MR investigation of the coupling between myocardial fiber architecture and cardiac contraction

Theme: Engineering the Future of BiomedicineLeft ventricular structure has proved to be related with cardiac function; however the relation of myocardial fiber distribution with regional wall motion remains to be elucidated. In this study, both in vivo tagging and ex vivo DTI studies were performed in adult rats. LV circumferential strain, myocardium twist and myocardial fiber architecture were investigated. Results show that myocardial fiber distribution has direct relation with LV myocardium magnitude of circumferential strain and twist angle. Such integrated functional and structural analysis may provide more information for understanding the fundamental cardiac mechanics and assessment of pathological changes. ©2009 IEEE.published_or_final_versionThe 31st Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC 2009), Minneapolis, MN., 2-6 September 2009. In Proceedings of the 31st EMBC, 2009, p. 4395-439

MR study of myocardial fiber structure using diffusion tensor imaging

This paper discussed the left ventricular myocardium structure in both normal and pathological states using diffusion tensor imaging. Myocardial fiber pathway distribution was investigated in normal canine hearts, and effects of infarct size and location on myocardium structure remodeling were studied in LAD- and LCX-related myocardium infarct (MI) porcine models. Majority fiber pathways were found to have small helix angles and dominate the fiber architecture in normal myocardium. While in the two MI groups studied, substantial fiber quality degraded in infarct region with significant correlation with infarct size. The double-helical structure shifted towards more left-handed, especially in LAD-related MI group. The results suggest that both infarct size and location affect the myocardium structural remodeling. These studies not only provide supplemental information on myocardial fiber architecture and cardiac mechanics in normal hearts, but also revealed the alterations in myocardial fiber quality and structure in infarct hearts. ©2009 IEEE.published_or_final_versionThe 2nd International Congress on Image and Signal Processing (CISP 2009) and the 2nd International Conference on BioMedical Engineering and Informatics (BMEI 2009), Tianjin, China, 17-19 October 2009. In Proceedings of the 2nd BMEI, 2009, p. 1-

Diffusion tensor shape measurements of infarcted myocardium in porcine models using three phase geometric analysis

Posters - Myocardial Visibility: Experimental Models: No. 3642Previous DTI studies on infarcted LV myocardium structure usually investigated diffusivity and diffusion anisotropy. In current study, diffusion tensor shape with a combination of linear, planar and spherical measures are examined and illustrated on a three-phase space in porcine models. Results show that the measurements of tensor shape have significant alteration in infarcted myocardium and are more sensitive to detect subtle change of diffusion properties than conventionally used parameters. Infarct location shows no apparent influence on myocardium structural degradation. This study gives insights into myocardium structural alteration and demonstrates potential application of DTI in detecting infarcted heart remodeling.postprin

Diffusion imaging with balanced steady state free precession

Balanced steady state free precession (bSSFP) offers high signal efficiency and relative motion insensitivity. In this study, diffusion weighted bSSFP (DW-bSSFP) was introduced by modifying standard bSSFP sequence with two pairs of balanced bipolar diffusion gradients. The diffusion effect was analyzed and described in closed forms. It was found to be coupled to the transverse and longitudinal relaxation, flip angle and spin phase advance per TR. Such coupling was demonstrated in phantom experiment at 7T. Preliminary DW-bSSFP imaging experiment was performed in rat brain in vivo for diffusion tensor imaging, yielding parametric maps qualitatively similar to those obtained with an 8-shot DW-EPI protocol. The proposed DW-bSSFP approach can provide a new means of diffusion imaging with high resolution, relative motion insensitivity and short diffusion time. Such approach may lead to improved and new diffusion characterization of neural tissues, abdominal organs, myocardium and musculoskeletal tissues. © 2012 IEEE.published_or_final_versio

Effects of hypercapnia on DTI quantitation

Posters - Diffusion Perfusion: Animal Models: No. 4046The accuracy of DTI derived parameters can directly affect the interpretation of underlying biological microstructures. However, the diffusivity measurements are likely to be confounded by the presence of vasculature. Nevertheless, little is known about to what degree blood signal from vasculature affects the diffusion quantitation. In this study, we examined the effects of hypercapnia on DTI quantification indices in anesthetized rat brains. It was found statistically significant changes occurred in all parametric DTI maps indicating that hemodynamic alterations can potentially affect the DTI indices and detection of tissue microstructures. Therefore, cautions must be taken when interpreting DTI parameters in vivo.postprin

Manganese-enhanced MRI of hypoxic-ischemic brain injuries using Mn-DPDP

Theme: Engineering the Future of BiomedicineIn this study, Mn-dipyridoxaldiphosphate (MnDPDP), a clinically approved manganese contrast agent for hepatic and pancreatic imaging, was demonstrated for the first time for manganese-enhanced MRI (MEMRI) in brains of normal young rats (n=4) and rats with hypoxic-ischemic (H-I) insult at postnatal day 7 (n=8). After a single intraperitoneal injection of low dosage with 0.1μmol/g in postnatal 14 days, 2D T1-weighted image (T1WIs), T1 maps, T2-weighted images (T2WIs) and T2 maps were acquired at 7 Tesla 1 day before, 1 day and 7 days after MnDPDP injection. The image contrast changes induced by MnDPDP appeared as the hyperintensity in T1WIs and the hypointensity in T2WIs. T1and T2 values decreased in the regions of Mn enhancement. Such enhancement presented as a delayed pattern that was more pronounced in 7 day after MnDPDP injection, suggesting the sustained Mn accumulation due to MnDPDP. Moreover, the MnDPDP enhancement in H-I brains was more pronounced in the lesion sites and was easily detectable in T1WI, T1 map, T2WI and T2 map. The results demonstrated here support the possibility of using MnDPDP as a 'slow release' Mn2+ for clinical diagnosis of various neuropathologies. ©2009 IEEE.published_or_final_versionThe 31st Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC 2009), Minneapolis, MN., 3-6 September 2009. In Proceedings of the 31st EMBC, 2009, p. 4775-477

