Pressure Mapping and Hemodynamic Assessment of Intracranial Dural Sinuses and Dural Arteriovenous Fistulas with 4D Flow MRI.

The feasibility of 4D flow MR imaging to visualize flow patterns and generate relative pressure maps in the dural venous sinus in healthy subjects (n = 60) and patients with dural arteriovenous fistulas (n = 7) was investigated. Dural venous drainage was classified based on torcular Herophili anatomy by using 4D flow MR imaging-derived angiograms and magnitude images. Subjects were scanned in a 3T clinical MR imaging system. 4D flow MR imaging enabled noninvasive characterization of dural sinus anatomy and mapping of relative pressure differences.

MO-D-213CD-02: Non-Contrast-Enhanced Magnetic Resonance Angiography Methods for Assessment of Morphology and Flow.

Traditional clinical MR Angiography (MRA) provides volumetric datasets to characterize the vessel lumen. These MRA techniques can be generally separated into two categories: • contrast-enhanced MRA, which requires the venous injection of a paramagnetic contrast agent in form of a Gadolinium chelate and • non-contrast-enhanced MRA (NCE MRA), which relies on signal properties of the blood or the motion of the blood to create signal differences between the blood pool and the surrounding tissues. Time-of-Flight (TOF) and Phase- Contrast (PC) imaging have been developed as NCE techniques in the early days of MR imaging. However, widespread clinical adaptation of MRA did not occur until the introduction of CE-MRA in the mid-1990ies with significantly improved robustness. Recent developments have renewed the interest in imaging approaches that do not rely on any external contrast agents. Advances in hardware, especially gradient amplifiers and multi-channel coil technology, have reduced imaging times, improved the signal-to-noise ratio, and reduced artefacts so that NCE MRA is becoming competitive again. These approaches provide viable alternatives in patients that are at risk for nephrogenic systemic fibrosis (NSF) and should not receive a Gd-based contrast agent. In addition, some of those approaches provide insights in functional information beyond the standard luminography. For example, arterial spin labeling (ASL) imaging can be used as a 'pseudo arterial injection' by labeling blood in targeted volumes and tracking its distribution over time. Novel '4D MR Flow' imaging is an extension of traditional PC MRA to capture volumetric velocity vector fields throughout the cardiac cycle, thereby allowing for direct measures of hemdodynamic parameters such as pressure gradient, wall shear stress, pulse wave velocity, kinetic energy, and more. This lecture will provide an overview of the underlying contrast mechanisms of time-of-flight, phase-contrast, balanced steady state free precession (bSSFP), and ASL MRA. Current and potential future roles of these approaches in clinical imaging will also be discussed. LEARNING OBJECTIVES: 1. Understand the various origins of MRA contrast mechanisms that do not require a contrast agent. 2. Understand the issues related to NCE-MRA imaging including design, acquisition and processing. 3. Understand the benefits, pitfalls, and future potentials of these approaches. My research is sponsored by GE Healthcare.

Integrated head-thoracic vascular MRI at 3 T: assessment of cranial, cervical and thoracic involvement of giant cell arteritis.

Recently, high-resolution contrast-enhanced MRI has proven to be feasible for noninvasive diagnosis of giant cell arteritis in the cranium. In such examinations, thickening of the vessel wall and/or increased contrast enhancement demonstrate mural inflammation. Typically, the superficial cranial arteries with predominance of the superficial temporal artery are affected by the disease. However, giant cell arteritis can also involve other parts of the vascular system and an examination with extended coverage, including head, neck, and thorax would be advantageous. In this study, a novel approach for integrated head-thoracic vascular MRI at 3 T is presented. Combining first-pass imaging of a single-dose contrast agent with post-contrast imaging permits the assessment of both thoracic aortic geometry and wall, in addition to high-resolution head imaging needed for the analysis of the small superficial cranial arteries. Results from a patient feasibility study are presented and confirm that the protocol can successfully be completed in less than 40 min.

Classification of premature ventricular complexes using filter bank features, induction of decision trees and a fuzzy rule-based system.

The classification of heart beats is important for automated arrhythmia monitoring devices. The study describes two different classifiers for the identification of premature ventricular complexes (PVCs) in surface ECGs. A decision-tree algorithm based on inductive learning from a training set and a fuzzy rule-based classifier are explained in detail. Traditional features for the classification task are extracted by analysing the heart rate and morphology of the heart beats from a single lead. In addition, a novel set of features based on the use of a filter bank is presented. Filter banks allow for time-frequency-dependent signal processing with low computational effort. The performance of the classifiers is evaluated on the MIT-BIH database following the AAMI recommendations. The decision-tree algorithm has a gross sensitivity of 85.3% and a positive predictivity of 85.2%, whereas the gross sensitivity of the fuzzy rule-based system is 81.3%, and the positive predictivity is 80.6%.