Detecting Microcirculatory Dysfunction Of Small Intestinal Ischemia-reperfusion Injury Using MSCT Perfusion Imaging In Porcine Models

PART I Small Intestinal MSCT Perfusion Imaging:A Feasibility Study in Porcine ModelsObjective To investigate the feasibility of multi-slice CT (MSCT) perfusion imaging for evaluating hemodynamics of small intestine in porcine models.Materials and methods Fifteen pigs were fixed in a supine postion after anesthesia with intramuscular injection of ketamine and atropine sulphate. Abdominal belts were used to control respiratory artifacts. Small intestinal MSCT perfusion imaging was performed on 128-slice helical CT with a coverage of middile abdomen including most portions of small intestine. Fifty milliliters of iodine contrast media (370 mgl/ml) was administered with a flow rate of 5 ml/s through ear vein by a power injector. Quantitative perfusion parameters, blood flow (BF), blood volume (BV), mean transit time (MTT), and permeability surface (PS), were measured by two radiologists separately at an imaging postprocessing workstation. The quantitative perfusion parameters were compared between jejunum and ileum using paired-t test and measurement reproducibility was evaluated using Bland-Altman analyse. Results Small intestional anatomy of porcines was similar to that of human. MSCT perfusion color maps showed jejunum and ileum as homogeneous hypervascularity. Time-density curve (TDC) of small intestine appeared as a rapid rise at early phase and a long plateu at later phase. Jejunum had the slightly higher BF and BV values and the slightly lower PS and MTT values compared with ileum [(35.57±7.12) VS (33.81±8.96) ml/100ml/min, (10.56±1.40) ml/100ml VS (9.83±1.58) ml/100ml, (19.54±3.77)VS(21.02±4.46)s, and(22.25±5.71)VS(23.69±4.53)ml/1 OOml/min, respectively]. However, there were no stastistically significant differences (p=0.463, 0.284,0.464, and 0.72, respectively). Bland-Altman analyse showed a good measurement reproducibility of quantitative perfusion parameters between two separate readers (difference mean=0.7907,0.0068,-0.3139 and 0.745, respectively).Conclusion It is feasibility for MSCT perfusion imaging evaluating the hemodynamics of small intestine in porcine models. The small intestine are homogeneous hypervascularity without significant difference between jejunum and ileum in quantitative perfusion parameters. (33.81±8.96) ml/100ml/min, (10.56±1.40) ml/100ml VS (9.83±1.58) ml/100ml, (19.54±3.77)VS(21.02±4.46)s, and(22.25±5.71)VS(23.69±4.53)ml/1 OOml/min, respectively]. However, there were no stastistically significant differences (p=0.463, 0.284,0.464, and 0.72, respectively). Bland-Altman analyse showed a good measurement reproducibility of quantitative perfusion parameters between two separate readers (difference mean=0.7907,0.0068,-0.3139 and 0.745, respectively).PART II Visualizing Microcirculatory Dysfunction of Small Intestinal Ischemia-reperfusion Injury Using MSCT Perfusion ImagingObjective To investigate the value of multi-slice CT (MSCT) perfusion imaging to visualize microcirculatory dysfunction of small intestinal ischemia-reperfusion injury (IRI) in porcine models. Materials and methods Forty-eight pigs were included in the study. IRI animals were divided into four groups according to different reperfusion time point:IRI 1h group, IRI 2h group, IRI 3h group, and IRI 4h group (n=6, respectively). Control groups were composed as follows:sham-operated 3h group, sham-operated 4h group, sham-operated 5h group, sham-operated 5h group (n=5, respectively) and ischemia group (n=4). IRI groups were induced by separating and clamping super mesenteric artery (SMA) for 2 hours and declamping SMA for reperfusion for 1h,2h,3h and 4h, respectively. Sham-operated groups were produced by separating SMA without clamping and controled at corresponding postoperative 3h, 4h,5h and 6h. Ischemia group was produced by separating and clamping SMA without reperfusion. Abdominal belts were used to control respiratory artifacts. Tracheal intubation and mechanical ventilation were performed after general anesthesia. All animals underwent MSCT perfusion imaging using a 128-slice CT scanner. Scanning parameters, image postoprocessing and measurement were the same as listed in Part I. All subjects were sacrificed with IV injection of KCL after CT examination. Mucosal tissues were scraped with a glass slide and snap frozen in liquid nitrogen for testing amount of malondialdehyde (MDA) and activity of superoxide dismutase (SOD). Distal ileum segment was resected for HE staining to evaluate inteastinal wall injury according to Chiu’s morphologic standard. Correlation between MSCT perfusion parameters, blood flow (BF), blood volume (BV), mean transit time (MTT), and permeability surface (PS), and amount of MDA and SOD was confirmed by Spearman analysis method. Results BF value of IRI 4h group was significantly lower than that of sham-operated group [(18.832±4.687) VS (31.014±7.039) ml/100ml/min, p=0.018]. BV values of IRI 2h, IRI 3h and IRI 4h groups were significantly lower than those of sham-operated groups [(4.624±0.668) VS (9.160±1.887) ml/100ml, p=0.003; (5.015±1.203) VS (9.310±1.466) ml/100ml, p=0.000; (3.376±0.826) VS (9.188±0.785) ml/100ml, p=0.000, respectively]. MTT values of IRI 1h, IRI 2h, IRI 3h and IRI 4h groups were significantly lower than those of sham-operated groups (p=0.000,0.000,0.011 and 0.008, respectively). BF, BV, PS values between four IRI groups were