Demineralized bone matrix-induced ectopic bone formation in rats: in vivo study with follow-up by magnetic resonance imaging, magnetic resonance angiography, and dual-energy X-ray absorptiometry

The aim of this study was to further explore the use of magnetic resonance imaging (MRI), magnetic resonance angiography (MRA), and dual-energy X-ray absorptiometry (DEXA) to assess bone formation and blood circulation in a pedicled bone graft substitute. In 14 Wistar rats, initially 10 weeks old, heterogeneous demineralized femur bone matrix implants were wrapped in pedicled adductor thigh muscle flaps. One rat died after surgery. Subsequently, bone formation and maintenance of blood vessel functionality were evaluated in six rats 6 weeks postimplantation by means of in vivo MRI/MRA and postmortem histomorphometry. The other seven rats were left for 12 weeks, whereafter bone formation was evaluated by in vivo DEXA and postmortem histomorphometry. The results demonstrated that after 6 weeks bone formation was present in four of six animals, quantified as 42 (+/-35)% and 25 (+/-19)% by means of MRI and histomorphometry, respectively. MRA was able to show patency of the pedicles of these four rats only, which suggests that the lack of blood supply in the other two rats is the cause of the failure to form bone. In the 12-week group, histology showed increased bone formation without signs of osteolysis, which was quantified histomorphometrically to be as high as 48 (+/-15)%. DEXA failed to show bone formation. It is concluded that in vivo MRI proved to be a reliable method for monitoring ectopic bone formation in a rat model, whereas in vivo DEXA was unable to detect the implants. Furthermore, in vivo MRA proved to be a useful technique for studying the circulation of muscle flaps in this animal model.     

In vivo monitoring of age-related changes in rat brain using quantitative diffusion magnetic resonance imaging and magnetic resonance relaxometry

Ghrelin is a novel peptide that stimulates the release of growth hormone from the pituitary and is involved in hypothalamic feeding regulation. A pre-embedding immunostaining technique was used to study the ultrastructure and synaptic relationships of ghrelin-containing neurons in the rat arcuate nucleus (ARC). Ghrelin-like immunoreactive (ghrelin-LI) neurons were found in the ARC, and were especially abundant in its ventral part. At the electron microscopic level, ghrelin-LI neurons received afferent synapses from many unknown axon terminals. Ghrelin-LI products in the immunoreactive cell bodies, processes, and axon terminals were detected mainly in dense granular vesicles about 110 nm in diameter. Ghrelin-LI presynaptic axon terminals often made synapses with unknown immunonegative neurons. These results suggest that ghrelin acts to regulate food intake through synaptic connections in hypothalamic neuronal networks.     

In utero eyeball development study by magnetic resonance imaging

The aim of this study was to measure fetal ocular development and to determine a growth curve by means of measurements in utero. Fetal ocular development was recorded by analysis of the results of magnetic resonance imaging (MRI). An anatomic study allowed definition of the best contrasted MRI sequences for calculation of the ocular surface. Biometric analysis of the values of the ocular surface in the neuro-ocular plane in 35 fetuses allowed establishment of a linear model of ocular growth curve in utero. Evaluation of ocular development may allow the detection and confirmation of malformational ocular anomalies such as microphthalmia.     

Evaluation of ectopic pregnancy by magnetic resonance imaging.

Patients (n = 37) suspected of ectopic pregnancy were prospectively evaluated with magnetic resonance (MR) imaging to assess the capability of MR imaging in the diagnosis of ectopic pregnancy. Five levels of confidence were defined: diagnostic, suspicious, equivocal, questionable, and negative. Tubal wall enhancement and presence of tubal haematoma or gestational sac-like structure were considered diagnostic findings. There were 21 diagnostic, two suspicious, eight equivocal, and six negative findings. MR findings were compared with the surgical findings in 18 patients. Surgical confirmation was obtained in 12 diagnostic, two suspicious, and four equivocal studies. Using the MR diagnostic criteria for tubal pregnancy, MR had 12 true positive, three true negative, three false negative, and no false positive results for the diagnosis of tubal pregnancy. Retrospective analysis of the signal intensity of haematoma and ascites was performed for these 18 surgically confirmed cases. The predominant signal intensity of tubal haematoma was an intermediate signal on T1-weighted image (WI) and a low signal on T2WI. Ascites showed signal intensity higher than that of urine on T1WI in 100% of 13 cases. In conclusion, MR imaging with use of intravenous contrast material allows a specific diagnosis of tubal pregnancy, recognizing tubal wall enhancement and fresh tubal haematoma.     

