对比剂Gd-DTPA对肝外胆管癌磁共振扩散加权成像的影响

目的:探讨对比剂钆喷替酸葡甲胺(Gd-DTPA)对肝外胆管癌磁共振扩散加权成像(DWI)图像质量及表观扩散系数(ADC)的影响。方法:回顾性分析经病理证实并被DWI检出的57例肝外胆管癌患者的DWI图像资料,比较静脉注射对比剂Gd-DTPA增强前后及不同b值条件下肝外胆管癌病灶信噪比(SNR)、病灶与正常肝脏间对比信噪比(CNR)及ADC值的差异。结果:同一b值条件下,增强前后病灶SNR、CNR、ADC值的差异均无统计学意义(P>0.05);增强前后肝外胆管癌病灶SNR、CNR及ADC值均随着b值的增大而降低,其差异均有统计学意义(P<0.05)。结论:肝外胆管癌病灶的DWI图像质量及ADC值不受Gd-DTPA影响,所以选择合适b值的增强后DWI序列是可行的。     

静脉注射钆类对比剂对乳腺正常腺体及肿瘤组织MR扩散加权成像的影响

目的 探讨乳腺MR DWI质量及正常腺体与癌组织的ADC值是否受到钆类对比剂增强扫描的影响.方法 对25例已经针吸穿刺或粗针活检病理证实为乳腺癌的患者在静脉注射Gd-DTPA前、后行DWI扣描,将R01分别置于癌灶及正常腺体,应用配对t检验及非参数检验比较b值=0及1000 s/mm2时增强前后图像中癌灶和正常腺体的信噪比(SNR)、对比噪声比(CNR)及ADC值的变化.结果 增强前、后癌灶的SNR(34.56±11.34和33.60±14.34)与正常腺体的SNR(9.88±3.16和10.42±4.18)以及图像CNR(24.16±9.05和22.26±10.05)的差异无统计学意义(P癌灶SNR=0.70,P正常腺体SNR=0.11;PCNR=0.17);增强前后癌灶的ADC值分别为(0.96±0.13)×10-3和(0.95±0.14)×10-3mm2/s,正常腺体分别为(1.90±0.47)×10-3 和(1.91±0.61)×10-3mm2/s,两者在增强后ADC值与其增强前差异均无统计学意义(P=0.20和0.97).结论 乳腺痛组织和正常腺体DWI的质量及ADC测量值不会受到Gd-DTPA的影响,故在乳腺MR扫描中,DWI可以在增强扫描后进行.     

磁共振钆对比剂的不良反应

含钆对比剂是磁共振增强检查中最常使用的对比剂,其不良发应的发生率低,但是可引起严重的、甚至致死性的不良反应.本文主要对含钆对比剂不良反应的发生率、表现、危险因素、预防及治疗进行综述.     

磁共振扩散加权成像对帕金森病的研究进展

帕金森病(Parkinson's disease,PD)是一种常见于中老年人的慢性进行性中枢神经变性疾病,以静止性震颤、肌强直、运动迟缓及姿态异常等为典型的临床表现,其主要病理改变是黑质多巴胺能神经元(dopamine,DA)变性丢失及蓝斑区路易小体(Lewy body)形成.     

乳腺磁共振扩散加权成像的应用

目的：探讨乳腺磁共振扩散加权成像（DWI）检查的可行性,并重点探讨影响DWI图像质量的技术参数。方法：使用GE1．5T磁共振扫描仪及阵列线圈对32例乳腺疾病患者行常规SE序列扫描,其中19例为良性肿瘤,5例炎性病变,6例恶性肿瘤．均经手术及病理证实;另硅胶置入2例。使用体线圈行DWI序列扫描,采用全方位扩散梯度及5个b值扫描。DWI总的扫描时间40s。结果：在DWI序列扫描中,良性和恶性肿瘤均为高信号,计算ADC值可鉴别良性和恶性肿瘤．通过各种扫描参数的合理匹配,可使图像质量的信噪比达到最佳,并减少图像的几何变形。结论：DWI对于检查乳腺病变是一种快速可行并行之有效的技术。     

