Usefulness of Magnetic Particle Imaging for Predicting the Therapeutic Effect of Magnetic Hyperthermia

Purpose: To investigate the usefulness of magnetic particle imaging (MPI) for predicting the therapeutic effect of magnetic hyperthermia (MH). Materials and Methods: First, we performed phantom experiments to investigate the relationship between the MPI value and the temperature rise of magnetic nanoparticles (MNPs) under an alternating magnetic field (AMF). The MPI value was defined as the pixel value of the transverse image reconstructed from the third-harmonic signals. Samples filled with various iron concentrations of MNPs (Resovist®) were prepared and were imaged using our MPI scanner. These samples were also heated using the AMF, and the specific loss power (SLP) and volume-specific loss power (vSLP) were calculated from the initial slope of the time-dependent temperature rise. Second, we performed animal experiments using tumor-bearing mice, which were divided into untreated (n = 10) and treated groups (n = 20). The tumors in the treated group were injected with Resovist®?at an iron concentration of 250 mM (n = 10) or 500 mM (n = 10), and received MH for 20 min, during which the temperatures in the tumor and rectum were measured. The relative tumor volume growth (RTVG) was calculated from (V15 -?V0)/V0, where V0 and V15 represented the tumor volume on day 0 and day 15 after MH, respectively. Results: In phantom experiments, the MPI value had significant correlations with the iron concentration of MNPs (r = 0.997), temperature rise (r = 0.981), and vSLP (r = 0.961). In animal experiments, the MPI value had significant correlations with the temperature rise in the tumor (r = 0.731) and RTVG (r = ﹣0.687). Conclusion: Our preliminary results suggest that MPI is useful for predicting the therapeutic effect of MH.

Application of Magnetic Particle Imaging to Pulmonary Imaging Using Nebulized Magnetic Nanoparticles

Purpose: To investigate the feasibility of applying magnetic particle imaging (MPI) to pulmonary imaging using nebulized magnetic nanoparticles (MNPs) and to quantify the mucociliary clearance in the lung, using small animal experiments. Materials and Methods: Intrapulmonary administration of MNPs was performed in seven-week-old male ICR (Institute of Cancer Research) mice (n = 8) using a nebulized microsprayer connected to a high-pressure syringe containing 50 μL of MNPs (500 mM Resovist®). We imaged the lungs using our MPI scanner 2.5 hours, 1 day, 3 days, and 7 days after the intrapulmonary administration of MNPs. The average MPI value was calculated by drawing a region of interest (ROI) on the lungs by taking the threshold value for extracting the contour as 20% of the maximum MPI value within the ROI. The MPI value was defined as the pixel value of the transverse image reconstructed from the third-harmonic signals. Mice were sacrificed immediately after the last MPI and X-ray CT studies on day 7, and 5 lobes of the lung in each mouse were extracted to confirm the accumulation of iron using Berlin blue staining. Results: We could visualize the distribution of MNPs in the lungs as positive contrast using MPI with use of nebulized MNPs. The presence of iron in the lung was confirmed by Berlin blue staining. The average MPI value decreased with time and tended to saturate. The clearance rate was calculated to be 0.505 day−1 from the time course of the average MPI value in the lungs. Conclusion: Our preliminary results suggest that MPI can be applied to pulmonary imaging by nebulizing MNPs and can be useful for quantifying the mucociliary clearance in the lung.

Lock-in-Amplifier Model for Analyzing the Behavior of Signal Harmonics in Magnetic Particle Imaging

The purpose of this study was to present a lock-in-amplifier model for analyzing the behavior of signal harmonics in magnetic particle imaging (MPI) and some simulation results based on this model. In the lock-in-amplifier model, the signal induced by magnetic nanoparticles (MNPs) in a receiving coil was multiplied with a reference signal, and was then fed through a low-pass filter to extract the DC component of the signal (output signal). The MPI signal was defined as the mean of the absolute value of the output signal. The magnetization and particle size distribution of MNPs were assumed to obey the Langevin theory of paramagnetism and a log-normal distribution, respectively, and the strength of the selection magnetic field (SMF) in MPI was assumed to be given by the product of the gradient strength of the SMF and the distance from the field-free region (x). In addition, Gaussian noise was added to the signal induced by MNPs using normally-distributed random numbers. The relationships between the MPI signal and x were calculated for the odd- and even-numbered harmonics and were investigated for various time constants of the low-pass filter used in the lock-in amplifier and particle sizes and their distributions of MNPs. We found that the behavior of the MPI signal largely depended on the time constant of the low-pass filter and the particle size of MNPs. This lock-in-amplifier model will be useful for better understanding, optimizing, and developing MPI, and for designing MNPs appropriate for MPI.

