Background and Aims Advances in cancer treatment have improved survival; however, local recurrence and metastatic disease—the principal causes of cancer mortality—have limited the ability to achieve durable remissions. Local recurrences arise from latent tumor cells that survive therapy and are often not detectable by conventional clinical imaging techniques. Local recurrence after transarterial embolization (TAE) of hepatocellular carcinoma (HCC) provides a compelling clinical correlate of this phenomenon. In response to TAE‐induced ischemia, HCC cells adapt their growth program to effect a latent phenotype that precedes local recurrence. Approach and Results In this study, we characterized and leveraged the metabolic reprogramming demonstrated by latent HCC cells in response to TAE‐induced ischemia to enable their detection in vivo using dynamic nuclear polarization (DNP) magnetic resonance spectroscopic imaging (MRSI) of 13carbon‐labeled substrates. Under TAE‐induced ischemia, latent HCC cells demonstrated reduced metabolism and developed a dependence on glycolytic flux to lactate. Despite the hypometabolic state of these cells, DNP‐MRSI of 1‐13C‐pyruvate and its downstream metabolites, 1‐13C‐lactate and 1‐13C‐alanine, predicted histological viability. Conclusions These studies provide a paradigm for imaging latent, treatment‐refractory cancer cells, suggesting that DNP‐MRSI provides a technology for this application.

During dynamic nuclear polarization (DNP) at 1.5 K and 5 T, 129 Xe nuclear magnetic resonance (NMR) spectra of a homogeneous xenon/1-propanol/trityl-radical solid mixture exhibit a single peak, broadened by 1 H neighbors. A second peak appears upon annealing for several hours at 125 K. Its characteristic width and chemical shift indicate the presence of spontaneously formed pure Xe clusters. Microwave irradiation at the appropriate frequencies can bring both peaks to either positive or negative polarization. The peculiar time evolution of 129 Xe polarization in pure Xe clusters during DNP can be modelled as an interplay of spin diffusion and T 1 relaxation. Our simple spherical-cluster model offers a sensitive tool to evaluate major DNP parameters in situ, revealing a severe spindiffusion bottleneck at the cluster boundaries and a significant sample overheating due to microwave irradiation. Subsequent DNP system modifications designed to reduce the overheating resulted in four-fold increase of 129 Xe polarization, from 5.3% to 21%.

Purpose To investigate the feasibility of describing the impact of any flip angle–TR combination on the resulting distribution of the hyperpolarized xenon‐129 (HXe) dissolved‐phase magnetization in the chest using a single virtual parameter, TR90°,equiv. Methods HXe MRI scans with simultaneous gas‐ (GP) and dissolved‐phase (DP) excitation were performed using 2D projection scans in mechanically ventilated rabbits. Measurements with DP flip angles ranging from 6–90° and TRs ranging from 8.3–500 ms were conducted. DP maps based on acquisitions of similar radio frequency pulse‐induced relaxation rates were compared. Results The observed distribution of the DP magnetization was strongly affected by acquisition flip angle and TR. However, for flip angles up to 60°, measurements with the same radio frequency pulse‐induced relaxation rates, resulted in very similar DP images despite the presence of significant macroscopic gas transport processes. For flip angles approaching 90°, the downstream signal component decreased noticeably relative to acquisitions with lower flip angles. Nevertheless, the total DP signal continued to follow an empirically verified conversion equation over the entire investigated parameter range, which yields the equivalent TR of a hypothetical 90° measurement for any experimental flip angle–TR combination. Conclusion We have introduced a method for converting the flip angle and TR of a given HXe DP measurement to a standardized metric based on the virtual quantity, TR90°,equiv, using their equivalent RF relaxation rates. This conversion permits the comparison of measurements obtained with different pulse sequence types or by different research groups using various acquisition parameters.

Until recently, molecular imaging using magnetic resonance (MR) has been limited by the modality’s low sensitivity, especially with non-proton nuclei. The advent of hyperpolarized (HP) MR overcomes this limitation by substantially enhancing the signal of certain biologically important probes through a process known as external nuclear polarization, enabling real-time assessment of tissue function and metabolism. The metabolic information obtained by HP MR imaging holds significant promise in the clinic, where it could play a critical role in disease diagnosis and therapeutic monitoring. This review will provide a comprehensive overview of the developments made in the field of hyperpolarized MR, including advancements in polarization techniques and delivery, probe development, pulse sequence optimization, characterization of healthy and diseased tissues, and the steps made towards clinical translation.

Prone position limits the radiologic progression of early lung injury. Minimizing unstable inflation in this setting may alleviate the burden of acute respiratory distress syndrome.