Local excitation black blood imaging at 3T: Application to the carotid artery wall

Abstract

A novel approach for imaging large sections of the carotid artery wall at isotropic spatial resolution is presented. Local excitation by means of 2D excitation pulses was combined with a diffusion-prepared segmented steady-state black-blood gradient echo technique enabling the assessment of the carotid arterial wall over a range of up to 15 cm. The carotid arteries of five healthy volunteers were imaged with the proposed technique. Signal-to-noise ratio (SNR), wall-lumen contrast-tonoise ratio (CNR), and vessel dimensions were assessed and compared to conventional excitation techniques. In all experiments black-blood contrast could be realized over the covered carotid arteries with similar SNR and CNR as the conventional technique covering the region of the bulbus only. The well-established understanding of atherosclerosis as an important risk factor for the development of acute ischemic events like ischemic stroke has stimulated increasing interest in noninvasive assessment of the structure, composition, and burden of plaque depositions in the carotid artery wall. Over the last decade MRI has proven to contribute substantially to the noninvasive assessment and characterization of atherosclerotic plaque, especially in the aorta and the carotid arteries (1-3).Most commonly, vessel wall imaging has been achieved by combining a double-inversion recovery black-blood preparation (4) with 2D data acquisition by means of multi spin-echo (MSE) techniques (1-3). Without compromising spatial resolution due to severe T 2 apodization, this technique allows for the acquisition of a single slice in the minute time range, while providing excellent lumen-wall contrast and enabling differently weighted images including T 2 (T 2 W), proton density (PDW) and, limited by the required inversion recovery time for blood signal nulling and heart rate, T 1 weighting (T 1 W). The extension of this technique to 3D coverage of large sections of the artery of interest has been limited by the resulting long acquisition times, often causing image-distorting motion artifacts (5) due to swallowing, arterial pulsation, breathing, and suboptimal blood suppression (6,7) due to incomplete exchange of the blood in the entire volume. Improvement of blood suppression has been obtained by utilizing phasesensitive reconstruction techniques (8) and diffusion-prepared techniques (9,10,12), all relying rather on the motion of the blood than on complete blood exchange between preparation and readout. Swallowing motion artifacts have been addressed by utilization of navigators monitoring the position of the epiglottis (10,13) and the application of segmented gradient echo techniques has enabled time-efficient 3D imaging of the carotid and aortic arteries (9 -11). 2D excitation pulses have been applied in various fields for restricting the field-of-view (FOV) to a confined region-of-interest (ROI) (14,15).In this contribution the application of local excitation by means of 2D excitation pulses using variable-density spiral trajectories (16,17) in combination ...

Imaging biomarkers of cardiovascular disease

“…MSDE has been combined with 3D acquisition techniques for effective blood suppression in a large volume (37-38) because of its low dependency on flow direction. It can also be utilized post-contrast due to its T 1 insensitivity.…”

Diffusion-weighted echo planar imaging in patients with recent myocardial infarction

“…In addition, parts of the heart distant from the surface coils, such as the inferior and lateral walls, can induce myocardial signal loss and lead to false-negative diagnosis [11]. Some authors have reported that weak diffusion-sensitizing gradients can efficiently nullify the blood pool signal by dephasing all moving spins prior to the imaging sequence [13][14][15]. Recently, Nguyen et al reported that diffusion-weighted (DW) black blood imaging of the heart is feasible in healthy subjects, with reference to IR FSE T2-weighted sequences [16].…”

Imaging Cardiovascular Calcification

“…Moreover, the carotid arteries can be imaged using phased‐array coils and well‐tested multicontrast imaging protocols such as bright‐ and black‐blood techniques 82. All of these make the carotid artery the most commonly assessed vessel in MRI studies of atherosclerosis 23, 83, 84, 85…”