uu.seUppsala universitets publikationer
Ändra sökning
Avgränsa sökresultatet
1 - 22 av 22
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Träffar per sida
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sortering
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
Markera
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 1.
    Andersson, Jonathan
    et al.
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för kirurgiska vetenskaper, Radiologi.
    Ahlström, Håkan
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för kirurgiska vetenskaper, Radiologi. Antaros Med, Mölndal, Sweden.
    Kullberg, Joel
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för kirurgiska vetenskaper, Radiologi. Antaros Med, Mölndal, Sweden.
    Separation of water and fat signal in whole-body gradient echo scans using convolutional neural networks2019Ingår i: Magnetic Resonance in Medicine, ISSN 0740-3194, E-ISSN 1522-2594, Vol. 82, nr 3, s. 1177-1186Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Purpose: To perform and evaluate water–fat signal separation of whole‐body gradient echo scans using convolutional neural networks.

    Methods: Whole‐body gradient echo scans of 240 subjects, each consisting of 5 bipolar echoes, were used. Reference fat fraction maps were created using a conventional method. Convolutional neural networks, more specifically 2D U‐nets, were trained using 5‐fold cross‐validation with 1 or several echoes as input, using the squared difference between the output and the reference fat fraction maps as the loss function. The outputs of the networks were assessed by the loss function, measured liver fat fractions, and visually. Training was performed using a graphics processing unit (GPU). Inference was performed using the GPU as well as a central processing unit (CPU).

    Results: The loss curves indicated convergence, and the final loss of the validation data decreased when using more echoes as input. The liver fat fractions could be estimated using only 1 echo, but results were improved by use of more echoes. Visual assessment found the quality of the outputs of the networks to be similar to the reference even when using only 1 echo, with slight improvements when using more echoes. Training a network took at most 28.6 h. Inference time of a whole‐body scan took at most 3.7 s using the GPU and 5.8 min using the CPU.

    Conclusion: It is possible to perform water–fat signal separation of whole‐body gradient echo scans using convolutional neural networks. Separation was possible using only 1 echo, although using more echoes improved the results.

  • 2. Barral, Joëlle K.
    et al.
    Gudmundson, Erik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Avdelningen för systemteknik. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Reglerteknik.
    Stikov, Nikola
    Etezadi-Amoli, Maryam
    Stoica, Peter
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Avdelningen för systemteknik. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Reglerteknik.
    Nishimura, Dwight G.
    A Robust Methodology for In Vivo T1 Mapping2010Ingår i: Magnetic Resonance in Medicine, ISSN 0740-3194, E-ISSN 1522-2594, Vol. 64, nr 4, s. 1057-1067Artikel i tidskrift (Refereegranskat)
  • 3.
    Berglund, Johan
    et al.
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för radiologi, onkologi och strålningsvetenskap, Enheten för radiologi.
    Ahlström, Håkan
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för radiologi, onkologi och strålningsvetenskap, Enheten för radiologi.
    Johansson, Lars
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för radiologi, onkologi och strålningsvetenskap, Enheten för radiologi.
    Kullberg, Joel
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för radiologi, onkologi och strålningsvetenskap, Enheten för radiologi.
    Two-point dixon method with flexible echo times2011Ingår i: Magnetic Resonance in Medicine, ISSN 0740-3194, E-ISSN 1522-2594, Vol. 65, nr 4, s. 994-1004Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The two-point Dixon method is a proton chemical shift imaging technique that produces separated water-only and fat-only images from a dual-echo acquisition. It is shown how this can be achieved without the usual constraints on the echo times. A signal model considering spectral broadening of the fat peak is proposed for improved water/fat separation. Phase errors, mostly due to static field inhomogeneity, must be removed prior to least-squares estimation of water and fat. To resolve ambiguity of the phase errors, a corresponding global optimization problem is formulated and solved using a message-passing algorithm. It is shown that the noise in the water and fat estimates matches the Cramér-Rao bounds, and feasibility is demonstrated for in vivo abdominal breath-hold imaging. The water-only images were found to offer superior fat suppression compared with conventional spectrally fat suppressed images.

