Dual energy CT imaging is expected to play a major role in the diagnostic arena as it provides material
decomposition on an elemental basis. The purpose of this work is to investigate the use of dual energy micro-CT for
the estimation of vascular, tissue, and air fractions in rodent lungs using a post-reconstruction three-material
decomposition method. We have tested our method using both simulations and experimental work. Using
simulations, we have estimated the accuracy limits of the decomposition for realistic micro-CT noise levels. Next,
we performed experiments involving ex vivo lung imaging in which intact lungs were carefully removed from the
thorax, were injected with an iodine-based contrast agent and inflated with air at different volume levels. Finally, we
performed in vivo imaging studies in (n=5) C57BL/6 mice using fast prospective respiratory gating in endinspiration
and end-expiration for three different levels of positive end-expiratory pressure (PEEP). Prior to imaging,
mice were injected with a liposomal blood pool contrast agent. The mean accuracy values were for Air (95.5%),
Blood (96%), and Tissue (92.4%). The absolute accuracy in determining all fraction materials was 94.6%. The
minimum difference that we could detect in material fractions was 15%. As expected, an increase in PEEP levels for
the living mouse resulted in statistically significant increases in air fractions at end-expiration, but no significant
changes in end-inspiration. Our method has applicability in preclinical pulmonary studies where various
physiological changes can occur as a result of genetic changes, lung disease, or drug effects.
Micro-CT has become a powerful tool for small animal research. Many micro-CT applications require exogenous
contrast agents, which are most commonly based on iodine. Despite advancements in contrast agents, single-energy
micro-CT is sometimes limited in the separation of two different materials that share similar grayscale intensity values as
in the case of bone and iodine. Dual energy micro-CT offers a solution to this separation problem, while eliminating the
need for pre-injection scanning. Various dual energy micro-CT sampling strategies are possible, including 1) single
source sequential scanning, 2) simultaneous dual source acquisition, or 3) single source with kVp switching. But, no
commercial micro-CT system exists in which all these sampling strategies have been implemented. This study reports on
the implementation and comparison of these scanning techniques on the same small animal imaging system.
Furthermore, we propose a new sampling strategy that combines dual source and kVp switching. Post-sampling and
reconstruction, a simple two-material dual energy decomposition was applied to differentiate iodine from bone. The
results indicate the time differences and the potential problems associated with each sampling strategy. Dual source
scanning allows for the fastest acquisition, but is prone to errors in decomposition associated with scattering and
imperfect geometric alignment of the two imaging chains. KVp switching prevents these types of artifacts, but requires
more time for sampling. The novel combination between the dual source and kVp switching has the potential to reduce
sampling time and provide better decomposition performance.
Fluorescence diffuse optical tomography (FDOT) plays an important role in studying physiological and pathological
processes of small animals in vivo. The low spatial resolution, however, limits the ability of FDOT in resolving the biodistributions
of fluorescent markers. The anatomical information provided by X-ray computed tomography (CT) can be
used to improve the image quality of FDOT. However, in most hybrid FDOT/CT systems, the projection data sets of
optics and X-ray are acquired sequentially, which increases the acquisition time and bring in the unwanted soft tissue
displacement. In this paper, we evaluate the performance of a synchronous FDOT/CT system, which allows for faster
and concurrent imaging. Compared with previous FDOT/CT systems, the two subsystems (FDOT and CT) acquire
projection images in synchronous mode, so the body position can keep consistent in the same projection data acquired by
both subsystems. The experimental results of phantom and in vivo experiments suggest that the reconstruction quality of
FDOT can be significantly improved when structural a priori information is utilized to constrain the reconstruction
process. On the other hand, the synchronous FDOT/CT system decreases the imaging time.
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