| 1. |
- Marlevi, David, doktorand, et al.
(författare)
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Multigrid reconstruction in tomographic imaging
- 2020
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Ingår i: IEEE Transactions on Radiation and Plasma Medical Sciences. - : Institute of Electrical and Electronics Engineers (IEEE). - 2469-7311 .- 2469-7303. ; 4:3, s. 300-310
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we present an efficient methodology for multigrid tomographic image reconstruction from non-truncated projection data. By partitioning the reconstruction domain and adapting the forward and backward operators, an image can be reconstructed accurately within multiple domains of varying discretisation or regularisation. We demonstrate the efficacy of the multigrid reconstruction principle using simulated data for quantitative assessment and experimental measurements from a μ-CT scanner for a clinically relevant use case scenario. A major advantage of using multiple reconstruction grids is the possibility to drastically reduce the number of unknowns in the inverse problem, and thereby the associated computational cost. This cost reduction helps to enlarge the class of available algorithms in applications with strict limitations on computation time or resources, and it enables full system resolution reconstruction of subregions that would otherwise be infeasible for the full field of view. The numerical experiments, along with a brief error analysis, show that the expected artefacts from coarse discretisation outside the region of interest become noticeable only for large differences in discretisation between subregions.
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| 2. |
- Wallstén, Elin, 1985-, et al.
(författare)
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A Study of Dynamic PET Frame-Binning on the Reference Logan Binding Potential
- 2017
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Ingår i: IEEE Transactions on Radiation and Plasma Medical Sciences. - : IEEE. - 2469-7311 .- 2469-7303. ; 1:2, s. 128-135
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Tidskriftsartikel (refereegranskat)abstract
- Objective: The reference Logan plot is a tool for determining the non-displaceable binding potential for dynamic PET exams using tracers with reversible bindings. Dynamic frame protocols affect noise in PET images and short frames can lead to quantitative uncertainties and noise-induced reconstruction bias. The aim of this study was to analyze the effect of frame binning on 11C-Raclopride striatal binding potential from reference Logan analysis. Methods: 12 healthy volunteers were scanned in list mode using 11C-raclopride, and the image data were reconstructed into 9 different frame binning schemes whereof 3 clinical schemes. Reconstruction was performed with 3 different algorithms, one based on filtered back projection (FBP) and two based on ordered subset expectation maximization (OSEM); one including resolution recovery. Logan plots were used for calculating the non-displaceable binding potential. Variation in binding potential was evaluated using Students t-tests. Results: It was found that frame lengths of up to 60 s gave significantly different results compared to the reference clinical protocol for OSEM, both with and without resolution recovery (maximum deviation: 10.3 % for the 15 s protocol). For FBP, frame lengths of up to 30 s gave significantly different results with a maximum deviation of 2.8 %. The higher sampling dependence of OSEM compared to FBP is likely due to noise-dependent bias in the OSEM algorithm, most apparent at high noise levels. Conclusions: Bias related to OSEM reconstruction of high-noise data is an important factor for dynamic PET protocols. Time frames of 120 s or more generate the most stable values for the striatum binding potential with the reference Logan plot for 11C-Raclopride brain PET.
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| 3. |
- DrAdda, Ilenia, et al.
(författare)
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A Statistical DOI Estimation Algorithm for a SiPM-Based Clinical SPECT Insert
- 2022
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Ingår i: IEEE Transactions on Radiation and Plasma Medical Sciences. - 2469-7311. ; 6:7, s. 771-777
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Tidskriftsartikel (refereegranskat)abstract
- A prototype clinical brain SPECT insert has been designed for use in simultaneous SPECT/MRI. The system utilises novel slit-slat collimators which, like pinhole collimators, suffers from parallax errors due to the large incident angle of photons. A statistical algorithm has been developed to determine the depth-of-interaction (DOI) with a view to improving image performance. The importance of DOI correction was demonstrated using Monte Carlo simulation. This simulation also indicated that 4 DOI layers (3×1.5 mm+3.5 mm) may be sufficient. The improvement in event localisation was demonstrated on a single detector before implementing the algorithm on the full clinical prototype where some limitations in event localisation in layers close to the readout plane were observed. Nevertheless DOI enabled the rejection of poorly localised events with improved resolution in reconstructed line sources.
