The influence of contrast agent injection on physiological flow in the circle of Willis

X-ray videodensitometry allows in vivo flow measurements from gradients in contrast agent concentration. However, the injection of contrast agent alters the flow to be measured. Here, the temporal, spatial, and inter-patient variability of the response to injection are examined. To this purpose, an injection is prescribed in the internal carotid in a 1D wave propagation model of the arterial circulation. Although the resulting effect of injection is constant over a cardiac cycle, the response does vary with the location within the cerebral circulation and the geometry of the circle of Willis. At the injection site, the injection partly suppresses the incoming blood flow, such that the distal flow is increased by approximately 10%. This corresponds to approximately 20% of the injection rate added to the blood flow during injection, depending on the vascular geometry. In the communicating arteries, the flow direction is reversed during injection. Since the measured flow is not equal to the physiological blood flow, the effect of injection should be taken into account when deriving the flow from travelling contrast agent.     

The clearance of Xenon-133 following its parenchymal injection: a rapid method for estimating functional liver blood-flow

Portal venous flow, total hepatic blood-flow and hepatic artery flow were measured in healthy dogs by electromagnetic flowmetry and a double indicator dilution technique. Functional liver blood-flow was measured by the double indicator dilution technique. Functional hepatic blood-flow did not correlate with portal venous flow, total hepatic blood-flow or hepatic artery flow, measured by either electromagnetic flowmetry or a double indicator dilution technique. There was a good correlation (r = 0.83, P less than 0.001) between functional hepatic blood-flow and liver blood-flow, measured by the clearance of Xenon-133 injected directly into the liver parenchyma. It is concluded that the clearance of Xenon-133, injected directly into the liver parenchyma, is a rapid and simple method for measuring functional hepatic blood-flow.     

A digital-radiographic technique for in vitro tissue thickness measurement using iodine displacement.

A novel digital radiographic method has been developed for measuring the thickness of a tissue sample by iodine displacement. This simple, accurate method is useful both in medical research and in the comparison of pathological and clinical findings. Radiographic measurements of tissue samples in air suffer from the limitation that the quantity measured depends on the product of both thickness and radiographic attenuation coefficient. This technique allows one to obtain thickness measurements from a digital radiograph of a tissue sample suspended in a bath of radio-opaque contrast agent. The attenuation of the iodinated contrast agent is much higher than that of tissue or calcium. Thus the resulting image is determined largely by the contour of the surrounding bath, and is only slightly influenced by the composition of the tissue. This technique improves both the accuracy and precision of radiographic thickness determination. In this paper the iodine displacement technique is described and the accuracy and precision of thickness measurements in appropriate phantoms are quantified. This technique has been used with both image intensifier and screen-film based imaging systems to obtain thickness maps of calcified human aorta, with precision better than 4% and spatial resolution of 2.5 mm-1.     

Effects of Electromagnetic Field and Basic Fibroblast Growth Factor on Osteoblast＇s Growth

Osteoblasts of rat cultured in vitro were stimulated with pulsed 50 Hz electromagnetic field and basic fibroblast growth factor(bFGF). The MTT method, flow cytometry and histochemistry staining were used to detect cell proliferation, cell cycle and alkaline phosphatase. The results indicated : after stimulated by 1 mT electromagnetic field, the cells are more abundant,have more S phase percentages, 2 mT electromagnetic field have no evident effect on cells‘ growth;compared with electromagnetic field, the cells stimulated by bFGF are more abundant and have larger S phase ratios. Electromagnetic field and bFGF have no effect on cells, alkaline phosphatase. Therefore ,we concluded that electromagnetic field can enhance osteoblasts growth like some growth factor such as basic fibroblast growth factor, and the osteoblasts‘, characteristics was not changed.     

Stroke volumes and ventricular volumes determined from indicator dilution curves,Part 2

A flow simulator designed to produce well defined pulsatile flows of water through two series-connected compartments is used to simulate either the right or the left side of the heart. The stroke volume and the diastolic volume of one of the compartments can be preset to desired values. In 14 experiments comprising 102 indicator recordings cold 5% dextrose solution and ink, were used as indicators being injected as boli at a defined instant during the pumping cycle by means of a power injector. A data-retrieval procedure based on a mathematical two-compartment model is used to calculate stroke volumes and ventricular volumes using the indicator recordings as input data. The results are compared with the actual volumes and acceptable agreement was obtained in nine experiments.     

