Table 2.
Sensitivity and resolution of in vivo molecular imaging modalities available for monitoring endothelial-targeted nanoparticles.
| Imaging modality | Radiation Spectrum | Contrast Agents | Sensitivity | Spatial Resolution | Advantages | Disadvantages |
|---|---|---|---|---|---|---|
| PET | High energy gamma rays | Positron Emitters 18F, 124I, 64Cu | 10−11–10−12M | 1–2 mm | High sensitivity | Low resolution Requires cyclotron produced isotopes |
| SPECT | Low energy gamma rays | Photon Emitters 123I, 99mTc, 111 In | 10−10–10−11M | 1–2 mm | High sensitivity | Low resolution |
| MRI | Radiowaves | Gadolinium (Gd3+) chelates, iron oxide | 10−3–10−5Ma | 25–200 μm | High resolution | Low sensitivity; long image acquisition time and processing time |
| Ultrasound (US) | High-frequency sound | Gas-filled bubbles | 10−6–10−9Mb | 30–500 μmb | Low cost; realtime imaging; portability | Limited resolutionc; Difficulty imaging through bone and lungs |
| Optical Fluorescence | Visible or near-infrared light | Fluorophores | 10−9–10−12M | 1–10 mm | High sensitivity; low cost; high throughput | Low resolution; Limited depth to less than 1 cm |
a
With contrast-loaded nanoparticles the sensitivity can be enhanced to 10−9M.
b
[16]
c
The spatial resolution of US indicated is at the surface of the body. The sensitivity and resolution decreases as a function of depth of penetration of the acoustic signal.