MR imaging features of gadofluorine-labeled matrix-associated stem cell implants in cartilage defects.

OBJECTIVES: The purpose of our study was to assess the chondrogenic potential and the MR signal effects of GadofluorineM-Cy labeled matrix associated stem cell implants (MASI) in pig knee specimen. MATERIALS AND METHODS: Human mesenchymal stem cells (hMSCs) were labeled with the micelle-based contrast agent GadofluorineM-Cy. Ferucarbotran-labeled hMSCs, non-labeled hMSCs and scaffold only served as controls. Chondrogenic differentiation was induced and gene expression and histologic evaluation were performed. The proportions of spindle-shaped vs. round cells of chondrogenic pellets were compared between experimental groups using the Fisher's exact test. Labeled and unlabeled hMSCs and chondrocytes in scaffolds were implanted into cartilage defects of porcine femoral condyles and underwent MR imaging with T1- and T2-weighted SE and GE sequences. Contrast-to-noise ratios (CNR) between implants and adjacent cartilage were determined and analyzed for significant differences between different experimental groups using the Kruskal-Wallis test. Significance was assigned for p<0.017, considering a Bonferroni correction for multiple comparisons. RESULTS: Collagen type II gene expression levels were not significantly different between different groups (p>0.017). However, hMSC differentiation into chondrocytes was superior for unlabeled and GadofluorineM-Cy-labeled cells compared with Ferucarbotran-labeled cells, as evidenced by a significantly higher proportion of spindle cells in chondrogenic pellets (p<0.05). GadofluorineM-Cy-labeled hMSCs and chondrocytes showed a positive signal effect on T1-weighted images and a negative signal effect on T2-weighted images while Ferucarbotran-labeled cells provided a negative signal effect on all sequences. CNR data for both GadofluorineM-Cy-labeled and Ferucarbotran-labeled hMSCs were significantly different compared to unlabeled control cells on T1-weighted SE and T2*-weighted MR images (p<0.017). CONCLUSION: hMSCs can be labeled by simple incubation with GadofluorineM-Cy. The labeled cells provide significant MR signal effects and less impaired chondrogenesis compared to Ferucarbotran-labeled hMSCs. Thus, GadoflurineM-Cy might represent an alternative MR cell marker to Ferucarbotran, which is not distributed any more in Europe or North America.

Gadofluorine M-enhanced magnetic resonance imaging of inflammatory bowel disease: quantitative analysis and histologic correlation in a rat model.

OBJECTIVES: : To determine the colonic mural enhancement in a rat model of inflammatory bowel disease (IBD) using gadofluorine M- and diethylenetriamine pentaacetic acid (Gd-DTPA)-enhanced magnetic resonance (MR) imaging, and to correlate the degree of enhancement with the histopathologic severity of the disease. MATERIALS AND METHODS: : This study was approved by our hospital's institutional animal care and use committee. A total of 44 rats with 2 grades (mild, n = 17; and severe, n = 27) of dinitrobenzene sulfonic acid (DNBS)-induced IBD and 13 rats without IBD, were examined using a 2.4-T, small animal MR scanner. T2- and T1-weighted MR images were acquired, and sequential T1-weighted MR imaging was then performed immediately and again 15, 45, 60, and 90 minutes, and 24 hours after intravenous -injection of either gadofluorine M- or Gd-DTPA (0.1 mmol Gd/kg body weight). The signal-to-noise ratios and enhancement ratios (ER) of the colon wall were measured. For paired and group comparisons of the histopathology and MR imaging data, the Wilcoxon- and the Mann-Whitney U tests were used, and the multifactorial analysis of variance test was used to compare the time courses of the ERs. RESULTS: : Gadofluorine M injection resulted in significant differences in the ER of noninflamed, mildly inflamed, and severely inflamed colon wall at any time up to 24 hours after contrast injection (ER at 24 hours 2.0 ± 1.2; 10.1 ± 4.3; and 49.7 ± 10.8, respectively; P < 0.01). After Gd-DTPA injection, significant differences were observed in the ER of inflamed and noninflamed bowel at 15, 45, and 60 minutes (P < 0.01); however, no significant differences in mildly and severely inflamed bowel were observed at any time. In contrast to Gadofluorine M, there was no prolonged contrast enhancement in the inflamed colon wall after intravenous injection of Gd-DTPA (ER at 24 hours 1.6 ± 1.3; 3.4 ± 2.7; and 3.3 ± 1.6, respectively; n.s.). CONCLUSIONS: : Gadofluorine M-enhanced MR imaging shows a higher correlation of the wall enhancement and histopathology grading in an IBD rat model than does Gd-DTPA-enhanced imaging.

