Improved efficiency in double‐inversion fast spin‐echo imaging

Abstract

Double-inversion fast spin-echo (FSE) pulse sequences can be designed to provide excellent suppression of blood signal in black-blood MRI. However, because a nonselective inversion is used, these sequences typically have been highly inefficient. In this work it is demonstrated that the efficiency of double-inversion sequences can be greatly improved by a form of interleaving in which all of the slices to be imaged in a single pass are reinverted each time a signal is obtained from any single slice. Visualization of disease in the cervical carotid bifurcation has been improved by optimized "black-blood" techniques which suppress the signal from flowing blood and enhance the intensity of tissue, vessel wall, and plaque components. The quality of black-blood techniques depends on the extent to which the signal from blood is suppressed and does not contribute confounding signal to the vessel wall images. Blood suppression in black-blood imaging was improved with the introduction of selective preinversion pulses (1-3). In selective preinversion, the spins outside of the imaged slice are inverted while the spins within the slice are unaffected. This selective inversion is usually accomplished by a nonselective inversion of the entire volume, followed by a selective inversion of the imaged slice. The time between inversion and image acquisition is selected based on the time required to null the signal from blood. All blood that flows into the imaged slice produces no MR signal, and the contrast between stationary tissue and flowing blood is very high. Although initially applied to fast gradient-echo sequences (such as turbo fast imaging with steady precession (turboFISP)), the technique has also been applied successfully to fast spin-echo (FSE) sequences (4).Although the double-inversion technique provides excellent suppression of blood signal, and excellent contrast between the vessel wall and the lumen, the requirement of a nonselective inversion results in the limitation that slices can only be acquired sequentially. An improvement in efficiency was demonstrated recently by Song et al. (5), in which two widely separated slices are reinverted and imaged at each repetition time (TR). Although this technique doubles the efficiency of double-inversion FSE acquisition, only one of the slices imaged will have the appropriate inversion time to null the signal from blood.In this work, we present a modification of the efficient carotid imaging technique of Song et al. (5). In our modification two or more slices are selectively reinverted with each inversion time, but data is acquired from only one slice. The acquired slice is alternated between the selected slices such that the TR of each slice is maximized. The technique is described and results are given below. METHODS SubjectsTwo subjects (48 and 80 years old) with minor carotid artery disease were imaged. Both have flow patterns which lead to consistent lesion-mimicking blood signal in normal double-inversion FSE imaging techniques. The technique was also tested on at le...

In vivo and ex vivo measurements of the mean ADC values of lipid necrotic core and hemorrhage obtained from diffusion weighted imaging in human atherosclerotic plaques

“…The pulse diagram of 2D-ss-IMIV DWEPI sequence is shown in Figure 1. T1w images were acquired with 2D TSE using a time-efficient double inversion preparation (23,24) with TR ¼ 850 ms, TI ¼ 500 ms, TE ¼ 9.5 ms, and ETL ¼11, spatial resolution of 0.5 Â 0.5 Â 2 mm 3 . T2w images were acquired at the same slice locations using 2D TSE with 0.5 Â 0.5 Â 2 mm 3 , TR ¼ 2.0 s, TE ¼ 65 ms and ETL ¼ 15.…”

MRI of atherosclerosis in clinical trials

“…To improve the time efficiency of DIR, several multislice acquisition techniques have recently been proposed (38)(39)(40)(41)(42)(43). These methods employ consecutive (41,42) or simultaneous (43) re-inversion of a group of slices.…”

“…These methods employ consecutive (41,42) or simultaneous (43) re-inversion of a group of slices. Several slices can be imaged within a single repetition time (TR), either by applying several readout sequences (each for a specific slice) in rapid succession (42) or by reducing the inversion time and acquiring the signal for each slice at the zero-crossing point in the established pulsed steady state (41,43).…”

“…Several slices can be imaged within a single repetition time (TR), either by applying several readout sequences (each for a specific slice) in rapid succession (42) or by reducing the inversion time and acquiring the signal for each slice at the zero-crossing point in the established pulsed steady state (41,43). Starting from initial double-slice techniques (41,42), multi-slice DIR sequences progressed to 8-16 slice variants while using a combination of the above acquisition strategies (38,40,43). At the same time, it is worth noting that the increased time efficiency of multislice DIR (i.e.…”

Comparison of 2D and multislab 3D magnetic resonance techniques for measuring carotid wall volumes

“…Reading out several slices simultaneously increases coverage and thus reduces scan time (20 -24). Inversion time (TI) can be a challenge as it varies for each slice (20), but this can be overcome with interleaving (21). By most methods the number of slices that can be simultaneously acquired is limited to four by specific absorption rate (SAR) limits (21), saturation effects, and blood flow artifact (22,23).…”