Quantification of myocardial blood flow and assessment of its transmural distribution with real-time power modulation myocardial contrast echocardiography.

BACKGROUND: The purpose of this study was to examine the ability of real-time myocardial contrast echocardiography (MCE) with power modulation to quantitate myocardial blood flow (MBF) and to assess its transmural distribution in open-chest dogs undergoing partial or total coronary stenoses. METHODS AND RESULTS: MBF was measured in 12 dogs instrumented with a cuff occluder around the left anterior descending coronary artery at rest, during partial coronary stenosis (during infusion of adenosine), and during coronary occlusion. The MCE-derived rate of microbubble velocity, beta, and myocardial blood volume, A, were obtained by curve fitting of videointensity versus time plots, after the transient destruction of microbubbles by high-energy ultrasound. The data were compared with MBF measured with radiolabeled microspheres. Significant correlations were found between radiolabeled microsphere-derived MBF and both beta (r = 0.93) and the product of A x beta (r = 0.91). MCE beta reserve also correlated well with microsphere-derived flow reserve. Comparing endocardial/epicardial MCE ratios and microsphere-derived MBF ratios, significant correlation was also found between endomicropsheres/epimicrospheres MBF ratio and both endo/epi beta (r = 0.90) and endo/epi A x beta (r = 0.88). CONCLUSIONS: Real-time power modulation MCE allows for an accurate quantification of MBF and of its transmural distribution in open-chest dogs undergoing partial or total coronary stenoses.     

Quantification of myocardial perfusion and determination of coronary stenosis severity during hyperemia using real-time myocardial contrast echocardiography

Although regional myocardial perfusion can be currently quantified with myocardial contrast echocardiography (MCE) by using intermittent harmonic imaging (IHI), the method is tedious and time-consuming in the clinical setting. We hypothesized that regional myocardial perfusion can be quantified and the severity of coronary stenosis determined during hyperemia with MCE using real-time imaging (RTI) where microbubbles are not destroyed. Six open-chest dogs were studied during maximal hyperemia induced by adenosine in the absence or presence of coronary stenoses varying from mild to severe. Myocardial blood flow (MBF) was measured at each stage by using radiolabeled microspheres. MCE was performed using both IHI and RTI. Data for the latter were acquired in both end-systole and end-diastole. No differences were found between myocardial flow velocity (MFV) derived from IHI and RTI when end-systolic frames were used for the latter. MFV was consistently higher for RTI (P <.01) when end-diastolic frames were used. A linear relation was noted between MFV and radiolabeled microsphere-derived MBF ratios from the stenosed and the normal beds when end-systolic frames were used for RTI (r = 0.78, P <.001), whereas no relation was found when end-diastolic frames were used (r = 0.08, P =.78). The scatter for assessing MBF (A.beta) was minimal for IHI and RTI (9%-10%) with end-systolic frames, whereas that for RTI with end-diastolic frames was large (30%). Furthermore the correlation with radiolabeled microsphere-derived MBF was significantly (P <.01) weaker with RTI when end-diastolic frames were used (r = 0.53) than when end-systolic frames (r = 0.94) or IHI was used (r = 0.99). Data acquisition for IHI was 10 minutes, whereas it was 8 seconds for RTI. Thus, RTI can be used to quantify regional myocardial perfusion and stenosis severity during MCE. Only end-systolic frames, however, provide accurate data. RTI offers a rapid and easy means of assessing regional myocardial perfusion with MCE.     

Reproducible Computer-Assisted Quantification of Myocardial Perfusion with Contrast-Enhanced Ultrasound

Myocardial perfusion can be quantified by myocardial contrast echocardiography (MCE) and is used for the diagnosis of coronary artery disease (CAD). However, existing MCE quantification software is highly operator dependent and has poor reproducibility and ease of usage. The aim of this study was to develop robust and easy-to-use software that can perform MCE quantification accurately, reproducibly and rapidly. The developed software has the following features: (i) semi-automatic segmentation of the myocardium; (ii) automatic rejection of MCE data with poor image quality; (iii) automatic computation of perfusion parameters such as myocardial blood flow (MBF). MCE sequences of 18 individuals (9 normal, 9 with CAD) undergoing vasodilator stress with dipyridamole were analysed quantitatively using the software. When evaluated against coronary angiography, the software achieved a sensitivity of 71% and a specificity of 91% for hyperemic MBF. With the automatic rejection algorithm, the sensitivity and specificity further improved to 77% and 94%, respectively. For MBF reproducibility, the percentage agreement is 85% (κ = 0.65) for inter-observer variability and 88% (κ = 0.72) for intra-observer variability. The intra-class correlation coefficients are 0.94 (inter-observer) and 0.96 (intra-observer). The time taken to analyse one MCE sequence using the software is about 3 min on a PC. The software has exhibited good diagnostic performance and reproducibility for CAD detection and is rapid and user-friendly.     

