Valid and efficient manual estimates of intracranial volume from magnetic resonance images

Background: Manual segmentations of the whole intracranial vault in high-resolution magnetic resonance images are often regarded as very time-consuming. Therefore it is common to only segment a few linearly spaced intracranial areas to estimate the whole volume. The purpose of the present study was to evaluate how the validity of intracranial volume estimates is affected by the chosen interpolation method, orientation of the intracranial areas and the linear spacing between them. Methods: Intracranial volumes were manually segmented on 62 participants from the Gothenburg MCI study using 1.5 T, T-1-weighted magnetic resonance images. Estimates of the intracranial volumes were then derived using subsamples of linearly spaced coronal, sagittal or transversal intracranial areas from the same volumes. The subsamples of intracranial areas were interpolated into volume estimates by three different interpolation methods. The linear spacing between the intracranial areas ranged from 2 to 50 mm and the validity of the estimates was determined by comparison with the entire intracranial volumes. Results: A progressive decrease in intra-class correlation and an increase in percentage error could be seen with increased linear spacing between intracranial areas. With small linear spacing (<= 15 mm), orientation of the intracranial areas and interpolation method had negligible effects on the validity. With larger linear spacing, the best validity was achieved using cubic spline interpolation with either coronal or sagittal intracranial areas. Even at a linear spacing of 50 mm, cubic spline interpolation on either coronal or sagittal intracranial areas had a mean absolute agreement intra-class correlation with the entire intracranial volumes above 0.97. Conclusion: Cubic spline interpolation in combination with linearly spaced sagittal or coronal intracranial areas overall resulted in the most valid and robust estimates of intracranial volume. Using this method, valid ICV estimates could be obtained in less than five minutes per patient

Descartes "misstag"

Humanistiska fakulteten vid Göteborgs Universitet har erbjudit oss som visade upp vår forskning vid Humanistdagarna i april 2010 att också författa var sitt bidrag till föreliggande nätpublikation. Det visade sig vara inte helt enkelt att skriva en kort artikel som anknyter till båda de presentationer jag hade vid Humanistdagarna – Kropp, själ och psykisk sjukdom: ett möte mellan filosofi och psykiatri respektive Neurala nätverk och modeller för mänskligt tänkande. (De är båda tillgängliga på Internet som nr 54 och 55 i Filosofiska Meddelanden, Webserien, http://www.flov.gu.se/publikationer/fm/web/.) Men så småningom konvergerade tankarna på ett mycket naturligt sätt till min läromästare bland läromästare: René Descartes. Så den här lilla uppsatsen blir en betraktelse över Descartes, några av hans argument och en av hans belackare

Perceptual fulfilment and temporal sequence learning

What happens when an expectation of a certain perceptible event is fulfilled? Traditional empiricist theories about intentionality, as well as several recent theories about mental imagery, emphasise the concrete similarity between expectations and perceptions. For example, one can almost "hear in one's head" a melody which one is anticipating. This has been the starting point for many theories which postulate some kind of similarity matching between the expectation and its fulfilment. According to such theories, an analogue mental representation of the expected fact is "held up" against the incoming percept, and their similarity or non-similarity determines whether the expectation is or is not fulfilled. If such theories are taken as descriptions of phenomenologically accessible facts, they are difficult to defend. First, analogical expectations - when they do occur - usually do not persist into the fulfilment phase. And how could they be matched for similarity, if they are not available at the same time? Second, many cases of expectation do not involve any imagery at all but only reveal themselves as a feeling of surprise if they are not fulfilled. The philosophical literature abounds with arguments against the thesis that concrete similarity to a certain percept is essential for an expectation to have that percept as its object. But of course these are not arguments against cognitive and/or neural-network theories which entail that simultaneous matchings are performed below the introspectively accessible level; such an assumption is often used in explanations of perceptual learning. I here suggest a simple alternative theory of the nature of matching in such learning. Suppose that thought and perception alternate using the same representational medium, and that the contents of this medium are being continuously fed into the cognitive system which produces thought. Such a common feedback/input mechanism will, in itself, give rise to learning because at each alternation from expectation to perception, the system will perform an implicit matching. If the percept is sufficiently dissimilar to what would have occurred in the common medium without perception, the cognitive system will tend to switch to another region of its state-space, in which other kinds of expectations are produced

Quantifying Quality of Life

The concept of quality of life (QoL) which is most relevant to medical and medicopolitical decisions is QoL as goodness of life, e.g., the value of a life for the person who lives it. Mainly because of the interdependence of values, components of an individual human life cannot be ordered in such a way as to permit a complete and context-free ordinal scale. However, local orderings (given a set of fixed conditions) can often be found. Similarly, although local ratio scaling of the desirability of life components using direct ratio estimation seems to be possible, the scales cannot be made complete. Ratio scale values assigned by an individual to the goodness of life components by estimation need not always be even locally additive, since there may not exist any principle of composition. By statistical means, representations of (something like) the value of life components have been derived, which are locally near-additive and which may be useful on a population basis (the QUALY methodology). They are however not useful on an individual basis, nor outside the proven domain of additivity. The question whether the numbers representing the values of different lives can be added is wrongly put. There is no such thing as a composition of a supra-life from individual lives. The real question is whether the numbers should be added - whether the sum is the morally decisive arithmetical quantity to be calculated here. To this, utilitarianism answers Yes, while egalitarianism answers No. The measurement part of QUALY methodology must be kept conceptually apart from utilitarian ethics