Early recognition of hypertensive heart disease is needed to prevent macrovascular and microvascular damage. Hypertension (HTN) is a risk factor for coronary artery disease, and plays a prominent role in the development of adverse left ventricular (LV) remodeling and heart failure. Here, we review new knowledge on effects of HTN on cardiac geometry and function, obtained from multimodality cardiac imaging, including echocardiography, positron emission tomography and magnetic resonance imaging. Early recognition of changes in LV geometry and function induced by HTN could identify patients at risk for end-organ damage, who could be targeted for close monitoring and intensive therapy. Basal septal hypertrophy as the early imaging biomarker at the adaptive phase may be a specific aspect not only in hypertensive heart but stress-related conditions and called stressed heart morphology.

Purpose

To ameliorate tradeoffs between a fixed spatial resolution and signal-to-noise ratio (SNR) for hyperpolarized ¹³ C MRI.

Methods

In MRI, SNR is proportional to voxel volume but retrospective downsampling or voxel averaging only improves SNR by the square root of voxel size. This can be exploited with a metabolite-selective imaging approach that independently encodes each compound, yielding high-resolution images for the injected substrate and coarser resolution images for downstream metabolites, while maintaining adequate SNR for each. To assess the efficacy of this approach, hyperpolarized [1-¹³ C]pyruvate data were acquired in healthy Sprague-Dawley rats (n = 4) and in two healthy human subjects.

Results

Compared with a constant resolution acquisition, variable-resolution data sets showed improved detectability of metabolites in pre-clinical renal studies with a 3.5-fold, 8.7-fold, and 6.0-fold increase in SNR for lactate, alanine, and bicarbonate data, respectively. Variable-resolution data sets from healthy human subjects showed cardiac structure and neuro-vasculature in the higher resolution pyruvate images (6.0 × 6.0 mm² for cardiac and 7.5 × 7.5 mm² for brain) that would otherwise be missed due to partial-volume effects and illustrates the level of detail that can be achieved with hyperpolarized substrates in a clinical setting.

Conclusion

We developed a variable-resolution strategy for hyperpolarized ¹³ C MRI using metabolite-selective imaging and demonstrated that it mitigates tradeoffs between a fixed spatial resolution and SNR for hyperpolarized substrates, providing both high resolution pyruvate and coarse resolution metabolite data sets in a single exam. This technique shows promise to improve future studies by maximizing metabolite SNR while minimizing partial-volume effects from the injected substrate.