Modeling of micturition characteristics based on prostatic stiffness modulation induced using hormones and adrenergic antagonists

Quantitative estimation of brain stiffness measured using a tactile biosensor in animal models

AIMS

The purpose of this experimental study was to evaluate the clinical application of a tool equipped to measure the consistency of soft tissue.

METHODS AND RESULTS

We have measured three kinds of soft tissues with brain-like softness. Also, we evaluated the stiffness of an animal brain with intracranial hypertension. Next, we attempted to measure the mechanical properties of three materials using a tactile sensor. This sensor measures three parameters: depth, pressure, and the change in resonance frequency. The change in resonance frequency correlated linearly on a semi-log scale with the stiffness of the gelatin. Next, we measured brain stiffness using an epidural balloon expansion model in 28 rats. The rats were divided into five groups based upon the volume of saline solution infused into the balloon. Rat brain stiffness was measured using the tactile sensor. We then analyzed the relationship between change in resonance frequency in tactile sensor and the I-IV latency in brainstem evoked potentials under increased balloon volume. The value of change in resonance frequency decreased with the increment of volume (Spearman's test: R = 0.777).

CONCLUSION

The tactile sensor is an appropriate tool for quantitatively measuring the palpability of soft materials, which probably includes the brain and spinal cord.

Tactile resonance sensors in medicine

Tactile sensors in general are used for measuring the physical parameters associated with contact between sensor and object. Tactile resonance sensors in particular are based on the principle of measuring the frequency shift, Deltaf, defined as the difference between a freely vibrating sensor resonance frequency and the resonance frequency measured when the sensor makes contact to an object. Deltaf is therefore related to the acoustic impedance of the object and can be used to characterize its material properties. In medicine, tactile resonance sensor systems have been developed for the detection of cancer, human ovum fertility, eye pressure and oedema. In 1992 a Japanese research group published a paper presenting a unique phase shift circuit to facilitate resonance measurements. In this review we summarize the current state-of-the-art of tactile resonance sensors in medicine based on the phase shift circuit and discuss the relevance of the measured parameters for clinical diagnosis. Future trends and applications enabled by this technology are also predicted.

Impedance estimation of soft tissue using ultrasound signal

This paper proposes a new impedance estimation method for soft tissue using ultrasound. This method estimates the impedance distribution inside an object. An ultrasound probe, which is attached to a force sensor, compresses soft tissue and observes the deformation process of tissue while measuring reaction force. The impedance parameters are then estimated based on this information. Experiments were conducted under two conditions, a static analysis and a dynamic analysis. In the static analysis, the ultrasound probe compressed the soft tissue slowly while keeping a balance of the power. In the dynamic analysis, the probe compressed tissue dynamically, and the deformation process of the soft tissue was observed. Experimental results demonstrated that our method can estimate the impedance of a soft object.

High resolution regional elasticity mapping of the human prostate

What is it that the clinician "feels" during a digital rectal examination? To answer this question, it is necessary to measure the elastic properties of the prostate and verify the stiffness values with histological examination. Therefore, we devised an Elasticity Mapping System to evaluate the elastic properties of various histopathological grades of prostate cancer in relation to benign prostatic hyperplasia (BPH) and normal tissue. The system consists of a micro tactile sensor, a three-axis (XYZ) with one (fine Z) micromanipulation stage, a stereoscope camera and a measurement chamber. Using this methodology we mapped the elasticity of human prostate cancer (CaP) and it was obviously observed that the node was significantly harder than surrounding normal tissues and had some textures.

Computer-aided diagnosis of prostate cancer with emphasis on ultrasound-based approaches: a review

This paper reviews the state of the art in computer-aided diagnosis of prostate cancer and focuses, in particular, on ultrasound-based techniques for detection of cancer in prostate tissue. The current standard procedure for diagnosis of prostate cancer, i.e., ultrasound-guided biopsy followed by histopathological analysis of tissue samples, is invasive and produces a high rate of false negatives resulting in the need for repeated trials. It is against these backdrops that the search for new methods to diagnose prostate cancer continues. Image-based approaches (such as MRI, ultrasound and elastography) represent a major research trend for diagnosis of prostate cancer. Due to the integration of ultrasound imaging in the current clinical procedure for detection of prostate cancer, we specifically provide a more detailed review of methodologies that use ultrasound RF-spectrum parameters, B-scan texture features and Doppler measures for prostate tissue characterization. We present current and future directions of research aimed at computer-aided detection of prostate cancer and conclude that ultrasound is likely to play an important role in the field.