心肌造影超声心动图对糖尿病大鼠心肌微循环的评价

目的 研究心肌造影超声心动图(MCE)技术结合潘生丁负荷试验是否能够早期检测糖尿病(DM)大鼠左室心肌微循环的功能障碍.方法 雄性SD大鼠18只,腹腔注射链脲菌素复制DM模型,另12只体质量匹配的雄性SD大鼠腹腔注射生理盐水作为对照.分别在静息状态和潘生丁负荷后,对两组大鼠(12周)乳头肌水平左室短轴行MCE检查,测定各室壁感兴趣区域峰值声学强度(PI)、造影剂灌注速率(β)及声学强度达峰时间(TTP)等指标,计算心肌血流量(MBF)和心肌血流储备(MFR).MCE检查完毕后,对心肌组织分别行~(99m)Tc-MIBI核素摄取量及毛细血管密度测定.结果 无论静息状态还是负荷后,同组大鼠后壁的MBF较前壁、侧壁和室间隔的MBF显著减低(P<0.05);取前壁心肌进行组间比较,静息状态和负荷后,DM组的PI、MBF和MFR均较对照组显著减低(P<0.05).潘生丁负荷后,DM组β也较对照组显著减低,TTP显著延长(P<0.05).DM组各室壁的核素摄取量和毛细血管密度均显著减低(P<0.05).结论 MCE检测的PI、β、TTP、MBF及MFR等指标可以敏感地检测出DM早期的心肌微循环功能障碍.     

双嘧达莫与多巴酚丁胺负荷心肌超声造影探测冠脉狭窄的对比研究

目的对比双嘧达莫和多巴酚丁胺负荷心肌超声造影(MCE)探测静息状态下无心肌血流限制性冠脉狭窄的能力.方法用放置"水膨胀”式缩窄器于冠脉主干近端的方法,建立15只慢性多支冠脉狭窄闭胸犬模型.术后7～10d进行静息、双嘧达莫和多巴酚丁胺的小剂量微泡弹丸式注射法MCE,并同步用放射性标记微球测量心肌血流(MBF).以MBF储备≥3为正常和＜3为异常供血区.结果两种药物引起MBF增加,在正常和异常供血区均相近.两种药物负荷时,MCE示异常供血区灌注缺损的范围和程度相同.两种药物作用下异常供血区的峰值声强度(VI)均较正常供血区低(P＜0.05),异常和正常供血区峰值VI比值非常接近;且双嘧达莫和多巴酚丁胺的峰值VI比值均与相应的MBF比值呈良好的线性正相关(r=0.90和0.87,P＜0.0001).结论双嘧达莫和多巴酚丁胺负荷MCE探测冠脉狭窄的能力相近.因此,两者均可用于慢性冠脉狭窄的诊断.     

Effects of nitroglycerin on transmural myocardial blood flow in the unanesthetized dog.

This study was designed to determin the effect of nitroglycerin upon transmural distribution of myocardial blood flow in the awake dog during normal conditions and in the presence of ischemia-induced coronary vasodilation. Studies were performed in chronically prepared dogs with electromagnetic flowmeters and hydraulic occluders on the left circumflex coronary artery. Regional myocardial blood flow was estimated by using radionuclide-labeled microspheres, 7-10 mum in diameter, injected into the left atrium. During control conditions endocardial flow (0.86 plus or minus SEM 0.05 ml/min per g) slightly exceeded epicardial flow (0.72 plus or minus 0.03 ml/min per g, P smaller than 0.05), and this distribution of flow was not significantly altered by nitroglycerin. After a 5-s coronary artery occlusion, reactive hyperemia occurred with excess inflow of arterial blood effecting 360 plus or minus 15% repayment of the blood flow debt incurred during occlusion. When arterial inflow was limited to the preocclusion rate during coronary vasodilation after a 5-s total coronary artery occlusion, flow to the subepicardial myocardium was increased at the expense of underperfusion of the subendocardial myocardium, and the delayed reactive hyperemia was markedly augmented (mean blood flow debt repayment =775plus or minus 105%, P smaller than 0.01). Tese data suggested that subendocardial underperfusion during the interval of coronary vasodilation in the presence of a flow-limiting proximal coronary artery stenosis caused continuing subendocardial ischemia which resulted in augmentation of the reactive hyperemic response. In this experimental model both the redistribution of myocardial blood flow which occurred during an interval of restricted arterial inflow after a 5-s coronary artery occlusion and augmentation of the subsequent reactive hyperemic response were returned toward normal by nitroglycerin. This effect of nitroglycerin may have resulted, at least in part, from its ability to vasodilate the penetrating arteries which deliver blood from the epicardial surface to the subendocardium.     

