Evaluation of superparamagnetic iron oxide for MR imaging of liver injury: proton relaxation mechanisms and optimal MR imaging parameters.
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PURPOSE: To investigate the proton relaxation mechanisms and the optimal MR imaging parameters in superparamagnetic iron oxide (SPIO)-enhanced MR imaging of liver injury. METHODS: A liver injury model was created in the rat using carbon tetrachloride. The T1 and T2 relaxation effects of SPIO in normal and injured liver were estimated by ex vivo relaxometry. In vivo laser confocal microscopy of the liver was performed to simulate the distribution and clustering of SPIO particles in the hepatic macrophages. SPIO-enhanced MR imaging (1.5T) of normal and diseased rats was performed with variable parameters. The liver specimens were prepared for histopathological examination. RESULTS: Histopathological and laser confocal microscopic findings showed diffuse macrophage distribution but decreased intracellular clustering of SPIO in injured liver. Ex vivo relaxometry showed sustained T1 and T2 relaxation effects of SPIO in liver injury. On MR images obtained with moderate echo time (spin echo [SE] 2000/40 and gradient echo [GRE] 130/9.0/60 degrees), injured liver showed significantly lower decrease in signal-to-noise ratio (SNR) than the normal liver, whereas little difference in SNR was found between the normal and injured liver on heavily T2-(SE 2000/80) and T1-weighted (SE 300/11 and GRE 130/2.0/90 degrees) MR images. CONCLUSION: Pulse sequences with a moderately long echo time (TE) may be more appropriate than heavily T1- or T2-weighted images for distinguishing normal and injured liver in SPIO-enhanced MR imaging because of the maintained T1 and T2 relaxation effect but decreased T2* relaxation effect of SPIO in injured liver. (+info)
Local staging of rectal cancer: the current role of MRI.
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With the advent of powerful gradient coil systems and high-resolution surface coils, magnetic resonance imaging (MRI) has recently extended its role in the staging of rectal cancer. MRI is superior to endorectal ultrasound, the most widely used staging modality in patients with rectal tumors, in that it visualizes not only the intestinal wall but also the surrounding pelvic anatomy. The crucial advantage of MRI is not that it enables exact T-staging but precise evaluation of the topographic relationship of a tumor to the mesorectal fascia. This fascia is the most important anatomic landmark for the feasibility of total mesorectal excision, which has evolved into the standard operative procedure for the resection of cancer located in the middle or lower third of the rectum. MRI is currently the only imaging modality that is highly accurate in predicting whether or not it is likely that a tumor-free margin can be achieved and thus provides important information for planning of an effective therapeutic strategy, especially in patients with advanced rectal cancer. (+info)
Inflammatory response after ischemic stroke: a USPIO-enhanced MRI study in patients.
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BACKGROUND AND PURPOSE: The intensity of the inflammatory response may be related to the volume of acute infarction. Ultra-small superparamagnetic particles of iron oxide (USPIO) may enable assessment of neuroinflammation. We aimed to assess whether the intensity of the inflammatory response might be related to the subacute ischemic lesion volume. METHODS: We enrolled patients who presented with acute anterior circulation stroke. MRI was performed at day 0, day 6, and day 9. The MRI protocol included T1-weighted imaging, gradient-echo T2*-weighted imaging, diffusion-weighted imaging, perfusion-weighted imaging and MR angiography. Blood-brain barrier disruption was defined as post-gadolinium enhancement on T1-weighted images. USPIO was administered after day 6 MRI. USPIO enhancement ratios were defined as the ratio between USPIO-related signal volume on day 9 T1-weighted imaging (respectively T2*-weighted imaging) and day 6 diffusion-weighted imaging infarct volume. The relationship between day 6 infarct volume and the enhancement ratio was assessed using Pearson and Spearman correlation tests. RESULTS: The protocol was completed in 10 patients. Signal alterations after USPIO injection was observed in 9/10 patients on day 9 T1-weighted imaging and in 5/10 patients on day 9 T2*-weighted imaging. USPIO-related MRI enhancement was heterogeneous. Lesion volume on day 6 diffusion-weighted imaging had no impact on USPIO enhancement at day 9 according to the Pearson correlation test (P=0.39) or Spearman test (P=0.25). There was no relationship between blood-brain barrier disruption and USPIO enhancement. CONCLUSIONS: USPIO MRI enhancement is heterogeneous and not clearly related to subacute lesion volume. (+info)
Imaging inflammation in acute brain ischemia.
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Brain inflammation holds promise as a therapeutic target in subacute stages of ischemic stroke. At the cellular level, postischemic inflammation is dominated by cells of the innate immune system with resident microglia/brain macrophages and blood-derived monocytes/macrophages being the most important cell types involved. Iron oxide nanoparticles such as ultrasmall superparamagnetic iron oxide (USPIO) are novel cell-specific contrast agents for MRI. After intravenous injection USPIO is taken up by circulating phagocytic cells. USPIO-laden macrophages cause typical signal changes in MRI of infarcted brain parenchyma, which has been demonstrated in studies of both experimental ischemia and human stroke. USPIO-enhanced MRI may therefore represent an important tool to address the role of macrophages for ischemic lesion development both in basic science and clinical studies. (+info)
Superparamagnetic iron oxide (SPIO) MRI contrast agent for bone marrow imaging: differentiating bone metastasis and osteomyelitis.
