Constructing Hard Examples for Graph Isomorphism.

We describe a method for generating graphs that provide difficult examples for practical Graph Isomorphism testers. We first give the theoretical construction, showing that we can have a family of graphs without any non-trivial automorphisms which also have high Weisfeiler-Leman dimension. The construction is based on properties of random 3XOR-formulas. We describe how to convert such a formula into a graph which has the desired properties with high probability. We validate the method by experimental implementations. We construct random formulas and validate them with a SAT solver to filter through suitable ones, and then convert them into graphs. Experimental results demonstrate that the resulting graphs do provide hard examples that match the hardest known benchmarks for graph isomorphism

Eradication of advanced pelvic hydatid bone disease after limb salvage surgery - 5-year follow-up: a case report

Abstract INTRODUCTION: Echinococcosis is produced by the larval stage of Echinococcus granulosus; it is a parasitic disease which is seen rarely in humans and has adverse outcomes. We report a case of advanced pelvic hydatid bone disease with successful limb salvage surgery. Our patient had a 5-year follow-up without recurrence which is a rarity as per the literature. Early diagnosis and prompt medical therapy are necessary for effective management whereas delayed diagnosis is always fraught with the risk of recurrence and sepsis. CASE PRESENTATION: In 2009, a 30-year-old woman, native of Karachi (Sindhi ethnicity), presented at our clinic with history of a pathological fracture 11 years earlier. Her fracture was initially misdiagnosed and fixed. Subsequently she had persistent disease that progressed with time. Following this she underwent multiple surgeries and the diagnosis of hydatid disease was made but despite multiple debridements and medical therapy she was not cured and finally she was offered a hemipelvectomy (limb sacrifice). On presentation to our hospital she was counseled regarding options of hemipelvectomy versus a limb salvage form of modified internal hemipelvectomy and wide margin resection. She opted for limb salvage. She underwent internal hemipelvectomy with wide margin resection of soft tissue and proximal femur along with postoperative albendazole therapy. She was able to walk again after a very long period. Currently she is 5-years postreconstructive surgery. She is infection free and ambulant without support. CONCLUSIONS: Hydatid bone disease is a rare entity in our part of the world but a careful history and thorough look at the initial images of our patient would have led to the suspicion of pathologic fracture and subsequent early diagnosis of this difficult problem. A second important learning point in this case was the lack of early referral to a center where this difficult problem could have been handled effectively. This could have minimized the physical, mental and financial stress to the patient and her family

Multi Layered Multi Task Marker Based Interaction in Information Rich Virtual Environments

Simple and cheap interaction has a key role in the operation and exploration of any Virtual Environment (VE). In this paper, we propose an interaction technique that provides two different ways of interaction (information and control) on complex objects in a simple and computationally cheap way. The interaction is based on the use of multiple embedded markers in a specialized manner. The proposed marker like an interaction peripheral works just like a touch paid which can perform any type of interaction in a 3D VE. The proposed marker is not only used for interaction with Augmented Reality (AR), but also with Mixed Reality. A biological virtual learning application is developed which is used for evaluation and experimentation. We conducted our experiments in two phases. First, we compared a simple VE with the proposed layered VE. Second, a comparative study is conducted between the proposed marker, a simple layered marker, and multiple single markers. We found the proposed marker with improved learning, easiness in interaction, and comparatively less task execution time. The results gave improved learning for layered VE as compared to simple VE

Dr. KID: Direct Remeshing and K-set Isometric Decomposition for Scalable Physicalization of Organic Shapes

Dr. KID is an algorithm that uses isometric decomposition for the physicalization of potato-shaped organic models in a puzzle fashion. The algorithm begins with creating a simple, regular triangular surface mesh of organic shapes, followed by iterative k-means clustering and remeshing. For clustering, we need similarity between triangles (segments) which is defined as a distance function. The distance function maps each triangle's shape to a single point in the virtual 3D space. Thus, the distance between the triangles indicates their degree of dissimilarity. K-means clustering uses this distance and sorts of segments into k classes. After this, remeshing is applied to minimize the distance between triangles within the same cluster by making their shapes identical. Clustering and remeshing are repeated until the distance between triangles in the same cluster reaches an acceptable threshold. We adopt a curvature-aware strategy to determine the surface thickness and finalize puzzle pieces for 3D printing. Identical hinges and holes are created for assembling the puzzle components. For smoother outcomes, we use triangle subdivision along with curvature-aware clustering, generating curved triangular patches for 3D printing. Our algorithm was evaluated using various models, and the 3D-printed results were analyzed. Findings indicate that our algorithm performs reliably on target organic shapes with minimal loss of input geometry

Utility of limited protocol magnetic resonance imaging lumbar spine for nerve root compression in a developing country, is it accurate and cost effective?

