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Water–fat separation in magnetic resonance imaging and its application in studies of brown adipose tissue
Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för kirurgiska vetenskaper.ORCID-id: 0000-0001-6477-2331
2019 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Abstract [en]

Virtually all the magnetic resonance imaging (MRI) signal of a human originates from water and fat molecules. By utilizing the property chemical shift the signal can be separated, creating water- and fat-only images. From these images it is possible to calculate quantitative fat fraction (FF) images, where the value of each voxel is equal to the percentage of its signal originating from fat. In papers I and II methods for water–fat signal separation are presented and evaluated.

The method in paper I utilizes a graph-cut to separate the signal and was designed to perform well even for a low signal-to-noise ratio (SNR). The method was shown to perform as well as previous methods at high SNRs, and better at low SNRs.

The method presented in paper II uses convolutional neural networks to perform the signal separation. The method was shown to perform similarly to a previous method using a graph-cut when provided non-undersampled input data. Furthermore, the method was shown to be able to separate the signal using undersampled data. This may allow for accelerated MRI scans in the future.

Brown adipose tissue (BAT) is a thermogenic organ with the main purpose of expending chemical energy to prevent the body temperature from falling too low. Its energy expending capability makes it a potential target for treating overweight/obesity and metabolic dysfunctions, such as type 2 diabetes. The most well-established way of estimating the metabolic potential of BAT is through measuring glucose uptake using 18F-fludeoxyglucose (18F-FDG) positron emission tomography (PET) during cooling. This technique exposes subjects to potentially harmful ionizing radiation, and alternative methods are desired. One alternative method is measuring the BAT FF using MRI.

In paper III the BAT FF in 7-year olds was shown to be negatively associated with blood serum levels of the bone-specific protein osteocalcin and, after correction for adiposity, thigh muscle volume. This may have implications for how BAT interacts with both bone and muscle tissue.

In paper IV the glucose uptake of BAT during cooling of adult humans was measured using 18F-FDG PET. Additionally, their BAT FF was measured using MRI, and their skin temperature during cooling near a major BAT depot was measured using infrared thermography (IRT). It was found that both the BAT FF and the temperature measured using IRT correlated with the BAT glucose uptake, meaning these measurements could be potential alternatives to 18F-FDG PET in future studies of BAT.

sted, utgiver, år, opplag, sider
Uppsala: Acta Universitatis Upsaliensis, 2019. , s. 65
Serie
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 1589
Emneord [en]
brown adipose tissue, magnetic resonance imaging, water–fat signal separation, graph-cut, positron emission tomography, 18F-fludeoxyglucose, infrared thermography, machine learning, artificial neural networks, deep learning, convolutional neural networks
HSV kategori
Forskningsprogram
Radiologi
Identifikatorer
URN: urn:nbn:se:uu:diva-390436ISBN: 978-91-513-0718-3 (tryckt)OAI: oai:DiVA.org:uu-390436DiVA, id: diva2:1342910
Disputas
2019-09-13, Enghoffsalen, Entrance 50, Akademiska sjukhuset, Uppsala, 13:15 (svensk)
Opponent
Veileder
Tilgjengelig fra: 2019-08-23 Laget: 2019-08-14 Sist oppdatert: 2019-09-17
Delarbeid
1. Water-fat separation incorporating spatial smoothing is robust to noise
Åpne denne publikasjonen i ny fane eller vindu >>Water-fat separation incorporating spatial smoothing is robust to noise
2018 (engelsk)Inngår i: Magnetic Resonance Imaging, ISSN 0730-725X, E-ISSN 1873-5894, Vol. 50, s. 78-83, artikkel-id S0730-725X(18)30040-7Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

PURPOSE: To develop and evaluate a noise-robust method for reconstruction of water and fat images for spoiled gradient multi-echo sequences.

METHODS: The proposed method performs water-fat separation by using a graph cut to minimize an energy function consisting of unary and binary terms. Spatial smoothing is incorporated to increase robustness to noise. The graph cut can fail to find a solution covering the entire image, in which case the relative weighting of the unary term is iteratively increased until a complete solution is found. The proposed method was compared to two previously published methods. Reconstructions were performed on 16 cases taken from the 2012 ISMRM water-fat reconstruction challenge dataset, for which reference reconstructions were provided. Robustness towards noise was evaluated by reconstructing images with different levels of noise added. The percentage of water-fat swaps were calculated to measure performance.

RESULTS: At low noise levels the proposed method produced similar results to one of the previously published methods, while outperforming the other. The proposed method significantly outperformed both of the previously published methods at moderate and high noise levels.

CONCLUSION: By incorporating spatial smoothing, an increased robustness towards noise is achieved when performing water-fat reconstruction of spoiled gradient multi-echo sequences.

Emneord
Chemical shift imaging, Dixon, Graph cuts, Multi-scale, Quadratic pseudo-Boolean optimization, Water-fat separation
HSV kategori
Identifikatorer
urn:nbn:se:uu:diva-347450 (URN)10.1016/j.mri.2018.03.015 (DOI)000434750700011 ()29601865 (PubMedID)
Forskningsfinansiär
Swedish Research Council, 2016-01040
Tilgjengelig fra: 2018-04-03 Laget: 2018-04-03 Sist oppdatert: 2019-08-14bibliografisk kontrollert
2. Separation of water and fat signal in whole-body gradient echo scans using convolutional neural networks
Åpne denne publikasjonen i ny fane eller vindu >>Separation of water and fat signal in whole-body gradient echo scans using convolutional neural networks
2019 (engelsk)Inngår i: Magnetic Resonance in Medicine, ISSN 0740-3194, E-ISSN 1522-2594, Vol. 82, nr 3, s. 1177-1186Artikkel i tidsskrift (Fagfellevurdert) Published
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.