Resonance sensor measurements of stiffness variations in prostate tissuein vitro—a weighted tissue proportion model

Prostate cancer is the most common type of cancer in men in Europe and the US. The methods to detect prostate cancer are still precarious and new techniques are needed. A piezoelectric transducer element in a feedback system is set to vibrate with its resonance frequency. When the sensor element contacts an object a change in the resonance frequency is observed, and this feature has been utilized in sensor systems to describe physical properties of different objects. For medical applications it has been used to measure stiffness variations due to various patho-physiological conditions. In this study the sensor's ability to measure the stiffness of prostate tissue, from two excised prostatectomy specimens in vitro, was analysed. The specimens were also subjected to morphometric measurements, and the sensor parameter was compared with the morphology of the tissue with linear regression. In the probe impression interval 0.5-1.7 mm, the maximum R(2) > or = 0.60 (p < 0.05, n = 75). An increase in the proportion of prostate stones (corpora amylacea), stroma, or cancer in relation to healthy glandular tissue increased the measured stiffness. Cancer and stroma had the greatest effect on the measured stiffness. The deeper the sensor was pressed, the greater, i.e., deeper, volume it sensed. Tissue sections deeper in the tissue were assigned a lower mathematical weighting than sections closer to the sensor probe. It is concluded that cancer increases the measured stiffness as compared with healthy glandular tissue, but areas with predominantly stroma or many stones could be more difficult to differ from cancer.

Prostate cancer detection with an improved resonance sensor system: parameter evaluation in a silicone model and on human prostate tissue in vitro

The purpose of this study was to improve a resonance sensor system for prostate cancer detection and evaluate its performance on silicone with different hardness. Furthermore, to investigate if the instrument could distinguish between cancerous and normal prostate tissue in one in vitro prostate specimen. The system could measure the frequency shift, impression depth and the rise time of the force signal. The frequency shift, impression depth and the rise time described the relative hardness of silicone (n = 50, P < 0.05). The results from measurements on the prostate specimen indicated that there is a significant difference in the parameter data between cancerous and normal prostate tissue (n = 15, P < 0.05). The parameters' impression depth and force rise time adds important information for cancer detection. Further studies on prostate tissue with different tumour types must be performed in order to understand the full value of the new sensor system.

Prostate tissue stiffness as measured with a resonance sensor system: a study on silicone and human prostate tissue in vitro

Prostate cancer is the most common form of cancer in men in Europe and in the USA. Some prostate tumours are stiffer than the surrounding normal tissue, and it could therefore be of interest to measure prostate tissue stiffness. Resonance sensor technology based on piezoelectric resonance detects variations in tissue stiffness due to a change in the resonance frequency. An impression-controlled resonance sensor system was used to detect stiffness in silicone rubber and in human prostate tissue in vitro using two parameters, both combinations of frequency change and force. Variations in silicone rubber stiffness due to the mixing ratio of the two components could be detected (p<0.05) using both parameters. Measurements on prostate tissue showed that there existed a statistically significant (MANOVA test, p<0.001) reproducible difference between tumour tissue (n=13) and normal healthy tissue (n=98) when studying a multivariate parameter set. Both the tumour tissue and normal tissue groups had variations within them, which were assumed to be related to differences in tissue composition. Other sources of error could be uneven surfaces and different levels of dehydration for the prostates. Our results indicated that the resonance sensor could be used to detect stiffness variations in silicone and in human prostate tissue in vitro. This is promising for the development of a future diagnostic tool for prostate cancer.

