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Biomedical subjects

A Dobbeleir

Publications and source records attributed to A Dobbeleir.

33 records · Page 2Linked to original sources
PubMed1991

Technetium 99m mercaptoacetyltriglycine gamma camera clearance calculations: methodological problems.

Major sources of errors in the gamma-camera methods for the calculation of renal clearance are the accuracy of background correction for obtaining the true renal time-activity curve and the validity of the externally recorded pre-cordial activity as an estimate of the plasmatic time-activity curve. With technetium 99m mercaptoacetyltriglycine (99mTc-MAG3), because of its high protein plasma binding, one could expect minimal extravascular diffusion and hence a more accurate externally detected plasmatic curve. The high extraction rate should reduce the influence of the background, but, on the other hand, the effect of hepatobiliary excretion on the calculation of renal clearance might be significant. Our results suggest that the hepatobiliary excretion of 99mTc-MAG3 does not influence the gamma-camera renal clearance determination, even in patients with low renal function. However, the pre-cordial curve does not reflect accurately the plasmatic disappearance curve; its calibration with a single plasma sample taken at the 20th min is responsible for significant errors, probably because of an unfavourable ratio between the intravascular and extravascular activities at the 20th min.

Adult↗
PubMed1991

Performance of a single crystal digital gamma camera for first pass cardiac studies.

First pass radionuclide angiocardiography (FPRNA) has gained increasing interest because of the development of new 99Tcm-labelled perfusion agents and of new 191Os/191Irm generator systems. The aim of the study was to evaluate the performance capacities of a small field of view single crystal digital gamma camera for 99Tcm and 191Irm at high count rates. The camera dead time for 99Tcm (window 30%) was well corrected up to 300 kcps in fast acquisition mode using the relative decrease of a small shielded reference source. Using the decaying activity method for 191Irm the non-linearity response of the gamma camera was corrected by an 191Os reference soruce up to 210 kcps at 70 keV, 75 kcps at 129 keV and 320 kcps including both peaks. Saturation count rates were respectively 270 kcps, 150 kcps and 420 kcps and high count rate resolution (FWHM) 9.0, 7.3 and 10.3 mm. Since the accuracy of first pass measurements is more sensitive to count rate than to spatial resolution the 50-150 keV window was chosen for clinical studies. In data obtained from 32 ECG gated FPRNA patient studies, the whole field of view count rate during the left ventricular phase ranged from 100 to 250 kcps with 80 to 120 mCi (2960-4400 MBq) of 191Irm and 100 to 180 kcps with 20 to 25 mCi (750-925 MBq) of 99Tcm red blood cells permitting for both tracers accurate non-linearity correction.

Evaluation Studies as Topic↗
PubMed1990

Evaluation of reproducibility of solid-phase gastric emptying in healthy subjects.

Radionuclide gastric emptying studies are performed as a matter of clinical routine. Our aim was to evaluate the inter- and intra-individual variability and the reproducibility of gastric emptying studies in healthy young male volunteers using a single solid-phase, standard meal. The meal consisted of a pancake (500 KJ) tagged with technetium 99m sulphur colloid and no additional liquid. Continuous acquisitions of gastric activity in anterior projection were taken during 90 min, starting from the onset of the meal. Gastric emptying was evaluated three times in a 3-week period. Five different parameters were evaluated. Our results show that there is important inter- and intra-individual variability in normal volunteers. In spite of this variability, no significant difference between the different series of gastric emptying studies was observed.

Adult↗
PubMed1990

Effect of mild mental stress on solid phase gastric emptying in healthy subjects.

Radionuclide gastric emptying studies are performed in clinical routine but the possible influence of the mental state of the patient is never taken into account. We wanted to evaluate the effect of a mild psychological stress on solid phase gastric emptying in healthy young male volunteers. The standard meal consisted of a pancake (500 kJ) without additional liquid. Simultaneous dynamic acquisitions of gastric activity in anterior and posterior projection were taken during 90 min starting from the onset of the meal. Gastric emptying was evaluated three times in basal conditions and once under mental stress. Stress was induced by means of a dichotomous listening test, lasting for 30 min, starting at the end of the meal. The results of rest and stress studies were compared. Mild mental stress has a significant influence on gastric emptying. The lag phase increased from 11 +/- 3 min to 36 +/- 10 min (mean +/- S.D.) (p less than 0.005) and the gastric emptying rate from 79 +/- 13%/hour to 100 +/- 31%/hour (mean +/- S.D.) (not significant). During a stress period gastric emptying as a whole is delayed but this is mainly due to the prolongation of the lag phase. Our data also suggest that during the stress period gastric emptying is interrupted and reactivated once the stress period has ended.

Adult↗
PubMed1990

Effect of background correction on separate technetium-99m-DTPA renal clearance.

The estimation of the background constitutes the main difficulty in the accurate determination of the separate renal clearance, using the 99mTc-DTPA complex and the gamma camera. This is due to the low extraction rate of DTPA, giving an unfavorable signal-to-noise ratio, and to the fact that no background area can accurately represent both interstitial and vascular components of the renal curve. Several algorithms have been proposed in the literature for solving the problem of background but their effect on the calculated clearance value has not been sufficiently assessed. In this paper, it has been possible, using a theoretical approach, to predict the respective influence of the different algorithms on the renal clearance. These results were confirmed on the basis of clinical data obtained from 53 renal studies. It was shown that a double background correction, using successively the area ratio method followed by a linear fit method, is probably the most precise method and is less dependent on the choice of the background area.

