大鼠眼球的高场磁共振成像研究

该文旨在研究微型磁共振（MRI）对大鼠眼球的成像效果和应用. 通过对10只SD大鼠的20只眼球进行7.0 T MRI检查,应用常规T1WI和T2WI序列高分辨率扫描;观察MRI图像上大鼠眼球的结构,并比较MRI测量与组织学显微镜下测量视网膜厚度结果. 磁共振扫描清楚地显示了所有受试大鼠眼球的主要结构,包括角膜、晶状体、玻璃体、视网膜、巩膜、虹膜、睫状体、视神经. 球壁结构磁共振图像层次与组织学结构层次有良好对应性; 磁共振视网膜厚度测量值与显微镜下视网膜厚度测量数据进行配对 t 检验,P＞0.05,二者无显著差异. 由此得出的结论是小动物MRI可以对大鼠眼球细微解剖结构进行无创性的成像,为我们提供了一个研究大鼠眼科疾病模型的形态学及功能变化的手段.      

MR imaging findings in recurrent primary osseous Ewing sarcoma

The objective of this study was to determine the value of magnetic resonance (MR) imaging in diagnosing local recurrence of Ewing sarcoma. We retrospectively reviewed radiographs, Tc^99m-methylene diphosphonate (MDP) skeletal scintigraphy, computed tomography scans, and MR studies of 11 patients who had local recurrences of osseous Ewing sarcoma following initial responses to chemotherapy and local radiation. The MR images were compared to those of a control group of nine patients who had no evidence of relapse. T₁- and T₂-weighted MR images identified 9 of the 11 recurrences. Computed tomography was diagnostic in 4 of 6 cases evaluated, Tc^99m-MDP bone scintigraphy in 4 of 11 cases, and plain radiographs in 2 of 10. MR findings at relapse included changes in signal intensity, increased extent of abnormal marrow signal on T₁- and T₂-weighted images, and identification of a new soft tissue mass. These findings suggest that MR imaging is valuable in the routine follow-up of parimary osseous Ewing sarcoma.     

Serial MR imaging of intracranial metastases after radiosurgery

Purpose: To evaluate the spatiotemporal evolution of radiosurgical induced changes both in metastases and in normal brain tissue adjacent to the lesions by serial magnetic resonance (MR) imaging. Methods and Materials: Thirty-five intracranial metastases of different primaries were treated in 25 patients by single high-dose radiosurgery. MR images acquired before radiosurgery were available in all patients. Sixty-three follow-up MR studies were performed in these patients including T₂- and contrast-enhanced T₁-weighted MR images. The average follow-up time was 9 ± 5 months (mean ± standard deviation [SD]). Based on contrast-enhanced T₁-weighted MR images, tumor response was radiologically classified in the following four groups: stable disease was assumed if the average tumor diameter after treatment did not show a tumor shrinkage of more than 50% and an increase of more than 25%, partial remission as a shrinkage of tumor size of more than 50%, a disappearance of contrast-enhancing tumor as a complete remission, and an increase of tumor diameter of more than 25% as tumor progress. Moreover, we analysed signal changes on T₂-weighted images in brain parenchyma adjacent to the enhancing metastases. Results: The overall mean survival time was 10.5 ± 7 months, with a 1-year actuarial survival rate of 40%. Stable disease, partial or complete remission of the metastatic tumor was observed in 22 patients (88%). Central or homogeneous loss of contrast enhancement appeared to be a good prognostic sign for stable disease or partial remission. This association was statistically significant (p < 0.05). Three patients (12%) suffered from tumor progression. In eight patients (32%) with stable disease or partial remission, signal changes on T₂-weighted images were observed in tissue adjacent to the contrast enhancing lesions. A progression of the high signal on T₂-weighted images was seen in seven of the eight patients between 3 and 6 months after therapy, followed by a signal regression 6–18 months after irradiation. Conclusion: MR imaging is a sensitive imaging tool to evaluate tumor response as well as the presence or absence of adjacent parenchymal changes following radiosurgery. Loss of homogeneous or central contrast enhancement on Gd-enhanced MR images appeared to be a good prognostic sign for tumor response. Tumor shrinkage seems not to be dependent on time. In addition, most cases of radiation induced changes in normal brain parenchyma observed on T₂-weighted images seem to be self limited.     

