Dynamic Gd-DTPA enhanced MRI measurement of tissue cell volume fraction

A new technique for measuring tissue cellular volume fraction, based on an improved modeling of the dynamic distribution of Gd-DTPA and the effect of proton exchange, is described. This technique uses peak T₁ enhancement and blood Gd-DTPA concentration to compute tissue cellular volume fraction. The feasibility of this technique is demonstrated with computer simulations that explore the limits of the simplifying assumptions (small vascular space, slow vascular-extravascular proton exchange), and by direct comparison of MR and radionuclide cell fraction measurements made in muscle, liver, and tumor tissue in a rat model. The computer simulations demonstrate that with slow to intermediate vascular proton exchange and vascular fractions less than 10% the error in our cell fraction measurements typically remains less than 10%. Consistent with this prediction, a direct comparison between MR and radionuclide measurements of cell fraction demonstrates mean percent differences of less than 10%: 1.9% in muscle (n = 4); 9% in liver (n = 1) and 9.5% in tumor (n = 4). Similarly, for all rats studied, the MR-measured cell fractions (muscle (0.92 ± 0.04, n = 20); liver (0.76 ± 0.11, n = 9); whole tumor (0.69 ± 0.15, n = 22)) agree with the cell fraction values reported in the literature. In general, the authors' results demonstrate the feasibility of a simple method for measuring tissue cell fraction that is robust across a broad range of vascular volume, flow, and exchange conditions. Consequently, this method may prove to be an important means for evaluating the response of tumors to therapy.     

ΔR2* gadolinium‐diethylenetriaminepentacetic acid relaxivity in venous blood

The accuracy of perfusion measurements using dynamic, susceptibility‐weighted, contrast‐enhanced MRI depends on estimating contrast agent concentration in an artery, i.e., the arterial input function. One of the difficulties associated with obtaining an arterial input function are partial volume effects when both blood and brain parenchyma occupy the same pixel. Previous studies have attempted to correct arterial input functions which suffer from partial volume effects using contrast concentration in venous blood. However, the relationship between relaxation and concentration (C) in venous blood has not been determined in vivo. In this note, a previously employed fitting approach is used to determine venous relaxivity in vivo. In vivo relaxivity is compared with venous relaxivity measured in vitro in bulk blood. The results show that the fitting approach produces relaxivity calibration curves which give excellent agreement with arterial measurements. Magn Reson Med 69:1104–1108, 2013. © 2012 Wiley Periodicals, Inc.     

Regional measurement of the Gd-DTPA tissue partition coefficient in canine myocardium

Quantifiable MRI perfusion studies using the contrast agent Gd-DTPA require measurement or estimation of the tissue partition coefficient (λ) for tracer kinetic modeling. Radiotracer techniques were used to obtain regional λ measurements from the left ventricles of five dogs. Measurements were analyzed to determine whether spatial heterogeneity was a major component of λ variability. No systematic variations were identified in terms of radial position, short-axis slice location, or wall position. The high λ variability seen in this study and in cited data of others may be due in part to tissue heterogeneity in interstitial volume, plasma volume, and perfusate hematocrit.     

Quantitative CBV measurement from static T1 changes in tissue and correction for intravascular water exchange.

The steady-state (SS) approach has been proposed to measure quantitative cerebral blood volume (CBV). However, it is known that the CBV value in SS (CBVSS) is subject to error resulting from the effects of water diffusion from the intra- to extravascular space. CBVSS measurements were simulated in both fast- and no-water-exchange limits, and compared with measured CBVSS values to determine which limiting case is appropriate. Twenty-eight patients were scanned with a segmented Look-Locker echo-planar imaging (LL-EPI) sequence before and after the injection of 0.1 mmol/kg of a T1-shortening contrast agent. Signal changes and T1 values of brain parenchyma and the blood pool were measured pre- and postcontrast. These signal changes and T1 values, in combination with the simulated results, were used to estimate water-exchange rates. We found that the intra- to extravascular water-exchange rates in white matter (WM) and gray matter (GM) were 0.9 and 1.6 s-1, respectively. With these water-exchange rates, the fast-water-exchange limit of the CBV values showed good agreement with the simulation (r=0.86 in WM, and 0.78 in GM). The CBV values with the correction for water-exchange effects were recalculated as 2.73+/-0.44 and 5.81+/-1.12 of quantitative cerebral blood water volume (%) in WM and GM, respectively.     