Measurement of myocardial blood flow velocity reserve with myocardial contrast echocardiography in patients with suspected coronary artery disease: comparison with quantitative gated Technetium 99m sestamibi single photon emission computed tomography.

BACKGROUND: The ability of high and low mechanical index (MI) imaging methods during myocardial contrast echocardiography (MCE) to assess the physiologic significance of coronary stenoses were compared with technetium 99m sestamibi single photon emission computed tomography (SPECT) in patients. METHODS: Intermittent ultraharmonic imaging (high MI) and power modulation angio (low MI) were performed during continuous infusions of the echo-enhancing contrast agent, Optison, at rest and after dipyridamole stress in 39 patients. Technetium 99m sestamibi SPECT was performed simultaneously. Images from the 3 apical windows were divided into 6 walls. Myocardial blood flow (MBF) velocity and MBF velocity reserve were quantified from pulsing interval versus acoustic intensity MCE curves in each wall using postprocessed images. RESULTS: Approximately 25% of the myocardial walls could not be analyzed from MCE because of artifacts. MBF velocity and MBF derived from both MCE methods increased significantly after dipyridamole in healthy patients (n = 143 and 129 walls for high and low MI, respectively), compared with those with either reversible (n = 11 and 10 walls for high and low MI, respectively) or fixed defects (n = 18 and 14 walls for high and low MI, respectively) on SPECT. Consequently, MBF velocity and MBF reserve were significantly greater for patients with normal perfusion. Receiver operator characteristic curves obtained for MBF velocity reserve provided a sensitivity and specificity of 82% and 87%, respectively, for high MI; versus 64% and 96%, respectively, for low MI imaging after uninterpretable images were excluded from analysis. CONCLUSIONS: Both high and low MI MCE imaging techniques can be used to determine the presence of perfusion defects as identified by technetium 99m sestamibi SPECT. Low MI imaging methods have a number of drawbacks that limit its sensitivity compared with high MI techniques.     

A fast and effective method of quantifying myocardial perfusion by magnetic resonance imaging

The quantification of global myocardial blood flow (MBF) by measuring coronary sinus flow by magnetic resonance (MRI) was demonstrated to be very well correlated with positron emission tomography (PET). We proposed a new method for the quantification of regional myocardial perfusion with MRI by the integration of MBF and first pass technique. The aim of this study was to validate this new method for quantification of regional perfusion by comparing it with 13NH13-PET in swine models of myocardial infarction and in humans in resting and hyperemic conditions. MRI and 13NH3-PET was performed in 2 healthy swine, 11 swine models of myocardial infarction (5 reperfused, 6 non reperfused) and in 12 humans at rest and during hyperemia. MBF was estimated by MRI through the quantification of coronary sinus flow and left ventricular (LV) mass. The upslope of signal intensity (SI-upslope) of each myocardial segment was obtained by the first pass gadolinium technique. Regional SI-upslope was indexed by the upslope of the entire left ventricular myocardium (global upslope). Regional myocardial perfusion was estimated as the product of MBF and SI-upslope/global upslope. Regional perfusion was also estimated by 13NH3-PET. A close agreement of the MRI and PET techniques for measurement of regional myocardial perfusion was found in all myocardial segments by Bland–Altman analysis (mean difference 5.1 %; limits of agreement, ?37.2–27.5 %). With the integration of the first pass technique and the measurement of global MBF by coronary sinus flow/LV mass, MRI allows direct quantification of regional myocardial perfusion.     

Assessment of coronary stenoses of graded severity by myocardial contrast echocardiography.