Macroscopic tumor volume of malignant glioma determined by contrast-enhanced magnetic resonance imaging with and without magnetization transfer contrast

The purposes of this study were to compare the conspicuity and lesion volume of contrast-enhancing macroscopic malignant glioma determined by postcontrast magnetic resonance (MR) imaging with and without magnetization transfer (MT) saturation, and to discuss possible implications for radiotherapy planning. Nineteen patients (age 24–60 years) with histologically proven malignant glioma were prospectively examined by MR imaging. After the administration of gadolinium dimeglumine (0.1 mmol/kg body weight), the lesions were imaged with an MT-weighted FLASH (fast, low-angle shot) pulse sequence and with a conventional T₁-weighted spin-echo (SE) sequence without MT saturation. The mean tumor volumes of gliomas measured on MT-weighted FLASH images were significantly (p < .01) larger than those obtained from T₁-weighted SE images (45 ± 15 cm³ vs. 33 ± 10 cm³). The mean contrast-to-noise ratio of enhancing lesions on MT-weighted FLASH was 48 ± 14 compared with 30 ± 14 on SE images, representing a significant (p < .01) improvement. We conclude that the volume of contrast enhancement of malignant glioma identified on MT-weighted FLASH images represents the area of disrupted blood-brain barrier. If this volume of subtle contrast enhancement is caused by tumor infiltration and represents the boost target volume for stereotactic radiosurgery or brachytherapy, MT-weighted FLASH images would be better than T₁-weighted SE images to define these volumes. These improved delineation of areas at highest risk for recurrence following radiation therapy should enhance the efficacy of treatment planning for high-boost therapy.     

MRI of thermally denatured blood: methemoglobin formation and relaxation effects

Focal regions of T₁-shortening have been observed in magnetic resonance imaging (MRI)-monitored thermal ablations of perfused tissues. The aims of this study were two-fold: to find evidence for heat-induced conversion of hemoglobin (Hb) to methemoglobin (mHb), and to investigate the effects of heat treatment of in-vitro blood components upon their MR relaxation times. Spectrophotometric studies were performed to confirm the heat-induced formation of methemoglobin. Preparations of whole and fractionated blood, previously submitted to elevated temperatures of 40°C to 80°C, were imaged and the relaxation times were calculated. Optical absorption spectra of samples containing free Hb, heated to 60°C, showed increased light absorption at 630 nm, evident of mHb presence. Short T₁ values in whole blood (1.13 s) and packed red blood cell (0.65 s) compartments, heated at 60°C, compared to their baseline values (1.62 s and 0.83 s, respectively), were attributed to mHb formation. In relation to MRI-guided thermal interventions, these results suggest a possible explanation for observation of hyperintense regions on T₁-weighted images.     

基于MRI影像组学的BI-RADS 3-5类乳腺病变三分类

医生根据磁共振影像征象对患者的乳腺病变程度进行BI-RADS分类评估时存在一定的主观性,且 BI-RADS 3-5类病变的良恶性存在交叉,在临床诊断时极易发生因诊断类别较高而造成不必要的有创治疗．针对这些问题,本文应用影像组学技术对乳腺的T₁加权（T1W）和动态对比增强（DCE）磁共振图像进行特征提取和融合,采用最小绝对收缩和选择算子（LASSO）算法筛选出各特征集的最优特征集,并分别使用支持向量机（SVM）、随机森林（RF）、K最近邻（KNN）及逻辑回归（LR）算法进行BI-RADS 3-5类乳腺病变三分类,并且在此基础上实现乳腺良恶性分类．结果显示基于特征融合的四个影像组学模型对乳腺病变BI-RADS 3-5类的分类准确率分别为81.25%、87.50%、78.38%、81.25%;对乳腺病变良恶性鉴别的准确率分别为90.91%、93.55%、92.73%、94.55%. 这表明MRI影像组学结合机器学习的算法对乳腺病变BI-RADS分类效果及良恶性鉴别效果均较好,且特征融合可进一步提高分类预测的准确率．     