Gd—DTPAMRI在心绞痛中的作用

目的：探讨Ｇｄ－ＤＴＰＡ增强ＭＲＩ在心绞痛中的作用。材料和方法：２２例心绞痛作Ｇｄ－ＤＴＰＡ增强前后ＭＲＩ检查,其中１６例作冠状动脉造影检查,１１例作ＳＰＥＣＴ检查。结果：增强ＭＲＩ上,１８例（８２％）可见局部异常强化信号,其部位与临床ＥＣＧ吻合,与ＣＡ、ＳＰＥＣＴ所示心肌缺血部位一致。在ＭＲＩ上的异常强化信号与冠状动脉狭窄、ＳＰＥＣＴ显示灌注缺损密切有关。结论：Ｇｄ－ＤＴＰＡＭＲＩ为心绞痛的诊断提供有价值的依据。     

MRI增强检查在脊柱病变中的诊断价值

目的：讨论不同种类脊柱病变的ＭＲＩ表现及Ｇｄ－ＤＴＰＡ增强检查在脊柱病变中的意义。材料与方法：研究脊柱病变５７例,均行矢状位、轴位Ｔ１ＷＩ、Ｔ２ＷＩ及增强后Ｔ１ＷＩ扫描,其中１２例增强后采用脂肪抑制技术（ＣＨＥＳＳ法）扫描。结果：（１）不同的脊柱病变ＭＲＩ表现不同;（２）在增强后脂肪抑制组及未抑制组,显示脊柱病变与正常骨髓分界最清晰的序列中增强后Ｔ１ＷＩ分别占５１．１％、９２．７％;（３）所有病例在显示椎旁肿块与周围关系最明确的序列中增强后Ｔ１ＷＩ占８３．８％。结论：（１）增强检查对脊柱病变的诊断与鉴别诊断有重要价值;（２）它有利于显示椎旁肿块与椎管内结构的关系;（３）增强后Ｔ１ＷＩ脂肪抑制技术成像与平扫相结合是脊柱病变的首选扫描序列     

1H T1 and T2 measurements of the MR imaging contrast agents Gd-DTPA and Gd-DTPA BMA at 1.5T

We report in vitro T₁ and T₂ relaxation studies for the open-chain complexes Gd-DTPA and Gd-DTPA BMA. Measurements were performed on phantoms containing aqueous and plasma solutions of different concentrations by MR imaging in a 1.5T superconducting whole-body scanner. Longitudinal relaxation times T₁ were evaluated from serial turbo-FLASH experiments for concentrations less than 1 mM, whereas for larger concentrations the values were obtained from a standard inversion recovery (IR) sequence. Transverse relaxation times T₂ were determined using multi-echo spin-echo MRI protocols. The T₁ and T₂ relaxivities of the nonionic Gd-DTPA BMA are similar to those of the Gd-DTPA. The temperature dependencies of the relaxivities were determined over a temperature interval ranging from 21 to 50 °C and were found to be slightly different for the two contrast agents. In the case of Gd-DTPA BMA a larger deviation of the expected temperature behavior of the relaxivities was observed as compared with Gd-DTPA. Deviations from a strictly linear dependence of relaxation times on temperature were found at lower concentrations in aqueous solutions. In plasma solutions a high T₁/T₂ ratio was observed for low concentrations, which decreased monotonically with increasing concentrations. Received 2 October 1995; Revision received 17 April 1996; Accepted 24 April 1996     

