Clinical Cardiovascular Applications of Hyperpolarized Magnetic Resonance

LncRNA MALAT1's role in the development of retinopathy: A review

Long noncoding RNA (lncRNA) metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) and retinopathy are 2 distinct yet interconnected areas of research in the field of ocular studies. MALAT1, with its diverse biological functions, has been extensively studied and demonstrated to play a role in various diseases, including ocular pathologies. Its involvement in alternative splicing regulation, transcriptional control, and the competing endogenous RNA (ceRNA) network suggests its potential implication in retinopathy. Retinopathy refers to a group of disorders that affect the retina, leading to vision impairment and, in severe cases, even blindness. These conditions include diabetic retinopathy, retinoblastoma, proliferative vitreoretinopathy, retinopathy of prematurity, and retinal neurodegeneration. The understanding of the molecular mechanisms underlying the development and progression of retinopathy, along with the potential involvement of MALAT1, can provide valuable insights for the diagnosis and treatment of this condition. Retinopathy, characterized by various manifestations and underlying mechanisms, presents a significant challenge in the field of ophthalmology. As a complex disease, its pathogenesis involves multifactorial factors, including angiogenic dysregulation, inflammatory responses, oxidative stress, and cellular signaling abnormalities. The emerging role of long noncoding RNA MALAT1 in retinopathy has attracted considerable attention. MALAT1 has been found to participate in multiple cellular processes, including alternative splicing regulation and transcriptional control. Additionally, the competing endogenous RNA (ceRNA) network involving MALAT1 indicates its potential relevance as a regulator in retinopathy. Further investigations into the specific mechanisms underlying MALAT1's involvement in retinopathy pathogenesis may provide valuable insights into the development of diagnostic and therapeutic approaches for managing retinal disorders.

3D quantitative myocardial perfusion imaging with hyperpolarized HP001(bis-1,1-(hydroxymethyl)-[1-13C]cyclopropane-d8): Application of gradient echo and balanced SSFP sequences

PURPOSE

This study aims to show the viability of conducting three-dimensional (3D) myocardial perfusion quantification covering the entire heart using both GRE and bSSFP sequences with hyperpolarized HP001.

METHODS

A GRE sequence and a bSSFP sequence, both with a stack-of-spirals readout, were designed and applied to three pigs. The images were reconstructed using  13 $$ {}^{13} $$ C coil sensitivity maps measured in a phantom experiment. Perfusion was quantified using a constrained decomposition method, and the estimated rest/stress perfusion values from  13 $$ {}^{13} $$ C GRE/bSSFP and Dynamic contrast-enhanced MRI (DCE-MRI) were individually analyzed through histograms and the mean perfusion values were compared with reference values obtained from PET(  15 $$ {}^{15} $$ O-water). The Myocardial Perfusion Reserve Index (MPRI) was estimated for  13 $$ {}^{13} $$ C GRE/bSSFP and DCE-MRI and compared with the reference values.

RESULTS

Perfusion values, estimated by both DCE and  13 $$ {}^{13} $$ C MRI, were found to be lower than reference values. However, DCE-MRI's estimated perfusion values were closer to the reference values than those obtained from  13 $$ {}^{13} $$ C MRI. In the case of MPRI estimation, the  13 $$ {}^{13} $$ C estimated MPRI values (GRE/bSSFP: 2.3/2.0) more closely align with the literature value (around 3) than the DCE estimated MPRI value (1.6).

CONCLUSION

This study demonstrated the feasibility of 3D whole-heart myocardial perfusion quantification using hyperpolarized HP001 with both GRE and bSSFP sequences. The  13 $$ {}^{13} $$ C perfusion measurements underestimated perfusion values compared to the  15 $$ {}^{15} $$ O PET literature value, while the  13 $$ {}^{13} $$ C estimated MPRI value aligned better with the literature. This preliminary result indicates  13 $$ {}^{13} $$ C imaging may more accurately estimate MPRI values compared to DCE-MRI.

