BACKGROUND & AIMS: :The susceptibility gradients generated by super-paramagnetic iron oxide (SPIO) nanoparticles make them an ideal contrast agent in magnetic resonance imaging. Traditional quantification methods for SPIO nanoparticle-based contrast agents rely on either mapping T₂* values within a region or by modeling the magnetic field inhomogeneities generated by the contrast agent. In this study, a new model-based SPIO quantification method is introduced. The proposed method models magnetic field inhomogeneities by approximating regions containing SPIOs as ensembles of magnetic dipoles, referred to as the finite perturber method. The proposed method was verified using data acquired from a phantom and in vivo mouse models. The phantom consisted of an agar solution with four embedded vials, each vial containing known but different concentrations of SPIO nanoparticles. Gaussian noise was also added to the phantom data to test performance of the proposed method. The in vivo dataset was acquired using five mice, each of which was subcutaneously implanted in the flanks with 1 × 10(5) labeled and 1 × 10(6) unlabeled C6 glioma cells. For the phantom data set, the proposed algorithm was generate accurate estimations of the concentration of SPIOs. For the in vivo dataset, the method was able to give estimations of the concentration within SPIO-labeled tumors that are reasonably close to the known concentration.

背景与目标： : 超顺磁性氧化铁 (SPIO) 纳米颗粒产生的磁化率梯度使其成为磁共振成像中的理想造影剂。基于SPIO纳米颗粒的造影剂的传统定量方法依赖于在区域内映射t 2*值或通过对造影剂产生的磁场不均匀性进行建模。在这项研究中，介绍了一种新的基于模型的SPIO量化方法。所提出的方法通过近似包含SPIOs的区域作为磁偶极子的集合来建模磁场不均匀性，称为有限扰动法。使用从体模和体内小鼠模型获得的数据验证了所提出的方法。幻影由带有四个嵌入式小瓶的琼脂溶液组成，每个小瓶包含已知但浓度不同的SPIO纳米颗粒。还将高斯噪声添加到幻像数据中，以测试所提出方法的性能。使用五只小鼠获得体内数据集，每只小鼠皮下植入1 × 10(5) 标记和1 × 10(6) 未标记的C6神经胶质瘤细胞。对于幻像数据集，所提出的算法是生成SPIOs浓度的准确估计。对于体内数据集，该方法能够给出与已知浓度相当接近的SPIO标记肿瘤内浓度的估计值。

BACKGROUND & AIMS: PURPOSE:To label human monocytes with superparamagnetic iron oxide (SPIO) and compare labeling efficiency with that of ultrasmall SPIO (USPIO) and evaluate the effect of iron incorporation on cell viability, migratory capacity, and proinflammatory cytokine production. MATERIALS AND METHODS:The study was approved by the institutional ethics committee; informed consent was obtained from donors. Freshly isolated human monocytes were labeled with iron particles of two sizes, USPIOs of 30 nm and SPIOs of 150 nm, for 1.5 hours in culture medium containing 0.1, 0.5, 1.0, and 3.7 mg of iron per milliliter. Labeling efficiency was determined with relaxation time magnetic resonance (MR) imaging (4.7 T) and Prussian blue staining for presence of intracellular iron. Cell viability was monitored; migratory capacity of monocytes after labeling was evaluated by using an in vitro assay with monolayers of brain endothelial cells. Levels of proinflammatory cytokines, interleukin (IL) 1 and IL-6, were measured with enzyme-linked immunosorbent assay 24 hours after labeling. Data were analyzed with Student t test or two-way analysis of variance followed by a multiple-comparison procedure. RESULTS:R2 relaxation rates increased for cell samples incubated with SPIOs, whereas rates were not affected for samples incubated with highest concentration of USPIOs. Labeling monocytes with SPIOs (1.0 mg Fe/mL) resulted in an R2 of 13.1 sec(-1) +/- 0.8 (standard error of the mean) (7 sec(-1) +/- 0.2 for vehicle-treated cells, P < .05) and had no effect on cell viability. On the basis of T2 relaxation times, the in vitro MR detection limit of 58 labeled monocytes per 0.05 microL was calculated. Migration of labeled monocytes was not different from that of vehicle-treated cells. Intracellular iron had no effect on production of IL-1 and IL-6 24 hours after labeling. CONCLUSION:In vitro labeling of human monocytes is effective by using SPIOs, not USPIOs. Incubation with SPIOs (1.0 mg Fe/mL) results in efficient labeling detectable on MR images and does not affect cellular viability and activation markers such as cell migration and cytokine production.

