MR measurement of coronary blood flow.

The functional significance of coronary arterial stenosis can be evaluated by measuring the pharmacological flow reserve. Magnetic resonance (MR) imaging has a unique potential for noninvasive measurement of coronary blood flow and flow reserve in the native coronary artery and bypass graft. Restenosis after coronary balloon angioplasty and stenting in the left anterior descending artery can be detected noninvasively with serial MR measurements of the coronary flow reserve. Further refinement of the MR pulse sequences to improve spatial and temporal resolutions may permit accurate quantification of blood flow volume and flow reserve in all major coronary arterial branches. MR assessments of blood flow volume and flow pattern allow noninvasive detection of significant stenosis in the coronary artery bypass graft as well. By integrating MR blood flow measurement in the coronary sinus and cine MR assessment of left ventricular myocardial mass, altered myocardial micro-circulation in patients with diffuse myocardial diseases, such as hypertrophic cardiomyopathy and cardiac transplant, has been documented. J. Magn. Reson. Imaging 1999;10:728-733.     

PET心肌灌注显像测定心肌血流量及冠状动脉血流储备的研究进展

PET心肌灌注显像可绝对定量测定局部心肌血流量(MBF)和冠状动脉血流储备(CFR).由于显像剂半衰期短,允许在短时间内重复进行PET心肌灌注显像,获得静息态、冷加压试验和药物负荷试验等不同状态下的MBF,进而评价冠状动脉血管内皮依赖性和非依赖性的CFR功能.在早期诊断冠心病,准确诊断冠状动脉多支病变,评价微血管病变,早期检测冠状动脉内皮细胞功能异常及CFR功能的异常,估测预后,帮助临床治疗方案的制定以及检测疗效等方面,PET心肌灌注显像有重要的临床价值.该文将介绍PET心肌灌注显像相关知识及其在心血管领域的主要应用.     

Coronary vasodilator reserve and Framingham risk scores in subjects at risk for coronary artery disease

Background  The relationship between coronary vasodilator reserve and risk of coronary heart disease (CHD) in subjects without coronary artery disease (CAD) is not well known. Methods and Results  We studied 289 subjects (mean age, 58 ± 10 years) without overt CAD and at low (<10%) to intermediate risk (10%–20%) for CHD based on Framingham risk scores (RAMPART [Relative and Absolute Myocardial Perfusion changes as measured by Positron Emission Tomography to Assess the Effects of ACAT Inhibition: A Double-Blind, Randomized, Controlled, Multicenter Trial]). Coronary flow reserve (CFR) and coronary vascular resistance (CVR) were calculated from rest and adenosine nitrogen 13 ammonia positron emission tomography studies. Framingham-estimated CHD risk was used to as a surrogate for outcomes. Compared with subjects with low-risk scores (n = 150), those with intermediate-risk scores (n = 139) had a higher minimal CVR (49.3 ± 17.41 mm Hg · mL^-1 · min^-1 · g^-1 vs 52.4 ± 16.4 mm Hg · mL^-1 · min^-1 · g^-1, P = .05) and lower CFR (2.8 ± 1.0 vs 2.5 ± 0.8, P = .02). CFR was inversely related to CHD risk (R=-0.2, P = .006), and CVR was directly related to CHD risk (R = 0.2, P < .001). The mean CFR was significantly lower in patients in the first quartile of CHD risk compared with those in the fourth quartile (2.3 ± 0.7 vs 2.8 ± 1.0, P = .02), and the minimal CVR was significantly higher (44 ± 15 mm Hg · mL^-1 · min^-1 · g^-1 vs 53 ± 14 mm Hg · mL^-1 · min^-1 · g^-1, P < .05). Conclusions  In subjects without clinical CAD and at low to intermediate risk, CFR assessed by positron emission tomography is inversely related to estimated 10-year CHD risk.     

