Table 1.
Information ranges of common imaging techniques in anatomy, physiology, and biochemistry.
| Terms | ||
|---|---|---|
| Physiology and biochemistry | Anatomy | Functional significance |
| Short-range molecular interaction | Co-localization | Molecules in direct contact; diffusion in nanoseconds |
| Intermediate-range interaction | Close proximity/co-association | Subcellular; diffusion distances < 0.3 μ m; diffusion in microseconds to < 1 millisecond |
| Long-range interactions | Histological proximity | Diffusion in milliseconds to minutes; cellular level to histological level; transport may involve circulatory system |
FRET (fluorescence resonance energy transfer) identifies molecules that are in molecular contact or that are separated by < 10 nm (i.e., “short-range interactions’’). Spatial localization in X- and Y-coordinates is limited to > 300 nm by optical diffraction phenomena. Laser scanning confocal microscopy provides biochemical, immunocytochemical, and structural data in the X- and Y-axes from 300 nm to 30 millimeters, and from 0.6 μ m to ~600 μ m in the Z-axis. FRIL provides structural and immunocytochemical data from about 2 nm to 2 mm (six orders of magnitude). PET scans (positron emission tomography) have about 1 mm resolution and collect data over ~0.5 m2. Thus, FRIL spans the gap from FRET to PET scans.