Jakob Weiss1, Jana Taron1, Ahmed E. Othman1, Robert Grimm2, Petros Martirosian1, Christina Schraml1, Konstantin Nikolaou1, and Mike Notohamiprodjo1
1Diagnostic and Interventional Radiology, University of Tuebingen, Tuebingen, Germany, 2Siemens Healthcare, Erlangen, Germany
Synopsis
To evaluate
clinical performance of contrast-enhanced 3D-isotropic
radial volumetric interpolated breath-hold examination (VIBE) for late-phase MR
imaging of the liver. A prototype retrospective self-gating algorithm for more
motion-robust data acquisition was implemented and compared to standard Cartesian
VIBE. Utilization of self-gating VIBE provides significantly improved image quality,
especially in coronal reformations and Gd-EOB-DTPA-enhanced late-phase scans.
Moreover, in 11% only radial VIBE provided diagnostic image quality, thus having a
direct implication on patient care. Therefore, self-gated radial VIBE seems a
valuable approach to improve diagnostic accuracy in late-phase MR imaging of
the liver.Purpose
To
evaluate the clinical performance of a 3D-isotropic self-gated radial
volumetric interpolated breath-hold examination (VIBE) for late-phase MR
imaging of the liver.
Material and Methods
70 patients with suspected intrahepatic mass were
included and underwent liver MRI at 1.5T (Magnetom Aera, Siemens Healthcare, Germany).
Depending on the clinical indication, either Gd-EOB-DTPA (35 patients) or Gadobutrol
(35 patients) were administered. During late-venous (Gadobutrol) or
hepatocyte-specific phase (Gd-EOB-DTPA), a self-gated 3D-isotropic radial VIBE
prototype sequence was acquired. The acquisition principles of the underlying
k-space readout using the stack-of-stars scheme have been described recently in
detail [1-3]. In short:
Cartesian k-space sampling is only performed along the slice direction (kz)
whereas in-plane (kx; ky) readout is performed along rotated spokes. The
resulting spoke overlap in the center facilitates a more motion-robust data
acquisition. Two series were reconstructed from the data set: 1) Using the
complete data set (r-VIBE-100) and 2) prototype algorithm with implementation
of a retrospective self-gating approach that allows sorting the data into bins
according to the respiration phase. The self-gating signal was extracted from
the k-space center, which is crossed by every spoke in the central k-space
partition. For image reconstruction, 40% of the acquired data at the most
consistently visited respiratory position, typically close to end-expiration,
were used (r-VIBE-40) to further
reduce motion artifacts. Schemes of the stack-of-stars trajectory and the
self-gating algorithm are provided in Figure 1. A standard Cartesian VIBE
(std-VIBE) served as reference.
Images
were assessed qualitatively (overall image quality, sharpness,
lesion detection,
artifacts due to streak or motion, biliary tree) on a 5-point Likert-scale (5=excellent) and
quantitatively (coefficient of variation (CV); contrast-ratio) in axial and
coronal reformations by two readers independently. Statistical analyses were performed
using SPSS (Version 22, IMB, Armonk, USA). Non-parametric testing using
Friedman´s ANOVA was conducted for qualitative analysis. For quantitative
values ANOVA analysis and post-hoc testing were performed. P-values <0.05
were considered to indicate significance.
Results
In eight cases (11%) only radial VIBE provided
diagnostic image quality to detect relevant findings such as portal venous
thrombosis or liver lesions (Figure 2/3) whereas std-VIBE was considered
non-diagnostic.
Image quality (p<0.05) and sharpness (p<0.001)
of r-VIBE-40 were rated significantly superior in GD-EOB-DTPA-enhanced scans
and coronal reformations as compared to std-VIBE. Lesion detection was
significantly improved (p<0.05) in coronal reformations of
Gd-EOB-DTPA-enhanced r-VIBE-40 scans in comparison to std-VIBE. In axial planes streak artifacts were graded significantly higher (p<0.001)
in r-VIBE-40 as compared to r-VIBE-100 and std-VIBE. In coronal multiplanar
reformations, image scores for motion artifacts were significantly lower
(p<0.001) in r-VIBE-40 than in r-VIBE-100 and std-VIBE. No differences could
be observed in the depiction of the biliary tree.
CV was significantly higher in r-VIBE-40 as compared
to the other sequences (p<0.01). Highest contrast-ratios were found in r-VIBE-40
and std-VIBE with significant differences to r-VIBE-100 (p<0.001) in
Gadobutrol-enhanced scans, whereas no differences were found in
Gd-EOB-DTPA-enhanced examinations.
Discussion
This study demonstrates that 3D-isotropic self-gated
radial VIBE significantly improves image quality, especially in coronal
multiplanar reformations and late-phase Gd-EOB-DTPA-enhanced scans as compared
to non-gated radial VIBE and standard Cartesian VIBE. This has a significant
clinical impact, as patients with liver disease frequently are unable to
properly hold their breath. Therefore, based on the results of this study we
consider 3D-isotropic self-gated radial VIBE as a promising approach to reduce
the number of non-diagnostic examinations due to motion-induced impairment of
image quality. Moreover, in 11% of the cases only radial VIBE provided
sufficient image quality to detect relevant pathologies, thus having a direct
implication for patient care.
The improved robustness of the assessed self-gated 3D
radial prototype sequence also allows acquiring data during free breathing
beyond an individual patient´s breath-hold capability. This is especially
useful for the assessment of discrete anatomic and pathologic details. Furthermore,
the possibility of reconstructing arbitrary reformations of the 3D-isotropic
data sets without additional reconstruction time poses a viable strategy to
further increase diagnostic accuracy in liver imaging.
A
current disadvantage of radial VIBE is the relatively long acquisition time,
due to reduced sampling efficiency and the lack of parallel imaging. However, to
facilitate diagnostic image quality in dynamic contrast-enhanced MRI,
especially important for the diagnosis of hepatocellular carcinoma [4], different image
reconstruction approaches have been developed including k-space-weighted image
contrast reconstruction (r-VIBE-KWIC) [5] or extra-dimensional
golden-angle radial sparse parallel MRI (XD-GRASP) [6]. Thus, radial k-space
sampling combined with iterative reconstruction algorithms seems a valuable
approach for abdominopelvic and dynamic liver MRI.
Conclusion
Utilization of self-gated 3D-isotropic radial VIBE
provides significantly superior image quality as compared to the standard
Cartesian VIBE, especially in multiplanar reformations and Gd-EOB-DTPA-enhanced
late-phase examinations.
Acknowledgements
No acknowledgement found.References
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