35 research outputs found

    3D adaptive Wiener filter to restore brain SPECT image with reference MRI

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    Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal

    Quantitative Yttrium-90 Bremsstrahlung SPECT/CT and PET/CT Study for 3D Dosimetry in Radiomicrosphere Therapy

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    Liver cancer ranks the third most common cause of cancer related mortality worldwide. Radiomicrosphere therapy (RMT), a form of radiation therapy, involves administration of Yttrium-90 (90Y) microspheres to the liver via the hepatic artery. 90Y microspheres bremsstrahlung SPECT/CT or PET/CT imaging could potentially identify an extrahepatic uptake. An early detection of such an uptake, thus, could initiate preventative measures early on. However, the quantitative accuracy of bremsstrahlung SPECT/CT images is limited by the wide and continuous energy spectrum of 90Y bremsstrahlung photons. 90Y PET/CT imaging is also possible but limited by the extremely small internal pair production decay. These limitation lead to inaccurate quantitation of microsphere biodistribution especially in small tumors. SPECT/CT and PET/CT acquisition of a Jasczak phantom with eight spherical inserts filled with 90Y3Cl solution were performed to measure the quantitative accuracy of the two imaging modalities. 90Y microsphere SPECT/CT data of 17 patients who underwent RMT for primary or metastatic liver cancer were acquired. Technetium-99m macroaggregated albumin (99mTc-MAA) SPECT/CT scans were also collected, but available for only twelve of the patients. SPECT/CT images from phantoms were used to determine the optimal iteration number for the iterative spatial resolution recovery algorithm. Methods for image based calculation of calibration factors for activity estimation from the patient and phantom 90Y bremsstrahlung SPECT/CT images were developed. Tumor areas were segmented using an active contour method. The 99mTc-MAA and 90Y microsphere SPECT/CT images were co-registered a priori for correlation analysis. Comparison of uptake on 99mTc-MAA and 90Y microsphere SPECT/CT images was assessed using tumor to healthy liver ratios. Furthermore, a three dimensional absorbed dose estimation algorithm was developed using the voxel S-value method. Absorbed doses within the tumor and healthy part of the liver were investigated for correlation with administered activity. Improvement in contrast to noise ratio and contrast recovery coefficients (QH) on patient and phantom 90Y bremsstrahlung SPECT/CT images as well as PET/CT images were achieved. Total activity estimations in liver and phantom gave mean percent errors of -4 ± 12% and -23 ± 41% for patient and phantom SPECT/CT studies. The pre and post-treatment images showed significant correlation (r = 0.9, p \u3c 0.05) with mean TLR of 9.2 ± 9.4 and 5.0 ± 2.2 on 99mTc-MAA and 90Y microspheres SPECT/CT respectively. The correlation between the administered activity and tumor absorbed dose was weak (r = 0.5, p \u3e 0.05), however, healthy liver absorbed dose increased with administered activity (r = 0.8, p \u3c 0.05)

    Advanced Image Acquisition, Processing Techniques and Applications

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    "Advanced Image Acquisition, Processing Techniques and Applications" is the first book of a series that provides image processing principles and practical software implementation on a broad range of applications. The book integrates material from leading researchers on Applied Digital Image Acquisition and Processing. An important feature of the book is its emphasis on software tools and scientific computing in order to enhance results and arrive at problem solution

