Phase-contrast Technique Research Articles

Cardiovascular cine imaging and flow evaluation using Fast Interrupted Steady-State (FISS) magnetic resonance

BackgroundExisting cine imaging techniques rely on balanced steady-state free precession (bSSFP) or spoiled gradient-echo readouts, each of which has limitations. For instance, with bSSFP, artifacts occur from rapid through-plane flow and off-resonance effects. We hypothesized that a prototype cine technique, radial fast interrupted steady-state (FISS), could overcome these limitations. The technique was compared with standard cine bSSFP for cardiac function, coronary artery conspicuity, and aortic valve morphology. Given its advantageous properties, we further hypothesized that the cine FISS technique, in combination with arterial spin labeling (ASL), could provide an alternative to phase contrast for visualizing in-plane flow patterns within the aorta and branch vessels.Main bodyThe study was IRB-approved and subjects provided consent. Breath-hold cine FISS and bSSFP were acquired using similar imaging parameters. There was no significant difference in biplane left ventricular ejection fraction or cardiac image quality between the two techniques. Compared with cine bSSFP, cine FISS demonstrated a marked decrease in fat signal which improved conspicuity of the coronary arteries, while suppression of through-plane flow artifact on thin-slice cine FISS images improved visualization of the aortic valve. Banding artifacts in the subcutaneous tissues were reduced. In healthy subjects, dynamic flow patterns were well visualized in the aorta, coronary and renal arteries using cine FISS ASL, even when the slice was substantially thicker than the vessel diameter.ConclusionCine FISS demonstrates several benefits for cardiovascular imaging compared with cine bSSFP, including better suppression of fat signal and reduced artifacts from through-plane flow and off-resonance effects. The main drawback is a slight (~ 20%) decrease in temporal resolution. In addition, preliminary results suggest that cine FISS ASL provides a potential alternative to phase contrast techniques for in-plane flow quantification, while enabling an efficient, visually-appealing, semi-projective display of blood flow patterns throughout the course of an artery and its branches.

Dose and diagnostic performance comparison between phase-contrast mammography with synchrotron radiation and digital mammography: a clinical study report

Two dosimetric quantities [mean glandular dose (MGD) and entrance surface air kerma (ESAK)] and the diagnostic performance of phase-contrast mammography with synchrotron radiation (MSR) are compared to conventional digital mammography (DM). Seventy-one patients (age range, 41 to 82 years) underwent MSR after a DM examination if questionable or suspicious breast abnormalities were not clarified by ultrasonography. The MGD and the ESAK delivered in both examinations were evaluated and compared. Two on-site radiologists rated the images in consensus according to the Breast Imaging Reporting and Data System assessment categories, which were then correlated with the final diagnoses by means of statistical generalized linear models (GLMs). Receiver operating characteristic curves were also used to assess the diagnostic performance by comparing the area under the curve (AUC). An important MGD and ESAK reduction was observed in MSR due to the monoenergetic beam. In particular, an average 43% reduction was observed for the MGD and a reduction of more than 50% for the ESAK. GLM showed higher diagnostic accuracy, especially in terms of specificity, for MSR, confirmed by AUC analysis ([Formula: see text]). The study design implied that the population was characterized by a high prevalence of disease and that the radiologists, who read the DM images before referring the patient to MSR, could have been influenced in their assessments. Within these limitations, the use of synchrotron radiation with the phase-contrast technique applied to mammography showed an important dose reduction and a higher diagnostic accuracy compared with DM. These results could further encourage research on the translation of x-ray phase-contrast imaging into the clinics.

