64排螺旋CT下肢血管成像技术与DSA评估动脉狭窄的效果对比研究

目的探讨64排螺旋CTA评估下肢动脉狭窄闭塞性疾病的效果。方法对43例下肢动脉闭塞性疾病患者行64排螺旋CTA扫描,18例一周后行双下肢DSA检查,将每侧下肢血管分成8段,动脉狭窄程度分为：正常、轻度狭窄、中度狭窄、重度狭窄、闭塞5个级别。并以DSA为标准来评估。结果对18例患者双侧下肢共288段血管进行研究,CTA与DSA对血管狭窄程度显示一致的有275段,被CTA高估有ll段血管,低估有2段血管。结论64排螺旋CTA是下肢动脉狭窄硬化性疾病可靠的评估方法。     

Run-Off Computed Tomography Angiography (CTA) for Discriminating the Underlying Causes of Intermittent Claudication

AimTo evaluate run-off computed tomography angiography (CTA) of abdominal aorta and lower extremities for detecting musculoskeletal pathologies and clinically relevant extravascular incidental findings in patients with intermittent claudication (IC) and suspected peripheral arterial disease (PAD). Does run-off CTA allow image-based therapeutic decision making by discriminating the causes of intermittent claudication in patients with suspected peripheral arterial disease PAD?ResultsWhile focused on vascular imaging, CTA image quality was sufficient for evaluation of the MSK system in all cases. The underlying cause of IC was diagnosed in run-off CTA as vascular, MSK and a combination in n = 138 (65%), n = 10 (4%), and n = 66 (31%) cases, respectively. Specific vascular or MSK therapy was recorded in n = 123 and n = 9 cases. In n = 82, no follow-up was possible. Clinically relevant extravascular incidental findings were detected in n = 65 patients (30%) with neoplasia, ascites and pleural effusion being the most common findings.DiscussionRun-off CTA allows identification of vascular, MSK, and combined causes of IC in patients with suspected PAD and can guide specific therapy. CTA also allowed confident detection of crEVIF although detection did not necessarily trigger workup or treatment.     

A novel application of capnography during controlled human exposure to air pollution

Background

A detailed contrast bolus propagation model is essential for optimizing bolus-chasing Computed Tomography Angiography (CTA). Bolus characteristics were studied using bolus-timing datasets from Magnetic Resonance Angiography (MRA) for adaptive controller design and validation.

Methods

MRA bolus-timing datasets of the aorta in thirty patients were analyzed by a program developed with MATLAB. Bolus characteristics, such as peak position, dispersion and bolus velocity, were studied. The bolus profile was fit to a convolution function, which would serve as a mathematical model of bolus propagation in future controller design.

Results

The maximum speed of the bolus in the aorta ranged from 5–13 cm/s and the dwell time ranged from 7–13 seconds. Bolus characteristics were well described by the proposed propagation model, which included the exact functional relationships between the parameters and aortic location.

Conclusion

The convolution function describes bolus dynamics reasonably well and could be used to implement the adaptive controller design.     

Velocity field studies at surgically imposed arterial stenoses on the abdominal aorta in pigs

In order to describe velocity profiles and the size of deterministic and non-deterministic velocity disturbances at arterial stenoses, symmetrical and asymmetrical stenoses with intended area reductions of 50% (‘moderate’) and 85% (‘severe’) were applied on the abdominal aorta in six pigs. Blood velocities were registered by hot-film anemometry in 21 measuring points distributed across the vessel cross-sectional area in one pre-stenotic and three post-stenotic positions. Signal analysis included ensemble averaging, the high-pass filtering technique, and three-dimensional visualization. None of the stenoses affected the pre-stenotic velocity field. Downstream moderate stenoses flow separation and vortex formation were present. Moderate asymmetric stenoses induced turbulence in the post-stenotic velocity field. Immediately downstream of severe stenoses a prominent post-stenotic jet was present. Farther downstream, a multitude of coherent vortices and turbulence dominated the flow field. The transverse distribution of turbulence intensity parallelled with the peak systolic velocity profile, whereas transverse profiles of the relative turbulence intensity (turbulence intensity/mean velocity) revealed peak values in flow field locations with high velocity gradients. Velocity parameters for symmetric and asymmetric severe stenoses were highly comparable. However, the exact degree of stenosis was significantly higher for symmetrical (85%) than for asymmetrical (76%) stenoses. Therefore, recalling that stenosis severity strongly influences the development of velocity disturbances, this indicates that asymmetry of a stenosis is a predictor for blood velocity disturbances.     

