Moshi Geso

Potential dependent superiority of gold nanoparticles in comparison to iodinated contrast agents

PURPOSE To identify the benefits in image contrast enhancement using gold nanoparticles (AuNPs) compared to conventional iodinated contrast media. MATERIALS AND METHODS Gold nanoparticles and iodinated contrast media were evaluated for contrast enhancement at various X-ray tube potentials in an imaging phantom. Iopromide and AuNP suspension were equalized according to molar concentration of radiopaque element (0.5077 Mol/L). Contrast-to-noise ratio is used to quantify contrast enhancement. Both projectional radiographic (40-80 kVp) and computed tomography (CT) (80-140 kVp) imaging modalities were examined. RESULTS AND CONCLUSIONS Findings indicate 89% improvement in CNR at low energies near the mammographic range (40 kVp). However, as expected no significant difference in enhancement was observed at potentials commonly used for angiography (around 80 kVp) probably due to the k-edge influence for iodine. At the highest energies typically available in computed tomography, significant improvement in contrast enhancement using gold nanoparticles is obtained, 114% greater CNR than that produced by iodine at 140 kVp. Experimental findings for 70-120 kVp spectra correlate well with the theoretical calculations based on linear attenuation coefficients. Superior attenuation of gold nanoparticles at low and high kVp potentials support their further (pre)clinical evaluation.

Optimal energy for cell radiosensitivity enhancement by gold nanoparticles using synchrotron-based monoenergetic photon beams

Gold nanoparticles have been shown to enhance radiation doses delivered to biological targets due to the high absorption coefficient of gold atoms, stemming from their high atomic number (Z) and physical density. These properties significantly increase the likelihood of photoelectric effects and Compton scattering interactions. Gold nanoparticles are a novel radiosensitizing agent that can potentially be used to increase the effectiveness of current radiation therapy techniques and improve the diagnosis and treatment of cancer. However, the optimum radiosensitization effect of gold nanoparticles is strongly dependent on photon energy, which theoretically is predicted to occur in the kilovoltage range of energy. In this research, synchrotron-generated monoenergetic X-rays in the 30–100 keV range were used to investigate the energy dependence of radiosensitization by gold nanoparticles and also to determine the photon energy that produces optimum effects. This investigation was conducted using cells in culture to measure dose enhancement. Bovine aortic endothelial cells with and without gold nanoparticles were irradiated with X-rays at energies of 30, 40, 50, 60, 70, 81, and 100 keV. Trypan blue exclusion assays were performed after irradiation to determine cell viability. Cell radiosensitivity enhancement was indicated by the dose enhancement factor which was found to be maximum at 40 keV with a value of 3.47. The dose enhancement factor obtained at other energy levels followed the same direction as the theoretical calculations based on the ratio of the mass energy absorption coefficients of gold and water. This experimental evidence shows that the radiosensitization effect of gold nanoparticles varies with photon energy as predicted from theoretical calculations. However, prediction based on theoretical assumptions is sometimes difficult due to the complexity of biological systems, so further study at the cellular level is required to fully characterize the effects of gold nanoparticles with ionizing radiation.

A Novel Method for Respiratory Motion Gated With Geometric Sensitivity of the Scanner in 3D PET

PET image quality can be significantly affected by respiratory motion artifacts. To improve image quality, surveillance systems have been developed to track the movements of the subject during scanning. Gating techniques utilizing the tracking information, are able to compensate for subject motion, thereby improving lesion detection. In this paper, we present a gating method that utilizes the Geometric Sensitivity Gating (GSG) of a 3D-PET scanner system operating in list event acquisition mode. As a result of the non-uniform geometric sensitivity, the count rate from a given organ, will depend on the axial location of the organ. Consequently the respiratory phase can be determined from count rate changes which are determined by suitable temporal resolution from the list-mode data stream. The GSG method has several advantages over existing methods; it only uses LOR events. It is non-invasive, no additional hardware device systems and patient preparation required. Using GATE (GEANT4 Application Tomographic Emission) and NCAT (NURBs(Non Uniform Rational B-Splines) Cardiac Torso) software packages, realistic simulations of respiratory motion demonstrate that GSG can be used for respiratory gating. The validation on clinical data demonstrates that GSG is able to reduce respiratory motion artifacts.

VERIFICATION OF BRACHYTHERAPY DOSIMETRY WITH RADIOCHROMIC FILM

The aim of this work is to empirically validate the optimized dose distribution calculated by the Nucletron Brachytherapy Planning System (v. 13.3) at a distance of 1.0 cm from a stepping source of high-dose-rate-iridium 192 (192Ir). The longitudinal dose distribution at 1.0 cm from a straight pathway of multiple-source positions is measured using radiochromic film and compared with the planning systems calculated results. The optical density of the exposed films was determined with a modified Scanditronix film scanner, and the film was calibrated with 192Ir using manually calculated exposure times. A calibration equation was used to convert scanner output to dose. Our results illustrate the significance of exacting geometry in the experimental setup due to the inverse square law and the small distances involved. The dose distribution calculated by the Nucletron Brachytherapy Planning System (v. 13.3), at a distance of 1.0 cm, is validated to within +/-4% of the measured dose distribution. The advantages and limitations of radiochromic film as a dosimetry tool are also addressed in this work.

