Purpose
To allow for T1 mapping of the myocardium within 2.3 s for a 2D slice utilizing cardiac motion‐corrected, model‐based image reconstruction.
Methods
Golden radial data acquisition is ...continuously carried out for 2.3 s after an inversion pulse. In a first step, dynamic images are reconstructed which show both contrast changes due to T1 recovery and anatomical changes due to the heartbeat. An image registration algorithm with a signal model for T1 recovery is applied to estimate non‐rigid cardiac motion. In a second step, estimated motion fields are applied during an iterative model‐based T1 reconstruction. The approach was evaluated in numerical simulations, phantom experiments and in in‐vivo scans in healthy volunteers.
Results
The accuracy of cardiac motion estimation was shown in numerical simulations with an average motion field error of 0.7 ± 0.6 mm for a motion amplitude of 5.1 mm. The accuracy of T1 estimation was demonstrated in phantom experiments, with no significant difference (p = 0.13) in T1 estimated by the proposed approach compared to an inversion‐recovery reference method. In vivo, the proposed approach yielded 1.3 × 1.3 mm T1 maps with no significant difference (p = 0.77) in T1 and SDs in comparison to a cardiac‐gated approach requiring 16 s scan time (i.e., seven times longer than the proposed approach). Cardiac motion correction improved the precision of T1 maps, shown by a 40% reduced SD.
Conclusion
We have presented an approach that provides T1 maps of the myocardium in 2.3 s by utilizing both cardiac motion correction and model‐based T1 reconstruction.
Purpose
Subject‐tailored parallel transmission pulses for ultra‐high fields body applications are typically calculated based on subject‐specific B1+$$ {\mathrm{B}}_1^{+} $$‐maps of all transmit ...channels, which require lengthy adjustment times. This study investigates the feasibility of using deep learning to estimate complex, channel‐wise, relative 2D B1+$$ {\mathrm{B}}_1^{+} $$‐maps from a single gradient echo localizer to overcome long calibration times.
Methods
126 channel‐wise, complex, relative 2D B1+$$ {\mathrm{B}}_1^{+} $$‐maps of the human heart from 44 subjects were acquired at 7T using a Cartesian, cardiac gradient‐echo sequence obtained under breath‐hold to create a library for network training and cross‐validation. The deep learning predicted maps were qualitatively compared to the ground truth. Phase‐only B1+$$ {\mathrm{B}}_1^{+} $$‐shimming was subsequently performed on the estimated B1+$$ {\mathrm{B}}_1^{+} $$‐maps for a region of interest covering the heart. The proposed network was applied at 7T to 3 unseen test subjects.
Results
The deep learning‐based B1+$$ {\mathrm{B}}_1^{+} $$‐maps, derived in approximately 0.2 seconds, match the ground truth for the magnitude and phase. The static, phase‐only pulse design performs best when maximizing the mean transmission efficiency. In‐vivo application of the proposed network to unseen subjects demonstrates the feasibility of this approach: the network yields predicted B1+$$ {\mathrm{B}}_1^{+} $$‐maps comparable to the acquired ground truth and anatomical scans reflect the resulting B1+$$ {\mathrm{B}}_1^{+} $$‐pattern using the deep learning‐based maps.
Conclusion
The feasibility of estimating 2D relative B1+$$ {\mathrm{B}}_1^{+} $$‐maps from initial localizer scans of the human heart at 7T using deep learning is successfully demonstrated. Because the technique requires only sub‐seconds to derive channel‐wise B1+$$ {\mathrm{B}}_1^{+} $$‐maps, it offers high potential for advancing clinical body imaging at ultra‐high fields.
Purpose
Respiratory motion‐compensated (MC) 3D cardiac fat‐water imaging at 7T.
Methods
Free‐breathing bipolar 3D triple‐echo gradient‐recalled‐echo (GRE) data with radial phase‐encoding (RPE) ...trajectory were acquired in 11 healthy volunteers (7M\4F, 21–35 years, mean: 30 years) with a wide range of body mass index (BMI; 19.9–34.0 kg/m2) and volunteer tailored B1+ shimming. The bipolar‐corrected triple‐echo GRE‐RPE data were binned into different respiratory phases (self‐navigation) and were used for the estimation of non‐rigid motion vector fields (MF) and respiratory resolved (RR) maps of the main magnetic field deviations (ΔB0). RR ΔB0 maps and MC ΔB0 maps were compared to a reference respiratory phase to assess respiration‐induced changes. Subsequently, cardiac binned fat‐water images were obtained using a model‐based, respiratory motion‐corrected image reconstruction.
