We thank the support of National Natural Science Foundation of China (NSFC) - Excellent Young Scientists Fund (Hong Kong and Macau) (81922079), Hong Kong Research Grants Council General Research Fund (GRF 17121520 and 17123419), and Hong Kong Research Grants Council Collaborative Research Fund (CRF C7018-14E) for small animal imaging experiments.

The protocol described below follows the animal care guidelines of The University of Hong Kong. The animals used in the study were 8-week-old C57BL/6J mice.
1. Animal surgical procedures and cold challenge
<ol>
	<li>Perform interscapular BAT (iBAT) dissection.
	<ol>
		<li>Anesthetize the mice by intraperitoneal injection of ketamine/xylazine (100 mg/kg bodyweight ketamine and 10 mg/kg bodyweight xylazine). After anesthesia, shave the hair of the mouse from the neck to just below the scapulae.</li>
		<li>Place the mice on the heating pad after disinfection and make a 2 cm incision along the dorsal midline of the mice.</li>
		<li>Remove the iBAT pads (bilateral). In the sham-operated group, make the same incision but leave the iBAT pads intact.</li>
		<li>Close the incision using 7 mm stainless steel wound clips after the bleeding stops.</li>
		<li>After surgery, give meloxicam (5 mg/kg in drinking water) to the mice for 6 days and house them in an intensive care unit (ICU) for 14 days. Remove the clips as soon as the wound is healed (7-10 days).</li>
	</ol>
	</li>
	<li>Cold challenge of the mice: House the mice at thermoneutrality (30 &#176;C) for 14 days. On day 13, pre-chill the animal cages in cold (6 &#176;C) overnight. On day 14, put the mice at 6 &#176;C in the environmental chamber for 7 days. Place two mice in each cage.</li>
</ol>
2. Micro-PET/MR calibrations and workflow setup
NOTE: Micro-PET/MR imaging is performed using a sequential PET/MR system (see Table of Materials). Each mouse is placed on the imaging bed; first scan with the MR for an anatomical reference (scout view) before advancing to the center of the PET field-of-view (FOV) for a static [18F]FDG PET acquisition, followed by MR imaging for anatomic reference. An imaging workflow is created in the scanner-operating software (see Table of Materials) to enable automated, sequential PET/MR scans prior to the imaging session.
<ol>
	<li>Create an imaging workflow in the operating software that includes static PET acquisition, MRI acquisitions for attenuation correction, and anatomical reference using T1-weigthed 3D imaging and T2-weighted 2D imaging, respectively.</li>
	<li>To acquire PET, set 400-600 keV level discrimination, F-18 study isotope, 1-5 coincidence mode and 20 min scans.</li>
	<li>To acquire T1-weighted MR (for attenuation correction), set Gradient Echo-3D (TE = 4.3 ms, TR = 16 ms, FOV = 90 x 60 mm, number of excitations (NEX) = 3, 28 slices with 0.9 mm thickness, voxel size = 0.375 x 0.375 x 0.9 mm).</li>
	<li>To acquire T2-weighted MR (anatomical reference), set Fast-spin Echo 2D (TE = 71.8 ms, TR = 3000 ms, FOV = 90 x 60 mm, NEX = 5, 32 slices with 0.9 mm thickness, voxel size = 0.265 x 0.268 x 0.9 mm3).</li>
	<li>To reconstruct PET, use Tera-Tomo 3D (TT3D) algorithm (8 iterations, 6 subsets) with 1-3 coincidence mode, and with decay, dead-time, random, attenuation, and scatter corrections to create images with an overall of 0.3 mm3 voxel size.</li>
	<li>Perform a PET Activity Test of the micro-PET/MR scanner one day before the start of imaging study to check the accuracy of PET quantitation.
	<ol>
		<li>Prepare a 5 mL syringe filled with [18F]FDG as recommended by the manufacturer guidelines (140-220 &#956;Ci/5-8 MBq in water or saline).</li>
		<li>Record the activity of the syringe using a dose calibrator (see Table of Materials) and note the time of measurement.</li>
		<li>Select Interpolated Ellipse ROI to draw a volume-of-interest (VOI) on the reconstructed image to compare the recovered activity to the value measured as described above. The recovered activity for a well-calibrated scanner is accurate within &#177;5%.</li>
	</ol>
	</li>
</ol>
3. Injection of [18F]FDG
<ol>
	<li>Order a clinical dose of [18F]FDG (10 mCi/370 MBq) from the supplier for its arrival to the imaging lab approximately 30 min before the first scheduled injection. Make sure to wear appropriate personal protective equipment (PPE), such as a lab coat, gloves, personal radiation dosimeter e.g. Fingers, whole body when receiving the package containing radioactive materials. Change gloves regularly to prevent cross contamination of the radioactivity and increase distance from the radioactive source as much as possible.</li>
	<li>Use the forceps to carefully transfer the [18F]FDG stock vial behind an L-block table top shield.</li>
	<li>Dispense an aliquot of [18F]FDG and dilute with sterilized saline to give a total activity concentration at 200-250 &#956;Ci/7-9 MBq) in 100-150 &#956;L.</li>
	<li>Draw the [18F]FDG solution into a 1 mL syringe with needle (see Table of Materials), measure the radioactivity using a dose calibrator set to F-18, and record the time of measurement.</li>
	<li>Record the weight of the mouse prior to injection. Inject the prepared [18F]FDG solution via tail vein. Take note of the injection time and residue of the radioactivity of the syringe to enable decay correction.</li>
	<li>Put the mouse back in the cage and allow [18F]FDG uptake for 60 min before PET scans.</li>
	<li>Calculate the injected [18F]FDG activity using the following formula11: 
	Injected activity (&#956;Ci/MBq) 
	= Activity in the syringe before injection 
	- activity in the syringe after injection</li>
</ol>
4. Micro-PET/MR acquisition
<ol>
	<li>Turn on the air heater to the mouse bed to allow warm air to pass through it.</li>
	<li>Anesthetize the mouse using 5% isoflurane (1 L/min medical O2). Once induced, transfer the mouse to the warm mouse bed and maintain anesthesia at 2%-3 % isoflurane via a nose mask cone. Position the mouse head-prone onto the bite bar and make sure the mouse does not protrude outside of the diameter of the bed. Apply eye lubricant to avoid drying and formation of corneal ulcers.</li>
	<li>Monitor the body temperature and the respiratory rate by a thermal probe and a respiratory pad, respectively. Maintain the body temperature at 36-37 &#176;C, and the respiratory rate at 70-80 breaths per minute (bpm) by adjusting the isoflurane level.</li>
	<li>Perform a scout view to determine the mouse position. Adjust the mouse bed position to include the whole mouse body, and to ensure the center FOV of MR is in the center of mouse body.</li>
	<li>Under the PET Acquisition in the study list window, select Scan Range on Previous Acquisition to use the scout view position as described above. Click on Prepare to move the animal bed from MR to PET. Select OK to initiate the PET scan. Record the injection dose and time measured before and after [18F]FDG administration in the Radiopharmaceutical Editor. Enter the weight of the mouse under the Subject Information menu.</li>
	<li>Once the PET scan is completed, select Prepare to move to MR and complete all the MR acquisitions in the study list window. Select OK to start the MR scans.</li>
	<li>After the whole workflow is completed, briefly evaluate the quality of the acquired MR images using the post-processing software (see Table of Materials). Click on the Home button to move the mouse bed from MR to the original position.</li>
	<li>Carefully remove the mouse from the scanner and return it to a clean housing cage with a heated pad underneath to allow recovery in warm environment. Supply the mouse with food and water. The system is now ready for the next mouse in queue.</li>
	<li>To reconstruct data, select PET Acquisition under the Raw Scan menu to load the completed PET scan. Select T1-weighted MR Acquisition for material map creation. Reconstruct the data as described above (see step 2.5).</li>
	<li>Follow the local and institute regulations regarding the care and handling of post-PET imaging mouse. Consider all used syringes/needles, gloves, bedding, and fecal matter as radioactive waste that require special handling/disposal in accordance with the local regulations.</li>
</ol>
5. Post-imaging analysis
<ol>
	<li>Open the Image Analysis software (see Table of Materials) and click on Load DICOM Data to retrieve the corresponding MR and PET images.</li>
	<li>Perform co-registration of MR and PET image by dragging these images to the display window. Click on the Automatic Registration function.
	<ol>
		<li>Select Rigid transformation under the Registration Setup drop-down menu. Check Shift and Rotation under the Rigid/Affine menu.</li>
		<li>Select T1-weighted MR acquisition as the Reference and PET acquisition as the Reslice under the Global Role Selection menu.</li>
		<li>Inspect the registration in all three dimensions to make sure a perfect alignment between MR and PET images. To adjust it manually, click on Manual Registration.</li>
	</ol>
	</li>
	<li>Use Interpolated Ellipse ROI to draw VOI on the tissue of interest, i.e., iBAT and inguinal white adipose tissue (iWAT) using MR image for reference. Use the Brush Tool and Eraser Tool to define the VOI border; hence, the anatomy of tissues. Make sure there is no overlap uptake by using PET image to avoid spillover from the neighboring organs. Repeat the process slide-by-slide until the whole VOI is delineated. If necessary, edit the VOIs to maintain consistent VOI volumes between each mouse.</li>
	<li>Use Ellipsoid VOI to draw a 3 mm3 VOI on the lung as a reference organ. Avoid any spillover from the neighboring heart and muscle.</li>
	<li>Upon completion, click on Show ROI Table to rename each VOI. Record the mean radioactivity with the VOI and tissue volume into a spreadsheet. Archive the VOI drawings and the imaging data to a data storage device.</li>
	<li>Calculate the standardized uptake value (SUV) for all VOIs using the following equation11: 
	SUVmean&#160;= VOI radioactivity in kBq / (Decay - corrected injected dose in kBq / mouse body weight in kg), assuming a tissue density of 1 g/mL.&#160;</li>
</ol>

