Johan De Mey

Vascular Active Contour for Vessel Tree Segmentation

In this paper, a novel active contour model is proposed for vessel tree segmentation. First, we introduce a region competition-based active contour model exploiting the Gaussian mixture model, which mainly segments thick vessels. Second, we define a vascular vector field to evolve the active contour along its center line into the thin and weak vessels. The vector field is derived from the eigenanalysis of the Hessian matrix of the image intensity in a multiscale framework. Finally, a dual curvature strategy, which uses a vesselness measure-dependent function selecting between a minimal principal curvature and a mean curvature criterion, is added to smoothen the surface of the vessel without changing its shape. The developed model is used to extract the liver and lung vessel tree as well as the coronary artery from high-resolution volumetric computed tomography images. Comparisons are made with several classical active contour models and manual extraction. The experiments show that our model is more accurate and robust than these classical models and is, therefore, more suited for automatic vessel tree extraction.

Accelerated HF-rTMS in treatment-resistant unipolar depression: Insights from subgenual anterior cingulate functional connectivity

Abstract Objectives. Intensified repetitive transcranial magnetic stimulation (rTMS) applied to the left dorsolateral prefrontal cortex (DLPFC) may result in fast clinical responses in treatment resistant depression (TRD). In these kinds of patients, subgenual anterior cingulate cortex (sgACC) functional connectivity (FC) seems to be consistently disturbed. So far, no de novo data on the relationship between sgACC FC changes and clinical efficacy of accelerated rTMS were available. Methods. Twenty unipolar TRD patients, all at least stage III treatment resistant, were recruited in a randomized sham-controlled crossover high-frequency (HF)-rTMS treatment study. Resting-state (rs) functional MRI scans were collected at baseline and at the end of treatment. Results. HF-rTMS responders showed significantly stronger resting-state functional connectivity (rsFC) anti-correlation between the sgACC and parts of the left superior medial prefrontal cortex. After successful treatment an inverted relative strength of the anti-correlations was observed in the perigenual prefrontal cortex (pgPFC). No effects on sgACC rsFC were observed in non-responders. Conclusions. Strong rsFC anti-correlation between the sgACC and parts of the left prefrontal cortex could be indicative of a beneficial outcome. Accelerated HF-rTMS treatment designs have the potential to acutely adjust deregulated sgACC neuronal networks in TRD patients.

Using 3D-MRI to localize the dorsolateral prefrontal cortex in TMS research.

Transcranial magnetic stimulation (TMS) is currently used as a non-invasive treatment for depression. In most clinical trials, the left dorsolateral prefrontal cortex (DLPFC) has been selected as the target site for TMS treatment and this region is commonly determined by a “standard procedure”, using a fixed position with respect to the motor cortex. In this study, to evaluate the relevance of using individual anatomical data during coil positioning, we used a more individualized localization method, based on three-dimensional magnetic resonance imaging of the head (3D-MRI). We wanted to examine the intra-individual variability of the localization of the stimulation area using a method taking into account individual brain anatomy by 3D-MRI, by comparing this method to the “standard procedure”. As expected, even in a gender-controlled sample, our results demonstrate that the difference between the anatomical localization and the standard procedure of a well-defined part of the prefrontal cortex varies within subjects. Therefore, our results confirm the need for a TMS-coil positioning method which incorporates individual anatomical information.

Individual differences in local gray and white matter volumes reflect differences in temperament and character: A voxel-based morphometry study in healthy young females

The psychobiological personality model of Cloninger distinguishes four heritable temperament traits (harm avoidance (HA), novelty seeking (NS), reward dependence (RD) and persistence (P)) and three character traits (self-directedness (SD), cooperativeness (CO) and self-transcendence (ST)) which develop during lifetime. Prior research already showed that individual differences in temperament are reflected in structural variances in specific brain areas. In this study, we used voxel-based morphometry (VBM) to correlate the different temperament and character traits with local gray and white matter volumes (GMV and WMV) in young healthy female volunteers. We found correlations between the temperament traits and GMV and WMV in the frontal, temporal and limbic regions involved in controlling and generating the corresponding behavior as proposed in Cloningers theory: anxious for HA, impulsive for NS, reward-directed for RD and goal-directed for P. The character traits correlated with GMV and WMV in the frontal, temporal and limbic regions involved in the corresponding cognitive tasks: self-reflection for SD, mentalizing and empathizing with others for CO and religious belief for ST. This study shows that individual variations in brain morphology can be related to the temperament and character dimensions, and lends support to the hypothesis of a neurobiological basis of personality traits.

