RESUMEN
OBJECTIVE: This study compared quantitatively the efficacy of intravenous adenosine and dipyridamole for pharmacologic induction of myocardial hyperemia. BACKGROUND: Pharmacologic vasodilation is used increasingly for induction of myocardial hyperemia in conjunction with radionuclide imaging of myocardial blood flow. Although both intravenous dipyridamole and adenosine have been used, the magnitude of hyperemia induced by these agents and the hyperemia to baseline blood flow ratios have not been quantified and compared. METHODS: Twenty normal volunteers were studied with dynamic positron emission tomography (PET) and intravenous nitrogen-13 ammonia. Myocardial blood flow was quantified with a two-compartment tracer kinetic model. RESULTS: Myocardial blood flow at rest averaged 1.1 +/- 0.2 ml/min per g and increased significantly to 4.4 +/- 0.9 ml/min per g during adenosine and 4.3 +/- 1.3 ml/min per g after dipyridamole administration. Hyperemia to baseline flow ratios averaged 4.3 +/- 1.6 for adenosine and 4.0 +/- 1.3 for dipyridamole. The average flow ratios and the maximal flows achieved were similar for both agents, but there was considerable variation in the individual response to these agents, as indicated by the range of hyperemia to baseline flow ratios (from 2.0 to 8.4 for adenosine and from 1.5 to 5.8 for dipyridamole). In addition, the hyperemic responses to dipyridamole and to adenosine differed by greater than 1 ml/min per g in nine subjects. CONCLUSIONS: Despite these inter- and intraindividual differences, we conclude that both agents are equally effective in producing myocardial hyperemia.
Asunto(s)
Adenosina , Circulación Coronaria/efectos de los fármacos , Dipiridamol , Corazón/diagnóstico por imagen , Tomografía Computarizada de Emisión , Adulto , Prueba de Esfuerzo/métodos , Hemodinámica/efectos de los fármacos , Humanos , Procesamiento de Imagen Asistido por Computador , Masculino , Radioisótopos de NitrógenoRESUMEN
Reorientation of transaxial cardiac PET images into short-axis images has been shown by other investigators to improve visual identifiability of defects in myocardial tracer uptake. However, quantification of physiologic processes from such reoriented images may be complicated by errors introduced during the reorientation process. Therefore, a quantitative characterization of these errors is necessary. An annular phantom of human cardiac dimensions was imaged in a 15-plane positron emission tomograph at six angles (0 degrees, 5 degrees, 25 degrees, 45 degrees, 65 degrees, 85 degrees) and at two different axial sampling densities. In addition, two different reorientation interpolators were employed, one using three-dimensional linear interpolation and the other using a "hybrid" interpolation algorithm. Distortion of linear distances was variable but was minimized with denser axial sampling and the use of hybrid interpolation. Circumferential profile analysis, corrected for inhomogeneities in reoriented image spatial resolution, revealed a maximal loss of region of interest counts at 65 degrees of at least 14.4%. Reorientation errors were minimized by use of dense axial sampling, low angles of reorientation and use of the hybrid interpolation algorithm.
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Corazón/diagnóstico por imagen , Procesamiento de Imagen Asistido por Computador , Modelos Estructurales , Tomografía Computarizada de Emisión/métodos , Desoxiglucosa/análogos & derivados , Radioisótopos de Flúor , Fluorodesoxiglucosa F18 , HumanosRESUMEN
The utility of Patlak graphical analysis was investigated for quantification of regional myocardial blood flow (MBF) and for generating parametric images of MBF with 13N-ammonia and dynamic PET imaging in dogs and humans. MBF was estimated by a two-compartment model fit of the initial 2 min of the kinetic data and by Patlak graphical analysis of the initial 2, 3, or 4 min of data. In 11 dog studies, MBF by compartmental model fitting linearly correlated with MBF by microspheres (correlation coefficient (r) = 0.99, slope = 0.92) and by Patlak graphical analysis (r = 0.99, slope = 0.90). In 10 normal human studies, MBF obtained by the Patlak graphical analysis agreed well with MBF obtained by the compartmental model fitting (r = 0.96, slope = 1.04). Good agreement of the MBF estimates was also observed in 10 coronary artery disease patient studies (r = 0.96). Patlak graphical analysis permitted generation of parametric images of MBF. The parametric images of MBF, in units of ml/min/g, are of good image quality and have relatively low noise levels. We conclude that regional MBF can be noninvasively and conveniently measured with dynamic 13N-ammonia PET using either a two-compartment model or Patlak graphical analysis. MBF parametric images generated with the Patlak graphical analysis both map the distribution and quantitate the magnitude of myocardial perfusion abnormalities.
