| 1. |
- Ardonne, Eddy, et al.
(författare)
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Degeneracy of non-Abelian quantum Hall states on the torus : domain walls and conformal field theory
- 2008
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Ingår i: Journal of Statistical Mechanics. - 1742-5468. ; , s. P04016-
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Tidskriftsartikel (refereegranskat)abstract
- We analyze the non-Abelian Read–Rezayi quantum Hall states on the torus, where it is natural to employ a mapping of the many-body problem onto a one-dimensional lattice model. On the thin torus—the Tao–Thouless (TT) limit—the interacting many-body problem is exactly solvable. The Read–Rezayi states at filling ν = k/(kM+2) are known to be exact ground states of a local repulsive k+1-body interaction, and in the TT limit this is manifested in that all states in the ground state manifold have exactly k particles on any kM+2 consecutive sites. For M \neq 0 the two-body correlations of these states also imply that there is no more than one particle on M adjacent sites. The fractionally charged quasiparticles and quasiholes appear as domain walls between the ground states, and we show that the number of distinct domain wall patterns gives rise to the nontrivial degeneracies, required by the non-Abelian statistics of these states. In the second part of the paper we consider the quasihole degeneracies from a conformal field theory (CFT) perspective, and show that the counting of the domain wall patterns maps one to one on the CFT counting via the fusion rules. Moreover we extend the CFT analysis to topologies of higher genus
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| 2. |
- Bergholtz, E. J., et al.
(författare)
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Pfaffian quantum Hall state made simple : Multiple vacua and domain walls on a thin torus
- 2006
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 74:8, s. 081308-
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Tidskriftsartikel (refereegranskat)abstract
- We analyze the Moore-Read Pfaffian state on a thin torus. The known sixfold degeneracy is realized by two inequivalent crystalline states with a four- and twofold degeneracy, respectively. The fundamental quasihole and quasiparticle excitations are domain walls between these vacua, and simple counting arguments give a Hilbert space of dimension 2n−1 for 2n−k holes and k particles at fixed positions and assign each a charge ±e∕4. This generalizes the known properties of the hole excitations in the Pfaffian state as deduced using conformal field theory techniques. Numerical calculations using a model Hamiltonian and a small number of particles support the presence of a stable phase with degenerate vacua and quarter-charged domain walls also away from the thin-torus limit. A spin-chain Hamiltonian encodes the degenerate vacua and the various domain walls.
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| 3. |
- Birnbaum, Daniel, et al.
(författare)
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Thirteen questions about the object to Graham Harman
- 2020
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Ingår i: Artful objects : Graham Harman on art and the business of speculative realism. - Berlin ; Stockholm : Sternberg Press ; Stockholm School of Economics. - 9783956795244 ; , s. 43-72
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 4. |
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| 5. |
- Fischer, Sara, et al.
(författare)
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Comparisons of Intracranial Volume and Cephalic Index After Correction of Sagittal Craniosynostosis With Either Two or Three Springs
- 2021
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Ingår i: The Journal of craniofacial surgery. - 1536-3732. ; 32:8, s. 2636-2640
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Tidskriftsartikel (refereegranskat)abstract
- ABSTRACT: In this retrospective study, the authors determined changes in intracranial volume (ICV) and cephalic index (CI) in patients with sagittal craniosynostosis and operated with craniotomy combined with either 2 or 3 springs. The authors included patients (n=112) with complete follow-up that had undergone surgical correction for isolated sagittal craniosynostosis with craniotomy combined with springs between 2008 and 2017. All patients underwent computed tomography examination preoperative, at the time of spring extraction, and at 3years of age. Intracranial volume was measured using a semiautomatic MATLAB program, and CI was calculated as the width/length of the skull. The authors found that craniotomy combined with 2 springs increased the ICV from a preoperative value of 792±113mL (mean±standard deviation) to 1298±181mL at 3years of age and increased the CI from 72.1±4.1 to 74.6±4.3, whereas craniotomy combined with 3 springs increased the ICV from 779±128mL to 1283±136mL and the CI from 70.7±4.3 to 74.8±3.7. The relative increase in ICV was 65±21% in the two-spring group and 68±34% in the three-spring group (P value=0.559), and the relative increase in CI was 3.6±3.3% in the two-spring group as compared with 6.0±5.0% in the three-spring group (P=0.004). These findings demonstrated that use of 3 springs resulted in additional absolute and relative CI-specific effects as compared with 2 springs during the time when the springs were in place, with this effect maintained at 3years of age.
