Showing papers on "Perfusion scanning published in 1991"

Measurement of tissue perfusion by dynamic computed tomography

Abstract: A method for quantifying tissue perfusion by dynamic computed tomography (CT) is described. By applying a nuclear medicine data processing technique to time-density data from a single-location dynamic CT sequence, tissue perfusion can be determined from the maximum gradient of the tissue time-density curve divided by the peak enhancement of the aorta. Using this method, splenic perfusion was measured at 1.2 ml min-1 ml-1, normal renal cortical perfusion at 2.5 ml min-1 ml-1 and normal renal medullary perfusion at 1.1 ml min-1 ml-1. Changes in cortical and medullary perfusion in renal failure and hypertension were demonstrated. The ability of dynamic CT to provide quantitative functional information is not well recognized and is potentially of value when studying structures, such as the renal cortex and medulla, that cannot be anatomically resolved by standard functional imaging techniques.

Imaging of Diffusion and Microcirculation with Gradient Sensitization: Design, Strategy, and Significance'

Abstract: Recent developments in the use of magnetic resonance (MR) to measure and image diffusion and blood microcirculation (“perfusion”) are summarized. After a brief description of the effects of diffusion and perfusion on the MR signal, the different methods (conventional spin-echo, stimulated-echo, gradient-echo, and echo-planar imaging) that have been proposed and used to image and measure diffusion and perfusion by gradient sensitization are presented, along with their advantages and limitations. The difficulties of diffusion/ perfusion imaging related to both hardware and software are then discussed. Special attention is given to specific problems encountered with in vivo studies and data analysis. Finally, the potential biologic and clinical applications are outlined, and some examples are presented.

Brain perfusion is abnormal in cocaine-dependent polydrug users: a study using technetium-99m-HMPAO and ASPECT.

Abstract: Cocaine abuse is widespread and has been associated with serious neurovascular complications. We studied a group of cocaine-dependent polydrug users with 99mTc-HMPAO and high-resolution SPECT and compared their perfusion pattern to cerebral perfusion in a group of older control subjects. Sixteen of 18 cocaine-dependent polydrug users had abnormal perfusion characterized primarily as small focal defects involving inferoparietal, temporal, and anterofrontal cortex and basal ganglia. Psychometric testing was abnormal in all 18 cocaine-dependent subjects. No relation was found between the severity of SPECT abnormalities and mode of administration or frequency or length of cocaine use. All 15 older normal subjects had normal cerebral perfusion. While the focal perfusion abnormalities to the cortex and basal ganglia could be explained by the profound vasoconstrictor effects of cocaine, the combinational use of multiple substances including cannabis and alcohol may play a contributory role. This study documents the high incidence of functional brain abnormalities in cocaine-dependent chronic polydrug users without corresponding abnormalities on imaging studies of cerebral anatomy and morphology.

Diffusion/perfusion MR imaging of acute cerebral ischemia.

Abstract: In vivo echo-planar MR imaging was used to measure apparent diffusion coefficients (ADC) of cerebral tissues in a comprehensive noninvasive evaluation of early ischemic brain damage induced by occlusion of the middle cerebral artery (MCA) in a cat model of acute regional stroke. Within 10 min after arterial occlusion, ADC was significantly lower in tissues within the vascular territory of the occluded MCA than in normally perfused tissues in the contralateral hemisphere. Sequential echo-planar imaging was then used in conjunction with bolus injections of the magnetic susceptibility contrast agent, dysprosium DTPA-BMA, to characterize the underlying cerebrovascular perfusion deficits. Normally perfused regions of brain were identified by a dose-dependent 35–70% loss of signal intensity within 6–8 s of contrast administration, whereas ischemic regions appeared relatively hyperintense. These data indicate that sequential diffusion/perfusion imaging may be diagnostically useful in differentiating permanently damaged from reversibly ischemic brain tissue. © 1991 Academic Press, Inc.

