Numerical Study of the Features of Ti-Nb Alloy Crystallization during Selective Laser Sintering

The demand for implants with individual shape requires the development of new methods and approaches to their production. The obvious advantages of additive technologies and selective laser sintering are the capabilities to form both the external shape of the product and its internal structure. Recently appeared and attractive from the perspective of biomechanical compatibility are beta alloys of titanium-niobium that have similar mechanical properties to those of cortical bone. This paper studies the processes occurring at different stages of laser sintering using computer simulation on atomic scale. The effect of cooling rate on the resulting crystal structure of Ti-Nb alloy was analysed. Also, the dependence of tensile strength of sintered particles on heating time and cooling rate was studied. It was shown that the main parameter, which determines the adhesive properties of sintered particles, is the contact area obtained during sintering process. The simulation results can both help defining the technological parameters of the process to provide the desired mechanical properties of the resulting products and serve as a necessary basis for calculations on large scale levels in order to study the behaviour of actually used implants

NCOG-26. IMPACT OF GENDER ON TUMOR TREATING FIELDS COMPLIANCE IN PATIENTS WITH GLIOBLASTOMA

Abstract BACKGROUND Tumor treating fields (TTFields) has emerged as a novel antimitotic modality to treat glioblastoma (GBM). Recently, a positive association was reported between TTFields dose at the tumor bed and survival outcomes in GBM patients. Dose density depends upon power density and compliance rate (cumulative amount of time TTFields therapy is delivered to the patient). Increased compliance with TTFields has been proposed as an independent prognostic factor for improved clinical benefits. There is evidence that females tend to respond better than males to standard therapy. However, the impact of gender and age on TTFields compliance is not fully understood in GBM patients. OBJECTIVE To investigate potential interactions amongst age, gender and TTFields compliance in GBM patients. METHODS A cohort of 16 patients (males =9; females=7; mean-age=60.8±7.6years) with newly diagnosed and recurrent GBM receiving TTFields were analyzed retrospectively. Device usage time was collected from internal log files in each case. The mean duration of TTFields therapy in patients was 4 months. Chi-square and independent sample T-tests were performed to evaluate differences in compliance rates based on patient age and gender and to examine gender-age relationships. Additionally, Pearson correlation analyses were performed to determine associations between gender and compliance rates. The probability (p) value of 0.05 was considered significant. RESULTS A trend (p=0.067) towards greater TTFields compliance was observed in females (80.1±0.11%) versus males (63.0±0.22%). Additionally, there was a strong positive correlation (R=0.73; p=0.058) between age and compliance rates for female patients. There were 6 patients ≥ 65 years and 10 patients &amp;lt; 65 years. However, we did not find significant differences in compliance rate and gender variables between patients ≥ 65 years and &amp;lt; 65 years of age. CONCLUSIONS Our results demonstrate gender influences TTFields compliance amongst GBM patients. However, future studies with larger cohorts are warranted to validate these findings. </jats:sec

Abstract CT068: Tumor treating fields in patients with glioblastomas: Evaluation of treatment response using advanced mr imaging techniques

Abstract Introduction: Tumor treating fields (TTFields) is a new modality for the treatment of patients with newly diagnosed and recurrent glioblastomas (GBMs). TTFields system delivers low intensity, intermediate frequency alternating electric field directly to brain causing neoplastic cell death with minimal effect on the normal dividing cells. The purpose of present investigator sponsored trial was to evaluate the effects of TTFields in GBM patients using diffusion tensor imaging (DTI), perfusion weighted imaging (PWI) and 3D-echoplanar spectroscopic imaging (EPSI). Methods: Two patients with newly diagnosed GBM and six patients with recurrent GBMs previously treated with standard of care maximal safe resection and chemo-radiation therapy received TTFields. Patients underwent baseline (prior to TTFields) and two follow-up (one and two months post initiation of TTFields) MR imaging on a 3T MR system. DTI data were acquired using 30 directions with a single-shot spin-echo EPI sequence. After motion and eddy current correction of raw DTI data, parametric maps [mean diffusivity (MD), fractional anisotropy (FA)] were generated using in-house developed algorithm. For PWI, T2* weighted gradient-echo EPI sequence was acquired with a temporal resolution of 2.1s. Leakage corrected cerebral blood volume (CBV) maps were constructed. 3D-EPSI was acquired using a spin-echo based sequence. EPSI data were processed using metabolic imaging and data analysis system (MIDAS) package. DTI (MD, FA), EPSI [choline (Cho)/creatine(Cr)], CBV maps and FLAIR images were co-registered to post-contrast T1-weighted images and a semi-automated algorithm was used to segment the contrast-enhancing region of neoplasms. Median values of MD, FA, relative CBV (rCBV) and Cho/Cr were computed at each time point. The 90th percentile rCBV (rCBVmax) values were also measured. Percent changes of each parameter between baseline and follow-up time points were evaluated. Results and Discussion: In general, there was an increasing trend in MD (~3%) and steadily decline trend in FA (~8%) at the 2 month follow-up relative to baseline. Additionally, from baseline to post- TTFields, reductions in Cho/Cr and rCBVmax were also observed from most of the patients. Clinically, all these patients were stable at 2 month follow-up. The inhibited cellular growth may account for large increase in MD and decrease in FA and Cho/Cr as observed in the current study. Reducing trends in rCBVmax at the follow-up may indicate anti- angiogenetic effects of TTFields and tissue perfusion within the tumor bed after the therapy. Conclusion: Our preliminary data suggest that advanced MR imaging may be useful in evaluating treatment response to TTFields in patients with GBMs. Inclusion of more patients is warranted to validate our findings. Acknowledgement: Support of NovoTTF-100A system (Novocure Ltd., Haifa, Israel) is gratefully acknowledged. Citation Format: SANJEEV CHAWLA, Sumei Wang, Gaurav Verma, Aaron Skolnik, Lauren Karpf, Lisa Desiderio, Steven Brem, Katherine Peters, Harish Poptani, Suyash Mohan. Tumor treating fields in patients with glioblastomas: Evaluation of treatment response using advanced mr imaging techniques [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr CT068. doi:10.1158/1538-7445.AM2017-CT068</jats:p

