Prediction of experimental cardiac magnetostimulation thresholds using pig-specific body models

PURPOSE

Modern high-amplitude gradient systems can be limited by the International Electrotechnical Commission 60601-2-33 cardiac stimulation (CS) limit, which was set in a conservative manner based on electrode experiments and E-field simulations in uniform ellipsoidal body models. Here, we show that coupled electromagnetic-electrophysiological modeling in detailed body and heart models can predict CS thresholds, suggesting that such modeling might lead to more detailed threshold estimates in humans. Specifically, we compare measured and predicted CS thresholds in eight pigs.

METHODS

We created individualized porcine body models using MRI (Dixon for the whole body, CINE for the heart) that replicate the anatomy and posture of the animals used in our previous experimental CS study. We model the electric fields induced along cardiac Purkinje and ventricular muscle fibers and predict the electrophysiological response of these fibers, yielding CS threshold predictions in absolute units for each animal. Additionally, we assess the total modeling uncertainty through a variability analysis of the 25 main model parameters.

RESULTS

Predicted and experimental CS thresholds agree within 19% on average (normalized RMS error), which is smaller than the 27% modeling uncertainty. No significant difference was found between the modeling predictions and experiments (p < 0.05, paired t-test).

CONCLUSION

Predicted thresholds matched the experimental data within the modeling uncertainty, supporting the model validity. We believe that our modeling approach can be applied to study CS thresholds in humans for various gradient coils, body shapes/postures, and waveforms, which is difficult to do experimentally.

Dynamics of Collagen Oxidation and Cross Linking in Regenerating and Irreversibly Infarcted Myocardium

In mammalian hearts myocardial infarction produces a permanent collagen-rich scar. Conversely, in zebrafish a collagen-rich scar forms but is completely resorbed as the myocardium regenerates. The formation of cross-links in collagen hinders its degradation but cross-linking has not been well characterized in zebrafish hearts. Here, a library of fluorescent probes to quantify collagen oxidation, the first step in collagen cross-link (CCL) formation, was developed. Myocardial injury in mice or zebrafish resulted in similar dynamics of collagen oxidation in the myocardium in the first month after injury. However, during this time, mature CCLs such as pyridinoline and deoxypyridinoline developed in the murine infarcts but not in the zebrafish hearts. High levels of newly oxidized collagen were still seen in murine scars with mature CCLs. These data suggest that fibrogenesis remains dynamic, even in mature scars, and that the absence of mature CCLs in zebrafish hearts may facilitate their ability to regenerate.

Measurement of magnetostimulation thresholds in the porcine heart

PURPOSE

Powerful MRI gradient systems can surpass the International Electrotechnical Commission (IEC) 60601-2-33 limit for cardiac stimulation (CS), which was determined by simple electromagnetic simulations and electrode stimulation experiments. Only a few canine studies measured magnetically induced CS thresholds in vivo and extrapolating them to human safety limits can be challenging.

METHODS

We measured cardiac magnetostimulation thresholds in 10 healthy, anesthetized pigs using capacitors discharged into a flat spiral coil to produce damped sinusoidal waveforms with effective stimulus duration ts,eff  = 0.45 ms. Electrocardiography (ECG), blood pressure, and peripheral oximetry signals were recorded to determine threshold coil currents yielding cardiac capture. Dixon and CINE MR volumes from each animal were segmented to generate porcine-specific electromagnetic models to calculate dB/dt and E-field values in the porcine heart at threshold. For comparison, we also simulated maximum dB/dt and E-field values created by three MRI gradient systems in the heart of a human body model.

RESULTS

The average dB/dt threshold estimated in the porcine heart was 1.66 ± 0.23 kT/s, which is 11-fold greater than the IEC dB/dt limit at ts,eff  = 0.45 ms, and 31-fold greater than the maximum value created by the investigated MRI gradients in the human heart. The average E-field threshold estimated in the porcine heart was 92.9 ± 13.5 V/m, which is 6-fold greater than the IEC E-field limit at ts,eff  = 0.45 ms and 37-fold greater than the maximum gradient-induced E-field in the human heart.

CONCLUSION

This first measurement of cardiac magnetostimulation thresholds in pigs indicates that the IEC cardiac safety limit is conservative for the investigated stimulus duration (ts,eff  = 0.45 ms).

A nanoparticle probe for the imaging of autophagic flux in live mice via magnetic resonance and near-infrared fluorescence

Autophagy-the lysosomal degradation of cytoplasmic components via their sequestration into double-membraned autophagosomes-has not been detected non-invasively. Here we show that the flux of autophagosomes can be measured via magnetic resonance imaging or serial near-infrared fluorescence imaging of intravenously injected iron oxide nanoparticles decorated with cathepsin-cleavable arginine-rich peptides functionalized with the near-infrared fluorochrome Cy5.5 (the peptides facilitate the uptake of the nanoparticles by early autophagosomes, and are then cleaved by cathepsins in lysosomes). In the heart tissue of live mice, the nanoparticles enabled quantitative measurements of changes in autophagic flux, upregulated genetically, by ischaemia-reperfusion injury or via starvation, or inhibited via the administration of a chemotherapeutic or the antibiotic bafilomycin. In mice receiving doxorubicin, pre-starvation improved cardiac function and overall survival, suggesting that bursts of increased autophagic flux may have cardioprotective effects during chemotherapy. Autophagy-detecting nanoparticle probes may facilitate the further understanding of the roles of autophagy in disease.

Neutrophils incite and macrophages avert electrical storm after myocardial infarction

Sudden cardiac death, arising from abnormal electrical conduction, occurs frequently in patients with coronary heart disease. Myocardial ischemia simultaneously induces arrhythmia and massive myocardial leukocyte changes. In this study, we optimized a mouse model in which hypokalemia combined with myocardial infarction triggered spontaneous ventricular tachycardia in ambulatory mice, and we showed that major leukocyte subsets have opposing effects on cardiac conduction. Neutrophils increased ventricular tachycardia via lipocalin-2 in mice, whereas neutrophilia associated with ventricular tachycardia in patients. In contrast, macrophages protected against arrhythmia. Depleting recruited macrophages in Ccr2 -/- mice or all macrophage subsets with Csf1 receptor inhibition increased both ventricular tachycardia and fibrillation. Higher arrhythmia burden and mortality in Cd36 -/- and Mertk -/- mice, viewed together with reduced mitochondrial integrity and accelerated cardiomyocyte death in the absence of macrophages, indicated that receptor-mediated phagocytosis protects against lethal electrical storm. Thus, modulation of leukocyte function provides a potential therapeutic pathway for reducing the risk of sudden cardiac death.

Biomedical Imaging in Experimental Models of Cardiovascular Disease

Major advances in biomedical imaging have occurred over the last 2 decades and now allow many physiological, cellular, and molecular processes to be imaged noninvasively in small animal models of cardiovascular disease. Many of these techniques can be also used in humans, providing pathophysiological context and helping to define the clinical relevance of the model. Ultrasound remains the most widely used approach, and dedicated high-frequency systems can obtain extremely detailed images in mice. Likewise, dedicated small animal tomographic systems have been developed for magnetic resonance, positron emission tomography, fluorescence imaging, and computed tomography in mice. In this article, we review the use of ultrasound and positron emission tomography in small animal models, as well as emerging contrast mechanisms in magnetic resonance such as diffusion tensor imaging, hyperpolarized magnetic resonance, chemical exchange saturation transfer imaging, magnetic resonance elastography and strain, arterial spin labeling, and molecular imaging.

