Real-time integration of ultrasound into neuronavigation: technical accuracy using a light-emitting-diode-based navigation system

Summary. Background. In brain surgery, intraoperative brain deformation is the major source of postimaging inaccuracy of neuronavigation. For intraoperative imaging of brain deformation, we developed a platform for the integration of ultrasound imaging into a navigation system.Method. A commercially available ultrasound system was linked to a light-emitting-diode- (LED) based neuronavigation system via rigid fixation of a position localiser to the ultrasound probe and ultrasound image transfer into the navigation system via a S-VHS port. Since the position of the ultrasound image co-ordinate system is not readily defined within the navigation reference co-ordinate system (REF CS), a transformation which links both co-ordinate systems has to be defined by a calibration procedure. Calibration of the ultrasound probe within the REF CS was performed via a cross-wire phantom. The phantom target was defined within the navigation co-ordinate system (by pointer under microscopic control) and imaged by ultrasound. Ultrasound presets were optimised (digital beam focusing, gain intensity) to attain a small echoic target for manual target definition. The transformation was derived from 150 ultrasound measures and iteration. Accuracy was calculated as mean linear error (LE; in X_REF, Y_REF, or Z_REF direction), overall mean LE (linear errors of all axes X_REF to Z_REF) and Euclidean error (EE; vectorial distance from the physical target).Findings. Optimised ultrasound presets (8MHz frequency, digital beam focusing, 20% gain intensity) enabled a low interobserver error (mean: 0.5mm, SD: 0.28) for target definition within the 2-D ultrasound image. Mean accuracy of pointer-based physical target definition in the REF CS was 0.7mm (RMSE; SD: 0.23mm). For navigated ultrasound, the overall mean LE was 0.43mm (SD: 1.36mm; 95%CL: 3.13mm) with a mean EE of 2.26mm (SD: 0.97mm; 95%CL: 4.21mm).Interpretation. Using a single target cross-wire phantom, a highly accurate integration of ultrasound imaging into neuronavigation was achieved. The phantom accuracy of integration lies within the range of application accuracy of navigation systems and warrants clinical studies.     

Accurate pedicle screw insertion under the control of a computer-assisted image guiding system: Laboratory test and clinical study

We used a commercially available computer-assisted navigation system (StealthStation; Sofamor Danek, Memphis, TN, USA) in both an in-vitro and a clinical study performed in 1996–1998. The basic data used for navigation were preoperative computed tomography (CT) scan imaging data. The position of the probe or drill guide was superimposed in real-time on a monitor. For the in-vitro study, ten plastic lumbar spine models (50 vertebrae) were used. The entrance hole for the screw was made by drilling, following navigation. Using the navigation system, we drilled 88 holes through the pedicles into the vertebral bodies of 44 vertebral models. All 88 pedicle holes were contained within the pedicle without perforation. The mean deviation of the hole positions from the surgical plan was 1.78 ± 0.81 mm, and the mean angular deviation was 2.28°± 1.92°. In 29 patients, using the navigation system, we introduced 169 pedicle screws at the planned position. Fifty-one screws were used for thoracic and 118 screws for lumbar spinal fixation. All screws correctly passed through the pedicles. There were no neurological complications after surgery. Using this guided surgery system, we achieved satisfactory results both in the laboratory and in a clinical setting. Received for publication on April 17, 1998; accepted on Oct. 30, 1998     

Functional neuronavigation combined with intra-operative 3D ultrasound: Initial experiences during surgical resections close to eloquent brain areas and future directions in automatic brain shift compensation of preoperative data

