Gallbladder bile: an experimental study in dogs using MR imaging and proton MR spectroscopy

Magnetic resonance (MR) imaging, proton MR spectroscopy, and biochemical analysis were performed to investigate MR signal intensity (SI) differences between concentrated and dilute gallbladder bile of seven fasting and five sincalide-treated dogs. MR images revealed high SI from bile of fasting dogs and low to medium SI in sincalide-treated dogs when spin-echo (SE) pulse sequences with repetition rates of 0.5 and 2.0 sec were used. Proton MR spectra were similar for fasting and sincalide-treated dogs. In fasting dogs, water content in the bile was slightly lower, and cholesterol, phospholipid, and bile acid concentrations were higher. More than 90% of proton signals in all Fourier transform free induction decay spectra emanated from water molecules, and no lipid proton resonances were detected in Fourier transform SE spectra after tau delays of 7 msec. These results indicate that the differences in SI are caused by alterations in relaxation times of water protons, possibly resulting from the interactions of water protons and macromolecules.     

Cine-gradient-refocused MR imaging of central pulmonary emboli

We studied the use of MR imaging with a limited-flip-angle, gradient-refocused pulse sequence to show central pulmonary emboli in 11 patients and to distinguish acute from chronic emboli. The central pulmonary vasculature was imaged by using a cine-limited-flip-angle (cine-MR) pulse sequence with 63/13 (TR/TE) and a 30 degrees flip angle (theta), as well as standard spin-echo sequences. Patients were selected on the basis of suspicion of central pulmonary embolism and correlative studies done within 24 hr of the MR examination. Correlations with other studies were based on the original MR report and blinded review of the MR images by two observers in consensus. Emboli were shown in all cases by cine-MR, and they corresponded to the locations of angiographic abnormalities and mismatched perfusion defects on scintigraphy. In three patients considered to have acute pulmonary embolus on the basis of angiography, the cine-MR studies were consistent with acute pulmonary embolus in two patients and chronic pulmonary embolus in one patient (however, in that patient pathologic examination showed chronic embolism). In one case in which angiography led to the diagnosis of acute and chronic pulmonary embolism, the cine-MR study showed acute embolism. In three patients thought to have chronic pulmonary embolus on the basis of angiography, the cine-MR study was interpreted as representing acute embolus in one patient and chronic embolus in two patients. In this highly selected, small group of patients, cine-MR imaging was accurate in showing central pulmonary embolism.     

MR imaging of pulmonary arterial hypertension and pulmonary emboli

Intraluminal signal in the pulmonary arteries on spin-echo, ECG-gated MR images is limited to the diastolic phase of the cardiac cycle in normal subjects. Initial experience has indicated that signal persisting during systole may be characteristic of slow blood flow associated with pulmonary arterial hypertension (PAH) or of thrombotic material secondary to pulmonary embolism. This study analyzes our cumulative experience (31 patients) with multiphasic, double spin-echo MR for assessing PAH and/or suspected pulmonary embolism. In PAH, the abnormal systolic signal showed an intensity increase from first to second echo. This pattern was observed in 92% of PAH patients, including 100% of patients with pulmonary systolic pressures greater than or equal to 80 mm Hg and 60% of patients with pressures less than 80 mm Hg. At any focus in the pulmonary arteries, such signal disappeared at some phase of the cardiac cycle. In patients with pulmonary embolism, signal from thrombus was fixed throughout the cardiac cycle and showed little or no increase in relative intensity change from first- to second-echo image. Using this guideline, MR made six confirmed positive and four confirmed negative diagnoses of proximal pulmonary embolism, while it failed to identify thrombus in the one patient with a peripheral pulmonary embolism. Intraluminal signal in the pulmonary arteries caused by PAH or pulmonary embolism can be differentiated in most instances using multiphasic, double spin-echo, ECG-gated MR. However, at its current stage of development, the procedure does not appear to be useful for the evaluation of peripheral pulmonary embolism.     