脉冲电磁场对人单核细胞激活的影响

研究不同参数的脉冲电磁场(PEMF)干预对人单核(THP-1)细胞激活的影响。将体外培养的THP-1细胞分别以频率为32Hz或64Hz、强度为1mT的PEMF进行干预,2次/d,30min/次,间隔8h,共3d,以频率为0Hz作为对照组。采用计数法观察PEMF处理后THP-1细胞与人脐静脉内皮细胞(HUVECs)之间的黏附变化;ELISA法检测THP-1细胞培养基中单核细胞趋化因子1(MCP-1)的分泌情况;荧光定量PCR法观察THP-1细胞MCP-1基因表达改变。结果观察到,PEMF干预能明显抑制THP-1细胞与HUVECs间黏附,降低THP-1细胞MCP-1基因表达及其蛋白分泌水平。本实验提示,频率为32Hz或64Hz、场强为1mT的PEMF干预3d后,能明显抑制THP-1细胞激活。     

Do contrast agents affect ultrasound flow measurements?

The use of iodine contrast agents during angiography can put patients at risk. The replacement of angiography through duplex ultrasound methods would, therefore, be of great interest. Even when duplex sonography is used however, an x-ray angiography is often performed afterwards to verify the diagnosis. This causes complications in an unacceptable number of patients. The safety of duplex ultrasound sonography diagnosis can be improved by using low-risk Doppler contrast agents. Slow blood flow through vessels with a high degree stenosis and intracerebral flow can be more easily and accurately detected using these agents. However, amplification of the Doppler echo alters the measurements during both high and low flow, so that the flow rate cannot be recorded very precisely. Our goal was to study the effect of a contrast agent on velocity measurements with color-coded Doppler ultrasonography and on pulsed, one-goal measurements. We used a laser-Doppler-anemometer (LDA) with high temporal and spatial resolution as a reference method to compare the measurements.     

On the use of R1 and R2* for measurement of contrast agent concentration in isolated perfused rat liver

We present experimental MRI protocols at 4.7 T for quantitative determination of the Dotarem distribution volume in isolated perfused rat liver. The procedures involved either constant contrast agent (CA) concentration or bolus administration conditions. R1 and R2* effects of the CA in liver and perfusate were measured using gradient echo fast imaging (GEFI) experiments by varying either the excitation angle or the echo time. CA concentrations in liver and perfusate were also measured after MRI by inductively coupled plasma atomic emission spectroscopy, in order to determine in situ relaxivities in the perfusate (r1=4.2 +/- 0.1 s(-1) mm(-1), r2*=17 +/- 2 s(-1) mm(-1)) and in the liver (r1=7.2 +/- 0.2 s(-1) mm(-1), r2*=99 +/- 5 s(-1) mm(-1)). When CA concentrations were estimated from R1 measurements and r1, the CA distribution volume estimations in liver resulting from bolus (0.31 +/- 0.01) and stationary (0.32 +/- 0.05) experiments were not significantly different. In contrast, after a bolus, CA concentrations derived from R2* and r2* were overestimated in liver and even more in perfusate. However, with R1 and R2* being measured before CA bolus administration, zero echo time signal intensities computed from multiple TE measurements during multiple boli yielded good estimations of R1 and thus correct CA concentrations in liver and in perfusate. Under these conditions, a single multi-echo GEFI acquisition should be sufficient to determine the concentration-time curves. Consequently, this protocol should be appropriate to rapidly estimate the distribution volume in vivo when multiple boli have to be avoided.     

The ramp injection of radiotracers for blood flow measurement by emission tomography

A prototype instrument based on the coincidence detection of annihilation radiation was built to control the arterial concentration of a radionuclide as a uniformly increasing ramp function over a preset injection interval (ranging from 1.6 min to 13.6 h). The device was designed to accommodate radionuclides of different physical and biological half-life, and the physiological characteristics of the system being studied. A kinetic model based on the Kety-Schmidt integral was developed to permit the determination of cerebral blood flow (CBF). Both the kinetic model and the ramp injector were tested in cats studied with the PETT III positron emission tomograph and 4-(18F)-fluoroantipyrine as the CBF tracer. The ratio lambda/f of the brain-to-blood partition coefficient (lambda) and blood flow (f) were determined simultaneously by serial measurements with positron emission tomography.     