significantly different (F=9.965,10.856 and 5.511, respectively; p=0.005,0.000 and 0.007, respectively). MTT values between four IRI groups showed no significant difference (F=1.760, p=0.191). There were a good negative correlation between BF, BV values and MDA (r=-0.714, p=0.000; r=-0.713, p=0.000; respectively) and a good positive correlation between BF, BV values and SOD (r=0.641, p=0.001; r=0.677, p=0.000; respectively). The 2-hour ischemic loops were not significantly exacerbated with reperfusion. Conclusion MSCT perfusion imaging could be a valuable tool for detecting microcirculatory dysfunction and dynamic surveillance of small intestinal IRI.PART Ⅲ MSCT Imaging Findings of Small Intestinal Ischemia-reperfusion Injury:Correlation with HistopathologyObjective To investigate multi-slice CT (MSCT) imaging findings of small intestinal ischemia-reperfusion injury (IRI) and correlate with histopathology.Materials and methods Twenty pigs were randomly divided into four groups according to different reperfusion time point:IRI 1h group, IRI 2h group, IRI 3h group, and IRI 4h group (n=5, respectively). Abdominal belts were used to reduce respiratory artifacts. Tracheal intubation and mechanical ventilation were performed after general anesthesia. All animals underwent double-phase dynamic contrast 128-slice CT scanning with coverage of whole abdomen. Iodine contrast media (370 mgl/ml) was administered at a rate of 3 ml/s with a volume of 2ml/kg through ear vein by a power injector. The delay time of arterial and venous phase was 38s and 72s, respectively. MSCT scanning was first performed 3 days before completing animal models as baseline images. Mesenteric attenuation, wall thickness, enhancement,and dilation of bowel, intraluminal fluid were reviewed. All animals were sacrificed with IV injection of KCL after CT terminal examination. Distal ileum segment was resected for HE staining to evaluate intestinal wall injury according to Chiu’s morphologic standard. Results Mesenteric edema was only seen in IRI 4h group. There were no significant differences for intestinal wall enhancement value at arterial phase between IRI 1h group, IRI 2h group, IRI 3h group, IRI 4h group and their baseline values (p=0.340,0.810,0.169 and 0.071, respectively). There were no significant differences for intestinal wall enhancement values at venous phase of IRI 1h,2h,3h group compared with their baseline values (p=0.608、0.659 and 0.343, respectively). However, intestinal wall enhancement value at venous phase of IRI 4h group was significantly lower than baseline values (p=0.013). Intestinal dilation and intraluminal fluid were visualized in 15 pigs, most obvious in IRI 4h group although no significant difference compared with other 3 groups. At histopotholgy, intestinal wall changes mainly localized in mucosal layer, which appeared as mucosa shed, neutrophil infiltration, interstital edema and dilation of capillaries. However, there were no significant differences for Chiu’s scores among IRI 1h,2h,3h and 4h groups (p=0.797). Conclusion MSCT could detect morphologic changes of small intestinal IRI which appear as bowel dilation and intraluminal fluid from IRI 1h to 4h, decreased enhancement and mesenteric edema on IRI 4h. No bowel wall injury aggravates histopathologically during the reperfusion process.PART IV Secondary Lung Injury of Small Intestinal Ischemia-reperfusion Injury:MSCT Imaging Findings and Histopathologic CorrelationObjective To investigate multi-slice CT (MSCT) imaging findings secondary lung injury of small intestinal ischemia-reperfusion injury (IRI) and correlate with histopathologic results. Materials and methods Sixteen pigs were randomly divided into lung injury group (n=8) and sham-operated group (n=8). Lung injury group was produced by clamping super mesenteric artery (SMA) for 2 hours and declamping SMA for 4 hours. Sham-operated group was produced by separating SMA without clamping. Chest CT scans were performed with parameters as follows: collimation,0.6mm; slice thickness, 1mm; slice gap,0.7mm; field of view,294 mm; 122 kv and 99 mAS. Axial images were used to evaluate lung abnormalities. All animals were scarificed with IV injection of KCL after CT examination. Bronchoaveolar lavage fluid, permeability index and the wet/dry radio of the lung were analyzed and compared. Histopathological changes were observed after HE staining. Results MSCT showed lung abnormalities in 5 pigs, which appeared as increased attenuation, patchy ground-glass opacities, consolidation, interlobular septa and bronchovascular bundles thickening, and reticular opacities. There were no obvious lung abnormalities in remaining 3 pigs. Lung parenchymal injury was visualized at histopathology. Alveolar septal thickening, interstitial edema and capillary dilation were seen in 5 pigs. There were severe alveolar wall distruction, coalescene, alveolar and intertitial exudation in 2 pigs. Only capillary congestion and interstitial edema were showed in the remaining 3 pigs. The wet/dry ratio and lung permeability index in IRI group were significantly higher than those of control group. No lung structural abnormalies were detected in contral group. MSCT showed a sensitivity of 62.5% and specificity of 100% respectively for diagnosing secondary lung injury of small intestine IRI. Conclusion MSCT could accurately visualize secondary lung injury of small intestine IRI and is a useful tool for one-stop imaging evaluation for small intestine IRI.