Quality Assessment of Computed Tomography Images using a Channelized Hoteling Observer: Optimization of Protocols in Clinical Practice.

Background: This study investigated the feasibility of channelized hoteling observer (CHO) model in computed tomography (CT) protocol optimization regarding the image quality and patient exposure. While the utility of using model observers such as to optimize the clinical protocol is evident, the pitfalls associated with the use of this method in practice require investigation. Materials and Methods: This study was performed using variable tube current and adaptive statistical iterative reconstruction (ASIR) level (ASIR 10% to ASIR 100%). Various criteria including noise, high-contrast spatial resolution, CHOs model were used to compare image quality at different captured levels. For the implementation of CHO, we first tuned the model in a restricted dataset and then it to the evaluation of a large dataset of images obtained with different reconstruction ASIR and filtered back projection (FBP) levels. Results: The results were promising in terms of CHO use for the stated purposes. Comparisons of the noise of reconstructed images with 30% ASIR and higher levels of noise in rebuilding images using the FBP approach showed a significant difference (P < 0.05). The spatial resolution obtained using various ASIR levels and tube currents were 0.8 pairs of lines per millimeter, which did not differ significantly from the FBP method (P > 0.05). Conclusions: Based on the results, using 80% ASIR can reduce the radiation dose on lungs, abdomen, and pelvis CT scans while maintaining image quality. Furthermore using ASIR 60% only for the reconstruction of lungs, abdomen, and pelvis images at standard radiation dose leads to optimal image quality.

Pragmatic Approaches to Reducing Radiation Dose in Brain Computed Tomography Scan using Scan Parameter Modification.

Background: High radiation dose of patients has become a concern in the computed tomography (CT) examinations. The aim of this study is to guide the radiology technician in modifying or optimizing the underlying parameters of the CT scan to reduce the patient radiation dose and produce an acceptable image quality for diagnosis. Methods: The body mass measurement device phantom was repeatedly scanned by changing the scan parameters. To analyze the image quality, software-based and observer-based evaluations were employed. To study the effect of scan parameters such as slice thickness and reconstruction filter on image quality and radiation dose, the structural equation modeling was used. Results: By changing the reconstruction filter from standard to soft and slice thickness from 2.5 mm to 5 mm, low-contrast resolution did not change significantly. In addition, by increasing the slice thickness and changing the reconstruction filter, the spatial resolution at different radiation conditions did not significantly differ from the standard irradiation conditions (P > 0.05). Conclusion: In this study, it was shown that in the brain CT scan imaging, the radiation dose was reduced by 30%-50% by increasing the slice thickness or changing the reconstruction filter. It is necessary to adjust the CT scan protocols according to clinical requirements or the special conditions of some patients while maintaining acceptable image quality.

Introduction of a New Parameter for Evaluation of Digital Radiography System Performance.

BACKGROUND: The aim of this study was to compare the image quality and radiation doses in various digital radiography systems using contrast-detail radiography (CDRAD) phantom. METHODS: The image quality and radiation dose for seven different digital radiography systems were compared using the CDRAD phantom. Incident air kerma (IAK) values were measured for certain exposure settings in all digital radiography systems. The images from the CDRAD phantom were evaluated by three observers. The results were displayed in the form of a contrast-detail (CD) curve. In addition, the inverse image quality figure (IQFinv)-to-IAK ratios were used for quantitative comparison of different digital radiography system performance. RESULTS: Results of this study showed that the CD curves cannot be suitable criterion for determining the performance of digital radiography systems. For this reason, IQFinv-to-radiation dose (IAK) ratios in a fixed radiation condition were used. The highest performance in terms of producing high-quality images and low radiation dose was related to X-ray unit 1 and the lowest performance was for X-ray unit 5. CONCLUSION: The ratio of IQFinv to IAK for performance evaluation of digital radiography systems is an innovation of this study. A digital radiography system with a higher IQFinv-to-IAK ratio is associated with lower patient dose and better image quality. Therefore, it is recommended to equip the new imaging centers with the systems that have higher IQFinv-to-IAK ratios.

Granulocyte-macrophage colony-stimulating factor, a potent adjuvant for polarization to Th-17 pattern: an experience on HIV-1 vaccine model.

Cytokines are mediators for polarization of immune response in vaccines. Studies show that co-immunization of DNA vaccines with granulocyte-macrophage colony-stimulating factor (GM-CSF) can increase immune responses. Here, experimental mice were immunized with HIV-1tat/pol/gag/env DNA vaccine with GM-CSF and boosted with recombinant vaccine. Lymphocyte proliferation with Brdu and CTL activity, IL-4, IFN-γ, IL-17 cytokines, total antibody, and IgG1 and IgG2a isotypes were assessed with ELISA. Results show that GM-CSF as adjuvant in DNA immunization significantly increased lymphocyte proliferation and IFN-γ cytokines, but CTL response was tiny increased. Also GM-CSF as adjuvant decreased IL-4 cytokine vs mere vaccine group. IL-17 in the group that immunized with mixture of DNA vaccine/GM-CSF was significantly increased vs DNA vaccine group. Result of total antibody shows that GM-CSF increased antibody response in which both IgG1 and IgG2a increased. Overall, results confirmed the beneficial effect of GM-CSF as adjuvant to increase vaccine immunogenicity. The hallmark result of this study was to increase IL-17 cytokine with DNA vaccine/GM-CSF immunized group. This study for the first time provides the evidence of the potency of GM-CSF in the induction of IL-17 in response to a vaccine, which is important for control of infection such as HIV-1.

Therapeutic protein deimmunization by T-cell epitope removal: antigen-specific immune responses in vitro and in vivo.

Hirudin III is an effective anti-coagulant; however, in 40% of treated patients, a high-titer of anti-Hirudin III IgG antibodies is observed. Development of antibody responses requires the activation of helper T lymphocyte (HTL), which is dependent on peptide epitopes binding to HLA class II molecules. Based on computational prediction softwares, four new mutants of Hirudin III, T4K, S9G, V21G, and V21K, had been designed with the aim of reducing the binding affinity of these HTL epitopes. The constructed mutants have been purified and assayed for bioactivity. Finally in vitro and in vivo cell-mediated responses were assessed and humoral immune assays were performed. All modified forms of Hirudin III were active, and showed significantly reduced human T-cell responses. All mutants indicated lower human IFN-γ level compared to native Hirudin, and V21K indicated lowest IFN-γ level. Mice immunized with T4K and V21K showed a significant reduction in total antibody responses and mouse IFN-γ levels. Mice immunized with V21K after 3rd immunization had lower T-cell proliferation compared to native Hirudin and other mutants. Based on these results, V21K is proposed as the best alternate Hirudin III candidate with lowest antigenicity. These findings validate our rational design strategy aimed at providing new active analogs of therapeutic proteins with reduced immunogenicity.