Biomedical subjects

H Wijkstra

Publications and source records attributed to H Wijkstra.

At least 37 records · Page 2Linked to original sources

PubMed2000

Intraprostatic temperature monitoring during transurethral microwave thermotherapy: status and future developments.

Transurethral microwave thermotherapy is being applied as a minimally invasive treatment for alleviating the symptoms of urinary outlet obstruction associated with benign prostatic hyperplasia. Treatment progress has traditionally been guided in its effective power by rectally and urethrally measured temperatures, whereas intraprostatic temperatures would be preferred for feedback purposes. A critical evaluation is presented of intraprostatic thermometry techniques that have been suggested, the techniques currently being used and investigated, and the problems that remain to be solved. Techniques for noninvasive temperature measurement and detecting tissue response during thermal therapy are discussed in more detail. Results presented in the literature have shown magnetic resonance imaging and ultrasonic imaging to be adequate thermometry modalities. For treatment monitoring of transurethral microwave thermotherapy, ultrasonic imaging is especially promising. Future research will indicate whether the promise evolves into a sound clinical technique.

Body Temperature↗

PubMed2000

The application of three-dimensional contrast-enhanced ultrasound to measure volume of affected tissue after HIFU treatment for localized prostate cancer.

INTRODUCTION: Adequate monitoring of volume and location of affected tissue might provide helpful information when performing localized ablative therapy for prostate cancer. We hypothesize that the change in blood flow patterns after therapy in comparison to the blood flow pattern prior to therapy can be used to locate and quantify the amount of affected tissue due to the therapy. We describe the use of three-dimensional contrast-enhanced power Doppler ultrasound (3D-CE-PDU) to determine its additive value to visualize the extent of tissue defects created by high-intensity focused ultrasound (HIFU) in correlation with the histopathology of the prostatectomy specimen. MATERIALS AND METHODS: Nine patients with biopsy-proven localized prostate cancer, who gave informed consent, were included in the protocol. HIFU treatment was performed 1 week in advance of radical retropubic prostatectomy (RRP) as part of a protocol to study the value of HIFU treatment as local ablative therapy for clinical T(1-2)N(0)M(0) prostate carcinoma. 3D-CE-PDU was performed 1 day prior to unilateral HIFU treatment of the affected lobe on biopsy indication and 1 day before RRP using 2.5 g Levovist((R)) (Schering AG, Germany) microbubble ultrasound contrast agent and a Kretz((R)) Voluson 530D ultrasound scanner (Kretztechnik AG, Austria). Ultrasound data and pathology whole-mount sections were stored digitally to allow off-line processing. Human interpretations of HIFU measurements in three-dimensional ultrasound data were based on gray-scale information (local increase in gray level) in combination with power Doppler mode (absence of blood flow). Histopathological analysis of the whole-mount section revealed a broad band of hemorrhagic necrosis in the HIFU-treated area. Using both the ultrasound data and the pathology sections, the total volume of the prostate and of the HIFU-treated area was measured, and relative volumes were obtained. RESULTS: Visual inspection of the three-dimensional reconstruction of contrast-enhanced Doppler measurements revealed the HIFU-affected prostate tissue by the absence of a blood flow pattern. Paired t tests of the relative HIFU volume indicated that Doppler results (mean 21.7%, SD +/-10.8%) differed from the pathology results (mean 32.6%, SD +/-16.0%), but a good correlation was found between the relative pathology HIFU volume (Pearson correlation r = 0.94, p<0.0015) and mean 3D-CE-PDU HIFU. Closer inspection of the pathology specimen revealed that the outer ring of the macroscopic hemorrhagic necrosis overestimated the actually dead tissue. On microscopy, the border of dead tissue appeared to be 1-2 mm inside the macroscopically identified red hemorrhagic band. 3D-CE-PDU HIFU volumes indicated by the single observers were not statistically different and correlated very well (Pearson correlation r = 0.98, p<0.001). CONCLUSION: The results illustrate that 3D-CE-PDU is a promising method to determine the size of the defect of HIFU ablative therapy for prostate carcinoma. The absence of blood flow indicated by three-dimensional power Doppler ultrasound images reflects affected tissue after HIFU treatment, and volume measurements of these areas can quantify the amount of affected tissue.

