William D. K. Green

A feature space for edgels in images with landmarks

In many current medical applications of image analysis, objects are detected and delimited by boundary curves or surfaces. Yet the most effective multivariate statistics available pertain to labeled points (landmarks) only. In the finite-dimensional feature space that landmarks support, each case of a data set is equivalent to a deformation map deriving it from the average form. This paper introduces a new extension of the finite-dimensional spline-based approach for incorporating edge information. In this implementation edgels are restricted to landmark loci: they are interpreted as pairs of landmarks at infinitesimal separation in a specific direction. The effect of changing edge direction is a singular perturbation of the thin-plate spline for the landmarks alone. An appropriate normalization yields a basis for image deformations corresponding to changes of edge direction without landmark movement; this basis complements the basis of landmark deformations ignoring edge information. We derive explicit formulas for these edge warps, evaluate the quadratic form expressing bending energies of their formal combinations, and show the resulting spectrum of edge features in typical scenes. These expressions will aid all investigations into medical images that entail comparisons of anatomical scene analyses to a normative or typical form.

A Feature Space for Derivatives of Deformations

Applications of image deformation to averaging or the description of clinically interesting variation require that expert knowledge be concentrated into feature vectors of substantially lower dimension. For “images” of discrete, individually labelled points, or landmarks, the quasilinear procedures of the interpolating thin-plate spline conveniently exemplify these vectors as explicit deformations, and its energetics supplies a basis for the shape space they span. Recent work by our group extended these strengths of the thinplate spline to incorporate information about edge directions at landmarks, or edgels. This paper shows how linear combinations of up to four of these edgel specifications at a point can constrain a splined deformation to accord with arbitrary specifications of the affine derivative there. Any such constrained deformation may be computed in closed algebraic form as a singular perturbation of the underlying landmark-driven spline. Local scale change, local rotation, and unidimensional local dilatation follow as special cases. The resulting synthesis of the landmark-based and image-based approaches to analysis of deformations seems to us much more promising than either approach separately.

Edgewarp: a flexible program package for biometric image warping in two dimensions

Edgewarp, a program in C and XWindows, is a wholly graphical interface for managing the complicated algebra by which thin- plate splines are applied in contemporary biomedical image analysis. This flexible warping package permits the free specification of deformations by arbitrary combinations of landmark point correspondences and constraints. Its parameters may be forwarded for rigorous multivariate statistical analysis at the same time that the associated images can be averaged or correlated after unwarping. This paper describes the kinematics of the interface by which clinical users can exploit these graphics and biometrics. Even though we show an actual clinical finding arrived at by these means, our main purpose is to inveigle the reader into playing with our shareware.

Effects of anesthetic technique on side effects associated with fentanyl oralet premedication

STUDY OBJECTIVES To evaluate the efficacy of 5 to 10 micrograms/kg of oral transmucosal fentanyl citrate (OTFC) as an anesthetic premedication, and to determine whether propofol induction reduces postoperative nausea and vomiting (PONV) in pediatric patients premedicated with OTFC undergoing outpatient surgery. DESIGN Prospective, randomized, double-blinded study. SETTINGS University of Michigan Health Care Systems and University of Arizona. PARTICIPANTS 62 ASA physical status I and II children aged 4 to 14 years (8.9 +/- 0.5 years). INTERVENTIONS Subjects were randomly assigned to one of four groups: (1) OTFC premedication and halothane induction; (2) OTFC premedication and propofol induction; (3) placebo premedication and halothane induction; and (4) placebo premedication and propofol induction. OTFC or placebo was administered 30 minutes prior to induction, and activity (sedation), apprehension, and cooperation scores were recorded before, at 15 and 30 minutes after study drug, and on induction. All perioperative adverse events were recorded. MEASUREMENTS AND MAIN RESULTS Children who received OTFC became drowsier and had a significant change from baseline in combined activity, apprehension, and cooperation scores, whereas those who received placebo became less cooperative at induction. Patients who received OTFC experienced more adverse events overall (p < 0.001) than patients who received placebo. Additionally, OTFC patients experienced more vomiting (p < 0.001) and pruritus (p = 0.049) than controls. The incidence of PONV in patients who received OTFC and halothane induction was 50%, compared to 30% in patients receiving OTFC and a propofol induction (p = NS). CONCLUSIONS OTFC in doses of 5 to 10 micrograms/kg was effective in producing sedation and facilitating cooperation with induction; however, it was associated with significant PONV in our study. Although propofol induction did not significantly reduce PONV in our study, further study with a larger sample, and with propofol as the sole anesthetic, may be warranted.

A symmetrical Waxholm canonical mouse brain for NeuroMaps

NeuroMaps (2010) is a Web-based application that enables investigators to map data from macaque studies to a canonical atlas of the macaque brain. It currently serves as an image processor enabling them to create figures suitable for publication, presentation and archival purposes. Eventually it will enable investigators studying any of several species to analyze the overlap between their data and multimodality data mapped by others. The purpose of the current project was to incorporate the Waxholm canonical mouse brain (Harwylycz, 2009) into NeuroMaps. An enhanced gradient echo (T2*) magnetic resonance image (MRI) of the Waxholm canonical brain (Johnson et al., 2010) was warped to bring the irregular biological midplane of the MRI into line with the mathematically flat midsagittal plane of the Waxholm space. The left hemisphere was deleted and the right hemisphere reflected to produce a symmetrical 3D MR image. The symmetrical T2* image was imported into NeuroMaps. The map executing this warp was applied to four other voxellated volumes based on the same canonical specimen and maintained at the Center for In-Vitro Microscopy (CIVM): a T2-weighted MRI, a T1-weighted MRI, a segmented image and an image reconstructed from Nissl-stained histological sections of the specimen. Symmetric versions of those images were returned to the CIVM repository where they are made available to other laboratories. Utility of the symmetric atlas was demonstrated by mapping and comparing a number of cortical areas as illustrated in three conventional mouse brain atlases. The symmetric Waxholm mouse brain atlas is now accessible in NeuroMaps where investigators can map image data to standard templates over the Web and process them for publication, presentation and archival purposes: http://braininfo.rprc.washington.edu/MapViewData.aspx.

Spline-based deformable models

There are well established techniques for the biomathematical analysis of sets of homologous images with landmarks. These include the construction of the average configuration of landmarks, the statistical analysis of the procrustes residuals of the landmark positions and the averaging of the images themselves. This paper outlines a method of performing similar steps on sets of images with homologous 1D features as well as landmarks. The basis of the method is the expanded and consistent application of the thin-plate spline, a tool already used in the analysis of landmark images.