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| 6. |
- Fischer, Sara, et al.
(författare)
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Intracranial volume is normal in infants with sagittal synostosis.
- 2015
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Ingår i: Journal of plastic surgery and hand surgery. - 2000-6764. ; 49:1, s. 62-64
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Tidskriftsartikel (refereegranskat)abstract
- Abstract Premature sagittal synostosis results in an elongated, narrow skull shape, scaphocephaly. It has been unclear whether the intracranial volume (ICV) of these children is different from that of normal children. The aim of the present study was to precisely determine the ICV in a large cohort of children with premature sagittal synostosis and to compare it to the ICV of a sex- and age-matched control group. All patients (n = 143) with isolated sagittal synostosis registered in the Göteborg Craniofacial Registry until the end of 2012 with a preoperative CT examination were identified. For each case, a sex- and age- (±30 days) matched control was identified from children who had undergone CT for post-traumatic or neurological reasons. The ICV was measured in a semi-automatic MATLAB program with functions such as region growing, watershed, and thresholding in axial CT slices. The ICV was calculated using the Cavalieri principle. The mean (± SEM) values of ICV for children with sagittal synostosis and for corresponding controls were 866 ± 13 ml and 870 ± 15 ml, respectively. The mean ages of these groups were 173 ± 8 days and 172 ± 8 days, respectively. Subgroup analysis of sex and age at CT (≤180 days and >180 days) did not reveal any differences in ICV between cases and controls. Precise determination of ICV in addition to the use of adequate controls has made it possible to conclude that children with premature isolated sagittal synostosis have a normal ICV.
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| 7. |
- Hagmarker, Linn, et al.
(författare)
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A new quantitative image-based method for evaluation of bony temporal hollowing in metopic synostosis
- 2016
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Ingår i: Journal of Plastic Surgery and Hand Surgery. - : Medical Journals Sweden AB. - 2000-656X .- 2000-6764. ; 50:6, s. 343-348
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Tidskriftsartikel (refereegranskat)abstract
- Objective: Premature craniosynostosis is a congenital disorder causing a skull deformity. For both functional and cosmetic reasons, the deformity is surgically treated with a cranioplasty before the age of 1 year. Temporal hollowing is a common and undesirable remaining deformity after cranioplasty for metopic synostosis. The most common method to determine the degree of temporal hollowing is subjective judgement of the temporal region. The aim of the present project was to develop a quantitative semi-automatic computer tool for objective measurement of bony temporal hollowing. Methods: Using MATLAB, a tool was developed to segment computed tomography images, defining the outermost contour. The images were dorsally limited to the widest point of the head. In each case, a sex-and age-matched control was identified and the contours compared. The bony temporal hollowing of the cases was calculated. Results: The intra-user coefficient of variation (CV) was 5.0% (95% CI = 4.2%-6.2%) and the inter-user CV was 3.0% (95% CI = 2.1%-8.6%). For clinical testing purposes, the tool was used in 14 patients, seven of whom had been operated on with a spring-assisted cranioplasty and seven with a cranioplasty using a bone graft. Conclusions: In summary, this study presents a new tool for objective measurement of the surgical result after cranioplasty for metopic synostosis.
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| 8. |
- Levin, Sofia, et al.
(författare)
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Kreativitet och kapital på arkitektkontoret
- 2013
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Ingår i: Kreativt kapital: ledning och organisering i kulturella och kreativa näringar. - Stockholm : 8tto. - 9789187419065
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 9. |
- Magnander, Tobias, et al.