In vivo 19F nuclear magnetic resonance spectroscopy of trifluorinated neuroleptics in the rat

In vivo 19F NMR measurements of trifluorinated neuroleptics in the rat brain were made using a 13 x 18 mm surface coil at 4.7 T. The signal of fluphenazine was obtained within 8-15 min from brains of living rats treated chronically with drug doses of 5-30 mg/kg. Following the intravenous injection of a single dose of trifluoperazine (30 mg/kg), brain levels could be monitored with a time resolution of 30 min. The data demonstrate the possibility of obtaining in vivo pharmacokinetics of fluorinated agents in the rat brain. 19F NMR is expected to become an important tool in neurochemical research.     

In vivo magnetic resonance imaging and relaxometry study of a porous hydrogel implanted in the trapezius muscle of rabbits

In vivo magnetic resonance imaging (MRI) and relaxometry were performed to assess noninvasively the tissue reaction and the biological integration of hydrogels made of poly[N-(2-hydroxypropyl) methacrylamide] (PHPMA) after implantation in the trapezius muscle of rabbits. The benefits of incorporating RGD peptide sequences in the polymer backbone were also investigated. The histological status of each implant was probed by the trend of their transversal relaxation times, T(2), while their biocompatibility was evaluated by analyzing the host tissue response through the evolution of the relaxation times of the adjacent muscle tissue. MR results showed the good acceptability of both hydrogels by the host tissue. The transversal relaxation curves of each implant exhibited two distinct phases as a function of implantation time: (1) a monoexponential phase, dominated by the influx of fluids inside the implants; and (2) a biexponential phase related to the infiltration of cells and the granulation tissue formation within the porous structure of each polymer. These MR findings were correlated with the results of conventional histological analyses. The present study demonstrates the effectiveness of MR methods in noninvasively monitoring the biocompatibility and histological status of implanted porous biomaterials.     

In vivo magnetic resonance spectroscopy and dynamic contrast enhanced imaging of the prostate gland

The quantitation of in vivo 1H MR spectroscopy and dynamic contrast enhanced MR imaging is described for patients with histologically confirmed prostate adenocarcinoma and benign prostatic hypertrophy (BPH). Results are presented which suggest that combined use of these techniques may be helpful in improving the characterization of prostate pathologies and ultimately increase the staging accuracy of magnetic resonance.     

MRI活体示踪超顺磁性氧化铁标记兔骨髓间充质干细胞的自体皮下移植

背景：高磁场MRI已被成功应用于示踪移植超顺磁性氧化铁标记骨髓基质干细胞的研究,但目前还有应用低磁场MRI示踪移植干细胞的报道。 目的：探讨用0.2 T MRI活体示踪自体皮下移植磁化标记骨髓基质干细胞的分布和迁移的可行性。 方法：从兔骨髓中分离培养骨髓基质干细胞,采用超顺磁性氧化铁和BrdU双重标记后,与壳聚糖复合植入兔自体大腿皮下。自体皮下移植未标记骨髓基质干细胞和皮下单纯注射超顺磁性氧化铁为对照。 结果与结论：超顺磁性氧化铁标记骨髓基质干细胞经普鲁士蓝染色和电镜检查证实细胞胞浆含致密铁颗粒。超顺磁性氧化铁标记后自体皮下移植的兔骨髓基质干细胞在GRET2*WI序列成像时产生特征性的低信号改变至少维持8周,且信号逐渐从移植部位进入组织深处。但普鲁士蓝染色和BrdU免疫组化显示大部分的移植细胞仍停留在原移植部位。提示体外超顺磁性氧化铁能有效地标记骨髓基质干细胞,利用0.2 T MRI活体示踪自体皮下移植的超顺磁性氧化铁标记兔骨髓基质干细胞分布和迁移是可行的。     

In vivo chlorine‐35, sodium‐23 and proton magnetic resonance imaging of the rat brain

