Carotid Intraplaque Hemorrhage Imaging with Quantitative Vessel Wall T1 Mapping: Technical Development and Initial Experience

Abstract

Purpose To develop a three-dimensional (3D) high-spatial-resolution time-efficient sequence for use in quantitative vessel wall T1 mapping. Materials and Methods A previously described sequence, simultaneous noncontrast angiography and intraplaque hemorrhage (SNAP) imaging, was extended by introducing 3D golden angle radial k-space sampling (GOAL-SNAP). Sliding window reconstruction was adopted to reconstruct images at different inversion delay times (different T1 contrasts) for voxelwise T1 fitting. Phantom studies were performed to test the accuracy of T1 mapping with GOAL-SNAP against a two-dimensional inversion recovery (IR) spin-echo (SE) sequence. In vivo studies were performed in six healthy volunteers (mean age, 27.8 years ± 3.0 [standard deviation]; age range, 24–32 years; five male) and five patients with atherosclerosis (mean age, 66.4 years ± 5.5; range, 60–73 years; five male) to compare T1 measurements between vessel wall sections (five per artery) with and without intraplaque hemorrhage (IPH). Statistical analyses included Pearson correlation coefficient, Bland-Altman analysis, and Wilcoxon rank-sum test with data permutation by subject. Results Phantom T1 measurements with GOAL-SNAP and IR SE sequences showed excellent correlation (R2 = 0.99), with a mean bias of −25.8 msec ± 43.6 and a mean percentage error of 4.3% ± 2.5. Minimum T1 was significantly different between sections with IPH and those without it (mean, 371 msec ± 93 vs 944 msec ± 120; P = .01). Estimated T1 of normal vessel wall and muscle were 1195 msec ± 136 and 1117 msec ± 153, respectively. Conclusion High-spatial-resolution (0.8 mm isotropic) time-efficient (5 minutes) vessel wall T1 mapping is achieved by using the GOAL-SNAP sequence. This sequence may yield more quantitative reproducible biomarkers with which to characterize IPH and monitor its progression.

Simultaneous T1 and T2 mapping of the carotid plaque (SIMPLE) with T2 and inversion recovery prepared 3D radial imaging

“…In vivo T2 mapping of plaque has been shown to be able to quantify lipid-rich core in carotid atherosclerosis (13,17). On the other hand, T1 mapping may be the preferred way to monitor the IPH progression (15,30,31), which is a key risk factor for clinical events. To fulfill these needs, this study proposed the SIMPLE sequence for simultaneous plaque T1 and T2 quantification in a single 3D large coverage scan with the advantage of relative short scan time and good accuracy.…”

“…Following T2IR preparation, 3D radial sampling is adopted for 3D isotropic acquisition. The 3D golden angle radial order proposed for the GOAL-SNAP sequence (15) is modified for SIMPLE to achieve an uniform distribution of spokes used for reconstruction at a certain TI and TE prep . Specifically, spokes acquired at the same TI in the shots with the same TE prep (S1, S1′, Fig1a), conform to the golden angle distribution, with the azimuthal angle and polar angle increments ( Δτ and Δυ ) defined by the 2D golden angle means ϕ 1 =0.4656, ϕ 2 =0.6823 (18): Δυ(normalS1,normalS1′)=anormalcos(ϕ1),0.5emΔτ(S1,S1′)=2π⋅ϕ2while for adjacent spokes in one shot (S1, S2, Fig.…”

“…For carotid wall depiction, similar to the GOAL-SNAP work (15), a black-blood image with near-zero luminal signal (Fig. 1b) was reconstructed using KWIC technique to achieve both high spatial resolution and high SNR (25).…”

“…By utilizing 3D black-blood preparation of variable preparation times, Yuan et al proposed a 3D T2 mapping sequence with larger coverage and thinner slices (16). By utilizing inversion recovery (IR) prepared 3D golden angle radial sampling, Qi et al developed a 3D T1 mapping technique (GOAL-SNAP) with large coverage and isotropic spatial resolution (15). Coolen et al were the first to develop a combined 3D vessel wall T1 and T2 mapping technique (14).…”

Free‐running 3D whole heart myocardial T1 mapping with isotropic spatial resolution

“…The contrast of a specific TI frame is given by the average of all the radial spokes binned into the corresponding frame. The signal of each radial spoke is calculated using Bloch equation, which has been previously described for 3D radial‐based carotid quantitative mapping and is also provided in the Supporting Information file. The singular values by SVD of the dictionary are shown in Figure A.…”