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Biomedical subjects

M Razavi

Publications and source records attributed to M Razavi.

At least 37 records · Page 2Linked to original sources
PubMed1993

An automatic method for enhancing the display of different tissue densities in digital chest radiographs.

Digital chest radiographs are often too bright and/or lack contrast when viewed on a video display. This often occurs in radiographs taken of patients with dense lungs, or when incorrect x-ray exposure techniques or inappropriate image preprocessing operations are performed (eg, by the computed radiography system or laser scanner). This article describes a method to automatically provide brightness and contrast adjustments to selectively enhance either soft or dense tissues. This method reduces viewer interaction and improves displayed image quality. The algorithm analyzes the gray-level histogram of a chest radiograph and determines the breakpoints that separate the region outside the patient (background), the radiographically soft tissues, and the radiographically dense tissues. From these breakpoints, a series of piecewise linear look-up tables (LUTs) is generated to selectively enhance either the soft tissues or the dense tissues. This is performed by: (1) varying the contrast in the patient background to achieve the desired overall brightness, (2) selectively increasing the contrast of the tissue region of interest, and (3) reducing or maintaining the contrast of the remaining region. The resulting LUTs are applied to the original image via video display.

Algorithms↗
PubMed1993

Nephrolithiasis in Iranian sheep.

Out of 500 Iranian sheep examined, six revealed the presence of lithiasis in their kidneys. Nephroliths in three animals were composed of ammonium magnesium phosphates and in the others of calcium carbonates and calcium phosphates. Interestingly sodium and ammonium urate crystals were present in the kidneys of three animals.

Abattoirs↗
PubMed1992

Receiver-operating-characteristic study of chest radiographs in children: digital hard-copy film vs 2K x 2K soft-copy images.

Two methods are commonly used to visualize digital radiologic imaging data: (1) hard-copy viewing, in which the digital data are used to modulate the intensity of a laser beam that exposes an analog film and (2) soft-copy viewing, in which the digital data are converted to an analog video signal and presented on a CRT monitor. The film method allows new digital imaging systems to be easily integrated into conventional radiologic management and viewing methods. The second method, soft-copy viewing, allows digital imaging data to be managed and viewed electronically in a picture archiving and communication system (PACS). These PACS systems are hypothesized to have improved operational efficiency and enhanced image-analysis capabilities. The quality of soft-copy images is still not widely accepted. This article reports on the results of a large-scale receiver-operating-characteristic study comparing observers' performance in detecting various pediatric chest abnormalities on soft-copy 2048 x 2048K byte displays with their performance with digital laser-printed film from computed radiography. The disease categories studied were pneumothorax, linear atelectasis, air bronchogram, and interstitial disease. The selected data set included 239 images; 77 contained no proved abnormality and 162 contained one or more of the abnormalities mentioned. Seven pediatric radiologists participated in the study, two as judges and five as observers. Our results show no significant difference between viewing images on digital hard copy and soft copy for the detection of pneumothoraces and air bronchograms. A slight performance edge for soft copy was seen for interstitial disease and linear atelectasis. This result indicates that computed chest radiographs in children viewed in a soft-copy PACS environment should result in diagnoses similar to or slightly more accurate than those obtained in a laser-printed film-based environment.

Child↗
PubMed1991

Adenine and hypoxanthine transport in human erythrocytes: distinct substrate effects on carrier mobility.

