Daniela Franz, Presenter: Travel support, Bayer AG

Ernst J. Rummeny MD, Abstract Co-Author: Nothing to Disclose

Dimitrios C. Karampinos, Abstract Co-Author: Research Grant, Koninklijke Philips NV

Michael Souvatzoglou, Abstract Co-Author: Nothing to Disclose

Stephan G. Nekolla PhD, Abstract Co-Author: Nothing to Disclose

Markus Schwaiger MD, Abstract Co-Author: Research Grant, Siemens AG

Matthias Johannes Eiber MD, Abstract Co-Author: Speaker, Siemens AG Speaker, Astellas Group Speaker, Johnson & Johnson

To describe the value of a 2-point VIBE Dixon sequence acquired for attenuation correction in whole-body simultaneous PET/MRI investigating fat- and water-signal of metabolically active and inactive adipose tissue in pediatric patients.

19 PET/MRI (Siemens Biograph mMR) examinations of 10 patients (7 male, 3 female; mean age 13.5) with oncological diagnoses were retrospectively enrolled in the study. PET/MRI acquisition included a 2D VIBE Dixon sequence (TR/TE 3.60/1.23,2.46, SL 3.12, matrix 191x121, FOV 500) used for attenuation correction with calculation of fat- and water-images. In each patient ROIs were placed into supraclavicular and gluteal fat depots bilaterally and signal intensities on fat and water images as well as the SUVmean were determined. Fat-fraction was calculated from the ratio of the fat signal over the summed water- and fat signal. Standard of reference for metabolically active brown supraclavicular fat was at least one PET examination in every patient showing the characteristic pattern of high uptake in the typical regions of brown fat.

The fat-fraction was significantly lower (p<0.0001) in supraclavicular brown adipose tissue (BAT) (range: 0.53-0.83, Mean: 0.69) compared to gluteal white adipose tissue (WAT) (range: 0.85-0.96, Mean: 0.92). Mean SUVmean for BAT was 4.67 (range: 0.29-18.25), for WAT 0.19 (range: 0.08-0.5).  No significant correlation between SUVmean and fat-fraction could be observed- neither for BAT (R=-0.06, p=0.73) nor for WAT (R=-0.10, p=0.57). 

Fat-fraction-analysis of Dixon VIBE images anyway acquired for attenuation correction in PET/MRI can potentially be used to assess composition of fat and differentiate between brown and white fat tissue. Metabolic activity as determined by SUV-analysis showed no correlation with fat-fraction using Dixon VIBE sequences.  

1) Fat-fraction-analysis of MR Dixon images in fat depots of different regions of the body can potentially help identify different types of adipose tissue thus may help identify regions of brown fat, even without PET. 2) In pediatric patients showing PET-uptake in PET/MRI inconclusive for brown fat vs. malignant lesions fat-fraction-analysis can possibly help for further differentiation.  

Franz, D, Rummeny, E, Karampinos, D, Souvatzoglou, M, Nekolla, S, Schwaiger, M, Eiber, M, Preliminary Results Using VIBE Dixon Sequences in Simultaneous PET/MRI for Discrimination between Metabolic Active and Inactive Adipose Tissue.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14011545.html