Results
The 3D cardiac fat‐water imaging at 7T was successfully demonstrated. Local respiration‐induced frequency shifts in MC ΔB0 maps are small compared to the chemical shifts used in the multi‐peak model. Compared to the reference exhale ΔB0 map these changes are in the order of 10 Hz on average. Cardiac binned MC fat‐water reconstruction reduced respiration induced blurring in the fat‐water images, and flow artifacts are reduced in the end‐diastolic fat‐water separated images.
Conclusion
This work demonstrates the feasibility of 3D fat‐water imaging at UHF for the entire human heart despite spatial and temporal B1+ and B0 variations, as well as respiratory and cardiac motion.
Purpose
Myocardial fat infiltrations are associated with a range of cardiomyopathies. The purpose of this study was to perform cardio‐respiratory motion‐correction for model‐based water‐fat ...separation to image fatty infiltrations of the heart in a free‐breathing, non‐cardiac‐triggered high‐resolution 3D MRI acquisition.
Methods
Data were acquired in nine patients using a free‐breathing, non‐cardiac‐triggered high‐resolution 3D Dixon gradient‐echo sequence and radial phase encoding trajectory. Motion correction was combined with a model‐based water‐fat reconstruction approach. Respiratory and cardiac motion models were estimated using a dual‐mode registration algorithm incorporating both motion‐resolved water and fat information. Qualitative comparisons of fat structures were made between 2D clinical routine reference scans and reformatted 3D motion‐corrected images. To evaluate the effect of motion correction the local sharpness of epicardial fat structures was analyzed for motion‐averaged and motion‐corrected fat images.
Results
The reformatted 3D motion‐corrected reconstructions yielded qualitatively comparable fat structures and fat structure sharpness in the heart as the standard 2D breath‐hold. Respiratory motion correction improved the local sharpness on average by 32% ± 24% with maximum improvements of 81% and cardiac motion correction increased the sharpness further by another 15% ± 11% with maximum increases of 31%. One patient showed a fat infiltration in the myocardium and cardio‐respiratory motion correction was able to improve its visualization in 3D.
Conclusion
The 3D water‐fat separated cardiac images were acquired during free‐breathing and in a clinically feasible and predictable scan time. Compared to a motion‐averaged reconstruction an increase in sharpness of fat structures by 51% ± 27% using the presented motion correction approach was observed for nine patients.
Abstract
Purpose
Depicting the stiffness of biological soft tissues, MR elastography (MRE) has a wide range of diagnostic applications. The purpose of this study was to improve the temporal ...resolution of 2D hepatic MRE in order to provide more rapid feedback on the quality of the wavefield and ensure better temporal sampling of respiration‐induced stiffness changes.
Methods
We developed a rapid MRE sequence that uses 2D segmented gradient‐echo spiral readout to encode 40 Hz harmonic vibrations and generate stiffness maps within 625 ms. We demonstrate the use of this technique as a rapid test for shear wave amplitudes and overall MRE image quality and as a method for monitoring respiration‐induced stiffness changes in the liver in comparison to 3D MRE and ultrasound‐based time‐harmonic elastography.
Results
Subsecond MRE allowed monitoring of increasing shear wave amplitudes in the liver with increasing levels of external stimulation within a single breath‐hold. Furthermore, the technique detected respiration‐induced changes in liver stiffness with peak values (1.83 ± 0.22 m/s) at end‐inspiration, followed by softer values during forced abdominal pressure (1.60 ± 0.22 m/s) and end‐expiration (1.49 ± 0.22 m/s). The effects of inspiration and expiration were confirmed by time‐harmonic elastography.
Conclusion
Our results suggest that subsecond MRE of the liver is useful for checking MRE driver settings and monitoring breathing‐induced changes in liver stiffness in near real time.
To provide high-resolution cardiac T
mapping of various cardiac phases and cine imaging within a single breath-hold using continuous golden ratio-based radial acquisition and model-based iterative ...image reconstruction.
Data acquisition was performed continuously using golden ratio-based radial sampling and multiple inversion pulses were applied independent of the heart rate. Native T
maps of diastole and systole were reconstructed with in-plane resolution of 1.3 × 1.3 mm
using model-based iterative image reconstruction. Cine images with 30 cardiac phases were reconstructed from the same data using kt-SENSE. The method was evaluated in a commercially available T
phantom and 10 healthy subjects. In vivo T
assessment was carried out segment-wise.
Evaluation in the phantom demonstrated accurate T
times (R
> 0.99) and insensitivity to the heart rate. In vivo T
values did not differ between systole and diastole, and T
times assessed by the proposed approach were longer than measured with a modified Look-Locker inversion recovery (MOLLI) sequence, except for lateral segments. Cine images had a consistent dark-blood contrast and functional assessment was in agreement with assessment based on Cartesian cine scans (difference in ejection fraction: 0.26 ± 2.65%, P = 0.65).