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PURPOSE: We explored appropriate scan timing for bone marrow imaging enhanced using superparamagnetic iron oxide (SPIO) and evaluated the usefulness of SPIO in differentiating metastasis and osteomyelitis in patients. METHODS: To determine the adequate scan timing after administration of SPIO, 5 healthy subjects were examined using a 1.5T magnetic resonance (MR) imaging scanner. Sagittal images of their lumbar spines were obtained using short-TI inversion recovery (STIR) sequence before and 3, 6, 9, 24, and 48 hours after intravenous injection of 8 micromol Fe/kg SPIO (ferucarbotran). MR signal intensities (SIs) were evaluated. Based on the results, 12 patients, five with bone metastasis and seven with vertebral osteomyelitis, were examined using the same procedure before and 3 hours after intravenous injection of ferucarbotran at the same dose. SIs of the bone metastases, osteomyelitis, and surrounding normal bone marrow were measured, and relative enhancement (RE) was calculated for each lesion. RESULTS: In the healthy volunteers, maximum reduction in signal was observed 3 to 24 hours (P<0.05) after administration of SPIO; thereafter and up to 48 hours, the SI gradually recovered. In the patients, the RE of the bone metastases was -12.2%, which was significantly higher than that in the osteomyelitis (-35.0%, P<0.001) and normal bone marrow (-46.6%, P<0.0005). CONCLUSION: Maximum suppression of signal intensity in bone marrow was seen 3 hours after injection of ferucarbotran, the point at which ferucarbotran allows differentiation of bone metastasis from ostoemyelitis. (+info)
Magnetic resonance evaluation of human mesenchymal stem cells in corpus cavernosa of rats and rabbits.
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AIM: To investigate whether the biological process of superparamagnetic iron oxide (SPIO)-labeled human mesenchymal stem cells (hMSCs) may be monitored non-invasively by using in vivo magnetic resonance (MR) imaging with conventional 1.5-T system examinations in corpus cavernosa of rats and rabbits. METHODS: The labeling efficiency and viability of SPIO-labeled hMSCs were examined with Prussian blue and Tripan blue, respectively. After SPIO-labeled hMSCs were transplanted to the corpus cavernosa of rats and rabbits, serial T2-weighted MR images were taken and histological examinations were carried out over a 4-week period. RESULTS: hMSCs loaded with SPIO compared to unlabeled cells had a similar viability. For SPIO-labeled hMSCs more than 1 X 10 (5) concentration in vitro, MR images showed a decrease in signal intensity. MR signal intensity at the areas of SPIO-labeled hMSCs in the rat and rabbit corpus cavernosa decreased and was confined locally. After injection of SPIO-labeled hMSCs into the corpus cavernosum, MR imaging demonstrated that hMSCs could be seen for at least 12 weeks after injection. The presence of iron was confirmed with Prussian blue staining in histological sections. CONCLUSION: SPIO-labeled hMSCs in corpus cavernosa of rats and rabbits can be evaluated non-invasively by molecular MR imaging. Our findings suggest that MR imaging has the ability to test the long-term therapeutic potential of hMSCs in animals in the setting of erectile dysfunction. (+info)
Long-term monitoring of transplanted human neural stem cells in developmental and pathological contexts with MRI.
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Noninvasive monitoring of stem cells, using high-resolution molecular imaging, will be instrumental to improve clinical neural transplantation strategies. We show that labeling of human central nervous system stem cells grown as neurospheres with magnetic nanoparticles does not adversely affect survival, migration, and differentiation or alter neuronal electrophysiological characteristics. Using MRI, we show that human central nervous system stem cells transplanted either to the neonatal, the adult, or the injured rodent brain respond to cues characteristic for the ambient microenvironment resulting in distinct migration patterns. Nanoparticle-labeled human central nervous system stem cells survive long-term and differentiate in a site-specific manner identical to that seen for transplants of unlabeled cells. We also demonstrate the impact of graft location on cell migration and describe magnetic resonance characteristics of graft cell death and subsequent clearance. Knowledge of migration patterns and implementation of noninvasive stem cell tracking might help to improve the design of future clinical neural stem cell transplantation. (+info)
Comparison of the inflammatory burden of truly asymptomatic carotid atheroma with atherosclerotic plaques contralateral to symptomatic carotid stenosis: an ultra small superparamagnetic iron oxide enhanced magnetic resonance study.
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BACKGROUND: Inflammation is a recognised risk factor for the vulnerable atherosclerotic plaque. The aim of this study was to explore whether there is a difference in the degree of magnetic resonance (MR) defined inflammation using ultra small superparamagnetic iron oxide (USPIO) particles within carotid atheroma in completely asymptomatic individuals and the asymptomatic carotid stenosis contralateral to the symptomatic side. METHODS: 20 symptomatic patients with contralateral disease and 20 completely asymptomatic patients underwent multi-sequence MR imaging before and 36 h after USPIO infusion. Images were manually segmented into quadrants and signal change in each quadrant was calculated following USPIO administration. Mean signal change was compared across all quadrants in the two groups. RESULTS: The mean percentage of quadrants showing signal loss was 53% in the contralateral group compared with 31% in completely asymptomatic individuals (p = 0.025). The mean percentages showing enhancement were 44% and 65%, respectively (p = 0.024). The mean signal difference between the two groups was 8.6% (95% CI 1.6% to 15.6%; p = 0.017). CONCLUSIONS: Truly asymptomatic plaques seem to demonstrate inflammation but not to the extent of the contralateral asymptomatic stenosis to the symptomatic side. Inflammatory activity may be a significant risk factor in asymptomatic disease. (+info)