磁共振扩散加权成像对前列腺癌的诊断价值

目的:评价MR扩散加权成像对前列腺癌的诊断价值。方法:搜集有手术或穿刺病理结果的前列腺疾病患者15例,其中前列腺癌10例,前列腺炎5例。所有病例均行MR常规T1WI、T2WI及DWI扫描。回顾性分析各组病例的MR常规表现及DWI表现。结果:在MR扩散加权图像上,8例前列腺癌表现为外周带内局限性显著高信号,其余病变在扩散加权成像上为低信号或等信号。结论:MR扩散加权成像对前列腺癌有重要的鉴别诊断价值。     

肝脏磁共振扩散加权成像技术探讨

磁共振水分子扩散加权成像(diffusion-weighted imaging, DWI)能够无创性探测活体组织内水分子的布朗运动,最初应用于颅脑.近年来随着技术的进步,DWI逐渐被应用于腹部脏器,例如:肝脏.     

卵巢肿瘤磁共振扩散加权成像初步研究

目的探讨磁共振扩散加权成像(DWI)对卵巢肿瘤的鉴别诊断价值。资料与方法回顾分析经病理证实的15例卵巢良性肿瘤和20例卵巢恶性肿瘤患者的影像资料,分别比较良恶性肿瘤的实性部分及囊性部分的表观扩散系数(ADC)值并进行统计学分析。结果卵巢良性肿瘤囊性部分ADC值(2.40±0.99)×10-3mm2/s与恶性肿瘤的囊性部分ADC值(2.46±0.87)×10-3mm2/s差异无统计学意义(P=0.922>0.05)。而卵巢良性肿瘤实性部分ADC值(1.48±0.54)×10-3mm2/s与恶性肿瘤的实性部分ADC值(0.99±0.28)×10-3mm2/s差异具有统计学意义(P=0.013<0.05)。结论卵巢肿瘤实性部分DWI的定量分析有助于卵巢肿瘤的鉴别诊断。     

全身磁共振扩散加权成像应用进展

在临床实际工作中,CT作为对病变部位横断面成像一直占据着统治地位,但是,病变功能和代谢的改变往往在其形态学改变之前已经发生.磁共振扩散加权成像(DWI)是近十年来兴起的一种功能成像技术,它具有早期诊断价值及能够在常规影像形态学发生肉眼可视的改变前探测到病变异常特点[1],现已较广泛应用于临床各系统病变.全身扩散加权成像(WB-DWI)能够提供全身肿瘤性和非肿瘤性病变的功能信息(水分子的扩散),并且能使这些病变凸现得更加清晰.笔者结合相关文献对DWI的基本原理、WB-DWI发展过程、临床应用及存在的局限性和挑战进行阐述.     

注射钆剂后弥散加权成像对乳腺肿瘤诊断的影响

目的：评估1.5 T MRI中乳腺肿瘤患者使用钆对比剂是否对弥散加权成像（DWI）有显著性影响。方法行乳腺MRI检查的女性患者40例（共计44个病灶）,分别测量增强前后DWI图像信噪比（SNR）和对比噪声比（CNR）、病灶增强前后的表观扩散系数（ADC）及指数表观扩散系数（eADC）。结果给药前后DWI图像的SNR及CNR差异无统计学意义。乳腺癌给药前后的ADC值（t=-4.023, P=0.001）及eADC值（t=4.082, P=0.001）差异有统计学意义,良性肿瘤给药前后的ADC值（t=-1.700, P=0.103）及eADC值（t=1.341, P=0.194）差异无统计学意义。结论增强后行DWI是可行的,并且有助于提高其鉴别乳腺良恶性肿瘤的能力。     

Arachnoid granulations on high-resolution MR images and diffusion-weighted MR images: normal appearance and frequency

Arachnoid granulations (AGs), protrusions into the cerebral venous sinus lumen, have been reported on cerebral venography, contrast enhanced CT, and conventional MR imaging. Although thin-sliced high-resolution MR images and diffusion-weighted images are frequently obtained, there have been no detailed reports concerning AGs on these images. In this study, the frequency and positional distribution of AGs in the transverse sinus was investigated on thin-sliced high-resolution MR images, and their appearance on diffusion-weighted MR images was evaluated. At least one AG was found in 107 of 151 subjects (70.9%). No statistically significant differences were noticed between males and females or between the right and left sides. No significant correlations between age and size or between age and the number of AGs were noted. On diffusion-weighted images, all AGs showed iso-intensity to normal brain tissue, which was higher than the reported signal intensity of arachnoid cyst and lower than that of epidermoids. In conclusion, AGs are normal structures that are frequently found in the cerebral venous sinuses on high-resolution MR images. Knowledge regarding their frequency and normal appearance would be helpful to avoid confusion between pathological processes and AGs. It is also important to know that AGs are frequently found even in the younger population.     

