| Superparamagnetic iron oxide (SPIO) is a new-style tissue specific MR contrast agent. It is completely different from the conventional Gd-DTPA in the principles of enhancement and clinical application. The purpose of this study is: 1. To establish a curve of dosage gradient-liver signal intensity on SPIO enhanced MR imaging of normal rats and find a safe and effective dose for enhancement. 2. To compare the contrast noise ratio (CNR) of lesion to liver and the detecting ability on MR imaging between before and after SPIO administration in model of implanted liver adenocarcinoma rats. 3. To evaluate the potentiality of SPIO enhanced MR imaging in differentiation hepatocellular carcinomas (HCC) from hyperplastic nodules in rats model of chemically induced liver tumors and to compare the sensitivity of detection for different HCC in size before and after SPIO adiministration. 4. To evaluate the efficacy of SPIO enhanced MR imaging in the detection and characterization of focal hepatic lesions, compared with Gd-DTPA enhanced MR images. 5. To study the affection of different field strength and various sequences in detecting hepatic carcinoma using SPIO enhanced MR imaging.Part I: Superparamagnetic iron oxide-enhanced MR imaging in rat liver Objective: To establish a curve of dosage gradient-liver signal intensity of SPIO in normal rats and to find an appropriate dose for enhancement. Methods: 72 normal SD rats, 4 rats a group at random, underwent MR enhancement with 0, 2, 5, 8, 10, 12, 15, 20, 30, 40, 50, 60, 70, 80, 100, 140, 210, 280 (mol/kg SPIO respectively after planeexamination. The signal-to-noise ratio of liver was measured and a curve of dosage gradient-liver signal intensity was made. Results: ⑴Along with the increase of the dose of SPIO, the signal intensity of both T1 and T2 weighted images of liver declined. ⑵T2 weighted images is more sensitive than T1 weighted images in small dose, the ED50 of T1 weighted is 8 (mol/kg, and the ED50 of T2 weighted is 5 (mol/kg. ⑶ When the dose is greater than 15 (mol/kg, the signal intensity of T1 weighted images declined more rapidly than T2 weighted, the effect of enhanced T1 weighted images resemble T2 weighted ones, and it's images with more fine resolution. ⑷At the dose of 40 (mol/kg, the signal intensity of T1 weighted images approach the background noise, and at the dose of 15 (mol/kg, the signal intensity of T2 weighted images approach the background noise. Conclusion: Good effect of T1 and T2 enhanced MR imaging can be acquired at the dose of 20~10 (mol/kg SPIO respectively, the best contrast-to-noise ratio is found on T2-weighted enhanced MR image.Part II: Hepatic implanted tumor in rat: superparamagnetic iron oxide-enhanced MR imagingObjective: To compare the lesion to liver CNR and the detecting ability on MR imaging between before and after SPIO injection in model of implanted liver adenocarcinoma rats. Materials and methods: 38 implanted liver adenocarcinoma rats with 43 tumors underwent T1 and T2-weighted MR imaging before and after the injection of SPIO agent. Evaluations included enhancing characteristics of the tumors, counting the number of lesions and statistical analysis of quantitative changes in the signal intensity of both lesions and normal liver. Results: The highest CNR can be acquired on the dose of 20(mol Fe/kg on enhanced T2-weighted MR images. Its CNR almost doubled compared with that of enhanced T1-weighted and unenhanced T2-weighted MR images. The CNR of unenhanced T1-weighted MR images was lowest. The number of lesions detected onenhanced MR imaging was the same with that of the pathology, and enhanced MR imaging was superior to unenhanced MR imaging in tumors smaller than 3mm, the ratio of leave out on unenhanced MR images was 36.3 percent. Conclusion: Good effect of SPIO enhanced T1 and T2-weighted MR imaging can both be acquired at the dose of 20(mol Fe/kg, its detecting ability was the same with pathology, and the best contrast-to-noise ratio was found on T2-weighted enhanced MR image.
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