Cerebrospinal fluid flowmetry using phase-contrast MRI technique and its clinical applications

Background and aim and aim Cine phase-contrast (PC) MRI is a useful noninvasive imaging technique in evaluating the dynamics of cerebrospinal fluid (CSF) in the evaluation, follow-up, surgical decision, and postoperative survey of certain disease processes, such as normal pressure hydrocephalus, aqueduct stenosis (AS), postendoscopic third ventriculostomy, and arachnoid cysts cases. The aim of this study was to determine the value of cardiac-gated cine-PC-MRI in characterizing CSF flow in patients with CSF flow disorders. Patients and methods The study included 30 patients with 10 persons as the control group and 20 patients who were suspected to have CSF flow abnormalities. Two imaging techniques were applied: the axial plane for flow quantification and the sagittal plane for a qualitative assessment. Results Among the 30 patients, quantitative analysis revealed the mean value to be 22 μl as the average aqueductal stroke volume in the control group. In the normal pressure hydrocephalus group, systolic velocities as well as stroke volume values were higher than those of the controls. In the AS group, lack of significant aqueductal CSF flow was noticeable. Both peak systolic and diastolic velocities were found to be statistically significantly lower in patients with AS than in the control group. In arachnoid cyst cases, CSF flow study with cine PC-MRI enables visualization of flow communication between cysts and neighboring CSF compartments. Two cases were assigned as communicating cysts and four cases were noncommunicating. Conclusion Assessment of CSF flow indicates the potentials of using PC-MRI adjunct to routine MR for the clinical study of CSF-related diseases.

Mathematical Modelling of CSF Pulsatile Flow in Aqueduct Cerebri.

The phase-contrast MRI technique permits the non-invasive assessment of CSF movements in cerebrospinal fluid cavities of the central nervous system. Of particular interest is pulsatile cerebrospinal fluid (CSF) flow through the aqueduct cerebri. It is allegedly increased in hydrocephalus, having potential diagnostic value, although not all scientific reports contain unequivocally positive conclusions. For the mathematical simulation of CSF flow, we used a computational model of cerebrospinal blood/fluid circulation designed by a former student as his PhD project. With this model, cerebral blood flow and CSF may be simulated in various vessels using a system of non-linear differential equations as time-varying signals. The amplitude of CSF flow seems to be positively related to the amplitude of pulse waveforms of intracranial pressure (ICP) in situations where mean ICP increases, such as during simulated infusion tests and following step increases of resistance to CSF outflow. An additional positive association between the pulse amplitude of ICP and CSF flow can be seen during simulated increases in the amplitude of arterial pulses (without changes in mean arterial pressure, MAP). The opposite effect can be observed during step increases in the resistance of the aqueduct cerebri and with decreasing elasticity of the system, where the CSF flow amplitude and the ICP pulse amplitude are related inversely. Vasodilatation caused by both gradual decreases in MAP and by increases in PaCO2 provokes an elevation in the observed amplitude of pulsatile CSF flow. Preliminary results indicate that the pulsations of CSF flow may carry information about both CSF-circulatory and cerebral vasogenic components. In most cases, the pulsations of CSF flow are positively related to the pulse amplitudes of both arterial pressure and ICP and to a degree of cerebrovascular dilatation.

Cardiovascular magnetic resonance elastography: A review.

Cardiovascular diseases are the leading cause of death worldwide. These cardiovascular diseases are associated with mechanical changes in the myocardium and aorta. It is known that stiffness is altered in many diseases, including the spectrum of ischemia, diastolic dysfunction, hypertension and hypertrophic cardiomyopathy. In addition, the stiffness of the aortic wall is altered in multiple diseases, including hypertension, coronary artery disease and aortic aneurysm formation. For example, in diastolic dysfunction in which the ejection fraction is preserved, stiffness can potentially be an important biomarker. Similarly, in aortic aneurysms, stiffness can provide valuable information with regard to rupture potential. A number of studies have addressed invasive and non-invasive approaches to test and measure the mechanical properties of the myocardium and aorta. One of the non-invasive approaches is magnetic resonance elastography (MRE). MRE is a phase-contrast magnetic resonance imaging technique that measures tissue stiffness non-invasively. This review article highlights the technical details and application of MRE in the quantification of myocardial and aortic stiffness in different disease states.

