Sharif Digital Repository

Magnetic Resonance Imaging is one of the most advanced medical imaging procedure that noninvasively played in most applications. However, this imaging method is a good resolution, but not in the conventional high speed imaging method, in fact, the main problem is slow. In recent years many studies have been done to accelerate MRI that compressed sensing can be mentioned among them. Such methods, however, have had very good results but MRI systems are very complex. This project investigates the reconstruction of MR images using data from partial non-Cartesian samples aimed at reducing sampling time and also speed up the process of reconstruction of MR images have been studied. In this regard,... 

Computerized tomography (CT) is a powerful tool among existing bioimaging techniques for capturing bio-images. In fact, CT imaging systems have attracted great attention in the last decades, because of their fast and high-quality reconstruction, low complexity and low-cost hardware solutions. In a CT scan procedure, linear sensors receive x-ray radiations, passed through the patient’s body and The quality of the reconstructed image is essentially influenced by the number of captured line projections. Nevertheless, gathering the adequate amount of data requires the patient to being exposed to X-ray radiations for a long time. However, the intensification of x-ray radiations could lead to... 

Frequency-scan millimeter-wave imaging systems are of high interest due to their low cost and acceptable performance in many applications such as concealed-weapon-detection. In recent years, the performance of this system in view of imaging time, image quality and cost has been improved via its implementation based on metamaterial apertures. These structures take advantage from the famous theory of single pixel imaging in optics. Through using the compressive sensing principle, the number of required imaging modes for obtaining diffraction limited resolution is reduced which in turn lessens the imaging time and more importantly the required bandwidth. Still, the image quality and resolution... 

Magnetic Resonance Imaging ,MRI, although as one of the most advanced medical imaging equipment is well known but compared to other medical imaging systems needs more time to imaging, so it has caused the patient dissatisfaction. According to the recently researches, filling the image data in a space of information that called ‘k-space’, in the process of image reconstruction, is the main reason of slow MRI. Image reconstruction methods for accelerating like half scan based on image reconstruction by using only a part of k-space is used in MRI systems today, but this method is associated with lower SNR image. Recent research on the theory of compressed sensing has been opened a new approach... 

Recently, there has been an increasing trend towards the use of millimeter-wave (MMW) imaging in various detection applications. This is mainly due to two factors: first, the radiation in the MMW band (30–300 GHz) is nonionizing and safe to use and second, it is able to penetrate through most dielectric materials as well as poor weather conditions, such as smoke and fog. With these potentials, MMW imaging has been used in a variety of applications, including target surveillance and precision target imaging, safe aircraft landing, highway traffic monitoring in fog, remote sensing for civil applications and concealed threat object detection for security concerns. Moreover, it can also find... 

Each year, large quantities of low/intermediate operational radioactive wastes are produced in different matrices. Usually, these wastes are temporarily stored within the plants and after a certain period, they have to be transferred to landfill sites for final disposal. According to international regulations recommended by IAEA as well as, requirements imposed by national regulatory bodies, waste packages must clear certain requirments called Waste Acceptance Criteria. As such, all waste packages are subject to certain inspections in plant or at disposal facilities. Computerized Tomography (CT) is proven to be one of the most efficient inspection tools for waste packages that can reveal... 

Nowadays, millimeter-wave imaging is widely used in security and medical applications. The growing threat from terrorist attacks is driven research on novel ways to enhance security inspection systems. Millimeter-wave imaging not only is an effective option of penetrating into dielectric materials including cloth, but also provides suitable imaging resolution. Moreover, millimeter-wave imaging is capable of identifying different materials making it a promising option for concealed weapon detection. In spite of X-ray, millimeter-wave imaging is non-ionizing, allowing for non-invasive imaging. In this thesis, first we investigate different millimeter-wave imaging systems and reconstruction... 

Today digital imaging systems have been widely used due to their ease of use and proper costs, but still they suffer from low contrast and resolution. Because of technical limits and expensiveness of hardware, software techniques like super resolution have been used. By super resolution we mean increasing the density of an image’s pixels. Super resolution can be categorized as “single image super resolution” and “multi-image super resolution”. Single image super resolution is applied on a low quality image which has blur and/or noise of environment and imaging system and increases its quality and density to an acceptable level. In multi-image super resolution some auxiliary images captured... 

