Biomedical subjects
Publications and source records attributed to E Riihimäki.
A prototype device consisting of a focused array of several scanning collimator plates that produce multiple pencil beams has been constructed for radiographic imaging. Under normal imaging conditions, the scatter-to-primary ratio resulting from this device is less than 10%. High-contrast radiographs can be produced without increasing patient radiation dose.
Simultaneous assessment of coronary flow and flow-volume relation makes it possible to evaluate the dilatatory responses of coronary vasculature. A new set up of methods for investigation of the coronary circulation was employed to study the nature of the coronary flow and volume responses to dipyridamole in dogs. The turnover rate of coronary blood, the reciprocal value of the mean transit time, can be accurately determined by computer simulation analysis of coronary dye dilution curves. After intravenous dipyridamole (0.5 mg/kg) both coronary turnover rate and electromagnetically assessed blood flow were observed to increase in parallel and to the same degree (+55%). This indicates that no increase in the coronary vascular volume and, accordingly, no significant overall coronary dilatation takes place. The effective coronary blood flow in relation to the myocardial oxygen consumption, i.e. the nutritional flow, and the myocardial oxygen consumption decreased by 25% concomitant to a corresponding fall in myocardial oxygen requirements. Thus, the increase in total coronary flow after dipyridamole is useless for myocardial metabolism, and may properly be denoted as luxury perfusion or throughput flow.
The body disappearances and the liver mean transit times of a hepatobiliary tracer, 99mTc-diethyl IDA, were measured from 100 cholescintigraphies of 98 patients. Fifteen patients had no hepatobiliary disease; their mean body disappearance was 6.6, SD 1.1%/min, and mean liver mean transit time 32, SD 19 min. The values within 2 SDs, disappearance greater than or equal to 4.4%/min and mean transit time less than or equal to 70 min, were used as reference values. Disappearance constants below 4.4%/min were observed 29% and mean transit times exceeding 70 min in 49% of the examinations performed on patients with some hepatobiliary abnormality. The calculated parameters were compared with the levels of serum bilirubin and ASAT. Disappearance constants below 4.4%/min were seen in 33% and mean transit times exceeding 70 min in 55% of the patients who had either abnormal serum bilirubin or ASAT due to a hepatobiliary disease. The correlation between the serum bilirubin and the disappearance was -0.13, and between ASAT and body disappearance it was -0.28. The corresponding correlation coefficients of serum bilirubin and ASAT with the liver mean transit times were 0.33 and 0.44. Long mean transit times in relation to bilirubin and ASAT were seen in some acute cases. Short mean transit times in relation to bilirubin and ASAT were seen with falling serum levels of the latter.
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The effect of beta-blockade by acebutolol on global and regional myocardial perfusion (133Xenon wash-out) was studied in 10 patients with coronary artery disease. Another group of 10 similar patients was used to study the effect of acebutolol on left ventricular cavity size (metal markers--spot film camera). Global perfusion responses roughly paralleled the changes in rate-pressure variable which decreased in 8 patients and increased in 2 who had spontaneous angina pectoris. Regional perfusion decreased more in areas distal to less than 75% stenoses than in those distal to less than 75% stenoses (29 vs 12%; p = 0.10 less than 0.20). Left ventricular asynergy did not modify the response, nor did the presence or absence of collateral vessels. No evidence was found to support the thesis that beta-blockade may evoke a redistribution in perfusion which favours the potentially ischaemic areas of myocardium. Left ventricular cavity size remained unchanged after acebutolol, a cardioselective beta-blocking compound with some degree of agonist activity.
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With use of semiselective xenon-133 injections and gamma camera recording, myocardial scintigrams were obtained in a series of 20 patients with angina pectoris, abnormal exercise electrocardiograms and normal coronary arteries. Ten patients (Group I) exhibited localized perfusion defects and the other 10 (Group II) a hjemogenous uptake of the tracer. Group I was characterized by more past myocardial infarctions and, most significantly, by male preponderance (P less than 0.001). Computer analysis of regional xenon-133 washout curves revealed that every patient in Group I had a reduced flow rate in the area of the perfusion defect (P less than 0.001). A comparison of this group with 26 patients with similarly abnormal scintigrams but coronary arterial obstruction revealed that myocardial perfusion was 16 to 18 percent greater in the group with normal coronary arteries. In three patients of this group, myocardial perfusion rates were not augmented by atrial pacing in contrast to the response in patients with coronary arterial obstruction. The data demonstrated localized perfusion abnormalities in half of the patients with angina pectoris and normal coronary arteries and constitute evidence that a metabolic disorder is not the sole mechanism for ischemia in this syndrome.
