Relationship between the Number of SPIO-labeled Macrophage and MR Signal Intensity

PURPOSE: For the in vivo imaging of macrophages using MRI, the feasibility of labeling macrophages with iron oxide and the number of SPIO-labeled macrophage detected in 1.5 T MR, were assessed. MATERIALS AND METHODS: The MR signal intensity was measured with variable concentrations of iron oxide, ranging from 112 to 2.384x10-7 μgFe/mL. The macrophages were incubated in SPIO solution (112 μgFe/mL) for 24 hours. The MR signal intensity was measured in variable numbers of SPIO-labeled macrophages. RESULTS: The MR image signal intensity gradually increased with decreasing SPIO concentration, and reached a plateau at a concentration of 0.219 μgFe/mL. After incubation with iron oxide, the compact uptake of SPIO was detected in the cytoplasm of the macrophages using Prussian blue staining. No susceptibility effect was detected in the tubes of more than 122 macrophages. CONCLUSION: The MR signal intensity was dependent on the number of macrophages. No susceptibility effect due to a cluster of SPIO-labeled macrophages was detected in more than 488 cells.

The Effect of Micro-Particles of Linoleic Acid Emulsion on the Blood-Brain Barrier in Cats

PURPOSE: The purpose of this study was to investigate the permeability change of the blood-brain barrier and the reversibility of the embolized lesions induced with a fat-emulsion technique by using magnetic resonance imaging (MRI), and we also wished to evaluate the resultant histologic findings in cat brains. MATERIALS AND METHODS: MR imaging was scheduled serially at 1 hour, day 1, day 4 and day 7 after infusion of linoleic acid-emulsion (0.05 ml linoleic acid+20 ml saline) to the internal carotid artery in 12 cats. Abnormal signal intensity or contrast enhancement was evaluated on diffusion-weighted images (DWIs), the apparent diffusion coefficient (ADC) maps, and gadolinium-enhanced T1-weighted images (Gd-T1WIs) at the stated times. MR imaging was stopped if the lesion shows isointensity and no contrast enhancement was observed at the acquisition time, and then brain tissue was harvested and examined. Light microscopic (LM) and electron microscopic (EM) examinations were performed. RESULTS:The embolized lesions appeared as isointensities (n=7) or mild hyperintensities (n=5) on DWIs, as isointensities (n=12) on the ADC maps, and as contrast enhancements (n=12) on Gd-T1WIs at 1 hour. The lesions showed isointensity on DWIs and the ADC maps, and as no contrast enhancement for all cats at day 1. The LM findings revealed small (< 1 cm) focal necrosis and demyelination in three cats. EM examinations showed minimal findings of small (< 3 micrometer) fat globules within the endothelial wall (n=10) and mild swelling of the neuropils (< 5 micrometer). Widening of the interstitium or morphologic disruption of the endothelial wall was not seen. CONCLUSION: Cerebral fat embolism induced by linoleic acid emulsion revealed vasogenic edema and reversible changes as depicted on the MR images. These results might help us to understand the mechanisms of fat on the blood-brain barrier, and this technique could be used as a basic model for research of the effects of drugs on the disrupted blood-brain barrier, and also as a research model for the chemotherapeutic effects of drugs of the brain tumors.

Proton MR Spectroscopic Features According to Change of Hepatic Parenchymal Iron Content after SPIO Injection

PURPOSE: To determine the effect of iron on proton MR spectra (1H-MRS) by evaluating changes in 1H-MRS of the liver according to changes in hepatic parenchymal iron content. MATERIALS AND METHODS: We evaluated serial changes in 1H-MRS of the liver after intravenous infusion of SPIO in 40 rabbits. These were divided into eight groups of five, and in each group, respectively, 1H-MRS and T2WI MR images were acquired prior to SPIO infusion, just after infusion, and at 15 minutes and 1, 2, 4, 24 and 96 hours after infusion. MR spectra were evaluated with particular attention to the curve pattern observed at specific times after the infusion of SPIO, and the results were correlated with the signal intensity observed on T2W1 images and the histologic giade of ilon content of samples of resected liver parenchyma. RESULTS: As observed on T2WI, the mean signal intensity of rabbit liver in its pre-SPIO infusion state, just after infusion, at 15 minutes, and at 1, 2, 4, 24 and 96 hours after SPIO infusion was 121.3 +/-15.5, 41.5 +/-12.7, 30.3 +/-7.9, 31.3 +/-3.5, 33.6 +/-9.4, 45.5 +/-10.9, 80.3 +/-15.7 and 110.4 +/-22.9, respectively(p<0.05). Mean standard deviation of the ratio of the area of the peak (3.9-4.1 ppm) / lipid peak (1.3 ppm) peak at each of the above times except for the pre-infusion state was 1.10 +/-0.13, 1.86 +/-0.21, 1.80 +/-0.30, 1.76 +/-0.27, 1.74 +/-0.20, 0.07 +/-0.02 and 0.03 +/-0.01, respectively(p<0.05). The hepatic parenchymal iron content increased rapidly from just after SPIO infusion, reaching its maximal level (as revealed by histologic specimens) at 15 minutes, sustaining this for up to 4 hours, and then decreasing gradually over periods of 24 and 96 hours. These results show that serial changes in patterns of MR spectra and the signal intensity seen on T2WI images correlate closely with changes in hepatic parenchymal iron content. CONCLUSION: Elevated hepatic parenchymal iron content leads to increases in the relative intensity of unknown peaks at around 4.0 ppm and decreases in the relative intensity of lipid peaks.