(författare)
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A novel statistical analysis method to improve the detection of hepatic foci of (111)In-octreotide in SPECT/CT imaging.
- 2016
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Ingår i: EJNMMI physics. - : Springer Science and Business Media LLC. - 2197-7364. ; 3:1
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Tidskriftsartikel (refereegranskat)abstract
- Low uptake ratios, high noise, poor resolution, and low contrast all combine to make the detection of neuroendocrine liver tumours by (111)In-octreotide single photon emission tomography (SPECT) imaging a challenge. The aim of this study was to develop a segmentation analysis method that could improve the accuracy of hepatic neuroendocrine tumour detection.
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| 10. |
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| 11. |
- Magnander, Tobias, et al.
(författare)
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Improved detection rate and visualization of liver uptake foci in diagnostic 111In-octreotide SPECT/CT investigations with a novel segmentation analysis
- 2015
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Ingår i: Optimisation in X-ray and Molecular Imaging 2015 - the Fourth Malmö Conference on Medical Imaging, Gothenburg, Sweden, 28-30 May 2015.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Purpose: Detection of liver tumors will change the course of treatment of neuroendocrine tumours. In nuclear medicine 111In-octreoscan is of high value for detection of neuroendocrine tumours. However, neuroendocrine tumours disseminated to the livers is often challenging to detect from 111In-octreoscan SPECT images due to low uptake, high noise, poor resolution and low contrast. The aim of the present study was to develop a segmentation analysis method for increased diagnostic accuracy of neuroendocrine liver tumours. Methods: For the SPECT reconstruction 120 projections are acquired with 3 degrees spacing around the patient injected with 111In-octreoscan. The projections are reconstructed into a 128x128x128 voxel matrix using OSEM with CT based attenuation correction. The liver is segmented from the SPECT or CT using either an isosurface, region growing or a GPU accelerated level set algorithm. Manual editing finishes the segmentation of the liver. The segmented liver volume of interest, liver VOI, is thresholded at 125 equidistant threshold values between 0 and the maximum voxel value. At each threshold value a connected component labeling algorithm is used to calculate the number of uptake foci (NUF). The normalized NUF (nNUF) is then plotted against the threshold index (ThI), defined as ThI=(cmax-cthr)/cmax, where cmax is the maximal voxel value in the VOI, and cthr is the voxel threshold value. The method is named nNUFTI - normalized Number of Uptake Foci vs ThI. The ThI at 0.25 nNUF was used for analysis of liver tumour involvement. SPECT images from 53 patients without tumour involvement (i.e SPECT negative) in the liver were analysed with nNUFTI. A three year follow up with MRI, SPECT, PET/CT and CT was used to separate the patients into two groups: the healthy group, with still no liver tumours, and the malignant group, shown to have developed tumours in the liver. Results: 40 patients ended up in the healthy group and 13 in the malignant group. The ThI at 0.25 nNUF was significantly different between the groups (p<0.01). A probability function for the ThI values was constructed from the obtained data. This relationship might be a useful guide in the diagnostic decision making. Conclusions: Our new developed method nNUFTI has been shown to perform well. More studies on the nNUFTI method are needed.
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| 12. |
- Maltese, Giovanni, 1974, et al.
(författare)
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Intracranial volume before and after surgical treatment for isolated metopic synostosis.
- 2014
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Ingår i: The Journal of craniofacial surgery. - 1536-3732. ; 25:1, s. 262-266
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Tidskriftsartikel (refereegranskat)abstract
- Metopic synostosis results in a keel-shaped forehead, hypotelorism, and an increased interparietal width. This study aimed to measure the frontal and total intracranial volume in patients with metopic synostosis before and after surgery and to compare the effect of 2 different operation methods. All patients operated for isolated metopic synostosis between 2002 and 2008 at Sahlgrenska University Hospital who had undergone preoperative and/or postoperative computed tomographic examination (at 3 y of age) were included. The patients were grouped according to operation method: (1) forehead remodeling in combination with a bone graft or (2) forehead remodeling in combination with a spring. Sex- and age-matched controls were identified. A previously developed MATLAB computer program was used to measure the frontal and total intracranial volumes. Sixty patients and 198 controls were included. Preoperatively, the patients with metopic synostosis had significantly lower frontal volumes than those of the controls (P < 0.001) but equal total intracranial volumes. The operations redistributed the intracranial volume and resulted in an improved, frontal-total intracranial volume ratio. However, at 3 years of age, the frontal volume (P < 0.001), total intracranial volume (P ≤ 0.002), and ratio between the 2 (P < 0.001) were significantly lower in the patients than in the controls. The 2 operation methods were equally efficient in creating an improved frontal-total ratio. Surgery for metopic synostosis improves the distribution of the intracranial volume but does not result in normal total intracranial volume or frontal volume at 3 years of age.