  • 4.
    Berglund, Johan
    et al.
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för radiologi, onkologi och strålningsvetenskap, Enheten för radiologi.
    Ahlström, Håkan
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för radiologi, onkologi och strålningsvetenskap, Enheten för radiologi.
    Kullberg, Joel
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för radiologi, onkologi och strålningsvetenskap, Enheten för radiologi.
    Model-based mapping of fat unsaturation and chain length by chemical shift imaging: phantom validation and in vivo feasibility2012Ingår i: Magnetic Resonance in Medicine, ISSN 0740-3194, E-ISSN 1522-2594, Vol. 68, nr 6, s. 1815-1827Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Knowledge about the triglyceride (fat) 1H spectrum enables quantitative determination of several triglyceride characteristics. This work describes a model-based chemical shift imaging method that separates water and fat signal and provides maps of three triglyceride quantities: fatty acid carbon chain length (CL), number of double bond pairs (ndb), and number of methylene-interrupted double bonds (nmidb). The method was validated by imaging a phantom containing ten different oils using 1.5 T and 3.0 T clinical scanners, with gas-liquid chromatography (GLC) as reference. Repeated acquisitions demonstrated high reproducibility of the method. Statistical tests of correlation and linear regression were performed to examine the accuracy of the method. Significant correlation was found at both field strengths for all three quantities, and high correlation (r2 > 0.96) was found for measuring ndb and nmidb. Feasibility of the method for in vivo imaging of the thigh was demonstrated at both field strengths. The estimates of ndb and nmidb in subcutaneous adipose tisse were in agreement with literature values, while CL appears overestimated. The method has potential use in large-scale cross-sectional and longitudinal studies of triglyceride composition, and its relation to diet and various diseases.

  • 5.
    Berglund, Johan
    et al.
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för onkologi, radiologi och klinisk immunologi, Enheten för radiologi.
    Johansson, Lars
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för onkologi, radiologi och klinisk immunologi, Enheten för radiologi.
    Ahlström, Håkan
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för onkologi, radiologi och klinisk immunologi, Enheten för radiologi.
    Kullberg, Joel
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för onkologi, radiologi och klinisk immunologi, Enheten för radiologi.
    Three-point Dixon method enables whole-body water and fat imaging of obese subjects2010Ingår i: Magnetic Resonance in Medicine, ISSN 0740-3194, E-ISSN 1522-2594, Vol. 63, nr 6, s. 1659-1668Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Dixon imaging techniques derive chemical shift-separated water and fat images, enabling the quantification of fat content and forming an alternative to fat suppression. Whole-body Dixon imaging is of interest in studies of obesity and the metabolic syndrome, and possibly in oncology. A three-point Dixon method is proposed where two solutions are found analytically in each voxel. The true solution is identified by a multiseed three-dimensional region-growing scheme with a dynamic path, allowing confident regions to be solved before unconfident regions, such as background noise. 2 pi-Phase unwrapping is not required. Whole-body datasets (256 x 184 x 252 voxels) were collected from 39 subjects (body mass index 19.8-45.4 kg/m(2)), in a mean scan time of 5 min 15 sec. Water and fat images were reconstructed offline, using the proposed method and two reference methods. The resulting images were subjectively graded on a four-grade scale by two radiologists, blinded to the method used. The proposed method was found superior to the reference methods. It exclusively received the two highest grades, implying that only mild reconstruction failures were found. The computation time for a whole-body dataset was 1 min 51.5 sec +/- 3.0 sec. It was concluded that whole-body water and fat imaging is feasible even for obese subjects, using the proposed method.

  • 6.
    Berglund, Johan
    et al.
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för radiologi, onkologi och strålningsvetenskap, Enheten för radiologi.
    Kullberg, Joel
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för radiologi, onkologi och strålningsvetenskap, Enheten för radiologi.
    Three-dimensional water/fat separation and T2* estimation based on whole-image optimization: application in breathhold liver imaging at 1.5 T2012Ingår i: Magnetic Resonance in Medicine, ISSN 0740-3194, E-ISSN 1522-2594, Vol. 67, nr 6, s. 1684-1693Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The chemical shift of water and fat resonances in proton MRI allows separation of water and fat signal from chemical shift encoded data. This work describes an automatic method that produces separate water and fat images as well as quantitative maps of fat signal fraction and T2* from complex multi-echo gradient recalled datasets. Accurate water and fat separation is challenging due to signal ambiguity at the voxel level. Whole-image optimization can resolve this ambiguity, but might be computationally demanding, especially for three-dimensional (3D) data. In this work, periodicity of the model fit residual as a function of the off-resonance was utilized to modify a previously proposed formulation of the problem. This gives a smaller solution space and allows rapid optimization. Feasibility and accurate separation of water and fat signal was demonstrated in breathhold 3D liver imaging of ten volunteer subjects, with both acquisition and reconstruction times below 20 seconds.

