Quantification of myocardial blood flow with 82Rb positron emission tomography: clinical validation with 15O-water

PURPOSE: Quantification of myocardial blood flow (MBF) with generator-produced (82)Rb is an attractive alternative for centres without an on-site cyclotron. Our aim was to validate (82)Rb-measured MBF in relation to that measured using (15)O-water, as a tracer 100% of which can be extracted from the circulation even at high flow rates, in healthy control subject and patients with mild coronary artery disease (CAD). METHODS: MBF was measured at rest and during adenosine-induced hyperaemia with (82)Rb and (15)O-water PET in 33 participants (22 control subjects, aged 30 ± 13 years; 11 CAD patients without transmural infarction, aged 60 ± 13 years). A one-tissue compartment (82)Rb model with ventricular spillover correction was used. The (82)Rb flow-dependent extraction rate was derived from (15)O-water measurements in a subset of 11 control subjects. Myocardial flow reserve (MFR) was defined as the hyperaemic/rest MBF. Pearson's correlation r, Bland-Altman 95% limits of agreement (LoA), and Lin's concordance correlation ρ (c) (measuring both precision and accuracy) were used. RESULTS: Over the entire MBF range (0.66-4.7 ml/min/g), concordance was excellent for MBF (r = 0.90, [(82)Rb-(15)O-water] mean difference ± SD = 0.04 ± 0.66 ml/min/g, LoA = -1.26 to 1.33 ml/min/g, ρ(c) = 0.88) and MFR (range 1.79-5.81, r = 0.83, mean difference = 0.14 ± 0.58, LoA = -0.99 to 1.28, ρ(c) = 0.82). Hyperaemic MBF was reduced in CAD patients compared with the subset of 11 control subjects (2.53 ± 0.74 vs. 3.62 ± 0.68 ml/min/g, p = 0.002, for (15)O-water; 2.53 ± 1.01 vs. 3.82 ± 1.21 ml/min/g, p = 0.013, for (82)Rb) and this was paralleled by a lower MFR (2.65 ± 0.62 vs. 3.79 ± 0.98, p = 0.004, for (15)O-water; 2.85 ± 0.91 vs. 3.88 ± 0.91, p = 0.012, for (82)Rb). Myocardial perfusion was homogeneous in 1,114 of 1,122 segments (99.3%) and there were no differences in MBF among the coronary artery territories (p > 0.31). CONCLUSION: Quantification of MBF with (82)Rb with a newly derived correction for the nonlinear extraction function was validated against MBF measured using (15)O-water in control subjects and patients with mild CAD, where it was found to be accurate at high flow rates. (82)Rb-derived MBF estimates seem robust for clinical research, advancing a step further towards its implementation in clinical routine

Twenty-three unsolved problems in hydrology (UPH) – a community perspective

This paper is the outcome of a community initiative to identify major unsolved scientific problems in hydrology motivated by a need for stronger harmonisation of research efforts. The procedure involved a public consultation through on-line media, followed by two workshops through which a large number of potential science questions were collated, prioritised, and synthesised. In spite of the diversity of the participants (230 scientists in total), the process revealed much about community priorities and the state of our science: a preference for continuity in research questions rather than radical departures or redirections from past and current work. Questions remain focussed on process-based understanding of hydrological variability and causality at all space and time scales. Increased attention to environmental change drives a new emphasis on understanding how change propagates across interfaces within the hydrological system and across disciplinary boundaries. In particular, the expansion of the human footprint raises a new set of questions related to human interactions with nature and water cycle feedbacks in the context of complex water management problems. We hope that this reflection and synthesis of the 23 unsolved problems in hydrology will help guide research efforts for some years to come

