无对比剂增强的磁共振血管成像技术

钆对比剂目前被广泛应用于全身血管磁共振成像,但是由于它在肾功能不全的患者身上可出现肾源性系统性纤维化,基于安全的考虑,无对比剂增强的血管成像技术受到关注。西门子磁共振事业部独家推出的无对比剂磁共振血管成像软件包syngo NATIVE,用以满足客户的临床需求。syngo NATIVE包括两种不同的技术：syngo NATIVE TrueFISP和syngo NATIVE SPACE,前者用于腹部动脉（特别是肾动脉）成像,后者主要用于外周动脉的成像。本文分别对这两种技术的背景以及当前的临床应用进行介绍。     

A pre-operative CT and non-contrast-enhanced C-arm CT registration framework for trans-catheter aortic valve implantation

Contrast-enhanced C-arm CT is routinely used for intra-operative guidance during the trans-catheter aortic valve implantation (TAVI); however, the requirement for contrast agent injection is not preferable, especially for patients with renal insufficiencies. To address this problem, we present a novel framework for fully automatic registration of pre-operative CT and non-contrast-enhanced C-arm CT. The proposed framework provides an improved workflow and minimizes the usage of contrast agent in the TAVI procedure. Our framework consists of three steps: coarse rigid-body alignment, anatomical knowledge-based prior deformation field generation, and fine deformable registration. We validated the proposed framework on 20 real patient data sets. Based on the 20 data sets, the mesh-to-mesh errors at the aortic root from different methods are measured. Our proposed method significantly outperforms the other state-of-the-art methods. Specifically, we achieve the registration accuracy at 1.76 ± 0.43 mm which is clinically plausible. Quantitative evaluation on real non-contrast enhanced C-arm CT data sets confirms the applicability in the clinical usage. The proposed heart registration method is generic and hence can be easily applied to other cardiac applications.     

Non-contrast-enhanced hepatic MR angiography with true steady-state free-precession and time spatial labeling inversion pulse: optimization of the technique and preliminary results

Objective

To selectively visualize the hepatic arteries using the respiratory-triggered three-dimensional (3D) true steady-state free-precession (SSFP) projection magnetic resonance angiographic sequence with time spatial labeling inversion pulse (T-SLIP), and describe the optimization of this protocol.

Materials and methods

Twenty healthy volunteers were examined in this study. A respiratory-triggered 3D true SSFP combined with T-SLIP was performed. Among several key factors that affect the image quality, the most important is the inversion time (TI). Therefore, according to the difference in TI, four image groups: group A (TI of 800 ms), group B (TI of 1000 ms), group C (TI of 1200 ms), and group D (TI of 1400 ms), were assigned and compared to detect the optimal TI for hepatic artery visualization. For quantitative assessment, the relative signal intensity, i.e., Cv–l (vessel-to-liver contrast) of the right hepatic artery was measured. For qualitative evaluation, the quality of vessel visualization and the order of identified hepatic artery branches were evaluated by two radiologists.

Results

Selective and high-contrast visualization of the hepatic arteries was acquired in all cases. Regarding the quantitative assessment, Cv–l decreased in group D due to background signal recovery, but there was no significant difference between groups (p-value >0.05). Regarding the qualitative evaluation, there were significant differences between group A and the other groups (p-value <0.01) and between groups B and C (p-value <0.05). In group C, both the image quality score and mean value for the order of the hepatic artery branches were highest, and a TI of 1200 ms was thought to be optimal regarding the balance between vessel-to-liver contrast and peripheral hepatic artery visualization.

Conclusion

The MR angiographic technique using true SSFP with T-SLIP enabled the selective visualization of hepatic arteries without the need for an exogenous contrast agent or breath-hold.     

Non-contrast-enhanced magnetic resonance venography using magnetization-prepared rapid gradient-echo (MPRAGE) in the preoperative evaluation of living liver donor candidates: Comparison with conventional computed tomography venography

ObjectiveTo compare the diagnostic performance of non-contrast-enhanced magnetic resonance venography using magnetization-prepared rapid gradient-echo (MPRAGE-MRV) and conventional computed tomography venography (CTV) in preoperative evaluation of venous tributaries for living donor liver transplantation.Materials and methodsInstitutional review board approval and written informed consent were obtained for this prospective study of 73 donor candidates. Of these, 23 underwent right-sided graft hepatectomy without middle hepatic vein. One or more tributaries, other than the right hepatic vein, were reconstructed for 20 of the 23 grafts. For these 20 grafts, the number and location of the tributaries requiring reconstruction were evaluated based on venography, and diagnostic performance was analyzed using surgical records as a reference standard. For each candidate, the number of small tributaries directly joining the inferior vena cava was counted in each venographic image; a paired-sample t-test was used to assess differences. The severity of respiratory artifacts in MPRAGE-MRV was qualitatively evaluated, and compared using Wilcoxon's rank-sum test.ResultsAll reconstructed venous tributaries were prospectively identified using both methods. MPRAGE-MRV tended to provide a greater number of small tributaries than conventional CTV (mean: 2; 95% CI: [1.66, 2.34], and 1.74; [1.44, 2.04], respectively), although the difference was not significant (P = 0.10); MPRAGE-MRV was superior or equal to CTV in 52 subjects (71.2%), and inferior in 21 subjects (28.8%). Respiratory artifacts were significantly less severe in the former subjects (P < 0.0001).ConclusionsMPRAGE-MRV has the potential to replace conventional CTV in the preoperative evaluation of living liver donor candidates.     

Non-contrast-enhanced hepatic MR angiography: Do two-dimensional parallel imaging and short tau inversion recovery methods shorten acquisition time without image quality deterioration?

Objective

To study whether shortening the acquisition time for selective hepatic artery visualization is feasible without image quality deterioration by adopting two-dimensional (2D) parallel imaging (PI) and short tau inversion recovery (STIR) methods.

Materials and methods

Twenty-four healthy volunteers were enrolled. 3D true steady-state free-precession imaging with a time spatial labeling inversion pulse was conducted using 1D or 2D-PI and fat suppression by chemical shift selective (CHESS) or STIR methods. Three groups of different scan conditions were assigned and compared: group A (1D-PI factor 2 and CHESS), group B (2D-PI factor 2 × 2 and CHESS), and group C (2D-PI factor 2 × 2 and STIR). The artery-to-liver contrast was quantified, and the quality of artery visualization and overall image quality were scored.

Results

The mean scan time was 9.5 ± 1.0 min (mean ± standard deviation), 5.9 ± 0.8 min, and 5.8 ± 0.5 min in groups A, B, and C, respectively, and was significantly shorter in groups B and C than in group A (P < 0.01). The artery-to-liver contrast was significantly better in group C than in groups A and B (P < 0.01). The scores for artery visualization and overall image quality were worse in group B than in groups A and C. The differences were statistically significant (P < 0.05) regarding the arterial branches of segments 4 and 8. Between group A and group C, which had similar scores, there were no statistically significant differences.

Conclusion

Shortening the acquisition time for selective hepatic artery visualization was feasible without deterioration of the image quality by the combination of 2D-PI and STIR methods. It will facilitate using non-contrast-enhanced MRA in clinical practice.