Diffusion-Weighted MR Imaging in Animal Model with Acute Ischemic Brain Infarction: Evaluation of Reversible Brain Injury

PURPOSE: To determine whether the analysis of abnormally high signal intensities in ischemic tissue, as revealed by diffusion-weighted MR imaging (DWI) can be used to evaluate reversible brain lesions in a cat model of acute ischemia. MATERIALS AND METHODS: Ten cats were divided into two groups of five (Group I and Group II), and in all animals the middle cerebral artery was temporarily occluded. Group I underwent T2-DWI 30 minutes after occlusion, and Group II 120 minutes after occlusion. In both groups, DWI was performed one hour and 24 hours after reperfusion (at one hour, non-T2-weighted; at 24 hours, T2-weighted). Both occlusion and reperfusion were monitored by 99m TC-ECD brain perfusion SPECT. All animals were sacrificed 24 hours later and their brain tissue was stained with TTC. Signal intensity ratios (SIR, signifying average signal intensity within the region of interest divided by that in the contralateral, nonischemic, homologous region) of the two groups, as seen on DWI were compared. The percentage of hemispheric lesions occurring in the two groups was also compared. RESULTS: SIR after occlusion of the middle cerebral artery was 1.29 in Group I and 1.59 in Group II. Twenty-four hours after reperfusion, SIR in Group I was higher than in Group II (p<0.01). After occlusion and reperfusion, the percentage of hemispheric lesions in Group I was less than in Group II. For the latter, the percentage of these lesions revealed by TTC staining and T2-weighted imaging was 48% and 59%, respectively, findings distinctly different from those for Group I. In addition, in group I, infarction was revealed by neither TTC staining nor T2-weighted imaging (p<0.01). CONCLUSION: The use of DWI to evaluate signal intensity ratios can help determine whether or not brain injury after temporary cerebral ischemia is reversible.

Analysis of Signal Intensity Curve on Dynamic Contrast-Enhanced MR Imaging of Postoperative Scars in Rabbits:Comparison of Gadopentetate Dimeglumine and 24-gadolinium-tetraazacy-clododecanetetraacetic acid (DOTA)-dendrimer

PURPOSE: To compare the enhancement patterns of 24-gadolinium-tetrazacyclodode-cane tetracetic acid (DOTA)-dendrimer (Gadomer-17) with those of gadopentetate dimeglumine (Magnevist) in postoperative scars in rabbits. MATERIALS AND METHODS: Twelve rabbit thighs with experimentally induced postoperative scars underwent dynamic contrast-enhanced MR imaging with both Gadomer-17 and gadopentetate dimeglumine at a 24-hr interval at one (n = 10), two (n = 8) and three months (n=4) after scar induction. The enhancement and the ratios of lesions at each time point, peak enhancement ratios, and the slope and shape of curves were assessed. RESULTS: At all time points, enhancement ratios were significantly lower after the injection of Gadomer-17 than with gadopentetate dimeglumine (p<0.05). Peak enhancement ratios were significantly lower with Gadomer-17 (1.29+/-0.15) than with gadopentetate dimeglumine (1.61+/-0.31) (p<0.01). The slope values were 2.99%/min+/-2.72 after Gadomer-17 injection and 8.99%/min+/-7.32 after gadopentetate dimeglumine injection (p<0.01). The enhancement ratio curves showed mostly the plateau pattern with Gadomer-17 (90.9%), while for gadopentetate dimeglumine, the curve pattern was either plateau (50%) or washout (50%). Difference in enhancement characteristics between the two contrast agents were most pronounced for one-month scars. CONCLUSION: With Gadomer-17, weaker enhancement and the plateau pattern were found in postoperative scars, whereas stronger enhancement and either washout or the plateau pattern were found with gadopentetate dimeglumine.