Tc-99m sestamibi myocardial imaging at rest for evaluation of cocaine-induced myocardial ischemia and infarction.

Many clinical cases of cocaine-induced myocardial infarction have been reported in the literature. Of the reported cases, patients tend to be young (in the third decade of life), chronic abusers with myocardial infarction typically involving the anterior left ventricular wall. This case report demonstrates the usefulness of two-phase (symptomatic and asymptomatic) Tc-99m sestamibi myocardial imaging at rest for definitive diagnosis of cocaine-induced myocardial ischemia and infarction.     

Transmural metabolite distribution in regional myocardial ischemia as studied with 31P NMR

Phosphorus-31 nuclear magnetic resonance (31P NMR) has been applied to study the canine heart prior to and during regional myocardial ischemia induced by partial flow reduction in the left anterior descending coronary artery (LAD). NMR data were acquired in a transmural fashion by restricting the signal to a column perpendicular to the heart wall using B0 gradients and obtaining spectroscopic spatial resolution along the third dimension using the B1 gradient and adiabatic excitation. With this approach, transmural spectra were accumulated in five separate voxels spanning the wall of the left ventricle from the epicardium to the endocardium. In the normal canine myocardium the levels of high-energy phosphates CP and ATP were relatively constant throughout the left ventricular wall, with only minor evidence of free inorganic phosphate in any of the transmural voxels. However, during sustained partial occlusion of the LAD, significant regional differences between the epi- and the endocardium were noted. The data demonstrate the importance of studying cardiac bioenergetics with transmural differentiation.     

Assessment of global and regional myocardial function in the mouse using cine and tagged MRI.

Mouse models are expected to play an important role in future investigations of human cardiac diseases. In the present report, MRI methods for determining global and regional cardiac function in the mouse are demonstrated. ECG-gated cine images were acquired in five C57BL/6 mice at physiological temperatures (37 degrees C) and heart rates of 500 +/- 50 beats per minute. Left ventricular mass, ejection fraction, and cardiac output were estimated from the resulting images. Regional myocardial function was also determined in three animals by application of 2D SPAtial Modulation of Magnetization (SPAMM) in combination with the cine protocol. The quality of the tagged images was sufficient to allow mapping of myocardial strains and displacements. The results of the regional strain analysis were consistent with similar studies in larger animals. This work demonstrates the first characterization of regional myocardial function in the mouse via SPAMM techniques.     

Imaging of regional metabolic activity by 18F-FDG/PET in rats with transient cerebral ischemia

Changes in regional metabolic activities induced by middle cerebral artery occlusion (MCAO) can influence patient outcome. Our aim was to demonstrate in a rat model that ¹⁸F-FDG with positron emission tomography (PET) imaging is a quantitative, reproducible approach for identifying acute and sub-acute metabolic variations in infarct regions. We found that imaging with ¹⁸F-FDG/PET enabled detection and quantification of ischemia-induced metabolic deficits and provided a sensitive and reliable means of assessing cerebral ischemic lesions compared with conventional neurological scoring systems in rodents.     

Time course of regional myocardial glucose metabolism after transient ischemia assessed by positron emission tomography]

The purpose of this study was to examine the significance of glucose metabolism in ischemic canine myocardium after reperfusion. Transient ischemia was induced by 90 or 180 minutes occlusion of the left anterior descending coronary artery. Twelve hours and 4 weeks after reperfusion, myocardial blood flow (MBF) and glucose metabolism were assessed (with H2(15)O and 18F-FDG, respectively) by positron emission tomography (PET) under the fasting state, and the metabolic findings were compared with the histologic examination. Glucose metabolism in ischemic regions was inversely related to the amount of tissue necrosis 12 hours and 4 weeks after reperfusion (r = -0.89 and r = -0.82, respectively). The perfusion-metabolism mismatch pattern was seen in the area with less than 10 percent necrosis 12 hours after reperfusion, but this pattern disappeared after 4 weeks. The area with 10 to 50 percent necrosis showed the mismatch pattern until 4 weeks after reperfusion, and in the area with more than 50 percent necrosis, perfusion-metabolism concordantly decreased. Thus, metabolic index assessed early after reperfusion by PET identified myocardial viability, and the perfusion-metabolism mismatch pattern sustained in relation to the degree of ischemic injury. Since some regions estimated to be irreversible by PET were viable by the histologic examination, PET study might underestimate the myocardial viability.     

