Biomedical subjects

A van Aswegen

Publications and source records attributed to A van Aswegen.

At least 19 recordsLinked to original sources

PubMed1997

Radiation dose estimates of 186Re-hydroxyethylidene diphosphonate for palliation of metastatic osseous lesions: an animal model study.

A common complication in patients with breast or prostate cancer is bone metastases causing pain. New radionuclide therapy methods have recently been proposed for palliation, including 186Re-hydroxyethylidene diphosphonate (186Re-HEDP). This paper reports on the local development of 186Re-HEDP and the biodistribution studied in animals for eventual use in patients. Adult dose was computed assuming a 70 kg standard man. The 186Re was labelled to HEDP using standard techniques. The biodistribution in five Chacma baboons (Papio ursinus) was studied. Doses ranging from 39.4 to 44.9 MBq kg(-1) (mean 43.6 +/- 2.8 MBq kg[-1]) were administered, corresponding to an adult human dose of 2960 MBq (80 mCi). Whole-body images of the animals were obtained with a dual-headed scintillation camera on an hourly basis for 6 h post-injection and then daily for 3 days. The bone, soft tissue, kidneys and urinary bladder were considered source organs and data from these organs were used in a compartmental model to obtain the mean residence times of the radionuclide in the different source organs. Radiation dose estimates for 186Re-HEDP were subsequently obtained with the MIRDOSE 3 program. The estimated absorbed radiation doses to some of the organs (expressed in mGy MBq[-l]) were as follows: bone surface 1.69; kidneys 0.09; liver 0.04; ovaries 0.04; red marrow 0.75; total body 0.12; urinary bladder wall 0.43. 186Re-HEDP yielded an effective dose of 0.17 mSv MBq(-1). The radiation dose delivered to the bone marrow in this study did not cause any detrimental effect to the baboons, indicating that locally produced 186Re-HEDP is suitable for clinical use.

Adult↗

PubMed1996

Evaluation of samarium-153 and holmium-166-EDTMP in the normal baboon model.

Bone-seeking radiopharmaceuticals such as ethylenediaminetetramethylene phosphonate (EDTMP) complexes of samarium-153 and holmium-166 are receiving considerable attention for therapeutic treatment of bone metastases. In this study, using the baboon experimental model, multicompartmental analysis revealed that with regard to pharmacokinetics, biodistribution, and skeletal localisation, 166Ho-EDTMP was significantly inferior to 153Sm-EDTMP and 99mTc-MDP. A more suitable 166Ho-bone-seeking agent should thus be sought for closer similarity to 153Sm-EDTMP to exploit fully the therapeutic potential of its shorter half-life and more energetic beta radiation.

Absorption↗

PubMed1996

A Monte Carlo evaluation of the channel ratio scatter correction method.

Several methods exist to eliminate the contribution of scattered photons during imaging. One of these, the channel ratio (CR) scatter correction technique, uses the change in the ratio of counts from two symmetrical adjacent energy windows straddling the energy photopeak. The accuracy of the results depends upon the assumption that the ratio of the scatter components in the two windows (H value) is constant and is independent of the relative size of the scatter contribution. In this study a Monte Carlo simulation was used to investigate the behaviour of the scatter component for different source sizes at different depths. Four disc sources containing a 99Tcm solution were simulated at different depths as imaged with a scintillation camera. Two 10% energy windows with 5% offsets to either side of the 140 keV photopeak of 99Tcm were used. The ratio of the scattered counts in the lower energy window to the scattered counts in the upper window (true H value) was determined from the simulation for each source at every depth. Since it is impossible to measure the true H value at different organ depths during a clinical study, the use of an average H value was considered. Scatter correction was applied to the images simulated at the various depths in water. The geometric mean was calculated and attenuation correction performed assuming mono-exponential attenuation. For quantitation purposes the corrected counts were expressed in terms of a references source. The choice of the reference source yielding the best quantitative results was also investigated. Results of this Monte Carlo simulation study show that although the true H value depends on both source size and depth of the source in the scattering medium, the CR scatter correction technique can be applied successfully when an average H value is used.

