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Biomedical subjects

P C Minnaar

Publications and source records attributed to P C Minnaar.

At least 19 recordsLinked to original sources
PubMed1990

A comparison of the clinical relevance of thallium-201 and technetium-99m-methoxyisobutyl-isonitrile for the evaluation of myocardial blood flow.

Thallium-201 is at present the radiotracer of choice for the clinical evaluation of myocardial blood flow. Although different technetium-99m-isonitrile agents have been synthesised recently, only 99mTc-methoxyisobutyl-isonitrile (99mTc-MIBI) has proved to hold promise for clinical implementation. The myocardial distribution of 201Tl and 99mTc-MIBI was compared in a group of 20 patients, who underwent both 201Tl single photon emission computed tomography and 99mTc-MIBI study as well as coronary angiography. The sensitivity for predicting a lesion ranged from 25% to 88% in different areas of the heart and was comparable for the two radiopharmaceuticals. The specificity was greater than 80% for all regions except the inferior region where a specificity of 58% obtained by 99mTc-MIBI was better than the low specificity of 17% obtained with 201Tl (P less than 0.008).

Angiocardiography↗
PubMed1989

99mTc ethoxy methylpropyl isonitrile: a radioactive tracer for myocardial perfusion imaging.

The initial experience with a new 99mTc labelled myocardial perfusion agent, ethoxy methylpropyl isonitrile (EMI), is described in the primate as model. Rapid biliary clearance of EMI ensures low radionuclide concentration in the liver and lungs after 60 min. Adequate visualization of the myocardium is therefore possible. Heart-to-lung and heart-to-liver ratios of 1.52 and 2.45 respectively were obtained. EMI is an efficient imaging agent to evaluate myocardial ischemia and infarction.

Animals↗
PubMed1988

Investigation into the effect of Fenoterol on mucociliary clearance in patients with chronic bronchitis.

We investigated the effect of Fenoterol, a selective beta 2 adrenoceptor stimulant, on mucociliary clearance in 12 patients with chronic bronchitis. Mucociliary clearance was measured with a scintillation camera after inhalation of a 99mTc labelled aerosol. Fenoterol was administered one h after acquisition commenced and imaging was maintained for a further two h. Three regions of interest (ROI) were selected over each lung to generate time activity curves. Corrections for decay, alveolar deposition (using 24 h image), cough and movement of activity through each ROI were carried out. An exponential function was fitted to the clearance curves to determine clearance rates. The increase in percentage clearance after Fenoterol administration for the left and right whole lung ROI was 35% and 36% per h respectively (P = 0.006 and 0.020). Fenoterol enhances cilial clearance in chronic bronchitis patients.

Adult↗
PubMed1988

A computer program in compiled BASIC for the IBM personal computer to calculate the mean platelet survival time with the multiple-hit and weighted mean methods.

We developed an easy-to-operate computer program for the IBM personal computer to calculate, display and store in a database platelet kinetic data determined by analysis of the rate of clearance of radiolabeled blood platelets from the circulation. This was done by curve fitting using the weighted mean method and multiple-hit model. These models are complementary and calculating the mean platelet survival time with both is recommended. Improvement of the weighted mean method was investigated. The optimized weighting and fitting the exponential function with the Marquardt non-linear least squares method improved the weighted mean method. The weighted mean and multiple-hit models fit the survival curve data equally well. The calculation of the mean platelet survival time with the weighted mean method was very fast. The duration of calculation with the multiple-hit model could take up to 2 minutes. Calculation of the mean platelet survival time using both models has the advantage that conditions when calculation of the mean platelet survival time would be invalid, can be detected. The computer program will promote the valid comparison of results obtained at different institutions.

Blood Platelets↗
PubMed1988

A new approach to NEMA scintillation camera count rate curve determination.