STUDY Design: Cross sectional study.PURPOSE: To determine the accuracy of the screening magnetic resonance study of the lumbar spine in the diagnosis of nerve root compression in cases of low back pain as compared to the routine magnetic resonance imaging (MRI) study of the lumbar spine.OVERVIEW OF LITERATURE: No local study has been conducted for this purpose. In an international study, the reported sensitivity and specificity of screening MRI lumbar spine protocol in the detection of nerve root compression are 54% and 100% respectively.Methods: Patients of both genders older than 20 years of age with low back pain of any duration or any severity who were referred to the radiology department of Aga Khan University Hospital for MRI of their lumbar spine were evaluated. Two sets of MRI imaging were recruited for each patient: one labeled as \u27screening\u27 and the other labeled as \u27routine\u27. The findings of screening MRI were compared with the findings of the routine MRI study.Results: A total of 109 patients fulfilling the inclusion criteria were included in this study. The diagnostic accuracy, specificity and sensitivity of the screening protocol in our study was 100%, 100% and 100%, respectively in comparison with the routine MRI lumbar spine study for the detection of nerve root compression.CONCLUSIONS: Our data proved that the MRI screening study is a highly accurate tool, and its findings are comparable to the routine study for the detection of nerve root compression especially in cases of lumbar spondylosis

Torsion of wandering spleen with Infarction.

Wandering spleen is a rare entity that results from the absence or maldevelopment of the ligaments that support the spleen in its normal location. As a result, the spleen is hypermobile and may be predisposed to hilar torsion and subsequent infarction, making it a potentially fatal abdominal emergency. We present a case of a 36-year-old Afghan female who presented with an acute abdomen, and was radiologically and surgically confirmed to have a wandering spleen with torsion and complete infarction. Knowledge of this condition and its radiological findings can play a crucial role in making a correct and timely diagnosis

Role of early contrast enhanced CT scan in severity prediction of acute pancreatitis

Abstract Severe pancreatitis occurs in approximately 15-25% of patients with acute pancreatitis. The objective of our study was to compare the CTSeverity Index (CTSI) with a clinical score (BISAP score) to predict severity of acute pancreatitis. Forty-eight consecutive patients with acutepancreatitis who underwent contrast enhanced CT scan within 72 hours of presentation were included. Results of our study showed that both CTSI and BISAP score were reliable predictors of mortality (p value = 0.019 and \u3c0.001 respectively) and need for mechanical ventilation (p value = .002 and .006 respectively). Positive predictive value of CTSI to predict recovery without intervention was 91.4% as compared to 78% for that of BISAP score. Receiver Operating Characteristics (ROC) Curves showed CT scan was superior to BISAP Score in predicting need of percutaneous or surgical intervention. Early CT scan may be utilized for prediction of clinical course of patients with acute pancreatitis

Interobserver reliability of the renal nephrometry scoring system: Experience from a developing nation

Introduction: The RENAL (radius, exophytic/endophytic properties, nearness of tumor to the collecting system or sinus in millimeters, anterior/posterior, location relative to polar lines) nephrometry score (RENAL-NS) has been described as a structured and quantifiable method to describe a renal tumor’s relevant anatomic features as they relate to the complexity of the lesion. We aim to evaluate a tumor’s RENAL-NS and to assess the reproducibility of the score among different observers.Methods: This retrospective study included 49 patients diagnosed with renal cell carcinoma (RCC) who had complete computed tomography (CT) data, RENAL-NS, and histopathology results. All patients underwent renal surgery/intervention at our center between January 2008 and December 2018. The radius of the lesion, exophytic/endophytic properties, nearness to the collecting system, anterior or posterior description, and location relative to the polar lines was used to calculate the score. Tumor complexity was graded as low, intermediate, or high. Two body imaging radiologists evaluated the data independently.Results: Interobserver agreement for each of the RENAL-NS parameters, respectively, and overall complexity was calculated. The total agreement was 82%, 51%, 84%, 69%, 73%, and 90%, corresponding to Kappa values of 0.72, 0.33, 0.44, 0.49, 0.58, and 0.83, respectively. The radius, nearness to the collecting system, and total complexity showed the best agreement. Exophytic properties of the lesion showed the least agreement. For cases that were discordant in terms of the final score, no major implications in surgical planning were observed.Conclusion: The results of this study show that the RENAL-NS is a useful tool to assess the anatomical features of renal tumors and it is easily reproducible, even for less experienced radiologists in a developing nation

Cholecystocolonic Fistula

Cholecystocolonic fistula (CCF) is a rare complication of gallstone disease with a variable clinical presentation. It is difficult to diagnose CCF pre-operatively despite modern diagnostic and imaging modalities as they are often asymptomatic or incidentally discovered, often peri-operatively. However, management of this uncommon yet important finding is not very well described in the literature. The most common fistula is the cholecystoduodenal fistula, followed by the cholecystocolonic fistula; the cholecystogastric fistula is reportedly the least commonly reported. We report our experience with three cases of cholecystocolonic fistula discovered on imaging which were subsequently confirmed through surgery