Aged↗

PubMed1999

Contrast-enhanced three-dimensional power Doppler angiography of the human prostate: correlation with biopsy outcome.

OBJECTIVES: To determine the feasibility of contrast-enhanced three-dimensional (3D) imaging of the prostatic vasculature using power Doppler imaging and to analyze whether semiquantitative judgments of 3D images with respect to symmetry and distribution of vascular structures correlated with biopsy outcome. METHODS: 3D power Doppler images were obtained before and after intravenous administration of 2.5 g Levovist. Subsequently, random and/or directed transrectal ultrasound (TRUS)-guided biopsies were performed. Vascular images were analyzed by two experts. Prostate vasculature was judged with respect to symmetry and vessel distribution using a (scale) grading system. RESULTS: Eighteen patients with a suspicion of prostate cancer either because of an elevated prostate-specific antigen (greater than 4.0 ng/mL; Tandem-R-assay) or an abnormal digital rectal examination were included in the study. Prostate cancer was detected in 13 patients. Vascular anatomy was judged abnormal in unenhanced images in 6 cases, of which 5 proved malignant. Enhanced images were considered suspicious for malignancy in 12 cases, including 1 benign and 11 malignant biopsy results. Sensitivity of enhanced images was 85% (specificity 80%) compared with 38% for unenhanced images (specificity 80%) and 77% for conventional gray-scale TRUS (specificity 60%). Of 6 patients who showed no B-mode abnormalities, vascular patterns were judged abnormal in 4 cases, of which 3 were malignant. CONCLUSIONS: Contrast-enhanced 3D power Doppler angiography is feasible in patients with suspicion of prostate cancer who are scheduled for prostate biopsies. The sensitivity of power Doppler 3D imaging for the detection of prostate malignancy increased from 38% (5 of 13) to 85% (11 of 13) after administration of intravascular microbubble contrast (Levovist), and specificity was found to be 80% (4 of 5) for both imaging modalities. Thus, the use of Levovist when combined with the power Doppler display mode and 3D image reconstruction offers a promising new research area that might prove useful in prostate cancer detection in the future.

Angiography↗

PubMed1999

Transrectal ultrasound imaging of the prostate: review and perspectives of recent developments.

We present a critical review of the recent literature and discuss the development and prospective view of the evaluations of transrectal ultrasound with regard to prostate malignancy. We illustrate this with personal experiences. Material and Methods: Based on a critical evaluation of clinical data we address the apparent shortcoming of greyscale transrectal ultrasonography in the assessment of prostate cancer. New developments and future possibilities are also discussed. Evaluation of the value of greyscale transrectal ultrasonography in the diagnosis of prostate cancer indicates a limited role, because of the non-uniform appearance of prostate cancer on the ultrasound images. Ameliorating of transrectal ultrasound, like the use of contrast ultrasonography, could improve the detection of prostate cancer. Although the use of greyscale transrectal ultrasonography lacks sensitivity and specificity for the diagnosis of prostate cancer, its use in volume measurement of the prostate and biopsy guidance is unquestionable. The first results of the application of contrast ultrasonography are promising, both in detection of prostate cancer as in treatment follow up. Other developments like improvement of transducer and computer technology could make the use of ultrasound more versatile. However, future research will indicate whether all these improvements will lead to clinical applications.

Journal Article↗

PubMed1999

A computer model for describing the effect of urethral afferents on simulated lower urinary tract function.

