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Biomedical subjects

F Pedersen

Publications and source records attributed to F Pedersen.

At least 19 recordsLinked to original sources
PubMed1994

Principal component analysis of dynamic positron emission tomography images.

Multivariate image analysis can be used to analyse multivariate medical images. The purpose could be to visualize or classify structures in the image. One common multivariate image analysis technique which can be used for visualization purposes is principal component analysis (PCA). The present work concerns visualization of organs and structures with different kinetics in a dynamic sequence utilizing PCA. When applying PCA on positron emission tomography (PET) images, the result is initially not satisfactory. It is illustrated that one major explanation for the behaviour of PCA when applied to PET images is that it is a data-driven technique which cannot separate signals from high noise levels. With a better understanding of the PCA, gained with a strategy of examining the image data set, the transformations, and the results using visualization tools, a surprisingly easily understood methodology can be derived. The proposed methodology can enhance clinically interesting information in a dynamic PET imaging sequence in the first few principal component images and thus should be able to aid in the identification of structures for further analysis.

Artifacts↗
PubMed1994

MUSE--a new tool for interactive image analysis and segmentation based on multivariate statistics.

MUSE--a new software tool for the interactive exploration of multivariate images and the development of image segmentation methods has been designed, implemented, and tested in a number of real application projects. The multivariate statistical classification and projection methods in MUSE can be used not only to analyze multispectral images but also, in special cases, multitemporal images and volume images. Additionally MUSE can be applied to normal greyscale images provided they are made multivariate through an initial processing step. This step may consist in the application of filters designed to enhance any existing texture differences between different regions in the images. MUSE has been successfully applied to medical images (color photographs, MR, PET, SPECT) as well as to satellite images (Landsat TM).

Diagnostic Imaging↗
PubMed1994

Is there a relationship between the acoustic occlusion effect and the sensation of occlusion?

The objective of the present investigation was to examine the relationship between the acoustic occlusion effect and the subjective occlusion sensation when using ear moulds. The material comprises 45 subjects (19M and 26F, at a median age of 76 years, range 38-88 years) subgrouped according to the classification of their hearing disorder into two group: N = 22 subjects with conductive hearing loss (1); N = 21 subjects with sensorineural hearing loss (2). The side effects caused by an ear mould were evaluated at an interview, based on a structured questionnaire, two months after the hearing aid fitting. The comparative investigation showed that when the outer ear canal was occluded with an ear mould there were no significant differences between the two groups of subjects in the frequency of sensation of occlusion, in the sound quality of environmental sound or own voice, in hearing problems when chewing, or in ventilation problems. Neither were significant differences in the magnitude of the acoustic occlusion effect present between those answering yes and those answering yes and those answering no to a change in the sound quality of own voice in the group with sensorineural hearing loss. Although the number of subjects is limited, it is concluded that no relationship exists between the acoustic occlusion effect and the perceived sound quality, thus leaving no physical basis for the claim that this side effect is caused by an ear mould.

Adult↗
PubMed1993

Effects of atenolol and diltiazem on exercise tolerance and ambulatory ischaemia.

Twenty-five normotensive patients with stable angina, angiographically documented coronary disease and normal left ventricular function were randomized to a crossover study comparing atenolol 100 mg x 1, sustained-release diltiazem 120 mg x 2, and their combination. A maximal symptom limited bicycle exercise test and a 24-h ambulatory electrocardiographic (ECG) monitoring were performed at the end of each treatment period. Exercise duration was increased equally in the different treatment groups. Time to onset of 1-mm ST-segment depression was longer with atenolol (P < 0.02) and combination therapy (P < 0.01) than with diltiazem. The maximal ST-segment depression was decreased with atenolol (P < 0.05) and combination therapy (P < 0.02), whereas, time to onset of angina was prolonged only with combination therapy (P < 0.03). The number of ischaemic episodes during ambulatory monitoring was lower with atenolol and combination therapy than with diltiazem (P < 0.01). The difference between atenolol and diltiazem was mainly due to lower ischaemic activity with atenolol between 06:00 h and 12:00 h (P < 0.05). Anginal frequency (P < 0.01) and nitroglycerin consumption (P < 0.05) were lower with combination therapy than with monotherapy. Thus, while comparable effects were achieved on clinical variables, atenolol appeared to be more effective than diltiazem, reducing myocardial ischaemia during exercise and ambulatory monitoring. With combination therapy, both clinical and electrocardiograph signs of ischaemia were improved.

