2D sense for faster 3D MRI

Sensitivity encoding in two spatial dimensions (2D SENSE) with a receiver coil array is discussed as a means of improving the encoding efficiency of three-dimensional (3D) Fourier MRI. it is shown that in Fourier imaging with two phase encoding directions, 2D SENSE has key advantages over one-dimensional parallel imaging approaches. By exploiting two dimensions for hybrid encoding, the conditioning of the reconstruction problem can be considerably improved, resulting in superior signal-to-noise behavior. As a consequence, 2D SENSE permits greater scan time reduction, which particularly benefits the inherently time-consuming 3D techniques. Along with the principles of 2D SENSE imaging, the properties of the technique are discussed and investigated by means of simulations. Special attention is given to the role of the coil configuration, yielding practical setups with four and six coils. The in vivo feasibility of the two-dimensional approach is demonstrated for 3D head imaging, permitting four-fold scan time reductio

Investigation of ventricular cerebrospinal fluid flow phase differences between the foramina of Monro and the aqueduct of Sylvius

In this paper, phase contrast magnetic resonance flow measurements of the foramina of Monro and the aqueduct of Sylvius of seven healthy volunteers are presented. Peak volume flow rates are of the order of 150 mm3/s for the aqueduct of Sylvius and for the foramina of Monro. The temporal shift between these volume flows is analyzed with a high-resolution cross-correlation scheme which reveals high subject-specific phase differences. Repeated measurements show the invariability of the phase differences over time for each volunteer. The phase differences as a fraction of one period range from -0.0537 to 0.0820. A mathematical model of the pressure dynamics is presented. The model features one lumped compartment per ventricle. The driving force of the cerebrospinal fluid is modeled through pulsating choroid plexus. The model includes variations of the distribution of the choroid plexus between the ventricles. The proposed model is able to reproduce the measured phase differences with a very small (5%) variation of the distribution of the choroid plexus between the ventricles and, therefore, supports the theory that the choroid plexus drives the cerebrospinal fluid motio

Adaptive metabolic changes in CADASIL white matter

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is an important genetic cause of stroke, but pathogenic mechanisms and functional alterations remain poorly characterized. The purpose of this study was to investigate adaptive metabolic and functional changes in white matter hyperintensities and normal-appearing white matter in CADASIL patients using 1H-magnetic resonance spectroscopic imaging (MRSI). Eight CADASIL patients and eight matched healthy controls were studied. 1H-MRSI data were acquired on a 3T scanner using high-resolution multi-spin echo spectroscopic imaging (T E=288ms) and non-accelerated medium-resolution MRSI (T E=35ms). MRI of all CADASIL patients demonstrated characteristic white matter hyper-intensities (WMH) in the subcortical periventricular white matter. Cre/Cho, Glx/Cho and Glx/Cre ratios were significantly decreased in WMH compared to normal-appearing white matter (NAWM) in patients, while Glx/Cre and mI/Cho ratios in NAWM showed a significant increase compared to healthy controls. In severely affected patients derived spectra reflected a decrease of NAA concentrations inside WMH when compared to healthy white matter. Metabolic abnormalities in WMH of CADASIL patients are compatible with axonal loss due to chronic micro-infarctions. Increased Glx/Cre and mI/Cho ratios in NAWM indicate an augmented glial cell density and decreased neuronal cell density. This altered tissue composition might be interpreted as adaptation to hypoperfusion and impaired vasoreactivity in NAWM of CADASIL patients. Our data might contribute to the general understanding of adaptive processes induced by hypoperfusion and chronic ischemi

MRI-based inverse finite element approach for the mechanical assessment of patellar articular cartilage from static compression test

The mechanical property of articular cartilage determines to a great extent the functionality of diarthrodial joints. Consequently, the early detection of mechanical and, thus, functional changes of cartilage is crucial for preventive measures to maintain the mobility and the quality of life of individuals. An alternative to conventional mechanical testing is the inverse finite element approach, enabling non-destructive testing of the tissue. We evaluated a method for the assessment of the equilibrium material properties of the patellar cartilage based on magnetic resonance imaging during patellofemoral compression. We performed ex vivo testing of two equine patellas with healthy cartilage, one with superficial defects, and one with synthetically degenerated cartilage to simulate a pre-osteoarthritic stage. Static compression with 400N for 2h resulted in morphological changes comparable to physiological in vivo deformations in humans. We observed a decrease of the equilibrium Young's modulus of the degenerated cartilage by -59%, which was in the range of the results from indentation (-74%) and confined compression tests (-58%). With the reported accuracy of magnetic resonance imaging and its reproducibility, the results indicate the potential to measure differences in Young's modulus with regard to cartilage degeneration and consequently to distinguish between healthy and pre-osteoarthritic cartilag

Impact of fMRI-guided advanced DTI fiber tracking techniques on their clinical applications in patients with brain tumors

Introduction: White matter tractography based on diffusion tensor imaging has become a well-accepted non-invasive tool for exploring the white matter architecture of the human brain in vivo. There exist two main key obstacles for reconstructing white matter fibers: firstly, the implementation and application of a suitable tracking algorithm, which is capable of reconstructing anatomically complex fascicular pathways correctly, as, e.g., areas of fiber crossing or branching; secondly, the definition of an appropriate tracking seed area for starting the reconstruction process. Large intersubject, anatomical variations make it difficult to define tracking seed areas based on reliable anatomical landmarks. An accurate definition of seed regions for the reconstruction of a specific neuronal pathway becomes even more challenging in patients suffering from space occupying pathological processes as, e.g., tumors due to the displacement of the tissue and the distortion of anatomical landmarks around the lesion. Methods: To resolve the first problem, an advanced tracking algorithm, called advanced fast marching, was applied in this study. The second challenge was overcome by combining functional magnetic resonance imaging (fMRI) and diffusion tensor imaging (DTI) in order to perform fMRI-guided accurate definition of appropriate seed areas for the DTI fiber tracking. In addition, the performance of the tasks was controlled by a MR-compatible power device. Results: Application of this combined approach to eight healthy volunteers and exemplary to three tumor patients showed that it is feasible to accurately reconstruct relevant fiber tracts belonging to a specific functional system. Conclusion: fMRI-guided advanced DTI fiber tracking has the potential to provide accurate anatomical and functional information for a more informed therapeutic decision makin

Myocardial tagging for the analysis left ventricular function

8. Conclusions: Based on our measurements following observations were made: (1) The left ventricle performs a systolic wringing motion which occurs mainly during isovolumic contraction. (2) Diastolic untwisting is found predominantly during isovolumic relaxation and occurs opposite to systolic rotation. (3) After myocardial infarction regional shortening is reduced in infarcted and remote regions. Predominantly diastolic untwisting is delayed and prolonged. (4) In patients with aortic stenosis apical rotation is enhanced, whereas diastolic untwisting is significantly inhibited, which explains the diastolic dysfunction in these patients. Myocardial tagging makes an accurate regional wall motion analysis and the assessment of cardiac rotation possible and, thus, allow new insight into the mechanical function of the hear