Cardiac First-Pass and Myocardial Perfusion in Normal Subjects Assessed by Subsecond Gd-DTPA Enhanced MR Imaging

Abstract: To evaluate first pass in the right ventricular (RV) and left ventricular (LV) cavities and myocardial perfusion, subsecond MR imaging was performed in seven normal subjects following intravenous bolus injection of Gd-DTPA. After the baseline scans, sequential ECG-triggered images were obtained every three to four RR intervals. The procedure consisted of an initial presaturation pulse (150 degrees), and the acquisition time for one image was approximately 500 ms with 64 phase-encoding steps. After bolus administration of Gd-DTPA (0.05 mmol/kg body wt), progressively increasing signal intensities were observed in the RV cavity, the LV cavity, and the myocardial wall. Gadolinium DTPA enhanced subsecond MR offers temporal information of the first transit in the cardiac chambers and may provide useful clinical reference data for assessment of myocardial perfusion in patients with coronary artery disease.

Exercise thallium-201 perfusion scintigraphy in the assessment of coronary artery disease

Abstract: Exercise thallium-201 perfusion scintigraphy has been used extensively over the last decade for the detection and localization of coronary artery disease. Single-photon emission computed tomography (SPECT) is a refinement of presently avallable techniques, offering improved identification over planar imaging of individual vessel stenosis and quantification of the extent of abnormally perfused myocardium. In this review, the planar and SPECT techniques are discussed in light of the most recently published large patient series, and with regard to the many factors that affect the sensitivity and specificity of perfusion imaging in identifying coronary artery disease. The clinical implications of exercise perfusion scintigraphy and its future applications in cardiology practice are discussed.

Coronary artery stenosis

Abstract: Anatomic and functional characteristics of coronary artery stenosis physiology of coronary circulation methods for pressure-flow analysis and arteriography interactions with the coronary vascular bed phasic pressure flow and fluid dynamic analysis phasic pressure flow and arteriographic geometry collapsing stenoses coronary flow reserve quantitative coronary arteriography reversal by risk factor modication positron emission tomography of the heart prinicples of cardiac PET PET perfusion imaging quantitation of PET perfusion images coronary collateral function assessed by PET assessing myocardial infarction, ischemia and viability PET compared to other imaging modalities accuracy and performance of the positron scanner economics of cardiac PET radiation burden, facilities and regulatory status clinical case studies with PET

Technetium-99m-sestamibi myocardial perfusion imaging in detection of coronary artery disease: comparison between initial (1-hour) and delayed (3-hour) postexercise images.

Abstract: Technetium-99m-sestamibi, a new myocardial perfusion imaging agent, does not show significant or rapid myocardial redistribution following its intravenous injection at stress. The purpose of this study was to evaluate the myocardial clearance of 99mTc-sestamibi and ischemic/normal wall ratios at 1 hr and at 3 hr after injection at stress in patients with significant coronary artery disease. Twenty-five patients with ischemic defects on 201Tl scans (n = 15) and/or significant disease on coronary angiogram (n = 18) were prospectively studied. Planar images were obtained at 65 and at 190 min after an injection at stress of 20-25 mCi of 99mTc-sestamibi. A rest study was performed 1-6 days later. Ischemic/normal wall ratios were 0.73 +/- 0.10 and 0.83 +/- 0.12 (p less than 0.05) at 1 and 3 hr, respectively (0.98 +/- 0.15 at rest). Myocardial washout was 26% +/- 12% for normal walls and 15% +/- 8% for ischemic walls (p less than 0.001). Segmental analysis showed 48 and 46 ischemic segments at 1 and 3 hr, respectively. In conclusion, although only a few ischemic segments were missed at 3 hr, significantly lower ischemic/normal wall ratios were found at 1 hr. Faster myocardial washout from normal walls is responsible for the partial reduction of this ratio.

PET Perfusion Imaging and Nuclear Cardiology

Abstract: population have coronary atherosclerosis, most of it din ically silent (3,4). Silent myocardial ischemia is increas ingly recognized in symptomatic and asymptomatic mdi viduals (5—14).It has an unfavorable prognosis when occurring during exercise testing (7) in patients with recent unstable angina (8) or in asymptomatic patients with perfusion defects after dipyridamole (11-14). Up to 48% of asymptomatic subjects with silent ischemia have a cardiac event (angina pectoris, myocardial infarction, or sudden death)within 4—6 yr(7,9). Fortyto 60%of patients with sudden death or myocardial infarction pre sent no previous symptoms (15—18).Therefore, silent coronary atherosclerosis remains a particular problem in cardiovascular medicine because there are no warning symptoms until a major cardiac event occurs. The major questions for cardiovascular medicine are how to identify silent coronary artery disease (CAD) in specific individuals, how to define its severity in either the symptomatic or asymptomatic patient, how to decide ob jectively among dietary, medical, and mechanical inter ventions, how to assess the results itivasively and nonin vasively, and how to reduce unnecessary invasive proce dures by accurately selecting appropriate patients. At the other end of the clinical spectrum, in patients with myo cardial infarction and myocardial salvage by thrombolysis, percutaneous transluminal coronary angioplasty (PTCA) or bypass surgeryrequiresreliable measures of myocardial viability and involvement of other coronary arteries to determine definitive mechanical interventions having sig nificant risks.