The method of determining count rate curves suggested by the National Electrical Manufacturers Association (NEMA) is based upon a single reference count rate. Inaccuracies in the reference value are propagated to the rest of the curve values. NEMA also requires the measurement of individual attenuation factors for every absorber. Errors can easily occur during the measurement and during the subsequent calculations which utilize these factors. An alternative approach is suggested: count rate curves are based upon at least five low count rate values and the determination of individual attenuation factors is eliminated. Count rate curves are generated from graphs of the 1n of the observed count rate against the number of equally thick copper absorber plates, by back-extrapolation of a line which is fitted to the linear low count rate data. The method was successfully implemented in practice. Agreement was found between the results of the NEMA method and the alternative method suggested.

Scintillation Counting↗
PubMed1987

Absolute left ventricular volume changes after sublingual nitroglycerine and nifedipine intervention.

The haemodynamic effects of two vasodilators, sublingual nitroglycerine and nifedipine, on absolute end-diastolic volume, end-systolic volume, stroke volume (SV), heart rate, systolic blood pressure (SBP), cardiac output (CO) and corresponding cardiac indices were measured in two different groups, each consisting of 20 ischaemic heart disease patients, with gated blood pool scintigraphy. A control study was done in 5 ischaemic heart disease patients without intervention. Direct measurement of left ventricular (LV) volume was done by correcting LV activity for tissue attenuation utilising a geometric method. With nifedipine intervention only SBP (125.25 +/- 19.8 mmHg) showed a significant mean decrease (11 mmHg). The other measured parameters did not change significantly. With nitroglycerine all the parameters except LV ejection fraction showed significant changes. Mean CO decreased by 8% while mean SV decreased by 16%. The results in the control group showed excellent repeatability. The absolute haemodynamic changes of future cardiac drugs might easily be measured in vivo by this non-invasive technique.

Administration, Oral↗
PubMed1986

Radionuclide evaluation of left ventricular function in a distantly located intensive coronary care unit.

Regular evaluation of left ventricular (LV) function is important in assessing patients in an intensive coronary care unit (ICCU). An adapted first-transit (FT) technique was applied to 21 patients for calculation of LV ejection fraction (LVEF). In this method the radionuclide is administered directly into the right pulmonary artery through a Swan-Ganz catheter. High-quality LV images are obtained because of minimal activity in the right ventricle and left lung. Data were acquired on a distantly located on-line computer system to restrict equipment in the ICCU. LVEF from FT compared well with LVEF from gated blood pool studies (r = 0.91) but gave consistently lower values. The adapted FT method ensures improved counting statistics during LVEF determination and facilitates evaluation of LV wall motion in the ICCU patient.

Adult↗
PubMed1986

Radionuclide cholescintigraphic imaging: an evaluation of several 99mTc labelled hepatobiliary radiopharmaceuticals.

Recently, much interest has been shown in the development of 99mTc labelled cholescintigraphic agents for imaging the hepatobiliary tract. In this study six cholescintigraphic agents were compared in rabbits with respect to transit efficiency through the liver and the halftime on the washout portion of the liver time-activity curve. The agents compared were p-butyl-IDA (PBIDA), diisopropyl-IDA (DISIDA), two mebrofenin (MBF) agents and two pyridoxylaminates (PDA). Best transit efficiencies were obtained with MBF (34.1 and 31.2%) followed by PDA (27.7 and 24.9%) while DISIDA (23%) and PBIDA (19.3%) were the lowest. The same phenomenon was observed regarding the washout halftime, with MBF the most rapid (6.3 and 5.9 min), PDA more prolonged (10.1 and 12.0 min) and DISIDA and PBIDA the slowest (23.0 and 23.2 min). This study confirms the difference in physiological behaviour of the various cholescintigraphic agents and shows identical flow patterns for locally produced and imported compounds.

Aniline Compounds↗
PubMed1986

Radionuclide determination of absolute LV volumes: interstudy, interobserver and intraobserver variances.

