Biomedical subjects

M Bajka

Publications and source records attributed to M Bajka.

18 recordsLinked to original sources

PubMed2006

Tumor growth models to generate pathologies for surgical training simulators.

Many virtual reality based surgical training simulators have been presented in the last few years. These systems promise to alleviate the lack of realistic training possibilities common to minimally invasive procedures. Virtual reality allows for riskless training on a wide range of findings in a condensed period of time. We investigated different methods for the generation of tumor models suitable for surgical training simulators. The goal of our research is a high fidelity hysteroscopy simulator which provides an individual surgical scene for every training. Emphasis was placed on the modeling of growth processes leading to the generation of macroscopically realistic findings of the most common pathologies in hysteroscopy, namely polyps and myomas found in the uterine cavity. Both a cellular automaton and a particle based tumor growth model are presented and discussed.

Cell Proliferation↗

PubMed2006

Generation of variable anatomical models for surgical training simulators.

The generation of variable surgical scenes is a key element for effective training with surgery simulators. Our current research aims at a high fidelity hysteroscopy simulator which challenges the trainee with a new surgical scene in every training session. We previously reported on methods able to generate a broad range of pathologies within an existing healthy organ model. This paper presents the methods necessary to produce variable models of the healthy organ. In order to build a database of uteri, a volunteer study was conducted. The segmentation was carried out interactively, also covering the establishment of an anatomically meaningful correspondence between the individual organs. The variability of the shape parameters has been characterized by principal component analysis. A new method has been developed and tested, allowing the derivation of realistic new instances based on the stochastic model and complying with non-linear shape constraints which are defined and interactively controlled by medical experts.

Computer Graphics↗

PubMed2005

[Contraception and bleeding disorders--diagnostic contributions by ultrasound].

Practically all widely used and safe and reversible methods of contraception exert a direct (or at least an indirect) impact on the endometrium. Not surprisingly, abnormal uterine bleeding is a frequent adverse reaction associated with contraception. In this situation sonography--in particular transvaginal sonography--offers the physician a practically non-invasive imaging technique for determining the etiology of abnormal uterine, cervical or vaginal bleeding. Ultrasonographic imaging provides the physician with a detailed picture of the internal reproductive organs. It can also be used to monitor the efficacy of the particular contraceptive method. e.g. to check the position of IUDs, confirm the suppression of ovarian follicle activity in women taking ovulation inhibitors, detect ovarian cysts as a focus of undesirable hormonal activity, etc. In some cases, the failure of contraception, namely pregnancy, can be diagnosed by ultrasound. By using high-frequency linear ultrasonographic probes, the physician can verify the position of subcutaneous contraceptive implants on the medial upper arm. Therapeutic consequences can be derived, in particular, from the ultrasonographic measurement of the total thickness of the endometrial layer.

Adult↗

PubMed2005

Hydrometra simulation for VR-based hysteroscopy training.

During hysteroscopy a hydrometra is maintained, i.e. the uterus is distended with liquid media to access and visualize the uterine cavity. The pressure and flow induced by the liquid are crucial tools for he gynecologists during surgery to obtain a clear view of the operation site. This paper presents two different aspects of hydrometra simulation, namely the distension of the uterine muscle and the liquid flow simulation in the cavity. The deformation of the organ's shape is computed offline based on finite element calculations whereas the flow is approximated on the fly by solving the simplified Navier-Stokes equations. The real-time capabilities of the presented algorithms as well as the level of fidelity achieved by the proposed methods are discussed.

Body Fluids↗

PubMed2004

[Differential diagnosis of acute pelvic pain in gynecology].

Differential diagnosis of acute pelvic pain in gynecology has to respect the four pillars anamnesis, laboratory, clinical investigation and ultrasonographic evaluation. Besides, no findings should be evaluated independently. A meaningful general attempt to the diagnostics in gynecology is the partitioning in pregnancy test-positive (known pregnancy respectively) and pregnancy test-negative (postmenopausal respectively). Further important findings are clear inflammation markers and free blood in the abdominal cavity. If an extensive basic clarification should not allow conclusive diagnosis, the judgement of the dynamism of the complaints by short term controls or an interdisciplinary cooperation may be helpful. Sometimes, several relevant causes may be identified as reason of acute pelvic pain.

Acute Disease↗

PubMed2004

Detailed anatomy of the abdomen and pelvis of the visible human female.

