| 1. |
- Bae, Cheolyong, 1989-, et al.
(författare)
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High-Speed Chromatic Dispersion Compensation Filtering in FPGAs for Coherent Optical Communication
- 2020
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Ingår i: 2020 30th International Conference on Field-Programmable Logic and Applications (FPL). - : IEEE. - 9781728199023 - 9781728199030 ; , s. 357-358
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Konferensbidrag (refereegranskat)abstract
- Chromatic dispersion is one of the error sources limiting the transmission capacity in coherent optical communication that can be mitigated with digital signal processing. In this paper, the current status and plans of implementation of chromatic dispersion compensation (CDC) filters on FPGAs are discussed. As these high-speed filters are most efficiently implemented in the frequency-domain, different approaches for high-speed FFT-based architectures are considered and preliminary results of fully parallel FFT implementation by utilizing FPGA hardware features are presented.
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| 2. |
- Bae, Cheolyong, 1989-, et al.
(författare)
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Overlap-Save Commutators for High-Speed Streaming Data Filtering
- 2021
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Ingår i: 2021 IEEE International Symposium on Circuits and Systems (ISCAS). - : IEEE. - 9781728192017
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Overlap-save and overlap-add methods enable efficient implementation of FIR filters. In this paper, a compact method for handling the overlap and shuffle of samples for realtime processing using pipelined FFT architectures is presented. It is suitable for cases when the sample rate is equal to or higher than the clock frequency
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| 3. |
- Gustafsson, Oscar, 1989, et al.
(författare)
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An assessment of Bayesian IVIM model fitting
- 2016
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Ingår i: ISMRM 2016 Annual Meeting. 7-13 May, Singapore. - : International Society for Magnetic Resonance in Medicine.
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Konferensbidrag (refereegranskat)abstract
- Bayesian model fitting has been proposed as an alternative to the commonly used least squares fitting of the IVIM model. In this work we used Monte Carlo simulations to study the convergence of a Markov Chain Monte Carlo implementation of Bayesian model fitting and compared the resulting model parameters to two least squares model fitting methods. We saw that the convergence of the Bayesian model fitting procedure was affected by noise and compartment sizes. Bayesian model fitting was beneficial for the diffusion coefficient and the perfusion fraction, especially at low SNR
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| 4. |
- Gustafsson, Oscar, 1989, et al.
(författare)
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Can Cramer-Rao Lower Bound be used to find optimal b-values for IVIM?
- 2016
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Ingår i: ISMRM 2016 Annual Meeting. 7-13 May, Singapore. - : International Society for Magnetic Resonance in Medicine.
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Konferensbidrag (refereegranskat)abstract
- Cramer-Ráo Lower Bound is commonly used in experiment design optimization. Here we use it to find optimal b-value schemes for IVIM imaging. The optimization was generalized with regard to averaging and the characteristics of the results, given the input and the constraints, were studied. The resulting schemes never included more than the minimum number of four unique b-values, even though multiple sets of tissue parameters were included in the optimization. The optimized b-value schemes were compared to a typical one using simulations.
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| 7. |
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| 8. |
- Gustafsson, Oscar, 1989, et al.
(författare)
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Impact of prior distributions and central tendency measures on Bayesian intravoxel incoherent motion model fitting
- 2018
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Ingår i: Magnetic Resonance in Medicine. - : Wiley. - 0740-3194 .- 1522-2594. ; 79:3, s. 1674-1683
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Tidskriftsartikel (refereegranskat)abstract
- © 2017 International Society for Magnetic Resonance in Medicine.Purpose: Bayesian model fitting has been proposed as a robust alternative for intravoxel incoherent motion (IVIM) model-fitting parameter estimation. However, consensus regarding choice of prior distribution and posterior distribution central tendency measure is needed. The aim of this study was to compare the quality of IVIM parameter estimates produced by different prior distributions and central tendency measures, and to gain knowledge about the effect of these choices. Methods: Three prior distributions (uniform, reciprocal, and lognormal) and two measures of central tendency (mean and mode) found in the literature were studied using simulations and in vivo data from a tumor mouse model. Results: Simulations showed that the uniform and lognormal priors were superior to the reciprocal prior, especially for the parameters D and f and clinically relevant SNR levels. The choice of central tendency measure had less effect on the results, but had some effects on estimation bias. Results based on simulations and in vivo data agreed well, indicating high validity of the simulations. Conclusions: Choice of prior distribution and central tendency measure affects the results of Bayesian IVIM parameter estimates. This must be considered when comparing results from different studies. The best overall quality of IVIM parameter estimates was obtained using the lognormal prior.