  • 7.
    Berglund, Johan
    et al.
    Karolinska Univ Hosp, Dept Med Radiat Phys, P9 02, SE-17176 Stockholm, Sweden.;Karolinska Inst, Dept Clin Sci Intervent & Technol, Stockholm, Sweden..
    Skorpil, Mikael
    Department of Radiology, Uppsala University Hospital; Umea Univ, Dept Radiat Sci, Umea, Sweden..
    Multi-scale graph-cut algorithm for efficient water-fat separation2017Ingår i: Magnetic Resonance in Medicine, ISSN 0740-3194, E-ISSN 1522-2594, Vol. 78, nr 3, s. 941-949Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Purpose

    To improve the accuracy and robustness to noise in water-fat separation by unifying the multiscale and graph cut based approaches to B-0-correction.

    Methods

    A previously proposed water-fat separation algorithm that corrects for B-0 field inhomogeneity in 3D by a single quadratic pseudo-Boolean optimization (QPBO) graph cut was incorporated into a multi-scale framework, where field map solutions are propagated from coarse to fine scales for voxels that are not resolved by the graph cut. The accuracy of the single-scale and multi-scale QPBO algorithms was evaluated against benchmark reference datasets. The robustness to noise was evaluated by adding noise to the input data prior to water-fat separation.

    Results

    Both algorithms achieved the highest accuracy when compared with seven previously published methods, while computation times were acceptable for implementation in clinical routine. The multi-scale algorithm was more robust to noise than the single-scale algorithm, while causing only a small increase (+10%) of the reconstruction time.

    Conclusion

    The proposed 3D multi-scale QPBO algorithm offers accurate water-fat separation, robustness to noise, and fast reconstruction. The software implementation is freely available to the research community. Magn Reson Med 78:941-949, 2017.

  • 8.
    Björk, Marcus
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Avdelningen för systemteknik. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Reglerteknik.
    Ingle, R. Reeve
    Gudmundson, Erik
    Stoica, Peter
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Avdelningen för systemteknik. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Reglerteknik.
    Nishimura, Dwight G.
    Barral, Joëlle K.
    Parameter estimation approach to banding artifact reduction in balanced steady-state free precession2014Ingår i: Magnetic Resonance in Medicine, ISSN 0740-3194, E-ISSN 1522-2594, Vol. 72, nr 3, s. 880-892Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Purpose: The balanced steady-state free precession (bSSFP) pulse sequence has shown to be of great interest due to its high signal-to-noise ratio efficiency. However, bSSFP images often suffer from banding artifacts due to off-resonance effects, which we aim to minimize in this article. Methods: We present a general and fast two-step algorithm for 1) estimating the unknowns in the bSSFP signal model from multiple phase-cycled acquisitions, and 2) reconstructing band-free images. The first step, linearization for off-resonance estimation (LORE), solves the nonlinear problem approximately by a robust linear approach. The second step applies a Gauss-Newton algorithm, initialized by LORE, to minimize the nonlinear least squares criterion. We name the full algorithm LORE-GN. Results: We derive the Cramer-Rao bound, a theoretical lower bound of the variance for any unbiased estimator, and show that LORE-GN is statistically efficient. Furthermore, we show that simultaneous estimation of T-1 and T-2 from phase-cycled bSSFP is difficult, since the Cramer-Rao bound is high at common signal-to-noise ratio. Using simulated, phantom, and in vivo data, we illustrate the band-reduction capabilities of LORE-GN compared to other techniques, such as sum-of-squares. Conclusion: Using LORE-GN we can successfully minimize banding artifacts in bSSFP.