Significant regional heterogeneity of coronary flow reserve in paediatric hypertrophic cardiomyopathy

Previous studies have indicated that cardiac events in young patients with hypertrophic cardiomyopathy (HCM) are related to ischaemia rather than to arrhythmia. We measured coronary flow reserve in paediatric HCM and compared the values with those in adult HCM. We studied 12 patients with HCM including six paediatric (<20 years old; mean 13 years) and six adult patients (>20 years old: mean 62 years), and six healthy young adults (mean 29 years) as controls. Every patient underwent magnetic resonance imaging (MRI) for anatomical assessment. Myocardial blood flow at rest and after dipyridamole infusion was measured with dynamic nitrogen-13 ammonia positron emission tomography (PET). Partial volume effect was corrected for using the anatomical data obtained with MRI. In adult patients with HCM, coronary flow reserve in the hypertrophied septal region was not significantly different from that in the non-hypertrophied lateral wall (1.38+/-0.29 vs 1.77+/-0.39, respectively). In the paediatric patients, coronary flow reserve in the hypertrophied septal region was significantly lower than in the non-hypertrophied lateral wall (0.84+/-0.33 vs 2.74+/-0.90, respectively, P<0.01). In addition, coronary flow reserve in adult patients was lower than in control subjects both in the septal wall (1.38+/-0.29 vs 2.94+/-0.35, respectively, P<0.0001) and in the lateral wall (1.77+/-0.39 vs 2.85+/-0.69, respectively, P<0.05). In contrast, coronary flow reserve in paediatric patients was not significantly different from that in control subjects in the lateral wall (2.74+/-0.90 vs 2.85+/-0.69, respectively), while absolute reduction of myocardial blood flow was noted after pharmacological vasodilatation in the hypertrophied septal region. In conclusion, significant regional differences of coronary flow reserve were present in the paediatric patients with HCM. These results suggest that paediatric patients with HCM intrinsically have the potential to experience significant regional ischaemia even in the absence of coronary stenosis.     

Significant regional heterogeneity of coronary flow reserve in paediatric hypertrophic cardiomyopathy

Previous studies have indicated that cardiac events in young patients with hypertrophic cardiomyopathy (HCM) are related to ischaemia rather than to arrhythmia. We measured coronary flow reserve in paediatric HCM and compared the values with those in adult HCM. We studied 12 patients with HCM including six paediatric (<20 years old; mean 13 years) and six adult patients (>20 years old: mean 62 years), and six healthy young adults (mean 29 years) as controls. Every patient underwent magnetic resonance imaging (MRI) for anatomical assessment. Myocardial blood flow at rest and after dipyridamole infusion was measured with dynamic nitrogen-13 ammonia positron emission tomography (PET). Partial volume effect was corrected for using the anatomical data obtained with MRI. In adult patients with HCM, coronary flow reserve in the hypertrophied septal region was not significantly different from that in the non-hypertrophied lateral wall (1.38ǂ.29 vs 1.77ǂ.39, respectively). In the paediatric patients, coronary flow reserve in the hypertrophied septal region was significantly lower than in the non-hypertrophied lateral wall (0.84ǂ.33 vs 2.74ǂ.90, respectively, P<0.01). In addition, coronary flow reserve in adult patients was lower than in control subjects both in the septal wall (1.38ǂ.29 vs 2.94ǂ.35, respectively, P<0.0001) and in the lateral wall (1.77ǂ.39 vs 2.85ǂ.69, respectively, P<0.05). In contrast, coronary flow reserve in paediatric patients was not significantly different from that in control subjects in the lateral wall (2.74ǂ.90 vs 2.85ǂ.69, respectively), while absolute reduction of myocardial blood flow was noted after pharmacological vasodilatation in the hypertrophied septal region. In conclusion, significant regional differences of coronary flow reserve were present in the paediatric patients with HCM. These results suggest that paediatric patients with HCM intrinsically have the potential to experience significant regional ischaemia even in the absence of coronary stenosis.     

Portal blood flow: measurement with MR imaging

Portal blood flow was measured by means of direct bolus imaging (DBI), a method of measuring flow velocity with magnetic resonance imaging. DBI allows immediate visualization of fluid movement, thereby enabling calculation of a flow velocity from fluid displacement. In a study of 14 healthy male volunteers, portal blood flow was measured with electrocardiographic gating during the 18 seconds subjects could suspend respiration. These measurements showed a close correlation (r = .968) with those obtained by means of Doppler ultrasound (US). Increases in portal blood flow after oral administration of ethanol and glucose were measured with DBI. Glucose caused a statistically greater increase in portal blood flow volume in healthy control subjects than in patients with chronic hepatitis. Blood sugar, on the other hand, showed a significantly greater increase in these patients, possibly reflecting the greater vascular resistance of the liver. DBI is a useful noninvasive method of measuring portal blood flow without the limitations imposed on Doppler US by obesity and intestinal gas.     

