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Biomedical subjects

K S Nikita

Publications and source records attributed to K S Nikita.

At least 19 recordsLinked to original sources
PubMed2004

A digital subtraction radiography scheme based on automatic multiresolution registration.

OBJECTIVES: To establish a digital subtraction radiography scheme for aligning clinical in vivo radiographs based on the implementations of an automatic geometric registration method and a contrast correction technique. METHODS: Thirty-five pairs of in vivo dental radiographs from four clinical studies were used in this work. First, each image pair was automatically aligned by applying a multiresolution registration strategy using the affine transformation followed by the implementation of the projective transformation at full resolution. Then, a contrast correction technique was applied in order to produce subtraction radiographs and fused images for further clinical evaluation. The performance of the proposed registration method was assessed against a manual method based on the projective transformation. RESULTS: The qualitative assessment of the experiments based on visual inspection has shown advantageous performance of the proposed automatic registration method against the manual method. Furthermore, the quantitative analysis showed statistical difference in terms of the root mean square (RMS) error estimated over the whole images and specific regions of interest. CONCLUSIONS: The proposed automatic geometric registration method is capable of aligning radiographs acquired with or without rigorous a priori standardization. The methodology is pixel-based and does not require the application of any segmentation process prior to alignment. The employed projective transformation provides a reliable model for registering intraoral radiographs. The implemented contrast correction technique sequentially applied provides subtraction radiographs and fused images for clinical evaluation regarding the evolution of a disease or the response to a therapeutic scheme.

Algorithms↗
PubMed2003

A 3D high-resolution gamma camera for radiopharmaceutical studies with small animals.

The results of studies conducted with a small field of view tomographic gamma camera based on a Position Sensitive Photomultiplier Tube are reported. The system has been used for the evaluation of radiopharmaceuticals in small animals. Phantom studies have shown a spatial resolution of 2mm in planar and 2-3mm in tomographic imaging. Imaging studies in mice have been carried out both in 2D and 3D. Conventional radiopharmaceuticals have been used and the results have been compared with images from a clinically used system.

Algorithms↗
PubMed2003

A scenario for a web-based radiation treatment planning structure: A new tool for quality assurance procedure?

The desire to develop web-based platforms for remote collaboration among physicians and technologists is becoming a great challenge. In this paper we describe a web-based radiotherapy treatment planning (WBRTP) system to facilitate decentralized radiotherapy services by allowing remote treatment planning and quality assurance (QA) of treatment delivery. Significant prerequisites are digital storage of relevant data as well as efficient and reliable telecommunication system between collaborating units. The system of WBRTP includes video conferencing, display of medical images (CT scans, dose distributions etc), replication of selected data from a common database, remote treatment planning, evaluation of treatment technique and follow-up of the treated patients. Moreover the system features real-time remote operations in terms of tele-consulting like target volume delineation performed by a team of experts at different and distant units. An appraisal of its possibilities in quality assurance in radiotherapy is also discussed. As a conclusion, a WBRTP system would not only be a medium for communication between experts in oncology but mainly a tool for improving the QA in radiotherapy.

Cooperative Behavior↗
PubMed2002

Intraoperative hyperthermia and chemoradiotherapy for inoperable pancreatic carcinoma.

The aim of this study was to evaluate the tolerability and the possible clinical benefit of intraoperative hyperthermia combined with multischedule chemotherapy and bypass surgery for the palliative treatment of inoperable pancreatic cancer. Ten patients with unresectable adenocarcinoma of the pancreas received preoperative chemotherapy [5-fluorouracil (5-FU)], bypass surgery and postoperative chemotherapy (5-FU, doxorubicin and cisplatin) plus sandostatin and radiotherapy (45 Gy, 25 fractions, 5 days a week). A single session of intraoperative hyperthermia was performed, by using a waveguide-type applicator (433 MHz). The tumour region was heated to 43-45 degrees C for up to 60 min, while 500 mg 5-FU was infused simultaneously through the gastroduodenal into the splenic artery. Postoperative recovery was uneventful for all patients. A brief instrument was developed for evaluating patients' quality of life. Chemotherapy-related toxicity included myelosuppression, vomiting, alopecia and increase in blood urea nitrogen (BUN), creatinine, SGOT and SGPT. Glucose and amylase determinations remained within normal limits throughout the whole treatment. There was a significant improvement before and 1 month after combined treatment in Eastern Cooperative Oncology Group (ECOG) status (1.8 +/- 0.4), Scott-Huskinsson pain scale (3.2 +/- 0.8) and quality of life score (30.5 +/- 6.7). No progressive disease was noticed and the median overall survival was 11 (SE = 2.4) months. There was also a significant (P = 0.002, Wilcoxon test) decrease in values of both serum carcinoembryonic antigen (CEA) and carbohydrate antigen (CA19-9), from 7.6 +/- 1.3 ng/mL and 875.7 +/- 104.8 U/mL to 3.5 +/- 0.7 ng/mL and 65.3 +/- 14.1 U/mL respectively. The first clinical results suggest a potential advantage of using combined intraoperative hyperthermia, chemotherapy and postoperative radiotherapy in the palliative treatment of the adenocarcinoma of the pancreas. The whole procedure seems to be free of perioperative morbidity, while the chemotherapy toxicity was rather moderate. However, the preliminary nature limits the general applicability of our results.