Liposomal Gd-DTPA: preparation and characterization of relaxivity

Gadolinium diethylenetriaminepentaacetic acid (DTPA) has not proved particularly useful for hepatosplenic magnetic resonance imaging. However, by entrapping the Gd-DTPA within lipid vesicles, one may exploit the ability of the reticuloendothelial system to endocytose particulates, permitting passive delivery of contrast agent to the liver and spleen while decreasing the rate of clearance of Gd-DTPA from the vasculature. Liposomes of 70-400 nm diameter containing Gd-DTPA were prepared by a freeze-thaw extrusion process. These exhibited high trapping efficiencies and excellent stability during storage. For all sizes of liposomes, the relaxivity of the entrapped Gd-DTPA was less than that of free Gd-DTPA. Relaxivity varied linearly with the surface-area-to-volume ratio of the liposomes; the smaller the liposomes, the greater the relaxivity. Liposomes containing cholesterol had a lower relaxivity than liposomes without cholesterol. The authors suggest this reflects the decrease in the water permeability coefficient caused by the presence of cholesterol in the liposome membrane.     

In vivo imaging of extraction fraction of low molecular weight mr contrast agents and perfusion rate in rodent tumors

Tissue uptake of a fully extractable MR detectable tracer, deuterated water (D₂O), was compared with that of a less extractable contrast agent, Gadolinium-DTPA-dimeglumine (Gd-DTPA), in rodent tumor and muscle tissue. This dual tracer method allowed calculation of relative (to muscle) tissue perfusion and extraction fraction of Gd-DTPA in each image pixel in vivo. Solutions of Gd-DTPA and D₂O were injected intravenously into Fisher female rats (n = 9) with R3230 mammary adenocarcinomas implanted in the hind limb. Perfusion rate was approximately two times greater (P < 0.005 by paired t test) in tumor than in muscle. Gd-DTPA extraction fraction at the interface between tumor and muscle was 2.0 times the extraction fraction in normal muscle (P <0.005 by paired t test). Extraction fraction at the tumor center was 1.6 times the extraction fraction in muscle (P <0.01 by paired t test). High extraction fraction of Gd-DTPA correlated with high capillary permeability determined from Evans Blue staining. Low molecular weight Gd-DTPA derivatives are widely used in clinical practice, and their extraction fractions are crucial determinants of image contrast during the first few passes of the contrast agent bolus. Therefore spatially resolved measurements of contrast agent extraction fractions obtained in vivo have significant clinical utility. The data demonstrate that extraction of low molecular weight tracers is sensitive to increased permeability in tumor vasculature and that this increased permeability can be imaged.     

国产钆喷酸葡胺在脑肿瘤诊断中的作用

目的：探讨国产钆喷酸葡胺在脑肿瘤诊断中的价值。材料和方法：回顾分析８２例脑肿瘤的ＭＲＩ增强表现,其中脑胶质细胞瘤２８例;脑膜瘤１３例;垂体微腺瘤１６例;脑转移瘤１５例;颅咽管瘤２例;松果体瘤２例;三叉神经瘤２例;听神经瘤３例;颅底脊索瘤１例。结果：８２例脑肿瘤病人注射造影剂后,有轻度强化９例,中度强化２９例,明显强化２３例,增强效果达７４．４％,其中脑膜瘤、胶质细胞瘤、脊索瘤强化明显;垂体微腺瘤不强化,而正常垂体组织强化明显,从而把肿瘤组织勾描清楚,与ＣＴ的增强表现相类似。增强病例中有轻微反应３例。结论：国产钆喷酸葡胺在脑肿瘤诊断中是一种较为理想的造影剂     