We report on a virtual anatomical preparation of the abdomen and pelvis of the Visible Human Female (VHF) for laparoscopic surgery training. The detailed cross-sectional image data set from the U.S. National Library of Medicine was used as the basis to build an exemplary model of the female abdomen and pelvis. Segmentation software was developed to delineate organ outlines and more than 300 structures of interest, including organs, blood vessels, bones, muscles, and ligaments, have been segmented and three-dimensionally reconstructed. Analyzing the normal anatomy we found several variations and pathologies of the VHF, such as missing muscles (gemellus superior, psoas minor), additional veins as well as spondylophytes (vertebral column, pubic bone), and colon diverticula. The complete data set may be viewed on the home page of the project (http://www.vision.ee.ethz.ch/projects/Lasso/start.html).

Abdomen↗

PubMed2004

New nomogram for foetal weight estimation based on Hadlock's two-parameter formula.

AIM: To develop and validate a graphical method for ultrasonic foetal weight estimation with predictive qualities comparable to state-of-the-art computational methods. METHOD: Study data were obtained from 3839 consecutive singleton pregnancies with ultrasound examination within 7 days of delivery. We translated the well established Hadlock 2-parameter formula based on abdomen circumference and femur length into a nomogram [corrected]. We compared the measured foetal weight with estimations obtained from this new nomogram and three other methods. RESULTS: Measured by the foetal weight percentage error the new nomogram underestimates the foetal weight on average by 2.5 % (9.86) (mean [SD]) with uniform results over the complete birth weight spectrum. By the same measurement the Hadlock 4-parameter formula underestimates the foetal weight by 1.2 % (9.3) whereas the Hansmann nomogram overestimates the foetal weight by 14.5 % (16.1) The difference between the estimated foetal weight percentage error obtained from the new nomogram and from the Hadlock 2-parameter formula is 0.06 % (0.27) and hence clinically irrelevant. CONCLUSION: The new nomogram has predictive qualities comparable to state-of-the-art computational methods and is thus not only as reliable but also easy to use in situations when computers are not available. It can be recommended for foetal weight estimation over the whole spectrum of birth weight.

Embryonic and Fetal Development↗

PubMed2004

A finite element model for the simulation of hydrometra.

The behaviour of the human uterus under an internal (intracavital) pressure of 150 mm Hg (20 kPa) was modelled. The application of such an intracavital or intrauterine pressure corresponds to the procedure which is performed at the beginning of hysteroscopy (hydrometra). Homogenous, isotropic material laws were implemented in a three dimensional, finite element model. The volume of the distended uterine cavity was calculated with different parameters obtained from in vivo aspiration experiments on human uteri as well as from ex vivo tensile tests on rabbit uteri for comparison purposes. The calculated results were in general agreement with in vivo measurements of hydrometra performed at the University Hospital of Zurich.

Animals↗

PubMed2002

Inverse finite element characterization of soft tissues.

In this work a tissue aspiration method for the in vivo determination of biological soft tissue material parameters is presented. An explicit axisymmetric finite element simulation of the aspiration experiment is used together with a Levenberg-Marquardt algorithm to estimate the material model parameters in an inverse parameter determination process. An optimal fit of the simulated experiment and the real experiment is sought with the parameter estimation algorithm. Soft biological tissue is modelled as a viscoelastic, non-linear, nearly incompressible, isotropic continuum. Viscoelasticity is accounted for by a quasi-linear formulation. The aspiration method is validated experimentally with a synthetic material. In vivo (intra-operatively during surgical interventions) and ex vivo experiments were performed on human uteri.

Algorithms↗

PubMed2001

[Adnexal findings].

The female small pelvis is usually explored by conventional clinical examination. Adnexal masses found are assessed first by ultrasound. Thereby, sonographic findings should be documented and committed in a purely descriptive manner. It is not advisable to establish a histopathologic diagnosis, but to assign sonographic findings to one of the following three major groups: "simple cyst", "benign lesion", "malignant lesion". The SGUMGG recommends the Mainz-Score for the assessment of adnexal tumours, performed by transvaginal ultrasonography. Usually, a new adnexal tumour without symptoms may be evaluated after an interval of approx. six weeks without additional danger for the patient. A comprehensive Swiss guideline to adnexal tumours is in preparation by the Schweizerische Gesellschaft für Gynäkologie und Geburtshilfe. Its release is expected to be in the ongoing year 2001.