Summary Objective. The aims of this study were: 1) To develop protocols for, integration and assessment of the usefulness of high quality fMRI (functional magnetic resonance imaging) and DTI (diffusion tensor imaging) data in an ultrasound-based neuronavigation system. 2) To develop and demonstrate a co-registration method for automatic brain-shift correction of pre-operative MR data using intra-operative 3D ultrasound. Methods. Twelve patients undergoing brain surgery were scanned to obtain structural and fMRI data before the operation. In six of these patients, DTI data was also obtained. The preoperative data was imported into a commercial ultrasound-based navigation system and used for surgical planning and guidance. Intra-operative ultrasound volumes were acquired when needed during surgery and the multimodal data was used for guidance and resection control. The use of the available image information during planning and surgery was recorded. An automatic voxel-based registration method between preoperative MRA and intra-operative 3D ultrasound angiography (Power Doppler) was developed and tested postoperatively. Results. The study showed that it is possible to implement robust, high-quality protocols for fMRI and DTI and that the acquired data could be seamlessly integrated in an ultrasound-based neuronavigation system. Navigation based on fMRI data was found to be important for pre-operative planning in all twelve procedures. In five out of eleven cases the data was also found useful during the resection. DTI data was found to be useful for planning in all five cases where these data were imported into the navigation system. In two out of four cases DTI data was also considered important during the resection (in one case DTI data were acquired but not imported and in another case fMRI and DTI data could only be used for planning). Information regarding the location of important functional areas (fMRI) was more beneficial during the planning phase while DTI data was more helpful during the resection. Furthermore, the surgeon found it more user-friendly and efficient to interpret fMRI and DTI information when shown in a navigation system as compared to the traditional display on a light board or monitor. Updating MRI data for brain-shift using automatic co-registration of preoperative MRI with intra-operative ultrasound was feasible. Conclusion. In the present study we have demonstrated how both fMRI and DTI data can be acquired and integrated into a neuronavigation system for improved surgical planning and guidance. The surgeons reported that the integration of fMRI and DTI data in the navigation system represented valuable additional information presented in a user-friendly way and functional neuronavigation is now in routine use at our hospital. Furthermore, the present study showed that automatic ultrasound-based updates of important pre-operative MRI data are feasible and hence can be used to compensate for brain shift. Rasmussen and Lindseth have contributed equally to this paper.     

Accuracy of angiography and Doppler ultrasonography in the detection of carotid stenosis: a histopathological study of 123 cases

Summary Background. A prospective study was performed comparing the accuracy of digital subtraction angiography (DSA) and Doppler ultrasonography (DUS) stenosis findings with measurements on histological specimens. Method. DSA and DUS were used to evaluate carotid stenosis and were compared with measurements on histological specimens. Intact carotid plaques from 123 cases were removed in one piece during surgery. The specimens were histologically processed and examined in transverse sections. The smallest inner and correlating outer diameters were measured and the extent of stenosis was calculated. Carotid artery stenoses were compared and statistics done. Specimens in symptomatic cases were divided into 3 groups: stenosis 30–49% (Group 1), stenosis 50–69% (Group 2) and stenosis 70–99% (Group 3). Specimens in asymptomatic cases were divided into two groups: stenosis ≤59% (Group A) and stenosis ≥60% (Group B). Findings. Wilcoxon paired tests revealed significant differences between DSA, DUS and measurements on histological specimens. In severe stenoses only, no significant difference was observed between stenosis measurement according to the European Carotid Surgery Trial (ECST) angiography methodology and measurements on histological specimens. The most pronounced differences were found between angiography methodology of the North American Symptomatic Carotid Endarterectomy Trial (NASCET) and measurements on histological specimens. When investigating how often preoperative measurement classified stenosis into the same Group of stenoses as postoperative measurement, DUS was the most accurate diagnostic tool. Conclusions. This study confirmed our previous results, i.e., angiography underestimates the degree of carotid artery stenosis. DUS seems to be more accurate in classifying stenoses into different groups to the extent of narrowing of the carotid arteries. These results make the position of angiography in diagnostic algorithm of carotid stenoses investigations even more questionable.     

The evaluation and comparison of cerebellar mutism in children and adults after posterior fossa surgery: report of two adult cases and review of the literature

Summary. Summary.   Background: Although there are some cases of cerebellar mutism in adults after posterior fossa surgery for cerebellar tumour it generally occurs in children. Reversible pathophsiology and the anatomical substrate of this syndrome still remain unclear. The predominance of cerebellar mutism in children is suggested to be related to the higher incidence of posterior fossa tumours in children. However, the question regarding the reason for the obvious difference in the incidence of this syndrome between the paediatric and adult population still remaing unanswered. The aim of this study was to evaluate and compare children and adult groups separately to understand the incidence and the clinical characteristics better and to elucidate the pathophysiological basis and predictive factors for this syndrome.   Method: We reviewed, analysed, and compared the cases of cerebellar mutism individually in children and in adults reported in the English literature. We found 106 reported cases in children and 11 cases in adults which were suitable for analysis. We added two adult cases to these.   Findings: The ages of the patients ranged from 2 to 16 (mean, 6.4 year) in children and from 17 to 74 (mean, 38.7 year) in adults. Although vermis was the main location in both groups, the incidence of vermis lesions was considered higher in the paediatric population (%91.5 versus %69.2). The rate of brain stem invasion was prominent in children (%31.1) when compared with adults (%7.6). The latency for the development of mutism and the duration of the mutism were similar in children and adults (mean, 1.4 d versus 2 d and mean, 5.07 wk versus 4.2 wk respectively). Mutism was transient in all the cases of both groups.   Interpretation: Recent concepts of cerebellar physiology disclose the importance of the cerebellum in learning, language, and mental and social functions. Pontine nuclei, the thalamus, motor and sensory areas and supplementary motor areas have been proven necessary for the initiation of speech. It can be hypothesized that uncompleted maturation of the reciprocal links in childhood connecting the cerebellum to these structure makes the children more vulnerable to have postoperative cerebellar mutism in comparison to the adult population.     

