Stable xenon CT cerebral blood flow imaging: rationale for and role in clinical decision making

The stable xenon CT method of measuring cerebral blood flow has been investigated in research studies for over 10 years. Recently, it has been gaining clinical acceptance, primarily owing to a combination of several unique advantages it holds over other cerebral blood flow measurement techniques. The accuracy of this technique in quantifying low cerebral blood flow gives it a unique application in cases of brain death and acute stroke and it can be repeated after an interval of 20 min. making it possible to evaluate autoregulation and cerebrovascular reserve. Furthermore, cerebral blood flow information is directly coupled to CT anatomy. Although it is more difficult to administer than a standard CT scan, careful monitoring can ensure patient safety during the examination. In this article we review the physiologic and technical bases for the clinical application of xenon CT-derived quantitative cerebral blood flow information and discuss the advantages and disadvantages of the technique. We also describe its current clinical applications, including its usefulness in the evaluation of acute stroke, occlusive vascular disease, carotid occlusion testing, vasospasm, arteriovenous malformations, and head trauma management.     

Quantitative applications of Doppler cardiography in congenital heart disease

Doppler ultrasound has rapidly become a valuable tool in the noninvasive investigation of cardiac hemodynamics. Although based on secure principles, accurate application of this methodology to quantitative measurements necessitates a thorough understanding of both Doppler physics and instrumentation. Over the past several years a large body of clinical and animal data verifying the accuracy of Doppler determination of pressure and flow data at various sites in the cardiovascular system, as well as the potential sources of error in acquisition and interpretation of blood velocity recordings, has been published. Quantitative use of Doppler in congenital heart disease, with emphasis on limitations of existing studies and issues particular to this patient population, is reviewed.     

CT fluoroscopy for thoracic interventional procedures

In the past several years, CT fluoroscopy has proved a valuable new technique in guiding the performance of intrathoracic procedures. Several approaches to using CT fluoroscopy are discussed. We have found an interrupted, real-time technique optimal to facilitate biopsy of percutaneous lung nodules, particularly small lesions. The technique is also valuable in assisting thoracic drainage procedures. This article also discusses the use of CT fluoroscopy to guide transbronchial needle aspiration, which is another potentially important application.     

冠状动脉内多普勒超声研究冠状动脉血流速度

目的:评价冠状动脉内多普勒超声测量冠脉血流速度的应用价值。材料和方法:利用冠状动脉内多普勒血流钢丝(FloWire) 测量21 例冠状动脉狭窄患者和12 例正常冠状动脉的血流速度。结果:左前降支冠脉狭窄远端的平均最大血流速度(APV) 、舒张期最大血流速度(DPV) 和舒张期与收缩期流速比值(DSVR) 均显著低于正常组测值。结论:应用冠脉内多普勒超声技术可评价正常和冠脉狭窄病变患者的冠脉血流速度,这为定量研究冠脉血流动力学提供了新方法。     

Interventional endoscopic ultrasound

Endoscopic ultrasound (EUS) has been used in clinical practice for the past two decades, mainly for staging upper gastrointestinal tract tumours. More recently the technique has been used to guide interventional procedures, particularly EUS-guided biopsy. In this review we describe the equipment and technique required for interventional EUS. We also discuss with illustrations the current clinical applications, potential complications and developments for the future.     

Intravascular ultrasound imaging of peripheral arteries as an adjunct to balloon angioplasty and atherectomy