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| 11. |
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IVIM reveals increased blood perfusion of liver metastases after oral intake of Salovum®
- 2015
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Ingår i: Magnetic Resonance Materials in Physics, Biology and Medicine. - : Springer Science and Business Media LLC. - 0968-5243 .- 1352-8661.
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Proceedings (redaktörskap) (övrigt vetenskapligt/konstnärligt)abstract
- Introduction Elevated interstitial fluid pressure (IFP) of tumours impairs perfusion, which hinders anti-cancer drugs and oxygen to reach tumour cells1-3. AF-16, a 16 amino acid long sequence from the amino terminal end of the endogenous protein Antisecretory Factor (AF), supresses IFP in animal models of solid tumours4, and could improve drug delivery to tumour cells. Salovum®, a spray-dried egg yolk powder with high content of antisecretory peptides, should be tested on humans, but requires non-invasive tumour IFP/perfusion assessment methods. The IntraVoxel Incoherent Motion (IVIM) model applied to multi-b DWI enables measurement of tissue diffusion (D), pseudo-diffusion (D*) and voxel volume fraction of actively perfused capillaries (f) 5. The aim of this study was to investigate if f could be used to monitor changes induced by Salovum® in colorectal liver metastases in vivo Subjects and Methods Previously untreated patients (n=6) with colorectal liver metastases were imaged before, and 24h after intake of Salovum®, using IVIM-MRI (3T Philips, 16‐channel receiver; Single-shot, SE‐EPI (breath-hold); FOV covering liver, 3x3x5mm3 voxels; TR/TE/NSA/SENSE=1900ms/50ms/2/2; 11 b‐values (0-600); acquisition~10 min. MATLAB-based images processing comprised 1) Inter-scan image registration (volume preserving free-form deformation6); 2) Voxelwise fitting of D and A [eq.2] to S(b200-600) (for b>200, [eq.1] reduces to [eq.2], assuming D<2cm) on DWI (b=600), transfer of ROIs to corresponding f-maps for calculation of median ROI f before and after Salovum® intake and 4) Mann-Whitney U-test for statistical significance (α-level=0.05). Results Liver and metastases were well visualised on DWIs and f-maps Median f in metastatic tissue increased after intake of Salovum® in 5/6 patients, but decreased in one patient (Fig.2) (p<0.0001). Discussion/Conclusion The increased perfusion fraction on day 2 may offer a “window of opportunity” for improved transport of drugs to tumour cells. The increase in f was small, and perhaps not clinically significant, suggesting that additional time points after Salovum® intake and dose escalation be investigated, as well as intra-tumour effect heterogeneity. The proposed IVIM approach is a promising, non-invasive method for studying Salovum® induced changes in liver metastases in vivo. Further optimisation and fractionation studies should be conducted, and IVIM derived parameters should be compared to other techniques for perfusion or IFP measurements. References 1Rofstad,E.K.,et al.,Neoplasia. 2009;11(11):1243-51. 2Milosevic,M.F.,et al.,1999;43(5):1111-23. 3Wiig, H.,et al.,1982;42(2):159-64. 4Al-Olama, M.et al., 2011;50(7):1098-104. 5Le Bihan, D., et al., 1988;168(2):497-505. 6Rueckert, D., et al., 1999;18(8):712-21.
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| 12. |
- Lilja, Ylva, et al.
(författare)
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Impact of region-of-interest method on quantitative analysis of DTI data in the optic tracts
- 2016
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Ingår i: Bmc Medical Imaging. - : Springer Science and Business Media LLC. - 1471-2342. ; 16
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Tidskriftsartikel (refereegranskat)abstract
- Background: To extract DTI parameters from a specific structure, a region of interest (ROI) must be defined. ROI selection in small structures is challenging; the final measurement results could be affected due to the significant impact of small geometrical errors. In this study the optic tracts were analyzed with the aim to assess differences in DTI parameters due to ROI method and to identify the most reliable method. Methods: Images of 20 healthy subjects were acquired. Fractional anisotropy (FA) was extracted from the optic tracts by four different ROI methods. Manual tracing was performed in 1) the b0 image and 2) a T1-weighted image registered to the FA image. Semi-automatic segmentation was performed based on 3) tractography and 4) the FA-skeleton algorithm in the tract-based spatial statistics (TBSS) framework. Results were analyzed with regard to ROI method as well as to inter-scan, intra-rater and inter-rater reliability. Results: The resulting FA values divided the ROI methods into two groups that differed significantly: 1) the FA-skeleton and the b0 methods showed higher FA values compared to 2) the tractography and the T1-weighted methods. The intra-and inter-rater variabilities were similar for all methods, except for the tractography method where the inter-rater variability was higher. The FA-skeleton method had a better reproducibility than the other methods. Conclusion: Choice of ROI method was found to be highly influential on FA values when the optic tracts were analyzed. The FA-skeleton method performed the best, yielding low variability and high repeatability.