MR imaging of acute spinal cord injury: results of an experimental study in dogs

A weight-drop model was used to induce 16 acute lesions of varying severity in the spinal cords of eight mongrel dogs. The subsequent 3- to 7-hr postinjury MR images (0.5 T) were assessed. T1-weighted images contributed little information. Injection of gadolinium tetra-azacyclododecane tetraacetic acid did not result in significant enhancement. T2-weighted sequences offered precise detection and delineation of the lesions, displaying fusiform hyperintense signal abnormalities that corresponded to both edema and hemorrhage. In low-impact injuries, abnormalities were small and centrally located, sparing the periphery of the spinal cord. In these cases hemorrhage was minimal and limited to the center of the lesion. In severe-impact injuries, MR showed widespread longitudinal extension with involvement of the periphery of the spinal cord. In the most severe injuries, a central heterogeneous signal component was frequently observed opposite the site of impact because of important hemorrhage within the cord. Overall, hyperintense areas correlated closely with lesion severity, as demonstrated by pathologic findings. T2-weighted MR images obtained at 0.5 T were found to be reliable in the evaluation of acute spinal cord trauma.     

In vivo MR imaging of pulmonary arteries of normal and experimental emboli in small animals

PURPOSE: To demonstrate the feasibility of pulmonary MRA in living rodents. MATERIALS AND METHODS: A three-dimensional (3D) gradient echo sequence was adapted to perform a time-of-flight (TOF) angiography of rat lung. Angiogram with a spatial resolution of 195 x 228 x 228 microm(3) was acquired in around 33 minutes. The method was then applied in animals before and after pulmonary embolism (PE) induction. Section of the proximal right pulmonary artery was measured and compared between the two populations. RESULTS: Good quality images were obtained with a contrast-to-noise ratio (CNR) of 9 +/- 3 in the proximal part of the pulmonary artery. Cross-section areas of the right main artery are statistically different before (3.45 +/- 0.69 mm(2)) and after induction of PE (4.3 +/- 0.86 mm(2)). CONCLUSION: This noninvasive tool permits angiogram acquisition at around 200 microm spatial resolution and objective distinction between healthy and embolized arteries.     

经皮肺动脉瓣置换动物实验研究

目的 探讨新型带瓣膜雕刻支架经皮植入置换肺动脉瓣的可行性和疗效.方法 自行设计圆柱状网状支架,用医用316 L不锈钢激光雕刻而成.将新鲜的猪心包经脱细胞处理后置0.6%戊二醛浸泡36 h,生理盐水洗净,裁剪成人工瓣膜,缝合在不锈钢支架上,制成带瓣膜肺动脉支架.手术前将带瓣膜支架压缩至定制的相应大小的球囊导管上.选择健康犬8只,体重(15.5 ± 3.1)kg,穿刺右股静脉,将带瓣膜支架经导管植入至肺动脉瓣处,置换自身肺动脉瓣膜.手术后通过DSA和超声等方法即刻观察实验效果.结果 1只犬死于术中麻醉意外,7只犬经皮瓣膜置换术均获得成功,术后即时影像和超声检查结果表明人工肺动脉瓣膜功能正常.结论 自制新型带瓣膜支架经导管植入置换肺动脉瓣方法可行,效果理想.     

经动脉磁共振门静脉成像的实验研究

目的在犬模型上评价不同的造影动脉、对比剂剂量及血管扩张剂应用与否对经动脉磁共振门静脉成像(MR imaging during arterial portography,MRAP)图像的影响,总结出MRAP的最佳技术参数,为下一步的临床应用做准备.方法健康成犬16条,通过随机化分组表法分配到造影动脉、对比剂剂量及有无血管扩张剂3个研究组中.每条犬行腹腔麻醉后,在X线监视下经股动脉穿刺插管至肠系膜上动脉或脾动脉,行MRAP检查.计算增强前后肝实质信号强度的相对增强值,比较各因素不同水平间的相对增强值之间差异有无统计学意义.分析时间-增强曲线,总结MRAP的最佳技术参数.结果在16条犬上均获得了较为理想的MRAP图像.肠系膜上动脉组肝实质相对增强峰值为29.3%～106.0%,脾动脉组为29.5%～105.0%,肠系膜上动脉组达到肝实质相对增强峰值的时间为24～27 s,而脾动脉组为24～28 s,两组间差异无显著性意义(F=0.03,P>0.05).0.025 mmol/kg组的相对增强峰值为29.3%～30.9%,与0.050 mmol/kg组的95.5%～98.8%,0.100 mmol/kg组的102.0%～106.0%和0.200 mmol/kg组的104.0%～105.0%比较,除后两组之间差异无显著性意义(P>0.05)外,其他各组间差异均有非常显著性意义(P<0.01).有血管扩张剂组达到肝实质相对增强峰值的时间为21～27 s,早于无血管扩张剂组的24～28 s(P<0.05),但两组肝实质相对增强峰值差异无显著性意义(P>0.05).结论 (1)MRAP是一项新的安全可行的肝脏影像学检查技术,20 ml 钆喷替酸葡甲胺(Gd-DTPA)混合液(0.050～0.100 mmol/kg)以1 ml/s注射速度经造影动脉注入,在注射开始后21～28 s即可获得实验动物肝实质的最佳门静脉增强MRAP图像.(2)肠系膜上动脉或脾动脉作为造影动脉,在MRAP影像和时间-增强曲线上无差别.(3)0.050～0.100 mmol/kg的Gd-DTPA剂量完全可以引起肝实质足够的增强(95.5%～106.0%).(4)血管扩张剂的应用并不影响MRAP图像肝实质增强峰值达到的时间和峰值的大小.     