Magnetic Particle Imaging for Magnetic Hyperthermia Treatment: Visualization and Quantification of the Intratumoral Distribution and Temporal Change of Magnetic Nanoparticles in Vivo

Purpose: Magnetic hyperthermia treatment (MHT) is a strategy for cancer therapy using the tem-perature rise of magnetic nanoparticles (MNPs) under an alternating magnetic field (AMF). Re-cently, a new imaging method called magnetic particle imaging (MPI) has been introduced. MPI allows imaging of the spatial distribution of MNPs. The purpose of this study was to investigate the feasibility of visualizing and quantifying the intratumoral distribution and temporal change of MNPs and predicting the therapeutic effect of MHT using MPI. Materials and Methods: Colon-26 cells (1 × 106 cells) were implanted into the backs of eight-week-old male BALB/c mice. When the tumor volume reached approximately 100 mm3, mice were divided into untreated (n = 10) and treated groups (n = 27). The tumors in the treated group were directly injected with MNPs (Resovist?) with iron concentrations of 500 mM (A, n = 9), 400 mM (B, n = 8), and 250 mM (C, n = 10), respectively, and MHT was performed using an AMF with a frequency of 600 kHz and a peak amplitude of 3.5 kA/m. The mice in the treated group were scanned using our MPI scanner immediately before, immediately after, 7 days, and 14 days after MHT. We drew a region of interest (ROI) on the tumor in the MPI image and calculated the average, maximum, and total MPI values and the number of pixels by taking the threshold value for extracting the contour as 40% of the maximum MPI value (pixel value) within the ROI. These parameters in the untreated group were taken as zero. We also measured the relative tumor volume growth (RTVG) defined by (V-V0)/V0, where V0 and V are the tumor volumes immediately before and after MHT, respectively. Results: The average, maximum, and total MPI values decreased up to 7 days after MHT and remained almost constant thereafter in all groups, whereas the number of pixels tended to increase with time. The RTVG values in Groups A and B were significantly lower than those in the control group 3 days or more and 5 days or more after MHT, respectively. The above four parameters were significantly inversely correlated with the RTVG values 5, 7, and 14 days after MHT. Conclusion: MPI can visualize and quantify the intratumoral distribution and temporal change of MNPs before and after MHT. Our results suggest that MPI will be useful for predicting the therapeutic effect of MHT and for the treatment planning of MHT.

Usefulness of Magnetic Particle Imaging for Monitoring the Effect of Magnetic Targeting

Purpose: Magnetic targeting refers to the attachment of therapeutic agents to magnetizable particles such as magnetic nanoparticles (MNPs) and then applying magnetic fields to concentrate them to the targeted region such as solid tumors. The purpose of this study was to investigate the usefulness of magnetic particle imaging (MPI) for monitoring the effect of magnetic targeting using tumor-bearing mice. Materials and Methods: Colon-26 cells (1 × 106 cells) were implanted into the backs of eight-week-old male BALB/c mice. When the tumor volume reached approximately 100 mm3, the mice were divided into treated (n = 8) and untreated groups (n = 8). The tumors in the treated group were directly injected with MNPs (Resovist?, 250 mM) and a neodymium magnet was attached to the tumor surface, whereas the magnet was not attached to the tumor in the untreated group. The mice were imaged using our MPI scanner and the average and maximum MPI values were obtained by drawing a region of interest (ROI) on the tumor, with the threshold value for extracting the contour of the tumor being taken as 40% of the maximum MPI value in the ROI. The relative tumor volume growth (RTVG) was calculated from (V ? V0)/V0, where V0 and V represented the tumor volume immediately before and after the injection of MNPs, respectively. Results: The average and maximum MPI values in the treated group were significantly higher than those in the untreated group 3 days after the injection of MNPs, suggesting the effectiveness of magnetic targeting. There were no significant differences in RTVG between the two groups. Conclusion: Our preliminary results suggest that MPI is useful for monitoring the effect of magnetic targeting.

