Molecular imaging: the emerging role of optical imaging in nuclear medicine

Through its role in (routine) patient care, nuclear medicine has set the standard for molecular imaging: the sensitivity and specificity of the available (multimodality) nuclear imaging technologies (SPECT/CT, PET/CTand PET/MR) are superior to those of any other clinical imaging modality. Nevertheless, efforts are ongoing to apply ultrasound, magnetic resonance and/or optical imaging techniques to molecular imaging in the clinic. A careful look at the theoretical detection sensitivities of the individual modalities readily confirms that especially ultrasound, optical and radionuclide techniques currently have the potential to visualize (low) biomarker expression levels using imaging probes [1]. Having said this, there are also activities regarding the development of MR contrast agents. Since the value of ultrasound technologies remains confined to the vascular network and the sensitivity of MR is still relatively low, only optical imaging can, in theory, match the sensitivity performance of nuclear medicine techniques.