Biometry↗

PubMed1995

The effect of exercise on normal splenic volume measured with SPECT.

In a study group of 20 healthy young men, splenic volume was determined with SPECT before and after exercise. A randomly chosen control group of 10 comparable men was studied similarly, but without exercise intervention. The mean splenic volume did not change significantly in the control group (i.e., from 292.9 ml to 282.1 ml [P = 0.75]). The mean splenic volume decreased 60.1 ml from 279.4 to 219.3 ml (21.5%) in the study group and this was highly significant (P = 0.01). Although exercise induced splenic autotransfusion is generally considered to be unimportant in humans, significant splenic contractility was observed with this technique. In the normal individual with a large spleen or with functional splenomegaly, the contractility response may become more important and can now be measured in a quick and easy manner.

Adolescent↗

PubMed1995

Quantitation of SPECT performance: Report of Task Group 4, Nuclear Medicine Committee.

A comprehensive performance testing program is an essential ingredient of high-quality single-photon emission computed tomography (SPECT). Many of the procedures previously published are complicated, time consuming, or require a special testing environment. This Task Group developed a protocol for evaluating SPECT imaging systems that was simple, practical, required minimal test equipment, and could be performed in a few hours using processing software available on all nuclear medicine computers. It was designed to test rotational stability of uniformity and sensitivity, tomographic spatial resolution, uniformity and contrast, and the accuracy of attenuation correction. It can be performed in less than three hours and requires only a Co-57 flood source, a line source, and a tomographic cylindrical phantom. The protocol was used 51 times on 42 different cameras (seven vendors) by four different individuals. The results were used to establish acceptable ranges for the measured parameters. The variation between vendors was relatively small and appeared to reflect slight differences in basic camera performance, collimation, and reconstruction software. Individuals can use the tabulated values to evaluate the performance of individual systems.

Cobalt Radioisotopes↗

PubMed1995

Determination of glomerular filtration rate with radionuclide renography and direct urinary activity quantitation.

OBJECTIVE: The direct urinary activity quantitation method is quick (approximately 40 minutes), requires only a single blood sample, is performed as part of standard renal scanning and shows high accuracy compared with 24-hour creatinine clearance. The purpose was to evaluate the practical application and accuracy of this technique at our clinic. DESIGN: Direct urinary activity quantitation was done in patients scheduled for routine radionuclide renography and compared to standard multiple-blood-sample techniques by means of Cr-51-EDTA and Tc-99m-DTPA. SETTING: Academic Medical Complex, Department of Nuclear Medicine, Universitas Hospital, Bloemfontein. PARTICIPANTS: Fifteen patients scheduled for routine radionuclide renography (glomerular filtration rate (GFR) determination) were voluntarily enrolled in the study. The GFRs of selected patients varied over a wide range. Possible obstructive uropathy was excluded. MAIN OUTCOME MEASURES: GFRs obtained by the direct urinary method were compared with GFRs determined by multisample Cr-51-EDTA and Tc-99m DTPA. RESULTS: GFRs from the direct urinary method compared with multisample Tc-99m-DTPA showed differences from -19.85 to 22.95 ml/min with a mean of 0.2 (+/- 12.25) ml/min (r = 0.93). When compared with multisample Cr-51 EDTA, differences ranged from -34.35 to 21.05 ml/min with a mean of -4.25 (+/- 16.08) ml/min (r = 0.90). CONCLUSION: The direct urinary activity technique is CONCLUSION: The direct urinary activity technique is easily applied and highly accurate compared with previous standardised multisample radionuclide techniques for determination of GFR.

Adolescent↗

PubMed1993

The channel ratio method of scatter correction for radionuclide image quantitation.