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| 13. |
- Lilja, Ylva, et al.
(författare)
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Impact of ROI method on quantitative analysis of DTI
- 2015
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Ingår i: Magnetic Resonance Materials in Physics, Biology and Medicine. - : Springer Science and Business Media LLC. - 0968-5243 .- 1352-8661. ; 28:suppl 1
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Konferensbidrag (refereegranskat)
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| 14. |
- Lilja, Ylva, et al.
(författare)
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Visual pathway impairment by pituitary adenomas: quantitative diagnostics by diffusion tensor imaging.
- 2017
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Ingår i: Journal of neurosurgery. - 1933-0693. ; 127:3, s. 569-579
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE Despite ample experience in surgical treatment of pituitary adenomas, little is known about objective indices that may reveal risk of visual impairment caused by tumor growth that leads to compression of the anterior visual pathways. This study aimed to explore diffusion tensor imaging (DTI) as a means for objective assessment of injury to the anterior visual pathways caused by pituitary adenomas. METHODS Twenty-three patients with pituitary adenomas, scheduled for transsphenoidal tumor resection, and 20 healthy control subjects were included in the study. A minimum suprasellar tumor extension of Grade 2-4, according to the SIPAP (suprasellar, infrasellar, parasellar, anterior, and posterior) scale, was required for inclusion. Neuroophthalmological examinations, conventional MRI, and DTI were completed in all subjects and were repeated 6 months after surgery. Quantitative assessment of chiasmal lift, visual field defect (VFD), and DTI parameters from the optic tracts was performed. Linear correlations, group comparisons, and prediction models were done in controls and patients. RESULTS Both the degree of VFD and chiasmal lift were significantly correlated with the radial diffusivity (r = 0.55, p < 0.05 and r = 0.48, p < 0.05, respectively) and the fractional anisotropy (r = -0.58, p < 0.05 and r = -0.47, p < 0.05, respectively) but not with the axial diffusivity. The axial diffusivity differed significantly between controls and patients with VFD, both before and after surgery (p < 0.05); however, no difference was found between patients with and without VFD. Based on the axial diffusivity and fractional anisotropy, a prediction model classified all patients with VFD correctly (sensitivity 1.0), 9 of 12 patients without VFD correctly (sensitivity 0.75), and 17 of 20 controls as controls (specificity 0.85). CONCLUSIONS DTI could detect pathology and degree of injury in the anterior visual pathways that were compressed by pituitary adenomas. The correlation between radial diffusivity and visual impairment may reflect a gradual demyelination in the visual pathways caused by an increased tumor effect. The low level of axial diffusivity found in the patient group may represent early atrophy in the visual pathways, detectable on DTI but not by conventional methods. DTI may provide objective data, detect early signs of injury, and be an additional diagnostic tool for determining indication for surgery in cases of pituitary adenomas.
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| 15. |
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| 16. |
- Montelius, Mikael, 1979, et al.
(författare)
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Multiparametric MRI with spatiotemporal evaluation reveals potential therapy response biomarkers for 177Lu-octreotate therapy of mice with human neuroendocrine tumor
- 2017
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Ingår i: ISMRM 25th Annual Meeting. 22-27 April 2017, Honolulu, Hawaii, USA.
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Konferensbidrag (refereegranskat)abstract
- Tissue parameters derived from multiparametric MRI were evaluated as potential imaging biomarkers for therapy response assessment in mice with human neuroendocrine tumor treated with 177Lu-octreotate. Animals were imaged before and repeatedly after 177Lu-octreotate treatment, using T2w, IVIM-DWI, DCE-MRI, T1- and T2*-mapping techniques. MR-parameters were evaluated regionally and longitudinally, and quantitative proteomics was used to evaluate underlying biological response in central and peripheral tumor separately. Several MR-parameters showed strong correlation with tumor response, as verified by MRI-based tumor volume measurements, but also with proteins associated with radiobiological effects on tumor tissue. Spatial and temporal evaluation increased sensitivity of the methods.
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