Effects of asymmetric load carrying on the biomechanics of walking

The purpose of the study was to investigate the effects of an asymmetric sidepack carrying system on frontal plane joint moments of force in both lower extremities and in the L5/S1 joint during level walking. Ground reaction force data and frontal plane film records were obtained from five males performing three walking conditions: 0, 10 and 20% bodyweight loads in a sidepack supported by the left shoulder. Inverse dynamics were used to calculate the lower extremity moments during stance and a static model of the pelvis was used to calculate the L5/S1 moments during single support for each limb. Normal walking was characterized by symmetric kinetics between left and right limbs and around the L5/S1 joint. The asymmetric loads produced unbalanced lateral trunk muscle dominance between left and right limb stance phases, increased right hip and knee moments and decreased left hip and knee moments. During normal walking, the L5/S1 moment was dominant on the contralateral trunk side for both limbs. The asymmetric loads applied to the left side caused a shift in L5/S1 moment dominance to the right side during left and right single support phases.     

Certain aspects of acute arterial thrombosis]

An analysis included 228 patients with the acute arterial thrombosis in the extremities. Over 33% of patients reported to the treatment later than 24 hours after the onset. This delay markedly worsened the results of therapy. Sixty two percent of limbs was saved. Mortality rate was 15%. The author analyse the results of therapy in relation to the localization of thrombi and type of the treatment--surgical, use of vasodilators with heparin or streptokinase. In case of thrombosis localized in the end segment of aorta the results were less promising than in case of more peripheral arterial involvement. Excellent and favourable results in this group amounted to 32%, the limb was amputated in 13% of patients and 28% of patients died. Hundred eighty patients were operated. Arteriosclerotic lesions to the arterial wall were detected in 97%. Excellent and favourable results of surgery were achieved in 45%, amputations amounted to 22%, and mortality rate was 16%. Vasodilators combined with heparin produced an improvement in 13% of patients in whom surgery could be postponed. The best results were achieved in patients treated with fibrinolytic agents with subsequent surgery or without it. In this group excellent and favourable results amounted to 57%, amputations--24%, and mortality rate--8%.     

Acute occlusion of an abdominal aortic aneurysm complicated by bilateral lower extremity venous thrombosis: A case report

Acute occlusion of an abdominal aortic aneurysm is a rare phenomenon. Its possible complications include distal spasm followed by arterial thrombosis, ischemia of the distal limbs, distal embolization, acidosis, hyperkalemia, and the development of venous thrombosis of the lower limbs. Surgical correction is often complicated by cardiac decompensation, renal failure, fatal pulmonary embolism, and metabolic derangements related to toxins released from the revascularized limb. Unless contraindicated, immediate systemic heparinization must be undertaken when the diagnosis is first suspected. We present a case of sudden occlusion of an abdominal aortic aneurysm complicated by venous thrombosis involving both lower extremities. After undergoing surgical revascularization, the patient sustained massive fatal pulmonary emboli. Prophylactic interruption of the inferior vena cava may be indicated in patients who present with this complication of abdominal aortic aneurysm.     