Assessment of myocardial perfusion during CABG surgery with two-dimensional transesophageal contrast echocardiography.

Abstract: No reliable, quantifiable index of tissue perfusion is currently available to assess the efforts of coronary artery bypass graft (CABG) surgery. We used two-dimensional transesophageal contrast echocardiography with sonicated Renografin-76 microbubbles to determine the distribution of myocardial blood flow during coronary artery bypass graft surgery in 15 patients. Sonicated Renografin-76 contrast agent was injected into the aortic root of all patients after institution of cardiopulmonary bypass and application of the aortic occlusive clamp. Eight patients had contrast agent injected directly into the free proximal end of the vein-CABG anastomosis. All patients again received aortic root injections during reperfusion after anastomosis of the proximal aortovein and distal coronary artery. Echocardiographic images of the left ventricle short axis at the level of the papillary muscles were obtained in real time and analyzed retrospectively from videotape. Injection of contrast provided information about the magnitude and geometric distribution of coronary artery-vein bypass run-off and enabled identification of poorly perfused myocardial regions. When predicted myocardial perfusion patterns, based on preoperative evaluation of epicardial vessel distribution derived from coronary angiography, were compared to actual perfusion patterns assessed with intraoperative echocardiography, contrast regional myocardial perfusion patterns were predicted 84% of the time (71-97%, 95% confidence limit). Regional myocardial perfusion deficits detected after coronary bypass grafting were associated with regional wall motion abnormalities detected after separation from cardiopulmonary bypass. Our technique makes possible on-line visualization of changes in regional blood flow in the heart before, during, and after CABG.(ABSTRACT TRUNCATED AT 250 WORDS)

Recent advances in MR imaging/spectroscopy of cerebral ischemia.

Abstract: Recent advances in high-resolution MR imaging and multinuclear spectroscopy have stimulated studies of the functional relationships between tissue hypoperfusion, cellular energy depletion, and brain edema associated with cerebral ischemia. The very slow (microns/sec) random translational motion of water protons in various brain tissues and intracranial fluid compartments can now be assessed with MR diffusion imaging. More slowly diffusing protons in ischemic tissues can be differentiated from normal parenchyma, CSF, and flowing blood, enabling the detection and localization of ischemic regions within minutes of the onset of stroke. Perfusion imaging "snapshots," obtained in as little as 25 msec with echoplanar MR methods, permit the evaluation of tissue washin/washout kinetics of contrast agents in the microvasculature, and thus the quantification of brain perfusion on a regional basis. Also, delineation of major intra- and extracranial arterial and venous structures with MR angiography, acquired with two...

Clinical cardiac positron emission tomography: state of the art.

Abstract: Cardiac positron emission tomography (PET) has evolved rapidly from a relatively esoteric research tool into clinical applications providing unique, quantitative information on myocardial perfusion, metabolism, and cell membrane function and having a potentially significant impact on cardiovascular medicine. Although there are many different positron radionuclides for imaging diverse myocardial behavior, three radionuclides have reached accepted clinical utility. Cardiac PET using nitrogen-13-ammonia, rubidium-82, and fluoro-18-deoxyglucose has proved accurate and definitive in multiple university and private-practice sites for diagnosing and assessing severity and location of coronary artery disease in symptomatic or asymptomatic patients, for identifying injured but viable myocardium potentially salvageable by revascularization, and for ruling out clinically significant coronary artery stenosis with a high specificity in patients who might otherwise undergo coronary arteriography to document the absence of significant disease. 89 references.

SPECT evaluation of brain perfusion reserve by the acetazolamide test using Tc-99m HMPAO.

