Showing papers on "Perfusion scanning published in 1994"

Prognosis of patients with left ventricular dysfunction, with and without viable myocardium after myocardial infarction. Relative efficacy of medical therapy and revascularization.

Abstract: BACKGROUNDThe uptake of F-18 deoxyglucose into dysfunction segments after myocardial infarction identifies metabolically active (FDG+) or inactive (FDG-) myocardium Although patients with FDG+ segments have been found to be at risk for adverse events, the prognostic significance of viable myocardium in relation to other influences on postinfarction prognosis, including revascularization, remain ill defined The purpose of this study was to investigate the relative prognostic significance of FDG+ tissue and to establish whether myocardial revascularization in patients with viable tissue attenuates the risk of adverse outcomeMETHODS AND RESULTSOne hundred thirty-seven patients with left ventricular dysfunction and resting perfusion defects after myocardial infarction underwent positron emission tomography with both dipyridamole stress Rb-82 perfusion imaging and FDG imaging After the exclusion of 4 patients proceeding to transplantation, 2 with uninterpretable scans and 2 lost to follow-up, 129 patients

Tissue specific perfusion imaging using arterial spin labeling.

Abstract: Quantitative magnetic resonance measurements of regional tissue perfusion can be obtained using magnetically labeled arterial water as a diffusable tracer. Continuous labeling is achieved in flowing spins using adiabatic inversion. The effects of continuous labeling of proximal arterial spins and T1 relaxation in distal tissue magnetization result in a steady-state change in tissue magnetization which is tissue specific, i.e., it can be quantified in units of blood flow per gram of tissue per unit time. This magnetization is sampled using standard imaging sequences. The theoretical basis for this method, including the effects of macromolecular spin saturation, is reviewed. Recent results demonstrating the successful implementation of this technique in vitro and in vivo in rat brain, heart, and kidney, and in human brain and kidney are presented, as well as the use of a separate RF coil for arterial labeling to produce selective perfusion images in rat brain. This approach allows quantitative perfusion images to be obtained completely non-invasively at the resolution of 1H MRI, and is useful in the clinical and investigational evaluation of organ physiology.

Correlation of pharmacological 99mTc-sestamibi myocardial perfusion imaging with poststenotic coronary flow reserve in patients with angiographically intermediate coronary artery stenoses.

Abstract: BACKGROUND The physiological assessment of angiographically intermediate-severity stenoses remains problematic. Functional measurements of poststenotic intracoronary Doppler coronary flow reserve can be performed in humans but have not been correlated with hyperemic myocardial perfusion imaging or angiographic data in this patient population. METHODS AND RESULTS Thirty-three patients undergoing diagnostic quantitative coronary angiography (QCA) for assessment of intermediate-severity coronary artery disease (mean QCA percent diameter stenosis, 56 +/- 14%) were studied. Proximal and distal poststenotic Doppler coronary flow velocities were measured (left anterior descending coronary artery, 16; right coronary artery, 10; left circumflex artery, 7 patients) before and during peak maximal hyperemia with intracoronary adenosine (8 to 12 micrograms). Intravenous pharmacological stress (adenosine, 20 patients; dipyridamole, 13 patients) 99mTc-sestamibi tomographic perfusion imaging was performed within 1 week of coronary flow-velocity studies. kappa statistics were calculated to measure the strength of correlation among coronary flow velocities, perfusion imaging data, and QCA results. QCA stenosis severity (abnormal, > or = 50% diameter stenosis) and poststenotic Doppler coronary flow reserve (ratio of abnormal distal hyperemic to basal flow, < or = 2.0) were correctly correlated in 20 of 27 patients (74%; kappa = .48). QCA stenosis severity and 99mTc-sestamibi imaging (abnormal if one or more reversible myocardial segments were present in the poststenotic zone) were correlated in 28 of 33 patients (85%; kappa = .63). 99mTc-sestamibi imaging results agreed with the basal (nonhyperemic) proximal-to-distal velocity ratio (normal, < 1.7) in 15 of 31 patients (48%; kappa = .17). The strongest correlation occurred between hyperemic distal flow-velocity ratio measurements and 99mTc-sestamibi perfusion imaging results in 24 of 27 patients (89%; kappa = .78). All 14 patients with abnormal distal hyperemic flow-velocity values had corresponding reversible 99mTc-sestamibi tomographic defects. More reversibly hypoperfused segments were present in patients with abnormal poststenotic hyperemic flow-velocity ratios (abnormal, 2.4 +/- 0.7 segments; normal, 0.6 +/- 1.0 segments; P < .05). The number of poststenotic myocardial 99mTc-sestamibi perfusion defects was correlated with the QCA percent cross-sectional area reduction (P < .02) and with minimal luminal diameter (P < .05) of intermediate-severity coronary artery stenoses. CONCLUSIONS Two technologically diverse functional measures of stenosis severity--Doppler-derived poststenotic hyperemic intracoronary flow reserve and vasodilator stress 99mTc-sestamibi myocardial perfusion imaging--are highly (89%) correlated. The physiological assessment of coronary stenoses of angiographically intermediate severity may be improved by the use of these techniques.