Validation of cardiac diffusion tensor imaging sequences: A multicentre test-retest phantom study

Cardiac diffusion tensor imaging (DTI) is an emerging technique for the in vivo characterisation of myocardial microstructure, and there is a growing need for its validation and standardisation. We sought to establish the accuracy, precision, repeatability and reproducibility of state-of-the-art pulse sequences for cardiac DTI among 10 centres internationally. Phantoms comprising 0%-20% polyvinylpyrrolidone (PVP) were scanned with DTI using a product pulsed gradient spin echo (PGSE; N = 10 sites) sequence, and a custom motion-compensated spin echo (SE; N = 5) or stimulated echo acquisition mode (STEAM; N = 5) sequence suitable for cardiac DTI in vivo. A second identical scan was performed 1-9 days later, and the data were analysed centrally. The average mean diffusivities (MDs) in 0% PVP were (1.124, 1.130, 1.113) x 10^-3  mm² /s for PGSE, SE and STEAM, respectively, and accurate to within 1.5% of reference data from the literature. The coefficients of variation in MDs across sites were 2.6%, 3.1% and 2.1% for PGSE, SE and STEAM, respectively, and were similar to previous studies using only PGSE. Reproducibility in MD was excellent, with mean differences in PGSE, SE and STEAM of (0.3 ± 2.3, 0.24 ± 0.95, 0.52 ± 0.58) x 10^-5  mm² /s (mean ± 1.96 SD). We show that custom sequences for cardiac DTI provide accurate, precise, repeatable and reproducible measurements. Further work in anisotropic and/or deforming phantoms is warranted.

Detection and Characterization of Thrombosis in Humans Using Fibrin-Targeted Positron Emission Tomography and Magnetic Resonance

OBJECTIVES

The authors present a novel technique to detect and characterize LAA thrombus in humans using combined positron emission tomography (PET)/cardiac magnetic resonance (CMR) of a fibrin-binding radiotracer, [⁶⁴Cu]FBP8.

BACKGROUND

The detection of thrombus in the left atrial appendage (LAA) is vital in the prevention of stroke and is currently performed using transesophageal echocardiography (TEE).

METHODS

The metabolism and pharmacokinetics of [⁶⁴Cu]FBP8 were studied in 8 healthy volunteers. Patients with atrial fibrillation and recent TEEs of the LAA (positive n = 12, negative n = 12) were injected with [⁶⁴Cu]FBP8 and imaged with PET/CMR, including mapping the longitudinal magnetic relaxation time (T₁) in the LAA.

RESULTS

[⁶⁴Cu]FBP8 was stable to metabolism and was rapidly eliminated. The maximum standardized uptake value (SUV_Max) in the LAA was significantly higher in the TEE-positive than TEE-negative subjects (median of 4.0 [interquartile range (IQR): 3.0-6.0] vs 2.3 [IQR: 2.1-2.5]; P < 0.001), with an area under the receiver-operating characteristic curve of 0.97. An SUV_Max threshold of 2.6 provided a sensitivity of 100% and specificity of 84%. The minimum T₁ (T_1Min) in the LAA was 970 ms (IQR: 780-1,080 ms) vs 1,380 ms (IQR: 1,120-1,620 ms) (TEE positive vs TEE negative; P < 0.05), with some overlap between the groups. Logistic regression using SUV_Max and T_1Min allowed all TEE-positive and TEE-negative subjects to be classified with 100% accuracy.

CONCLUSIONS

PET/CMR of [⁶⁴Cu]FBP8 is able to detect acute as well as older platelet-poor thrombi with excellent accuracy. Furthermore, the integrated PET/CMR approach provides useful information on the biological properties of thrombus such as fibrin and methemoglobin content. (Imaging of LAA Thrombosis; NCT03830320).

Cardiac Alterations on 3T MRI in Young Adults With Sedentary Lifestyle-Related Risk Factors

Background

Young adult populations with the sedentary lifestyle-related risk factors overweight, hypertension, and type 2 diabetes (T2D) are growing, and associated cardiac alterations could overlap early findings in non-ischemic cardiomyopathy on cardiovascular MRI. We aimed to investigate cardiac morphology, function, and tissue characteristics for these cardiovascular risk factors.

Methods

Non-athletic non-smoking asymptomatic adults aged 18-45 years were prospectively recruited and underwent 3Tesla cardiac MRI. Multivariate linear regression was performed to investigate independent associations of risk factor-related parameters with cardiac MRI values.

Results

We included 311 adults (age, 32 ± 7 years; men, 49%). Of them, 220 subjects had one or multiple risk factors, while 91 subjects were free of risk factors. For overweight, increased body mass index (per SD = 5.3 kg/m2) was associated with increased left ventricular (LV) mass (+7.3 g), biventricular higher end-diastolic (LV, +8.6 ml), and stroke volumes (SV; +5.0 ml), higher native T1 (+7.3 ms), and lower extracellular volume (ECV, -0.38%), whereas the higher waist-hip ratio was associated with lower biventricular volumes. Regarding hypertension, increased systolic blood pressure (per SD = 14 mmHg) was associated with increased LV mass (+6.9 g), higher LV ejection fraction (EF; +1.0%), and lower ECV (-0.48%), whereas increased diastolic blood pressure was associated with lower LV EF. In T2D, increased HbA1c (per SD = 9.0 mmol/mol) was associated with increased LV mass (+2.2 g), higher right ventricular end-diastolic volume (+3.2 ml), and higher ECV (+0.27%). Increased heart rate was linked with decreased LV mass, lower biventricular volumes, and lower T2 values.

Conclusions

Young asymptomatic adults with overweight, hypertension, and T2D show subclinical alterations in cardiac morphology, function, and tissue characteristics. These alterations should be considered in cardiac MRI-based clinical decision making.

Manifold-based respiratory phase estimation enables motion and distortion correction of free-breathing cardiac diffusion tensor MRI

PURPOSE

For in vivo cardiac DTI, breathing motion and B₀ field inhomogeneities produce misalignment and geometric distortion in diffusion-weighted (DW) images acquired with conventional single-shot EPI. We propose using a dimensionality reduction method to retrospectively estimate the respiratory phase of DW images and facilitate both distortion correction (DisCo) and motion compensation.

METHODS

Free-breathing electrocardiogram-triggered whole left-ventricular cardiac DTI using a second-order motion-compensated spin echo EPI sequence and alternating directionality of phase encoding blips was performed on 11 healthy volunteers. The respiratory phase of each DW image was estimated after projecting the DW images into a 2D space with Laplacian eigenmaps. DisCo and motion compensation were applied to the respiratory sorted DW images. The results were compared against conventional breath-held T₂ half-Fourier single shot turbo spin echo. Cardiac DTI parameters including fractional anisotropy, mean diffusivity, and helix angle transmurality were compared with and without DisCo.

