Regional changes in the contralateral “healthy” hemisphere after ischemic lesions evaluated by quantitative T2 parametric maps

Modifications in the contralateral “healthy” hemisphere in a population of rats bearing cortical infarction were studied in vivo by magnetic resonance imaging (MRI) with the aim to investigate whether cerebral areas not directly involved in the lesion react at the presence of an ischemic lesion. The study was performed in rats in which a transtemporal approach was adopted to occlude the right middle cerebral artery (MCA). For MRI, the animals were examined at 4.7 Tesla and quantitative T2 parametric images were obtained by a multiecho sequence. Healthy rats and sham‐operated animals were used as control groups. The quantitative T2 parametric images showed that in the first week after the ischemia a significant increase in the mean T2 was seen in the lesioned parietal cortex, compared to the corresponding region of healthy rats (106 msec vs. 68 msec, P < 0.001). The contralateral “healthy” hemisphere showed T2 mean values not significantly different from the corresponding hemisphere of healthy rats (71 msec vs. 70 msec). However, a statistically significant increase in the T2 values was evident in the hypothalamic region (74 msec vs. 66 msec, P < 0.001). In rats examined 1 month after the ischemia, the T2 values of the hypothalamus were lower than those observed one week after ischemia (69 msec) but remained higher than in controls. The present study demonstrates that after a cerebral ischemia areas of secondary involvement distant from the lesion are present and can be studied in vivo by quantitative MRI. Anat Rec 266:118–122, 2002. © 2002 Wiley‐Liss, Inc.     

Manganese ions as intracellular contrast agents: proton relaxation and calcium interactions in rat myocardium

Paramagnetic manganese (Mn) ions (Mn(2+)) are taken up into cardiomyocytes where they are retained for hours. Mn content and relaxation parameters, T(1) and T(2), were measured in right plus left ventricular myocardium excised from isolated perfused rat hearts. In the experiments 5 min wash-in of MnCl(2) were followed by 15 min wash-out to remove extracellular (ec) Mn(2+) MnCl(2), 25 and 100 micro M, elevated tissue Mn content to six and 12 times the level of control (0 micro M MnCl(2)). Variations in perfusate calcium (Ca(2+)) during wash-in of MnCl(2) and experiments including nifedipine showed that myocardial slow Ca(2+) channels are the main pathway for Mn(2+) uptake and that Mn(2+) acts as a pure Ca(2+) competitor and a preferred substrate for slow Ca(2+) channel entry. Inversion recovery analysis at 20 MHz revealed two components for longitudinal relaxation: a short T(1 - 1) and a longer T(1 - 2). Approximate values for control and Mn-treated hearts were in the range 600-125 ms for T(1 - 1) and 2200-750 ms for T(1 - 2). The population fractions were about 59 and 41% for the short and the long component, respectively. The intracellular (ic) R(1 - 1) and R(2 - 1) correlated best with tissue Mn content. Applying two-site exchange analyses on the obtained T(1) data yielded results in parallel to, but also differing from, results reported with an ec contrast agent. The calculated lifetime of ic water (tau(ic)) of about 10 s is compatible with a slow water exchange in the present excised cardiac tissue. The longitudinal relaxivity of Mn ions in ic water [60 (s mM)(-1)] was about one order of magnitude higher than that of MnCl(2) in water in vitro [6.9 (s mM)(-1)], indicating that ic Mn-protein binding is an important potentiating factor in relaxation enhancement.     

Quantitative manganese tract tracing: dose-dependent and activity-independent terminal labelling in the mouse visual system

