FMT-XCT: in vivo animal studies with hybrid fluorescence molecular tomography–X-ray computed tomography

Abstract

The development of hybrid optical tomography methods to improve imaging performance has been suggested over a decade ago and has been experimentally demonstrated in animals and humans. Here we examined in vivo performance of a camera-based hybrid fluorescence molecular tomography (FMT) system for 360° imaging combined with X-ray computed tomography (XCT). Offering an accurately co-registered, information-rich hybrid data set, FMT-XCT has new imaging possibilities compared to stand-alone FMT and XCT. We applied FMT-XCT to a subcutaneous 4T1 tumor mouse model, an Aga2 osteogenesis imperfecta model and a Kras lung cancer mouse model, using XCT information during FMT inversion. We validated in vivo imaging results against post-mortem planar fluorescence images of cryoslices and histology data. Besides offering concurrent anatomical and functional information, FMT-XCT resulted in the most accurate FMT performance to date. These findings indicate that addition of FMT optics into the XCT gantry may be a potent upgrade for small-animal XCT systems.

Characterizing EPR-mediated passive drug targeting using contrast-enhanced functional ultrasound imaging

“…To address the shortcomings associated with standard FMT, we (and others) have developed protocols for the co-registration of CT and FMT data sets [30][31][32]. The advantage of such co-registered images is the addition of anatomical information, allowing for a much more precise 3D segmentation of tumors (and other organs of interest) on the basis of the CT images, yielding a highly reproducible method for biodistribution analyses [32].…”

“…We here used ~70 kDa-sized near-infrared fluorophore (NIRF) -labeled HPMA copolymers (which are known to efficiently accumulate in subcutaneous CT26 tumors in mice via EPR [29]), hybrid computed tomography-fluorescence molecular tomography (CT-FMT; [30][31][32]) and microbubble (MB) -based contrast-enhanced functional ultrasound (ceUS) imaging [33,34], to demonstrate that the degree of tumor vascularization correlates with the degree of EPR-mediated passive drug targeting. These findings indicate that relatively easily imageable vascular parameters, such as tumor blood volume and tumor blood flow, can be used to characterize EPR, and to on the basis of this preselect patients likely to respond to passively tumor-targeted nanomedicine therapies.…”

“…Clinically, however, due to the abovementioned large inter-and intraindividual variability in EPR, the efficacy of passively tumor-targeted nanomedicines is compromised, with often significant improvements in tolerability, but hardly any increases in efficacy [9,10,14]. Consequently, there seems to be a clear need to develop methods to visualize and characterize the EPR effect, in order to preselect patients presenting with sufficiently high levels of EPR, to thereby (pre-) stratify responders and non-responders, and to thereby individualize and improve nano-chemotherapeutic treatments.We here used ~70 kDa-sized near-infrared fluorophore (NIRF) -labeled HPMA copolymers (which are known to efficiently accumulate in subcutaneous CT26 tumors in mice via EPR [29]), hybrid computed tomography-fluorescence molecular tomography (CT-FMT; [30][31][32]) and microbubble (MB) -based contrast-enhanced functional ultrasound (ceUS) imaging [33,34], to demonstrate that the degree of tumor vascularization correlates with the degree of EPR-mediated passive drug targeting. These findings indicate that relatively easily imageable vascular parameters, such as tumor blood volume and tumor blood flow, can be used to characterize EPR, and to on the basis of this preselect patients likely to respond to passively tumor-targeted nanomedicine therapies.…”

“…Depth cannot be determined, and has to be estimated on the basis of the FMT signal. This approach consequently results in a relatively subjective interpretation of the data, and may give rise to biased, inaccurate and/or incorrect outcomes (depending on the observer's experience, expertise and expectations).To address the shortcomings associated with standard FMT, we (and others) have developed protocols for the co-registration of CT and FMT data sets [30][31][32]. The advantage of such co-registered images is the addition of anatomical information, allowing for a much more precise 3D segmentation of tumors (and other organs of interest) on the basis of the CT images, yielding a highly reproducible method for biodistribution analyses [32].…”

Hybrid µCT-FMT imaging and image analysis

“…In contrast to non-invasive microscopy techniques, which allow imaging of superficial targets at subcellular resolution 1 , FMT allows three-dimensional reconstruction of fluorescent sources in depths of several centimeters, albeit at lower resolution 2 . Many targeted fluorescent probes are available to image angiogenesis, apoptosis, inflammation, and others [2][3][4][5] . Some probes are activatable, e.g., by specific enzyme cleavage leading to unquenching of fluorochromes.…”