Table 2.
Major variants of optical brain mapping techniques
| Optical Brain Mapping Technique | Mapping Signal | Validation in Animal or Human Brain | Required Hardware, | Advantages | Disadvantages | ~Spatial Resolution | ~Temporal Resolution | ~Field of View |
|---|---|---|---|---|---|---|---|---|
| Optical Imaging of Intrinsic Signals (OIS) (44–46) | HbR, HbT, light- scattering | Both | CCD, visible light source, lens/microscope, optical filter. | Relatively simple, used intraoperatively already | Requires exposed brain. Mapping signals have mixed sources. | 10−5 m | 10−2 s | Surface, ~cm2, larger FOV with poorer spatial resolution |
| Diffuse optical Tomography (DOT, NIRS) (92, 121–123) | HbR, HbO, HbT, light- scattering | Both | Fiber-optic near- infrared light source and detector array. | Non-invasive, feasibility demonstrated in human subjects, compatible with fMRI | Low resolution and low signal-to- noise ratio | 10−2 m | 10−2 s | Can be hemispheric or whole brain, ~2 cm depth |
| Optical Spectrosocopy (39, 40, 124, 125) | HbR, HbO, HbT, light- scattering, tumor auto- fluorescence | Both | Visible light spectroscopic device, 337nm laser. | Tumor and radiation necrosis delineation | May require contact of probe onto brain | 10−5 m | 10−3 s | Probe tip |
| 2D-Optical Spectroscopy (2DOS) (10, 72–74) | HbR, HbO, HbT, light- scattering | Animal | CCD, light source, lens/microscope, filterwheel or image splitter. | Best overall resolutions, may be ideal intraoperative technique | Requires exposed brain. | 10−5 m | 10−2 s | Surface, ~cm2, larger FOV with poorer spatial resolution |
| Laser Doppler flowmetry/imaging (LDF/LDI) (16, 87, 126) | CBF | Animal (LDI in human skin) | Laser, detector | Clinical device is available. | Requires exposed brain | 10−3 m | ~10−1 s (dependent on field of view) | Surface, 2D with scanning |
| Laser Speckle Imaging (LSI) (109–111, 127) | CBF | Animal (LSI in human skin) | Laser, microscope, CCD | Real-time 2D imaging of CBF | Requires exposed brain | 10−5 m | 10−3 s | Surface, ~cm2, larger FOV with poorer spatial resolution |
| Optical Coherence/Doppler Tomography (OCT/ODT) (65, 66, 128) | CBF | OCT in both, ODT in animal | Laser, detector | 3D imaging of blood flow, clinical OCT device is available. | Requires exposed brain | 10−6 m | ~10−1 s (dependent on field of view) | 3D with scanning, ~2mm depth |
| Laminar Optical Tomography (LOT) (114) | HbR, HbO, HbT | Animal | Photodiode array, lens/optics, 473 + 532nm lasers | 3D imaging | Requires exposed brain | 10−4 m | ~10−1 s (dependent on field of view) | Planar, 3D with scanning, ~2mm depth |
| Dye Imaging, e.g. Voltage-Sensitive Dyes (VSD; (129- 131)) or 5-amino levilinic acid (5- AL (64)) | VSD: Voltage, (as well as intrinsic signals, 5-AL: gliomas | VSD in animal, 5-AL in both | CCD or Photodiode Array, Dye | VSD maps subthreshold electrical changes. 5-AL maps gliomas borders | Toxicity of dyes, and bleaching of dyes. Requires exposed brain | 10−5 m | 10−3 s | ~mm2, larger FOV with poorer spatial resolution |
| Multi-Photon Microscopy (113, 119, 132, 133) | CBF, HbT, vessel diameter | Animal | Ti:Sapphire Laser, microscope | Microscopic resolution | Requires exposed brain, limited depth, tracer injection | 10−8 m | 10−3 s | ~0.3 mm2, ~0.3 mm depth |