This article reviews many of the applications of intravascular ultrasound (US) imaging for peripheral arterial diseases. In vitro studies demonstrate an excellent correlation between ultrasound measurements of lumen and plaque crossectional area compared with histologic sections. In vivo clinical studies reveal the enhanced diagnostic capabilities of this technology compared with angiography. Intravascular US imaging can provide valuable information on the degree, eccentricity, and histologic type of stenosis before intervention, and on the morphological changes in the arterial wall and the extent of excision after intervention. Intravascular US may also serve as a superior index for gauging the diameter of balloon, stent, laser probe, and/or atherectomy catheter appropriate for a proposed intervention. Significant new insights into the mechanisms of balloon angioplasty and atherectomy have been established by intravascular US findings. Intravascular US imaging has been shown to be a more accurate method than angiography for determining the cross-sectional area of the arterial lumen, and for assessing severity of stenosis. Quantitative assessment of the luminal cross-sectional area after the balloon dilatation should be more accurate than angiography as intimal tears or dissections produced by the dilatation may not be accurately evaluated with angiography. At the present time, intravascular US is still a controversial imaging technique. Outcome studies are currently being organized to assess the clinical value and cost effectiveness of intravascular ultrasound in the context of these interventional procedures.     

Use of a Doppler guide wire for intravascular blood flow measurements: a validation study for potential neurologic endovascular applications.

PURPOSETo conduct a validation study of a Doppler guide wire for potential neuroendovascular applications.METHODSA 12-MHz, 0.018-inch Doppler guide wire was evaluated in eight swine under various blood flow conditions using two types of in vivo cerebrovascular models (physiologic and arteriovenous shunting). Flow conditions were mechanically and pharmacologically altered. Doppler average peak velocity was compared with volumetric blood flow, and flow profile corrections were calculated and analyzed. Qualitative aspects of the Doppler guide wire spectra were also assessed.RESULTSPlots of average peak velocity versus volumetric blood flow showed excellent linear relationships (r2 > 0.94), which were maintained at high flow conditions (average peak velocity, 99 to 236 cm/sec; volumetric blood flow, 392 to 889 mL/min). Values of flow profile correction varied from 0.43 to 0.94 and showed no consistent relationship to changes in volumetric blood flow.CONCLUSIONSThe excellent correlation between average peak velocity and volumetric blood flow over a wide range of blood flow conditions and the additional qualitative information of the Doppler guide wire spectra establish a foundation for clinical implementation. The unpredictable variations of flow profile corrections remain obstacles for calculating volumetric blood flow based on Doppler guide wire average peak velocity.     

Assessment of coronary flow reserve using single photon emission computed tomography with technetium 99m-labeled tracers

The quantitative assessment of coronary flow reserve (CFR) may be useful for the functional evaluation of coronary artery disease (CAD), allowing judgment of its severity, tracking of disease progression, and evaluation of the anti-ischemic efficacy of therapeutic strategies. Invasive techniques, such as intracoronary Doppler ultrasound and the pressure-derived method, which directly assess CFR velocity and fractional flow reserve, have been used for the evaluation of the physiologic significance of coronary lesions. Considerable progress has been made in the improvement of technologies directed toward the noninvasive quantification of myocardial blood flow and CFR. Positron emission tomography has emerged as an accurate technique to quantify CFR. The absolute measurements obtained with this noninvasive approach have been widely validated. Nevertheless, it has not been applied to routine studies because of its high cost and complexity. On the other hand, technetium 99m-labeled tracers have been largely used for the evaluation of myocardial perfusion with single photon emission computed tomography (SPECT) imaging in patients with suspected or known CAD. Recently, attempts to estimate CFR with SPECT tracers have been made to obtain, with noninvasive methods, data for quantitative functional assessment of CAD. This review analyzes the relative merit and limitations of CFR measurements by cardiac SPECT imaging with Tc-99m-labeled tracers and describes the potential clinical applications of this technique.     