Volumetric Patch-Based Super-Resolution Reconstruction of Hyperpolarized 13C Cardiac MRI

The achievable spatial resolution of 13C metabolic images acquired with hyperpolarized 13C-pyruvate is worse than 1H images typically by an order of magnitude due to the rapidly decaying hyperpolarized signals and the low gyromagnetic ratio of 13C. This study is to develop and characterize a volumetric patch-based super-resolution reconstruction algorithm that enhances spatial resolution 13C cardiac MRI by utilizing structural information from 1H MRI. The reconstruction procedure comprises anatomical segmentation from high-resolution 1H MRI, calculation of a patch-based weight matrix, and iterative reconstruction of high-resolution multi-slice 13C MRI. The method was tested with a multi-compartmental digital phantom for optimizing the patch size and an anthropomorphic cardiac MR phantom for validating the performance. Finally, the method was applied to human cardiac 13C images, acquired with an injection of hyperpolarized [1-13C]pyruvate. The phantom studies demonstrated that high-resolution multi-slice 13C images, reconstructed from a single-slice low-resolution input 13C image, retained the signal intensity range. The reconstruction accuracy was asymptotically improved as the patch size increased whereas intra-segmental spatial fluctuations were preserved better with smaller patches. However, a structurally non-identified tissue region was not restored regardless of the patch size. The cardiac MR phantom and the human cardiac images demonstrated improved spatial resolutions in the reconstructed images (10 × 10 × 30 mm3/voxel to 2 × 2 × 5 mm3/voxel). The volumetric patch-based super-resolution method reconstructs multi-slice high-resolution of 13C images, enhancing the cardiac structure, while preserving the quantitative accuracy. The proposed method is applicable to other multi-modal images that suffer from limited spatial resolution.

CMR to characterize myocardial structure and function in heart failure with preserved left ventricular ejection fraction

Despite remarkable progress in therapeutic drugs, morbidity, and mortality for heart failure (HF) remains high in developed countries. HF with preserved ejection fraction (HFpEF) now accounts for around half of all HF cases. It is a heterogeneous disease, with multiple aetiologies, and as such poses a significant diagnostic challenge. Cardiac magnetic resonance (CMR) has become a valuable non-invasive modality to assess cardiac morphology and function, but beyond that, the multi-parametric nature of CMR allows novel approaches to characterize haemodynamics and with magnetic resonance spectroscopy (MRS), the study of metabolism. Furthermore, exercise CMR, when combined with lung water imaging provides an in-depth understanding of the underlying pathophysiological and mechanistic processes in HFpEF. Thus, CMR provides a comprehensive phenotyping tool for HFpEF, which points towards a targeted and personalized therapy with improved diagnostics and prevention.

Review of Myocardial Ischemia, Scar, and Viability Estimation with Molecular Magnetic Resonance Imaging

BACKGROUND

Cardiovascular diseases, particularly myocardial ischemia from coronary artery obstruction, remain a leading cause of global morbidity. This review explores cardiac molecular magnetic resonance imaging (mMRI) and other molecular imaging techniques for the evaluation of myocardial ischemia, scarring, and viability.

RESULTS AND FINDINGS

mMRI imaging methods provide detailed information on myocardial ischemia, edema, and scar tissue using techniques like cine imaging, T1 and T2 mapping, and gadolinium-based contrast agents. These methods enable the precise assessment of the myocardial tissue properties, crucial in diagnosing and treating cardiovascular diseases. Advanced techniques, such as the T1ρ and RAFFn methods, might provide enhanced contrast and sensitivity for the detection of myocardial scarring without contrast agents. Molecular probes, including gadolinium-based and protein-targeted contrast agents, improve the detection of molecular changes, facilitating early diagnosis and personalized treatment. Integrating MRI with positron emission tomography (PET) combines the high spatial and temporal resolution with molecular and functional imaging.

CONCLUSION

Recent advancements in mMRI and molecular imaging have changed the evaluation of myocardial ischemia, scarring, and viability. Despite significant progress, extensive research is needed to validate these techniques clinically and further develop imaging methods for better diagnostic and prognostic outcomes.