Visualising the 3D microstructure of stained and native intervertebral discs using X-ray microtomography

Intervertebral disc degeneration (IVDD) is linked to low back pain. Microstructural changes during degeneration have previously been imaged using 2D sectioning techniques and 3D methods which are limited to small specimens and prone to inducing artefacts from sample preparation. This study explores micro computed X-ray tomography (microCT) methods with the aim of resolving IVD 3D microstructure whilst minimising sample preparation artefacts. Low X-ray absorption contrast in non-mineralised tissue can be enhanced using staining and phase contrast techniques. A step-wise approach, including comparing three stains, was used to develop microCT for bovine tail IVD using laboratory and synchrotron sources. Staining successfully contrasted collagenous structures; however not all regions were stained and the procedure induced macroscopic structural changes. Phase contrast microCT of chemically fixed yet unstained samples resolved the nucleus pulposus, annulus fibrosus and constituent lamellae, and finer structures including collagen bundles and cross-bridges. Using the same imaging methods native tissue scans were of slightly lower contrast but free from sample processing artefacts. In the future these methods may be used to characterise structural remodelling in soft (non-calcified) tissues and to conduct in situ studies of native loaded tissues and constructs to characterise their 3D mechanical properties.

Fast X-ray imaging of cavitating flows

A new method based on ultra-fast X-ray imaging was developed in this work for the investigation of the dynamics and the structures of complex two-phase flows. In this paper, cavitation was created inside a millimetric 2D Venturi-type test section, while seeding particles were injected into the flow. Thanks to the phase-contrast enhancement technique provided by the APS (Advanced Photon Source) synchrotron beam, high definition X-ray images of the complex cavitating flows were obtained. These images contain valuable information about both the liquid and the gaseous phases. By means of image processing, the two phases were separated, and velocity fields of each phase were, therefore, calculated using image cross-correlations. The local vapour volume fractions were also obtained, thanks to the local intensity levels within the recorded images. These simultaneous measurements, provided by this new technique, afford more insight into the structure and the dynamic of two-phase flows as well as the interactions between them, and hence enable to improve our understanding of their behaviour. In the case of cavitating flows inside a Venturi-type test section, the X-ray measurements demonstrate, for the first time, the presence of significant slip velocities between the phases within sheet cavities for both steady and unsteady flow configurations.

Recent advances in edge illumination x-ray phase-contrast tomography.

.Edge illumination (EI) is an x-ray phase-contrast imaging technique, exploiting sensitivity to x-ray refraction to visualize features, which are often not detected by conventional absorption-based radiography. The method does not require a high degree of spatial coherence and is achromatic and, therefore, can be implemented with both synchrotron radiation and commercial x-ray tubes. Using different retrieval algorithms, information about an object’s attenuation, refraction, and scattering properties can be obtained. In recent years, a theoretical framework has been developed that enables EI computed tomography (CT) and, hence, three-dimensional imaging. This review provides a summary of these advances, covering the development of different image acquisition schemes, retrieval approaches, and applications. These developments constitute an integral part in the transformation of EI CT into a widely spread imaging tool for use in a range of fields.

Quantifying musculoskeletal motion using dynamic MRI techniques: A systematic review of validity and perspectives for musculoskeletal disorder evaluation

This systematic review reports the evidence of validity and reliability of dynamic MRI (dMRI) techniques in quantifying in vivo skeletal joint movement (kinematics) or muscle tracking and to propose recommendations of use for the assessment of normal and impaired musculoskeletal function. A systematic search was conducted on six bibliographic databases (Web of science, PubMed, Scopus, Academic search Premier, Pascal, and Cochrane Library) for articles published between 1990 and January 2017. Prospective studies that reported the concurrent validity and/or reliability of determining in vivo skeletal joint or muscle motion using dMRI techniques were included after assessment by two independent reviewers for inclusion and exclusion criteria. Selected articles were assessed using an adapted quality assessment tool and a data extraction process. Concurrent validity and reliability measurement results were categorized as poor, moderate, or excellent for this review. Bibliographic search identified 20 articles that met the inclusion and exclusion criteria. The mean quality assessment score for all the selected articles was 66% (±10.4). Concurrent validity and/or reliability of eight dMRI techniques evaluating the musculoskeletal motion were reported. Selected studies spanned various joints and muscles with knee joint being the most evaluated joint (seven studies), followed by ankle and temporomandibular joint (two studies each). Moderate to excellent concurrent validity and reliability were reported for most of the dMRI techniques. Based on the current level of metrological evidence Cine Phase-Contrast and Real-time MRI techniques stand out for determining skeletal joint motion whereas Spin tag MRI technique stands out for determining muscle motion. dMRI techniques can be effectively applied to understand in vivo skeletal joint and muscle movement mechanics for both healthy and pathological populations. However, caution must be exercised as the evidence of validity and reliability of using these techniques in all the skeletal joints and muscles have not been systematically evaluated. Furthermore, clinical utility of the techniques in impaired population is not addressed yet in terms of concurrent validity and reliability measures setting up a good research direction for future studies. Examples of the best available techniques and outcomes for rehabilitation application will be provided during the presentation.