Gadofosveset-enhanced magnetic resonance imaging of human carotid atherosclerotic plaques: a proof-of-concept study.

OBJECTIVE: To investigate the potential of gadofosveset-enhanced MR imaging for the characterization of human carotid atherosclerotic plaques. MATERIALS AND METHODS: Sixteen (9 symptomatic, 7 asymptomatic) patients with 70% to 99% carotid stenosis (according to NASCET criteria) were included (13 men, 3 women, mean age 67.6 years). All patients underwent baseline precontrast MR imaging of the carotid plaque. Immediately after completion of the baseline examination, 0.03 mmol/kg gadofosveset was administered. At 24 hours postinjection, the acquisition was repeated. Twelve patients were scheduled for carotid endarterectomy. Carotid endarterectomy specimens were HE-, CD31-, CD68-, and albumin-stained to correlate signal enhancement with plaque composition, intraplaque microvessel density, and macrophage and albumin content. A random intercept model was used to compare signal enhancement between symptomatic and asymptomatic patients, adjusting for size of various plaque components. This study was approved by the institutional medical ethics committee. All participants gave written informed consent. RESULTS: Signal enhancement (SE) of the plaque was significantly higher in symptomatic patients compared with asymptomatic patients (median log SE 0.182 vs. -0.109, respectively, P < 0.001). A positive association (as expressed by a regression coefficient beta = 0.0035) was found between signal enhancement on the log scale and intraplaque albumin content (P = 0.038). There was no association between signal enhancement and various other plaque components. CONCLUSION: In this study, the potential of gadofosveset-enhanced human carotid plaque MR imaging for identification of high-risk plaques was demonstrated. Signal enhancement of the plaque after administration of gadofosveset was associated with differences in intraplaque albumin content. Although promising, we emphasize that these results are based on a small patient population. Larger prospective studies are warranted.

Evaluation of rHA labeled with Gd-DTPA for blood pool imaging and targeted contrast delivery.

A new contrast agent was developed by linking Gd-DTPA chelate to recombinant human albumin in the laboratory. The molar relaxivity of the new agent was tested in aqueous solution at B(0) 1.5 T and temperature 20 degrees C. The soluble compound had a higher molar longitudinal relaxivity and molar transverse relaxivity in water (r(1) = 7.2 s(-1) mM(-1), r(2) = 18.4 s(-1) mM(-1)) than those measured for Gd-DTPA solution (r(1) = 3.5 s(-1) mM(-1), r(2) = 5.5 s(-1) mM(-1)). The performance of the compound as a blood pool agent was investigated with soluble and microparticulate forms of the compound and comparisons were made with Gd-DTPA and the polymeric blood-pool agent, Gadomer. T(1)-weighted imaging experiments show that the soluble compound acts as a highly effective blood pool agent with hyperintensity in the vasculature persisting beyond 2 h post administration, compared with free Gd-DTPA, which was cleared from the blood pool after approximately 10 min. The clearance kinetics of the new agents were examined, due to the incomplete elimination within 14 days post injection; both rHA labeled compounds are probably not suitable for development as routine blood pool contrast media. However, with free sites on the Gd-loaded rHA molecule, there are possibilities for binding the agent to antibodies in the laboratory, which was demonstrated, and thus there exist potential applications for in vivo molecular imaging with this agent.

Roles of myocardial blood volume and flow in coronary artery disease: an experimental MRI study at rest and during hyperemia.

