MRI simulation-based evaluation of ECV calculation using MOLLI T1 maps

Quantification of myocardial extracellular volume (ECV) fraction based on pre- and post-gadolinium MOLLI T1 maps is a research tool that has the potential to become an important prognostic tool for assessing specific cardiomyopathies. In this study, we utilized advanced MR simulations of the MOLLI pulse sequence for a wide range of physiological T2 values for pre-gadolinium blood and myocardium in order to investigate the dependency of MOLLI-based ECV measurements on T2. Simulations show that MOLLI underestimates ECV measurements in shorter pre-gadolinium myocardial T2 and longer pre-gadolinium blood T2 values with the ECV underestimation error being higher with pre-gadolinium myocardial T2 values than with pre-gadolinium blood T2 values. © 2015 CCAL

Massively parallel CUDA simulations of cardiac and embryonic MRI on a cloud-based cluster

Embryonic and cardiovascular Magnetic Resonance Imaging (MRI) in both clinic and research environments is confronted by challenges like motion, flow and low resolution. MRI simulations can be used as a valuable tool against these challenges but they are characterized by high computational intensity. In this study we implemented cardiac and embryonic MR simulations on a cloud-based cluster. For this purpose, an anatomical model of a human embryo was split over a variable number of computer nodes on the cloud. Simulation of a Gradient-Echo pulse sequence was performed and the partial results were aggregated in a central node to produce the simulated MR image, following the MapReduce paradigm. The measured execution times and speedups demonstrated the benefits of this cloud-based approach. © 2015 CCAL

Using a modified 3D-printer for mapping the magnetic field of RF coils designed for fetal and neonatal imaging

An experimental setup for characterizing the magnetic field of MRI RF coils was proposed and tested. The setup consisted of a specially configured 3D-printer, a network analyzer and a mid-performance desktop PC. The setup was tested on a single loop RF coil, part of a phased array for fetal imaging. Then, the setup was used for determining the magnetic field characteristics of a high-pass birdcage coil used for neonatal MR imaging with a vertical static field. The scattering parameter S21, converted into power ratio, was used for mapping the B1 magnetic field. The experimental measurements from the loop coil were close to the theoretical results (R = 0.924). A high degree of homogeneity was measured for the neonatal birdcage RF coil. The development of MR RF coils is time consuming and resource intensive. The proposed experimental setup provides an alternative method for magnetic field characterization of RF coils used in MRI. © 2016 Published by Elsevier Inc

Parallel simulations for QUAntifying RElaxation magnetic resonance constants (SQUAREMR): An example towards accurate MOLLI T1 measurements

Background: T1 mapping is widely used today in CMR, however, it underestimates true T1 values and its measurement error is influenced by several acquisition parameters. The purpose of this study was the extraction of accurate T1 data through the utilization of comprehensive, parallel Simulations for QUAntifying RElaxation Magnetic Resonance constants (SQUAREMR) of the MOLLI pulse sequence on a large population of spins with physiologically relevant tissue relaxation constants. Methods: A CMR protocol consisting of different MOLLI schemes was performed on phantoms and healthy human volunteers. For every MOLLI experiment, the identical pulse sequence was simulated for a large range of physiological combinations of relaxation constants, resulting in a database of all possible outcomes. The unknown relaxation constants were then determined by finding the simulated signals in the database that produced the least squared difference to the measured signal intensities. Results: SQUAREMR demonstrated improvement of accuracy in phantom studies and consistent mean T1 values and consistent variance across the different MOLLI schemes in humans. This was true even for tissues with long T1s and MOLLI schemes with no pause between modified-Look-Locker experiments. Conclusions: SQUAREMR enables quantification of T1 data obtained by existing clinical pulse sequences. SQUAREMR allows for correction of quantitative CMR data that have already been acquired whereas it is expected that SQUAREMR may improve data consistency and advance quantitative MR across imaging centers, vendors and experimental configurations. While this study is focused on a MOLLI-based T1-mapping technique, it could however be extended in other types of quantitative MRI throughout the body. © 2015 Xanthis et al