Recent developments of the reconstruction in magnetic particle imaging

Magnetic particle imaging(MPI)is an emerging molecular imaging technique with high sensitivity and temporal-spatial resolution.Image reconstruction is an important research topic in MPI,which converts an induced voltage signal into the image of superparamagnetic iron oxide particles concentration distribution.MPI reconstruction primarily involves system matrix-and x-space-based methods.In this review,we provide a detailed overview of the research status and future research trends of these two methods.In addition,we review the application of deep learning methods in MPI reconstruction and the current open sources of MPI.Finally,research opinions on MPI reconstruction are presented.We hope this review promotes the use of MPI in clinical applications.

Effect of Signal Filtering on Image Quality of Projection-Based Magnetic Particle Imaging

Purpose: Magnetic particle imaging (MPI) allows for imaging of the spatial distribution of magnetic nanoparticles (MNPs) in positive contrast, with high sensitivity, high spatial resolution, and high imaging speed. It is necessary to increase the signal-to-noise ratio to enhance the reliability of MPI. The purpose of this study was to investigate the effect of signal filtering on the image quality and quantitativity in projection-based MPI using phantoms. Materials and Methods: We fabricated two kinds of phantom (cylindrical tube phantom with a diameter of 6 mm and A-shaped phantom) and evaluated the effect of signal filtering in terms of root-mean-square (RMS) granularity and the correlation coefficient between iron concentrations of MNPs and average MPI values for four filter modes (THRU, BPF, BEF, and LPF). In the THRU mode, the signal input was output without passing through the filter. In the BPF mode, only the third-harmonic signal was passed using a band-pass filter (central frequency: 1200 Hz, band width: 1/3 octave). In the BEF mode, the first-harmonic signal was eliminated using a band-elimination filter (central frequency: 400 Hz, band width: 1/3 octave). In the LPF mode, only the signal with a frequency less than the third-harmonic frequency was passed using a low-pass filter (cut-off frequency: 1200 Hz, -24 ± 2 dB/octave). The RMS granularity was obtained by calculating standard deviations of the pixel values in the MPI image without MNPs, whereas average MPI values were obtained by drawing a circular region of interest with a diameter of 6 mm on the MPI image of the cylindrical tube phantom. Results: When using the filtered back-projection (FBP) method with a ramp filter for image reconstruction, the RMS granularity and correlation coefficient decreased in the order of THRU, BPF, BEF, and LPF. In the BPF mode, however, some artifacts were observed. When using the maximum likelihood-expectation maximization (ML-EM) algorithm with an iteration number of 15, the correlation coefficient decreased in the order of THRU, BPF, BEF, and LPF, whereas the RMS granularity did not largely depend on the filter mode and was significantly (p Conclusion: The BEF mode is adequate for the FBP method in projection-based MPI, whereas THRU is a best option in use of the ML-EM algorithm.

Comparative Study of Extracellular and Intracellular Magnetic Hyperthermia Treatments Using Magnetic Particle Imaging