At concentrations sufficient for visualisation using MRI, manganese (Mn) is believed to behave as a calcium analogue. This study examines different concentrations of Mn for enhanced MR tract tracing. The premise of activity-dependent axonal transport was also examined by partial or complete blockade of retinal ganglion cell activity. Quantitative T(1) maps and semi-quantitative normalised signal intensities in the superior colliculi facilitated assessment of applied intraocular concentrations and activity dependence, respectively. Varying the concentration of applied Mn revealed a non-monotonic profile, with optimal, unfavourable and undesirable effects noted: 25 mM proved optimal, showing a maximal decrease in T(1), whereas 400 mM was associated with no terminal-field enhancement. The estimated vitreal concentration for optimal transport of Mn (2 mM) is substantially lower than that used in previous studies of the mouse. Both the partial blockade of inputs to 50% of retinal ganglion cells by a mGluR6 glutamate agonist and the complete blockade of all retinal ganglion cell activity with tetrodotoxin failed to decrease the relative enhancement in the superior colliculus. The failure to prevent axonal transport of Mn by blocking activity (and therefore theoretically the intracellular influx) appeared to be paradoxical. The optimal vitreal concentration of Mn has previously been shown to facilitate massive intracellular uptake of Mn, competitively blocking calcium, and 1 mM Mn blocks neurotransmission pre-synaptically. These results suggest that, at concentrations required for optimal Mn-enhanced MRI tract tracing in the visual system of the mouse, the uptake and transport of Mn may be dominated by passive mechanisms, which may also block neurotransmission. Copyright (c) 2008 John Wiley & Sons, Ltd.     

Monitoring dynamic alterations in calcium homeostasis by T (1)-weighted and T (1)-mapping cardiac manganese-enhanced MRI in a murine myocardial infarction model

Manganese has been used as a T(1)-weighted MRI contrast agent in a variety of applications. Because manganese ions (Mn(2+)) enter viable myocardial cells via voltage-gated Ca(2+) channels, manganese-enhanced MRI is sensitive to the viability and inotropic state of the heart. In spite of the established importance of Ca(2+) regulation in the heart both before and after myocardial injury, monitoring strategies to assess Ca(2+) homeostasis in affected cardiac tissues are limited. This study implements a T(1)-mapping method to obtain quantitative information both dynamically and over a range of MnCl(2) infusion doses. To optimize the current Mn(2+) infusion protocols, we performed both dose-dependent and temporal washout studies. A non-linear relationship between infused MnCl(2) solution dose and increase in left ventricular wall relaxation rate (DeltaR(1)) was observed. Control mice also exhibited significant Mn(2+) clearance over time, with a decrease in DeltaR(1) of approximately 50% occurring in just 2.5 h. The complicated efflux time dependence possibly suggests multiple efflux mechanisms. With the use of the measured relationship between infused Mn(2+) dose, DeltaR(1), and inductively coupled plasma mass spectrometry data analysis provided a means of estimating the absolute heart Mn concentration in vivo. We show that this technique has the sensitivity to observe or monitor potential alterations in Ca(2+) handling in vivo because of the physiological remodeling after myocardial infarction. Left ventricular free wall DeltaR(1) values were significantly lower (P = 0.005) in the adjacent zone, surrounding the injured myocardial tissue, than in healthy tissue. This inferred reduction in Mn concentration can be used to estimate potentially salvageable myocardium in vivo for future treatment or evaluation of disease progression.     

Cell labeling for magnetic resonance imaging with the T1 agent manganese chloride

There is growing interest in using MRI to track cellular migration. To date, most work in this area has been performed using ultra-small particles of iron oxide. Immune cells are difficult to label with iron oxide particles. The ability of adoptively infused tumor specific T cells and N cells to traffic to the tumor microenvironment may be a critical determinant of their therapeutic efficacy. We tested the hypothesis that lymphocytes and B cells would label with MnCl2 to a level that would allow their detection by T1-weighted MRI. Significant signal enhancement was observed in human lymphocytes after a 1 h incubation with 0.05-1.0 mM MnCl2. A flow cytometry-based evaluation using propidium iodide and Annexin V staining showed that lymphocytes did not undergo apoptosis or necrosis immediately after and 24 h following a 1 h incubation with up to 1.0 mM MnCl2. Importantly, NK cells and cytotoxic T cells maintained their in vitro killing capacity after being incubated with up to 0.5 mM MnCl2. This is the first report to describe the use of MnCl2 to label lymphocytes. Our data suggests MnCl2 might be an alternative to iron oxide cell labeling for MRI-based cell migration studies.     