Remote sensing of mechanical properties of materials using a novel ultrasound transducer and signal processing

An ultrasound-based remote sensing method to evaluate the mechanical properties of materials is presented. This method consists of a disk-shaped, piezoelectric transducer, operating at its resonance frequency, and a phase-shifted, feedback circuit. Mechanical parameters are derived by analyzing the signal contained in the phase-shifted values of the reflected signal. It is concluded that, using this novel transducer system and signal processing, remote mechanical measurements can be made. Such measurements obviate the need to apply the force-deformation approach and may be used to enable stiffness imaging.

Considerations in the design and sensitivity optimization of the micro tactile sensor

Although miniaturization has been considered the only technology with which to increase sensitivity of tactile sensors, we recently developed the micro tactile sensor (MTS) that performs with high sensitivity without microfabrication. In this study, we examined design and sensitivity optimization of the MTS using theory based upon Mason's equivalent circuit. The touch probe, which is attached to the lead zirconate titanate (PZT) element, was expressed as a purely inductive circuit component. Resonance frequency was calculated as a function of the length of the touch probe, and sensitivity was predicted to be dependent on the length. Furthermore, many kinds of MTS were fabricated with different touch probe lengths, and actual sensitivity was measured as phase shift between nonloaded and loaded conditions. And, from the consideration of theory and experimental data, a sensitivity coefficient was proposed and found to be useful.

Development of a vibratory microinjection method

To reduce cellular damage by pronuclear microinjection and nuclear transfer, we have recently developed a vibratory microinjection method. A micropipette was fixed to a piezoelectric ceramic with a resonance frequency of 70 kHz. When this micropipette was vibrated, it easily entered a mouse-fertilized egg without any sharp depression of the cell body, whereas a sharp, deep depression at the insertion site was observed when the micropipette was not vibrated. A depression rate defined as a rate of a depth of depression over an original cell diameter was utilized as an index of cellular deformation. The depression rates with and without vibration were 11.1 +/- 5.2% (N = 24) and 40.4 +/- 8.8% (N = 16), respectively (P < 0.0001, Student's t-test). In conclusion, the vibratory microinjection method is a new, useful option for gene transfer because it resulted in much less cellular deformation, therefore implicating less cellular damage.

A resonator sensor for measurement of intraocular pressure--evaluation in an in vitro pig-eye model

Intraocular pressure (IOP) measurement is performed routinely at every eye clinic. High IOP, which can be a sign of glaucoma, can lead to degeneration of the retina and can cause blindness. In this study we developed a resonator sensor for IOP measurement based on an oscillator consisting of a piezoelectric element made of lead zirconate titanate, a flat contact piece of nylon and a feedback circuit. The aim of this study was to evaluate the new sensor's ability to determine lOP in an in vitro pig-eye model. Six eyes from four pigs were removed and fixed in agar. They were then pressurized by a saline column (10-35 cm H2O) through a cannula inserted into the vitreous chamber. The IOP was measured with the resonator sensor applied to cornea. An Alcon applanation pneumatonometer and a standard Viggo-Spectramed pressure sensor connected to the saline column were used as references. The IOP as measured with the resonator sensor correlated well with the pressure elicited by the saline column for individual eyes (r = 0.96-0.99, n = 60) and for all eyes (r = 0.92, n = 360). The correlation between the resonance sensor and the pneumatonometer was r = 0.92 (n = 360). The pneumatonometer also showed a good correlation with the saline column (r = 0.98, n = 360). We conclude that our in vitro pig-eye model made it possible to induce reproducible variation in IOP, and measurement of that pressure with the newly developed resonator sensor gave very promising results for development of a clinically applicable IOP tonometer with unique properties.

Myocardial tactile stiffness during acute reduction of coronary blood flow

BACKGROUND

Evaluation of regional myocardial contractile function is of clinical importance. We have developed a new tactile sensor system for accurate measurement of myocardial stiffness in situ. We found that the myocardial stiffness measured by this sensor, which we call tactile stiffness, can be a very useful index for accurate quantification of regional myocardial function. In this study, we used a coronary stenosis model to investigate regional myocardial tactile stiffness under conditions of reduced coronary blood flow.

METHODS

The myocardial tactile stiffness, coronary blood flow, and ventricular pressure and volume, of five open chest mongrel dogs weighing 15 to 17 kg, were measured. After measuring the baseline myocardial stiffness, coronary arterial stenosis was induced with a balloon occluder.