The accuracy of quantitation of radionuclide distributions in human tissue with the scintillation camera is decreased by attenuation and scatter of photons. If scatter correction is applied satisfactorily, narrow beam attenuation can be applied. In this article, a scatter correction technique, the channel ratio (CR) method, is introduced. The CR scatter correction method is proposed for quantitation of the radionuclide distribution in organs. The improvement in the geometrical resolution was measured and examples of clinical images are presented. In this method, the change in the ratio of counts from two symmetrical adjacent energy windows straddling the energy photopeak was used to eliminate the contribution of scattered photons during imaging with 99mTc. The theory and methods for the empirical affirmation are described. To apply the CR scatter correction method, two constants, the ratio of primary photons G and the ratio of scattered photons H in the same windows, were determined. Different sized sources in varying depths of water were imaged. When the source activities were quantified after scatter correction with the CR method, the measurements ranged from 96%-108% in comparison to the reference value in 100 mm water. The scatter fraction increased from 0.20 in 10 mm water to 1.44 in 200 mm water. The geometrical resolution expressed as full width at tenth maximum in 150 mm water improved by 30.4% and was restored to the value of the geometrical resolution in air. The CR scatter correction method is a simple method to correct for scatter in order to facilitate accurate quantitation of the radionuclide distribution during imaging with a scintillation camera.

Humans↗

PubMed1993

Verification of a varying threshold edge detection SPECT technique for spleen volume: a comparison with computed tomography volumes.

SPECT enables quantitation of organ volume with radionuclide techniques using threshold edge detection methods. Previous phantom studies showed that a negative correlation exists between volume and threshold value. In those studies, the use of calibration curves were believed to correct for volume dependence on threshold values. The aim of this study was to evaluate the accuracy of spleen volume determination in 20 patients with SPECT by employing a varying threshold edge detection technique with volumes derived from CT. All patients had both radionuclide and CT examinations that were reconstructed with a filtered backprojection algorithm. During SPECT reconstruction, transverse slices were obtained with attenuation correction (Method A) and without attenuation correction (Method B). CT volumes were calculated from manually drawn regions of interest, whereas SPECT volumes were calculated with an automated algorithm using previously determined calibration curves. A confidence interval for calculated SPECT volumes also was calculated because of possible errors in the threshold value. The spleen volumes studied ranged from 91.2 ml to 1660.1 ml. Regression analysis yielded equations of CT = 0.97 SPECT + 7.07 (r = 0.996) and CT = 1.05 SPECT - 19.25 (r = 0.990) between CT and SPECT spleen volumes with a standard error of the y estimates of 31.10 ml and 54.47 ml, respectively. A mean percentage difference of 10.5% +/- 7.6% and 11.4% +/- 6.6% in spleen volume was obtained for Methods A and B in comparison with CT spleen volumes. The threshold value varied between 40.9% and 32.4% for Method A and between 41.2% and 28.5% for Method B because the spleen volume is increased. The varying threshold edge detection technique described in this paper can be implemented successfully in the clinical setting.

Adult↗

PubMed1990

[A comparison of three different techniques for measuring glomerular filtration rate].

The clearance of inulin, creatinine and radioactive tracers from the blood may be used to measure glomerular filtration rate (GFR). These techniques, however, are usually invasive and time-consuming. Although the clearance of a radioactive tracer is usually applied in nuclear medicine for the determination of GFR, it is also possible to convert the concentration of the tracer in the kidneys to absolute GFR by means of a regression equation. As this new technique is much faster, we have compared it with the conventional technique. A good correlation was found with the standard radionuclide techniques (r = 0.91), but the reference method was under-estimated on the average by 14 ml/min. The new regression equation derived in our clinic will ensure future accurate GFR measurements within 6 minutes.

Chromium Radioisotopes↗

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

Daily serial evaluation of left ventricular function with equilibrium radionuclide ventriculography following thrombolysis during acute myocardial infarction.