    Enhancement of noisy planar nuclear medicine images using mean field annealing

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    Abstract Nuclear Medicine (NM) images inherently suffer from large amounts of noise and blur. The purpose of this research is to reduce the noise and blur while maintaining image integrity for improved diagnosis. The proposal is to further improve image quality after the standard pre- and post-processing undertaken by a gamma camera system. Mean Field Annealing (MFA), the image processing technique used in this research is a well known image processing approach. The MFA algorithm uses two techniques to achieve image restoration. Gradient descent is used as the minimisation technique, while a deterministic approximation to Simulated Annealing (SA) is used for optimisation. The algorithm anisotropically diffuses an image, iteratively smoothing regions that are considered non-edges and still preserving edge integrity until a global minimum is obtained. A known advantage of MFA is that it is able to minimise to this global minimum, skipping over local minima while still providing comparable results to SA with significantly less computational effort. Image blur is measured using either a point or line source. Both allow for the derivation of a Point Spread Function (PSF) that is used to de-blur the image. The noise variance can be measured using a flood source. The noise is due to the random fluctuations in the environment as well as other contributors. Noisy blurred NM images can be difficult to diagnose particularly at regions with steep intensity gradients and for this reason MFA is considered suitable for image restoration. From the literature it is evident that MFA can be applied successfully to digital phantom images providing improved performance over Wiener filters. In this paper MFA is shown to yield image enhancement of planar NM images by implementing a sharpening filter as a post MFA processing technique

    Development Of A Scintillation Detector And The Influence On Clinical Imaging

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    The detector is the functional unit within a Positron Emission Tomography (PET) scanner, serving to convert the energy of radiation emitted from a patient into positional information, and as such contributes significantly to the performance of the scanner. While modern whole-body scanners use detectors composed of very many (i.e., 20000-30000) small pixels, typically ~4x4x20mm3 in size, several groups are actively investigating the performance of continuous crystals coupled to position sensitive photodetectors as an alternative detector design with a number of potential advantages, including improved spatial resolution and position sampling. This work in particular focuses on thick (≥14mm) continuous crystals in order to maintain the sensitivity of modern scanners. Excellent spatial resolution in continuous detectors that are thick, however, has proven difficult to achieve using simple positioning algorithms, leading to research in the field to improve performance. This thesis aims to investigate the effect of modifications to the scintillation light spread within the bulk of the scintillator to improve performance, focusing on the use of laser induced optical barriers (LIOBs) etched within thick continuous crystals, and furthermore aims to translate the effect on detector performance to scanner quantitation in patient studies. The conventional continuous detector is first investigated by analyzing the various components of the detector as well as its limitations. It is seen that the performance of the detector is affected by a number of variables that either cannot be improved or may be improved only at the expense of greater complexity or computing time; these include the photodetector, the positioning algorithm, and Compton scatter in the detector. The performance of the detectors, however, is fundamentally determined by the light spread within the detector, and limited by the depth-dependence of the light spread and poor performance in the entrance region, motivating efforts to modify this aspect of the detector. The feasibility and potential of LIOBs to fine-tune this light spread and improve these limitations is then studied using both experiments and simulations. The behavior of the LIOBs in response to optical light is investigated, and the opacity of the etchings is shown to be dependent on the parameters of the etching procedure. Thick crystals were also etched with LIOBs in their entrance region in a grid pattern in order to improve the resolution in the entrance region. Measurements show an overall improvement in spatial resolution: the resolution in the etched region of the crystals is slightly improved (e.g., ~0.8mm for a 25mm thick crystal), though in the unetched region, it is slightly degraded (e.g., ~0.4mm for a 25mm thick crystal). While the depth-dependence of the response of the crystal is decreased, the depth-of-interaction (DOI) performance is degraded as well. Simulation studies informed by these measurements show that the properties of the LIOBs strongly affect the performance of the crystal, and ultimately further illustrate that trade-offs in spatial resolution, position sampling, and DOI resolution are inherent in varying the light spread using LIOBs in this manner; these may be used as a guide for future experiments. System Monte Carlo simulations were used to investigate the added benefit of improved detector spatial resolution and position sampling to the imaging performance of a whole-body scanner. These simulations compared the performance of scanners composed of conventional pixelated detectors to that of scanners using continuous crystals. Results showed that the improved performance (relative to that of 4-mm pixelated detectors) of continuous crystals with a 2-mm resolution, pertinent to both the etched 14mm thick crystal studied as well as potential designs with the etched 25mm thick crystal, increased the mean contrast recovery coefficient (CRC) of images by ~22% for 5.5mm spheres. Last, a set of experiments aimed to test the correspondence between quantification in phantom and patient images using a lesion embedding methodology, so that any improvements determined using phantom studies may be understood clinically. The results show that the average CRC values for lesions embedded in the lung and liver agree well with those for lesions embedded in the phantom for all lesion sizes. In addition, the relative changes in CRC resulting from application of post-filters on the subject and phantom images are consistent within measurement uncertainty. This study shows that the improvements in CRC resulting from improved spatial resolution, measured using phantom studies in the simulations, are representative of improvements in quantitative accuracy in patient studies. While unmodified thick continuous detectors hold promise for both improved image quality and quantitation in whole-body imaging, excellent performance requires intensive hardware and computational solutions. Laser induced optical barriers offer the ability to modify the light spread within the scintillator to improve the intrinsic performance of the detector: while measurements with crystals etched with relatively transmissive etchings show a slight improvement in resolution, simulations show that the LIOBs may be fine-tuned to result in improved performance using relatively simple positioning algorithms. For systems in which DOI information is less important, and transverse resolution and sensitivity are paramount, etching thick detectors with this design, fine-tuned to the particular thickness of the crystal and application, is an interesting alternative to the standard detector design