The results of 22 absolute left ventricular volume (LVV) determinations by a radionuclide (RN) method are compared to the results obtained by contrast ventriculography (CV). Another 10 patients were analysed in order to evaluate the interstudy, interobserver and intraobserver variances. Good correlation was shown between the RN and CV measurements of the end diastolic volume (EDV), end systolic volume (ESV), stroke volume (SV) and ejection fraction (EF), but the RN method overestimates the EDV and ESV. The EF was underestimated, but no difference could be shown for the SV. On the inter- and intraobserver levels, regression analysis yielded excellent correlation (r greater than 0.99 in all cases) with no statistically significant difference (P less than 0.05). The interstudy variance was minimal as indicated by regression analysis (r greater than 0.87) and no statistically significant difference (P less than 0.05) could be shown between studies. The results indicate that the RN method of LVV determination can be used in intervention studies over a limited period.

Adult↗
PubMed1986

Left ventricular function evaluation using radionuclide methods in the intensive coronary care unit.

We describe an adapted first-transit (FT) technique to perform left ventricular ejection fraction (LVEF) measurements on patients with Swan-Ganz catheters in the intensive cardiac care unit (ICCU). The radionuclide is introduced directly into the right pulmonary artery through the catheter. High-quality images of the left ventricle are obtained owing to minimal activity in the right ventricle and left lung. LVEF measurements obtained by FT compared well with measurements obtained from gated blood pool studies (r = 0.91) but gave consistently lower values. The adapted FT method improves LVEF determination and left-ventricular wall motion evaluation in the ICCU patient.

Cardiac Catheterization↗
PubMed1986

Evaluation of mathematic models to assess platelet kinetics.

Twelve mathematic methods used to calculate the mean platelet survival time were compared by determining the "goodness of fit" of the models to the platelet survival curves of 15 reference subjects and 54 patients. Platelets were labeled with [111In]oxine. The linear (LN), exponential, weighted mean, multiple hit (MH), Dornhorst (DH), Meuleman (ML), alpha order (AO), and polynomial (PO) mathematic models were investigated. The goodness of fit for the exponential model was determined by the nonlinear least squares method (EP), and also by the linear least squares method on logarithmically transformed data (EX) as is recommended. The modified weighted mean (MWM) and the usual weighted mean method (WM) obtained with these exponential models were tested. The Dornhorst (DH10) and Meuleman (ML10) models, where the potential age-dependent platelet survival times were kept constant at 10 days, were also evaluated. The goodness of fit results, expressed as % s.d. indicated that the LN (5.2%), EX (5.0%), EP (4.4%), WM (3.7%), DH10 (3.7%), and ML10 (3.7%) models all fitted the data significantly worse than the MWM, MH, DH, ML, AO, and PO models (range 3.2-3.3%). The mean platelet survival time determined with the MH model differed significantly from the results with the DH, ML, and AO models. The results of mean platelet survival time calculated with different mathematic models cannot, therefore, be compared directly. The models that fitted the platelet survival curve well varied slightly in sensitivity to noise as is indicated by the coefficient of variation of the mean platelet survival time estimates for the reference subjects (range 7.9-12.0%). Fitting data to at least two mathematic models has definite advantages. Data on which the calculations are based are probably invalid if the following are true: (a) if the mean platelet survival time estimated with the alpha order model is shorter than that estimated with the EP, MWM, or MH models, or (b) the mean platelet survival time estimated with either the DH, ML, AO, or PO models, is longer than the LN, MWM, or MH estimate of the mean platelet survival time. We conclude that the mean platelet survival time can be reliably estimated by fitting the data to either the MWM method (if limited computing facilities are available) or the MH model. Confidence in the result will be increased if considered in conjunction with the finding obtained with one other model; in those cases where the platelet survival time is very short, the alpha order model is recommended.(ABSTRACT TRUNCATED AT 400 WORDS)

Blood Platelets↗
PubMed1985

Evaluation of (o)-[77Br]bromohippuran as renal tubular function agent.