Asunto(s)
Amoníaco , Circulación Coronaria , Radioisótopos de Nitrógeno , Tomografía Computarizada de Emisión , Adulto , Anciano , Anciano de 80 o más Años , Animales , Perros , Femenino , Corazón/diagnóstico por imagen , Humanos , Masculino , Persona de Mediana EdadRESUMEN
Preserved glucose metabolism in ischemically injured, dysfunctional myocardial tissue as demonstrated on PET imaging predicts functional improvement after revascularization. To characterize more precisely the relationship between regional myocardial blood flow, viability and extent and severity of flow and metabolism abnormalities, we developed a PC-based semiquantitative analysis technique using 13N-ammonia and 18F-deoxyglucose polar map displays. A data base for mean values (m) and standard deviations (s.d.) for relative 13N activities reflecting regional myocardial blood flow, relative 18F activities normalized to normal flow regions reflecting regional glucose utilization and the difference of normalized 18F and 13N activities as an index of a flow-metabolism mismatch was established in 11 normals. Parametric polar maps were derived by comparing patient data to a normal range defined as greater than m - 2 s.d. for relative myocardial blood flow and less than m + 2 s.d. for both relative glucose utilization and the difference between normalized 18F and 13N activities. Semiquantitative indices of extent and severity of blood flow defects, of relative increases in glucose utilization and of flow-metabolism mismatch areas are generated for the entire myocardium and the three coronary territories. The approach promises to be clinically useful to confirm presence and absence of flow and metabolic abnormalities and to assess their extent as a potential predictor of functional outcome after therapy.
Asunto(s)
Circulación Coronaria , Glucosa/metabolismo , Corazón/diagnóstico por imagen , Interpretación de Imagen Asistida por Computador , Tomografía Computarizada de Emisión/métodos , Adulto , Anciano , Algoritmos , Amoníaco/metabolismo , Enfermedad Coronaria/diagnóstico por imagen , Enfermedad Coronaria/fisiopatología , Desoxiglucosa/metabolismo , Femenino , Radioisótopos de Flúor , Humanos , Masculino , Persona de Mediana Edad , Radioisótopos de Nitrógeno , Valores de Referencia , Función Ventricular IzquierdaRESUMEN
To determine if dynamic PET and 13N-ammonia can be utilized to quantitate regional hepatic arterial blood flow (rHABF) noninvasively, eight anesthetized dogs and eight human volunteers were examined with PET following intravenous bolus administration of 13N-ammonia. Hepatic time-activity curves and the arterial input function were derived from ROIs drawn over the right lateral superior segment of the liver and the left ventricle of the heart, respectively. rHABF was quantitated using a two-compartment model, with comparison with simultaneously acquired microsphere blood flow measurement (MS) in the canine studies. rHABF derived from canine dynamic PET with 13N-ammonia were linearly related to microsphere values (rHABF = 0.92 x MS + 0.04, r = 0.98), with a mean of 0.40 ml/min/g. The results in eight normal volunteers gave a rHABF value of 0.26 +/- 0.07 ml/min/g. Dynamic 13N-ammonia hepatic PET allows noninvasive quantification of rHABF.