RESULTS

The left-ventricular geometries after DisCo and motion compensation resulted in significantly improved alignment of DW images with T₂ reference. DisCo reduced the distance between the left-ventricular contours by 13.2% ± 19.2%, P < .05 (2.0 ± 0.4 for DisCo and 2.4 ± 0.5 mm for uncorrected). DisCo DTI parameter maps yielded no significant differences (mean diffusivity: 1.55 ± 0.13 × 10^-3 mm² /s and 1.53 ± 0.13 × 10^-3 mm² /s, P = .09; fractional anisotropy: 0.375 ± 0.041 and 0.379 ± 0.045, P = .11; helix angle transmurality: 1.00% ± 0.10°/% and 0.99% ± 0.12°/%, P = .44), although the orientation of individual tensors differed.

CONCLUSION

Retrospective respiratory phase estimation with LE-based DisCo and motion compensation in free-breathing cardiac DTI resulting in significantly reduced geometric distortion and improved alignment within and across slices.

Accelerated in Vivo Cardiac Diffusion-Tensor MRI Using Residual Deep Learning-based Denoising in Participants with Obesity

Purpose

To develop and assess a residual deep learning algorithm to accelerate in vivo cardiac diffusion-tensor MRI (DT-MRI) by reducing the number of averages while preserving image quality and DT-MRI parameters.

Materials and Methods

In this prospective study, a denoising convolutional neural network (DnCNN) for DT-MRI was developed; a total of 26 participants, including 20 without obesity (body mass index [BMI] < 30 kg/m²; mean age, 28 years ± 3 [standard deviation]; 11 women) and six with obesity (BMI ≥ 30 kg/m²; mean age, 48 years ± 11; five women), were recruited from June 19, 2019, to July 29, 2020. DT-MRI data were constructed at four averages (4Av), two averages (2Av), and one average (1Av) without and with the application of the DnCNN (4Av_DnCNN, 2Av_DnCNN, 1Av_DnCNN). All data were compared against the reference DT-MRI data constructed at eight averages (8Av). Image quality, characterized by using the signal-to-noise ratio (SNR) and structural similarity index (SSIM), and the DT-MRI parameters of mean diffusivity (MD), fractional anisotropy (FA), and helix angle transmurality (HAT) were quantified.

Results

No differences were found in image quality or DT-MRI parameters between the accelerated 4Av_DnCNN DT-MRI and the reference 8Av DT-MRI data for the SNR (29.1 ± 2.7 vs 30.5 ± 2.9), SSIM (0.97 ± 0.01), MD (1.3 µm²/msec ± 0.1 vs 1.31 µm²/msec ± 0.11), FA (0.32 ± 0.05 vs 0.30 ± 0.04), or HAT (1.10°/% ± 0.13 vs 1.11°/% ± 0.09). The relationship of a higher MD and lower FA and HAT in individuals with obesity compared with individuals without obesity in reference 8Av DT-MRI measurements was retained in 4Av_DnCNN and 2Av_DnCNN DT-MRI measurements but was not retained in 4Av or 2Av DT-MRI measurements.

Conclusion

Cardiac DT-MRI can be performed at an at least twofold-accelerated rate by using DnCNN to preserve image quality and DT-MRI parameter quantification.Keywords: Adults, Cardiac, Obesity, Technology Assessment, MR-Diffusion Tensor Imaging, Heart, Tissue CharacterizationSupplemental material is available for this article.© RSNA, 2021.

Optimized 64-channel array configurations for accelerated simultaneous multislice acquisitions in 3T cardiac MRI

PURPOSE

Three 64-channel cardiac coils with different detector array configurations were designed and constructed to evaluate acceleration capabilities in simultaneous multislice (SMS) imaging for 3T cardiac MRI.

METHODS

Three 64-channel coil array configurations obtained from a simulation-guided design approach were constructed and systematically evaluated regarding their encoding capabilities for accelerated SMS cardiac acquisitions at 3T. Array configuration A_Uni-sized consists of uniformly distributed equally sized loops in an overlapped arrangement, B_Gapped uses a gapped array design with symmetrically distributed equally sized loops, and C_Dense has non-uniform loop density and size, where smaller elements were centered over the heart and larger elements were placed surrounding the target region. To isolate the anatomic variation from differences in the coil configurations, all three array coils were built with identical semi-adjustable housing segments. The arrays' performance was compared using bench-level measurements and imaging performance tests, including signal-to-noise ratio (SNR) maps, array element noise correlation, and SMS acceleration capabilities. Additionally, all cardiac array coils were evaluated on a healthy volunteer.

RESULTS

The array configuration C_Dense with the non-uniformly distributed loop density showed the best overall cardiac imaging performance in both SNR and SMS encoding power, when compared to the other constructed arrays. The diffusion weighted cardiac acquisitions on a healthy volunteer support the favorable accelerated SNR performance of this array configuration.

CONCLUSION

Our results indicate that optimized highly parallel cardiac arrays, such as the 64-channel coil with a non-uniform loop size and density improve highly accelerated SMS cardiac MRI in comparison to symmetrically distributed loop array designs.

Free-breathing diffusion tensor MRI of the whole left ventricle using second-order motion compensation and multitasking respiratory motion correction

PURPOSE

We aimed to develop a novel free-breathing cardiac diffusion tensor MRI (DT-MRI) approach, M2-MT-MOCO, capable of whole left ventricular coverage that leverages second-order motion compensation (M2) diffusion encoding and multitasking (MT) framework to efficiently correct for respiratory motion (MOCO).

METHODS

Imaging was performed in 16 healthy volunteers and 3 heart failure patients with symptomatic dyspnea. The healthy volunteers were scanned to compare the accuracy of interleaved multislice coverage of the entire left ventricle with a single-slice acquisition and the accuracy of the free-breathing conventional MOCO and MT-MOCO approaches with reference breath-hold DT-MRI. Mean diffusivity (MD), fractional anisotropy (FA), helix angle transmurality (HAT), and intrascan repeatability were quantified and compared.

RESULTS

In all subjects, free-breathing M2-MT-MOCO DT-MRI yielded DWI of the entire left ventricle without bulk motion-induced signal loss. No significant differences were seen in the global values of MD, FA, and HAT in the multislice and single-slice acquisitions. Furthermore, global quantification of MD, FA, and HAT were also not significantly different between the MT-MOCO and breath-hold, whereas conventional MOCO yielded significant differences in MD, FA, and HAT with MT-MOCO and FA with breath-hold. In heart failure patients, M2-MT-MOCO DT-MRI was feasible yielding higher MD, lower FA, and lower HAT compared with healthy volunteers. Substantial agreement was found between repeated scans across all subjects for MT-MOCO.

CONCLUSION

M2-MT-MOCO enables free-breathing DT-MRI of the entire left ventricle in 10 min, while preserving quantification of myocardial microstructure compared to breath-held and single-slice acquisitions and is feasible in heart failure patients.

Magnetic Resonance-Based Characterization of Myocardial Architecture

Advances in technology have made it possible to image the microstructure of the heart with diffusion-weighted magnetic resonance. The technique provides unique insights into the cellular architecture of the myocardium and how this is perturbed in a range of disease contexts. In this review, the physical basis of diffusion MRI and the challenges of implementing it in the beating heart are discussed. Cutting edge acquisition and analysis techniques, as well as the results of initial clinical studies, are reported.

