When Is a Positive Test for Pediatric Growth Hormone Deficiency a True-Positive Test?

BACKGROUND: In most cases, the growth hormone stimulation test is a necessary component for the diagnosis of growth hormone deficiency (GHD) in children. Diagnostic testing can lead to unnecessary treatment of children with false-positive test results and omission of treatment in children with false-negative results. False-positive results are suggested by the absence of typical growth responses in treated children and false-negative results are suggested by continued growth failure in those left untreated. SUMMARY: The probability that a positive test result indicates the presence of the condition (true positive) depends on the prevalence of that condition in the test population and the false positive rate of the test. This probability has been estimated using published data on the prevalence of GHD in children and the false positive rates estimated from performance of stimulation tests in normally growing children and from repeated testing in short children. Because of the low prevalence of GHD and the substantial false positive rate of the test, the probability of a true-positive result in a child with short stature is 0.028, or about 1 in 36 cases. Key Messages: In children with short stature, most positive growth hormone stimulation test results will be false-positive results, resulting in growth hormone treatment of children misdiagnosed as growth hormone deficient. Additional information is required for accurate diagnosis and prediction of successful treatment outcomes in children. Improvements in diagnostic accuracy and treatment outcome predictions can be anticipated from the use of additional predictive enrichment markers identified and evaluated in broadly based studies of growth hormone treatment in children.

Imaging Bell-type nonlocal behavior.

The violation of a Bell inequality not only attests to the nonclassical nature of a system but also holds a very unique status within the quantum world. The amount by which the inequality is violated often provides a good benchmark on how a quantum protocol will perform. Acquiring images of such a fundamental quantum effect is a demonstration that images can capture and exploit the essence of the quantum world. Here, we report an experiment demonstrating the violation of a Bell inequality within observed images. It is based on acquiring full-field coincidence images of a phase object probed by photons from an entangled pair source. The image exhibits a violation of a Bell inequality with S = 2.44 ± 0.04. This result both opens the way to new quantum imaging schemes based on the violation of a Bell inequality and suggests promise for quantum information schemes based on spatial variables.

Experimental Limits of Ghost Diffraction: Popper's Thought Experiment.

Quantum ghost diffraction harnesses quantum correlations to record diffraction or interference features using photons that have never interacted with the diffractive element. By designing an optical system in which the diffraction pattern can be produced by double slits of variable width either through a conventional diffraction scheme or a ghost diffraction scheme, we can explore the transition between the case where ghost diffraction behaves as conventional diffraction and the case where it does not. For conventional diffraction the angular extent increases as the scale of the diffracting object is reduced. By contrast, we show that no matter how small the scale of the diffracting object, the angular extent of the ghost diffraction is limited (by the transverse extent of the spatial correlations between beams). Our study is an experimental realisation of Popper's thought experiment on the validity of the Copenhagen interpretation of quantum mechanics. We discuss the implication of our results in this context and explain that it is compatible with, but not proof of, the Copenhagen interpretation.

Resolution limits of quantum ghost imaging.

Quantum ghost imaging uses photon pairs produced from parametric downconversion to enable an alternative method of image acquisition. Information from either one of the photons does not yield an image, but an image can be obtained by harnessing the correlations between them. Here we present an examination of the resolution limits of such ghost imaging systems. In both conventional imaging and quantum ghost imaging the resolution of the image is limited by the point-spread function of the optics associated with the spatially resolving detector. However, whereas in conventional imaging systems the resolution is limited only by this point spread function, in ghost imaging we show that the resolution can be further degraded by reducing the strength of the spatial correlations inherent in the downconversion process.

Imaging with a small number of photons.

Low-light-level imaging techniques have application in many diverse fields, ranging from biological sciences to security. A high-quality digital camera based on a multi-megapixel array will typically record an image by collecting of order 10(5) photons per pixel, but by how much could this photon flux be reduced? In this work we demonstrate a single-photon imaging system based on a time-gated intensified camera from which the image of an object can be inferred from very few detected photons. We show that a ghost-imaging configuration, where the image is obtained from photons that have never interacted with the object, is a useful approach for obtaining images with high signal-to-noise ratios. The use of heralded single photons ensures that the background counts can be virtually eliminated from the recorded images. By applying principles of image compression and associated image reconstruction, we obtain high-quality images of objects from raw data formed from an average of fewer than one detected photon per image pixel.