Marcel Dominik Nickel

Liver fat quantification using a multi‐step adaptive fitting approach with multi‐echo GRE imaging

The purpose of this study was to develop a multi‐step adaptive fitting approach for liver proton density fat fraction (PDFF) and R2* quantification, and to perform an initial validation on a broadly available hardware platform.

Quantification of Hepatic Steatosis With a Multistep Adaptive Fitting MRI Approach: Prospective Validation Against MR Spectroscopy

OBJECTIVE. The purpose of this study is to prospectively compare hybrid and complex chemical shift-based MRI fat quantification methods against MR spectroscopy (MRS) for the measurement of hepatic steatosis. SUBJECTS AND METHODS. Forty-two subjects (18 men and 24 women; mean ± SD age, 52.8 ± 14 years) were prospectively enrolled and imaged at 3 T with a chemical shift-based MRI sequence and a single-voxel MRS sequence, each in one breath-hold. Proton density fat fraction and rate constant (R2*) using both single- and dual-R2* hybrid fitting methods, as well as proton density fat fraction and R2* maps using a complex fitting method, were generated. A single radiologist colocalized volumes of interest on the proton density fat fraction and R2* maps according to the spectroscopy measurement voxel. Agreement among the three MRI methods and the MRS proton density fat fraction values was assessed using linear regression, intraclass correlation coefficient (ICC), and Bland-Altman analysis. RESULTS. Correlation between the MRI and MRS measures of proton density fat fraction was excellent. Linear regression coefficients ranged from 0.98 to 1.01, and intercepts ranged from -1.12% to 0.49%. Agreement measured by ICC was also excellent (0.99 for all three methods). Bland-Altman analysis showed excellent agreement, with mean differences of -1.0% to 0.6% (SD, 1.3-1.6%). CONCLUSION. The described MRI-based liver proton density fat fraction measures are clinically feasible and accurate. The validation of proton density fat fraction quantification methods is an important step toward wide availability and acceptance of the MRI-based measurement of proton density fat fraction as an accurate and generalizable biomarker.

Ultrafast dynamic contrast-enhanced mri of the breast using compressed sensing: breast cancer diagnosis based on separate visualization of breast arteries and veins

To evaluate the feasibility of ultrafast dynamic contrast‐enhanced (UF‐DCE) magnetic resonance imaging (MRI) with compressed sensing (CS) for the separate identification of breast arteries/veins and perform temporal evaluations of breast arteries and veins with a focus on the association with ipsilateral cancers.

Application of whole-lesion histogram analysis of pharmacokinetic parameters in dynamic contrast-enhanced MRI of breast lesions with the CAIPIRINHA-Dixon-TWIST-VIBE technique.

To investigate the application of whole‐lesion histogram analysis of pharmacokinetic parameters for differentiating malignant from benign breast lesions on dynamic contrast‐enhanced magnetic resonance imaging (DCE‐MRI).

Gd-EOB-DTPA-enhanced T1 relaxometry for assessment of liver function determined by real-time 13 C-methacetin breath test

ObjectivesTo determine whether liver function as determined by intravenous administration of 13C-methacetin and continuous real-time breath analysis can be estimated quantitatively from gadoxetic acid (Gd-EOB-DTPA)-enhanced magnetic resonance (MR) relaxometry.MethodsSixty-six patients underwent a 13C-methacetin breath test (13C-MBT) for evaluation of liver function and Gd-EOB-DTPA-enhanced T1-relaxometry at 3 T. A transverse 3D VIBE sequence with an inline T1 calculation based on variable flip angles was acquired prior to (T1 pre) and 20 min post-Gd-EOB-DTPA (T1 post) administration. The reduction rate of T1 relaxation time (rrT1) and T1 relaxation velocity index (∆R1) between pre- and post-contrast images was evaluated. 13C-MBT values were correlated with T1post, ∆R1 and rrT1, providing an MRI-based estimated 13C-MBT value. The interobserver reliability was assessed by determining the intraclass correlation coefficient (ICC).ResultsStratified by three different categories of 13C-MBT readouts, there was a constant increase of T1 post with increasing progression of diminished liver function (p ≤ 0.030) and a constant significant decrease of ∆R1 (p ≤ 0.025) and rrT1 (p < 0.018) with progression of liver damage as assessed by 13C-methacetin breath analysis. ICC for all T1 relaxation values and indices was excellent (> 0.88). A simple regression model showed a log-linear correlation of 13C-MBT values with T1post (r = 0.57; p < 0.001), ∆R1 (r = 0.59; p < 0.001) and rrT1 (r = 0.70; p < 0.001).ConclusionLiver function as determined using real-time 13C-methacetin breath analysis can be estimated quantitatively from Gd-EOB-DTPA-enhanced MR relaxometry.Key Points• Gd-EOB-DTPA-enhanced T1 relaxometry quantifies liver function• Gd-EOB-DTPA-enhanced MR relaxometry may provide parameters for assessing liver function before surgery• Gd-EOB-DTPA-enhanced MR relaxometry may be useful for monitoring liver disease progression• Gd-EOB-DTPA-enhanced MR relaxometry has the potential to become a novel liver function index

