Improved blood suppression in three-dimensional (3D) fast spin-echo (FSE) vessel wall imaging using a combination of double inversion-recovery (DIR) and diffusion sensitizing gradient (DSG) preparations

Abstract

Purpose: To provide improved blood suppression in three-dimensional inner-volume fast spin-echo (3D IV-FSE) carotid vessel wall imaging by using a hybrid preparation consisting of double inversion-recovery (DIR) and diffusion sensitizing gradients (DSG).

Materials and methods: Multicontrast black-blood MRI is widely used for vessel wall imaging and characterization of atherosclerotic plaque composition. Blood suppression is difficult when using 3D volumetric imaging techniques. DIR approaches do not provide robust blood suppression due to incomplete replacement of blood spins, and DSG approaches compromise vessel wall signal, reducing the lumen-wall contrast-to-noise ratio efficiency (CNR(eff)). In this work a hybrid DIR+DSG preparation is developed and optimized for blood suppression, vessel wall signal preservation, and vessel-wall contrast in 3D IV-FSE imaging. Cardiac gated T(1)-weighted carotid vessel wall images were acquired in five volunteers with 0.5 x 0.5 x 2.5 mm(3) spatial resolution in 80 seconds.

Results: Data from healthy volunteers indicate that the proposed method yields a statistically significant (P < 0.01) improvement in blood suppression and lumen-wall CNR(eff) compared to standard DIR and standard DSG methods alone.

Conclusion: A combination of DIR and DSG preparations can provide improved blood suppression and lumen-wall CNR(eff) for 3D IV-FSE vessel wall imaging.

Figure 1

Timing of the proposed pulse sequence. Imaging is performed using a 3D fat-saturated inner-volume fast spin-echo (IV-FSE) pulse sequence. Blood suppression is achieved by a combination of double inversion recovery (DIR) and diffusion sensitizing gradient (DSG) preparations. FATSAT = fat saturation.

Figure 2

Scatter plots of the velocity (cm/second) of unsuppressed luminal blood. Each color represents one volunteer. a: Projection onto the YZ plane, with $\left({\overline{V}}_y,{\overline{V}}_z\right).=\left(-0.8,-1.4\right)$ and $\left({\sigma }_{V_y},{\sigma }_{V_z}\right)=\left(2.96,1.41\right)$. b: Projection onto the XZ plane, with $\left({\overline{V}}_x,{\overline{V}}_z\right).=\left(-2.7,-1.4\right)$ and $\left({\sigma }_{V_x},{\sigma }_{V_z}\right)=\left(1.51,1.41\right)$. c: Projection onto the XY plane, $\left({\overline{V}}_x,{\overline{V}}_y\right).=\left(\left[-2.3,-2.2\right],\left[-3.9,3.6\right]\right)$ and $\left({\sigma }_{V_x},{\sigma }_{V_y}\right)=\left(1.04,1.64\right),\left(2.09,1.34\right)$. Maximum likelihood was used to estimate the mean and standard deviation of one or two component Gaussian mixture distributions for each plot (gray ellipses). Note that ${\sigma }_{V_y}>{\sigma }_{V_z}$ but ${\sigma }_{V_x}\sim {\sigma }_{V_z}$, hence stronger dephasing is required along the imaging slab (XY or L/R-A/P) rather than perpendicular to the imaging slab (Z or S/I).

Figure 3

Blood and vessel wall SNR from a single volunteer, when using 3D IV-FSE DIR+DSG imaging with a range of b-values. Blood signal (solid) decreases with higher b-value. Vessel wall signal (dashed) decreases significantly for b-value > 1 second/mm². This is due to increased DSG duration and therefore significant T₂-weighting. A b-value of 0.1 second/mm² was used in subsequent studies (black arrow).

Figure 4

T₁-weighted images from a healthy volunteer at the bifurcation of carotid artery using the proposed 3D IV-FSE DIR+DSG, 3D IV-FSE DIR, and 2D multislice FSE DIR acquisitions. a: Full FOV single slice just above the bifurcation. The DIR only methods suffer from artifacts due to incomplete blood suppression at the bifurcation (arrow). b: Zoomed in view from all the slices around the right carotid artery, highlighted box indicates the slices with significant residual blood signal when using DIR alone. The arrow clearly indicates the presence of significant residual luminal blood signal when using 3D IV-FSE DIR.

Figure 5

T₁-weighted images from five volunteers at the bifurcation of the left carotid artery using the proposed 3D IV-FSE DIR+DSG, 3D IV-FSE DIR, and 2D multislice FSE DIR acquisitions. The highlighted box indicates studies with significant residual blood signal when using DIR alone. The arrows clearly indicate the presence of significant residual luminal blood signal when using 3D IV-FSE DIR.

Figure 6

Scatter plots showing in vivo measurements of the wall and lumen SNR, and wall to lumen CNR efficiency on a per subject basis. Each color represents one volunteer. a: Measurements from carotid segments only corresponding to the central slices at the bifurcation are plotted. b: Measurements from all carotid segments across all the acquired slices are averaged per subject and then plotted. The proposed method provides improved blood suppression and wall to lumen CNR_eff, for all subjects when compared to the 3D DIR IV-FSE.