急性、亚急性、慢性心肌梗塞在Gd－DTPA增强MRI上的信号表现

通过对Ｇｄ－ＤＴＰＡ增强前后ＭＲＩ上急性、亚急性和慢性心肌梗塞区的心肌信号变化规律的总结，期望对心肌梗塞作出定性定量的诊断。材料和方法：３２例不同时期心肌梗塞及１２例正常心脏做了Ｇｄ－ＤＴＰＡ增强前后ＭＲＩ扫描，增强后为动态观察。结果：１０例急性心肌梗塞和１０例亚急性心肌梗塞均见到心肌的异常强化信号：１２例慢性心肌梗塞中仅４例（３３％）见到异常强化信号。正常心肌为均匀一致的轻度信号增强。不同时期的心肌梗塞异常信号范围不同，信号率的动态变化规律也不同。结论：Ｇｄ－ＤＴＰＡ增强ＭＲＩ及动态观察可以显示心肌梗塞的部位、范围及为心肌梗塞的分期提供依据。     

钆喷酸葡胺对比剂不良反应3例报告及文献复习

目的　加深对磁共振成像钆喷酸葡胺对比剂不良反应的认识。方法　报道 3例钆喷酸葡胺对比剂不良反应 ,观察 1例重度不良反应及抢救经过 ;复习钆对比剂不良反应的相关文献。结果　钆喷酸葡胺对比剂有不良反应 ,我院发生率为 0 .2 0 6%。结论　钆喷酸葡胺对比剂不良反应发生率虽低 ,但在患者对医疗质量要求较高的今天也应引起足够的重视     

Gadodiamide T1 relaxivity in brain tissue in vivo is lower than in saline.

In vivo measurements of gadodiamide (Gd-DTPA-BMA) T(1) relaxivity were performed at 4.7 T in injured and normal rat brains. Cerebral lesions were induced in nine rats by a localized freezing method. T(1) maps of the lesions were generated before and after injection of Gd-DTPA-BMA (0.1-0.6 mmol/kg). Samples of normal and necrotic brain were collected postmortem; the wet and dry weights were determined, and Gd content was measured by inductively coupled plasma mass spectroscopy. The in vivo relaxivity was determined by a linear fit of a plot of the change in relaxation rate following injection of the contrast agent as a function of Gd content. This analysis yielded a relaxivity in the injured brain of 2.8 sec(-1) mmol(-1) kg tissue water at 36 degrees C. The water weight fraction was 0.90 +/- SD 0.02 wt/wt in injured brain and 0.79 +/- 0.02 in normal brain. Relaxivity measurements were also performed on solutions of Gd-DTPA-BMA (0.0-0.6 mmol) and albumin (0-30% wt/wt) in normal saline at room and physiologic temperatures. The relaxivity in the albumin/saline increased with increasing solids content with values of 4.0-4.9 sec(-1) mmol(-1)kg at 21 degrees C and 3.4-4.5 sec(-1) mmol(-1) kg at 37 degrees C. The relaxivity of the tissues differed significantly from that of the saline solutions of comparable solids content, suggesting that the solids content of a tissue is not the only factor that determines in vivo relaxivity.     

钆剂对T2 WI脑肿瘤1H-MRSI代谢物波峰面积的影响

目的:探讨钆剂对T2WI脑肿瘤1H-MRSI代谢物波峰面积有无影响,为钆剂增强波谱的应用提供依据。材料和方法:在钆剂注射前后,对高级别和低级别星形细胞瘤、脑膜瘤及正常对照各4例行T2WI长TE(TE=144ms,PRESS)MRSI成像,分别记录感兴趣区内肿瘤的实性区、周围水肿区及正常表现体素的Cho、Cr及NAA代谢物波谱数据(共643个有效体素),分析增强前后代谢物波峰面积的变化。结果:钆剂注射后5-10min的长TE(TE=144ms,PRESS)MRSI显示,仅脑膜瘤组Cho峰面积下降的程度(<10%)相比正常组有显著性差异(P<0.05),余各组之间差异无显著意义。总体上Cho、Cr及NAA波峰的面积无明显变化。结论:钆剂注射后,脑膜瘤Cho波峰面积稍有下降,其影响机制可归于T2*敏感效应;总体上钆剂对T2WI长TE脑肿瘤MRSI主要代谢物波峰面积的影响甚微,可以忽略;增强波谱以Cho/Cr比值反映脑肿瘤Cho水平的变化较为可靠;应用增强后波谱完全可行。     

