Explanatory models for a tactile resonance sensor system—elastic and density-related variations of prostate tissuein vitro

A tactile resonance sensor for prostate cancer detection - evaluation on human prostate tissue

Prostate cancer surgery risks erectile problems and incontinence for the patient. An instrument for guiding surgeons to avoid nerve bundle damage and ensure complete cancer removal is desirable. We present a tactile resonance sensor made of PZT ceramics, mounted in a 3D motorized translation stage for scanning and measuring tissue stiffness for detecting cancer in human prostate. The sensor may be used during surgery for guidance, scanning the prostate surface for the presence of cancer, indicating migration of cancer cells into surrounding tissue. Ten fresh prostates, obtained from patients undergoing prostate cancer surgery, were cut into 0.5 cm thick slices. Each slice was measured for tissue stiffness at about 25 different sites and compared to histology for validation cancer prediction by stiffness. The statistical analysis was based on a total of 148 sites with non-cancer and 40 sites with cancer. Using a generalized linear mixed model (GLMM), the stiffness data predicted cancer with an area under the curve of 0.74, after correcting for overfitting using bootstrap validation. Mean prostate stiffness on the logarithmic scale (p = 0.015) and standardized Z-scores (p = 0.025) were both significant predictors of cancer. This study concludes that stiffness measured by the tactile resonance sensor is a significant predictor of prostate cancer with potential for future development towards a clinical instrument for surgical guidance.

Design and analysis of an ultrasonic tactile sensor using electro-mechanical analogy

This paper proposed a hybrid design approach of a vibro-concentrator, a vital component of an ultrasonic tactile sensor, by using electro-mechanical analogy. Lab experiments on soft materials with elastic modulus from 14 kPa to 150 kPa were conducted using the tactile sensor installed with the vibro-concentrator to verify the performance of the design. Various mechanical and electrical parameters, such as resonance frequency shift and equivalent conductance, were discussed, focusing on their feasibility as new stiffness indicators. As a variant of tactile sensors, ultrasonic tactile sensors have the advantage of high sensitivity and minimal contact with the object over traditional tactile sensors based on force-displacement principle. They detect the changes in mechanical vibration characteristics, mostly resonance frequency shift of the sensor, as an indicator of the mechanical properties of the object. A vibro-concentrator has been frequently adopted to improve the performance an ultrasonic tactile sensor, but its design has yet been systematically considered. We propose a hybrid design approach based on electro-mechanical analogy for both mechanical and electrical analyses. Mechanically, impedance analogy was adopted to design an ultrasonic vibration concentrator for the sensor to localize the contact and reinforce the vibration behavior at ~40 kHz. Electrically, we used mobility analogy to derive electrical parameters from the tactile sensing tests in lab environment. The competence of the design was demonstrated by mechanical and electrical characteristic tests. By investigating various electrical parameters from tactile sensing tests, the equivalent conductance determined by the electro-mechanical analysis was found to have almost perfectly linear relationship (R² = 0.9998) with the samples' elastic modulus ranging from 10 kPa to 70 kPa, and showed its potential as a new stiffness indicator for soft materials. Further analyses suggested that the electrically determined series resonance frequency shift, parallel resonance frequency shift, and maximum phase angle frequency shift also had excellent linearities (R² = 0.9947, 0.9842, and 0.9935, respectively) with sample's modulus and can be considered as indicator candidates.

Quantitative mechanical assessment of the whole prostate gland ex vivo using dynamic instrumented palpation

An instrumented palpation sensor, designed for measuring the dynamic modulus of tissue in vivo, has been developed and trialled on ex vivo whole prostate glands. The sensor consists of a flexible membrane sensor/actuator with an embedded strain gauge and is actuated using a dynamically varying airflow at frequencies of 1 and 5 Hz. The device was calibrated using an indentation stiffness measurement rig and gelatine samples with a range of static modulus similar to that reported in the literature for prostate tissue. The glands were removed from patients with diagnosed prostate cancer scheduled for radical prostatectomy, and the stiffness was measured within 30 min of surgical removal. Each prostate was later examined histologically in a column immediately below each indentation point and graded into one of the four groups; normal, benign prostatic hyperplasia, cancerous and mixed cancer and benign prostatic hyperplasia. In total, 11 prostates were assessed using multiple point probing, and the complex modulus at 1 and 5 Hz was calculated on a point-by-point basis. The device yielded values of quasi-static modulus of 15 ± 0.5 kPa and dynamic modulus of 20 ± 0.5 kPa for whole prostates, and a sensitivity of up to 80% with slightly lower specificity was achieved on diagnosis of prostate cancer using a combination of mechanical measures. This assessment did not take into account some obvious factors such as edge effects, overlap and clinical significance of the cancer, all of which would improve performance. The device, as currently configured, is immediately deployable in vivo. A number of improvements are also identified which could improve the sensitivity and specificity in future embodiments of the probe.