A computer model of mechanical properties of the bladder, the urethra and the rhabdosphincter, as well as their neural control is presented in this paper. The model has a rather simple design and processes sensory information from both the bladder wall tension and urethral stretch. It is assumed that afferent signals from the urethra are involved in a sacral excitatory reflex and a supraspinal inhibitory reflex. Pressure and flow signals that resemble experimentally measured normal human behaviour could be simulated with this model. From these simulations the relation between the neural control mechanisms used in the model and the neural control mechanism in vivo cannot be judged entirely because similar behaviour could be simulated with models that are bas ed on different neural control mechanisms. Also behaviour that resembles detrusor overactivity was simulated with our model after an externally induced rise in detrusor pressure was added. Detrusor overactivity, sometimes in combination with urethral relaxation, can occur during a urodynamic investigation. A possible explanation for this detrusor overactivity might be that the micturition reflex is triggered by unknown disturbances and is inhibited immediately after by the same mechanism that normally ceases voiding. The described model provides such a mechanism. Based on these simulations, therefore, it is concluded that urethral afferent signals might be important in lower urinary tract control.

Afferent Pathways↗

PubMed1999

Aspects of imaging in the assessment and follow up of benign prostatic hyperplasia.

For assessing patients suffering from benign prostatic hyperplasia and monitoring subsequent treatment, symptom questionnaires, uroflowmetry, prostate volume measurements, postvoiding residual urine volume measurements and pressure-flow studies may be used. This review highlights aspects of imaging in the assessment of benign prostatic hyperplasia, including volume determinations of prostate and postvoiding residual urine, texture imaging and biopsy guidance. Future developments are also briefly discussed.

Animals↗

PubMed1999

Contrast angiosonography: a technology to improve Doppler ultrasound examinations of the prostate.

OBJECTIVES: A feasibility study to evaluate whether analysis techniques adapted from X-ray angiography can be used to analyze the transient enhancement of prostate blood flow patterns in color Doppler maps as obtained after administering ultrasound contrast agents. METHODS: Injections of ultrasound contrast agents were given to dogs and humans, and color Doppler blood flow patterns in fixed transverse sections through the prostate were recorded on video tape. Computer assistance of Doppler signals over time is used to evaluate the transient enhancement of flow patterns obtained with contrast-enhanced Doppler ultrasound. Results are compared to indicator dilution curve theory as used in, e.g., X-ray angiography. RESULTS: Administering a contrast agent to improve color Doppler evaluation of prostate blood flow resulted in clear enhancement of Doppler signal intensities without unwanted side effects. Using the computer, the perfused area of the prostate could be obtained quantitatively over time showing profiles of individual heartbeats. Averaging the perfused area over one heartbeat resulted in an indicator dilution curve, and correlation with dilution theory indicated the feasibility of applying wash-in and wash-out analysis of contrast agents in color Doppler images. CONCLUSION: Frame-by-frame interpretation by the computer indicated the feasibility of analyzing the transient enhancement of blood flow visibility in the Doppler image over time using techniques such as wash-in and wash-out time. This technology provides researchers in the field of ultrasound evaluation of the prostate the opportunity to apply a new diagnostic tool, contrast angiosonography, in their research. This method for analysis of prostatic blood flow can be helpful in any application that affects the blood supply of the prostate such as heat treatments and hormonal treatments.

Aged↗

PubMed1998

A computer model of the neural control of the lower urinary tract.

Better understanding of the underlying working mechanism of the neural control of the lower urinary tract will facilitate the treatment of dysfunction with a neurogenic cause. We developed a computer model to study the effect of a neural control system on lower urinary tract behavior. To model the mechanical properties and neural control, assumptions had to be made. These assumptions were based, as much as possible, on knowledge and hypotheses taken from the literature. With valid assumptions, it should be possible to simulate normal as well as pathological behavior. To test the computer model, first, normal behavior of the lower urinary tract was simulated, and secondly, the known features of bladder outlet obstruction were simulated after the properties of the urethra were changed. The simulation results are comparable with measured data, so the assumptions on which the model is based could be valid. If the assumptions are valid, the feedback loops used in the model are also important feedback loops in vivo, and the model can be used to gain insight into the underlying mechanism of neural control.

Computer Simulation↗

PubMed1998

Selective detrusor activation by sacral ventral nerve-root stimulation: results of intraoperative testing in humans during implantation of a Finetech-Brindley system.

