GIST: an interactive, GPU-based level set segmentation tool for 3D medical images

While level sets have demonstrated a great potential for 3D medical image segmentation, their usefulness has been limited by two problems. First, 3D level sets are relatively slow to compute. Second, their formulation usually entails several free parameters which can be very difficult to correctly tune for specific applications. The second problem is compounded by the first. This paper describes a new tool for 3D segmentation that addresses these problems by computing level-set surface models at interactive rates. This tool employs two important, novel technologies. First is the mapping of a 3D level-set solver onto a commodity graphics card (GPU). This mapping relies on a novel mechanism for GPU memory management. The interactive rates level-set PDE solver give the user immediate feedback on the parameter settings, and thus users can tune free parameters and control the shape of the model in real time. The second technology is the use of intensity-based speed functions, which allow a user to quickly and intuitively specify the behavior of the deformable model. We have found that the combination of these interactive tools enables users to produce good, reliable segmentations. To support this observation, this paper presents qualitative results from several different datasets as well as a quantitative evaluation from a study of brain tumor segmentations.     

Investigating the assumptions of the self‐controlled case series method

We describe some simple techniques for investigating 2 key assumptions of the self‐controlled case series (SCCS) method, namely, that events do not influence subsequent exposures and that events do not influence the length of observation periods. For each assumption, we propose some simple tests based on the standard SCCS model, along with associated graphical displays. The methods also enable the user to investigate the robustness of the results obtained using the standard SCCS model to failure of assumptions. The proposed methods are investigated by simulations and applied to data on measles, mumps and rubella vaccine, and antipsychotics.     

In vitro effect of antibodies to dna on the template activity of DNA

Blood samples containing antibodies to DNA were obtained from patients with systemic lupus erythematosus (SLE) and rabbits immunized with denatured DNA complexed to methylated bovine serum albumin. The immunoglobulin fractions from these sources did not decrease the over-all template activity of singlestranded DNA with DNA polymerase or DNA-dependent RNA polymerase. In competition studies, both DNA polymerase and DNA-dependent RNA polymerase inhibited the binding of DNA antibodies to single-stranded DNA, as evidenced by inhibition of micro-complement fixation. These findings suggest that antibodies to DNA fail to decrease denatured DNA template activity because the enzymes which use a single-stranded DNA template can displace or block the antibodies from the denatured DNA as a result of greater binding affinity to the denatured DNA. The anti-DNA antibodies associated with SLE, therefore, may not be involved in the pathogenesis of the intracellular abnormalities associated with the disease.     

Predictors of the Need for Critical Care After Total Joint Arthroplasty: An Update of Our Institutional Risk Stratification Model

Based on our previously published risk stratification model, 295 (19%) of a consecutive series of 1594 TJA patients were triaged to the ICU. However, only 67 patients (22%) required intensive care interventions. We identified 5 independent multivariate predictors (P < 0.001) including COPD, CAD, CHF (1 point each), EBL > 1000 mL, and intraoperative vasopressors (2 points each) to form the Penn Arthroplasty Risk Score (PARS). Patients with a score of 0 through 7 had a probability of requiring critical care of 7.0%, 13.2%, 23.5%, 38.1%, 55.4%, 71.4%, 83.4%, and 91.1% respectively. Based on these results, our previous risk stratification protocol is overly sensitive and non-specific. Any risk stratification algorithm for ICU admission should include intraoperative risk factors in order to be fully predictive.     

Use of the exercise maximal ST segment/heart rate slope in assessing the results of coronary angioplasty.

A new exercise test was used to assess the effects of coronary angioplasty in 22 patients. Twenty five angioplasty procedures were performed and the exercise maximal ST segment/heart rate slope was measured before and after operation on 23 occasions; in two patients treated for unstable angina the slope was measured only after the two procedures. Successful angioplasty (23 of the 25 procedures) resulted in a significant reduction of the maximal ST/HR slope, usually falling by the equivalent of single vessel disease according to previously published criteria. When angioplasty produced little angiographic change (two of the 25 procedures) the maximal ST/HR slope was not significantly altered. A second, and successful, angioplasty for these two patients led to a significant reduction of the maximal ST/HR slope. Twelve patients were restudied by coronary angiography and exercise testing approximately six months after angioplasty. Of these, six had experienced recurrent chest pain, and the exercise test successfully identified the three who had restenoses and the three who did not. Thus the maximal ST/HR slope was useful as a non-invasive and accurate method for following the progress of individual patients after coronary angioplasty.