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Purpose To determine the diagnostic value of a new ultrasmall superparamagnetic iron oxide Clariscan®, (NC100150) for the evaluation of renal perfusion in an animal model using a 3D-FFE-EPI sequence. Materials and Methods Four groups of four rabbits each were imaged after bolus injection of NC100150, using a 1.5 T MR system (Gyroscan ACS-NT). T2*w MR images in the coronal plane were acquired over 60 seconds with an echo-shifted 3D-FFE-EPI sequence (TR/TE/α = 18/25 msec/8°). Data were transferred to a workstation and converted into concentration curves. Based on the fitted concentration time curves, parameter maps were calculated pixelwise: bolus arrival time (T0), time-to-peak (TTP), mean transit time (MTT), and relative bolus volume (rBV). Maximum signal decrease was determined with respect to the baseline value. Results Mean MTT increased from 4.2 seconds at a dose of 0.25 mg to 5.9 seconds at 1.0 mg (P < .0001). The maximum signal decrease was observed at 0.75 mg, corresponding to 85% of the baseline value. Transit times of the contrast bolus were accurately calculated for the cortex and the outer medulla, but at the level of the inner medulla no arterial flow profile was identified. No significant difference between the cortex and the outer medulla was found for either T0 or rBV, but medullar TTP and MTT were prolonged with regard to cortical TTP and MTT (6.3 seconds vs. 5.7 seconds, P < .001; 5.7 seconds vs. 4.2 seconds, P < .0001). Conclusion The employed intravascular contrast agent is well suited to assess renal perfusion. By the use of a T2*w3D perfusion sequence, cortical and medullar transit times can be quantified and physiologic information on regional perfusion differences can be obtained. J. Magn. Reson. Imaging 2002;16:190–195. © 2002 Wiley-Liss, Inc.

The purpose of this study was to determine the diagnostic value of the superparamagnetic iron oxide NSR 0430 for the detection of focal liver lesions in the presence of advanced cirrhosis. Cirrhosis and growth of cholangiofibromas were induced in 22 rats by administration of thioacetamide. Sixteen non-cirrhotic animals served as controls. T1 and T2 relaxation times of liver and tumor tissue of 12 animals were measured spectroscopically. In 10 animals in vivo MRI was performed before and 1 hour after contrast administration, and then the tumor-to-liver contrast-to-noise ratio (CNR) was calculated. All specimens were evaluated histologically. After contrast administration, T1 and T2 values of liver tissue showed a significant decrease of 18% (P = 0.01) and 31% (P = 0.009), respectively, whereas relaxation times of tumor tissue did not change. On precontrast turbo spin-echo images, 40 tumors could be identified; after contrast administration, 95 lesions were visible. CNR increased significantly after contrast administration by 297% at a TE of 50 msec and by 254% at a TE of 90 msec. In conclusion, our in vitro and in vivo results demonstrate that administration of NSR 0430 substantially improves liver-to-tumor CNR and lesion detection on T2-weighted magnetic resonance images even in the presence of severe cirrhosis.

The efficacy of the superparamagnetic contrast agent magnetic starch microspheres (MSM) was evaluated in vitro by NMR relaxometry and in vivo by MR imaging using T2-weighted spin-echo (SE) and turbo spin-echo (TSE) sequences at 0.5 T and 1.5 T in 60 normal rats who received MSM in doses of 10-50 mu mol/kg. MR imaging was performed using T2-weighted SE and TSE sequences. The relaxation rates 1/T1 and 1/T2 for liver and spleen increased linearly with MSM concentrations up to 30 mu mol/kg body weight, and approached almost constant levels for higher doses. The slopes in the linear part of the 1/T2 diagram were 0.62 Hz +/- 0.03 for the liver and 0.51 Hz +/- 0.06 x kg/mu mol for the spleen. On all T2-weighted sequences at 0.5 T and 1.5 T, liver signal-to-noise ratio (SNR) decreased by a factor of 2-3 already at the lowest dose of 10 mu mol/kg. SNR values of TSE sequences exceeded values for SE sequences by 50-80%. The SNR decrease was not significantly different between SE and TSE sequences. Our results show that MSM is well suited as a T2 contrast agent at both magnetic field strengths when using conventional SE and fast TSE sequences.

The diagnostic value of magnetic starch microspheres (MSM), a new superparamagnetic contrast agent, was studied in experimental models of diffuse and focal splenic disease in rats by means of ex vivo relaxometry and in vivo magnetic resonance (MR) imaging. Owing to small differences in unenhanced T1 and T2 values between diffuse lymphoma and normal spleen, MR imaging failed to distinguish tumor-bearing animals from control animals by signal-to-noise ratios (SNRs) obtained with T1- and T2-weighted spin-echo sequences. One hour after injection of 20 mumol/kg MSM, lymphomatous spleen showed significantly (P < .001) reduced enhancement relative to normal splenic tissue. As a result, animals with diffuse lymphoma (SNR: 10.3 +/- 1.7) could be easily differentiated from control animals (SNR: 5.5 +/- 0.6) on T2-weighted (TR msec/TE msec = 2,000/45) images. In focal splenic disease, MSM produced normal enhancement of nontumorous splenic tissue, whereas relaxation times of tumors were not different before and after contrast agent injection. On T2-weighted images (2,000/45), the tumor-spleen contrast-to-noise ratio increased from 4.8 +/- 1.6 to 21.8 +/- 1.9 (+354%), improving conspicuity of splenic tumors. The results show that MSM-enhanced MR imaging improves the detection of diffuse and focal splenic disease.