OBJECTIVE: To validate fast perfusion mapping techniques in a setting of coronary artery stenosis, and to further assess the relationship of absolute myocardial blood volume (MBV) and blood flow (MBF) to global myocardial oxygen demand. METHODS: A group of 27 mongrel dogs were divided into 10 controls and 17 with acute coronary stenosis. On 1.5-T MRI, first-pass perfusion imaging with a bolus injection of a blood-pool contrast agent was performed to determine myocardial perfusion both at rest and during either dipyridamole-induced vasodilation or dobutamine-induced stress. Regional values of MBF and MBV were quantified by using a fast mapping technique. Color microspheres and (99m)Tc-labeled red blood cells were injected to obtain respective gold standards. RESULTS: Microsphere-measured MBF and (99m)Tc-measured MBV reference values correlated well with the MR results. Given the same changes in MBF, changes in MBV are twofold greater with dobutamine than with dipyridamole. Under dobutamine stress, MBV shows better association with total myocardial oxygen demand than MBF. Coronary stenosis progressively reduced this association in the presence of increased stenosis severity. CONCLUSIONS: MR first-pass perfusion can rapidly estimate regional MBF and MBV. Absolute quantification of MBV may add additional information on stenosis severity and myocardial viability compared with standard qualitative clinical evaluations of myocardial perfusion.

Quantification of regional myocardial oxygenation by magnetic resonance imaging: validation with positron emission tomography.

BACKGROUND: A comprehensive evaluation of myocardial ischemia requires measures of both oxygen supply and demand. Positron emission tomography (PET) is currently the gold standard for such evaluations, but its use is limited because of its ionizing radiation, limited availability, and high cost. A cardiac MRI method was developed for assessing myocardial oxygenation. The purpose of this study was to evaluate and validate this technique compared with PET during pharmacological stress in a canine model of coronary artery stenosis. METHODS AND RESULTS: Twenty-one beagles and small mongrel dogs without coronary artery stenosis (controls) or with moderate to severe acute coronary artery stenosis underwent MRI and PET imaging at rest and during dipyridamole vasodilation or dobutamine stress to induce a wide range of changes in cardiac perfusion and oxygenation. MRI first-pass perfusion imaging was performed to quantify myocardial blood flow and volume. The MRI blood oxygen level-dependent technique was used to determine the myocardial oxygen extraction fraction during pharmacological hyperemia. Myocardial oxygen consumption was determined by the Fick law. In the same dogs, (15)O-water and (11)C-acetate were used to measure myocardial blood flow and myocardial oxygen consumption, respectively, by PET. Regional assessments were performed for both MR and PET. MRI data correlated nicely with PET values for myocardial blood flow (R(2)=0.79, P<0.001), myocardial oxygen consumption (R(2)=0.74, P<0.001), and oxygen extraction fraction (R(2)=0.66, P<0.01). CONCLUSIONS: Cardiac MRI methods may provide an alternative to radionuclide imaging in settings of myocardial ischemia. Our newly developed quantitative MRI oxygenation imaging technique may be a valuable noninvasive tool to directly evaluate myocardial energetics and efficiency.

Myocardial blood volume is associated with myocardial oxygen consumption: an experimental study with cardiac magnetic resonance in a canine model.

Understanding the oxygen consumption of the left ventricular myocardium provides important insight into the relationship between myocardial oxygen supply and demand. In other territories, cardiac magnetic resonance has been utilized to measure myocardial oxygen consumption with a blood level oxygen dependent (BOLD) technique. The BOLD technology requires repetitive sampling of stationary tissues and is frequently implemented in areas such as the brain. A limitation to utilizing BOLD cardiac magnetic resonance techniques in the heart has been cardiac motion. In this study, we document a methodology for acquiring BOLD images in the heart and demonstrate the utility of the technique for identifying associations between myocardial oxygen consumption and blood flow.

Comparison of gadofluorine-M and Gd-DTPA for noninvasive staging of atherosclerotic plaque stability using MRI.

BACKGROUND: Inflammation and neovascularization play critical roles in the stability of atherosclerotic plaques. Whole-body quantitative assessment of these plaque features may improve patient risk-stratification for life-threatening thromboembolic events and direct appropriate intervention. In this report, we determined the utility of the MR contrast agent gadofluorine-M (GdF) for staging plaque stability and compared this to the conventional agent Gd-DTPA. METHODS AND RESULTS: Five control and 7 atherosclerotic rabbits were sequentially imaged after administration of Gd-DTPA (0.2 mmol/kg) and GdF (0.1 mmol/kg) using a T(1)-weighted pulse sequence on a 3-T MRI scanner. Diseased aortic wall could be distinguished from normal wall based on wall-to-muscle contrast-to-noise values after GdF administration. RAM-11 (macrophages) and CD-31 (endothelial cells) immunostaining of MR-matched histological sections revealed that GdF accumulation was related to the degree of inflammation at the surface of plaques and the extent of core neovascularization. Importantly, an MR measure of GdF accumulation at both 1 and 24 hours after injection but not Gd-DTPA at peak enhancement was shown to correlate with a quantitative histological morphology index related to these 2 plaque features. CONCLUSIONS: GdF-enhanced MRI of atherosclerotic plaques allows noninvasive quantitative information about plaque composition to be acquired at multiple time points after injection (within 1 and up to 24 hours after injection). This dramatically widens the imaging window for assessing plaque stability that is currently attainable with clinically approved MR agents, therefore opening the possibility of whole-body (including coronary) detection of unstable plaques in the future and potentially improved mitigation of cataclysmic cardiovascular events.