Evaluation of 2-point, 3-point, and 6-point Dixon magnetic resonance imaging with flexible echo timing for muscle fat quantification

The purpose of this study is to evaluate and compare 2-point (2pt), 3-point (3pt), and 6-point (6pt) Dixon magnetic resonance imaging (MRI) sequences with flexible echo times (TE) to measure proton density fat fraction (PDFF) within muscles. Two subject groups were recruited (G1: 23 young and healthy men, 31 ± 6 years; G2: 50 elderly men, sarcopenic, 77 ± 5 years). A 3-T MRI system was used to perform Dixon imaging on the left thigh. PDFF was measured with six Dixon prototype sequences: 2pt, 3pt, and 6pt sequences once with optimal TEs (in- and opposed-phase echo times), lower resolution, and higher bandwidth (optTE sequences) and once with higher image resolution (highRes sequences) and shortest possible TE, respectively. Intra-fascia PDFF content was determined. To evaluate the comparability among the sequences, Bland-Altman analysis was performed. The highRes 6pt Dixon sequences served as reference as a high correlation of this sequence to magnetic resonance spectroscopy has been shown before. The PDFF difference between the highRes 6pt Dixon sequence and the optTE 6pt, both 3pt, and the optTE 2pt was low (between 2.2% and 4.4%), however, not to the highRes 2pt Dixon sequence (33%). For the optTE sequences, difference decreased with the number of echoes used. In conclusion, for Dixon sequences with more than two echoes, the fat fraction measurement was reliable with arbitrary echo times, while for 2pt Dixon sequences, it was reliable with dedicated in- and opposed-phase echo timing.

Clinical Feasibility of Free-Breathing Dynamic T1-Weighted Imaging With Gadoxetic Acid–Enhanced Liver Magnetic Resonance Imaging Using a Combination of Variable Density Sampling and Compressed Sensing

Objectives The purpose of the study was to investigate the clinical feasibility of free-breathing dynamic T1-weighted imaging (T1WI) using Cartesian sampling, compressed sensing, and iterative reconstruction in gadoxetic acid–enhanced liver magnetic resonance imaging (MRI). Materials and Methods This retrospective study was approved by our institutional review board, and the requirement for informed consent was waived. A total of 51 patients at high risk of breath-holding failure underwent dynamic T1WI in a free-breathing manner using volumetric interpolated breath-hold (BH) examination with compressed sensing reconstruction (CS-VIBE) and hard gating. Timing, motion artifacts, and image quality were evaluated by 4 radiologists on a 4-point scale. For patients with low image quality scores (<3) on the late arterial phase, respiratory motion-resolved (extradimension [XD]) reconstruction was additionally performed and reviewed in the same manner. In addition, in 68.6% (35/51) patients who had previously undergone liver MRI, image quality and motion artifacts on dynamic phases using CS-VIBE were compared with previous BH-T1WIs. Results In all patients, adequate arterial-phase timing was obtained at least once. Overall image quality of free-breathing T1WI was 3.30 ± 0.59 on precontrast and 2.68 ± 0.70, 2.93 ± 0.65, and 3.30 ± 0.49 on early arterial, late arterial, and portal venous phases, respectively. In 13 patients with lower than average image quality (<3) on the late arterial phase, motion-resolved reconstructed T1WI (XD-reconstructed CS-VIBE) significantly reduced motion artifacts (P < 0.002–0.021) and improved image quality (P < 0.0001–0.002). In comparison with previous BH-T1WI, CS-VIBE with hard gating or XD reconstruction showed less motion artifacts and better image quality on precontrast, arterial, and portal venous phases (P < 0.0001–0.013). Conclusions Volumetric interpolated breath-hold examination with compressed sensing has the potential to provide consistent, motion-corrected free-breathing dynamic T1WI for liver MRI in patients at high risk of breath-holding failure.