Prediction of human orthostatic tolerance by changes in arterial and venous hemodynamics in the microgravity environment

In this article, we intentionally present exclusively the results of our recent studies of arterial and venous hemodynamics as predictors of human orthostatic tolerance during space flight and after the return to Earth. The possibility of in-flight orthostatic tolerance prediction by arterial hemodynamic responses to the lower body negative pressure (LBNP) and venous hemodynamic changes in response to occlusion of the lower extremities is demonstrated. For the first time, three levels of cerebral blood flow deficits during the determination of orthostatic tolerance in the course of the LBNP test performed in microgravity. We offer quantitative arguments for the dependence of the cerebral blood flow deficit on the degree of tolerance of the LBNP test. Patterns of arterial hemodynamics during LBNP were successfully used to diagnose the actual orthostatic tolerance and to follow its trend during flight, which testifies to the possibility of predicting orthostatic tolerance changes in an individual cosmonaut during space flight. Occlusion plethysmography of the legs revealed three levels of response of the most informative venous parameters (capacity, distensibility, and rate of filling) of the lower extremities correlated to the severity of decrease in orthostatic tolerance.     

Assessment of brachial artery blood flow across the cardiac cycle: retrograde flows during cycle ergometry.

We describe a novel software system that utilizes automated algorithms to perform edge detection and wall tracking of high-resolution B-mode arterial ultrasound images, combined with synchronized Doppler waveform envelope analysis, to calculate conduit arterial blood flow (BF) across the cardiac cycle. Furthermore, we describe changes in brachial arterial BF to the resting forearm during incremental cycle ergometry in eight subjects. During exercise, peak BF during the cardiac cycle increased at each workload (P < 0.001), because of increased velocity in the presence of unaltered cross-sectional area. In contrast, mean BF calculated across each cardiac cycle decreased at lower workloads before increasing at 100 and 160 W (P < 0.001). Differences in the pattern of peak and mean cardiac cycle flows were due to the influence of retrograde diastolic flow, which had a larger impact on mean flows at lower workloads. In conclusion, BF can be measured with high temporal resolution across the cardiac cycle in humans. Resting brachial arterial flow, including retrograde flow, increases during lower limb exercise.     

CT检查中造影剂不良反应的预防、处理及对影像学检查 的影响分析

目的：在CT 等医学影像检查过程中,常需要应用造影剂。在造影剂的使用常常发生不良反应,掌握不良反应的发生率,减少 或减轻患者的不良反应,能够使CT 增强扫描顺利进行,提高检查安全性。方法：搜集我院2011 年10 月至2012 年9 月间的1500 例CT 造影增强检查患者,包括冠状动脉CT 血管成像（冠脉CTA）、头部CT 血管成像（头CTA）、肝脏增强、泌尿系三维成像 （CTU）以及双下肢血管成像（双下肢CTA）,进行造影剂的不良反应类型、造影剂药物剂量、注射速度等统计分析,总结造成不良 反应发生的因素及处理方法。结果：不良反应的类型包括发热、呕吐、荨麻疹、面色潮红、局部疼痛、流泪、血压下降、喉头水肿、休 克等。使用非离子型造影剂出现不良反应者85 例,占5.67 %。其中轻度反应65 例,占4. 33%;中度反应16 例,占1.06%;重度4 例,占0. 27 %。结论：在CT 增强扫描过程中,造影剂的用量及注射速度与不良反应的发生有相关性。ＣＴ 检查过程总应该认真 执行操作流程,密切观察病人情况,积极防治,正确处理,将造影剂不良反应降低到最低程度,使患者更加安全。     

CT检查中造影剂不良反应的预防、处理及对影像学检查的影响分析

目的：在CT等医学影像检查过程中,常需要应用造影剂。在造影剂的使用常常发生不良反应,掌握不良反应的发生率,减少或减轻患者的不良反应,能够使CT增强扫描顺利进行,提高检查安全性。方法：搜集我院2011年10月至2012年9月间的1500例CT造影增强检查患者,包括冠状动脉CT血管成像（冠脉CTA）、头部CT血管成像（头CTA）、肝脏增强、泌尿系三维成像（CTU）以及双下肢血管成像（双下肢CTA）,进行造影剂的不良反应类型、造影剂药物剂量、注射速度等统计分析,总结造成不良反应发生的因素及处理方法。结果：不良反应的类型包括发热、呕吐、荨麻疹、面色潮红、局部疼痛、流泪、血压下降、喉头水肿、休克等。使用非离子型造影剂出现不良反应者85例,占5．67％。其中轻度反应65例,占4．33％;中度反应16例,占1．06％;重度4例,占0．27％。结论：在CT增强扫描过程中,造影剂的用量及注射速度与不良反应的发生有相关性。cT检查过程总应该认真执行操作流程,密切观察病人情况,积极防治,正确处理,将造影剂不良反应降低到最低程度,使患者更加安全。     

Age and regional specificity of peak limb vascular conductance in women.