<ol>
	<li>Rosen, E. D., Spiegelman, B. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=What+we+talk+about+when+we+talk+about+fat.">What we talk about when we talk about fat.</a> Cell. 156 (1-2), 20-44 (2014).</li><li>Cannon, B., Brown Nedergaard, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=adipose+tissue:+function+and+physiological+significance.">adipose tissue: function and physiological significance.</a> Physiological Review. 84 (1), 277-359 (2004).</li><li>Jal Wu, ., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Beige+adipocytes+are+a+distinct+type+of+thermogenic+fat+cell+in+mouse+and.">Beige adipocytes are a distinct type of thermogenic fat cell in mouse and.</a> 150 (2), 366-376 (2012).</li><li>Cypess, A. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Activation+of+human+brown+adipose+tissue+by+a+beta3-adrenergic+receptor+agonist.">Activation of human brown adipose tissue by a beta3-adrenergic receptor agonist.</a> Cell Metabolism. 21 (1), 33-38 (2015).</li><li>Ishibashi, J., Seale, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Beige+can+be+slimming.">Beige can be slimming.</a> Science. 328 (5982), 1113-1114 (2010).</li><li>Jal Schulz, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Brown-fat+paucity+due+to+impaired+BMP+signalling+induces+compensatory+browning+of+white+fat.">Brown-fat paucity due to impaired BMP signalling induces compensatory browning of white fat.</a> Nature. 495 (7441), 379-383 (2013).</li><li>Pal Cohen, ., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ablation+of+PRDM16+and+beige+adipose+causes+metabolic+dysfunction+and+a+subcutaneous+to+visceral+fat+switch.">Ablation of PRDM16 and beige adipose causes metabolic dysfunction and a subcutaneous to visceral fat switch.</a> Cell. 156 (1-2), 304-316 (2014).</li><li>Mal Cypess, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Identification+and+importance+of+brown+adipose+tissue+in+adult+humans.">Identification and importance of brown adipose tissue in adult humans.</a> New England Journal of Medicine. 360 (15), 1509-1517 (2009).</li><li>Aal vander Lans, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cold+acclimation+recruits+human+brown+fat+and+increases+nonshivering+thermogenesis.">Cold acclimation recruits human brown fat and increases nonshivering thermogenesis.</a> Journal of Clinical Investigation. 123 (8), 3395-3403 (2013).</li><li>Jal Hanssen, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Short-term+cold+acclimation+improves+insulin+sensitivity+in+patients+with+type+2+diabetes+mellitus.">Short-term cold acclimation improves insulin sensitivity in patients with type 2 diabetes mellitus.</a> Nature Medicine. 21 (8), 863-865 (2015).</li><li>Wang, X., Minze, L. J., Shi, Z. Z. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Functional+imaging+of+brown+fat+in+mice+with+18F-FDG+micro-PET/CT.">Functional imaging of brown fat in mice with 18F-FDG micro-PET/CT.</a> Journal of Visualized Experiments: JoVE. 69, (2012).</li><li>Greenwood, H. E., Nyitrai, Z., Mocsai, G., Hobor, S., Witney, T. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High-throughput+PET/CT+imaging+using+a+multiple-mouse+imaging+system.">High-throughput PET/CT imaging using a multiple-mouse imaging system.</a> Journal of Nuclear Medicine: Official Publication, Scoiety of Nuclear Medicine. 61 (2), 292-297 (2020).</li><li>Carter, L. M., Henry, K. E., Platzman, A., Lewis, J. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=3D-printable+platform+for+high-throughput+small-animal+imaging.">3D-printable platform for high-throughput small-animal imaging.</a> Journal of Nuclear Medicine: Official Publication, Scoiety of Nuclear Medicine. 61 (11), 1691-1692 (2020).</li><li>Jal Andersson, ., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Estimating+the+cold-induced+brown+adipose+tissue+glucose+uptake+rate+measured+by+(18)F-FDG+PET+using+infrared+thermography+and+water-fat+separated+MRI.">Estimating the cold-induced brown adipose tissue glucose uptake rate measured by (18)F-FDG PET using infrared thermography and water-fat separated MRI.</a> Scientific Reports. 9 (18), 12358 (2019).</li><li>Eal Lundstrom, ., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Brown+adipose+tissue+estimated+with+the+magnetic+resonance+imaging+fat+fraction+is+associated+with+glucose+metabolism+in+adolescents.">Brown adipose tissue estimated with the magnetic resonance imaging fat fraction is associated with glucose metabolism in adolescents.</a> Pediatric Obesity. 14 (9), (2019).</li><li>Eal Lundstrom, ., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Magnetic+resonance+imaging+cooling-reheating+protocol+indicates+decreased+fat+fraction+via+lipid+consumption+in+suspected+brown+adipose+tissue.">Magnetic resonance imaging cooling-reheating protocol indicates decreased fat fraction via lipid consumption in suspected brown adipose tissue.</a> PLoS One. 10 (4), 0126705 (2015).</li><li>Nakamura, Y., Yanagawa, Y., Morrison, S. F., Nakamura, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Medullary+reticular+neurons+mediate+neuropeptide+Y-induced+metabolic+inhibition+and+mastication.">Medullary reticular neurons mediate neuropeptide Y-induced metabolic inhibition and mastication.</a> Cell Metabolism. 25 (2), 322-334 (2017).</li><li>Jal Fueger, B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Impact+of+animal+handling+on+the+results+of+18F-FDG+PET+studies+in+mice.">Impact of animal handling on the results of 18F-FDG PET studies in mice.</a> Journal of Nuclear Medicine: Official Publication, Scoiety of Nuclear Medicine. 47 (6), 999-1006 (2006).</li><li>Vines, D. C., Green, D. E., Kudo, G., Keller, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evaluation+of+mouse+tail-vein+injections+both+qualitatively+and+quantitatively+on+small-animal+PET+tail+scans.">Evaluation of mouse tail-vein injections both qualitatively and quantitatively on small-animal PET tail scans.</a> Journal of Nuclear Medicine Technology. 39 (4), 264-270 (2011).</li></ol>

