Measurement of vascular volume fraction and blood-tissue permeability constants with a pharmacokinetic model: Studies in rat muscle tumors with dynamic Gd-DTPA enhanced MRI

We propose a compartmental model to explain the signal enhancement curves following the bolus injection of Gd-DTPA. The model incorporates vascular volume fraction contribution, and the possibility of having different transport constants between the plasma and extravascular components. A Walker 256 carcinoma grown in rat muscle was used to demonstrate the capability of this model. Several different types of tissues were included in the measurements: normal, quickly enhanced, slowly enhanced, and necrotic tissues. Blood volume and blood-tissue permeability information can be derived from the dynamic contrast-enhanced MRI study employing the proposed model. In the tissue contrast enhancement curve, the initial rising slope after injection is related to the blood volume (or, vascular volume fraction), the maximum enhancement ratio is related to the uptake of tissue, and the decay rate is related to the clearance of tracer from tissue. The measured permeability constant is not the conventional permeability; instead they are contrast agents uptake and clearance rates, which are limited by the blood perfusion. These parameters can be used to characterize different enhancement patterns.     

口服Gd—DTPA造影剂溶液在上腹部磁共振成像中的价值

为提高磁共振成像（ＭＲＩ）在腹部检查中的价值，采用口服Ｇｄ－ＤＴＰＡ溶液作为胃肠道磁共振造影剂。结果显示，日服０．０９％ＧｄＤＴＰＡ溶液５ｍｌ／ｋｇ，进行Ｔ１加权成像，能起到良好的胃肠造影增强对比作用。以不同溶剂配制的Ｇｄ－ＤＴＰＡ造影剂，对上腹部磁共振检查，效果满意，组间无显著差异。从经济、实用角度考虑以冷开水为溶剂的Ｇｄ－ＤＴＰＡ溶液为宜。对提高上腹部磁共振成像质量有重要价值。     

MRI增强扫描对脑转移瘤的诊断价值

目的 总结磁共振增强扫描在脑转移瘤诊断中的重要价值。方法 脑转移瘤32例，均经病理和临床证实，全部病例均做了Gd-DTPA增强前后扫描。结果 脑转移瘤单发15例，多发17例，发生在幕上26例，幕下6例，幕上幕下并存4例。病灶最大径在0．5cm～6cm，平均2．4cm。发现病灶数：T1WI40个，T2WI56个，增强后发现116个。结论 增强扫描发现的脑转移瘤病灶明显多于平扫，并且能分清病灶与瘤周水肿的界限，从而明确其发生的部位、数目、形态、和大小，结合临床和影像学特征，容易作出正确诊断。     

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。     

MRI of spondylodiscities: contribution of gadolinium-DTPA and fat suppression sequence

Twenty-six patients with a clinical diagnosis of spondylodiscitis were examined with non-contrast and contrast-enhanced MRI in order to define the contribution of gadolinium-DTPA (Gd-DTPA) and different pulse sequences, including a fat suppression sequence (SPIR). Spin echo (SE) T1-weighted images before and after Gd-DTPA injection and SE T2-weighted images were obtained in all patients. Twelve patients were also examined using the SPIR sequence following Gd-DTPA injection. Signal intensity and morphological features of the disc and vertebral lesions were then evaluated. The SE T1-weighted sequence with Gd-DTPA was very effective in showing the pathological changes at the level of the disc as an area of low signal intensity surrounded by a peripheral rim of enhancement in 24 of 26 cases (92%). This feature was not visible on non-enhanced images. As regards contiguous vertebral lesions this sequence was less informative, since in 8 of 26 cases (31%) the vertebral lesions became isointense and therefore not detectable. In 12 cases there was extension into the surrounding structures (spinal canal and/or paravertebral tissues). An enhanced SE T1-weighted sequence provided good anatomical definition of the extension of the infection in the spinal canal in all cases with this type of involvement (7 of 12). Regarding the 7 cases with paravertebral extension, no extension was visible in 1 case due to the reduced contrast with the surrounding fat following Gd-DTPA injection. The enhanced SPIR sequence was very effective, particularly in detecting the lesions in the vertebral bodies, avoiding the limitation of the enhanced SE T1-weighted sequence. The SPIR sequence was also effective in showing the extension within the spinal canal and the paravertebral fat. On the basis of our results the combination of a SE T1-weighted sequence without contrast and SPIR sequence with Gd-DTPA seems to be the best approach in cases of spondylodiscitis. Correspondence to : M. A. Cova     

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.     

Effect of vitreous fluidity on the measurement of blood-retinal barrier permeability using contrast-enhanced MRI

Breakdown of the blood-retinal barrier (BRB), frequently an early clinical sign in retinopathy, can be accurately determined using contrast-enhanced MRI. However, increased vitreous fluidity with age and disease may affect the accuracy of the MRI method. We compared the permeability surface area product per area of leaky retina in eyes with normal vitreous (5.42 ± 0.48 × 10^?4 cm/min, mean ± SEM, n = 5) to the contralateral gas-compressed vitrectomized eyes (5.41 ± 0.54 × 10^?4 cm/min, n = 5). The effect of vitrectomy was not significant (P = 0.325) using a Wilcoxon matched pairs signed rank test on the signed differences of the PS' values.     

增强磁共振成象动态扫描显示心绞痛病灶的初步研究

通过总结22例心绞痛患者经钆－二乙烯三胺五乙酸（Gd－DTPA）增强磁共振成象（MRI）动态扫描的研究结果，提出Gd－DTPA增强MRI动态扫描可以显示心绞痛病灶。22例心绞涌患者均为临床证实。增强检查方法为ECG门控，同一检查区域连续扫描4次，时间间隔为5、10、20和30min。信号测量由MRI机内在测量功能完成。结果：22例中有18例表现为增强后心肌局灶性高信号区。通过分析病灶区动态信号变化曲线并与正常心肌对比，发现其特点为病灶区增强后10min最高，信号增强率和信号对比率的最高峰也都在10min左右。而正常心肌的最高峰出现在5min时。这个结果与急、慢性心肌梗死MRI动态曲线的变化情况也不相同。表示心绞痛病灶区增强的原理和心肌梗死的增强原理并不完全相同。结论：Gd－DTPA增强MRI动态扫描完全可以定位和定量地显示心绞痛的病灶，但对它的增强原理目前尚不完全了解。     

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.     

钆贝葡胺与钆喷酸葡胺对单发脑转移瘤患者MRI T1WI增强扫描诊断价值的对比

目的 比较钆贝葡胺与钆喷酸葡胺在脑内单发转移瘤增强扫描中的价值.方法 选择81例单发脑转移瘤患者,首先行钆喷酸葡胺增强扫描,剂量0.1 mmol/kg;2 d后行钆贝葡胺增强扫描,剂量0.1 mmol/kg.结果 ①钆贝葡胺强化后,病变形态、病变边缘、强化程度及增强范围均显著优于钆喷酸葡胺,差异具有统计学意义（z=12.3232,14.43534,11.4536,12.4232,P＜0.05）;②增强扫描后,钆贝葡胺强化图像对比信噪比均显著高于钆喷酸葡胺,强化病灶/正常脑组织增强比均显著高于钆喷酸葡胺,差异具有统计学意义（t=12.3456,12.3465,11.2675,3.7865,3.8796,3.8781,P＜0.05）.结论 钆贝葡胺增强扫描对单发脑转移瘤病变形态、病变边缘、强化程度及增强范围显示更优,其图像对比信噪比及病灶/正常脑组织增强比更高.