背景与目标：

BACKGROUND & AIMS: MRI of superparamagnetic iron oxide (SPIO)-labeled cells has become a valuable tool for studying the in vivo trafficking of transplanted cells. Cellular detection with MRI is generally considered to be orders of magnitude less sensitive than other techniques, such as positron emission tomography (PET), single photon emission-computed tomography (SPECT), or optical fluorescence microscopy. However, an analytic description of the detection threshold for single SPIO-labeled cells and the parameters that govern detection has not been adequately provided. In the present work, the detection threshold for single SPIO-labeled cells and the effect of resolution and SNR were studied for a balanced steady-state free precession (SSFP) sequence (3D-FIESTA). Based on the results from both theoretical and experimental analyses, an expression that predicts the minimum detectable mass of SPIO (m(c)) required to detect a single cell against a uniform signal background was derivedm(c) = 5v/(K(fsl) x SNR), where v is the voxel volume, SNR is the image signal-to-noise ratio, and K(fsl) is an empirical constant measured to be 6.2 +/- 0.5 x 10(-5) microl/pgFe. Using this expression, it was shown that the sensitivity of MRI is not very different from that of PET, requiring femtomole quantities of SPIO iron for detection under typical micro-imaging conditions (100 microm isotropic resolution, SNR = 60). The results of this work will aid in the design of cellular imaging experiments by defining the lower limit of SPIO labeling required for single cell detection at any given resolution and SNR.

背景与目标： 超顺磁性氧化铁 (SPIO) 标记细胞的MRI已成为研究移植细胞体内运输的有价值的工具。MRI的细胞检测通常被认为比其他技术 (例如正电子发射断层扫描 (PET)，单光子发射计算机断层扫描 (SPECT) 或光学荧光显微镜) 的敏感性低几个数量级。但是，尚未充分提供单个SPIO标记细胞的检测阈值和控制检测的参数的分析描述。在当前工作中，研究了平衡稳态自由进动 (SSFP) 序列 (3D-FIESTA) 的单个SPIO标记细胞的检测阈值以及分辨率和SNR的影响。根据理论和实验分析的结果，可以预测在均匀信号背景下检测单个细胞所需的SPIO (m(c)) 的最小可检测质量的表达式为dm(c) = 5v/(K(fsl) x SNR)，其中v是体素体积，SNR是图像信噪比，K(fsl) 是测量为6.2 +/- 0.5 × 10(-5) microl/pgFe的经验常数。使用该表达式，表明MRI的灵敏度与PET的灵敏度没有太大差异，需要在典型的微成像条件下 (100微m各向同性分辨率，SNR = 60) 检测SPIO铁的飞度量。这项工作的结果将通过定义在任何给定分辨率和SNR下进行单细胞检测所需的SPIO标记的下限来帮助细胞成像实验的设计。

BACKGROUND & AIMS: PURPOSE:Magnetic resonance imaging (MRI) has been used to track magnetically labeled human bone marrow-derived mesenchymal stem cells (hBMSCs) in vivo after COX-2 silencing and transplantation into nude rats via tail vein injection. METHODS:In the present study, we knocked down COX-2 expression in hBMSCs through lentivirus transduction. The COX-2 knockdown was confirmed by real-time PCR and Western blotting analyses. Subsequently, we labeled cells with the novel reagent SPIO-Molday ION Rhodamine-B™ (MIRB). The viability, proliferation and differentiation of these cells were assessed in vitro. Labeled lenti-shCOX2 hBMSCs, unlabeled hBMSCs and phosphate-buffered saline (PBS) were individually injected into the tail veins of nude rat models, forming three treatment groups. All nude rats underwent GRE T2*-weighted MRI at 1 h, 7 days and 14 days post-injection. After MRI examination, the animals were sacrificed, and the brain and liver were examined by fluorescence microscopy and Prussian Blue staining. RESULTS:Our results confirmed the successful down-regulation of COX-2 at the mRNA and protein levels in hBMSCs by lentivirus transduction. The viability and differentiation of hBMSCs were not affected by MIRB labeling. After 7 days, hypointense signal void areas in the rat livers were observed on MRI. After 14 days, iron particles were detected in the blood vessels, sinusoids, interlobular septum and capsule tissues of the liver. CONCLUSION:The MIRB-labeled lenti-shCOX2 hBMSCs transplanted into nude rat models via tail vein injection can be detected and monitored in vivo using 3.0 T clinical MRI for up to 14 days after cell transplantation.