Electrical sacral nerve-root stimulation can be used to induce bladder contraction. However, bladder emptying is hampered by simultaneous contraction of the external urethral sphincter. Voiding may improve when using a stimulation method that allows selective detrusor activation. Both theoretical and animal studies have demonstrated that it is possible to obtain selective detrusor activation by sacral root stimulation using an selective anodal block. The objective of this paper is to demonstrate the feasibility of this stimulation method in humans. For investigation of the stimulation method, intraurethral and intravesical pressure responses to sacral root stimulation were measured in acute experiments on 12 patients. The results show that selective detrusor activation is possible in patients. Future perspectives are discussed.

Electric Stimulation↗

PubMed1998

Edge detection in prostatic ultrasound images using integrated edge maps.

OBJECTIVE: We investigated an algorithm to detect grey level transitions with multiple scales of resolution to improve edge detection and localisation in ultrasound images of the prostate. INTRODUCTION: We had developed a non-analytical operator for prostate contour determination implemented with minimum and maximum filters and locate edges. We implemented a technique for improved determination of boundary parts in prostatic ultrasound images by adjusting the edge detection parameter to signal information. METHODS: First the influence of prefilter settings and edge detection parameters is investigated in a test image and a real ultrasound image. Then, local standard deviation is used to identify or fewer homogeneous regions that are filtered with course resolution, while areas with larger deviation that grey level transitions occur, which should be preserved using smaller filter sizes to improve edge localisation. RESULTS: Analysis of images with different filter sizes indicated that areas are merged for increasing filter sizes: less pronounced edges disappear or displace for larger filters. Two scales of resolution lead to an improved localisation of edges when smaller filter sizes are used in areas with an increased local standard deviation. CONCLUSIONS: This paper illustrates an edge detection method suitable as pre-processing step in interpretation of medical images. By adapting input parameters to signal information, object recognition can be applied in images from different imaging modalities. Also, disadvantages are discussed, resulting in a new application combining a localisation algorithm to find the initial contour and a delineation algorithm to improve the outlining of the resulting contour.

Algorithms↗

PubMed1998

Transrectal ultrasound of the prostate: innovations and future applications.

PURPOSE: We present a critical evaluation of the use of ultrasound for prostate disease examination in urological practice, and provide perspectives on ultrasound applications that may become important for the future evaluation of prostate problems. MATERIALS AND METHODS: Based on an evaluation of clinical data in cases suspicious for prostatic malignancy, we addressed the apparent shortcomings of transrectal ultrasound for accurately diagnosing prostate cancer. Future applications presented in the literature were noted. RESULTS: Evaluating the ultrasound data in cases suspicious for malignancy indicated that imaging has little advantage over digital rectal examination for detecting malignant areas. The new applications of ultrasound that hold great promise for use in the urology clinic include the injection of contrast agents to obtain information on blood supply, temperature estimation for the noninvasive assessment of temperature distributions during heat treatment and a therapeutic application for local treatment of prostate cancer. CONCLUSIONS: While differential diagnosis with ultrasound appears to result in disappointing sensitivity and specificity values, its use in volume measurement and biopsy guidance is unquestioned. The development of new applications may improve the clinical value of ultrasound in urological practice. The application of ultrasound contrast agents for the detection and clinical staging of prostate cancer is especially promising. Future research will indicate whether the promise evolves in clinical applications.

Animals↗

PubMed1998

Computerized artifact detection and correction of uroflow curves: towards a more consistent quantitative assessment of maximum flow.

