Focusing Ultrasound Through the Skull: The Promise and Challenge of Transcranial Focused Ultrasound

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The ED/CAS Chapter of the Pikes Peak Section of the IEEE is pleased to invite you to a talk given by Dr. Taylor D. Webb on Focusing Ultrasound Through the Skull: The Promise and Challenge of Transcranial Focused Ultrasound.

The Transcranial focused ultrasound (FUS) is a class of ultrasound techniques with the potential to provide a variety of new non-invasive treatment options for pathologies ranging from cancer to depression. At high energies, FUS can destroy diseased tissue through thermal ablation, a technique that was recently approved by the FDA to treat essential tremor. At lower energies, FUS can reversibly open the blood brain barrier for the delivery of chemotherapeutic agents to tumors and it can modulate neural activity, suggesting the possibility of using FUS to treat mental illness and study neural function.

However, delivery of the acoustic energy to the desired location of the brain is difficult because heterogeneity in the acoustic properties of the skull causes alterations to the size, shape, and location of the beam’s focus. Compensating for these distortions requires knowledge of the acoustic velocity in the patient’s skull. Clinically, the velocity is estimated using a CT scan of the patient, but there is disagreement about the correct method for obtaining the acoustic velocity from the CT image and, because FUS procedures are often performed under MR guidance, there is interest in estimating the velocity with MRI.

We are developing models relating the acoustic velocity of human skull bone to CT Hounsfield Units (HU) and two different parameters measured with ultra short echo time (UTE) MRI. These models allow us to estimate the acoustic velocity in individual patient skulls using either a CT or MR image. They are generated using measurements from 100 fragments taken from two ex-vivo human skulls. Our results show that velocity is strongly correlated with both HU and the measured MR parameters. These models will improve the accuracy of CT based velocity estimates and, by allowing the use of MRI instead of CT, eliminate the need for ionizing radiation, leading to improved treatment efficacy and more widespread application of FUS.

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