Ioannis Pechlivanis

Registration of CT and Intraoperative 3-D Ultrasound Images of the Spine Using Evolutionary and Gradient-Based Methods

A system for the registration of computed tomography and 3-D intraoperative ultrasound images is presented. Three gradient-based methods and one evolutionary algorithm are compared with regard to their suitability to solve this image registration problem. The system has been developed for pedicle screw insertion during spinal surgery. With clinical preoperative and intraoperative data, it is demonstrated that precise registration is possible within a realistic range of initial misalignment. Significant differences can be observed between the optimization methods. The covariance matrix adaptation evolution strategy shows the best overall performance, only four of 12 000 registration trials with patient data failed to register correctly.

Percutaneous placement of pedicle screws in the lumbar spine using a bone mounted miniature robotic system: first experiences and accuracy of screw placement.

Study Design. A prospective analysis. Objective. The idea of this study was to evaluate a new miniature robotic system providing passive guidance for pedicle screw placement at the lumbar spine. Special focus was laid on the postoperative accuracy of screw placement. Summary and Background Data. Recent technical developments lead to a minimization of pedicle screw fixation techniques. However, the use of navigational techniques is still under controversy. Methods. Patients selected for a minimal invasive posterior lumbar interbody fusion received a spiral computer tomographic scan before surgery. The miniature hexapod robot was mounted to the spinous process and the system moves to the exact entry point according to the trajectory of the surgeon’s preoperative plan. After minimal invasive screw placement all patients received routinely a postoperative spiral computer tomographic scan. Screws placed exactly within the pedicle were evaluated as group A, screws deviating <2 mm were evaluated as group B, ≥2 mm to <4 mm (group C); ≥4 mm to <6 mm (group D); and more than 6 mm (group E). Results. Thirty-one patients received a PLIF with percutaneous posterior pedicle screw insertion using the bone mounted miniature robotic device. A total of 133 pedicle screws were placed. The majority of the screws were placed in L5 (58 screws; 43.6%). In axial plane, 91.7% of the screws were evaluated as group A and 6.8% were evaluated as group B. In longitudinal plane, 81.2% of the screws were evaluated as group A and 9.8% were evaluated as group B. In 1 screw (L5 right) the postoperative evaluation was done as group C (axial plane) and D (longitudinal plane). In 29/31 cases the integration of the miniature robotic system was successful. Conclusion. In our study the first clinical assessment of a new bone mounted robot system guiding percutaneous pedicle screw placement was done. A deviation <2 mm to the surgeon ′s plan in 91.0% to 98.5% verifies the system’s accuracy.

3-Dimensional computed tomographic angiography for use of surgery planning in patients with intracranial aneurysms

SummaryBackground. After subarachnoid haemorrhage (SAH) diagnostic evaluation of the underlying cause is warranted since the rebleeding rate is high. The objective of the study was to answer the question, whether 3-Dimensional computed tomographic angiography (3D-CTA) is able to accurately determine the surgical indications in patients with intracranial aneurysms.Methods. After performing 3D-CTA the size of the aneurysm, direction of the aneurysmal dome, neck position and variants of the circle of Willis were analysed. Surgery was performed solely on CTA data in those cases, where the aneurysm was clearly visible. If the findings were negative or inconclusive, intra-arterial digital subtraction angiography (DSA) was also done.Findings. Between January 2001 and December 2002 100 patients (68 F, 32 M) were examined and 123 aneurysms (86 ruptured and 37 unruptured) were diagnosed. All patients received CTA preoperatively and in 27 patients selective DSA was additionally performed. Postoperatively in 34 patients the operative result was checked by DSA.A good correlation between CTA and the intra-operative findings was present in 92 of 100 patients. One aneurysm was not seen on CTA, but was on DSA. In four cases we could confirm DSA findings in CTA after re-evaluation of the data. In three cases neither CTA nor DSA clearly showed an aneurysm, but it was confirmed during surgery.A good correlation between CTA and DSA was found in 60 of 61 patients (98%). The correlation between CTA and intra-operative findings was good as expected in 92 patients, in 5 patients an aneurysm was detected on re-evaluation. Only one aneurysm could not be demonstrated by CTA but in DSA.Conclusion. CTA is less invasive, less time consuming, cheaper and easier to demonstrate the essential information regarding the aneurysm than DSA. We therefore recommend that following a careful analysis most aneurysms – 92% – can be operated solely on CTA data.

Non-fusion rates in anterior cervical discectomy and implantation of empty polyetheretherketone cages.

