The purpose of these guidelines is to assist physicians in recommending, performing, interpreting and reporting the results of FDG PET/CT for oncological imaging of adult patients. PET is a quantitative imaging technique and therefore requires a common quality control (QC)/quality assurance (QA) procedure to maintain the accuracy and precision of quantitation. Repeatability and reproducibility are two essential requirements for any quantitative measurement and/or imaging biomarker. Repeatability relates to the uncertainty in obtaining the same result in the same patient when he or she is examined more than once on the same system. However, imaging biomarkers should also have adequate reproducibility, i.e. the ability to yield the same result in the same patient when that patient is examined on different systems and at different imaging sites. Adequate repeatability and reproducibility are essential for the clinical management of patients and the use of FDG PET/CT within multicentre trials. A common standardised imaging procedure will help promote the appropriate use of FDG PET/CT imaging and increase the value of publications and, therefore, their contribution to evidence-based medicine. Moreover, consistency in numerical values between platforms and institutes that acquire the data will potentially enhance the role of semiquantitative and quantitative image interpretation. Precision and accuracy are additionally important as FDG PET/CT is used to evaluate tumour response as well as for diagnosis, prognosis and staging. Therefore both the previous and these new guidelines specifically aim to achieve standardised uptake value harmonisation in multicentre settings.

Neural precursors often generate distinct cell types in a specific order, but the intrinsic or extrinsic cues regulating the timing of cell fate specification are poorly understood. Here we show that Drosophila neural precursors (neuroblasts) sequentially express the transcription factors Hunchback --> Krüppel --> Pdm --> Castor, with differentiated progeny maintaining the transcription factor profile present at their birth. Hunchback is necessary and sufficient for first-born cell fates, whereas Krüppel is necessary and sufficient for second-born cell fates; this is observed in multiple lineages and is independent of the cell type involved. We propose that Hunchback and Krüppel control early-born temporal identity in neuroblast cell lineages.

The Drosophila embryonic central nervous system (CNS) develops from a bilateral neuroectoderm that forms adjacent to the specialized cells of the ventral midline. Neuroectoderm on each side of the ventral midline can be subdivided, on the basis of patterns of gene expression and neuroblast formation, into an orthogonal grid of four rows (1, 3, 5, 7) along the anteroposterior (AP) axis and three columns (ventral, intermediate, and dorsal) along the DV axis. The earliest neuroblast array has four neuroblasts in the ventral column, two in the intermediate column, and four in the dorsal column. Neuroblasts divide repeatedly to produce a series of smaller ganglion mother cells (GMCs), each of which produce two postmitotic neurons or glia. Every neuroblast is uniquely identifiable on the basis of its AP and DV position, and each generates a characteristic family of neurons and glia.Neuroblast formation is regulated by the proneural genes achaete, scute, and lethal of scute (for review, see Campos-Ortega 1993). Each of these proneural genes is expressed in clusters of 4-6 cells at different positions within the neuroectoderm (e.g., achaete is expressed in four clusters, in the ventral and dorsal columns of rows 3 and 7). Proneural genes promote the formation of neuroblasts, whereas Delta-Notch signaling inhibits neuroblast formation; the balance of proneural and Notch activity results in the formation of a single neuroblast from each cluster (for review, see Campos-Ortega 1993).What are the cues that specify correct neuroblast identity along the AP and DV axes? The segment polarity genes wingless, hedgehog, gooseberry, and engrailed are expressed in stripes in the neuroectoderm and specify the AP row identity of neuroblasts (Chu-LaGraff and Doe 1993;Zhang et al. 1994;Skeath et al. 1995;Bhat 1996;Matsuzaki and Saigo 1996;Bhat and Schedl 1997). Conditional inactivation (for wingless; Chu-LaGraff and Doe 1993) or misexpression (for gooseberry; Skeath et al. 1995) experiments show that segment polarity gene function is required in the neuroectoderm, prior to neuroblast delamination, for the proper specification of neuroblast identity.Less is known about how neuroectoderm and neuro-

Motoneurons are an essential component of all metazoan nervous systems, but it is unknown whether there is an evolutionarily conserved mechanism for generating motoneurons during neurogenesis. In the vertebrate CNS, HB9/MNR2 transcription factors are specifically expressed in all somatic motoneurons and are necessary to distinguish motoneurons from interneurons, in part by repressing interneuron-specific gene expression. Here, we identify and characterize the single Drosophila ortholog of the HB9/MNR2 gene family. Drosophila HB9 is detected in a subset of motoneurons with ventral muscle targets and in a small group of interneurons, including the well characterized serotonergic interneurons. RNA interference knockdown of HB9 levels leads to defects in motoneuron ventral muscle target recognition, ectopic expression of a marker for dorsally projecting motoneurons (Even-skipped), and defects in serotonergic interneuronal projections. Conversely, ectopic HB9 expression causes an expansion of ventral motoneuron projections and repression of Even-skipped. Thus, Drosophila HB9 is required in a subset of motoneurons and interneurons for establishing proper axon projections but does not have a general role in distinguishing motoneuron and interneuron cell types.