Biomedical subjects

H Wijkstra

Publications and source records attributed to H Wijkstra.

At least 73 records · Page 4Linked to original sources

PubMed1995

Computerized analysis of transrectal ultrasonography images in the detection of prostate carcinoma.

OBJECTIVE: To report on the use of automated image analysis in the interpretation of transrectal ultrasonographic images of the prostate. PATIENTS AND METHODS: During transrectal ultrasonography, images were recorded from biopsies performed in 127 patients. Subsequently in the image, the puncture place was marked and analysed. Analysis of the images was performed with the Automated Urologic Diagnostic Expert (AUDEX) system, consisting of a personal computer connected to the ultrasound machine. From the images collected, parameters can be calculated for image classification. The parameters obtained with this procedure were correlated with the histological result. RESULTS: Evaluation showed a sensitivity of 84.8% and specificity of 87.5%. The positive and negative predictive values, to predict prostate carcinoma, were 84.8% and 87.5%, respectively. CONCLUSION: Automated image analysis can help in the diagnosis of prostate carcinoma. In patients with non-palpable lesions or with poorly visualized tumours, image analysis is superior to the standard current diagnostic techniques.

Humans↗

PubMed1995

Urodynamic assessment in the laser treatment of benign prostatic enlargement.

OBJECTIVE: To determine if bladder outlet obstruction can be adequately relieved after laser prostatectomy. PATIENTS AND METHODS: Since November 1992, a total of 105 patients underwent laser treatment of the prostate because of complaints related to benign prostatic enlargement (BPE). To date, urodynamic data from a study of pressure flow analysis are available for 79 patients both at baseline and at 6 months after treatment. Patients were evaluated using changes in symptoms (IPSS symptom score), peak flow rate (Qmax), post-voiding residual volume (PVR), detrusor pressure at maximum flow (Pdet at Qmax), and the linear passive urethral resistance relation (LPURR). Moreover, patients with minimal bladder outlet obstruction were compared to patients with severe bladder outlet obstruction. RESULTS: There was a significant improvement in mean IPSS score from 21.3 at baseline to 5.3 at the 6-month follow-up. The Qmax improved from 7.9 mL/s to 17.8 mL/s, and the PVR decreased from 91.6 mL to 15.6 mL. At baseline, > 80% of the patients were considered obstructed according to the analysis of pressure flow, whereas 6 months after laser treatment, only 5% of the patients were still considered obstructed. A comparison of the outcome between minimally obstructed patients and severely obstructed patients showed comparable improvements. CONCLUSION: Laser therapy of the prostate was, according to urodynamic parameters, capable of relieving outlet obstruction and minimally obstructed patients also showed a significant relief of outlet obstruction.

Humans↗

PubMed1995

Automated analysis and interpretation of transrectal ultrasonography images in patients with prostatitis.

Transrectal ultrasound (TRUS) offers a valuable complement to digital rectal examination (DRE) in diagnosing prostate diseases. However, in case of prostatitis syndromes, contradictions are found with regard to characteristic ultrasound features in these patients. Therefore we sought for better imaging techniques. This paper describes a study on the automated analysis of ultrasonographic prostate images (AUDEX). With image processing, in the present study, tissue characterization is performed to predict the probability of the presence of inflammated prostate tissue. This technique already proved its validity in patients with prostate cancer. During prostate examinations, images were recorded with clear indication of the puncture position. Only patients with an unambiguously inflamed or noninflamed benign histologic result were included. Evaluation showed that a sensitivity of 90.6% and a specificity of 64.2% was reached. Finally, the prospective positive and negative predictive value for prostatitis was 50.0% and 94.6%, respectively. This means that AUDEX predicts the diagnosis 'prostatitis' in a large number of patients with no infection. In case of prostatitis, however, this prediction is almost always right.

Data Interpretation, Statistical↗

PubMed1995

Analysis of maximum detrusor contraction power in relation to bladder emptying in patients with lower urinary tract symptoms and benign prostatic enlargement.

PURPOSE: We evaluate the relationship among post-voiding residual urine volume, bladder outlet obstruction and maximum detrusor contractility power. MATERIALS AND METHODS: We investigated urodynamically and retrospectively 242 elderly men with various grades of bladder outlet obstruction and symptoms. RESULTS: Residual urine predominantly correlated with bladder outlet obstruction and not with maximum detrusor contractility power. Maximum detrusor contractility power showed significant positive correlation with bladder outlet obstruction. Urodynamically, the detrusor compensates for bladder outlet obstruction with elevated maximum detrusor contractility power. Decay of contraction during micturition however, hampers effective emptying. CONCLUSIONS: Maximum detrusor contractility power limits for normal detrusor contractility must be related to bladder outlet obstruction grade. Based on the results of our analysis, new limits showing improved correlation with complete emptying were derived.

