Dynamic Liver Magnetic Resonance Imaging During Free Breathing: A Feasibility Study With a Motion Compensated Variable Density Radial Acquisition and a Viewsharing High-Pass Filtering Reconstruction.

OBJECTIVE: Robust dynamic contrast-enhanced T1-weighted images are crucial for accurate detection and categorization of focal liver lesions in liver/abdominal magnetic resonance imaging (MRI). As optimal dynamic imaging usually requires multiple breath-holds, its inherent susceptibility to motion artifacts frequently results in degraded image quality in incompliant patients. Because free-breathing imaging may overcome this drawback, the intention of this study was to evaluate a dynamic MRI sequence acquired during free breathing using the variable density, elliptical centric golden angle radial stack-of-stars radial sampling scheme, which so far has not been implemented in 4-dimensional applications. MATERIALS AND METHODS: In a prospective pilot study, 27 patients received a routine abdominal MRI protocol including the prototype free-breathing sequence (4DFreeBreathing) for dynamic imaging. This enables more convenient and faster reconstruction through variable density, elliptical centric golden angle radial stack-of-stars without the use of additional reconstruction hardware, and even higher motion robustness through soft-gating. A standard breath-hold sequence performed subsequently served as reference standard. Of the continuous dynamic data sets, each dynamic phase was analyzed regarding image quality, motion artifacts and vessel conspicuity using 5-point Likert scales. Furthermore, correct timing of the late arterial phase was compared with the preexaminations. RESULTS: 4DFreeBreathing delivered motion-free dynamic images with high temporal resolution in each subject. Overall image quality scores were rated good or excellent for 4DFreeBreathing and the gold standard without significant differences (P = 0.34). There were significantly less motion artifacts in the 4DFreeBreathing sequence (P < 0.0001), whereas vessel conspicuity in each dynamic phase was comparable for both groups (P = 0.45, P > 0.99, P = 0.22, respectively). Correct timing of the late arterial phase could be achieved in 27 of 27 (100%) examinations using 4DFreeBreathing versus 35 of 53 (66%) preexaminations using gold standard (P < 0.001). CONCLUSION: The benefit of convenient and fast image reconstruction combined with the superiority in motion robustness and timing compared with standard breath hold sequences renders 4DFreeBreathing an attractive alternative to existing free-breathing techniques in dynamic liver MRI.

Clinical Evaluation of Free-Breathing Contrast-Enhanced T1w MRI of the Liver using Pseudo Golden Angle Radial k-Space Sampling.

PURPOSE: Contrast-enhanced T1-weighted MR imaging of the liver is typically acquired using breath-hold techniques to reduce motion artifacts and to allow for optimal diagnostic image quality. Insufficient breath-holds during MR data collection can cause severe reduction of image quality up to the point of being non-diagnostic. The aim of this study was to evaluate the subjective and objective clinical image quality of a novel free-breathing radial k-space sampling MR technique. MATERIALS AND METHODS: Consent for this study was given by the local IRB committee. 86 patients who underwent both breath-hold (BH) and free-breathing (FB) late-phase contrast T1w-FS-FFE liver MRI using conventional BH Cartesian (Cartesian-eTHRIVE) and FB "pseudo golden angle" radial k-space sampling (Radial-eTHRIVE) were included in this retrospective analysis. Subjective analysis comprised 5-point Likert scale ratings (1 = very good; 5 = non-diagnostic) for "artifact impact", "anatomic sharpness", "vessel sharpness", "contrast impression", and "overall diagnostic quality". Relative signal intensities in different ROIs were compared between Cartesian-eTHRIVE and Radial-eTHRIVE. For statistical differences paired Wilcoxon test and paired t-test have been performed (p < 0.05). RESULTS: The MR scan time was significantly longer for FB Radial-eTHRIVE (2 min, 54 s) compared to BH Cartesian-eTHRIVE (0 min 15 s). Cartesian-eTHRIVE demonstrated a superior subjective contrast impression and objective measurements revealed an increased lesion-to-liver-contrast for hypointense liver lesions (Hypo-LTLC: 0.33 ±â€Š0.19 vs. 0.20 ±â€Š0.11; p = 0.000), while no difference was observed for hyperintense liver lesions (Hyper-LTLC). Subjective evaluation showed superior anatomic sharpness ratings by both readers for Radial-eTHRIVE. Most importantly, in a subgroup analysis of patients who were unable to perform adequate breath-holds, free-breathing Radial-eTHRIVE still demonstrated good subjective image quality. CONCLUSION: Free-breathing, radial k-space sampling T1w MRI of the liver delivers high diagnostic image quality, especially in patients who are unable to adequately perform breath-hold maneuvers. Thus, Radial-eTHRIVE can be an important clinical alternative in patients with impaired respiration status. KEY POINTS: · Delayed-phase contrast-enhanced MRI of the liver can be robustly performed using a "pseudo golden angle" Radial-eTHRIVE sequence.. · Free-breathing Radial-eTHRIVE yields good diagnostic image quality in case of a high artifact burden in breath-hold Cartesian-eTHRIVE and thus could be used as a "back-up" for patients with impaired respiratory capacity.. · A lower lesion-to-liver-contrast ratio is observed for hypointense liver lesions in free-breathing Radial-eTHRIVE sequence.. CITATION FORMAT: · Hedderich DM, Weiss K, Spiro JE et al. Clinical Evaluation of Free-Breathing Contrast-Enhanced T1w MRI of the Liver using Pseudo Golden Angle Radial k-Space Sampling. Fortschr Röntgenstr 2018; 190: 601 - 609.

