Advantages of the nested case-control design in diagnostic research

Abstract Background Despite its benefits, it is uncommon to apply the nested case-control design in diagnostic research. We aim to show advantages of this design for diagnostic accuracy studies. Methods We used data from a full cross-sectional diagnostic study comprising a cohort of 1295 consecutive patients who were selected on their suspicion of having deep vein thrombosis (DVT). We draw nested case-control samples from the full study population with case:control ratios of 1:1, 1:2, 1:3 and 1:4 (per ratio 100 samples were taken). We calculated diagnostic accuracy estimates for two tests that are used to detect DVT in clinical practice. Results Estimates of diagnostic accuracy in the nested case-control samples were very similar to those in the full study population. For example, for each case:control ratio, the positive predictive value of the D-dimer test was 0.30 in the full study population and 0.30 in the nested case-control samples (median of the 100 samples). As expected, variability of the estimates decreased with increasing sample size. Conclusion Our findings support the view that the nested case-control study is a valid and efficient design for diagnostic studies and should also be (re)appraised in current guidelines on diagnostic accuracy research.</p

High-speed drilling of metals with a long-pulse XeCl excimer laser

Studies of the influence of pulse length on material processing with different lasers have shown that a long pulse is beneficial for processing speed. In this paper a technique of pulse length variation is used in which the pulse length is the only varied parameter. Pulses between 5 and 150 ns length are sliced out of the 175 ns pulse of a long pulse excimer laser. The beam quality for each sliced pulse length is similar. In this paper the results are shown of hole drilling experiments in 125 micron aluminium foil with pulses of 10 and 100 ns length. The influence of the pulse length on material processing is discussed in relationship with equal energy and equal power density of the pulses. This study shows that in both cases long pulses remove more material than short pulses

Shadowgraphic imaging of metal drilling with a long pulse excimer laser

A shadowgraphic imaging technique is used for studying the interaction between the laser beam and the material during laser drilling. The used laser is a XeCl excimer laser with a nearly diffraction limited beam and 175 ns pulse length. We studied how and when the material is removed. Holes are drilled with a series of pulses in aluminum and Hastelloy X. The shadowgraphic images show the development of a shockwave whose expansion is in agreement with theory. Both the removal of material at different times after the start of the laser pulse and the material removal for different pulses during the drilling process are shown. Material removal occurs by vaporization as well as melt ejection. Our experiments show the same amount of removed material for drilling with different cover gases. The shadowgraphic images show that the larger part of the material is removed after the end of the laser pulse

Evaluation of adrenal function using the human corticotrophin-releasing hormone test, low dose Synacthen test and 9am cortisol level in children and adolescents with central adrenal insufficiency

Background The insulin tolerance test (ITT) has become less popular in paediatrics because of the risks associated with hypoglycaemia. Human corticotrophin-releasing hormone (hCRH) test results correlate with the ITT and may be an acceptable method to test for central adrenal insufficiency (CAI). Simpler tests, such as the low dose Synacthen test (LDST) and 9am cortisol, have also been proposed. Objective To compare the ability of the hCRH test, LDST, 9am cortisol level and 24-h cortisol profiles to diagnose CAI in a paediatric population. Design and setting A cross-sectional study in a tertiary paediatric endocrine clinic. Participants Thirty-one children and adolescents (aged 2·3–18·3 years) with CAI risk factors had an hCRH test, LDST, 9am cortisol and 24-h cortisol profile performed. Results Of 23 patients with confirmed CAI (hCRH peak cortisol 381 nmol/l are highly suggestive of normal hypothalamic–pituitary–adrenal (HPA) function, stimulation testing need only be performed if 9am cortisol is 108–381 nmol/l. The LDST should be interpreted cautiously because mild CAI may be missed. When stimulation results are marginal, 24-h cortisol profiles can provide reassurance of normal cortisol status

An individual participant data meta-analysis of psychological interventions for preventing depression relapse

Major depressive disorder is a leading cause of disability worldwide; identifying effective strategies to prevent depression relapse is crucial. This individual participant data meta-analysis addresses whether and for whom psychological interventions can be recommended for relapse prevention of major depressive disorder. One- and two-stage individual patient data meta-analyses were conducted on 14 randomized controlled trials (N = 1,720). The relapse risk over 12 months was substantially lower for those who received a psychological intervention versus treatment as usual, antidepressant medication, or evaluation-only control (hazard ratio, 0.60; 95% confidence interval, 0.48–0.74). The number of previous depression episodes moderated the treatment effect, with psychological interventions demonstrating greater efficacy for patients with three or more previous episodes. Our results suggest that adding psychological interventions to current treatment to prevent depression relapse is recommended. For patients at lower risk of relapse, less-intensive approaches may be indicated