The purpose of this study was to evaluate the effectiveness of intracellular magnetic hyperthermia treatment (MHT) in comparison with that of extracellular MHT using magnetic particle imaging (MPI). Colon-26 cells were implanted subcutaneously into the backs of 8-week-old male BALB/c mice. When the tumor volume reached approximately 100 mm3, the mice were divided into control (n = 10), extracellular MHT (n = 8), and intracellular MHT groups (n = 7). In the control group, MHT was not performed. In the extracellular MHT and intracellular MHT groups, the tumors were injected directly with magnetic nanoparticles (MNPs) (400 mM Resovist®) and were heated for 20 min using an alternating magnetic field. During MHT, the temperatures of the tumor and rectum were measured using optical fiber thermometers. In the extracellular MHT group, MHT was performed 15 min after the injection of MNPs, whereas MHT was performed one day after the injection of MNPs in the intracellular MHT group. In both groups, MPI images were obtained using our MPI scanner immediately before, immediately after, and 7 and 14 days after MHT. After the MPI studies, we drew a region of interest (ROI) on the tumor in the MPI image and calculated the average, maximum, and total MPI values and the number of pixels within the ROI. Transmission electron microscopic (TEM) images were also obtained from resected tumors. In all groups, tumor volume was measured every day and the relative tumor volume growth (RTVG) was calculated. The TEM images showed that almost all the MNPs were aggregated in the extracellular space in the extracellular MHT group, whereas they were contained within the intracellular space in the intracellular MHT group. Although the temperature of the tumor in the intracellular MHT group was significantly lower than that in the extracellular MHT group, the RTVG value in the intracellular MHT group was significantly lower than that in the control group 2 days or more after MHT and that in the extracellular MHT group 3, 4, and 5 days after MHT. The average MPI value normalized by that immediately before MHT in the intracellular MHT group was significantly higher than that in the extracellular MHT group immediately and 7 days after MHT. The maximum and total MPI values normalized by those immediately before MHT in the intracellular MHT group were significantly higher than those in the extracellular MHT group 7 days after MHT, suggesting that the temporal change of MNPs within the tumor in the intracellular MHT group was smaller than that in the extracellular MHT group. Our results suggest that intracellular MHT is more cytotoxic than extracellular MHT in spite of a lower temperature rise of tumors, and that MPI is useful for evaluating the difference in the temporal change of MNPs in the tumor between extracellular MHT and intracellular MHT.

Visualization of Magnetic Nanofibers Using Magnetic Particle Imaging

Purpose: Magnetic nanofibers (MNFs) are nanofibers impregnated with magnetic nanoparticles (MNPs). Magnetic particle imaging (MPI) is a recently introduced imaging method that allows im-aging of the spatial distribution of MNPs. The purpose of this study was to develop MNFs and to investigate the feasibility of visualizing them using MPI and of heating them using an alternating magnetic field (AMF). Materials and Methods: First, chitosan nanofibers were cross-linked with glu-taraldehyde vapor in a sealed vial for 24 hours. Next, they were mixed with various concentrations of MNPs and the mixture was stirred for 1 hour using a magnetic stirrer. After the mixture was re-frigerated at –80&#8451 for 24 hours, it was freeze-dried for 24 hours. The morphology of the resultant MNFs was characterized by scanning electron microscopy, and the magnetic properties were meas-ured using a vibrating sample magnetometer. After these measurements, we imaged the MNFs us-ing our MPI scanner, and investigated the correlation between the pixel values of the MPI image and the concentration of MNPs or the number of MNF sheets. We also heated the MNFs using AMF, and measured the temperature rise using an infrared thermometer. Results: The MNFs were suc-cessfully visualized using our MPI scanner, and the pixel values of the MPI image showed excellent correlation with the concentration of MNPs (r = 0.992) and the number of MNF sheets (r = 0.997). A significant temperature rise was observed under AMF, and the initial slope of the time-dependent temperature rise showed excellent correlation with the concentration of MNPs (r = 0.994) and the number of MNF sheets (r = 0.979). Conclusion: The MNFs developed in this study can be visualized using MPI and can be applied to magnetic hyperthermia. They will be useful in biomedicine including cancer therapy and tissue regeneration.

In vivo tracking of human adipose-derived stem cells labeled with ferumoxytol in rats with middle cerebral artery occlusion by magnetic resonance imaging