Multisegment and halfscan reconstruction of 16-slice computed tomography for assessment of regional and global left ventricular myocardial function

RATIONALE AND OBJECTIVES: We sought to prospectively compare multisegment and halfscan reconstruction of 16-slice computed tomography (CT) for the assessment of regional and global left ventricular myocardial function with magnetic resonance imaging (MRI) as the reference standard. MATERIALS AND METHODS: Forty-two patients underwent CT with 16 x 0.5-mm detector collimation. Electrocardiogram-gated reconstructions were generated with multisegment reconstruction (using up to 4 segments correlated with the raw data of up to 4 heartbeats) and standard halfscan reconstruction. Steady-state free-precession cine MRI was acquired within 24 hours. RESULTS: More normal myocardial segments were identified correctly with multisegment (95%, 620/656) compared with halfscan reconstruction (88%, 582/656) of CT (P < 0.001). Also, the accuracy (92% [657/714] vs. 87% [620/714]) and rate of nondiagnostic segments (0% vs. 5% [33/714]) were significantly better when using multisegment reconstruction (P < 0.001). The image quality with multisegment reconstruction was significantly superior to that achieved with halfscan reconstruction (P < 0.001). In the assessment of global left ventricular function, multisegment and halfscan reconstruction of CT showed high correlations for all parameters with MRI, whereas Bland-Altman analysis revealed smaller limits of agreement for assessment of myocardial mass with multisegment reconstruction (P = 0.025), but no significant differences between both reconstruction techniques in the measurement of left ventricular volumes as compared with MRI. CONCLUSIONS: Multisegment reconstruction of 16-detector row CT improves image quality and assessment of regional wall motion compared with standard halfscan reconstruction.     

Simultaneous cardiac mechanics and phosphorus-31 NMR spectroscopy during global myocardial ischemia and reperfusion in the intact dog

To investigate the high-energy phosphate metabolic correlates of left ventricular (LV) dysfunction during the onset and recovery from severe, global myocardial ischemia in vivo, seven preinstrumented closed-chest dogs had ECG-gated phosphorus-31 (31P) NMR-spectroscopy (NMR-S) studies performed and LV micromanometer and sonomicrometer data measured before, during, and every 5 min following severe occlusive global myocardial ischemia. Ischemic LV + dP/dtmax fell from 2396 +/- 576 mm Hg/s at baseline to 2185 +/- 478 mm Hg/s (p less than 0.05) and did not normalize until after 30 min of reperfusion. LV ejection fraction (EF) decreased significantly (0.32 +/- 0.07 EF units to 0.12 +/- 0.13 EF units; p less than 0.05) and did not recover by 30 min of reperfusion (0.27 +/- 0.09 units; P less than 0.05 vs baseline). Simultaneous 31P NMR-S studies demonstrated excellent beta-ATP signal-to-noise (10 +/- 4:1). Myocardial acidosis occurred during global ischemia (delta pH = -0.22 +/- 0.23 units; p less than 0.05), with recovery at 30 min of reperfusion. Inorganic phosphate/phosphocreatine ratio (Pi/PCr) increased significantly during ischemia (0.46 +/- 0.07 to 0.61 +/- 0.07; P less than 0.05), with delayed normalization of this ratio at 30 min of reperfusion. beta-ATP peak area did not change during ischemia. Pi/PCr and LV contractility (+dP/dtmax) were significantly correlated at baseline (r = -0.70) and during global ischemia (r = -0.78; p less than 0.01), but not during recovery (r = 0.006; p = NS). Therefore, the simultaneous evaluation of high-fidelity hemodynamic data and topical 31P NMR-S can be performed in the intact state.     

Imaging of myocardial metabolism

There is compelling evidence that alterations in myocardial substrate use play a key role in a variety of normal and abnormal cardiac conditions such as aging, left ventricular hypertrophy, and diabetic heart disease. However, it is unclear whether the metabolic changes are adaptive or maladaptive. Development of transgenic models targeting key aspects of myocardial substrate use, such as uptake, oxidation, and storage, is accelerating our understanding of the metabolic perturbations of cardiac disease. However, whether the metabolic phenotype in these models is relevant to the human condition is frequently unknown. The importance of altered myocardial metabolism in the pathogenesis of cardiac disease is underscored by the current robust development of novel therapeutics that target myocardial substrate use. Currently, magnetic resonance spectroscopy, single photon emission computed tomography, and positron emission tomography are the 3 methods available to image myocardial substrate metabolism. In this review the role of metabolic imaging in the study of specific cardiac disease processes will be discussed. Both the current and future capabilities of metabolic imaging to furthering our understanding of cardiac disease are highlighted.     