背景与目标：

BACKGROUND & AIMS: :There has been recent interest in positive-contrast MRI methods for noninvasive tracking of cells labeled with superparamagnetic iron-oxide nanoparticles. Low-tip-angle balanced steady-state free precession sequences have been used for fast, high-resolution, and flow-insensitive positive-contrast imaging; however, the contrast can be compromised by the limited suppression of the on-resonant and fat signals. In this work, a new technique that produces positive contrast with alternating repetition time steady-state free precession is proposed to achieve robust background suppression for a broad range of tissue parameters. In vitro and in vivo experiments demonstrate the reliability of the generated positive contrast. The results indicate that the proposed method can enhance the suppression level by up to 18 dB compared with conventional balanced steady-state free precession.

背景与目标： : 最近对正对比MRI方法进行非侵入性追踪用超顺磁性氧化铁纳米颗粒标记的细胞产生了兴趣。低尖端角度平衡的稳态自由进动序列已用于快速，高分辨率和对流动不敏感的正对比度成像; 但是，对共振和脂肪信号的有限抑制可能会损害对比度。在这项工作中，提出了一种通过交替重复时间稳态自由进动产生正对比的新技术，以实现对广泛组织参数的鲁棒背景抑制。体外和体内实验证明了产生的阳性对比的可靠性。结果表明，与传统的平衡稳态自由进动相比，该方法可以将抑制水平提高多达18 dB。

BACKGROUND & AIMS: :This study evaluates the robustness of a magnetic resonance (MR) fat quantification method to changes in R2* caused by an intravenous infusion of superparamagnetic iron oxide (SPIO) contrast agent. The R2* and proton density fat fraction (PDFF) were measured in liver and spine in 14 subjects using an investigational sequence (IDEAL IQ) provided by the MR scanner vendor. Measurements were made before and after SPIO infusion. Results showed SPIO significantly increased R2* in both liver (p=8.8×10(-8)) and spine (p=1.3×10(-2)) but PDFFs were not significantly different in either the liver (p=5.5×10(-1)) or the spine (p=5.6×10(-1)). These results confirm that the IDEAL IQ method of fat quantification is robust to changes in R2*.

背景与目标： : 这项研究评估了磁共振 (MR) 脂肪定量方法对静脉输注超顺磁性氧化铁 (SPIO) 造影剂引起的R2 * 变化的鲁棒性。使用MR扫描仪供应商提供的研究序列 (理想智商) 在14名受试者的肝脏和脊柱中测量R2 * 和质子密度脂肪分数 (PDFF)。在SPIO输注之前和之后进行测量。结果显示，SPIO在肝脏 (p = 8.8 × 10(-8)) 和脊柱 (p = 1.3 × 10(-2)) 中均显着增加R2 *，但PDFFs在肝脏 (p = 5.5 × 10(-1)) 或脊柱 (p = 5.6 × 10(-1))。这些结果证实了理想的IQ脂肪定量方法对R2 * 的变化是稳健的。