MR imaging of the uterus: low-signal-intensity abnormalities of the endometrium and endometrial cavity

T2-weighted magnetic resonance (MR) images showing focal areas of low signal intensity involving the endometrium or endometrial cavity were analyzed retrospectively in 28 women. The causes of the hypointense foci were disclosed histologically in 25 patients and by follow-up MR examinations in the other 3. The low signal intensity foci were due to submucosal leiomyoma (11 patients), blood clot (7 patients), endometrial carcinoma (4 patients), early intrauterine pregnancy (3 patients), retained products of conception (2 patients), and endometrial hamartoma (1 patient). The correct diagnosis was made on the basis of MR findings alone in 9 of the 11 submucosal leiomyomas. MR findings were nonspecific in the remainder of the cases. The results indicate that, on MR images, hypointense foci within the endometrium or endometrial cavity can arise from a variety of causes. Often, a specific diagnosis is not possible, and correlation with clinical history is essential.     

Superparamagnetic iron oxide particles and positive enhancement for myocardial perfusion studies assessed by subsecond T1-weighted MRI

Superparamagnetic iron oxide particles (SPIOs) are usually referred to as T₂ MR contrast agents, reducing signal intensity (SI) on T₂-weighted MR images (negative enhancement). This study reports the original use of SPIOs as T₁-enhancing contrast agents, primarily assessed in vitro, and then applied to an in vivo investigation of a myocardial perfusion defect. Using a strongly T₁-weighted subsecond MR sequence with SPIOs intravenous (IV) bolus injection, MR imaging of myocardial vascularization after reperfusion was performed, on a dog model of coronary occlusion followed by reperfusion. Immediately after the intravenous bolus injection of 20 μmol/kg of SPIOs, a positive signal intensity enhancement was observed respectively, in the right and left ventricular cavity and in the nonischemic left myocardium. Moreover, compared to normal myocardium, the remaining ischemic myocardial region (anterior wall of the left ventricle) appeared as a lower and delayed SI enhancing area (cold spot). Mean peak SIE in the nonischemic myocardium (posterior wall) was significantly higher than in the ischemic myocardium (anterior wall) (110 ± 23% vs. 74 ± 22%, Mann-Whitney test < 1%, n₁ = 6, n₂ − n₁ = 0, U > 2). In conclusion, the T₁ effect of SPIOs at low dose, during their first intravascular distribution, suggests their potential use as positive markers to investigate the regional myocardial blood flow and some perfusion defects such as the “no-reflow phenomenon”.     

Detection of late epilepsy by the texture analysis of MR brain images in the lithium-pilocarpine rat model

The aim of the study was to detect by texture analysis non easily visible anomalies of magnetic resonance (MR) images of piriform and entorhinal cortices relevant to the lithium-pilocarpine (Li-Pilo) model of temporal lobe epilepsy in rats. Status epilepticus was induced by Li-Pilo in twenty male rats 21 day-old. T₂-weighted MR images of their brain, were obtained before injection of Li-Pilo and one day after status epilepticus. An hyperintense signal was found in the piriform and entorhinal cortices of six rats, which developed chronic epilepsy after a latent period of one to three months. Among the 14 other rats which displayed images similar to those obtained before injection, four remained healthy but 10 rats developed late epileptic symptoms, raising the problem of hidden cortical damage which may be too subtle to be detected by classic MRI examination. A numeric treatment of digital images was then undertaken by texture analysis, to derive image information from a purely computational point of view. The combined texture and discriminant analyses based on pixels pattern anomalies, selected 3 texture parameters derived from co-occurrence matrix which characterized structural abnormalities relevant to the hyperintense signal, not only in the modified images of 6 rats but also in images of 10 rats with apparently non modified images. These three texture’s parameters allowed to classify the twenty rats of our experiment as follows: sixteen epileptic rats were effectively classified with cortical lesions, two non epileptic were correctly classified with healthy cortex, but two healthy rats were not correctly classified. This misclassification is discussed on the basis of the time dependence of the onset of seizure in the Li-Pilo model. These promising results suggest to apply this method to MRI examinations for an improvement of the early diagnostic of human epilepsy.     