Quantitative magnetic resonance imaging of human brain perfusion at 1.5 T using steady-state inversion of arterial water

Abstract: We report our experience using a noninvasive magnetic resonance technique for quantitative imaging of human brain perfusion at 1.5 T. This technique uses magnetically inverted arterial water as a freely diffusible blood flow tracer. A perfusion image is calculated from magnetic resonance images acquired with and without arterial blood inversion and from an image of the apparent spin-lattice relaxation time. Single-slice perfusion maps were obtained from nine volunteers with approximately 1 x 2 x 5-mm resolution in an acquisition time of 15 min. Analysis yielded average perfusion rates of 93 +/- 16 ml.100 g-1.min-1 for gray matter, 38 +/- 10 ml.100 g-1.min-1 for white matter, and 52 +/- 8 ml.100 g-1.min-1 for whole brain. Significant changes in perfusion were observed during hyperventilation and breath holding. This technique may be used for quantitative measurement of perfusion in human brain without the risks and expense of methods which use exogenous tracers.

Relationship between brain blood flow and carotid arterial flow in the sheep fetus.

Abstract: The present study investigates whether changes in total brain blood flow can be reliably estimated by changes in carotid arterial blood flow in fetal and perinatal lambs. We therefore compared carotid arterial blood flow, measured with implanted transit-time ultrasound transducers, with brain blood flow, measured by radioactive microspheres in fetal lambs during normal oxygenation and during pulmonary ventilation with oxygen, with Po: ranging from levels normal for the healthy fetus to levels normally seen postnatally. Cerebral perfusion pressure was modified over a wide range to alter brain blood flow: it was decreased by balloon occlusion of the brachiocephalic trunk and increased by a balloon occluder around the aortic isthmus. Carotid arterial blood flow and brain blood flow were closely related (r = 0.97, p < 0.0001). The relationship was not altered at different levels of oxygenation. However, measurements during higher cerebral perfusion pressures, obtained during aortic isthmus occlusion, had a negative influence on the agreement between carotid arterial blood flow and brain blood flow. When excluding values obtained by aortic isthmus occlusion, changes of 20% or more in brain blood flow could be predicted with carotid arterial blood flow within a confidence limit of 95%. Blood flow measurements in the carotid artery may be useful to estimate changes in brain perfusion.

Concepts of myocardial perfusion imaging in magnetic resonance imaging.

Abstract: Based on the major innovations in ultrafast magnetic resonance (MR) imaging in recent years, myocardial perfusion imaging with MR has become the focus of many investigators. Two major approaches to myocardial perfusion imaging involve either exogenous or endogenous contrast agents. For the first category of perfusion experiments, we review the characteristics of the common contrast agents and MR techniques for experimental and clinical first-pass studies and in particular address the question of extracting quantitative estimates for myocardial blood flow (milliliters per minute per gram) and volume (milliliters per gram). We demonstrated quantitative perfusion analysis using intravascular relaxation agents and heavily T1-weighted ultrafast gradient echo sequences. Signal time curves need to be transformed to content time curves and the resulting residue functions were analyzed with a multiple-pathway, axially distributed perfusion model. These preliminary results suggest that quantitative assessment of myocardial perfusion is feasible, but additional studies should provide further confidence for this novel MR approach. The exact sensitivity and specificity of MR first-pass imaging in conjunction with extracellular contrast agents in patient studies and its diagnostic accuracy as judged against coronary angiography and scintigraphic perfusion imaging remain yet undefined. The second category of perfusion experiments does not require exogenous contrast agents and has not yet been tested in patient studies. Progress is reported on several MR perfusion-sensitive methods that use the tissue water as an endogenous contrast agent in combination with magnetization transfer techniques as well as paramagnetic deoxyhemoglobin for measuring tissue oxygenation using heavily T2*-weighted sequences for blood oxygen-level-dependent contrast. Possible future directions and developments toward further improvements for MR myocardial perfusion measurements and contraction-perfusion matching are also addressed.