BACKGROUND & AIMS: PURPOSE:To evaluate the efficacy of ferucarbotran in T2-weighted (T2W) fast spin-echo (FSE) and T2*W gradient-echo (GRE) sequences for characterizing focal liver lesions. MATERIALS AND METHODS:In 68 patients, 46 malignant and 22 benign focal liver lesions were evaluated. Precontrast (NCE) T2W FSE images and contrast-enhanced (CE) T2W FSE and T2*W GRE images were obtained on a 1.5T MR system. Based on signal intensity (SI) measurements in focal lesions and liver parenchyma, the signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated for all sequences. The percentage of SI loss (PSIL) in focal lesions after contrast agent (CA) application was calculated for the T2W FSE sequence. Qualitative analyses were performed to assess image quality and lesion conspicuity obtained with the CE-T2W FSE and CE-T2*W GRE sequences. RESULTS:The mean PSIL was higher in solid benign lesions than in malignant lesions (39.6% vs. 3.2%, P<0.05). With a threshold PSIL of 25%, the sensitivity and specificity for characterizing malignant lesions were 97.8% and 92.9%, respectively. The mean CNR of the malignant lesions was higher in the CE-T2*W sequence than in the CE- and NCE-T2W FSE sequences (29.9 vs. 22.7 (P<0.01) vs. 12.8 (P<0.01)). CE-T2*W images showed a superior image quality and lesion conspicuity (P<0.05) compared to the CE-T2W FSE sequence. CONCLUSION:The PSIL can be an accurate tool for characterizing benign and malignant lesions. The addition of a CE-T2*W GRE sequence is helpful for the detection and characterization of malignant lesions.

背景与目标：

BACKGROUND & AIMS: OBJECTIVE:To evaluate transplanted porcine pancreatic islets in the kidney capsules of diabetic mice using a clinically approved superparamagnetic iron oxide (SPIO) and a 1.5T MR scanner. MATERIALS AND METHODS:Various numbers of porcine pancreatic islets labeled with Resovist, a carboxydextran-coated SPIO, were transplanted into the kidney capsules of normal mice and imaged with a 3D FIESTA sequence using a 1.5T clinical MR scanner. Labeled (n = 3) and unlabeled (n = 2) islets were transplanted into the kidney capsules of streptozotocin-induced diabetic mice. Blood glucose levels and MR signal intensities were monitored for 30 days post-transplantation. RESULTS:There were no significant differences in viability or insulin secretion between labeled and unlabeled islets. A strong correlation (r(2) > 0.94) was evident between the number of transplanted islets and T(2) relaxation times quantified by MRI. Transplantation with labeled or unlabeled islets helped restore normal sustained glucose levels in diabetic mice, and nephrectomies induced the recurrence of diabetes. The MR signal intensity of labeled pancreatic islets decreased by 80% over 30 days. CONCLUSION:The transplantation of SPIO-labeled porcine islets into the kidney capsule of diabetic mice allows to restore normal glucose levels, and these islets can be visualized and quantified using a 1.5T clinical MR scanner.

背景与目标：

BACKGROUND & AIMS: BACKGROUND:The objective of our study was to assess the negative predictive value (NPV) of double-contrast MRI (DC-MRI) with SPIO and gadolinium, and to determine the role of DC-MRI in screening for hepatocellular carcinoma (HCC) in cirrhotic patients. METHODS:We retrospectively included 160 DC-MRI scans done as second-line investigations in 119 patients with cirrhosis over a 25-month period. Two radiologists independently classified the MRI scans as strongly suggesting HCC (HCC Group), showing benign nodules (benign nodules Group), showing no nodules (no-nodules Group) or indeterminate; they assigned a diagnostic confidence score (DCS) using a 0-10 scale. The reference standard was histology or results of follow-up investigations. Mean follow-up was 16.9 months (12-28 months). RESULTS:The radiologists disagreed for two scans (kappa = 0.98). Of 112 scans [benign nodules Group (n = 32) and no-nodules Group (n = 80)], 11 were excluded (3 patients lost to follow-up and 8 who died with no known cancer) while a HCC was detected during follow-up in 8 patients, yielding a NPV of 92% (93/101) (95% confidence interval, 85%-97%). The DCS was in the 4-6 range (indicating uncertainty) for only 6 (3.75%) scans. CONCLUSIONS:DC-MRI is reliable and reproducible. Its high NPV suggests a role as a second-line investigation after ultrasonography, for HCC screening.