Spatial diversity of blood-brain barrier alteration and macrophage invasion in experimental autoimmune encephalomyelitis: a comparative MRI study.

Inflammation plays a central role in the development of numerous disorders of the central nervous system (CNS) such as multiple sclerosis (MS). For a long time it was assumed that recruitment of macrophages into the CNS and breakdown of the blood-brain barrier (BBB) are closely linked. In the present study we challenge this concept. We used small superparamagnetic iron oxide particles (SPIO)-enhanced T2-weighted (T2-w) magnetic resonance imaging (MRI) on a routine 1.5 T MRI unit to follow macrophage infiltration in experimental autoimmune encephalomyelitis (EAE), the animal model of MS. After an initial SPIO-enhanced MRI, gadofluorine M (Gf), an experimental contrast agent which proved to be more sensitive in detecting BBB leakage than gadolinium (Gd)-DTPA (Bendszus, M., Ladewig, G., Jestaedt, L., Misselwitz, B., Solymosi, L., Toyka, K.V., Stoll, G., Gadofluorine-M enhancement allows more sensitive detection of inflammatory CNS lesions than T2-w imaging: a quantitative MRI study. Brain 2008; 1-12), was applied to the same animals followed by a second scan. Areas with SPIO-induced signal loss on T2-w MRI indicative of recent macrophage infiltration were matched with areas showing Gf enhancement as a measure of BBB disturbance. Overall 87 EAE lesions showed iron-related signal loss, while 57 lesions showed Gf enhancement. By direct comparison we could detect concomitant SPIO-induced signal loss and Gf enhancement only in a small minority of lesions. In conclusion, our findings show macrophage infiltration in the CNS during EAE in areas with a closed BBB for humoral factors. This holds true despite the use of a more sensitive MR contrast agent for BBB disruption than Gd-DTPA. Our experimental observations may have implications for disease monitoring in MS patients by MRI which guides treatment decisions.

MRI-based biomechanical imaging: initial study on early plaque progression and vessel remodeling.

The goal of the study is to develop a noninvasive magnetic resonance imaging (MRI)-based biomechanical imaging technique to address biomechanical pathways of atherosclerotic progression and regression in vivo using a 3D fluid-structure interaction (FSI) model. Initial in vivo study was carried out in an early plaque model in pigs that underwent balloon-overstretch injury to the left carotid arteries. Consecutive MRI scans were performed while the pigs were maintained on high cholesterol (progression) or normal chow (regression), with an injection of a plaque-targeted contrast agent, Gadofluorine M. At the end of study, the specimens of carotid arterial segments were dissected and underwent dedicated mechanical testing to determine their material properties. 3D FSI computational model was applied to calculate structure stress and strain distribution. The plaque structure resembles early plaque with thickened intima. Lower maximal flow shear stress correlates with the growth of plaque volume during progression, but not during regression. In contrast, maximal principle structure stress/stain (stress-P1 and strain-P1) were shown to correlate strongly with the change in the plaque dimension during regression, but moderately during progression. This MRI-based biomechanical imaging method may allow for noninvasive dynamic assessment of local hemodynamic forces on the development of atherosclerotic plaques in vivo.

Atherosclerosis: contrast-enhanced MR imaging of vessel wall in rabbit model--comparison of gadofosveset and gadopentetate dimeglumine.