Abstract: This report describes a new approach to the evaluation of brain perfusion reserve using Tc-99m HMPAO SPECT. Consecutive brain Tc-99m HMPAO SPECT studies before and after acetazolamide (Diamox) administration were performed within 30 minutes on 19 patients with significant vascular occlusive lesions. Thirteen patients showed decreased perfusion reserve and four patients maintained perfusion reserve in the affected vascular territories after Diamox administration, providing additional information to baseline Tc-99m HMPAO SPECT in 17 (89%) patients. Although flow augmentation post-Diamox was underestimated, possibly due to the nonproportionality of Tc-99m HMPAO activity to true blood flow, significant changes in the brain perfusion pattern were both visually and quantitatively determined using an image subtraction technique. This consecutive Tc-99m HMPAO SPECT technique seems to be of practical use for the evaluation of brain perfusion reserve and for the improvement of the sensitivity of detecting pathologic areas.

Evaluation of right ventricular regional perfusion with technetium-99m-sestamibi SPECT.

Abstract: To evaluate technetium-99m-sestamibi as a right ventricular perfusion imaging agent, 25 normal volunteers and 25 patients with suspected coronary disease were studied with both sestamibi and thallium-201 SPECT. All patients underwent cardiac characterization. Compared to thallium-201 images, visualization of the right ventricle was superior for sestamibi in all cases. After computer masking of the left ventricle, count profiles for each 6-mm right ventricular short-axis slice were extracted and plotted in a bull's-eye type polar map with images normalized to maximal right ventricular counts. On sestamibi right ventricular polar maps, 7 of 11 patients (64%) with right coronary stenosis had fixed or reversible inferior right ventricular defects. None of the 25 volunteers or patients without right coronary stenosis had right ventricular defects (true-negative rate = 100%). We conclude that sestamibi SPECT provides an accurate means to assess right ventricular regional perfusion, with data presentation and interpretation facilitated by the polar map display.

Nuclear cardiac imaging.

Abstract: Important developments in the field of nuclear cardiac imaging include increasing use of single-photon emission computed tomography; the availability of pharmacologic stress testing; the introduction of newer technetium-labeled perfusion imaging agents; and a number of other newer imaging agents and imaging techniques. Tomographic imaging improves image quality as well as sensitivity. This improvement is probably more noticeable with pharmacologic stress testing and with the newer technetium agents. A number of pharmacologic stress agents are now being used. These include dipyridamole, adenosine, and dobutamine. In our experience, thallium tomographic imaging during adenosine-induced coronary hyperemia has resulted in a high degree of accuracy in the diagnosis of coronary artery disease. Both 99mTc-sestaMIBI (hexakis-2-methoxyisobutyl-isonitrile) and 99mTc-teboroxime may be used for simultaneous assessment of perfusion and function. These agents, although similar to thallium in many aspects, differ in many other aspects as they differ from each other. For example, sestaMIBI has a long retention time, but teboroxime has a very rapid washout time. Therefore, the imaging protocols using these two agents are considerably different. Assessment of myocardial viability has been an area of interest; specifically, the use of the reinjection technique has improved the ability to differentiate between scar tissue and viable myocardium.

Myocardial perfusion imaging with technetium-99m-labeled agents.

Abstract: Thallium-201 (201Tl) is suboptimal as a single-photon emitting agent for myocardial perfusion imaging, in view of its low-energy photons and long half-life. To circumvent these limitations, two new myocardial perfusion imaging agents labeled with technetium-99m (99mTc) have been developed. They are Tc-sestamibi and Tc-teboroxime. Clinical trials of myocardial perfusion with both tracers have shown results similar to those obtained with 201Tl for detection of coronary artery disease. Results to date indicate that Tc-sestamibi accurately detects and locates myocardial infarction and can accurately assess both left and right ventricular ejection fractions by the first-pass technique. In addition, research has shown that rest-stress studies can be performed on the same day and that Tc-sestamibi can be used to assess the results of thrombolytic therapy. Tc-teboroxime has excellent myocardial tracer uptake characteristics but is cleared very rapidly from the myocardium. These features make Tc-teboroxime well suited to rapid serial studies. These new technetium myocardial perfusion agents have just become available for routine clinical use and are likely to replace 201Tl in many of its clinical applications.

Increased rCBF in gray matter heterotopias detected by SPECT using 99mTc hexamethyl-propylenamine oxime.