缺血后处理对急性心肌缺血／再灌注家猪心脏的作用

目的研究缺血后处理对实验家猪心肌梗死范围及血压心率的影响,探讨在体条件下,缺血后处理是否具有缩小家猪缺血心脏的心肌梗死范围。方法采用标准家猪缺血／再灌注模型,在缺血后再灌前,分别给予4个周期和8个周期的短暂再灌注／再缺血作缺血后处理,TTC法确定心肌梗死范围。结果缺血后处理组8-30PostC心肌梗死范围（10．5±0．5）％,缺血后处理组4-30PostC心肌梗死范围及对照组分别为（36．7±3．7）％和（33．5±7．6）％（P〈0．01）,8个周期的缺血后处理组家猪心肌梗死面积明显小于对照组以及4个周期组,各组家猪的心率和平均动脉压无明显差异。结论缺血后处理可明显缩小家猪缺血心脏的心肌梗死范围。     

IR-SE and IR-MEMRI allow in vivo visualization of oscine neuroarchitecture including the main forebrain regions of the song control system

Songbirds share with humans the capacity to produce learned vocalizations (song). Recently, two major regions within the songbird's neural substrate for song learning and production; nucleus robustus arcopallii (RA) and area X (X) are visualized in vivo using Manganese Enhanced MRI (MEMRI). The aim of this study is to extend this to all main interconnected forebrain Song Control Nuclei. The ipsilateral feedback circuits allow Mn2+ to reach all main Song Control Nuclei after stereotaxic injection of very small doses of MnCl2 (10 nl of 10 mM) into HVC of one and MAN (nucleus magnocellularis nidopallii anterioris) of the other hemisphere. Application of a high resolution (80 micron) Spin Echo Inversion Recovery sequence instead of conventional T1-weighted Spin Echo images improves the image contrast dramatically such that some Song Control Nuclei, ventricles, several laminae, fibre tracts and other specific brain regions can be discerned. The combination of this contrast-rich IR-SE sequence with the transsynaptic transport property of Manganese (Inversion Recovery based MEMRI (IR-MEMRI)) enables the visualization of all main interconnected components of the Song Control System in telencephalon and thalamus.     

Evaluation of infarcted murine heart function: comparison of prospectively triggered with self-gated MRI

Measurement of cardiac function is often performed in mice after, for example, a myocardial infarction. Cardiac MRI is often used because it is noninvasive and provides high temporal and spatial resolution for the left and right ventricle. In animal cardiac MRI, the quality of the required electrocardiogram signal is variable and sometimes deteriorates over time, especially with infarcted hearts or cardiac hypertrophy. Therefore, we compared the self‐gated IntraGateFLASH method with a prospectively triggered FLASH (fast low‐angle shot) method in mice with myocardial infarcts (n = 16) and in control mice (n = 21). Mice with a myocardial infarct and control mice were imaged in a vertical 9.4‐T MR system. Images of contiguous 1‐mm slices were acquired from apex to base with prospective and self‐gated methods. Data were processed to calculate cardiac function parameters for the left and right ventricle. The signal‐to‐noise and contrast‐to‐noise ratios were calculated in mid‐ventricular slices. The signal‐to‐noise and contrast‐to‐noise ratios of the self‐gated data were higher than those of the prospectively gated data. Differences between the two gating methods in the cardiac function parameters for both left and right ventricle (e.g. end‐diastolic volumes) did not exceed the inter‐observer variability in control or myocardial infarcted mice. Both methods gave comparable results with regard to the cardiac function parameters in both healthy control mice and mice with myocardial infarcts. Moreover, the self‐gated method provided better signal‐to‐noise and contrast‐to‐noise ratios when the acquisition time was equal. In conclusion, the self‐gated method is suitable for routine use in cardiac MRI in mice with myocardial infarcts as well as in control mice, and obviates the need for electrocardiogram triggering and respiratory gating. In both gating methods, more than 10 frames per cardiac cycle are recommended. Copyright © 2010 John Wiley & Sons, Ltd.     

Cyclooxygenase products are not involved in the protection against myocardial infarction afforded by preconditioning in rabbit. Cyclooxygenase pathway's involvement in preconditioning.