OBJECTIVES: To evaluate a computerized method of artifact detection and correction of uroflow and compare the quantitative assessment of maximum flow obtained by the computer with visual correction by experts. METHODS: A total of 90 randomly chosen flows was scanned into the computer whereafter automated artifact detection and correction was performed according to pre-established rules implemented in the software. Three experts visually corrected the flows using the same artifact detection and correction specifications as the computer. Measuring agreement between different methods of assessment of maximum flow was evaluated by calculating the difference and the standard deviation (SD) of the differences. The repeatability of assessing the maximum flow value by the computer and by expert 1 was assessed by calculating the difference between 2 readings and the coefficient of repeatability. RESULTS: The coefficient of repeatability of maximum flow after detection and correction of artifacts by the computer (0.38 ml/s) was slightly better when compared with the coefficient of repeatability between 2 observations by 1 expert (1.12 ml/s). The interobserver variation for the quantitative assessment of maximum flow appeared to be great. A total of 51% of the maximum flow values assessed by expert 2 was 1 ml/s or more greater than those assessed by expert 1. When comparing the results of the computer with those of the experts, the mean value of maximum flow from expert 1 was 0.71 ml/s smaller than the computer value (p < 0.01), the mean value from expert 2 was 0.53 ml/s greater (p < 0.01) and the mean value from expert 3 was not significantly different (0.25 ml/s greater). The SD of maximum flow after correction by the computer was 0.3 ml/s smaller than the SD of the raw data from the flowmeter and the corrected values by 2 experts. CONCLUSIONS: Computerized artifact detection and correction eliminates an important fraction of the variability of manually corrected maximum flow values. This may lead to smaller sample size requirements, especially in studies where the primary objective is to assess a small (+/- 1 ml/s) difference in mean maximum flow between groups.

Adrenergic alpha-Antagonists↗

PubMed1997

Urinary bladder control by electrical stimulation: review of electrical stimulation techniques in spinal cord injury.

Evacuation of urine in paraplegics without the need for catheters would be possible when voiding could be induced by eliciting a bladder contraction. A challenging option to obtain detrusor contraction is electrical stimulation of the detrusor muscle or its motor nerves. This article reviews the 4 possible stimulation sites where stimulation would result in a detrusor contraction: the bladder wall, the pelvic nerves, the sacral roots, and the spinal cord. With respect to electrode application, sacral root stimulation is most attractive. However, in general, sacral root stimulation results in simultaneous activation of both the detrusor muscle and the urethral sphincter, leading to little or no voiding. Several methods are available to overcome the stimulation-induced detrusor-sphincter dyssynergia and allow urine evacuation. These methods, including poststimulus voiding, fatiguing of the sphincter, blocking pudendal nerve transmission, and selective stimulation techniques that allow selective detrusor activation by sacral root stimulation, are reviewed in this paper.

Electric Stimulation↗

PubMed1997

Quantitative assessment of uroflow: is there a circadian rhythm?

OBJECTIVES: To investigate if the circadian rhythm of urinary flow values varies within groups of patients with varying degrees of bladder outlet obstruction. METHODS: A total of 170 patients with lower urinary tract symptoms suggestive of bladder outlet obstruction used a home-based uroflowmeter and produced a total of 1670 correctly measured flows at home. These patients also underwent a screening program with free urinary flowmetry in the hospital and a urodynamic pressure and flow study. RESULTS: There is a circadian variability in urinary flow values in men with higher grades of obstruction. These men have a higher peak urinary flow with a smaller voided volume and thus a shorter flow time in the early afternoon when compared with late evening, early morning, and the midnight to morning periods. CONCLUSIONS: This significantly greater maximum flow in the afternoon in men with higher grades of obstruction can be an important bias in studies where the primary end point is to assess a small improvement in maximum flow. Therefore, the circadian rhythm of uroflow has to be taken into account in the evaluation of the efficacy of treatment. Patients participating in clinical research studies should produce their urinary flow in the clinic always during the same time period, either in the morning or in the afternoon, and should not switch their appointment time.

Adult↗

PubMed1997

The correlation between prostate volume, transition zone volume, transition zone index and clinical and urodynamic investigations in patients with lower urinary tract symptoms.