Ferumoxytol, an iron replacement product, is a new type of superparamagnetic iron oxide ap- proved by the US Food and Drug Administration. Herein, we assessed the feasibility of tracking transplanted human adipose-derived stem cells labeled with ferumoxytol in middle cerebral artery occlusion-injured rats by 3.0 T MRI in vivo. 1 × 104 human adipose-derived stem cells labeled with ferumoxytol-heparin-protamine were transplanted into the brains of rats with middle cerebral artery occlusion. Neurologic impairment was scored at 1, 7, 14, and 28 days after transplantation. T2-weighted imaging and enhanced susceptibility-weighted angiography were used to observe transplanted cells. Results of imaging tests were compared with results of Prussian blue staining. The modified neurologic impairment scores were significantly lower in rats transplanted with cells at all time points except I day post-transplantation compared with rats without transplantation. Regions with hypointense signals on T2-weighted and enhanced susceptibility-weighted angiography images corresponded with areas stained by Prussian blue, suggesting the presence of superparamagnetic iron oxide particles within the engrafted cells. Enhanced susceptibility-weighted angiography image exhibited better sensitivity and contrast in tracing ferumoxytol-heparin-protamine-labeled human adipose-derived stem ceils compared with T2-weighted imaging in routine MRI.

In Vitro Targeted Magnetic Delivery and Tracking of Superparamagnetic Iron Oxide Particles Labeled Stem Cells for Articular Cartilage Defect Repair

To assess a novel cell manipulation technique of tissue engineering with respect to its ability to augment superparamagnetic iron oxide particles （SPIO） labeled mesenchymal stem cells （MSCs） density at a localized cartilage defect site in an in vitro phantom by applying magnetic force. Meanwhile, non-invasive imaging techniques were use to track SPIO-labeled MSCs by magnetic resonance imaging （MRI）. Human bone marrow MSCs were cultured and labeled with SPIO. Fresh degenerated human osteochondral fragments were obtained during total knee arthroplasty and a cartilage defect was created at the center. Then, the osteochondral fragments were attached to the sidewalls of culture flasks filled with phosphate-buffered saline （PBS） to mimic the human joint cavity. The SPIO-labeled MSCs were injected into the culture flasks in the presence of a 0.57 Tesla （T） magnetic force. Before and 90 min after cell targeting, the specimens underwent T2-weighted turbo spin-echo （SET2WI） sequence of 3.0 T MRI. MRI results were compared with histological findings. Macroscopic observation showed that SPIO-labeled MSCs were steered to the target region of cartilage defect. MRI revealed significant changes in signal intensity （P0.01）. HE staining exibited that a great number of MSCs formed a three-dimensional （3D） cell ＂sheet＂ structure at the chondral defect site. It was concluded that 0.57 T magnetic force permits spatial delivery of magnetically labeled MSCs to the target region in vitro. High-field MRI can serve as an very sensitive non-invasive technique for the visualization of SPIO-labeled MSCs.

A Novel Therapeutic Strategy Combining Use of Intracellular Magnetic Nanoparticles under an Alternating Magnetic Field and Bleomycin

Purpose: The purpose of this study was to present a novel therapeutic strategy combining use of intracellular magnetic nanoparticles (MNPs) under an alternating magnetic field (AMF) and bleomycin (BLM), and to evaluate its therapeutic effect using tumor-bearing mice. Materials and Methods: MNPs (Resovist?, 1.05 mg iron) were incorporated into the hemagglutinating virus of Japan-envelope (HVJ-E) vector (~5 × 109 particles) (HVJ-E/MNPs) by centrifugation at 10,000 × g for 5 min at 4°C. Tumor-bearing mice were prepared by inoculating Colon-26 cells subcutaneously into the backs of BALB/c mice. When the tumor volume reached ~100 mm3, HVJ-E/MNPs and/or BLM were injected directly into the tumor. The AMF was applied to the mice one hour after the injection of agents (AMF treatment). The mice injected with HVJ-E/MNPs were imaged using our magnetic particle imaging (MPI) scanner immediately (13 min) before, immediately (22 min) after, and 3, 7, and 14 days after the injection of agents, and the temporal changes of the average and maximum MPI pixel values in the tumor were quantitatively evaluated. The therapeutic effect was evaluated by calculating the relative tumor volume growth (RTVG) from the tumor volumes measured each day. Transmission electron microscopic (TEM) observation of resected tumors was also performed to confirm the intracellular distribution of MNPs. Results: The AMF treatment combined with BLM significantly decreased the RTVG value compared with AMF treatment alone at 9 to 14 days, and BLM alone at 3 to 5 days after AMF treatment. The average and maximum MPI pixel values in the tumor were almost constant for 14 days. TEM observation confirmed that most of the HVJ-E/MNPs were internalized into tumor cells within one hour after injection. Conclusion: A novel therapeutic strategy with use of AMF treatment and BLM was presented, and the time-dependent change of MNPs in tumors was evaluated using MPI. The present results suggest that this novel strategy can suppress tumor volume growth over AMF treatment or BLM alone, and can be performed repeatedly with a single injection of HVJ-E/MNPs. They also suggest that HVJ-E is effective for internalizing MNPs into cancer cells and that MPI allows for longitudinal monitoring of the distribution of MNPs in tumors.