Sickle cell disease and transcranial Doppler imaging: inter-hemispheric differences in blood flow Doppler parameters.

BACKGROUND AND PURPOSE: to establish reference values of interhemispheric differences and ratios of blood flow Doppler parameters in the terminal internal carotid artery, middle cerebral artery, and anterior cerebral artery in children with sickle cell anemia. METHODS: fifty-seven out of 74 recruited children (mean age, 7.8 ± 3.4 years; range limits, 3-14 years), who were free of neurological deficits and intracranial narrowing detectable by MRA and had flow velocities \u3c 170 cm/s by conventional transcranial Doppler ultrasound, underwent transcranial color-coded duplex ultrasonography. Reference limits of flow parameters corrected and uncorrected for the angle of insonation were estimated using tolerance intervals, with P=0.90 for all possible data values from 95% of a population. RESULTS: reference limits for left-to-right differences in cm/s in the mean angle-corrected and uncorrected flow velocities were -56 to 53 and -72 to 75 for middle cerebral artery, -49 to 57 and -81 to 91 for anterior cerebral artery, and -55 to 64 and -73 to 78 for terminal internal carotid artery, respectively. Respective reference limits for left-to-right velocity ratios were 0.31 to 1.84 and 0.38 to 1.75 for middle cerebral artery, 0.48 to 2.99 and 0.46 to 2.89 for anterior cerebral artery, and 0.61 to 2.56 and 0.56 to 2.23 for terminal internal carotid artery. CONCLUSIONS: the study provides reference limits of interhemispheric differences and ratios of blood flow Doppler parameters that may be helpful in identification of intracranial arterial narrowing in children with sickle cell disease undergoing ultrasound screening for stroke prevention

Enrollment in a brain magnetic resonance study: results from the Women's Health Initiative Memory Study Magnetic Resonance Imaging Study (WHIMS-MRI)

RATIONALE AND OBJECTIVES: The rates of enrollment of volunteers for brain magnetic resonance imaging (MRI) studies vary by demographic and clinical characteristics. We use data from a large MRI study to identify factors associated with differential enrollment and to examine potential biases this may produce in study results. MATERIALS AND METHODS: Results from recruitment of 1,431 women into the MRI substudy of the Women's Health Initiative Memory Study (WHIMS-MRI) are described. A sensitivity analysis was conducted to estimate the degree of bias associated with missing data on estimates of risk factor relationships. RESULTS: Of 2,345 women contacted from an established cohort of women older than 70 years of age, 72% consented to undergo screening for WHIMS-MRI. Scanning was ultimately completed on 61%. Completion rates varied according to a range of sociodemographic, lifestyle, and clinical characteristics that may be related to study outcomes. Plausible levels of selective enrollment in magnetic resonance imaging studies may produce moderate biases (< +/-20%) in characterizations of risk factor relationships. Adverse events, such as claustrophobia, occurred during 1.7% of the attempted scans and, in 0.8% of instances, led to lost data. CONCLUSIONS: Enrollment of older women into brain imaging studies is feasible, although selection biases may limit how well study cohorts reflect more general populations