A variable resolution approach for improved acquisition of hyperpolarized ¹³C metabolic MRI

Abstract

Purpose To ameliorate tradeoffs between a fixed spatial resolution and signal‐to‐noise ratio (SNR) for hyperpolarized 13C 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 [1‐13C]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 13C 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.

Characterization and compensation of inhomogeneity artifact in spiral hyperpolarized13C imaging of the human heart

“…SNR currently limits pushing this resolution further, as other authors have reported the need to degrade resolution in order to encode bicarbonate with reliable SNR. 24 f 0 correction improved some apparent regional defects in the bicarbonate images, but other factors such as transmit and receive B 1 inhomogeneity may contribute to signal dropout. Based on measurements of B 1 transmit and receive profiles of the coils used in this study, B 1 inhomogeneities impart much less signal shading, while f 0 artifact tends to manifest as a blur or a signal dropout.…”

“…However, the challenge remains to achieve a point spread that preserves the myocardial wall thickness with 13 C bicarbonate images. SNR currently limits pushing this resolution further, as other authors have reported the need to degrade resolution in order to encode bicarbonate with reliable SNR 24 f0 correction improved some apparent regional defects in the bicarbonate images, but other factors such as transmit and receive inhomogeneity may contribute to signal dropout.…”

Differences in molecular phenotype in mouse and human hypertrophic cardiomyopathy

“…Since correlations between tissue mRNA and protein expression/function can vary, parallel metabolic flux/metabolomics studies in HCM mouse models and human hearts would be ideal to examine the contribution of abnormalities in cardiac metabolism to the genesis of cardiac HCM phenotype. Advances in hyperpolarized 13C-MRI 62 provide the opportunity for non-invasive metabolic imaging in human hearts 63 and experimental models.…”

Pilot Study of Hyperpolarized 13C Metabolic Imaging in Pediatric Patients with Diffuse Intrinsic Pontine Glioma and Other CNS Cancers

“…Freedom in positioning the paddle 13 C receivers helped reduce this issue by maximizing the proximity to the anatomic lesion; 18 however, other pediatric indications may benefit from custom-designed detector arrays that better conform to the surface of the head. While the spatial resolution was relatively low in this study (3.38-8 cm 3 ), variable resolution acquisition strategies 25 and maintaining a short time to injection through quality control practices should greatly improve this issue.…”