A comparison between 6-point dixon mri and mr spectroscopy to quantify muscle fat in the thigh of subjects with sarcopenia

BackgroundChanges in muscle fat composition as for example observed in sarcopenia, affect physical performance and muscular function, like strength and power.ObjectivesThe purpose of this study was to compare 6-point Dixon magnetic resonance imaging and multi-echo magnetic resonance spectroscopy sequences to quantify muscle fat.Setting, participants and measurementsTwo groups were recruited (G1: 23 healthy young men (28 ± 4 years), G2: 56 men with sarcopenia (80 ± 5 years)). Proton density fat fraction was measured with a 6-point product and a 6-point prototype Dixon sequence in the left thigh muscle and with a highspeed multi-echo T2*-corrected H1 magnetic resonance spectroscopy sequence within the semitendinosus muscle of the left thigh. To evaluate the comparability among the different methods, Bland-Altman and linear regression analyses of the proton density fat fraction results were performed.ResultsMean differences ± 1.96 * standard deviation between spectroscopy and 6pt Dixon sequences were 1.9 ± 3.3% and 1.5 ± 3.6% for the product and prototype sequences, respectively. High correlations were measured between the proton density fat fraction results of the 6-point Dixon sequences and spectroscopy (R = 0.95 for the product sequence and R = 0.97 for the prototype sequence).ConclusionsDixon imaging and spectroscopy sequences show comparable accuracy for fat measurements in the thigh. Spectroscopy is a local measurement, whereas Dixon sequences provide maps of the fat distribution. The high correlations of the 6-point Dixon sequences with spectroscopy support their clinical use. They provide higher spatial resolution than spectroscopy, but are not suitable for a more complicated spectral analysis to separate extra- and intramyocellular lipids.

A novel framework for evaluating the image accuracy of dynamic MRI and the application on accelerated breast DCE MRI

ObjectiveTo develop a novel framework for evaluating the accuracy of quantitative analysis on dynamic contrast-enhanced (DCE) MRI with a specific combination of imaging technique, scanning parameters, and scanner and software performance and to test this framework with breast DCE MRI with Time-resolved angiography WIth Stochastic Trajectories (TWIST).Materials and methodsRealistic breast tumor phantoms were 3D printed as cavities and filled with solutions of MR contrast agent. Full k-space raw data of individual tumor phantoms and a uniform background phantom were acquired. DCE raw data were simulated by sorting the raw data according to TWIST view order and scaling the raw data according to the enhancement based on pharmaco-kinetic (PK) models. The measured spatial and temporal characteristics from the images reconstructed using the scanner software were compared with the original PK model (ground truth).ResultsImages could be reconstructed using the manufacturer’s platform with the modified ‘raw data.’ Compared with the ‘ground truth,’ the RMS error in all images was <10% in most cases. With increasing view-sharing acceleration, the error of the initial uptake slope decreased while the error of peak enhancement increased. Deviations of PK parameters varied with the type of enhancement.ConclusionA new framework has been developed and tested to more realistically evaluate the quantitative measurement errors caused by a combination of the imaging technique, parameters and scanner and software performance in DCE-MRI.

Self-gated 4D-MRI of the liver: Initial clinical results of continuous multiphase imaging of hepatic enhancement

To evaluate the feasibility of a self‐gated free‐breathing volume‐interpolated breath‐hold examination (VIBE) sequence using compressed sensing (CS) for contrast‐enhanced multiphase liver MRI.