Ferrite-enhanced MR imaging of hepatic lymphoma: an experimental study in rats

The purpose of this investigation was to define the potential of unenhanced and ferrite-enhanced MR to detect hepatic lymphoma. Rats were implanted with diffuse and focal hepatic lymphoma. Both in vitro measurements of relaxation times and in vivo MR imaging of normal liver and of diffuse and focal hepatic lymphoma were compared. Diffuse infiltrative hepatic lymphoma showed increased T1 (45%) and T2 (41%) relaxation times in vitro, but could not be distinguished from normal control livers on in vivo spin echo (SE) images with a repetition time of 500 msec and an echo time of 30 msec (SE 500/30) or SE 1500/60 images. Focal hepatic lymphoma showed increased T1 (185%) and T2 (115%) relaxation times relative to normal liver tissue. Focal hepatic lymphoma was undetectable on unenhanced SE 500/30 MR images (contrast-to-noise ratio, C/N = 0.4) and was slightly hyperintense on SE 1500/60 images (C/N = 1.1). Ferrite (50 mumol Fe/kg) was administered to improve tissue contrast. In normal control animals, T2 of liver in vitro decreased from 29.3 +/- 3.3 msec to 11.1 +/- 1.2 msec, and image signal-to-noise ratio (S/N) of liver in vivo decreased from 16.1 +/- 2.4 to 2.8 +/- 0.3 (p less than .005). Ferrite-enhanced diffuse hepatic lymphoma showed in vitro T2 values and in vivo MR image S/N values indistinguishable from those of normal control animals. The T2 of focal hepatic lymphoma was essentially unaltered by ferrite. On SE 500/30 images, focal hepatic lymphoma became readily detectable, quantitated by a 35-fold increase in tumor-liver C/N. We conclude that clinical studies are warranted to determine the value of ferrite enhanced MR as a technique for the enhanced detection of focal hepatic lymphoma.     

Acute cerebral infarction in monkeys: an experimental study using MR imaging

Magnetic resonance (MR) imaging was performed in five monkeys with experimentally induced acute cerebral infarction to define the MR imaging features and correlate these with computed tomographic (CT) findings, laboratory analysis, and histopathologic studies. Acute infarct (2-4 hours after embolization) was generally visible on MR images but not on CT scans. CT at 24 and 48 hours did show the infarcts. In all cases the infarct was more clearly depicted with MR imaging and was visualized as an area of high signal intensity on T2-weighted images. Spectrometric nuclear MR measurements of the postmortem cerebral tissue confirmed prolongation of both T1 and T2 values similar to that calculated from MR images. At postmortem laboratory testing, the area of infarction detected with MR imaging had decreased specific gravity and increased water content, reflecting edema.     

