Biomedical subjects

G Sakas

Publications and source records attributed to G Sakas.

7 recordsLinked to original sources

PubMed2006

Magnetic resonance imaging of freely moving objects: prospective real-time motion correction using an external optical motion tracking system.

Subject motion and associated artefacts limit the applicability of MRI and the achievable quality of the images acquired. In this paper, a fully integrated method for prospective correction of arbitrary rigid body motion employing an external motion tracking device is demonstrated for the first time. The position of the imaging volume is updated prior to every excitation of the spin system. The performance of the available tracking hardware and its connection to the MR imager is analyzed in detail. With the introduction of a novel calibration procedure the accuracy of motion correction is improved compared to previous approaches. Together with the high geometry update rate even freely moving objects can be imaged without motion related artefacts. The high performance and image quality improvement in case of subject motion are demonstrated for various imaging techniques such as gradient and spin echo, as well as echo planar imaging.

Artifacts↗

PubMed2005

Telemonitoring of medication adherence in patients with schizophrenia.

Nonadherence to medication is a widespread problem in schizophrenia and is associated with poor clinical outcomes and inappropriate management and utilization of resources. The aim of the current investigation was to assess the impact of telemonitoring of medication adherence on symptomatology and service use in patients with schizophrenia. A total of 108 schizophrenia patients were randomized into three equal groups according to the approaches used to assess medication adherence; self-report, pill counting, and telemonitoring. Telementoring was achieved through an innovative new platform called @HOME. This platform offers clinicians early warnings about impeding nonadherence as well as information about the pattern of medication taking. Patient's adherence was observed over an 8-week period, during which patient's clinical status and service use were recorded. In comparison to the other two groups, patients using @HOME showed improvement in the Global Clinical Impression Scale and a significant reduction in emergency visits and medical appointments. The @HOME platform was highly acceptable by patients, caregivers, and professionals, and required minimal training for implementation. The results of the study suggest that the use of telemonitoring in psychiatric settings was both feasible and acceptable and may be associated with significant clinical and service related benefits.

Adult↗

PubMed2000

Reconstruction and navigation system for intraoperative brachytherapy using the flab technique for colorectal tumor bed irradiation.

PURPOSE: To present the development of a new navigation and reconstruction system based on an electromagnetic free-hand tracker and on CT imaging for treatment planning of intraoperative high-dose-rate brachytherapy (IORT-HDRB) in the sacral region. Our aim is to improve accuracy and to enable individualized treatment planning and dose documentation to be performed for IORT-HDRB using a flab technique. METHODS AND MATERIALS: The material consists of an electromagnetic 3D tracker system, a PC workstation with Microsoft Windows NT 4.0 operating system, and a recognition program for continuous speech. In addition, we designed an external reference system constructed of titanium and Perspex, which is positioned in the pelvis, and a special digitizer pen for reconstruction of the flab geometry. The flab design incorporates a series of silicon 10-mm-diameter spherical pellets. Measurements were made with a pelvic phantom in order to study the accuracy of the system. The reconstruction results are stored and can be exported via network or floppy to our different treatment planning systems. RESULTS: Our results for the reconstruction of a flab with six catheters and a total of 100 spherical pellets give mean errors in the range (2.5 +/- 0.6) mm to (3.5 +/- 0.8) mm depending on the positions of the pelvic phantom and transmitter relative to the operation table. These errors are calculated by comparing the reconstruction results of our system with those using a CT-based reconstruction of the flab geometry. For the accuracy of the navigation system for the pelvic phantom, we obtained mean errors in the range (2.2 +/- 0.7) mm to (3. 1 +/- 1.0) mm. CONCLUSIONS: The new system we have developed enables navigation and reconstruction within the surgical environment with a clinically acceptable level of accuracy. It offers the possibility of individualized treatment planning and effective documentation of the 3D dose distribution in IORT-HDRB using a flab technique.