The authors have no conflicts of interest to disclose.

In this study, a PET/MR -based imaging and quantification of functional brown and beige adipose tissue in small animal was described. This method uses the non-metabolizable glucose analog [18F]FDG as an imaging biomarker so as to identify the adipose tissues with high glucose-demand in a non-invasive manner. MR offers good soft tissue contrast and can better differentiate adipose fat tissues from the neighboring soft tissues and muscle. When combined with PET, this enables imaging and quantifying of the activated adipocytes as a result of high glucose utilization in an accurate manner. The experimental conditions outlined here highlights the feasibility of using [18F]FDG PET to study up-regulation of iBAT and iWAT in vivo, and is potentially useful for evaluation of the thermogenic impact of new drug candidates. In addition, this protocol can be easily modified into high throughput format by simultaneously imaging multiple mice using a specially designed animal bed, thereby increasing the statistical power and confidence in the imaging data at a reduced cost and time12,13.
Currently, [18F]FDG PET/CT remains the most common approach to visualize BAT in humans and rodents and standard protocols have been well established8,11. In recent years, there are also several studies using [18F]FDG PET/MR imaging to assess BAT in humans14,15,16. In contrast, no detailed description on [18F]FDG PET/MRI for small animals is available. Described here is a detailed protocol that relies on the use of a combined PET and MR imaging system in mice. This method takes advantage of the higher resolution of MRI, especially on the detection of fat tissues, making them easy to identify and segment compared to the commonly used CT method. Therefore, the current approach enables an improved accuracy of PET quantification compared to the PET/CT method, which is of great value for studies in small animals with more delicate adipose depots. When analyzing the results of tissues of interest at their baseline uptake, MRI becomes an essential tool to accurately draw the VOIs to ensure consistency of their volumes between mice and avoid inclusion of neighboring organs. In addition, accurate image processing such as image registration and VOI delineation are important to allow reliable quantification. The anatomical location of the glucose-responsive BAT is distinct between humans and mouse. While the functional BAT locates at the interscapular region, [18F]FDG PET/MR imaging-based analysis mainly identify functional BAT in the supraclavicular region in humans14,15,16.
The fasting or fed status of the mice should also be taken into consideration when performing the [18F]FDG uptake experiment. In some studies, the mice are fasted for several hours or even overnight before the uptake experiment since it is supposed that endogenous glucose will compete with [18F]FDG. In the protocol, the [18F]FDG at fed status was measured and strong uptake signal was still observed in both iBAT and iWAT. This, thus, demonstrates that it is not necessary to put the mice at a fasted status for robust uptake signals, which is less physiologically relevant. Actually, caution should be taken when examining BAT and beige adipocytes in fasted animals since a previous finding has reported that the hypothalamic neuropeptide Y (NPY)-mediated hunger signal acts on the medullary motor systems to inhibit BAT thermogenesis by reducing the sympathetic innervation17. Consistently, in humans, it is suggested that upon high calorigenic diets, the thermogenic adipocytes burn out extra calories so as to maintain energy balance. In contrast, upon nutrient deprivation, counter-regulatory mechanisms are activated to suppress energy waste.
Another consideration for [18F]FDG PET imaging involves the routes for radiotracer administration into mice. Intraperitoneal and intravenous techniques are two common ways to inject [18F]FDG into mice, and both methods result in a relatively similar biodistribution of [18F]FDG in mice 60 min post injection18. While the intraperitoneal method is relatively easy to perform and the injection can be done quickly to avoid unwanted stress imposed onto the mice, direct injection accidentally into the bowel is common and is not immediately identified, leading to unreliable PET results19. Intravenous method is the preferred method and employed in this study. Successful tail vein injection can be determined when a visible blood flashback is observed prior to infusion, indicating that the needle is properly positioned inside the vein for infusion. One limitation to this technique is the difficulty to notice a visible blood flashback, potentially due to low blood pressure and the presence of dark hair on the tails. This can be overcome by warming the tail with a warm washcloth to increase the blood flow, hence improving the visibility of the vein for needle insertion.
An accurate scanner and a relevant equipment are other important factors for reliable PET image quantification. It is imperative to perform routine quality control examinations on PET and MR components of the scanner. MR quality control involves the signal-to-noise ratio assessment on different T1- and T2-weighted sequences, which should be performed on a weekly basis as recommended by the scanner manufacturer. For PET, accuracy of activity must be determined using a syringe containing a known concentration of radioactivity on a weekly basis or before the start of an important study. This quality control test also allows determination of co-registration of PET and MR images. Calibration must be performed if the recovered activity falls outside the recommended range or mis-registration between PET and MR images is found. In addition, the dose calibrator should be regularly calibrated according to the manufacturer guidelines since this is an important tool for quality control of the scanner as well as radioactivity measurement for PET imaging.
This study shows that the activation of adipose depots in both iBAT and iWAT in mice can be visualized and quantified using [18F]FDG PET/MR imaging upon exposure to cold temperature. However, the current study is limited by the fact that [18F]FDG uptake in iWAT was relatively low unless in the absence of iBAT. This indicates that compared to the iBAT that is readily activated by cold stimulus, beige adipocytes are relatively reluctant to be mobilized and act more like a backup thermogenic depot of iBAT in mice. More efficient methods to induce the [18F]FDG signal in the iWAT and/or other adipose depots in normal mice, such as the use of beige-specific activators or stronger cold challenge condition, are to be identified, which is beyond the scope of the current study.

