  Transcranial focused ultrasound can deliver energy to the brain in a
minimally invasive manner for a variety of clinical applications. However,
acoustic inhomogeneities within the skull cause significant wave interactions,
leading to difficulties in predicting the energy delivered to the target. We
present a comprehensive examination of intracranial acoustic fields generated
by focused ultrasound transducers and assess the characteristics of cranial
bone that affect acoustic transmission. Acoustic field maps were generated at
88 regions of interest across 10 historical and 2 Thiel-embalmed human skull
specimens with sonication at frequencies of 220 kHz, 650 kHz, and 1000 kHz. The
average peak pressure attenuation was $3.1 \pm 1.4$ dB, $9.0 \pm 1.7$ dB, and
$14.6 \pm 4.1$ dB, respectively. The average power attenuation was $5.0 \pm
2.4$ dB, $14.9 \pm 3.2$ dB, and $24.1 \pm 6.3$ dB, respectively. The effect of
skull thickness, skull density ratio, and skull curvature on intracranial peak
pressure and power was investigated and linear fits produced. Our results
demonstrate that Thiel-embalmed samples fall within the confidence intervals of
fits for historical samples. The effects of angulation and spacing between the
transducer and the skull were also investigated. Results indicate that wave
superposition resulting from skull and transducer spacing could lead to a
30-40% uncertainty in peak recorded intracranial pressure.