Eccentric needle motion effect on near-nozzle dynamics of diesel spray

The eccentric needle motion has been regarded as an important cause of in-nozzle flow disturbances and hole-to-hole spray variations of modern fuel injectors. However, the experimental investigations on this subject have rarely been reported due to great difficulties in the direct measurements of eccentric needle motion and the flow characteristics of individual holes in an injection nozzle. In this study, the axial and eccentric needle motion and the near-nozzle spray dynamics of 3-hole, 5-hole and 8-hole diesel injection nozzles were investigated in varied injection pressure conditions using an X-ray phase-contrast imaging technique. The eccentric needle motion and near-nozzle spray axial velocity showed temporal oscillations during the injection with different oscillation frequencies. The frequencies of these two oscillations were independent to the nozzle hole number and injection pressure. To discuss the mutual dependency of these two oscillations, the time traces of the spray axial velocity were measured for individual holes. The results showed that the oscillation phase, frequency and amplitude of the spray axial velocity were almost identical for all holes, which indicated that the sac pressure variation rather than hole-to-hole flow variation can be the primary cause of the spray axial velocity oscillation by the eccentric needle motion. The adequacy of this consideration was thoroughly discussed using a mass balance model in the nozzle sac that predicted the sac pressure variation during an injection event.

MRI-based assessment of acute effect of head-down tilt position on intracranial hemodynamics and hydrodynamics.

To quantify the acute effect of the head-down tilt (HDT) posture on intracranial hemodynamics and hydrodynamics. We evaluated the intracranial physiological parameters, blood flow-related parameters, and brain morphology in the HDT (-6° and -12°) and the horizontal supine (HS) positions. Seven and 15 healthy subjects were scanned for each position using 3.0 T magnetic resonance imaging system. The peak-to-peak intracranial volume change, the peak-to-peak cerebrospinal fluid (CSF) pressure gradient (PGp-p ), and the intracranial compliance index were calculated from the blood and CSF flow determined using a cine phase-contrast technique. The brain volumetry was conducted using SPM12. The measurements were compared using the Wilcoxon signed-rank test or a paired t-test. No measurements changed in the -6° HDT. The PGp-p and venous outflow of the internal jugular veins (IJVs) in the -12° HDT were significantly increased compared to the HS (P < 0.001 and P = 0.025, respectively). The cross-sectional areas of the IJVs were significantly larger (P < 0.001), and the maximum, minimum, and mean blood flow velocity of the IJVs were significantly decreased (P = 0.003, < 0.001, and = 0.001, respectively) in the -12° HDT. The mean blood flow velocities of the internal carotid arteries were decreased (P = 0.023). Neither position affected the brain volume. Pressure gradient and venous outflow were increased in accordance with the elevation of the intracranial pressure as an acute effect of the HDT. However, the CSF was not constantly shifted from the spinal canal to the cranium. 2 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2018;47:565-571.

Implication of pulmonary-systemic flow information in the management of complex presentation of pulmonary arterial hypertension: exploring role of phase contrast MRI technique.

Phase-contrast (PC) cardiovascular magnetic resonance (MR) is an established technique which can measure, non-invasively, all three directional components of the velocities of blood flow relative to all four spatio-temporal dimensions of the heart and great vessels (1-4). The mapping of single component of “time-resolved velocity” directed perpendicularly through a 2D plane is extensively used for clinical measurements of flow volume (1-4). This technique provides measurements of forward, regurgitant and shunt flows in cardiovascular disease (5). Application of the same technology enables evaluation of flow across large aortic collaterals. Thus a measure of shunting between systemic to pulmonary (S-P) circulation or otherwise can be quantitatively obtained. Here we present a clinical example wherein information obtained from PC technique greatly assisted in the better understanding of patho-physiological basis of a uncommon clinical presentation.