In response to changing nutritional needs, adipose tissue serves as an energy cache to adopt either lipid storage or mobilization mode to meet the needs of the body1. Moreover, adipose tissue also plays a key function in thermoregulation, via a process called non-shivering thermogenesis, also called facultative thermogenesis. This is typically achieved by the brown adipose tissue (BAT), which expresses abundant level of mitochondria membrane protein uncoupling protein 1 (UCP1). As a proton carrier, UCP1 generates heat by uncoupling the proton transport and ATP production2. Upon cold stimulation, thermogenesis in BAT is set in motion by activation of the sympathetic nervous system (SNS), followed by release of norepinephrine (NE). NE binds to the &#946;3 adrenergic receptors and leads to elevation of intracellular cyclic AMP (cAMP). As a consequence, cAMP/PKA-dependent engagement of CREB (cAMP response element-binding protein) stimulates Ucp1 transcription via direct binding on CREB-response elements (CRE)2. In addition to BAT, brown-like adipocytes are also found within white adipose tissue and are therefore named beige or brite (brown-in-white) cells1,3. In response to specific stimuli (such as cold), these otherwise quiescent beige cells are remodeled to exhibit multiple brown-like features, including multilocular lipid droplets, densely-packed mitochondria, and augmented UCP1 expression3,4,5.
Animal studies have demonstrated that brown and beige adipocytes possess multiple metabolic benefits beyond its fat-reducing effect, including insulin-sensitization, lipid-lowering, anti-inflammation, and anti-atherosclerosis6,7. In humans, the amount of beige/brown fat is inversely correlated with age, insulin resistance index, and cardiometabolic disorders8. Moreover, activation of beige/brown adipocytes in humans by either cold acclimation or &#946;3 adrenergic receptor agonist confers protection against a series of metabolic disorders4,9,10. These pieces of evidence collectively indicate that induction of brown and beige adipose tissue is a potential therapeutic strategy for management of obesity and its related medical complications8.
Interestingly, although they share similar function, beige and classical brown adipocytes are derived from different precursors and activated by overlapping but distinct mechanisms1. Therefore, in vivo imaging and quantification of brown and beige adipocytes are essential to achieve a better understanding of the molecular control of these adipose tissues. Currently 18F-fluorodeoxyglucose ([18F]FDG) positron emission tomography (PET) scan combined with computed tomography (CT) remains the gold standard for characterization of thermogenic brown and beige cells in clinical studies8. Magnetic resonance imaging (MRI) uses powerful magnetic fields and radio frequency pulses to produce detailed anatomical structures. Compared to CT scan, MRI generates images of organs and soft tissues with a higher resolution. Provided here is a protocol for visualization and quantification of functional brown and beige adiposes in mouse models after acclimation to cold exposure, a common and most reliable way to induce adipose browning. This method can be applied to characterize the thermogenic adipose depots in small animal models with high precision.

<table><tbody><tr><td>0.9% sterile saline</td><td>BBraun</td><td></td><td>0.9% sodium chloride intravenous infusion, 500 mL</td></tr><tr><td>5 mL syringe</td><td>Terumo</td><td>SS05L</td><td>5 mL syringe Luer Lock</td></tr><tr><td>Dose Calibrator</td><td>Biodex</td><td></td><td>Atomlab 500</td></tr><tr><td>Eye lubricant</td><td>Alcon Duratears</td><td></td><td>Sterile ocular lubricant ointment, 3.5 g</td></tr><tr><td>Insulin syringe</td><td>Terumo</td><td>10ME2913</td><td>1 mL insulin syringe with needle</td></tr><tr><td>InterView Fusion software</td><td>Mediso</td><td>Version 3.03</td><td>Post-processing and image analysis software</td></tr><tr><td>Isoflurane</td><td>Chanelle Pharma</td><td></td><td>Iso-Vet, inhalation anesthetic, 250 mL</td></tr><tr><td>Ketamine</td><td>Alfasan International B.V.</td><td>HK-37715</td><td>Ketamine 10% injection solution, 10 mL</td></tr><tr><td>Medical oxygen</td><td>Linde HKO</td><td>101-HR</td><td>compressed gas, 99.5% purity</td></tr><tr><td>Metacam</td><td>Boehringer Ingelheim</td><td></td><td>5 mg/mL Meloxicam solution for injection for dogs and cats, 10 mL</td></tr><tr><td>nanoScan PET/MR Scanner</td><td>Mediso</td><td></td><td>3 Tesla MR</td></tr><tr><td>Nucline nanoScan software</td><td>Mediso</td><td>Version 3.0</td><td>Scanner operating software</td></tr><tr><td>Wound clips</td><td>Reflex 7</td><td>203-100</td><td>7mm Stainless steel wound clips, 20 clips</td></tr><tr><td>Xylazine</td><td>Alfasan International B.V.</td><td>HK-56179</td><td>Xylazine 2% injection solution, 30 mL</td></tr></tbody></table>

visualization and quantification of brown and beige adipose tissues in mice using [18f]fdg micro-pet/mr imaging