PURPOSE: To investigate the potential of gadofosveset for contrast material-enhanced magnetic resonance (MR) imaging of plaque in a rabbit model of atherosclerosis. MATERIALS AND METHODS: All experiments were approved by the animal ethics committee. Thirty-one New Zealand White rabbits were included in one of four study groups: animals with atherosclerosis imaged with gadofosveset (n = 10) or gadopentetate dimeglumine (n = 7) and control animals imaged with gadofosveset (n = 7) or gadopentetate dimeglumine (n = 7). Aortic atherosclerosis was induced through endothelial denudation combined with a cholesterol-enriched diet. Control rabbits underwent a sham surgical procedure and received a regular diet. After 8 weeks, pre- and postcontrast T1-weighted MR images of the aortic vessel wall were acquired. Relative signal enhancement was determined with dedicated software. Statistical analysis was performed by using a generalized linear mixed model. Immunohistochemical staining with CD31 and albumin was used to assess microvessel density and the albumin content of the vascular wall. Group differences were analyzed by using a chi(2) test. Gadofosveset spatial distribution and content within the vessel wall were determined with proton-induced x-ray emission (PIXE) analysis. RESULTS: Postcontrast signal enhancement was significantly greater for atherosclerotic than for control animals imaged with gadofosveset (P = .022). Gadopentetate dimeglumine could not enable discrimination between normal and atherosclerotic vessel walls (P = .428). PIXE analysis showed higher amounts of gadopentetate dimeglumine than gadofosveset in both atherosclerotic and normal rabbit aortas. Immunohistochemical staining revealed the presence of albumin and increased microvessel density in the vascular walls of atherosclerotic rabbits. CONCLUSION: These results suggest that gadofosveset can be used to differentiate between atherosclerotic and normal rabbit vessel walls. SUPPLEMENTAL MATERIAL: http://radiology.rsnajnls.org/cgi/content/full/250/3/682/DC1.

Magnetic resonance imaging of experimental inflammatory bowel disease: quantitative and qualitative analyses with histopathologic correlation in a rat model using the ultrasmall iron oxide SHU 555 C.

OBJECTIVES: To quantitatively and qualitatively characterize the MR findings of inflammatory bowel disease in a rat model after i.v. injection of the reticuloendothelial system cell specific ultrasmall iron oxide SHU 555 C. MATERIALS AND METHODS: Colitis was induced in 15 rats using dinitrobenzene sulfonic acid instillation. Five rats served as controls. T1- and T2-weighted spin-echo- and T2*-weighted gradient-echo-sequences were acquired at 2.4 Tesla before and immediately, 15, 45, 60, and 90 minutes, and 24 hours after i.v.-injection of SHU 555 C (0.1 mmol Fe/kg). MR images were evaluated quantitatively regarding thickness and signal-to-noise ratio (SNR) of the bowel wall and qualitatively regarding overall bowel wall signal intensity and the occurrence of bowel wall ulcerations. MR findings were correlated to histology. RESULTS: The inflamed bowel wall was significantly thicker than the noninflamed bowel wall and 90 minutes after contrast injection it showed a significant reduction of SNR in T1- (94 +/- 27 vs. 61 +/- 29; P < 0.01), T2- (67 +/- 26 vs. 28 +/- 17; P < 0.05), and T2*- (92 +/- 57 vs. 10 +/- 7; P < 0.05) weighted images as compared with unenhanced images. At 24 hours, the respective SNR values remained significantly reduced. The signal loss was homogeneous in 12 and focal in 3 of the 15 rats with colitis. Nine rats showed colonic wall ulcerations. In all but one animal (missed focal ulceration) MR findings correlated to the histologic findings. CONCLUSIONS: SHU 555 C leads to a significant signal intensity loss of the inflamed bowel wall in T1-, T2- and T2*-weighted images. SHU 555 C enhanced MRI findings correlate well with histologic findings.

Dysferlin-deficient muscular dystrophy: gadofluorine M suitability at MR imaging in a mouse model.

