Molecular imaging agents can be targeted to a specific receptor or protein on the cardiomyocyte surface, or to enzymes released into the interstitial space, such as cathepsins, matrix metalloproteinases and myeloperoxidase. Molecular imaging of the myocardium, however, requires the imaging agent to be small, sensitive (nanomolar levels or better), and able to gain access to the interstitial space. Several novel agents that fulfill these criteria have been used for targeted molecular imaging applications in the myocardium.
Recent advances in molecular imaging have permitted the noninvasive imaging of apoptosis, a critical process underlying the pathogenesis of many diseases of the cardiovascular system including atherosclerotic vascular disease, myocardial ischemia and reperfusion injury, chronic heart failure, myocarditis, and cardiac allograft rejection. Multiple molecular targets including phosphatidylserine, phosphatidylinositol 3-kinase, and caspases have been targeted by a variety of imaging agents and modalities such as nuclear scintigraphy, PET, MRI, and fluorescent and bioluminescent imaging.
Inflammatory responses after myocardial infarction profoundly impact tissue repair. Yet, efficient tools to serially and noninvasively assess cellular and molecular functions in postinfarct inflammation are lacking. Here we use multichannel fluorescent molecular tomography (FMT) for spatiotemporal resolution of phagocytic and proteolytic activities mediated by macrophages and neutrophils in murine infarcts. We performed FMT imaging to compare the course of efficient and impaired healing in wild-type and FXIII-/- mice, respectively.
A new approach to MR trabecular bone characterization is presented. This method probes the diffusion of spins through internal magnetic field gradients due to the susceptibility contrast between the bone and water (or marrow) phases. The resulting spin magnetization decay encodes properties of the underlying structure. This method, termed decay due to diffusion in the internal field (DDIF), is well established as a probe of pore size and structure. In the present work its application is shown for in vitro experiments on excised bovine tibiae samples.
Trabecular bone structure is known to play a crucial role in the overall strength, and thus fracture risk, of such areas of the skeleton as the vertebrae, spine, femur, tibiae, or radius. Several MR methods devoted to probing this structure depend upon the susceptibility difference between the solid bone matrix and the intervening fluid/marrow/fat, usually in the context of a linewidth (1/T(2)') measurement or mapping technique.
We demonstrate that CPMG sequences with phase-modulated refocusing pulses of the same duration as the standard 180° pulses can generate echo trains with significantly increased amplitudes compared to the standard CPMG sequence in the case when there is a large range of Larmor frequencies across the sample. The best performance is achieved with symmetric phase-alternating (SPA) composite refocusing pulses of the form α-yβ+yα-y.
This paper describes an NMR method capable of determining the diffusion constant of a material within a few milliseconds and without the need of multiple scans. The method can be used with static or pulsed magnetic field gradients. It may be used to detect time-dependent processes, such as in chemical reactions, production monitoring, and medical MRI.
NMR can probe the microstructures of anisotropic materials such as liquid crystals, stretched polymers and biological tissues through measurement of the diffusion propagator, where internal structures are indicated by restricted diffusion. Multi-dimensional measurements can probe the microscopic anisotropy, but full sampling can then quickly become prohibitively time consuming. However, for incompletely sampled data, compressed sensing is an effective reconstruction technique to enable accelerated acquisition.
Remote detection nuclear magnetic resonance and magnetic resonance imaging can be used to study fluid flow and dispersion in a porous medium from a purely Eulerian point of view (i.e., in a laboratory frame of reference). Information about fluid displacement is obtained on a macroscopic scale in a long-time regime, while local velocity distributions are averaged out.
Spatially resolved MRI measurements of porosity and relaxation time have been performed on a series of sandstone and carbonate rock cores in order to assess spatial heterogeneity in these samples. Geostatistical techniques such as the construction of experimental variograms provide a quantitative measure of heterogeneity, although the interpretation of standard techniques is at times ambiguous. Here, we attempt to resolve some of that ambiguity by addressing the influence of regularization (spatial averaging over the volume of a voxel) on the variogram.