Retrieving the Ultrasmall-Angle X-Ray Scattering Signal with Polychromatic Radiation in Speckle-Tracking and Beam-Tracking Phase-Contrast Imaging

Ultrasmall-angle x-ray scattering (USAXS) is sensitive to microstructures that are smaller than the imaging system's resolution, and therefore inaccessible via other contrast mechanisms. This comparison of two phase-contrast imaging techniques focuses on their differences in the retrieved absorption and USAXS signals. The results indicate that the retrieval method for speckle tracking needs revision, while beam tracking extracts the correct signal. This is a key result for implementing the beam-tracking method with laboratory (not beamline) x-ray sources, for tomographic applications from materials science to medicine.

Anticancer properties of Semen Euphorbiae towards ACHN human renal adenocarcinoma cells by inducing apoptosis.

The main objective of the present research work was to evaluate the antitumor effects of ethanol extract of Semen Euphorbiae (EESE) in ACHN human renal carcinoma cells. The effects on apoptosis induction, cell cycle phase distribution and livin protein expression were also evaluated. MTT assay was used to assess cytotoxic effects of the extract while as clonogenic assay was used to evaluate effects on colony formation tendency. Inverted phase contrast and fluorescence microscopic techniques were used to evaluate effects of EESE on cellular morphology and apoptosis. Flow cytometry using annexin V-FITC and propidium iodide were used to quantify the extent of apoptosis and also to evaluate effects on cell cycle. Results indicate that ethanol extract of Semen Euphorbiae exhibited potent cytotoxic effects in ACHN human renal cancer cells. These effects were found to be dose-dependent as well as time dependent. Clonogenic assay revealed that EESE led to dose-dependent inhibition of colony formation in these cells. EESE-treated cells also showed evident signs of alterations and deformations in cell morphology including detachment of cells from one another forming small cluster of cells. In contrast to untreated control cells, EESE-treated cells with 10, 100 and 200 µg/ml dose showed an increase in the number of cells emitting red/orange fluorescence indicating onset and execution of apoptosis. EESE extract also led to G2/M cell cycle arrest in these cells.

Automated Liver Elasticity Calculation for 3D MRE.

Magnetic Resonance Elastography (MRE) is a phase-contrast MRI technique which calculates quantitative stiffness images, called elastograms, by imaging the propagation of acoustic waves in tissues. It is used clinically to diagnose liver fibrosis. Automated analysis of MRE is difficult as the corresponding MRI magnitude images (which contain anatomical information) are affected by intensity inhomogeneity, motion artifact, and poor tissue- and edge-contrast. Additionally, areas with low wave amplitude must be excluded. An automated algorithm has already been successfully developed and validated for clinical 2D MRE. 3D MRE acquires substantially more data and, due to accelerated acquisition, has exacerbated image artifacts. Also, the current 3D MRE processing does not yield a confidence map to indicate MRE wave quality and guide ROI selection, as is the case in 2D. In this study, extension of the 2D automated method, with a simple wave-amplitude metric, was developed and validated against an expert reader in a set of 57 patient exams with both 2D and 3D MRE. The stiffness discrepancy with the expert for 3D MRE was -0.8% ± 9.45% and was better than discrepancy with the same reader for 2D MRE (-3.2% ± 10.43%), and better than the inter-reader discrepancy observed in previous studies. There were no automated processing failures in this dataset. Thus, the automated liver elasticity calculation (ALEC) algorithm is able to calculate stiffness from 3D MRE data with minimal bias and good precision, while enabling stiffness measurements to be fully reproducible and to be easily performed on the large 3D MRE datasets.