Validation of a new t2∗ algorithm and its uncertainty value for cardiac and liver iron load determination from MRI magnitude images

Purpose To validate an automatic algorithm for offline T2∗ measurements, providing robust, vendor-independent T2∗, and uncertainty estimates for iron load quantification in the heart and liver using clinically available imaging sequences. Methods A T2∗ region of interest (ROI)-based algorithm was developed for robustness in an offline setting. Phantom imaging was performed on a 1.5 Tesla system, with clinically available multiecho gradient-recalled-echo (GRE) sequences for cardiac and liver imaging. A T2∗ single-echo GRE sequence was used as reference. Simulations were performed to assess accuracy and precision from 2000 measurements. Inter- and intraobserver variability was obtained in a patient study (n = 23). Results Simulations: Accuracy, in terms of the mean differences between the proposed method and true T2∗ ranged from 0-0.73 ms. Precision, in terms of confidence intervals of repeated measurements, was 0.06-4.74 ms showing agreement between the proposed uncertainty estimate and simulations. Phantom study: Bias and variability were 0.26 ± 4.23 ms (cardiac sequence) and -0.23 ± 1.69 ms (liver sequence). Patient study: Intraobserver variability was similar for experienced and inexperienced observers (0.03 ± 1.44 ms versus 0.16 ± 2.33 ms). Interobserver variability was 1.0 ± 3.77 ms for the heart and -0.52 ± 2.75 ms for the liver. Conclusion The proposed algorithm was shown to provide robust T2∗ measurements and uncertainty estimates over the range of clinically relevant T2∗ values. © 2015 The Authors. Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine

Bright-blood T2-weighted MRI has high diagnostic accuracy for myocardial hemorrhage in myocardial infarction: a preclinical validation study in swine

<p>Background: Myocardial hemorrhage after myocardial infarction (MI) usually goes undetected. We investigated the diagnostic accuracy of bright-blood T2-weighted cardiac MRI for myocardial hemorrhage in experimental MI.</p> <p>Methods and Results: MI was created in swine by occluding the left anterior descending (n=10) or circumflex (n=5) coronary arteries for 90 minutes followed by reperfusion for ≤3 days (n=2), 10 days (n=7), or 60 days (n=6). MRI was performed at 1.5 T, using bright-blood T2-prepared steady-state free-precession, T2* and early (1 minute) and late (10–15 minutes) gadolinium enhancement (EGE, LGE, respectively) MRI. Left ventricular sections and histology were assessed for hemorrhage by an experienced cardiac pathologist blinded to the MRI data. Hypointense regions on T2-weighted and contrast-enhanced MRI were independently determined by 3 cardiologists experienced in MRI who were also blinded to the pathology results. Eighty ventricular pathological sections were matched with MRI (n=68 for EGE MRI). All sections with evidence of MI (n=63, 79%) also exhibited hyperintense zones consistent with edema on T2-weighted MRI and infarct on LGE MRI. Myocardial hemorrhage occurred in 49 left ventricular sections (61%) and corresponded with signal voids on 48 T2-weighted (98%) and 26 LGE-MRI (53%). Alternatively, signal voids occurred in the absence of hemorrhage in 3 T2-weighted (90% specificity) and 5 LGE MRI (84% specificity). On EGE MRI, 27 of 43 cases of early microvascular obstruction corresponded with hemorrhage (63% sensitivity), whereas 5 of 25 defects occurred in the absence of hemorrhage (80% specificity). The positive and negative predictive values for pathological evidence of hemorrhage were 94% and 96% for T2-weighted, 84% and 55% for LGE MRI, and 85% and 56% for EGE MRI.</p> <p>Conclusions: Bright-blood T2-weighted MRI has high diagnostic accuracy for myocardial hemorrhage.</p&gt