The mechanism whereby preconditioning with a transient period of ischemia renders the heart resistant to infarction from a subsequent ischemic insult is unknown. The purpose of this study was to determine whether cyclooxygenase pathways are involved in preconditioning's protection. Two inhibitors of that pathway, meclofenamate (MEC) and aspirin (ASP), were test in an in situ and a blood perfused isolated heart model, respectively. Preconditioning was achieved with 5 minute ischemia and 10 minutes reperfusion. All in situ hearts underwent 30 minute ischemia followed by 180 minute reperfusion, while the isolated hearts experienced 45 minute ischemia plus 120 minute reperfusion. Infarct size was measured with TTC stain. In the in situ model, 39.9% +/- 4.2% of the ischemic zone was infarcted in control hearts but only 8.8% +/- 2.2% in preconditioning hearts. Pretreatment with MEC (5 mg/Kg) caused no alteration of infarct size in either non preconditioned (34.3% +/- 8.3%) or preconditioned hearts (6.7% +/- 3.3%). In isolated hearts, 45 minute ischemia caused 31.0% +/- 5.9% of the ischemic zone to be infarcted in control hearts and only 5.4% +/- 2.2% in preconditioned hearts. Pretreatment with ASP (1 mg/Kg) failed to affect infarct size in either non preconditioned (35.7% +/- 3.7%) or preconditioned hearts (10.2% +/- 1.9%). The data indicate that cyclooxygenase pathways are not involved in the preconditioning's protection.     

Survey of gross anatomy,microscopic anatomy,neuroscience, and embryology courses in medical school curricula in the United States

Modifications in the contralateral "healthy" hemisphere in a population of rats bearing cortical infarction were studied in vivo by magnetic resonance imaging (MRI) with the aim to investigate whether cerebral areas not directly involved in the lesion react at the presence of an ischemic lesion. The study was performed in rats in which a transtemporal approach was adopted to occlude the right middle cerebral artery (MCA). For MRI, the animals were examined at 4.7 Tesla and quantitative T2 parametric images were obtained by a multiecho sequence. Healthy rats and sham-operated animals were used as control groups. The quantitative T2 parametric images showed that in the first week after the ischemia a significant increase in the mean T2 was seen in the lesioned parietal cortex, compared to the corresponding region of healthy rats (106 msec vs. 68 msec, P < 0.001). The contralateral "healthy" hemisphere showed T2 mean values not significantly different from the corresponding hemisphere of healthy rats (71 msec vs. 70 msec). However, a statistically significant increase in the T2 values was evident in the hypothalamic region (74 msec vs. 66 msec, P < 0.001). In rats examined 1 month after the ischemia, the T2 values of the hypothalamus were lower than those observed one week after ischemia (69 msec) but remained higher than in controls. The present study demonstrates that after a cerebral ischemia areas of secondary involvement distant from the lesion are present and can be studied in vivo by quantitative MRI.     

Characterisation of in vivo ovarian cancer models by quantitative 1H magnetic resonance spectroscopy and diffusion-weighted imaging

Magnetic resonance imaging (MRI) and spectroscopy (MRS) offer powerful approaches for detecting physiological and metabolic alterations in malignancies and help investigate underlying molecular mechanisms. Research on epithelial ovarian carcinoma (EOC), the gynaecological malignancy with the highest death rate characterised by frequent relapse and onset of drug resistance, could benefit from application of these molecular imaging approaches. In this study, MRI/MRS were used to characterise solid tumour models obtained by subcutaneous (s.c.) or intraperitoneal (i.p.) implantation of human SKOV3.ip cells in severe combined immunodeficiency (SCID) mice. In vivo MRI/MRS, ex vivo magic-angle-spinning (MAS), and in vitro (1)H-NMR measurements were carried out at 4.7 T, 9.4 T, and 9.4/16.5 T, respectively. MRI evaluation was performed by T1-, T2-, and diffusion-weighted (DW) multislice spin-echo imaging. The in vivo (1)H spectra of all tumour models showed a prominent resonance of total choline-containing metabolites (tCho). Quantitative in vivo MRS of both i.p. and s.c. SKOV3.ip xenografts showed that the mean tCho content was in the 2.9-4.5 mM range, with a mean PCho/tCho ratio of 0.99 ± 0.01 [23 examinations, 14-34 days post injection (dpi)], in good agreement with ex vivo and in vitro analyses. Myo-inositol ranged between 11.7 and 17.0 mM, with a trend towards higher values in i.p. xenografts at 14-16 dpi. The average apparent diffusion coefficient (ADC) values of SKOV3.ip xenografts [1.64 ± 0.11 (n = 9, i.p.) and 1.58 ± 0.03 x10(-3) mm(2)/s (n = 7, s.c.)] were in agreement with values reported for tumours from patients with EOC, while the mean vascular signal fraction (VSF) was lower (≤ 4%), probably due to the more rapid growth of preclinical models. Both s.c. and i.p. xenografts are valuable preclinical models for monitoring biochemical and physiopathological changes associated with in vivo EOC tumour growth and response to therapy, which may serve as the basis for further clinical development of noninvasive MR approaches.     