Hemodynamic response changes in cerebrovascular disease: implications for functional MR imaging

BACKGROUND AND PURPOSE: Patients with cerebrovascular occlusive disease may develop compensatory changes in local cerebral vasculature with a resultant loss of vascular reactivity. These alterations can affect the blood oxygen level-dependent (BOLD) signal that is the basis for functional MR imaging. We investigated the BOLD signal in patients with unilateral cerebrovascular disease to ascertain the clinical utility of functional MR imaging in these patients. METHODS: Five healthy volunteers and three patients with cerebro-occlusive disease were imaged with both a block and an event-related design of a visually cued bilateral motor task. Activation maps were calculated, and individual hemodynamic response curves were generated for left and right primary motor cortices. Vascular reserve was determined for the relevant vascular territory by using transcranial Doppler ultrasonography (US). RESULTS: In the event-related data, the amplitude of the BOLD response was significantly decreased in the motor cortex ipsilateral to the stenosis and showed significant delays in the timing of the hemodynamic response. In contrast, the longer duration stimulus and longer TR of the block design showed significant decreases in the BOLD amplitude but no significant interhemispheric temporal differences. Corroborating the hemodynamic status, transcranial Doppler US analysis showed diminished vascular reserve ipsilateral to the lesion. CONCLUSION: Differences in the results between the event-related and block paradigms reflect the sensitivity to alterations in autoregulation or vascular compliance. These changes in the vasculature directly affect the BOLD contrast underlying functional MR imaging. Thus, while this technique remains a useful clinical tool, caution is warranted when studying patients with cerebrovascular disease.     

Blood flow volume quantification of cerebral ischemia: comparison of three noninvasive imaging techniques of carotid and vertebral arteries

OBJECTIVE: Determination of blood flow volume is useful in assessing ischemic cerebrovascular disease. We compared the blood flow volume measurement of three noninvasive imaging techniques, namely color velocity imaging quantification, spectral Doppler imaging quantification, and MR phase-contrast flow quantification, to see how well the flow values determined by each technique agreed with one another. SUBJECTS AND METHODS: Flow volume quantification was tested experimentally using a flow simulator and by the three techniques in the vertebral and internal carotid arteries of 40 patients with histories of cerebral ischemia. In the flow simulation study, the flow values in each technique were compared with the phantom flow by the Wilcoxon's signed rank test. In the patient study, the flow values between each paired technique were compared by paired t test. The significance level was taken at p less than 0.05. RESULTS: Flow volumes were measured by color velocity imaging quantification. MR phase-contrast flow quantification agreed with the phantom flow simulation within the tested range, and spectral Doppler imaging quantification values were significantly overestimated. In patients, a large variation of the blood flow volume was obtained between each technique (p < 0.05). Among them, spectral Doppler imaging quantification showed the highest flow values in the vessels (internal carotid arteries, 312.6 mL/min; vertebral arteries, 112.0 mL/min), followed by color velocity imaging quantification (internal carotid arteries, 216.8 mL/min; vertebral arteries, 58.1 mL/min) and MR phase-contrast flow quantification (internal carotid arteries, 169.1 mL/min; vertebral arteries, 66.5 mL/min). CONCLUSION: Blood flow volume measurements determined by the three noninvasive imaging techniques on the same vessel can differ widely, and spectral Doppler imaging quantification consistently overestimated the flow volume. It is, therefore, essential that the same technique, preferably color velocity imaging quantification or MR phase-contrast flow quantification, be used for clinical follow-up investigations in the future.     

Sonography of the hepatic vascular system

The possibility of blood-flow analysis with Doppler techniques is a valuable addition to B-mode real-time scanning and enhances the role of sonography as the primary noninvasive imaging method for the liver and its vessels. Duplex sonography has already proved useful for qualitative assessment of hepatic blood flow in clinical practice. Preliminary experience with color Doppler flow imaging suggests that this technique may make assessment of the presence and direction of blood flow in intra- and perihepatic vessels easier and less time-consuming.     

Assessment of functional MR imaging in neurosurgical planning.