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| 13. |
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| 14. |
- Ryden, T., et al.
(författare)
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IMPROVEMENTS OF (IN)-I-111 SPECT IMAGES RECONSTRUCTED WITH SPARSELY ACQUIRED PROJECTIONS BY DEEP LEARNING GENERATED SYNTHETIC PROJECTIONS
- 2021
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Ingår i: Radiation Protection Dosimetry. - : Oxford University Press (OUP). - 0144-8420 .- 1742-3406. ; 195:3-4, s. 152-157
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Tidskriftsartikel (refereegranskat)abstract
- The aim was to improve single-photon emission computed tomography (SPECT) quality for sparsely acquired In-111 projections by adding deep learning generated synthetic intermediate projections (SIPs). Method: The recently constructed deep convolutional network for generating synthetic intermediate projections (CUSIP) was used for improving 20 sparsely acquired In-111-octreotide SPECTs. Reconstruction was performed with 120 (120P) or 30 (30P) projections, or 120 projections with 90 SIPs generated from 30 projections (30-120SIP). The SPECT reconstructions were performed with attenuation, scatter and collimator response corrections. Postfiltered 30P reconstructed SPECT was also analyzed. Image quality were quantitatively evaluated with root-mean-square error, peak signal-to-noise ratio and structural similarity index metrics. Result: The 30-120SIP reconstructed SPECT had statistically significant improved image quality parameters compared to 30P reconstructed SPECT with and without post filtering. The images visual appearance was similar to slightly filtered 120P SPECTs. Thereby, substantial acquisition time reduction with SIPs seems possible without image quality degradation.
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| 15. |
- Söfteland, Madiha Bhatti, 1977, et al.
(författare)
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Temporal Deformity Objectively Measured before and after Surgery for Metopic Synostosis: Retrusion Rather than Hollowing
- 2017
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Ingår i: Journal of Craniofacial Surgery. - 1049-2275. ; 28:7, s. 1757-1760
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Tidskriftsartikel (refereegranskat)abstract
- The temporal contour deformity typical of metopic synostosis is often referred to as temporal hollowing, but has not been quantitatively defined. This deformity is present before surgery and remains to a varying extent at long-term follow-up. The present study aimed to objectively evaluate the degree of this contour deformity in metopic synostosis before and after surgical correction. All children surgically treated for metopic synostosis at Sahlgrenska University Hospital between 2002 and 2014 (n = 120) with appropriate computed tomography scans (n = 160) performed preoperatively and/or at follow-up at 3 years of age were included. Depending on age, 1 of 2 surgical techniques was used. Children presenting before the age of 6 months were treated with frontal remodeling in combination with a spring (S group), whereas children older than 6 months were treated with a bone transplant (BT group). The bony temporal deformity was measured with a semiautomatic MATLAB program and patients were compared to sex-and age-matched controls. The deformity was significantly reduced in both groups (P < 0.001). In the S group, it was reduced from a mean ± standard deviation of 3.6 ± 1.9% to 1.0 ± 1.2% and in the BT group, it was reduced from 3.3% ± 1.4% to 1.1% ± 0.8%. The contour deformity in metopic synostosis is present both before and after surgery and should therefore be termed temporal retrusion (TR). This assessment method enables objective comparison of TR before and after surgical correction and is a potential tool to evaluate TR in metopic synostosis. © 2017 by Mutaz B. Habal, MD.