Adult↗
PubMed1993

Planar 201Tl scintigraphy in ischaemic heart disease: a critical re-evaluation of qualitative and quantitative data analysis.

The aims of the present study were to examine the observer agreement of qualitative (visual) and quantitative (computer-assisted) analysis of planar 201Tl imaging and to compare the diagnostic values of these methods in the detection of infarcted and exercise-induced ischaemic myocardium. The study population comprised of 119 patients (aged 24-77 years) referred consecutively for stress thallium scintigraphy for either diagnostic reasons (n = 42, 35%) or for further evaluation of known coronary artery disease (CAD) (n = 77, 65%). The interobserver agreement was low with the qualitative method and significantly higher with the quantitative method: Kappa-values 0.29-0.39 vs. 0.80-0.92, P < 0.00001. Sensitivity and specificity for the detection of previous Q-wave infarct was significantly higher with the quantitative method (94% and 94%) compared to the qualitative method (77% and 74%), P < 0.01. The corresponding predictive values of a positive and a negative test were 96% and 92% vs. 80% and 70% (P < 0.01). In 86 patients in whom coronary angiography was performed the two methods did not differ significantly regarding sensitivity, specificity and predictive values for the diagnosis of reversible ischaemia or rather CAD. However, when 22 patients with a maximal exercise heart rate < 80% of the predicted target heart rate were excluded the sensitivity was increased with both techniques and was significantly higher with the quantitative method. We conclude that qualitative image analysis has an unacceptably low reproducibility and that quantitative image analysis increases the diagnostic value of 201Tl scintigraphy considerably in both the detection of previous infarcts and, provided a sufficient exercise level is achieved, in the disclosure of reversible myocardial ischaemia.

Adult↗
PubMed1992

[Magnesium and ischemic heart disease].

Our knowledge about magnesium in health and disease has increased during the past ten years. Many authors have demonstrated possible magnesium depletion in the population as a whole and particularly among cardiac patients receiving diuretics. Evidence suggests that this magnesium depletion may play a role in the development of arteriosclerosis. It has been demonstrated that long term supplementation of the diet with magnesium reduces the frequency of heart disease. However, the matter is still not proven. It is postulated further that magnesium depletion aggravates the outcome of acute myocardial infarct and has a tendency to provoke arrhythmia. Finally, it has been shown that the potassium depletion frequently observed among cardiac patients may actually arise from magnesium depletion. On this basis, many authors have employed magnesium therapy in various cardiac diseases. Some authors have demonstrated that magnesium therapy reduces the mortality in AMI patients. These studies are, however, too few and too limited to be conclusive. In order to investigate this question, an international multicentre trial (ISIS-4) will be conducted to investigate the influence of magnesium therapy on the mortality after acute myocardial infarction.

Coronary Disease↗
PubMed1992

Effect of thrombolytic therapy on exercise response during early recovery from acute myocardial infarction: a placebo controlled study.

Several studies have shown that infarct size is reduced following thrombolytic treatment in patients with acute myocardial infarction. Exercise test variables, such as an impaired heart rate response during exercise, are known to be related to left ventricular function and patient prognosis following acute myocardial infarction. The present study was performed to compare exercise test variables in acute myocardial infarction patients following either intravenous thrombolysis or placebo. Symptom-limited bicycle ergometer tests, carried out 1-2 weeks from the infarction, were performed in 85 patients randomized to intravenous streptokinase (N = 41) or placebo (N = 44) given within 12 h from onset of symptoms. At rest heart rate, systolic blood pressure and rate-pressure product were similar in the two groups. At maximum workload the streptokinase treated patients had a higher median maximal heart rate than controls (136 vs. 126 b.min-1, P less than 0.01) but only a trend towards higher systolic blood pressure was seen (175 vs. 163 mmHg, P = 0.09). Rate-pressure product at maximal exercise was 23,620 vs. 20,100 mmHg.b.min-1 respectively, (P less than 0.01). Total exercise time, ST-segment deviation, occurrence of angina pectoris and left ventricular ejection fraction were similar in the two groups. The trend towards an increased heart rate at maximum workload in streptokinase-treated patients was seen at all levels of left ventricular ejection fraction, and at all levels of exercise capacity.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Pressure↗
PubMed1991

Prevalence and significance of an abnormal exercise ECG in asymptomatic males. Outcome of thallium myocardial scintigraphy.

