All work was performed at the Duke Center for In Vivo Microscopy, an NIH/NIBIB national Biomedical Technology Resource Center (P41 EB015897) and NCI Small Animal Imaging Resource Program (U24 CA092656). Additional support was provided from NSF Graduate Research Fellowship (2003014921).

1. Assemble and Calibrate Ultrasound System
<ol>
	<li>The ultrasound system begins with a single-element ultrasound transducer with a diameter wide enough to cover the mouse brain and a center frequency in the range of 2 MHz. The transducer is driven by a 50-dB-power amplifier, which is connected to a signal generator that produces the ultrasound pulse sequence.</li>
	<li>To calibrate the acoustic pressure of the ultrasound system, use a hydrophone to relate the applied voltage to the resultant acoustic pressure. Place...

<ol>
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Here, a method was presented for noninvasively opening the BBB throughout the whole mouse brain with ultrasound and microbubbles (BOMUS). With the BBB open, Mn2+ was administered and activation-induced manganese-enhanced MRI (AIM MRI) was used to image neuronal response to short-duration stimulation in lightly sedated mice.
Adequate BBB opening was achieved with a peak-negative acoustic pressure of 0.36 MPa. Note, this is the pressure at scalp surface at the center of the ultrasound...

<table border="1">
 <tbody>
 <tr>
 <td>Name of the reagent</td>
 <td>Company</td>
 <td>Catalog number</td>
 <td>Comments </td>
 </tr>
 <tr>
 <td>Hydrophone</td>
 <td>Sonora Medical Systems, Longmont, CA</td>
 <td>SN S4-251</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>Translation stage</td>
 <td>Newport Corporation, Irvine, CA</td>
 <td>&nbsp;</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>Ultrasound transducer</td>
 <td>Olympus NDT, Inc., Waltham MA</td>
 <td>A306S-SU</td>
 <td>Review the manufacturer's test sheet that accompanies the transducer to find the exact center frequency of that particular transducer, which may differ from the nominal frequency listed in the catalog. (e.g., the nominal frequency of our transducer was 2.25 MHz, but the actual center frequency was 2.15 MHz.)</td>
 </tr>
 <tr>
 <td>Vevo Imaging Station</td>
 <td>VisualSonics, Inc. Toronto, Canada</td>
 <td>&nbsp;</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>50 dB power amplifier</td>
 <td>E&amp;I, Rochester, NY</td>
 <td>model 240L</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>Signal generator</td>
 <td>Agilent Technologies, Santa Clara, CA</td>
 <td>model 33220A</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>MnCl2-(H2O)4</td>
 <td>Sigma</td>
 <td>&nbsp;</td>
 <td>Molecular weight varies by batch, call manufacturer for exact measurement</td>
 </tr>
 <tr>
 <td>Perflutren lipid microspheres</td>
 <td>Lantheus Medical Imaging, N. Billerica, MA</td>
 <td>DEFINITY</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>Microsphere agitator</td>
 <td>Lantheus Medical Imaging, N. Billerica, MA</td>
 <td>VIALMIX</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>MR imaging coil</td>
 <td>m2m Imaging Corp., Hillcrest, OH</td>
 <td>&nbsp;</td>
 <td>35 mm diameter quadrature transmit/receive volume coil</td>
 </tr>
 <tr>
 <td>MRI system</td>
 <td>GE Healthcare, Milwaukee, WI</td>
 <td>&nbsp;</td>
 <td>GE EXCITE console operating a 7-T horizontal bore magnet</td>
 </tr>
 <tr>
 <td>Image analysis environment</td>
 <td>Visage Imaging, San Diego, CA, MathWorks, Natick MA</td>
 <td>Amira 
 MATLAB</td>
 <td>&nbsp;</td>
 </tr>
 </tbody>
</table>

functional neuroimaging using ultrasonic blood-brain barrier disruption and manganese-enhanced mri

Although mice are the dominant model system for studying the genetic and molecular underpinnings of neuroscience, functional neuroimaging in mice remains technically challenging. One approach, Activation-Induced Manganese-enhanced MRI (AIM MRI), has been used successfully to map neuronal activity in rodents 1-5. In AIM MRI, Mn2+ acts a calcium analog and accumulates in depolarized neurons 6,7. Because Mn2+ shortens the T1 tissue property, regions of elevated neuronal activity will enhance in MRI. Furthermore, Mn2+ clears slowly from the activated regions; therefore, stimulation can be performed outside the magnet prior to imaging, enabling greater experimental flexibility. However, because Mn2+ does not readily cross the blood-brain barrier (BBB), the need to open the BBB has limited the use of AIM MRI, especially in mice.
One tool for opening the BBB is ultrasound. Though potentially damaging, if ultrasound is administered in combination with gas-filled microbubbles (i.e., ultrasound contrast agents), the acoustic pressure required for BBB opening is considerably lower. This combination of ultrasound and microbubbles can be used to reliably open the BBB without causing tissue damage 8-11.
Here, a method is presented for performing AIM MRI by using microbubbles and ultrasound to open the BBB. After an intravenous injection of perflutren microbubbles, an unfocused pulsed ultrasound beam is applied to the shaved mouse head for 3 minutes. For simplicity, we refer to this technique of BBB Opening with Microbubbles and UltraSound as BOMUS 12. Using BOMUS to open the BBB throughout both cerebral hemispheres, manganese is administered to the whole mouse brain. After experimental stimulation of the lightly sedated mice, AIM MRI is used to map the neuronal response.
To demonstrate this approach, herein BOMUS and AIM MRI are used to map unilateral mechanical stimulation of the vibrissae in lightly sedated mice 13. Because BOMUS can open the BBB throughout both hemispheres, the unstimulated side of the brain is used to control for nonspecific background stimulation. The resultant 3D activation map agrees well with published representations of the vibrissae regions of the barrel field cortex 14. The ultrasonic opening of the BBB is fast, noninvasive, and reversible; and thus this approach is suitable for high-throughput and/or longitudinal studies in awake mice.

Watch this Scientific Journal Video about Functional Neuroimaging Using Ultrasonic Blood-brain Barrier Disruption and Manganese-enhanced MRI at JoVE.com

Functional Neuroimaging Using Ultrasonic Blood-brain Barrier Disruption and Manganese-enhanced MRI

A technique is described for broadly opening the blood-brain barrier in the mouse using microbubbles and ultrasound. Using this technique, manganese can be administered to the mouse brain. Because manganese is an MRI contrast agent that accumulates in depolarized neurons, this approach enables imaging of neuronal activity.

Although mice are the dominant model system for studying the genetic and molecular underpinnings of neuroscience, functional neuroimaging in mice remains ...

functional-neuroimaging-using-ultrasonic-blood-brain-barrier

Research

JoVE Journal

Neuroscience

14.9K visualizações.  Stanford University. Uma técnica é descrita para amplamente abertura da barreira sangue-cérebro no ratinho usando microbolhas e ultra-som. Usando esta técnica, o manganês pode ser administrada para o cérebro do rato. Porque o manganês é um agente de contraste para IRM que se acumula nos neurónios despolarizadas, esta abordagem permite imagiologia de actividade neuronal.