Evaluation of the radiation dose in micro-CT with optimization of the scan protocol

INTRODUCTION Micro-CT provides non-invasive anatomic evaluation of small animals. Serial micro-CT measurements are, however, hampered by the severity of ionizing radiation doses cumulating over the total period of follow-up. The dose levels may be sufficient to influence experimental outcomes such as animal survival or tumor growth. AIM This study was designed to evaluate the radiation dose of micro-CT and to optimize the scanning protocol for longitudinal micro-CT scans. METHODS AND MATERIALS Normal C57Bl/6 mice were euthanized. Radiation exposure was measured using individually calibrated lithium fluoride thermoluminescent dosimeters (TLDs). Thirteen TLDs were placed in the mice at the thyroid, lungs, liver, stomach, colon, bladder and near the spleen. Micro-CT (SkyScan 1178) was performed using two digital X-ray cameras which scanned over 180 degrees at a resolution of 83 microm, a rotation step of 1.08 degrees , 50 kV, 615 microA and 121 s image acquisition time. The TLDs were removed after each scan. CTDI(100) was measured with a 100 mm ionization chamber, centrally positioned in a 2.7 cm diameter water phantom, and rotation steps were increased to reduce both scan time and radiation dose. RESULTS Internal TLD analysis demonstrated median organ dose of 5.5 +/- 0.6 mGy per mA s, confirmed by CTDI(100) with result of 6.6 mGy per mA s. A rotation step of 2.16 resulted in qualitatively accurate images. At a resolution of 83 microm the scan time is reduced to 63 s with an estimated dose of 2.9 mGy per mA s. At 166 microm resolution, the scan time is limited to 27 s, with a concordant dose of 1.2 mGy per mA s. CONCLUSIONS The radiation dose of a standard micro-CT scan is relatively high and could influence the experimental outcome. We believe that the presented adaptation of the scan protocol allows for accurate imaging without the risk of interfering with the experimental outcome of the study.

HF-rTMS treatment in medication-resistant melancholic depression: results from 18FDG-PET brain imaging.

INTRODUCTION High frequency repetitive transcranial magnetic stimulation (HF-rTMS) of the left dorsolateral prefrontal cortex (DLPFC) might be a promising strategy to treat depression, but not all patients show a positive outcome. OBJECTIVE In this open study, we evaluate whether a favorable HF-rTMS treatment outcome could be predicted by baseline prefrontal brain glucose metabolism (CMRglc), measured by 18fluorodeoxyglucose positron emission tomography (18FDG-PET). METHODS A sample of 21 antidepressant-free, treatment-resistant depression (TRD) patients of the melancholic subtype received 10 sessions of HF-rTMS delivered on the left DLPFC. Patients underwent a static 18FDG-PET before and after HF-rTMS treatment. RESULTS Forty-three percent of the patients showed a reduction of at least 50% on their Hamilton Rating Scale for Depression scores. Higher baseline metabolic activities in the DLPFC and the anterior cingulate cortex (ACC) were associated with better clinical outcome. Successful HF-rTMS treatment was related to metabolic changes in subdivisions of the ACC (Brodmann areas 24 and 32). CONCLUSION This biological impact of HF-rTMS on regional brain CMRglc explains to some extent how HF-rTMS may improve moods in TRD patients. Larger sham-controlled HF-rTMS treatment studies are needed to confirm these results.

Deconvolution-based Dynamic Contrast-enhanced MR Imaging of Breast Tumors: Correlation of Tumor Blood Flow with Human Epidermal Growth Factor Receptor 2 Status and Clinicopathologic Findings—Preliminary Results

PURPOSE To prospectively determine whether breast carcinomas possess characteristic values of tumor blood flow (TBF) that correlate with pathologic and molecular prognostic markers. MATERIALS AND METHODS The institutional ethics committee approved this study. After informed consent was obtained, 57 women (age range, 31-80 years) with histologically proved breast cancer underwent routine magnetic resonance (MR) mammography, which included a whole-breast dynamic contrast material-enhanced (DCE) sequence. A second contrast material bolus was injected during dynamic single-section turbo field-echo imaging of the section where the lesion was maximally enhanced. The relative signal intensity changes were deconvolved in a pixelwise fashion to yield the TBF. Formalin-fixed paraffin-embedded tumor specimens on slides were evaluated for histologic size and grade, as well as for estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) protein. In patients with a HER2 protein score of 2+ or 3+, HER2 gene status was assessed. For all prognostic parameters, the Mann-Whitney U test was used to compare median TBF in the HER2-positive group with that in the HER2-negative group. RESULTS Significantly higher TBF was observed in tumors larger than 2 cm in diameter and in PR-negative and HER2 gene-amplified tumors (P < .05). In the HER2-positive and HER2-negative groups, ER-positive PR-positive tumors had a lower median TBF than did ER-negative PR-negative tumors, and the difference was significant in the HER2-positive group (P < .05). CONCLUSION Pixelwise deconvolution analysis of DCE MR data in patients with breast cancer can provide preoperative information regarding TBF. These results also support the hypothesis that there is increased TBF in HER2-positive tumors.

