Biomedical subjects

George Nikiforidis

Publications and source records attributed to George Nikiforidis.

15 recordsLinked to original sources

PubMed2006

Level of consciousness as a conditioning factor of F wave generation in stroke patients.

OBJECTIVE: The current study aimed to investigate whether the level of consciousness influenced the F wave generation, as an independent factor. METHODS: Forty three patients with acute stroke were divided according to their level of consciousness in two groups; to those with Glasgow scale (GCS) score 3-7 indicating coma (group I) and those with GCS score 8-15 (group II). A series of 40 electrical stimuli were delivered to the ulnar nerve bilaterally in order to obtain F waves. The following variables were estimated and then compared between groups: F persistence, F wave latency, amplitude and duration. All studies were performed within 3 days from the onset of the stroke symptoms. RESULTS: The main finding to emerge was the significantly reduced F wave persistence in the group of patients with low GCS score as opposed to patients allocated in the group with GCS score 8-15. This result is referred to F waves obtained from both the affected and unaffected limb. F wave minimum latency was also prolonged in the group with low GCS score, whilst the comparison of all other F wave variables revealed no significant differences between groups I and II. F wave persistence measurements did not differ between the affected and unaffected sides. Stroke location and type (ischemic or hemorrhagic) were not associated with alterations of F wave measurements. CONCLUSIONS: Our results on stroke patients suggest that generation of F waves, expressed by the F wave persistence is associated with the level of consciousness. SIGNIFICANCE: F wave study may be useful as an objective measure in documenting the severity of consciousness impairment.

Action Potentials↗

PubMed2006

Digital subtraction angiography and computer assisted image analysis for the evaluation of the antiangiogenetic effect of ionizing radiation on tumor angiogenesis.

PURPOSE: The aim of the present study was to evaluate and quantify the antiangiogenetic effect of ionizing radiation on tumor angiogenesis using digital subtraction angiography (DSA) in conjunction with computer assisted image analysis (CAIA). METHODS: Walker 256 carcinosarcoma was inoculated in both glutei of 12 Wistar rats. When the tumors reached a diameter of 1.5 cm, local irradiation of the right gluteus was performed. The left gluteus of each animal served as a control. After 24 hours of irradiation, angiography was performed, and images where digitized and subsequently processed. The effect of irradiation was observed both in big and small vessels (smaller or greater than 200 microm). RESULTS: Irradiated areas of both small and big vessels showed a statistically significant reduction in both total vessel area and length. Small vessels showed a greater trend toward suppression by irradiation (not statistically significant). CONCLUSION: Irradiation had a deleterious effect in both macro- and micro-blood supply of a tumor. The use of CAIA enhanced the efficacy of DSA and enabled the in vivo identification of the effect of irradiation on various caliber vessels as well as the ratios of total length and total area of small and big vessels.

Angiography, Digital Subtraction↗

PubMed2005

Development of a support vector machine-based image analysis system for assessing the thyroid nodule malignancy risk on ultrasound.

An SVM-based image analysis system was developed for assessing the malignancy risk of thyroid nodules. Ultrasound images of 120 cytology confirmed thyroid nodules (78 low-risk and 42 high-risk of malignancy) were manually segmented by a physician using a custom developed software in C++. From each nodule, 40 textural features were automatically calculated and were used with the SVM algorithm in the design of the image analysis system. Highest classification accuracy was 96.7%, misdiagnosing two high-risk and two low-risk thyroid nodules. The proposed system may be of value to physicians as a second opinion tool for avoiding unnecessary invasive procedures.

Algorithms↗

PubMed2004

Design and implementation of a web-enabled haematological system.

This paper describes the design and the implementation of a web-enabled integrated haematological system, named e-HS. The proposed system runs on a set of distributed network nodes providing useful haematological services. These services include patient-oriented data management, digitized histopathological slides (DHS) acquisition, teleconsulting facilities, etc. The objective of e-HS is to supply web-enabled services according to haematological requirements, implement a distributed storage scheme for DHS, and provide a common database containing all haematological laboratory results by using eXtensible Markup Language (XML) and web technologies. Our implementation can be accessible to every authorized physician at the distributed nodes without any additional software. The only software required for the user is the widely used browser (e.g. MS Internet Explorer v 3.02 or higher). Besides, by using a self-explaining user interfaces and HTML-techniques, such as hyperlinks, the necessary amount of training at the physicians-side is reduced to a minimum. A first implementation of the e-HS, has been established at the Medical Physics Department of the University of Patras (master node of the system), and has been tested with success by the medical staff of the Hospital Departments of the University of Patras and Thessalonica that served as distributed nodes of the system.

Clinical Laboratory Information Systems↗

PubMed2004

Virtual endoscopy in renal artery stenosis: an innovative approach for diagnosis and follow-up.