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| 16. |
- Söfteland, Madiha Bhatti, 1977, et al.
(författare)
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The Degree of Surgical Frontal Volume Correction in Metopic Synostosis Determines Long-Term Outcomes
- 2017
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Ingår i: Journal of Craniofacial Surgery. - : Ovid Technologies (Wolters Kluwer Health). - 1049-2275. ; 28:5, s. 1161-1163
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Tidskriftsartikel (refereegranskat)abstract
- Metopic synostosis results in a keel-shaped forehead, reduced frontal intracranial volume (ICV), and lower frontal to total volume ratio. The ratio improves with cranioplasty, but at 3 years of age, the ratio is still not normalized when compared to that in normal children. The aim of the present study was to investigate whether a low frontal to total ICV ratio at 3 years of age was due to relapse or insufficient correction.All children surgically treated for metopic synostosis in combination with a spring at Sahlgrenska University Hospital with subsequent spring extraction between 2002 and 2008 (n=20) were included. A MATLAB program was used to measure frontal and total ICV.Preoperatively, the frontal to total ICV ratio was 9.81.3% (mean +/- standard deviation). At spring removal, 6 months after cranioplasty, the ratio had increased to 11.8 +/- 2.4%. At 3 years of age, the ratio was 11.6 +/- 1.9%. In age-matched normal children, the ratio was 14.4 +/- 1.9% preoperatively, 15.3 +/- 2.2% at time of spring extraction, and 13.4 +/- 1.4% at 3 years of age.Cranioplasty thus improved the frontal to total ICV ratio, but did not normalize it. The ratio did not change from 6 months after the cranioplasty to 3 years of age. These results indicate that a more pronounced frontal volume correction during cranioplasty is necessary to achieve a normalized distribution of ICV in metopic synostosis.
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| 17. |
- Tovetjärn, Robert, 1982, et al.
(författare)
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Intracranial volume in 15 children with bilateral coronal craniosynostosis.
- 2014
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Ingår i: Plastic and reconstructive surgery. Global open. - 2169-7574. ; 2:11
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Tidskriftsartikel (refereegranskat)abstract
- Intracranial volume (ICV) growth in patients with bilateral coronal craniosynostosis (BCS) is not well described. It is therefore important to evaluate the consequences of cranial surgery in children with this condition. The aim of the present study was to evaluate ICVs in patients operated on for BCS.
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| 18. |
- Unander-Scharin, Jesper, et al.
(författare)
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Springs produce favorable morphological outcomes compared to H-Craniectomy in a two-center comparison of matched cases
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- AbstractSagittal synostosis is the most common type of premature suture closure and many surgical techniques are used for correction of the scaphocephalic skull shape. Direct comparisons of the outcome of different surgical techniques for correction of craniosynostosis are rare. The aim of the present study was to compare the outcome of craniotomy combined with springs and H-craniectomy for non-syndromic sagittal synostosis. This study was enabled by the synchronization of pre- and postoperative imaging, follow-up and data collection for the two craniofacial national referral centers in Sweden, using two fundamentally different surgical techniques - Craniotomy with springs (Gothenburg) and H-Craniectomy (Uppsala). Twenty-three pairs of patients matched for sex and preoperative cephalic index (CI) were included. CI, total intracranial volume and partial intracranial volumes were measured before surgery and at 3 years of age. Perioperative data including operation time, blood loss, volume of transfused blood and length of hospital stay were also gathered.Craniotomy with springs had less bleeding and lower transfusion rates than H-craniectomy. However, the spring-assisted surgery requires two operations. Three spring-related complications occurred . The total surgery time was similar for both groups. Most importantly, in the compiled analysis of changes in CI and partial volume distribution, the craniotomy combined with springs was demonstrated to produce a superior morphological correction.
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| 19. |
- Wikberg, Emma, et al.
(författare)
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A new computer tool for systematic evaluation of intracranial volume and its capacity to evaluate the result of the operation for metopic synostosis.