Hyperpolarized Water for Coronary Artery Angiography and Whole-Heart Myocardial Perfusion Quantification

Purpose: Water freely diffuses across cell membranes, making it suitable for measuring absolute tissue perfusion. In this study, we introduce an imaging method for conducting coronary artery angiography and quantifying myocardial perfusion across the entire heart using hyperpolarized water. Methods:1H was hyperpolarized using dissolution dynamic nuclear polarization (dDNP) with UV-generated radicals. Submillimeter resolution coronary artery images were acquired as 2D projections using a spoiled GRE (SPGRE) sequence gated on diastole. Dynamic perfusion images were obtained with a multi-slice SPGRE with diastole gating, covering the entire heart. Perfusion values were analyzed through histograms, and the most frequent estimated perfusion value (the mode of the distribution), was compared with the average values for 15O water PET from the literature. Results: A liquid state polarization of 10% at the time of the injection and a 30 s T1 in D2O TRIS buffer were measured. Both coronary artery and dynamic perfusion images exhibited good quality. The main and small coronary artery branches were well resolved. The most frequent estimated perfusion value is around 0.6 mL/g/min, which is lower than the average values obtained from the literature for 15O-water PET (around 1.1 and 1.5 mL/g/min). Conclusions: The study successfully demonstrated the feasibility of achieving high-resolution, motion-free coronary artery angiography and 3D whole-heart quantitative myocardial perfusion using hyperpolarized water.

Delivering Robust Proton-Only Sensing of Hyperpolarized [1,2-13C2]-Pyruvate Using Broad-Spectral-Range Nuclear Magnetic Resonance Pulse Sequences

Hyperpolarized [1-13C]pyruvate is the leading hyperpolarized injectable contrast agent and is currently under evaluation in clinical trials for molecular imaging of metabolic diseases, including cardiovascular disease and cancer. One aspect limiting broad scalability of the technique is that hyperpolarized 13C MRI requires specialized 13C hardware and software that are not generally available on clinical MRI scanners, which employ proton-only detection. Here, we present an approach that uses pulse sequences to transfer 13C hyperpolarization to methyl protons for detection of the 13C-13C pyruvate singlet, employing proton-only excitation and detection only. The new pulse sequences are robust to the B1 and B0 magnetic field inhomogeneities. The work focuses on singlet-to-magnetization (S2M) and rotor-synchronized (R) pulses, both relying on trains of hard pulses with broad spectral width coverage designed to effectively transform hyperpolarized 13C2-singlet hyperpolarization to 1H polarization on the CH3 group of [1,2-13C2]pyruvate. This approach may enable a broader adoption of hyperpolarized MRI as a molecular imaging technique.

Proton-Only Sensing of Hyperpolarized [1,2-13C2]Pyruvate

Hyperpolarized MRI is emerging as a next-generation molecular imaging modality that can detect metabolic transformations in real time deep inside tissue and organs. 13C-hyperpolarized pyruvate is the leading hyperpolarized contrast agent that can probe cellular energetics in real time. Currently, hyperpolarized MRI requires specialized "multinuclear" MRI scanners that have the ability to excite and detect 13C signals. The objective of this work is the development of an approach that works on conventional (i.e., proton-only) MRI systems while taking advantage of long-lived 13C hyperpolarization. The long-lived singlet state of [1,2-13C2]pyruvate is hyperpolarized with parahydrogen in reversible exchange, and subsequently, the polarization is transferred from the 13C2 spin pair to the methyl protons of pyruvate for detection. This polarization transfer is accomplished with spin-lock induced crossing pulses that are only applied to the methyl protons yet access the hyperpolarization stored in the 13C2 singlet state. Theory and first experimental demonstrations are provided for our method, which obviates 13C excitation and detection for proton sensing of 13C-hyperpolarized pyruvate with an overall experimental-polarization transfer efficiency of ∼22% versus a theoretically predicted polarization transfer efficiency of 25%.