BACKGROUND: Myocardial contrast echocardiography (MCE) has potential value in the assessment and quantitation of myocardial perfusion defects. However, the severity of stenosis detectable by MCE and its diagnostic accuracy remain undefined. Thus, we produced coronary stenoses of variable severity and quantified their effect on MCE. METHODS AND RESULTS: Three grades of left anterior descending (LAD) obstructions were produced in 7 open-chest swine. The stenoses were nonflow-limiting at rest, but decreased coronary hyperemia by 31.3% +/- 4.7%, 69.9% +/- 5.3% and 98.9% +/- 1.1%, respectively. Regional myocardial blood flow (RBF) was measured with fluorescent microspheres and was expressed as the ratio of LAD and control (LCx) beds. MCE was performed with 0.3 mg/kg intravenous AF0150 during ECG-gated harmonic imaging in short-axis view. Background-subtracted peak intensity (PI) was expressed as the ratio of LAD/LCx beds. Both RBF and PI ratios progressively decreased with increasing grades of stenosis. MCE showed a significant correlation with RBF (r = 0.74; P <.0001). Ratios of both PI and RBF differed significantly from baseline when coronary hyperemia was reduced more than 50%. An LAD/LCx ratio less than 0.6 by MCE yielded 61% and 83% sensitivity and 85% and 76% specificity with stenosis that reduced coronary hyperemia more than 50% and more than 75%, respectively. CONCLUSION: MCE with intravenous AF0150 during vasodilation correctly depicted the progressive reduction of flow ratios produced by graded coronary stenoses. A significant reduction of PI ratio was observed with stenosis causing more than 50% reduction of coronary hyperemia. An MCE ratio in stenosed/control beds could be selected, which exhibited good sensitivity and specificity in the identification of coronary stenosis.     

Early impairment of myocardial blood flow reserve in men with essential hypertension: a quantitative myocardial contrast echocardiography study.

OBJECTIVE: Aims of this study were to: (1) demonstrate whether quantitative myocardial contrast echocardiography could detect an index of myocardial blood flow reserve through the analysis of refilling curves generated by microbubble transit into myocardium both at rest and after vasodilatation induced by dipyridamole; and (2) explore with this method myocardial microcirculatory function in two different models (ie, patients with essential hypertension and control subjects). METHODS: Two groups of strictly age-matched men were studied (case-control study): 12 patients who were adults (28.2 +/- 0.2 years) and asymptomatic with never-treated essential hypertension, a mild degree of left ventricular hypertrophy, and normal left ventricular function; and 12 control subjects. Quantitative myocardial contrast echocardiography was performed in all study participants. We used second-generation ultrasound microbubbles as echocardiography contrast agent. Real-time color-coded power modulation was performed with a phased-array system interfaced to a S3 transducer (1.3-3.6 MHz). RESULTS: In control subjects there was little increase in myocardial blood volume (30%) between basal and hyperemic status (P <.05); in patients with hypertension this parameter increased by 22% (P <.05). Myocardial blood velocity increased after dipyridamole by 270% in control subjects (P <.01), whereas for patients with hypertension this parameter increased only by 150% (P <.02). The index of myocardial blood flow reserve was significantly lower for patients with hypertension than in control subjects (3.3 +/- 0.3 vs 4.4 +/- 0.3, respectively; P <.01). CONCLUSION: Results of our study documented that myocardial microcirculation in young adult patients with hypertension showed an early impairment in the vasodilatation capacity of the resistance arterioles under dipyridamole-induced hyperemia, as demonstrated by a reduction of myocardial blood flow reserve. Myocardial blood velocity increased after dipyridamole induction in control subjects, whereas patients with hypertension showed a significantly lesser increase. Myocardial blood flow reserve was significantly lower for patients with hypertension because of an early impairment in vasodilatation capacity of resistance arterioles under dipyridamole-induced hyperemia.     

Mechanism of myocardial dysfunction in the presence of chronic coronary stenosis and normal resting myocardial blood flow: clinical implications.