Aged↗

PubMed1995

Variability of pressure-flow analysis parameters in repeated cystometry in patients with benign prostatic hyperplasia.

Urodynamic investigation becomes increasingly important in the diagnosis of bladder outflow obstruction in patients with benign prostatic hyperplasia. To date, different methods for evaluation of the pressure-flow relationship and quantification of the grade of obstruction are available. Models for pressure-flow analysis are briefly explained. The variability of the parameters is investigated by evaluation of 75 patients in whom 2 sequential voidings during urodynamic investigation were analyzed. The results showed that in 87% of these patients individual maximum flow differences of first and second voidings were less than 2 ml. per second. Individual detrusor pressure at maximum flow differences were less than 15 cm. water in 80% of these patients, while in 80% the intra-individual variation of the pressure-flow results was less than 15 cm. water for the minimal voiding pressure parameters (minimal urethral opening detrusor pressure and urethral resistance factor). For the pressure-flow parameter that defines the theoretical urethral lumen during voiding, the variation was less than 1.5 mm.2 in 84% of the patients. Patients with larger intra-individual differences are discussed. We concluded that the observed, aforementioned differences can be regarded as an indication of normal intra-individual variability of voiding during urodynamic investigation. This intra-individual variability, however, seldom leads to a change in the clinical grade of bladder outflow obstruction. We conclude that investigators involved in therapeutic trials of benign prostatic hyperplasia must be aware of this intra-individual variability of micturition, since this variability is greater than the refined scale of the pressure-flow analysis models.

Humans↗

PubMed1995

Automated prostate volume determination with ultrasonographic imaging.

A method for automated determination of the prostate volume based on planimetric volumetry was developed to overcome subjectivity in prostate volume measurements using ultrasonography. An edge detection method is applied to locate the prostate boundary in sequential ultrasonographic images. During regular examinations, the volume was assessed automatically in 55 patients. The Pearson correlation coefficient of the automated volume compared to the reference prostate volume was 0.93. The estimated ratio of the automated volume to the reference volume was 0.92. This method overcomes the individual subjectivity when interpreting ultrasonographic images, and provides accurate and objective results for followup of benign prostatic hyperplasia treatments and for comparison of multicenter trials. Also, this method is a useful tool for objective determination of prostate specific antigen in proportion to the volume (prostate specific antigen density).

Aged↗

PubMed1995

Computer analysis of transrectal ultrasound images of the prostate for the detection of carcinoma: a prospective study in radical prostatectomy specimens.

PURPOSE: The reliability and objectivity of computer assisted transrectal ultrasound are examined. MATERIALS AND METHODS: Pathological examination of radical prostatectomy specimens was compared prospectively to automated cancer detection in corresponding transrectal ultrasound images. RESULTS: For automated cancer detection, a sensitivity of 0.75 and a specificity of 0.78 were obtained. Moreover, 74% of human interpretation of the percentage of malignancy in the analyzed images was equal to the actual calculated percentage (Pearson's product moment correlation coefficient 0.85). CONCLUSIONS: Comparing these results to those obtained with normal transrectal ultrasound, automated analysis provides additional information in the interpretation of transrectal ultrasound images by color coding them in an objective manner according to the probability of malignancy.

Aged↗

PubMed1995

Semi-automated database design by the end-user.

An information system was developed to manage the data for a large number of research projects simultaneously. The system, called URIS, has facilitated the management of research data in an academic urological department. It enables end-users, who are not necessarily skilled computer scientists, to design their own databases semi-automatically, by supporting data entry screen design and the specification of research items. The system creates the database tables automatically after these activities. The specification of research items is the most important but also most difficult part in this process.

Computer Literacy↗

PubMed1994

Analysis of ultrasonographic prostate images for the detection of prostatic carcinoma: the automated urologic diagnostic expert system.