常规MPI及MPA结合磁敏感加权成像技术对脑血管畸形诊断的价值分析

目的分析常规MPI及MPA结合磁敏感加权成像技术对脑血管畸形诊断的价值。方法收集我院2011年2月～2014年7月期间诊治的36例脑血管畸形患者作为研究对象,所有患者均实施磁共振检查,并磁敏感加权成像序列与T1WI、T1WI、T2WI增强扫描、MRA等常规MRI序列进行对比。结果本组中有20例患者为动静脉畸形,其中有18例患者位于大脑,另外2例患者位于小脑半球;有6例患者静脉畸形,其中有4名患者位于右额顶叶及左顶叶,另外2例患者位于右颞叶且为多发;10例海绵状血管瘤,其中有6例患者位于大脑,另外4例患者位于小脑。结论与常规的磁共振序列相比,磁敏感加权成像序列能够将更多的脑血管畸形清晰的显示出来,在诊断和鉴别诊断脑血管畸形只能够具有非常重要的诊断价值。

基于Kaczmarz算法的磁粒子成像快速重建算法研究

目的:为了解决磁粒子断层成像中系统矩阵方法成像时间长、计算复杂的问题,提出一种基于Kaczmarz算法的磁粒子成像快速重建算法。方法:首先,分析经典Kaczmarz算法及其变体算法的收敛速度,并计算在任意矩阵下的迭代次数和计算时间;其次,比较欧氏距离和余弦距离对系统数据的区分能力,并运用基于余弦距离的K-means算法来增强块Kaczmarz算法的运算能力,缩短系统矩阵重建时间并最终实现磁粒子成像快速重建。最后,通过计算机仿真实验验证提出的算法的有效性。结果:提出的算法大幅缩短了重建时间,提高了重建图像的空间分辨力和质量。结论:提出的算法可以实现磁粒子成像的快速重建,并且在处理含有噪声的数据时具备较强的重建能力。

基于超导的小型化磁粒子成像系统仿真构建

针对磁粒子成像技术尚停留在实验室鼠用设备阶段,传统线材线圈过大,无法在可接受的设备体量内达到临床人体检测所需磁场强度的问题,提出了一种基于超导技术构建高场强、小型化磁粒子成像设备的方法。采用高温超导MgB_(2)线圈替代传统铜线圈,构建磁粒子成像选择场与驱动场。结果表明,在达到相同磁通量的情况下,超导磁粒子成像系统可将两组功能区总质量降低为0.01 kg,设备体积缩小至7 L。在此基础上,采用超导线圈构建梯度磁场还能够获得更高的变化斜率,使零磁扫描区边缘更为清晰规则,移动过程中形态更为稳定,平均直径缩小近二分之一。

Multifunctional Fluorescent Magnetic Nanoparticles： Synthesis, Characterization and Targeted Cell Imaging Applications

Multifunctional fluorescent magnetic nanoparticles （Fe3O4@SiO2-PLLA-RhB/FA） with cell recognition ability were synthesized through conjugation of magnetic nanoparticles with folic acid （FA） and Rhodamine B. To verity their potential biomedical applications, biocompatibility as well as cell imaging applications of the multifunctional nanoparticles were further investigated. Results showed that these fluorescent magnetic nanoparticles are well bio- compatible with NIH-3T3 cells and HeLa cells. More importantly, these nanoparticles could be selectively taken up by HeLa cells （FA receptor positive） as evidenced by laser scanning confocal microscopy, suggesting their potential for biological imaging applications. Given their excellent biocompatibility and multifunctional characteristics, weexpect that the fluorescent magnetic nanoparticles could be promising for various biomedical applications.

