title: Investigations into pulsed high-intensity focused ultrasound-enhanced delivery: preliminary evidence for a novel mechanism.
abstract: Pulsed high-intensity focused ultrasound (HIFU) exposures without ultrasound contrast agents have been used for noninvasively enhancing the delivery of various agents to improve their therapeutic efficacy in a variety of tissue models in a nondestructive manner. Despite the versatility of these exposures, little is known about the mechanisms by which their effects are produced. In this study, pulsed-HIFU exposures were given in the calf muscle of mice, followed by the administration of a variety of fluorophores, both soluble and particulate, by local or systemic injection. In vivo imaging (whole animal and microscopic) was used to quantify observations of increased extravasation and interstitial transport of the fluorophores as a result of the exposures. Histological analysis indicated that the exposures caused some structural alterations such as enlarged gaps between muscle fiber bundles. These effects were consistent with increasing the permeability of the tissues; however, they were found to be transient and reversed themselves gradually within 72 h. Simulations of radiation force-induced displacements and the resulting local shear strain they produced were carried out to potentially explain the manner by which these effects occurred. A better understanding of the mechanisms involved with pulsed HIFU exposures for noninvasively enhancing delivery will facilitate the process for optimizing their use.
authors.affiliation: Department of Radiology and Imaging Sciences, Clinical Center, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Hilary A
authors.initials: HA
authors.lastname: Hancock
authors.forename: Lauren H
authors.initials: LH
authors.lastname: Smith
authors.forename: Julian
authors.initials: J
authors.lastname: Cuesta
authors.forename: Amir K
authors.initials: AK
authors.lastname: Durrani
authors.forename: Mary
authors.initials: M
authors.lastname: Angstadt
authors.forename: Mark L
authors.initials: ML
authors.lastname: Palmeri
authors.forename: Eitan
authors.initials: E
authors.lastname: Kimmel
authors.forename: Victor
authors.initials: V
authors.lastname: Frenkel
mesh_terms: D000818:Animals; D005119:Extravasation of Diagnostic and Therapeutic Materials / Q000000981:diagnostic imaging; D005260:Female; D057086:High-Intensity Focused Ultrasound Ablation / Q000295:instrumentation* / Q000379:methods; D037102:Lectins / Q000008:administration & dosage; D051379:Mice; D008809:Mice, Inbred C3H; D018485:Muscle Fibers, Skeletal / Q000000981:diagnostic imaging; D018482:Muscle, Skeletal / Q000000981:diagnostic imaging / Q000502:physiology; D054118:Nanospheres / Q000008:administration & dosage; D010539:Permeability; D012709:Serum Albumin / Q000008:administration & dosage; D013314:Stress, Mechanical; D014463:Ultrasonography
chemical_list: D037102:Lectins; D012709:Serum Albumin