Algorithms↗
PubMed1989

Continuous anterior acquisitions in gastric emptying: comparison with the mean.

Depth correction is necessary when gastric emptying is studied by means of a labeled meal. In this study continuous anterior images were acquired from the onset of the food ingestion. Differences in depth were measured using a left lateral view. A minimal and crude depth correction was performed. The results obtained with this correction method were compared with those obtained using the depth correction technique of the mean. The results obtained in the anterior projection without any depth correction were also compared with those obtained using the method of the mean. The results obtained with both correction techniques were identical in 18 gastric emptying studies. This approach also permits the creation of a time-activity curve over the duodenum in the anterior projection. In this way the lag phase can easily be assessed.

Adult↗
PubMed1988

Assessment of vertebral mineral content by means of a single-crystal scintillation camera.

Increasing interest in bone mass has led to dedicated commercial dual photon absorptiometry (DPA) instruments. We describe a method for the measurement of the mineral content of the lumbar spine using a scintillation camera. The most appropriate source(s) and collimator were investigated. An especially constructed arm placed the sources in the focal point of a converging collimator. Two single-peak sources, 99Tcm and 241Am, were used instead of dual-peak 153Gd source. Phantom studies showed no degradation of the results in water depths of up to 26 cm. Acquiring 10 Mcounts per image over a 300 cm2 field, a coefficient of variation (c.v.) of 1.7% was obtained. Reducing the total counts per image to 1 Mcount gave rise to a c.v. of 6.2%. Long-term measurements showed a c.v. of 1.1% for density, with a mean value of 0.98 gHa cm-2 compared to 0.90 for a commercial DPA instrument. Repeated measurements of the lumbar spine on 10 patients with a 2 week interval showed a c.v. of 5%. Comparative measurements were made between the scintillation camera and a commercial DPA instrument on six volunteers. Systematic higher results, similar to those observed with the phantom, were obtained with the scintillation camera. The reproducibility on a phantom and in patients is in the same range as commercial DPA instruments. The low cost related to the use of standard nuclear medicine equipment and to inexpensive radioactive sources represent definite advantages.

Humans↗
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↗
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

Influence of statistical noise on the determination of the single kidney 99Tcm-DTPA clearance.

Single kidney clearance can be obtained using the 99Tcm-DTPA complex and the scintillation camera. In order to evaluate the influence of statistical noise on the determination of the clearance, several non-noisy curves were constructed, simulating renal, background and precordial curves. Poisson noise was added to these curves and the clearance results were compared to those obtained on the original curves. It was shown that, in so far as a moderate curve smoothing was used, the statistical noise did not interfere considerably with the results of the renal clearance.

Glomerular Filtration Rate↗
PubMed1981

Radionuclide quantitation of left-to right cardiac shunts using deconvolution analysis: concise communication.

Quantitative radionuclide angiocardiography (QRAC) was performed with and without deconvolution analysis (DA) in 87 children with various heart disorders. QRAC shunt quantitation was possible without DA in 70% of the cases and with DA in 95%. Among 21 patients with prolonged bolus injections, quantitation of the shunt was possible in 52% of the cases without DA an in all cases with DA. Correlation between oximetry and QRAC with DA was better than between oximetry and QRAC without DA. It is concluded that QRAC with DA is a more reliable, noninvasive means for detection and quantitation of left-to-right cardiac shunts than QRAC without DA.

Adolescent↗
PubMed1978

A simple method for measuring separate glomerular filtration rate using a single injection of 99mTc-DTPA and the scintillation camera.

A new technique for measuring glomerular filtration in each kidney has been developed using a scintillation camera and the 99mTc-DTPA complex. The technique has been applied to 101 children with various uropathies. Correlations with the total and separate creatinine clearance, the HgCl2 uptake test, and the maximal urinary concentration have been good. The reproducibility of the method has been satisfactory in a small number of patients. The test is particularly adapted to children because of its simplicity, reduced trauma, short duration (20 minutes) and low-radiation dose. In contrast to some other radioisotope techniques, it can be carried out in infants.

Adolescent↗
PubMed1977

Measurement of separate kidney clearance by means of 99mTc-DTPA complex and a scintillation camera.

A new radioisotopic method of determining the separate glomerular clearance of the kidneys is described. After injection of 99mTc-DTPA, the data from a scintillation camera are recorded by computer. The renal curves are corrected for extrarenal activity and the plasma curve is obtained from a precordial curve. At each instant the slope of the renal curve divided by the corresponding plasma concentration gives the separate clearance value, in the period extending from 80 to 180 s after injection of the tracer. The error and correction factors introduced are discussed. Normal values are established on 25 patients and correspond to inulin clearance values. Left kidney: 60 ml/min (SD=13). Right kidney: 57 ml/min (SD=12). The method is simple for the patient, takes only 20 min, is not dangerous, is particularly applicable to young children and can be repeated frequently in the same patient.

Adolescent↗