Study Design. A prospective analysis. Objective. Our aim was to assess the radiographically detectable bony fusion in patients with anterior cervical discectomy (ACD) and polyetheretherketone (PEEK)-cage implantation without additional filling. Furthermore, clinical data of patients with and without fusion were compared. Summary of Background Data. PEEK-cage implantation is performed in cervical spinal surgery because of its benefits. However, fusion rates without filling of the cage have not been reported. Methods. Patients selected for ACD with PEEK-cage implantation prospectively underwent plain radiography in anterior-posterior and lateral projections during the postoperative hospital stay and at follow-up. Furthermore, clinical status was evaluated using the Odom scale, the Short Form-36, the Visual Analog Scale (VAS) for arm and neck pain, and the cervical Oswestry score. Fusion status, migration, and subsidence of the PEEK cage were evaluated on the basis of the lateral radiographs. Fusion was confirmed by presence of continuous trabecular bone bridges in the disc space. To exclude an influence of the cage on the evaluation of fusion rates, fusion was evaluated in analogous fashion retrospectively in a control group. Results. A total of 52 patients underwent ACD and interbody fusion. One-level surgery was performed in 44 patients and 2-level surgery in 8 patients. A total of 60 ACD and interbody fusions with a PEEK cage were analyzed. A majority of operations were at the C5/6 level (40 patients, 77%). Cage height was 4 mm in 32 cases, 5 mm in 23 cases, and 6 mm in 5 cases. Bony fusion was present at 43 treated levels (71.7%), whereas at 17 levels (28.3%) no fusion was found. Statistical analysis revealed no significant difference between the fusion and non-fusion groups regarding time to follow-up, implanted cage height. Short Form-36, cervical Oswestry score, VAS arm and neck, or Odom criteria. In the control group, ACD was performed in 29 patients (42 levels; 18 one-level and 12 two-level operations). Bony fusion was present at 30 levels (71.4%), whereas non-fusion was present at 12 treated levels (28.6%). Statistically analysis revealed no significant difference between the study group and the control group regarding time to follow-up or fusion rates. Conclusion. Implantation of empty PEEK cages after ACD shows an unexpectedly low rate effusion according to radiologic criteria, although no statistically significant difference could be observed clinically.

Vibrography During Tumor Neurosurgery

The aim of this study was to determine whether elastography, a sonographically based real‐time strain imaging method for registering the elastic properties of tissue, can be used in brain tumor surgery.

Computed tomographic angiography in the evaluation of clip placement for intracranial aneurysm

SummaryBackground. Computed tomographic angiography (CTA) has been shown to reliably detect aneurysms pre-operatively. The aim of this study was to compare the ability of post-operative CTA to detect aneurysmal remnants in connection with clip placement compared with digital subtraction angiography (DSA). Furthermore, special attention was paid to identifying factors influencing the image quality of CTA. Method. Between January 2005 and January 2006 a total of 76 patients with intracranial aneurysms were treated in our department. Thirty-two patients with a total of 33 clipped aneurysm were included in this study. All patients underwent CTA and DSA after surgery. Two investigators, each blinded to the classifications of the other, assessed image quality and clip placement. Findings. In three patients aneurysmal remnants could be detected with CTA and DSA. One 2-mm aneurysmal remnant was not clearly identified on CTA; two small (<2-mm) aneurysmal remnants were definitely not seen on CTA. A single titanium clip was used for aneurysmal clipping in 26 patients, two clips were needed in six patients and one aneurysm required three clips being used. Overall, use of one titanium clip tended to result in better image quality. In addition, clip-gantry angles between 30° and 60° tended to yield better image quality. Conclusion. Post-operatively, CTA can be recommended as a reliable non-invasive diagnostic tool only with optimal image quality and with this criterion up to 66% of the aneurysms can be evaluated. Titanium artefacts, especially in the important zone (<2 mm) around the clip in which small aneurysmal remnants can occur, can render adequate evaluation impossible. CTA image quality depends on the number of titanium clips used, but clip-gantry-angle does not significantly influence the image quality.