Measurement of myocardial infarct size at early and late time intervals using MR imaging: an experimental study in dogs

The current study assessed the capability of ECG-gated MR imaging to quantitate both the percentage of the left ventricle involved by acute myocardial infarction and the mass of acute myocardial infarction at 3 and 21 days after coronary occlusion in dogs. Infarct mass was measured from gated transverse MR images using computer-generated calculated-T2 images. T2 images provided accentuation of the boundary between infarcted and normal myocardium as well as objective, reproducible calculation of image voxels representing infarcted myocardium. Postmortem and in vivo MR infarct mass and percentage correlated closely at 3 days (r = .98, SEE = 0.73 g; r = .97, SEE = 1.2%), and 21 days (r = .94, SEE = 1.54 g; r = .95, SEE = 1.61%). Left ventricular mass, infarct mass, and percentage of infarct were measured on end-diastolic MR images. Infarct mass at 3 and 21 days was not significantly different, with a mean deviation of 0.63 g. There was close intra- and interobserver reproducibility (r = .99 and r = .90, respectively) for measurement of infarct mass. The quantitative technique employed for determining the mass of acute myocardial infarctions, based on the different T2 relaxation times of infarcted and normal myocardium, provides for objective analysis and reproducibility. With this technique, MR provides an accurate method for assessing the mass of acute infarcts and the percentage of the left ventricle involved by the infarct both early and late after coronary occlusion.     

肺栓塞MR增强肺灌注成像与核素肺灌注显像对比实验研究

目的:比较MR及SPECT核素肺灌注显像诊断肺栓塞的价值。方法:24只大白兔建立肺栓塞模型,栓塞后6h采用3D-FLASH序列,从耳缘静脉注入Gd-DTPA行肺灌注扫描,应用Evaluation自动生成肺灌注曲线,在冠状位原始图像上两侧对称性选取正常与病变区肺实质的ROI测量时间-信号强度曲线。从耳缘静脉注入99Tcm-MAA111-148MBq0·3ml8体位显像。病理学检查:分别于栓塞后分批处死实验动物,光学显微镜下观察栓塞肺组织及正常肺组织的表现。统计学采用t检验和χ2检验。结果:成功建立20只兔肺栓塞模型,栓塞后6hMR增强肺灌注成像正常和栓塞区肺实质增强率分别为317·5%和45·1%;正常肺组织灌注曲线峰值明显,栓塞区灌注曲线低平或峰值延迟(t=11·52,P<0·01)。MR增强肺灌注成像对肺栓塞模型检测的敏感性为95%,特异性为85%;SPECT肺灌注显像敏感性100%,特异性65%,统计学分析二者检查结果差异不具有统计学意义(χ2=2·06,P>0·05)。病理显示:梗死区可见大量的纤维素渗出,肺间质增厚,动脉腔内可见红细胞和血栓形成,其周围白细胞浸润伴肺淤血,部分可见点状出血及肺淤血。结论:Gd-DTPAMR增强肺灌注成像诊断肺栓塞是可行的;MR诊断肺栓塞与SPECT具有较好的一致性。     

正常乳猪骨骺及干骺端骨髓的增强MR成像研究

目的 :探讨正常乳猪骨骺及干骺端骨髓的增强MR表现特征及不同年龄阶段的骨髓转化特征。方法 :8头乳猪 ,分别在出生 2、4、6和 8周的时间对双侧股骨近段及远段进行增强前后T1WIMR扫描 ,分析不同时间骨骺二次骨化中心骨髓和干骺端骨髓增强MR表现特征及增强率的变化 ,并与相应组织学发现进行对照研究。结果 :干骺端骨髓和骨骺二次骨化中心周边骨髓为含有丰富血管的红骨髓 ,增强后呈显著强化 ,且干骺端增强率较骨骺骨髓更高 ,但随年龄增长 ,两者的增强率均逐渐减低。骨干中央和二次骨化中心中央为黄骨髓 ,强化不明显。结论 :Gd DTPA增强在干骺端红骨髓与二次骨化中心周边红骨髓比在骨骺二次骨化中心中央区域黄骨髓强化更明显 ,其强化程度随年龄的增长逐渐减弱。     

三维增强磁共振肺动脉血管造影诊断急性肺栓塞的实验研究

目的 探讨钆喷替酸葡甲胺（Ｇｄ－ＤＴＰＡ）三维增强共振肺动脉血管造影成像（３ＤＣＥＭＲＰＡ）在急性肺栓塞（ｐｕｌｍｏｎａｒｙ ｅｍｂｏｌｉｓｍ,ＰＥ）中的诊断价值。方法 对１７只自体血栓引发的犬急性肺栓塞模型,利用３Ｄ快速扰相梯度回波序列（ＦＳＰＧＲ）行３Ｄ ＣＥＭＲＰＡ检查和Ｘ线肺动脉血管造影（Ｘ－ｒａｙ ｐｕｌｍｏｎａｒｙ ａｎｇｉｏｇｒａｐｈｙ,ＸＰＡ）检查,并与病理解剖对照。     