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Amoníaco , Circulación Hepática , Tomografía Computarizada de Emisión , Adulto , Animales , Perros , Humanos , Masculino , Matemática , Modelos Biológicos , Radioisótopos de NitrógenoRESUMEN
UNLABELLED: PET permits the quantification of myocardial blood flow, but is hampered by the limited spatial resolution of PET images. METHODS: We evaluated two methods for the correction of resolution effects in PET perfusion 13NH3-ammonia images. In one model, the spillover and recovery coefficients are estimated in the kinetic modeling analysis. The new, second model uses an explicit delineation of the left ventricular wall and a convolution model for the system point spread function to compute the regional values of the spillover and recovery coefficients. RESULTS: The new method is validated with phantom measurements. The two methods are evaluated on animal experiments using 13NH3-ammonia. Both two- and three- compartment models were used to compute absolute flow values. Excellent linear correlations with microsphere data were obtained. The slope of the regression line was lower for corrections based on kinetic modeling as compared to convolution-based correction. In animal experiments, recovery coefficients of 59% for the myocardial wall and 86% for the blood pool were obtained. Spillover from the blood pool into the myocardial was was 14%. CONCLUSION: The new correction method strongly suppresses spillover and recovery effects due to limited resolution.
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Algoritmos , Amoníaco , Artefactos , Corazón/diagnóstico por imagen , Radioisótopos de Nitrógeno , Tomografía Computarizada de Emisión , Animales , Circulación Coronaria/fisiología , Perros , Femenino , Humanos , Modelos Lineales , Masculino , Modelos Cardiovasculares , Fantasmas de Imagen , Función Ventricular/fisiologíaRESUMEN
UNLABELLED: The purpose of this study was to apply and validate a previously developed model-based image analysis technique which derives estimates of regional myocardial wall thickness and the left ventricular radius directly from gated cardiac PET images. METHODS: In 11 normal volunteers, gated myocardial 18F-deoxyglucose (FDG) images with 16 equal gates spanning the entire cardiac cycle were acquired for 20 min. To improve count statistics and thus image quality, 3 and 5 of 16 gates were summed to obtain systolic and diastolic images. Based on a five-parameter model, radial profiles from systolic and diastolic PET images were fit by nonlinear regression for myocardial wall thickness, left ventricular radius and tracer activities in the blood pool, the myocardial tissue and the extracardiac background. Echocardiography and gated magnetic resonance imaging (MRI) were performed in 11 and 7 volunteers, respectively. RESULTS: We observed a significant (p < 0.001) correlation between measurements obtained by gated PET imaging and the correlative imaging modalities for myocardial wall thickness and left ventricular radius. While good agreement was observed between measurements of average radial shortening, estimates of average wall thickening differed significantly. CONCLUSION: This model-based analysis offers accurate estimates of regional recovery coefficients directly from gated cardiac PET images and may also prove useful for the assessment of myocardial contractile function. These recovery coefficients are essential for the correction of partial volume effects when quantitative PET studies are performed.
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Ecocardiografía , Electrocardiografía , Corazón/diagnóstico por imagen , Imagen por Resonancia Magnética , Tomografía Computarizada de Emisión , Desoxiglucosa/análogos & derivados , Radioisótopos de Flúor , Fluorodesoxiglucosa F18 , Corazón/anatomía & histología , Humanos , Contracción Miocárdica , Análisis de RegresiónRESUMEN
UNLABELLED: In this study, factor analysis of dynamic structures (FADS) was used to extract the "pure" blood-pool time-activity curves (TACs) and to generate parametric myocardial blood flow (MBF) images (pixel unit: ml/min/g). METHODS: Ten dynamic 13N-ammonia dog PET studies (three baseline, five hyperemia and two occlusion) were included. Three factors (TACs) and their corresponding factor images (the right ventricular and left ventricular blood pools and myocardial activities) were extracted from each study. The left ventricular factors matched well with the plasma TACs. The factor images of myocardium were then converted to a parametric images of MBF using a relationship derived from a two-compartment model. RESULTS: MBF estimates obtained from FADS correlated well with MBF estimates obtained with the two-compartment model (r = 0.98, slope = 0.84) and microsphere techniques (r = 0.96, slope = 0.94). FADS-generated MBF parametric images have better image quality and lower noise levels compared to those generated with Patlak graphical analysis. CONCLUSION: Regional MBF can be measured accurately and noninvasively with 13N-ammonia dynamic PET imaging and FADS. The method is simple, accurate and produces parametric images of MBF without requiring blood sampling and spillover correction.
