Silvester Czanner

Reliability of MRI-derived measurements of human cerebral cortical thickness: the effects of field strength, scanner upgrade and manufacturer.

In vivo MRI-derived measurements of human cerebral cortex thickness are providing novel insights into normal and abnormal neuroanatomy, but little is known about their reliability. We investigated how the reliability of cortical thickness measurements is affected by MRI instrument-related factors, including scanner field strength, manufacturer, upgrade and pulse sequence. Several data processing factors were also studied. Two test-retest data sets were analyzed: 1) 15 healthy older subjects scanned four times at 2-week intervals on three scanners; 2) 5 subjects scanned before and after a major scanner upgrade. Within-scanner variability of global cortical thickness measurements was <0.03 mm, and the point-wise standard deviation of measurement error was approximately 0.12 mm. Variability was 0.15 mm and 0.17 mm in average, respectively, for cross-scanner (Siemens/GE) and cross-field strength (1.5 T/3 T) comparisons. Scanner upgrade did not increase variability nor introduce bias. Measurements across field strength, however, were slightly biased (thicker at 3 T). The number of (single vs. multiple averaged) acquisitions had a negligible effect on reliability, but the use of a different pulse sequence had a larger impact, as did different parameters employed in data processing. Sample size estimates indicate that regional cortical thickness difference of 0.2 mm between two different groups could be identified with as few as 7 subjects per group, and a difference of 0.1 mm could be detected with 26 subjects per group. These results demonstrate that MRI-derived cortical thickness measures are highly reliable when MRI instrument and data processing factors are controlled but that it is important to consider these factors in the design of multi-site or longitudinal studies, such as clinical drug trials.

Reliability in multi-site structural MRI studies: Effects of gradient non-linearity correction on phantom and human data

Longitudinal and multi-site clinical studies create the imperative to characterize and correct technological sources of variance that limit image reproducibility in high-resolution structural MRI studies, thus facilitating precise, quantitative, platform-independent, multi-site evaluation. In this work, we investigated the effects that imaging gradient non-linearity have on reproducibility of multi-site human MRI. We applied an image distortion correction method based on spherical harmonics description of the gradients and verified the accuracy of the method using phantom data. The correction method was then applied to the brain image data from a group of subjects scanned twice at multiple sites having different 1.5 T platforms. Within-site and across-site variability of the image data was assessed by evaluating voxel-based image intensity reproducibility. The image intensity reproducibility of the human brain data was significantly improved with distortion correction, suggesting that this method may offer improved reproducibility in morphometry studies. We provide the source code for the gradient distortion algorithm together with the phantom data.

MRI-derived measurements of human subcortical, ventricular and intracranial brain volumes: Reliability effects of scan sessions, acquisition sequences, data analyses, scanner upgrade, scanner vendors and field strengths

Automated MRI-derived measurements of in-vivo human brain volumes provide novel insights into normal and abnormal neuroanatomy, but little is known about measurement reliability. Here we assess the impact of image acquisition variables (scan session, MRI sequence, scanner upgrade, vendor and field strengths), FreeSurfer segmentation pre-processing variables (image averaging, B1 field inhomogeneity correction) and segmentation analysis variables (probabilistic atlas) on resultant image segmentation volumes from older (n=15, mean age 69.5) and younger (both n=5, mean ages 34 and 36.5) healthy subjects. The variability between hippocampal, thalamic, caudate, putamen, lateral ventricular and total intracranial volume measures across sessions on the same scanner on different days is less than 4.3% for the older group and less than 2.3% for the younger group. Within-scanner measurements are remarkably reliable across scan sessions, being minimally affected by averaging of multiple acquisitions, B1 correction, acquisition sequence (MPRAGE vs. multi-echo-FLASH), major scanner upgrades (Sonata-Avanto, Trio-TrioTIM), and segmentation atlas (MPRAGE or multi-echo-FLASH). Volume measurements across platforms (Siemens Sonata vs. GE Signa) and field strengths (1.5 T vs. 3 T) result in a volume difference bias but with a comparable variance as that measured within-scanner, implying that multi-site studies may not necessarily require a much larger sample to detect a specific effect. These results suggest that volumes derived from automated segmentation of T1-weighted structural images are reliable measures within the same scanner platform, even after upgrades; however, combining data across platform and across field-strength introduces a bias that should be considered in the design of multi-site studies, such as clinical drug trials. The results derived from the young groups (scanner upgrade effects and B1 inhomogeneity correction effects) should be considered as preliminary and in need for further validation with a larger dataset.

