Category Archives: research

Review of brown fat imaging

In this Radiology paper we review the origins of BAT imaging, discuss current preclinical and clinical strategies for imaging BAT, and discuss imaging methods that will provide crucial insight into metabolic disease and how it may be treated by modulating BAT activity. Please follow this link to Radiology.

FDG PET CT with uptake in BAT (white arrow).

FDG PET CT with uptake in BAT (arrows).

Marrow fat measures by DECT and MRS

In this study published in Radiology, MMIC investigator Miriam Bredella tested the performance of dual-energy computed tomography (CT) in the assessment of marrow adipose tissue (MAT) content of the lumbar spine by using proton (hydrogen 1 [(1)H]) magnetic resonance (MR) spectroscopy as a reference standard and to determine the influence of MAT on the assessment of bone mineral density (BMD). She found that dual-energy CT can be used to assess MAT content and BMD of the lumbar spine in a single examination and provides data that closely agree and correlate with (1)H MR spectroscopy data. Read the full article here.

Fat accumulation in the tongue

In this paper published in Metabolism, MMIC research fellow Ivan Godoy sought to examine associations between tongue adiposity with upper airway measures, whole-body adiposity and gender. We hypothesized that increased tongue adiposity is higher in males and positively associated with abnormal upper airway measures and whole-body adiposity. We found that increased tongue adiposity is influenced by gender and is associated with abnormal upper airway patency and body composition parameters. Here is link to the full abstract.

Cross sectional area of the tongue on sagittal CT.

Cross sectional area of the tongue on sagittal CT.

Measures of airway potency on sagittal CT.

Measures of airway potency on sagittal CT.

Dysfunctional fat in HIV patients

MMIC Director Martin Torriani, in a study funded by the Harvard Center for AIDS Research, set out to investigate adipose tissue in HIV patients. HIV patients are at an increased risk for cardiometabolic disease secondary to depot-specific alterations in adipose function, but mechanisms remain poorly understood. The endoribonuclease Dicer has been linked to the modulation of brown and white adipocyte differentiation. We previously demonstrated that Dicer knockout mice undergo transformation of brown adipose tissue to white adipose tissue and develop a lipodystrophic phenotype. We hypothesized reduced Dicer and brown adipose tissue gene expression from nonlipomatous sc fat among HIV patients with a lipodystrophic phenotype. Our results demonstrate dysfunctional sc adipose tissue marked by reduced Dicer in relationship to the down-regulation of brown and beige fat-related genes in lipodystrophic HIV patients and may provide a novel mechanism for metabolic dysregulation. A strategy to increase browning of white adipose tissue may improve cardiometabolic health in HIV. Read the full paper here.

Neck fat compartments in obesity

In a recent publication in the American Journal of Clinical Nutrition, Martin Torriani et al. used whole-body CT imaging to show that fat accumulation in the neck is correlated with cardiovascular risk and has different patterns in men and women. Further, neck fat accumulation involved specific neck compartments as adiposity increases. Read more here.

(A) Anatomic compartments of the neck at the level of C5. Tracings delimit subcutaneous (NATsc), posterior (NATpost), and perivertebral (NATperivert) compartments. (B) NAT compartments in a lean female without metabolic syndrome (27 years, BMI 23 kg/m2). (C) NAT accumulation in an obese female with metabolic syndrome (61 years, BMI 30 kg/m2).

(A) Anatomic compartments of the neck at the level of C5. Tracings delimit subcutaneous (NATsc), posterior (NATpost), and perivertebral (NATperivert) compartments. (B) NAT compartments in a lean female without metabolic syndrome (27 years, BMI 23 kg/m2). (C) NAT accumulation in an obese female with metabolic syndrome (61 years, BMI 30 kg/m2).

VAT and SAT FDG activity in metabolically health obese

In this study published in Obesity, MMIC research fellow Adriana Oliveira et al. sought to  measure FDG uptake in visceral (VAT) and subcutaneous (SAT) adipose tissue of metabolically healthy obese (MHO) and metabolically abnormal obese (MAO) compared to metabolically healthy lean (MHL) subjects. Given that MHO has increased metabolic risk, it was hypothesized that MHO and MAO display similar VAT FDG uptake. We found that FDG uptake in VAT of MHO is similar to MAO and lower than MHL, suggesting these subjects may present similar VAT dysfunction. You can read the full article here.

FDG PET CT of VAT/SAT

FDG PET CT of VAT/SAT

T2 mapping of adipose tissue fibrosis

IFP_T2map_combo

Panels A and B show a non-operated knee, with normal appearance of the infrapatellar fat and corresponding T2 map. Panels C and D are from the contra-lateral operated knee, with fibrosis (arrow) and T2 map showing lower values.

In a recent study by our group, Torriani and collaborators showed T2 mapping of infrapatellar adipose tissue was sensitive to detect fibrotic changes from arthroscopic surgery. This is a first step in quantitative assessment of adipose tissue fibrosis and future studies will perform T1rho and T2* adipose tissue relaxometry to further develop this research.

Fibrosis is an important feature of adipose tissue in obesity. Divoux et al. found that adipose tissue fibrosis limits omental adipocyte hypertrophy and hampers subcutaneous fat mass loss induced by bariatric surgery.

Brown adipose tissue has a positive effect on bone

BAT_bone_combo

Quantification of brown adipose tissue (BAT) within red region of interest. BAT in the supraclavicular region shows as dark nodular areas of increased activity in PET (Panel A) that correspond to orange areas in fused PET/CT (Panel B).

Investigators from our group, including Miriam Bredella and Corey Gill, performed a study in adults that measured brown adipose tissue (BAT) by 18F-FDG positron emission tomography/computed tomography and found it is a positive predictor of femoral bone structure, correlating with thigh muscle and subcutaneous fat.

This work expands that by Ponrartana et al., who found a similar positive relationship between BAT volume and bone cross sectional area in children. Given that the pediatric population is more likely to have higher quantities of BAT, our work suggests this positive relationship between BAT and bone also remains influential in adults.