(o)-[77Br]bromohippuran (BHIP) was developed as renal tubular function agent due to its favourable chemical and physical properties and compared to (o)-[131I]iodohippuran (IHIP). Renograms obtained from baboons were compared and absorbed radiation dose calculations performed. Although BHIP showed a delayed kidney uptake and washout pattern, good kidney clearance of the radionuclide was obtained after 30 min. Radiation dose values for BHIP were markedly lower than for IHIP indicating that larger activities of BHIP could be administered to increase counting statistics. BHIP imaging in normal volunteers did however not substantiate the favourable behaviour obtained in the primate.

Animals↗
PubMed1985

Persistent left superior vena cava detected with radionuclide angiocardiography.

A 28-year-old man presented with paresthesias, fatigue, central cyanosis, and erythrocytosis. A first pass flow study with Tc-99m as free pertechnetate was done, among other tests, to exclude a central shunt when a persistent left superior vena cava was incidentally detected. The value of radionuclide angiocardiography to examine the central circulation noninvasively was again illustrated in this case.

Adult↗
PubMed1983

Variation in left ventricular ejection fraction determination at rest and during exercise.

The results of multi-gated blood pool imaging (MBPI) for determination of left ventricular ejection fraction (LVEF) in 48 patients at rest and during exercise were analysed in order to evaluate observer variance and interstudy variance. Twenty-three MBPI studies carried out with the patient at rest and 37 studies carried out during graded ergometer exercise were analysed by two independent observers in order to determine intra- and inter-observer variance. On the intra-observer level regression analysis yielded excellent correlation between rest and exercise studies (r = 0,998 at rest, r = 0,964 during exercise), and showed no statistically significant difference (P less than 0,01); this was also true of the inter-observer measurements (r = 0,999 at rest, r = 0,988 during exercise). In order to evaluate interstudy variance, MBPI was repeated in 15 patients at rest. Interstudy variation of the LVEF was minimal as indicated by regression analysis (r = 0,98), and showed no statistically significant difference (P less than 0,01). During the repeat study a mean increase in the LVEF of 2,1% was obtained, but this difference was not statistically significant.

Adolescent↗
PubMed1983

Determination of right ventricular ejection fraction utilising a radionuclide washout technique.

A radionuclide washout technique (WO), for calculation of the right ventricular ejection fraction (RVEF) which is independent of the exact position of the right ventricular region of interest was evaluated and results compared with first pass (FP) and equilibrium gated blood pool (GBP) values. Regression analysis between RVEF values of 24 patients obtained from FP and WO yielded a correlation coefficient (r) of 0.89, while a slightly poorer correlation coefficient was obtained when FP and GBP were compared (r = 0.79) and between WO and GBP (r = 0.71). No significant difference between RVEF values calculated from the three techniques was found (P less than 0.05) on inter- and intraobserver level. The radionuclide washout technique yields an accurate determination of RVEF without the necessity of outlining the RV accurately.

Adult↗
PubMed1982

Kinetics and fate of indium 111 oxine-labeled platelets in patients with aortic aneurysms.

The survival and sites of sequestration of indium 111 oxine-labeled autologous platelets were studied quantitatively in six patients with aortic aneurysms. The in vivo distribution was quantitated daily with a scintillation camera and a computer-assisted imaging system. Data of platelet survival curves were fitted to a gamma function model. Mean platelet survival was shortened and the disappearance curves were exponential in all but two patients who had normal platelet survival. Platelet radioactivity in the aneurysm was 5.1 +/- 3% of whole-body radioactivity at the end of platelet survival. Platelet were sequestered in the spleen, liver, and bone marrow. Accumulation of platelets, presumably due to microembolization, was prominent in the lower limbs. This indicates that although platelets were deposited in the aneurysm, many are damaged and are eventually sequestered in the reticuloendothelial system.

Aged↗