Water Diffusion In Tissue Research Articles

Optimization of a free water elimination two-compartment model for diffusion tensor imaging

Diffusion tensor imaging is used to measure the diffusion of water in tissue. The diffusion properties carry information about the relative organization and structure of the underlying tissue. In the case of a single voxel containing both tissue and a fast diffusing component such as free water, a single diffusion tensor is no longer appropriate. A two-tensor free water elimination model has previously been proposed to correct for the case of volume mixing. Here, this model was implemented in a straightforward but novel manner without the use of spatial constraints. The optimal acquisition parameters were investigated through Monte Carlo simulations and human brain imaging studies. At a signal-to-noise ratio of 40 with 64 diffusion-weighted encoding images, the most accurate estimates of fast diffusion signal were obtained with two diffusion-weighted shells (b-value in s/mm2×number of directions) of 500×32 and 1500×32. The potential bias in fractional anisotropy induced by this two-compartment model was more than an order of magnitude less than the error of using the single diffusion tensor model in the presence of partial volume effects with free water. This strategy may be useful for characterizing the diffusion of tissues adjacent to cerebral spinal fluid (CSF), tissues affected by edema, and removing artifacts from blurring and ghosting of the CSF signal.

A proposed role for efflux transporters in the pathogenesis of hydrocephalus.

Hydrocephalus is a common brain disorder that is treated only with surgery. The basis for surgical treatment rests on the circulation theory. However, clinical and experimental data to substantiate circulation theory have remained inconclusive. In brain tissue and in the ventricles, we see that osmotic gradients drive water diffusion in water-permeable tissue. As the osmolarity of ventricular CSF increases within the cerebral ventricles, water movement into the ventricles increases and causes hydrocephalus. Macromolecular clearance from the ventricles is a mechanism to establish the normal CSF osmolarity, and therefore ventricular volume. Efflux transporters, (p-glycoprotein), are located along the blood brain barrier and play an important role in the clearance of macromolecules (endobiotics and xenobiotics) from the brain to the blood. There is clinical and experimental data to show that macromolecules are cleared out of the brain in normal and hydrocephalic brains. This article summarizes the existing evidence to support the role of efflux transporters in the pathogenesis of hydrocephalus. The location of p-gp along the pathways of macromolecular clearance and the broad substrate specificity of this abundant transporter to a variety of different macromolecules are reviewed. Involvement of p-gp in the transport of amyloid beta in Alzheimer disease and its relation to normal pressure hydrocephalus is reviewed. Finally, individual variability of p-gp expression might explain the variability in the development of hydrocephalus following intraventricular hemorrhage.

