Per Larsen

AMP‐activated protein kinase regulates nicotinamide phosphoribosyl transferase expression in skeletal muscle

•  NAD is a substrate for sirtuins (SIRTs), which regulate gene transcription in response to specific metabolic stresses. •  Nicotinamide phosphoribosyl transferase (Nampt) is the rate‐limiting enzyme in the NAD salvage pathway. •  Using transgenic mouse models, we tested the hypothesis that skeletal muscle Nampt protein abundance would increase in response to metabolic stress in a manner dependent on the cellular nucleotide sensor, AMP‐activated protein kinase (AMPK). •  Exercise training, as well as repeated pharmacological activation of AMPK by 5‐amino‐1‐β‐d‐ribofuranosyl‐imidazole‐4‐carboxamide (AICAR), increased Nampt protein abundance. However, only the AICAR‐mediated increase in Nampt protein abundance was dependent on AMPK. •  Our results suggest that cellular energy charge and nutrient sensing by SIRTs may be mechanistically related, and that Nampt may play a key role for cellular adaptation to metabolic stress.

The visible ear: A digital image library of the temporal bone

High-fidelity computer-based modeling, simulation and visualization systems for the study of temporal bone anatomy and training for middle ear surgery are based on a sequence of digital anatomical images, which must cover a large tissue volume and yet display details in high resolution and with high fidelity. However, the use of existing image libraries by independent developers of virtual models of the ear is limited by copyright protection and low image resolution. A fresh frozen human temporal bone was CT-scanned and serially sectioned at 25 µm and digital images of the block surface were recorded at 50- to 100-µm increments with a Light PhaseTM single-shot camera back attachment. A total of 605 images were recorded in 24-bit RGB resolution. After color correction and elimination of image size variation by differential cropping to 15.4 cm × 9.7 cm, all images were resampled to 3,078 × 1,942 pixels at a final resolution of 50 µm/pixel and stored as 605 one-Mb JPEG files together with a three-dimensional viewer. The resulting complete set of image data provides: (1) a source material suitable for generating computer models of the human ear; (2) a resource of high-quality digital images of anatomical cross sections from the human ear, and (3) a PC-based viewer of the temporal bone in three perpendicular planes of section.

Hepatic NAD salvage pathway is enhanced in mice on a high-fat diet.

Nicotinamide phosphoribosyltransferase (Nampt) is the rate-limiting enzyme for NAD salvage and the abundance of Nampt has been shown to be altered in non-alcoholic fatty liver disease. It is, however, unknown how hepatic Nampt is regulated in response to accumulation of lipids in the liver of mice fed a high-fat diet (HFD). HFD mice gained more weight, stored more hepatic lipids and had an impaired glucose tolerance compared with control mice. NAD levels as well as Nampt mRNA expression, protein abundance and activity were significantly increased in HFD mice. Enhanced NAD levels were associated with deacetylation of p53 and Nfκb indicating increased activation of Sirt1. Despite impaired glucose tolerance and increased hepatic lipid levels in HFD mice, NAD metabolism was significantly enhanced. Thus, improved NAD metabolism may be a compensatory mechanism to protect against negative impact of hepatic lipid accumulation.

A Pilot Study on the Influence of Facial Expression on Measurements in Three-Dimensional Digital Surfaces of the Face in Infants With Cleft Lip and Palate

Objective Three-dimensional surface imaging is an increasingly popular modality for face measurements in infants with cleft lip and palate. Infants are noncompliant toward producing specific facial expressions, and selecting the appropriate moment of acquisition is challenging. The objective was to estimate amount and spatial distribution of deformation of the face due to facial expression in infants with cleft lip and palate and provide recommendations for an improved acquisition protocol, including a method of quality control in terms of obtaining images with true neutral expression. Material and Methods Three-dimensional surface images of ten 4-month-old infants with unrepaired cleft lip and palate were obtained using a 3dMDface stereophotogrammetric system. For each subject, five surface images judged as representing a neutral expression were obtained during the same photo session. Mean and maximum deformations were calculated. A formalized review was performed, allowing the image exhibiting the “best” neutral expression to be selected, thus decreasing errors due to residual facial expression. Results Deformation due to facial expression generally increased from forehead to chin. The amount of deformation in three selected regions were determined: nose (mean, 1 mm; maximum = 3 mm); cleft region (mean, 2 mm; maximum = 5 mm); chin region (mean, 5 mm; maximum = 12 mm). Analysis indicated that introduction of a formalized review of images could reduce these errors by a factor of 2. Conclusions The continuous change of facial expression in infants represents a substantial source of error; however, this may be reduced by incorporating a formalized review into the acquisition protocol.

Sparse statistical deformation model for the analysis of craniofacial malformations in the Crouzon mouse

Crouzon syndrome is characterised by the premature fusion of cranial sutures. Recently the first genetic Crouzon mouse model was generated. In this study, Micro CT skull scannings of wild-type mice and Crouzon mice were investigated. Using nonrigid registration, a wild-type craniofacial mouse atlas was built. The atlas was registered to all mice providing parameters controlling the deformations for each subject. Our previous PCA-based statistical deformation model on these parameters revealed only one discriminating mode of variation. Aiming at distributing the discriminating variation over more modes we built a different model using Independent Component Analysis (ICA). Here, we focus on a third method, sparse PCA (SPCA), which aims at approximating the properties of a standard PCA while introducing sparse modes of variation. The results show that SPCA outperforms both ICA and PCA with respect to the Fisher discriminant, although many similarities are found with respect to ICA.