RESULTS

Reducing the coronary flow to 50% and 25% of the baseline level reduced the end-systolic tactile stiffness significantly from 2.20+/-0.16 g/mm2 to 2.05+/-0.20 g/mm2 (p<0.05) and from 2.21+/-0.16 g/mm2 to 1.96+/-0.18 g/mm2 (p<0.01), respectively. Reducing the flow, to 50% and 25%, increased the end-diastolic stiffness significantly from 1.29+/-0.15 g/mm2 to 1.39+/-0.14 g/mm2 (p<0.01) and from 1.30+/-0.16 g/mm2 to 1.46+/-0.14 g/mm2 (p<0.05), respectively.

CONCLUSIONS

We consider that the regional myocardial tactile stiffness will be a useful index sensitive enough to detect changes in regional contractile function under conditions of reduced coronary blood flow.

A catheter tactile sensor for measuring hardness of soft tissue: measurement in a silicone model and in an in vitro human prostate model

Tissue hardness is related to tissue composition, and this is often changed by disease. It is therefore of interest to measure the hardness in an objective and non-invasive way. A tactile sensor based on a vibrating piezoelectric ceramic element in a feedback loop is described. When the sensor touches an object it produces a frequency shift related to the hardness of the object. The aim of this study was to develop an in vitro hardness measurement method using a catheter type version of the sensor. The method was evaluated in an established silicone tissue model and on human prostate tissue in vitro. A linear relationship was found with a high degree of explanation (R2 = 0.98) between a cone penetration hardness standard (DIN ISO 2137) applied to the silicone model and the corresponding frequency shift. The results from measurements on a human prostate tissue sample, fixed with formalin, showed that the relative hardness measured with the tactile sensor correlated (R = -0.96, p < 0.001, N = 60) with the proposed hardness related to the histological composition of the prostate tissue. The results indicated that hardness of prostate tissue, and maybe hardness of human tissue in general, can be expressed according to the cone penetration standard and that the hardness can be measured with this tactile sensory system. These findings hold the promise of further development of a non-invasive tool for hardness measurement in a clinical situation.

A tactile sensor for detection of physical properties of human skin in vivo

A spring loaded tactile sensor with displacement sensing has been evaluated for non-invasive assessment of physical properties, stiffness and elasticity, of human skin in vivo. The tactile sensor consists of a peizoelectric vibrator (61 kHz) with a vibration pickup, electronics and PC with software for measurement of the change in frequency when the sensor is attached to an object. Integrated with the tactile sensor is a displacement sensor that shows the compression of the spring that loads the sensor element against the object during measurement. Under certain conditions (e.g. fixed contact pressure) this change in frequency monitors the acoustic impedance of the object and is related to the stiffness of soft tissue. The experimental results on silicone gum and on healthy Japanese and Swedish women indicated that the instrument was able to detect changes in stiffness and elastic related properties of human skin, related to age, day-to-day variations and application of cosmetics. The instrument was concluded to be easy to handle and suitable for field work.

Myocardial tactile stiffness: a variable of regional myocardial function

OBJECTIVES

We developed a new sensor system for in situ measurement of myocardial tactile stiffness-stiffness in a direction perpendicular to the wall-and validated its use for providing a reasonable estimation of regional myocardial function.

BACKGROUND

Numerous attempts have been made to directly assess regional myocardial function. The complexity and highly invasive nature of the measuring devices have hampered their in situ application.

METHODS

In open chest mongrel dogs, myocardial tactile stiffness, ventricular pressure and ventricular volume were monitored. Under the preload reduction, these variables were measured to determine the relation between the end-systolic pressure-volume relation (ESPVR) and the end-systolic tactile stiffness-volume relation (ESSVR). The changes in myocardial tactile stiffness were monitored in the regional ischemic myocardial model and infarcted model to evaluate their usefulness as indexes of regional myocardial function.

RESULTS

Myocardial tactile stiffness changed cyclically and followed a time course similar to left ventricular pressure. When preload was altered, the ESSVR was as linear as the ESPVR. The slope of the ESSVR and that of the ESPVR showed a strong correlation over a wide range of contractility. These results suggest that myocardial tactile stiffness can be a good index of regional wall stress or fiber stress. End-systolic myocardial tactile stiffness of ischemic and infarcted regions decreased significantly, with a concomitant increase in end-diastolic stiffness compared with that of intact myocardium.