In this study we demonstrate the feasibility of combined chlorine‐35, sodium‐23 and proton magnetic resonance imaging (MRI) at 9.4 Tesla, and present the first in vivo chlorine‐35 images obtained by means of MRI. With the experimental setup used in this study all measurements could be done in one session without changing the setup or moving the subject. The multinuclear measurement requires a total measurement time of 2 h and provides morphological (protons) and physiological (sodium‐23, chlorine‐35) information in one scanning session. Chlorine‐35, sodium‐23 and high resolution proton images were acquired from a phantom, a healthy rat and from a rat displaying a focal cerebral infarction. Compared to the healthy tissue a signal enhancement of a factor of 2.2 ± 0.2 in the chlorine‐35 and a factor of 2.9 ± 0.6 in the sodium‐23 images is observed in the areas of infarction. Exemplary unlocalized measurement of the in vivo longitudinal and transversal relaxation time of chlorine‐35 in a healthy rat showed multi‐exponential behaviour. A biexponential fit revealed a fast and a slow relaxing component with T_1,a = (1.7 ± 0.4) ms, T_1,b = (25.1 ± 1.4) ms, amplitudes of A = 0.26 ± 0.02, (1–A) = 0.74 ± 0.02 and T_2,a = (1.3 ± 0.1) ms, T_2,b = (11.8 ± 1.1) ms, A = 0.64 ± 0.02, (1–A) = 0.36 ± 0.02. Combined proton, sodium‐23 and chlorine‐35 MRI may provide a new approach for non‐invasive studies of ionic regulatory processes under physiological and pathological conditions in vivo. Copyright © 2010 John Wiley & Sons, Ltd.     

In vivo, trans-synaptic tract-tracing utilizing manganese-enhanced magnetic resonance imaging (MEMRI)

It is well established that manganese ion (Mn2+) can access neurons through voltage-gated calcium (Ca2+) channels. Based upon this fundamental principle, Mn2+ has long been used in biomedical research as an indicator of Ca2+ influx in conjunction with fluorescent microscopy. Additionally, after entry into neurons, Mn2+ is transported down axons via microtubule based fast axonal transport. Furthermore, Mn2+ is paramagnetic, resulting in a shortening of the spin-lattice relaxation time-constant, T1, which yields positive contrast enhancement in T1-weighted MRI images, specific to tissues where the ion has accumulated. Manganese-enhanced MRI (MEMRI) utilizes a combination of these properties of Mn2+ to trace neuronal pathways in an MRI-detectable manner. The focus of this review will detail some of the current MEMRI tract-tracing methodologies in mice and non-human primates as well as biological applications of MEMRI tract-tracing.     

Changes of meniscal interhorn distances: an in vivo magnetic resonance imaging study

The aim of this study was to evaluate the changes of the internal (IID) and external meniscal interhorn distance (EID) of the medial and the lateral meniscus under loading. Sagittal magnetic resonance images of 15 knees were studied. The medial and lateral meniscus were examined with the knee at 0° and 30° of flexion, under no load, with load equal to 50% of body weight and with load equal to 100% of body weight. Under no load, the mean IID was 19.9 mm for the medial meniscus and 12.3 mm for the lateral meniscus and the mean EID was 44.6 mm for the medial meniscus and 34.4 mm for the lateral meniscus. Under load equal to 50% and 100% of patient's body weight, there was a significant increase in both distances (p < 0.05). Under constant loading, flexion of the knee from 0° to 30°, decreased the EID of both menisci. In conclusion, loading increases both IID and EID. Knee position affects only the EID. The quality of magnetic resonance images may affect the reliability of such measurements.     

消旋聚乳酸/ 羟基磷灰石复合材料成骨性的体内实验研究

 目的 探讨消旋聚乳酸/羟基磷灰石（PDLLA/HA）复合材料在动物体内的生物相容性和成骨性。 方法 将 66 只日本大耳兔随机为 3 组，每组 22 只。其中 2 组分别于股骨髁间植入 PDLLA/HA 复合材料圆柱棒（PDLLA/HA 组）和 PDLLA 圆柱棒（PDLLA 组），1 组仅手术而不植入材料作为对照组。术后 3、6 周植入部位摄 X 线片观察植入材料的变化及其与周围组织的结合情况；术后 3、6、12、24 周每组各处死 5 只兔，进行植入部位大体解剖学观察和组织病理学观察。 结果 术后 X 线观察显示 PDLLA/HA 组植入材料显影良好，与周围组织有明显界限；而 PDLLA 组可以看到明显的孔道。大体解剖学和组织病理学观察显示 PDLLA/HA 组术后早期局部炎症反应明显轻于 PDLLA 组，材料与周围组织结合紧密，膜外有少许新骨生成；6 周时膜外新骨增多；12 周时复合螺钉周围有少量新生骨小梁形成，边缘附有大量的成骨细胞；24 周时可见纤维组织长入材料，材料色、形、质与周围结缔组织相近。而 PDLLA 组材料降解明显，12 周后已不能维持棒体形状。 结论 PDLLA/HA 复合材料具有良好的生物相容性和体内成骨性。     