PURPOSE: To compare the usefulness of gadofluorine M with that of Gadomer in assessment of dysferlin-deficient muscular dystrophy at 7.0-T magnetic resonance (MR) imaging. MATERIALS AND METHODS: All experiments were approved by local review boards. SJL/J mice (n = 24) with dysferlin-deficient muscular dystrophy and C57BL/6 control mice (n = 24) were imaged at 12-15 weeks (young) or older than 30 weeks (old) by using dynamic contrast material-enhanced imaging with inversion-prepared steady-state free-precession sequence before, during, and after administration of gadofluorine M at 2 micromol or Gadomer at 4 micromol intravenously. After imaging, regions of interest were determined from the upper extremity and left ventricular chamber; fractional extravascular extracellular volume, v(e), and permeability surface tissue density product, PS rho, were measured by using a two-compartment pharmacokinetic model. The natural history of muscular dystrophy was assessed histologically in 70 mice (seven five-mouse groups each of SJL/J mice and of control mice) at 4-week intervals from 8 to 32 weeks. In addition, three SJL/J mice and three control mice at age 33 weeks were sacrificed, and fluorescence microscopy was performed for visualization of intravenously administered carbocyanine-labeled gadofluorine M in muscle cells. Statistical analysis was performed by using the t test. RESULTS: Gadofluorine M enhancement was significantly greater in skeletal muscle of 30-week-old mice with dysferlin-deficient muscular dystrophy, compared with control mice. Gadofluorine M demonstrated both increased rate of enhancement (PS rho sec(-1) +/- standard error of the mean: 0.004 e(-)(4) +/- 3 vs 0.002 e(-)(4) +/- 3; P < .05) and increased level of enhancement (v(e) +/- standard error of the mean: 0.035 +/- 0.004 vs 0.019 +/- 0.004; P < .05). Gadomer showed no differential enhancement in the two mouse groups. Histologic examination confirmed the presence of labeled gadofluorine M in muscle cells. CONCLUSION: Gadofluorine M-enhanced MR imaging may be of value in monitoring dysferlin-deficient muscular dystrophy disease progression in this animal model and could prove to be a useful tool in following the course of chronic muscle diseases in humans.

Gadofluorine M enhancement allows more sensitive detection of inflammatory CNS lesions than T2-w imaging: a quantitative MRI study.

Magnetic resonance imaging plays a pivotal role in the diagnosis and treatment monitoring of multiple sclerosis. Currently available magnetic resonance-techniques only partly reflect the extent of tissue inflammation and damage. In the present study, application of the experimental magnetic resonance-contrast agent Gadofluorine M significantly increased the sensitivity of lesion detection in myelin-oligodendrocyte glycoprotein-induced experimental autoimmune encephalomyelitis, an animal model for multiple sclerosis. Gadofluorine M-enhancement on T(1)-weighted (T(1)-w) images utilizing a clinical 1.5 T magnetic resonance unit showed numerous lesions in optic nerve, spinal cord and brain, the majority of which were not detectable on standard T(2)-weighted (T(2)-w) and Gd-DTPA enhanced T(1)-w sequences. Quantitative assessment by pixel counts revealed highly significant differences in sensitivity in favour of Gadofluorine M. Gadofluorine uptake closely corresponded to inflammation and demyelination on tissue sections. These unique features of Gadofluorine M in visualizing inflammatory CNS lesions hold promise for future clinical development in multiple sclerosis.

Fast mapping of myocardial blood flow with MR first-pass perfusion imaging.

Accurate and fast quantification of myocardial blood flow (MBF) with MR first-pass perfusion imaging techniques on a pixel-by-pixel basis remains difficult due to relatively long calculation times and noise-sensitive algorithms. In this study, Zierler's central volume principle was used to develop an algorithm for the calculation of MBF with few assumptions on the shapes of residue curves. Simulation was performed to evaluate the accuracy of this algorithm in the determination of MBF. To examine our algorithm in vivo, studies were performed in nine normal dogs. Two first-pass perfusion imaging sessions were performed with the administration of the intravascular contrast agent Gadomer at rest and during dipyridamole-induced vasodilation. Radiolabeled microspheres were injected to measure MBF at the same time. MBF measurements in dogs using MR methods correlated well with the microsphere measurements (R2=0.96, slope=0.9), demonstrating a fair accuracy in the perfusion measurements at rest and during the vasodilation stress. In addition to its accuracy, this method can also be optimized to run relatively fast, providing potential for fast and accurate myocardial perfusion mapping in a clinical setting.

In vitro labeling of glioma cells with gadofluorine M enhances T1 visibility without affecting glioma cell growth or motility.