Reversible impairment of coronary flow reserve in takotsubo cardiomyopathy: A myocardial PET study

Background. The precise etiology of takotsubo cardiomyopathy remains unclear. The study of myocardial blood flow (MBF) and coronary flow reserve (CFR) by use of positron emission tomography might help in understanding this syndrome. Methods and Results. Three postmenopausal women underwent adenosine/rest perfusion with nitrogen 13 ammonia and metabolism with fluorine 18 fluorodeoxyglucose positron emission tomography, coronary angiography, cardiac magnetic resonance, and echocardiography in the acute phase of takotsubo cardiomyopathy and at 3 months’ follow-up, after normalization of left ventricular function. PET study was performed in 2 parts: the perfusion analysis with nitrogen ammonia and the metabolism of the heart using FDG. MBF and CFR were analyzed quantitatively in the acute phase and at follow-up. The images highlighted the impairment of tissue metabolism in the dysfunctioning left ventricular segments in the acute phase, mainly in the apical segments and progressively less in the medium segments. At the same time, a clear inverse metabolic/perfusion mismatch emerged, which normalized 3 months later. The quantitative analysis of MBF showed a reduction in the acute phase in apical segments in comparison to basal segments without differences between midventricular and basal segments. In the acute phase CFR proved to be reduced in apical versus basal segments. CFR impairment of apical segments recovered completely after 3 months. Conclusion. The acute phase of takotsubo cardiomyopathy is characterized by an inverse perfusion/metabolism mismatch with a reduction in CFR in the apical segments. However, the impairment of CFR and the reduction of metabolism in the apical segments recovered completely after 3 months.     

Splenic artery and superior mesenteric artery blood flow: nonsurgical Doppler US measurement in healthy subjects and patients with chronic liver disease

The accuracy of the duplex Doppler ultrasound system in the measurement of blood flow in the splenic artery and the superior mesenteric artery was evaluated in seven anesthetized dogs by comparing blood flow recordings obtained simultaneously with the electromagnetic flowmeter, with those obtained with the combination of B-mode and M-mode scanning. Various flow rates were produced by the infusion of dopamine. Splenic artery blood flow and superior mesenteric artery blood flow measured with the duplex system exhibited significant correlations with corresponding values obtained with electromagnetic flow measurements (r = .93 and r = .93, respectively). Changes in splanchnic circulation with the progression of chronic liver disease in humans were then investigated with the use of the duplex system. Splenic artery blood flow and superior mesenteric artery blood flow were significantly increased in patients with cirrhosis compared with patients with chronic hepatitis and healthy subjects. These results indicate that a hyperdynamic circulatory state may develop in the splanchnic circulation of the intestine and spleen in cirrhotic patients.     

Carotid and vertebral artery blood flow in left- and right-handed healthy subjects measured with MR velocity mapping

The goal of the study was to establish normal carotid artery flow rates in left-handed and right-handed individuals as a standard against which patients with carotid artery disease could be compared. Antegrade and retrograde flow were measured in the ascending aorta, in the right and left common, internal, and external carotid arteries, and in the vertebral arteries of 12 healthy subjects. Five subjects were right-handed, five left-handed, and two ambidextrous. Measured flow rates were as follows: common carotid arteries, 360–557 mL/min (mean [± standard deviation], 465 mL/min ± 52); internal carotid arteries, 132–367 mL/min (mean, 265 mL/min ± 60); external carotid arteries, 113–309 mL/min (mean, 186 mL/min ± 51); vertebral arteries from 133–308 mL/min (mean, 244 mL/min ± 43); and cerebral circulation, 546–931 mL/min (mean, 774 mL/min ± 134). All right-handed subjects had higher flow rates in the left internal carotid artery than in the right, and all left-handed subjects had higher flow rates in the right internal carotid artery (P =.007). There were no significant differences in left and right common carotid artery flow rates between left- and right-handed subjects. The standard deviation of a single measurement was 5%. The flow rates were similar to those obtained previously with other techniques and could be used as a normal standard.     