- 2012
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Ingår i: Journal of plastic surgery and hand surgery. - 2000-6764. ; 46:6, s. 393-8
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Tidskriftsartikel (refereegranskat)abstract
- Abstract The aim of this project was to develop a tool for systematic evaluation of volumetric changes after surgery for craniosynostosis. A computer program using MATLAB was developed to measure total intracranial volume and frontal volume, anterior to the coronary sutures, by multiplying the area with slice thickness of each slice from just above foramen magnum to just beneath the vertex in CT examinations. The ratio between frontal volume and total volume was used for evaluation of the clinical result in 12 patients operated on for metopic synostosis. In 0.625 and 5 millimetre slices the coefficients of variation were 0.00049 and 0.00058, respectively, for measurements of total volume. The highest coefficient of variation was found in postoperative measurements of the frontal volume and was 0.014 in 0.625 millimetre slices. Measurements in 5 millimetre slices resulted in 3.8% ± 1.5% (mean ± SD) lower total volumes and 5.8% ± 5.3% lower frontal volumes than measurements in 0.625 millimetre slices. In patients operated on for metopic synostosis the ratio between frontal volume and total volume increased 25% ± 16% for patients operated on with cranioplasty in combination with a spring (n = 6) and 20% ± 13% for patients operated on with cranioplasty in combination with a bone transplant (n = 6). In summary, this study has developed a tool that can determine frontal and total intracranial volume with little variation. This tool can be used for systematic evaluation of the result of the operation for metopic synostosis.
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| 20. |
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| 21. |
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| 22. |
- Wikberg, Emma, et al.
(författare)
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Evaluation of reconstruction methods and image noise levels concerning visual assessment of simulated liver lesions in In-111-octreotide SPECT imaging
- 2023
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Ingår i: EJNMMI Physics. - 2197-7364. ; 10:1
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Tidskriftsartikel (refereegranskat)abstract
- Background: Early cancer detection is crucial for patients' survival. The image quality in In-111-octreotide SPECT imaging could be improved by using Monte Carlo (MC)-based reconstruction. The aim of this observational study was to determine the detection rate of simulated liver lesions for MC-based ordered subset expectation maximization (OSEM) reconstruction compared to conventional attenuation-corrected OSEM reconstruction.MethodsThirty-seven SPECT/CT examinations with In-111-octreotide were randomly selected. The inclusion criterion was no liver lesions at the time of examination and for the following 3 years. SPECT images of spheres representing lesions were simulated using MC. The raw data of the spheres were added to the raw data of the established healthy patients in 26 of the examinations, and the remaining 11 examinations were not modified. The images were reconstructed using conventional OSEM reconstruction with attenuation correction and post filtering (fAC OSEM) and MC-based OSEM reconstruction without and with post filtering (MC OSEM and fMC OSEM, respectively). The images were visually and blindly evaluated by a nuclear medicine specialist. The criteria evaluated were liver lesion yes or no, including coordinates if yes, with confidence level 1-3. The percentage of detected lesions and accuracy (percentage of correctly classified cases), as well as tumor-to-normal tissue concentration (TNC) ratios and signal-to-noise ratios (SNRs), were evaluated.ResultsThe detection rates were 30.8% for fAC OSEM, 42.3% for fMC OSEM, and 50.0% for MC OSEM. The accuracies were 45.9% for fAC OSEM, 45.9% for fMC OSEM, and 54.1% for MC OSEM. The number of false positives was higher for fMC and MC OSEM. The observer's confidence level was higher in filtered images than in unfiltered images. TNC ratios were significantly higher, statistically, with MC OSEM and fMC OSEM than with AC OSEM, but SNRs were similar due to higher noise with MC OSEM.ConclusionOne in two lesions were found using MC OSEM versus one in three using conventional reconstruction. TNC ratios were significantly improved, statistically, using MC-based reconstruction, but the noise levels increased and consequently the confidence level of the observer decreased. For further improvements, image noise needs to be suppressed.
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| 23. |
- Wikberg, Emma, et al.