The changes in ventricular function after reperfusion by coronary thrombolysis are important when deciding about further definitive treatment necessary to ensure long-term vessel patency. The purpose of this study was to evaluate the early changes in left ventricular function after reperfusion. Left ventricular function was serially evaluated for 10 days in a group of 18 patients receiving intracoronary thrombolytic therapy for an acute myocardial infarction. Comparison of the global ventricular function in the successfully and unsuccessfully reperfused groups of patients showed significantly better function in the successful group than the unsuccessful group after the first day, which was maintained for the entire study period. Global and regional ventricular function in the successfully reperfused patients showed significant early improvement during the initial 72 h with maintenance of this improvement for the study period of 10 days. In the patients in whom reperfusion was unsuccessful, regional ventricular function showed no change, while the global function declined from day 5 to day 8 of the study period. This study then confirms the significant improvement in ventricular function after successful reperfusion. The time course pattern of the change in ventricular function indicates that the most significant improvement occurs within the first 72 h after reperfusion. These changes are similar to those previously reported in experimental animals.

Angioplasty, Balloon↗

PubMed1988

The effects of nisoldipine on left ventricular filling rate in patients with ischemic heart disease measured with radionuclide gated blood pool scintigraphy.

Nisoldipine is a newly developed calcium channel blocker with outstanding vasodilatory properties especially with regard to the coronary arteries. Thus it may find wide-spread application as a therapeutic agent in various ischemic heart disease syndromes. The purpose of this study was to evaluate the effect of nisoldipine on the diastolic function of the left ventricle (LV) in the clinical situation. A patient group on nisoldipine treatment was compared to a control group. In the nisoldipine group a maximum decrease of 17 mmHg in the mean systolic blood pressure with an increase in the mean peak ejection rate (0.78 EDV/s) and peak filling rate (0.52 EDV/s) were observed. Mean LV ejection fraction increased by 6.4% and the time to peak filling rate decreased by 36.5 ms. After eight weeks of treatment the acute effects of nisoldipine were similar to the previous study. Nisoldipine therefore tends to improve both the diastolic and systolic function of the left ventricle.

Adult↗

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↗

PubMed1987

A comparison of the acute hemodynamic effects of nifedipine and nisoldipine in patients with ischemic reduced left ventricular function.

Nisoldipine (BAY k 5552) like nifedipine, is a dihidropyridine compound with strong calcium blocking activity. The purpose of this study was to measure and compare the absolute hemodynamic effects of these two drugs before and at 30 min, 60 min and 120 min after oral intake in 20 ischemic heart disease patients with radionuclide gated cardiac scintigraphy. No significant change was seen in end diastolic volume index with either of the drugs. With nifedipine the stroke volume index (SVI) increased significantly from the basal value at 30 min (P = 0.004) and 60 min (P = 0.034) yet not significantly at 120 min. The same trend was seen in left ventricular ejection fraction (LVEF) with significant increases at 30 min (P = 0.02) and 60 min (P = 0.025) yet not at 120 min. The cardiac index increased significantly at 30 min (P = 0.001), 60 min (P = 0.002) and 120 min (P = 0.025) but the latter value was significantly lower than the 30 min value indicating the maximal effect had already passed. With nisoldipine the SVI increased significantly at 60 min (P = 0.004) and 120 min (P = 0.001) but not at 30 min. These changes were again reflected by a significant increase in LVEF at 60 min (P = 0.021) and 120 min (P = 0.002) without significant increase at 30 min. The increase in CI was highly significant at 60 min (P = 0.003) and 120 min (P = 0.001) without significant change at 30 min. Nisoldipine proved to be a potent calcium antagonist with slower onset and longer duration of action than nifedipine.

Aged↗

PubMed1987

Comparative radionuclide and thermodilution determinations of cardiac output and stroke volume in the baboon (Papio ursinus).

Thermodilution cardiac output determinations and multigated equilibrium blood-pool scintigraphy were performed in ten healthy chacma baboons (Papio ursinus). The correlation was moderately good between both the radionuclide and thermodilution stroke volume (r = 0.58, SEE = 3 ml; SVth = 0.78SVr + 15.6 ml) as well as the cardiac output (r = 0.72, SEE = 0.2 liter/min; COth = 0.56 Cor + 2.1 liter/min). The attenuation depth dr as determined by radionuclide techniques was found to correlate well with the radiologically determined values dx (r = 0.8, SEE = 0.4 cm; dx = 0.87dr + 0.72 cm) which validated the depth values used in the calculations.

Animals↗

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↗