Contrast-enhanced cardiac MR imaging in the detection of reduced coronary flow velocity reserve

PURPOSE: To prospectively evaluate the accuracy of contrast material-enhanced cardiac magnetic resonance (MR) imaging for determining impaired coronary flow velocity reserve (CFR) by using Doppler flow measurement as the reference standard. MATERIALS AND METHODS: The study was approved by the institutional ethics committee, and all patients gave written informed consent. Eligible patients underwent contrast-enhanced cardiac MR imaging and invasive measurement of CFR. For contrast-enhanced MR imaging, a three-section single-shot saturation recovery gradient-recalled echo sequence with steady-state free precession was used. Sections were divided into six segments. For each segment, a transmural and subendocardial myocardial perfusion reserve index (MPRI) was calculated by using the upslope of the signal intensity-time curve during the first pass of contrast material at rest and during adenosine infusion (140 microg per kilogram body weight per minute). MPRIs of vascular regions were compared with the corresponding CFR. Receiver operating characteristic (ROC) analysis was performed to find the number of segments needed for best diagnostic accuracy of MPRI and to find a cutoff value for MPRI in the detection of a reduced CFR. RESULTS: Thirty-five patients were evaluated (male-to-female ratio, 27:8; mean age +/- standard deviation, 63.5 years +/- 8.2; mean body mass index, 28.8 kg/m(2) +/- 3.8), and 43 vascular regions were analyzed. A linear correlation was found between the MPRI and CFR (r = 0.44, P < .05). The MPRI was significantly lower in vascular regions with a CFR of less than 2.00 than in regions with a CFR of 2.00 or greater (P < .05). Detection of a CFR of less than 2.00 was more accurate with subendocardial MPRI measurements than with transmural measurements. The mean subendocardial MPRI of the segments with the three lowest MPRIs of a vascular region showed the best diagnostic performance in the detection of a CFR of less than 2.00 (area under the ROC curve, 0.85; sensitivity, 84%; specificity, 75%) by using a cutoff value of 1.21. CONCLUSION: The diagnostic accuracy of subendocardial perfusion analysis in contrast-enhanced cardiac MR imaging is higher than that of transmural analysis.     

Gated MR imaging of the heart: intracardiac signals in patients and healthy subjects

The appearance of intraluminal signal in the cardiac chambers, the descending aorta, and blood vessels was studied in healthy subjects and patients with myocardial disease on first and second spin-echo gated magnetic resonance images. Signal was present in the cardiac chambers and the aorta at various phases of the cardiac cycle when physiological or pathological slow flow conditions are expected in healthy subjects and in patients. Healthy individuals tended to show signal in the ventricles and aorta during end-diastole, and signal was less likely to be present at higher heart rates and in systolic images. In patients with regional or global left ventricular dysfunction, intraventricular signal tended to persist into systole. Surprisingly, intraventricular signal was not present with increased frequency adjacent to infarcted regions of the myocardial wall. Thus, the mere presence of intracavitary signal cannot be used as an indicator of either regional or global cardiac contraction abnormalities. In the left atrium, signal was often present during systole. Physical factors determining the appearance of signal of flowing blood are discussed in an Appendix.     

心肌桥患者冠状动脉血流储备研究

目的　评估心肌桥对冠状动脉 (冠脉 )血流储备的作用。方法　 2 0 0 0年 9月至 2 0 0 3年 1月 ,13例冠脉造影显示心肌桥患者即刻测定冠脉血流储备 ,与同期 32例冠脉造影正常对照者比较。结果　两组患者一般情况无差异。 13例心肌桥患者临床均有稳定型心绞痛 ;心肌桥均位于左前降支 (中段 11例 ,中远段 2例 ) ,收缩期及舒张期冠脉狭窄分别为 78%± 7%和 15 %± 5 % ,血流储备较对照组显著降低 (2 .0± 0 .3和 3.3± 0 .6 ,P <0 .0 0 1)。结论　心肌桥使冠脉血流储备降低 ,这可能是患者发生心绞痛的原因     

MR imaging of the cochlear modiolus: area measurement in healthy subjects and in patients with a large endolymphatic duct and sac