自动胰岛素注射器的设计

设计了一种全自动胰岛素注射器.利用变化电磁场使针管运动完成自动注射穿刺,利用微型步进电机精确控制注射药量,利用微处理器控制注射推药过程和存储每天用药信息.此全自动胰岛素注射器将为需要长期注射胰岛素来调节血糖的糖尿病患者提供方便和减轻痛苦.     

脉冲电磁场防治骨质疏松的动物实验装置研制及实验观察

目的根据脉冲电磁场治疗骨质疏松的原理，设计用于动物实验的脉冲电磁场治疗装置．并用该装置观察在脉冲电磁场作用下实验动物力学特性和骨组织形态的变化。方法设计了强度为11MT．频率12Hz／8Hz自动跳变的脉冲电磁场发生装置和专用的动物实验装置，并将磁场作用于去势大鼠的骨质疏松模型。结果实验装置运行时．对各参数检测表明，实验装置满足设计的要求：经脉冲电磁场装置治疗的大鼠骨形态和力学特性与未经治疗的模型组都有明显改善。结论实验装置满足设计要求，脉冲电磁场可以改善骨的形态和骨骼的力学特性。     

Effect of contrast agent viscosity and injection flow velocity on bolus injection pressures for peripheral venous injection in first-pass myocardial perfusion studies.

Myocardial perfusion imaging using Gd contrast agents is typically performed with bolus injections of the contrast agent using a power injector to provide for consistent and sufficiently rapid injection rates for all patients. For protocols in which a peripheral venous injection is called for (e.g. antecubital vein) injection catheters of 18 ga are used where vessel geometry permits. In some patients, particularly women with smaller veins, 20 and 22 ga catheters are used. The effect of catheter size and pressure tubing length can result in high injection pressures that occasionally cause leakage or connector failure. The viscosity of the contrast agent also impacts injection pressure. In this study, a simulation of the injection pathway was constructed with time resolved pressures measured at two points in the pathway. Pressure drops were calculated for a typical MR perfusion injection protocol.     

低频脉冲电磁场治疗骨质疏松的机制及临床应用

BACKGROUND: The most commonly used physiotherapies for osteoporosis include low-frequency pulsed electromagnetic field, ultrashort wave therapy, and extracorporeal shock wave therapy. Because of the uncertain intensity of extracorporeal shock wave and uncertain efficacy of ultrasound therapy, low-frequency pulsed electromagnetic fields have become the most widely used treatment for osteoporosis in clinic. OBJECTIVE: To review the mechanism and clinical application of low-frequency pulsed electromagnetic fields in the treatment of osteoporosis. METHODS: A computer search by the first author of PubMed and CNKI databases was performed for relevant articles using the keywords of “pulsed electromagnetic fields and osteoporosis” or “osteoblast or osteoclast” in English and “osteoporosis; pulsed pulsed electromagnetic fields; osteoblasts; osteoclasts” in Chinese, respectively. After initial search, there were 169 articles, and according to the inclusion criteria, 29 highly relevant articles that are authentic and have clear views were analyzed. RESULTS AND CONCLUSION: The pulsed electromagnetic field as a non-drug therapy is characterized by no trauma, no infection, simple operation, low cost, long-term use, and good safety. Its efficacy has been increasingly affirmed by researchers and clinicians. Pulsed electromagnetic fields can promote the synthesis of DNA, influence the proliferation and differentiation of osteoblasts, increase the apoptosis of osteoclasts, and have a certain window effect. Pulsed electromagnetic fields can effectively relieve pain and increase bone density level in patients with osteoporosis, which can increase its efficacy in combination with other drugs and have a wide range of clinical applications.        

External field electromagnetic measurement of blood flow

Summary An electromagnetic intravascular rate of volume flow meter of minimal dimensions is described. It is activated by an extracorporeal magnetic field. The location at the apex of the aortic arch minimizes ECG artifacts and circumvents the problem of securing a zero-flow baseline which is given by the lowest mid-diastolic flow level. The magnetic field at the electrodes is maximized by placing the subject axially into the magnetic coil. The flow transducer also offers a means of measuring the artery diameter and its pulsations. The electromagnetic flow measurements of cardiac output agree within about 20% with dyedilution technique determinations.This work has been supported by Medical Testing Systems, Inc.     