Brown and beige adipocytes are now recognized as potential therapeutic targets for obesity and metabolic syndromes. Non-invasive molecular imaging methods are essential to provide critical insights into these thermogenic adipose depots. Here, the protocol presents a PET/MR imaging-based method to evaluate the activity of brown and beige adipocytes in mouse interscapular brown adipose tissue (iBAT) and inguinal subcutaneous white adipose tissue (iWAT). Visualization and quantification of the thermogenic adipose depots were achieved using [18F]FDG, the non-metabolizable glucose analog, as the radiotracer, when combined with the precise anatomical information provided by MR imaging. The PET/MR imaging was conducted 7 days after cold acclimation and quantitation of [18F]FDG signal in different adipose depots was conducted to assess the relative mobilization of thermogenic adipose tissues. Removal of iBAT substantially increased cold-evoked [18F]FDG uptake in iWAT of the mice.

Three groups of mice (n = 3 per group) underwent micro-PET/MR imaging in this study, where they were housed at either thermoneutrality (30 &#176;C) or cold (6 &#176;C) for 7 days. One group of mice (n = 3) had their iBAT removed (iBATx) prior to cold treatment (Figure 1A). This method led to an alteration to the white adipose tissue activity in all three mice. In particular, a remarkable increase in [18F]FDG uptake was observed in iWAT using micro-PET/MR imaging (Figure 1B-C). This co-registered imaging data is demonstrated as maximal intensity projection (MIP), where iWAT was clearly delineated to allow quantification of the [18F]FDG uptake. Consistently, the multilocular adipocytes, which are characteristic morphology for beige adipocytes, were more pronounced in iWAT from iBATx mice, compared to the sham operated group (Figure 1D).
To verify whether changes on iBAT and iWAT activities upon this prolonged cold induction can be monitored by micro-PET/MR imaging, imaging studies were performed on the mice exposed to 30 &#176;C and 6 &#176;C and the results between groups were compared. PET/MR imaging also demonstrated that mice subjected to 6 &#176;C have markedly elevated [18F]FDG uptake on iBAT in sham operated mice (Figure 2A), which is consistent with the previous reported literature11. Mice with their iBAT removed (iBATx) prior to cold treatment showed the highest [18F]FDG uptake in the iWAT among the 30 &#176;C and 6 &#176;C group (Figure 2B). PET images were further quantified using an SUV-based approach. In iBAT, cold exposure caused a 7-fold increase in [18F]FDG uptake when compared to the 30 &#176;C group. In iWAT, [18F]FDG uptake was higher&#160;in cold-acclimated iBATx mice than the remaining groups (Figure 2C). Removal of iBAT in the cold-induced mice resulted in an 8-fold increase in the uptake of iWAT compared to the thermoneutrality mice, whereas only a modest increase (2-fold) was observed when iBAT was present in mice.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/62460/62460fig1v3.jpg" /> 
Figure 1: Micro-PET/MR Imaging of inguinal white adipose tissue (iWAT) in mice. Interscapular brown adipose tissue was surgically removed (iBATx). After recovery, the mice were housed at 6 &#176;C for 7 days before analysis. (A) Flow chart for the surgical and the subsequent procedures. (B) Illustration of the position of the mouse and the PET/MR scanner. (C) Maximal intensity projection (MIP) of co-registered PET/MR images. White arrows: Location of iWAT. A: Anterior L: Left. (D) Hematoxylin and Eosin (HE) staining of iWAT in sham and iBATx mice after cold exposure. Scale bar = 100 &#181;m. <a href="https://www-jove-com.bdigitaluss.remotexs.co/files/ftp_upload/62460/62460fig1v3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/62460/62460fig02.jpg" /> 
Figure 2: Representative in vivo [18F]FDG uptake in brown adipose tissue at the interscapular region (iBAT) and inguinal subcutaneous white adipose tissue (iWAT). Mice housed at thermoneutrality (30 &#176;C), cold-acclimated (6 &#176;C) and cold-acclimated + iBATx were subjected to [18F]FDG PET/MR imaging. (A) Sagittal section of PET/MR images showing iBAT in mice. (B) Axial section of PET/MR images showing bilateral iWAT. (C) Quantitative analysis of [18F]FDG uptake in iBAT (left) and iWAT (right). Yellow arrows: Location of iBAT. White arrows: Location of iWAT. n = 3 for each group. Values of SUVratio are presented as mean &#177;SD. <a href="https://www-jove-com.bdigitaluss.remotexs.co/files/ftp_upload/62460/62460fig02large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Visualization and Quantification of Brown and Beige Adipose Tissues in Mice using [18F]FDG Micro-PET/MR Imaging at JoVE.com

Visualization and Quantification of Brown and Beige Adipose Tissues in Mice using [18F]FDG Micro-PET/MR Imaging

Functional imaging and quantitation of thermogenic adipose depots in mice using a micro-PET/MR imaging-based approach.

Visualization and Quantification of Brown and Beige Adipose Tissues in Mice using [18F]FDG Micro-PET/MR Imaging

Brown and beige adipocytes are now recognized as potential therapeutic targets for obesity and metabolic syndromes. Non-invasive molecular imaging methods ...

visualization-quantification-brown-beige-adipose-tissues-mice-using

Universidad San Sebastian

Research

JoVE Journal

Biology

3.0K Views.  The University of Hong Kong. Functional imaging and quantitation of thermogenic adipose depots in mice using a micro-PET/MR imaging-based approach.