PURPOSE: To evaluate the cochlear modiolus with thin-section magnetic resonance (MR) imaging in healthy subjects and patients with a large endolymphatic duct and sac, and to assess whether the cochlea is normal or abnormal in patients with a large endolymphatic duct and sac. MATERIALS AND METHODS: MR images were obtained in 10 ears in five volunteers (group 1), 40 ears in 20 patients with bilateral sensory hearing loss (group 2), three ears in two patients with Mondini malformation (group 3), and 12 ears in seven patients with a large endolymphatic duct and sac (group 4). RESULTS: In groups 1 and 2, all modiolar areas were larger than 4.0 mm2. In group 3, each modiolus was smaller than 2.0 mm2. In group 4, modiolar areas were smaller than 2.0 mm2 in eight ears and were larger than 4.0 mm2 in four ears. CONCLUSION: Findings in this study confirm that a large endolymphatic duct and sac is frequently associated with modiolar deficiency, but the modiolar area is normal in some cases. This result does not support the recently proposed hypothesis that hearing loss with a large endolymphatic duct and sac is caused by the transmission of subarachnoid pressure forces into the labyrinth through a deficient modiolus.     

Higher skeletal muscular metabolic reserve capacity in COPD patients than healthy subjects

We investigated the interaction between skeletal muscle exercise capacity and central restrictions using exercise modalities, which recruit differing levels of muscle mass in eight patients chronic obstructive lung disease (COPD) (FEV₁% of predicted; 35 [SE 4%]) and eight healthy controls. Subjects performed conventional bicycling, two‐leg knee extensor (2‐KE) and single‐leg knee extensor (1‐KE) exercises. Maximal values for pulmonary V?O₂ (VO_2max), power output, blood lactate, heart rate, blood pressure, and arterial oxygen saturation of hemoglobin were registered. VO_2max in controls was 2453 (210), 1468 (124), and 976 (76) mL/min during bicycling, 2‐KE and 1‐KE, respectively. The COPD patients achieved 48% (P<0.05), 62% (P<0.05), and 81% (P=0.10) of the control values. The mass‐specific VO_2max (VO_2max/exercising muscle mass) during 1‐KE was 345 (25) and 263 (30) mL/kg/min (P<0.05) in controls and COPD patients, respectively. During 2‐KE the controls and COPD patients achieved 85% (4%) and 67% (5%) (P=0.06) of the mass‐specific V?O₂ during 1‐KE, while during bicycling they achieved 31% (2%) and 17% (1%) (P<0.05), respectively. The COPD patients have central restrictions when exercising with a relatively small muscle mass (2‐KE) and have a higher muscular metabolic reserve capacity than controls during whole body exercise.     

MR measurement of blood flow in the cardiovascular system.

Methods for measurement of blood flow with MR were devised many years ago but have been used for diagnosis in only the past few years. The two methods of measurement that have been used most extensively are based on the principles of time of flight and phase shift. A number of factors can influence the accuracy of MR measurements of blood flow. In vitro studies using flow phantoms have verified the accuracy of the phase-shift technique for measuring flow velocities exceeding 5 m/sec, which for practical purposes, encompasses the peak flow encountered in cardiovascular disorders. The flow measurements have been used to quantify valvular heart disease, congenital heart disease, pulmonary arterial disease, thoracic aortic disease, and peripheral vascular disease.     

Renal arterial blood flow measurement by breath‐held MRI: Accuracy in phantom scans and reproducibility in healthy subjects

This study evaluates reliability of current technology for measurement of renal arterial blood flow by breath‐held velocity‐encoded MRI. Overall accuracy was determined by comparing MRI measurements with known flow in controlled‐flow‐loop phantom studies. Measurements using prospective and retrospective gating methods were compared in phantom studies with pulsatile flow, not revealing significant differences. Phantom study results showed good accuracy, with deviations from true flow consistently below 13% for vessel diameters 3mm and above. Reproducibility in human subjects was evaluated by repeated studies in six healthy control subjects, comparing immediate repetition of the scan, repetition of the scan plane scouting, and week‐to‐week variation in repeated studies. The standard deviation in the 4‐week protocol of repeated in vivo measurements of single‐kidney renal flow in normal subjects was 59.7 mL/min, corresponding with an average coefficient of variation of 10.55%. Comparison of renal arterial blood flow reproducibility with and without gadolinium contrast showed no significant differences in mean or standard deviation. A breakdown among error components showed corresponding marginal standard deviations (coefficients of variation) 23.8 mL/min (4.21%) for immediate repetition of the breath‐held flow scan, 39.13 mL/min (6.90%) for repeated plane scouting, and 40.76 mL/min (7.20%) for weekly fluctuations in renal blood flow. Magn Reson Med 63:940–950, 2010. © 2010 Wiley‐Liss, Inc.