. Author manuscript; available in PMC: 2014 Dec 1.

Published in final edited form as: NMR Biomed. 2013 Oct 3;26(12):1609–1629. doi: 10.1002/nbm.3025

Table 2.

Select literature reports summarizing progress in MR of BAT morphology and metabolic activity.

MR Technique(s)	First-Author (Ref. Number)	Morphology, Metabolic Activity	Magnetic Field Strength	Rodent, Human	MR Findings	Significance to MR
* Proton MRS and T₁/T₂-Weighted MRI Proton MRS * Proton MRS and CSI	* Osculati (181, 182)	Morphology	7.0 Tesla	rodent ex vivo specimen / in vivo	Higher water content in BAT. BAT is consistently hypointense to WAT on conventional MRI.	Difference in fat-to-water ratio of BAT and WAT contributes to difference in signal intensities in MR BAT intensity potentially indicative of underlying adipocyte structure and fat content. Physiology and metabolism-mediated differences in TG properties between BAT and WAT exist and can be quantified by MR.
	** Zancanaro (186)		11.7 Tesla	rodent ex vivo specimen	BAT is more saturated. Unsaturation levels vary with age, temperature, and stimulation.
	** Strobel (60)		7.0 Tesla	rodent in vivo	BAT and WAT have different water and fat contents. BAT is more saturated than WAT. Measured T₂ of individual TG peaks.
	** Hamilton (185)		3.0 Tesla	rodent ex vivo specimen	BAT and WAT have different water and fat contents. BAT is more saturated than WAT. Measured T₁ and T₂ of individual peaks.
	*** Lunati (75)		4.7 Tesla	rodent post-mortem / in vivo	BAT is more polyunsaturated than WAT. Polyunsaturation degree is more uniform in BAT.
* T₁/T₂-weighted MRI and Frequency-Selective MRI ** T₁/T₂- weighted MRI	* Dundamadappa (179)		not reported	human in vivo	BAT hyperintense versus muscle. BAT signal intensity is variable on fat-suppressed images.	BAT can be visualized on T₁ and T₂ weighted images and exhibit signal intensity differences in comparison to muscle and WAT.
	** Carter (180)		not reported	human in vivo	BAT iso- and hyperintense to muscle and hypointense to fat on T₁ and T₂ -weighted images.
	** Sbarbati (183)	Morphology and Metabolic Activity	4.7 Tesla	rodent in vivo	BAT exhibits lower signals in cold-acclimated animals than those at thermoneutrality. BAT shows decrease in signal after stimulation.	BAT MR signals sensitive to temperature and stimulation.
	* Chen (184)	Morphology and Metabolic Activity	9.4 Tesla		BAT has a shorter T₂ than WAT, and is less affected by fat-suppression. BAT perfusion visible with MR contrast agent; hemodynamics visible with fMRI.	Characterization of BAT morphology and function is feasible with MR.
* Proton MRS and Frequency-Selective MRI ** Frequency-Selective MRI	* Sbarbati (187)	Morphology	4.7 Tesla		Evident differences in water-fat spectra and signals between muscle, BAT, and WAT.	Works posit and reinforce fat-signal fraction as a useful biomarker for comparing BAT and WAT and for comparing BAT between groups.
	** Lunati (188)		4.7 Tesla		Interscapular BAT has varying fat-signal fractions from surface to intermediate and deep layers.
	* Peng (189)		7.0 Tesla		Consistent cross-sectional differences in BAT and WAT fat-signal fractions between groups.
Proton Spectroscopy	Branca (202)		7.0 Tesla	rodent ex vivo specimen / in vivo	Novel approach exploits proximity of water and fat in BAT to generate spectral signal. Relies also on the presence of water and fat in BAT.	Method overcomes intrinsic limitation of spatial resolution and partial-volume effects.
Chemical-Shift-Encoded Water-Fat MRI	Hu (190, 191)		3.0 Tesla	rodent ex vivo specimen / post-mortem / in vivo	BAT consistently occupies a lower and broader fat-signal fraction range than WAT.	Reinforces earlier works that fat-signal fraction contrast between BAT and WAT is potentially a useful biomarker, and that signal trends are consistent between rodents and humans. BAT fat-signal fraction potentially useful in cross-sectional group comparisons.
	Smith (192)		9.4 Tesla	rodent in vivo
	Holstila (193)		1.5 Tesla	rodent - post-mortem human - in vivo
	Hu (194, 195, 196)		3.0 Tesla	human post-mortem / in vivo
	Lidell (197)			human post-mortem
	Gifford (198)			human in vivo
	Wayte (199)
	Lundström (200)		1.5 Tesla
*T₂-weighted MRI**	Khanna (228)	Metabolic Activity	7.0 Tesla	rodent in vivo	Variations in BAT metabolic activity due to temperature and drug stimulations are detectable by dynamic T₂* MRI, relying on the BOLD effects of hemoglobin and tissue perfusion.	BAT function and hemo-dynamics can be monitored using MRI, without the use of a contrast agent.
*T₂-weighted MRI**	van Rooijen (201)		3.0 Tesla	human in vivo
13-Carbon Spectroscopy and CSI	Lau (230)			rodent in vivo	BAT metabolic activity can be quantified with hyperpolarized 13C-pyruvate and its downstream products, bicarbonate, alanine, and lactate.	BAT metabolism and function can be quantified with MR with the administration of emerging exogenous contrast agents.
13-Carbon Spectroscopy and CSI	Friesen-Waldner (231)
129-Xenon Spectroscopy and CSI	Branca (232, 233)		9.4 Tesla		BAT metabolic activity can be quantified with 129Xe in gas, lipid-, and cytoplasm-dissolved phases, and the chemical-shift of 129Xe due to temperature.