Definition of liver tumors in the presence of diffuse liver disease: comparison of findings at MR imaging with positive and negative contrast agents.

PURPOSE: The potential to define liver tumors at magnetic resonance (MR) imaging was compared with a positive and a negative contrast agent (gadoxetic acid disodium, or gadolinium EOB-DTPA [a hepatocyte-directed agent], and ferumoxides, or superpara-magnetic iron oxide particles [a Kupffer cell-directed agent], respectively) in normal rats and in rats with induced acute hepatitis, fatty liver, or cirrhosis. MATERIALS AND METHODS: Rats with implanted liver adenocarcinomas were divided into four groups: no diffuse liver disease ("normal" [n = 6]) and diffuse liver diseases (induced acute hepatitis [n = 6], fatty liver [n = 6], or cirrhosis [n = 6]). Rats first received gadoxetic acid disodium (50 mumol/kg) and then, 45 minutes later, ferumoxides (10 mumol/kg). Liver signal intensity enhancement and tumor-to-liver contrast-to-noise ratio (C/N) were measured in each group. RESULTS: Mean liver signal intensity enhancement values with gadoxetic acid disodium and ferumoxides were excellent in the normal liver model (176% and -62%, respectively; P < .01) but were significantly reduced in the acute hepatitis model (82% and -36%, respectively). In the fatty livers compared with the normal livers, enhancement with gadoxetic acid disodium was reduced (57%) but with ferumoxides was excellent (-55%). In the cirrhotic livers compared with the normal livers, enhancement with gadoxetic acid disodium (174%) was virtually the same but was impaired with ferumoxides (-43%). CONCLUSION: Hepatic enhancement and tumor-to-liver C/N with either positive or negative liver-enhancing agents can be impaired by the presence of underlying liver disease. Prior knowledge of the type of diffuse liver disease may influence the choice of contrast agent for tumor detection.

MR imaging of blood oxygenation-dependent changes in focal renal ischemia and transplanted liver tumor in rat.

The potential of using fast magnetic resonance (MR) imaging in conjunction with apnea-induced blood deoxygenation for the noninvasive monitoring of relative perfusion in the rat abdomen has been studied with two experimental models: glycerol-induced focal renal ischemia and transplanted liver tumor. Gradient-echo echo-planar imaging (GRE-EPI) (TE of 20 msec at 2T) of liver and kidney was performed before, during, and after a 60-second apnea episode and then was followed in the same rat by contrast-enhanced (a) GRE-EPI and (b) T1-weighted spin-echo imaging (TR msec/TE msec = 200/6) with polylysine-(gadolinium-DTPA [diethylenetriaminepentaacetic acid]). The results indicate that a noninvasive vascular challenge due to apnea can be used for the detection of focal tissue perfusion abnormalities in rat kidney and liver tumor.

Comparison of Gd-EOB-DTPA and Gd-DTPA for contrast-enhanced MR imaging of liver tumors.

A new hepatobiliary contrast agent for magnetic resonance (MR) imaging, gadolinium-ethoxybenzyl (EOB)-diethylemetriaminepentaacetic acid (DTPA), was compared with Gd-DTPA to define the potential for improving tumor-liver contrast in a rodent liver adenocarcinoma model. With a T1-weighted spin-echo sequence, the contrast-to-noise ratio (C/N) for tumor before contrast agent administration was 5 (arbitrary units), the tumor appearing slightly hypo-intense with respect to liver parenchyma. After Gd-DTPA injection (0.1 mmol/kg), tumor enhanced more strongly than liver, resulting in an equalization of tumor and liver signal intensities and a decline in C/N to zero at 3 minutes after injection. After Gd-EOB-DTPA injection (0.1 mmol/kg), liver enhanced more strongly than tumor. Five minutes after injection, C/N increased from 5 to 25 and remained above 17 for 50 minutes. The data indicate that Gd-EOB-DTPA yields higher and more prolonged tumor-liver contrast than Gd-DTPA on T1-weighted spin-echo images. The high liver-tumor contrast after Gd-EOB-DTPA administration should prove clinically advantageous for MR imaging detection of focal hepatic masses.

Magnetic resonance imaging demonstration of pharmacologic-induced myocardial vasodilatation using a macromolecular gadolinium contrast agent.

RATIONALE AND OBJECTIVES: Adenosine is a potent vasodilator used clinically in nuclear scintigraphy to assess coronary artery reserves. The potential to identify this vasodilating effect of adenosine using magnetic resonance imaging (MRI), which is superior in spatial resolution to nuclear scintigraphy, combined with a blood-pool MRI contrast agent, was investigated in normal rats. METHODS: Groups of Sprague-Dawley rats received successive infusions of either adenosine (3 mg/kg/minute; n = 7) or dipyridamole (negative control; up to 1.0 mg/kg/minute; n = 9), both before and after contrast enhancement, with a macromolecular blood-pool MRI contrast agent, albumin-gadolinium-DTPA35 (Gd-DTPA35) (4.0 mumol Gd per kilogram). Electrocardiographically (ECG) gated MRIs (2.0 Tesla), acquired serially before and after contrast enhancement, and with and without either adenosine or dipyridamole infusions, to monitor potential pharmacologic responses. RESULTS: During repeated infusions of adenosine, the postcontrast myocardial enhancement, reflecting blood volume, increased significantly (P < .05), up to 150%, compared with pre-adenosine enhancement. Infusions of dipyridamole, pharmacologically inactive in rats, produced no change in myocardial enhancement. CONCLUSIONS: The increased myocardial signal intensity observed during adenosine infusions after enhancement of the blood pool can be attributed to increased blood volume accompanying coronary vasodilatation. The method, which does not require a continuous infusion of contrast agent, has potential for the clinical evaluations of coronary artery reserves.

Evaluation of radiation-induced liver injury with MR imaging: comparison of hepatocellular and reticuloendothelial contrast agents.

Gadolinium (4s)-4-(4-ethoxybenzyl-3,6,9-tris(carboxylato-methyl)-3,6,9- triazaudecandioic acid (EOB) diethylenetriaminepentaacetic acid (DTPA), a hepatocellular-directed magnetic resonance (MR) contrast agent, and coated superparamagnetic iron oxide particles (SPIO), a Kupffer cell-directed contrast agent, were compared for uptake and enhancement in a rodent model of radiation-induced liver injury. A single x-irradiation exposure (50-70 Gy) was delivered to one side of the liver in 18 rats. MR imaging was performed 3 days after x irradiation with sequential injections of the two contrast agents in the same rats. Additionally, biliary excretion of Gd-EOB-DTPA was quantified after whole-liver irradiation in five rats. Electron microscopy of the irradiated liver demonstrated mitochondrial injury in both hepatocyte and Kupffer cell populations. With Gd-EOB-DTPA, however, liver enhancement and biliary excretion were not affected by irradiation. Uptake of SPIO was decreased in the irradiated portion of the liver, with a precise demarcation between irradiated and nonirradiated zones at MR imaging.