OBJECTIVE: To determine if, in patients with lower urinary tract symptoms (LUTS), measurement of the transition zone (TZ) of the prostate by transrectal ultrasonography (TRUS) and the ratio between the TZ volume and total prostate volume (TZ index) correlates better with clinical and urodynamic investigations than total prostate volume alone. PATIENTS AND METHODS: In total, 150 consecutive patients with LUTS underwent a standardized screening programme including the International Prostate Symptom Sore (IPSS), a physical examination, TRUS of the prostate and urodynamic investigations with pressure-flow studies. The total prostate volume and TZ volume were assessed from TRUS using the ellipsoid formula. Spearman's rank correlation coefficients were calculated between different prostate volume measurements and specific symptomatic and urodynamic variables. RESULTS: The relationships between specific IPSS symptoms, symptom scores and the prostate volume measurements were not statistically significant except for one domain, nocturia, that appeared to be statistically significantly correlated with the TZ index (r = 0.25). The correlations for free flow, pressure-flow variables and prostate volume measurements were stronger, but only moderate at best. The highest correlations were between TZ volume and the linear passive urethral resistance obstruction category, urethral resistance factor and detrusor pressure at maximum flow (r = 0.43, 0.44 and 0.40, respectively). The differences between the correlations of prostate volume and TZ index and these variables were small (r = 0.39, 0.38 and 0.37, respectively for prostate volume and r = 0.38, 0.40 and 0.33 respectively for TZ index). CONCLUSIONS: There were very small differences between the correlations of total prostate volume, TZ volume and TZ index, and clinical and pressure-flow variables. In the assessment of the last two, the estimation of the total prostate volume by TRUS was a reasonable way to obtain the required information about prostate size and measuring TZ volume and calculating TZ index was of limited additional value. Symptoms and bladder outlet obstruction were mainly determined by other factors than the prostate and, specifically, TZ volume. As earlier studies have indicated that including pressure-flow data in the pre-operative evaluation and selection of patients for interventional therapies may improve the overall clinical results, we think that prostate volume, TZ volume or symptoms alone should not be used as the main indication for deciding on the appropriate invasive treatment options.

Adult↗

PubMed1997

Selective detrusor activation by electrical stimulation of the human sacral nerve roots.

The purpose of this study was to investigate the feasibility of selective detrusor activation without activation of the urethral sphincter by sacral root stimulation in patients. The sacral roots were stimulated using a tripolar electrode. An anodal block was used to prevent the urethral sphincter from contraction. Using square current pulses (700 microseconds, 6-7 mA), no increase in intraurethral pressure was measured, while a normal increase in intravesical pressure occurred. The minimum pulse duration to obtain a complete block was 550 microseconds. The study shows that anodal blocking of action potentials is possible in humans and can result in selective detrusor activation when used in sacral root stimulation.

Action Potentials↗

PubMed1997

Selective detrusor activation by electrical sacral nerve root stimulation in spinal cord injury.

Electrical sacral nerve root stimulation can be used in spinal cord injury patients to induce urinary bladder contraction. However, existing stimulation methods activate simultaneously both the detrusor muscle and the urethral sphincter. Urine evacuation is therefore only possible using poststimulus voiding. Micturition would improve if the detrusor muscle could selectively be activated. The purpose of this study was to demonstrate selective detrusor activation in patients by ventral sacral root stimulation. The stimulation method involves selective activation of the small diameter myelinated nerve fibers and consists of a combination of cathodal excitation and selective anodal blocking using a tripolar electrode. To investigate anodal blocking, the intraurethral pressure response to stimulation was measured in acute experiments performed on 12 patients. The influence of both pulse amplitude and pulse duration on the pressure response was analyzed. In 8 out of 12 patients anodal blocking of somatic motor fibers was possible. This study also indicates the feasibility of selective detrusor activation by sacral root stimulation.

Electric Stimulation Therapy↗

PubMed1997

[Diagnosis of prostate cancer in urination disorders in urological practice: current status and future developments].

This paper presents the current diagnostics of patients with prostate related problems (lower urinary tract symptoms) who visit the urology clinic. The diagnostic triad for prostate cancer detection is presented, consisting of a serum Prostate-Specific Antigen test, a digital rectal examination to palpate the prostate, and transrectal ultrasound of the prostate to visualise internal structures and guide the urologist in taking biopsies. The results of the tests for a biopsied population of 232 patients illustrate the shortcomings of the individual tests in predicting the presence of a malignancy. Biopsies are needed to prove or rule out prostate cancer in case of a suspicion. Future developments in early detection of prostate cancer are directed to improve the clinical use of the current diagnostic triad, and to identify new diagnostic tools.

Aged↗