Table 1.
Method | Sampling time Spatial resolution Agent [C] |
Advantages and disadvantages | Reference |
Microelectrode | Fast, sec Localized measurement No agent required |
Fast; accurate if calibrated with an external buffer Limited to surface-accessible tumors; requires MRI to guide electrodes into tumors |
[16–18] |
Fluorescence imaging | Fast, sec 5 μm μM–nM |
Sensitive; low cost; can be used during clinical fluorescence guided surgery Limited to surface-accessible tumors |
[14,19–21, 25–29] |
PET | 10 min 2 mm nM |
Fast; whole body imaging Requires radioactive isotope; coarse resolution; and limited accuracy |
[22–24, 31] |
1H MRS | >30 min 1mm3 mM |
Simultaneous measurement of pHe and detection of metabolites Poor sensitivity; some agents are pH buffers that change tissue pHe |
[34, 39, 40] |
31P MRS | 40 min 1cm3 mM |
Can simultaneously measure pHi and pHe Requires a 31P MRI transceiver coil |
[41, 43–46] |
19F MRS | 5 min 1cm3 μM–mM |
Fast; good sensitivity Requires a 19F MRI transceiver coil |
[42, 47, 49] |
Hyperpolarized 13C MRS | 5 sec 0.375 mm3 mM |
Very fast Requires a 13C MRI transceiver coil; requires a hyperpolarizer instrument Short hyperpolarized 13C life time; Measures pHi and pHe |
[48] |
pH dependent T1 relaxation | <1 min 0.1 mm3 mM |
Fast; high resolution Requires a cocktail of contrast agents |
[50–53] |
CEST MRI | ~5 min μm–mm mM |
Good specificity Poor sensitivity |
[37] |