In vivo morphometry and functional morphology of brown adipose tissue by magnetic resonance imaging

Brown adipose tissue (BAT) is the main effector of nonshivering thermogenesis and diet-induced thermogenesis in mammals. Assessment of the magnitude and perturbations of BAT deposits in the intact, living body would be of much relevance for quantitative studies of BAT functions, but such studies have been impossible to date. In this paper it is shown that magnetic resonance imaging (MRI) morphometry can provide the means for accurate, repeated determinations of the volume of BAT deposits in a living animal; moreover, tissue modifications due to acclimation at different ambient temperatures are revealed in vivo by MRI, which correlates with histology and ultrastructure. Furthermore, MRI differentiates areas of BAT responsive to acute adrenergic stimulation, thereby giving information on the thermogenetically active tissue in the intact animal. Therefore, MRI represents a reliable tool for correlative morphological and functional studies of BAT in the living animal.     

Fetal programming of hepatic lobular architecture in the rat demonstrated ex vivo with magnetic resonance imaging

We demonstrate that MRI imaging at sub-millimetre resolution can distinguish between periportal and perivenous zones of the rat liver lobule. This made it possible to measure the hepatic lobular radius in ex-vivo perfused fixed livers using MRI. Comparisons of histomorphometric and MRI measurements of lobular radius were in good agreement, although MRI measurements were significantly smaller (P< 0.001). Male rats whose mothers were fed 40% of the protein of controls during gestation and lactation, had a significantly larger hepatic lobular radius than that of controls [449+/-11 microm vs. 373+/-9 microm (mean +/- SEM), respectively, p<0.001, n = 12; histomorphometry data]. The proton T(2) in periportal and perivenous zones was mapped both before and after antegrade or retrograde perfusion of 10 ml of digitonin (4 mg ml(-1)). Only the T(2) of the hypointense regions increased significantly following antegrade perfusion of digitonin and conversely only that of the intense regions following retrograde perfusion. Digitonin causes permeabilization of cells in specific hepatic zones, determined by the direction of perfusion. The intense and hypointense regions of the hepatic MR images thus arise from the perivenous and periportal zones of the hepatic lobule, respectively.     

In vivo magnetic resonance imaging of dendritic cell migration into the draining lymph nodes of mice

Dendritic cell (DC) migration into the draining lymph nodes is critical for T cell priming. Here, we show that magnetic resonance imaging (MRI) can be used to visualize DC migration in vivo. We combined clinically approved small particles of iron oxide (SPIO) with protamine sulfate to achieve efficient uptake by murine bone marrow-derived DC. SPIO-DC were largely unaltered and after injection into the footpads of mice, they migrated into the T cell areas of the draining lymph nodes, which could be visualized by MRI. Distinct MRI signal reduction patterns correlated with the detection of SPIO-DC mainly within Thy-1.2+ B220- T cell areas, as confirmed by iron staining and immunohistology. Clear signal reduction patterns could still be observed with 1x10(6) injected SPIO-DC at high resolution, resulting in the detection of about 2000 DC. Control injections of homing-incompetent SPIO-DC derived from CCR7-/- mice or SPIO alone did not reach the T cell areas. Taken together, the results demonstrate that clinically approved contrast agents allow the non-invasive visualization of DC migration into the draining lymph node by MRI in vivo at high resolution. This protocol therefore also allows dynamic imaging of immune responses and MRI-based tracking of human DC in patients.     

In vivo magnetic resonance imaging and spectroscopy of humans with a 4 T whole-body magnet

A research-type 4 T whole-body magnet, built by Siemens AG, Erlangen, FRG, was used to investigate magnetic resonance at high field strengths. Designs for head and body coils operating at 170 MHz are described. Proton images of the human head and body are degraded by dielectric resonances and penetration effects. The nature of the dielectric resonances was demonstrated in phantoms containing distilled and saline doped water. Radiation damping at 170 MHz generates secondary echoes after a spin echo sequence. This effect was observed in phantoms and with reduced amplitude in the human head. Hydrogen spectra of the human head were selected utilizing stimulated and spin echoes. The latter technique allows the volume size to be reduced to 1 cm3. Examples of brain tumors that have been routinely investigated with volumes of 8 cm3 are given. Natural abundance carbon and phosphorus spectra of muscle and liver demonstrate the expected increase in spectral resolution and signal to noise ratio. Carbon spectra from the liver show the glycogen signal. Fluorine spectroscopy was used to study the time course of the absorption and emptying of a fluorinated antibiotic from the human stomach.     