MP7-03 IMAGING MICROSTRUCTURAL PROPERTIES OF THE KIDNEYS USING DIFFUSION TENSOR- MRI

You have accessJournal of UrologyImaging/Radiology II1 Apr 2014MP7-03 IMAGING MICROSTRUCTURAL PROPERTIES OF THE KIDNEYS USING DIFFUSION TENSOR- MRI Sophie van Baalen, Martijn Froeling, Alexander Leemans, Bennie ten Haken, Aart Klijn, Tom de Jong, and Pieter Dik Sophie van BaalenSophie van Baalen More articles by this author , Martijn FroelingMartijn Froeling More articles by this author , Alexander LeemansAlexander Leemans More articles by this author , Bennie ten HakenBennie ten Haken More articles by this author , Aart KlijnAart Klijn More articles by this author , Tom de JongTom de Jong More articles by this author , and Pieter DikPieter Dik More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2014.02.326AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES Acute Pyelonephritis (APN) is a common disease in children: about 2.7% of girls and 1% of boys have an APN by the age of 7. APN can result in irreversible damage to the renal parenchyma, affecting the growth and development of the kidney and possibly leading to renal insufficiency, protein loss and hypertension. All children receive a DMSA scintigraphy 6 months after an APN episode to assess the occurrence and extent of renal scars. The radiation dose of 1 mSv/examination imposes a long-term risk in young children. Replacing the DMSA scan with an MRI scan for children with APN would eliminate the risks associated with using ionizing radiation. A promising MRI technique is Diffusion Tensor Imaging (DTI). DTI enables measuring the direction and extend of water diffusion in renal tissue, without using contrast agents. In this study, MRI-DTI was used for kidney imaging to evaluate whether this technology can visualize the microstructural architecture of healthy kidney tissues. METHODS Ten healthy volunteers were scanned on a 3 Tesla MRI scanner. The resulting images were processed to enable Diffusion-Tensor based tractography, visualizing the 3D tissue structure of the kidney. The diffusion parameters Fractional Anisotropy (FA) and Mean Diffusivity (MD) were measured by drawing regions of interest in the medulla and cortex. This study was approved by the ethical committee of our institution. RESULTS The radial orientation of the medullar tissue was visualized and the pyelum contour was segmented. Tracts originate in the cortex and convolute in multiple papillae, at the edge of the pyelum contour, reflecting the microstructure of medulla, consisting of radially oriented straight tubules and vascular network. Differentiation of cortical and medullary tissue based on FA and MD measurement was possible. One volunteer happened to have a dysplastic kidney with evident disturbed microstructural properties on the MRI-DTI tractography image. CONCLUSIONS MRI-DTI is able to visualize the microstructural architecture, especially the renal pyramids, the papillae and major and minor calyxes of the kidney. We are sure that in near future we will be able to visualize alterations in the microstructure e.g. scar tissue formation using this method. © 2014FiguresReferencesRelatedDetails Volume 191Issue 4SApril 2014Page: e65-e66 Advertisement Copyright & Permissions© 2014MetricsAuthor Information Sophie van Baalen More articles by this author Martijn Froeling More articles by this author Alexander Leemans More articles by this author Bennie ten Haken More articles by this author Aart Klijn More articles by this author Tom de Jong More articles by this author Pieter Dik More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

Visualization, imaging and new preclinical diagnostics in radiation oncology

Innovative strategies in cancer radiotherapy are stimulated by the growing knowledge on cellular and molecular tumor biology, tumor pathophysiology, and tumor microenvironment. In terms of tumor diagnostics and therapy monitoring, the reliable delineation of tumor boundaries and the assessment of tumor heterogeneity are increasingly complemented by the non-invasive characterization of functional and molecular processes, moving preclinical and clinical imaging from solely assessing tumor morphology towards the visualization of physiological and pathophysiological processes. Functional and molecular imaging techniques allow for the non-invasive characterization of tissues in vivo, using different modalities, including computed tomography (CT), magnetic resonance imaging (MRI), ultrasound, positron emission tomography (PET) and optical imaging (OI). With novel therapeutic concepts combining optimized radiotherapy with molecularly targeted agents focusing on tumor cell proliferation, angiogenesis, and cell death, the non-invasive assessment of tumor microcirculation and tissue water diffusion, together with strategies for imaging the mechanisms of cellular injury and repair is of particular interest. Characterizing the tumor microenvironment prior to and in response to irradiation will help to optimize the outcome of radiotherapy. These novel concepts of personalized multi-modal cancer therapy require careful pre-treatment stratification as well as a timely and efficient therapy monitoring to maximize patient benefit on an individual basis. Functional and molecular imaging techniques are key in this regard to open novel opportunities for exploring and understanding the underlying mechanisms with the perspective to optimize therapeutic concepts and translate them into a personalized form of radiotherapy in the near future.

Spatial Mapping of Translational Diffusion Coefficients Using Diffusion Tensor Imaging: A Mathematical Description.

In this article, we discuss the theoretical background for diffusion weighted imaging and diffusion tensor imaging. Molecular diffusion is a random process involving thermal Brownian motion. In biological tissues, the underlying microstructures restrict the diffusion of water molecules, making diffusion directionally dependent. Water diffusion in tissue is mathematically characterized by the diffusion tensor, the elements of which contain information about the magnitude and direction of diffusion and is a function of the coordinate system. Thus, it is possible to generate contrast in tissue based primarily on diffusion effects. Expressing diffusion in terms of the measured diffusion coefficient (eigenvalue) in any one direction can lead to errors. Nowhere is this more evident than in white matter, due to the preferential orientation of myelin fibers. The directional dependency is removed by diagonalization of the diffusion tensor, which then yields a set of three eigenvalues and eigenvectors, representing the magnitude and direction of the three orthogonal axes of the diffusion ellipsoid, respectively. For example, the eigenvalue corresponding to the eigenvector along the long axis of the fiber corresponds qualitatively to diffusion with least restriction. Determination of the principal values of the diffusion tensor and various anisotropic indices provides structural information. We review the use of diffusion measurements using the modified Stejskal-Tanner diffusion equation. The anisotropy is analyzed by decomposing the diffusion tensor based on symmetrical properties describing the geometry of diffusion tensor. We further describe diffusion tensor properties in visualizing fiber tract organization of the human brain.