Magnetic scanning gate microscopy of CoFeB lateral spin valve

Devices comprised of CoFeB nanostructures with perpendicular magnetic anisotropy and non-magnetic Ta channel were operated in thermal lateral spin valve (LSV) mode and studied by magnetotransport measurements and magnetic scanning gate microscopy (SGM). Due to the short spin diffusion length of Ta, the spin diffusion signal was suppressed, allowing the study of the contribution from the anomalous Nernst (ANE) and anomalous Hall effects (AHE). The magnetotransport measurements identified the switching fields of the CoFeB nanostructures and demonstrated a combination of AHE and ANE when the devices were operated in thermally-driven spin-injection mode. Modified scanning probe microscopy probes were fabricated by placing a NdFeB magnetic bead (MB) on the apex of a commercial Si probe. The dipole magnetic field distribution around the MB was characterized by using differential phase contrast technique and direct measurement of the switching field induced by the bead in the CoFeB nanodevices. Using SGM we demonstrate the influence of localized magnetic field on the CoFeB nanostructures near the non-magnetic channel. This approach provides a promising route towards the study of thermal and spin diffusion effects using local magnetic fields.

Orbital angular momentum light in microscopy.

Light with a helical phase has had an impact on optical imaging, pushing the limits of resolution or sensitivity. Here, special emphasis will be given to classical light microscopy of phase samples and to Fourier filtering techniques with a helical phase profile, such as the spiral phase contrast technique in its many variants and areas of application.This article is part of the themed issue 'Optical orbital angular momentum'.

Analyzer-based imaging system performance in a synchrotron clinical environment: a feasibility study

X-ray phase contrast imaging arises from changes of the propagation direction of the radiant wave field when traversing the object and it can yield higher contrast for soft tissues than conventional x-ray radiology based on attenuation. Commonly intermediate steps are required to transform wave front modulations into intensity modulations measurable by the detection system. One of these phase contrast techniques is analyzer-based imaging (ABI), which utilizes an analyzer crystal as angular filter with a bandwidth in the micro-radian regime placed between the sample and the detector. Furthermore employing appropriate algorithms, attenuation, refraction and scattering/dark field images can be extracted providing complementary information. The implementation of ABI requires X-ray optics with very high stability and micro-radian resolution. In return, this method possesses an extremely high sensitivity among the phase contrast techniques. At the medical beamline of the Italian synchrotron ELETTRA, a patient room has been implemented in order to perform clinical mammography with free-space propagation phase contrast. In this work we have tested the feasibility of ABI in a preclinical set-up implementing the system in the patient room. High quality images of breast tissues samples are presented and compared to images acquired at a conventional mammography unit. The system has shown excellent stability and imaging performances.

Table-top phase-contrast imaging employing photon-counting detectors towards mammographic applications

In mammography the difficult task to detect microcalcifications (≈ 100 μm) and low contrast structures in the breast has been a topic of interest from its beginnings. The possibility to improve the image quality requires the effort to employ novel X-ray imaging techniques, such as phase-contrast, and high resolution detectors. Phase-contrast techniques are promising tools for medical diagnosis because they provide additional and complementary information to traditional absorption-based X-ray imaging methods. In this work a Hamamatsu microfocus X-ray source with tungsten anode and a photon counting detector (Timepix operated in Medipix mode) was used. A significant improvement in the detection of phase-effects using Medipix detector was observed in comparison to an standard flat-panel detector. An optimization of geometrical parameters reveals the dependency on the X-ray propagation path and the small angle deviation. The quantification of these effects was achieved taking into account the image noise, contrast, spatial resolution of the phase-enhancement, absorbed dose, and energy dependence.

Single-shot edge illumination x-ray phase-contrast tomography enabled by joint image reconstruction.

Edge illumination x-ray phase-contrast tomography (EIXPCT) is an emerging x-ray phase-contrast tomography technique for reconstructing the complex-valued x-ray refractive index distribution of an object. Conventional image reconstruction approaches for EIXPCT require multiple images to be acquired at each tomographic view angle. This contributes to prolonged data-acquisition times and elevated radiation doses, which can hinder in vivo applications. In this work, a new "single-shot" method is proposed for joint reconstruction (JR) of the real and imaginary-valued components of the refractive index distribution from a tomographic data set that contains only a single image acquired at each view angle. The proposed method is predicated on a nonlinear formulation of the inverse problem that is solved by using a gradient-based optimization method. The method is validated and investigated using computer-simulated and experimental EIXPCT data sets.