  • 9.
    Björk, Marcus
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Avdelningen för systemteknik. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Reglerteknik.
    Zachariah, Dave
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Avdelningen för systemteknik. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Reglerteknik.
    Kullberg, Joel
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för kirurgiska vetenskaper, Radiologi.
    Stoica, Peter
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Avdelningen för systemteknik. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Reglerteknik.
    A multicomponent T2 relaxometry algorithm for myelin water imaging of the brain2016Ingår i: Magnetic Resonance in Medicine, ISSN 0740-3194, E-ISSN 1522-2594, Vol. 75, nr 1, s. 390-402Artikel i tidskrift (Refereegranskat)
  • 10.
    Björnerud, Atle
    et al.
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för radiologi, onkologi och strålningsvetenskap, Enheten för radiologi.
    Bjerner, Tomas
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för radiologi, onkologi och strålningsvetenskap, Enheten för radiologi.
    Johansson, Lars
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för radiologi, onkologi och strålningsvetenskap, Enheten för radiologi.
    Ahlström, Håkan
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för radiologi, onkologi och strålningsvetenskap, Enheten för radiologi.
    Assessment of myocardial blood volume and water exchange: theoretical considerations and in vivo results.2003Ingår i: Magnetic Resonance in Medicine, ISSN 0740-3194, E-ISSN 1522-2594, Vol. 49, nr 5, s. 828-837Artikel i tidskrift (Refereegranskat)
  • 11.
    Bjørnerud, Atle
    et al.
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för radiologi, onkologi och strålningsvetenskap, Enheten för radiologi.
    Johansson, Lars O.
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för radiologi, onkologi och strålningsvetenskap, Enheten för radiologi.
    Ahlström, Håkan K.
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för radiologi, onkologi och strålningsvetenskap, Enheten för radiologi.
    Renal T(*)(2) perfusion using an iron oxide nanoparticle contrast agent: influence of T(1) relaxation on the first-pass response2002Ingår i: Magnetic Resonance in Medicine, ISSN 0740-3194, E-ISSN 1522-2594, Vol. 47, nr 2, s. 298-304Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Quantitative perfusion measurements require accurate knowledge of the correlation between first-pass signal changes and the corresponding tracer concentration in tissue. In the present study, a detailed analysis of first-pass renal cortical changes in T(1) and T(*)(2) following bolus injection of the iron oxide nanoparticle NC100150 Injection was investigated in a pig model using a double-echo gradient-echo sequence. The estimated change in 1/T(*)(2) during first pass calculated from single-echo sequences was compared to the true double-echo-derived 1/T(*)(2) curves. Using a single-echo (TE = 6 ms) spoiled gradient-echo sequence, the first-pass 1/T(*)(2) response following a bolus injection of 1 mg Fe/kg of NC100150 Injection was significantly underestimated due to counteracting T(1) effects. Signal response simulations showed that the relative error in the first-pass response decreased with increasing TE and contrast agent dose. However, both the maximum TE and the maximum dose are limited by excessive cortical signal loss, and the maximum TE is further limited by high temporal resolution requirements. The problem of T(1) contamination can effectively be overcome by using a double-echo gradient-echo sequence. This yields a first-pass response that truly reflects the tissue tracer concentration, which is a critical requirement for quantitative renal perfusion assessment.

  • 12.
    Bjørnerud, Atle
    et al.
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för onkologi, radiologi och klinisk immunologi. Radiologi.
    Johansson, Lars O.
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för radiologi, onkologi och strålningsvetenskap, Enheten för radiologi.
    Briley-Sæbø, Karen
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för onkologi, radiologi och klinisk immunologi. Radiologi.
    Ahlström, Håkan K.
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för radiologi, onkologi och strålningsvetenskap, Enheten för radiologi.
    Assessment of T1 and T2* effects in vivo and ex vivo using iron oxide nanoparticles in steady state: dependence on blood volume and water exchange2002Ingår i: Magnetic Resonance in Medicine, ISSN 0740-3194, E-ISSN 1522-2594, Vol. 47, nr 3, s. 461-471Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Accurate knowledge of the relationship between contrast agent concentration and tissue relaxation is a critical requirement for quantitative assessment of tissue perfusion using contrast-enhanced MRI. In the present study, using a pig model, the relationship between steady-state blood concentration levels of an iron oxide nanoparticle with a hydrated diameter of 12 nm (NC100150 Injection) and changes in the transverse and longitudinal relaxation rates (1/T2* and 1/T1, respectively) in blood, muscle, and renal cortex was investigated at 1.5 T. Ex vivo measurements of 1/T2* and 1/T1 were additionally performed in whole pig blood spiked with different concentrations of the iron oxide nanoparticle. In renal cortex and muscle, 1/T2* increased linearly with contrast agent concentration with slopes of 101 +/-22 s(-1)mM(-1) and 6.5 +/-0.9 s(-1)mM(-1) (mean +/- SD), respectively. In blood, 1/T2* increased as a quadratic function of contrast agent concentration, with different quadratic terms in the ex vivo vs. the in vivo experiments. In vivo, 1/T1 in blood increased linearly with contrast agent concentration, with a slope (T1-relaxivity) of 13.9 +/- 0.9 s(-1)mM(-1). The achievable increase in 1/T1 in renal cortex and muscle was limited by the rate of water exchange between the intra- and extravascular compartments and the 1/T1-curves were well described by a two-compartment water exchange limited relaxation model.

