Neurosurgery is performed with extremely low margins of error. Surgical inaccuracy may
have disastrous consequences. The overall aim of this thesis was to improve accuracy in
cranial neurosurgical procedures by the application of new technical aids. Two technical
methods were evaluated: augmented reality (AR) for surgical navigation (Papers I-II) and the
optical technique of diffuse reflectance spectroscopy (DRS) for real-time tissue identification
(Papers III-V).
Minimally invasive skull-base endoscopy has several potential benefits compared to
traditional craniotomy, but approaching the skull base through this route implies that at-risk
organs and surgical targets are covered by bone and out of the surgeon’s direct line of sight.
In Paper I, a new application for AR-navigated endoscopic skull-base surgery, based on an
augmented-reality surgical navigation (ARSN) system, was developed. The accuracy of the
system, defined by mean target registration error (TRE), was evaluated and found to be
0.55±0.24 mm, the lowest value reported error in the literature.
As a first step toward the development of a cranial application for AR
navigation, in Paper II this ARSN system was used to enable insertions of biopsy needles
and external ventricular drainages (EVDs). The technical accuracy (i.e., deviation from the
target or intended path) and efficacy (i.e., insertion time) were assessed on a 3D-printed
realistic, anthropomorphic skull and brain phantom; Thirty cranial biopsies and 10 EVD
insertions were performed. Accuracy for biopsy was 0.8±0.43 mm with a median insertion
time of 149 (87-233) seconds, and for EVD accuracy was 2.9±0.8 mm at the tip with a median
angular deviation of 0.7±0.5° and a median insertion time of 188 (135-400) seconds.
Glial tumors grow diffusely in the brain, and patient survival is correlated with
the extent of tumor removal. Tumor borders are often invisible. Resection beyond borders as
defined by conventional methods may further improve a patient’s prognosis. In Paper III,
DRS was evaluated for discrimination between glioma and normal brain tissue ex vivo. DRS
spectra and histology were acquired from 22 tumor samples and 9 brain tissue samples
retrieved from 30 patients. Sensitivity and specificity for the detection of low-grade gliomas
were 82.0% and 82.7%, respectively, with an AUC of 0.91.
Acute ischemic stroke caused by large vessel occlusion is treated with
endovascular thrombectomy, but treatment failure can occur when clot composition and
thrombectomy technique are mismatched. Intra-procedural knowledge of clot composition
could guide the choice of treatment modality. In Paper IV, DRS, in vivo, was evaluated for
intravascular clot characterization. Three types of clot analogs, red blood cell (RBC)-rich,
fibrin-rich and mixed clots, were injected into the external carotids of a domestic pig. An
intravascular DRS probe was used for in-situ measurements of clots, blood, and vessel walls,
and the spectral data were analyzed. DRS could differentiate clot types, vessel walls, and
blood in vivo (p<0,001). The sensitivity and specificity for detection were 73.8% and 98.8%
for RBC clots, 100% and 100% for mixed clots, and 80.6% and 97.8% for fibrin clots,
respectively.
Paper V evaluated DRS for characterization of human clot composition ex
vivo: 45 clot units were retrieved from 29 stroke patients and examined with DRS and
histopathological evaluation. DRS parameters correlated with clot RBC fraction (R=81,
p<0.001) and could be used for the classification of clot type with sensitivity and specificity
rates for the detection of RBC-rich clots of 0.722 and 0.846, respectively. Applied in an
intravascular probe, DRS may provide intra-procedural information on clot composition to
improve endovascular thrombectomy efficiency