Systolic cardiac function is typically preserved in obese adults, potentially masking underlying declines in cardiomyocyte metabolism that may contribute to heart failure. We used chemical exchange saturation transfer (CEST) MRI, a sensitive method for measurement of myocardial creatine, to examine whether myocardial creatine levels correlate with cardiac structure, contractile function, or visceral fat mass in obese adults. In this study, obese (body mass index, BMI > 30, n = 20) and healthy (BMI < 25, n = 11) adults were examined with dual‐energy x‐ray absorptiometry to quantify fat masses. Cine MRI and myocardial tagging were performed at 1.5 T to measure ventricular structure and global function. CEST imaging with offsets in the range of ±10 parts per million (ppm) were performed in one mid‐ventricular slice, where creatine CEST contrast was calculated at 1.8 ppm following field homogeneity correction. Ventricular structure, global function (ejection fraction 69.4 ± 4.3% healthy versus 69.6 ± 9.3% obese, NS), and circumferential strain (−17.0 ± 2.3% healthy versus −16.5 ± 1.5% obese, NS) and strain rate were preserved in obese adults. However, creatine CEST contrast was significantly reduced in obese adults (6.8 ± 1.3% healthy versus 4.1 ± 2.7% obese, p = 0.001). Creatine CEST contrast was inversely correlated with total body fat% (ρ = −0.45, p = 0.011), visceral fat mass (ρ = −0.58, p = 0.001), and septal wall thickness (ρ = −0.44, p = 0.013), but uncorrelated to ventricular function or contractile function. In conclusion, creatine CEST‐MRI reveals a strong correlation between heightened body and visceral fat masses and reduced myocardial metabolic function that is independent of ventricular structure and global function in obese adults.

Patients with end stage renal disease (ESRD) suffer high mortality from arrhythmias linked to fibrosis, but are contraindicated to late gadolinium enhancement magnetic resonance imaging (MRI). We present a quantitative method for gadolinium-free cardiac fibrosis imaging using magnetization transfer (MT) weighted MRI, and probe correlations with widely used surrogate markers including cardiac structure and contractile function in patients with ESRD. In a sub-group of patients who returned for follow-up imaging after one year, we examine the correlation between changes in fibrosis and ventricular structure/function. Quantification of changes in MT revealed significantly greater fibrotic burden in patients with ESRD compared to a healthy age matched control cohort. Ventricular mechanics, including circumferential strain and diastolic strain rate were unchanged in patients with ESRD. No correlation was observed between fibrotic burden and concomitant measures of either circumferential or longitudinal strains or strain rates. However, among patients who returned for follow up examination a strong correlation existed between initial fibrotic burden and subsequent loss of contractile function. Gadolinium-free myocardial fibrosis imaging in patients with ESRD revealed a complex and longitudinal, not contemporary, association between fibrosis and ventricular contractile function.

Purpose: Gene therapy employing AAV vector-mediated gene delivery has undergone substantial growth in recent years with promising results in both preclinical and clinical studies, as well as emerging regulatory approval. However, the lack of methods for quantifying the efficacy of gene therapy from cellular delivery of gene editing technology to specific functional outcomes remains an obstacle for the efficient development of gene therapy treatments. Building upon prior works that utilized a genetically encoded Lysine Rich Protein as a chemical exchange saturation transfer (CEST) reporter, we hypothesized that AAV viral capsids may generate endogenous CEST contrast from the large number of surface lysine residues. Methods: Water-suppressed NMR and NMR-CEST experiments were performed on isolated solutions of AAV serotypes 1-9 on a Bruker 800MHz vertical scanner. A series of in vitro experiments were performed for thorough testing of NMR-CEST contrast of AAV2 capsids under varying pH, density, biological transduction stage, and later across multiple serotypes and mixed biological media. Reverse transcriptase (RT)-polymerase chain reaction (PCR) was used to quantify virus concentration. Subsequent experiments determined the pH-dependent exchange rate and optimized CEST saturation schemes for AAV contrast detection at 7 T. Results: NMR-CEST experiments revealed CEST contrast up to 52% for AAV2 viral capsids between 0.6-0.8 ppm. Evaluation of CEST contrast generated by AAV2 demonstrates high levels of CEST contrast across a variety of chemical environments, concentrations, and saturation schemes. AAV2 CEST contrast displayed significant positive correlations with capsid density (R2>0.99, P<0.001), pH (R2=0.97, P=0.01), and viral titer per cell count (R2=0.92, P<0.001). Transition to a preclinical field strength yielded up to 11.8% CEST contrast following optimization of saturation parameters. Conclusion: AAV2 viral capsids exhibit strong capacity as an endogenous CEST contrast agent and can potentially be used for monitoring and evaluation of AAV vector-mediated gene therapy protocols.

PurposeCEST MRI has been used to probe changes in cardiac metabolism via assessment of CEST contrast from Cr. However, B1 variation across the myocardium leads to spatially variable Cr CEST contrast in healthy myocardium.MethodsWe developed a spatial–spectral (SPSP) saturation pulsed CEST protocol to compensate for B1 variation. Flip angle maps were used to individually tailor SPSP pulses comprised of a train of one‐dimensional spatially selective subpulses selective along the principal B1 gradient dimension. Complete Z‐spectra in the hearts of (n = 10) healthy individuals were acquired using conventional Gaussian saturation and SPSP schemes and supported by phantom studies.ResultsIn simulations, the use of SPSP pulses reduced the average SD of the effective saturation B1 values within the myocardium (n = 10) from 0.12 ± 0.02 μT to 0.05 ± 0.01 μT (p < 0.01) and reduced the average SD of Cr CEST contrast in vivo from 10.0 ± 4.3% to 6.1 ± 3.5% (p < 0.05). Results from the hearts of human subjects showed a significant reduction of CEST contrast distribution at 2 ppm, as well as amplitude, when using SPSP saturation. Corresponding phantom experiments revealed PCr‐specific contrast generation at body temperature when SPSP saturation was used but combined PCr and Cr contrast generation when Gaussian saturation was used.ConclusionThe use of SPSP saturation pulsed CEST resulted in PCr‐specific contrast generation and enabled ratiometric mapping of PCr to total Cr CEST contrast in the human heart at 3T.

We hypothesized that AAV2 capsids may generate endogenous CEST contrast similar to LRP. We tested this using NMR CEST under varying pH, density, biological transduction stage, across serotypes and mixed biological media. Subsequent experiments determined the pH-dependent exchange rate and optimized CEST saturation schemes for AAV contrast detection at 7T. The results of this study reveal that AAV capsids generate endogenous CEST contrast around 0.6-0.8ppm. Exchangeable protons are likely from serine and threonine residues on the AAV capsid. Based on calculated fast exchange rates, an optimized CEST saturation scheme generated robust CEST contrast in mixed biological media phantoms at 7T.