Abstract: Imaging findings of morphology and regional cerebral blood flow in two patients suffering from epileptic seizures are presented. CT and MRI revealed heterotopic gray matter as a probable structural correlate, causing the seizure disorder.99mTc hexamethyl-propylenamine oxime (HM-PAO) SPECT demonstrated focally increased regional cerebral blood flow in both patients in the areas of their heterotopic lesions. Heterotopic and orthotopic gray matter seem to have similar features in terms of regional perfusion. A focally increased brain perfusion in interictal epileptic patients may indicate an underlying migration anomaly.

Myocardial perfusion by contrast echocardiography. From off-line processing to radio frequency analysis.

Abstract: In the last decade, many efforts have been made to study myocardial perfusion by contrast echocardiography. The possibility of differentiating normal from nonperfused myocardium and measuring the extent of the area at risk and myocardial infarction size has already been demonstrated. The aim of this paper is to review the approaches to quantitation of coronary blood flow by contrast echocardiography. In a series of studies, echocardiographic contrast agents have been treated like "deposit tracers." After an upstream contrast injection, myocardial contrast intensity (according to the partition principle) hypothetically reflects the fraction of contrast, and consequently of flow, distributed to the myocardium. A good correlation was found between changes in peak myocardial contrast intensity and corresponding changes in coronary blood flow (r = 0.83). However, this approach is limited by electronic signal distortion and attenuation artifacts. In other studies contrast agents have been treated as intravascular "free-passing" tracers, and (according to the dilution principle) their myocardial transit times hypothetically reflect coronary blood flow. A prolonged myocardial washout halftime with coronary underperfusion has been documented in animal experiments and patients with severe coronary stenosis. However, the majority of contrast agents have intermediate characteristics and do not belong to either category of tracers; furthermore, signal distortion and attenuation phenomena affect the washout phase. The time of myocardial contrast appearance, which is independent of tracer characteristics, permitted the differentiation of baseline conditions from coronary underperfusion but seemed inaccurate in the quantitation of coronary blood flow (r = 0.60).(ABSTRACT TRUNCATED AT 250 WORDS)

Single photon emission computed tomography in cerebrovascular disease

Abstract: Every year, nearly half a million people in the United States have a stroke. Cerebrovascular disease is the third leading cause of death in the country, and it costs the economy approximately $25 billion annually. SPECT perfusion imaging is a sensitive indicator of stroke. Abnormal patterns of blood flow are recognized either as areas of hypoactivity (focal or diffused) or hyperactivity (hyperemia or luxury perfusion). Lesions are demonstrated earlier by SPECT than by CT or MRI, and the physiologic information from flow imaging is not available from such anatomic studies. Given the significance of stroke and the early sensitivity of SPECT, why do most neurologists not include SPECT in the evaluation of their patients? The authors feel that the answer is that most neurologists do not view SPECT flow imaging as providing additional information beyond the standard clinical and radiologic work-up. This article therefore concentrates on ways in which SPECT imaging can be useful in stroke, identifying the major concerns of clinicians, and demonstrating how some of these concerns can be addressed by SPECT. The goal is to expand the perspective of the nuclear-medicine physician and encourage investigations on urgent clinical problems in the diagnosis and management of patients withmore » cerebrovascular diseases. Additional information may be obtained from several excellent reviews of SPECT imaging in stroke. 73 refs.« less

Tc-99m HMPAO SPECT analysis of neuroleptic effects on regional brain function.

Abstract: This report describes a new approach to the evaluation of neuroleptic effects on regional brain function. Using Tc-99m HMPAO SPECT imaging, consecutive brain perfusion studies before and after acute haloperidol administration were performed on three schizophrenic patients and two normal volunteers. The antipsychotic drug ameliorated the hypoactivity in the frontal lobe and suppressed the hyperactivity in the temporo-occipito-pa-rietal lobe selectively in the dominant hemisphere in the schizophrenic patients. It did not exert a significant influence on the brain perfusion pattern in normal volunteers. This nuclear medicine technique seems to be useful for the evaluation of drug effects in psychiatric diseases.

Imaging, measurements, and analysis of the heart

Abstract: Ventricular function - imaging and quantification ventricular function - measurement and analysis perfusion - measurement and analysis circulation and perfusion - imaging and imagination metabolism electrocardiology - imaging, analysis and simulation.

