Using synchrotron radiation angiography with a highly sensitive detector to identify impaired peripheral perfusion in rat pulmonary emphysema

A new method for visualizing pulmonary artery microvasculature using synchrotron radiation pulmonary microangiography: the measurement of pulmonary arterial blood flow velocity in the high pulmonary blood flow rat model

BACKGROUND

Increased pulmonary blood flow (PBF) and shear stress may provoke irreversible vascular remodeling, yet invasive visualization of the microvasculature complicates monitoring. A non-invasive imaging methodology would therefore safely provide mechanistic insights into the progression of high PBF-induced vascular remodeling.

PURPOSE

To establish a novel microvasculature visualization method using synchrotron radiation pulmonary microangiography (SRPA) that can also calculate PBF velocity in vivo.

MATERIAL AND METHODS

A high PBF rat model was established by making a fistula between the abdominal aorta and inferior vena cava. After eight weeks, SRPA was performed and the dynamic density changes in the right lower pulmonary artery (PA) were calculated by software. SRPA was performed with a HARP (High-Gain Avalanche Rushing amorphous Photoconductor) receiver. PBF velocity was calculated by contrast medium transit time within the PA. All data were presented as mean ± standard error (SE). Student's t-test was used for comparison between the two groups.

RESULTS

High dynamic spatial and contrast resolution from SRPA in the PA allowed for clear pulmonary microangiography and accurate detection of higher PBF in the rat model (82.3 ± 8.5 mm/s high-PBF group vs. 46.1 ± 4.3 mm/s control group, P < 0.01).

CONCLUSIONS

These novel results demonstrate that SRPA was useful in both visualizing the dynamic flow distribution within the microvasculature and calculating PBF velocity. This newly developed, non-invasive technology may become a powerful tool in clarifying the mechanism of vascular remodeling associated with high PBF-induced shear stress.

How high resolution 3-dimensional imaging changes our understanding of postnatal lung development

During the last 10 + years biologically and clinically significant questions about postnatal lung development could be answered due to the application of modern cutting-edge microscopic and quantitative histological techniques. These are in particular synchrotron radiation based X-ray tomographic microscopy (SRXTM), but also ³Helium Magnetic Resonance Imaging, as well as the stereological estimation of the number of alveoli and the length of the free septal edge. First, the most important new finding may be the following: alveolarization of the lung does not cease after the maturation of the alveolar microvasculature but continues until young adulthood and, even more important, maybe reactivated lifelong if needed to rescue structural damages of the lungs. Second, the pulmonary acinus represents the functional unit of the lung. Because the borders of the acini could not be detected in classical histological sections, any investigation of the acini requires 3-dimensional (imaging) methods. Based on SRXTM it was shown that in rat lungs the number of acini stays constant, meaning that their volume increases by a factor of ~ 11 after birth. The latter is very important for acinar ventilation and particle deposition.

Association between endothelial function and micro-vascular remodeling measured by synchrotron radiation pulmonary micro-angiography in pulmonary arterial hypertension

OBJECTIVES

Pulmonary arterial hypertension (PAH) is a progressive disease which causes increased vascular resistance. In this study, our purpose was to quantify the micro-vascular remodeling in monocrotaline-induced PAH rats using synchrotron radiation pulmonary micro-angiography (SRPA), a method we have previously established in an in vivo rat model. To determine the relationship between endothelial function and vascular remodeling, the local expression of endothelin-1 (ET-1), endothelial nitric oxide synthase (eNOS) and vascular endothelial growth factor (VEGF) was evaluated using immunohistochemical staining.

METHODS

Monocrotaline-induced PAH rats were created by subcutaneous injection of monocrotaline. After 2 weeks, SRPA was performed at the Photon Factory of the High Energy Accelerator Research Organization. The internal diameters of pulmonary arterioles were measured using SRPA images. Semi-quantified analyses of ET-1, eNOS and VEGF expression in pulmonary arterioles were performed by immunohistochemical staining.

RESULTS

Micro-vascular density and the internal diameters of pulmonary arterioles were significantly decreased in PAH. ET-1 expression was significantly increased in PAH compared with the control (1.53 ± 0.45 vs. 0.80 ± 0.14) and eNOS expression was significantly decreased in PAH compared with the control (1.12 ± 0.59 vs. 1.91 ± 0.66), although VEGF expression did not differ between the groups.

CONCLUSIONS

SRPA can be effectively used for visualizing the decreased pulmonary micro-vasculature associated with PAH. Increased ET-1 expression and decreased eNOS expression may contribute to the proliferation and vasospasm of pulmonary arterioles induced by endothelial dysfunction due to PAH. This SRPA technology may help to identify a correlation between endothelial function and micro-vasculature remodeling in PAH.