Non-contrast enhanced 4D intracranial MR angiography based on pseudo-continuous arterial spin labeling with the keyhole and view-sharing technique.

PURPOSE: 4D dynamic MR angiography (4D-MRA) using pseudo-continuous arterial spin labeling (pCASL), combined with Keyhole and View-sharing (4D-PACK) for scan acceleration, is introduced. Its validity for arterial inflow dynamics visualization was investigated through comparison with 4D-pCASL and contrast inherent inflow enhanced multiphase angiography (CINEMA). METHODS: Six healthy volunteers were included in the study. The arterial transit time (ATT) in 4D-PACK was measured at multiple regions in middle cerebral artery (MCA), and Pearson's correlation coefficient with ATT in 4D-pCASL was calculated. The contrast-to-noise ratio (CNR) in 4D-PACK was measured in four MCA segments and compared with that in 4D-pCASL and CINEMA. Arterial visualization in 4D-PACK was assessed qualitatively in patients with moyamoya disease and arteriovenous malformation by comparing with CINEMA. RESULTS: 4D-PACK achieved a 36% scan time reduction compared with 4D-pCASL. The correlation coefficient for ATT measured by 4D-pCASL and 4D-PACK was greater than 0.96. The CNR was significantly higher using 4D-PACK compared with CINEMA in the M4 segment (P < 0.01). In patient examinations, the flow in the collateral artery or draining vein was better visualized in 4D-PACK compared with CINEMA. CONCLUSION: 4D-PACK accelerates 4D-pCASL, shows similar inflow dynamics as 4D-pCASL and shows better peripheral visualization compared with CINEMA. Magn Reson Med 80:719-725, 2018. © 2018 International Society for Magnetic Resonance in Medicine.

Contrast-enhanced timing robust acquisition order with a preparation of the longitudinal signal component (CENTRA plus) for 3D contrast-enhanced abdominal imaging.

PURPOSE: To investigate a new image acquisition method that enables an accurate hepatic arterial phase definition and the visualization of contrast agent uptake processes in abdominal organs like liver, spleen, and pancreas. MATERIALS AND METHODS: A 3D turbo gradient echo method where a fat suppression prepulse is followed by the acquisition of several profiles was combined with an elliptical centric k-space ordering technique and 3D dynamic elliptical centric keyhole. The new k-space ordering method (CENTRA+) was validated experimentally. In an initial clinical evaluation phase the method was employed in five patients to assess the accuracy of the hepatic arterial phase definition and the visualization of the contrast uptake processes in dynamic scanning in abdominal organs like liver, spleen, and pancreas. RESULTS: In total, five patients were evaluated using the new k-space order. Our initial results indicate that the new k-space order allows consistent capture of the hepatic arterial phase. In dynamic scanning the extreme short temporal resolution obtained with 3D elliptical centric keyhole enables contrast enhancement to be followed in organs with fast contrast uptake characteristics. CONCLUSION: The elliptical centric nature of the new image acquisition method effectively allows capture of the contrast enhancement processes with good fat suppression.