Myocardial perfusion imaging with PET.

Abstract: Although SPECT has become an accepted imaging technique for myocardial perfusion studies, there are several advantages to evaluating coronary artery disease (CAD) with PET. CAD is a complex, dynamic disease and quantitative measurements of myocardial blood flow by PET can improve the functional characterization of CAD. The major advantage of PET over SPECT is its ability to provide attenuation-corrected images, which decreases incidence of attenuation artifacts and increases specificity. Myocardial perfusion imaging with PET can also provide more accurate information on localization of disease, as well as quantitative assessment, in absolute values, of myocardial blood flow. The measurement of regional flow reserve allows for physiologic characterization of stenosis severity, and may provide early detection of CAD as well as prognostic information. The disadvantage of PET, compared to SPECT, is that the equipment and operations are more expensive. As more accurate diagnostic and prognostic data lead to improved patient management, the cost-to-benefit ratios of PET and SPECT in the clinical setting need to be further analyzed to determine which diagnostic test is most efficient in the work-up of patients with suspected or known CAD.

Myocardial perfusion imaging with thallium-201.

Abstract: Over the past 15 yr, numerous clinical studies have validated the use of myocardial perfusion imaging with 201Tl for detection and evaluation of coronary artery disease (CAD). In addition, 201Tl scintigraphy plays a valuable role in the risk stratification of patients with suspected or known CAD to determine prognosis. Typical protocols involve a comparison of stress and rest images to locate regions of myocardial ischemia. Results are comparable from protocols that employ either exercise stress or pharmacologic stress. By combining 201Tl scintigraphic criteria with electrocardiographic (ECG) data, the sensitivity for detection of ischemia may be increased by as much as 25%-30%. The introduction of quantitative interpretation and SPECT has increased the accuracy of myocardial perfusion imaging with 201Tl. With respect to prognosis, several 201Tl scan variables, such as multiple perfusion defects and abnormal 201Tl lung uptake, are associated with high risk. Even when cardiac catheterization findings are known, 201Tl scintigraphy provides important supplementary information for identifying high-risk subgroups of patients with CAD.

Perfusion imaging of the rat kidney with MR.

Abstract: PURPOSE: To develop a technique for measurement of regional renal perfusion with magnetic resonance (MR) imaging. MATERIALS AND METHODS: Quantitative renal perfusion images in rats were obtained by measurement of the reduction in kidney MR image signal intensity after steady state magnetic labeling of arterial blood in the suprarenal aorta. Labeling was achieved with adiabatic fast passage inversion of arterial water. RESULTS: Cortical renal blood flow was 4.9 mL/g/min +/- 0.15 (12 rats), which correlated well with previous measurements obtained with other techniques. Serial perfusion images obtained every 5 minutes during intravenous infusion of either acetylcholine or angiotensin II showed that one increased and the other decreased renal blood flow, respectively, also correlating with previous measurements. CONCLUSION: Quantitative measurement of cortical renal blood flow can be obtained with proton MR imaging techniques, with use of endogenous arterial water as a tracer. This technique should be readil...

The role of single photon emission computed tomography brain imaging with 99mTc-bicisate in the localization and definition of mechanism of ischemic stroke

Abstract: 99mTc-bicisate (99mTc-ECD) is a new brain perfusion imaging agent formulated from a radiochemically stable kit (Neurolite). A multicenter trial was conducted to determine the sensitivity and specificity of single photon emission computed tomography (SPECT) imaging with 99mTc-bicisate in the localization of ischemic stroke; 170 subjects were enrolled, 128 patients with stroke and 42 controls. Imaging results from 148 subjects (107 stroke patients and 41 controls) were considered evaluable. In the evaluable subjects, SPECT brain imaging with 99mTc-bicisate (21.0 +/- 2.5 mCi) was interpreted without clinical information and was compared with a final assessment using all clinical, diagnostic, and laboratory procedures except the 99mTc-bicisate SPECT results. 99mTc-bicisate was safe and well-tolerated. SPECT imaging with 99mTc-bicisate demonstrated a specificity of 98% and a sensitivity of 86% for localization of strokes (kappa, 0.75; 95% confidence interval, 0.64-0.86). Results were unchanged over time and were similar for all stroke mechanisms except for lacunar disease (sensitivity, 58%). In a secondary analysis, a normal image or small, deep (e.g., subcortical) perfusion defect was highly predictive of a lacunar mechanism. Defects involving the cortical surface were strongly associated with nonlacunar mechanisms. SPECT imaging with 99mTc-bicisate is a sensitive marker in the localization of perfusion defects associated with ischemic stroke and may assist in the determination of the underlying mechanism of a stroke.

