Browsing by Author "Alqahtani, Nasser"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Eletromagnetic Detection of Mild Brain Injury: A Novel Imaging Approach to Post Concussive Syndrome
    (Scientific Research Publishing, 2021-11) Rizkalla, James; Botros, David; Alqahtani, Nasser; Patnala, Mounica; Salama, Paul; Perez, Felipe Pablo; Rizkalla, Maher; Medicine, School of Medicine
    Introduction: Mild traumatic brain injury (mTBI) is a common injury, with nearly 3 - 4 million cases annually in the United States alone. Neuroimaging in patients with mTBI provides little benefit, and is usually not indicated as the diagnosis is primarily clinical. It is theorized that microvascular trauma to the brain may be present in mTBI, that may not be captured by routine MRI and CT scans. Electromagnetic (EM) waves may provide a more sensitive medical imaging modality to provide objective data in the diagnosis of mTBI. Methods: COMSOL simulation software was utilized to mimic the anatomy of the human skull including skin, cranium, cerebrospinal fluid (CSF), gray-matter tissue of the brain, and microvasculature within the neural tissue. The effects of penetrating EM waves were simulated using the finite element analysis software and results were generated to identify feasibility and efficacy. Frequency ranges from 7 GHz to 15 GHz were considered, with 0.6 and 1 W power applied. Results: Variations between the differing frequency levels generated different energy levels within the neural tissue-particularly when comparing normal microvasculature versus hemorrhage from microvasculature. This difference within the neural tissue was subsequently identified, via simulation, serving as a potential imaging modality for future work. Conclusion: The use of electromagnetic imaging of the brain after concussive events may play a role in future mTBI diagnosis. Utilizing the proper depth frequency and wavelength, neural tissue and microvascular trauma may be identified utilizing finite element analysis.
  • Thumbnail Image
    Item
    Optical properties Of CAD-CAM lithium disilicate glass-ceramic in different firing temperatures and thicknesses
    (2016) Alqahtani, Nasser; Chu, Tien-Min Gabriel; Phasuk, Kamolphob; Morton, Dean; Levon, John A.
    Background: With the emerging of digital dentistry, IPS e.max® CAD lithium disilicate (LD) glass-ceramic material has become one of the most popular esthetic restorative materials in digital assisted dental esthetic restoration. The mechanical and optical properties of this material have been investigated in several studies. However, there is a lack of information and consensus regarding the optical properties of IPS e.max® LD glass-ceramic materials. Objectives: 1) To investigate the optical properties as translucency parameters (TP), Contrast ratio (CR), light transmissions (Lt) and color changes (CC) between high-translucent (HT) and low-translucent (LT) IPS e.max® CAD LD glass-ceramic materials with different crystalline phases and thickness in different firing stages. 2) To investigate the optical properties as TP, CR, Lt and CC of each translucent (HT and LT) IPS e.max® CAD LD glass-ceramic materials with different crystalline phases and thickness in different firing stages. 3) To determine the mathematical relationships of thicknesses of IPS e.max® CAD LD glass-ceramics materials with TP and Lt. Materials and methods: The total of 120 of shade A2 IPS max CAD samples (HT and LT) were prepared into square shape (15.25 mm X 15.25 mm) and were divided into two main groups according to the material translucency (HT and LT) (n=60). Each main group was further divided into 5 sub-groups according to the thickness (1.00, 1.25, 1.5, 1.75, and 2.00 mm) (n=12). Each thickness group was assigned into three groups based on different crystallization (firing) temperatures (750, 820 °C in single stage heating schedule with 1 second and 10 second holding times, respectively, and 840 °C with two-stage heating schedule (RECOM) (820°C, 840 °C with 10 second and 7 min holding time, respectively) as recommended by manufacturer (n=4). CIEL*a*b*, TP, CR, and Lt were measured and calculated for all samples. Statistical analysis: The effects of the test results were evaluated using 3-way ANOVA with factors for Translucency (HT and LT), Firing Temperature (750, 850, and RECOM) and Thickness (1, 1.25, 1.5, 1.75, and 2), as well as all two-way and three-way interactions among the factors. Pair-wise comparisons were made using Least Significant Differences to control the overall significance level at 5%. Results: The mean irradiance and TP for both HT and LT decrease as the thickness of the samples increases from 1 to 2mm with significant difference between the thickness groups within each material translucency groups (HT and LT) and between both HT and LT. The coefficients of absorption (c) of the two materials were calculated. The effective incidence irradiance when material thickness approaches zero (Ie) was also calculated. There is an unexpected spectral peak shift as the thickness of the samples increases. There is no statistically significant difference in Ie at 750˚C and 820 ˚C between the HT and LT. However, there is a statistically significant higher Ie in HT at the recommended firing temperature as expected. Coefficients of translucency parameter (p) of the materials in various firing temperature were defined and the TP of the material as the thickness approaches zero were calculated (TP0). The TP of the materials is directly correlated to the mean irradiance passing through the samples. There is no statistically significant difference in the TP0 and Ie of the HT and LT groups at the recommended firing temperature. Conclusion: In this project we developed modified Beer-Lambert law to describe the parameters governing the effect of thickness on light transmission in dental ceramic material. We also applied the same equation to describe the translucency parameter. The parameters defined in these equations allow us to compare the optical property of dental ceramic material independent of the thickness of the samples.