PubMed Health⌕ Search

Biomedical subjects

A Cuarón

Publications and source records attributed to A Cuarón.

At least 37 records · Page 2Linked to original sources
PubMedDate not supplied

[Evaluation of the experience of the observer in the interpretation of myocardial scintillography with radioactive phosphates].

Two-hundred-and five myocardial scans with radioactive phosphates, performed in 185 patients interned at the Coronary Care Unit due to acute chest pain (147 myocardial infarcts: 58 coronary heart disease), were independently interpreted by six observers with different degrees of experience on the lectures of these kind of images (two nuclear physicians, two cardiologists, and two fellows of the Nuclear Medicine Unit). A series of six different grades of myocardial concentration of the radioactive phosphates, related to its osseous concentration were followed. Each observer reported the grade of concentration he found in each image. The fraction of myocardial infarcts and of coronary heart disease found by each observer in every grade of concentration were calculated. With these data, it was determined the optimal criterion level of each observer by which he attained the minor incidence of false negative and false positive results. Four observers found their optimal criterion level on 2F, where grades 0-2D are considered as negative, and grades 2F-4 are considered as positive. One observer found his optimal level at 2D (0-1: -; 2D-4: +) and other at 1 (0: -; 1-4: +. By using a decision matrix which relates results of the test with a binary outcome (normal, abnormal) to the actual diagnosis, also with a binary outcome (infarct, no infarct), the ratios for "sensitivity", "specificity" and "accuracy" were derived for each observer performing at his particular optimal criterion level. Our results suggests that the observer performance depends on his particular degree of experience in interpreting nuclear medical images and on his visual perception. It was concluded that it is necessary to periodically evaluate the individual optimal criterion level of the physicians in charge of the lectures of the myocardial images with radioactive phosphates, liable to shift with time in relation to the experience of the observer. The need of a more objective procedure to quantitate myocardial concentration of the radioactive phosphates is also implied.

Acute Disease↗
PubMedDate not supplied

[Evaluation of radioactive phosphate scintillography in relation to time elapsed after acute myocardial infarct].

A consecutive series of 205 myocardial scans, performed with 99mTc-labeled phosphates, in 185 patients with acute chest pain, were independently evaluated by comparing myocardial concentration intensity of the tracer to that in bone, and by rating this intensity by a six-category rating scale, which imply five criterion levels for calling an image "positive". The optimal criterion level was determined for each day of evolution of illness, as the one in which a shift to a more lax criterion level produces a bigger increment in false-positive results than in True-positive results, and in which a shift to a stricter criterion level causes a greater decrease in true positive results than in false-negative results. In all instances, the optimal criterion level was that with a moderate (2+) myocardial tracer concentration, lower than rib uptake, but with a focal pattern of myocardial distribution of the tracer (2F). By using this optimal criterion level, our results agree with the general consensus in that the procedure's usefullness is restricted to the first five days of evolution of illness. However, our daily statistical analysis showed that the best period to obtain the maximal diagnostic efficiency lies between the third and fourth days after the onset of acute chest pain. A negative result during this period, in patients with ECG and CPK serum concentration compatible with acute myocardial infarction, should be considered of prognostic significance, since it may translate a defficient colateral coronary circulation.

Acute Disease↗
PubMedDate not supplied

[Pulmonary perfusion scintigraphy. Feasibility of quantitative thoracic tomography using the detection of gamma ray dispersion from technetium-99m].

Attenuation of gama radiation (140 KeV) from a punctual source of 99mTc was investigated in materials with a similar density to that of human chest tissues: air, saw dust (lungs), and water (chest wall and mediastinic organs). Half-value thickness (A 1/2) and linear attenuation coefficients (u) were measured for each material. With these experimental data, attenuation of the primary radiation beam and intensity of Compton effect at an angle of 90 degrees were calculated at different depths of a theoretical model of a human chest, assuming a primary radiation beam with a direction from right-to-left, and the inverse. The results demonstrated the theoretical possibility of obtaining quantitative tomographic bidimensional images of the tissular densitometry of the hemi-tórax near the radiation source, by means of the detection of the gama photons scattered al 90 degrees as a result of Compton effect. Attenuation of the primary beam prevents the obtaintion of information from the far sided hemitorax. Theoretical considerations for the correction of this defect of the low energy gama photons from 99mTc are discussed. It was decided to design and built a system for the experimental evaluation of this new principle for clinical exploration, which can be used as a low cost and simple adjuvant to increase the specificity of perfusion lung scintigraphy.

Densitometry↗
PubMedDate not supplied

[Myocardial ischemia in hypertension heart disease (author's transl)].