The influence of age on limb vasodilator capacity in women is unclear. The objectives of this study were to characterize and compare age-associated changes in forearm and calf peak vascular conductance (VC(peak); a functional index of arterial structure) in women and to identify physiological characteristics predictive of variation in limb-specific VC(peak). Peak conductance (plethysmographic flow/mean arterial pressure), VC(peak) of the forearm (forearm VC(peak)), and calf (calf VC(peak)) after 10 min of arterial occlusion were measured in 58 healthy, normally active women aged 21-79 yr. Aerobic capacity (cycle peak oxygen uptake), arterial health (pulse-wave velocity, ankle-brachial index), total cholesterol, limb-specific tissue composition (dual-energy X-ray absorptiometry), and isometric strength (handgrip, plantar flexion) were also assessed. The relative decline in calf VC(peak) with age (-6.8% per decade, P < 0.001) was greater than the forearm (-4.4% per decade, P = 0.004), in contrast to results previously reported for men (forearm decline > calf decline). Limb VC(peak) per kilogram muscle declined with age in the calf (-6.0% per decade; P = 0.002), but not the forearm (P = 0.12). Age, cholesterol, and regional tissue composition were significant predictors of peak conductance in both limbs; however, age was a stronger predictor of peak conductance in the calf. These results suggest that healthy aging is associated with a linear decline in limb vasodilator capacity in women, but the magnitude of this effect is region specific. Further research will be required to determine whether the decline in lower extremity vasodilator capacity with age explains diminished exercising leg vasodilation in older women.     

DCE-MRI of the Liver: Reconstruction of the Arterial Input Function Using a Low Dose Pre-Bolus Contrast Injection

Purpose

To assess the quality of the arterial input function (AIF) reconstructed using a dedicated pre-bolus low-dose contrast material injection imaged with a high temporal resolution and the resulting estimated liver perfusion parameters.

Materials and Methods

In this IRB–approved prospective study, 24 DCE-MRI examinations were performed in 21 patients with liver disease (M/F 17/4, mean age 56 y). The examination consisted of 1.3 mL and 0.05 mmol/kg of gadobenate dimeglumine for pre-bolus and main bolus acquisitions, respectively. The concentration-curve of the abdominal aorta in the pre-bolus acquisition was used to reconstruct the AIF. AIF quality and shape parameters obtained with pre-bolus and main bolus acquisitions and the resulting estimated hepatic perfusion parameters obtained with a dual-input single compartment model were compared between the 2 methods. Test–retest reproducibility of perfusion parameters were assessed in three patients.

Results

The quality of the pre-bolus AIF curve was significantly better than that of main bolus AIF. Shape parameters peak concentration, area under the time activity curve of gadolinium contrast at 60 s and upslope of pre-bolus AIF were all significantly higher, while full width at half maximum was significantly lower than shape parameters of main bolus AIF. Improved liver perfusion parameter reproducibility was observed using pre-bolus acquisition [coefficient of variation (CV) of 4.2%–38.7% for pre-bolus vs. 12.1–71.4% for main bolus] with the exception of distribution volume (CV of 23.6% for pre-bolus vs. 15.8% for main bolus). The CVs between pre-bolus and main bolus for the perfusion parameters were lower than 14%.

Conclusion

The AIF reconstructed with pre-bolus low dose contrast injection displays better quality and shape parameters and enables improved liver perfusion parameter reproducibility, although the resulting liver perfusion parameters demonstrated no clinically significant differences between pre-bolus and main bolus acquisitions.     

Orthostasis fails to produce active limb venoconstriction in adolescents.

