Texture Feature Comparison Between Step-and-Shoot and Continuous-Bed-Motion 18F-FDG PET
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Abstract:
Our objective was to investigate the differences in texture features between step-and-shoot (SS) and continuous-bed-motion (CBM) imaging in phantom and clinical studies. Methods: A National Electrical Manufacturers Association body phantom was filled with 18F-FDG solution at a sphere-to-background ratio of 4:1. SS and CBM were performed using the same acquisition duration, and the data were reconstructed using 3-dimensional ordered-subset expectation maximization with time-of-flight algorithms. Texture features were extracted using the software LIFEx. A volume of interest was delineated on the 22-, 28-, and 37-mm spheres with a threshold of 42% of the maximum SUV. The voxel intensities were discretized using 2 resampling methods, namely a fixed bin size and a fixed bin number discretization. The discrete resampling values were set to 64 and 128. In total, 31 texture features were calculated with gray-level cooccurrence matrix (GLCM), gray-level run length matrix, neighborhood gray-level different matrix, and gray-level zone length matrix. The texture features of the SS and CBM images were compared for all settings using the paired t test and the coefficient of variation. In a clinical study, 27 lesions from 20 patients were examined using the same acquisition and image processing as were used during the phantom study. The percentage difference (%Diff) and correlation between the texture features from SS and CBM images were calculated to evaluate agreement between the 2 scanning techniques. Results: In the phantom study, the 11 features exhibited no significant difference between SS and CBM images, and the coefficient of variation was no more than 10%, depending on resampling conditions, whereas entropy and dissimilarity from GLCM fulfilled the criteria for all settings. In the clinical study, the entropy and dissimilarity from GLCM exhibited a low %Diff and excellent correlation in all resampling conditions. The %Diff of entropy was lower than that of dissimilarity. Conclusion: Differences between the texture features of SS and CBM images varied depending on the type of feature. Because entropy for GLCM exhibits minimal differences between SS and CBM images irrespective of resampling conditions, entropy may be the optimal feature to reduce the differences between the 2 scanning techniques.Keywords:
Resampling
Texture (cosmology)
We present a method for automated brain-tissue segmentation through voxelwise classification. Our algorithm uses manually labeled training images to train a support vector machine (SVM) classifier, which is then used for the segmentation of target images. The classification incorporates voxel intensities from a T1-weighted scan, an IR scan, and a FLAIR scan; features to encode the voxel position in the image; and Gaussian-scale-space features and Gaussian-derivative features at multiple scales to facilitate a smooth segmentation. An experiment on data from the MRBrainS13 brain-tissue-segmentation challenge showed that our algorithm produces reasonable segmentations in a reasonable amount of time.
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Purpose: Nasopharnx carcinoma (NPC) treatment is being carried out using Ir-192 HDR seeds in Mehdieh Hospital in Hamadan, Iran. The Oncentra™ TPS is based on optimized TG-43 formalism which disregards heterogeneity in the treatment area. Due to abundant heterogeneity in head and neck, comparison of the Oncentra™ TPS dose evaluation and an accurate dose calculation method in NPC brachytherapy is the objective of this study. Methods: CT DICOMs of a patient with NPC obtained from Mehdieh Hospital used to create 3D voxel phantom with CTCREATE utility of EGSnrc code package. The voxel phantom together with Ir-192 HDR brachytherapy source were the input to DOSXYZnrc to calculate the 3D dose distribution. The sources were incorporate with type 6 source in DOSXYZnrc and their dwell times were taken into account in final dose calculations. Results: The direct comparison between isodoses as well as DVHs for the GTV, PTV and CTV obtained by Oncentra™ and EGSnrc Monte Carlo code are made. EGSnrc results are obtained using 5×109 histories to reduce the statistical error below 1% in GTV and 5% in 5% dose areas. The standard ICRP700 cross section library is employed in DOSXYZnrc dose calculation. Conclusion: A direct relationship between increased dose differences and increased material density (hence heterogeneity) is observed when isodoses contours of the TPS and DOSXYZnrc are compared. Regarding the point dose calculations, the differences range from 1.2% in PTV to 5.6% for cavity region and 7.8% for bone regions. While Oncentra™ TPS overestimates the dose in cavities, it tends to underestimate dose depositions within bones.