Chapter 14 - Affective Brain Areas and Sleep-Disordered Breathing

The neural damage accompanying the hypoxia, reduced perfusion, and other consequences of sleep-disordered breathing, found in obstructive sleep apnea, heart failure, and congenital central hypoventilation syndrome (CCHS), appears in areas that serve multiple functions, including emotional drives to breathe, and involve systems that serve affective, cardiovascular, and breathing roles. The damage, assessed with structural magnetic resonance imaging (MRI) procedures, shows tissue loss or water content and diffusion changes indicative of injury, and impaired axonal integrity between structures; damage is preferentially unilateral. Functional MRI responses in affected areas also are time- or amplitude-distorted to ventilatory or autonomic challenges. Among the structures injured are the insular, cingulate, and ventral medial prefrontal cortices, as well as cerebellar deep nuclei and cortex, anterior hypothalamus, caudal raphé, ventrolateral medulla, portions of the basal ganglia and, in CCHS, the locus coeruleus. Caudal raphé and locus coeruleus injury have the potential to modify serotonergic and adrenergic modulation of upper airway and arousal characteristics, as well as affective drive to breathe. Since both axons and gray matter show injury, the consequences to function, especially to autonomic, cognitive, and mood regulation, are major. Several of the affected rostral sites mediate aspects of dyspnea, especially in CCHS, while others participate in initiation of inspiration after central breathing pauses, and the medullary injury can impair baroreflex and breathing control. The ancillary injury associated with sleep-disordered breathing to central structures can elicit multiple other distortions in cardiovascular, cognitive, and emotional functions in addition to effects on breathing regulation.

Numerical simulation of diffusion MRI signals using an adaptive time-stepping method

The effect on the MRI signal of water diffusion in biological tissues in the presence of applied magnetic field gradient pulses can be modelled by a multiple compartment Bloch–Torrey partial differential equation. We present a method for the numerical solution of this equation by coupling a standard Cartesian spatial discretization with an adaptive time discretization. The time discretization is done using the explicit Runge–Kutta–Chebyshev method, which is more efficient than the forward Euler time discretization for diffusive-type problems. We use this approach to simulate the diffusion MRI signal from the extra-cylindrical compartment in a tissue model of the brain gray matter consisting of cylindrical and spherical cells and illustrate the effect of cell membrane permeability.

Association of Metabolite Concentrations and Water Diffusivity in Normal Appearing Brain Tissue with Glioma Grade

Studies of brain tumors have identified altered tissue metabolism and water diffusion in MRI normal appearing tissue regions. In this retrospective study the relationship of these imaging measures with tumor grade in gliomas was investigated. MR spectroscopic imaging of whole brain and mean diffusivity (MD) measurements were obtained in subjects with untreated glioma and from normal control subjects. Mean metabolite values for N-acetylaspartate (NAA), total creatine (Cre), and total choline (Cho) were obtained in gray- and white-matter regions for the hemisphere contralateral to the tumor location, and MD values were obtained from contralateral normal-appearing white matter. Analyses tested for differences in mean values between subject groups while accounting for age. Analysis demonstrated increased NAA/Cre and MD, and decreased Cho/NAA for all tumor grades relative to control values. Differences between tumor grades were also observed for NAA, NAA/Cre, and Cho/NAA. Abnormal values of water diffusion were also observed, but with only a weak association between alterations in diffusion and tissue metabolites. This study supports previous observations of altered tissue metabolism and water diffusion in normal-appearing white matter while additionally finding differences of metabolite values in gray matter and an association with tumor grade.