During a 3-year period 2500 asymptomatic male aviators were screened routinely for coronary artery disease by maximal bicycle exercise testing. In 55 cases (2.1%) the exercise ECG was abnormal (40 subjects exhibited ST depression, 14 ventricular ectopic activity and in one subject both abnormalities were observed). Further non-invasive studies (Thallium scintigraphy, echocardiography and ambulatory ECG monitoring for arrhythmias) identified nine out of the 55 aviators (16%, 95% CL = 7-26%) with an abnormal exercise test as having cardiac disease. We conclude that standard exercise ECG by itself is a poor predictor of coronary artery disease in asymptomatic subjects because of too many false-positives when the pre-test likelihood of disease is low. Therefore, exercise electrocardiography cannot be recommended as the single routine screening test for coronary artery disease in such individuals.

Adult↗
PubMed1991

Continuous oral N-acetylcysteine treatment and development of nitrate tolerance in patients with stable angina pectoris.

The presence of sulfhydryl (SH) groups appears to be fundamental to nitrate-induced vasodilation and N-acetylcysteine (NAC), a sulfhydryl (SH)-donor substance, potentiates hemodynamic responsiveness to nitrates. We investigated the effect of simultaneous administration of NAC and isosorbide dinitrate (ISDN) on development of nitrate tolerance. In a double-blind, randomized, placebo-controlled cross-over study, seven patients with stable angina pectoris were treated for two 8-day periods with ISDN (40 mg four times daily, q.i.d.) together with NAC (controlled release 600 mg q.i.d.) or matching placebo. Bicycle exercise tests were performed before treatment was started, 1 h after treatment was started, and at day 8. After 8-day treatment with ISDN + placebo, responses determined by exercise testing were diminished as compared with responses obtained during acute therapy and did not differ from baseline values, suggesting development of tolerance to ISDN. During treatment with ISDN + NAC, time to 1-mm ST depression was significantly prolonged (441 +/- 44 vs. 381 +/- 40 s, mean +/- SEM) and total ST segment depression significantly reduced (1.9 +/- 0.7 vs. 3.5 +/- 0.8 mm) as compared with baseline values. The reduction in ST segment depression was significantly more pronounced during ISDN + NAC (46%) as compared with ISDN + placebo (23%). Although exercise time and time to angina pectoris were unaffected. NAC augmented the antiischemic effects of ISDN as assessed by ECG. This finding may suggest that development of nitrate tolerance is modified by chronic oral high-dose NAC administration.

Acetylcysteine↗
PubMed1991

High-frequency amplification with ITC-HA and BTE-HA. A comparative investigation.

The purpose of the present investigation was to evaluate the magnitude of selective high-frequency amplification obtained by an in-the-canal hearing aid (ITC-HA), and to compare it with that obtained with a conventional behind-the-ear hearing aid (BTE-HA) with an open mould. 22 subjects (20 males, 2 females) at a median age of 66 years (range 46-84) were included in the investigation. All suffered from a bilateral high-frequency hearing loss with normal or near-normal hearing thresholds at 0.5 and 1 kHz. Insertion gain measurements demonstrated that the ITC-HA gives a significantly higher amplification in the high-frequency area, when compared with the BTE-HA, though neither of the hearing aids amplified as much as indicated by the POGO strategy. Although a better amplification in the high-frequency area was obtained with the ITC-HA, it did not result in significantly better speech recognition when compared with the BTE-HA. At the hearing aid fitting, all subjects preferred the ITC-HA, and after an observation period of one year, 68% of those fitted used the aid continuously. Based on the investigation it is concluded that hearing-impaired persons can be fitted with an ITC-HA, even if they have pronounced high-frequency hearing loss, and that this type of aid is preferred by the hearing-impaired to the conventional BTE-HA.

Aged↗
PubMed1991

Microvascular right-to-left pulmonary shunt demonstrated by a radionuclide method.

