|
|
Cone Be am CT in dentistry: Motion artifacts and their reduction
Hanzelka, Tomáš ; Beneš, Jiří (advisor) ; Charvát, František (referee) ; Mazánek, Jiří (referee)
Cone Beam Computed Tomography (CBCT) allows effective 3D imaging in dentistry. CBCT consists of a planar detector and a x-ray source that rotate once around patient`s head. The x-ray beam is cone-shaped and is directed through the whole volume of interest. All the data needed are obtained during a single rotation of the source and detector. This rotation takes from several to several tens of seconds, and during this time the CBCT captures several hundred of 2D images. They represent different points of view on the region of interest and are later reconstructed to form a 3D data set. The biggest advantage of CBCT is that it can produce 3D image using at radiation doses similar to those of conventional diagnostic methods used in dentistry (Pauwels et al., 2010). In the experimental part of our experiment, we address one of the biggest weaknesses of CBCT - patient movement during scanning which has a major impact on the image quality and is currently the main limiting factor in the further development of this technology. In the first part of our experiment, we recorded movements of patients and CBCT scanner using a high speed camera and subsequently analyzed the data in MatLab program. Significant level of patient motion as well as motion of CBCT scanner was demonstrated. Motion was highest at the...
|
|
|
Effect of resolution recovery on image quality in myocardial perfusion SPECT
Skibová, Daniela ; Šámal, Martin (advisor) ; Judas, Libor (referee) ; Zimák, Jaroslav (referee)
Objectives: Resolution recovery algorithms (IR-RR) were recently proposed as tools to improve quality of SPECT images through better resolution. The aim of the presented study was to investigate the effect of IR-RR on myocardial perfusion SPECT studies. Methods: Phantom and clinical studies were performed using SPECT-CT Infinia/Hawkeye (GE Healthcare). NEMA triple line phantom was scanned according to NEMA procedures. Cold sphere and cardiac phantom were scanned under clinical conditions (900 -angled detectors, 60 views and circular orbit) and reconstructed via IR-RR (Evolution for Cardiac, GE, 12 iterations and 10 subsets), OSEM (ordered subset expectation maximization, 2 iterations and 10 subsets) and FBP (filtered back projection). IR-RR and OSEM reconstructions were used with/without attenuation and scatter correction (ACSC). The effect of post-reconstruction filtering was evaluated. In clinical studies two data-sets were used (half-time and full-time). Conventional scan using full-time (20 sec per stress projection and 25 sec per rest projection) was reconstructed via FBP and IR-RR; half-time scan (10 sec stress, 12 sec rest studies) was reconstructed via IR-RR. End-diastolic volume (EDV), end-systolic volume (ESV) and left ventricular ejection fraction (EF) were calculated using two software...
|
|
|
Performance analysis of the newest video encoding standards
Klejmová, Eva ; Polák, Ladislav (referee) ; Slanina, Martin (advisor)
The aim of this work is to describe state-of-the-art high-definition video compression algorithms. The thesis focuses on the differences between algorithms and their functionality. Procedures for video sequences compression based on reference implementations of selected codecs are being proposed and their important parameters are being discussed. Bachelor's thesis deals with comparison of reference implementations based on subjective and objective video quality measurements and time requirements. The graphic interface for selected codecs has been also designed.
|
|
|
Quality measurement of analog and digital terrestrial television broadcasting
Zach, Ondřej ; Polák, Ladislav (referee) ; Slanina, Martin (advisor)
This bachelor‘s thesis deals with the description of basic features of the analog and digital television broadcasting and suggestion of a method for objective video quality evaluation at both broadcasting types. The base of this thesis is description of picture broadcast technology in analog and digital form. Also principles of some video quality evaluation metrics are described. In this thesis, a method for video quality comparison is suggested, including a verifying of this method. According to this method, sequences at changing broadcasting conditions were recorded for both broadcasting types. The quality factors of these sequences were computed and on the basis of these factors, the analog and digital TV broadcasting were compared.