BACKGROUND AND PURPOSE: Presurgical sensorimotor mapping with functional MR imaging is gaining acceptance in clinical practice; however, to our knowledge, its therapeutic efficacy has not been assessed in a sizable group of patients. Our goal was to identify how preoperative sensorimotor functional studies were used to guide the treatment of neuro-oncologic and epilepsy surgery patients. METHODS: We retrospectively reviewed the medical records of 46 patients who had undergone preoperative sensorimotor functional MR imaging to document how often and in what ways the imaging studies had influenced their management. Clinical management decisions were grouped into three categories: for assessing the feasibility of surgical resection, for surgical planning, and for selecting patients for invasive functional mapping procedures. RESULTS: Functional MR imaging studies successfully identified the functional central sulcus ipsilateral to the abnormality in 32 of the 46 patients, and these 32 patients are the focus of this report. In epilepsy surgery candidates, the functional MR imaging results were used to determine in part the feasibility of a proposed surgical resection in 70% of patients, to aid in surgical planning in 43%, and to select patients for invasive surgical functional mapping in 52%. In tumor patients, the functional MR imaging results were used to determine in part the feasibility of surgical resection in 55%, to aid in surgical planning in 22%, and to select patients for invasive surgical functional mapping in 78%. Overall, functional MR imaging studies were used in one or more of the three clinical decision-making categories in 89% of tumor patients and 91% of epilepsy surgery patients. CONCLUSION: Preoperative functional MR imaging is useful to clinicians at three key stages in the preoperative clinical management paradigm of a substantial percentage of patients who are being considered for resective tumor or epilepsy surgery.     

Retrieval of intravascular foreign bodies with goose neck snare

PURPOSE: to evaluate the efficacy and advantages of the snare systems in the retrieval of foreign bodies from vascular system. MATERIALS AND METHODS: the snare technique has been used for intravascular foreign body retrieval. We performed percutaneous extraction of intravascular foreign bodies using combination multipurpose catheters and a nitinol snare loop. In this report, we evaluated the patients who had performed endovascular device reposition or foreign body retrieval from 1998 to 2001. RESULTS: foreign body retrieval was performed in 15 patients. The foreign bodies consisted of seven fractured port catheters, one sheath fragment, one embolization coil, four wire fragments, one pace-maker transducer and one dislocated endovascular stent. In no case were surgical procedures required, and no complications were encountered. CONCLUSION: the snare technique is a useful and a safe method as an alternative procedure to surgery. This technique is highly effective with low rate complications.     

静注手振氟碳微泡增强肝脏彩色血流信号的实验研究

目的探讨静注手振氟碳微泡造影剂增强肝脏彩色血流信号的能力.材料和方法应用彩色多普勒血流图观察5只兔子静注3种2个剂量手振氟碳微泡造影剂前后肝脏彩色血流变化.结果30次注射中29次肝脏彩色血流信号增强.结论静注手振氟碳微泡造影剂能增强肝脏彩色血流信号,具有较大的潜在应用价值.     

Use of intravascular stents in the treatment of internal carotid and extracranial vertebral artery pseudoaneurysms.

The management of extracranial carotid or vertebral artery pseudoaneurysms is controversial. Although some of these lesions resolve spontaneously, many clinicians opt to treat them with trapping procedures that result in vessel sacrifice. We describe two cases in which an intravascular stent was used to obliterate an aneurysm of the extracranial vertebral artery and the internal carotid artery, respectively, while maintaining the patency of the parent vessel. The technique, which has been successful in experimental animal models, shows promise for application in humans.     

Amplitude-coded color Doppler: clinical applications

Amplitude-coded color Doppler sonography (ACD) has become an useful adjunct to gray-scale US and conventional color Doppler sonography (CD) for the assessment of vascular diseases and pathologic conditions that might affect or alter tissue vascularization or perfusion. Basically, all US units that generate conventional color Doppler information through autocorrelation technique are capable of displaying ACD. This technique is also referred to as power Doppler, amplitude-mode color Doppler US, color Doppler energy (CDE), or US angiography. Amplitude-coded color Doppler sonography has already emerged as a valuable adjunct to conventional CD, particularly for evaluating flow in parts of the body where CD signal is weak because of slow flow, small blood vessels, or both. Received: 1 December 1997; Revision received: 26 March 1998; Accepted: 2 June 1998     

