The K-Space segmentation tool set

In this paper we describe two applications, created as part of the K-Space Network of Excellence, designed to allow researchers to use and experiment with state-of-the-art methods for spatial segmentation of images and video sequences. The first of these tools is an _Interactive Segmentation Tool_, developed to allow accurate human-guided segmentation of semantic objects from images using different segmentation algorithms. The tool is particularly useful for generating ground-truth segmentations, extracting objects for further processing, and as a general image processing application.The second tool we developed is designed for fully automatic spatial region segmentation of image and video. The tool is web-based; usage only requires a browser. Both the automatic and interactive segmentation tools have been made available online; we anticipate they will be a valuable resource for other researchers

MRI Techniques for Cardiovascular Imaging

Over the last several years, cardiovascular MRI has benefited from a number of technical advances which have improved routine clinical imaging techniques. As a result, MRI is now well positioned to realize its longstanding promise of becoming the comprehensive cardiac imaging test of choice in many clinical settings. This may be achieved using a combination of basic advanced techniques. In this overview, the basic cardiac MRI techniques which are clinically useful are reviewed, and the recent technical advances which are clinically promising are described. These advances include routine black blood and cine bright blood techniques that are high speed (slice), multislice whole heart perfusion imaging methods, and recently emerging real-time imaging methodologies. J Magn. Reson. Imaging 1999;10:590–601. © 1999 Wiley-Liss, Inc

Reliable In-Plane Velocity Measurements With Magnetic Resonance Velocity Imaging

Magnetic resonance (MR) imaging is a well-known diagnostic imaging modality. In addition to its high-quality imaging capabilities, hydrogen-based MR can also provide non-invasively the velocity of water-based fluids in all three spatial directions (through-plane and in-plane) in an image. Many previous studies showed that MR velocity imaging can accurately measure the through-plane velocity. The aim of this study was to evaluate how reliable are the in-plane velocity measurements in an image. The axial velocity of water in horizontal tubes (inner diameter: 14.7–26.2 mm) was measured with segmented (fast) and non-segmented (slow) k-space MR velocity imaging using: (a) an imaging slice placed perpendicular to the tube axis with through-plane velocity-encoding; and (b) an imaging slice placed parallel to the tube axis with in-plane velocity-encoding. The two planes intersected along the vertical tube-centerline. The flow rate was accurately quantified (mean error plane velocity profiles were not significantly different from the through-plane profiles (mean difference =6%, correlation coefficients \u3e0.98). There was no significant difference between the velocity profiles from the segmented and the non-segmented sequences (mean difference 0.95). The results of this study suggest that fast MR velocity imaging can measure the in-plane velocity in an image with reliability

Sub Millimeter Analysis of Specificity of SE, GE, and ASE BOLD Responses in the Human Visual Cortex

Sub-millimeter spatial resolution applications are becoming of increasing interest in fMRI. Several animal and human studies have successfully mapped high resolution functional organizations. However, it is not known which fMRI technique (which depends on field strength), maximizes contrast to noise as well as specificity to capillaries for sub-millimeter functional mapping. In this work we examine this problem by comparing functional maps, at 0.5mm in plane resolution, of gradient echo BOLD, spin echo BOLD, and asymmetric echo BOLD in human visual cortex at 7 Tesla

Fast Measurements of Flow Through Mitral Regurgitant Orifices With Magnetic Resonance Phase Velocity Mapping

Magnetic-resonance (MR) phase velocity mapping (PVM) shows promise in measuring the mitral regurgitant volume. However, in its conventional nonsegmented form, MR-PVM is slow and impractical for clinical use. The aim of this study was to evaluate the accuracy of rapid, segmented k-spaceMR-PVM in quantifying the mitral regurgitant flow through a control volume (CV) method. Two segmented MR-PVM schemes, one with seven (seg-7) and one with nine (seg-9) lines per segment, were evaluated in acrylic regurgitant mitral valve models under steady and pulsatile flow. A nonsegmented (nonseg) MR-PVM acquisition was also performed for reference. The segmented acquisitions were considerably faster (min) than the nonsegmented (\u3e45 min). The regurgitant flow rates and volumes measured with segmented MR-PVM agreed closely with those measured with nonsegmented MR-PVM (differences 0.05), when the CV was large enough to exclude the region of flow acceleration and aliasing from its boundaries. The regurgitant orifice shape (circular vs. slit-like) and the presence of aortic outflow did not significantly affect the accuracy of the results under both steady and pulsatile flow (p\u3e0.05). This study shows that segmented k-space MR-PVM canaccurately quantify the flow through regurgitant orifices using the CV method and demonstrates great clinical potential

Improved Techniques for Acquisition and Analysis of Dynamic Contrast-Enhanced Magnetic Resonance Imaging for Detecting Vascular Permeability in the Central Nervous System

Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) is a noninvasive technique for quantitative assessment of the integrity of blood-brain barrier and blood-spinal cord barrier (BSCB) in the presence of central nervous system pathologies. However, the results of DCE-MRI show substantial variability. The high variability can be caused by a number of factors including inaccurate T1 estimation, insufficient temporal resolution and poor contrast-to-noise ratio. My thesis work is to develop improved methods to reduce the variability of DCE-MRI results. To obtain fast and accurate T1 map, the Look-Locker acquisition technique was implemented with a novel and truly centric k-space segmentation scheme. In addition, an original multi-step curve fitting procedure was developed to increase the accuracy of T1 estimation. A view sharing acquisition method was implemented to increase temporal resolution, and a novel normalization method was introduced to reduce image artifacts. Finally, a new clustering algorithm was developed to reduce apparent noise in the DCE-MRI data. The performance of these proposed methods was verified by simulations and phantom studies. As part of this work, the proposed techniques were applied to an in vivo DCE-MRI study of experimental spinal cord injury (SCI). These methods have shown robust results and allow quantitative assessment of regions with very low vascular permeability. In conclusion, applications of the improved DCE-MRI acquisition and analysis methods developed in this thesis work can improve the accuracy of the DCE-MRI results

MRI of the lung (1/3):methods

Proton magnetic resonance imaging (MRI) has recently emerged as a clinical tool to image the lungs. This paper outlines the current technical aspects of MRI pulse sequences, radiofrequency (RF) coils and MRI system requirements needed for imaging the pulmonary parenchyma and vasculature. Lung MRI techniques are presented as a “technical toolkit”, from which MR protocols will be composed in the subsequent papers for comprehensive imaging of lung disease and function (parts 2 and 3). This paper is pitched at MR scientists, technicians and radiologists who are interested in understanding and establishing lung MRI methods. Images from a 1.5 T scanner are used for illustration of the sequences and methods that are highlighted. Main Messages • Outline of the hardware and pulse sequence requirements for proton lung MRI • Overview of pulse sequences for lung parenchyma, vascular and functional imaging with protons • Demonstration of the pulse-sequence building blocks for clinical lung MRI protocol