Transcutaneous Viscoelastic Properties of Brain through Cranial Defects

Abstract

Decompressive craniectomy is a procedure necessary for preventing brain herniation due to brain edema in patients with acute intracranial hypertension. We transcutaneously palpated brain stiffness through cranial defects in order to evaluate brain edema of such patients for one month until cranioplasty. However, there are no instruments designed to quantitatively evaluate brain stiffness in the decompressive cranial defect. This study attempted to evaluate brain stiffness under normal conditions by using a palpation-like tactile resonance sensor that measured penetrating depth (Dp), pressure (Pr), and change in frequency (dF). For this purpose, we studied seven patients, who had undergone unilateral decompressive craniectomy, and measured the viscoelastic properties of cranial defects using the sensor. The patients meeting our inclusion criteria underwent haptic measurements and head CT scans within three days before cranioplasty. We compared the data sets obtained from the seven subjects with clinical factors including physical data, neurological parameters, and CT images. We found that under stable conditions, the clinical factors did not have an impact on brain stiffness. Then, we selected data sets from six patients with the same maximum depth (h = 3.0 mm) and treated them as one group. In addition, we analyzed the hysteresis graphs obtained. The estimated mean values of the transcutaneous viscoelastic properties in the cranial defects were as follows: stiffness = 28.37 gf/mm and shear modulus = 1.94 kPa. The correlation between Pr and dF indicated linear elasticity in a loading state (Pr = 0.853*dF + 2.729, R2 = 0.997).