  • 13. Ericsson, A
    et al.
    Weis, J
    Hemmingsson, A
    Wikström, M
    Sperber, G O
    Measurements of magnetic field variations in the human brain using a 3D-FT multiple gradient echo technique.1995Ingår i: Magnetic Resonance in Medicine, ISSN 0740-3194, E-ISSN 1522-2594, Vol. 33, nr 2, s. 171-7Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A magnetic resonance 3DFT multiple gradient-echo technique was used for measurements of the proton spectrum for each voxel in the measured slice. Water, fat, magnetic field and T2 distributions in the head of a normal volunteer and a patient with intracerebral hematoma were computed. Magnetic field variations caused by the head were calculated after correction for the static magnetic field inhomogeneity. Large local magnetic field variations up to 3 ppm were found in the human brain near interfaces between air or bone and brain tissues and 0.5 ppm between hematoma and brain tissue. Information about magnetic field variations could be useful for shimming procedures in vivo and for correcting artifacts in imaging and spectroscopy.

  • 14.
    Juul, Troels
    et al.
    Aarhus Univ, Dept Clin Med, MR Res Ctr, Aarhus, Denmark.
    Palm, Fredrik
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för medicinsk cellbiologi, Integrativ Fysiologi.
    Nielsen, Per Mose
    Aarhus Univ, Dept Clin Med, MR Res Ctr, Aarhus, Denmark.
    Bertelsen, Lotte Bonde
    Aarhus Univ, Dept Clin Med, MR Res Ctr, Aarhus, Denmark.
    Laustsen, Christoffer
    Aarhus Univ, Dept Clin Med, MR Res Ctr, Aarhus, Denmark.
    Ex vivo hyperpolarized MR spectroscopy on isolated renal tubular cells: A novel technique for cell energy phenotyping.2017Ingår i: Magnetic Resonance in Medicine, ISSN 0740-3194, E-ISSN 1522-2594, Vol. 78, nr 2, s. 457-461Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    PURPOSE: It has been demonstrated that hyperpolarized (13) C MR is a useful tool to study cultured cells. However, cells in culture can alter phenotype, which raises concerns regarding the in vivo significance of such findings. Here we investigate if metabolic phenotyping using hyperpolarized (13) C MR is suitable for cells isolated from kidney tissue, without prior cell culture.

    METHODS: Isolation of tubular cells from freshly excised kidney tissue and treatment with either ouabain or antimycin A was investigated with hyperpolarized MR spectroscopy on a 9.4 Tesla preclinical imaging system.

    RESULTS: Isolation of tubular cells from less than 2 g of kidney tissue generally resulted in more than 10 million live tubular cells. This amount of cells was enough to yield robust signals from the conversion of (13) C-pyruvate to lactate, bicarbonate and alanine, demonstrating that metabolic flux by means of both anaerobic and aerobic pathways can be quantified using this technique.

    CONCLUSION: Ex vivo metabolic phenotyping using hyperpolarized (13) C MR in a preclinical system is a useful technique to study energy metabolism in freshly isolated renal tubular cells. This technique has the potential to advance our understanding of both normal cell physiology as well as pathological processes contributing to kidney disease.

  • 15.
    Langner, Taro
    et al.
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för kirurgiska vetenskaper, Radiologi.
    Hedström, Anders
    BioVenture Hub, Antaros Med, Molndal, Sweden.
    Mörwald, Katharina
    Paracelsus Med Univ, Dept Pediat, Salzburg, Austria; Paracelsus Med Univ, Obes Res Unit, Salzburg, Austria.
    Weghuber, Daniel
    Paracelsus Med Univ, Dept Pediat, Salzburg, Austria; Paracelsus Med Univ, Obes Res Unit, Salzburg, Austria.
    Forslund, Anders
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för kvinnors och barns hälsa, Forskargrupper (Inst. för kvinnor och barns hälsa), Pediatrisk inflammationsforskning.
    Bergsten, Peter
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för medicinsk cellbiologi. Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för kvinnors och barns hälsa, Forskargrupper (Inst. för kvinnor och barns hälsa), Pediatrisk inflammationsforskning.
    Ahlström, Håkan
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för kirurgiska vetenskaper, Radiologi. BioVenture Hub, Antaros Med, Mölndal, Sweden.
    Kullberg, Joel
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för kirurgiska vetenskaper, Radiologi. BioVenture Hub, Antaros Med, Mölndal, Sweden.
    Fully convolutional networks for automated segmentation of abdominal adipose tissue depots in multicenter water–fat MRI2019Ingår i: Magnetic Resonance in Medicine, ISSN 0740-3194, E-ISSN 1522-2594, Vol. 81, nr 4, s. 2736-2745Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Purpose: An approach for the automated segmentation of visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT) in multicenter water–fat MRI scans of the abdomen was investigated, using 2 different neural network architectures.