Successive Cambia: A Developmental Oddity or an Adaptive Structure?

Background Secondary growth by successive cambia is a rare phenomenon in woody plant species. Only few plant species, within different phylogenetic clades, have secondary growth by more than one vascular cambium. Often, these successive cambia are organised concentrically. In the mangrove genus Avicennia however, the successive cambia seem to have a more complex organisation. This study aimed (i) at understanding the development of successive cambia by giving a three-dimensional description of the hydraulic architecture of Avicennia and (ii) at unveiling the possible adaptive nature of growth by successive cambia through a study of the ecological distribution of plant species with concentric internal phloem. Results Avicennia had a complex network of non-cylindrical wood patches, the complexity of which increased with more stressful ecological conditions. As internal phloem has been suggested to play a role in water storage and embolism repair, the spatial organisation of Avicennia wood could provide advantages in the ecologically stressful conditions species of this mangrove genus are growing in. Furthermore, we could observe that 84.9% of the woody shrub and tree species with concentric internal phloem occurred in either dry or saline environments strengthening the hypothesis that successive cambia provide the necessary advantages for survival in harsh environmental conditions. Conclusions Successive cambia are an ecologically important characteristic, which seems strongly related with water-limited environments.

Validity of perfusion parameters obtained using the modified Tofts model: A simulation study

The two‐compartment Tofts model (2CTM) has had widespread use in research and clinical practice. It assumes there is no broadening associated with the bolus transit through the capillary bed of the tissue under study. This assumption is often violated, with consequences that are hard to predict intuitively. The two‐compartment exchange model is a generalization of 2CTM obtained by dropping the zero‐broadening hypothesis, making it suitable for estimating the impact of violating this assumption. Using data simulated on the basis of the two‐compartment exchange model, the correspondence between the hemodynamic parameters serving as input for the two‐compartment exchange model and the parameters resulting from fitting the data with the 2CTM was investigated. The influence of tissue type and experimental setup was studied. Generally, a large tissue and setup dependent bias of the 2CTM fitting results with respect to the two‐compartment exchange model input was observed. Extreme caution is needed when interpreting 2CTM data. Magn Reson Med, 2011.

Postmastectomy lymphoedema: different patterns of fluid distribution visualised by ultrasound imaging compared with magnetic resonance imaging

OBJECTIVES Postmastectomy lymphoedema remains a disabling complication caused by treatment for breast cancer. The increased thickness of the dermal layer and the increased volume of the subcutis represent the most important contributions to the total swelling of the arm. Ultrasound imaging of the subcutaneous layer results in different patterns of reflected ultrasound waves depending on the morphological alternations that occurred due to impaired lymphatic drainage. The aim of this study was to compare these echographic images with those obtained using magnetic resonance imaging to explain the nature of the morphological changes. DESIGN Observational study. SETTING Patients were recruited from the Breast Clinic at the University Hospital Brussels. PARTICIPANTS Seven women (mean age 60 years) with unilateral breast cancer who subsequently developed lymphoedema. MAIN OUTCOME MEASURES The water displacement technique was applied to determine arm volumes, and echographic and magnetic resonance images were used to evaluate changes in tissue structures. RESULTS Volumetric measurements of the arm (mean affected arm 3241 ml vs unaffected arm 2538 ml) showed a significant increase in total arm volume of 703 ml (95% confidence interval 324 to 1084 ml). Using echography, the thickness of the dermal and subcutaneous layers showed an average increase of 0.2 to 0.8mm and 3.9 to 7.2mm, respectively. The differences between the affected arm and the unaffected arm for all upper and lower arm measurements (i.e. volumetry, dermal and subcutaneous thickness) were significant, but no significant differences were registered for hand measurements. On echography, the dermis showed uniform changes, with a homogenous hypo-echogenic appearance compared with the contralateral side due to water influx. Different patterns of structural changes could be visualised within the subcutis: (1) uniformly hypo-echogenic due to the diffuse spread of water through the subcutis; (2) hyperechogenic areas surrounded by hypo-echogenic streaks visualised on magnetic resonance imaging as adipose tissue surrounded by fluid embedded in fibrous tissue; and (3) homogenously hyperechogenic due to the overgrowth of adipose tissue with a minimal amount of water. CONCLUSIONS Echographic images can help to determine the likelihood that complex physical therapy will reduce lymphoedema, and evaluate treatment results by measuring tissue thickness and evaluating tissue consistency.