The measurement of brain tissue stiffness in-vivo

There is considerable interest in surgical decompression as a management strategy (RescueICP) for intractable intracranial hypertension. After such an operation measurements of intracranial pressure (ICP) and thus cerebral perfusion pressure (CPP) become less meaningful. Measurements of the biomechanical properties of the brain may be one measure capable of detecting changing status of such patients. However these properties of the brain are neither documented or well understood. We have developed an indentation probe capable of making measurements of human brain stiffness.

The device consists of an indenting tip of depth 2 mm and diameter 12 mm surrounded by an annular body of 20 mm diameter. Measurements are made by two load cells, connected through interface electronics to a laptop computer.

Laboratory measurements show the probe to provide accurate and repeatable measurements over a range of zero to 10N. Inter-operator variability from six healthcare professionals had a coefficient of variance of 8.75%. Measurements obtained during surgery from a patient undergoing tumour resection were towards the lower end of the device's measurable range.

We have determined that this indentation device has a linear response and that the inter- and intra-operator variability is low. Although the device is still in an early stage of development, preliminary results during intracranial surgery demonstrate that this device is capable of measuring in-vivo tissue stiffness. Further work is required to derive a quantitative "stiffness index" from the two load curves. In addition a standard operation method is required so that consistent and repeatable measurements are made. The device may be of value in assessing patients after decompressive craniectomy.