A 37-yr-old man with angiolymphoid hyperplasia (Kimura's syndrome), who had been treated unsuccessfully for suspected asthma, was investigated due to a decrease in arterial oxygen saturation (86%). Right heart catheterization and angiography of the pulmonary artery failed to demonstrate any right-to-left shunts. However, simultaneous scintigraphy over the lungs, kidneys, and head after injection of 150 MBq technetium-99m-labeled macroaggregated albumin i.v. and inhalation of 150 MBq krypton-81m demonstrated a right-to-left shunt in the lungs probably caused by precapillary pulmonary arteriovenous shunts.

Adult↗
PubMed1990

[Use of fibrinolytics in the treatment of acute myocardial infarction in Denmark. A questionnaire study].

Questionnaires were sent to all Danish departments admitting patients with acute myocardial infarction (AMI) in order to investigate the attitudes of the departments to thrombolytic therapy in AMI. Two questionnaires were used: one with few questions which was answered by all 68 departments, and a more comprehensive questionnaire which was answered by 51 departments. The study shows that thrombolytic therapy now is use in all departments as opposed to 25% two years ago. In connection with introduction of thrombolytic therapy scientific studies are performed in 75% of the departments. In all departments, streptokinase (SK) is the drug of first choice and recombinant tissue plasminogen activator (rt-PA) is used in 2/3 of the departments in cases where SK-antibodies are suspected.

Denmark↗
PubMed1990

ECG and enzymatic indicators of therapeutic success after intravenous streptokinase for acute myocardial infarction.

Thrombolytic therapy has been documented to result in reperfusion of jeopardized myocardium and reduction in the size of the acute myocardial infarction (AMI). The effect of intravenous streptokinase on a creatine kinase-MB (CK-MB) reperfusion index and an ECG estimate of myocardial salvage was therefore studied in 65 patients with a first AMI, randomized to treatment with streptokinase (n = 33) or placebo (control group, n = 32). Reperfusion was defined as a CK-MB appearance rate constant (k1) greater than 0.185. The final AMI size was first predicted from the admission standard ECG by previously developed formulas based on ST segment elevation. The final AMI size was estimated from the QRS score on the predischarge ECG. Myocardial salvage was defined as a greater than or equal to 20% decrease from predicted to final AMI size. The k1 value in the control group was significantly lower than that in the streptokinase group (median 0.157 versus 0.328; p = 0.0001). Accordingly the reperfusion rate was higher in the streptokinase group than in the control group (88% versus 34%; p = 0.0002). The difference in AMI size (final-predicted) was significantly greater in the streptokinase group than in the control group (median -7% versus +1%; p = 0.0001). Myocardial salvage occurred in 60% and 19%, respectively (p = 0.004). A significant correlation was found between CK-MB reperfusion and ECG salvage: 19 of 20 streptokinase-treated patients with salvage also had reperfusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Creatine Kinase↗
PubMed1990

Effect of intravenous streptokinase on the relation between initial ST-predicted size and final QRS-estimated size of acute myocardial infarcts.

Thrombolytic therapy has been documented to reduce acute myocardial infarct size. The previously established relation between initial ST segment elevation and final electrocardiographic (ECG) myocardial infarct size in patients without coronary reperfusion might therefore be altered by thrombolytic therapy. The effect of intravenous streptokinase on this relation was therefore studied in 73 patients with initial acute myocardial infarction who had participated in the Second International Study of Infarct Survival (ISIS-2). Patients who received streptokinase were considered as one group and patients who did not receive streptokinase as a control group. Final myocardial infarct size, which was estimated from the QRS score, was predicted from the admission standard ECG by previously developed formulas based on ST segment elevation. In the 40 control patients there was no change from ST-predicted to final QRS-estimated infarct size (median 17.7% versus 18.3%; p = NS). In the 33 patients in the streptokinase group, there was a highly significant decrease from predicted to final myocardial infarct size (median 21.9% versus 16.2%; p less than 0.0002). This decrease was found for both anterior (median 23.7% versus 19.5%; p less than 0.03) and inferior (median 21.9% versus 12.0%; p = 0.001) infarct locations. Multiple regression analysis adjusting for differences in predicted infarct size confirmed the significance of streptokinase on the difference in infarct size (p = 0.006). Based on the variability of the percent change from predicted to final infarct size in the control group, a threshold decrease greater than or equal to 20% is required for identification of salvage.(ABSTRACT TRUNCATED AT 250 WORDS)

Aspirin↗