PURPOSE: We investigated the utility of virtual endoscopy (VE) as a diagnostic and follow-up tool in patients with renal artery stenosis, especially as a means of defining vascular patency. PATIENTS AND METHODS: We performed VE in 24 patients with ostial atherosclerotic renal artery stenosis and correlated the results with those of conventional angiography. The patients were treated successfully by placement of metal stents and conventional catheter angiography and VE for patency assessment 6 and 12 months after stent insertion. RESULTS: In all patients, the stenotic segment was identified, and VE findings were concordant with those of angiography. The average degree of stenosis was estimated to be 70% +/- 20% when angiography was used and 62% +/- 15% when VE was used. After metal stent insertion, the 12-month patency rate was 83.3% (20 patients). Angiography and VE findings remained concordant during the follow-up period, but VE provided more information beyond the stenotic segment, allowing examination of the arterial lumen both cephalad and caudal to the point of obstruction. CONCLUSION: Virtual endoscopy provided a more dynamic, direct, minimally invasive approach that was equal to or better than angiography for both the verification of the vascular stenosis and the evaluation of the arterial lumen.

Aged↗

PubMed2004

Tele-diagnostic and therapeutic guidance in urology.

PURPOSE: To design a Web-based network for diagnostic and therapeutic guidance in urology. MATERIALS AND METHODS: We designed an architectural model of a low-cost multimedia Web platform that runs on a collection of distributed collaborative network nodes to provide a set of urologist-oriented Web-enabled services. Any node of the platform was able to share patient-oriented data via automated processes with appropriate authorization, confidentiality, and high-security protocols. The urologist can show the details of the records of patients and additionally enrich the world experience with his or her own cases. Video clips maintained locally at the nodes will be accessible by clinicians in a trouble-free way with MS Windows Media player and a relatively small amount of source code. RESULTS AND CONCLUSIONS: The primary advantage of this architectural model is that it provides Web-enabled integrated urologic services while using a distributed storage scheme for urological video files (AVI format) and a global repository of laboratory results using Extensible Markup Language (XML) and Data Grid technologies. In addition, this model provides decision-support services (knowledge from a global database and predefined procedures). The architecture model is based entirely on HTTP, XML, GRID-like environment and DotNet technologies. Finally, the platform provides extensibility and scalability targeted to large-scale Web-enabled global urologic databases.

Decision Support Techniques↗

PubMed2004

Computer-based malignancy grading of astrocytomas employing a support vector machine classifier, the WHO grading system and the regular hematoxylin-eosin diagnostic staining procedure.

OBJECTIVE: To investigate and develop an automated technique for astrocytoma malignancy grading compatible with the clinical routine. STUDY DESIGN: One hundred forty biopsies of astrocytomas were collected from 2 hospitals. The degree of tumor malignancy was defined as low or high according to the World Health Organization grading system. From each biopsy, images were digitized and segmented to isolate nuclei from background tissue. Morphologic and textural nuclear features were quantified to encode tumor malignancy. Each case was represented by a 40-dimensional feature vector. An exhaustive search procedure in feature space was utilized to determine the best feature combination that resulted in the smallest classification error. Low and high grade tumors were discriminated using support vector machines (SVMs). To evaluate the system performance, all available data were split randomly into training and test sets. RESULTS: The best vector combination consisted of 3 textural and 2 morphologic features. Low and high grade cases were discriminated with an accuracy of 90.7% and 88.9%, respectively, using an SVM classifier with polynomial kernel of degree 2. CONCLUSION: The proposed methodology was based on standards that are common in daily clinical practice and might be used in parallel with conventional grading as a second-opinion tool to reduce subjectivity in the classification of astrocytomas.

Artificial Intelligence↗

PubMed2004

Automated segmentation of routinely hematoxylin-eosin-stained microscopic images by combining support vector machine clustering and active contour models.

OBJECTIVE: To develop a method for the automated segmentation of images of routinely hematoxylin-eosin (H-E)-stained microscopic sections to guarantee correct results in computer-assisted microscopy. STUDY DESIGN: Clinical material was composed 50 H-E-stained biopsies of astrocytomas and 50 H-E-stained biopsies of urinary bladder cancer. The basic idea was to use a support vector machine clustering (SVMC) algorithm to provide gross segmentation of regions holding nuclei and subsequently to refine nuclear boundary detection with active contours. The initialization coordinates of the active contour model were defined using a SVMC pixel-based classification algorithm that discriminated nuclear regions from the surrounding tissue. Starting from the boundaries of these regions, the snake fired and propagated until converging to nuclear boundaries. RESULTS: The method was validated for 2 different types of H-E-stained images. Results were evaluated by 2 histopathologists. On average, 94% of nuclei were correctly delineated. CONCLUSION: The proposed algorithm could be of value in computer-based systems for automated interpretation of microscopic images.