Video: Visualization and Quantification of Brown and Beige Adipose Tissues in Mice using [18F]FDG Micro-PET/MR Imaging

Utilizing 18F-FDG PET/CT Imaging and Quantitative Histology to Measure Dynamic Changes in the Glucose Metabolism in Mouse Models of Lung Cancer

A hallmark of advanced tumors is a switch to aerobic glycolysis that is readily measured by [18F]-2-fluoro-2-deoxy-D-glucose positron emission tomography (18F-FDG PET) imaging. Co-mutations in the KRAS proto-oncogene and the LKB1 tumor suppressor gene are frequent events in lung cancer that drive hypermetabolic, glycolytic tumor growth. A critical pathway regulating the growth and metabolism of these tumors is the mechanistic target of the rapamycin (mTOR) pathway, which can be effectively targeted using selective catalytic mTOR kinase inhibitors. The mTOR inhibitor MLN0128 suppresses glycolysis in mice bearing tumors with Kras and Lkb1 co-mutations, referred to as KL mice. The therapy response in KL mice is first measured by 18F-FDG PET and computed tomography (CT) imaging before and after the delivery of MLN0128. By utilizing 18F-FDG PET/CT, researchers are able to measure dynamic changes in the glucose metabolism in genetically engineered mouse models (GEMMs) of lung cancer following a therapeutic intervention with targeted therapies. This is followed by ex vivo autoradiography and a quantitative immunohistochemical (qIHC) analysis using morphometric software. The use of qIHC enables the detection and quantification of distinct changes in the biomarker profiles following treatment as well as the characterization of distinct tumor pathologies. The coupling of PET imaging to quantitative histology is an effective strategy to identify metabolic and therapeutic responses in vivo in mouse models of disease.

Utilizing 18F-FDG PET/CT Imaging and Quantitative Histology to Measure Dynamic Changes in the Glucose Metabolism in Mouse Models of Lung Cancer

In this protocol, we describe how to utilize [18F]-2-fluoro-2-deoxy-D-glucose positron emission tomography and computed tomography (18F-FDG PET/CT) imaging to measure the tumor metabolic response to the targeted therapy MLN0128 in a Kras/Lkb1 mutant mouse model of lung cancer and coupled imaging with high resolution ex vivo autoradiography and quantitative histology.

A hallmark of advanced tumors is a switch to aerobic glycolysis that is readily measured by [18F]-2-fluoro-2-deoxy-D-glucose positron emission tomography ...

Cancer Research

Segmentation and Measurement of Fat Volumes in Murine Obesity Models Using X-ray Computed Tomography

Obesity is associated with increased morbidity and mortality as well as reduced metrics in quality of life.1 Both environmental and genetic factors are associated with obesity, though the precise underlying mechanisms that contribute to the disease are currently being delineated.2,3 Several small animal models of obesity have been developed and are employed in a variety of studies.4 A critical component to these experiments involves the collection of regional and/or total animal fat content data under varied conditions.
Traditional experimental methods available for measuring fat content in small animal models of obesity include invasive (e.g. ex vivo measurement of fat deposits) and non-invasive (e.g. Dual Energy X-ray Absorptiometry (DEXA), or Magnetic Resonance (MR)) protocols, each of which presents relative trade-offs. Current invasive methods for measuring fat content may provide details for organ and region specific fat distribution, but sacrificing the subjects will preclude longitudinal assessments. Conversely, current non-invasive strategies provide limited details for organ and region specific fat distribution, but enable valuable longitudinal assessment. With the advent of dedicated small animal X-ray computed tomography (CT) systems and customized analytical procedures, both organ and region specific analysis of fat distribution and longitudinal profiling may be possible. Recent reports have validated the use of CT for in vivo longitudinal imaging of adiposity in living mice.5,6 Here we provide a modified method that allows for fat/total volume measurement, analysis and visualization utilizing the Carestream Molecular Imaging Albira CT system in conjunction with PMOD and Volview software packages.

Fat content analysis is routinely conducted in studies utilizing murine obesity models. Emerging methods in small animal CT imaging and analysis are providing for longitudinal detail rich fat content analysis. Here we detail step by step procedures for performing small animal CT imaging, analysis, and visualization.

Obesity is associated with increased morbidity and mortality as well as reduced metrics in quality of life.1 Both environmental and genetic factors are ...

Medicine

Non-Invasive PET/MR Imaging in an Orthotopic Mouse Model of Hepatocellular Carcinoma

Preclinical experimental models of hepatocellular carcinoma (HCC) that recapitulate human disease represent an important tool to study tumorigenesis and evaluate novel therapeutic approaches. Non-invasive whole-body imaging using positron emission tomography (PET) provides critical insights into the in vivo characteristics of tissues at the molecular level in real-time. We present here a protocol for orthotopic HCC xenograft creation with and without hepatic artery ligation (HAL) to induce tumor hypoxia and the assessment of their tumor metabolism in vivo using [18F]Fluoromisonidazole ([18F]FMISO) and [18F]Fluorodeoxyglucose ([18F]FDG) PET/magnetic resonance (MR) imaging. Tumor hypoxia could be readily visualized using the hypoxia marker [18F]FMISO, and it was found that the [18F]FMISO uptake was higher in HCC mice that underwent HAL than in the non-HAL group, whereas [18F]FDG could not distinguish tumor hypoxia between the two groups. HAL tumors also displayed a higher level of hypoxia-inducible factor (HIF)-1&#945; expression in response to hypoxia. Quantification of HAL tumors showed a 2.3-fold increase in [18F]FMISO uptake based on the standardized value uptake (SUV) approach.

Here, we present a protocol to create orthotopic hepatocellular carcinoma xenografts with and without hepatic artery ligation and perform non-invasive positron emission tomography (PET) imaging of tumor hypoxia using [18F]Fluoromisonidazole ([18F]FMISO) and [18F]Fluorodeoxyglucose ([18F]FDG).

Preclinical experimental models of hepatocellular carcinoma (HCC) that recapitulate human disease represent an important tool to study tumorigenesis and ...

Cerenkov Luminescence Imaging of Interscapular Brown Adipose Tissue

Brown adipose tissue (BAT), widely known as a &#8220;good fat&#8221; plays pivotal roles for thermogenesis in mammals. This special tissue is closely related to metabolism and energy expenditure, and its dysfunction is one important contributor for obesity and diabetes. Contrary to previous belief, recent PET/CT imaging studies indicated the BAT depots are still present in human adults. PET imaging clearly shows that BAT has considerably high uptake of 18F-FDG under certain conditions. In this video report, we demonstrate that Cerenkov luminescence imaging (CLI) with 18F-FDG can be used to optically image BAT in small animals. BAT activation is observed after intraperitoneal injection of norepinephrine (NE) and cold treatment, and depression of BAT is induced by long anesthesia. Using multiple-filter Cerenkov luminescence imaging, spectral unmixing and 3D imaging reconstruction are demonstrated. Our results suggest that CLI with 18F-FDG is a practical technique for imaging BAT in small animals, and this technique can be used as a cheap, fast, and alternative imaging tool for BAT research.

In this video report, we show the application of Cerenkov Luminescence Imaging (CLI) for interscapular brown adipose tissue in mice under activated and depressed conditions.

