Full-dose PET Synthesis from Low-dose PET Using High-efficiency Diffusion Denoising Probabilistic Model

To reduce the risks associated with ionizing radiation, a reduction of radiation exposure in PET imaging is needed. However, this leads to a detrimental effect on image contrast and quantification. High-quality PET images synthesized from low-dose data offer a solution to reduce radiation exposure. We introduce a diffusion-model-based approach for estimating full-dose PET images from low-dose ones: the PET Consistency Model (PET-CM) yielding synthetic quality comparable to state-of-the-art diffusion-based synthesis models, but with greater efficiency. There are two steps: a forward process that adds Gaussian noise to a full dose PET image at multiple timesteps, and a reverse diffusion process that employs a PET Shifted-window Vision Transformer (PET-VIT) network to learn the denoising procedure conditioned on the corresponding low-dose PETs. In PET-CM, the reverse process learns a consistency function for direct denoising of Gaussian noise to a clean full-dose PET. We evaluated the PET-CM in generating full-dose images using only 1/8 and 1/4 of the standard PET dose. Comparing 1/8 dose to full-dose images, PET-CM demonstrated impressive performance with normalized mean absolute error (NMAE) of 1.233+/-0.131%, peak signal-to-noise ratio (PSNR) of 33.915+/-0.933dB, structural similarity index (SSIM) of 0.964+/-0.009, and normalized cross-correlation (NCC) of 0.968+/-0.011, with an average generation time of 62 seconds per patient. This is a significant improvement compared to the state-of-the-art diffusion-based model with PET-CM reaching this result 12x faster. In the 1/4 dose to full-dose image experiments, PET-CM is also competitive, achieving an NMAE 1.058+/-0.092%, PSNR of 35.548+/-0.805dB, SSIM of 0.978+/-0.005, and NCC 0.981+/-0.007 The results indicate promising low-dose PET image quality improvements for clinical applications

Quantitative performance characterization of image quality and radiation dose for dental CBCT machine (CS9300)

Purpose: To characterize the performance of cone beam CT (CBCT) used in dentistry, investigating quantitatively the image quality and radiation dose during dental CBCT over different settings for partial rotation of the x-ray tube. Methods: Image quality and dose measurements were done on a variable field of view (FOV) dental CBCT (Carestream 9300). X-ray parameters for clinical settings were adjustable for 2-10 mA, 60-90 kVp, and two optional voxel size values, with fixed time for each protocol and FOV. The phantoms were positioned in the FOV to imitate clinical positioning. Image quality was assessed by scanning a cylindrical poly-methyl methacrylate (PMMA) image quality phantom (SEDENTEXCT IQ), and the images were analyzed using ImageJ to calculate image quality parameters such as noise, uniformity, contrast to noise ratio (CNR), and spatial resolution. A protocol proposed by SEDENTEXCT, dose index 1 (DI1), was applied to dose measurements obtained using a thimble ionization chamber and cylindrical PMMA dose index phantom (SEDENTEXCT DI). Dose distributions were obtained using Gafchromic film. Results: The image noise was 6-12.5% which, when normalized to the difference of mean voxel value of PMMA and air, was comparable between different FOVs. Uniformity was 93.5-99.7% across the images. CNR was 0.5-4.2, 0.2-4.6, 3.7-11.7, 4.3-17.8, and 6.3-14.3 for LDPE, POM, PTFE, air, and aluminum, respectively. The measured FWHM and spatial resolution were larger than the voxel size. FWHM were 0.49-0.65 mm; spatial resolution was 194.81-467.68. Dose distributions were symmetric about the rotation angle’s bisector. For large and medium FOVs at 4 mA, 80-90 kVp, and 180-250 μm, DI1 values were in the range of 1.26-3.23 mGy. DI1 values were between 1.01-1.93 mGy for small FOV (5x5 cm²) at 4-5 mA,75-84 kVp, and 200 μm. Conclusion: Noise and spatial resolution decreased and the CNR increased by increasing kVp; the geometric distortion, AAV, FWHM were very similar or the same when increasing the kVp. When FOV size increased, image noise increased and CNR decreased. FWHM and spatial resolution have no correlation with the voxel size. DI1 values were increased by increasing tube current (mA), tube voltage (kVp), and/or FOV.Science, Faculty ofPhysics and Astronomy, Department ofGraduat

Optimization of multimodal OCT for early cancer detection and diagnosis

In this thesis, I present improved optical imaging modalities for early cancer detection, diagnosis and prognosis of lung and cervical cancers in a minimally invasive fashion. Optical coherence tomography (OCT), which is based on low coherence interferometry of backscattered light, offers high resolution three-dimensional visualization of structures below the tissue surface. In contrast, autofluorescence imaging (AFI) detects spectral differences in fluorescence and absorption characteristics of endogenous fluorophores. A combined OCT–AFI system uses both complementary modalities to examine structural and molecular information, which may enable increased detection and characterization of features associated with disease. The motivation of this thesis is to improve the capabilities of OCT and OCT-AFI for the in vivo detection and localization of early cancers. Rotary-pullback catheter-based OCT or OCT-AFI systems suffer from motion-induced artifacts. In this thesis, I developed a method for the correction of these motion artifacts present in both 2D and 3D images collected with an endoscopic OCT-AFI system. I optimized and demonstrated the suitability of this method using real and simulated NURD (non-uniform rotation distortion) phantoms and in vivo endoscopic pulmonary OCT-AFI. Presented is a qualitative evaluation of this method showing an enhancement of the image quality and a proposed metric to quantitatively evaluate the correction method. Next, I evaluated a high resolution OCT system for early cervical cancer screening and diagnosis. My work characterized diagnostic OCT features of normal cervix as well as low-grade squamous intraepithelial lesions (LSIL), and high-grade squamous intraepithelial lesions (HSIL). We determined the sensitivity (100%), specificity (83%) and accuracy (85%) of this diagnostic technique in differentiating low-risk and high-risk cervical lesions. Lastly, I present a design for a forward-viewing fiber scanning high resolution OCT probe for in vivo cervical imaging in the clinic. To enable high resolution imaging but allow for sufficient depth penetration into tissue, OCT systems use near-infrared light ~1000 nm in wavelength. As well, I have investigated the suitability of a new supercontinuum light source for this application.Science, Faculty ofPhysics and Astronomy, Department ofGraduat

Trehalose: A promising new treatment for traumatic brain injury? A systematic review of animal evidence

Background: TBI is a major global health issue due to its high morbidity and mortality rates. Persistent neurodegeneration following secondary brain injuries is a significant concern. Trehalose, a naturally occurring disaccharide, has shown potential therapeutic effects in preclinical TBI models. This study systematically reviews the preclinical and clinical data on trehalose as a potential TBI treatment. Methods: We conducted a systematic review of trehalose’s role in TBI treatment following PRISMA guidelines. Our search spanned from the inception of PubMed, EMBASE, SCOPUS, and Web of Science until August 2023. Google Scholar was also manually searched. The quality of the studies was assessed using SYRCLE’s risk of bias tool for animal studies. Results: Out of sixty-six records reviewed, four animal studies were included. These studies indicated that trehalose enhanced motor and cognitive functions, reduced oxidative damage and inflammation, regulated metal dyshomeostasis, increased neurotrophic factors and synaptic proteins, and improved autophagy and mitochondrial function in mouse/rat TBI models. However, a significant risk of bias was noted. Conclusion: Trehalose demonstrates potential as a TBI treatment. However, more rigorous, and comprehensive research is needed to confirm its safety and efficacy in humans