Analysis of the distribution of MRI contrast agents in the livers of small animals by means of complementary microscopies.

BACKGROUND: Magnetic resonance imaging (MRI) contrast agents contain magnetic molecules such as iron (Fe) or gadolinium (Gd) that are injected in vivo into rats or mice to study their distribution inside the liver. Fluorescent europium (Eu) can be used as a model of Gd to obtain comparable information of this distribution of corresponding contrast agents. In a similar approach, Fe can be attached to Texas Red and used as a model of ferumoxides and be detected by fluorescence. METHODS: To combine and compare the advantages of different microscopic imaging modes, characterization studies were carried out by means of a confocal laser scanning microscope (CLSM), a secondary ion mass spectrometric (SIMS) microscope, and an electron energy loss spectrometric (EELS) microscope. In the case of CLSM, the locations of fluorescent signals inside preparations were determined by factor analysis of biomedical image sequences (FAMIS) and selection of image sequences at emission. RESULTS: By CLSM and FAMIS, we distinguished chelated Eu and Texas Red attached to Fe. By SIMS microscopy, we distinguished Eu and Gd of chlorides and chelates and Fe of a ferumoxide. By EELS microscopy, we distinguished Eu and Gd of chlorides. CONCLUSIONS: Analysis of compounds inside correlative specimens by means of CLSM, SIMS, and EELS microscopes provided complementary results.

Mechanisms of action of liver contrast agents: impact for clinical use.

New contrast agents for magnetic resonance imaging are continually being developed by pharmaceutical companies in order to better image the liver. These agents can be divided into hepatobiliary agents directed to the hepatocytes and nanoparticulate agents directed to the reticulo-endothelial system. After intravenous injection, all these agents concentrate in the liver and induce profound changes in signal intensity. Particulate agents induce predominantly a darkening of the liver parenchyma, while hepatobiliary agents induce a brightening. In both cases, liver-lesion conspicuity is enhanced, leading to a better visualization of the lesion. After a brief description of the principal characteristics of the agents, this paper will attempt to summarize the utility of these agents for the detection and characterization of focal liver disease.

Measurement of liver blood volume using a macromolecular MRI contrast agent at equilibrium.

Liver regional blood volume (LRBV) is altered by several disease states and various drugs. Preliminary studies in the rat, using research MR imaging instruments at 2T and vascular contrast agents, have suggested that MRI may be used to measure LRBV. Our goal was to develop a technique for measuring LRBV using a clinical machine at 1.5 T. This study was performed in the rabbit, using CarboxyMethylDextran Gd-DTPA, a macromolecular contrast agent with a molecular weight of 158 kDa. MRI was performed at 1.5 T, in the plane of the inferior vena cava, with and without flow compensation, before contrast injection and in the steady state after injection. Accuracy and stability of LRBV measurement, over 2 h and with various doses (0.01-0.05 mmol/kg), was tested against a standard Evan's Blue dye-indicator technique. LRBV was 28 +/- 2 mL/100 g when measured by MRI with flow compensation, which is in good agreement with the literature and with the 26 +/- 6 mL/100 g, measured by the Evan's Blue dilution technique. Measurements varied less than 7% over time and less than 9% over the range of doses. LRBV was overestimated using a sequence without flow compensation especially when large doses of contrast agent were injected. This noninvasive MRI technique provides a simple method for measuring liver LRBV and offers new prospects for future physiological and pathological studies.

[Digitized intravenous angiography in Takayasu's disease. Apropos of 44 cases]. / Place de l'angiographie numérisée intraveineuse dans la maladie de Takayasu. A propos de 44 cas.

Forty-four patients with Takayasu's disease were investigated by digitised intravenous angiography (DIVA) during a diagnostic and pretherapeutic work up (N = 29) or at surgery (N = 15); the aim of this retrospective study was to assess the role of DIVA in the investigation of this condition. The patients were 36 women, 6 men and 2 children; the average age was 31 years. The intravenous injections were performed in a central vein in 74% and in a peripheral vein in 26% of patients; the average amount of contrast medium injected was 140 ml per investigation (32 g of iodine %). Depending on the site of the lesions, the distribution of the 43 successfully investigated patients was as follows: Type I: 13 (20%), Type II: 6 (14%), Type III: 12 (28%), Type IV: 12 (28%). In the group of patients managed medically (N = 14) no other angiographic investigations were considered. In the group with an indication for surgery or percutaneous angioplasty (N = 15), the procedure was carried out without further angiography in 13 cases; in 2 patients the imaging of the distral vessels was inadequate and complementary angiography was required. All postoperative controls (N = 15) but one were satisfactory. These results show that DIVA is sufficiently reliable for it to be considered as an investigation of first intent in patients with suspected Takayasu's disease. The investigation is well tolerated and can be repeated when necessary to determine the optimal time for surgery. Arterial angiography should seem only to be indicated when the venous approach has failed, which was rare in this series.