Abstract 4310: Assessing PK parameters using dynamic contrast enhanced multispectral optoacoustic tomography (DCE-MSOT)
Authors: Morscher Stefan , Driessen Wouter H. , Burton Neal C. , Sardella Thomas , Razansky Daniel , Ntziachristos Vasilis 
Published: May 2015

Abstract
Pharmacokinetic imaging is a powerful platform for evaluating new candidate drugs and imaging agents, and multitude of applications have been demonstrated in DCE MRI. Interesting parameters such as Ktrans, half-life and Tmax can be retrieved for a tumor region after injection of a perfusion agent, allowing one to draw important conclusions on tumor growth, vascularization or therapy response. DCE MRI however is to a certain extent limited to magnetic agents and provides limited spatial and temporal resolution.
Multispectral Optoacoustic Imaging (MSOT) is an emerging modality that combines ultrasound resolution of 150 µm and acquisition times of a few microseconds with optical contrast in the near infrared (NIR) spectral region. Multispectral imaging allows the localization of injected fluorophores without necessity of a baseline scan before injection, while a core imaging rate of 10 images/second allows the acquisition of a multispectral image within a second or even less. This enables fast image acquisition to support pharmacokinetic imaging, where the temporal profile of individual pixels is fit to a model equation and resulting parameters are plotted as parametric maps. Using targeted agents, binding specificity and its kinetics can be evaluated, while perfusion agents allow the assessment of perfusion and tissue uptake through Ktrans. One advantage in regards to DCE-MRI is the ability to extract the arterial input function from the data itself by monitoring a single cross-section with maximal temporal resolution. Another important feature is the use of intrinsic contrast that allows blood oxygenation quantification, enabling the co-registration of functional oxygenation measurements with DCE perfusion measurements.
In particular, various algorithms can be applied in order to visualize blood oxygenation as a result from tissue intrinsic optoacoustic contrast without the injection of additional agents. These can be evaluated for pixel dependent temporal changes using the fast image acquisition techniques described above, which allows for tumor delineation and assessment of perfusion in a CO2 challenge experiment by visualizing the localized change in blood oxygenation. This can be cross-validated by the subsequent injection of a perfusion agent and evaluation of its transfer coefficient using DCE-MSOT techniques to paint a complete picture of the evaluated tumor microenvironment. The presented work uses the U87-MG glioblastoma and 4T1 tumors to illustrate the abilities of the technique in both subcutaneous and orthotopic settings.
The extension of contrast-enhanced kinetic modeling to the optoacoustic imaging regime allows access to a library of optical probes that are otherwise unavailable to traditional DCE-MRI, while maintaining high spatial resolution and providing access to functional hemodynamic parameters.
Citation Format: Stefan Morscher, Wouter HP Driessen, Neal C. Burton, Thomas Sardella, Daniel Razansky, Vasilis Ntziachristos. Assessing PK parameters using dynamic contrast enhanced multispectral optoacoustic tomography (DCE-MSOT). [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4310. doi:10.1158/1538-7445.AM2014-4310