Gadofluorine is a novel macrocyclic, amphiphilic gadolinium-based contrast agent. We found that malignant glioma cells could be labeled in vitro using Gadofluorine without the need for transfection agents or any other additional means. Labeling with Gadofluorine enhanced the visualization of glioma cells in T(1)-weighted sequences, even if the cells had been cultured in medium without Gadofluorine over several days. The intracellular uptake of Gadofluorine was measured and the loss of relevant amounts of Gadofluorine into the cell culture medium was ruled out by MRI. Confocal laser fluorescence microscopy revealed Cy-5-labeled Gadofluorine in the perinuclear cytoplasmic region, but neither within the nucleus nor bound to the cell membrane. Adverse effects of cellular Gadofluorine uptake were ruled out by proliferation and migration assays. Finally, in vivo analyses provided good visibility of labeled glioma cells in T(1)-weighted sequences after intracerebral injection in mice for more than 2 weeks. We thus conclude that Gadofluorine can easily be used to label glioma cells in vitro without affecting glioma cell biology. Gadofluorine provides an interesting alternative for cellular labeling if iron oxide particles are incorporated insufficiently by target cells or if the vicinity of susceptibility artifacts prohibits the use of signal-decreasing contrast agents.

Targeted contrast agent helps to monitor advanced plaque during progression: a magnetic resonance imaging study in rabbits.

OBJECTIVE: Gadofluorine M has been reported to enhance early atherosclerotic plaque signals in magnetic resonance imaging (MRI). The aim of this study was to examine the use of Gadofluorine M to monitor the progression of advanced plaques in a rabbit model. METHODS: Focal advanced atherosclerosis was induced in the right femoral arteries of 6 New Zealand white rabbits using a combination of cholesterol-enriched diet, and sequential air-desiccation, and balloon-overstretch injury. MRI with conventional 3 contrasts (T1, T2, and proton density [PD]) was performed to monitor the progression of the atherosclerotic plaques with 2 MRI scans separated by 4 to 8 weeks. Gadofluorine M was given intravenously to the rabbits 24 hours before the first MRI scans, and before (n = 3) or during (n = 3) the second MRI scan. The left femoral arteries were used as a control. Histopathologic images localized individual plaque components. RESULTS: The advanced plaque displayed multilayered neointima that included foam cells, smooth muscle cells, and extracellular matrix. The separate image contrasts offered similar T1-weighted enhancement patterns, but the combination of all 3 contrasts helped to delineate plaque and lumen boundaries. Gadofluorine M strongly enhanced neointima areas with an image contrast (contrast-to-noise ratio [CNR]) of approximately 15, versus 2 in the control femoral arterial wall. With improved images, significant changes in neointima and total plaque volumes over the 4 to 8 weeks between scans could be identified. Gadofluorine M remained within the plaques with significant image enhancements (contrast-to-noise ratio = 5.8) for 2 months after a single injection. CONCLUSION: This preliminary study in rabbits indicated that Gadofluorine M provides specific enhancements of components associated with advanced atherosclerotic plaques and may help to monitor the progression of the plaque in a rabbit model of atherogenesis.

Quantification of myocardial blood volume during dipyridamole and doubtamine stress: a perfusion CMR study.

PURPOSE: Myocardial blood volume (MBV) may provide complementary information about myocardial oxygen needs and viability. The aim of this study is to examine a Cardiovascular Magnetic Resonance (CMR) perfusion method to quantify the changes in MBV, in comparison with the radiolabeled 99mTc-Red-Blood-Cell (RBC) method. METHODS: Normal mongrel dogs (n=12) were used in this study. Eight dogs were injected intravenously with dipyridamole, and 4 dogs were given dobutamine during the MR scans. CMR first-pass perfusion imaging was performed at rest and during the pharmacological stress. An intravascular contrast agent, Gadomer (Schering AG, Berlin, Germany), was injected (0.015 mmol/kg) as a bolus during the scans. A perfusion quantification method was applied to obtain MBV maps. Radiolabeled-RBCs were injected at the end of the study to measure reference MBV at rest (n=4), during dipyridamole vasodilation (n=4), and during dobutamine stress (n=4). RESULTS: Myocardial blood flow (MBF) increased approximately 3-fold with both dipyridamole and dobutamine injections. Transmural MBV values measured by CMR were closely correlated with those measured by 99mTc method (CMR:MBV=6.2+/-1.3, 7.2+/-0.8, and 8.3+/-0.5 mL/100 g, at rest, with dipyridamole, and with dobutamine, respectively. 99mTc-RBC: MBV=6.1+/-0.5, 7.0+/-0.9, and 8.6+/-0.7 mL/100 g). Dobutamine stress significantly increased MBV by CMR (33%) and 99mTc methods (35%). During dipyridamole induced vasodilation, MBV increased non-significantly by 14% with the 99mTc method and 1% with CMR method, which agreed well with other reports. CONCLUSION: First-pass perfusion CMR with the injection of intravascular contrast agents is a promising non-invasive approach for the assessment of MBV both at rest and pharmacologically induced stress.