Craniofacial Statistical Deformation Models of Wild-type mice and Crouzon mice

Crouzon syndrome is characterised by premature fusion of cranial sutures and synchondroses leading to craniofacial growth disturbances. The gene causing the syndrome was discovered approximately a decade ago and recently the first mouse model of the syndrome was generated. In this study, a set of Micro CT scans of the heads of wild-type (normal) mice and Crouzon mice were investigated. Statistical deformation models were built to assess the anatomical differences between the groups, as well as the within-group anatomical variation. Following the approach by Rueckert et al. we built an atlas using B-spline-based nonrigid registration and subsequently, the atlas was nonrigidly registered to the cases being modelled. The parameters of these registrations were then used as input to a PCA. Using different sets of registration parameters, different models were constructed to describe (i) the difference between the two groups in anatomical variation and (ii) the within-group variation. These models confirmed many known traits in the wild-type and Crouzon mouse craniofacial anatomy. However, they also showed some new traits.

Genus zero graph segmentation

Fully automatic segmentation of intracranial volume.Equidistant subsampling with Delaunay tetrahedralisation for dense neighborhood connectivity without blocky grid-bias.Node clamping forces the segmentation to be consistent and of genus 0.Dice scores above 98% compared to manual reference. The intracranial volume (ICV) in children with premature fusion of one or more sutures in the calvaria is of interest due to the risk of increased intracranial pressure. Challenges for automatic estimation of ICV include holes in the skull e.g. the foramen magnum and fontanelles. In this paper, we present a fully automatic 3D graph-based method for segmentation of the ICV in non-contrast CT scans. We reformulate the ICV segmentation problem as an optimal genus 0 segmentation problem in a volumetric graph. The graph is the result of a volumetric spherical subsampling. The equidistantly sampled data points are connected using Delaunay tetrahedralisation creating a highly connected neighborhood. A Markov Random Field (MRF) is constructed on the graph with probabilities learned from an Expectation Maximisation algorithm matching a Mixture of Gaussians to the data. The result of the MRF segmentation is compared to manual segmentations performed by an expert. We have achieved very high Dice scores ranging from 98.14% to 99.00%, while volume deviation from the manual segmentation ranges from 0.7% to 3.7%. The Hausdorff distance, which shows the maximum error from automatic to manual segmentation, ranges from 4.73 to 9.81mm. Since this is sensitive to single error, we have also found the 95% Hausdorff distance, which ranges from 1.10 to 3.65mm. The segmentation is very consistent with the reference and differs only in difficult areas, where it seems that our method is much more slice-wise consistent than a manual segmentation. The proposed method is expected to perform well for other volumetric segmentations.

ESTIMATION OF INDEPENDENT NON-LINEAR DEFORMATION MODES FOR ANALYSIS OF CRANIOFACIAL MALFORMATIONS IN CROUZON MICE

Crouzon syndrome is a genetic disease resulting in premature fusion of cranial sutures and synchondroses causing craniosynostosis. A decade ago the Crouzon gene was discovered, and recently the first mouse model of the syndrome was generated. In this study, a set of micro CT scannings of the heads of wild-type (normal) mice and Crouzon mice were investigated. We present for what we believe is the first time, a statistical deformation model based on independent component analysis (ICA). A set of deformation parameters for each mouse was calculated using a B-spline-based non-rigid registration. From the parameters controlling the deformations for each subject, the statistical model was estimated. ICA is demonstrated to provide localized deformation components, many of which give a clear separation between Crouzon and wild-type mice. This is a clear improvement of a previous principal component-based model, which only provided one global deformation component describing the disease. The ICA components allow interpretation of each deformation feature to be carried out independently of other features, and provides a basis for linking the observed craniofacial malformations to the fusing of sutures. ICA revealed an interesting new finding, not previously reported in the literature, namely asymmetries in the head in Crouzon mice. This phenomenon is probably caused by asymmetric closure of craniofacial sutures

Genus Zero Graph Segmentation: Estimation of Intracranial Volume

The intracranial volume (ICV) in children with premature fusion of one or more sutures in the calvaria is of interest due to the risk of increased intracranial pressure. Challenges for automatic estimation of ICV include holes in the skull e.g. the foramen magnum and fontanelles. In this paper, we present a fully automatic 3D graph-based method for segmentation of the ICV in non-contrast CT scans. We reformulate the ICV segmentation problem as an optimal genus 0 segmentation problem in a volumetric graph. The graph is the result of a volumetric spherical subsample from the data connected using Delaunay tetrahedralisation. A Markov Random Field is constructed on the graph with probabilities learned from an Expectation Maximisation algorithm matching a Mixture of Gaussians to the data. Results are compared to manual segmentations performed by an expert. We have achieved very high Dice scores ranging from 98.14% to 99.00%, while volume deviation from the manual segmentation ranges from 0.7%-3.7%. The Hausdorff distance, which shows the maximum error from automatic to manual segmentation ranges, from 4.73-9.81mm. Since this is sensitive to single error, we have also found the 95% Hausdorff distance, which ranges from 1.10-3.65mm. The proposed method is expected to perform well for other volumetric segmentations.