Fabrication of carbon coated gadolinia particles for dual-mode magnetic resonance and fluorescence imaging

In the present study,we report a fabrication of dual-mode carbon coated gadolinia C@Gd_(2)O_(3)particles by a facile hydrothermal synthesis method without using any organic solvents.The prepared C@Gd_(2)O_(3)particles have a core-shell structure and a narrow size distribution in the range of 261±27 nm.The fluorescent properties of the prepared C@Gd_(2)O_(3)particles were accessed by a room-temperature photoluminescence study,while the longitudinal relaxivity(r1)was examined by using a clinical 1.5 T MRI scanner.A murine fibroblast L-929 cell line was used to examine the cytotoxicity and capability of the prepared C@Gd_(2)O_(3)particles for the fluorescent labeling.The obtained results show that the prepared C@Gd_(2)O_(3)particles could be used as a dual-mode contrast agent for magnetic resonance and fluorescence imaging.

Advances in magnetic particle imaging and perspectives on liver imaging

Magnetic particle imaging(MPI)is an emerging technique to visualize the spatial distribution of super-paramagnetic iron oxide with high temporal–spatial resolution,high sensitivity,unlimited image depth,and true quantitative information.MPI is based on the nonlinear response of superparamagnetic iron oxide in an alter-nating magnetic field without tissue background noise.It is a promising imaging modality for various applica-tions,including vascular imaging,cell tracking,tumor imaging,and catheter navigation.Many applications of liver imaging could be improved or created with MPI.In this review,we cover the principle and construction of MPI,we evaluate the features and advantages of MPI with relation to its own rationale and via comparison with other imaging modalities,and we review MPI liver imaging applications with a view toward assisting hepatic researchers in drawing inspiration.

体外纳米磁标记骨髓间充质干细胞生物学特性及其MR成像

目的研究超顺磁性氧化铁粒子(superparamagnetic iron oxide particles,SPIO)体外标记兔骨髓间充质干细胞(mesenchymal stem cells,MSCs)及MR细胞成像示踪可行性。方法从兔骨髓中分离培养MSCs,体外不同浓度SPIO联合硫酸鱼精蛋白标记,未标记细胞设为对照组。普鲁士蓝染色和电镜检查鉴定细胞内铁颗粒,台盼蓝染色检测细胞存活,MTT法测定细胞生长曲线的变化,磁标记MSCs转入成骨、成脂肪培养基中进行诱导培养后进行鉴定,应用1.5TMR梯度回波T2加权(GRET2*WI)扫描序列和自旋回波T2加权(SET2WI)扫描序列对磁标记细胞成像示踪。结果普鲁士蓝染色和电镜检查显示细胞质内含致密铁颗粒,磁标记对MSCs活性和增殖无统计学差异(P>0·05),标记细胞可正常成骨、成脂肪分化。GRET2*WI序列和SET2WI序列提示与未标记细胞信号强度(SI)相比,1×106(标记细胞)、5×105(标记细胞)SI均显著性下降(P<0·05),其中GRET2*WI的信号强度衰减率(△SI)显著高于T2WI序列(P<0·05)。在2个序列中1×106(标记细胞)△SI均高于5×105(标记细胞)△SI,但不具有显著性差异(P>0·05)。结论SPIO联合硫酸鱼精蛋白转染剂能成功标记MSCs,磁标记对细胞存活、增殖及潜在多向分化能力无影响。磁标记细胞在MR上产生特征性的低信号改变。应用1.5TMR成像示踪标记细胞可行,以GRET2*WI序列成像最为敏感。

荧光磁粉探伤智能图像识别技术研究

针对荧光磁粉探伤中人工观察识别工作量大、效率低、难以保证检测质量一致性及健康危害严重等问题,提出一种具备机器自主学习能力的智能图像识别方法。结合人工识别磁痕缺陷的工艺方法分析磁痕图像,基于图像形态学提取荧光磁粉缺陷多项特征建立专家知识库,同时根据人员对图像识别结果的判定情况自动修正专家知识库。实验证明该方法可有效识别车削类工件中存在的缺陷,鲁棒性较强。