Background-Microcomputed tomography (micro-CT) has been used extensively in research to generate high-resolution 3D images of calcified tissues in small animals nondestructively. It has been especially useful for the characterization of skeletal mutations but limited in its utility for the analysis of soft tissue such as the cardiovascular system. Visualization of the cardiovascular system has been largely restricted to structures that can be filled with radiopaque intravascular contrast agents in adult animals. Recent ex vivo studies using osmium tetroxide, iodinated contrast agents, inorganic iodine, and phosphotungstic acid have demonstrated the ability to stain soft tissues differentially, allowing for high intertissue contrast in micro-CT images. In the present study, we demonstrate the application of this technology for visualization of cardiovascular structures in developing mouse embryos using Lugol solution (aqueous potassium iodide plus iodine). Methods and Results-We show the optimization of this method to obtain ex vivo micro-CT images of embryonic and neonatal mice with excellent soft-tissue contrast. We demonstrate the utility of this method to visualize key structures during cardiovascular development at various stages of embryogenesis. Our method benefits from the ease of sample preparation, low toxicity, and low cost. Furthermore, we show how multiple cardiac defects can be demonstrated by micro-CT in a single specimen with a known genetic lesion. Indeed, a previously undescribed cardiac venous abnormality is revealed in a PlexinD1 mutant mouse. Conclusions-Micro-CT of iodine-stained tissue is a valuable technique for the characterization of cardiovascular development and defects in mouse models of congenital heart disease. (Circ Cardiovasc Imaging. 2010;3:314-322.)Key Words: micro-CT Ⅲ iodine Ⅲ mouse Ⅲ development Ⅲ PlexinD1 Ⅲ congenital heart disease T he ability to genetically manipulate the mouse has resulted in a powerful model system for the investigation of many disease processes. In particular, genetic studies in the mouse have enhanced our understanding of embryonic development, and by extension, of congenital defects. In humans, cardiac defects are the most common serious anomalies among live births with an estimated frequency of 0.6%. 1 Numerous mouse models of congenital heart disease have been generated and characterized, adding greater insight into the molecular and cellular origins of these defects. 2 In addition, current research in the area of targeted gene deletions holds great promise to further elucidate mechanisms of cardiac development. Editorial see p 228 Clinical Perspective on p 322Although structurally similar to the human, the significantly reduced size of the murine cardiovascular system presents a number of technical challenges when attempting to stage anatomic features such as vascular structures. Identification and characterization of the phenotype of cardiovascular defects in mice traditionally has relied on histological analysis of sectioned specimens. Histology,...

Purpose The purpose of this work was to develop and demonstrate feasibility and initial clinical validation of quantitative susceptibility mapping (QSM) in the abdomen as an imaging biomarker of hepatic iron overload. Theory In general, QSM is faced with the challenges of background field removal and dipole inversion. Respiratory motion, the presence of fat, and severe iron overload further complicate QSM in the abdomen. We propose a technique for QSM in the abdomen that addresses these challenges. Methods Data were acquired from 10 subjects without hepatic iron overload and 33 subjects with known or suspected iron overload. The proposed technique was used to estimate the susceptibility map in the abdomen, from which hepatic iron overload was measured. As a reference, spin-echo data were acquired for R2-based LIC estimation. Liver R2* was measured for correlation with liver susceptibility estimates. Results Correlation between susceptibility and R2-based LIC estimation was R2 = 0.76 at 1.5T and R2 = 0.83 at 3T. Further, high correlation between liver susceptibility and liver R2* (R2 = 0.94 at 1.5T; R2 = 0.93 at 3T) was observed. Conclusion We have developed and demonstrated initial validation of QSM in the abdomen as an imaging biomarker of hepatic iron overload.

Purpose To compare the performance of fat fraction quantification using single-R2* and dual-R2* correction methods in patients with fatty liver, using MR spectroscopy (MRS) as the reference standard. Materials and Methods From a group of 97 patients, 32 patients with hepatic fat fraction greater than 5%, as measured by MRS, were identified. In these patients, chemical shift encoded fat-water imaging was performed, covering the entire liver in a single breath-hold. Fat fraction was measured from the imaging data by post-processing using 6 different models: single- and dual-R2* correction, each performed with complex fitting, magnitude fitting and mixed magnitude/complex fitting to compare the effects of phase error correction. Fat fraction measurements were compared to co-registered spectroscopy measurements using linear regression. Results Linear regression demonstrated higher agreement with MRS using single-R2* correction compared with dual-R2* correction. Among single-R2* models, all 3 fittings methods performed similarly well (slope = 1.0 ± 0.06, r2=0.89–0.91). Conclusion Single-R2* modeling is more accurate than dual-R2* modeling for hepatic fat quantification in patients, even in those with high hepatic fat concentrations.

Purpose To evaluate the accuracy of R2* models (1/T2* = R2*) for chemical shift-encoded magnetic resonance imaging (CSE-MRI)-based proton density fat-fraction (PDFF) quantification in patients with fatty liver and iron overload, using MR spectroscopy (MRS) as the reference standard. Materials and Methods Two Monte Carlo simulations were implemented to compare the root-mean-squared-error (RMSE) performance of single-R2* and dual-R2* correction in a theoretical liver environment with high iron. Fatty liver was defined as hepatic PDFF >5.6% based on MRS; only subjects with fatty liver were considered for analyses involving fat. From a group of 40 patients with known/suspected iron overload, nine patients were identified at 1.5T, and 13 at 3.0T with fatty liver. MRS linewidth measurements were used to estimate R2* values for water and fat peaks. PDFF was measured from CSE-MRI data using single-R2* and dual-R2* correction with magnitude and complex fitting. Results Spectroscopy-based R2* analysis demonstrated that the R2* of water and fat remain close in value, both increasing as iron overload increases: linear regression between R2*W and R2*F resulted in slope = 0.95 [0.79–1.12] (95% limits of agreement) at 1.5T and slope = 0.76 [0.49–1.03] at 3.0T. MRI-PDFF using dual-R2* correction had severe artifacts. MRI-PDFF using single-R2* correction had good agreement with MRS-PDFF: Bland–Altman analysis resulted in −0.7% (bias) ± 2.9% (95% limits of agreement) for magnitude-fit and −1.3% ± 4.3% for complex-fit at 1.5T, and −1.5% ± 8.4% for magnitude-fit and −2.2% ± 9.6% for complex-fit at 3.0T. Conclusion Single-R2* modeling enables accurate PDFF quantification, even in patients with iron overload.