Gd-DTPA对前列腺3T氢质子波谱影响的初步研究

目的:用高场MR仪研究对比剂(Gd-DTPA)是否会影响前列腺氧质子MR波谱(<'1>H-MRS)的线宽(LW)、抑水率(WS%)及谱线质量.方法:对连续30例行前列腺MR波谱检查的患者分别于增强扫描前、后行<'1>H-MRS检查,比较扫描前、后两次LW、WS%及谱线质量.结果:增强后LW(14.41±1.78)较增强前(12.25±1.36)增高(P<0.05).增强后WS%(97.75±0.45)与增强前(97.50±0.25)比较,其变化无统计学意义(P>0.05).增强后的谱线质量降低(P<0.05).结论:Gd-DTPA影响前列腺<'1>H-MRS的LW及谱线质量.     

Gd-DTPA增强磁共振成像在诊断肝细胞肝癌中的价值

目的：评价Gd-DTPA增强磁共振成像在诊断肝细胞肝癌中的价值。资料与方法：经手术病理或临床证实的肝细胞肝癌53例行磁共报检查，成像序列为：自旋回波T1WI，脂肪抑制PD、T2WI及Gd-DTPA增强T1WI（T1WI＋C）。总结各序列图像对病体、子灶、假包膜、肿瘤镶嵌样结构、门静脉瘤栓等结构显示率。结果：T1WI、T2WI、T1WI＋C对病体的显示率分别为66％、100％、66％，显示的子灶数分别为28、52、22个，假包膜的显示率为39％、43％、75％，对肿瘤镶嵌样结构的显示率分别为20％、62％、73％，对门静脉瘤栓的显示率各为25％、100％、31％。结论：Gd-DTPA增强MRI对肝细胞肝癌的定性诊断有一定的帮助，而在确定主瘤、子灶、与门脉瘤栓存在与否方面不如T2WI。Gd-DIPA增强在肝细胞肝癌诊断中应选择使用而不必作为常规序多列。     

Quantitative Analysis of Dynamic Gd-DTPA Enhancement in Breast Tumors Using a Permeability Model

The MRI signal enhancement in a breast tumor, measured as a function of time after a bolus injection of Gd-DTPA, may contain enough information to differentiate malignant from benign tissue. We find a physiological model for measuring capillary permeability and leakage space (P. S. Tofts, A. G. Kermode, measurement of the blood-brain barrier permeability and leakage space using dynamic MR imaging. 1. Fundamental concepts. Magn. Reson. Med. 17, 357–367 (1991)) fits the data well. The enhancement curve is particularly sensitive to the preinjection T₁, of the tumor, the dose, and the time of injection. This model may provide a means of characterizing the pathophysiology of breast tumors from the Gd-DTPA enhancement curve.     

动态Gd-DTPA增强MRI对肝局灶性病变的诊断价值

目的：探讨动态Ｇｄ－ＤＴＰＡＭＲ扫描对肝局灶性病变的诊断价值。方法：对４１例肝局灶病变进行常规Ｔ１Ｗ、Ｔ２Ｗ和动态Ｇｄ－ＤＴＰＡ增强扫描，比较两种方法对肝局灶病变和诊断正确率，并对动态增强的类型和血液动力学改变进行分析。结果：平扫诊断率为８０％，单纯动态增强为９３％，两者结合起来则正确率提高到１００％（ｐ＜０．０５）。动态增强上，９４％的恶性肿瘤表现为早期强化，后期消退（Ⅰ型）；９０％血管表现为进行性强化（Ⅱ型）；而表现为轻度强化（Ⅲ型）者１００％为恶性肿瘤。不强化（Ⅳ型）者主要为良性病变，占７７％（ｐ＜０．０５）。结论：动态增强扫描对肝局灶病变诊断正确率优于平扫，尤其结合平扫则更能提高对肝局灶病变的诊断和鉴别诊断能力。