Detection of necrotic neural response in super‐acute cerebral ischemia using activity‐induced manganese‐enhanced (AIM) MRI

Immediate and certain determination of the treatable area is important for choosing risky treatments such as thrombolysis for brain ischemia, especially in the super‐acute phase. Although it has been suggested that the mismatch between regions displaying ‘large abnormal perfusion’ and ‘small abnormal diffusion’ indicates a treatable area on an MRI, it has also been reported that the mismatch region is an imperfect approximation of the treatable region named the ‘penumbra’. Manganese accumulation reflecting calcium influx into cells was reported previously in a middle cerebral artery occlusion (MCAO) model using activity‐induced manganese‐enhanced (AIM) MRI. However, in the super‐acute phase, there have been no reports about mismatches between areas showing changes to the apparent diffusion coefficient (ADC) and regions that are enhanced in AIM MRI. It is expected that the AIM signal can be enhanced immediately after cerebral ischemia in the necrotic core region due to calcium influx. In this study, a remote embolic rat model, created using titanium‐oxide macrospheres, was used to observe necrotic neural responses in the super‐acute phase after ischemia. In addition, images were evaluated by comparison between ADC, AIM MRI, and histology. The signal enhancement in AIM MRI was detected at 2 min after the cerebral infarction using a remote embolic method. The enhanced area on the AIM MRI was significantly smaller than that on the ADC map. The tissue degeneration highlighted by histological analysis corresponded more closely to the enhanced area on the AIM MRI than that on the ADC map. Thus, the manganese‐enhanced region in brain ischemia might indicate ‘necrotic’ irreversible tissue that underwent calcium influx. Copyright © 2009 John Wiley & Sons, Ltd.     

Photoacoustic tomography of ex vivo mouse hearts with myocardial infarction

In the present study, we evaluated the applicability of ex vivo photoacoustic imaging (PAI) on small animal organs. We used photoacoustic tomography (PAT) to visualize infarcted areas within murine hearts and compared these data to other imaging techniques [magnetic resonance imaging (MRI), micro-computed tomography] and histological slices. In order to induce ischemia, an in vivo ligation of the left anterior descending artery was performed on nine wild-type mice. After varying survival periods, the hearts were excised and fixed in formaldehyde. Samples were illuminated with nanosecond laser pulses delivered by a Nd:YAG pumped optical parametric oscillator. Ultrasound detection was achieved using a Mach-Zehnder interferometer (MZI) working as an integrating line detector. The voxel data were computed using a Fourier-domain based reconstruction algorithm, followed by inverse Radon transforms. The results clearly showed the capability of PAI to visualize myocardial infarction and to produce three-dimensional images with a spatial resolution of approximately 120 μm. Regions of affected muscle tissue in PAI corresponded well with the results of MRI and histology. Photoacoustic tomography utilizing a MZI for ultrasound detection allows for imaging of small tissue samples. Due to its high spatial resolution, good soft tissue contrast and comparatively low cost, PAT offers great potentials for imaging.     

Higher Lesion Detection by 3.0T MRI in Patient with Transient Global Amnesia

Purpose

Transient global amnesia (TGA) patients were retrospectively reviewed to determine the usefulness of high-field strength MRI in detecting probable ischemic lesions in TGA.

