| PARTâ… MDCT and CTA of Acute Mesenteric Ischemia Induced by Embolization of SMA in an Experimental Porcine ModelObjective To assess the usefulness of multidetector row CT (MDCT) and CT angiography (CTA) for detecting the early sign of acute mesenteric ischemia (AMI) in experimental porcine model. Materials and Methods 12 pigs were assigned to four groups with 3 pigs in each group. The digital subtraction angiography (DSA) of superior mesenteric artery (SMA) and the embolization of branches of SMA were performed using a percutaneous Seldinger technique, with gel foam and blood clot. MDCT pre- and postcontrast with arterial, venous and delay phase scans, and CTA with three-dimentional reconstrations were carried out at preoperation, 3 h, 6 h, 9 h, and 12 h after occlusion. The normal mesenteric vascular anatomy, arterial occlusion, mesentery and bowel changes, and dynamic evolution were evaluated. Results AMI changes were identified pathologically in all 12 experimental pigs, with the severity corresponding to the time of embolization. CTA showed all 57 embolized branches of SMA and 29 of 34 unoccluded arterial branches with 5 false-positive vessel occlusions. Its sensitivity and specificity were 100% and 85.3% respectively. Thin-slab maximum intensity projection (TSMIP) identified the disappearance of distal combed vessel branches and brush vasa recta, which were clearly delineated in normal bowel segment. Using this criterion, TSMIP correctly defined 23 of 24 ischemic bowel segments and all 12 normal bowel segments with 95.8% of sensitivity and 100% specificity. The early direct ischemic signs were occluded vessels, the disappearance of distal combed or brushy vasa recta, and poor bowel enhancement. The early indirect sign was bowel dilatation with fluid. Conclusion MDCT and CTA reliably define normal and occluded mesenteric vessels in the pig. It can easily detecte ischemic bowel segment by identified early changes of ischemia.PARTâ…¡MDCT Evaluation of Acute Mesenteric Ischemia Induced by Ligation of SMV in an Experimental Porcine ModelObjective To evaluate MDCT for detecting the early sign and dynamic evolution of AMI induced by occlusion of SMV in experimental porcine model. Materials and Methods 12 pigs were assigned randomly to three experimental groups and one control group with 3 pigs in each group. After performing laparotomy, SMV was separated and ligated in 9 pigs, and separated wothout ligation in 3 control pigs. MDCT pre- and postcontrast with arterial, venous and delay phase scans, and CTA reconstrations of mesenteric vessels were carried out at preoperation, 6 h, 12 h and 18h after ligation. The changes of mesenteric vessels, bowel, abdominal cavity pre-and post-operation, and dynamic evolution were evaluated. The results were compared with those of pathology. Results AMI changes were identified pathologically in all 9 experimental pigs. The congestion, edema and venular engorgement were found limiting to submucosa at 6h, and involving all layers with thicken wall, hemorrhage, and loss of some mucosa at 12h ligation of SMV. Diffuse necrosis, loss, ulcer and hemorrhage of mucosa, degeneration and fragmentation of muscular fibers, and fibrinous effusion, with bowel dilatation, fluid and thinness were seen at 18h. MDCTA clearly delineated main trunk of SMV, peripheral major and minor tributaries up to brushy vasa recta. It correctly identified the location and shape of ligation. The early ischemic findings were bowel wall thickness, mesenteric stranding, ascites and pronounced bowel enhancement. SMA and its major branches appeared spasm which displaying poor filling and delayed and prolonged visualization, and SMV and its tributaries appeared poor and delayed opacification. With time lapse, thinning bowel wall, dilatating bowel with fluid, aggravating edema of mesentery and acites and poor enhanced bowel were identified. Conclusion Human venous occlusive AMI can be duplicated successfully by the ligation of porcine SMV tributaries. MDCT can reliably define normal and occluded mesenteric vessels, detecte early changes mesenteric ischemia and evolution, and diagnosis venous occlusive AMI.PARTâ…¢The Optimization of Parameters and Anatomical Evaluation of Mesenteric Vessels with MDCT AngiographyObjective To optimize the parameters of multidetector row CT (MDCT) angiography in demonstrating mesenteric