Showing papers on "Perfusion scanning published in 1978"

Noninvasive assessment of coronary stenoses by myocardial perfusion imaging during pharmacologic coronary vasodilatation. I. Physiologic basis and experimental validation.

Abstract: This study was undertaken to establish the basic hemodynamic conditions necessary to cause abnormalities in external myocardial perfusion images of thallium-201 and technetium-99M-labeled particles as a result of defined coronary stenoses ranging from mild to severe narrowing. Twenty dogs underwent long-term instrumentation with a flow transducer and adjustable constrictor on the left circumflex coronary artery. Catheters were implanted in the aortic root and distal left circumflex coronary artery to measure pressure loss across the stenosis and in the pulmonary artery and left atrium for the injection of drugs or radionuclides, or both. All data were obtained in intact unsedated trained animals. The results from 145 images obtained at rest, during exercise or after coronary vasodilators in dogs with mild to severe coronary stenoses demonstrate the following: (1) The ratio of maximal flow in a normal to stenotic coronary artery must be at least 2:1 before defects appear in the myocardial perfusion image of thallium-201. (2) A diagnostic technique that utilizes a maximal stimulus for increasing coronary flow and an imaging agent that is distributed to the myocardium in linear proportion to coronary flow at flow rates up to 4 or 5 times resting levels will be the most sensitive method for detecting mild coronary stenoses; a diagnostic technique utilizing a submaximal stimulus for coronary flow or an imaging agent whose distribution is not proportional to flow at high flow rates will be least sensitive. (3) Myocardial perfusion imaging during coronary vasodilatation induced with intravenously administered dipyridamole is a better method for identifying moderate coronary stenoses than perfusion imaging during exercise stress in experimental animals. (4) The effect of intravenously administered dipyridamole on the coronary circulation can be closely regulated by adjusting the dose rate of infusion and can be instantaneously reversed with intravenous administration of aminophylline, a dipyridamole antagonist; dipyridamole infusion does not increase myocardial oxygen demands as much as exercise and does not Invoke myocardial ischemia as a diagnostic end point. This stimulus may therefore be more readily controlled than exercise stress and is not subject to the effects on treadmill testing of motivation, chronic lung disease, peripheral vascular disease or musculoskeletal impairment.

Noninvasive assessment of coronary stenoses with myocardial perfusion imaging during pharmacologic coronary vasodilatation. V. Detection of 47 percent diameter coronary stenosis with intravenous nitrogen-13 ammonia and emission-computed tomography in intact dogs.

Abstract: To determine the minimal coronary lesions detectable with perfusion imaging, 16 stenoses of 43 to 66 percent diameter narrowing were applied to the left circumflex coronary artery of three chronically instrumented intact dogs. Orthogonal diastolic coronary arteriograms, obtained on cut film by triggering X-ray exposures from the electrocardiogram while injecting contrast medium through a chronically implanted coronary arterial catheter, were analyzed quantitatively by computer. Fifteen millicuries of nitrogen-13 ammonia was injected intravenously during resting conditions, and emission-computed tomography was performed without electrocardiographic gating. One hour later, after residual nitrogen-13 ammonia had decayed, 15 mg of intravenous dipyridamole was given followed by a second dose of intravenous nitrogen-13 ammonia and repeat performance of emission-computed tomography. The cross-sectional tomographs of the heart were of high quality and revealed in the images obtained with dipyridamole definite perfusion defects with coronary stenoses of 47 percent or greater diameter narrowing. Stenoses of 45 percent diameter narrowing or less did not produce perfusion defects. Quantitative perfusion abnormalities approximated the quantitative severity of stenoses. It is concluded that noninvasive myocardial emission-computed tomography with nitrogen-13 ammonia during dipyridamole-induced coronary vasodilatation detects mild coronary stenoses for purposes of potential medical intervention.