背景与目标：

BACKGROUND & AIMS: PURPOSE:The purpose of this study was to determine whether MR with and without SPIO (AMI-25) could replace spiral-CTAP in the staging of colorectal adenocarcinoma. MATERIAL AND METHODS:Thirty-five patients were studied prospectively by means of i.v. contrast-enhanced spiral-CT, spiral-CTAP, and MR of the liver. MR imaging was performed before and after infusion of AMI-25. Diagnoses were compared to intraoperative findings (n = 35) which included intraoperative ultrasound (n = 21), and follow-up CT (n = 18). RESULTS AND CONCLUSION:Fifteen patients were found to have a total number of 53 liver metastases and 43 benign lesions were detected. Evaluation was performed in four different ways: 1) i.v. contrast-enhanced spiral-CT; 2) i.v. contrast-enhanced spiral-CT + spiral-CTAP; 3) plain MR; 4) plain MR + SPIO-enhanced MR. I.v. contrast-enhanced spiral-CT, spiral-CTAP and SPIO-enhanced MR identified patients with liver metastases with equal sensitivity. However, owing to its significantly higher sensitivity, based on a lesion-by-lesion analysis, spiral-CTAP cannot be replaced by SPIO-enhanced MR in patients who are to undergo liver resection. A limitation in spiral-CTAP is its relatively low specificity.

背景与目标：

BACKGROUND & AIMS: :Multifunctional nanoparticles combining therapy and imaging have the potential to improve cancer treatment by allowing personalized therapy. Herein, we aimed to compare in vivo different strategies in terms of targeting capabilities: (1) passive targeting via the EPR effect, (2) active targeting of αvβ3 integrin via RGD grafting, (3) magnetic targeting via a magnet placed on the tumor and (4) the combination of magnetic targeting and active targeting of αvβ3 integrin. For a translational approach, PLGA-based nanoparticles loaded with paclitaxel and superparamagnetic iron oxides were used. Electron Spin Resonance spectroscopy and Magnetic Resonance Imaging (MRI) were used to both quantify and visualize the accumulation of multifunctional nanoparticles into the tumors. We demonstrate that compared to untargeted or single targeted nanoparticles, the combination of both active strategy and magnetic targeting drastically enhanced (i) nanoparticle accumulation into the tumor tissue with an 8-fold increase compared to passive targeting (1.12% and 0.135% of the injected dose, respectively), (ii) contrast in MRI (imaging purpose) and (iii) anti-cancer efficacy with a median survival time of 22 days compared to 13 for the passive targeting (therapeutic purpose). Double targeting of nanoparticles to tumors by different mechanisms could be a promising translational approach for the management of therapeutic treatment and personalized therapy.

背景与目标： : 结合治疗和成像的多功能纳米颗粒有可能通过允许个性化治疗来改善癌症治疗。在此，我们旨在比较体内靶向能力方面的不同策略 :( 1) 通过EPR效应进行被动靶向，(2) 通过RGD移植对 αvβ3整联蛋白进行主动靶向，(3) 通过放置在肿瘤上的磁体进行磁靶向，以及 (4) 磁靶向和 αvβ3整合素的主动靶向的组合。对于翻译方法，使用了载有紫杉醇和超顺磁性氧化铁的基于PLGA的纳米颗粒。电子自旋共振波谱和磁共振成像 (MRI) 用于量化和可视化多功能纳米颗粒在肿瘤中的积累。我们证明，与非靶向或单一靶向纳米颗粒相比，主动策略和磁靶向的组合大大增强了 (i) 纳米颗粒积累到肿瘤组织中，与被动靶向相比增加了8倍 (分别为注射剂量的1.12% 和0.135%)，(ii) MRI (成像目的) 和 (iii) 抗癌疗效的对比，中位生存时间为22天，而被动靶向 (治疗目的) 为13天。通过不同的机制将纳米颗粒双重靶向肿瘤可能是治疗治疗和个性化治疗管理的一种有前途的转化方法。

BACKGROUND & AIMS: :The tumor-detecting capacity and clinical usefulness of superparamagnetic iron oxide (SPIO) magnetic resonance imaging (MRI) were examined in patients with hepatocellular carcinoma. The tumor detection rate of SPIO-MRI (64.5%) was comparable to those of dynamic computed tomography (CT) and plain MRI, but lower than that for Gd dynamic MRI (93.5%; P < 0.01%). A combination of Gd dynamic MRI and SPIO-MRI improved the detection rate; further, the tumor stage with respect to tumor blood-flow pattern was predicted by combining plain MRI with SPIO-MRI. This combination procedure may also be useful for selecting therapeutic strategies.