In chronic coronary artery disease, resting myocardial dysfunction can exist despite normal resting transmural myocardial blood flow (MBF). We hypothesized that this phenomenon occurs because of diminished endocardial MBF reserve. MBF (measured with radiolabeled microspheres) and wall thickening (WT) (measured with echocardiography) were assessed in 7 dogs after the development of severe left ventricular dysfunction caused by placement of ameroid constrictors on the left anterior descending (LAD) and left circumflex arteries and 3 weeks after selective bypass surgery to the LAD. Before surgery, the mean transmural MBF at rest and at peak dobutamine dose in the LAD bed were 1.1 +/- 0.5 and 3.0 +/- 1.5 mL/min per gram, respectively, and were not significantly changed after LAD bypass. The resting endocardial-to-epicardial MBF ratio (EER) was also normal before bypass (1.5 +/- 0.6) and remained unchanged after surgery. The prebypass EER at peak dobutamine dose, however, was markedly diminished in the LAD bed (0.7 +/- 0.3) and improved significantly (1.3 +/- 0.8, P <.01) after surgery. Resting WT in the LAD bed also improved to normal levels (36% +/- 4% versus 13% +/- 6%, P =.0001) and no longer demonstrated a biphasic response to dobutamine. In comparison, the nonbypassed left circumflex bed continued to show reduced resting WT (12% +/- 6%), a biphasic response to dobutamine, and abnormal EER during rest and dobutamine (0.7 +/- 0.3). We conclude that persistent myocardial dysfunction in the presence of normal resting transmural MBF can occur as a result of diminished endocardial MBF reserve, with transmural MBF reserve remaining normal.     

Assessment of flow mismatch with pharmacologic stress test on myocardial contrast echocardiography in a model of critical stenosis: adenosine triphosphate and dipyridamole.

Although adenosine triphosphate (ATP) is a favorable vasodilator because of its short-acting duration, the agent's effectiveness in facilitating the diagnosis of myocardial ischemia with myocardial contrast echocardiography (MCE) is not fully understood. The goal of this study was to examine the efficacy of intravenous ATP administration (0.15 to 0.30 mg/kg/min for 5 minutes) in diagnosing the flow mismatch with MCE. To achieve this, a critical stenosis was produced in the left circumflex artery in 10 anesthetized dogs. The peak intensity ratio of risk area to control area was reduced by ATP from 0.51 +/- 0.19 to 0.31 +/- 0.12 (P <.05). Systolic wall thickening of the risk area did not change significantly (32.8% +/- 9.8% to 27.5% +/- 12.8%). These changes did not differ from those obtained after dipyridamole. We conclude that MCE with intravenous ATP administration is as useful as the dipyridamole method for diagnosing critical coronary stenosis.     

A minimally-invasive closed chest myocardial occlusion-reperfusion model in rhesus monkeys (<Emphasis Type="Italic">Macaca mulatta</Emphasis>): monitoring by contrast-enhanced ultrasound imaging

Myocardial infarction is frequently developed in canine and porcine models but exceptionally in non-human primates. The aim of this study was to develop a minimally invasive myocardial ischemic/reperfusion model in the monkey intended to be combined with imaging techniques, in particular myocardial contrast echocardiography (MCE). A balloon-tipped catheter was advanced via the femoral artery into the left anterior descending artery (LAD) under fluoroscopic guidance in ten anaesthetized male rhesus monkeys (Macaca mulatta). The balloon was inflated to completely occlude the vessel. Coronary angiography (CA) was performed to control the reality of the LAD occlusion/reperfusion. The ischemia period was followed by 3–6 h of reperfusion. Myocardial perfusion was evaluated during ischemia and at reperfusion by MCE using a novel ultrasound contrast agent (BR38). Occlusion was successfully induced during 18–50 min in nine out of the ten evaluated monkeys. ST segment elevation indicated myocardial ischemia. MCE showed complete transmural arrest of myocardial blood flow during the ischemia period and no persistent microvascular perfusion defects during reperfusion. A minimally invasive closed-chest model was successfully developed for creating myocardial ischemia in the rhesus monkey (Macaca mulatta). This technique could have an important role in mimicking acute coronary syndrome under physiologically and ethically-acceptable conditions. MCE provides non-invasively information on myocardial perfusion status, information not available from CA.     