Cerebrospinal fluid-iophendylate contrast on gradient-echo MR images

The effect on the signal intensities of cerebrospinal fluid (CSF) and iophendylate (Pantopaque) and on CSF-iophendylate contrast was studied in vitro with a small-nutation-angle (alpha) gradient refocused magnetic resonance (MR) imaging technique (GRASS) as alpha, repetition time (TR), and echo time (TE) were varied. CSF signal intensity was consistently greater than that of iophendylate. Therefore, retained intraspinal iophendylate may be considered in the differential diagnosis of focal areas of low signal intensity at the periphery of the spinal canal on GRASS images. At constant TE and TR, an increase in alpha from 6 degrees to 45 degrees increased the signal intensities of CSF and iophendylate but decreased CSF-iophendylate contrast. At constant alpha and TR, an increase in TE from 13 to 28 msec decreased the signal intensities of CSF and iophendylate but increased contrast. At constant alpha and TE, an increase in TR from 50 to 400 msec increased the signal intensities of CSF and iophendylate, as well as contrast. Clinical examples of the contrast behavior of retained intraspinal iophendylate on both spin-echo and GRASS images corroborate the experimental findings. Retained intraspinal iophendylate may mimic the appearance of intra-or extra-dural lesions, magnetic susceptibility artifact, and flow on gradient-echo MR images of the spine.     

Fundamental study of DSA images using gadolinium contrast agent

Most contrast agents used in digital subtraction angiography (DSA) are non-ionic iodinated contrast agents, which can cause severe side effects in patients with contraindications for iodine or allergic reactions to iodine. Therefore, DSA examinations using carbon dioxide gas or examinations done by magnetic resonance imaging (MRI) and ultrasound (US) were carried out in these patients. However, none of these examinations provided images as clear as those of DSA with an iodinated contrast agent. We experienced DSA examination using a gadolinium contrast agent in a patient contraindicated for iodine. The patient had undergone MRI examination with a gadolinium contrast agent previously without side effects. The characteristics of gadolinium and the iodinated contrast agent were compared, and the DSA images obtained clinically using these media were also evaluated. The signal-to-noise (SN) ratio of the gadolinium contrast agent was the highest at tube voltages of 70 to 80 kilovolts and improved slightly when the image intensifier (I.I.) entrance dose was greater than 300 microR (77.4 nC/kg). The dilution ratios of five iodinated contrast agents showed the same S/N value as the undiluted gadolinium contrast agent. Clinically, the images obtained showed a slight decrease in contrast but provided the data necessary to make a diagnosis and made it possible to obtain IVR without any side effects. DSA examinations using a gadolinium contrast agent have some benefit with low risk and are thought to be useful for patients contraindicated for iodine.     

The effect of susceptibility of gadolinium contrast media on diffusion-weighted imaging and the apparent diffusion coefficient

RATIONALE AND OBJECTIVES: The development of parallel magnetic resonance imaging has resulted in the frequent use of diffusion-weighted imaging (DWI) in clinical medicine, which usually involves the use of contrast medium. However, gadolinium (Gd) contrast medium may have some effect on DWI and the apparent diffusion coefficient (ADC). The present study was performed to determine whether the magnetic susceptibility of contrast medium alters the DWI signal and the value of ADC in some imaging techniques. MATERIALS AND METHODS: Nonfat suppression DWI, short-time inversion recovery (STIR) combination, and chemical shift selective (CHESS) combination DWI were performed to examine 10 phantoms with gadolinium-meglumine gadopentetate (Gd-DTPA) dissolved at concentrations from 0.0005 to 0.1 mmol in physiologic saline as a contrast medium. The average pixel value and ADC of each method were determined. RESULTS: ADC showed no differences between before and after treatment with contrast medium for all imaging techniques with Gd considered distributed over the whole tumor. The signal intensity did not change on nonfat suppression or CHESS combination DWI, but deteriorated on STIR. CONCLUSIONS: ADC was not influenced by the magnetic susceptibility of contrast medium. In addition, it was suggested that the ability of tumor detection may be reduced if STIR is used as fat suppression.     