Endosonography↗

PubMed2001

[Ultrasound endometrium follow-up during tamoxifen treatment: Really not reliable or useful after all?].

AIM: To investigate whether an examination of the endometrium of women treated with tamoxifen (TAM) is useful or not. METHOD: 40 breast cancer patients who displayed a thickened endometrium of > 8 mm and/or vaginal bleeding were included in the study. They received daily TAM adjuvantly. Histologic clarification by hysteroscopy and D&C was recommended for patients with an endometrium of > 8 mm or vaginal bleeding. RESULTS: In our collective, the mean endometrial thickness was 13.7 +/- 5.6 mm (SD). 32 patients underwent a histological examination. Most had a benign lesion; in 2 cases we merely found a cystic atrophy (11 mm, 18 mm), 2 displayed atypical tissue (13 mm, 25 mm) and 2 an endometrial cancer (19 mm, 33 mm). All patients with atypical tissue or cancer had an endometrial thickness markedly above the norm, but 3 of them were not bleeding. No linear correlation between thickness of the endometrium and duration of TAM intake was found. CONCLUSION: To detect early premalignant or malignant changes of the endometrium, we recommend histological examination by hysteroscopy and dilatation and curettage when the endometrium is > 8 mm thick, even in the absence of symptoms. Therefore, these patients should have regular examinations by transvaginal ultrasound once or twice a year. Moreover, continuing regular screening of the endometrium for years after termination of tamoxifen-therapy is also to be recommended.

Adult↗

PubMed1999

[Krukenberg syndrome in metastatic gallbladder adenocarcinoma with unknown primary tumor].

The casuistic describes a female patient, in whom a metastatic adenocarcinoma of the ovary was diagnosed 3 years after cholecystectomy due to cholecystolithiasis, which was compatible with metastases of a carcinoma of the gallbladder or the bile ducts. While clinical and imaging results suggested a primary ovarian carcinoma with inapparent primary tumor, the final diagnosis was obtained on the basis of histological findings. The case demonstrates that an ovarian metastasis can simulate a primary tumor according to clinical and imaging results. This fact can be of serious therapeutic consequences for the respective patient. Therefore, in the presence of a clinically inapparent primary tumor, the differential diagnosis of unclear ovarian masses should include metastatic adenocarcinoma in addition to primary ovarian carcinoma and other ovarian lesions.

Adenocarcinoma↗

PubMed1999

Virtual reality based surgery simulation for endoscopic gynaecology.

Virtual reality (VR) based surgical simulator systems offer very elegant possibilities to both enrich and enhance traditional education in endoscopic surgery. However, while a wide range of VR simulator systems have been proposed and realized in the past few years, most of these systems are far from able to provide a reasonably realistic surgical environment. We explore the basic approaches to the current limits of realism and ultimately seek to extend these based on our description and analysis of the most important components of a VR-based endoscopic simulator. The feasibility of the proposed techniques is demonstrated on a first modular prototype system implementing the basic algorithms for VR-training in gynaecologic laparoscopy.

Computer Graphics↗

PubMed1996

[Analysis of indications and results of fractional curettage in a large gynecological cohort].

AIM: To determine whether the term "fractional D&C" is justified with respect to the uterine cervix and corpus fractions, and what indications and results are found when a large population at a university hospital is analyzed. METHODS: In this retrospective study covering a 3-year period at the Department of Gynecology, University Hospital of Zurich, indications and results of fractional D&C were obtained from hospital records stored in a data bank. The curettage results of hysterectomized women were compared with the histological findings of the hysterectomy specimens. RESULTS: 938 women (mean age 52 years) underwent fractional D&C. 38% had postmenopausal, 36% premenopausal and 13% perimenopausal abnormal bleeding. For 5% there was a sonographic finding without bleeding disorders, 4% had cervical polyps, 1% breast cancer, and 3% other diagnoses. In 13% of the cases the corpus curettage material could not be evaluated. For 43%, the corpus material appeared normal and in 5% a malignancy was found. In 74% of the cervical fractions nothing abnormal was detected, in 14% no conclusive evaluation of the material was possible, and in 3% the histological report showed a malignancy. In 20% of the cases the cervix curettage material was contaminated with material from the uterus cavum. CONCLUSIONS: For cases with cancer of the cervix, the sensitivity of fractional D&C was 80%, compared with a specificity of 66.7%. With a positive predictive value of 52.2%, the term "fractional D&C" is in many cases not justified. Our data and recent literature have prompted us to draw up new criteria for evaluation of abnormal vaginal bleeding, or a new set of indications for fractional D&C and hysteroscopy.