Compton imaging is an imaging technique in which Compton scattering is used to produce images from a gamma-ray source. Compton imaging systems are also known as Compton cameras. The basic design of Compton imaging systems consists of two-position detectors that are sensitive to the position and energy scattered from gamma rays. The gamma rays collide with the Compton scatterer detector and the scattered photons are absorbed in the absorber detector. Compton imaging performs well the ground radiation during the scattering processes through the separation of energy. The quality of images produced by Compton imaging depends on a variety of factors including detector energy resolution,... 

3D reconstruction of digital images is one of the sub- branches of computer vision which is used in various fields such as computer graphics, compute animation, etc. in general, two approaches exist for solving 3D structure problem. In the first approach to obtain the model, we need a certain distance of the whole object level at a certain point and to do so, a sensor is used which is directly interacting with the object. For instance, we use lasers and estimate the depth using that depth to make 3 D model. In the second approach we use the images we have at different instaces of an object (sensor is the camera that is sensitive to light). Using these data and the machine learning... 

Increasing advances in millimeter-wave imaging have given the new technology a special place in military and civilian activities. A very important advantage of this imaging system, which has led to its rapid development and growth, is that unlike methods such as X-ray imaging, the millimeter-wave signal is completely harmless to the human body. Because millimeter-wave imaging is non-ionizing, allowing for non- invasive imaging. Also, the millimeter-wave easily passes through human clothing and is reflected when it hits the human body, metal and ceramic objects, and some other objects. As a result, it can be used to photograph underwear, insensitive and safe places such as airports. In this... 

Sight is probably our most important sense. Every day, humans are exposed to many visual stimuli in their surroundings. The human brain is able to identify and prioritize important and valuable stimuli and memorize them. Identifying and remembering these valuable stimuli is vital to meeting the needs and maintaining survival. The aim of the proposed research is to find the effect of reward learning on the coding of visual objects in the human brain. Previous results have shown that long-term reward-object association make valuable objects more recognizable behaviorally. Studies have also shown that visual stimuli and the pattern of activity of primary visual cortex neurons are closely... 

The fast-growing development of engineering and medical sciences leads to the diagnosis and treatment of diseases with higher accuracy and in the early stages of the disease. Medical imaging systems are considered as a crucial and effective tool in this field that based on the principle of technology used, are able to image various tissues with high quality. In recent years, photoacoustic imaging has attracted the attention of many researchers and engineers, because it able to image different tissues with good resolution and penetration depth non-invasively and without the use of ionizing radiation. The photoacoustic system response is a low-pass filter that passes only low-frequency... 

In recent years, optical biomedical imaging techniques show great potential in noninvasive imaging. Although these methods have many advantages over other biomedical imaging methods (such as Computerized Tomography (CT), Magnetic Resonance Imaging (MRI) and etc.), these techniques confront with some problems such as optical scattering, light absorption and etc. For in vivo imaging, the short-wavelength infrared region (SWIR; 1,000–2,000 nm) provides several advantages over the visible and near-infrared regions: general lack of auto-fluorescence, low light absorption by blood and tissue, and reduced scattering. In this thesis we want to analyze the traditional IR imaging techniques and... 

X-ray Computed Tomography (CT) is a widely used medical imaging technique that provides cross-sectional images by measuring the attenuation of X-rays in the body. However, the increasing use of CT has raised concerns about the potential long-term risks associated with radiation exposure. Various approaches have been proposed to reduce radiation dose, and one of the latest methods is sparse-view CT, which has gained popularity due to its lower challenges compared to other techniques. In sparse-view CT, data acquisition is restricted to specific angles, resulting in a significant reduction in radiation dose. However, this approach can introduce streak artifacts in the reconstructed images due... 

e study of the brain’s neural activity is an active research area in computational neuroscience aiming to provide insights about the functionality of the brain as well as dysfunctions that underlie disorders. Functional Magnetic Resonance Imaging (fMRI) plays an important role in brain studies by providing non-invasive records of neural activities during a specific task with location sensitivity. Recent advances in statistics and machine learning offer powerful tools for paern recognition and processing of fMRI data. In this thesis, we decode information recorded via fMRI from the visual cortex to reconstruct images presented to subjects. Current reconstruction methods face numerous...