Effect of thin-section diffusion-weighted MR imaging on stroke diagnosis

BACKGROUND AND PURPOSE: Diffusion-weighted (DW) imaging has limited spatial resolution, especially in the z direction. We decreased the section thickness of DW imaging to 3 mm to determine if this change improves the depiction of small infarcts and if it affects stroke diagnosis. METHODS: We studied conventional (5-mm section thickness, 1-mm intersection gap) and thin-section (3-mm section thickness, no intersection gap) DW imaging data in 49 patients with symptoms of acute cerebral ischemia. Two radiologists who were not aware of the clinical findings reviewed all images and diagnosed the stroke subtype according to the Trial of Org 10172 in Acute Stroke Treatment (TOAST) method. Accuracies of stroke diagnosis with an experienced neuroradiologist and with a second-year radiology resident were compared. To quantify lesion conspicuity, contrast-to-noise ratios (CNRs) were measured. The CNR of thin-section DW imaging was then divided by the CNR of conventional DW imaging to yield the relative CNR (rCNR). RESULTS: The experienced neuroradiologist made the correct final diagnoses in 78% of cases with conventional DW imaging, improving to 100% with thin-section DW imaging. The resident made the correct diagnoses in 71% of cases with conventional DW imaging, improving to 94% with thin-section DW imaging. Lesion conspicuity was improved on thin-section DW imaging (rCNR = 1.47 +/- 0.63), especially for supratentorial lesions (rCNR = 1.51 +/- 0.63). CONCLUSION: Compared with conventional DW imaging, thin-section DW imaging permitted better lesion conspicuity and more precise stroke diagnosis.     

Effect of field strength on gadolinium enhancement in MR imaging

This studv was designed to evaluate the influence of magnetic field strength on the relative enhancement effect (RE) of gadolinium (Gd)-chelates. Dilution series of two paramagnetic contrast agents (Gd-DTPA and Gd-DOTA) were examined in three commercially available MR systems. operating at different field strengths (02 T, 1. T, and 1.5 T). The RE was plotted against Gd concentration. The highest increases in signal intensity occurred with Gd concentrations of approximately L.0 mmol/L. No significant difference in RE was observed between MR systems ranging in field strength from 0.? T to 1.5 T. The RE of Gd-DTPA and Gd-DOTA was found to he equivalent.     

Posterior reversible encephalopathy syndrome: prognostic utility of quantitative diffusion-weighted MR images

BACKGROUND AND PURPOSE: The recently described posterior reversible encephalopathy syndrome (PRES) classically consists of reversible vasogenic edema in the posterior circulation territories, although conversion to irreversible cytotoxic edema has been described. We hypothesized that the extent of edema has prognostic implications and that diffusion-weighted MR imaging (DWI) can help predict the progression to infarction. METHODS: Twenty-two patients with PRES and 18 control subjects were examined with isotropic DWI. Nineteen regions of interest (ROIs) were systematically placed, and apparent diffusion coefficients (ADCs) were computed and correlated with T2 and DWI signal intensity in each ROI. RESULTS: T2 signal abnormalities were always present in territories of the posterior circulation. Anterior circulation structures were involved in 91% of patients. ADC values in areas of abnormal T2 signal were high. More extensive T2 signal abnormalities were seen in patients with a poor outcome than in patients who recovered. In six patients (27%), areas of high DWI signal intensity were seen with ADC values that were paradoxically normal, which we called pseudonormalized. Abnormal T2 signal intensity and high ADC values surrounded these areas. Follow-up images in two patients showed progression to infarction in pseudonormalized regions. CONCLUSION: Vasogenic edema in PRES involves predominantly the posterior circulation territories, but anterior circulation structures are also frequently involved. The extent of combined T2 and DWI signal abnormalities correlate with patient outcome. High DWI signal intensity and pseudonormalized ADC values are associated with cerebral infarction and may represent the earliest sign of nonreversibility as severe vasogenic edema progresses to cytotoxic edema.