MR imaging of nitrosyl-iron complexes: experimental study in rats

PURPOSE: To assess the influence of several nitrosyl-iron complexes on proton nuclear spin relaxation rates to establish a magnetic resonance (MR) imaging technique for nitric oxide. MATERIALS AND METHODS: The influence of aqueous phantom solutions of nitrosyl-iron complexes on proton relaxation rates was analyzed for signal enhancement at conventional 1.5-T MR imaging. To induce formation of nitrosyl-iron complexes in a biologic tissue, isolated rat liver was perfused with a saline solution of the NO donor sodium nitroprusside (SNP), and the MR signal intensity was examined thereafter. RESULTS: All investigated nitrosyl-iron complexes shortened the longitudinal, or T1, and transverse, or T2, relaxation times in a concentration-dependent fashion. Relaxivities were highest with a dinitrosyl-iron complex bound to albumin and with a water-soluble mononitrosyl-iron dithiocarbamate complex. The contrast properties of 240 micromol/L of a paramagnetic nitrosyl-iron complex were sufficient to substantially enhance the signal intensity of SNP-perfused rat livers at hydrogen 1 MR imaging. CONCLUSION: Nitrosyl-iron complexes exhibit a contrast effect at MR imaging that can be exploited for NO imaging in living animals and patients with conventional (1)H MR imaging techniques.     

Sequential MR imaging of denervated muscle: experimental study

BACKGROUND AND PURPOSE: MR changes in denervated muscles have been reported to occur within days up to several weeks after peripheral nerve damage. The purpose of this experimental study was to investigate the longitudinal changes in denervated muscles by using MR imaging. METHODS: In 12 Lewis rats, the left sciatic nerve was transected at the level of the proximal thigh. MR imaging of both legs was performed before and 1 hour, 24 hours, 48 hours, 7 days, 14 days, 28 days, and 2 months after the procedure. The MR protocol included T1-weighted spin-echo, T2-weighted double turbo spin-echo, and turbo inversion recovery magnitude (TIRM) sequences obtained in the axial plane. Signal intensities (T2-weighted double turbo spin-echo and TIRM sequences) and the T2 TR (T2-weighted double turbo spin-echo sequence) were recorded for the soleus, peroneal, and gracilis muscles of both sides. Moreover, the circumferences of both lower legs were determined on the basis of T1-weighted images. RESULTS: Twenty-four hours after denervation, a signal intensity increase in the denervated peroneal and soleus muscles was present on TIRM images. On T2-weighted images, only the peroneal muscle exhibited slightly increased signal intensities and T2 TR. Forty-eight hours after nerve transection, the denervated soleus and peroneal muscles revealed prolonged T2 TR and marked increased signal intensities on T2-weighted and TIRM images when compared with the contralateral side, which further increased at or less than 2 months after denervation. Muscle atrophy of the denervated muscles was present as early as 7 days after denervation and was also increased at follow-up examinations. CONCLUSION: The TIRM sequence is more sensitive than is T2-weighted imaging in the detection of signal intensity changes in denervated muscle. These changes occur as early as 24 (TIRM sequence) and 48 (T2-weighted sequence) hours, respectively, after complete transection of the sciatic nerve in rats and precede muscle atrophy. The sensitivity to early signal intensity changes in denervated muscles may support the use of MR imaging in the diagnosis of peripheral nerve lesions.     