Detection of brain maturation: DTI with different b-values versus diffusion kurtosis imaging

Session 37: HARDI & Higher Order Descriptions of Diffusion - Oral presentationThis study aims to investigate the effects of different b-values in detecting microstructural changes during well-controlled rodent brain maturation. The results are also compared to the diffusion kurtosis indices obtained by diffusion kurtosis imaging (DKI) that characterizes the restricted diffusion by fitting multiple b-value DW measurements to a quadratic-exponential model. The results indicate that the b-value for optimal DTI detection of microstructural changes depends on the specific physiological or pathological processes targeted. High-order diffusion imaging, such as DKI, is therefore essential for more robust MR diffusion characterization of neural tissues.published_or_final_versionThe 17th Scientific Meeting & Exhibition of the International Society of Magnetic Resonance in Medicine (ISMRM), Honolulu, HI., 18-24 April 2009. In Proceedings of ISMRM 17th Scientific Meeting & Exhibition, 2009, p. 36

Diffusion tensor MRI study of myocardium structural remodeling after infarction in porcine model

Conference theme: Engineering Revolution In BioMedicineInvestigation of infarct myocardium structure will lead to better understanding of functional adaptation and remodeling. Diffusion tensor magnetic resonance imaging (DTI) provides a means for rapid and nondestructive characterization of the three-dimensional fiber architecture of myocardium. DTI studies were performed on 10 excised, formalin-fixed hearts of both Infarct (two months after left anterior descending coronary artery (LAD) occlusion surgery, n = 4) and control (n = 6) porcine. Each slice was divided into eight segments, and fractional anisotropy (FA) value and helix angle were measured in multiples short-axis slices, respectively. Infarct myocardium exhibited decreased FA value, flatter helix angle courses fluctuating around small helix angle with greater standard error of the mean (SEM) and smaller range of helix angle. The results provide structure information of infarct myocardium. © 2006 IEEE.published_or_final_versio

In vivo manganese-enhanced MRI for visuotopic brain mapping

This study explored the feasibility of localized manganese-enhanced MRI (MEMRI) via 3 different routes of Mn(2+) administrations for visuotopic brain mapping of retinal, callosal, cortico-subcortical, transsynaptic and horizontal connections in normal adult rats. Upon fractionated intravitreal Mn(2+) injection, Mn enhancements were observed in the contralateral superior colliculus (SC) and lateral geniculate nucleus (LGN) by 45-60% at 1-3 days after initial Mn(2+) injection and in the contralateral primary visual cortex (V1) by about 10% at 2-3 days after initial Mn(2+) injection. Direct, single-dose Mn(2+) injection to the LGN resulted in Mn enhancement by 13-21% in V1 and 8-11% in SC of the ipsilateral hemisphere at 8 to 24 hours after Mn(2+) administration. Intracortical, single-dose Mn(2+) injection to the visual cortex resulted in Mn enhancement by 53-65% in ipsilateral LGN, 15-26% in ipsilateral SC, 32-34% in the splenium of corpus callosum and 17-25% in contralateral V1/V2 transition zone at 8 to 24 hours after Mn(2+) administration. Notably, some patchy patterns were apparent near the V1/V2 border of the contralateral hemisphere. Laminar-specific horizontal cortical connections were also observed in the ipsilateral hemisphere. The current results demonstrated the sensitivity of MEMRI for assessing the neuroarchitecture of the visual brains in vivo without depth-limitation, and may possess great potentials for studying the basic neural components and connections in the visual system longitudinally during development, plasticity, pharmacological interventions and genetic modifications.published_or_final_versio

Gas-filled microbubbles: a novel susceptibility contrast agent for brain and liver MRI

Theme: Engineering the Future of BiomedicineGas-filled microbubbles have the potential to become a unique intravascular MR contrast agent due to their magnetic susceptibility effect, biocompatibility and localized manipulation via ultrasound cavitation. However, in vivo demonstration of microbubble susceptibility effect is limited so far and microbubble susceptibility effect is relatively weak when compared with other intravascular MR susceptibility contrast agents. In this study, two types of microbubbles, custom-made albumin-coated microbubbles (AMBs) and a commercially available lipid-based clinical ultrasound contrast agent (SonoVue® ), were investigated with in vivo dynamic brain and liver MRI in Sprague-Dawley rats at 7 Tesla. Transverse relaxation rate enhancements (ΔR2*) maps were computed for brain and liver, yielding results similar to those obtained with a common MR blood pool contrast agent. These results indicate that gas-filled microbubbles can serve as an intravascular MR contrast agent at high field. Enhancement of microbubble susceptibility effect by entrapping monocrystalline iron oxide nanoparticles (MIONs) into microbubbles was also investigated at 7 T in vitro. This is the first experimental demonstration of microbubble susceptibility enhancement for MRI application. This study indicates that gas-filled microbubble susceptibility effect can be substantially increased using iron oxides nanoparticles. With such approach, microbubbles can potentially be visualized with higher sensitivity and lower concentrations by MRI. Such capability has the potential to lead to real-time MRI guidance in various microbubble-based drug delivery and therapeutic applications. ©2009 IEEE.published_or_final_versionThe 31st Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC 2009), Minneapolis, MN., 3-6 September 2009. In Proceedings of the 31st EMBC, 2009, p. 4049-405