背景与目标： : 在肝细胞癌患者中检查了超顺磁性氧化铁 (SPIO) 磁共振成像 (MRI) 的肿瘤检测能力和临床实用性。SPIO-MRI (64.5%) 的肿瘤检出率与动态计算机断层扫描 (CT) 和普通MRI相当，但低于Gd动态MRI (93.5%; P <0.01%)。Gd动态MRI和SPIO-MRI的组合提高了检出率; 此外，通过将普通MRI与SPIO-MRI相结合，可以预测肿瘤血流模式的肿瘤分期。此组合程序也可能有助于选择治疗策略。

BACKGROUND & AIMS: :The survivin gene is highly expressed in pancreatic cancer. The purpose of this study was to design and synthesize functionalized magnetic iron oxide nanoparticles (MNPs) targeting survivin gene for the detection of pancreatic cancer. The pancreatic cancer cell line BxPC-3 with survivin gene expression was selected in this study. The healthy lung fibroblast cell was used as a control. Chitosan-coated MNPs (CS@MNPs) and antisense oligodeoxynucleotide of survivin gene were conjugated to MNPs to give Sur-MNPs. Fourier transform infrared spectroscopy was performed to confirm the conjunction of chitosan. The interactions of MNPs, CS@MNPs, and Sur-MNPs in BxPC-3 cells were observed, recorded and analyzed. The size, morphology, cell uptake, cytotoxicity and stability of those particles were assessed by transmission electron microscope, Prussian blue staining, MTT assay and agarose gel electrophoresis. The magnetic resonance signal intensities of pancreatic cells labeled with CS@MNPs and MNPs, and Sur-MNPs, were compared on T₂-weighted images. The results demonstrated that the level of cellular uptake of CS@MNPs was higher than that of naked MNPs. The Sur-MNPs had a suitable size (12 nm sized core), high stability, no cytotoxicity and good water dispersion. Sur-MNPs did not accumulate in healthy lung fibroblast cells, while being taken up by BxPC-3 cells. The Sur-MNPs in BxPC-3 cells could be visualized on T₂-weighted images, which suggested that Sur-MNPs could be used to detect the expression of survivin gene. Thus, Sur-MNPs may be a potential molecular imaging probe targeting survivin gene for early detection of pancreatic cancer cells.

背景与目标： : survivin基因在胰腺癌中高表达。目的设计并合成靶向survivin基因的功能化磁性氧化铁纳米颗粒 (MNPs)，用于胰腺癌的检测。本研究选择了BxPC-3 survivin基因表达的胰腺癌细胞系。健康的肺成纤维细胞用作对照。壳聚糖包被的MNPs (CS @ MNPs) 和survivin基因的反义寡核苷酸与MNPs偶联，得到Sur-MNPs。进行傅里叶变换红外光谱以确认壳聚糖的结合。观察、记录和分析BxPC-3细胞中MNPs、CS @ MNPs和Sur-MNPs的相互作用。通过透射电子显微镜，普鲁士蓝染色，MTT测定和琼脂糖凝胶电泳评估这些颗粒的大小，形态，细胞摄取，细胞毒性和稳定性。在t 2加权图像上比较了用CS @ MNPs和MNPs以及Sur-MNPs标记的胰腺细胞的磁共振信号强度。结果表明，CS @ MNPs的细胞摄取水平高于裸MNPs。Sur-MNPs具有合适的尺寸 (12  nm大小的芯)，高稳定性，无细胞毒性和良好的水分散性。Sur-MNPs在健康的肺成纤维细胞中没有积累，而被BxPC-3细胞占据。BxPC-3细胞中的Sur-MNPs可以在t 2加权图像上显示，这表明Sur-MNPs可用于检测survivin基因的表达。因此，Sur-MNPs可能是靶向survivin基因的潜在分子成像探针，可用于早期检测胰腺癌细胞。