Prospective comparison of MR phase-contrast velocimetry with intravascular doppler US during infrainguinal artery angioplasty

PURPOSE: To evaluate the accuracy of magnetic resonance (MR) velocimetry for quantitative assessment of stenosis in patients undergoing percutaneous transluminal angioplasty (PTA). MATERIALS AND METHODS: Thirty patients underwent PTA of the infrainguinal region. To assess hemodynamic parameters of lesions, MR phase-contrast velocimetry with a circular-polarized extremity receiver coil and a cardiac gated gradient echo sequence was conducted before and 1 day after PTA. Additionally, all lesions were examined by means of intravascular Doppler flow measurements (0.018-inch wire, 12 MHz). From these data, the degree of stenosis was calculated and a comparison of MR velocimetry with intravascular Doppler US was undertaken. RESULTS: Correlation between calculated grade of stenosis for MR velocimetry and intravascular Doppler US was good and significant (r = 0.74; P <.001). Calculated luminal stenosis grade were similar for both methods before PTA (intravascular Doppler US: 0.62 +/- 0.18, MR velocimetry: 0.54 +/- 0.19; P =.17 with paired Student t-test) and after PTA (0.25 +/- 0.23 and 0.3 +/- 0.2, respectively; P =.56). CONCLUSION: MR velocimetry results in reliable noninvasive in vivo flow measurements and allows accurate assessment of stenosis in a clinical setting.     

经颅多普勒超声诊断糖尿病性脑血管病变

目的:研究经颅多普勒超声检查对诊断糖尿病性脑血管病的价值。材料与方法:39例糖尿病患者进行经颅多普勒超声检查。结果:89.7％患者表现有脉动指数增高等脑动脉硬化的脑血液动力学改变。结论:经颅多普勒超声检查对诊断糖尿病性脑血管病有重要价值。     

A model of blood-brain barrier permeability to water: accounting for blood inflow and longitudinal relaxation effects.

A noninvasive technique for measuring the permeability of the blood-brain barrier (BBB) to water could help to evaluate changes in the functional integrity of the BBB that occur in different pathologies, such as multiple sclerosis or growth of brain tumor. Recently, Schwarzbauer et al. (Magn Reson Med 1997;37:769-777) proposed an MR method to measure this permeability based on the T(1) reductions induced by injecting various doses of paramagnetic contrast agent. However, this method may be difficult to implement in a clinical environment. Described here is a two-point technique, in which a spatially selective inversion is used to measure T(1) prior to and after injection of an intravascular contrast agent. Measurements made in the rat brain are compared to numerical simulations generated with a physiological model that accounts for blood flow and includes two different blood volumes: nonexchanging and exchanging blood volumes. Our results suggest that BBB permeability could be evaluated from the change in T(1) caused by the vascular contrast agent. This technique might provide an approach for monitoring changes in BBB permeability to water in clinical studies.     

The relationship between venous gas bubbles and adverse effects of decompression after air dives.

The presence of gas bubbles in the vascular system is often considered a sign of decompression stress and several studies in the existing literature have addressed the relationship between the amount of bubbles detected by ultrasound Doppler systems and the incidence of decompression sickness. The use of ultrasound imaging has some important advantages to Doppler systems, and here we have looked at the relationship between the amount of intravascular gas bubbles detected by ultrasound echocardiography and the incidence of signs and symptoms of decompression stress after 203 air dives. The results show that venous gas bubbles detected by ultrasound imaging is a highly sensitive, although not specific, predictor of such adverse effects of decompression. Our results agree with the published concordance between Doppler detected bubbles and decompression sickness. We conclude that bubble detection by ultrasonic scanning of the heart can be used as a tool to assess the safety of decompression procedures for air dives.