Risk stratification after myocardial infarction with exercise and Doppler echocardiography.

Abstract: Exercise testing early after myocardial infarction has been shown to be of further risk stratification value among otherwise low-risk patients on the basis of an uncomplicated clinical course. The addition of cardiac imaging modalities to exercise testing has augmented this capacity. Exercise echocardiographic imaging before and immediately after treadmill exercise can be accomplished in 85-95% of patients. New or worsening wall motion abnormalities identify 63-80% of patients who will suffer cardiac events and correctly predict 78-95% of those who will not. In addition, exercise echocardiography can detect multivessel coronary artery disease with a sensitivity of 80% and a specificity of 90%. These results are superior to those obtained by analyzing global left ventricular function during exercise, exercise aortic Doppler velocity profiles, or exercise electrocardiography. How exercise echocardiography compares with 201Tl perfusion imaging after myocardial infarction awaits a systematic study. Therefore, the choice between exercise echocardiography and perfusion imaging depends on physician preference, availability, cost, and service.

Brain death : determination with brain stem evoked potentials and radionuclide isotope studies

Abstract: Thirty-three patients fulfilling the clinical criteria for brain death were tested by Brainstem Auditory Evoked Potentials (BAEP) and Radionuclide Cerebral Angiography and Brain Perfusion Studies. There was a significant correlation between the BAEP and radionuclide study outcomes. All patients with absence of BAEP showed no cerebral perfusion. These findings, added to the clinical findings, resulted in a final diagnosis of brain death in all patients. It is concluded that BAEP and Radionuclide Cerebral Perfusion studies are useful adjuncts for proving that brain death has really occurred.

Tomographic myocardial perfusion imaging with technetium-99m-teboroxime at rest and after dipyridamole.

Abstract: This study was done to determine whether the rapidly clearing myocardial perfusion agent 99mTc-teboroxime (SQ 30217, Cardiotec®) could be combined with tomographic imaging to accurately quantify regional myocardial blood flow distribution in anesthetized dogs. Following stenosis of the anterior descending (LAD, n = 10) or circumflex (LCX, n = 5) coronary arteries, teboroxime was administered simultaneously with radioactive microspheres, at rest and following infusion of dipyridamole (0.15 mg/kg/min × 4 min). Tomographic imaging began 1 min after each teboroxime injection and continued for 12 min. For LAD stenosis, when the dipyridamole study was performed first, teboroxime activity in the center of the ischemic region was closely correlated with tissue microsphere content. However, the severity of the dipyridamole-induced flow deficit was underestimated by teboroxime when the rest study was performed first. Our results show that despite rapid myocardial clearance, tomographic imaging of 99mTc-teboroxime provides reasonably accurate quantitation of dipyridamole-induced anterior wall perfusion defects, but that the flow deficit is underestimated when a rest study is performed first or when the defect is located in the inferior wall.

New perspectives for perfusion imaging in echocardiography

Abstract: The rapid injection into the coronary circulation of solutions containing microbubbles produces an ultrasonic contrast effect in the myocardium. The time-intensity curves generated by sequential videodensitometric analysis of contrast intensity, which is corrected for myocardial background intensity, resembles the curves used in indicator dilution techniques. Studies done in vitro have demonstrated a direct relation between contrast intensity and amount of microbubbles. In animal studies, measurements derived from these curves correlated with changes in myocardial blood flow assessed by microspheres but with varying controversial results. Differences between investigators in technique of injection and size of microbubbles injected are among the list of factors that will alter the time-intensity curve and explain some of the differences in results between investigators. Several factors limit the application of myocardial contrast echocardiography (MCE) to the quantitation of myocardial blood flow. Nevertheless, the results from multiple investigations suggest that the technique is sensitive to changes in perfusion and may be applicable to the evaluation of regional coronary reserve and assessment of the results of revascularization procedures. Peak intensity and area under the time-intensity curve have provided consistent results between investigators; therefore, these measurements have been used to assess regional coronary reserve in experimental studies and patients with coronary artery disease. Although the results are encouraging, they cannot distinguish well between normal and mild impairments in coronary reserve and are subject to larger reproducibility errors.(ABSTRACT TRUNCATED AT 250 WORDS)