Rapid T1 quantification based on 3D phase sensitive inversion recovery

<p>Abstract</p> <p>Background</p> <p>In Contrast Enhanced Magnetic Resonance Imaging fibrotic myocardium can be distinguished from healthy tissue using the difference in the longitudinal <it>T</it>₁relaxation after administration of Gadolinium, the so-called Late Gd Enhancement. The purpose of this work was to measure the myocardial absolute <it>T</it>₁post-Gd from a single breath-hold 3D Phase Sensitivity Inversion Recovery sequence (PSIR). Equations were derived to take the acquisition and saturation effects on the magnetization into account.</p> <p>Methods</p> <p>The accuracy of the method was investigated on phantoms and using simulations. The method was applied to a group of patients with suspected myocardial infarction where the absolute difference in relaxation of healthy and fibrotic myocardium was measured at about 15 minutes post-contrast. The evolution of the absolute <it>R</it>₁relaxation rate (1/<it>T</it>₁) over time after contrast injection was followed for one patient and compared to <it>T</it>₁mapping using Look-Locker. Based on the <it>T</it>₁maps synthetic LGE images were reconstructed and compared to the conventional LGE images.</p> <p>Results</p> <p>The fitting algorithm is robust against variation in acquisition flip angle, the inversion delay time and cardiac arrhythmia. The observed relaxation rate of the myocardium is 1.2 s^-1, increasing to 6 - 7 s^-1after contrast injection and decreasing to 2 - 2.5 s^-1for healthy myocardium and to 3.5 - 4 s^-1for fibrotic myocardium. Synthesized images based on the <it>T</it>₁maps correspond very well to actual LGE images.</p> <p>Conclusions</p> <p>The method provides a robust quantification of post-Gd <it>T</it>₁relaxation for a complete cardiac volume within a single breath-hold.</p

Magnetic resonance multitasking for motion-resolved quantitative cardiovascular imaging.

Quantitative cardiovascular magnetic resonance (CMR) imaging can be used to characterize fibrosis, oedema, ischaemia, inflammation and other disease conditions. However, the need to reduce artefacts arising from body motion through a combination of electrocardiography (ECG) control, respiration control, and contrast-weighting selection makes CMR exams lengthy. Here, we show that physiological motions and other dynamic processes can be conceptualized as multiple time dimensions that can be resolved via low-rank tensor imaging, allowing for motion-resolved quantitative imaging with up to four time dimensions. This continuous-acquisition approach, which we name cardiovascular MR multitasking, captures - rather than avoids - motion, relaxation and other dynamics to efficiently perform quantitative CMR without the use of ECG triggering or breath holds. We demonstrate that CMR multitasking allows for T1 mapping, T1-T2 mapping and time-resolved T1 mapping of myocardial perfusion without ECG information and/or in free-breathing conditions. CMR multitasking may provide a foundation for the development of setup-free CMR imaging for the quantitative evaluation of cardiovascular health

Hybrid-State Free Precession in Nuclear Magnetic Resonance

The dynamics of large spin-1/2 ensembles in the presence of a varying magnetic field are commonly described by the Bloch equation. Most magnetic field variations result in unintuitive spin dynamics, which are sensitive to small deviations in the driving field. Although simplistic field variations can produce robust dynamics, the captured information content is impoverished. Here, we identify adiabaticity conditions that span a rich experiment design space with tractable dynamics. These adiabaticity conditions trap the spin dynamics in a one-dimensional subspace. Namely, the dynamics is captured by the absolute value of the magnetization, which is in a transient state, while its direction adiabatically follows the steady state. We define the hybrid state as the co-existence of these two states and identify the polar angle as the effective driving force of the spin dynamics. As an example, we optimize this drive for robust and efficient quantification of spin relaxation times and utilize it for magnetic resonance imaging of the human brain

Evaluation and Validation of clinical 4.23 T sodium MRI in animals and human: Application of oblique multi-slice spin-echo pulse sequence