心肌声学造影定量急性心肌梗塞后心肌血流量的实验研究

目的　评价心肌声学造影定量心肌梗塞心肌血流灌注的价值。方法　对６条犬急性心肌梗塞模型进行心肌声学造影, 采用自身对照的方法分析缺血区和非缺血区心肌显影时间－强度曲线各参数之比与心肌血流量的关系。结果　梗塞区时间－强度曲线各参数中, 曲线下面积（ＡＵＣ）和峰值强度（ＰＩ）与心肌相对血流量高度相关（ｒ＝ ０．９２和０．８４, Ｐ＜ ０．０１）, 与心肌绝对血流量相关性良好（ｒ＝ ０．７７和０．７１, Ｐ＜ ０．０１）。不同水平心肌血流量间的ＡＵＣ、ＰＩ均存在显著性差异（Ｐ均小于０．０１）, 且随着血流量的减少而呈下降趋势。三项时间指标与心肌绝对血流量无直接关系。结论　心肌造影时间－强度曲线参数中的曲线下面积和峰值强度可准确定量心肌梗塞后局部心肌血流量。     

二维应变超声心动图结合实时心肌超声造影评价冠状动脉不同狭窄程度对心肌灌注和心功能的影响

目的 应用二维应变超声心动图(2D-Strain)结合实时心肌超声造影(MCE)评价静息状态下冠状动脉(冠脉)不同程度狭窄患者局部心肌血流灌注和应变的变化及两者之间的关系.方法 对25例冠心病患者及15例健康志愿者行MCE和2D-Strain检查.血供异常的心肌节段按供血冠狭窄程度分为轻度狭窄组(50%～75%)、中度狭窄组(76%～89%)和重度狭窄组(≥90%).从MCE再灌注允盈曲线获得A值和β值分析心肌灌注;应用2D-Strain测量心肌纵向收缩期峰值应变(SL)分析心功能.结果 在异常冠脉供血区,随着冠脉狭窄程度的加重;各组的A值与对照组相比呈递减趋势,但差异无统计意义(P>0.05);而中度狭窄组和重度狭窄组的β值和SL值均显著低于对照组(β值:0.75±0.67和0.67±0.53对0.97±0.65;SL值:11.60±5.89和9.58±6.51对19.46±6.17,均P<0.05).β值与SL值有相关性(r=0.65,P<0.05).结论 MCE的再灌注参数β值和2D-Strain测量的SL值均可发现静息状态下>75%的冠脉狭窄引起的心肌缺血,且两者具有较好的相关性.     

Myocardial blood flow measurements in rats with simple pulsing contrast echocardiography

Relationship between contrast intensity and ultrasound (US) pulsing interval has been utilized to quantify myocardial blood flow (MBF) during myocardial contrast echocardiography (MCE). We tested if an MCE method employing a simple pulsing sequence during intravenous contrast infusion has the ability to quantify MBF in rats. We performed MCE in 17 rats using a 5- to 12-MHz broadband transducer during microbubble infusion via the femoral vein. Acoustic density (AD) from the anterior wall of the left ventricle imaged in the short axis plane was plotted against the frame number after shortening the pulsing interval (PI) from 1:20 to 1:1 end-systolic ECG gating. The relation between AD and frame number was fitted to a decay function. The rate of the AD decay was decreased during dipyridamole infusion, but was increased by causing coronary stenosis. The AD during long PI imaging remained unchanged during the interventions. Estimated MBF by MCE after correction by heart rate exhibited a close correlation (r = 0.83) with the present "gold standard" of colored microsphere-derived MBF. Thus, the decay rate of the contrast intensity obtained with the high-frequency transducer after abrupt shortening of PI during intravenous microbubble infusion may provide for noninvasive measurement of MBF in rats.     

Real-time myocardial blood flow imaging in normal human beings with the use of myocardial contrast echocardiography.

Triggered myocardial contrast echocardiography (MCE) has been used successfully to quantify myocardial blood flow and assess coronary stenosis in animal models, but practical considerations have limited its broad clinical use. Real-time MCE may have practical advantages to assess perfusion and real time myocardial blood flow in human beings. We compared real-time MCE with triggered imaging in 23 normal human volunteers by using an investigational ultrasound contrast agent (DMP-115) and a commercially available ultrasound platform (Acuson Sequoia). Peak myocardial opacification (reflecting myocardial blood volume) after contrast infusion was quantified digitally in gray scale units (GU). In 13 subjects, myocardial blood flow reserve was assessed during dipyridamole infusion with the use of intermittent destruction-replenishment techniques. Real-time MCE resulted in a 30- to 45-GU increase from baseline compared with a 20- to 70-GU increase with triggered imaging. Real-time MCE showed no statistical difference in opacification (P = .131 by analysis of variance) among any of the myocardial regions of interest. Triggered imaging resulted in heterogeneous opacification among the regions of interest (P < .05 by analysis of variance). Dipyridamole did not significantly change peak myocardial opacification (myocardial blood volume) for either technique. Quantification of flow reserve revealed that myocardial blood flow reserve for the dipyridamole group was 3.6 +/- 0.4 (mean +/- 1 standard error of the mean). Real-time MCE is feasible in normal human volunteers and provides homogenous opacification of the myocardium. Furthermore, quantification of myocardial blood flow with real-time MCE in normal human beings produces results that are consistent with the known physiology of the coronary microcirculation.     