|
|
|
Transmission analysis and measurements in digital television DVB-S/S2
Kaller, Ondřej ; Ulovec,, Karel (referee) ; Kratochvíl, Tomáš (advisor)
This master’s theses consists of theoretical introduction which includes basic search of referenced literature about digital television systems and picture quality classification. The results of signal character measurement of selected TV channels from satellites ASTRA 1E (DVB-S) and ASTRA 1L (DVB-S2) are provided. The energy budget calculation of downlink and results of 24-hour TS error rate measurement is included as well. The video quality by DVQL metric for each particular program of CS link stream was measured during full 24 hours.
|
|
|
Enhancement of bio-medical image signals
Gregor, Michal ; Šmirg, Ondřej (referee) ; Přinosil, Jiří (advisor)
When scanning biomedical images by magnetic resonance or ultrasound, unwanted elements in the form of noise are entered to the image. With help of various methods it is possible the noise from the image partially remove. There are many methods for noise reduction and every one works on a different principle. As a result of this the results of these methods are different and is necessary for them to be objectively assessed. There is use for the adjustment of the images wavelet transformation and some treshold techniques in the work. The quality of the resulting pictures is tested by the methods for objective quallity tests. Testing was done in the MATLAB program environment on the pictures from magnetic resonance and pictures from ultrasound.
|
|
|
Picture Quality Analysis in Digital Television Systems
Bednarz, Robin ; Slanina, Martin (referee) ; Kratochvíl, Tomáš (advisor)
Diploma thesis deals with the analysis of quality in digital television systems and contains theoretical description of subjective and objective assessment of quality picture methods. The thesis contains short-term and long-term analysis of quality picture of terrestrial television DVB-T. Measurements and experimentations were carried out with the help of Rohde&Schwarz DVQ analyzer of picture quality and software MPEG-2 Quality Monitor and MPEG-2 Elementary stream analyzer.
|
|
|
Simulation of the HVS characterstics in Matlab
Ševčík, Martin ; Slanina, Martin (referee) ; Kratochvíl, Tomáš (advisor)
In theoretical part Diploma thesis deals with the model of human vision HVS (Human Visual System), which can be used for image quality assessment in TV technique area. It has been described calculations of selected JND (Just Noticeable Difference) metrics, used in evaluation of HVS. In practical part of the thesis it has been suggested and realized simulation model in Matlab, which may be used for evaluation of three JND metrics from color and grayscale images and evaluation in spatial a frequency domain. Results of JND models have been compared to another objective image quality evaluation metrics (MSE, NMSE, SNR and PSNR). For interpretation of dependencies it has been used images with different defined content.
|
|
|
Monitoring the effects of new exposure parameters after transition to CR digital image processing in the Radiodiagnostic Department at Sušice Hospital, o.p.s.
KLIMENT, Karel
At the current time, doses of radiation caused by medical exposure make up the largest part of peoples' exposure to artificial sources of ionising radiation (SIR). Every medical exposure must be justified as of benefit to the individual subject to it. Radiation protection at the workplace is subject to the principle of optimisation. One of the paths leading to optimisation of radiation protection is the specification of the Local Diagnostic Reference Level (LDRL). The objective of this thesis was to test and evaluate whether and how transition to indirect digitisation affects image quality. According to model examinations on a water phantom, the lowest possible dose for which image quality would be preserved was to be determined. If the dose could be reduced, it would be possible to specify a new LDRL. The dose can be reduced, amongst other things, by making appropriate adjustment to exposure parameters on the control unit. I tested how changes in the exposure parameters set affected the quality of the resulting image. I used the water phantom for each examination which corresponded to the thickness of the area to be examined for a standard patient. For constant default voltage, first of all changes to the settings were made to reduced blackening and increase electrical charge. Subsequently, voltage was increased and reduced with a constant blackening level. Image quality was evaluated according to the measured values for noise, and high and low contrast resolution. I used the results to determine recommendations for specific examinations in terms of exposure parameters to be set. I worked out the LDRL for the new exposure parameter settings and compared it to the current LDRL values at the workplace and with the NDRL (National Diagnostic Reference Level).
|
guest ::