Emneord
Dixon, convolutional neural network, deep learning, magnetic resonance imaging, neural network, water-fat separation
HSV kategori
Identifikatorer
urn:nbn:se:uu:diva-382933 (URN)10.1002/mrm.27786 (DOI)000485077600026 ()31033022 (PubMedID)
Forskningsfinansiär
Swedish Research Council, 2016-01040
Tilgjengelig fra: 2019-05-07 Laget: 2019-05-07 Sist oppdatert: 2019-10-15bibliografisk kontrollert
3. MRI estimates of brown adipose tissue in children - Associations to adiposity, osteocalcin, and thigh muscle volume
Åpne denne publikasjonen i ny fane eller vindu >>MRI estimates of brown adipose tissue in children - Associations to adiposity, osteocalcin, and thigh muscle volume
Vise andre…
2019 (engelsk)Inngår i: Magnetic Resonance Imaging, ISSN 0730-725X, E-ISSN 1873-5894, Vol. 58, s. 135-142Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Context: Brown adipose tissue is of metabolic interest. The tissue is however poorly explored in children.

Methods: Sixty-three 7-year old subjects from the Swedish birth-cohort Halland Health and Growth Study were recruited. Care was taken to include both normal weight and overweight children, but the subjects were otherwise healthy. Only children born full term were included. Water-fat separated whole-body MRI scans, anthropometric measurements, and measurements of fasting glucose and levels of energy homeostasis related hormones, including the insulin-sensitizer osteocalcin, were performed. The fat fraction (FF) and effective transverse relaxation time (T-2(star)) of suspected brown adipose tissue in the cervical-supraclavicular-axillary fat depot (sBAT) and the FFs of abdominal visceral (VAT) and subcutaneous adipose tissue (SAT) were measured. Volumes of sBAT, abdominal VAT and SAT, and thigh muscle volumes were measured.

Results: The FF in the sBAT depot was lower than in VAT and SAT for all children. In linear correlations including sex and age as explanatory variables, sBAT FF correlated positively with all measures of adiposity (p < 0.01), except for VAT FF and weight, positively with sBAT T-2* (p = 0.036), and negatively with osteocalcin (p = 0.017). When adding measures of adiposity as explanatory variables, sBAT FF also correlated negatively with thigh muscle volume (p < 0.01).

Conclusions: Whole-body water-fat MRI of children allows for measurements of sBAT. The FF of sBAT was lower than that of VAT and SAT, indicating presence of BAT. Future studies could confirm whether the observed correlations corresponds to a hormonally active BAT.

sted, utgiver, år, opplag, sider
ELSEVIER SCIENCE INC, 2019
Emneord
Brown adipose tissue, Magnetic resonance imaging, Adiposity, Osteocalcin, Muscle volume, Quantitative MRI
HSV kategori
Identifikatorer
urn:nbn:se:uu:diva-380416 (URN)10.1016/j.mri.2019.02.001 (DOI)000461412300018 ()30742901 (PubMedID)
Forskningsfinansiär
Swedish Research Council, 2013-3013Swedish Research Council, 2016-01040Region Västra Götaland
Tilgjengelig fra: 2019-04-02 Laget: 2019-04-02 Sist oppdatert: 2019-08-14bibliografisk kontrollert
4. Estimating the cold-induced brown adipose tissue glucose uptake rate measured by 18F-FDG PET using infrared thermography and water-fat separated MRI
Åpne denne publikasjonen i ny fane eller vindu >>Estimating the cold-induced brown adipose tissue glucose uptake rate measured by 18F-FDG PET using infrared thermography and water-fat separated MRI
Vise andre…
2019 (engelsk)Inngår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, artikkel-id 12358Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Brown adipose tissue (BAT) expends chemical energy to produce heat, which makes it a potential therapeutic target for combating metabolic dysfunction and overweight/obesity by increasing its metabolic activity. The most well-established method for measuring BAT metabolic activity is glucose uptake rate (GUR) measured using 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET). However, this is expensive and exposes the subjects to potentially harmful radiation. Cheaper and safer methods are warranted for large-scale or longitudinal studies. Potential alternatives include infrared thermography (IRT) and magnetic resonance imaging (MRI). The aim of this study was to evaluate and further develop these techniques. Twelve healthy adult subjects were studied. The BAT GUR was measured using 18F-FDG PET during individualized cooling. The temperatures of the supraclavicular fossae and a control region were measured using IRT during a simple cooling protocol. The fat fraction and effective transverse relaxation rate of BAT were measured using MRI without any cooling intervention. Simple and multiple linear regressions were employed to evaluate how well the MRI and IRT measurements could estimate the GUR. Results showed that both IRT and MRI measurements correlated with the GUR. This suggest that these measurements may be suitable for estimating the cold-induced BAT GUR in future studies.

Emneord
brown adipose tissue, 18F-FDG positron emission tomography, infrared thermography, magnetic resonance imagingm PET/MRI, water–fat signal separation
HSV kategori
Forskningsprogram
Radiologi
Identifikatorer
urn:nbn:se:uu:diva-390410 (URN)10.1038/s41598-019-48879-7 (DOI)000482564800014 ()31451711 (PubMedID)
Forskningsfinansiär
Swedish Research Council, 2016-01040Swedish Heart Lung Foundation, 2170492EXODIAB - Excellence of Diabetes Research in Sweden
Tilgjengelig fra: 2019-08-09 Laget: 2019-08-09 Sist oppdatert: 2019-10-18bibliografisk kontrollert

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