Brown adipose tissue (BAT), widely known as a &#8220;good fat&#8221; plays pivotal roles for thermogenesis in mammals. This special tissue is closely ...

Human Brown Adipose Tissue Depots Automatically Segmented by Positron Emission Tomography/Computed Tomography and Registered Magnetic Resonance Images

Reliably differentiating brown adipose tissue (BAT) from other tissues using a non-invasive imaging method is an important step toward studying BAT in humans. Detecting BAT is typically confirmed by the uptake of the injected radioactive tracer 18F-Fluorodeoxyglucose (18F-FDG) into adipose tissue depots, as measured by positron emission tomography/computed tomography (PET-CT) scans after exposing the subject to cold stimulus. Fat-water separated magnetic resonance imaging (MRI) has the ability to distinguish BAT without the use of a radioactive tracer. To date, MRI of BAT in adult humans has not been co-registered with cold-activated PET-CT. Therefore, this protocol uses 18F-FDG PET-CT scans to automatically generate a BAT mask, which is then applied to co-registered MRI scans of the same subject. This approach enables measurement of quantitative MRI properties of BAT without manual segmentation. BAT masks are created from two PET-CT scans: after exposure for 2 hr to either thermoneutral (TN) (24 &#176;C) or cold-activated (CA) (17 &#176;C) conditions. The TN and CA PET-CT scans are registered, and the PET standardized uptake and CT Hounsfield values are used to create a mask containing only BAT. CA and TN MRI scans are also acquired on the same subject and registered to the PET-CT scans in order to establish quantitative MRI properties within the automatically defined BAT mask. An advantage of this approach is that the segmentation is completely automated and is based on widely accepted methods for identification of activated BAT (PET-CT). The quantitative MRI properties of BAT established using this protocol can serve as the basis for an MRI-only BAT examination that avoids the radiation associated with PET-CT.

The method presented here uses 18F-Fluorodeoxyglucose (18F-FDG) positron emission tomography/computed tomography (PET-CT) and fat-water separated magnetic resonance imaging (MRI), each scanned following 2 hr exposure to thermoneutral (24 &#176;C) and cold conditions (17 &#176;C) in order to map brown adipose tissue (BAT) in adult human subjects.

Reliably differentiating brown adipose tissue (BAT) from other tissues using a non-invasive imaging method is an important step toward studying BAT in ...

Determining Glucose Metabolism Kinetics Using 18F-FDG Micro-PET/CT

This paper describes the use of 18F-FDG and micro-PET/CT imaging to determine in vivo glucose metabolism kinetics in mice (and is transferable to rats). Impaired uptake and metabolism of glucose in multiple organ systems due to insulin resistance is a hallmark of type 2 diabetes. The ability of this technique to extract an image-derived input function from the vena cava using an iterative deconvolution method eliminates the requirement of the collection of arterial blood samples. Fitting of tissue and vena cava time activity curves to a two-tissue, three compartment model permits the estimation of kinetic micro-parameters related to the 18F-FDG uptake from the plasma to the intracellular space, the rate of transport from intracellular space to plasma and the rate of 18F-FDG phosphorylation. This methodology allows for multiple measures of glucose uptake and metabolism kinetics in the context of longitudinal studies and also provides insights into the efficacy of therapeutic interventions.

Determining Glucose Metabolism Kinetics Using 18F-FDG Micro-PET/CT

This study describes a protocol that uses 18F-FDG and positron emission tomography/computed tomography (PET/CT) imaging, together with kinetic modelling, to quantify the in vivo, real-time uptake of 18F-FDG into tissues.

This paper describes the use of 18F-FDG and micro-PET/CT imaging to determine in vivo glucose metabolism kinetics in mice (and is transferable to rats). ...

Functional Imaging of Brown Fat in Mice with 18F-FDG micro-PET/CT

Brown adipose tissue (BAT) differs from white adipose tissue (WAT) by its discrete location and a brown-red color due to rich vascularization and high density of mitochondria. BAT plays a major role in energy expenditure and non-shivering thermogenesis in newborn mammals as well as the adults 1. BAT-mediated thermogenesis is highly regulated by the sympathetic nervous system, predominantly via &beta; adrenergic receptor 2, 3. Recent studies have shown that BAT activities in human adults are negatively correlated with body mass index (BMI) and other diabetic parameters 4-6. BAT has thus been proposed as a potential target for anti-obesity/anti-diabetes therapy focusing on modulation of energy balance 6-8. While several cold challenge-based positron emission tomography (PET) methods are established for detecting human BAT 9-13, there is essentially no standardized protocol for imaging and quantification of BAT in small animal models such as mice. Here we describe a robust PET/CT imaging method for functional assessment of BAT in mice. Briefly, adult C57BL/6J mice were cold treated under fasting conditions for a duration of 4 hours before they received one dose of 18F-Fluorodeoxyglucose (FDG). The mice were remained in the cold for one additional hour post FDG injection, and then scanned with a small animal-dedicated micro-PET/CT system. The acquired PET images were co-registered with the CT images for anatomical references and analyzed for FDG uptake in the interscapular BAT area to present BAT activity. This standardized cold-treatment and imaging protocol has been validated through testing BAT activities during pharmacological interventions, for example, the suppressed BAT activation by the treatment of &beta;-adrenoceptor antagonist propranolol 14, 15, or the enhanced BAT activation by &beta;3 agonist BRL37344 16. The method described here can be applied to screen for drugs/compounds that modulate BAT activity, or to identify genes/pathways that are involved in BAT development and regulation in various preclinical and basic studies.

Functional Imaging of Brown Fat in Mice with 18F-FDG micro-PET/CT

A method of functional imaging of mouse brown adipose tissue (BAT) is described in which cold-stimulated uptake of 18F-Fluorodeoxyglucose (FDG) in BAT is non-invasively assessed with a standardized micro-PET/CT protocol. This method is robust and sensitive to detect differences in BAT activities in mouse models.

Brown adipose tissue (BAT) differs from white adipose  tissue (WAT) by its discrete location and a brown-red color due to rich  vascularization and high ...