Algorithms↗

PubMed2003

Ureteral metallic stents: application of virtual endoscopy for ureteral patency control.

OBJECTIVE: In the present study we have applied virtual endoscopy (VE) in patients with ureteral metallic stents as a follow-up tool study especially in the need to define ureteral patency. METHODS: We performed the suggested technique in 6 patients with malignant ureteral obstruction treated successfully by placement of Wallstent intraureteral metallic stents, and correlated the results with antegrade nephrostomography 48 hours after initial stent placement. RESULTS: In 2 patients restenosis was observed, and in the remaining 4 patients the stented ureters remained patent during the follow up evaluation. VE and antegrade nephrostomography, were concurrent as to their findings. Moreover, VE proceeds beyond the stenotic segment, allowing visualization of the ureteral lumen both cephalad and caudal to the point of obstruction. CONCLUSION: VE is providing indeed a more accurate, direct and dynamic approach in the evaluation of a strictured ureteral lumen within the metallic stent.

Female↗

PubMed2003

A novel spectral microscope system: application in quantitative pathology.

In this paper, a novel spectral microscope system is presented together with a method for the quantitative assessment of the uptake by histologic samples of stains used in pathology to label tissue features of diagnostic importance. The critical component of the microscope is a variable interference filter-based monochromator. The system is capable of performing real-time spectral imaging in a plurality of spectral bands and micro-spectroscopy in any image pixel, in the spectral range 400-1000 nm. The wavelength-tuning step is 2.4-2.6 nm, while the full-width at half maximum in each step is about 1.5% of the operating central wavelength. The developed system integrates algorithms and calibration procedures for the calculation of the stain-uptake by the tissue. The acquired spectra from both stained tissue and calibration stain solutions enable the calculation of the concentration maps of the stains, even if the latter are multiple and overlap spatially and spectrally. The system was used for the quantitative mapping of the expression of estrogen and progesterone receptors in breast cancer cells. In this particular case, model validation shows that although two stains are employed, capturing of their transmittance at more than ten wavelengths is required in order to obtain an acceptable accuracy. These findings highlight the need for the development and implementation of spectral microscopy in pathology and its potential to introduce novel more reliable diagnostic criteria.

Algorithms↗

PubMed2002

Ureteropelvic junction obstruction: an innovative approach combining metallic stenting and virtual endoscopy.

PURPOSE: We report our experience with auto-expandable metallic stents for treating ureteropelvic junction obstruction. MATERIALS AND METHODS: We treated 4 patients with a mean age of 45 years who had ureteropelvic junction obstruction with placement of a self-expandable intraureteral metallic stent (Wallstent, Schneider, Zurich, Switzerland). All patients presented with recurrent ureteropelvic junction obstruction after open pyeloplasty. Excretory urography and 3-dimensional reconstruction computerized tomography were performed 1 and 6 months after stent insertion. Virtual endoscopy images were obtained at followup due to the need to define ureteral patency. RESULTS: Mean followup was 16 months (range 9 to 24). Wallstent placement was successful and immediate patency was achieved in all cases. During followup 3 patients required no further intervention and the stented ureteropelvic junction remained patent. In the remaining patient stricture recurred 2 months after initial stent insertion due to the ingrowth of scar tissue through the prosthesis. Additional intervention was deemed necessary after placing a longer 6 cm., completely coaxial overlapping metal stent. Virtual endoscopy and excretory urography findings concurred. Virtual endoscopy allows visualization of the stented ureteropelvic junction lumen cephalad and caudal to the prosthesis. It also enables easy navigation within the stent at different angles of view. CONCLUSIONS: The concept of applying metallic stents for ureteropelvic junction obstruction and adjacent adynamic ureteral segments combined with virtual endoscopy is strengthened by the results of this study.

Adult↗

PubMed2002

Comparison of nutritional deficiencies after Roux-en-Y gastric bypass and after biliopancreatic diversion with Roux-en-Y gastric bypass.