    Methods: The 2 fully convolutional network architectures U‐Net and V‐Net were trained, evaluated, and compared using the water–fat MRI data. Data of the study Tellus with 90 scans from a single center was used for a 10‐fold cross‐validation in which the most successful configuration for both networks was determined. These configurations were then tested on 20 scans of the multicenter study beta‐cell function in JUvenile Diabetes and Obesity (BetaJudo), which involved a different study population and scanning device.

    Results: The U‐Net outperformed the used implementation of the V‐Net in both cross‐validation and testing. In cross‐validation, the U‐Net reached average dice scores of 0.988 (VAT) and 0.992 (SAT). The average of the absolute quantification errors amount to 0.67% (VAT) and 0.39% (SAT). On the multicenter test data, the U‐Net performs only slightly worse, with average dice scores of 0.970 (VAT) and 0.987 (SAT) and quantification errors of 2.80% (VAT) and 1.65% (SAT).

    Conclusion: The segmentations generated by the U‐Net allow for reliable quantification and could therefore be viable for high‐quality automated measurements of VAT and SAT in large‐scale studies with minimal need for human intervention. The high performance on the multicenter test data furthermore shows the robustness of this approach for data of different patient demographics and imaging centers, as long as a consistent imaging protocol is used.

  • 16. Schoenberg, Stefan O
    et al.
    Aumann, Silke
    Just, Armin
    Bock, Michael
    Knopp, Michael V
    Johansson, Lars
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för radiologi, onkologi och strålningsvetenskap, Enheten för radiologi.
    Ahlström, Håkan
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för radiologi, onkologi och strålningsvetenskap, Enheten för radiologi.
    Quantification of renal perfusion abnormalities using an intravascular contrast agent (part 2): results in animals and humans with renal artery stenosis2003Ingår i: Magnetic Resonance in Medicine, ISSN 0740-3194, E-ISSN 1522-2594, Vol. 49, nr 2, s. 288-298Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The interrelation between the morphologic degree of renal artery stenosis and changes in parenchymal perfusion is assessed using an intravascular contrast agent. In seven adult foxhounds, different degrees of renal artery stenosis were created with an inflatable clamp implanted around the renal artery. Dynamic susceptibility-weighted gradient-echo imaging was used to measure signal-time curves in the renal artery and the renal parenchyma during administration of 1.5 mg/kg BW of an intravascular ultrasmall particle iron oxide (USPIO) contrast agent. From the dynamic series, regional renal blood volume (rRBV), regional renal blood flow (rRBF), and mean transit time (MTT) were calculated. The morphologic degree of stenosis was measured in the steady state using a high-resolution 3D contrast-enhanced (CE) MR angiography (MRA) sequence (voxel size = 0.7 x 0.7 x 1 mm(3)). Five patients with renoparenchymal damage due to long-standing renal artery stenosis were evaluated. In the animal stenosis model, cortical perfusion remained unchanged for degrees of renal artery stenosis up to 80%. With degrees of stenoses > 80%, cortical perfusion dropped to 151 +/- 54 ml/100 g of tissue per minute as compared to a baseline of 513 +/- 76 ml/100 g/min. In the patients, a substantial difference in the cortical perfusion of more than 200 +/- 40 ml/100 g/min between the normal and the ischemic kidneys was found. The results show that quantitative renal perfusion measurements in combination with 3D-CE-MRA allow the functional significance of a renal artery stenosis to be determined in a single MR exam. Differentiation between renovascular and renoparenchymal disease thus becomes feasible.

