Magnetic resonance urography: initial experience of a low-dose Gd-DTPA-enhanced technique

Contrast-enhanced magnetic resonance urography (MRU) is a promising tool in the evaluation of the renal collecting system, but it can be limited by T2^* effects resulting from hyperconcentrated gadolinium chelates. The aim of this study was to evaluate a low-dose dimeglumine gadopentetate (Gd-DTPA) MRU technique consisting of a dynamic fast low-angle-shot (FLASH) 2D sequence and a static fast imaging in steady state precession (FISP) 3D sequence for depicting the kidneys and urinary tract. The Gd-DTPA dose (0.01 mmol/kg) was established experimentally in a healthy volunteer study. Ninety-one patients presenting with various renal disorders were examined with a low-dose Gd-DTPA MRU and a T2-weighted turbo spin echo (TSE) MRU technique on a 1.5-T system. Image quality and diagnostic value were considered at least satisfactory in 98.9 % of the FLASH 2D studies, 83.5 % of the FISP 3D studies and 78.5 % of the TSE T2-weighted studies. Typical enhancement patterns were established for the renal cell carcinoma and transitional cell carcinoma. The major limitations were motion artefacts and insufficient hydration of the patients. Low-dose Gd-DTPA MRU appears to be a useful technique in the evaluation of the kidneys and urinary tract, especially in cases of renal tumours. Received: 26 February 1998; Revised: 25 January 1999; Accepted: 14 June 1999     

常规Gd-DTPA增强后脑DWI检查的可行性研究

目的探讨常规增强扫描之后行DWI检查的可行性。方法采用西门子1．5T超导型MR扫描系统对86例颅内病变患者进行检查，先行常规T1WI、T2WI及DWI（b=0、1000s／mm^2）横断面扫描，然后行常规增强T1WI扫描，对比剂为钆喷替酸葡甲胺（Gd—DTPA），剂量为0．1mmol／kg，注药速度为1ml／s，注入对比剂4min后以相同的参数再行一次DWI扫描，将增强前后的DWI原始图像均输入工作站获得表观弥散系数图。分别计算出肿瘤强化实质区、坏死囊变区、脑梗死区、正常脑灰质区、正常脑白质区，正常神经核团区域增强前后的DWI信号噪声比（SNR）、对比噪声比（CNR）、ADC值。采用配对t检验比较不同区域增强前、后SNR、CNR及ADC值的差别。结果正常脑组织DWI的SNR和ADC值于增强前后均无明显差别，P〉0．05；增强前后肿瘤强化实质区、囊变坏死区、脑梗死DWI的SNR、CNR以及ADC值的差别也无统计学意义（P〉0．05）。结论常规Gd—DTPA增强4min后，正常脑组织和不同的病变组织的DWI（b=0、1000s／mm。）SNR、CNR及ADC值无明显改变，常规Gd—DTPA增强4min后行脑DWI（b=0、1000s／mm^2）扫描是可行的。     

Magnetic resonance imaging and histopathology of cerebral gliomas

Summary The correlation of magnetic resonance imaging (MRI) with histopathological findings was analysed in 26 patients with untreated cerebral gliomas. In low-grade gliomas, T2-weighted images demonstrated relatively homogeneous high-intensity lesions involving both the grey and the white matter. In high-grade gliomas, especially grade IV, T2-weighted images demonstrated prominent heterogeneity in signal intensity, which consisted of a hyperintense core, less hyperintense or normal intensity rim and surrounding finger-like areas of high intensity. Marked and irregular contrast enhancement was evident in all but one case of these high-grade gliomas in which gadolinium-DTPA was used. Histological examination revealed tumour cells extending as far as the borders of the high-intensity areas shown on T2-weighted images in both high-and low-grade gliomas, but in 5 of 8 low-grade and 4 of 18 high-grade gliomas, isolated tumour cells extended beyond the hyperintense areas shown on T2-weighted images.     

Echoplanar diffusion-weighted MRI with intravenous gadolinium-DTPA

It is occasionally necessary to repeat diffusion weighted imaging (DWI) after giving intravenous contrast medium (CM). However, the effects of CM on DWI and apparent diffusion coefficients (ADC) have not been fully examined. The aim of this prospective study was to investigate whether there are any diagnostically significant differences between echo-planar imaging (EPI)-DWI before and after intravenous CM. EPI-DWI was acquired twice in 203 consecutive patients before and after i.v. CM. Three blinded readers rated the diagnostic image quality. Quantitative ADC calculations were performed before and after CM in all 72 patients with lesions sufficiently large for quantification, and in 72 normal brain regions. Of the 203 patients, 127 had abnormalities on MRI, including ischaemic stroke (52), bleeding (nine), brain tumour with disturbed blood-brain barrier (BBB) (18) and other lesions (48). There were no significant signal differences on isotropic DWI before and after CM, even in lesions with definite disturbance of the BBB. No statistically significant difference between ADC of lesions and contralateral normal brain was observed.     