Adolescent↗

PubMed1996

[Gynecological management of patients over 80 years old. Results of a prospective study].

OBJECTIVE: Diagnosis and therapy of gynecologic inpatients who were over 80 years of age were analyzed with respect to the desired and the actual management. METHODS: A general assessment protocol for diagnostic and therapeutic steps which were not carried out in individual cases was drawn up and used for the 96 patients analyzed. The desired therapy corresponded to the ideal management of a 60-year-old patient. RESULTS: In two thirds of the cases, the desired therapy could be given. For 32 patients, there was a reduction of 5-50%; for only 2 patients one of > 50%. The most frequent deviation from the ideal therapy was for the oncologic patients. CONCLUSIONS: Our conclusions agree with those reported in the literature, namely that age alone can not be taken as an argument against standard treatment of a patient with a gynecologic disorder. For patients over 80 years of age, the individual risks and benefits of a particular therapy, especially when surgery is involved, should be carefully considered.

Aged↗

PubMed1995

[Placental site trophoblastic tumor. Morphology, differential diagnosis and prognosis].

A placental-site trophoblastic tumor is a rare neoplasia that is derived from the cells of the intermediate trophoblast. Morphological, biochemical, and Doppler ultrasound findings are presented regarding differential diagnosis using material from three recent cases. Essentially, placental-site trophoblastic tumors can be diagnosed if infiltration of the myometrium is seen by a monomorphic trophoblastic proliferation that is not interrupted by decidual cells. Necrosis and hemorrhages are not features of placental-site trophoblastic tumors. However, there is a peculiar behavior towards the uterine vasculature as spiral arteries are dilated and transformed the same way as occurs at the site of physiological implantation of pregnancy. It appears that as a result of this phenomenon there is a characteristic finding in ultrasound. Examination of this type of tumor demonstrates cystic spaces that can be defined as blood vessels by their Doppler signal. In two of the three cases a hysterectomy was performed, and criteria for the assumption of malignant placental-site tumors are therefore presented. However, only the mitosis rate seems to possess some predictive value.

Adult↗

PubMed1995

[Measuring the death of invasion of endometrial carcinoma. Preoperative transvaginal ultrasound and correlation with intraoperative and histopathologic findings--a prospective study].

AIM: Determination of the correlation of the assessment of depth of invasion in endometrial cancer by transvaginal ultrasound, and by intraoperative assessment with histopathology. METHOD: In this study 25 patients with endometrial cancer diagnosed by dilatation and curettage were examined by means of transvaginal ultrasound. The sonographically assessed depth of invasion (inner or outer half of the uterus wall) was compared with the intraoperatively determined depth of invasion in the sectioned uterus. Finally, we correlated these findings with histopathology. RESULTS: Transvaginal ultrasound and the intraoperative assessment of depth of invasion had and accuracy of 80% if correlated with the definitive histopathology. The result of the frozen section was correct in all analysed cases. We also evaluated the wrong assessments in the ultrasound group and in those patients who were assessed intraoperatively. In all these cases there were additional pathological findings, such as polyps, fibroids and uterus retroflexus. CONCLUSION: We conclude that especially in such cases frozen section analyses yield helpful information on the depth of invasion and should be performed routinely.

Adult↗

PubMed1995

[Transvaginal ultrasound of "placental-site trophoblastic tumor"].

The case of a placental-site trophoblastic tumor (PSTT) is described. Transvaginal sonography revealed a vascularized tumor mass with a deep invasion of the myometrium, partly with echogenic, solid parts and partly multiple echo-free cystic lesions. The maximum size of an echo-free cystic lesion was 4.4 cm. Doppler exploration indicated the presence of blood flow in all these cystic lesions. Distinctly abnormal low flow indices were prominent in the whole tumor area. According to the clinical results and the slightly positive levels of human chorionic beta-gonadotropin (100-1,000 IU/l postpartum), this tumor was classified as malignant trophoblastic disease, most likely PSTT. The authors conclude that, in the case of a patient with suspected trophoblastic disease and in view of the sonographic findings, PSTT may be a valid differential diagnosis, particularly if larger cystic lesions of more than 3 cm in diameter are found in the tumor bed together with evident blood flow at a low vascular resistance.

Adult↗