Brachytherapy↗

PubMed2000

[3D models for diagnosis and treatment planning in cardiology].

Due to the development new of imaging devices which produce a large number of tomographic slices, advanced techniques for the evaluation of the large amount of data are required. Computer supported extraction of dynamic 3D-models of the patients anatomy from temporal series thus is highly desirable. Since the diagnostician should be able to quickly make sensible decisions based on the models, high accuracy is required within a minimum of time. We present modeling and visualization techniques that are realized within the Cardiac Station. Results for the application of these techniques to cardiac image data demonstrate their usability. Besides giving information about the patients morphology functional parameters can be derived from the data and visualized together with the model. In order to verify the model with the original image data and for the planning of real intervention interaction techniques are presented.

Anatomy, Cross-Sectional↗

PubMed2000

[Free hand acquisition, reconstruction and visualization of 3D and 4D ultrasound].

3D Ultrasound will find in the next years a wide popularity under the medical imaging applications. The method expands the well-known sonography on the third dimension, therefore it becomes possible to generate spatial 3D views of internal organs. It is further possible to display static (3D) as well as dynamic organs (4D, e.g. pulsating heart). The clarity of the three-dimensional presentation supports very effectively the navigation. In this article we review the upgrading of conventional ultrasound devices on 3D and 4D capabilities, as well as the display of the datasets by corresponding visualisation and filtering approaches.

Computer Graphics↗

PubMed2000

Navigation system for interstitial brachytherapy.

PURPOSE: To develop a computed tomography (CT) based electromagnetic navigation system for interstitial brachytherapy. This is especially designed for situations when needles have to be positioned adjacent to or within critical anatomical structures. In such instances interactive 3D visualisation of the needle positions is essential. METHODS AND MATERIALS: The material consisted of a Polhemus electromagnetic 3D digitizer, a Pentium 200 MHz laptop and a voice recognition for continuous speech. In addition, we developed an external reference system constructed of Perspex which could be positioned above the tumour region and attached to the patient using a non-invasive fixation method. A specially designed needle holder and patient bed were also developed. Measurements were made on a series of phantoms in order to study the efficacy and accuracy of the navigation system. RESULTS: The mean navigation accuracy of positioning the 20.0 cm length metallic needles within the phantoms was in the range 2.0-4.1 mm with a maximum of 5.4 mm. This is an improvement on the accuracy of a CT-guided technique which was in the range 6.1-11.3 mm with a maximum of 19.4 mm. The mean reconstruction accuracy of the implant geometry was 3.2 mm within a non-ferromagnetic environment. We found that although the needles were metallic this did not have a significant influence. We also found for our experimental setups that the CT table and operation table non-ferromagnetic parts had no significant influence on the navigation accuracy. CONCLUSIONS: This navigation system will be a very useful clinical tool for interstitial brachytherapy applications, particularly when critical structures have to be avoided. It also should provide a significant improvement on our existing technique.

Brachytherapy↗

PubMed1995

Complete versus incomplete nonviable amputations of the thumb. Comparison of the survival rate and functional results.

81 patients with 84 complete (55) or incomplete (29) nonviable amputations of the thumb were studied to compare the survival rate and functional results between the two groups. 3 of these patients had bilateral thumb amputations. Of the 55 completely amputated thumbs, 43 survived (78 percent), while of the 29 incomplete nonviable amputations, 25 were salvaged (86 percent). Excluding patients with an amputation at the level of or distal to the interphalangeal (IP) joint, motion at the IP joint which did not exceed 40 degrees flexion even when a secondary procedure was done, did not show a statistical difference between the 2 groups. Average two-point discrimination was 14 mm for patients with complete amputations and 11 mm for patients with incomplete nonviable amputations. We conclude that incomplete nonviable amputations of the thumb are associated with a higher survival rate and better sensibility than complete thumb amputations, while motion at the IP joint does not differ between the two groups of patients.

Activities of Daily Living↗