Longitudinal quantitative MRI in multiple system atrophy and progressive supranuclear palsy

ObjectiveMRI has been used in parkinsonism to assess atrophy, tissue water diffusivity, and mineral deposition but usually at a single time-point. However, multiple system atrophy (MSA) and progressive supranuclear palsy (PSP) are progressive diseases. This study assessed the value of longitudinal MRI in characterizing the time course of the degenerative process. MethodsTwo serial MRIs (mean 23 months apart) were retrospectively analyzed in 12 MSA, 6 PSP, and 18 age and sex matched controls. Assessment included selected cross-sectional areas, regional apparent diffusion coefficient (ADC) and gradient echo (GRE) intensity ratios of the lateral ventricles, caudate, putamen, middle cerebellar peduncle, pons and midbrain. ResultsOn follow-up imaging, there was a larger ADC increase in the putamen in PSP over time compared to controls (p = 0.02). In MSA there was greater volume loss in the pons over time compared to controls (p = 0.002). In MSA the changes in middle cerebellar peduncle ADC were correlated with motor symptom severity according to the Unified Parkinson's Disease Rating Scale Part III (p = 0.005). ConclusionsEvidence of progressive neurodegeneration can be observed on MRI in MSA and PSP within two years consisting of increasing putaminal ADC in PSP and pontine atrophy in MSA.

Direct visualization and quantitative analysis of water diffusion in complex biological tissues using CARS microscopy

To date, it has not been possible to measure microscopic diffusive water movements in epithelia and in the interstitial space of complex tissues and organs. Diffusive water movements are essential for life because they convey physiologically important small molecules, e.g. nutrients and signaling ligands throughout the extracellular space of complex tissues. Here we report the development of a novel method for the direct observation and quantitative analysis of water diffusion dynamics in a biologically organized tissue using Coherent Anti-Stokes Raman Scattering (CARS) microscopy. Using a computer simulation model to analyze the CARS O-H bond vibration data during H2O/D2O exchange in a 3D epithelial cyst, we succeeded in measuring the diffusive water permeability of the individual luminal and basolateral water pathways and also their response to hormonal stimulation. Our technique will be applicable to the measurement of diffusive water movements in other structurally complex and medically important tissues and organs.

Avian egg latebra as brain tissue water diffusion model

Simplified models of non-monoexponential diffusion signal decay are of great interest to study the basic constituents of complex diffusion behavior in tissues. The latebra, a unique structure uniformly present in the yolk of avian eggs, exhibits a non-monoexponential diffusion signal decay. This model is more complex than simple phantoms based on differences between water and lipid diffusion, but is also devoid of microscopic structures with preferential orientation or perfusion effects. Diffusion scans with multiple b-values were performed on a clinical 3 Tesla system in raw and boiled chicken eggs equilibrated to room temperature. Diffusion encoding was applied over the ranges 5-5,000 and 5-50,000 s/mm(2). A low read-out bandwidth and chemical shift was used for reliable lipid/water separation. Signal decays were fitted with exponential functions. The latebra, when measured over the 5-5,000 s/mm(2) range, exhibited independent of preparation clearly biexponential diffusion, with diffusion parameters similar to those typically observed in in vivo human brain. For the range 5-50,000 s/mm(2), there was evidence of a small third, very slow diffusing water component. The latebra of the avian egg contains membrane structures, which may explain a deviation from a simple monoexponential diffusion signal decay, which is remarkably similar to the deviation observed in brain tissue.

Denoising and fast diffusion imaging with physically constrained sparse dictionary learning

Diffusion-weighted imaging (DWI) allows imaging the geometry of water diffusion in biological tissues. However, DW images are noisy at high b-values and acquisitions are slow when using a large number of measurements, such as in Diffusion Spectrum Imaging (DSI). This work aims to denoise DWI and reduce the number of required measurements, while maintaining data quality. To capture the structure of DWI data, we use sparse dictionary learning constrained by the physical properties of the signal: symmetry and positivity. The method learns a dictionary of diffusion profiles on all the DW images at the same time and then scales to full brain data. Its performance is investigated with simulations and two real DSI datasets. We obtain better signal estimates from noisy measurements than by applying mirror symmetry through the q-space origin, Gaussian denoising or state-of-the-art non-local means denoising. Using a high-resolution dictionary learnt on another subject, we show that we can reduce the number of images acquired while still generating high resolution DSI data. Using dictionary learning, one can denoise DW images effectively and perform faster acquisitions. Higher b-value acquisitions and DSI techniques are possible with approximately 40 measurements. This opens important perspectives for the connectomics community using DSI.