Seventeen hypertensive patients with EKG evidence of left ventricular hypertrophy and subendocardial ischemia were studied. The following tests were performed: cine-ventriculography, coronary arteriography, ejection fraction, ventricular pressures, left ventricular mass, EKG stress test and atrial stimulation. In 10 cases cardiac scintigraphy with intracoronary injection of albumin-macro-aggregates marked with TC 99m, was obtained. EKG stress and atrial stimulation tests were positive in all cases, with ST depression greater than 1mm, or accentuation of previous ST depression. 83.7% of the patients had permeable coronary arteries, with "corkscrew' tortuosity. Left ventricular mass was increased in all cases (119 +/- 28.5% m2 s/c). Ejection fraction (74.2 +/- 8.1), and left ventricular diastolic pressures were normal. Cardiac scintigraphy showed uniform distribution of the radioisotope in the right ventricle and poor concentration with better dispersion and distribution in the left ventricle. It is concluded that subendocardial ischemia in these subjects is not produced by obstruction of the main coronary trunks and is associated to a significant increment of left ventricular mass which possibly produce a poor coronary reserve, and a potentially high risk condition.

Adult↗
PubMedDate not supplied

[Tomographic densitometry of the human thorax].

We show the first clinical images obtained by a new tomographic system based on the detection of the scattered gamma photons of 99mTc by the chest tissues. These images show satisfactory contrast and tomographic effect on the half-chest near the radioactive source. Both effects tend to decrease on the contralateral half-chest. The images rendered important data in differential diagnosis of perfusion defects evident by lung scintigraphy with macroaggregated albumin labeled with 99mTc. Pulmonary density was normal and homogeneous in a healthy volunteer and also in a patient with pulmonary embolism. It demonstrated a hyperdense pulmonary mass in a patient with tumor of the right lung, which produced a perfusion defect evident in the conventional lung scintiscan, and a shadow in the gamma ray transmission image.

Female↗
PubMedDate not supplied

[Fundamental bases of digital information processing in nuclear cardiology (III)].

This article describes the transformation of the gamma-camera images into digital form. The incidence of a gamma photon on the detector, produces two voltage pulses, which are proportional to the coordinates of the incidence points, and a digital pulse, indicative of the occurrence of the event. The coordinate pulses passes through a analog-digital converter, that is activated by the pulse. The result is the appearance of a digital number at the out-put of the converter, which is proportional to the voltage at its in-put. This number, is stored on the accumulation memory of the system, either on a list mode or on a matrix mode. Static images can be stored on a single matrix. Dynamic data can be stored on a series of matrixes, each representing a different period of acquisition. It is also possible to capture information on a series of matrixes syncronized with the electrocardiogram of the patient. In this instance, each matrix represents a distinct period of the cardiac cycle. Data stored on the memory, can be used to process and display images and quantitative histograms on a video screen. In order to do that, it is necessary to translate the digital data on the memory to voltage levels, and to transform these on light levels on the screen. This, is achieved through a digital analog converter. The reading of the digital memory must be syncronic with the electronic scanning of the video screen.

Analog-Digital Conversion↗
PubMedDate not supplied

[Experimental evaluation of a tomographic system of the thorax by detection of the dispersion of technetium-99m radiation].

Based on a previous theoretical study, a simple device for the acquisition of bidimensional tomographic images of the human chest densitometry was designed. A radioactive linear source (99mTc) was adapted to the lateral aspect of a gamma camera detector in order to register only those photons scattered at 90 degrees. Resulting images from a liver phantom stuffed with saw dust, showed an evident tomographic effect and a satisfactory contrast between the structures sited at less than 20 cm from the source. These effects tend to decrease with distance. The causes of these deficiencies of the system and their possible corrections are discussed.

Evaluation Studies as Topic↗
PubMedDate not supplied

[Formation and migration of radioactive microemboli to the lung during radiovenography].

Two patients with lower extremity thrombophlebitis were studied by radionuclide venography with macroaggregated albumin labelled with 99mTc. Data analysis was performed with a new method. It generated sequential series of imagen (1-2 sec/frame) of the transit of the tracer through leg, thigh, and abdomen, allowing a more precise definition of temporal changes on regional radioactivity. This method rendered the first real evidence of the binding of the tracer to pre-existent venous thrombi, of the dislodgement of these and their gradual fragmentation during their transit to the lungs. The patients had no complaints during or after the study. Lung scanning, performed 24 hours later, showed slight alteration on regional lung perfusion in one case, and none in the other. It is concluded that radioactive microemboli to the lungs is a minor complication of radionuclide venography, which does not justify prevention. This could only nullify the sensitivity of the procedure.

Adult↗
PubMedDate not supplied

[Usefulness of technetium 99m diphosphate scintellography in the diagnosis of acute myocardial infarction. Electrocardiographic correlation].

We made myocardial gammagraphies on a group of 141 patients with acute thoracic pain, using 99 mtc diphosphonates. We obtained images with three projections (LOA, LL and PA); for reading the gammagraphy we used the diagnostic criteria of Berman and Cols. Studying 106 patients with acute myocardial infarction we found affirmative diagnosis in 89 cases (83.93%). In another group, 32 patients with chest angina, the results were negative in 20 cases (62.5%). We got a total of eight false positive images in patients showing post-infarction aneurism, post-defibrillation damage, and myocardial metastatic tumors. This method showed a specificity of 62.9%. Correlation with the electrocardiogram refering to the localization of the infarction, was of 85.39%. This method proved to be of high sensibility and specificity in confirming the diagnosis of acute myocardial infarction or establishing it with certainty in some patients when the electrocardiogram fails and, in some cases, to find out about the evolution and prognostic of the acute myocardial infarction.

