Eric M Schrauben

Four‐dimensional phase contrast MRI With accelerated dual velocity encoding

To validate a novel approach for accelerated four‐dimensional phase contrast MR imaging (4D PC‐MRI) with an extended range of velocity sensitivity.

Quantitative cerebrovascular 4D flow MRI at rest and during hypercapnia challenge.

UNLABELLED Non-invasive measurement of cerebral blood flow (CBF) in humans is fraught with technologic, anatomic, and accessibility issues, which has hindered multi-vessel hemodynamic analysis of the cranial vasculature. Recent developments in cardiovascular MRI have allowed for the measurement of cine velocity vector fields over large imaging volumes in a single acquisition with 4D flow MRI. The purpose of this study was to develop an imaging protocol to simultaneously measure pulsatile flow in the circle of Willis as well as the carotid and vertebrate arteries at rest and during increased CO2 (hypercapnia). METHODS 8 healthy adults (3 women, 26±0.4years) completed this study. Heart rate (pulse oximetry), arterial oxygen saturation (pulse oximetry), blood pressure (MAP, sphygmomanometry), and end-tidal CO2 (capnograph) were measured at rest (baseline) and during hypercapnia. Hypercapnia was induced via breathing a mixed gas of 3% CO2 and 21% O2 (balance N2) in the MR magnet. CBF and vessel cross-sectional area were quantified in 11 arteries using a 4D flow MRI scan, lasting 5-6min with a radially undersampled acquisition and an isotropic spatial resolution of 0.7mm. RESULTS Baseline total CBF was 665±54ml • min(-1). Hypercapnia increased total CBF 9±3% to 721±61ml • min(-1). Hypercapnic increases in CBF ranged from 7 to 36% by artery, with the largest increases in the left anterior cerebral artery. Increases in artery cross-sectional area were observed in basilar and vertebral arteries. CONCLUSION 4D flow MRI methods are sensitive enough to detect non-uniform changes in CBF and cross-sectional area to a mild yet clinically relevant CO2 stimulus. 4D flow MRI is a non-invasive reliable tool providing high spatio-temporal resolution in clinically feasible scan times without contrast agent. This approach can be used to interrogate regional cerebrovascular control in health and disease.

Phase unwrapping in 4D MR flow with a 4D single-step laplacian algorithm

To introduce and demonstrate a method for unwrapping 4D flow data by utilizing continuity constraints in all four available dimensions.

Fast 4D flow MRI intracranial segmentation and quantification in tortuous arteries

To describe, validate, and implement a centerline processing scheme (CPS) for semiautomated segmentation and quantification in carotid siphons of healthy subjects. 4D flow MRI enables blood flow measurement in all major cerebral arteries with one scan. Clinical translational hurdles are time demanding postprocessing and user‐dependence induced variability during analysis.

Respiratory‐induced venous blood flow effects using flexible retrospective double‐gating

To demonstrate a novel velocity sensitive acquisition and retrospective cardiorespiratory double‐gated reconstruction scheme to examine respiratory effect on venous blood flow in healthy volunteers.

Four-dimensional flow magnetic resonance imaging and ultrasound assessment of cerebrospinal venous flow in multiple sclerosis patients and controls.

A possibly causal relationship between multiple sclerosis and chronic cerebrospinal venous insufficiency has recently been hypothesized. Studies investigating chronic cerebrospinal venous insufficiency have reported conflicting results and few have employed multiple diagnostic imaging modalities across a large patient and control population. In this study, three complementary imaging modalities were used to investigate the chronic cerebrospinal venous insufficiency hypothesis in patients with multiple sclerosis and two age- and sex-matched control groups: healthy volunteers and patients with other neurological diseases. Strictly blinded Doppler ultrasound according to the original chronic cerebrospinal venous insufficiency hypothesis; four-dimensional flow magnetic resonance imaging of venous flow in the head, neck, and chest; and contrast-enhanced magnetic resonance venography for neck and chest venous luminography were acquired. An internal jugular vein stenosis evaluation was also performed across modalities. Percentage of subjects meeting ultrasound-based chronic cerebrospinal venous insufficiency criteria was small and similar between groups. In group-wise and pairwise testing, no four-dimensional flow magnetic resonance imaging variables were statistically significantly different, for any measurement location. In contrast-enhanced magnetic resonance venography of the internal jugular and azygos veins, no statistically significant differences were observed in stenosis scores between groups. These results represent compelling evidence against the chronic cerebrospinal venous insufficiency hypothesis in multiple sclerosis.