BACKGROUND & AIMS: PURPOSE:To compare conspicuity of zones of ablation on nonenhanced, gadopentetate dimeglumine-(Gd-DTPA) and ferucarbotran-(SPIO)-enhanced magnetic resonance (MR) images. MATERIALS AND METHODS:In all, 33 radiofrequency ablations (RFA) were performed in 17 healthy porcine livers at 1.5T MR imaging 1 day and 2 and 4 weeks after RFA: T2-weighted (w) ultra turbo spin echo (UTSE), proton density (PD)-w UTSE, T1-w gradient echo (GRE) pre- and 5 minutes postcontrast administration, dynamic T1-w GRE during Gd-DTPA (Magnevist) or SPIO (Resovist) administration, T2-w UTSE, and PD-w UTSE sequences 10 minutes after SPIO administration. Regions of interest (ROIs) for contrast-to-noise ratio (CNR) and signal-to-noise ratio (SNR) were drawn in consensus by two radiologists. RESULTS:PD-w SPIO-enhanced images (23.5 +/- 5.5) showed higher liver-to-lesion CNR than T1-w GRE Gd-DTPA-enhanced images (13.5 +/- 6.1) 1 day after RFA (P < or = 0.05). At all other timepoints, liver-to-lesion CNR of PD-w and T2-w SPIO-enhanced images did not differ significantly from T1-w GRE Gd-DTPA-enhanced images (P > or = 0.05). Nonenhanced T2-w images revealed lower liver-to-lesion CNR (7.0 +/- 7.5/6.5 +/- 5.9/6.8 +/- 5.0, 1 day/2 weeks/4 weeks, respectively) than T2-w SPIO-enhanced (17.4 +/- 4.8/15.3 +/- 4.5/14.2 +/- 5.7), PD-w SPIO-enhanced (23.5 +/- 5.5/16.9 +/- 3.6, 1 day/2 weeks), and T1-w Gd-DTPA-enhanced (15.3 +/- 3.6/12.7 +/- 3.5, 2/4 weeks) images (P < or = 0.05). Liver-to-lesion CNR of SPIO-enhanced dynamic T1-w GRE images after 30, 80, 150, and 240 seconds did not change significantly over time (P > or = 0.05). CONCLUSION:One day after RFA lesion conspicuity on PD-w ferucarbotran-enhanced images is better than on T1-w GRE Gd-DTPA-enhanced images. At all other timepoints, ferucarbotran is not superior to gadolinium. Ferucarbotran- and gadolinium-enhanced images improve lesion conspicuity compared with nonenhanced T2-w images at all timepoints.

背景与目标：

BACKGROUND & AIMS: :Along with the development of modern imaging technologies, contrast agents play increasingly important roles in both clinical applications and scientific research. Super-paramagnetic iron oxide (SPIO) nanoparticles, a negative contrast agent, have been extensively used in magnetic resonance imaging (MRI), such as in vivo labeling and tracking of cells. However, there still remain many challenges, such as in vivo quantification of SPIO nanoparticles. In this work, an MR phase gradient-based method was proposed to quantify the SPIO nanoparticles. As a calibration, a phantom experiment using known concentrations (10, 25, 50, 100, 150 and 250 µg/ml) of SPIO was first conducted to verify the proposed quantification method. In a following in vivo experiment, C6 glioma cells labeled with SPIO nanoparticles were implanted into flanks of four mice, which were scanned 1-3 days post-injection for in vivo quantification of SPIO concentration. The results showed that the concentration of SPIO nanoparticles could be determined in both phantom and in vivo experiments using the developed MR phase gradients approach.

背景与目标： 随着现代成像技术的发展，造影剂在临床应用和科学研究中发挥着越来越重要的作用。超顺磁性氧化铁 (SPIO) 纳米颗粒是一种阴性造影剂，已广泛用于磁共振成像 (MRI)，例如细胞的体内标记和跟踪。然而，仍然存在许多挑战，例如SPIO纳米颗粒的体内定量。在这项工作中，提出了一种基于MR相位梯度的方法来量化SPIO纳米颗粒。作为校准，首先进行使用已知浓度 (10、25、50、100、150和250 μ g/ml) 的SPIO的幻像实验，以验证所提出的定量方法。在随后的体内实验中，将用SPIO纳米颗粒标记的C6神经胶质瘤细胞植入四只小鼠的侧面，在注射后1-3天对其进行扫描，以体内定量SPIO浓度。结果表明，使用开发的MR相位梯度方法，可以在体模实验和体内实验中确定SPIO纳米颗粒的浓度。