Heat Source Modeling and Residual Stress Analysis for Metal Directed Energy Deposition Additive Manufacturing

The advancement in additive manufacturing encourages the development of simplified tools for deep and swift research of the technology. Several approaches were developed to reduce the complexity of multi-track modeling for additive manufacturing. In the present work, a simple heat source model called concentrated heat source was evaluated for single- and multi-track deposition for directed energy deposition. The concentrated heat source model was compared with the widely accepted Goldak heat source model. The concentrated heat source does not require melt pool dimension measurement for thermal model simulation. Thus, it reduces the considerable time for preprocessing. The shape of the melt pool and temperature contour around the heat source was analyzed for single-track deposition. A good agreement was noticed for the concentrated heat source model melt pool, with an experimentally determined melt pool, using an optical microscope. Two heat source models were applied to multi-track 3D solid structure thermo-mechanical simulation. The results of the two models, for thermal history and residual stress, were compared with experimentally determined data. A good agreement was found for both models. The concentrated heat source model reported less than the half the computational time required for the Goldak model. The validated model, for 3D solid structure thermo-mechanical simulation, was used to analyze thermal stress evolution during the deposition process. The material deposition on the base plate at room temperature results in lower peak temperatures in the layers near the base plate. Consequently, the higher thermal stress in the layers near the base plate was found, compared to the upper layers during the deposition process.     

Paediatric obstructive sleep apnoea: is a polysomnogram always necessary?

Obstructive sleep apnoea (OSA) is a common entity in children, most present with sleep disturbances such as snoring, choking during sleep, enuresis, restless sleep, or apnoeic spells. Other symptoms include poor school performance, hyperactivity, failure to thrive, heart failure and cor pulmonale. Most authors would concur that the polysomnogram (PSG) is the gold standard for the diagnosis of OSA, and that adenotonsillectomy is the surgical procedure of choice, with high curative rates and relatively low morbidity. Close post-operative monitoring of all children with OSA cannot be over-emphasized. The focus has been, traditionally, to anticipate post-operative airway and respiratory complications in this group of children. We present 73 children with clinical OSA and 36 children with proven OSA on PSG, with only one child having respiratory complications (mixed apnoea), and all with uneventful recovery. In view of our low complication rates, low post-operative morbidity, cost and facility factor, the need for a mandatory overnight PSG pre-operatively is questioned, and clinical criteria for performing a PSG preoperatively are suggested.     

Plumbagin induces reactive oxygen species, which mediate apoptosis in human cervical cancer cells

There is an emerging evidence that plumbagin (5-hydroxy-2-methyl-1, 4-naphthoquinone) may have potential as a chemotherapeutic agent. However, the growth inhibitory mechanisms of plumbagin have remained unexplored. The aim of the study was to determine whether plumbagin-induced cell death in human cervical cancer cell line, ME-180, exhibited biochemical characteristics of apoptosis and to check whether N-acetyl-l-cysteine (NAC), which is a free radical scavenger, can reverse the cytotoxic effects of plumbagin. It can be concluded from the results that plumbagin inhibits the growth of ME-180 cells in a concentration and time-dependent manner. The cytotoxic effect of plumbagin induced cell death is through the generation of reactive oxygen species (ROS) and subsequent induction of apoptosis as demonstrated by the present data. Treatment of cells with plumbagin caused loss of mitochondrial membrane potential (DeltaPsi(m)), and morphological changes characteristic of apoptosis, such as the translocation of phosphatidyl serine, nuclear condensation, and DNA fragmentation. Moreover, plumbagin-induced apoptosis involved release of mitochondrial cytochrome c and apoptosis inducing factor (AIF), thus activation of caspase-dependent and -independent pathways, as shown by the plumbagin-mediated activation of caspase-3 and -9. Our results also show that pretreatment of ME-180 cells with NAC blocks plumbagin-induced loss of DeltaPsi(m) and subsequent release of cytochrome c, AIF, and caspase-9 and -3 activation, thus inhibiting the apoptotic ability of plumbagin.     

Activities of daily living in patients with dementia: clinical relevance, methods of assessment and effects of treatment

Disability, characterised by the loss of ability to perform activities of daily living (ADL), is a defining feature of dementia that results in growing caregiver burden and the eventual need for alternative care or nursing home placement. Functional decline in patients with dementia can also result from causes other than dementia, such as comorbid medical and psychiatric illnesses and sensory impairment. ADL consists of instrumental ADL (IADL) [complex higher order skills, such as managing finances] and basic ADL (BADL) [self-maintenance skills, such as bathing]. Assessment of IADL and BADL is recommended to establish a diagnosis of dementia. Functional assessment also helps the healthcare provider to offer appropriate counselling regarding safety concerns and need for custodial care. Functional capacity measures have been used increasingly in pharmacological trials of patients with Alzheimer's disease (AD) and related dementias, although at the present time these measures are generally not primary outcome measures. Functional impairment is not a uniform construct; rather, it is multifaceted and can be measured with various clinical instruments. Many scales have been validated for use in patients with AD for characterising functional impairment and evaluating the efficacy of treatment. Research to date indicates that cholinesterase inhibitors have the potential for modest but meaningful beneficial effects on ADL in patients with mild-to-moderate AD. Memantine also has promising beneficial effects on functional abilities in persons with moderate-to-severe AD. Assessment of ADL as a primary efficacy measure using a validated scale that is non-gender biased and cross-nationally relevant is recommended in new treatment trials of patients with AD and related dementias.     