Diffusion Tensor Imaging and Related Techniques In Tuberous Sclerosis Complex: Review and Future Directions

In this article, the authors aim to introduce the nonradiologist to diffusion tensor imaging (DTI) and its applications to both clinical and research aspects of tuberous sclerosis complex. Tuberous sclerosis complex is a genetic neurocutaneous syndrome with variable and unpredictable neurological comorbidity that includes refractory epilepsy, intellectual disability, behavioral abnormalities and autism spectrum disorder. DTI is a method for modeling water diffusion in tissue and can noninvasively characterize microstructural properties of the brain. In tuberous sclerosis complex, DTI measures reflect well-known pathological changes. Clinically, DTI can assist with detecting the epileptogenic tuber. For research, DTI has a putative role in identifying potential disease biomarkers, as DTI abnormalities of the white matter are associated with neurocognitive morbidity including autism. If indeed DTI changes parallel phenotypical changes related to the investigational treatment of epilepsy, cognition and behavior with mTOR inhibitors, it will facilitate future clinical trials.

Characterisation of Endothelin-1-Induced Intrastriatal Lesions Within the Juvenile and Adult Rat Brain Using MRI and 31P MRS

Improved non-invasive magnetic resonance (MR) characterisation of in vivo models of focal ischaemic insults such as transient ischaemic attack (TIA) and perinatal arterial ischaemic stroke (AIS) may assist diagnosis, outcome prediction and treatment design. The classic middle cerebral artery occlusion (MCAO) model of ischaemic stroke is well documented in MR studies but generates extensive and complex lesions involving an acute inflammatory response and de-occlusion that immediately restores circulation. By contrast, intrastriatal microinjection of the potent vasoconstrictor, endothelin-1 (ET-1), induces a focal, reversible and low-flow ischaemia in the absence of a typical inflammatory response, which gradually restores blood flow over several hours and may be more relevant to TIA and AIS pathology. This study presents the first comprehensive longitudinal MR characterisation of the real-time anatomical [T1-weighted (T1-w)/T2-weighted (T2-w)], pathophysiological [apparent diffusion coefficient (ADC), cerebral blood volume, gadolinium contrast imaging of blood-brain barrier (BBB) integrity] and metabolic [phosphorus magnetic resonance spectroscopy (31P MRS)] evolution of a purely ischaemic ET-1-induced lesion within the juvenile and adult rat brain. ET-1-induced cytotoxic oedema was visualised on T2-w magnetic resonance imaging (MRI), inconsistent with the conventional notion that it cannot be detected using anatomical MRI. There was no immunohistochemical evidence of an acute inflammatory response or loss of BBB integrity, thus excluding a vasogenic oedema contribution to the pathology. Maximal T2-w intensity correlated with the lowest ADC value in both age groups, re-emphasising the purely ischaemic nature of the lesion and the absence of vasogenic oedema. Furthermore, extensive acute T1-w hypointensity was observed in the presence of cytotoxic oedema-induced T2-w changes, whereas other authors have shown that increased T1 values following MCAO reflect vasogenic oedema. Intriguingly, the lesion border exhibited hyperintensity on T2-w and ADC MRI at later time points, and the former may be a consequence of phagocytosis-induced fatty droplet deposition by macrophages detected immunohistochemically. In spite of a chronically reduced ADC, typically associated with ischaemia-induced energy failure, a 31P MRS-detectable reduction in the phosphocreatine (PCr) to gamma adenosine triphosphate (γATP) ratio was not observed at any time point in either age group, suggesting dissociation of tissue water diffusion and metabolic changes within the ET-1-induced lesion.

The role of tissue microstructure and water exchange in biophysical modelling of diffusion in white matter