A high-fidelity virtual environment for the study of paranoia

Psychotic disorders carry social and economic costs for sufferers and society. Recent evidence highlights the risk posed by urban upbringing and social deprivation in the genesis of paranoia and psychosis. Evidence based psychological interventions are often not offered because of a lack of therapists. Virtual reality (VR) environments have been used to treat mental health problems. VR may be a way of understanding the aetiological processes in psychosis and increasing psychotherapeutic resources for its treatment. We developed a high-fidelity virtual reality scenario of an urban street scene to test the hypothesis that virtual urban exposure is able to generate paranoia to a comparable or greater extent than scenarios using indoor scenes. Participants (n = 32) entered the VR scenario for four minutes, after which time their degree of paranoid ideation was assessed. We demonstrated that the virtual reality scenario was able to elicit paranoia in a nonclinical, healthy group and that an urban scene was more likely to lead to higher levels of paranoia than a virtual indoor environment. We suggest that this study offers evidence to support the role of exposure to factors in the urban environment in the genesis and maintenance of psychotic experiences and symptoms. The realistic high-fidelity street scene scenario may offer a useful tool for therapists.

The Playability Evaluation of Virtual Baby Feeding Application

This paper describes the playability evaluation of serious game application, which has been developed to significantly improve a new parent’s understanding and treatment of infants with feeding disorders. Feeding problems and the associated crying are a major cause of anxiety in new parents and substantial time and effort is spent by health care visitors in helping parents to tackle these issues. In this paper, the insights from the design and implementation of the application are provided. The engagement of users and their emotional immersion are discussed. Main findings of application evaluation are presented.

A study of visual perception: social anxiety and virtual realism

Virtual reality exposure therapy offers the possibility of tackling social anxiety in an efficient, safe and controlled manner. A key question, however, is what is the level of realism required in virtual environments to ensure the environment is effective in helping the participant to deal with their anxiety. One concern which affects a lot of people from all walks of life is the fear of a job interview. In this paper we investigate the relationship between anxiety and varying levels of realistic fidelity. We recruited 60 volunteers and studied their anxiety levels via randomised block design, where each block was exposed to a different level of fidelity of the virtual avatars: realistic 3D human avatar, cartoon-like 3D avatar, and human photographs. We measured the social anxiety of all participants via a measure of eyes avoidance behaviour. Our main findings are that the participants exhibited more anxiety in accordance with the attitude of virtual avatars than the avatars level of realism.

High dynamic range video for cultural heritage documentation and experimental archaeology

Video recording and photography are frequently used to document Cultural Heritage (CH) objects and sites. High Dynamic Range (HDR) imaging is increasingly being used as it allows a wider range of light to be considered that most current technologies are unable to natively acquire and reproduce. HDR video content however has only recently become possible at desirable, high definition resolution and dynamic range. In this paper we explore the potential use of a 20 f-stop HDR video camera for CH documentation and experimental archaeology purposes. We discuss data acquisition of moving caustics, flames, distant light and in participating media. Comparisons of Low Dynamic Range (LDR) and HDR content are made to illustrate the additional data that this new technology is able to capture, and the benefits this is likely to bring to CH documentation and experimental archaeology.

Assessing a virtual baby feeding training system

Currently a considerable amount of time and resources are spent helping parents overcome issues related to feeding young infants. Designing interactive virtual feeding scenarios is a preventative means to reduce the adaptation process time for newly made parents, but also help new parents improve their approach to feeding their children. In this paper, we present a case study on using and assessing a virtual reality infant feeding application. Our results show that virtual training can increase the efficiency of feeding depending on the different behaviour of the child.

Applet Competition as an Educational Tool in Creating Novel e-Textbook

We introduce a long-term competition-oriented project, using learning by doing (applets). The output of this project is updated every year at http://www.netgraphics.sk/. Many undergraduate students at the University of Warwick and the Comenius University compete in developing the e-Textbook, called Computer Graphics Virtual Textbook. The current version offers supplementary material for particular CG courses but it is also an independent source of information for all people interested in CG. There is currently 126 students enrolled for this competition. Every year, the number of valuable applets or applet innovations is lower than the total number of students. The three winners of 2008 round of applet competition will be announced before Christmas (and their creations will be presented at the SCCG09 conference). The best units of this project will be submitted to CGEMS.

Computer graphics virtual textbook

In this paper we present a project entitled Computer Graphics Virtual Textbook, which should be both locally and globally useful. The objective of this project is twofold. First, it enhances the undergraduate research activity at the University of Warwick and the Comenius University by involving more than one hundred undergraduate students in developing the Computer Graphics Virtual Textbook. Second objective of the project is to create an interactive series of web pages called Computer Graphics Virtual Textbook with Computer Graphics (CG) content. It will be used as a supplementary material for CG courses but it will also be an independent source of information for all people interested in CG. It contains descriptions of the very basic CG methods such as the plot of a point, a line, and a circle and also the advanced methods such as the modeling, rendering and visualization techniques, fractals, etc. To support the interactions the small interactive java applets are used. Java applets allow users to try and see how the described algorithm/method is working in real time.