BACKGROUND: Patients undergoing either Roux-en-Y gastric bypass (RYGBP) or biliopancreatic diversion (BPD) with RYGBP are at risk of developing metabolic sequelae secondary to malabsorption. We compared the differences in nutritional complications between these two bariatric operations. METHODS: A retrospective analysis of a prospective database was done. From June 1994 to December 2001, 243 morbidly obese patients underwent various bariatric procedures at our institution. Of these patients, 79 (BMI 45.6 +/- SD = 4.9) who underwent RYGBP (gastric pouch 15 +/- 5 ml, biliopancreatic limb 60-80 cm, alimentary limb 80-100 cm and common limb the remainder of the small intestine), and 95 super obese (BMI 57.2 +/- 6.1) who underwent a BPD (gastric pouch 15 +/- 5 ml, biliopancreatic limb 150-200 cm, common limb 100 cm and alimentary limb the remainder of the small intestine), were selected and studied for the incidence of micronutrient deficiencies and level of serum albumin at yearly intervals postoperatively. A variety of nutritional parameters including Hb, Fe, ferritin, folic acid, vitamin B12 and serum albumin were measured preoperatively and compared postoperatively at 1, 3, 6, 12, 18 and 24 months, and yearly thereafter. RESULTS: Nutritional parameters were compared preoperatively and at similar periods postoperatively. No statistically significant (P < 0.05) difference in the occurrence of deficiency was observed between the groups for any of the nutritional parameters studied, except for ferritin, which showed a significant difference at the 2-year follow-up (37.7% low ferritin levels after RYGBP vs. 15.2% after BPD, P = 0.0294). All of these deficiencies were mild, without clinical symptomatology and were easily corrected with additional supplementation of the deficient micronutrient, with no need for hospitalization. Regarding serum albumin, there was only one patient with a level below 3 g/dl in the RYGBP group and two in the BPD group. These three patients were hospitalized and received total parenteral nutrition for 3 weeks, without further complications. CONCLUSION: There was no significant difference in the incidence of deficiency of the nutritional parameters studied, except for ferritin, following RYGBP vs. BPD with RYGBP. The most common deficiencies encountered were of iron and vitamin B12. The incidence of hypoalbuminemia was negligible in both groups, with mean values above 4 g/dl.

Adult↗

PubMed2002

Neural network-based segmentation and classification system for automated grading of histologic sections of bladder carcinoma.

OBJECTIVE: To develop an image analysis system for automated nuclear segmentation and classification of histologic bladder sections employing quantitative nuclear features. STUDY DESIGN: Ninety-two cases were classified into three classes by experienced pathologists according to the WHO grading system: 18 cases as grade 1, 45 as grade 2, and 29 as grade 3. Nuclear segmentation was performed by means of an artificial neural network (ANN)-based pixel classification algorithm, and each case was represented by 36 nuclei features. Automated grading of bladder tumor histologic sections was performed by an ANN classifier implemented in a two-stage hierarchic tree. RESULTS: On average, 95% of the nuclei were correctly detected. At the first stage of the hierarchic tree, classifier performance in discriminating between cases of grade 1 and 2 and cases of grade 3 was 89%. At the second stage, 79% of grade 1 cases were correctly distinguished from grade 2 cases. CONCLUSION: The proposed image analysis system provides the means to reduce subjectivity in grading bladder tumors and may contribute to more accurate diagnosis and prognosis since it relies on nuclear features, the value of which has been confirmed.

Algorithms↗

PubMedDate not supplied

Virtual endoscopy: navigation within pelvicaliceal system.

PURPOSE: To evaluate the use of virtual endoscopy (VE) for the investigation of the pelvicaliceal unit and the depiction of its anatomic deformities. PATIENTS AND METHODS: Two study groups were prospectively enrolled in our protocol: ten patients with nonurologic pathologies, and thus without any known deformity of the pelvicaliceal unit (group A), and five patients with caliceal obstruction (group B). Virtual endoscopy represented a non-invasive technique providing amplification of the image in three-dimensional space. RESULTS: Virtual endoscopy was feasible in all patients, and in all cases succeeded in demonstrating the threedimensional morphology of the region of interest. The entire processing time ranged from 10 to 15 minutes (mean 12.6 minutes), and the three-dimensional image could be viewed from different angles, allowing better evaluation of the collecting system and its deformities than is possible with conventional intravenous urography or percutaneous nephrostomography. CONCLUSION: Virtual endoscopy enabled the creation of endoluminal views of the renal pelvis and calices from spiral tomographic images, thereby allowing diagnostic-preoperative and postoperative evaluation of the pelvicaliceal unit.

Adult↗

PubMedDate not supplied

Automated diagnosis of brain tumours astrocytomas using probabilistic neural network clustering and support vector machines.

A computer-aided diagnosis system was developed for assisting brain astrocytomas malignancy grading. Microscopy images from 140 astrocytic biopsies were digitized and cell nuclei were automatically segmented using a Probabilistic Neural Network pixel-based clustering algorithm. A decision tree classification scheme was constructed to discriminate low, intermediate and high-grade tumours by analyzing nuclear features extracted from segmented nuclei with a Support Vector Machine classifier. Nuclei were segmented with an average accuracy of 86.5%. Low, intermediate, and high-grade tumours were identified with 95%, 88.3%, and 91% accuracies respectively. The proposed algorithm could be used as a second opinion tool for the histopathologists.

Algorithms↗