Multi-contrast Acquisition in a Single Scan (MASS) for Three-dimensional Quantitative T1 Mapping of Carotid Atherosclerosis
Haikun Qi1, Huiyu Qiao1, Shuo Chen1, Zechen Zhou2, Xinlei Pan1, Yishi Wang1, Chun Yuan1,3, and Huijun Chen1

1Center for Biomedical Imaging Research, School of Medicine, Tsinghua University, Beijing, People's Republic of China, 2Philips Research China, Shanghai, People's Republic of China, 3Department of Radiology, University of Washington School of Medicine, Seattle, WA, United States


Intra-plaque hemorrhage (IPH) is a dynamic process and change of the IPH MR signal was found to be correlated with plaque developments. So quantitative T1 mapping of plaque is essential to monitor plaque progression. In this study, we proposed an IR prepared 3D golden angle radial sampling sequence, enabling multiple T1 contrasts acquisition in a single scan (MASS) with application to carotid artery T1 mapping. The accuracy and feasibility of MASS was demonstrated in phantom studies and in vivo imaging experiments on healthy volunteers and carotid atherosclerosis patients. MASS may be a one-stop solution to carotid atherosclerotic plaque imaging.


Carotid atherosclerosis has become the major cause of ischemic cerebrovascular event (1). Intra-plaque hemorrhage (IPH) is considered a characterization of vulnerable plaque, and can be detected by T1 weighted (T1W) MR sequences, such as MPRAGE (2), or SNAP (3). Recently, studies found that the T1 signal of IPH is changing across time (4), indicating IPH is a dynamic process. Moreover, the signal change of IPH on T1W MR images was found to be associated with plaque developments (5). Therefore, quantitative T1 mapping of plaque is important to better assess atherosclerotic plaque. In this study, we have developed a sequence enabling Multiple T1 contrasts Acquisition in a Single Scan (MASS) for 3D T1 mapping of carotid vessel wall.


Sequence Design: The proposed sequence consists of an IR preparation pulse and a 3D radial sampling acquisition (Fig. 1). Spokes of the same Inversion Time (TI) in different IRTRs conform to the golden angle distribution (6), to achieve a uniformly distributed k-space at certain TI for reconstruction. Water excitation pulse was used to suppress fat signal. MR Imaging: All scans were performed on a 3T Philips Scanner. For phantom studies, 9 tubes containing diluted Gd-DTPA with different concentrations were designed. T1 mapping of phantoms were performed using both MASS and a standard 2D IR-SE sequence (7). For in vivo experiments, after institutional review board approval, 6 healthy volunteers and 5 patients with carotid atherosclerotic plaques were imaged using a custom-designed 36-channel neurovascular coil (8). The scan included the T1W QIR-TSE black-blood sequence (9), SNAP (3), and a 5 min MASS scan with imaging parameters shown in Table 1. Image Reconstruction: Sliding window and narrow-KWIC filter with CG-SENSE (10) were used together to generate image series along the inversion recovery curve. For coil sensitivities estimation, MASS image at TI=1300ms was reconstructed with temporal window width (TW)=35 and KWIC filter (11). Because image contrast is dominated by the central parts of k-space, the reconstructed image intensity is determined by averaging the signal at spoke number of n to n+TW-1, where n is the start spoke index, ranging from 1 to N-TW+1 with an interval of TW, and N is the TFE factor. By setting TW=19, 8 frames of images were reconstructed. The last frame was used to remove the background phase in phase-sensitive reconstruction. Then, T1 mapping was performed by fitting the signal curve from the reconstructed image series to the theoretically calculated signal equation (3) voxel-by-voxel. Image Analysis: MASS images were reformatted to 2mm axial slices with the same geometry to QIR-TSE, and matched to QIR-TSE based on carotid bifurcation. Then, for healthy arteries, 5 axial slices were selected from CCA. For atherosclerotic arteries, 5 axial slices centered at the carotid bifurcation were selected. The lumen, outer wall and adjacent muscle contours were drawn on QIR-TSE images of the selected slices. Then the mean T1 of the carotid vessel wall or plaque, and muscle region were calculated for each slice. The slice-averaged T1 values for healthy vessel wall and muscle were reported. For each atherosclerotic artery, the mean T1 of the slices with plaque were averaged to generate the overall T1 of the plaque. Moreover, the corresponding SNAP images were reviewed to identify IPH.


The T1 mapping results of phantom are shown in Fig. 2. The T1 values from MASS were in good agreement with 2D IR-SE with measurement bias of 4.3%±2.5%. For in vivo imaging, 7 carotid arteries were detected with plaque in the 5 patients, among which 3 arteries were identified to have IPH on SNAP images. An example of MASS images at multiple TIs and the generated T1 map of an artery with IPH are shown in Fig. 3. Strong hyperintensities were seen in the plaque on the SNAP image, and the IPH regions showed strongly reduced values on the T1 map (IPH1: 412ms; IPH2: 353ms). The T1 measurements were summarized in Table 2. The plaque with IPH has lower T1 value than healthy vessel wall and the plaque without IPH.

Discussion and Conclusions

In this study, we have developed a 3D technique that can acquire co-registered images with multiple T1 contrasts in a single scan in short scan time (5min). The feasibility of MASS in quantitative T1 mapping of carotid artery has been demonstrated in healthy volunteers and atherosclerotic patients. In conclusion, MASS may be a useful tool to detect T1 changes of atherosclerotic plaque, and thus monitor its progression.


No acknowledgement found.


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FIG. 1. The schematic diagram of the proposed IR 3D golden angle radial sequence.

Table 1: Imaging parameters of MASS

FIG. 2. a: The T1 maps of phantom estimated by 2D IR-SE and MASS. b: Comparison of the mean T1 values of each tube measured by 2D IR-SE and MASS.

FIG. 3. a: The black-blood QIR-TSE and SNAP images of a carotid atherosclerosis patients with IPH. b: The five selected images (frames 1, 2, 4, 6, 8) along the IR curve reconstructed by MASS. c: The estimated carotid artery T1 map by MASS. The red arrows indicate the two IPH regions with reduced T1 values.

Table 2: Summary of T1 measurements

Proc. Intl. Soc. Mag. Reson. Med. 25 (2017)