Table 1.
Characteristics of clinical molecular imaging modalities in oncology.
| PET | SPECT | CT | MRI | US | OPTICAL | |
|---|---|---|---|---|---|---|
| Signal Used | High-energy γ-ray | Low-energy γ-ray | X-rays | Radio waves | High-frequency sound waves | Visible light or near-infrared |
| Contrast agents/Tracers | β+ emitting Radioisotope | γ- emitting Radioisotope | Krypton, Xenon, Barium and iodinated molecules | Gadolinium chelates/ superparamagnetic agents (SPIONs) | Microbubbles | Fluorescent probes/ dyes |
| Sensitivitya (mol/L) | 10-11-10-12 | 10-10-10-11 | Not well characterized | 10-3-10-5 | Not well characterized | 10-9-10-12 |
| Spatial Resolutionb | 1-2 mm | 1-2 mm | 50-200 μm | 25-100 μm | 50-500 μm | 2-3 mm |
| Temporal Resolutionc | 10 seconds to minutes | Mins | Mins | Mins-Hrs | Sec-Min | Sec-Min |
| Depth of Penetration | No limit | No limit | No limit | No limit | mm-cm | < 1 cm |
| Advantages | High sensitivity, can be used for whole body imaging | High resolution, can be used for whole body imaging, fast acquisition time | High spatial resolution, no ionizing radiation, high soft tissue contrast |
Fast acquisition time, real-time imaging, no ionizing radiation, cost-effective | Fast acquisition time, no ionizing radiation, real-time imaging, high sensitivity, cost-effective | |
| Disadvantages | Ionizing radiations, low resolution, expensive, long acquisition time | Ionizing radiations, low sensitivity, poor soft tissue demarcation | Poor sensitivity, long acquisition time, expensive | Poor contrast, low resolution | Low Resolution | |
aSensitivity is the ability of imaging technique to detect or identify the presence of a molecular probe when it is truly present, relative to its background.
bSpatial resolution is a measure of the accuracy or detail of image. It is mainly based on its detection ability to distinguish two adjacent structures as separate entities.
cTemporal resolution is the frequency at which the images are be recorded or captured. It is also represented as single acquisition time.
PET: Positron Emission Tomography; SPECT: Single-Photon Emission Computerized Tomography; CT: Computed tomography; MRI: Magnetic Resonance Imaging; US: Ultrasound