Materials and Methods

We investigated the lesion detection rate in patients with TGA using 1.5T and 3.0T MRI. Acute probable ischemic lesions were defined as regions of high-signal intensity in diffusion weighted image with corresponding low-signal intensity in apparent diffusion coefficient map.

Results

3.0T MRI showed 11 out of 32 patients with probable ischemic lesions in the hippocampus with mean lesion size of 2.8 ± 0.6 mm, whereas 1.5T MRI detected no lesion in any of 11 patients. There were no significant differences in clinical characteristics between the groups of 1.5 and 3.0T MRI.

Conclusion

High-field strength MRI has a higher detection rate of probable ischemic lesions than low-field strength MRI in patients with TGA.     

A Reproducible and Translatable Model of Focal Ischemia in the Visual Cortex of Infant and Adult Marmoset Monkeys

Models of ischemic brain injury in the nonhuman primate (NHP) are advantageous for investigating mechanisms of central nervous system (CNS) injuries and testing of new therapeutic strategies. However, issues of reproducibility and survivability persist in NHP models of CNS injuries. Furthermore, there are currently no pediatric NHP models of ischemic brain injury. Therefore, we have developed a NHP model of cortical focal ischemia that is highly reproducible throughout life to enable better understanding of downstream consequences of injury. Posterior cerebral arterial occlusion was induced through intracortical injections of endothelin‐1 in adult (n = 5) and neonatal (n = 3) marmosets, followed by magnetic resonance imaging (MRI), histology and immunohistochemistry. MRI revealed tissue hyperintensity at the lesion site at 1–7 days followed by isointensity at 14–21 days. Peripheral macrophage and serum albumin infiltration was detected at 1 day, persisting at 21 days. The proportional loss of total V1 as a result of infarction was consistent in adults and neonates. Minor hemorrhagic transformation was detected at 21 days at the lesion core, while neovascularization was detected in neonates, but not in adults. We have developed a highly reproducible and survivable model of focal ischemia in the adult and neonatal marmoset primary visual cortex, demonstrating similar downstream anatomical and cellular pathology to those observed in post‐ischemic humans.     

Fractionated manganese-enhanced MRI

We investigated the use of manganese-enhanced MRI (MEMRI) with fractionated doses as a way to retain the unique properties of manganese as a neuronal contrast agent while lessening its toxic effects in animals. First, we followed the signal enhancement on T1-weighted images of the brains of rats receiving 30 mg/kg fractions of MnCl2 . 4H2O every 48 h and found that the signal increased in regions with consecutive fractionated doses and ultimately saturated. Second, we used T1 mapping to test whether the amount of MRI-visible manganese that accumulated depended on the concentration of manganese in the fractions. For a fixed cumulative dose of 180 mg/kg MnCl2 . 4H2O, increasing fraction doses of 6 x 30 mg/kg, 3 x 60 mg/kg, 2 x 90 mg/kg and 1 x 180 mg/kg produced progressively shorter T1 values. The adverse systemic health effects, including complications at the injection site and poor animal well-being, also rose with the fraction dose. Thus, fractionated MEMRI can be used to balance the properties of manganese as a contrast agent in animals against its toxic effects.     

The Correlation of 3D DT-MRI Fiber Disruption with Structural and Mechanical Degeneration in Porcine Myocardium

Evaluation of structural parameters following a myocardial infarction (MI) is important to assess left ventricular function and remodeling. In this study, we assessed the capability of 3D diffusion tensor magnetic resonance imaging (DT-MRI) to assess tissue degeneration shortly after an MI using a porcine model of infarction. Two days after an induced infarction, hearts were explanted and immediately scanned by a 3T MRI scanner with a diffusion tensor imaging protocol. 3D fiber tracks and clustering models were generated from the diffusion-weighted imaging data. We found in a normal explanted heart that DT-MRI fibers showed a multilayered helical structure, with fiber architecture and fiber density reflecting the integrity of muscle fibers. For infarcted heart explants, we observed either a lack of fibers or disruption of fibers in the infarcted regions. Contours of the disrupted DT-MRI fibers were found to be consistent with the infarcted regions. Both histological and mechanical analysis of the infarcted hearts suggested DT-MRI fiber disruption correlated with altered microstructure and tissue mechanics. The ability of 3D DT-MRI to accurately distinguish viable myocardium from dead myocardium only 2 days post infarct without the use of radioisotopes or ionotropic agents makes it a promising approach to evaluate cardiac damage early post-MI.     