Correction to: Cardiovascular magnetic resonance native T2 and T2* quantitative values for cardiomyopathies and heart transplantations: a systematic review and meta-analysis

An amendment to this paper has been published and can be accessed via the original article.

Validation of thoracic aortic dimensions on ECG-triggered SSFP as alternative to contrast-enhanced MRA

Objectives

Assessment of thoracic aortic dimensions with non-ECG-triggered contrast-enhanced magnetic resonance angiography (CE-MRA) is accompanied with motion artefacts and requires gadolinium. To avoid both motion artefacts and gadolinium administration, we evaluated the similarity and reproducibility of dimensions measured on ECG-triggered, balanced steady-state free precession (SSFP) MRA as alternative to CE-MRA.

Methods

All patients, with varying medical conditions, referred for thoracic aortic examination between September 2016 and March 2018, who underwent non-ECG-triggered CE-MRA and SSFP-MRA (1.5 T) were retrospectively included (n = 30). Aortic dimensions were measured after double-oblique multiplanar reconstruction by two observers at nine landmarks predefined by literature guidelines. Image quality was scored at the sinus of Valsalva, mid-ascending aorta and mid-descending aorta by semi-automatically assessing the vessel sharpness.

Results

Aortic dimensions showed high agreement between non-ECG-triggered CE-MRA and SSFP-MRA (r = 0.99, p < 0.05) without overestimation or underestimation of aortic dimensions in SSFP-MRA (mean difference, 0.1 mm; limits of agreement, − 1.9 mm and 1.9 mm). Intra- and inter-observer variabilities were significantly smaller with SSFP-MRA for the sinus of Valsalva and sinotubular junction. Image quality of the sinus of Valsalva was significantly better with SSFP-MRA, as fewer images were of impaired quality (3/30) than in CE-MRA (21/30). Reproducibility of dimensions was significantly better in images scored as good quality compared to impaired quality in both sequences.

Conclusions

Thoracic aortic dimensions measured on SSFP-MRA and non-ECG-triggered CE-MRA were similar. As expected, SSFP-MRA showed better reproducibility close to the aortic root because of lesser motion artefacts, making it a feasible non-contrast imaging alternative.

Key Points

• SSFP-MRA provides similar dimensions as non-ECG-triggered CE-MRA.

• Intra- and inter-observer reproducibilities improve for the sinus of Valsalva and sinotubular junction with SSFP-MRA.

• ECG-triggered SSFP-MRA shows better image quality for landmarks close to the aortic root in the absence of cardiac motion.

Electronic supplementary material

The online version of this article (10.1007/s00330-020-06963-x) contains supplementary material, which is available to authorized users.

Cardiovascular magnetic resonance native T2 and T2* quantitative values for cardiomyopathies and heart transplantations: a systematic review and meta-analysis

BACKGROUND

The clinical application of cardiovascular magnetic resonance (CMR) T2 and T2* mapping is currently limited as ranges for healthy and cardiac diseases are poorly defined. In this meta-analysis we aimed to determine the weighted mean of T2 and T2* mapping values in patients with myocardial infarction (MI), heart transplantation, non-ischemic cardiomyopathies (NICM) and hypertension, and the standardized mean difference (SMD) of each population with healthy controls. Additionally, the variation of mapping outcomes between studies was investigated.

METHODS

The PRISMA guidelines were followed after literature searches on PubMed and Embase. Studies reporting CMR T2 or T2* values measured in patients were included. The SMD was calculated using a random effects model and a meta-regression analysis was performed for populations with sufficient published data.

RESULTS

One hundred fifty-four studies, including 13,804 patient and 4392 control measurements, were included. T2 values were higher in patients with MI, heart transplantation, sarcoidosis, systemic lupus erythematosus, amyloidosis, hypertrophic cardiomyopathy (HCM), dilated cardiomyopathy (DCM) and myocarditis (SMD of 2.17, 1.05, 0.87, 1.39, 1.62, 1.95, 1.90 and 1.33, respectively, P <  0.01) compared with controls. T2 values in iron overload patients (SMD = - 0.54, P = 0.30) and Anderson-Fabry disease patients (SMD = 0.52, P = 0.17) did both not differ from controls. T2* values were lower in patients with MI and iron overload (SMD of - 1.99 and - 2.39, respectively, P <  0.01) compared with controls. T2* values in HCM patients (SMD = - 0.61, P = 0.22), DCM patients (SMD = - 0.54, P = 0.06) and hypertension patients (SMD = - 1.46, P = 0.10) did not differ from controls. Multiple CMR acquisition and patient demographic factors were assessed as significant covariates, thereby influencing the mapping outcomes and causing variation between studies.

CONCLUSIONS

The clinical utility of T2 and T2* mapping to distinguish affected myocardium in patients with cardiomyopathies or heart transplantation from healthy myocardium seemed to be confirmed based on this meta-analysis. Nevertheless, variation of mapping values between studies complicates comparison with external values and therefore require local healthy reference values to clinically interpret quantitative values. Furthermore, disease differentiation seems limited, since changes in T2 and T2* values of most cardiomyopathies are similar.

Blood Oxygen Level-Dependent MRI of the Myocardium with Multiecho Gradient-Echo Spin-Echo Imaging

Background Myocardial oxygenation imaging could help determine the presence of microvascular dysfunction associated with increased cardiovascular risk. However, it is challenging to depict the potentially small oxygenation alterations with current noninvasive cardiac MRI blood oxygen level-dependent (BOLD) techniques. Purpose To demonstrate the cardiac application of a gradient-echo spin-echo (GESE) echo-planar imaging sequence for dynamic and quantitative heartbeat-to-heartbeat BOLD MRI and evaluate the sequence in populations both healthy and with hypertension in combination with a breath hold-induced CO2 intervention. Materials and Methods GESE echo-planar imaging sequence was performed in 18 healthy participants and in eight prospectively recruited participants with hypertension on a 3.0-T MRI system. T2 and T2* maps were calculated per heartbeat with a four-parameter fitting technique. Septal regions of interests were used to determine T2 and T2* values per heartbeat and examined over the course of a breath hold to determine BOLD changes. T2 and T2* changes of healthy participants and participants with hypertension were compared by using a nonparametric Mann-Whitney test. Results GESE echo-planar imaging approach gave spatially stable T2 and T2* maps per heartbeat for healthy participants and participants with hypertension, with mean T2 values of 43 msec ± 5 (standard deviation) and 46 msec ± 9, respectively, and mean T2* values of 28 msec ± 5 and 22 msec ± 5, respectively. The healthy participants exhibited increasing T2 and T2* values over the course of a breath hold with a mean positive slope of 0.2 msec per heartbeat ± 0.1 for T2 and 0.2 msec per heartbeat ± 0.1 for T2*, whereas for participants with hypertension these dynamic T2 and T2* values had a mean negative slope of -0.2 msec per heartbeat ± 0.2 for T2 and -0.1 msec per heartbeat ± 0.2 for T2*. The difference in these mean slopes between healthy participants and participants with hypertension was significant for both T2 (P < .001) and T2* (P < .001). Conclusion Gradient-echo spin-echo echo-planar imaging sequence provided quantitative T2 and T2* maps per heartbeat and enabled dynamic heartbeat-to-heartbeat blood oxygen level-dependent (BOLD)-response imaging by analyzing changes in T2 and T2* over the time of a breath-hold intervention. This approach could identify differences in the BOLD response between healthy participants and participants with hypertension. © RSNA, 2020 Online supplemental material is available for this article. See also the editorial by Friedrich in this issue.

