Rapid ultrasonic stimulation of inflamed tissue with diagnostic intent.
Previous studies have observed that individual pulses of intense focused ultrasound (iFU) applied to inflamed and normal tissue can generate sensations, where inflamed tissue responds at a lower intensity than normal tissue. It was hypothesized that successively applied iFU pulses will generate sensation in inflamed tissue at a lower intensity and dose than application of a single iFU pulse. This hypothesis was tested using an animal model of chronic inflammatory pain, created by injecting an irritant into the rat hind paw. Ultrasound pulses were applied in rapid succession or individually to rats' rear paws beginning at low peak intensities and progressing to higher peak intensities, until the rats withdrew their paws immediately after iFU application. Focused ultrasound protocols consisting of successively and rapidly applied pulses elicited inflamed paw withdrawal at lower intensity and estimated tissue displacement values than single pulse protocols. However, both successively applied pulses and single pulses produced comparable threshold acoustic dose values and estimates of temperature increases. This raises the possibility that temperature increase contributed to paw withdrawal after rapid iFU stimulation. While iFU-induction of temporal summation may also play a role, electrophysiological studies are necessary to tease out these potential contributors to iFU stimulation.
Applied Physics Laboratory, University of Washington, 1013 NE 40th Street, Seattle, Washington 98105, USA.
Abbi M
AM
McClintic
Trevor C
TC
Dickey
Michael
M
Gofeld
P Ray
PR
Illian
Michel
M
Kliot
John C
JC
Kucewicz
John D
JD
Loeser
Philippe G
PG
Richebe
Pierre D
PD
Mourad
D000818:Animals; D001522:Behavior, Animal; D059350:Chronic Pain / Q000139:chemically induced / Q000175:diagnosis* / Q000503:physiopathology / Q000523:psychology; D004195:Disease Models, Animal; D005620:Freund's Adjuvant; D006614:Hindlimb / Q000294:innervation*; D007249:Inflammation / Q000139:chemically induced / Q000175:diagnosis* / Q000503:physiopathology / Q000523:psychology; D008297:Male; D010147:Pain Measurement / Q000379:methods*; D058748:Pain Perception; D017288:Pain Threshold; D059227:Postsynaptic Potential Summation; D051381:Rats; D011916:Rats, Inbred F344; D011930:Reaction Time; D013997:Time Factors; D014465:Ultrasonics / Q000379:methods*
D005620:Freund's Adjuvant