Adenocarcinoma↗
PubMed2001

Abnormal P600 in heroin addicts with prolonged abstinence elicited during a working memory test.

The P600 component of event-related potentials, believed to be generated by anterior cingulate gyrus and basal ganglia, is considered as an index of aspects of second-pass parsing processes of information processing, having much in common with working memory (WM) systems. Moreover, dysfunction of these brain structures as well as WM deficits have been implicated in the pathophysiology of opioid addicts. The present study is focused on P600 elicited during a WM test in twenty heroin addicts with prolonged abstinence compared with an equal number of healthy controls. The results showed significantly prolonged latencies at right hemisphere, specifically at Fp2 abduction. Moreover, memory performance of patients did not differ from that of normal controls. These findings may indicate that abstinent heroin addicts manifest abnormal aspects of second-pass parsing processes as are reflected by the P600 latencies, elicited during a WM test. Additionally, the P600 might serve as a valuable investigative tool for a more comprehensive understanding of the neurobiological substrate of drug abuse.

Adult↗
PubMed2001

Cytoreductive surgery combined with intraoperative chemo-hyperthermia and postoperative radiotherapy in the management of advanced pancreatic adenocarcinoma: feasibility aspects and efficacy.

BACKGROUND/PURPOSE: The aim of our study was to evaluate the feasibility and the efficacy of cytoreductive surgery (CS) with intraoperative chemo-hyperthermia in the management of advanced stage IVA (T4N0M0) pancreatic cancer. METHODS: From August 1995 through March 1996, seven patients with unresectable adenocarcinoma of the pancreas underwent CS, with preoperative chemotherapy (5-fluorouracil [FU] for 96 h), plus 45-Gy external beam postoperative irradiation with a 6-MeV linear accelerator (1.8 Gy per fraction, 5 days per week). A single session of intraoperative hyperthermia was performed with a waveguide-type applicator operating at 433 MHz, and temperature was measured by inserting a flexiguide needle catheter carrying a thermometry probe with three measuring points into the tumor. The tumor region was heated to 43 degrees C-45 degrees C for up to 60 min, while 5-FU 500 mg was injected simultaneously through the gastroduodenal artery into the splenic artery (intraoperative regional chemotherapy). RESULTS: Postoperative recovery was uneventful for all patients. After the combined treatment, there was a significant decrease in the values of both serum carcinoembryonic antigen (CEA; P = 0.017, Wilcoxon test) and carbohydrate antigen (CA)19-9 ( P = 0.016; Wilcoxon test), from 7.6 +/- 1.5 ng/ml CEA and 869.6 +/- 126.9 U/ml CA to 3.5 +/- 0.8 ng/ml CEA and 104.7 +/- 35.4 U/ml CA19-9. Moreover, there was a significant improvement ( P = 0.016; Wilcoxon test) in Eastern Cooperative Oncology Group performance status, pain score, and body mass index. The median overall survival was 18.5 (SE, 1.8) months. CONCLUSIONS: Our preliminary clinical results suggest the tolerability and the considerable potential advantage of using cytoreductive resection with preoperative chemotherapy, intraoperative chemo-hyperthermia, and external beam postoperative radiotherapy for the management of advanced adenocarcinoma of the pancreas.

Adenocarcinoma↗
PubMed2001

Modeling tumor growth and irradiation response in vitro--a combination of high-performance computing and web-based technologies including VRML visualization.

A simplified three-dimensional Monte Carlo simulation model of in vitro tumor growth and response to fractionated radiotherapeutic schemes is presented in this paper. The paper aims at both the optimization of radiotherapy and the provision of insight into the biological mechanisms involved in tumor development. The basics of the modeling philosophy of Duechting have been adopted and substantially extended. The main processes taken into account by the model are the transitions between the cell cycle phases, the diffusion of oxygen and glucose, and the cell survival probabilities following irradiation. Specific algorithms satisfactorily describing tumor expansion and shrinkage have been applied, whereas a novel approach to the modeling of the tumor response to irradiation has been proposed and implemented. High-performance computing systems in conjunction with Web technologies have coped with the particularly high computer memory and processing demands. A visualization system based on the MATLAB software package and the virtual-reality modeling language has been employed. Its utilization has led to a spectacular representation of both the external surface and the internal structure of the developing tumor. The simulation model has been applied to the special case of small cell lung carcinoma in vitro irradiated according to both the standard and accelerated fractionation schemes. A good qualitative agreement with laboratory experience has been observed in all cases. Accordingly, the hypothesis that advanced simulation models for the in silico testing of tumor irradiation schemes could substantially enhance the radiotherapy optimization process is further strengthened. Currently, our group is investigating extensions of the presented algorithms so that efficient descriptions of the corresponding clinical (in vivo) cases are achieved.