Transabdominal ultrasonography in the evaluation of patients with advanced prostatic carcinoma: effects of castration and of chronic administration of a gonadotropin releasing hormone agonistic analogue

Twenty-two patients with advanced prostatic carcinoma were subjected either to orchiectomy (group I, n = 5) or to chronic administration of a gonadotropin releasing hormone agonistic analogue D, Ser (TBU)6, des Gly-NH2(10) LHRH nonapeptide (HOE 766) (group 2, n = 17). Plasma testosterone was similar in both groups prior to treatment (group 1: 636 +/- 129.29, group 2: 580.85 +/- 37.57; X +/- SE). The levels attained in group I were significantly lower (P less than .05) than those of group 2 through eight weeks of follow-up but were similar by the third month. Prostatic size (cm2) as estimated by transabdominal ultrasonography did not differ between the two groups prior to treatment (group 1: 23.6 +/- 3.35, group 2: 21.4 +/- 1.97; X +/- SE). Both therapies resulted in a decrease of prostatic size that was significantly more pronounced (P less than .05) in group I compared with group 2 by the first and third month; by the six month, there was no statistical difference in the prostatic size attained with either therapeutic modality. Persistent suppression of prostatic size was documented in all patients of group 2 chronically (up to 24 months) treated with HOE 766 even when there was evidence of uninhibited or progressive bony metastases. The above data 1) indicate the efficacy of the HOE 766 in inducing medical castration and prostatic shrinkage in advanced carcinoma of the prostate, 2) document the usefulness of transabdominal ultrasound in the follow-up of such patients, and 3) suggest a relationship between the rapidity of tumor shrinkage and Leydig cell suppression.     

Five-year outcome of normal pressure hydrocephalus with or without a shunt: predictive value of the clinical signs,neuropsychological evaluation and infusion test

Summary. Summary.   Background: Between 1993–1995, 51 patients under 75 years of age with clinical symptoms and CT-based diagnosis of normal pressure hydrocephalus were investigated prospectively in order to clarify the value of neuropsychological tests, clinical symptoms and signs and infusion test in the differential diagnosis and prediction of outcome in normal pressure hydrocephalus.   Methods: Patients had a thorough neurological examination, and neuropsychological evaluation. A 24-hour intraventricular ICP-measurement, infusion test, neurophysiological investigations and MRI study were performed, and a cortical biopsy was obtained. The ICP measurement defined the need for a shunt. All 51 patients were re-examined three and twelve months later. The final follow-up was accomplished five years postoperatively.   Findings: 25 of the patients needed a shunt operation. One year after a shunt placement 72% of these patients had a good recovery concerning activities of daily living, 58% benefited in their urinary incontinence and 57% walked better. During the 5 years of follow-up 8 patients with shunt and 9 without shunt had died. Positive effect of shunting remained. Only one neuropsychological test, recognition of words test, distinguishes the patients with the need for a shunt. Simple mini mental examination test was not different in those who improved. In the postoperative follow-up patients with shunt showed no change in neuropsychological tests even if they were subjectively better. The infusion test was of no value in diagnosing NPH. The 16 patients with Alzheimer's disease did worse after one year than those without pathological changes, but the mortality was not increased.   Interpretation: Specific neuropsychological tests are of little value in diagnosing NPH. Mini-Mental status examination was neither of value in diagnosing NPH nor in prediction of the outcome. In this study the infusion test did not improve diagnostic accuracy of NPH, but shunt placement relieves urinary incontinence and walking disability in patients with increased ICP. The patients with positive Alzheimer diagnosis on biopsy did not improve. Published online June 20, 2002