Stroke is the third leading cause of death and a significant contributor of morbidity in the United States. In humans, suboptimal cerebral collateral circulation within the circle of Willis (CW) predisposes to ischemia and stroke risk in the setting of occlusive carotid artery disease. Unique genes or developmental pathways responsible for proper CW formation are unknown. Herein we characterize a mouse model lacking Notch signaling in vascular smooth muscle cells (vSMCs), in which the animals are intolerant to reduced cerebral blood flow. Remarkably, unilateral carotid artery ligation results in profound neurological sequelae and death. After carotid ligation, perfusion of the ipsilateral cerebral hemisphere was markedly diminished, suggesting an anastomotic deficiency within the CW. High-resolution microcomputed tomographic (-CT) imaging revealed profound defects in cerebrovascular patterning, including interruption of the CW and anatomic deformity of the cerebral arteries. These data identify a vSMC-autonomous function for Notch signaling in patterning and collateral formation within the cerebral arterial circulation. The data further implicate genetic or functional deficiencies in Notch signaling in the pathogenesis of anatomic derangements underlying cerebrovascular accidents.angiogenesis ͉ cerebrovascular accident ͉ vascular patterning ͉ mastermind

Purpose To validate the utility and performance of a T2* correction method for hepatic fat quantification in an animal model of both steatosis and iron overload. Materials and Methods Mice with low (n=6), medium (n=6) and high (n=8) levels of steatosis were sedated and imaged using a chemical shift-based fat-water separation method to obtain MRI fat-fraction measurements. Imaging was performed before and after each of two superparamagnetic iron oxide injections to create hepatic iron overload. Fat-fraction maps were reconstructed with and without T2* correction. Fat-fraction with and without T2* correction, and T2* measurements were compared after each injection. Liver tissue was harvested and imaging results were compared to triglyceride extraction and histology grading. Results Excellent correlation was seen between MRI fat-fraction and tissue-based fat quantification. Injections of SPIOs led to increases in R2* (=1/T2*). Measured fat-fraction was unaffected by the presence of iron when T2* correction was used, whereas measured fat-fraction dramatically increased without T2* correction. Conclusion Hepatic fat-fraction measured using a T2*-corrected chemical shift-based fat-water separation method was validated in an animal model of steatosis and iron overload. T2* correction enables robust fat-fraction estimation in both the presence and absence of iron, and is necessary for accurate hepatic fat quantification.

Purpose The purpose of this work was to improve the robustness of existing chemical shift encoded water-fat separation methods by incorporating object-based information of the B0 field inhomogeneity. Theory The primary challenge in water-fat separation is the estimation of phase shifts that arise from B0 field inhomogeneity, which is composed of the background field and susceptibility-induced field. The susceptibility-induced field can be estimated if the susceptibility distribution is known or can be approximated. In this work, the susceptibility distribution is approximated from the source images using the known susceptibility values of water, fat, and air. The field estimate is then demodulated from the source images prior to water-fat separation. Methods Chemical shift encoded source images were acquired in anatomical regions that are prone to water-fat swaps. The images were processed using algorithms from the ISMRM Fat-Water Toolbox, with and without the object-based field map information. The estimates were compared to examine the benefit of using the object-based field map information. Results Multiple cases are shown in which water-fat swaps were avoided by using the object-based information of the B0 field map. Conclusion Object-based information of the B0 field may improve the robustness of existing chemical shift encoded water-fat separation methods.

Background: The smaller airways, , 2 mm in diameter, offer little resistance in normal lungs, but become the major site of obstruction in chronic obstructive pulmonary disease (COPD). Objective: To examine bronchiolar remodeling and alveolar destruction in COPD using micro-computed tomography (micro-CT). Methods: Micro-CT was used to measure the number and crosssectional lumen area of terminal bronchioles (TB) and alveolar mean linear intercept (Lm) in 4 lungs removed from patients with very severe (GOLD-4) COPD and 4 unused donor lungs that served as controls. These lungs were inflated with air to a transpulmonary pressure (P L ) of 30 cm H 2 O and held at P L 10 cm H 2 O while they were frozen solid in liquid nitrogen vapor. A high resolution CT scan was performed on the frozen specimen prior to cutting it into 2-cm thick transverse slices. Representative core samples of lung tissue 2 cm long and 1 cm in diameter cut from each slice were fixed at 2808C in a 1% solution of gluteraldehyde in pure acetone, post-fixed in osmium, critically point dried, and examined by micro-CT. Results: A 10-fold reduction in terminal bronchiolar number and a 100-fold reduction in their minimal cross-sectional lumen area were measured in both emphysematous and non-emphysematous regions of the COPD lungs. Conclusions: The centrilobular emphysematous phenotype of COPD is associated with narrowing and obliteration of the terminal bronchioles that begins prior to the onset of emphysematous destruction.