Acute Disease↗
PubMedDate not supplied

[Predictive value of 99m-Tc-Sn(II) methylene diphosphonate in the study of acute myocardial infarction].

Myocardial scintigraphy with 99mTc-Sn (II)-Methylenediphosphonate (MDP) was performed in 90 patients with proven acute myocardial infarction (AMI), and in 37 subjects with acute chest pain of a different etiology, during the first five days after the onset of their illness. The procedure was 82.2% sensitive, 86.5% specific, and 83.5 accurate for the diagnosis of AMI. Based on the usual clinical, electrocardiographic and biochemical criteria, the likelihood of AMI in this population was of 70.9% before the scintigraphic test. Application of Bayes' Theorem showed an increase in the likelihood of AMI, from 70.9% to 93.7%, when myocardial scintigraphy was positive, an incremental ruling-in-gain of 22.8%. A normal scintigraphy, on the other hand, reduced the likelihood of AMI, from 70.9% to 33.4%, an incremental ruling-out gain of 37.5%. It is concluded that myocardial scintigraphy with MDP is an important clinical procedure for the study of patients with acute chest pain: a positive test tends to confirm AMI, while a normal image, although it reduces the likelihood of this disease, is not particularly helpful in ruling it out.

Bayes Theorem↗
PubMedDate not supplied

[Bayesian analysis of myocardial scintigraphy using 99mTc-Sn(II)-methylenediphosphonate and using 99mTc-Sn(II)-pyrophosphate].

Myocardial scintigraphy with 99mTc-Sn (II)-Methylenediphosphonate (MDP) and with 99mTc-Sn (II) pyrophosphate (PPi) was performed in 185 patients with proven acute myocardial infarction (90 with MDP; 95 with PPi), and in 65 subjects with acute chest pain of a different etiology (37 with MDP; 28 with PPi), during the first five days after the onset of illness. Sensitivity, specificity and accuracy of the procedure were higher with PPi (0.895, 0.893, 0.894) than with MDP (0.822, 0.865, 0.835) in the diagnosis of AMI. Based on the usual clinical electrocardiographic and biochemical criteria, the likelihood of AMI on the population studied with MDP was of 70.9% and with PPi of 77.2%. Application of Bayes' theorem showed an increase in the likelihood of AMI, when myocardial scintigraphy was positive, from 70.9% to 93.7% when MDP was used, and from 77.2% to 96.6 when PPi was the tracer, with incremental ruling in gaings of 22.8% and 19.4%) respectively. A normal scintigraphy, on the other hand, reduced the likelihood of AMI from 70.9% to 33.4% when MDP was used, and from 77.2% to 29.2% when PPi was the tracer, with respective incremental ruling-out gains of 37.5% and 48.0%. Although homogeinity between the populations studied with each tracer was not proven, existing practical, clinical and biochemical evidence allows the conclusion that PPi is a better agent than MDP in the study of patients with acute chest pain.

Adolescent↗
PubMedDate not supplied

[Hepato-splenic scintigraphy in finding indications of bacterial endocarditis. Preliminary report].

Hepato-splenic scintigraphy with 99mTc-S-colloid was performed in twelve patients with bacterial endocarditis. These images showed that the size of the liver varied from normal to a severe hepatomegaly, depending on the presence of congestive heart failure. Intrahepatic distribution of the radiocolloid was slighty irregular in all cases. The spleen was conspicuously enlarged, and showed irregular distribution of the radiopharmaceutical. In some cases intrasplenic concentration defects caused by infarcts, abscesses or cysts, were observed. The relative uptake of radiocolloid by the spleen, varied from hypo- to hyperconcentration according to the degree of lymphoid hyperplasia caused by the infection. In two cases, both with congestive heart failure, concentration of the radiocolloid was evident in the bone marrow. The scintigraphic pattern observed in these patients with bacterial endocarditis can be easily differentiated from that caused by only congestive heart failure, which is similar to the observed in patients with cirrhosis of the liver and/or portal hypertension.

Adolescent↗
PubMedDate not supplied

[Myocardial damage following cardioversion].

In order to ascertain myocardial damage secondary to D.C. cardioversion, we studied 20 patients from the National Institute of Cardiology Ignacio Chávez, in whom an elective electric countershock was applied because of rythm abnormalities. We studied the patients before and after the procedure with E.C.G., enzyme levels (SGOT, LDH, CKMB), and myocardial scintigraphy to detect possible myocardial lesions. Only in two patients the CKMB rose to a significant level. The ECG changes were significant in 40 per cent, and myocardial scintigraphy was positive in a diffuse pattern in 50 per cent of the cases. The interpretation of the three studies as a whole, showed an absolute lack of correlation between them. We conclude that DC countershock is a safe and innocuous procedure, to which no myocardial damage can be attributed, if it is used within the normal limits of clinic.

Adult↗