CONCLUSIONS

Using our tactile sensor system, regional myocardial tactile stiffness of a beating heart was measured with reasonable temporal resolution. We consider myocardial tactile stiffness to be a useful index of regional myocardial function.

Influence of hormone treatment on prostate growth and micturition characteristics of the rat

The influence of dihydrotestosterone propionate (DHT) and estradiol (E) on prostate growth and micturition was evaluated. Complete studies were carried out on 49 Sprague-Dawley rats over a 14-day period. Rats were divided into three groups: (1) controls, (2) DHT, and (3) DHT + E. All groups were injected daily with 0.1 ml of sesame oil, together with 1.25 mg/kg of DHT for group 2 and 1.25 DHT + 0.125 mg/kg E for group 3. Physiological measurements of micturition were done weekly by subcutaneously administering a fluid loading dose consisting of 10 mg/kg furosemide + 5 ml saline. Parameters of micturition frequency, volume, and prostate weight were calculated. Prostate weight values for controls were 0.89 +/- 0.06 g while those treated with DHT increased significantly to 1.26 +/- 0.10 g (P < 0.05) and those treated with DHT + E also increased significantly to 1.24 +/- 0.09 g (P < 0.05). There was no significant difference in prostate weight between the DHT and DHT + E groups. Analysis of micturition data shows that the mean volume voided per micturition decreases in both the DHT and DHT + E treated rats. At between 7 and 14 days of DHT and DHT + E treatment, rats micturated at significantly reduced mean volumes. The lowest mean volume per micturition was detected on the 14th day of DHT treatment, showing a significant reduction from control values of 3.05 +/- 0.27 to 1.68 +/- 0.05 ml. The corresponding value of the mean micturated volume in the DHT + E groups was 1.86 +/- 0.31 ml. Control values for frequency of micturition was 3.25 +/- 0.52/hr, while for rats treated with DHT it was 3.62 +/- 0.38/hr and for DHT + E it was 4.0 +/- 0.54/hr. Evidence is provided to demonstrate that 14 day DHT, and particularly DHT + E, stimulation produces significant alterations in prostate weight and micturition characteristics of unanesthetized rats. On the basis of these observations it is proposed that the hormonally enlarged prostate promotes stimuli to trigger the spinal micturition reflex, thereby producing increased frequency of micturition.

Analysis of the relative biomechanical effects of alpha 1 and alpha 2 antagonists in modifying the compliance of the prostate and micturition parameters of the hormonally manipulated male rat

The potential of the alpha 1 and alpha 2 antagonists to modify prostate compliance, and micturition characteristics of rats with hormonally enlarged prostates was studied. Prostate growth was induced in Sprague-Dawley rats using dihydrotestosterone (DHT) and estradiol (E) by daily subcutaneous injections of DHT 1.25 mg/kg and E 0.25 mg/kg together with 0.1ml of sesame oil, as a vehicle, for a period of 3 weeks. A control group of six rats was used wherein the vehicle alone was administered. Dose levels of 3, 10, 30, and 300 micrograms/kg of alpha 1 or alpha 2 antagonist were given at weekly intervals to each of the groups defined above. Voiding characteristics, in terms of micturition frequency and volume per micturition, were measured and correlated with the pharmacological and hormonal stimulus. Prostate compliance and weight was evaluated in each of the groups after rats were terminated and the ventral prostate was dissected and removed in in toto. Compliance measurements were made using a new biosensor system which is based on the principle of detecting the shift in the resonance frequency of the biosensor produced by the hormones on the acoustic impedance of prostate. The results show that DHT and [DHT+E] significantly increased prostate weight and decreased prostate compliance. The alpha 2 antagonist atipamezole significantly increased the compliance of all prostates, including controls, while the alpha 1 antagonist did not alter the compliance. It is concluded that this alpha 2 antagonist is more effective than the prazosin in reversing the hardening effect of hormones on the prostate.