Transport of adenine and hypoxanthine in human erythrocytes proceeds via two mechanisms: (1) a common carrier for both nucleobases and (2) unsaturable permeation 4-5-fold faster for adenine for hypoxanthine. The latter process was resistant to inactivation by diazotized sulfanilic acid. Carrier mediated transport of both substrates was investigated using zero-trans and equilibrium exchange protocols. Adenine displayed a much higher affinity for the carrier (Km approximately 5-8 microM) than hypoxanthine (Km approximately 90-120 microM) but maximum fluxes at 25 degrees C were generally 5-10-fold lower for adenine (Vmax approximately 0.6-1.4 pmol/microliters per s) than for hypoxanthine (Vmax approximately 9-11 pmol/microliters per s). The carrier behaved symmetrically with respect to influx and efflux for both substrates. Adenine, but not hypoxanthine reduced carrier mobility more than 10-fold. The mobility of the unloaded carrier, calculated from the kinetic data of either hypoxanthine or adenine transport, was the same thus providing further evidence that these substrates share a common transporter and that their membrane transport is adequately described by the alternating conformation model of carrier-mediated transport.

Adenine↗
PubMed1988

Myocardial infarction and normal coronary arteriography: a 10 year clinical and risk analysis of 74 patients.

Myocardial infarction with normal coronary arteries was identified in 74 patients with a mean age of 43 years (range 19 to 66). A mean follow-up period of 10.5 years after documented myocardial infarction and 8.6 years after cardiac catheterization was obtained. The survival rate was 85% (n = 63). There were no statistical differences in age or clinical risk factor prevalence between survivors and nonsurvivors. Moderate (55%) to severe (27%) left ventricular impairment was more common in nonsurvivors. Nine of 11 deaths were cardiovascular, 6 were sudden and 8 occurred in patients with moderate to severe global left ventricular impairment. Seventy-six percent of survivors were asymptomatic and 86% were fully active at follow-up. Two survivors and three nonsurvivors experienced a second myocardial infarction. The clinical risk factors of the study group (Group I) were compared by age, sex and year of catheterization with risk factors in two matched groups. Group II consisted of 74 patients with coronary occlusive disease and myocardial infarction and Group III consisted of 148 patients with normal arteriograms. Group I differed from Group II in having fewer clinical risk factors (p = 0.01 to less than 0.0001). Cigarette smoking did not differ significantly between Group I (72%) and Group II (69%) but was less common in Group III (45%) (p less than 0.001). Hormone therapy or the peripartum state was more common in women in Group I (34%) than in women in Group III (14%) (p = 0.03).(ABSTRACT TRUNCATED AT 250 WORDS)

Actuarial Analysis↗
PubMed1986

Development of severe left ventricular outflow tract obstruction over the course of 14 years: an unusual natural history of hypertrophic obstructive cardiomyopathy.

A patient with hypertrophic obstructive cardiomyopathy who when first seen had a normal physial examination, chest x-ray, and electrocardiogram, and no provokable gradient with isoproterenol at cardiac catheterization, was re-evaluated after 14 years. At the time of re-evaluation, she was found to have a typical systolic ejection murmur, cardiomegaly, left ventricular hypertrophy, a pseudoinfarction pattern on electrocardiography, and a significant subaortic gradient both by catheterization and by doppler. This case demonstrates that hypertrophic obstructive cardiomyopathy can be a progressive disease and that patients with this condition warrant careful follow-up. Echocardiography with doppler may provide an excellent noninvasive method of following these patients.

Cardiomegaly↗
PubMed1985

The surgical treatment of atrial myxomas. Clinical experience and late results in 33 patients.

Thirty-three patients (28 female and five male) from 17 to 70 years of age (mean age 48 years) underwent excision of left atrial myxomas between 1957 and 1981 at The Cleveland Clinic Foundation. Twenty-four patients presented with congestive heart failure, three with tachyarrhythmias, two with syncope, and one each with angina, peripheral embolization, hemoptysis, and recurrent pleural effusions. Symptoms were present from 1 to 72 months before operation (mean 11.2 months). Thirty-one tumors originated from the atrial septum and two from the mitral valve anulus. Twenty-nine tumors were pedunculated, and four were sessile; they weighed from 20 to 112 gm (mean 57 gm). No right atrial or ventricular tumors were identified. The myxomas were successfully removed in all patients, either by shaving them from the atrial septum (n = 17) or by excising a portion of normal atrial septum with the tumor (n = 16). One death (3.0%) occurred 8 days after operation as a result of multiple tumor emboli to the coronary circulation. Follow-up is current and complete in all cases (range 1 to 25 years, mean 6.7 years). Twenty-eight patients are in New York Heart Association Class I, and the remaining four patients are in Class II. No recurrent myxomas have been identified clinically or by echocardiography in any patient. Altogether, 24 patients have been studied by two-dimensional echocardiography up to 20 years after operation (mean 4.0 years). In this series, excellent results were obtained by simple excision of the tumor, with or without a margin of normal atrial septum. Long-term clinical and echocardiographic follow-up is recommended since late recurrence, although rare, has been reported.