Carcinoma, Small Cell↗
PubMed2000

A neural network approach for insulin regime and dose adjustment in type 1 diabetes.

BACKGROUND: A decision support system based on a neural network approach is proposed to advise on insulin regime and dose adjustment for type 1 diabetes patients. METHOD: The system consists of two feed-forward neural networks, trained with the back-propagation algorithm with momentum and adaptive learning rate. The input to the system consists of patient's glucose levels, insulin intake, and observed hypoglycemia symptoms during a short time period. The output of the first neural network provides the insulin regime, which is applied as input to the second neural network to estimate the appropriate insulin doses for a short time period. RESULTS: The system's ability in order to recommend on insulin regime is excellent, while its performance in adjusting the insulin dosages for a specific patient is highly dependent on the data set used during the training procedure. CONCLUSIONS: Despite the limitations of computer-based approaches, this study shows that artificial neural networks can assist diabetes patients in insulin adjustment.

Blood Glucose↗
PubMed2000

Reengineering the biomedical-equipment procurement process through an integrated management information system.

The design of each new hospital site is typically preceded by decisions on the most appropriate level of biomedical equipment which significantly influences the layout of the hospital departments which are under construction. The most appropriate biomedical equipment should ideally be decided upon considering a series of demographic and social parameters of the hospital and international regulations and standards. This information should ultimately be distilled to proper technical specifications. This paper proposes a streamlined management process related to the procurement of biomedical equipment for new hospital sites or for those under expansion. The new management process aims to increase the efficiency of the experts involved in the definition of the most appropriate level of equipment and its technical specifications. It also addresses all aspects of the biomedical equipment-selection cycle, including the evaluation of the bids submitted by the equipment suppliers. The proposed process is assisted by a management information system, which integrates all related data-handling operations. It provides extensive decision-support facilities to the expert and a platform for the support of knowledge re-use in the field of biomedical-equipment selection.

Competitive Bidding↗
PubMed1999

Automatic retinal image registration scheme using global optimization techniques.

Retinal image registration is commonly required in order to combine the complementary information in different retinal modalities. In this paper, a new automatic scheme to register retinal images is presented and is currently tested in a clinical environment. The scheme considers the suitability and efficiency of different image transformation models and function optimization techniques, following an initial preprocessing stage. Three different transformation models--affine, bilinear and projective--as well as three optimization techniques--downhill simplex method, simulated annealing and genetic algorithms--are investigated and compared in terms of accuracy and efficiency. The registration of 26 pairs of Fluoroscein Angiography and Indocyanine Green Chorioangiography images with the corresponding Red-Free retinal images, showed the superiority of combining genetic algorithms with the affine and bilinear transformation models. A comparative study of the proposed automatic registration scheme against the manual method, commonly used in the clinical practice, is finally presented showing the advantage of the proposed automatic scheme in terms of accuracy and consistency.

Algorithms↗
PubMed1998

Optimization of the deposited power distribution inside a layered lossy medium irradiated by a coupled system of concentrically placed waveguide applicators.

A method is proposed for controlling the deposited power distribution in a layered cylindrical lossy model, irradiated by a phased-array hyperthermia system consisting of four waveguide applicators. A rigorous electromagnetic model of the heated tissue, which takes into account coupling phenomena between system elements, is used for predicting the electric field at any point inside tissue. The relative amplitudes and relative phases of the array elements are optimized in order to attain desired specific absorption rate (SAR) distributions inside and outside malignant tissues. A constrained nonlinear optimization problem is solved by using the penalty function method and the resulting unconstrained minimization of the penalty function is carried out by the downhill simplex method. Two practical phased-array hyperthermia systems have been studied and numerical results are presented.

Algorithms↗
PubMed1993

Optimal steady-state temperature distribution for a phased array hyperthermia system.

A method is presented for the evaluation of optimal amplitude and phase excitations for the radiating elements of a phased array hyperthermia system, in order to achieve desired steady-state temperature distributions inside and outside of malignant tissues. Use is made of a detailed electromagnetic and thermal model of the heated tissue in order to predict the steady-state temperature at any point in tissue. Optimal excitations are obtained by minimizing the squared error between desired and model predicted temperatures inside the tumor volume, subject to the constraint that temperatures do not exceed an upper bound outside the tumor. The penalty function technique is used to solve the constrained optimization problem. Sequential unconstrained minima are obtained by a modified Newton method. Numerical results for a four element phased array hyperthermia system are presented.

Electromagnetic Phenomena↗