A technique for semiautomatic segmentation of echogenic structures in 3D ultrasound,applied to infant hip dysplasia

Purpose

Automatic segmentation of anatomical structures and lesions from medical ultrasound images is a formidable challenge in medical imaging due to image noise, blur and artifacts. In this paper we present a segmentation technique with features highly suited to use in noisy 3D ultrasound volumes and demonstrate its use in modeling bone, specifically the acetabulum in infant hips. Quantification of the acetabular shape is crucial in diagnosing developmental dysplasia of the hip (DDH), a common condition associated with hip dislocation and premature osteoarthritis if not treated. The well-established Graf technique for DDH diagnosis has been criticized for high inter-observer and inter-scan variability. In our earlier work we have introduced a more reliable instability metric based on 3D ultrasound data. Visualizing and interpreting the acetabular shape from noisy 3D ultrasound volumes has been one of the major roadblocks in using 3D ultrasound as diagnostic tool for DDH. For this study we developed a semiautomated segmentation technique to rapidly generate 3D acetabular surface models and classified the acetabulum based on acetabular contact angle (ACA) derived from the models. We tested the feasibility and reliability of the technique compared with manual segmentation.

Methods

The proposed segmentation algorithm is based on graph search. We formulate segmentation of the acetabulum as an optimal path finding problem on an undirected weighted graph. Slice contours are defined as the optimal path passing through a set of user-defined seed points in the graph, and it can be found using dynamic programming techniques (in this case Dijkstra’s algorithm). Slice contours are then interpolated over the 3D volume to generate the surface model. A three-dimensional ACA was calculated using normal vectors of the surface model.

Results

The algorithm was tested over an extensive dataset of 51 infant ultrasound hip volumes obtained from 42 subjects with normal to dysplastic hips. The contours generated by the segmentation algorithm closely matched with those obtained from manual segmentation. The average RMS errors between the semiautomated and manual segmentation for the 51 volumes were 0.28 mm/1.1 voxel (with 2 node points) and 0.24 mm/0.9 voxel (with 3 node points). The semiautomatic algorithm gave visually acceptable results on images with moderate levels of noise and was able to trace the boundary of the acetabulum even in the presence of significant shadowing. Semiautomatic contouring was also faster than manual segmentation at 37 versus 56 s per scan. It also improved the repeatability of the ACA calculation with inter-observer and intra-observer variability of \(1.4 \pm 0.9\) degree and \(1.4 \pm 1.0\) degree.

Conclusion

The semiautomatic segmentation technique proposed in this work offers a fast and reliable method to delineate the contours of the acetabulum from 3D ultrasound volumes of the hip. Since the technique does not rely upon contour evolution, it is less susceptible than other methods to the frequent missing or incomplete boundaries and noise artifacts common in ultrasound images. ACA derived from the segmented 3D surface was able to accurately classify the acetabulum under the categories normal, borderline and dysplastic. The semiautomatic technique makes it easier to segment the volume and reduces the inter-observer and intra-observer variation in ACA calculation compared with manual segmentation. The method can be applied to any structure with an echogenic boundary on ultrasound (such as a ventricle, blood vessel, organ or tumor), or even to structures with a bright border on computed tomography or magnetic resonance imaging.

     

Diagnosis of Wilms' tumor using near-infrared Raman spectroscopy

Purpose

Raman spectroscopy has distinguished malignant from normal tissues in several types of cancer. This is the first report of applying Raman spectroscopy to the diagnosis of Wilms' tumor.

Methods

Specimens of normal kidney, Wilms' tumor, xanthogranuloma, nephrogenic rests, and rhabdoid tumor were collected fresh from the operating room. Specimens of Wilms' tumor, normal kidney, and congenital mesoblastic nephroma were retrieved from the cryobank and thawed to room temperature. At least 12 Raman spectra were collected from each tissue sample. Histologic slides of each specimen were reviewed by pediatric pathologists. A computer algorithm based on discriminant function analysis (DFA) classified the Raman spectra of Wilms' tumor and the normal sample.

Results

Four hundred sixty-seven spectra were collected from 41 specimens. Using DFA, Raman spectroscopy differentiated Wilms' tumor from normal with 100% sensitivity and specificity and treated from untreated Wilms' tumor with 100% sensitivity and specificity. Using a DFA model built from cryopreserved specimens but applied to fresh Wilms' and normal samples, the sensitivity and specificity were 93.3% and 90.9%, respectively.

Conclusion

Raman spectroscopy is an accurate technique for differentiating Wilms' tumor from normal kidney and treated from untreated Wilms' tumor. It has potential to diagnose in minutes what currently takes several hours to days.