Characterization of brown adipose tissue by water-fat separated magnetic resonance imaging.
BACKGROUND
To evaluate the possibility of quantifying brown adipose tissue (BAT) volume and fat concentration with a high resolution, long echo time, dual-echo Dixon imaging protocol.


METHODS
A 0.42 mm isotropic resolution water-fat separated MRI protocol was implemented by using the second opposite-phase echo and third in-phase echo. Fat images were calibrated with regard to the intensity of nearby white adipose tissue (WAT) to form relative fat content (RFC) images. To evaluate the ability to measure BAT volume and RFC contrast dynamics, rats were divided into two groups that were kept at 4° or 22°C for 5 days. The rats were then scanned in a 70 cm bore 3.0 Tesla MRI scanner and a human dual energy CT. Interscapular, paraaortal, and perirenal BAT (i/pa/pr-BAT) depots as well as WAT and muscle were segmented in the MRI and CT images. Biopsies were collected from the identified BAT depots.


RESULTS
The biopsies confirmed that the three depots identified with the RFC images consisted of BAT. There was a significant linear correlation (P < 0.001) between the measured RFC and the Hounsfield units from DECT. Significantly lower iBAT RFC (P = 0.0064) and significantly larger iBAT and prBAT volumes (P = 0.0017) were observed in the cold stimulated rats.


CONCLUSIONS
The calibrated Dixon images with RFC scaling can depict BAT and be used to measure differences in volume, and fat concentration, induced by cold stimulation. The high correlation between RFC and HU suggests that the fat concentration is the main RFC image contrast mechanism.
Department of Biomedical Engineering, Linköping University, Linköping, Sweden.|Center for Medical Image Science and Visualization (CMIV), Linköping University, Linköping, Sweden.
Thobias
T
Romu
Center for Medical Image Science and Visualization (CMIV), Linköping University, Linköping, Sweden.|Linköping University, Department of Anaesthesiology and Intensive Care and Department of Medical and Health Sciences, Norrköping, Sweden.
Louise
L
Elander
Center for Medical Image Science and Visualization (CMIV), Linköping University, Linköping, Sweden.|Department of Medical and Health Sciences, Linköping University, Linköping, Sweden.
Olof Dahlqvist
OD
Leinhard
Department of Medical and Clinical Genetics, Institute of Biomedicine, The Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden.
Martin E
ME
Lidell
Department of Medical and Clinical Genetics, Institute of Biomedicine, The Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden.|Endocrine Research Unit, Medizinische Klinik und Poliklinik IV, Klinikum der Ludwig Maximilians University (LMU), Munich, Germany.
Matthias J
MJ
Betz
Center for Medical Image Science and Visualization (CMIV), Linköping University, Linköping, Sweden.|Department of Radiation Physics and Department of Medical and Health Sciences, Linköping University, Linköping, Sweden.
Anders
A
Persson
Department of Medical and Clinical Genetics, Institute of Biomedicine, The Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden.
Sven
S
Enerbäck
Department of Biomedical Engineering, Linköping University, Linköping, Sweden.|Center for Medical Image Science and Visualization (CMIV), Linköping University, Linköping, Sweden.
Magnus
M
Borga
D002001:Adipose Tissue, Brown / Q000033:anatomy & histology*; D052436:Adipose Tissue, White / Q000033:anatomy & histology*; D000328:Adult; D000818:Animals; D001834:Body Water / Q000166:cytology*; D002102:Cadaver; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013382:Subtraction Technique
Dixon imaging; brown adipose tissue; quantitative MRI; water fat MRI; white adipose tissue