    Advances in characterisation, calibration and data processing speed of optical coherence tomography systems

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    This thesis describes advances in the characterisation, calibration and data processing of optical coherence tomography (OCT) systems. Femtosecond (fs) laser inscription was used for producing OCT-phantoms. Transparent materials are generally inert to infra-red radiations, but with fs lasers material modification occurs via non-linear processes when the highly focused light source interacts with the materials. This modification is confined to the focal volume and is highly reproducible. In order to select the best inscription parameters, combination of different inscription parameters were tested, using three fs laser systems, with different operating properties, on a variety of materials. This facilitated the understanding of the key characteristics of the produced structures with the aim of producing viable OCT-phantoms. Finally, OCT-phantoms were successfully designed and fabricated in fused silica. The use of these phantoms to characterise many properties (resolution, distortion, sensitivity decay, scan linearity) of an OCT system was demonstrated. Quantitative methods were developed to support the characterisation of an OCT system collecting images from phantoms and also to improve the quality of the OCT images. Characterisation methods include the measurement of the spatially variant resolution (point spread function (PSF) and modulation transfer function (MTF)), sensitivity and distortion. Processing of OCT data is a computer intensive process. Standard central processing unit (CPU) based processing might take several minutes to a few hours to process acquired data, thus data processing is a significant bottleneck. An alternative choice is to use expensive hardware-based processing such as field programmable gate arrays (FPGAs). However, recently graphics processing unit (GPU) based data processing methods have been developed to minimize this data processing and rendering time. These processing techniques include standard-processing methods which includes a set of algorithms to process the raw data (interference) obtained by the detector and generate A-scans. The work presented here describes accelerated data processing and post processing techniques for OCT systems. The GPU based processing developed, during the PhD, was later implemented into a custom built Fourier domain optical coherence tomography (FD-OCT) system. This system currently processes and renders data in real time. Processing throughput of this system is currently limited by the camera capture rate. OCTphantoms have been heavily used for the qualitative characterization and adjustment/ fine tuning of the operating conditions of OCT system. Currently, investigations are under way to characterize OCT systems using our phantoms. The work presented in this thesis demonstrate several novel techniques of fabricating OCT-phantoms and accelerating OCT data processing using GPUs. In the process of developing phantoms and quantitative methods, a thorough understanding and practical knowledge of OCT and fs laser processing systems was developed. This understanding leads to several novel pieces of research that are not only relevant to OCT but have broader importance. For example, extensive understanding of the properties of fs inscribed structures will be useful in other photonic application such as making of phase mask, wave guides and microfluidic channels. Acceleration of data processing with GPUs is also useful in other fields