MR of an adrenal pseudocyst

We describe the appearance of an adrenal pseudocyst on MRI and CT. The MR characteristics of the lesion were noteworthy in that the lesion had two components with different imaging characteristics. The larger component was of low signal intensity on both T₁- and T₂-weighted images and might have been confused with an adrenal adenoma.     

MRI-monitored cryosurgery in the rabbit brain

The inability to observe the transient, irregular shape of the frozen region that develops during cryosurgery has inhibited the application of this surgical technique to the treatment of tumors in the brain and deep in visceral organs. We used proton NMR spin-echo and spoiled gradient-echo imaging to monitor the development of frozen lesions during cryosurgery in the rabbit brain and the resulting postervosurgical changes up to 4 hr after freezing. Spoiled gradient-echo images (TE = 14 ms; TR = 50 ms) were acquired during freezing and thawing at a rate of 15 s/slice. Although the frozen region itself is invisible in MR images, its presence is distinguished easily from the surrounding unfrozen soft tissue because of the large contrast difference between frozen and unfrozen regions. T₂-weighted spin-echo images (TE = 100 ms, TR = 2 s) obtained after thawing suggest that edema forms first at the margin of the region that was frozen (cryolesion) and then moves into the region's core. Histological examination showed complete necrosis in the cryolesion and a sharp transition to undamaged tissue at the margin of the lesion and its image. Blood-brain barrier (BBB) damage was investigated using gadolinium-DTPA. The region of edema in the T₂-weighted spin-echo images was coincident with the area of BBB damage in the Gd-DTPA-enhanced T₁-weighted spin-echo images (TE = 33 ms, TR = 400 ms) and both were distinguishable as areas of high signal relative to the surrounding normal tissue. The results of these experiments indicate that MR can both effectively monitor the cryosurgical freezing and thawing cycle and characterize the postcryosurgical changes in tissue during follow-up.     

Quantitative MRI of uterine leiomyomas during triptorelin treatment: Reproducibility of volume assessment and predictability of treatment response

Magnetic resonance (MR) imaging is increasingly applied for the quantitative evaluation of uterine leiomyomas. MR is thought to be more accurate in comparison to ultrasound (US) techniques. MR signal intensity (SI) may prove to be predictive of myoma response to GnRH agonist treatment. This study aimed to evaluate the precision of uterine volume assessment by a parallel planimetric MR method and the accuracy of the ellipsoid formula based calculations from MR and US images. It was also attempted to analyze the precision of MR leiomyoma volume measurements and examine the relation between pretreatment myoma SI patterns and the response to agonist therapy. Twenty-seven women with a myomatous uterus were scanned three times during GnRH agonist treatment for 6 months. T₁- and T₂-weighted, as well as T₁ contrast-enhanced sequences of the uterus were obtained in the transverse and sagittal plane. Abdominal US of the uterus was performed with a conventional sector scanner. By the use of a software system for analysis of three-dimensional images obtained by MR, uterine volume was measured by a parallel planimetric method (MR-ROI) as well as the use of the ellipsoid formula (MR-ELL). Myoma volume was assessed by the MR-ROI method. SI of the myomas was estimated from selected tissue samples as well as from the integral myoma region of interest. By abdominal US, volume was assessed by the ellipsoid equation (US-ELL). Within- and between-observer and method reliability (Rw/Rb) was calculated from mean squares obtained by analysis of variance. For uterine volume assessment, reliability between observers and between methods when the MR-ROI and MR-ELL methods were analyzed was excellent. For the US-ELL measurements, the between-observer reliability was limited. Moreover, the reliability of the US-ELL was low when the MR-ROI method was used as the standard. Myoma volume assessment with the MR-ROI method showed high between-observer and between-method agreement. The myoma/fat SI ratio and the mean SI coefficient of variation failed to show a correlation with the degree of response to triptorelin treatment of individual myomas. In MR uterine volume assessment the MR-ELL method is very accurate compared with the more complicated MR-ROI method. The agreement between MR and US is limited. Therefore, the ellipsoid method on MR images is to be regarded as the method of choice for quantitative assessment of uterine volume response to hormonal treatment. Myoma SI patterns were shown to be of no value in the response prediction of myomas to treatment with GnRH agonists.     