In vivo morphometry and functional morphology of brown adipose tissue by magnetic resonance imaging.

Brown adipose tissue (BAT) is the main effector of nonshivering thermogenesis and diet-induced thermogenesis in mammals. Assessment of the magnitude and perturbations of BAT deposits in the intact, living body would be of much relevance for quantitative studies of BAT functions, but such studies have been impossible to date. In this paper it is shown that magnetic resonance imaging (MRI) morphometry can provide the means for accurate, repeated determinations of the volume of BAT deposits in a living animal; moreover, tissue modifications due to acclimation at different ambient temperatures are revealed in vivo by MRI, which correlates with histology and ultrastructure. Furthermore, MRI differentiates areas of BAT responsive to acute adrenergic stimulation, thereby giving information on the thermogenetically active tissue in the intact animal. Therefore, MRI represents a reliable tool for correlative morphological and functional studies of BAT in the living animal.     

In vivo dynamics and distribution of intracerebroventricularly administered gadodiamide, visualized by magnetic resonance imaging

Direct injections into the cerebroventricles have been extensively utilized in neurophysiological studies. Mapping the distribution of injectate after intracerebroventricular injection has been made only by post mortem analysis, and the dynamic distribution of injectate within the brain has not been well characterized. In this report, we apply contrast-enhanced magnetic resonance imaging to study the pharmacokinetics and extent of non-ionic gadodiamide transport into brain tissue in vivo after intracerebroventricular administration. The results indicate that intracerebroventricular injectate travels quickly throughout the ventricular system from the lateral ventricular site of injection to the fourth ventricle and foramina of Luschka and Magendie within 2 min. After this, the signal intensity begins to increase in the periventricular and paraventricular brain parenchyma. Contrast enhancement is visible 2 mm into the brain tissue from the ventricles. Quantitative analysis of the data shows that the transport of gadodiamide across the ependymal layer that lines the cerebrospinal fluid space characterized a rate constant of 0.066+/-0.017 min(-1). These results provide a better understanding of chemical transport and diffusion following direct injection into the cerebroventricles. They provide information on the in vivo dynamics of injectate after intracerebroventricular administration, and show that contrast enhanced magnetic resonance imaging may be used to more precisely define the target sites of chemicals after intracerebroventricular administration into the brain.     

Simultaneous in vivo dynamic contrast-enhanced magnetic resonance and scintigraphic imaging

In this study, we investigated the in vivo application of an integrated small-animal magnetic resonance (MR) and gamma-ray imaging system that consists of a semiconductor-based radiation detector, a parallel-hole collimator, and a specialized radiofrequency coil. Gadodiamide and (99m)Tc sestimibi agents were injected simultaneously into a mouse, and simultaneous dynamic contrast-enhanced MR and scintigraphic images of the kidneys were acquired. The time curves of both the MR signal intensity and radioactivity indicate a rapid uptake of the agents followed by a more gradual excretion, consistent with the previously reported literature. Our results demonstrate the feasibility of measuring multiple biological processes at the same time using both MR contrast agents and radiotracers.     

In vivo manganese-enhanced magnetic resonance imaging reveals connections and functional properties of the songbird vocal control system

Injection of manganese (Mn(2+)), a paramagnetic tract tracing agent and calcium analogue, into the high vocal center of starlings labeled within a few hours the nucleus robustus archistriatalis and area X as observed by in vivo magnetic resonance imaging. Structures highlighted by Mn(2+) accumulation assumed the expected tri-dimensional shape of the nucleus robustus archistriatalis and area X as identified by classical histological or neurochemical methods. The volume of these nuclei could be accurately calculated by segmentation of the areas highlighted by Mn(2+). Besides confirming previously established volumetric sex differences, Mn(2+) uptake into these nuclei revealed new functional sex differences affecting Mn(2+) transport. A faster transport was observed in males than in females and different relative amounts of Mn(2+) were transported to nucleus robustus archistriatalis and area X in males as compared to females.This new in vivo approach, allowing repeated measures, opens new vistas to study the remarkable seasonal plasticity in size and activity of song-control nuclei and correlate neuronal activity with behavior. It also provides new insights on in vivo axonal transport and neuronal activity in song-control nuclei of oscines.