Imaging the Vascular Bone Marrow Niche During Inflammatory Stress

RATIONALE

Inflammatory stress induced by exposure to bacterial lipopolysaccharide causes hematopoietic stem cell expansion in the bone marrow niche, generating a cellular immune response. As an integral component of the hematopoietic stem cell niche, the bone marrow vasculature regulates the production and release of blood leukocytes, which protect the host against infection but also fuel inflammatory diseases.

OBJECTIVE

We aimed to develop imaging tools to explore vascular changes in the bone marrow niche during acute inflammation.

METHODS AND RESULTS

Using the TLR (Toll-like receptor) ligand lipopolysaccharide as a prototypical danger signal, we applied multiparametric, multimodality and multiscale imaging to characterize how the bone marrow vasculature adapts when hematopoiesis boosts leukocyte supply. In response to lipopolysaccharide, ex vivo flow cytometry and histology showed vascular changes to the bone marrow niche. Specifically, proliferating endothelial cells gave rise to new vasculature in the bone marrow during hypoxic conditions. We studied these vascular changes with complementary intravital microscopy and positron emission tomography/magnetic resonance imaging. Fluorescence and positron emission tomography integrin αVβ3 imaging signal increased during lipopolysaccharide-induced vascular remodeling. Vascular leakiness, quantified by albumin-based in vivo microscopy and magnetic resonance imaging, rose when neutrophils departed and hematopoietic stem and progenitor cells proliferated more vigorously.

CONCLUSIONS

Introducing a tool set to image bone marrow either with cellular resolution or noninvasively within the entire skeleton, this work sheds light on angiogenic responses that accompany emergency hematopoiesis. Understanding and monitoring bone marrow vasculature may provide a key to unlock therapeutic targets regulating systemic inflammation.

Abstract 434: Acidifying Nanoparticle Upregulates Autophagy and Enhances Cardiomyocyte Survival after Chemotherapy

Introduction: Chemotherapy-induced cardiotoxicity remains prevalent and deadly, with no effective therapy to slow the progression to irreversible heart failure, which in the case of doxorubicin (Dox) can reach 50% mortality. Dox impact on cardiomyocytes (CMs) is multifocal, including oxidative stress, lysosome alkalinization, and apoptosis. PLGAs, poly(DL-lactide-co-glycolide), are FDA-approved polymers, form defined nanoparticles (NPs). We hypothesize that PLGA NPs target the lysosomal compartments, restore lysosomal acidity after Dox, and confer cardioprotective effects.

Methods: We synthesized fluorescent PLGA NPs by click chemistry. In H9C2 myocytes exposed to 1-5 μM of Dox +/- 1 mg/ml of PLGA, we measured cell viability (MTT), lysosomal pH (OG-514), mitochondrial membrane potential (JC-1), and autophagy proteins (western blot). We further co-injected C57Bl6 mice with PLGA (10 mg/kg, i.v.) and Dox (15 mg/kg, i.p.), to image apoptosis (Annexin) and autophagy (cathepsin-activatable autophagy probe, ADN, unpublished) after 24 hrs, or 4 mg/kg Dox weekly, 5x, i.p. and echo after 3-4 weeks.

Results: PLGA NPs formulated are of controlled size and valency, emits near-infrared fluorescence (Fig. A). In H9C2s, PLGA significantly improved survival after Dox (Fig. B), acidified lysosomes (Fig. C), did not impact cell energetics (Fig. D), and further restored autophagic flux (Fig. E). Imaging in Dox mice revealed significant apoptosis reduction and autophagy activation (Fig. F-H), and cardiac function recovery (Fig. I).

Conclusions: PLGA NPs may represent a novel class of cardioprotective therapeutics of early chemotherapy stress, and with translational potential.

Multiplexed Optical Imaging of Energy Substrates Reveals That Left Ventricular Hypertrophy Is Associated With Brown Adipose Tissue Activation

BACKGROUND

Substrate utilization in tissues with high energetic requirements could play an important role in cardiometabolic disease. Current techniques to assess energetics are limited by high cost, low throughput, and the inability to resolve multiple readouts simultaneously. Consequently, we aimed to develop a multiplexed optical imaging platform to simultaneously assess energetics in multiple organs in a high throughput fashion.

METHODS AND RESULTS

The detection of 18F-Fluordeoxyglucose uptake via Cerenkov luminescence and free fatty acid uptake with a fluorescent C₁₆ free fatty acid was tested. Simultaneous uptake of these agents was measured in the myocardium, brown/white adipose tissue, and skeletal muscle in mice with/without thoracic aortic banding. Within 5 weeks of thoracic aortic banding, mice developed left ventricular hypertrophy and brown adipose tissue activation with upregulation of β₃AR (β₃ adrenergic receptors) and increased natriuretic peptide receptor ratio. Imaging of brown adipose tissue 15 weeks post thoracic aortic banding revealed an increase in glucose (P<0.01) and free fatty acid (P<0.001) uptake versus controls and an increase in uncoupling protein-1 (P<0.01). Similar but less robust changes were seen in skeletal muscle, while substrate uptake in white adipose tissue remained unchanged. Myocardial glucose uptake was increased post-thoracic aortic banding but free fatty acid uptake trended to decrease.

CONCLUSIONS

A multiplexed optical imaging technique is presented that allows substrate uptake to be simultaneously quantified in multiple tissues in a high throughput manner. The activation of brown adipose tissue occurs early in the onset of left ventricular hypertrophy, which produces tissue-specific changes in substrate uptake that may play a role in the systemic response to cardiac pressure overload.

Alteration in ventricular pressure stimulates cardiac repair and remodeling

The mammalian heart undergoes complex structural and functional remodeling to compensate for stresses such as pressure overload. While studies suggest that, at best, the adult mammalian heart is capable of very limited regeneration arising from the proliferation of existing cardiomyocytes, how myocardial stress affects endogenous cardiac regeneration or repair is unknown. To define the relationship between left ventricular afterload and cardiac repair, we induced left ventricle pressure overload in adult mice by constriction of the ascending aorta (AAC). One week following AAC, we normalized ventricular afterload in a subset of animals through removal of the aortic constriction (de-AAC). Subsequent monitoring of cardiomyocyte cell cycle activity via thymidine analog labeling revealed that an acute increase in ventricular afterload induced cardiomyocyte proliferation. Intriguingly, a release in ventricular overload (de-AAC) further increases cardiomyocyte proliferation. Following both AAC and de-AAC, thymidine analog-positive cardiomyocytes exhibited characteristics of newly generated cardiomyocytes, including single diploid nuclei and reduced cell size as compared to age-matched, sham-operated adult mouse myocytes. Notably, those smaller cardiomyocytes frequently resided alongside one another, consistent with local stimulation of cellular proliferation. Collectively, our data demonstrate that adult cardiomyocyte proliferation can be locally stimulated by an acute increase or decrease of ventricular pressure, and this mode of stimulation can be harnessed to promote cardiac repair.