Orthostasis is characterized by translocation of blood from the upper body and thorax into dependent venous structures. Although active splanchnic venoconstriction is known to occur, active limb venoconstriction remains controversial. Based on prior work, we initially hypothesized that active venoconstriction does occur in the extremities during orthostasis in response to baroreflex activation. We investigated this hypothesis in the arms and legs of 11 healthy volunteers, aged 13-19 yr, using venous occlusion strain gauge plethysmography to obtain the forearm and calf blood flows and to compute the capacitance vessel volume-pressure compliance relation. Subjects were studied supine and at -10, +20, and +35 degrees to load the baroreflexes. With +20 degrees of tilt, blood flow decreased and limb arterial resistance increased significantly (P < 0.05) compared with supine. With +35 degrees of tilt, blood flow decreased, limb arterial resistance increased, and heart rate increased, indicating parasympathetic withdrawal and sympathetic activation with arterial vasoconstriction. The volume-pressure relation was unchanged by orthostatic maneuvers. The results suggest that active venoconstriction in the limbs is not important to mild orthostatic response.     

Relationship between leg muscle capillary density and peak hyperemic blood flow with endurance capacity in peripheral artery disease

The aim of this study was to determine if skeletal muscle capillary density is lower in patients with peripheral artery disease (PAD) and if capillary density relates to functional limitations. PAD patients with intermittent claudication (IC) have a decreased exercise tolerance due to exercise-induced muscle ischemia. Despite the apparent role diminished arterial flow has in this population, the degree of walking pain and functional limitation is not entirely explained by altered hemodynamics of the affected limbs. We hypothesized that skeletal muscle capillary density is lower in PAD and is related to the functional impairment observed in this population. Sixty-four patients with PAD and 56 controls underwent cardiopulmonary exercise testing and a gastrocnemius muscle biopsy. A subset of these patients (48 PAD and 47 controls) underwent peak hyperemic flow testing via plethysmography. Capillary density in PAD patients was lower compared with controls (P < 0.001). After adjustment for several baseline demographic imbalances the model relating capillary density to peak oxygen consumption (Vo(2)) remained significant (P < 0.001). In PAD subjects, capillary density correlated with peak Vo(2), peak walking time (PWT), and claudication onset time (COT). Peak hyperemic blood flow related to peak Vo(2) in both PAD and control subjects. PAD is associated with lower capillary density, and capillary density is related to the functional impairment as defined by a reduced peak Vo(2), PWT, and COT. These findings suggest that alterations in microcirculation may contribute to functional impairment capacity in PAD.     

Wave intensity in the ascending aorta: effects of arterial occlusion

We examine the effects of arterial occlusion on the pressure, velocity and the reflected waves in the ascending aorta using wave intensity analysis. In 11 anaesthetised, open-chested dogs, snares were used to produce total arterial occlusion at 4 sites: the upper descending aorta at the level of the aortic valve (thoracic); the lower thoracic aorta at the level of the diaphragm (diaphragm); the abdominal aorta between the renal arteries (abdominal) and the left iliac artery, 2 cm downstream from the aorta iliac bifurcation (iliac). Pressure and flow in the ascending aorta were measured, and data were collected before and during the occlusion. During thoracic and diaphragm occlusions a significant increase in mean aortic pressure (46% and 23%) and in wave speed (25% and 10%) was observed, while mean flow rate decreased significantly (23% and 17%). Also, the reflected compression wave arrived significantly earlier (45% and 15%) and its peak intensity was significantly greater (257% and 125%), all compared with control. Aortic occlusion distal to the renal arteries, however, caused an indiscernible change in the pressure and velocity waveforms, and in the intensities and timing of the waves in the forward and backward directions. The measured pressure and velocity waveforms are the result of the interaction between the heart and the arterial system. The separated pressure, velocity and wave intensity are required to provide information about arterial hemodynamic such as the timing and magnitude of the forward and backward waves. The net wave intensity is simpler to calculate but provides information only about the predominant direction of the waves and can be misleading when forward and backward waves of comparable magnitudes are present simultaneously.     

