Introduction: The introduction of high frequency ultrasound (HFUS) transducers with central frequencies up to 70 MHz is particularly attractive for neurosurgery considering the potential for real-time microscopic visualization of the subsurface anatomy without exposing patients to radiation or disrupting surgical workflow. While most conventional ultrasound systems deliver image resolutions of 0.5–1mm at penetration depths greater than 100mm, HFUS provides spatial resolution on the order of 15–100µm with limited depth penetration up to 15mm. Although improvement in spatial resolution must be considered in concert with reduced penetration depth, the trade-off is adequate in the context of an open surgical field where the bone is removed and the ultrasound probe can be placed directly adjacent to the region of interest. Integration of HFUS into the operating room facilitates dynamic intra-operative feedback to surgeons, thus informing clinical decisions. We present our initial experience using high frequency ultrasound imaging during craniospinal procedures.
Methods: HFUS images were obtained in 5 craniospinal procedures under the Health Canada Special Access program. Medical rationale for use of HFUS was provided for each patient. Surgical procedures were performed using the standard clinical practice with bone removal to facilitate real-time ultrasound imaging of the soft tissue.
Results: Images obtained comprised 4 spinal decompression surgeries (2 tumor resections, 2 cystic syrinx/synovial mass) and 1 cranial procedure (parietal metastatic adenocarcinoma biopsy and resection). HFUS images obtained during spine surgery delineated exquisite detailing of the spinal anatomy including delineation of white matter and grey matter tracts and nerve roots (Figure 1) and allowed accurate assessment of the extent of decompression/tumor resection. For the cranial application, disruption of the grey-white matter interface by diseased tissue (Figure 2), characteristic lobular disease patterns, vessel calcification, and necrosis were distinguishable and correlated well with these features on histopathology.
Conclusions: HFUS images confer significant improvement over conventional ultrasound.
Patient Care: This research will provide feasibility for the use of high frequency ultrasound for neurosurgical procedures. This is the first report describing intraoperative use of high frequency ultrasound which provides feedback to surgeon not previously available using conventional ultrasound. Thus, this work has the potential to inform clinical decision making improving both surgical outcomes and patient care.
Learning Objectives: By the conclusion of this session participants should be able to: 1) Describe the importance of high frequency ultrasound for fine delineation of neurosurgical anatomy with spatial resolution of less than 100 micrometers. 2) Understand the trade-off between spatial resolution and penetration depth in the context of high frequency ultrasound and neurosurgery. 3) Identify the clinical indications for high frequency ultrasound for neurosurgical procedures.