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Biomedical subjects

H R Ham

Publications and source records attributed to H R Ham.

At least 109 records · Page 6Linked to original sources
PubMed1987

Measurement of right ventricular volumes from ECG-gated steady-state krypton-81m angiocardiography.

The physical characteristics of krypton-81m makes it particularly suited for the study of right ventricular function, but its ultrashort half-life (13.3 s) precludes in vitro measurements of blood pool specific activity needed for count based determination of ventricular volumes. A combined geometric count based method was developed to measure absolute right ventricular volumes during steady state krypton-81m angiocardiography: background corrected ventricular count rates were converted to volumes using a count to volume calibration factor calculated in an 'internal reference ROI' located in the right ventricular outflow tract. Stroke volumes calculated with this method were shown to be comparable to thermodilution determined stroke volumes and the ability of the method to monitor changes in right ventricular volumes was demonstrated during intervention studies.

Angiocardiography↗
PubMed1986

The clinical value of 201Tl per rectum scintigraphy in the work-up of patients with alcoholic liver disease.

The clinical value of thallium 201 per rectum scintigraphy in the work-up of patients with alcoholic liver disease was evaluated using data obtained in 104 patients. The 25th min ratio of heart to liver activities was used as an index of portal systemic shunting. This ratio was found to be normal in alcoholic patients with normal liver biopsy and also in those presenting only steatosis. It was slightly higher in patients with liver fibrosis and significantly higher values were observed in patients with liver cirrhosis. High values of the ratio were associated with a higher risk of portal systemic encephalopathy and/or gastrointestinal bleeding. The prognostic value of the test was supported by the fact that good correlations were observed between the ratio and widely accepted prognostic scores such as the Child score or the Orrego index. Moreover, high ratios were associated with an increased mortality risk at one year. We conclude that this simple test is interesting in the screening of cirrhotics at risk of encephalopathy, gastrointestinal hemorrhage, or early death.

Adult↗
PubMed1986

Right ventricular ejection fraction: comparison of technetium-99m first pass technique and ECG-gated steady state krypton-81m angiocardiography.

Right ventricular ejection fraction (RVEF) calculated from ECG-gated steady-state 81mKr angiocardiography and from 99mTc first-pass studies were compared in 30 patients using a digital, single crystal, gamma-camera. Despite the two entirely different approaches RVEF values obtained by the two methods were comparable (r = 0.97): the mean absolute difference between the two techniques was 2.5% +/- 1.5% and the largest observed absolute difference was 5%. In the absence of an accepted reference method for measuring RVEF, this close correlation provides indirect validation of both techniques. The choice of method will therefore depend on several factors, including radiotracer availability, the characteristics of the gamma-camera and the protocol of clinical investigation.

Adult↗
PubMed1986

Radioisotopic evaluation of the renal parenchymal function in children with ureteropelvic junction obstruction. A retrospective study.

Separate glomerular filtration rates were evaluated in 21 children with uni- or bilateral ureteropelvic junction stenosis, using the Tc-99m DTPA complex and the scintillation camera. The grade of alteration seen on urograms has influenced the surgeon in his decision to use a conservative or a surgical treatment, whereas the type of intervention (pyeloplasty or nephrectomy) was mainly based on the scintigraphic quantitation. The morphological data provided by an excretory urogram could not predict the degree of functional impairment. The scintigraphic evaluation of single kidney clearance was useful in the evaluation of the effects of medical and surgical treatment.

Adolescent↗
PubMed1986

Technetium-99m DMSA imaging and the obstructed kidney.

Although several authors have claimed that the function of an obstructed kidney could be overestimated on Tc-99m DMSA imaging, the clinical importance of such an overestimation has not been well documented. Partial obstruction of one ureter was created in a rat, and a relative Tc-99m DMSA uptake was obtained 4 hours after intravenous injection. By puncture of the isolated obstructed kidney, it was shown that the function of that kidney was overestimated by at least 17%.

Animals↗
PubMed1986

Thallium scintigraphy in the evaluation of portal systemic shunting. The problem of rectal absorption.

Thallium-201 scintigraphy is an attractive method for studying the portal systemic shunting. However, the technique is sometimes hampered by a low rectal absorption. The present work shows that cirrhotic patients present a significantly lower activity in the regions of interest in relation to the low absorption of the tracer as compared with non-cirrhotic subjects (p less than 0.01). This study also demonstrates that the dilution of the tracer in a large volume cannot be envisaged in order to increase the surface contact and secondarily the absorption, because part of the tracer can reach the inferior vena cava via portal systemic communications in the lower part of the rectum. Oral administration of the thallium was also attempted but this route cannot be used in relation to its poor absorption and due to the difficulty in separating liver from intestinal activity. The study also shows that even in the case of low activity in the regions of interest, the interpretation of the test in cirrhotic patients is usually possible on the condition that the curves of radioactivity in the liver and cardiac areas are ascending. Using these criteria, only 6.7% of the tests were in fact not interpretable in this study.