Myocardial velocity gradient imaging by phase contrast MRI with application to regional function in myocardial ischemia

Velocity-encoded phase contrast magnetic resonance imaging (MRI) has the potential to quantify regional myocardial contractile function with a sensitivity to motion comparable to implanted ultrasonic crystals. An MRI sequence and post-processing algorithm were developed to measure myocardial velocity gradients on a 1.5 T MRI scanner. These methods were validated on a rotating phantom and applied to dogs before (n = 11) and during prolonged coronary occlusion (n = 5). In phantom validation studies, the average absolute error corresponded to motion equivalent to 0.03 ± 0.04 mm (mean ± SD) during the repetition time of the experiment. Rigid body corrections during post-processing significantly simplified the interpretation of myocardial velocity vectors. In vivo, rigid body motion contributes substantially to the recorded myocardial velocities in systole and diastole and can give the false impression of regional wall motion abnormalities. After rigid body correction, normal systolic and diastolic velocity vectors in short-axis views of the left ventricle were primarily directed toward the center of the left ventricle. Transmural radial strain rate was 2.0 ± 0.6 sec⁻¹ during systole and −3.6 ± 1.1 sec⁻¹ during early diastole in normal canine hearts. Ischemic myocardium was easily discriminated from normal left ventricle by velocity-encoded phase contrast MRI both qualitatively and quantitatively (P < 0.01 in systole and P < 0.05 in early diastole). Although the myocardial velocity images have a spatial resolution on the order of a millimeter, the velocity encoding describes the mechanical consequences of focal myocardial ischemia with sensitivity to submillimeter displacement of the pixels. The three-dimensional nature of velocity-encoded MRI is particularly well suited to the study of the complex motion of the heart in vivo. Magn Reson Med 42:98–109, 1999. © 1999 Wiley-Liss, Inc.     

Early detection of regional myocardial ischemia in ex vivo piglet hearts: MR imaging with magnetization transfer

The effects of regional myocardial ischemia and reperfusion on magnetization transfer (MT) contrast were investigated in an ex vivo perfused piglet heart model. The extent of the ischemic area was defined with perfusion magnetic resonance (MR) studies performed with use of extracellular contrast agents. Relative MT contrast was calculated for a total of 106 regions of interest in nine hearts. In the areas defined as being severely ischemic in the perfusion studies, a small but significant increase in the MT contrast of 18% ± 9 (standard deviation) (n = 35) was found as early as 10 minutes after the start of ischemia. This contrast difference was reduced to 11% ± 10 after 2 hours of total occlusion. The contrast between normal and ischemic tissue can be explained in part by the effect of inflowing blood, which leads to changes in both equilibrium magnetization and the apparent T1 of the perfused tissue. However, theoretical estimation suggests that these flow-related changes would produce a maximal relative change in MT contrast of approximately 4%. The most likely explanation for the rest of the observed changes is alteration in the distribution of cellular water related to the so-called intracellular edema that is known to be associated with the acute phase of myocardial ischemia.     

Imaging of acute cerebral ischemia.

Until recently, there was no efficacious treatment for acute cerebral ischemia. As a result, the role of neuroimaging and the radiologist was peripheral in the diagnosis and management of this disease. The demonstration of efficacy using thrombolysis has redefined this role, with the success of intervention becoming increasingly dependent on timely imaging and accurate interpretation. The potential benefits of intervention have only begun to be realized. In this State-of-the-Art review of imaging of acute stroke, the role of imaging in the current and future management of stroke is presented. The role of computed tomography is emphasized in that it is currently the most utilized technique, and its value has been demonstrated in prospective clinical trials. Magnetic resonance techniques are equally emphasized in that they have the potential to provide a single modality evaluation of tissue viability and vessel patency in an increasingly rapid evaluation.     

The fate of inorganic phosphate and pH in regional myocardial ischemia and infarction: a noninvasive 31P NMR study

