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

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.

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.

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).

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.