This paper describes a study on the automated analysis of ultrasonographic prostate images. With image processing, tissue characterization in the prostate was performed to assess the probability of malignancy. During prostate examinations, images were recorded at the positions where biopsies were taken. The used samples were divided into three groups. Two of them were used for the construction of a classification tree, and the third was used for the evaluation of this classification. A sensitivity of 80.6% and specificity of 77.1% were reached retrospectively. In a prospective way, these results were 80.0% and 88.2%, respectively. The prospective predictive value for cancer detection was 85.7%. The presented prospective value for image analysis was almost twice as high as the values normally found for prostate examination.

Aged↗

PubMed1994

A practical clinical method for contour determination in ultrasonographic prostate images.

This paper describes a practical method for automated determination of the contour of the prostate in ultrasonographic images. In this method, we use specific edge detection techniques, based on nonlinear Laplace filtering. Possible edges are located at zero-crossings of the second derivative of the image. The strength of the edge is reflected by the value of the gradient of the image at that location. Combining the information about location and strength, an edge intensity image is constructed from the initial ultrasonographic image. In our method, edge enhancement techniques are performed on the edge intensity image. Edges that actually represent a boundary are selected and linked: interpolation techniques are used to fill the gaps between detected boundary edges. The method for contour determination in ultrasonographic images is used for accurate volume measurements in an everyday clinical environment. Its computer implementation is fast, accurate (mean difference within 6% of exact volume) and easy to use.

Humans↗

PubMed1994

The reliability of computer analysis of ultrasonographic prostate images: the influence of inconsistent histopathology.

This article describes a method to investigate the influence of inconsistent histopathology during the development of tissue discrimination algorithms. Review of the pathology is performed on the biopsies used as training set of a computer system for cancer detection in ultrasonographic prostate images. The influence of the discrepancies found between independent pathologists on the discriminating power of the system is investigated. A high diagnostic consistency in histopathology concerning only the categories malignant and nonmalignant is found. Therefore, review of the pathology does not significantly influence the results of tissue discrimination algorithms for cancer detection. However a high interobserver variability is obtained in the differentiation between more histology classes.

Biopsy↗

PubMed1994

Bladder compliance after posterior sacral root rhizotomies and anterior sacral root stimulation.

To evaluate the effects of central detrusor denervation on bladder compliance, we studied 27 patients with complete suprasacral spinal cord injury in whom intradural posterior sacral root rhizotomies from S2 to S5 in combination with implantation of an intradural Finetech-Brindley bladder stimulator were performed. All patients initially presented with detrusor hyperreflexia. A majority of these patients had a decreased bladder compliance 5 days postoperatively followed by a rapid increase in bladder compliance thereafter. All patients showed persistent detrusor areflexia after long-term followup. In 2 patients incomplete posterior sacral rhizotomies appeared to be performed. These patients had low bladder compliance, so that secondary posterior sacral root rhizotomies at the level of the conus medullaris were done. Intradural rhizotomies of all posterior sacral root components from S2 to S5 in combination with implantation of an anterior sacral root stimulator is a safe and effective procedure in spinal cord injury patients.

Adolescent↗

PubMed1994

Bladder pressure sensors in an animal model.

Urinary incontinence due to detrusor hyperreflexia might be inhibited on demand if changes in bladder pressure could be detected by sensors and transferred into pudendal nerve electrostimulation. The aim of this study is to investigate how the bladder wall reacts on different sensor implants. Sensors were implanted in twelve goats. In group 1 (n = 8) real sensors were placed on the peritoneal surface of the bladder dome, between the peritoneum and the muscular layer, and between the cervix and bladder. In group 2 (n = 4), dummy sensors were placed between the mucosal and muscular layers. During follow-up as long as 25 months, urodynamic studies, radiographic control and urine cultures were done. In group 1, sensors placed between the peritoneum and muscular layer gave the best results. In group 2, 11 of the 12 sensors eroded. The authors conclude that implantation of sensors in the bladder wall is feasible.

Animals↗

PubMed1994

Selective sacral root stimulation for bladder control: acute experiments in an animal model.

High bladder pressure is a potential side effect of poststimulus voiding, used to date for stimulation-induced bladder emptying in spinal cord injured patients. To prevent this side effect, selective activation of the bladder without activation of the urethral sphincter by selective stimulation of sacral roots was studied in a canine animal model. On-line registration of bladder, urethral and rectal pressure was performed, and EMG of tail muscles and urethral sphincter was recorded. After laminectomy, intradural left and right sacral root S2 were stimulated with a tripolar cuff electrode. A self-made stimulator generating adjustable pulse shapes was used. Using 200 microsec. rectangular pulses, contraction of bladder and urethral sphincter could be elicited. Selective activation of the bladder occurred with pulses of 600 to 800 microsec. due to anodal blocking of the large nerve fibers in the sacral roots. During acute animal experiments we were able to achieve selective activation of the detrusor without simultaneous activation of the external urethral sphincter, and complete, low-pressure voiding occurred.