To determine the characteristic appearance of phosphorus (31P) nuclear magnetic resonance spectra in acute and chronic myocardial infarction in situ, cardiac-gated depth-resolved surface coil spectroscopy (DRESS) at 1.5 T was used to monitor 31P NMR spectra from localized volumes in the left anterior canine myocardium for up to 5 days following permanent occlusion of the left anterior descending coronary artery. Coronary occlusion initially produced regional ischemia manifested as significant reductions in the phosphocreatine (PCr) to inorganic phosphate (Pi) ratios and intracellular pH (P less than 0.05, Student's t test) in endocardially displaced spectra acquired in periods as short as 50 to 150 s postocclusion. Spectra acquired subsequently revealed either (i) restoration of near-normal phosphate metabolism sometime between 10 and about 50 min postocclusion or (ii) advancing ischemic phosphate metabolism at about an hour postocclusion, and/or (iii) maintenance of depressed PCr/Pi ratios for up to 5 days postocclusion with a return of the apparent pH to near normal values between 6 and 15 h postocclusion. Postmortem examination of animals exhibiting the first type of behavior revealed the existence of coronary collateral vessels. The last type of behavior indicates that Pi remains substantially localized in damaged myocardium for days following infarction. The location and size of infarctions were determined postmortem by staining excised hearts. The smallest infarctions detected by 31P DRESS weighed 4.9 and 7.5 g. The most acidic pH measured in vivo was 5.9 +/- 0.2. Infarctions aged 1/2 day to 5 days were characterized by elevated but broad Pi resonances at 5.1 +/- 0.2 ppm relative to PCr and significantly depressed PCr/Pi ratios (P less than 0.002, Student's t test) relative to preocclusion values. Contamination of Pi resonances by phosphomonoester (PM) components is a significant problem for preocclusion Pi and pH measurements. These results should be applicable to the detection and identification of human myocardial infarction using 31P NMR and DRESS.     

Gated fluorine 18 fluorodeoxyglucose positron emission tomography: Determination of global and regional left ventricular function and myocardial tissue characterization

BACKGROUND: Our objectives were to investigate the accuracy of global and regional left ventricular (LV) function parameters determined from gated fluorine 18 deoxyglucose (FDG) positron emission tomography (PET) and to determine whether this approach complements viability imaging data for tissue characterization. Nongated FDG-PET is a clinical standard for viability imaging, but LV function is often determined with other techniques, which increases patient burden, expenditure, and co-registration errors. Better tissue characterization may be achieved if data were acquired with one test.Methods and results Forty-eight patients with LV dysfunction (including 35 with ejection fraction [EF] 相似文献   

眼球脉络膜血管瘤的影像学表现

目的：探讨眼球脉络膜血管瘤的CT、MRI表现及其诊断、鉴别诊断价值。方法：回顾性分析9例经病理（3例）和临床证实（6例）的脉络膜血管瘤。CT扫描6例，MR检查4例，9例均行B超检查，3例作了眼底荧光血管造影。结果：2例CT平扫示眼球后极球壁轻度或新月形增厚，与球壁呈等密度，5例（1例平扫＋增强）增强示眼球后极部高密度梭形或扁平状隆起均匀肿块，瘤体强化明显。与玻璃体比较3例MR T1WI呈高信号，T2WI呈低信号，与视神经、眼外肌相比呈等信号；1例较小肿瘤辅以增强T1WI脂肪抑制技术被清楚显示。渗出性视网膜脱离在T1WI、T2WI上均呈中、高信号；增强T1WI瘤体显著强化，边界清晰，且信号均匀。B超检查8例为实质不均质肿块占位，1例为均质肿块占位，9例均探及视网膜脱离光带。结论：CT＋MRI＋B超检查对脉络膜血管瘤可得到较为全面的影像学诊断资料，MRI在该病的诊断及鉴别诊断中较CT及B超更具敏感性和特异性。     

肠缺血的影像诊断和介入治疗

肠缺血（intestinal ischemia）属重症急腹症范畴，病死率可高达70％～90％。患者得不到早期诊断和有效治疗是导致死亡的主要原因。这就要求对本病有足够的警惕和认识，争取早期诊断、及时治疗，提高救治水平。对于肠缺血病变者，介入治疗是重要治疗手段之一，在未发生肠坏死前，应作为治疗肠系膜缺血症的首选方法。     

心安宁对大鼠心肌缺血模型的抗心肌缺血作用

目的:观察心安宁的抗心肌缺血作用,为其进一步开发利用提供实验依据.方法:健康大鼠40只随机分为5组,分别灌服蒸馏水(假手术组、模型组)、心安宁125、250 mg/kg(心安宁1组、心安宁2组)、硝苯地平10 mg/kg(硝苯地平组).连续3 d灌胃,末次给药后1 h,除假手术组外其余各组大鼠行、右冠状动脉前降支结扎术引起心肌缺血,记录心电图,测定并计算心肌梗死面积.结果:心安宁能明显抑制缺血性心电图ST段抬高,显著缩小心肌梗死范围.结论:心安宁对大鼠急性心肌缺血及梗死有较好的保护作用,为心安宁的进一步开发提供了实验依据.