Intracranial meningiomas: How frequent are indicative findings in CT and MRI?

Summary Frequencies of CT and MRI findings characteristic of meningiomas were compared in 50 cases. Plain and contrast enhanced examinations with CT and MRI were evaluated retrospectively regarding 12 criteria known to be indicative of the diagnosis of meningiomas. CT proved to be superior in demonstrating calcifications and a typical tumor density. On the other hand, MRI was better suited for identifying the extraaxial location of tumors, the broad contact of tumors to the meninges, tumor capsules and meningeal contrast enhancement adjacent to the tumor. Both methods provided nearly equal results in demonstrating mass effects, hyperostoses, intensive and homogeneous contrast enhancement, and smooth tumor contours after contrast administration. On the whole, neither of the two methods demonstrated a universal superiority for the diagnosis of intracranial meningiomas. Rather, each method displayed distinct advantages.     

Disease activity in multiple sclerosis studied by weekly triple-dose magnetic resonance imaging

This study assessed whether dysfunction of the blood-brain barrier is an obligatory early event in lesion formation in multiple sclerosis. Dual-echo and T1-weighted magnetic resonance imaging after the injection of a triple dose (0.3 mmol/kg) of gadolinium-DTPA were obtained from ten patients with relapsing-remitting multiple sclerosis every week for 2 months. Sixty-four newly active lesions were detected by the two techniques. All the 44 new lesions seen on dual-echo scans enhanced during the early phases of their formation: 33 at their first appearance, 10 1 week before their appearance on the dual-echo scans, and one the week thereafter. When the every fourth (monthly) scan was analyzed, a total of 55 newly active lesions were detected (i.e., 14% active lesions would have been missed compared to the number found on weekly scanning). Thirty-one of them were detected by both dual-echo and triple-dose scans, 15 only by enhanced scans, and nine only by dual-echo scans. This study confirms that with highly sensitive magnetic resonance imaging techniques dysfunction of the blood-brain barrier is an obligatory early event in new lesion formation in relapsing-remitting multiple sclerosis. Received: 9 September 1998 Received in revised form: 21 January 1999 Accepted: 2 February 1999     

钆喷酸葡铵和不同b值对肝扩散加权成像的影响

目的探讨钆喷酸葡胺(Gd-DTPA)和不同b值对肝脏扩散加权成像(DWI)的影响。方法收集20例健康志愿者和61例临床怀疑肝肿瘤的患者,均行增强前、后两次DWI扫描,对比分析DWI图的信噪比(SNR)、对比信噪比(CNR)以及表观扩散系数(ADC)值。结果最终44例患者共56个病灶和20例正常肝志愿者纳入研究,分为正常肝组(20例),肝囊肿组(16个病灶),肝海绵状血管瘤组(14个病灶),肝细胞癌(HCC)组(15个病灶),肝转移瘤组(11个病灶)。相同b值下比较,增强前后两次DWI各组SNR值、CNR值差异均无统计学意义(P0.05),增强后DWI所得平均ADC值较增强前DWI所得平均ADC值有所减小,但其差异无统计学意义(P0.05)。不同b值下比较,增强后DWI各组的SNR值、CNR值差异均有统计学意义(P0.05),各值随b值的增大而减小;ADC值差异除肝囊肿组、转移瘤组无统计学意义(P0.05)外,其余组均有统计学差异(P0.05),且ADC值随b值增大而减小。结论钆对比剂Gd-DTPA对肝脏DWI图像质量和ADC值无显著影响,注射钆对比剂后5 min行肝DWI是可行的;在满足肝DWI图SNR和CNR的前提下,选择小b值有利于病灶的检出。     

Serial quantitative MR assessment of optic neuritis in a case of neuromyelitis optica,using Gadolinium-“enhanced” STIR imaging

Summary A patient is presented with neuromyelitis optica. MR imaging, using a short inversion time inversion recovery (STIR) technique, clearly depicted the lesion in the left optic nerve. Subsequent serial STIR imaging, with and without Gadolinium-DTPA, allowed quantitative assessment of changes parallel to improved optic nerve function. STIR imaging is a sensitive technique to demonstrate optic nerve lesions, and enables quantitative assessment to be made of the effect of (steroid) medication.     

Cystic spinal cord tumors: Magnetic resonance imaging correlated to histopathological findings

We report the characteristics of magnetic resonance imaging (MRI) of cystic intradural extramedullary spinal cord tumors (cystic neurilemmoma, epidermoid cyst, and enterogeneous cyst). T1-weighted MRI enhanced with gadolinium-DTPA clearly demonstrated the rim morphology of these tumors. The comparison between the rim enhancement pattern and histopathological findings offered possible qualitative diagnosis of these cystic spinal cord tumors by MRI.