  • 17. Weis, J
    et al.
    Ericsson, A
    Hemmingsson, A
    Chemical shift artifact-free microscopy: spectroscopic microimaging of the human skin.1999Ingår i: Magnetic Resonance in Medicine, ISSN 0740-3194, E-ISSN 1522-2594, Vol. 41, nr 5, s. 904-8Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A spectroscopic imaging technique with high spatial resolution was used for the study of human skin in vivo. The measurements were performed using a whole-body magnetic resonance system (1.5 T) with standard gradients and a standard 8-cm diameter circular surface coil. A decisive gain in signal-to-noise ratio was achieved by reducing the receiver bandwidth of the imaging system to values less than +/-5 kHz. The chemical shift misregistration was eliminated by post-detection data processing. The method was tested on different kinds of skin, on the foot sole and head. Water, fat, and chemical shift artifact-free images were obtained with resolution 0.107 x 0.143 mm in plane and slice thickness 1 mm. A major advantage of the spectroscopic imaging procedure is that the pulse sequence can be optimized for the maximum signal-to-noise ratio. There is no need for special modification of the sequence to circumvent the chemical shift artifacts (water, fat suppression, etc.).

  • 18.
    Weis, Jan
    et al.
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för radiologi, onkologi och strålningsvetenskap, Enheten för radiologi.
    Courivaud, Frederic
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för radiologi, onkologi och strålningsvetenskap, Enheten för radiologi.
    Hansen, Michael Schacht
    Johansson, Lars
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för radiologi, onkologi och strålningsvetenskap, Enheten för radiologi.
    Ribe, Lars Riisgaard
    Ahlström, Håkan
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för radiologi, onkologi och strålningsvetenskap, Enheten för radiologi.
    Lipid content in the musculature of the lower leg: evaluation with high-resolution spectroscopic imaging2005Ingår i: Magnetic Resonance in Medicine, ISSN 0740-3194, E-ISSN 1522-2594, Vol. 54, nr 1, s. 152-158Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A novel spectroscopic imaging method with high spectral and spatial resolution was developed for the specific goal of assessing muscle fat. Sensitivity to the methylene and methyl protons of fatty acids was improved by the use of a binomial 1 excitation pulse instead of the standard radiofrequency (RF) pulse. Acceptable measurement time is achieved by using a narrow spectral bandwidth (6 ppm). The spectral resolution is sufficient to resolve extramyocellular (EMCL) and intramyocellular (IMCL) lipids. A post-detection data processing scheme that permits correction of spectral artifacts caused by chemical shifts, spectral line aliasing, and magnetic field inhomogeneities is suggested. The lipid content in different lower leg muscles was evaluated. Muscle fiber orientation was taken into account in assessing quantities of EMCL and IMCL. The proposed technique allows small amounts of inhomogeneously distributed muscle lipids to be quantified.

  • 19. Weis, Jan
    et al.
    Ericsson, Anders
    Hemmingsson, Anders
    Chemical shift artifact-free microscopy: spectroscopic microimaging of the human skin1999Ingår i: Magnetic Resonance in Medicine, ISSN 0740-3194, E-ISSN 1522-2594, Vol. 41, nr 5, s. 904-908Artikel i tidskrift (Refereegranskat)
  • 20.
    Weis, Jan
    et al.
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för onkologi, radiologi och klinisk immunologi, Enheten för radiologi. Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för medicinska vetenskaper, Biomedicinsk informatik och teknik.
    Johansson, Lars
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för onkologi, radiologi och klinisk immunologi, Enheten för radiologi.
    Courivaud, Frederic
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för onkologi, radiologi och klinisk immunologi, Enheten för radiologi.
    Karlsson, F. Anders
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för medicinska vetenskaper.
    Ahlström, Håkan
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för onkologi, radiologi och klinisk immunologi, Enheten för radiologi.
    Quantification of intramyocellular lipids in obese subjects using spectroscopic imaging with high spatial resolution2007Ingår i: Magnetic Resonance in Medicine, ISSN 0740-3194, E-ISSN 1522-2594, Vol. 57, nr 1, s. 22-28Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Quantification of intramyocellular lipids (IMCL) in obese subjects by single-voxel spectroscopy (SVS) or conventional spectroscopic imaging (SI) often fails due to overlap of IMCL spectral lines by extramyocellular lipids (EMCL), and signal contamination from subcutaneous fat and bone marrow. This study demonstrates that these problems can be solved by high-resolution SI with 128 phase-encoding steps and a read gradient during acquisition. The small voxels obtained in this way facilitated differentiation between EMCL and IMCL. This method offers the possibility of studying different muscle groups and the variation of lipids within one muscle.