极低频脉冲电磁场对新生大鼠成骨细胞的影响

目的：观察极低频脉冲电磁场（pulsed electromagnetic fields，PEMF）对体外培养成骨细胞增殖、分化、体外矿化的影响。方法：采用频率为15Hz、强度为5mT、占空比为15％的PEMF作用于成骨细胞，检测成骨细胞的增殖、碱性磷酸酶（alkaline phosphatase，ALP）活性以及体外矿化指标。结果与结论：PEMF显著促进成骨细胞增殖和体外矿化，抑制ALP活性作用。     

Intraluminal recording of cross-sectional blood velocity distribution of human ascending aorta by ultrasound Doppler technique

A pulsed Doppler ultrasound technique was used for mapping two-dimensional blood velocity profiles in the human ascending aorta during open-heart surgery. An electronic position-sensitive device was constructed and linked to an intraluminal 10 MHz Doppler ultrasound probe. From a plane perpendicular to the central direction of blood flow, velocity mapping was performed covering the entire cross-section of the ascending aorta 6–7 cm above the valve. This method is based on a sequential sampling of velocity from continuously changing locations during a stable haemodynamic period; typically velocity points are recorded from 150–300 beats. Further processing transformed data to suit a previously developed velocity distribution model for normal blood flow in the human ascending aorta, based on multiregression analyses. In this model, the time series of data from consecutive beats were computed into an average two-dimensional profile described through one cardiac cycle. This method allows high spatial resolution (1.5 mm), in addition to the high-frequency response (200 Hz) of the modified ultrasound Doppler meter. Together with the advantage of velocity directionality and minimal time interventions, this makes the method well suited for studies on normal flow conditions as well as flow velocity distribution distal to different heart valve prostheses.     

The effect of light exercise upon blood flow velocity determined by laser-Doppler flowmetry

PRIMARY OBJECTIVE: The dominant, 0.1 Hz frequency, Traube-Hering component of blood flow velocity, which is related to baroreflex activity, may be modulated through the established techniques of manipulative medicine. Light exercise programmes, appropriate for use by the elderly and collectively termed gymnastique douce, also are believed to impact the baroreflex in a positive manner. Our objective was to test the relationship between the Traube-Hering oscillation and light exercise. METHODS: Using laser-Doppler flowmetry to quantify the Traube-Hering and other components of the blood flow velocity oscillation, we compared flowmetry records of 10 subjects before and immediately following a light-exercise programme. RESULTS: The data show that the light exercise programme amplifies the 0.1 Hz component of the blood flowmetry record. CONCLUSIONS: The 0.1 Hz component of blood-flow velocity is physiologically linked to baroreflex activity. It is this component that is augmented by a light exercise programme.     

Superior sagittal sinus blood flow in the dog measured by an electromagnetic flow meter. A comparison with a radioactive gas elimination method

A simple method for continuous measurement of superior sagittal sinus blood flow (SSBF) in dogs, using an electromagnetic flow meter around the intact vessel, is presented. This method is compared with a procedure measuring radioactive gas elimination upon intra-arterial indicator injection. A good correlation between the cerebral blood flow (CBF), calculated from the fast component of the elimination curve and SSBF (r = 0.96) was found within a CBF range of 50-200 ml/100 g min.     

Correlation between fluorescein flowmetry, 133Xenon clearance and electromagnetic flow measurement: a study in the intestine of the pig

The purpose of the present study was to compare fluorescein flowmetry as a technique for measuring changes in intestine blood flow with electromagnetic blood flowmetry and the 133Xenon clearance technique. In eight anaesthetized pigs the blood flow in the superior mesenteric artery was reduced to 20-75% of basal flow as defined by electromagnetic flowmetry. The change in blood flow as calculated by fluorescein flowmetry correlated well with that obtained by electromagnetic blood flowmetry (correlation coefficient 0.86) and 133Xenon clearance technique (correlation coefficient 0.94). These findings indicate that fluorescein flowmetry can be considered a quantitative method for measurements of a relative blood flow.