Animals↗

PubMed1994

Selective stimulation of sacral nerve roots for bladder control: a study by computer modeling.

The aim of this study was to investigate theoretically the conditions for the activation of the detrusor muscle without activation of the urethral sphincter and afferent fibers, when stimulating the related sacral roots. Therefore, the sensitivity of excitation and blocking thresholds of nerve fibers within a sacral root to geometric and electrical parameters in tripolar stimulation using a cuff electrode, have been stimulated by a computer model. A 3-D rotationally symmetrical model, representing the geometry and electrical conductivity of a nerve root surrounded by cerebrospinal fluid and a cuff was used, in combination with a model representing the electrical properties of a myelinated nerve fiber. The electric behavior of nerve fibers having different diameters and positions in a sacral root was analyzed and the optimal geometric and electrical parameters to be used for sacral root stimulation were determined. The model predicts that an asymmetrical tripolar cuff can generate unidirectional action potentials in small nerve fibers while blocking the large fibers bidirectionally. This result shows that selective activation of the detrusor may be possible without activation of the urethral sphincter and the afferent fibers.

Animals↗

PubMed1994

Imaging in BPH patients.

Benign prostatic hyperplasia is one of the most common pathological processes to afflict men. Strikingly, there is a large variety of methods of evaluation and therapeutic strategies for BPH in various countries. Before adequate treatment is possible, the process of benign adenomatous hyperplasia has to be distinguished from malignant or inflammatory prostatic disease. Furthermore, secondary alterations of the bladder and upper urinary tract have to be evaluated. A wide range of imaging techniques of the lower and upper urinary tract have evolved over the years. The specific benefits and restrictions of each of them are discussed. Finally, the recent developments and possibilities of computer-aided tissue characterisation and volume determination are outlined. The development of imaging techniques for BPH has just begun...

Humans↗

PubMed1992

The step response of left ventricular pressure to ejection flow: a system oriented approach.

Left ventricular pressure is dependent on both ventricular volume and ventricular ejection flow. These dependencies are usually expressed by ventricular elastance, and resistance, respectively. Resistance is a one-valued effect only, when ejection flow either is constant or increases. Decreasing ejection flow elicits a third effect: a decrease of elastance. The effects of elastance, resistance and elastance depression were modeled in a three-compartment model consisting of a dead-volume compartment, an elastance compartment, and a second series-elastance compartment connected to the elastance compartment by a resistance. This model was identified with the pressure response determined experimentally by imposing pumped constant-flow ejection epochs on isolated rabbit hearts. The experimental flow epochs consisted of two phases of constant flow separated by an increasing or decreasing flow step. It was found that elastance is not changed after the flow step if this is positive or zero. Negative flow steps induced a deactivation of elastance that is linearly dependent on the difference between isovolumic pressure that would be developed at the volume existing at the time of measurement and actual pressure. The parameters found from the identification procedure are ventricular active volume, nondepressed elastance, series-elastance, resistance, and the elastance deactivation factor. The first four parameter values were found in agreement with other results reported in literature. The elastance depression factor is a new parameter that could be of physiological or clinical significance since it may be related to the inability of the force generators in the heart muscle to be restored to their full number, after being inactivated or decoupled by filament sliding associated with ejection. On the basis of the results, an alinear state-model of the ventricle, for arbitrary, including physiological flow patterns is proposed.

Animals↗

PubMed1992

Motor evoked potentials from the bladder on magnetic stimulation of the cauda equina: a new technique for investigation of autonomic bladder innervation.

Although neurophysiological techniques have become widely accepted in the diagnostic evaluation of urogenital tract dysfunction, arguments have been forwarded to question their validity. Current techniques merely deal with somatosensory nerves, whereas micturition and sexual functions depend on autonomic motor nerve function as well. This study presents a new technique of motor evoked potentials obtained after magnetic stimulation of the cauda equina. Bladder and pelvic floor motor evoked potentials could be measured with concentric needle electrodes. Mean latency was 35.6 msec. for bladder motor evoked potentials and 10.6 msec. for pelvic floor motor evoked potentials. The technique was easy to perform, and provided consistent and objective data. No harmful side effects were noted.

Adult↗