Respiratory effects on phase contrast imaging of the jugular vein.

An analysis of the effect of respiratory function on MR flow measures of the internal jugular vein (IJV) is presented. A novel 2D radial acquisition and reconstruction method allows for retrospective gating to both the cardiac and respiratory cycle. In-vivo scans of human volunteers verify the efficacy of the algorithm, showing increased IJV flow during inspiration and decreased flow during expiration for each cardiac time frame.

3D respiratory resolved phase contrast imaging of the aorta

Background Respiratory motion compensation is essential for reproducible and robust cardiovascular MRI. Traditionally, breathholds or prospective gating by bellows or navigator signals limit data acquisition to the quiescent phase of respiration [1]. These approaches do not capture any variations of blood flow over the respiratory cycle, yet respiration has been shown to significantly affect flow in the great vessels [2]. The purpose of this pilot study was to adapt a 3D radially undersampled PC MR sequence (PC VIPR [3,4]) for use with our retrospective dual-gated (cardiac and respiratory) reconstruction to evaluate respiratory effects on net flow and cardiac flow waveforms.

Left ventricular function and regional strain with subtly‐tagged steady‐state free precession feature tracking

To provide regional strain and ventricular volume from a single acquisition, using subtly tagged steady‐state free precession (SubTag SSFP) feature tracking.

Improvement in pulmonary hypertension discrimination using multiple MRA pant-leg parameters of pulmonary artery

Background Pulmonary arterial hypertension (PAH) is a potentially severe disease that can lead to exercise intolerance, venous congestion, and heart failure. As a result of increased pulmonary pressures, dilation of the pulmonary arterial vasculature occurs. The extraction of these anatomical changes from magnetic resonance angiogram (MRA) may eliminate the need for invasive measurements. The aim of this study was to explore the use of volumetric imaging of the pulmonary trunk and proximal right and left arteries using MRA as an ew metric for diagnosing PAH. Methods Following IRB approval, eight PAH patients referred for right heart catheterization (RHC) for systemic sclerosis were evaluated with 3D contrast-enhanced MRA. For comparison, eight healthy volunteers underwent the same MRA protocol. All MRA exams were performed on 3.0T clinical scanners (GE Healthcare, Waukesha, WI) following the administration of gadolinium-based contrast agent at 1.5 ml/sec (gadobenate dimeglumine, Bracco, Milan). Scan parameters of the SPGR sequence included TR/TE of 2.9/1.0 ms, average field of view = 34 × 27 cm, slice thickness = 2.0 mm, 140-160 slices, flip angle = 28°, and true spatial resolution of 1.3 × 1.8 × 2.0 mm 3 , which was interpolated to 0.7 × 0.7 × 1.0 mm 3 by zero-filling. Approximate breath-hold time was between 15-21 seconds for each scan. These exams were not cardiac gated. Post-processing was evaluated using dynamic magnitude images in a commercial software (Mimics, Materialise, Belgium) to calculate diameter (main, left, and right pulmonary artery: MPA, LPA, RPA), volume, surface area, branch sum, and area sum pant-leg (P-L) measurements (Figure 1a). Each P-L was obtained by centerline semi-automated measurements two centimeters in each direction of bifurcation (Figure 1b). These parameters were evaluated as mean ± standard deviation. Differences in these measurements were statistically analyzed using a paired Student’s t-test. Results