Evaluation of Geometrical Sensitivity for Respiratory Motion Gating by GATE and NCAT Simulation

Respiratory motion artifacts can be a significant factor that limits the PET image quality. To improve image quality, surveillance systems have been developed to track the movements of the subject during scanning. Gating techniques utilizing the tracking information, are able to compensate for subject motion, thereby improving lesion detection. In this paper, we present a gating method that utilizes the geometric sensitivity gating (GSG) of a 3D-PET scanner system operating in list event acquisition mode. GSG method has several advantages over the existing methods, it only uses LOR events and is non-invasive, no additional hardware device is required and there is no additional patient preparation required. Using GATE (GEANT4 Application Tomographic Emission) and NCAT (NURBs(Non Uniform Rational B-Splines) Cardiac Torso) software packages with an Allegro PET configuration, realistic simulations of respiratory motion demonstrate that GSG can be used for respiratory gating.

Enhancement of radiation effects by bismuth oxide nanoparticles for kilovoltage x-ray beams: A dosimetric study using a novel multi-compartment 3D radiochromic dosimeter

The aim of this study is to present the first experimental validation and quantification of the dose enhancement capability of bismuth oxide nanoparticles (Bi2O3-Nps). A recently introduced multi-compartment 3D radiochromic dosimeter for measuring radiation dose enhancement produced from the interaction of X-rays with metal nanoparticles was employed to investigate the 3D spatial distribution of ionizing radiation dose deposition. Dose-enhancement factor for the dosimeters doped with Bi2O3-NPs was ~1.9 for both spectrophotometry and optical CT analyses. Our results suggest that bismuth-based nanomaterials are efficient dose enhancing agents and have great potential for application in clinical radiotherapy.

Novel Multicompartment 3-Dimensional Radiochromic Radiation Dosimeters for Nanoparticle-Enhanced Radiation Therapy Dosimetry

PURPOSE Gold nanoparticles (AuNps), because of their high atomic number (Z), have been demonstrated to absorb low-energy X-rays preferentially, compared with tissue, and may be used to achieve localized radiation dose enhancement in tumors. The purpose of this study is to introduce the first example of a novel multicompartment radiochromic radiation dosimeter and to demonstrate its applicability for 3-dimensional (3D) dosimetry of nanoparticle-enhanced radiation therapy. METHODS AND MATERIALS A novel multicompartment phantom radiochromic dosimeter was developed. It was designed and formulated to mimic a tumor loaded with AuNps (50 nm in diameter) at a concentration of 0.5 mM, surrounded by normal tissues. The novel dosimeter is referred to as the Sensitivity Modulated Advanced Radiation Therapy (SMART) dosimeter. The dosimeters were irradiated with 100-kV and 6-MV X-ray energies. Dose enhancement produced from the interaction of X-rays with AuNps was calculated using spectrophotometric and cone-beam optical computed tomography scanning by quantitatively comparing the change in optical density and 3D datasets of the dosimetric measurements between the tissue-equivalent (TE) and TE/AuNps compartments. The interbatch and intrabatch variability and the postresponse stability of the dosimeters with AuNps were also assessed. RESULTS Radiation dose enhancement factors of 1.77 and 1.11 were obtained using 100-kV and 6-MV X-ray energies, respectively. The results of this study are in good agreement with previous observations; however, for the first time we provide direct experimental confirmation and 3D visualization of the radiosensitization effect of AuNps. The dosimeters with AuNps showed small (<3.5%) interbatch variability and negligible (<0.5%) intrabatch variability. CONCLUSIONS The SMART dosimeter yields experimental insights concerning the spatial distributions and elevated dose in nanoparticle-enhanced radiation therapy, which cannot be performed using any of the current methods. The authors concluded that it can be used as a novel independent method for nanoparticle-enhanced radiation therapy dosimetry.

Imaging characteristics of extrapulmonary tuberculosis lesions on dual time point imaging (DTPI) of FDG PET/CT.

Introduction: This study aimed to evaluate the diagnostic value of dual time point imaging (DTPI) of 18F‐fluorodeoxyglucose (FDG) positron emission tomography/CT (PET/CT) for detecting the infective lesions in patients with extrapulmonary tuberculosis (EPTB).

Evaluating the peak-to-valley dose ratio of synchrotron microbeams using PRESAGE fluorescence

The peak-to-valley dose ratio of a microbeam array can be measured by fluorescence of PRESAGE dosimeters. Peak-to-valley dose ratios are calculated using this new technique and also by EBT2 film.

The Application of GATE and NCAT to Respiratory Motion Simulation in Allegro PET

Respiratory motion artifacts can be a significant factor that limits the PET image quality. To compensate respiratory motion, simulation using software packages may provide a valuable tool for the assessment of respiratory motion detection and correction. In this study, we investigate respiratory motion by simulation using GATE (GEANT4 Application Tomographic Emission) [Jan, et al., 2005] and NCAT (NURBs(Non Uniform Rational B-Splines) Cardiac Torso) [Segars, et al., 2001] software packages.