Whole Body and Regional Quantification of Active Human Brown Adipose Tissue Using 18F-FDG PET/CT

In endothermic animals, brown adipose tissue (BAT) is activated to produce heat for defending body temperature in response to cold. BAT&#39;s ability to expend energy has made it a potential target for novel therapies to ameliorate obesity and associated metabolic disorders in humans. Though this tissue has been well studied in small animals, BAT&#39;s thermogenic capacity in humans remains largely unknown due to the difficulties of measuring its volume, activity, and distribution. Identifying and quantifying active human BAT is commonly performed using 18F-Fluorodeoxyglucose (18F-FDG) positron emission tomography and computed tomography (PET/CT) scans following cold-exposure or pharmacological activation. Here we describe a detailed image-analysis approach to quantify total-body human BAT from 18F-FDG PET/CT scans using an open-source software. We demonstrate the drawing of user-specified regions of interest to identify metabolically active adipose tissue while avoiding common non-BAT tissues, to measure BAT volume and activity, and to further characterize its anatomical distribution. Although this rigorous approach is time-consuming, we believe it will ultimately provide a foundation to develop future automated BAT quantification algorithms.

Whole Body and Regional Quantification of Active Human Brown Adipose Tissue Using 18F-FDG PET/CT

Using free, open-source software, we have developed an analytical approach to quantify total and regional brown adipose tissue (BAT) volume and metabolic activity of BAT using 18F-FDG PET/CT.

In endothermic animals, brown adipose tissue (BAT) is activated to produce heat for defending body temperature in response to cold. BAT&#39;s ability to ...

Infrared Thermography for the Detection of Changes in Brown Adipose Tissue Activity

Measuring brown adipose tissue (BAT) activity by positron emission tomography computed tomography (PET-CT) via the accumulation of 18F-fluorodeoxyglucose (FDG) after a meal or in obese or diabetic patients fails as the method of choice. The main reason is that 18F-FDG competes with the postprandial high glucose plasma concentration for the same glucose transporter on the membrane of BAT cells. In addition, BAT uses fatty acids as a source of energy as well, which is not visible with PET-CT and could be changed along with glucose concentration in obese and diabetic patients. Therefore, to estimate the physiological importance of BAT in animals and humans, a new infrared thermography method used in recent publications is applied.
After overnight fasting, BAT activity was measured by infrared thermography before and after a meal in human volunteers and&#160;female wild-type mice. The camera software calculates the object&#39;s temperature using distance from the object, skin emissivity, reflected room temperature, air temperature, and relative humidity. In mice, the shaved area above the BAT was a region of interest for which average and maximal temperatures were measured. The phase of the estrous cycle in female mice was determined after an experiment by vaginal smears stained with cresyl violet (0.1%) stain solution. In healthy volunteers, two skin areas of the neck were selected: the supraclavicular area (above the collarbone, where BAT cells are present) and the interclavicular area (between the collarbones, where there is no BAT tissue detected). BAT activity is determined by the subtraction of those two values. Also, the average and maximal temperatures of skin areas could be determined in animals and human participants.
Changes in BAT activity after a meal measured by infrared thermography, a non-invasive and more sensitive method, were shown to be sex, age, and phase of the estrous cycle dependent in laboratory animals. As part of diet-induced thermogenesis, BAT activation in humans was also proven to be sex, age, and body mass index dependent. Further determining the pathophysiological changes in BAT activity after a meal will be of great importance for participants with high glucose plasma concentrations (obesity and diabetes mellitus type 2), as well as in different laboratory animals (knock-out mice). This method is also a variable tool for determining possible activating drugs that could rejuvenate BAT activity.

Here, we present a protocol for measuring brown adipose tissue activity after a meal in humans and laboratory animals.

Measuring brown adipose tissue (BAT) activity by positron emission tomography computed tomography (PET-CT) via the accumulation of 18F-fluorodeoxyglucose ...

Using a Combination of Indirect Calorimetry, Infrared Thermography, and Blood Glucose Levels to Measure Brown Adipose Tissue Thermogenesis in Humans

In mammals, brown adipose tissue (BAT) is activated rapidly in response to cold in order to maintain body temperature. Although BAT has been studied greatly in small animals, it is difficult to measure the activity of BAT in humans. Therefore, little is known about the heat-generating capacity and physiological significance of BAT in humans, including the degree to which components of the diet can activate BAT. This is due to the limitations in the currently most used method to assess the activation of BAT-radiolabeled glucose (fluorodeoxyglucose or 18FDG) measured by positron emission tomography-computerized tomography (PET-CT).
This method is usually performed in fasted subjects, as feeding induces glucose uptake by the muscles, which can mask the glucose uptake into the BAT. This paper describes a detailed protocol for quantifying total-body human energy expenditure and substrate utilization from BAT thermogenesis by combining indirect calorimetry, infrared thermography, and blood glucose monitoring in carbohydrate-loaded adult males. To characterize the physiological significance of BAT, measures of the impact of BAT activity on human health are critical. We demonstrate a protocol to achieve this by combining carbohydrate loading and indirect calorimetry with measurements of supraclavicular changes in temperature. This novel approach will help to understand the physiology and pharmacology of BAT thermogenesis in humans.

Here, we present a protocol to quantify the physiological significance of the impact of brown adipose tissue (BAT) activity on human metabolism. This is achieved by combining carbohydrate loading and indirect calorimetry with measurements of supraclavicular changes in temperature. This novel approach can help develop a pharmacological target for BAT thermogenesis in humans.

In mammals, brown adipose tissue (BAT) is activated rapidly in response to cold in order to maintain body temperature. Although BAT has been studied ...

Visualization and Quantification of Brown and Beige Adipose Tissues in Mice using [¹⁸F]FDG Micro-PET/MR Imaging

Summary

Explore More Videos

Chapters in this video

Utilizing ¹⁸F-FDG PET/CT Imaging and Quantitative Histology to Measure Dynamic Changes in the Glucose Metabolism in Mouse Models of Lung Cancer

Segmentation and Measurement of Fat Volumes in Murine Obesity Models Using X-ray Computed Tomography

Non-Invasive PET/MR Imaging in an Orthotopic Mouse Model of Hepatocellular Carcinoma

Cerenkov Luminescence Imaging of Interscapular Brown Adipose Tissue

Human Brown Adipose Tissue Depots Automatically Segmented by Positron Emission Tomography/Computed Tomography and Registered Magnetic Resonance Images

Determining Glucose Metabolism Kinetics Using ¹⁸F-FDG Micro-PET/CT

Functional Imaging of Brown Fat in Mice with ¹⁸F-FDG micro-PET/CT

Whole Body and Regional Quantification of Active Human Brown Adipose Tissue Using ¹⁸F-FDG PET/CT

Infrared Thermography for the Detection of Changes in Brown Adipose Tissue Activity

Using a Combination of Indirect Calorimetry, Infrared Thermography, and Blood Glucose Levels to Measure Brown Adipose Tissue Thermogenesis in Humans