Detection of mild traumatic brain injury in rodent models using shear wave elastography: preliminary studies.

OBJECTIVES: Traumatic brain injury (TBI) can cause adverse physiologic changes in fluid content within the brain, which may lead to changes in tissue elasticity (eg, stiffness). This study evaluated the ability of ultrasonic shear wave elastography to observe these changes in the brain after TBI in vivo. METHODS: Mice and rats received a mild TBI or sham surgery and were imaged acutely or 24 hours after injury using shear wave elastography, and the hemispheric stiffness values were compared. RESULTS: Stiffness values were consistent across brain hemispheres of sham TBI rodents. By 24 hours after TBI, relative brain tissue stiffness values for mice and rats each decreased ipsilaterally and increased contralaterally, both relative to each other and compared to sham TBI rodents (P < .05). The absolute tissue elasticity value increased for rats (P < .05) but not for mice. CONCLUSIONS: Differences between intrahemispheric stiffness values of rodent brains by 24 hours after mild TBI may reflect the observed edema and hemorrhage ipsilateral to TBI and the known reduction of cerebral blood flow in both brain hemispheres. If these hypotheses hold true, ultrasonic shear wave elastography may offer a method for detecting adverse changes in fluid content within the brain after mild TBI.

Evidence of changes in brain tissue stiffness after ischemic stroke derived from ultrasound-based elastography.

OBJECTIVES: Ischemia, edema, elevated intracranial pressure, and reduced blood flow can occur in the brain as a result of ischemic stroke, including contralateral to the stroke via a process known as diaschisis. In this study, ultrasound elastography, an imaging process sensitive to the stiffness of tissue, including its relative fluid content, was used to study changes in the stiffness of individual cerebral hemispheres after transient ischemic injury. METHODS: Elastographic images of mouse brains were collected 24 and 72 hours after middle cerebral artery occlusion. The shear moduli of both ipsilateral and contralateral brain hemispheres for these mice were measured and compared to corresponding values of control animals. RESULTS: At 24 hours (but not 72 hours) after induction of ischemic stroke, there was a significant decrease in the shear modulus in the ipsilateral hemisphere (P < .01) and a significant increase in the shear modulus in the contralateral hemisphere compared to that of control animals (P < .01). Significant differences were also evident between ipsilateral and contralateral shear modulus values at 24 and 72 hours after infarction (P < .01 for both). CONCLUSIONS: The differences between intrahemispheric averages of shear moduli of the brains of animals with stroke at 24 and 72 hours after stroke induction likely reflect the initial formation of edema and reduction of cerebral blood flow known to develop ipsilateral to ischemic infarction, the known transient increase in intracranial pressure, as well as the known initial reduction of blood flow and subsequent development of edema in the contralateral hemisphere (diaschisis). Thus, elastography offers a possible method to detect subtle changes in brain after ischemic stroke.

Treatment of uterine fibroid tumors in an in situ rat model using high-intensity focused ultrasound.

OBJECTIVE: To determine the efficacy and safety of high-intensity focused ultrasound (HIFU) for the treatment of uterine fibroid tumors in an in situ animal model. DESIGN: High-intensity focused ultrasound was applied intraoperatively to uterine fibroid tumors in rats. SETTING: Department of Bioengineering, and Applied Physics Laboratory, University of Washington, Seattle, Washington. ANIMAL(S): Thirty-five tumors in 27 Eker rats that had spontaneous in situ uterine fibroids were randomly assigned into two groups receiving HIFU (n = 29) or sham (n = 6) treatments. INTERVENTION(S): Animals were anesthetized, and tumors were exposed surgically. The HIFU was applied at 3.5 MHz in 10-second bursts to produce coagulative necrosis lesions (3 mm by 10 mm), spaced 5 mm apart. Sham treatments consisted of exposing the tumors, and handling them similarly to those in the HIFU treatment group, but HIFU was not applied. MAIN OUTCOME MEASURE(S): Tumor volume was measured every week transabdominally using B-mode ultrasound imaging. Gross examination and histological analysis were performed after euthanasia. RESULT(S): More than half of the tumors in the HIFU treatment group showed significant tumor volume reduction. The average tumor volume in the sham treatment group increased 40-fold. Gross and histological analysis showed coagulative necrosis of tumor cells in the HIFU treatment group. CONCLUSION(S): The HIFU may provide an effective and safe method of treating uterine fibroid tumors.