Motion-Induced Signal Loss in In Vivo Cardiac Diffusion-Weighted Imaging

LEVEL OF EVIDENCE

5 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2020;51:319-320.

Myocardial Scar Delineation Using Diffusion Tensor Magnetic Resonance Tractography

Background

Late gadolinium enhancement (LGE) is the current standard for myocardial scar delineation. In this study, we introduce the tractographic propagation angle (PA), a metric of myofiber curvature (degrees/unit distance) derived from diffusion tensor imaging (DTI), and compare its use to LGE and invasive scar assessment by endocardial voltage mapping.

Methods and Results

DTI was performed on 7 healthy human volunteers, 5 patients with myocardial infarction, 6 normal mice, and 7 mice with myocardial infarction. LGE to delineate the infarct and border zones was performed with a 2‐dimensional inversion recovery gradient‐echo sequence. Ex vivo DTI was performed on 5 normal human and 5 normal sheep hearts. Endocardial electroanatomic mapping and subsequent ex vivo DTI was performed on 5 infarcted sheep hearts. PA in the normal human hearts varied smoothly and was generally <4. The mean PA in the infarct zone was significantly elevated (10.34±1.02 versus 4.05±0.45, P<0.05). Regions with a PA ≤4 consistently had a bipolar voltage ≥1.5 mV, whereas those with PA values between 4 and 10 had voltages between 0.5 and 1.5 mV. A PA threshold >4 was the most accurate DTI‐derived measure of infarct size and demonstrated the greatest correlation with LGE (r=0.95).

Conclusions

We found a strong correlation between infarct size by PA and LGE in both mice and humans. There was also an inverse relationship between PA values and endocardial voltage. The use of PA may enable myocardial scar delineation and characterization of arrhythmogenic substrate without the need for exogenous contrast agents.

Cardiac macrophages promote diastolic dysfunction

Hulsmans et al. show that cardiac macrophages expand in left ventricular diastolic dysfunction, a hallmark of heart failure with preserved ejection fraction (HFpEF) and cardiac aging. In HFpEF, macrophages shift toward a profibrotic subset that promotes ventricular stiffness.

Macrophages populate the healthy myocardium and, depending on their phenotype, may contribute to tissue homeostasis or disease. Their origin and role in diastolic dysfunction, a hallmark of cardiac aging and heart failure with preserved ejection fraction, remain unclear. Here we show that cardiac macrophages expand in humans and mice with diastolic dysfunction, which in mice was induced by either hypertension or advanced age. A higher murine myocardial macrophage density results from monocyte recruitment and increased hematopoiesis in bone marrow and spleen. In humans, we observed a parallel constellation of hematopoietic activation: circulating myeloid cells are more frequent, and splenic ¹⁸F-FDG PET/CT imaging signal correlates with echocardiographic indices of diastolic dysfunction. While diastolic dysfunction develops, cardiac macrophages produce IL-10, activate fibroblasts, and stimulate collagen deposition, leading to impaired myocardial relaxation and increased myocardial stiffness. Deletion of IL-10 in macrophages improves diastolic function. These data imply expansion and phenotypic changes of cardiac macrophages as therapeutic targets for cardiac fibrosis leading to diastolic dysfunction.

Highly potent visnagin derivatives inhibit Cyp1 and prevent doxorubicin cardiotoxicity

Anthracyclines such as doxorubicin are highly effective chemotherapy agents used to treat many common malignancies. However, their use is limited by cardiotoxicity. We previously identified visnagin as protecting against doxorubicin toxicity in cardiac but not tumor cells. In this study, we sought to develop more potent visnagin analogs in order to use these analogs as tools to clarify the mechanisms of visnagin-mediated cardioprotection. Structure-activity relationship studies were performed in a zebrafish model of doxorubicin cardiomyopathy. Movement of the 5-carbonyl to the 7 position and addition of short ester side chains led to development of visnagin analogs with 1,000-fold increased potency in zebrafish and 250-fold increased potency in mice. Using proteomics, we discovered that doxorubicin caused robust induction of Cytochrome P450 family 1 (CYP1) that was mitigated by visnagin and its potent analog 23. Treatment with structurally divergent CYP1 inhibitors, as well as knockdown of CYP1A, prevented doxorubicin cardiomyopathy in zebrafish. The identification of potent cardioprotective agents may facilitate the development of new therapeutic strategies for patients receiving cardiotoxic chemotherapy. Moreover, these studies support the idea that CYP1 is an important contributor to doxorubicin cardiotoxicity and suggest that modulation of this pathway could be beneficial in the clinical setting.

Native T1 reference values for nonischemic cardiomyopathies and populations with increased cardiovascular risk: A systematic review and meta-analysis

Background

Although cardiac MR and T₁ mapping are increasingly used to diagnose diffuse fibrosis based cardiac diseases, studies reporting T₁ values in healthy and diseased myocardium, particular in nonischemic cardiomyopathies (NICM) and populations with increased cardiovascular risk, seem contradictory.

Purpose

To determine the range of native myocardial T₁ value ranges in patients with NICM and populations with increased cardiovascular risk.

Study Type

Systemic review and meta‐analysis.

Population

Patients with NICM, including hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy (DCM), and patients with myocarditis (MC), iron overload, amyloidosis, Fabry disease, and populations with hypertension (HT), diabetes mellitus (DM), and obesity.

Field Strength/Sequence

(Shortened) modified Look–Locker inversion‐recovery MR sequence at 1.5 or 3T.

Assessment

PubMed and Embase were searched following the PRISMA guidelines.

Statistical Tests

The summary of standard mean difference (SMD) between the diseased and a healthy control populations was generated using a random‐effects model in combination with meta‐regression analysis.

Results

The SMD for HCM, DCM, and MC patients were significantly increased (1.41, 1.48, and 1.96, respectively, P < 0.01) compared with healthy controls. The SMD for HT patients with and without left‐ventricle hypertrophy (LVH) together was significantly increased (0.19, P = 0.04), while for HT patients without LVH the SMD was zero (0.03, P = 0.52). The number of studies on amyloidosis, iron overload, Fabry disease, and HT patients with LVH did not meet the requirement to perform a meta‐analysis. However, most studies reported a significantly increased T₁ for amyloidosis and HT patients with LVH and a significant decreased T₁ for iron overload and Fabry disease patients.

Data Conclusions

Native T₁ mapping by using an (Sh)MOLLI sequence can potentially assess myocardial changes in HCM, DCM, MC, iron overload, amyloidosis, and Fabry disease compared to controls. In addition, it can help to diagnose left‐ventricular remodeling in HT patients.