(författare)
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EVALUATION OF THE SPATIAL RESOLUTION IN MONTE CARLO-BASED SPECT/CT RECONSTRUCTION OF (IN)-I-111-OCTREOTIDE IMAGES
- 2021
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Ingår i: Radiation Protection Dosimetry. - : Oxford University Press (OUP). - 0144-8420 .- 1742-3406. ; 195:3-4, s. 319-326
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Tidskriftsartikel (refereegranskat)abstract
- The purpose was to evaluate the spatial resolution in In-111-octreotide single-photom emission computed tomography (SPECT)/computed tomography (CT) imaging following reconstructions with three different ordered subset expectation maximizations (OSEM) reconstruction algorithms; attenuation corrected (AC) OSEM, AC OSEM with resolution recovery (ACRR OSEM) and Monte Carlo-based OSEM reconstruction (MC OSEM). SPECT/CT imaging of a triple line phantom containing In-111 in air and water was performed. The spatial resolution, represented by the full width at half maximum (FWHM) of a line profile, was determined for each line, for X and Y direction and for all reconstructions. The mean FWHM was 12.2 mm (+/- standard deviation [SD] 3.7 mm) for AC OSEM, 9.3 mm (+/- SD 2.5 mm) for ACRR OSEM and 8.2 mm (+/- SD 2.0 mm) for MC OSEM. MC-based SPECT/CT reconstruction clearly improves the spatial resolution in In-111-octreotide imaging and since MC simulations can be performed for all photon energies MC OSEM has the potential to improve SPECT/CT imaging overall.
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| 24. |
- Wikberg, Emma, 1982-, et al.
(författare)
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Fractional domain walls from on-site softening in dipolar bosons
- 2012
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 85:3, s. 033607-
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Tidskriftsartikel (refereegranskat)abstract
- We study dipolar bosons in a 1D optical lattice and identify a region in parameter space-strong coupling but relatively weak on-site repulsion-hosting a series of stable charge-density-wave (CDW) states whose low-energy excitations, built from fractional domain walls, have remarkable similarities to those of non-Abelian fractional quantum Hall states. Here, a conventional domain wall between translated CDW's may be split by inserting strings of degenerate, but inequivalent, CDW states. Outside these insulating regions, we find numerous supersolids as well as a superfluid regime. The mentioned phases should be accessible experimentally and, in particular, the fractional domain walls can be created in the ground state using single-site addressing, i.e., by locally changing the chemical potential.
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| 25. |
- Wikberg, Emma, et al.
(författare)
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Improvements of 177Lu SPECT images from sparsely acquired projections by reconstruction with deep-learning-generated synthetic projections
- 2024
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Ingår i: EJNMMI PHYSICS. - 2197-7364. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- Background For dosimetry, the demand for whole-body SPECT/CT imaging, which require long acquisition durations with dual-head Anger cameras, is increasing. Here we evaluated sparsely acquired projections and assessed whether the addition of deep-learning-generated synthetic intermediate projections (SIPs) could improve the image quality while preserving dosimetric accuracy. Methods This study included 16 patients treated with Lu-177-DOTATATE with SPECT/CT imaging (120 projections, 120P) at four time points. Deep neural networks (CUSIPs) were designed and trained to compile 90 SIPs from 30 acquired projections (30P). The 120P, 30P, and three different CUSIP sets (30P + 90 SIPs) were reconstructed using Monte Carlo-based OSEM reconstruction (yielding 120P_rec, 30P_rec, and CUSIP_recs). The noise levels were visually compared. Quantitative measures of normalised root mean square error, normalised mean absolute error, peak signal-to-noise ratio, and structural similarity were evaluated, and kidney and bone marrow absorbed doses were estimated for each reconstruction set. Results The use of SIPs visually improved noise levels. All quantitative measures demonstrated high similarity between CUSIP sets and 120P. Linear regression showed nearly perfect concordance of the kidney and bone marrow absorbed doses for all reconstruction sets, compared to the doses of 120P_rec (R-2 >= 0.97). Compared to 120P_rec, the mean relative difference in kidney absorbed dose, for all reconstruction sets, was within 3%. For bone marrow absorbed doses, there was a higher dissipation in relative differences, and CUSIP_recs outperformed 30P_rec in mean relative difference (within 4% compared to 9%). Kidney and bone marrow absorbed doses for 30P_rec were statistically significantly different from those of 120_rec, as opposed to the absorbed doses of the best performing CUSIP_rec, where no statistically significant difference was found. Conclusion When performing SPECT/CT reconstruction, the use of SIPs can substantially reduce acquisition durations in SPECT/CT imaging, enabling acquisition of multiple fields of view of high image quality with satisfactory dosimetric accuracy.