Biophysical models that describe the outcome of white matter diffusion MRI experiments have various degrees of complexity. While the simplest models assume equal-sized and parallel axons, more elaborate ones may include distributions of axon diameters and axonal orientation dispersions. These microstructural features can be inferred from diffusion-weighted signal attenuation curves by solving an inverse problem, validated in several Monte Carlo simulation studies. Model development has been paralleled by microscopy studies of the microstructure of excised and fixed nerves, confirming that axon diameter estimates from diffusion measurements agree with those from microscopy. However, results obtained in vivo are less conclusive. For example, the amount of slowly diffusing water is lower than expected, and the diffusion-encoded signal is apparently insensitive to diffusion time variations, contrary to what may be expected. Recent understandings of the resolution limit in diffusion MRI, the rate of water exchange, and the presence of microscopic axonal undulation and axonal orientation dispersions may, however, explain such apparent contradictions. Knowledge of the effects of biophysical mechanisms on water diffusion in tissue can be used to predict the outcome of diffusion tensor imaging (DTI) and of diffusion kurtosis imaging (DKI) studies. Alterations of DTI or DKI parameters found in studies of pathologies such as ischemic stroke can thus be compared with those predicted by modelling. Observations in agreement with the predictions strengthen the credibility of biophysical models; those in disagreement could provide clues of how to improve them. DKI is particularly suited for this purpose; it is performed using higher b-values than DTI, and thus carries more information about the tissue microstructure. The purpose of this review is to provide an update on the current understanding of how various properties of the tissue microstructure and the rate of water exchange between microenvironments are reflected in diffusion MRI measurements. We focus on the use of biophysical models for extracting tissue-specific parameters from data obtained with single PGSE sequences on clinical MRI scanners, but results obtained with animal MRI scanners are also considered. While modelling of white matter is the central theme, experiments on model systems that highlight important aspects of the biophysical models are also reviewed.

Advantages and drawbacks of breast DTI

In 1965, Stejskal and Tanner developed the pulsed gradient spin echo (PGSE) technique for measuring the diffusion coefficient in solution [1]. The discovery of MRI led to the development of diffusion imaging sequences particularly sequences based on echo planar imaging – EPI that facilitate fast clinical diffusion measurements. As a result of gradient strength limitations in most human scanners, it is necessary to use long finite-width gradient pulses in order to achieve high b values and hence, the short gradient pulse approximation breaks down. Nevertheless, it was shown by Zielinski and Sen [2] that diffusion experiments with long diffusion gradient pulses still measure a physical parameter reflecting self diffusion in systems that have open geometry and large amount of restriction as is the case in most tissues. Water diffusion in tissues presents a highly complex process as the system is composed of several different compartments with partial restriction processes within the compartments. Water diffusion coefficients of tissues are not merely affected by Brownian motion, but also by additional contributions of flow, restriction by cell membrane, extracellular tortuosity and exchange between tissue compartments. Water diffusion in tissues is often anisotropic due to restriction by membranes and walls of various micro-structures. Namely, anisotropic diffusion leads to variable diffusion coefficients for various directions and hence the diffusion coefficients are described by a diffusion tensor. The diffusion of water molecules in the mammary tissue presents a particular example of restricted movement in well defined microstructures composed of the ductal/ glandular trees. The, diffusion in parallel to the walls of the ducts is free; however, it is restricted in the directions perpendicular to the walls. The extent of restriction will depend on the experimental diffusion time versus the size of the ductal and glandular regions. Blockage of the ducts by cancer cells predominantly affects the free diffusion in parallel to the walls, reducing the diffusion coefficient in all directions, and consequently the extent of anisotropy. We have applied an experimental protocol to track this anisotropic motion using diffusion gradients in 30 to 60 directions and two b-values with a relatively high diffusion time [3]. In voxels with anisotropic water diffusion the distribution of the fraction of change in signal intensity in all directions of the field gradients assumed an anisotropic ellipsoid form, whereas in voxels with isotropic

Nuclear Magnetic Resonance as a Diagnostic Tool in Breast Cancer

Nuclear Magnetic Resonance as a Diagnostic Tool in Breast CancerThe early detection and treatment of breast cancer is of direct benefit to patients. Magnetic resonance imaging (MRI) is a promising modality for detection, diagnosis, and staging of breast cancer. MRI enables two methods: the diffusion-weighted MRI (DW MRI) and the dynamic contrast enhanced MRI (DCE MRI). DW MRI reflects the diffusion of water molecules in the extracellular fluid space and allows the estimation of cellularity and tissue structure. The value of the diffusion of water in tissue is called the apparent diffusion coefficient (ADC). ADC values in malignant lesions are smaller than in benign tissue. DCE MRI yields appropriate pharmacokinetic data of physiological parameters that relate to tissue perfusion, microvascular vessel wall permeability and extracellular volume fraction. Gadolinium based contrast agent is usually used in breast DCE MRI diagnostics. Changes in the post-contrast signal intensity help to distinguish lesions according to characteristically enhanced accumulation of contrast agent. Malignant lesions are characterized by a faster and stronger signal enhancement than benign lesions which relate to their neoangiogenesis. Over the last few years, there has been appreciable interest in the use of magnetic resonance spectroscopy (MRS) for the non-invasive analysis of breast tisue metabolites. One of the spectroscopic hallmarks of the neoplastic process appears to be the presence of total choline signal in thein vivospectrum. Despite the fact that MRI and MRS achieve excellent results, they are still not so frequently used in comparison to mammography and breast ultrasound.

