Table 1 Clinical assessment methodologies for the cerebral circulation
From: Regulation of the cerebral circulation: bedside assessment and clinical implications
Method | Principle | Global or local CBF assessment | Robustness | Invasive | Bedside | Continuous | Advantage | Disadvantage |
|---|---|---|---|---|---|---|---|---|
TCD [33] | Doppler principle | Global (vascular territory) | Fair | No | Yes | Yes | High-frequency signal | Signal easily lost. Flow velocity assessment only |
NIRS [34] | Absorbance of oxygenated and deoxygenated haemoglobin | Local | Good | No | Yes | Yes | Easy application | Uncertain intracranial contribution to signal |
PBTO2 [37] | Clark electrode | Local | Excellent | Yes | Yes | Yes | Robust | Local |
LDF [36] | Doppler principle | Local | Excellent | Yes | Yes | Yes | Assessment of microcirculation | Unknown biological zero |
Thermal diffusion [35] | Thermal diffusion | Local | Excellent | Yes | Yes | Yes | Absolute CBF | Frequent calibrations |
Duplex neck US [106] | Doppler principle | Global | Poor | No | Potentially | No | Absolute and global CBF | Semi-continuous |
CT [107] | Time-dependent attenuation of iodine IV contrast bolus (perfusion CT) or Xe gas | Global and local | Excellent | No | Potentially | No | Global and regional CBF | Bulky and intermittent |
PET [108] | Radioactive tracers emit positrons dependent on perfusion | Global and local | Excellent | Minimal (venous access) | No | No | Regional CBF and metabolism | Radiation, requires a cyclotron |
MRI [109] | Perfusion-dependent decrease in T2 signal with gadolinium | Global and local | Excellent | Minimal (IV access) or no for arterial spin labelling technique | No | No | Absolute, regional and global CBF | Time-consuming, expensive, difficult to assess critically ill patients |