Level of Evidence: 2

Technical Efficacy: Stage 3

J. Magn. Reson. Imaging 2018;47:891–912.

A Manganese-based Alternative to Gadolinium: Contrast-enhanced MR Angiography, Excretion, Pharmacokinetics, and Metabolism

Purpose To compare intravascular contrast enhancement produced by the manganese-based magnetic resonance (MR) imaging contrast agent manganese-N-picolyl-N,N',N'-trans-1,2-cyclohexenediaminetriacetate (Mn-PyC3A) to gadopentetate dimeglumine (Gd-DTPA) and to evaluate the excretion, pharmacokinetics, and metabolism of Mn-PyC3A. Materials and Methods Contrast material-enhanced MR angiography was performed in baboons (Papio anubis; n = 4) by using Mn-PyC3A and Gd-DTPA. Dynamic imaging was performed for 60 minutes following Mn-PyC3A injection to monitor distribution and elimination. Serial blood sampling was performed to quantify manganese and gadolinium plasma clearance by using inductively coupled plasma mass spectrometry and to characterize Mn-PyC3A metabolism by using high-performance liquid chromatography. Intravascular contrast enhancement in the abdominal aorta and brachiocephalic artery was quantified by measuring contrast-to-noise ratios (CNRs) versus muscle at 9 seconds following Mn-PyC3A or Gd-DTPA injection. Plasma pharmacokinetics were modeled with a biexponential function, and data were compared with a paired t test. Results Aorta versus muscle CNR (mean ± standard deviation) with Mn-PyC3A and Gd-DTPA was 476 ± 77 and 538 ± 120, respectively (P = .11). Brachiocephalic artery versus muscle CNR was 524 ± 55 versus 518 ± 140, respectively (P = .95). Mn-PyC3A was eliminated via renal and hepatobiliary excretion with similar pharmacokinetics to Gd-DTPA (area under the curve between 0 and 30 minutes, 20.2 ± 3.1 and 17.0 ± 2.4, respectively; P = .23). High-performance liquid chromatography revealed no evidence of Mn-PyC3A biotransformation. Conclusion Mn-PyC3A enables contrast-enhanced MR angiography with comparable contrast enhancement to gadolinium-based agents and may overcome concerns regarding gadolinium-associated toxicity and retention. ^© RSNA, 2017 Online supplemental material is available for this article.

Microstructural characterization of myocardial infarction with optical coherence tractography and two-photon microscopy

Myocardial infarction leads to complex changes in the fiber architecture of the heart. Here, we present a novel optical approach to characterize these changes in intact hearts in three dimensions. Optical coherence tomography (OCT) was used to derive a depth‐resolved field of orientation on which tractography was performed. Tractography of healthy myocardium revealed a smooth linear transition in fiber inclination or helix angle from the epicardium to endocardium. Conversely, in infarcted hearts, no coherent microstructure could be identified in the infarct with OCT. Additional characterization of the infarct was performed by the measurement of light attenuation and with two‐photon microscopy. Myofibers were imaged using autofluorescence and collagen fibers using second harmonic generation. This revealed the presence of two distinct microstructural patterns in areas of the infarct with high light attenuation. In the presence of residual myofibers, the surrounding collagen fibers were aligned in a coherent manner parallel to the myofibers. In the absence of residual myofibers, the collagen fibers were randomly oriented and lacked any microstructural coherence. The presence of residual myofibers thus exerts a profound effect on the microstructural properties of the infarct scar and consequently the risk of aneurysm formation and arrhythmias. Catheter‐based approaches to segment and image myocardial microstructure in humans are feasible and could play a valuable role in guiding the development of strategies to improve infarct healing.

Uncoupling of the profibrotic and hemostatic effects of thrombin in lung fibrosis

Fibrotic lung disease, most notably idiopathic pulmonary fibrosis (IPF), is thought to result from aberrant wound-healing responses to repetitive lung injury. Increased vascular permeability is a cardinal response to tissue injury, but whether it is mechanistically linked to lung fibrosis is unknown. We previously described a model in which exaggeration of vascular leak after lung injury shifts the outcome of wound-healing responses from normal repair to pathological fibrosis. Here we report that the fibrosis produced in this model is highly dependent on thrombin activity and its downstream signaling pathways. Direct thrombin inhibition with dabigatran significantly inhibited protease-activated receptor-1 (PAR1) activation, integrin αvβ6 induction, TGF-β activation, and the development of pulmonary fibrosis in this vascular leak-dependent model. We used a potentially novel imaging method - ultashort echo time (UTE) lung magnetic resonance imaging (MRI) with the gadolinium-based, fibrin-specific probe EP-2104R - to directly visualize fibrin accumulation in injured mouse lungs, and to correlate the antifibrotic effects of dabigatran with attenuation of fibrin deposition. We found that inhibition of the profibrotic effects of thrombin can be uncoupled from inhibition of hemostasis, as therapeutic anticoagulation with warfarin failed to downregulate the PAR1/αvβ6/TGF-β axis or significantly protect against fibrosis. These findings have direct and important clinical implications, given recent findings that warfarin treatment is not beneficial in IPF, and the clinical availability of direct thrombin inhibitors that our data suggest could benefit these patients.

Evaluation of antitumor activity and cardiac toxicity of a bone-targeted ph-sensitive liposomal formulation in a bone metastasis tumor model in mice

Chemotherapy for bone tumors is a major challenge because of the inability of therapeutics to penetrate dense bone mineral. We hypothesize that a nanostructured formulation with high affinity for bone could deliver drug to the tumor while minimizing off-target toxicity. Here, we evaluated the efficacy and toxicity of a novel bone-targeted, pH-sensitive liposomal formulation containing doxorubicin in an animal model of bone metastasis. Biodistribution studies with the liposome showed good uptake in tumor, but low accumulation of doxorubicin in the heart. Mice treated with the bone-targeted liposome formulation showed a 70% reduction in tumor volume, compared to 35% reduction for free doxorubicin at the same dose. Both cardiac toxicity and overall mortality were significantly lower for animals treated with the bone-targeted liposomes compared to free drug. Bone-targeted, pH-sensitive, doxorubicin containing liposomes represent a promising approach to selectively delivering doxorubicin to bone tumors while minimizing cardiac toxicity.

Diffusion MRI in the heart

Diffusion MRI provides unique information on the structure, organization, and integrity of the myocardium without the need for exogenous contrast agents. Diffusion MRI in the heart, however, has proven technically challenging because of the intrinsic non-rigid deformation during the cardiac cycle, displacement of the myocardium due to respiratory motion, signal inhomogeneity within the thorax, and short transverse relaxation times. Recently developed accelerated diffusion-weighted MR acquisition sequences combined with advanced post-processing techniques have improved the accuracy and efficiency of diffusion MRI in the myocardium. In this review, we describe the solutions and approaches that have been developed to enable diffusion MRI of the heart in vivo, including a dual-gated stimulated echo approach, a velocity- (M1 ) or an acceleration- (M2 ) compensated pulsed gradient spin echo approach, and the use of principal component analysis filtering. The structure of the myocardium and the application of these techniques in ischemic heart disease are also briefly reviewed. The advent of clinical MR systems with stronger gradients will likely facilitate the translation of cardiac diffusion MRI into clinical use. The addition of diffusion MRI to the well-established set of cardiovascular imaging techniques should lead to new and complementary approaches for the diagnosis and evaluation of patients with heart disease. © 2015 The Authors. NMR in Biomedicine published by John Wiley & Sons Ltd.