The proposed approach provides native T
maps of diastole and systole with high spatial resolution and cine images simultaneously within 16 s, which could strongly improve the scan efficiency.
Stroke–Heart Syndrome: Recent Advances and Challenges Scheitz, Jan F.; Sposato, Luciano A.; Schulz‐Menger, Jeanette ...
Journal of the American Heart Association,
09/2022, Letnik:
11, Številka:
17
Journal Article
Recenzirano
Odprti dostop
After ischemic stroke, there is a significant burden of cardiovascular complications, both in the acute and chronic phase. Severe adverse cardiac events occur in 10% to 20% of patients within the ...first few days after stroke and comprise a continuum of cardiac changes ranging from acute myocardial injury and coronary syndromes to heart failure or arrhythmia. Recently, the term stroke–heart syndrome was introduced to provide an integrated conceptual framework that summarizes neurocardiogenic mechanisms that lead to these cardiac events after stroke. New findings from experimental and clinical studies have further refined our understanding of the clinical manifestations, pathophysiology, and potential long‐term consequences of the stroke–heart syndrome. Local cerebral and systemic mediators, which mainly involve autonomic dysfunction and increased inflammation, may lead to altered cardiomyocyte metabolism, dysregulation of (tissue‐resident) leukocyte populations, and (micro‐) vascular changes. However, at the individual patient level, it remains challenging to differentiate between comorbid cardiovascular conditions and stroke‐induced heart injury. Therefore, further research activities led by joint teams of basic and clinical researchers with backgrounds in both cardiology and neurology are needed to identify the most relevant therapeutic targets that can be tested in clinical trials.
Purpose
To provide high‐resolution cardiac T1 mapping of various cardiac phases and cine imaging within a single breath‐hold using continuous golden ratio‐based radial acquisition and model‐based ...iterative image reconstruction.
Methods
Data acquisition was performed continuously using golden ratio‐based radial sampling and multiple inversion pulses were applied independent of the heart rate. Native T1 maps of diastole and systole were reconstructed with in‐plane resolution of 1.3 × 1.3 mm2 using model‐based iterative image reconstruction. Cine images with 30 cardiac phases were reconstructed from the same data using kt‐SENSE. The method was evaluated in a commercially available T1 phantom and 10 healthy subjects. In vivo T1 assessment was carried out segment‐wise.
Results
Evaluation in the phantom demonstrated accurate T1 times (R2 > 0.99) and insensitivity to the heart rate. In vivo T1 values did not differ between systole and diastole, and T1 times assessed by the proposed approach were longer than measured with a modified Look‐Locker inversion recovery (MOLLI) sequence, except for lateral segments. Cine images had a consistent dark‐blood contrast and functional assessment was in agreement with assessment based on Cartesian cine scans (difference in ejection fraction: 0.26 ± 2.65%, P = 0.65).
Conclusion
The proposed approach provides native T1 maps of diastole and systole with high spatial resolution and cine images simultaneously within 16 s, which could strongly improve the scan efficiency.
Purpose
Traditional phase‐contrast MRI is affected by displacement artifacts caused by non‐synchronized spatial‐ and velocity‐encoding time points. The resulting inaccurate velocity maps can affect ...the accuracy of derived hemodynamic parameters. This study proposes and characterizes a 3D radial phase‐contrast UTE (PC‐UTE) sequence to reduce displacement artifacts. Furthermore, it investigates the displacement of a standard Cartesian flow sequence by utilizing a displacement‐free synchronized‐single‐point‐imaging MR sequence (SYNC‐SPI) that requires clinically prohibitively long acquisition times.
Methods
3D flow data was acquired at 3T at three different constant flow rates and varying spatial resolutions in a stenotic aorta phantom using the proposed PC‐UTE, a Cartesian flow sequence, and a SYNC‐SPI sequence as reference. Expected displacement artifacts were calculated from gradient timing waveforms and compared to displacement values measured in the in vitro flow experiments.
Results
The PC‐UTE sequence reduces displacement and intravoxel dephasing, leading to decreased geometric distortions and signal cancellations in magnitude images, and more spatially accurate velocity quantification compared to the Cartesian flow acquisitions; errors increase with velocity and higher spatial resolution.
Conclusion
PC‐UTE MRI can measure velocity vector fields with greater accuracy than Cartesian acquisitions (although pulsatile fields were not studied) and shorter scan times than SYNC‐SPI. As such, this approach is superior to traditional Cartesian 3D and 4D flow MRI when spatial misrepresentations cannot be tolerated, for example, when computational fluid dynamics simulations are compared to or combined with in vitro or in vivo measurements, or regional parameters such as wall shear stress are of interest.
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