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Developing of voxel phantoms has been an active field of research during the last decades and is receiving more attention nowadays. Reference phantoms for several ethnic groups have been developed recently as an extension to the ICRP reference phantoms that are based on Caucasian standard anatomical data,. This work reports an attempt to develop a tool for automatic slice-based adjustment of voxel phantoms. This tool achieves the adjustment process depending on anthropomorphic data extracted from anterior and lateral images for targeted body. The software was used to adjust Golem voxel model according to 23 Sudanese individuals. The weight, height, and age of these individuals vary from 52 to 113 Kg; from 166 to 188 cm and from 20 to 35 years, respectively. The maximum equivalent diameter, mean equivalent diameter, major axis length, minimum axis length, solidity and volume of brain, heart, kidneys, liver, lungs, spleen and bladder were calculated for all prepared models. For each organ, the mean value for each of these parameters was calculated and the deviation of each model from this value was evaluated. For the obtained data, we have calculated a global deviation of model (GDM) and selected the model with the smallest GDM to be the Sudanese voxel model. We have also compared volume, height and weight for 17 organs of the Sudanese voxel phantoms with ICRP phantom Golem ، visible human and voxel man model.
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Tumor and normal tissue doses in boron neutron capture therapy were calculated by using Korean adult female voxel phantom KRWOMAN. The phantom was constructed by processing whole-body MR images of healthy Korean female volunteer. Organs and tissues on MR images were manually segmented and indexed using a graphic digitizer. Due to limited resolution of the raw MR images, voxels of 4mm x 4mm x 8mm were used. Test tumor in the center of brain of KRWOMAN was defined, and tumor and normal tissue dose in BNCT were evaluated using general-purposed Monte Carlo code, MCNP4B. Fundamental dose calculation system in radiation therapy including BNCT was established in this study and more application to another radiation therapy will be done using the methodology.
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We propose a new type of computational phantom, the “4D voxel phantom,” for realistic modeling of continuous respiratory motion in Monte Carlo dose calculation. In this phantom, continuous respiratory motion is realized by linear interpolation of the deformation vector fields (DVFs) between the neighboring original phases in the 4D CT data of a patient and by subsequent application of the DVFs to the phase images or to the reference image to produce multiple inter-phase images between the neighboring original phase images. A 4D voxel phantom is a combination of high-temporal-resolution voxel phantoms and on-the-fly dose registration to the reference phase image. In the course of particle transport simulation, the dose or deposited energy is directly registered to the reference phase image on-the-fly (i.e., after each event) using a DVF for dose registration. In the present study, we investigated two methods - DRP (DIR [deformable image registration] with respect to Reference Phase image) and DNP (DIR with respect to Neighboring original Phase image) - for production of multiple inter-phase images or high-temporal-resolution voxel phantoms. Utilizing these two methods, two 4D voxel phantoms each with 100 phases were produced from the original 10-phase images of the 4D CT data of a real patient in order to compare the two methods and to test the feasibility of the 4D voxel phantom methodology in general. We found that it is possible to produce a 4D voxel phantom very rapidly (i.e., <;40 min on a 4-core personal computer for a 100-phase phantom) in a fully automated process. The dose calculation results showed that the constructed 100-phase 4D voxel phantoms provide cumulative-dose distributions very similar to those of the conventional 10-phase approach for stationary proton-beam irradiation. The passing rates of the dose distributions of the 4D voxel phantoms were higher than 99.9% according to the 3% and 3 mm gamma criteria, which results validate the 4D voxel phantom methodology. The point-and dose-tracking analysis data showed that the DRP method, which uses the minimal number of DIR operations but uses inverse DVFs, provides significantly better results than those of the DNP method, which uses only DIR to generate the DVFs for inter-phase image generation and dose registration. The present study also showed that the computation time does not significantly increase when the number of phases in the 4D voxel phantom is increased for more realistic representation of continuous respiratory motion; the only significant increase is in the memory occupancy, which grows almost linearly with the number of phases.
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Numerical models and anthropomorphic phantoms are frequently used in radiation protection studies for dose evaluation purposes. In the present paper an integrated tool consisting of a plastic phantom coupled with a voxel model is presented. The voxel model was created from the image data set of a CT scan of the plastic phantom. The model was validated through a procedure that consisted in irradiating the plastic phantom and simulating the same irradiation conditions with the voxel model. The possibility of employing such couple of models in radiation protection studies was demonstrated calculating the organ dose conversion coefficients and comparing them with those evaluated with voxel models derived from human tomographic scans.
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Voxel phantom,associated with Monte Carlo simulation methods,has been applied in researches of radiation protection.But the simulation is time consuming which limits the wide application of voxel phantom.This work studied the description of voxel phantom for simulation and presented a method to describe voxel phantom in MCNP(Monte Carlo N-particle) with a 3-D voxel combination algorithm.The results show that the time spent in transportation of particles decreases 32% but more time is needed to tally energy deposited in tissues or organs.
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