Theranostic Nucleic Acid Binding Nanoprobe Exerts Anti-inflammatory and Cytoprotective Effects in Ischemic Injury

Extracellular nucleic acids are proinflammatory molecules that have been implicated in a diverse range of diseases. We report here the development of a multivalent nucleic acid scavenging nanoprobe, where the fluorochrome thiazole orange (TO) is conjugated to a polymeric 40 kDa dextran carrier. Dextran-TO (Dex-TO) has nanomolar affinity for mammalian and bacterial nucleic acids and attenuates the production of inflammatory cytokines from activated macrophages exposed to DNA and RNA. Mice with myocardial ischemia reperfusion that were treated with Dex-TO showed a decrease in myocardial macrophage infiltration at 24 hours (p<0.05) and a decrease in infarct size (18% ± 9%, p<0.01) on day 7. Dex-TO allows sites of injury to be identified with fluorescence imaging, while simultaneously exerting an anti-inflammatory and cytoprotective effect. Dex-TO could be of significant diagnostic and therapeutic (theranostic) utility in a broad range of conditions including ischemia, trauma, burns, sepsis and autoimmune disease.

Diffusion Tractography of the Entire Left Ventricle by Using Free-breathing Accelerated Simultaneous Multisection Imaging

Purpose To develop a clinically feasible whole-heart free-breathing diffusion-tensor (DT) magnetic resonance (MR) imaging approach with an imaging time of approximately 15 minutes to enable three-dimensional (3D) tractography. Materials and Methods The study was compliant with HIPAA and the institutional review board and required written consent from the participants. DT imaging was performed in seven healthy volunteers and three patients with pulmonary hypertension by using a stimulated echo sequence. Twelve contiguous short-axis sections and six four-chamber sections that covered the entire left ventricle were acquired by using simultaneous multisection (SMS) excitation with a blipped-controlled aliasing in parallel imaging readout. Rate 2 and rate 3 SMS excitation was defined as two and three times accelerated in the section axis, respectively. Breath-hold and free-breathing images with and without SMS acceleration were acquired. Diffusion-encoding directions were acquired sequentially, spatiotemporally registered, and retrospectively selected by using an entropy-based approach. Myofiber helix angle, mean diffusivity, fractional anisotropy, and 3D tractograms were analyzed by using paired t tests and analysis of variance. Results No significant differences (P > .63) were seen between breath-hold rate 3 SMS and free-breathing rate 2 SMS excitation in transmural myofiber helix angle, mean diffusivity (mean ± standard deviation, [0.89 ± 0.09] × 10^-3 mm²/sec vs [0.9 ± 0.09] × 10^-3 mm²/sec), or fractional anisotropy (0.43 ± 0.05 vs 0.42 ± 0.06). Three-dimensional tractograms of the left ventricle with no SMS and rate 2 and rate 3 SMS excitation were qualitatively similar. Conclusion Free-breathing DT imaging of the entire human heart can be performed in approximately 15 minutes without section gaps by using SMS excitation with a blipped-controlled aliasing in parallel imaging readout, followed by spatiotemporal registration and entropy-based retrospective image selection. This method may lead to clinical translation of whole-heart DT imaging, enabling broad application in patients with cardiac disease. ^© RSNA, 2016 Online supplemental material is available for this article.

Functional and anatomical characterization of brown adipose tissue in heart failure with blood oxygen level dependent magnetic resonance

Recent studies have suggested that brown adipose tissue (BAT) plays an important role in obesity, insulin resistance and heart failure. The characterization of BAT in vivo, however, has been challenging. No technique to comprehensively image BAT anatomy and function has been described. Moreover, the impact on BAT of the neuroendocrine activation seen in heart failure has only recently begun to be evaluated in vivo. The aim of this study was to use MRI to characterize the impact of heart failure on the morphology and function of BAT. Mice subjected to permanent ligation of the left coronary artery were imaged with MRI 6 weeks later. T2 weighted MRI of BAT volume and blood oxygen level dependent MRI of BAT function were performed. T2 * maps of BAT were obtained at multiple time points before and after administration of the β3 adrenergic agonist CL 316 243 (CL). Blood flow to BAT was studied after CL injection using the flow alternating inversion recovery (FAIR) approach. Excised BAT tissue was analyzed for lipid droplet content and for uncoupling protein 1 (UCP1) mRNA expression. BAT volume was significantly lower in heart failure (51 ± 1 mm(3) versus 65 ± 3 mm(3) ; p < 0.05), and characterized by a reduction in lipid globules and a fourfold increase in UCP1 mRNA (p < 0.05). CL injection increased BAT T2 * in healthy animals but not in mice with heart failure (24 ± 4% versus 6 ± 2%; p < 0.01), consistent with an increase in flow in control BAT. This was confirmed by a significant difference in the FAIR response in BAT in control and heart failure mice. Heart failure results in the chronic activation of BAT, decreased BAT lipid stores and decreased BAT volume, and it is associated with a marked decrease in ability to respond to acute physiological stimuli. This may have important implications for substrate utilization and overall metabolic homeostasis in heart failure. Copyright © 2016 John Wiley & Sons, Ltd.

Visnagin protects against doxorubicin-induced cardiomyopathy through modulation of mitochondrial malate dehydrogenase

Doxorubicin is a highly effective anticancer chemotherapy agent, but its use is limited by its cardiotoxicity. To develop a drug that prevents this toxicity, we established a doxorubicin-induced cardiomyopathy model in zebrafish that recapitulates the cardiomyocyte apoptosis and contractility decline observed in patients. Using this model, we screened 3000 compounds and found that visnagin (VIS) and diphenylurea (DPU) rescue the cardiac performance and circulatory defects caused by doxorubicin in zebrafish. VIS and DPU reduced doxorubicin-induced apoptosis in cultured cardiomyocytes and in vivo in zebrafish and mouse hearts. VIS treatment improved cardiac contractility in doxorubicin-treated mice. Further, VIS and DPU did not reduce the chemotherapeutic efficacy of doxorubicin in several cultured tumor lines or in zebrafish and mouse xenograft models. Using affinity chromatography, we found that VIS binds to mitochondrial malate dehydrogenase (MDH2), a key enzyme in the tricarboxylic acid cycle. As with VIS, treatment with the MDH2 inhibitors mebendazole, thyroxine, and iodine prevented doxorubicin cardiotoxicity, as did treatment with malate itself, suggesting that modulation of MDH2 activity is responsible for VIS' cardioprotective effects. Thus, VIS and DPU are potent cardioprotective compounds, and MDH2 is a previously undescribed, druggable target for doxorubicin-induced cardiomyopathy.

Heat-Induced Radiolabeling of Nanoparticles for Monocyte Tracking by PET

Heat-induced radiolabeling (HIR) yielded (89) Zr-Feraheme (FH) nanoparticles (NPs) that were used to determine NP pharmacokinetics (PK) by positron emission tomography (PET). Standard uptake values indicated a fast hepatic uptake that corresponded to blood clearance, and a second, slow uptake process by lymph nodes and spleen. By cytometry, NPs were internalized by circulating monocytes and monocytes in vitro. Using an IV injection of HIR (89) Zr-FH (rather than in vitro cell labeling), PET/PK provided a view of monocyte trafficking, a key component of the immune response.