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| 26. |
- Wikberg, Emma, 1982-
(författare)
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Non-abelian quantum Hall states and fractional charges in one dimension
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The fractional quantum Hall effect has, since its discovery around 30 years ago, been a vivid field of research—both experimentally and theoretically. In this thesis we investigate certain non-abelian quantum Hall states by mapping the two-dimensional system onto a thin torus, where the problem becomes effectively one-dimensional and hopping is suppressed, meaning that the classical electrostatic interaction dominates. The approach assists with a simplified view of ground states and their degeneracies, as well as of the nature of the fractionally charged, minimal excitations of the corresponding quantum Hall states. Similar models are also relevant for cold atoms trapped in one-dimensional optical lattices, where interaction parameters are available for tuning, which opens up for realizing interesting lattice states in controllable environments. The diverse applicability of the one-dimensional electrostatic lattice hamiltonian motivates the exploration of the systems and models treated in this work.In the absence of hopping or tunneling, the low-energy behavior of the one-dimensional lattice system is ultimately dependent on the nature of the electrostatic interaction present. For ordinary interactions such as Coulomb, the ground state at particle filling fraction ν= p/q has a well-known q-fold center-of-mass degeneracy and the elementary excitations are domain walls of fractional charge e* = ±e/q. These appear in abelian quantum Hall systems and are known since earlier. In this work, we show how other types of interaction give rise to increased ground state degeneracies and, as a result, to the emergence of split fractional charges recognized from non- abelian quantum Hall systems.
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| 27. |
- Wikberg, Emma, 1982-
(författare)
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Nontrivial ground-state degeneracies and generalized fractional excitations in the 1D lattice
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We study a 1D lattice Hamiltonian, relevant for a wide range of interesting physical systems like, e.g., the quantum-Hall system, cold atoms or molecules in optical lattices, and TCNQ salts. Through a tuning of the interaction parameters and a departure from a strictly convex interaction, nontrivial ground-state degeneracies and fractionally charged excitations emerge. The excitations, being a generalization of the fractional charges known from the fractional quantum-Hall effect, appear as domain walls between inequivalent ground states and carry the charge ± e/mq , where m is an integer and associated with the specified interaction, and ν = p/q is the filling fraction in the lattice. The description points at an interesting resemblance to states connected to non-Abelian statistics, which is central for the concept of topological quantum computing.
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| 28. |
- Wikberg, Emma, 1982-, et al.
(författare)
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Spin chain description of rotating bosons at v = 1
- 2009
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Ingår i: Journal of Statistical Mechanics. - 1742-5468. ; , s. P07038-
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Tidskriftsartikel (refereegranskat)abstract
- We consider bosons at Landau level filling ν = 1 on a thin torus. In analogy with previous work on fermions at filling ν = 1/2, we map the low-energy sector onto a spin-1/2 chain. While the fermionic system may realize the gapless XY phase, we show that typically this does not happen for the bosonic system. Instead, both delta function and Coulomb interaction lead to gapped phases in the bosonic system, and in particular we identify a phase corresponding to the non-Abelian Moore–Read state. In the spin language, the Hamiltonian is dominated by a ferromagnetic next-nearest-neighbor interaction, which leads to a description consistent with the non-trivial degeneracies of the ground and excited states of this phase of matter. In addition we comment on the similarities and differences of the two systems mentioned above and fermions at ν = 5/2.
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