基于MRI和深度学习的桥小脑角区脑膜瘤与听神经瘤分类算法研究

桥小脑角区脑膜瘤与听神经瘤是两种常见的脑部肿瘤,它们的临床表现和影像学表现极为相似,在临床诊断时极易发生误诊．将影像数据与深度学习方法相结合,建立脑膜瘤与听神经瘤的判别模型,可以为两种脑肿瘤的及时准确诊断提供重要手段．本文采集了307名脑肿瘤患者的T₁W-SE序列图像,通过对原始图像进行限制对比度自适应直方图均衡化（Contrast Limited Adaptive Histogram Equalization,CLAHE）等预处理,提升数据集图像质量,再经过建立的三维卷积神经网络（3-Dimensional Convolutional Neural Network,3D CNN）深度学习框架中图像特征的学习,实现对脑膜瘤与听神经瘤的分类．图像增强参数与网络结构参数经过优化后,对脑膜瘤与听神经瘤分类的准确率达到0.918 0,曲线下面积（Area Under Curve,AUC）为0.913 4,实现了对桥小脑角区脑膜瘤与听神经瘤的有效判别．     

Retroperitoneal ancient schwannoma presenting as an adrenal incidentaloma: CT and MR findings

A 35-year-old woman was referred to our institution for additional examinations to evaluate bilateral suprarenal masses incidentally found on abdominal ultrasonographic images obtained during an annual medical health checkup. Our computed tomographic scans showed bilateral and well-circumscribed low-density suprarenal masses, while MRI revealed the tumors to be heterogeneous with low intensity on T₁-weighted images and high intensity on T₂-weighted images. A laparoscopic adrenalectomy was performed under the suspicion of a malignant tumor, such as a malignant fibrous histiocytoma. Pathologic findings indicated a retroperitoneal ancient schwannoma of two histologic types: Antoni A and Antoni B. We considered that elucidation of the characteristic features of a schwannoma would provide helpful preoperative information for diagnosis.     

Changes in MR signal intensity and contrast enhancement of therapeutically irradiated soft tissue

Increased MR signal intensity was observed on T₂-weighted, STIR, and Gadolinium-DTPA-enhanced T₁-weighted images of subcutaneous and muscular soft tissue in 9 of 10 children treated with combination chemotheraphy and radiation therapy (RT) for malignancy in the pelvis or an extremity. Total radiation doses ranged from 59.5 to 65 Gy. Eight of the patients with these changes received hyperfractionated RT (seven for Ewing sarcoma and one for perineal rhabdomyosarcoma); one was treated for pelvic hemangiopericytoma with once-daily fractions. Evidence of soft tissue damage became apparent as early as the sixth week of RT and was seen for up to 69 wk post-RT. There was no clear MR evidence of RT-induced soft tissue damage in one patient, who underwent hyperfractionated RT for pelvic rhabdomyosarcoma. Other MR findings in this group included evidence of bladder wall thickening in three of the seven patients given pelvic RT and increased T₁-weighted signal of irradiated marrow in nine patients. All patients had clinical evidence of skin, soft tissue, or epithelial radiation effects. Increased MR signal intensity secondary to RT-induced damage can be differentiated from widespread tumor by geometric borders that conform to the margins of the radiation field.     