Insights Into the Metabolic Aspects of Aortic Stenosis With the Use of Magnetic Resonance Imaging

Pressure overload in aortic stenosis (AS) encompasses both structural and metabolic remodeling and increases the risk of decompensation into heart failure. A major component of metabolic derangement in AS is abnormal cardiac substrate use, with down-regulation of fatty acid oxidation, increased reliance on glucose metabolism, and subsequent myocardial lipid accumulation. These changes are associated with energetic and functional cardiac impairment in AS and can be assessed with the use of cardiac magnetic resonance spectroscopy (MRS). Proton MRS allows the assessment of myocardial triglyceride content and creatine concentration. Phosphorous MRS allows noninvasive in vivo quantification of the phosphocreatine-to-adenosine triphosphate ratio, a measure of cardiac energy status that is reduced in patients with severe AS. This review summarizes the changes to cardiac substrate and high-energy phosphorous metabolism and how they affect cardiac function in AS. The authors focus on the role of MRS to assess these metabolic changes, and potentially guide future (cellular) metabolic therapy in AS.

Metabolism of hyperpolarised [1-13 C]pyruvate in awake and anaesthetised rat brains

The use of hyperpolarised ¹³ C pyruvate for nononcological neurological applications has not been widespread so far, possibly due to delivery issues limiting the visibility of metabolites. First proof-of-concept results have indicated that metabolism can be detected in human brain, and this may supersede the results obtained in preclinical settings. One major difference between the experimental setups is that preclinical MRI/MRS routinely uses anaesthesia, which alters both haemodynamics and metabolism. Here, we used hyperpolarised [1-¹³ C]pyruvate to compare brain metabolism in awake rats and under isoflurane, urethane or medetomidine anaesthesia. Spectroscopic [1-¹³ C]pyruvate time courses measured sequentially showed that pyruvate-to-bicarbonate and pyruvate-to-lactate labelling rates were lower in isoflurane animals than awake animals. An increased bicarbonate-to-lactate ratio was observed in the medetomidine group compared with other groups. The study shows that hyperpolarised [1-¹³ C]pyruvate experiments can be performed in awake rats, thus avoiding anaesthesia-related issues. The results suggest that haemodynamics probably dominate the observed pyruvate-to-metabolite labelling rates and area-under-time course ratios of referenced to pyruvate. On the other hand, the results obtained with medetomidine suggest that the ratios are also modulated by the underlying cerebral metabolism. However, the ratios between intracellular metabolites were unchanged in awake compared with isoflurane-anaesthetised rats.

Temperature Cycling Enables Efficient 13C SABRE-SHEATH Hyperpolarization and Imaging of [1-13C]-Pyruvate

Molecular metabolic imaging in humans is dominated by positron emission tomography (PET). An emerging nonionizing alternative is hyperpolarized MRI of 13C-pyruvate, which is innocuous and has a central role in metabolism. However, similar to PET, hyperpolarized MRI with dissolution dynamic nuclear polarization (d-DNP) is complex costly, and requires significant infrastructure. In contrast, Signal Amplification By Reversible Exchange (SABRE) is a fast, cheap, and scalable hyperpolarization technique. SABRE in SHield Enables Alignment Transfer to Heteronuclei (SABRE-SHEATH) can transfer polarization from parahydrogen to 13C in pyruvate; however, polarization levels remained low relative to d-DNP (1.7% with SABRE-SHEATH versus ≈60% with DNP). Here we introduce a temperature cycling method for SABRE-SHEATH that enables >10% polarization on [1-13C]-pyruvate, sufficient for successful in vivo experiments. First, at lower temperatures, ≈20% polarization is accumulated on SABRE catalyst-bound pyruvate, which is released into free pyruvate at elevated temperatures. A kinetic model of differential equations is developed that explains this effect and characterizes critical relaxation and buildup parameters. With the large polarization, we demonstrate the first 13C pyruvate images with a cryogen-free MRI system operated at 1.5 T, illustrating that inexpensive hyperpolarization methods can be combined with low-cost MRI systems to obtain a broadly available, yet highly sensitive metabolic imaging platform.