Magnetic resonance imaging of atherosclerosis by targeting extracellular matrix deposition with Gadofluorine M.

As previously reported, Gadofluorine M-enhanced magnetic resonance imaging clearly demarcates atherosclerotic plaques from the normal vessel wall. To date, the underlying mechanism has remained unknown. Gadofluorine M is a gadolinium-containing macrocyclic contrast agent containing hydrophilic and hydrophobic moieties. To elucidate the mechanism of accumulation, fluorescently labeled and radioactively labeled derivates of Gadofluorine M were used to determine affinity and specificity of Gadofluorine M binding to blood serum and plaque components in vitro and for the distribution within the plaque of WHHL rabbits in vivo. Gadofluorine M binds to serum albumin, leading to a breakdown of micelles after intravenous injection. The affinity of Gadofluorine M to serum albumin is k(D) = 2 micromol/l. Gadofluorine then penetrates the atherosclerotic plaque while bound to albumin and then accumulates within the extracellular, fibrous parts of the plaque by binding to collagens, proteoglycans and tenascin, having the same affinity to these plaque constituents as to albumin. In contrast, weak binding was determined to LDL (k(D) = 2 mmol/l) and even no binding to hyaluronic acid. The driving force of binding and accumulation is the hydrophobic moiety of the molecules interacting with hydrophobic plaque materials. Thus, Gadofluorine M accumulates within the fibrous plaque or in the fibrous cap of a plaque containing high amounts of extracellular matrix components, but not in the lipid-rich areas. In combination with high-resolution MRI, Gadofluorine M might enable the detection of thin-cap fibroatheromas, also named the vulnerable plaque.

MRI tumor characterization using Gd-GlyMe-DOTA-perfluorooctyl-mannose-conjugate (Gadofluorine M), a protein-avid contrast agent.

The rationale and objectives were to define the MRI tumor-characterizing potential of a new protein-avid contrast agent, Gd-GlyMe-DOTA-perfluorooctyl-mannose-conjugate (Gadofluorine M; Schering AG, Berlin, Germany) in a chemically induced tumor model of varying malignancy. Because of the tendency for this agent to form large micelles in water and to bind strongly to hydrophobic sites on proteins, it was hypothesized that patterns of dynamic tumor enhancement could be used to differentiate benign from malignant lesions, to grade the severity of malignancies and to define areas of tumor necrosis. Gadofluorine M, 0.05 mmol Gd kg(-1), was administered intravenously to 28 anesthetized rats that had developed over 10 months mammary tumors of varying degrees of malignancy as a consequence of intraperitoneal administration of N-ethyl-N-nitrosourea (ENU), 45-250 mg kg(-1). These tumors ranged histologically from benign fibroadenomas to highly undifferentiated adenocarcinomas. Dynamic enhancement data were analyzed kinetically using a two-compartment tumor model to generate estimates of fractional plasma volume (fPV), apparent fractional extracellular volume (fEV*) and an endothelial transfer coefficient (K(PS)) for this contrast agent. Tumors were examined microscopically for tumor type, degree of malignancy (Scarff-Bloom-Richardson score) and location of necrosis. Eighteen tumor-bearing rats were successfully imaged. MRI data showed an immediate strong and gradually increasing tumor enhancement. K(PS) and fEV*, but not fPV obtained from tumors correlated significantly (p < 0.05) with the SBR tumor grade, r = 0.65 and 0.56, respectively. Estimates for K(PS) and fEV* but not fPV were significantly lower in a group consisting of benign and low-grade malignant tumors compared with the group of less-differentiated high-grade tumors (1.61 +/- 0.64 vs 3.37 +/- 1.49, p < 0.01; 0.45 +/- 0.17 vs 0.78 +/- 0.24, p < 0.01; and 0.076 +/- 0.048 vs 0.121 +/- 0.088, p = 0.24, respectively). It is concluded that the protein-avid MRI contrast agent Gadofluorine M enhances tumors of varying malignancy depending on the tumor grade, higher contrast agent accumulation for more malignant lesions. The results show potential utility for differentiating benign and low-grade malignant lesions from high-grade cancers.