

Diffusion and solubility of helium in Ce_0.8Gd_0.2O_{1.9 − δ} ceramics (δ = 0, 0.015) with a submicrocrystal structure are studied by thermodesorption of helium from preliminarily saturated (in the gas phase) crystals at temperatures of 613 and 673 K in the saturated pressure range 0–21 MPa. It is shown that, in this ceramics (δ = 0), the defect-trap diffusion mechanism operates. The main positions for dissolution are neutral anion vacancies formed as a result of thermal dissociation of impurity-vacancy complexes and saturated up to ∼1 × 10¹⁹ cm⁻³ at P = 6 MPa and T = 673 K. The dissociation energy of the complex and the energy of helium dissolution in the neutral anion vacancy are estimated at ∼2 eV and below −0.3 eV, respectively.     

MR digital subtraction angiography with three-dimensional data acquisition in the diagnosis of brain tumors: preliminary experience

MR digital subtraction angiography (DSA) visualizes intracranial vasculature using a rapid T1-weighted sequence and a bolus injection of gadolinium. Although two-dimensional sequences are most frequently used, we applied a three-dimensional technique in combination with a fast method of k-space filling to improve both the temporal and spatial resolutions. In this preliminary study, we assessed the feasibility of using this technique for the diagnosis of brain tumors in 21 patients by reviewing the obtained images and, in 10 patients, comparing the images with conventional angiograms. MR DSA visualized a tumor stain in 11 patients, a tumor mass effect in 9, and tumor-related vessels in 5. In 9 of the 10 patients for whom conventional angiograms were available, the two kinds of angiograms corresponded well. Three-dimensional MR DSA using our technique is a useful adjunct to conventional MR imaging for the visualization of tumor hemodynamics and, in some cases, tumor-related vessels and mass effects.     

White matter changes in multiple sclerosis: correlation of q-space diffusion MRI and 1H MRS

OBJECTIVE: To explore the diagnostic usefulness of high b-value diffusion magnetic resonance brain imaging ("q-space" imaging) in multiple sclerosis (MS). More specifically, we aimed at evaluating the ability of this methodology to identify tissue damage in the so-called normal-appearing white matter (NAWM). DESIGN: In this study we examined the correlation between q-space diffusion imaging and magnetic resonance spectroscopy (MRS)-based two-dimensional 1H chemical shift imaging. Eight MS patients with different degree of disease severity and seven healthy subjects were scanned in a 1.5-T magnetic resonance imaging (MRI) scanner. The MRI protocol included diffusion tensor imaging (DTI) (with bmax of 1000 s/mm2), high b-value diffusion-weighted imaging (with bmax of 14,000 s/mm2) and 2D chemical shift imaging. The high b-value data set was analyzed using the q-space methodology to produce apparent displacement and probability maps. RESULTS: We found that the q-space diffusion displacement and probability image intensities correlated well with N-acetylaspartate levels (r=.61 and .54, respectively). Furthermore, NAWM that was abnormal on MRS was also found to be abnormal using q-space diffusion imaging. In these areas, the q-space displacement values increased from 3.8+/-0.2 to 4.6+/-0.6 microm (P<.02), the q-space probability values decreased from 7.4+/-0.3 to 6.8+/-0.3 (P<.002), while DTI revealed only a small, but still significant, reduction in fractional anisotropy values from 0.40+/-0.02 to 0.37+/-0.02 (P<.05). CONCLUSION: High b-value diffusion imaging can detect tissue damage in the NAWM of MS patients. Despite the theoretical limitation of this method, in practice it provides additional information which is clinically relevant for detection of tissue damage not seen in conventional imaging techniques.     

Motion artifacts reduction in brain MRI by means of a deep residual network with densely connected multi-resolution blocks (DRN-DCMB)

Objective: Magnetic resonance imaging (MRI) acquisition is inherently sensitive to motion, and motion artifact reduction is essential for improving image quality in MRI. Methods: We developed a deep residual network with densely connected multi-resolution blocks (DRN-DCMB) model to reduce the motion artifacts in T1 weighted (T1W) spin echo images acquired on different imaging planes before and after contrast injection. The DRN-DCMB network consisted of multiple multi-resolution blocks connected with dense connections in a feedforward manner. A single residual unit was used to connect the input and output of the entire network with one shortcut connection to predict a residual image (i.e. artifact image). The model was trained with five motion-free T1W image stacks (pre-contrast axial and sagittal, and post-contrast axial, coronal, and sagittal images) with simulated motion artifacts. Results: In other 86 testing image stacks with simulated artifacts, our DRN-DCMB model outperformed other state-of-the-art deep learning models with significantly higher structural similarity index (SSIM) and improvement in signal-to-noise ratio (ISNR). The DRN-DCMB model was also applied to 121 testing image stacks appeared with various degrees of real motion artifacts. The acquired images and processed images by the DRN-DCMB model were randomly mixed, and image quality was blindly evaluated by a neuroradiologist. The DRN-DCMB model significantly improved the overall image quality, reduced the severity of the motion artifacts, and improved the image sharpness, while kept the image contrast. Conclusion: Our DRN-DCMB model provided an effective method for reducing motion artifacts and improving the overall clinical image quality of brain MRI.     

A method to investigate intervertebral disc morphology from MRI in early idiopathic scoliosis: a preliminary evaluation in a group of 14 patients

The aim of the study was to implement a methodology to quantify in vivo and from magnetic resonance imaging (MRI) the 3D geometrical properties of intervertebral discs (IVDs) in early idiopathic scoliosis with small curves. MRI data were posttreated using a custom-made image processing software to semiautomatically determine the location of disc centres, the location of the nucleus pulposus (NP) and the ratio between the NP volume and the disc volume. MRI was performed in a clinical protocol involving 14 patients having an early idiopathic scoliosis. First, the 3D reconstruction errors were quantified using a reproducibility test (intraoperator and interoperator) in one IVD (L5-S1). The maximal errors in location were 0.79 mm in the frontal plane, 1.84 mm in the sagittal plane and 0.76 mm in the vertical plane. The maximal error in relative volume was 42%. Second, the nucleus migration and relative volume were quantified in discs T5-T6 to L5-S1. No significant relative volume variation was detected. Concerning the disc migration, no significant differences were found in the sagittal and axial planes. In the frontal plane, significant differences were observed at the apex of the scoliotic curvature when the Cobb angle was > or =20 degrees . This innovative study in early scoliosis showed reproducible preliminary results, and its application to improve diagnosis and follow-up will be established in an enlarged patient database.