Clinical application and quantitative evaluation of generator-produced copper-62-PTSM as a brain perfusion tracer for PET.

Abstract: UNLABELLED Copper-62-pyruvaldehyde bis(N4-methylthiosemicarbazone) copper II (62Cu-PTSM) has been proposed as a generator-produced positron-emitting tracer for perfusion imaging. To evaluate the characteristics of 62Cu-PTSM as a cerebral perfusion tracer, brain PET images of 62Cu-PTSM were compared with cerebral blood flow (CBF). METHODS Following an intravenous injection of 62Cu-PTSM, a serial dynamic PET scan was performed for 10 min with arterial sampling in 10 subjects. CBF was measured by 15O-labeled water before the 62Cu-PTSM study. RESULTS Dynamic PET scan with octanol-extracted arterial input function indicated the presence of significant back-diffusion of 62Cu-PTSM from the brain within 3 min after injection, followed by stable activity from 3 to 10 min. Comparison with 15O-water PET demonstrated less contrast between high- and low-flow regions in 62Cu-PTSM image and a nonlinear relationship of flow and 62Cu-PTSM uptake, which suggests the underestimation of CBF in high-flow regions due to the existence of back-diffusion. CONCLUSION Although 62Cu-PTSM can be used widely for evaluation of brain perfusion with PET, kinetic analysis and correction may be needed to quantify regional CBF.

Dipyridamole Myocardial Perfusion Imaging

Abstract: Dipyridamole is a pharmacologic stressor used in place of exercise for myocardial perfusion imaging in patients who cannot exercise due to various physical limitations. Perfusion studies with dipyridamole can identify coronary artery disease (CAD) as accurately as maximal exercise stress testing. In addition, dipyridamole myocardial perfusion studies are useful to stratify patients according to risk of subsequent cardiac events. As dipyridamole is infused, it blocks the reabsorption and metabolism of adenosine normally produced in the body, producing the desired effect on the heart, coronary hyperemia. Dipyridamole can be used with 201Tl and 99mTc myocardial perfusion tracers, for either planar or SPECT imaging, in patients who cannot exercise or who can only exercise at submaximal levels.

Contrast agents for cerebral perfusion MR imaging

Abstract: Keywords: Brain, MR, 10.12143; Brain, perfusion, 10.12143; Contrast media; Perfusion studies

Assessment of cerebral perfusion using quantitative EEG cordance

Abstract: Brain electricaI activity is related to cerebral perfusion. The nature of this relationship is unclear, however, and surface-recorded activity has not been a reliable indicator of brain perfusion. We studied 27 subjects, all of whom were examined with single photon emission tomography (SPECT) and quantitative electroencephalography (QEEG), to assess associations between QEEG cordance and relative brain perfusion" Cordance has two indicator states: concordance, which may indicate high perfusion; and discordance, which may indicate low perfusion. We used multiple linear regression to assess the association between cordance and SPECT values, and found that cordance values were strongly associ- ated with tissue perfusion. Concordance in the a band was associated both with mean tissue perfusion and the volume of normally perfused tissue, and it had a stronger association with perfusion than any other QEEG variable. Discordance in the fi, band was associated with mean perfusion, and it had a stronger association than did relative but not absolute power. These data suggest that cordance may be useful for the noninvasive assessment of brain perfusion.

Kinetic properties of 99mTc-Q12 in canine myocardium.

Abstract: BACKGROUND99mTc-Q12 is a new Tc(III) perfusion imaging agent that permits prompt myocardial visualization in humans. We postulated that 99mTc-Q12 myocardial activity is related to actual myocardial blood flow during conditions of myocardial ischemia and pharmacological coronary artery vasodilation and that 99mTc-Q12 shows little or no myocardial redistribution as long as 4 hours after intravenous injection.METHODS AND RESULTSIn seven anesthetized, open chest dogs, the left circumflex coronary artery was occluded, and dipyridamole (0.32 or 0.56 mg/kg) was infused into the right atrium, followed by 10 mCi of 99mTc-Q12. Myocardial blood flow was measured by radiolabeled microspheres. The animals were euthanized, and a total of 315 myocardial samples were assayed in a well counter for 99mTc activity. One week later, radiolabeled microsphere activity was determined, and myocardial blood flow was calculated. 99mTc activity (y) was related to myocardial blood flow (x) from 0 to 2 mL.g-1 x min-1 by the relation y...