Bowel MR imaging with oral Gastrografin: an experimental study with healthy volunteers

Our objective was to evaluate Gastrografin for MR bowel imaging. Twenty-three healthy volunteers in two randomised groups received 300 or 400 ml 50% Gastrografin, drunk continuously during 2 and 3 h, respectively. Images were applied during breath-hold in three orthogonal orientations. The balanced fast-field echo (BFFE) and balanced turbo field-echo (BTFE) sequences, with acquisition times from 13 to 25 s, were used before gadolinium (Gd) DTPA implying 1- to 2-mm-thick slices locally or 6-mm-thick slices through the entire gastrointestinal tract. The Gd-enhanced images were performed using a 3D T1-weighted FFE sequence with water selective excitation (Proset). Image quality, including bowel distention, homogeneity of opacification and wall conspicuity, were evaluated by two experienced reviewers, and the adverse reactions were recorded. Very good or excellent distention, homogeneity and wall conspicuity were achieved in the central segments from the ileum to the left colon flexure in 83–96% of cases, due to the adequate contrast media supply in these regions. Distention, homogeneity and delineation were good in the central segments of the remaining bowels. Diarrhoea was a major problem affecting all participants, followed by nausea. Provided that there is modern fast sequential technology, excellent MR imaging of the bowel can be achieved by the oral administration 50% diluted Gastrografin. Further studies are needed to refine the technique and optimise the quantity and concentration of Gastrografin in order to avoid or reduce adverse reactions. Electronic Publication     

Efficacy of contrast-enhanced MR imaging in cardiomyopathy: an experimental study using Bio14.6 hamsters

RATIONALE AND OBJECTIVES: Myocardial fibrosis was evaluated with magnetic resonance (MR) imaging in Bio14.6 hamsters. MATERIALS AND METHODS: Gated gradient-echo T1-weighted images and spin-echo images with gadopentetate dimeglumine enhancement (0.2 mmol/kg) were obtained. RESULTS: Myocardial enhancement persisted for 13 minutes after administration of gadopentetate dimeglumine, and myocardial signal intensity peaked at 13 minutes on gradient-echo T1-weighted images. The enhanced areas were greater in Bio14.6 hamsters at 25-42 weeks than at 10 weeks. Pathologic data revealed enhancement with inflammation at 10 weeks and fibrosis with vessel proliferation at 25-42 weeks. Pathologic fibrotic change was greater at 32-42 weeks than at 10 weeks. The myocardium of 42-week-old Bio14.6 hamsters showed remarkable contrast enhancement, which continued for 13 minutes. There was no correlation between gadolinium enhancement and pathologic findings in the evaluation of myocardial degeneration and fibrosis. CONCLUSION: Gadolinium-enhanced MR imaging was useful for estimating myocardial fibrotic changes with vessel proliferation and myocardial damage.     

实时MR成像引导下猪脑动脉导管插管的验研究

目的 探讨实时MR成像引导下在猪脑动脉内进行导管插管的可行性.方法 选用10只美国产的雌性小型猪作为实验对象.经皮穿刺股动脉,在实时MR成像引导下,将3 F主动追踪微导管分别插至双侧咽升动脉内.解剖其主动脉弓、头臂动脉、颈动脉和咽升动脉,用肉眼观察有无穿孔、夹层等损害.结果 MR血管成像证实,猪主要由双侧咽升动脉在颅底形成微血管网供应脑的血供.在实时MR(rtMR)成像引导下,对10只猪舣侧咽升动脉进行插管操作,均操作成功,单次操作费时为4～12 min.所有实验动物的主动脉弓、头臂动脉、颈动脉和咽升动脉的内壁均光滑完整,未发现血管壁损伤.结论 实时MR成像引导下,可以将导管迅速、准确地插至猪脑动脉.     

Ventilation-perfusion lung imaging and selective pulmonary angiography in dogs with experimental pulmonary embolism

To determine the accuracy and limitations of Xe-133 ventilation and Tc-99m perfusion lung images (V-P images) in detecting pulmonary emboli (PE), these studies were performed in 23 dogs after experimental production of PE by a modified Wessler technique. Fourteen of the animals also underwent selective pulmonary angiography. Xenon-133 abnormalities were seen immediately after embolization in two of the 23 animals (8.7%). Perfusion images revealed the location of 83% of emboli that completely obstructed pulmonary vessels, but only 26% of those that partially obstructed flow. Defects were seen with 97% of emboli that completely occluded vessels larger than 2.0 mm in diameter, but in only 66% of those occluding smaller vessels. Oblique perfusion images provided the only evidence of the perfusion defect associated with five of 88 (5.7%) angiographically proven emboli. V-P imaging is a sensitive technique for detecting PE unless the emboli lodge in very small vessels or incompletely obstruct a vessel. Xenon-133 abnormalities occur infrequently following PE, and should not be a common cause for a false-negative V-P match in clinical practice.