Diffuse cerebral ischemia in the cat: I. Local blood flow during severe ischemia and recirculation

Abstract: The effects of severe cerebral ischemia on postischemic brain perfusion were examined in a series of pentobarbital-anesthetized cats. Ischemia of 15 or 30 minutes' duration was produced by occlusion of both common carotid arteries and the basilar artery and was coupled with mild systemic hypotension. A 90-minute period of normotensive postischemic recirculation was permitted in some animals. In 9 of 10 animals studied at the end of the ischemic insult and not allowed to recover, blood flow in the cerebral hemispheres was greatly reduced, with minimal flow (0.01 to 0.11 ml gm-1 min-1) persisting only in scattered perisulcal regions in 4 animals. Following 15 minutes of ischemia, blood flow was restored uniformly during recirculation, though at subnormal levels (31 to 35% of control). In contrast, 30 minutes of prior ischemia led to marked heterogeneities of local cerebral perfusion during recirculation, with multiple zones of persistent severe ischemia. Thus, while recirculation was suboptimal following both 15 and 30 minutes of ischemia, the 30-minute insult led to focal postischemic perfusion abnormalities that were sufficiently severe to make the possibility of functional recovery appear unlikely.

81mKr ventilation and 99mTc perfusion scans in chest disease: comparison with standard radiographs.

Abstract: In 75 patients with various pulmonary disorders, ventilation and perfusion scans were obtained in multiple views with the 81mKr/99mTc technique and compared with an evaluation of regional ventilation and perfusion derived from the standard chest radiograph. In emphysema, the chest film correlated poorly with ventilation-perfusion scans, showing a trend to underestimate the functional impairment. In chronic bronchitis and asthma, large segmental defects observed on both ventilation and perfusion scans were associated with a normal chest radiograph. Typical findings in pulmonary embolism were segmental defects on perfusion scan with normal ventilation scan and clear lung fields on the chest film. In chronic left heart disease, plain films were inaccurate in predicting alteration of the base-to-apex perfusion gradient observed on the scan.

Scintigraphic Detection of Pulmonary Emboli by Serial Positron Imaging of Inhaled 15O-Labeled Carbon Dioxide

Abstract: Inhaled radioactive carbon dioxide is retained in pulmonary blood distal to embolic obstruction and appears as an area of increased radioactivity that delineates the site and magnitude of the affected zone. The scintigraphic detection of pulmonary emboli by serial imaging of inhaled carbon dioxide labeled with cyclotron-produced 15O2 was evaluated in 27 patients undergoing conventional pulmonary ventilation/perfusion imaging and pulmonary arteriography. Fifteen patients proved to have pulmonary emboli on arteriography. Sensitivity (87%) and specificity (92%) rates for inhalation imaging were superior to those of conventional ventilation/perfusion imaging (P less than 0.05). Clearance of 15O2 activity was markedly delayed over embolized pulmonary segments (mean half time of 47.0 +/- 11.1 seconds [S.E.M.]) in comparison to normal segments (mean of 3.6 +/- 0.08 seconds; P less than 0.001). Pulmonary imaging by this method provides an approach to the detection of pulmonary emboli that is relatively sensitive and specific and permits analysis of persisting perfusion in embolized pulmonary segments. A major practical limitation, however, is the necessity of a nearby cyclotron.

Ultrasonography of the testis--correlation with radiotracer perfusion.

Abstract: Ultrasonic study of testicular disease and paratesticular masses was carried out in 20 cases. In eight of these, comparison was made with pertechnetate perfusion studies performed concurrently. Testicular torsion was well revealed by both techniques. Acute orchitis, in the early stages, was shown more clearly by radiotracer, unless there was associated epididymal swelling or hydrocele. Chronic complications of inflammation, particularly abscess formation, were seen best by ultrasonography. Paratesticular masses could be studied only by ultrasound. These included both solid and cystic masses due to chronic epididymitis.

Pulmonary embolism associated with elective surgery, detected by ventilation-perfusion scintigraphy.