Female↗
PubMed1986

Evaluation of the accuracy of steady-state krypton-81m method for calculating right ventricular ejection fraction.

The accuracy of a steady-state 81mKr method for calculating the right ventricular ejection fraction (RVEF) has been examined in this study. Causes of errors using this method and their effects on the calculated RVEF were evaluated. The results suggested that mixing in the right ventricle during continuous infusion of 81mKr was homogenous, allowing for the calculation of ejection fraction using the count rate ratio. Lung activity was quite important and could not be neglected in computing RVEF, but the use of [99mTc]MAA lung perfusion scanning seemed to allow a correct subtraction of this background activity. The delineation of right ventricular regions of interest (ROIs) was complicated by the translation movements of the right ventricle during heart contraction. These ROIs should be drawn carefully on the count density distribution images and data shown by parametric images; such as first and second harmonic phase, amplitude images, and composite stroke volume image should be considered. Furthermore, this study demonstrates the superiority of the 81mKr technique compared with 99mTc methods for computing RVEF. In conclusion, even if the true accuracy of the 81mKr method for calculating RVEF cannot be proven due to the lack of reference methods, strong, suggestive evidence that the technique should be accurate is shown here.

Adult↗
PubMed1985

Ventilation-perfusion patterns in lung diseases (with reference to those observed in pulmonary embolism).

The frequency distributions of ventilation-perfusion (V-P) patterns in various lung diseases were compared to those observed in pulmonary embolism in order to determine whether the specific V-P patterns for pulmonary embolism constituted a frequent finding in these disorders. The results showed that a segmental or lobar perfusion defect with normal ventilation, was associated with a high probability of thromboembolic lung disease, and was not present in any of the other lung diseases studied.

Humans↗
PubMed1985

Amplitude distribution in the right ventricle.

Amplitude distribution in the right ventricle obtained from ECG-gated ventriculography has been reviewed and six amplitude distribution patterns were identified. Homogeneous distribution was rarely observed even in patients without any cardiac or pulmonary diseases. Furthermore, there was no difference in frequency distribution of the amplitude distribution patterns between the control group, patients with coronary diseases, and those with recent inferior myocardial infarction. It was concluded that amplitude distribution could not be used to detect hypokinetic areas in the right ventricle.

Angina Pectoris↗
PubMed1985

Evaluation of methods for qualitative and quantitative assessment of esophageal transit of liquid.

The aim of this work was to compare the advantages and the limitations of several data processing techniques for the assessment of esophageal transit. The following qualitative methods were evaluated: scintigraphic image, cine-display, regional time-activity curve, and condensed image. The quantitative methods evaluated were the pixel to pixel presentation of parameters of the time-activity curves such as time of arrival, time to maximum, and several downslope parameters, mean transit time, mean time, and a new transit parameter based on the radioactive decay. The study allowed us to conclude that for the detection and the quantitation of esophageal transit the method of choice was the combined use of the condensed image and the pixel to pixel mean time image. The parametric image using the transit parameter calculated from decay was shown as a valuable alternative if an ultra-short half-life radionuclide was used as the tracer.

Esophagus↗
PubMed1985

Evaluation of esophageal transit in children and in infants by means of Krypton-81m.

This paper presents the results of Krypton-81m esophageal transit study in a series of children and infants presenting various esophageal disorders. The advantage of Kr-81m, compared to other radionuclides, is that the radiation dose to the patient is extremely low. The study can therefore be repeated as often as necessary and a high dose can be given to ensure good quality results. The method is very easy to perform and allows a quantitative assessment of esophageal transit in physiological conditions. The method gives information about the severity of altered transit and it is particularly useful in studying the effects of treatment.

Adolescent↗
PubMed1985

Oesophageal transit of liquid: effects of single or multiple swallows.

The effects of single and multiple swallowing on oesophageal transit have been evaluated in healthy subjects. It was shown that the transit patterns observed after multiple swallowing were different from that observed after a single swallow. It was concluded that for the detection of oesophageal transit abnormalities, the test should be performed using a single swallowed bolus.

Deglutition↗