Microscopic diffusion anisotropy in formalin fixed prostate tissue: Preliminary findings

Diffusion tensor microimaging at 16.4 T with 40 μm isotropic voxels was used to investigate anisotropic water diffusion in prostate tissue at spatial resolution approaching the cellular scale. Nine normal glandular tissue samples were collected from the peripheral zone of six formalin fixed radical prostatectomy specimens. Fibromuscular stromal tissue exhibited microscopic diffusion anisotropy (mean fractional anisotropy range 0.47-0.66) significantly higher (P < 0.01, Student's t-test) than in epithelium-containing voxels (mean fractional anisotropy range 0.31-0.54) in six of the seven normal tissue samples in which both compartments could be measured. Fiber tracking demonstrated principle stromal fiber directions consistent with myocyte orientation seen on light microscopy of the same sample. Diffusion tensor microimaging may be valuable for investigation of variable results from attempts to measure diffusion anisotropy in the prostate in vivo.

複数機種において同一被験者群を用いて得られた Fractional Anisotropy値の比較

The fractional anisotropy (FA) is calculated by using diffusion tensor imaging (DTI) with multiple motion probing gradients (MPG). While FA has become a widely used tool to detect moderate changes in water diffusion in brain tissue, the measured value is sensitive to scan parameters (e.g. MPG-direction, signal to noise ratio, etc.). Therefore, it is paramount to address the reproducibility of DTI measurements among multiple centers. The purpose of this study was to assess the inter-center variability of FA. We studied five healthy volunteers who underwent DTI brain scanning three times at three different centers (I-III), each with a 1.5 T scanner having a different MPG-schema. Then, we compared the FA and eigenvalue from the three centers measured in seven brain regions: splenium of corpus callosum (CCs), genu of corpus callosum (CCg), putamen, posterior limb of internal capsule, cerebral peduncle, optic radiation, and middle cerebellar peduncle. At the CCs and CCg, there was a statistical difference (p<0.05) between center Iand center IIfor the same MPG-directions. Furthermore, at CCs and CCg, there was a statistical difference (p<0.05) between center II and center III for different MPG-directions. Conversely, no statistical differences were found between center I and center III for the different MPG-directions for all regions. These results indicate that the FA value was affected by the MPG-schema as well as by the MPG-directions.

Microscopic diffusivity compartmentation in formalin‐fixed prostate tissue

MR microimaging at 16.4 T with 40-μm isotropic voxels was used to investigate compartmentation of water diffusion in formalin-fixed prostate tissue. Ten tissue samples (~ 28 mm(3) each) from five organs were imaged. The mean diffusivity of epithelial, stromal, and ductal/acinar compartments was estimated by two methods: (1) manual region of interest selection and (2) Gaussian fitting of voxel diffusivity histograms. For the region of interest-method, the means of the tissue sample compartment diffusivities were significantly different (P < 0.001): 0.54 ± 0.05 μm(2)/ms for epithelium-containing voxels, 0.91 ± 0.17 μm(2)/ms for stroma, and 2.20 ± 0.04 μm(2)/ms for saline-filled ducts. The means from the histogram method were also significantly different (P < 0.001): 0.45 ± 0.08 μm(2)/ms for epithelium-containing voxels, 0.83 ± 0.16 μm(2)/ms for stroma, 2.21 ± 0.02 μm(2)/ms for duct. Estimated partial volumes of epithelial, stromal, and ductal/acinar compartments in a "tissue only" subvolume of each sample were significantly different (P < 0.02) between cancer and normal tissue for all three compartments. It is concluded that the negative correlation between apparent diffusion coefficient and cancer Gleason grade observed in vivo results from an increase of partial volume of epithelial tissue and concomitant decrease of stromal tissue and ductal space.