Using a gamma camera and the Xenon-133 washout method the reduction in lung function during unilateral bronchography was assessed in eleven patients. A considerable reduction in the washout rate was observed in the lung examined with bronchography both absolutely and compared with the opposite lung. Some improvement occurred after coughing out the contrast medium. It is concluded that the ventilatory function of the lungs is considerably impaired during bronchography and this should be borne in mind when referring patients with reduced lung function for this examination.
A new method of processing digital images consists of a numerical filter which suppresses normal features producing an enhancement of the abnormality. The resulting filtered image aids the observer in the recognition of the abnormality. The filter is developed from verified normal images in the computer memory. The enhancement of pathologic accumulations with respect to surrounding activity was improved on the average by a factor of 2.6 for 13 lateral brain images.
Twelve patients with tumors and three with osteitis of the extremities were studied using 99mTc-labelled tetracycline in order to image the process with gamma camera. The diagnosis of all cases were verified histologically. The labelled tetracycline was found to give positive images for the most malignant tumors and active osteitis which together comprised about half of the studied cases.
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Studies were made using ordinary selective coronary angiography and angiography during ischaemia produced by right atrial pacing, on a series of 41 patients with ischaemic heart disease, to examine the response of the collaterals to the ischaemia stimulus. Regional myocardial perfusion was determined under the same circumstances by measuring regional 133Xenon washout curves. No collaterals were found in 8 patients, none of whom demonstrated collaterals when angiography was repeated during ischaemia. Eleven of the 33 patients with prepacing collaterals (33%) responded to ischaemia with an increase in the collaterals, 16 patients (49%) showed no change, 5 patients (15%) showed a decrease in the collaterals, and one patient exhibited a bidirectional change. Regional myocardial perfusion responses closely paralleled the angiographic changes, yielding suggestive evidence that the collaterals were intimately involved in the enhancement of the flow. Despite different collateral and flow responses to ischaemia, the data on exercise tolerance, left ventricular end-diastolic pressure, ejection fraction, prevalence of left ventricular asynergy, and the topographic relation between synergy and collaterals, were largely similar. The data show that in some patients the collateral circulation reacts to ischaemia by enhancement, but the functional significance of this response is obscure.
After selective coronary arteriography 150 muCi of Thallium-201 was injected into each coronary artery. Scintigraphy of the myocardium was performed about half an hour after the injection. In a series of ten patients the myocardium was clearly visualized in the gamma images. No adverse effects were noted.
By employing 133 Xenon injections and a gamma camera recording of the initial uptake and subsequent disappearance of the tracer, regional myocardial perfusion rates were determined in 38 patients with ischaemic heart disease. Areas supplied by collaterals and areas devoid of them were analyzed separately. In addition to determining basal flow rates, the regional perfusion was studied by repeated 133Xenon scintigrams during pacing-induced ischaemia. The data were grouped and analyzed according to the visual assessment of collateral response as observed in the angiograms performed under the same circumstances. Eleven patients who did not have collaterals on their angiograms were excluded, as were three patients in whom the collaterals were supplying segments distal to only subtotal obstructions leaving 24 patients to the study proper. Angiographic appraisal disclosed two different responses to ischaemia: ten patients exhibited an increase in the collateral pattern (responders) and 14 patients showed no change or reduction in the collaterals (nonresponders). The prepacing grading of the collaterals was similar in the subgroups. Under basal conditions the regional myocardial flow rates in areas supplied by collaterals or devoid of them were roughly similar. Upon ischaemia the greatest regional flow increment occurred in the responders. The data demonstrate a reasonable agreement between the visual assessment of collateral response to ischaemia and a change in the regional perfusion. The data further indicate that similar collateral patterns observed by routine coronary angiography are not functionally equipotent.
The series consisted of eight cases of severe serum alpha1-antitrypsin deficiency (Piz homozygosity) and eight lung patients with a heterozygous level of the compound. The regional blood pulsation pattern in the lungs in the recumbent position was compared with the pattern in a group of normal controls using a cinedensigraphic device specially constructed for lung circulation studies. In the homozygous group, pulsation in the lower part of the lungs was significantly weakened to the benefit of the apical part. Individual variations occurred. The disturbance observed was not altered with oxygen breathing. This phenomenon is analogous to the redistribution of the blood flow demonstrated by scintigraphic methods. The heterozygous group did not differ significantly from the normal controls with regard to regional pulsation pattern.
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Renal blood flow measurements in three regions of each kidney were carried out in eighteen hypertensive patients using the radioactive Xenon-133 washout technique in conjunction with renal angiography. It was found that the regional differences were generally small but differences existed in four patients significant in spite of normal angiographic findings. The reduction in blood flow in the two kidneys was generally of the same degree which implies a uniform response to the elevated blood pressure.