57 research outputs found
Novel Computer-Aided Detection of Respiratory Misregistration Artifacts in PET/CT
https://openworks.mdanderson.org/sumexp23/1083/thumbnail.jp
Investigating the Optimum Lower Energy Threshold of a New Research PET/CT Scanner
An investigation of the optimum 3D lower energy threshold (LET) setting of the Discovery-RX, a new LYSO based GE research PET/CT scanner is conducted. Sensitivity and noise equivalent count rate (NECR) performance of the scanner in 3D mode were evaluated at multiple LET settings: 400, 425, 450, 460, 470 and 480 KeV. The performance evaluations were conducted according to the NEMA NU2-2001 standard. In addition, the NECR was also evaluated for the same LET settings using the Data Spectrum whole body phantom in order to more accurately simulate a true clinical setting. For the sensitivity measurements, the line source was filled with 9.25 MBq of F-18. For the NECR measurements, the NEMA and the Data Spectrum phantoms were fitted with a line source having an initial activity of 1400 MBq of F-18. As expected, the sensitivity decreases with increasing LET. The sensitivity at 400 and 450 keV was 13.2% higher and 18.9% lower than the sensitivity at the scanners default LET of 425 keV. Also as expected, the scatter fraction (SF) decreased with increasing LET for both NECR phantoms. The NECR curve corresponding to the 450 keV had the highest values over the clinical range of activity concentration usually used. Initial performance evaluation suggests that a LET of 450 keV is the best setting for the phantoms tested. Further clinical tests are needed to validate this observation
Extracting respiratory signals from thoracic cone beam CT projections
Patient respiratory signal associated with the cone beam CT (CBCT)
projections is important for lung cancer radiotherapy. In contrast to
monitoring an external surrogate of respiration, such signal can be extracted
directly from the CBCT projections. In this paper, we propose a novel local
principle component analysis (LPCA) method to extract the respiratory signal by
distinguishing the respiration motion-induced content change from the gantry
rotation-induced content change in the CBCT projections. The LPCA method is
evaluated by comparing with three state-of-the-art projection-based methods,
namely, the Amsterdam Shroud (AS) method, the intensity analysis (IA) method,
and the Fourier-transform based phase analysis (FT-p) method. The clinical CBCT
projection data of eight patients, acquired under various clinical scenarios,
were used to investigate the performance of each method. We found that the
proposed LPCA method has demonstrated the best overall performance for cases
tested and thus is a promising technique for extracting respiratory signal. We
also identified the applicability of each existing method.Comment: 21 pages, 11 figures, submitted to Phys. Med. Bio
Spach Transformer: Spatial and Channel-wise Transformer Based on Local and Global Self-attentions for PET Image Denoising
Position emission tomography (PET) is widely used in clinics and research due
to its quantitative merits and high sensitivity, but suffers from low
signal-to-noise ratio (SNR). Recently convolutional neural networks (CNNs) have
been widely used to improve PET image quality. Though successful and efficient
in local feature extraction, CNN cannot capture long-range dependencies well
due to its limited receptive field. Global multi-head self-attention (MSA) is a
popular approach to capture long-range information. However, the calculation of
global MSA for 3D images has high computational costs. In this work, we
proposed an efficient spatial and channel-wise encoder-decoder transformer,
Spach Transformer, that can leverage spatial and channel information based on
local and global MSAs. Experiments based on datasets of different PET tracers,
i.e., F-FDG, F-ACBC, F-DCFPyL, and Ga-DOTATATE,
were conducted to evaluate the proposed framework. Quantitative results show
that the proposed Spach Transformer can achieve better performance than other
reference methods.Comment: 10 page
GPU-based Low Dose CT Reconstruction via Edge-preserving Total Variation Regularization
High radiation dose in CT scans increases a lifetime risk of cancer and has
become a major clinical concern. Recently, iterative reconstruction algorithms
with Total Variation (TV) regularization have been developed to reconstruct CT
images from highly undersampled data acquired at low mAs levels in order to
reduce the imaging dose. Nonetheless, TV regularization may lead to
over-smoothed images and lost edge information. To solve this problem, in this
work we develop an iterative CT reconstruction algorithm with edge-preserving
TV regularization to reconstruct CT images from highly undersampled data
obtained at low mAs levels. The CT image is reconstructed by minimizing an
energy consisting of an edge-preserving TV norm and a data fidelity term posed
by the x-ray projections. The edge-preserving TV term is proposed to
preferentially perform smoothing only on non-edge part of the image in order to
avoid over-smoothing, which is realized by introducing a penalty weight to the
original total variation norm. Our iterative algorithm is implemented on GPU to
improve its speed. We test our reconstruction algorithm on a digital NCAT
phantom, a physical chest phantom, and a Catphan phantom. Reconstruction
results from a conventional FBP algorithm and a TV regularization method
without edge preserving penalty are also presented for comparison purpose. The
experimental results illustrate that both TV-based algorithm and our
edge-preserving TV algorithm outperform the conventional FBP algorithm in
suppressing the streaking artifacts and image noise under the low dose context.
Our edge-preserving algorithm is superior to the TV-based algorithm in that it
can preserve more information of fine structures and therefore maintain
acceptable spatial resolution.Comment: 21 pages, 6 figures, 2 table
Imaging Long-Term Fate of Intramyocardially Implanted Mesenchymal Stem Cells in a Porcine Myocardial Infarction Model
The long-term fate of stem cells after intramyocardial delivery is unknown. We used noninvasive, repetitive PET/CT imaging with [18F]FEAU to monitor the long-term (up to 5 months) spatial-temporal dynamics of MSCs retrovirally transduced with the sr39HSV1-tk gene (sr39HSV1-tk-MSC) and implanted intramyocardially in pigs with induced acute myocardial infarction. Repetitive [18F]FEAU PET/CT revealed a biphasic pattern of sr39HSV1-tk-MSC dynamics; cell proliferation peaked at 33–35 days after injection, in periinfarct regions and the major cardiac lymphatic vessels and lymph nodes. The sr39HSV1-tk-MSC–associated [18F]FEAU signals gradually decreased thereafter. Cardiac lymphography studies using PG-Gd-NIRF813 contrast for MRI and near-infrared fluorescence imaging showed rapid clearance of the contrast from the site of intramyocardial injection through the subepicardial lymphatic network into the lymphatic vessels and periaortic lymph nodes. Immunohistochemical analysis of cardiac tissue obtained at 35 and 150 days demonstrated several types of sr39HSV1-tk expressing cells, including fibro-myoblasts, lymphovascular cells, and microvascular and arterial endothelium. In summary, this study demonstrated the feasibility and sensitivity of [18F]FEAU PET/CT imaging for long-term, in-vivo monitoring (up to 5 months) of the fate of intramyocardially injected sr39HSV1-tk-MSC cells. Intramyocardially transplanted MSCs appear to integrate into the lymphatic endothelium and may help improve myocardial lymphatic system function after MI
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