Prostate Cancer Detection with a Tactile Resonance Sensor-Measurement Considerations and Clinical Setup

Tumors in the human prostate are usually stiffer compared to surrounding non-malignant glandular tissue, and tactile resonance sensors measuring stiffness can be used to detect prostate cancer. To explore this further, we used a tactile resonance sensor system combined with a rotatable sample holder where whole surgically removed prostates could be attached to detect tumors on, and beneath, the surface ex vivo. Model studies on tissue phantoms made of silicone and porcine tissue were performed. Finally, two resected human prostate glands were studied. Embedded stiff silicone inclusions placed 4 mm under the surface could be detected in both the silicone and biological tissue models, with a sensor indentation of 0.6 mm. Areas with different amounts of prostate cancer (PCa) could be distinguished from normal tissue (p < 0.05), when the tumor was located in the anterior part, whereas small tumors located in the dorsal aspect were undetected. The study indicates that PCa may be detected in a whole resected prostate with an uneven surface and through its capsule. This is promising for the development of a clinically useful instrument to detect prostate cancer during surgery.

Dual-modality probe intended for prostate cancer detection combining Raman spectroscopy and tactile resonance technology--discrimination of normal human prostate tissues ex vivo

Prostate cancer is the most common cancer for men in the western world. For the first time, a dual-modality probe, combining Raman spectroscopy and tactile resonance technology, has been used for assessment of fresh human prostate tissue. The study investigates the potential of the dual-modality probe by testing its ability to differentiate prostate tissue types ex vivo. Measurements on four prostates show that the tactile resonance modality was able to discriminate soft epithelial tissue and stiff stroma (p < 0.05). The Raman spectra exhibited a strong fluorescent background at the current experimental settings. However, stroma could be discerned from epithelia by integrating the value of the spectral background. Combining both parameters by a stepwise analysis resulted in 100% sensitivity and 91% specificity. Although no cancer tissue was analysed, the results are promising for further development of the instrument and method for discriminating prostate tissues and cancer.

Comparative study of a muscle stiffness sensor and electromyography and mechanomyography under fatigue conditions

This paper proposes the feasibility of a stiffness measurement for muscle contraction force estimation under muscle fatigue conditions. Bioelectric signals have been widely studied for the estimation of the contraction force for physical human-robot interactions, but the correlation between the biosignal and actual motion is decreased under fatigue conditions. Muscle stiffness could be a useful contraction force estimator under fatigue conditions because it measures the same physical quantity as the muscle contraction that generates the force. Electromyography (EMG), mechanomyography (MMG), and a piezoelectric resonance-based active muscle stiffness sensor were used to analyze the biceps brachii under isometric muscle fatigue conditions with reference force sensors at the end of the joint. Compared to EMG and MMG, the change in the stiffness signal was smaller (p < 0.05) in the invariable contraction force generation test until failure. In addition, in the various contraction level force generation tests, the stiffness signal under the fatigue condition changed <10% (p < 0.05) compared with the signal under non-fatigue conditions. This result indicates that the muscle stiffness signal is less sensitive to muscle fatigue than other biosignals. This investigation provides insights into methods of monitoring and compensating for muscle fatigue.

Indentation loading response of a resonance sensor--discriminating prostate cancer and normal tissue

Prostate cancer is the most common type of cancer among men worldwide. Mechanical properties of prostate tissue are promising for distinguishing prostate cancer from healthy prostate tissue. The aim was to investigate the indentation loading response of a resonance sensor for discriminating prostate cancer tissue from normal tissue. Indentation measurements were done on prostate tissue specimens ex vivo from 10 patients from radical prostatectomy. The measurement areas were analysed using standard histological methods. The stiffness parameter was linearly dependent on the loading force (average R(2 )= 0.90) and an increased loading force caused a greater stiffness contrast of prostate cancer vs normal tissue. The accuracy of the stiffness contrast was assessed by the ROC curve with the area under the curve being 0.941 for a loading force of 12.8 mN. The results are promising for the development of a resonance sensor instrument for detecting prostate cancer.

Technologies for localization and diagnosis of prostate cancer

The gold standard for detecting prostate cancer (PCa), systematic biopsy, lacks sensitivity as well as grading accuracy. PSA screening leads to over-treatment of many men, and it is unclear whether screening reduces PCa mortality. This review provides an understanding of the difficulties of localizing and diagnosing PCa. It summarizes recent developments of ultrasound (including elastography) and MRI, and discusses some alternative experimental techniques, such as resonance sensor technology and vibrational spectroscopy. A comparison between the different methods is presented. It is concluded that new ultrasound techniques are promising for targeted biopsy procedures, in order to detect more clinically significant cancers while reducing the number of cores. MRI advances are very promising, but MRI remains expensive and MR-guided biopsy is complex. Resonance sensor technology and vibrational spectroscopy have shown promising results in vitro. There is a need for large prospective multicentre trials that unambiguously prove the clinical benefits of these new techniques.