Asunto(s)
Amoníaco , Circulación Coronaria/fisiología , Corazón/diagnóstico por imagen , Radioisótopos de Nitrógeno , Tomografía Computarizada de Emisión/métodos , Animales , Perros , Análisis Factorial , Procesamiento de Imagen Asistido por Computador , MicroesferasRESUMEN
The aims of this study were: (1) to measure noninvasively and near simultaneously myocardial blood flow, oxygen consumption, and contractile function and (2) to analyze myocardial energy expenditure and efficiency at rest and during dobutamine stress in normal humans. Dynamic and gated carbon-11 acetate positron emission tomography (PET) imaging was performed in 11 normal subjects. The initial uptake of (11)C-acetate was measured to estimate myocardial blood flow. Oxygen consumption was derived from the monoexponential slope of the (11)C-clearance curve recorded during myocardial washout. ECG-gated systolic and diastolic images were acquired during the peak myocardial (11)C activity to measure left ventricular radius, myocardial wall thickness, and long axis length. Myocardial oxygen consumption and parameters of cardiac geometry were used to determine myocardial energetics and cardiac efficiency by tension-area area analysis. Myocardial blood flow averaged 0. 8+/-0.06 ml min(-1) g(-1) at rest and 1.48+/-0.15 ml min(-1) g(-1) during dobutamine stress. Oxygen delivery and consumption were 151+/-13 and 88+/-15 microl O(2) min(-1) g(-1) at rest and increased to 291+/-31 and 216+/-31 microl O(2) min(-1) g(-1), respectively, during pharmacological stress (P<0.001). Oxygen extraction increased from 59%+/-8% at rest to 76%+/-9% during stress (P<0.001). Mechanical efficiency was 29%+/-6% at rest and 32%+/-6% during dobutamine stress (P=NS) while external work efficiency was 16%+/-6% at rest and increased to 21%+/-4% (P<0.01) during dobutamine stress. Stepwise linear regression analysis identified rate-pressure product and external cardiac work as major correlates of oxygen consumption. In summary, rapid dynamic and gated PET (11)C acetate imaging provides the unique capability to study noninvasively determinants of myocardial energy delivery, expenditure, and efficiency.
Asunto(s)
Corazón/diagnóstico por imagen , Miocardio/metabolismo , Tomografía Computarizada de Emisión , Acetatos , Adulto , Radioisótopos de Carbono , Cardiotónicos , Circulación Coronaria/fisiología , Dobutamina , Electrocardiografía , Metabolismo Energético , Femenino , Corazón/fisiología , Humanos , Procesamiento de Imagen Asistido por Computador , Masculino , Contracción Miocárdica/fisiología , Consumo de Oxígeno/fisiología , Función Ventricular Izquierda/fisiologíaRESUMEN
BACKGROUND: Regional myocardial blood flow has been quantified using transaxial positron emission tomographic (PET) imaging and tracer kinetic modeling. However, the use of transaxial images limits the accuracy of regional partial volume corrections and the localization of the quantified regional flow values. The purpose of the present study was to overcome both problems by calculating regional flows from reoriented short-axis PET images. METHODS AND RESULTS: Twelve experiments were performed in four dogs. 13N-ammonia was injected intravenously while microspheres were administered into the left atrium during baseline, hyperemic, and low-flow conditions. Serial transaxial frames were acquired with a 15-plane PET scanner and reoriented into short-axis frames. The arterial input function and eight regional myocardial tissue activity curves were derived from the reoriented frames. The arterial input functions were corrected for ammonia metabolites, and the myocardial tissue curves were corrected for spillover of activity, partial volume effects, and heterogeneities in the image's spatial resolution introduced during reorientation. Corrections for regional partial volume were based on estimates of the regional myocardial activity thickness derived from reoriented diastolic images of the heart. The myocardial 13N-ammonia kinetics were described with a two-pool compartmental model. Values of regional myocardial blood flow by PET correlated linearly with those by microspheres (slope, 0.94; y intercept, 0.06 ml/min/g; r = 0.93) over a wide range of flows. CONCLUSIONS: Regional myocardial blood flow can be measured accurately and noninvasively from serially acquired and reoriented short-axis 13N-ammonia images, thus overcoming limitations inherent to the use of transaxially acquired images and permitting a more complete evaluation of regional blood flows throughout the left ventricular myocardium.