Jens Toft

Electrolyte crystal growth kinetics

The growth rate of an electrolyte crystal in a supersaturated aqueous solution depends on the concentrations of the constituent ions. These concentrations may be varied independently when indifferent ions are present. For a binary electrolyte AαBβ the dependence of the rate on the concentrations of the ions A and B may be presented as isograms for constant growth rate in a diagram with the coordinates [A] and [B], or similar. The growth rate is controlled by the transport of the ions A and B through the solution by convection and diffusion, or by a process in the crystal surface, or by a combination hereof. The following surface controlled kinetics have been indentified: linear, parabolic, and exponential kinetics. They are related, respectively, to the adsorption process, to the integration of ions in screw dislocation centred surface spiral steps, and to the formation and growth of surface nuclei. Growth rates are reported for the following electrolytes: AgCl, CaF2, SrF2, Ag2C2O4, BaSO4, CaCO3, and CaC2O4·H2O.

Dobutamine-atropine stress echocardiography in asymptomatic healthy individuals : the relativity of stress-induced hyperkinesia

BACKGROUND Interpretation of dobutamine-atropine stress echocardiography (DASE) is based on the assumption that the normal response to dobutamine-atropine infusion is characterized by increased systolic thickening and motion of the left ventricular (LV) walls, whereas a reduction or no change is considered indicative of coronary artery disease. The aim of this study was to quantitatively assess changes in LV dimension and wall motion patterns during DASE in a healthy population. METHODS AND RESULTS Forty-two asymptomatic voluntary subjects (22 men) with a mean age of 59 years (range, 31 to 79 years) and a likelihood of < 5% for coronary artery disease underwent DASE with digital recording of two-dimensional and M-mode echocardiography at baseline and low-dose and peak infusion rates. Mean end-diastolic and end-systolic LV diameters and areas decreased and wall thicknesses increased progressively throughout the test. Wall motion and thickening increased from baseline to low-dose infusion in nearly all subjects. However, from low-dose to peak infusion, the mean absolute wall motion and relative wall thickening decreased by 13.1% (95% CI, 2.7 to 23.5) and 21.4% (95% CI, 6.4 to 36.4) regardless of age, sex, or use of atropine. Changes in fractional shortening and absolute wall thickening varied considerably, with a decrease observed in 15 and 13 individuals (36% and 31%), respectively. CONCLUSIONS In healthy subjects, measures of wall motion and wall thickening increased from baseline to low-dose infusion but decreased from low-dose to peak infusion. These findings call for revision of the assumptions on which the common analysis of DASE is based.

The occurrence of false-positive technetium-99m sestamibi bull's eye defects in different reference databases. A study of an age- and gender-stratified healthy population.

Myocardial perfusion single-photon emission tomographic (SPET) imaging has been shown to be sensitive in the detection of coronary artery disease (CAD), whereas its specificity has been suboptimal. The aim of the present study was to study the frequency of abnormal bulls eye perfusion defects in a large age-stratified group of healthy subjects undergoing myocardial SPET assessed by comparison with two existing commercially available reference databases. One hundred and twenty-eight healthy volunteers (76 males and 52 females) with a less than 5% likelihood of CAD underwent rest and exercise technetium-99m sestamibi SPET. The false-positive response rate, defined as a significant reversible defect, was 12% when compared to the CEqual database and 29% when compared to the Cedars-Sinai database. With the CEqual program, rest defects occurred in 12% of the subjects. Defects occurred more often in women than in men, but the difference did not attain statistical significance. Significant defects were most frequent in the inferior wall and in women in the anterior wall as well. The distribution of defects was independent of age. Our results suggest that the specificity of99mTc-sestamibi myocardial SPET using commercially available reference files is suboptimal. The risk of obtaining a falsepositive test result in subjects undergoing99mTc-sestamibi myocardial SPET with a very low likelihood of CAD was higher than anticipated. With both reference files false-positive test results were most frequently observed in the inferior wall. Our data suggest that commercial reference files for myocardial SPET need to be optimised, and should be used with caution. The use of attenuation correction may prove to be a major step forward.

The optimal reference population for cardiac normality in myocardial SPET in the detection of coronary artery stenoses: patients with normal coronary angiography or subjects with low likelihood of coronary artery disease?

Abstract. Both subjects with a low likelihood for coronary artery disease (CAD) and patients with normal findings on coronary angiography have been used as reference populations in non-invasive stress testing, including myocardial perfusion scintigraphy. Both of these criteria of normality – low likelihood of CAD and normal coronary angiography – have been criticised, and consensus on this issue is lacking. The aim of this study was to compare two different reference populations by testing the performance of artificial neural networks designed to interpret myocardial scintigrams. The networks were trained on myocardial perfusion scintigrams from 87 patients with angiographically documented CAD and on studies from one of two different reference groups: 48 patients with no signs of CAD based on angiography or 128 healthy volunteers with a likelihood for CAD <5%. The performance of the two different networks was then tested using scintigrams from a separate test group of 68 patients. Coronary angiography was used as the gold standard in this group. The network trained on patients with no signs of CAD based on angiography showed an area under the receiver operating characteristic (ROC) curve of 93%. The ROC area for the network trained on healthy volunteers was 72%, and this difference was statistically significant (P=0.03). The results of this study using artificial neural networks suggest that normal angiography should be preferred as the reference standard in myocardial scintigraphy when a patient is examined for CAD prior to possible angiography. Whether the same is true for other indications, e.g. in prognostic evaluation, is unknown.

Myocardial sestamibi single-photon emission tomography: variations in reference values with gender, age and rest versus stress?

Reference data files support the evaluation of myocardial perfusion single-photon emission tomography (SPET). The aim of this study was to create a large reference data base for technetium-99m sestamibi SPET, age and gender matched to the general patient population. One hundred and twenty-eight healthy volunteers (76 males and 52 females) with a likelihood of coronary artery disease of less than 5% underwent rest and maximal exercise99mTc-sestamibi SPET with a 2-day protocol and 180° elliptical rotation. The normalized activity values of99mTc-sestamibi in the inferior wall differed significantly between men and women. Age variations were found for men in the anterior wall. Normalized activity values in all four walls were strikingly similar during rest and stress. Our results suggest that the use of reference files in99mTc-sestamibi SPET requires a gender- and, for males, possibly an age-matched reference population. Different reference files at rest and during stress might not be necessary.