Minimization of diffusive attenuation in T2-weighted NMR images of porous solids using turboSPI

This communication presents the results of T₂-weighted nuclear magnetic resonance imaging (MRI) of a water saturated porous volcanic rock using a fast single point imaging technique (turboSPI). Imaging porous materials with heterogeneously distributed mineral products, and air voids, using conventional imaging methods, which introduce T₂-weighting by increasing the time between the excitation and refocusing pulses, often results in high diffusive signal losses and susceptibility distortion. T₂-weighted images acquired of a water saturated porous rock using turboSPI with an effective echo time of 8.1 ms (actual inter-echo time of 0.9 ms) exhibit significantly decreased diffusive attenuation, compared to analogous images obtained with an inter-echo time of 8.1 ms.     

MR Imaging of metastatic pancreatic VIPoma

The MR findings in a 32-year-old man with pancreatic VIPoma and liver metastases are described. A 2-cm mass was present in the region of the tail of the pancreas that was best shown on T₁-weighted fat-suppressed images as a low-signal intensity mass. Multiple liver metastases were present that showed intense peripheral ring enhancement on immediate post gadolinium spoiled gradient echo images.     

Phantom and in vivo study of the Look-Locher T1 mapping method

This paper describes and tests the LL-EPI method for obtaining quantitative T₁ estimates in a few seconds thereby allowing dynamic T₁ studies. It is shown that the method works even when there is an inflow into the imaged volume, e.g., in a vessel. No calibration is needed. The method has been tested in a phantom study with several different scan parameter set-ups, with and without inflow. The method shows robustness and individual scan parameters and inflow rates do not influence the ability to calculate the Gd-DTPA concentration. Linearity prevail between the measured 1/T₁ and the Gd-DTPA concentration in the range 150 < T₁ < 2500 ms. In a dynamic Gd-DTPA phantom study, it was shown that the dynamic LL-EPI T₁ mapping technique was three times more sensitive than the signal from a T^*₂-weighted EPI sequence. In an in vivo study, dynamic T₁ mapping of the Gd-DTPA uptake in a meningioma was performed. Inspection of the uptake curves indicates that the method is feasible in clinical perfusion studies.     

慢性电刺激海马结构诱发大鼠脑磁共振成像异常信号分析

为探讨海马结构(hippocampal formation)功能失衡与癫痫源性脑损伤的关系,本工作采用 慢性强直电刺激大鼠海马(hippocampus, HPC) CA1顶树突区（apical dendrite region, A DR）或齿状回（dentate gyrus, DG）诱发大鼠癫痫模型,一天一次,连续刺激6～8天后, 观察人工致痫灶以外的横向弛豫时间加权的核磁共振(T₂ weighted magnetic reson ance im age, T₂-WI) 绝对信号值变化（片厚1mm）,以及深部电图和原发性湿狗颤抖（pri mary wet dog shakes, WEDS）,并对被检测动物T₂-WI信号异常的相应脑区进行组织学鉴定. 结果表明：（1）电 刺激大 鼠ADR或DG的作用基本相似,引起深部电图的癫痫样电活动和侧脑室区域T₂值增强.（2）含有电极尖端痕迹的核磁共振（magnetic resonance image,MRI）脑切片出现对称性腹部侧脑室区域T₂值增强,连续向后1mm取MRI脑切片进行观察发现,对侧腹部侧脑室区域信号异常. （3）组织学切片观察到：MRI检测的侧脑室区域T₂-WI信号增强与组织切片的侧脑室扩大相吻合,可见扩大的侧脑室中脉络丛上皮细胞病理性增生现象. 提示：在大鼠癫痫点燃现象出现之前,过度激活DG或ADR均可引起相似的早期癫痫源性脑损伤.     

多甘醇-磷酸酯-EDTA酯共聚物铁(Ⅲ)配合物的合成和磁共振成象增强作用

通过乙二胺四乙酸双酸酐、二氯磷酸酯与多甘醇共缩聚,制得一系列三元共聚物配体.用配体与三氯化铁反应,得到相应的铁配合物.表征了配体和配合物的化学结构,测试了配合物的纵向弛豫速率,并考察了配合物的急性毒性和磁共振成象增强作用.