Noninvasive assessment of intracranial pressure using subharmonic-aided pressure estimation: An experimental study in canines

BACKGROUND Intracranial hypertension is a common clinicopathological syndrome in neurosurgery, and a timely understanding of the intracranial pressure (ICP) may help guide clinical treatment. We aimed to investigate the correlation between subharmonic contrast-enhanced ultrasound (SHCEUS) parameters and ICP in experimental canines. METHODS A dynamic model of ICP change from 11 mm Hg to 50 mm Hg was established in experimental canines by placing a latex balloon into the epidural space and injecting saline into the balloon. In addition, a pressure sensor was placed in the brain parenchyma to record the changes in ICP. When the ICP stabilized after each increase, subharmonic-aided pressure estimation (SHAPE) technology was performed to obtain the SHCEUS parameters, including the basal venous and adjacent intracranial arterial subharmonic amplitude and SHAPE gradient (subharmonic amplitude in the intracranial artery minus that in the basal vein). The correlation between these parameters and ICP was analyzed. RESULTS The subharmonic amplitude of the basal vein was negatively correlated with the ICP (r = -0.798), and the SHAPE gradient was positively correlated with the ICP (r = 0.628). According to the guidelines for ICP monitoring in patients with traumatic brain injury, we defined 20 mm Hg, 25 mm Hg, and 30 mm Hg as the cutoff ICP levels. The area under the receiver operating characteristic curve of the basal venous subharmonic amplitude for diagnosing intracranial hypertension >= 20 mm Hg, >= 25 mm Hg, and >= 30 mm Hg was 0.867 (95% confidence interval [CI], 0.750-0.943), 0.884 (95% CI, 0.770-0.954), and 0.875 (95% CI, 0.759-0.948), respectively. The area under the receiver operating characteristic curve of the SHAPE gradient for diagnosing intracranial hypertension >= 20 mm Hg, >= 25 mm Hg, and >= 30 mm Hg was 0.839 (95% CI, 0.716-0.924), 0.842 (95% CI, 0.720-0.926), and 0.794 (95% CI, 0.665-0.890), respectively. CONCLUSION SHCEUS parameters are correlated with ICP. The SHAPE technique can assist in evaluating ICP changes in canines, which provides a new idea and method for evaluating ICP.