  • 21.
    Weis, Jan
    et al.
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för onkologi, radiologi och klinisk immunologi, Enheten för radiologi.
    Johansson, Lars
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för onkologi, radiologi och klinisk immunologi, Enheten för radiologi.
    Ortiz-Nieto, Francisco
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för onkologi, radiologi och klinisk immunologi, Enheten för radiologi.
    Ahlström, Håkan
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för onkologi, radiologi och klinisk immunologi, Enheten för radiologi.
    Assessment of lipids in skeletal muscle by high-resolution spectroscopic imaging using fat as the internal standard: comparison with water referenced spectroscopy2008Ingår i: Magnetic Resonance in Medicine, ISSN 0740-3194, E-ISSN 1522-2594, Vol. 59, nr 6, s. 1259-1265Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The main purpose of the study was to compare proton (1H) single-voxel MR spectroscopy (MRS) with high-spatial-resolution spectroscopic imaging (MRSI) to determine the lipid content in human skeletal muscle. Unsuppressed water line was used as a concentration reference in the processing of single-voxel spectra. The spectrum from yellow bone marrow with a 100% fat content and probe with the vegetable oil served as internal and external reference for high-spatial-resolution MRSI, respectively. Very good correlation was found between lipid concentrations measured by water referenced single-voxel MRS and high-spatial-resolution MRSI with yellow bone marrow as the internal standard. Excellent correlation was found between total lipid concentrations estimated by high-spatial-resolution MRSI with vegetable oil as the external fat standard and yellow bone marrow as the internal reference. From comparison of single-voxel MRS and MRSI approaches, it follows that relaxation correction of the reference water and methylene fat line is inevitable in processing the standard single-voxel spectra. The high-resolution MRSI approach is recommended to avoid the problem of relaxation corrections and enables using vegetable oil as the external fat standard.

  • 22.
    Wiesinger, Florian
    et al.
    GE Healthcare, Freisinger Landstr 50, D-85748 Munich, Germany.
    Bylund, Mikael
    Umea Univ, Umea, Sweden.
    Yang, Jaewon
    UCSF, San Francisco, CA USA.
    Kaushik, Sandeep
    GE Global Res, Bangalore, Karnataka, India.
    Shanbhag, Dattesh
    GE Global Res, Bangalore, Karnataka, India.
    Ahn, Sangtae
    GE Global Res, Niskayuna, NY USA.
    Jonsson, Joakim H.
    Umea Univ, Umea, Sweden.
    Lundman, Josef A.
    Umea Univ, Umea, Sweden.
    Hope, Thomas
    UCSF, San Francisco, CA USA.
    Nyholm, Tufve
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för immunologi, genetik och patologi, Medicinsk strålningsvetenskap. Umea Univ, Umea, Sweden.
    Larson, Peder
    UCSF, San Francisco, CA USA.
    Cozzini, Cristina
    GE Healthcare, Freisinger Landstr 50, D-85748 Munich, Germany.
    Zero TE-based pseudo-CT image conversion in the head and its application in PET/MR attenuation correction and MR-guided radiation therapy planning2018Ingår i: Magnetic Resonance in Medicine, ISSN 0740-3194, E-ISSN 1522-2594, Vol. 80, nr 4, s. 1440-1451Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Purpose: To describe a method for converting Zero TE (ZTE) MR images into Xray attenuation information in the form of pseudo-CT images and demonstrate its performance for (1) attenuation correction (AC) in PET/MR and (2) dose planning in MR-guided radiation therapy planning (RTP). Methods: Proton density-weighted ZTE images were acquired as input for MRbased pseudo-CT conversion, providing (1) efficient capture of short-lived bone signals, (2) flat soft-tissue contrast, and (3) fast and robust 3D MR imaging. After bias correction and normalization, the images were segmented into bone, soft-tissue, and air by means of thresholding and morphological refinements. Fixed Hounsfield replacement values were assigned for air (-1000 HU) and soft-tissue (142 HU), whereas continuous linear mapping was used for bone. Results: The obtained ZTE-derived pseudo-CT images accurately resembled the true CT images (i. e., Dice coefficient for bone overlap of 0.73 +/- 0.08 and mean absolute error of 123 +/- 25 HU evaluated over the whole head, including errors from residual registration mismatches in the neck and mouth regions). The linear bone mapping accounted for bone density variations. Averaged across five patients, ZTE-based AC demonstrated a PET error of -0.04 +/- 1.68% relative to CT-based AC. Similarly, for RTP assessed in eight patients, the absolute dose difference over the target volume was found to be 0.23 +/- 0.42%. Conclusion: The described method enables MR to pseudo-CT image conversion for the head in an accurate, robust, and fast manner without relying on anatomical prior knowledge. Potential applications include PET/MR-AC, and MR-guided RTP.

1 - 22 av 22
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf