In Vivo Tracking of Edema Development and Microvascular Pathology in a Model of Experimental Cerebral Malaria Using Magnetic Resonance Imaging

The overall goal of this method is to monitor pathological changes of experimental cerebral malaria in vivo. This method can help to answer key questions in the pathogenesis of experimental cerebral malaria as it allows us to visualize in vivo how pathology of the whole brain evolves in space and over time. The technique thereby allows a detailed assessment of brain pathology, and can be used to assess the efficacy of novel treatment strategies in cerebral malaria.

Performing the MRI setup will be Manuel Fischer, our lab manager. Begin by collecting female mosquitoes from their cage, 17 to 22 days after the blood meal. Use forceps to place three to four mosquitoes on a glass slide, combined with a drop of cold RPMI medium.

Then, place the slide under a microscope. Carefully stretch the mosquito between the head and body with forceps, and use a syringe and needle to isolate the salivary gland. Next, collect the salivary glands from the glass slide by sucking them up with a glass pipette, and transferring them into 1.5 milliliter centrifuge tube.

Then, use a small plastic stick to smash the isolated salivary glands within the centrifuge tube for three minutes in order to isolate the sporozoites from the salivary gland tissue. Centrifuge for three minutes at 1, 000 times g and four degrees Celsius to purify the sporozoites from the remaining tissue. Pipette the supernatant, which contains the sporozoites, to a new centrifuge tube, and count the purified sporozoites in a Neubauer hemocytometer.

Sporozoites show a typical counterclockwise movement. Next, adjust the concentration of the purified sporozoites to 10, 000 per milliliter by adding phosphate-buffered saline. Finally, place a C57BL/6 mouse in a restrainer, and put its tail into warm water to better visualize the tail vein.

Then, inject a total of 1, 000 sporozoites, or 0.1 milliliters, into the tail vein to initiate infection. Begin by bringing the mouse to a 9.4T small animal Magnetic Resonance Imaging, or MRI scanner, that uses a volume resonator for radiofrequency transmission. Then, apply dexpanthenol eye ointment to both eyes.

Turn on the temperature-controlled water bath to 42 degrees Celsius in order to maintain the body temperature of the mouse. Then, place a tail vein catheter into the mouse's tail vein. Next, position the mouse for the MRI by placing it prone and with a crunched back on an animal bed equipped with a headlock and tooth bar to minimize head motion.

Take care not to straighten the cervical spine of the mouse. Connect a contrast agent injection system filled with 0.3 millimole per kilogram Gd-DTPA to the tail vein catheter. Next, place the 4-Channel Phased Array Surface Receiver head coil onto the head of the mouse.

Finally, place a breathing pad onto the back of the mouse and check the respiration on the monitoring device. Turn on the positional laser by pressing F2 on the control panel, and move the mouse until the horizontal positional light is in the middle of the smaller part of the coil, which covers the head of the mouse. Turn off the positional laser by pressing F2 again, and then move the mouse into the final position by pressing F3 on the control panel.

Begin by performing a localizing scan to make sure that the mouse brain is in the isocenter of the magnet. Qualitatively assess vasogenic edema by using 3D T2-weighted imaging. Select a multi-slice RARE sequence, and adjust the slice position, making sure that the whole brain, from the nose to the cerebellum is covered.

After adjusting the saturation slices, start the sequence, and wait 10 minutes and 48 seconds to acquire the images. Next, perform T2 relaxometry to quantitatively assess vasogenic edema by selecting multi-slice, multiple-spin echo sequence. Adjust the slice position, and start the acquisition of the sequence, which takes eight minutes and 53 seconds.

To quantitatively assess both vasogenic edema and cytotoxic edema, carry out diffusion-weighted imaging by selecting a spin-echo EPI diffusion sequence. Adjust the slice position and saturation slice. Then start the sequence and wait seven minutes and 56 seconds until the raw images are acquired.

Following that, assess microhemorrhages, using 3D T2 star-weighted imaging. Select a flow-compensated FLASH sequence, adjust the slice position, and start the sequence, which runs for 15 minutes and 40 seconds. Afterwards, assess arterial patency using time of flight angiography by selecting a 3D FLASH sequence.

Adjust the slice position, start the sequence, and then wait seven minutes and 16 seconds until the images are acquired. Finally, assess the blood-brain barrier disruption. Select a 3D T1-weighted imaging with a FLASH sequence, adjust the slice position, and start the sequence.

Wait one minute and 14 seconds until images without contrast are acquired. Then, inject contrast of 0.3 millimole per kilogram and repeat the measurement. An increase in blood-brain barrier disruption and a fluid increase indicate early vasogenic edema in the olfactory bulb that is already present in mild disease, and starts to spread towards the brain stem as the severity of the disease increases.

On T2 maps, the severity of vasogenic edema can be quantified by drawing regions of interest into specific anatomical regions. For each region, a T2 relaxation time that increases with increasing edema can be obtained. Furthermore, brain volume indicative of edema starts to significantly increase in moderately sick mice as compared to baseline, and further increases in severely sick mice.

Lastly, microvascular pathology, as evidenced by microhemorrhages and an increase of vessel susceptibility contrast, occurs after the first signs of blood-brain barrier disruption in vasogenic edema. These microhemmorhages predominantly occur in the olfactory bulb. If the whole MRI protocol is obtained, all images including positioning can be obtained within one hour, if it is performed properly.

The minimal protocol should include a T2 weighted sequence or T2 relaxometry, and a T2 star-weighted sequence in order to judge the presence of vasogenic edema, microhemmorhage load, and microvascular impairment. After watching this video, you should have a good understanding how whole-brain MRI visualizes pathological changes in experimental cerebral malaria, including such changes as brain swelling, which is difficult to detect ex vivo.