Abstract: The frequency of clinical and sub-clinical postoperative pulmonary embolism, demonstrated by combined pulmonary ventilation-perfusion scanning, and the prophylactic effect of low-dose heparin, were assessed in a randomised double-blind study in 43 patients aged over 40 years Pulmonary embolism was demonstrated using combined ventilation-perfusion scanning in 4 out of 43 patients (9%) The incidence was 1 out of 19 patients in the heparin-treated group and 3 out of 24 patients in the placebo group This difference was not significant If post-operative perfusion scanning alone had been utilised for diagnosing pulmonary embolism, the frequency of pulmonary emboli would have been 33%, with 21% in the heparin group and 46% in the placebo group This difference is not significant It is concluded that perfusion scanning over-estimates the frequency of post-operative pulmonary embolism The use of the more specific combined ventilation-perfusion scanning shows that asymptomatic postoperative pulmonary embolism does occur, but that the frequency is considerably lower than indicated by perfusion scanning alone Combined ventilations-perfusion scanning must be performed in studies assessing the effects of various treatment regimes on the frequency of pulmonary embolism postoperatively The small number of patients included in the study do not permit any conclusions concerning any prophylactic effect of low-dose heparin against pulmonary embolism

Myocardial perfusion scanning with thallium--201 for the non-invasive diagnosis of coronary artery disease.

Abstract: Thallium--201 myocardial perfusion scanning has been evaluated in Australia in patients with coronary artery disease. Myocardial scans reliably detect both acute myocardial infarction and the transient myocardial ischaemia of angina pectoris. The non-invasive nature, ease of study, and the ability to scan patients with conventional cameras makes thallium--201 an attractive additional diagnostic agent for patients with suspected coronary artery disease. Although thallium--201 reliably indicates perfusion defects in the myocardium, its diagnostic use at the moment should be reserved to clarify such diagnostic problems in patients with coronary artery disease which cannot be satisfactorily explained by conventional investigation.

Clinical pulmonary perfusion imaging in the dog.

Abstract: Scintigraphic pulmonary perfusion imaging in the dog has been described for the clinically normal animal. The usefulness of this technique in the patient with pulmonary dysfunction was assessed by review of 76 consecutive clinical cases completed in a 6-month period. This review indicated that 3 basic patterns of perfusion defects are commonly seen in the dog. These were associated with (1) diffuse parenchymal metastatic disease, (2) mediastinal metastatic disease, and (3) heartworm disease. The technique has proved reliable as an aid in the staging of neoplastic disease and of some potential value in heartworm disease and is now performed on a routine basis at this institution for purposes of clinical diagnosis.

Intracoronary myocardial perfusion imaging: patterns in patients with coronary artery disease.

Abstract: Myocardial imaging following the intracoronary injection of radiolabeled particles is used to identify transmural scars in patients being evaluated for coronary atherosclerosis. Selective imaging of the microcirculation derived from each major coronary vessel is accomplished using a dual radionuclide technique. This report illustrates the various normal and abnormal imaging patterns encountered in patients with coronary artery disease. The regional myocardial nomenclature proposed by the American Heart Association Council on Cardiovascular Surgery is used. Correlation of the nuclear study with the contrast arteriogram and ventriculogram is essential for identifying both transmural scars and regions of collateral circulation. The procedure is safe and can be performed during routine coronary angiography.

Influenza A Infection Should Not Simulate Pulmonary Embolism

Abstract: To the Editor.— The article by Lynn et al (238:1166, 1977), entitled "Influenza A Infection Simulating Pulmonary Embolism" is misleading. The article states, "Pulmonary perfusion scans may demonstrate segmental, subsegmental, or nonspecific defects that represent relative reduction of regional pulmonary blood flow. These defects could be secondary to obstructive airway disease, pneumonia, atelectasis, effusion, and other acute or chronic pulmonary disease processes. In the absence of these concurrent abnormalities, the diagnosis of PE [pulmonary embolism] is established by perfusion defects demonstrated by pulmonary perfusion scan with the radioisotope-labeled particles [italics added]. The first two sentences are entirely correct. However, the third sentence is incorrect. Since the advent of the ventilation scan in the late 1960s, the diagnosis of pulmonary embolism is established by perfusion defects demonstrated by a pulmonary perfusion scan only when the concurrently performed ventilation scan does not show the same defects. Although the clinical absence of obstructive