Romhild M. Hoogeveen

Model-based quantitation of 3-D magnetic resonance angiographic images

Quantification of the degree of stenosis or vessel dimensions are important for diagnosis of vascular diseases and planning vascular interventions. Although diagnosis from three-dimensional (3-D) magnetic resonance angiograms (MRAs) is mainly performed on two-dimensional (2-D) maximum intensity projections, automated quantification of vascular segments directly from the 3-D dataset is desirable to provide accurate and objective measurements of the 3-D anatomy. A model-based method for quantitative 3-D MRA is proposed. Linear vessel segments are modeled with a central vessel axis curve coupled to a vessel wall surface. A novel image feature to guide the deformation of the central vessel axis is introduced. Subsequently, concepts of deformable models are combined with knowledge of the physics of the acquisition technique to accurately segment the vessel wall and compute the vessel diameter and other geometrical properties. The method is illustrated and validated on a carotid bifurcation phantom, with ground truth and medical experts as comparisons. Also, results on 3-D time-of-flight (TOF) MRA images of the carotids are shown. The approach is a promising technique to assess several geometrical vascular parameters directly on the source 3-D images, providing an objective mechanism for stenosis grading.

Implications of SENSE MR in routine clinical practice

Sensitivity encoding (SENSE) uses multiple MRI receive coil elements to encode spatial information in addition to traditional gradient encoding. Requiring less gradient encodings translates into shorter scan times, which is extremely beneficial in many clinical applications. SENSE is available to routine diagnostic imaging for the past 2 years. This paper highlights the use of SENSE with scan time reduction factors up to 6 in contrast-enhanced MRA, routine abdominal imaging, mammography, cardiac and neuro imaging. It is shown that SENSE has opened new horizons in both routine and advanced MR imaging.

Utilizing SENSE to achieve lower station sub-millimeter isotropic resolution and minimal venous enhancement in peripheral MR angiography†

To use the parallel imaging technique, sensitivity encoding (SENSE), to increase spatial resolution and decrease venous contamination in peripheral magnetic resonance angiography (MRA).

Flow Volume and Shunt Quantification in Pediatric Congenital Heart Disease by Real-Time Magnetic Resonance Velocity Mapping A Validation Study

Background—Flow quantification in real time by phase-contrast MRI (PC-MRI) may provide unique hemodynamic information in congenital heart disease, but available techniques have important limitations. We sought to validate a novel real-time magnetic resonance flow sequence in children. Methods and Results—In 14 pediatric patients (mean age 5.2±2.0 years) with cardiac left-to-right shunt, pulmonary (Qp) and aortic (Qs) flow rates were determined by nontriggered free-breathing real-time PC-MRI with single-shot echo-planar imaging combined with sensitivity encoding, which yielded 25 phase images per second at 2.7×2.7-mm in-plane resolution (field of view 30×34 cm2). Over a 9.5-second period that included 2 to 5 respiratory cycles, 16.6±2.6 subsequent stroke volumes (range 13 to 22) were acquired in each vessel. Results were compared with conventional retrospectively ECG-gated PC-MRI. Mean Qp/Qs by conventional PC-MRI was 1.91±0.64, and it was 1.94±0.68 (mean±SD) by real-time PC-MRI. For blood flow rate through pulmonary artery and aorta, we found differences of 2% to 3% (Bland-Altman analysis), with lower limits of agreement of −11% to −13% (mean−2 SD) and upper limits of 18% to 19% (mean±2 SD), which demonstrated good agreement between both methods. Mean difference for Qp/Qs was 1%, with limits of agreement ranging between −18% and 22% (mean±2 SD). High repeatability but some flow overestimation was observed in vitro (pulsatile flow phantom) with real-time PC-MRI, whereas conventional PC-MRI was accurate. Beat-to-beat stroke-volume variation was 6.1±2.3% in vivo and 3.7±0.3% in vitro. Conclusions—Beat-to-beat quantification of pulmonary and aortic flows and hence left-to-right shunt within a few seconds is reliable by nontriggered real-time PC-MRI with echo-planar imaging and sensitivity encoding. Good spatial/temporal resolution and a large field of view may render the sequence valuable for multiple applications in congenital heart disease.

4D time-resolved MR angiography with keyhole (4D-TRAK): More than 60 times accelerated MRA using a combination of CENTRA, keyhole, and SENSE at 3.0T†

To present a new 4D method that is designed to provide high spatial resolution MR angiograms at subsecond temporal resolution by combining different techniques of view sharing with parallel imaging at 3.0T.

Steady-state free precession MRA of the renal arteries: breath-hold and navigator-gated techniques vs. CE-MRA.

To explore the use of breath‐hold and navigator‐gated noncontrast Steady State Free Precession (SSFP) MR angiography (MRA) protocols for the evaluation of renal artery stenosis (RAS).

Construction of a protocol for measuring blood flow by two-dimensional phase-contrast MRA.

Our aim is to describe and demonstrate the steps we have found to be useful in the construction and evaluation of protocols for triggered and nontriggered measurement of blood flow by two‐dimensional phase‐contrast magnetic resonance angiography (MRA). To achieve this goal, we start with a survey of factors governing the accuracy (validity) and precision (repeatability) of MR flow measurements. This knowledge, combined with prior information regarding the diameter of the target vessel and the prevailing flow conditions, is then employed to define a protocol for measuring flow with negligible systematic error. In the absence of a gold standard for in vivo flow measurements, the protocol is subsequently validated for a range of flow conditions by representative phantom experiments. Precision is then calculated from the signal‐to‐noise ratio (SNR) of blood in the accompanying magnitude images or, less conveniently, estimated from the standard deviation of repeated measurements. The desired precision is finally achieved by adjusting the appropriate SNR parameters. All steps involved in protocol development are demonstrated for both flow‐independent and flow‐dependent acquisitions. J. Magn. Reson. Imaging 1999;9:119–127

Parallel imaging in MR angiography.

The recently developed techniques of parallel imaging with phased array coils are rapidly becoming accepted for magnetic resonance angiography (MRA) applications. This article reviews the various current parallel imaging techniques and their application to MRA. The increased scan efficiency provided by parallel imaging allows increased temporal or spatial resolution, and reduction of artifacts in contrast-enhanced MRA (CE-MRA). Increased temporal resolution in CE-MRA can be used to reduce the need for bolus timing and to provide hemodynamic information helpful for diagnosis. In addition, increased spatial resolution (or volume coverage) can be acquired in a breathhold (eg, in renal CE-MRA), or in otherwise limited clinically acceptable scan durations. The increased scan efficiency provided by parallel imaging has been successfully applied to CE-MRA as well as other MRA techniques such as inflow and phase contrast imaging. The large signal-to-noise ratio available in many MRA techniques lends these acquisitions to increased scan efficiency through parallel imaging.

Contrast‐enhanced peripheral MR angiography using SENSE in multiple stations: Feasibility study

To investigate if the use of parallel imaging is feasible and beneficial for peripheral contrast‐enhanced magnetic resonance angiography (CE‐MRA).

Contrast‐enhanced peripheral MR angiography at 3.0 Tesla: Initial experience with a whole‐body scanner in healthy volunteers

To report preliminary experience with contrast‐enhanced magnetic resonance angiography (CE‐MRA) of the peripheral arteries on a 3.0 T whole‐body scanner equipped with a prototype body coil.