| Background and ObjectiveGastric carcinoma is the most common malignant tumor of the digestive tract in China, and is the third leading cause of the cancer-related deaths, only inferior to lung cancer and hepatocellular carcinoma, and both the incidence and mortality of it is the first in malignant tumors in rural areas. And the stomach is the most common site of gastrointestinal stromal tumors(GISTs) and gastrointestinal lymphoma.The value of contrast-enhanced MSCT scan in diagnosis and differential diagnosis of gastric tumors has been proved by many researches, but the studies of gastric arterial CT angiography(CTA) are relatively fewer. To know the feeding arteries, vascular invasion and artery variation is essential for performing the best therapeutic regimen, avoiding vascular injury, reducing bleeding and shortening operation time.In the previous studies, the display rate of larger diameter arteries such as left gastric artery(LGA) and right gastroepiploic artery(RGEA) was nearly100%, but the display rate of smaller diameter arteries like right gastric artery(RGA), left gastroepiploic artery(LGEA), short gastric artery(SGA) and posterior gastric artery (PGA) was lower. Special imaging of GE Discovery CT750HD generates a set of single energy images. Recent study reveals that image quality of CTA of the optimal keV is better than that of the conventional polychromatic images.The aim of the study includes three aspects:First, to asess the value of special CT angiography on gastric arterial anatomy and artery variation. Second, to explore the effect of the optimal contrast-to-noise ratio(optimal CNR) technique on image quality of gastric arterial CTA in spectral imaging. Third, to evaluate the feeding arteries of gastric tumors.Materials and methods1Clinical datas64patients with clinically suspected gastric diseases from May2011to December2011were collected, including46males and18femals, excluding cases with histories of abdomen surgery. The range of age was between27and79, average at61.2. Pathological results:45cases were gastric cancer.9cases were gastric gastrointestinal stromal tumors(GISTs).6cases were gastric lymphoma, and4cases were chronic gastritis.2Scanning methodAll the subjects were asked to be fasting for8-12h, and the subjects without contraindications(such as benign prostate hypertrophy and glaucoma) were intramuscular injected654-220mg10-15min before the scanning, and were asked to drink water800～1000ml. All the patients took supine position, and underwent dual-phase enhanced gemstone spectral imaging examination, using a single tube, rapid dual kVp(80kVp and140kVp) switching technique on a high-definition Discovery CT750HD (GE Healthcare, Wisconsin, USA). The scanning range was from the top of liver to the inferior pole of kidney. The non-ionic contrast media Iohexol(Omnipaque350mgI/ml) at a dose of1.5ml/kg was injected with a high pressure syringe at a rate of4ml/s through median cubital vein. The arterial phase and portal venous phase scans were triggered when the aortic CT value was200HU and65s after the injection. The GSI scanning parameters:80kVp and140kVp switching per0.5ms, automatic tube current, the thickness and spacing:5mm, pitch:0.984:1, tube rotation time:0.8s. The reconstruction thickness was0.625mm, at an interval of0.625mm. 3Data processing and analysisData was sent to the GE ADW4.4workstation and data of the arterial phase was post-processed by an experienced radiologist using the GSI Viewer. The CNR plot of GSI viewer was used to select the optimal CNR for gastric artery. A circular region of interest(ROI) was placed within the base of the celiac trunk which we wanted to emphasize, and another ROI was placed within the gastric wall of the same slice which we wanted to contrast against. The GSI Viewer software package automatically calculated and displayed the CNR values for the101sets of monochromatic images, and from the CNR plot, the optimal monochromatic level for generating the best CNR between the gastric artery and the gastric wall could be selected. ROI was placed within the base of the celiac trunk, the gastric wall, and the subcutaneous fat tissue in the abdomen of the same slice to measure the CT value both in the optimal monochromatic images and in the140kVp polychromatic images. CNR was defined according to the formula: CNR=(ROIo-ROId)/SDn,(ROIo denoted CT value of the base of the celiac trunk, and ROId denoted the CT value of the gastric wall of the same slice, and SDn denoted the standard deviation of the subcutaneous fat tissue in the abdomen of the same slice). Measurements of all ROI were repeated for3times and the average value was chosen as the result.Both this monochromatic and the polychromatic image sets were post-processed with volume rendering(VR) and thin slice maximum intensity projection(TSMIP). Three experienced radiologists independently and subjectively graded overall noise and delineation of the left gastric artery(LGA), right gastric artery(RGA), left gastroepiploic artery(LGEA), right gastroepiploic artery(RGEA), short gastric artery (SGA) and posterior gastric artery(PGA) on CTA images with a4-point scale, and recorded the display rate of the arteries and the artery variation. Evaluation standard:4stood for excellent(arteries could be clearly shown and the margins were sharp);3stood for good(the arterial stem was clearly shown and the end was blurred);2stood for middle(the arteries were light);1stood for poor(only the distribution of the arteries were recognized);0arteries could not be recognized.Data was handled by SPSS13.0statistical package. The mean optimal keV for generating the best CNR was computed. Fisher’s exact probability was used to compare the display rate of gastric arteries on VR from the optimal monochromatic and the polychromatic images. Paired t-test or Wilcoxon matched-pairs signed ranks test was performed on CT value of the celiac trunk, contrast-to-noise ratio, image noise and subjective scores from the optimal monochromatic and the polychromatic images sets separately. P<0.05was defined as statistical significance.Results1. The monochromatic images at53±3keV was found to provide the best CNR for gastric arterial CTA. On monochromatic and the conventional140kVp VR images the display rate of LGA and RGEA were both100.0%; PGA, both10.9%; LGEA,85.9%and78.1%respectively; RGA,71.9%and65.6%; SGA21.9%and15.6%, but there was no significant difference(each P>0.05). At the same time, artery variation was found in35cases(in14cases, there was more than one kind of variation).2. The mean CT value, CNR of the celiac trunk and image noise at the optimal keV level(654.68±120.17HU,36.96±11.76,16.80±4.73) were higher, compared with those of the conventional polychromatic images(291.44±51.29HU,20.87±7.32,12.70±3.58)(each P<0.001). The mean CT value, CNR of the celiac trunk, image noise at the optimal keV level increased by124.6%,77.1%and32.3%respectively than those of the conventional polychromatic images.3. The subjective scores of the LGA, RGA, LGEA, RGEA, PGA, SGA and the total score of the CTA images at the optimal keV level(3.73±0.44,2.39±1.55,2.35±0.72,3.48±0.63,0.20±0.70,0.60±1.09,12.75±2.81) were all higher, compared with those of the conventional polychromatic images(2.97±0.55,1.64±1.33,1.5±0.77,2.89±0.79,0.12±0.44,0.38±0.85,9.4±2.43)(each P<0.05), increased by25.6%,45.7%,56.7%,20.4%,66.7%,57.9%and35.6%respectively.4. All the blood supply of60gastric tumors was displayed on CTA. In41cases, the feeding artery became dilatate; lost the adipose space, or the artery was wraped or penetrated into the tumors. VR can directly demonstrate anatomical structures and morphological changes of the arteries and TSMIP can clearly display the relationship between the arteries and the tumors. Conclusions1. Gastric arterial CTA of spectral CT can clearly and directly show the anatomy and vascular variation of the gastric arteries.2. The image quality of gastric arteries from the optimal monochromatic images was improved.3. Gastric arterial CTA of spectral CT can clearly and directly demonstrate the feeding arteries of the gastric tumors. |
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