Maximum likelihood fitting of FROC curves under an initial-detection-and-candidate-analysis model

We have developed a model for FROC curve fitting that relates the observer's FROC performance not to the ROC performance that would be obtained if the observer's responses were scored on a per image basis, but rather to a hypothesized ROC performance that the observer would obtain in the task of classifying a set of "candidate detections" as positive or negative. We adopt the assumptions of the Bunch FROC model, namely that the observer's detections are all mutually independent, as well as assumptions qualitatively similar to, but different in nature from, those made by Chakraborty in his AFROC scoring methodology. Under the assumptions of our model, we show that the observer's FROC performance is a linearly scaled version of the candidate analysis ROC curve, where the scaling factors are just given by the FROC operating point coordinates for detecting initial candidates. Further, we show that the likelihood function of the model parameters given observational data takes on a simple form, and we develop a maximum likelihood method for fitting a FROC curve to this data. FROC and AFROC curves are produced for computer vision observer datasets and compared with the results of the AFROC scoring method. Although developed primarily with computer vision schemes in mind, we hope that the methodology presented here will prove worthy of further study in other applications as well.     

Recirculating and germinal center B cells differentiate into cells responsive to polysaccharide antigens

Antibodies against bacterial capsular polysaccharides play a critical protective role. Responses to these antigens can occur without the help or control of T cells and are associated with marginal zone (MZ) B cells. Capsular antigens are diverse and some cross-react with self-carbohydrate epitopes. This diversity may explain the recruitment of non-autoreactive recirculating B cells and memory B cells to the MZ in addition to other B cells, some of which are weakly autoreactive cells, that are recruited to the MZ without entering the recirculating pool. To test whether memory B cells respond to polysaccharide-based antigens, mice with hapten-specific memory B cells were challenged with hapten-polysaccharide. Hapten-specific plasma cells producing high affinity antibody with Ig V-region mutations were induced. To test whether naive recirculating B cells can form MZ cells that respond to polysaccharide, recirculating B cells from lymph nodes were transferred into Rag-1-deficient mice. MZ cells differentiated from the donor cells without proliferation or T cell help and responded to polysaccharide-based antigen. The differentiation of B cells both from germinal centers and the recirculating pool to the MZ phenotype is likely to make an important contribution to the repertoire of B cells that respond to polysaccharide antigens.     

Case report: human herpesvirus 7 associated fatal encephalitis in a peripheral blood stem cell transplant recipient

Previous studies have suggested a neuroinvasive and neuropersistent potential of human herpesvirus 7 (HHV-7). In this report, a case of fatal encephalitis is described and its association with HHV-7 infection is discussed. An 8-year-old girl received a peripheral blood stem cell transplant for relapsed acute lymphoblastic leukaemia. The post-transplant period was uneventful and a course of intrathecal chemotherapy was given on Day-30. On Day-41, she developed acute encephalopathy with diplopia and nystagmus. She ran a rapid downhill course and succumbed despite antiviral treatment. The only positive pathological finding was the multiple microscopic foci of haemorrhage associated with neuronal degeneration detected in the brain stem. All microbiological investigations were negative, except for the presence of HHV-7 DNA in cerebrospinal fluid and brain stem tissue samples.     

Cognitive function in depression: a distinct pattern of frontal impairment in melancholia?

BACKGROUND: Although depressed patients demonstrate impaired performance on a range of neuropsychological tests, there is little research that examines either frontal cognitive deficits or possible differences in test performance between melancholic and non-melancholic subtypes. METHODS: Depressed subjects were administered a broad neuropsychological battery. In an overall analysis, 77 depressed subjects were compared with 28 controls. In a second set of analyses, the depressed sample was divided into melancholic and non-melancholic subsets according to DSM-III-R, the CORE system and the Newcastle scale. These depressed subsets were contrasted to controls and with each other using ANCOVA controlling for age, IQ, simple reaction time and Hamilton Depression scores where appropriate. RESULTS: The total depressed sample was impaired on most mnemonic tasks, simple reaction time and Trails B. Similar findings applied to DSM-III-R melancholic and non-melancholic subjects. When defined by the CORE and Newcastle (narrower definitions of melancholia), melancholic patients were additionally impaired on WCST (perseverative response) and (for Newcastle) digit symbol substitution. In contrast, the cognitive performance of the CORE and Newcastle-defined non-melancholic patients was largely unimpaired. CONCLUSIONS: Using narrower definitions of melancholia, i.e. CORE and (in particular) Newcastle, melancholic patients were impaired on mnemonic tasks and tasks of selective attention, and set-shifting while non-melancholic subjects were largely unimpaired in their cognitive performance. These differences may be due to impairment of specific neuroanatomical regions in narrowly defined melancholic patients, in particular the anterior cingulate.     

Whole body health

Alternative therapies, widely used by Americans, include yoga, relaxation techniques, and herbal medications, as well as less conventional and more experimental treatments. The AIDS Research Center in Seattle is conducting the largest study of alternative therapies. Many alternative therapies are used as complements to traditional treatments, and can make a disease easier to manage. Several categories of alternative medicines are detailed: acupuncture and other Chinese treatments, natural treatments including herbal medicine and aromatherapy, and mind-body treatments such as hypnosis and biofeedback. Patients are cautioned to avoid five dangerous therapies: chelation therapy, colonic irrigation, bee venom therapy, hydrogen peroxide injections, and unlabeled medicines. Contact telephone numbers for alternative therapies are listed.