Schulte R, Laustsen C. Comprehensive Literature Review of Hyperpolarized Carbon-13 MRI: The Road to Clinical Application

This review provides a comprehensive assessment of the development of hyperpolarized (HP) carbon-13 metabolic MRI from the early days to the present with a focus on clinical applications. The status and upcoming challenges of translating HP carbon-13 into clinical application are reviewed, along with the complexity, technical advancements, and future directions. The road to clinical application is discussed regarding clinical needs and technological advancements, highlighting the most recent successes of metabolic imaging with hyperpolarized carbon-13 MRI. Given the current state of hyperpolarized carbon-13 MRI, the conclusion of this review is that the workflow for hyperpolarized carbon-13 MRI is the limiting factor.

The use of hyperpolarised 13C-MRI in clinical body imaging to probe cancer metabolism

Metabolic reprogramming is one of the hallmarks of cancer and includes the Warburg effect, which is exhibited by many tumours. This can be exploited by positron emission tomography (PET) as part of routine clinical cancer imaging. However, an emerging and alternative method to detect altered metabolism is carbon-13 magnetic resonance imaging (MRI) following injection of hyperpolarised [1-13C]pyruvate. The technique increases the signal-to-noise ratio for the detection of hyperpolarised 13C-labelled metabolites by several orders of magnitude and facilitates the dynamic, noninvasive imaging of the exchange of 13C-pyruvate to 13C-lactate over time. The method has produced promising preclinical results in the area of oncology and is currently being explored in human imaging studies. The first translational studies have demonstrated the safety and feasibility of the technique in patients with prostate, renal, breast and pancreatic cancer, as well as revealing a successful response to treatment in breast and prostate cancer patients at an earlier stage than multiparametric MRI. This review will focus on the strengths of the technique and its applications in the area of oncological body MRI including noninvasive characterisation of disease aggressiveness, mapping of tumour heterogeneity, and early response assessment. A comparison of hyperpolarised 13C-MRI with state-of-the-art multiparametric MRI is likely to reveal the unique additional information and applications offered by the technique.

Hyperpolarized 13 C magnetic resonance imaging for noninvasive assessment of tissue inflammation

Inflammation is a central mechanism underlying numerous diseases and incorporates multiple known and potential future therapeutic targets. However, progress in developing novel immunomodulatory therapies has been slowed by a need for improvement in noninvasive biomarkers to accurately monitor the initiation, development and resolution of immune responses as well as their response to therapies. Hyperpolarized magnetic resonance imaging (MRI) is an emerging molecular imaging technique with the potential to assess immune cell responses by exploiting characteristic metabolic reprogramming in activated immune cells to support their function. Using specific metabolic tracers, hyperpolarized MRI can be used to produce detailed images of tissues producing lactate, a key metabolic signature in activated immune cells. This method has the potential to further our understanding of inflammatory processes across different diseases in human subjects as well as in preclinical models. This review discusses the application of hyperpolarized MRI to the imaging of inflammation, as well as the progress made towards the clinical translation of this emerging technique.

Metabolic and Molecular Imaging of the Diabetic Cardiomyopathy

The term diabetic cardiomyopathy is defined as the presence of abnormalities in myocardial structure and function that occur in the absence of, or in addition to, well-established cardiovascular risk factors. A key contributor to this abnormal structural-functional relation is the complex interplay of myocardial metabolic remodeling, defined as the loss the flexibility in myocardial substrate metabolism and its downstream detrimental effects, such as mitochondrial dysfunction, inflammation, and fibrosis. In parallel with the growth in understanding of these biological underpinnings has been developmental advances in imaging tools such as positron emission tomography and magnetic resonance imaging and spectroscopy that permit the detection and in many cases quantification, of the processes that typifies the myocardial metabolic remodeling in diabetic cardiomyopathy. The imaging readouts can be obtained in both preclinical models of diabetes mellitus and patients with diabetes mellitus facilitating the bi-directional movement of information between bench and bedside. Moreover, imaging biomarkers provided by these tools are now being used to enhance discovery and development of therapies designed to reduce the myocardial effects of diabetes mellitus through metabolic modulation. In this review, the use of these imaging tools in the patient with diabetes mellitus from a mechanistic, therapeutic effect, and clinical management perspective will be discussed.