64排螺旋CTA在下肢动脉闭塞及狭窄性病变中应用价值

目的：评价64排螺旋CT血管造影在下肢动脉闭塞性及狭窄性病变中应用价值。方法：采用美国GE公司生产LightSpeed VCT对52例患者进行下肢血管造影检查。扫描层厚0．625mm,管电压120KV、管电流130．205mAs,扫描时间约为10秒。图像后处理技术多采用VR、M1P、MPR、cMPR,图像分析密切结合原始轴位图像。结果：67支血管未见明确病变,CTA显示狭窄血管共77支,5支血管闭塞;狭窄≥50％,≤75％共21支;狭窄≤50％共51支。结论：64排CTA图像在发现闭塞远端血管方面优于DSA,可以清晰显示闭塞远端侧枝供血血管。随着64排螺旋CT临床广泛应用,在下肢血管疾病诊断方面的优势会得到长足发展。     

Does colonization asymmetry matter in metapopulations?

Despite the considerable evidence showing that dispersal between habitat patches is often asymmetric, most of the metapopulation models assume symmetric dispersal. In this paper, we develop a Monte Carlo simulation model to quantify the effect of asymmetric dispersal on metapopulation persistence. Our results suggest that metapopulation extinctions are more likely when dispersal is asymmetric. Metapopulation viability in systems with symmetric dispersal mirrors results from a mean field approximation, where the system persists if the expected per patch colonization probability exceeds the expected per patch local extinction rate. For asymmetric cases, the mean field approximation underestimates the number of patches necessary for maintaining population persistence. If we use a model assuming symmetric dispersal when dispersal is actually asymmetric, the estimation of metapopulation persistence is wrong in more than 50% of the cases. Metapopulation viability depends on patch connectivity in symmetric systems, whereas in the asymmetric case the number of patches is more important. These results have important implications for managing spatially structured populations, when asymmetric dispersal may occur. Future metapopulation models should account for asymmetric dispersal, while empirical work is needed to quantify the patterns and the consequences of asymmetric dispersal in natural metapopulations.     

Spiral blood flow in aorta–renal bifurcation models

The presence of a spiral arterial blood flow pattern in humans has been widely accepted. It is believed that this spiral component of the blood flow alters arterial haemodynamics in both positive and negative ways. The purpose of this study was to determine the effect of spiral flow on haemodynamic changes in aorta–renal bifurcations. In this regard, a computational fluid dynamics analysis of pulsatile blood flow was performed in two idealised models of aorta–renal bifurcations with and without flow diverter. The results show that the spirality effect causes a substantial variation in blood velocity distribution, while causing only slight changes in fluid shear stress patterns. The dominant observed effect of spiral flow is on turbulent kinetic energy and flow recirculation zones. As spiral flow intensity increases, the rate of turbulent kinetic energy production decreases, reducing the region of potential damage to red blood cells and endothelial cells. Furthermore, the recirculation zones which form on the cranial sides of the aorta and renal artery shrink in size in the presence of spirality effect; this may lower the rate of atherosclerosis development and progression in the aorta–renal bifurcation. These results indicate that the spiral nature of blood flow has atheroprotective effects in renal arteries and should be taken into consideration in analyses of the aorta and renal arteries.     

Ordering process of self-organizing maps improved by asymmetric neighborhood function

The Self-organizing map (SOM) is an unsupervised learning method based on the neural computation, which has found wide applications. However, the learning process sometime takes multi-stable states, within which the map is trapped to an undesirable disordered state including topological defects on the map. These topological defects critically aggravate the performance of the SOM. In order to overcome this problem, we propose to introduce an asymmetric neighborhood function for the SOM algorithm. Compared with the conventional symmetric one, the asymmetric neighborhood function accelerates the ordering process even in the presence of the defect. However, this asymmetry tends to generate a distorted map. This can be suppressed by an improved method of the asymmetric neighborhood function. In the case of one-dimensional SOM, it is found that the required steps for perfect ordering is numerically shown to be reduced from O(N ³) to O(N ²). We also discuss the ordering process of a twisted state in two-dimensional SOM, which can not be rectified by the ordinary symmetric neighborhood function.