Adolescent↗
PubMed1983

Long-term management of diaphragmatic paralysis complicating prosthetic valve replacement.

The exact incidence of diaphragmatic paralysis complicating secondary heart procedures is not known. The postoperative period can be complicated by difficulty in weaning from mechanical ventilation and misinterpretation of the clinical signs of respiratory muscle fatigue for congestive heart failure and acute bronchospasm. We present 3 patients, all of whom had right diaphragmatic paralysis and recurrent respiratory failure after a second mitral valve replacement. Long-term management with night-time ventilation in 2 patients resulted in no further episodes of respiratory failure and physical rehabilitation with exercise tolerance significantly greater than the preoperative state.

Aged↗
PubMed1975

Selection of the candidate for myocardial revascularization; a profile of high risk based on multivariate analysis.

A survey of 60 patients who died from cardiac related causes after vein or artery bypass operations alone (1967 to 1973) was made with respect to 26 clinical, angiographic, and operative variables. These factors were compared with identical characteristics of 1,188 survivors operated upon in 1973. Through discriminant analysis, the various characteristics, isolated or multiple in any combination, have been converted into risk related to operative death. The distinctive features of the mortality group were vastly different from those in the surviving group. Ten patients (16.67 per cent) of the mortality group were in the ninety-ninth percentile of risk, whereas these factors or variables of similar weight produced an equivalent risk of only 0.34 per cent of the survivors; thus, operative death in these circumstances could be predicted with an estimated 98.0 per cent assurance. Each of 6 patients with mortality risks above 0.99999 had (1) marked cardimegaly, (2) uncompensated congestive heart failure (CHF), (3) triple vessel coronary artery disease and/or obstruction of the left main coronary artery, (4) generalized impairment of left ventricular contraction or segmental left ventricular scar, and (5) evelated left ventricular end-diastolic pressure. As a single factor, congestive heart failure (CHF) exerted the most influence on the probability of dying. A new and more desctiptive statistical interpretation of the factors presumed to affect risk is presented.

Age Factors↗
PubMed1970

Cinecoronary arteriography in young men.

Of a group of 723 men less than 40 years old who underwent cinecoronary arteriography primarily for evaluation of chest pain, 357 (49%) were found to have at least 50% narrowing of one or more coronary arteries. The youngest person was 17 years old. The distribution of lesions in the young men was similar to that found earlier in a study of persons not selected by age. The anterior descending coronary artery was most frequently affected; the right coronary artery was most often totally occluded. No total occlusions of the left main coronary artery were seen. Electrocardiographic evidence of myocardial infarction, found in 109 patients, was less common with disease of the circumflex or right coronary arteries than with disease of the anterior descending coronary artery. This observation was confirmed by examination of left ventriculograms for areas of decreased contractility. Six patients had no significant arterial narrowing. The extent of arterial involvement seemed to be related to the duration of symptoms in patients who had angina pectoris or myocardial infarctions. Clinical diagnoses correlated well with the angiographic findings, particularly in those men considered to be normal and those with typical angina pectoris. Addition of atypical features or prolonged pain decreased the degree of correlation. Only 20% of those with cholesterol levels less than 200 mg/100 ml had significant lesions, whereas 81% with levels more than 275 mg/100 ml had such findings.

Adolescent↗