Iron particles for noninvasive monitoring of bone marrow stromal cell engraftment into, and isolation of viable engrafted donor cells from, the heart

Stem cells offer a promising approach to the treatment of myocardial infarction and prevention of heart failure. We have used iron labeling of bone marrow stromal cells (BMSCs) to noninvasively track cell location in the infarcted rat heart over 16 weeks using cine-magnetic resonance imaging (cine-MRI) and to isolate the BMSCs from the grafted hearts using the magnetic properties of the donor cells. BMSCs were isolated from rat bone marrow, characterized by flow cytometry, transduced with lentiviral vectors expressing green fluorescent protein (GFP), and labeled with iron particles. BMSCs were injected into the infarct periphery immediately following coronary artery ligation, and rat hearts were imaged at 1, 4, 10, and 16 weeks postinfarction. Signal voids caused by the iron particles in the BMSCs were detected in all rats at all time points. In mildly infarcted hearts, the volume of the signal void decreased over the 16 weeks, whereas the signal void volume did not decrease significantly in severely infarcted hearts. High-resolution three-dimensional magnetic resonance (MR) microscopy identified hypointense regions at the same position as in vivo. Donor cells containing iron particles and expressing GFP were identified in MR-targeted heart sections after magnetic cell separation from digested hearts. In conclusion, MRI can be used to track cells labeled with iron particles in damaged tissue for at least 16 weeks after injection and to guide tissue sectioning by accurately identifying regions of cell engraftment. The magnetic properties of the iron-labeled donor cells can be used for their isolation from host tissue to enable further characterization.     

MRI studies of cryoinjury infarction in pig hearts: ii. Effects of intrapericardial delivery of adipose-derived stem cells (ADSC) embedded in agarose gel

The purpose was to assess effects of intrapericardially deposited adipose‐derived stem cells (ADSC) as a source of angiogenic factors on cryoinjury infarction. To enhance this effect and reduce incorporation of ADSC into tissue, the cells were immobilized in agarose gel patches transplanted onto cryoinjured epicardium. In domestic pigs (15–20 kg) the left ventricular (LV) anterior wall of exposed hearts was cryoinjured using aluminum rod (Φ=25 mm) cooled in liquid nitrogen. Sterilized circular patches made of agarose gel were placed in a nylon bag and sutured to cryoinjured epicardium. In 4 pigs, the patches contained 650,000 human ADSCs; in control animals patches were cell‐free (n,=,2) or no patches were implanted (n,=,2). Cine and T₁‐weighted MRI was performed in vivo weekly (4 weeks) after injury using a 3 T imager. Following baseline imaging, a double bolus of gadopentate dimeglumine was injected (GdDTPA, 0.05 and 0.15 mmol/kg) and serial short axis images were acquired. In the 4‐week ADSC‐treated group, 2 pigs were assessed using GdDTPA and 2 pigs were assessed using MnCl₂ (70 micromol/kg/14 min). In all pigs, 5 × 10⁶ NIR fluorescent microspheres (15 µm FMS, 645/680 nm) were injected into the hearts, which were excised, sliced and examined with fluorescence imaging for FMS content. Triphenyltetrazolium chloride (TTC) staining was used to determine necrotic areas. Four‐week infarction areas were hypokinetic and appeared hyperintensive on Gd‐enhanced MR images, hypointensive on Mn‐enhanced images, and were TTC‐negative. First‐pass Gd enhancement kinetics was faster in the infarct area of ADSC‐treated hearts: 152 ± 89 vs 54 ± 5.3% of normal in control (p = 0.03). Accordingly, FMS fluorescence was much higher in the treated infarcts (144 ± 59% of remote, n = 4) relative to control hearts (58 ± 13%, n = 4), which correlated with 3 times higher microvascular density in treated hearts. LV wall thickening was partially restored by ADSC treatment. ADSC‐containing patches attached to cryoinjured epicardium greatly improved perfusion and microvascular density of scar tissue. Copyright © 2011 National Research Council Canada.