Table 1.

Comparison of major imaging techniques for studying cancer metabolism.

Imaging techniques	Advantages	Disadvantages	Clinical applications	References
Magnetic resonance spectroscopy (MRS)	(i) Widely used medical imaging technique (ii) Ability to assess multiple metabolites in one measurement (iii) No radiation concern	(i) It has relatively long acquisition time (ii) Data processing is not routine in the clinic (iii) Lack of familiarity with clinicians	Brain, head and neck, prostate, breast, and cervix	[39–46]
Dynamic nuclear polarization- (DNP-) MRS	(i) Signal enhancements of over 10,000-fold of magnitude for stable isotope carbon-13 (13C) enriched compounds (ii) Simultaneous detection of multiple hyperpolarized molecules allowed several metabolic pathways to be probed at the same time (iii) No radiation concern (iv) Short acquisition time (v) Real-time observation of not only the uptake of the targeted molecule but also its flux to produce downstream metabolic products	Hyperpolarized 13C-labelled substrates have very short half-life (in tens of seconds)	Prostate	[47]
Positron emission tomography (PET)	(i) Widely used in clinical applications (ii) High sensitivity	(i) Not all tumors show a significant increase in metabolic activity on FDG-PET imaging (ii) Difficult to evaluate malignant lesions in tissues that physiologically take up FDG (such as the central nervous system) or excrete FDG (such as the kidneys and bladder) or differentiate between inflammation and cancer (iii) Radiation concern (iv) It measures perfusion and accumulation of a tracer and does not differentiate between metabolites containing the radionuclide or tracer per se	Oral cancer, lymphoma, melanoma, lung cancer, esophageal cancer, and colorectal cancer Cervical Ovarian Pancreas Prostate	[48–57]
Mass spectrometry imaging (MSI)	(i) Highly sensitive (ii) It can be used to investigate both identified and unidentified molecules in spatial localized areas without any need for labeling or contrasting agents	Analytical technique of tissue section, not noninvasive imaging	Brain, oral, lung, breast, gastric, pancreatic, renal, ovarian, and prostate cancer	[58–66]