    Super-MeV Compton Imaging and 3D Gamma-Ray Imaging Using Pixelated CdZnTe

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    The dissertation presents work in gamma-ray imaging in the MeV range, 3D Compton imaging, and time encoded imaging. The first thrust in high energy gamma-ray imaging begins with analyzing the artifacts produced. These factors include the increase in pair-production events, incorrect event sequencing, and charge sharing due to the larger electron clouds. They all result in shift-variant artifacts that degrade the signal-to-noise ratio as well as create artifacts that might be mistaken for a hot spot. The degradation from artifacts is discussed and possible mitigation techniques are presented to allow for recovery of the Compton image. One of the presented mitigation techniques proposes a new sequencing algorithm for 3-or-more interaction events, called FIL-MSD. Missequencing presents one of the more dominant artifacts and by fixing the first interaction to be the largest deposited energy, the sequencing efficiency has increased by 20% in simulated data. Experimental results show an almost twofold increase in the signal to noise ratio (SNR) for simple backprojection images of a 22Na (1.7 MeV) source. The image resolution using filtered backprojection (FBP) was improved on by developing an analytical point spread function model for high energy 3-interaction events. Previous models did not account for missequencing effects in the model. Adding these effects into the model improved the resolution of the image, but at a cost of increased artifact production. In addition, the Wiener filter was formalized for spherical harmonics, which could be used for any number of interaction given an appropriate point spread function model. Next, demonstration of a 3D Compton imaging system is accomplished via sensor fusion of a foot-mounted odometer and a CdZnTe detector. A comparison between 3D Compton imaging and inverse-square image-reconstruction algorithms for certain measurement conditions is presented. The experiments demonstrate the advantage of 3D Compton imaging over traditional localization techniques in those scenarios. Improvements in time encoded imaging (TEI) were also made with advancements in the reconstruction algorithms and was done so in three thrusts: use of subpixel sensing, depth of interaction correction, and 3D imaging of extended sources. Complex 3D objects was accomplished via the use of magnification-parallax effects which allowed for the estimation of a source in distance away from the detector. Both the 3D Compton imaging and TEI techniques were explored at the Idaho National Laboratory.PHDNuclear ScienceUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/155099/1/shyd_1.pd

    Compact realizations of optical super-resolution microscopy for the life sciences

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    Sandmeyer A. Compact realizations of optical super-resolution microscopy for the life sciences. Bielefeld: Universität Bielefeld; 2019

    Toward the development of an economically viable digital x-ray imaging device

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    A project aimed at the development of a robot-based patient positioning system for high-precision proton radiotherapy is underway at iThemba LABS. Part of the project included the development of a portal digital x-ray imaging device that would be used to verify the patient treatment set-up. The imaging device consisted of a scintillation screen, front surface mirror and a high-resolution charged-couple device (CCD) camera. The total costs for the device were about 7 times less expensive than a commercial amorphous silicon flat panel detector. To improve the efficiency of the system, the CCD chip and scintillation screen were chosen so that the wavelength of the light from the screen closely matched the wavelength at which the CCD sensor has the maximum quantum efficiency. The digital images compared favourably with those of x-ray film. Although the digital images were of lower resolution due to the finite resolution of the CCD chip, they were considered satisfactory. The use of pixel binning allowed for the use of lower exposure settings when compared to exposure settings for un-binned images. This resulted in a reduction of patient dose without significantly compromising image quality. The device would not be used for diagnostic purposes, but only to verify patient position at treatment setup. As such, the digital images would be compared against digitally reconstructed radiographs (DRRs) of the fields and/or the treatment position, which are created from the treatment planning Computed Tomography (CT) images. In general, the spatial resolution of the DRRs is also comparably lower than digital x-ray images, as the resolution of the DRRs is limited to the voxel size of the CT images
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