FUS-mediated reversible modulation of region-specific brain function in animal model

FUS-mediated reversible modulation of region-specific

brain function in animal model

Jong-Hwan Lee*, Yongzhi Zhang*, Wonhye Lee*, Krisztina Fischer*, Alexander Bystritsky*, Nathan McDannold*, and

Ferenc A. Jolesz*, and Seung-Schik Yoo*,

*Department of Radiology, Brigham and Women’s Hospital, Harvard Medical School

Presented to Gerald J. & Dorothy R. Freidman Foundation Symposium 2008

Reversible and non-invasive regional modulation of cortical function

• Needed for short-term/long-term modulation of the brain function.

• Ultimately, it may provide non-pharmaceutical intervention of appetite control !

• Transcranial magnetic stimulation (TMS) suffers from limited penetration depth and lacks spatial specificity.

• Transcranial direct current stimulation (tDCS) lacks spatial specificity.

• Deep brain stimulation (DBS) is invasive.www.biomag.hus.fi/tms/Thesis/dt.html

Idea: Pulsed FUS (FUP)• Motivation and Earlier work

– Trans-skull delivery of FUS (Hynynen et al. 2004)– Reversible modulation of activity in ex vivo brain tissue

(Bachtold et al. 1998) – Previous works on animal sciatic nerves.

• Things to avoid;– Irreversible tissue damage or seizure induction.– BBB disruption.– Excessive heating.

• Proposed method: Instead of continuous application of HIFU, apply the low intensity FUS stimulation with sufficient inter-stimulation intervals as a train of pulses.

Initial excursion: Real-time fMRI during FUP

• Why real-time fMRI?– To monitor the blood-oxygenated-level-dependent

(BOLD) MRI signals that are associated with the activation in real-time, non-invasively.

– Allows the adjustment of the FUP parameters on-fly.

No stimulation stimulation

21 s 21 s12 s

T-1 signal equl

A

Detected activation at p<0.001 level and approximate location of the FUP application in yellow circle.

No stimulation stimulation

15 s 45s12 s

T-1 signal equl

15s

FUP application and intensity adjustment

50 W/cm2

Recovery

TRIAL EXAMPLE

Experimental flow1. Spotting of the FU ‘hot spot’ using phantom

– 690 KHz ultrasound transducer with 8 cm focal depth

2. Anatomical localization

3. Functional localization via fMRI– BOLD-sensitive EPI sequence to detect level of activation

4. Adjustment of positioning system

5. Application of FUP with fMRI

6. fMRI without FUP to monitor

7. MRI Thermometry– Fast SPGR sequence; phase

Dependent thermometry

8. [Group#1] Perfusion of Trypan blue to examine BBB disruption, followed by the histological analysis.

9. [Group #2] Survival for 1 week with behavior observation, followed by the histological analysis

Transducer

Ultrasound beam

Water tank

Water bag

Rabbit

Skull

Plastic plate

MRI Coil

Brain

Sonication target

Positioning system

Control Computer

Function Generator

Amplifier

Power Meter

MRI Room

Matching Network

Experimental setup

Power Monitor

Function Generator

Power Amplifier

Pulse Regulator

MRI Console rtfMRI Processor

Pulse Monitor

3T MRI

No stimulation

stimulation

15 s 9 s12 s 45 s

FUP application

Event-related response and FUP• In order to capture the effect of FUP during short-trial

based visual stimulation, event-related fMRI design was adapted.

• FUP (500 μs duration and 10 msec inter-pulse-interval) at 50W/cm2 intensity was applied for 9, 18, and 27 sec.

Temporal progression of activation

PreFUP

L R

FUP

3min

7min

11min

5min

BOLD Contrast (%) measured from each session

C

Presence of BBB disruption or tissue damage?

• Trypan Blue perfusion after FUP (within 30min) showed no apparent BBB disruption.

• Histological analysis (H&E stain) showed no tissue damage even at 350W/cm2 pulse (10 msec inter-pulse-interval) application of the FUP for 27 sec.

• Survival experiment showed normal post-FUP animal behavior and normal histology results.

McDannold et al. BWH, PNAS 2007

A B C D E

MR Thermometry

• No temperature rise during 27s application of FUP at 500 μs duration and 10 msec inter-pulse-interval at 50W/cm2 intensity. – Virtually no temperature change

• Even at higher level of energy at 350W/cm2 intensity, only 0.95 C rise of temperature was detected after 27s FUP application.

07019

077 sonication 1

Temperatures at 9.9 s.

P7.5

TR:39.2 TE:19.5

bw: 3.57 kHz

Img time: 4.0 s

FOV: 8 cm 256×256 (256×128)

FA: 30° ETL: 1 NEX: 1.00

coef: 0.01000 ppm/°C

Rabbit

Rabbit

08-03-08 2:14:01 PM

R14.8 L25.0

S23.8

I16.0

Tem

pe

ratu

re R

ise

(°C

)

1.8

1.4

1

0.6

0.2

-0.2

-0.6

-1

-1.4

-1.8

27s

18s

9s

Conclusions• Reversible modulation of region-specific brain function

was demonstrated via pulsed application of focused ultrasound energy.

• The given FUP parameter appears to be safe to be used, both short-term and long-term.

• The BOLD signal showed that the visual-stimulation-induced activation was enhanced during the FUP application, followed by the period of non-responsive stages, which suggest the ‘relative refractory period’.– More confirmatory study is needed using different stimulation parameters.

• Potential mechanism ? Temperature-mediation was ruled out. Possibly via mechanical modulation.

• Electrophysiological confirmation will be followed.

Future Direction• Application of the FUP to modulate neural

circuitries in hypothalamus (targeting ventromedial nucleus), and subsequent appetite control.

• Testing on obese ob/ob Leptin deficient mice– Effect of down-regulation ?– Effect of up-regulation ?

• Challenges– Size of region-of-interest in mouse is small.– Potential induction of modulation in other neuro-

endocrine systems.

From Harlan catalogue

Acknowledgement• Magdalini C. Pilatou, Ph.D.• Lisa Treat, M.S.• Jason White, Ph.D. and with the financial support from

– Gerald J. & Dorothy R. Freidman Foundation– Focused Ultrasound Surgery Foundation– Bystritsky Family Foundation

, and all anonymous rabbits…

Disclaimer: This rabbit was NOT used in the experiment