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| 4. |
- Kim, Michele M., et al.
(författare)
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Development of Ultra-High Dose Rate (FLASH) Particle Therapy
- 2022
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Ingår i: IEEE Transactions on Radiation and Plasma Medical Sciences. - 2469-7311. ; 6:3, s. 252-262
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Tidskriftsartikel (refereegranskat)abstract
- Research efforts in FLASH radiotherapy have increased at an accelerated pace recently. FLASH radiotherapy involves ultra-high dose rates and has shown to reduce toxicity to normal tissue while maintaining tumor response in pre-clinical studies when compared to conventional dose rate radiotherapy. The goal of this review is to summarize the studies performed to-date with proton, electron, and heavy ion FLASH radiotherapy, with particular emphasis on the physical aspects of each study and the advantages and disadvantages of each modality. Beam delivery parameters, experimental set-up, and the dosimetry tools used are described for each FLASH modality. In addition, modeling efforts and treatment planning for FLASH radiotherapy is discussed along with potential drawbacks when translated into the clinical setting. The final section concludes with further questions that have yet to be answered before safe clinical implementation of FLASH radiotherapy.
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| 5. |
- Ljungberg, M., et al.
(författare)
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3-D Image-Based Dosimetry in Radionuclide Therapy
- 2018
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Ingår i: IEEE Transactions on Radiation and Plasma Medical Sciences. - 2469-7311. ; 2:6, s. 527-540
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Forskningsöversikt (refereegranskat)abstract
- Radionuclide therapy is the use of radioactive drugs for internal radiotherapy, mainly for the treatment of metastatic disease. As opposed to systemic cancer therapies in general, the use of radioactively labeled drugs results not only in a targeted therapy but also the possibility of imaging the distribution of the drug during therapy. From such images, the absorbed doses delivered to tumors and organs at risk can be calculated. Calculation of the absorbed dose from 3-D images such as single-photon emission computed tomography (SPECT)/CT, and in some cases positron emission tomography (PET)/CT, relies on image-based activity quantification. Quantification is accomplished by modeling the physics involved in the image-formation process, and applying image-processing methods. From a time-sequence of such quantitative images, the absorbed doses are then calculated. Although individual-patient dosimetry is a standard component of other forms of radiotherapy, it is still overlooked in the majority of radionuclide therapies. In this review, we summarize the physical and technical problems that need to be addressed in image-based dosimetry. The focus is on SPECT, since most of the radionuclides used are single-photon emitters, although the use of PET is also discussed. Practical issues of relevance for the practical implementation of personalized dosimetry in radionuclide therapy are also highlighted.
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| 6. |
- Velo, Alexandre F., et al.
(författare)
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99mTc/123I Dual-Radionuclide Correction for Self-Scatter, Down-Scatter, and Tailing Effect for a CZT SPECT With Varying Tracer Distributions
- 2023
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Ingår i: IEEE Transactions on Radiation and Plasma Medical Sciences. - 2469-7311. ; 7:8, s. 839-850
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Tidskriftsartikel (refereegranskat)abstract
- Single-photon emission computed tomography systems distinguish radionuclides by using multiple energy windows. For cadmium zinc telluride (CZT) detectors, the energy spectrum has a low-energy tail leading to additional crosstalk between the radionuclides. Previous work developed models to correct the scatter and crosstalk for CZT-based dedicated cardiac systems with similar 99mTc/123I tracer distributions. These models estimate the primary and scatter components by solving a set of equations employing the maximum-likelihood expectation–maximization approach. A penalty term is applied to ensure convergence. The present work estimates the penalty term for any 99mTc/123I activity level. An iterative approach incorporating Monte Carlo into the iterative image reconstruction loops was developed to estimate the penalty terms. We used SIMIND and extended cardiac-torso phantoms in this study. Distribution of tracers in the myocardial tissue and blood pool was varied to simulate a dynamic acquisition. Evaluations of the estimated and the real penalty terms were performed using simulations and large animal data. The myocardium to blood pool ratio was calculated using regions of interests in the myocardial tissue and the blood pool for quantitative analysis. All corrected images yielded a good agreement with the gold standard images. In conclusion, we developed a CZT crosstalk correction method for quantitative imaging of 99mTc/123I activity levels by dynamically estimating the penalty terms.
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