Emerging Technologies to Image Tissue Metabolism

Abstract

Due to the implication of altered metabolism in a large spectrum of tissue function and disease, assessment of metabolic processes becomes essential in managing health. In this regard, imaging can play a critical role in allowing observation of biochemical and physiological processes. Nuclear imaging methods, in particular positron emission tomography, have been widely employed for imaging metabolism but are mainly limited by the use of ionizing radiation and the sensing of only one parameter at each scanning session. Observations in healthy individuals or longitudinal studies of disease could markedly benefit from non-ionizing, multi-parameter imaging methods. We therefore focus this review on progress with the non-ionizing radiation methods of MRI, hyperpolarized magnetic resonance and magnetic resonance spectroscopy, chemical exchange saturation transfer, and emerging optoacoustic (photoacoustic) imaging. We also briefly discuss the role of nuclear and optical imaging methods for research and clinical protocols.

Multiplex SERS Detection of Metabolic Alterations in Tumor Extracellular Media

“…In fact, detection of specific metabolites within complex environments is considered as one of the major challenges to be addressed by optical‐based detection systems. [ 12,33 ] Although both plasmonic substrates were sufficiently efficient to identify Kyn in PBS, when we incubated varying concentrations of Kyn in cell media, discrepancies were observed between the spectra obtained using both substrates (see Figure S6a,b in the Supporting Information). As shown in Figure 1e, only the superlattice substrate was reliable toward the detection of kynurenine in complex media, whereas no significant bands at 560 cm −1 could be identified using LbL substrates.…”

“…[ 11 ] Hence, the development of alternative label‐free methods to rapidly detect multiple tumor‐secreted metabolites in extracellular media is required toward understanding metabolic interactions in the tumor niche. [ 12 ]…”

A Biomimetic Plasmonic Nanoreactor for Reliable Metabolite Detection

“…[ 1 ] Accurate profiling of medically relevant metabolites in human body fluids provides molecular information for deep understanding of pathological mechanism at a more distal level than genomic analysis, and enables precise diagnosis and treatment of the underling diseases. [ 2 ] Till now, different advanced techniques, including magnetic resonance spectroscopy, [ 3 ] mass spectrometry, [ 4 ] and chromatography coupled mass spectroscopy, [ 5 ] have been developed to measure metabolites in vitro and in vivo. While useful, these techniques require sophisticated and expensive equipment, hampering their use in rapid point‐of‐care clinical testing.…”

Responsive ParaCEST Contrast Agents

“…In order to observe a CEST effect, this exchange rate (k ex ) must be lower than the chemical shift difference between the exchangeable proton of the CEST agent and the bulk water proton (∆ω = |ω CEST − ω WAT |). Many diamagnetic CEST agents have been proposed, and certain metabolites can also act as endogenous contrast agents and be imaged by diaCEST [6]. These diamagnetic probes present small chemical shifts compared to bulk water, and in this chemical shift range, a strong background signal from the tissue magnetization transfer is present.…”