Prospective memory: Multiple retrieval processes

ABSTRACT—An interesting challenge for researchers who study prospective memory is to explain how people recognize environmental events as cues for actions. Whereas some theorists propose that a capacity-consuming monitoring process is the only means by which intentions can be retrieved, we argue that the cognitive system relies on multiple processes, including spontaneous processes that reflexively respond to the presence of target events. We present evidence for the existence of spontaneous retrieval processes and apply the idea of multiple processes to mixed findings on age-related decline in prospective memory. KEYWORDS—prospective memory; monitoring; spontaneous retrieval; automatic and controlled processes; aging and memory After a change in his usual routine, an adoring father forgot to turn toward the daycare center and instead drove his usual route to work at the university. Several hours later, his infant son, who had been quietly asleep in the back seat, was dead. Eight months after a hernia surgery, a patient complained of abdominal pain and nausea. A scan of his abdominal area revealed that a 16-cm clamp had been left from his previous surgery. Despite the best intentions of a surgical team of doctors and nurses, they had forgotten to remove the clamp. The above errors represent real failures of prospective memory (PM) or remembering to perform intended actions. Although they highlight the potentially disastrous consequences of some PM failures, it is important to realize that our daily lives are filled, and sometimes overflowing, with PM demands. From managing work activities (e.g., remembering to pack needed papers in the morning) to coordinating social relations (e.g., remembering to take children to parties) to handling healthrelated needs (e.g., remembering to take medication), good PM i

SUMMARY

Based on research showing that easing task demands improves prospective memory, we examined the effects of breaks and task switches on prospective memory. The first experiment suggested that people tend not to take advantage of breaks to improve prospective memory unless specifically instructed to do so. The next two experiments showed that both breaks and task switches interfered with prospective memory. The results indicate that work settings with frequent breaks and task switches may be especially susceptible to prospective memory failure. Copyright # 2006 John Wiley & Sons, Ltd. If we think about it even minimally, it is clear that our everyday lives are replete with prospective memory demands such as remembering to take vitamins, to give messages to various people, and to carry out errands. Prospective memory is also critical to many work settings. Loukopoulos, Dismukes, and Barshi (2001) have described the enormous number of prospective memory demands that occur in cockpit situations. Although many of these are scripted, they are still subject to failure under highly demanding situations, when routines are disrupted, and when there are interruptions. Prospective memory failures in these work settings can be catastrophic. For example, following a series of interruptions, a

Forgetting of Intentions in Demanding Situations Is Rapid

this article should be addressed to Gilles Einstein, Department of Psychology, Furman University, Greenville, South Carolina 29613. E-mail: [email protected] Journal of Experimental Psychology: Applied Copyright 2003 by the American Psychological Association, Inc. 2003, Vol. 9, No. 3, 147--162 1076-898X/03/$12.00 DOI: 10.1037/1076-898X.9.3.147 147 changes in the magnitude of demands throughout the work period (see Nowinski et al., in press). We developed this paradigm for exploration in the same sense that others have used simulated work environments to investigate performance and cognitive processes pertinent to applied settings (cf. Salthouse, Hambrick, Lukas, & Dell, 1996

Dual Pathways to Prospective Remembering

According to the multiprocess framework (McDaniel & Einstein, 2000), the cognitive system can support prospective memory (PM) retrieval through two general pathways. One pathway depends on top-down attentional control processes that maintain activation of the intention and/or monitor the environment for the triggering or target cues that indicate that the intention should be executed. A second pathway depends on (bottom-up) spontaneous retrieval processes, processes that are often triggered by a PM target cue; critically spontaneous retrieval is assumed to not require monitoring or active maintenance of the intention. Given demand characteristics associated with experimental settings, however, participants are often inclined to monitor, thereby potentially masking discovery of bottom-up spontaneous retrieval processes. In this article, we discuss parameters of laboratory PM paradigms to discourage monitoring and review recent behavioral evidence from such paradigms that implicate spontaneous retrieval in PM. We then re-examine the neuro-imaging evidence from the lens of the multiprocess framework and suggest some critical modifications to existing neuro-cognitive interpretations of the neuro-imaging results. These modifications illuminate possible directions and refinements for further neuro-imaging investigations of PM