vessels and investigate the imaging anatomy of mesenteric vessels. Materials and Method One hundred and forty patients with no abnormal alimentary tract were divided into seven groups with 20 cases each, according to the collimation, slice thickness, the concentration of contrast medium, injection rate and delay time. Enhanced MDCT of whole abdomen were performed, and CT angiograms of mesenteric vessels were reconstructed with volume rendering (VR), maximum intensity projection (MIP) and thin-slab maximum intensity projection (TSMIP). The margin and branches of vessels were scored. The parameters and reconstruction techniques were compared. Three-dimensional (3D) anatomical architectures of 100 cases of mesenteric vessels were analyzed. Results At 0.6mm collimation, CT angiography reconstructed with 1.0mm slice thickness had highest scores in demonstrating mesenteric arteries without statistically significant difference among different slice thickness. CT venography with1.0mm slice thickness was superior to 0.6mm and 1.5mm in demonstrating veins, with statistical difference in the former. CT angiography with 0.6mm collimation was better than that with 1.2mm, with no statistical difference. The 370mgI/ml contrast medium was better than 300mgI/ml in delineating mesenteric arteries as well as veins. The injection rate of 4.0ml/s and 5.0ml/s were superior to 3.0ml/s in demonstrating mesenteric arteries but veins. The optimal delay time of venous phase was 25s behind the arterial phase. Mesenteric vessels were well displayed in all 100 cases. The 3th to 4th -order branches of vessels could be identified in VR and MIP images with better whole view, and better 3D view in the former. In contrast, TSMIP could clearly show the 5th to 6th-order branches of vessels including the vasa recta at the margin of bowel. MDCT angiography clearly displayed the location, origin, diameter, direction, distribution, vascular anastomosis and variation of mesenteric vessels. Conclusion The optimal protocol of MDCT angiography for mesenteric vessels is 0.6mm collimation, 1.0mm slice thickness with 0.5mm increment, 370mgI/ml contrast medium at 4.0ml/s or 5.0ml/s injection rate, the delay time of arterial phase decided by test bolus, and venous phase being 25s behind arterial phase. MDCT with 3D reformatting can clearly visualize the anatomical features of mesenteric vessels; thus it is helpful for the early diagnosis and intervention of pancreatic cancer, ischemic or inflammatory bowel diseases. PARTâ…£The Application of MDCT Angiography of Mesenteric Vessels in Acute Mesenteric IschemiaObjective To evaluate mesenteeric MDCT angiography in the diagnosis of acute mesenteric ischemia (AMI). Materials and Method 43 cases of AMI proven by clinical criteria, or operation and pathology underwent whole abdomen MDCT precontrast, arterial phase and venous phase with 0.6mm collimation. The mesenteric arteries and veins were reconstructed by using VR, MIP, and TSMIP techniques, and abnormal CT angiography findings as well as abnormal bowel and mesentery were analyzed. Results 43 patients with AMI were resulted from SMA embolism (n=4), SMA thrombosis (n=6), mesenteric and portal venous thrombosis (n=13), SMA dissection (n=5), strangulated bowel obstruction (n=10) and vasculitis (n=5). Among 43 patients with AMI, 17 cases were managed by surgery, with 6 infarctions and 11 ischemias identified. 7 and 19 patients were managed by DSA guided interventional and internal conservative therapy respectively, with improvement in 24 cases, deterioration and death in one case respectively. MDCT angiography showed clearly the position, shape, severity and extent of the vascular occlusion, narrow and dissection. It could also demonstrate the abnormal course and direction of the vessels including vascular gather together, shift, tortuosity, retortion, and twist. Furthermore, the pathogenesis of various conditions leading to AMI including atherosclerotic plaque, emboli, thrombosis, dissection, tumorous invasion, strangulated bowel obstruction and vasculitis could identified by MDCT angiography. Conclusion MDCT angiography can clearly demonstrate the abnormal mesenteric vessels which is the direct sign leading to AMI, and identify AMI and its etiology at early stage, with the combination with its indirect findings. |
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