Objective: Application of high-field 4.23 T MRI clinical imager was demonstrated for sodium-magnetic resonance imaging (MRI) data acquisition. Primary hypothesis: Sodium [Na] in brain is MR visible. Secondary hypothesis was, if, application of multislice spin echo (MSSE) pulse sequence at selected scan parameters can sufficiently visualize the total sodium signal as indicator of sub-clinical activity. Material and Methods: MSSE pulse sequence technique was used to simulate sodium images of human brain. For validation purpose, inversion recovery pulse sequence was validated by optimization of scan inversion time (TI). Phantom of sodium and rat brain were imaged. Sodium images were validated and compared with proton MRI images. Results: MSSE pulse technique enabled to visualize the sodium signal at optimized scan parameters. Specifically, MSSE pulse technique enabled the identification of different sodium rich areas due to their subphysiological activity in the brain, comparable with proton MRI images. Reconstruction images of brain further enhanced the power to classify the brain tissue. Intracellular sodium images of agarose-saline solution filled-tube phantom were generated by use of inversion recovery pulse sequence. Conclusion: Using MSSE pulse sequence at 4.23 T, in vivo sodium images can be generated within acceptable scan time for routine clinical brain examination for achieving better sub-physiological information as obtained from proton MRI

T2 and T2⁎ mapping and weighted imaging in cardiac MRI

Cardiac imaging is progressing from simple imaging of heart structure and function to techniques visualizing and measuring underlying tissue biological changes that can potentially define disease and therapeutic options. These techniques exploit underlying tissue magnetic relaxation times: T1, T2 and T2*. Initial weighting methods showed myocardial heterogeneity, detecting regional disease. Current methods are now fully quantitative generating intuitive color maps that do not only expose regionality, but also diffuse changes – meaning that between-scan comparisons can be made to define disease (compared to normal) and to monitor interval change (compared to old scans). T1 is now familiar and used clinically in multiple scenarios, yet some technical challenges remain. T2 is elevated with increased tissue water – edema. Should there also be blood troponin elevation, this edema likely reflects inflammation, a key biological process. T2* falls in the presence of magnetic/paramagnetic materials – practically, this means it measures tissue iron, either after myocardial hemorrhage or in myocardial iron overload. This review discusses how T2 and T2⁎ imaging work (underlying physics, innovations, dependencies, performance), current and emerging use cases, quality assurance processes for global delivery and future research directions

Technological innovations in magnetic resonance for early detection of cardiovascular diseases

Most recent technical innovations in cardiovascular MR imaging (CMRI) are presented in this review. They include hardware and software developments, and novelties in parametric mapping. All these recent improvements lead to high spatial and temporal resolution and quantitative information on the heart structure and function. They make it achievable ambitious goals in the field of mapletic resonance, such as the early detection of cardiovascular pathologies. In this review article, we present recent innovations in CMRI, emphasizing the progresses performed and the solutions proposed to some yet opened technical problems

Myocardial t1 Mapping Techniques for Quantification of Myocardial Fibrosis

Identifying and quantifying diffuse myocardial fibrosis is important to provide insights into the relationship between myocardial fibrosis, diastolic and systolic dysfunction, as well as clinical outcomes. T1 mapping is a promising technique for noninvasively identifying diffuse myocardial fibrosis in heart failure. A quantitative T1 map provides sensitivity to the full range of T1 values and is advantageous over the traditional T1-weighted imaging by reducing the reliance on visual interpretation of the signal intensity in the myocardium. However, in-vivo myocardial T1 quantification is challenging because of cardiac and respiratory motion. During the past few years, a variety of T1 mapping techniques, including the modified Look Locker inversion recovery (MOLLI) sequence, have been developed and optimized to measure the myocardial T1 value. Importantly, there have been significant differences between the T1 values determined by various methods, and several aspects of T1 mapping are incompletely understood. The accuracy of T1 mapping is sensitive to several confounding factors, such as the types of T1 mapping acquisition sequence and individual physiologic parameters. It also remains unclear if myocardial T1 values are constant throughout the cardiac cycle or the cyclic variation from the error of the variable flip angle (VFA) technique. Lastly, it is necessary to validate these techniques against the endomyocardial biopsy. The work intends to validate several aspects of T1 mapping. Firstly, whether there is significant cyclic variation of myocardial T1 at 1.5T was assessed in healthy volunteers and patients without myocardial disease. Secondly, a fast 3D DFA technique with B1 correction was developed to measure T1 comparably with gold standard in a wide range of T1 values, which showed it is necessary to incorporate B1 correction at 3T. Thirdly, Look Locker and MOLLI were compared to evaluate their agreement and difference in 3 patient groups precontrast and postcontrast situations. Finally, the T1 mapping te