Brain perfusion SPECT in a patient with a subtle venous angioma

Abstract: Brain SPECT of regional cerebral blood flow using 1-123 IMP demonstrated a focally decreased perfusion area immediately adjacent to a venous angioma in a patient with simple partial seizures A positive correlation was obtained among the location of the venous angioma, the decreased perfusion area on SPECT images, and the electroencephalographic focus Anomalous venous drainage through a venous angioma may explain a perfusion disturbance in the surrounding brain of the angioma High-resolution SPECT imaging with magnetic resonance guidance provides useful information on the pathophysiology of venous angiomas

Functional imaging of changes in human intrarenal perfusion using quantitative dynamic computed tomography.

Abstract: Miles KA, Hayball MP, Dixon AK. Functional imaging of changes in human intrarenal perfusion using quantitative dynamic computed tomography. Quantitative dynamic computed tomography was used with perfusion imaging to characterize intrarenal variations in perfusion in normal and abnormal human kidneys. Perfusion images were obtained from 14 normal and four abnormal kidneys, comprising a renal tumor, an infarcted renal allograft, and two kidneys in a patient with cyclosporin toxicity. Images demonstrating quantifiable intrarenal variations in perfusion were consistently obtained. Normal cortical and medullary perfusion were 4.7 mL/min/mL and 1.1 mL/min/mL, respectively, consistent with accepted normal ranges. The changes in the abnormal kidneys corresponded with known pathophysiology. Computed tomography perfusion imaging creates quantifiable images of renal perfusion with a spatial resolution currently higher than any other functional imaging technique. It offers the opportunity to characterize renal diseases by their relative effects on cortical and medullary perfusion.

3D bolus tracking with frequency-shifted BURST MRI.

Abstract: Objective Our goal was to develop and test a 3D bolus-tracking MR technique for perfusion imaging of normal and pathological (infarcted) human brain. Materials and methods All experiments were performed on standard 1.5 T GE/Signa clinical scanners. Five normal volunteers and one patient with a subacute brain infarct were studied. Modified [frequency-shifted (FS)] BURST MRI was performed during injection of a bolus of Gd-DTPA (0.13 mmol/kg) in the antecubital vein. The 3D datasets were acquired with a time resolution of 2.2 s and an effective spatial resolution of 4.3 x 4.3 x 6.4 mm. Three-dimensional maps of blood volume and bolus arrival time were determined by fitting a synthetic curve to the intensity time course on a voxel-by-voxel basis. Results Both relative cerebral blood volume and arrival time maps demonstrated sensitivity to regional differences in blood supply in both normal brain and in the subacute brain infarction. The transit time maps showed arrival time delays of 5-7 s within and around the infarct and confirmed the diagnosis of left middle cerebral artery occlusion. Conclusion The results of the measurements on both normal and diseased human brain demonstrated the ability to acquire valuable 3D information about brain perfusion using FS BURST MRI.

Evaluation of cerebral vasospasm in patients with subarachnoid hemorrhage using single photon emission computed tomography.

Abstract: Cerebral vasospasm (CVS) occurs as a result of the breakdown in cerebral autoregulation mechanisms. Because cerebral vasospasm can occur after subrachnoid hemorrhage (SAH), it is important to evaluate borderline perfusion. Evaluation of borderline vascular insufficiency is important to reduce ischemic complications. In this study 25 patients with SAH were investigated by somatosensory evoked potentials (SEP), computed tomography (CT), digital subtraction angiography (DSA) and single photon emission computed tomography (SPECT) in order to predict borderline ischemic areas. Clinical grades were also correlated with these investigations. Thirteen patients had symptomatic vasospasm and 15 patients had angiographic vasospasm. SPECT showed hypoperfusion in 22 out of 25 patients. CT predicted CVS in 8 of these 22 patients. Our study shows that brain perfusion SPECT is a non-traumatic, non-invasive, non-allergic, inexpensive method for the prediction of cerebral vasospasm. We conclude that brain SPECT with Tc-99m HM-PAO is an accessible technique that can demonstrate varying degrees of regional tissue hypoperfusion in patients with delayed ischemic deficits due to CVS following SAH.