负荷心肌超声造影测定冠状动脉血流储备的临床应用

目的:探讨负荷心肌超声造影测定冠状动脉血流储备(Coronary flow reserve,CFR)的无创方法,并将其应用于评价冠状动脉微循环功能障碍(Coronary microcirculation dysfunction,CMD)。方法:人选161例因胸痛住院的非阻塞性冠状动脉疾病患者,所有患者均进行三磷酸腺苷负荷心肌造影,用QLab定量分析静息和负荷后平台期信号强度(A)和信号强度增加率(β)。心肌血流量(Myocardial blood flow,MBF)用A×β表示,CFR=MBF负荷/MBF静息。CMD定义为CFR<2.0。用Logistie多元回归分析筛选CMD的影响因素。结果:在非阻塞性胸痛患者中CMD发生率为51.6%;与冠状动脉微循环功能正常者相比,CMD中糖尿病高脂血症和E/e'>15比例明显增加,Logistic多元回归分析显示,E/e'>15是CMD发生的独立危险因素。结论:负荷心肌超声造影是测定CFR的有效无创方法;在非阻塞性胸痛患者中CMD发病率高,且与左室舒张末压升高有关。     

应用心肌超声造影首灌注成像时间参数定量评价心肌血流灌注的实验研究

目的 探讨首灌注血流通过冠状动脉时间(Tc)和心肌半灌注时间(Tm)评价缺血心肌血流灌注的价值.方法 18只健康杂种犬开胸后建立左前降支急性心肌梗死模型,180 min后经股静脉持续匀速推注造影剂(C3F8),应用实时三平面心肌超声造影(RT-TP-MCE)同步观察心肌内微气泡"从无到有再到稳定状态"的充填全过程(首灌注),然后行实时单平面心肌超声造影(RT-SP-MCE)观察心肌内微气泡被Flash破坏后再充填到稳定状态的过程(再灌注),两种方法均用单指数函数Y=A×(1-e-βt)+B来拟合时间-强度曲线.单平面法测量A值(平台期峰值强度)和β值(曲线斜率)来定量分析心肌血流量(A×β);RT-TP-MCE将左室心腔开始显影的时间标化为0点,测量Tc(即左室心肌开始显影的时间)、Tm(即心肌显影达50%平台期的时间).实验结束后处死犬,取出心脏行伊文思蓝和氯化三苯基四氮唑双重染色.结果 以染色结果为标准,将心肌节段分为正常组、缺血组和梗死组,分析正常组和缺血组.RT-TP-MCE正常组和缺血组Tc分别为(10.1±1.3)s和(20.4±7.1)s(P＜0.01),Tm分别为(17.1±2.2)s和(39.7±8.8)s(P＜0.01);缺血组心肌Tc、Tm与实时RT-SP-MCE测得的心肌血流量(A×β)均呈明显负性相关(r1=-0.876,P＜0.O1;r2=-0.894,P＜0.01).结论 RT_TP-MCE首灌注成像能同步定量评价心肌血流灌注;心肌缺血时,血流量越少,Tc和Tm越长.     

静脉输注国产声学造影剂定量心肌血流灌注的实验研究

目的：评价应用国产左心声学造影剂“全氟星”定量心肌血流灌注的可行性。方法：建立犬前降支缺血模型，经外周静脉持续匀速输注“全氟星”，存取不同触发间隔的造影图像，通过计算造影剂再充填曲线的平台声强度及微泡再充填速率估测心肌血流量。以正常区为参照、放射微球测定心肌血流量为“金标准”，判定应用国产左心声学造影剂定量心肌血流灌注的可行性。结果：放射微球测定心肌血流量与心肌声学造影定量结果相关良好（r=0.8913，P＜0．001）。结论：静脉均速输注“全氟显”可用于估测心肌血流量。