The subthalamic nucleus at 3.0 Tesla: choice of optimal sequence and orientation for deep brain stimulation using a standard installation protocol: Clinical article

OBJECT Reliable visualization of the subthalamic nucleus (STN) is indispensable for accurate placement of electrodes in deep brain stimulation (DBS) surgery for patients with Parkinson disease (PD). The aim of the study was to evaluate different promising new MRI methods at 3.0 T for preoperative visualization of the STN using a standard installation protocol. METHODS Magnetic resonance imaging studies (T2-FLAIR, T1-MPRAGE, T2*-FLASH2D, T2-SPACE, and susceptibility-weighted imaging sequences) obtained in 9 healthy volunteers and in 1 patient with PD were acquired. Two neuroradiologists independently analyzed image quality and visualization of the STN using a 6-point scale. Interrater reliability, contrast-to-noise ratios, and signal-to-noise ratios for the STN were calculated. For illustration of the anatomical accuracy, coronal T2*-FLASH2D images were fused with the corresponding coronal section schema of the Schaltenbrand and Wahren stereotactic atlas. RESULTS The STN was best and reliably visualized on T2*-FLASH2D imaging (in particular, the coronal view). No major artifacts in the STN were observed in any of the sequences. Susceptibility-weighted, T2-SPACE, and T2*-FLASH2D imaging provided significantly higher contrast-to-noise ratio values for the STN than standard T2-weighted imaging. Fusion of the coronal T2*-FLASH2D and the digitized coronal atlas view projected the STN clearly within the boundaries of the STN found in anatomical sections. CONCLUSIONS For 3.0-T MRI, T2*-FLASH2D (particularly the coronal view) provides optimal delineation of the STN using a standard installation protocol.

Toward Registration of 3D Ultrasound and CT Images of the Spine in Clinical Praxis: Design and Evaluation of a Data Acquisition Protocol

Recent work has demonstrated the accuracy and operational viability of an algorithm proposed by the authors that successfully registers 3-D ultrasound data with CT or MRI data. The successful application of this method to intraoperative navigation, however, depends critically on the quality of the acquired ultrasound data. This gives rise to two questions concerning the usability of the algorithm in clinical praxis. First, how can one guarantee high-quality, user-independent ultrasound registration data with this procedure? Second, can this approach work reliably in clinical practice, namely within the operating theater? To address both of these questions, we present an ultrasound data acquisition protocol that leads the user through the data acquisition process and also provides the criteria to adjust the relevant ultrasound parameters. We also evaluated criteria for the visual inspection of the suitability of the ultrasound data for the registration process. Results for this evaluation show that these visual criteria can be used to decide preoperatively if an ultrasound registration will be successful in a patient. The intraoperative evaluation of the protocol showed that high-quality registrations can be achieved under realistic conditions. This protocol and the visual inspection criteria, together with the ultrasound registration algorithm, provide a surgical team with a means of performing precise, cost-effective navigation in patients for whom a navigated intervention was previously impossible. We evaluated the proposed procedure in clinical practice.

Chronic subdural haematoma in patients with Huntington's disease

We studied the frequency of patients who had chronic subdural haematomas (CSDH) and Huntingtons disease (HD) in a 1-year study period. In our department a total of 58 patients with CSDH were treated. Four patients (6.9% of them) had HD. Surgical evacuation of the haematoma was performed in all four cases with the use of a twist drill trepanation without a drainage system.

Treatment of degenerative cervical disc disease with uncoforaminotomy--intermediate clinical outcome.

BACKGROUND Anterior cervical uncoforaminotomy (uncoforaminotomy) is an operative method intended to preserve the functional motion segment of the cervical spine while removing the underlying pathology. Controversy exists concerning the patients best suited for this treatment modality. Furthermore, no long-term outcome analyses have been published. METHODS Between November 2002 and June 2004, 96 patients underwent single-level uncoforaminotomy in our neurosurgical department for the treatment of cervical radiculopathy. The patients were divided into three groups: A, soft disc; B, hard disc; C, hard and soft disc. Follow-up was performed 2 years after surgery. Clinical outcome was classified according to Odom et al. and to the cervical Oswestry and 11-point box scales for arm and neck pain. RESULTS Ninety patients (92%) underwent intermediate follow-up examinations at an average of 33 months after surgery. Forty-nine patients were in group A, 24 in group B, and 17 in group C. At discharge, 98% of those in group A, 96% in group B, and 94% in group C showed excellent or good results. In two patients revision surgery was performed within 4 weeks due to recurrent disc herniation. In one patient revision was carried out due to a subcutaneous hematoma. In group B one case of vertebral artery injury occurred. Additionally in one patient of this group revision surgery was performed due to inadequate decompression of the neural foramen. At follow-up 94% of the patients in group A, 89% in group B, and 87% in group C had excellent or good results. The scores on the cervical Oswestry scale and the 11-point-box scale showed no significant differences among the groups. CONCLUSION Uncoforaminotomy, especially in patients with soft-disc pathologies, is a good operative method for the treatment of radicular pain.