| Objective:To evaluate the impact of different volume and injection rate of contrast medium on portal vein peak time、enhancement peak value and portography in animal.Materials and methods1. Experiment of portal vein’s enhancement peak time and enhancement value in different injection volumes and injection rate.Experiment objects:Selection of six normal Bama pigs:weights was about 20kg-40kg. Before CT scan, the animals were deprived of food for 10 hours, water for 4 hours before each MSCT examination and then weights were measured. Four of six pigs proceeded respectively CT scan with different volumes(2.0ml/kg,2.5ml/kg) and different injection rate (2.0ml/s, 2.5ml/s,3.0ml/s); compatible combination examination:24 times; the other two pigs proceeded only 3 times scan of different volume and injection rate, the compatibility of different combination a total of 27 scans. The minimum time delay between two consecutive examination in the same animal was 48h to allow complete renal excretion of contrast medium.CT scans:Experiment Bama pigs were first anesthetized, then were fixed in the prone position on a fixed plate, while establishing intravenous access behind the ear vein. Examination equipment is the 64-slice GE Light Speed VCT. Entire liver CT scan:selected thickness were 5mm with continuous scan. The images were browsed and the portal main trunk were selected (either throw out the first right branch of portal vein or upwards two levels) as the target level of continuous dynamic perfusion scan. By binoculars high pressure injection syringe, bolus contrast medium (diatrizoate 60%) injection was performed through ear vein, scans started 2s after injection of contrast medium,1 layer/time/sec, interval of Is, a total scan time of 80s, to obtain 40 images.CT image processing:After the perfusion scan data was introduced into GE Advantage Window4.4 workstations,ROI was placed in the portal vein area, Perfusion4 software or manual measurement and the mapping of the portal vein time-density curves (TDC) was used, and the portal vein reached peak time and peak enhancement were obtained.2. Experiment of portographyExperiment Objects:4 of the 6 experiment Bama pigs. Experimental Methods:The portal vein peak time of the experiment displayed the best scan baseline delay time, the same Bama pig consecutive scans separated time was at least 48hours, by using the same flow rate, contrast medium and dose calculation mode processed enhanced portal phase MSCT scan. Scan range included the entire liver parenchyma.Image processing and analysis:The scan data was introduced into the GE Advantage Window4.4 workstation and carried through VR, MIP imaging of portal vein post processing. Assess to the image quality of portography, based on a branch of portal vein and the opacification of portography, clarity of image was divided into the A, B, C, D grads. Data analysis was performed with SPSS 16.0 statistical software package (factorial design analysis of variance) and Microsoft Office Excel 2003.Result:1. When the injection rate was 2.0ml/s, the volume were 2.0ml/kg and 2.5ml/kg, Imax P were 187.9±13.3Hu,215.7±9.8Hu; when the injection rate was 2.5ml/s, the volume were 2.0ml/kg and 2.5ml/kg, Imax P were 188.1±24.4Hu,227.3±36.7Hu; when the injection rate was 3.0ml/s, the volume were 2.0ml/kg and 2.5ml/kg, Imax P were 214.5±17.0Hu, 235.3±11.5Hu.2.When the volume were different, the degree of maximum enhancement of portal vein showed significant difference (p<0.05). Without including the injection rate’s parameter, when comparing 2.5ml/kg with 2.0ml/kg volume intensity, portal vein enhancement peak value increased for 29.28Hu(p<0.05). When the injection rates were different, the degree of maximum enhancement of portal vein showed no statistical significance (p> 0.05).3. When the injection rate was 2.0ml/s, the volume were 2.0ml/kg and 2.5ml/kg, Tmax P were 43.4 ± 8.2 s,49.0 ± 8.2s; when the injection rate was 2.5ml/s, the volume were 2.0 ml/kg and 2.5ml/kg, Tmax P were 35.0 ± 4s, 39.5 ± 6.4s; when the injection rate was 3.0ml/s, the volume were 2.0ml/kg and 2.5ml/kg, Tmax P were 31.0 ± 5.9 s,38.0 ± 1.0s.4. With different injection rate and volume, the time to reach peak enhancement of portal vein showed significant difference (p<0.05). There was difference between 2.0ml/s and 2.5ml/s> 2.0ml/s and 3.0ml/s (p<0.05); no difference was shown between 2.5ml/s and 3.0ml/s (p> 0.05). Without considering the flow rate’s parameter, when comparing 2.5ml/kg with 2.0ml/kg, Tmax P extended for 5.73s (p> 0.05), no statistical significance.5. In the case of 2.5ml/kg:when the injection rate was 2.0ml/s,the obtained portography showed A grade one time, B grade three times; when the injection rate was 2.5ml/s, the portography showed grade A three times, grade B one time; when the injection rate was 3.0ml/s, the portography showed grade A three times, grade B one time. In the case of 2.5ml/kg:when the injection rate was 2.0ml/s, the portography showed grade A one time, grade B three times; when the injection rate was 2.5ml/s, the portography showed grade A three times, grade B one time; and when the injection rate was 3.0ml/s, the portography showed grade A three times, grade B one time.Conclusion:1.The increasing of the volume has impacts the degree of maximum enhancement and time to reach peak enhancement of portal vein. When the other parameters do not change, the increase the volume of injection prolongs the time-to-peak enhancement of portal vein and increase maximum portal vein enhancement.2. The increased of the injection rate affects the portal vein peak time, but has no effect on portal vein enhancement peak value. When the other parameters are constant, the increase of injection rate shortens the time-to-peak enhancement of portal vein and increase maximum portal vein enhancement.3. When the volume are constant, injection rate are 2.5ml/s and 3.0ml/s, MSCTP images have consistent quality; when the volume are 2.0ml/kg and 2.5ml/kg MSCTP images show mostly grade B and above. According to the diagnostic requirements, lowest contrast medium volume and minimum injection rate can be used as recommended parameters for multi slices spiral CT portal vein phase scan; this study suggests the best contrast medium volume at 2.0ml/kg and contrast medium injection rate at 2.5ml/s. |
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