Dynamic instrumented palpation (DIP)—a new method for soft tissue quality assessment; application to engineered mechanical phantom materials

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.

Dynamic instrumented palpation - a new method for soft tissue quality assessment: application to prostate disease diagnosis

The objective is to establish the feasibility of using dynamic instrumented palpation, a novel technique of low-frequency mechanical testing, applied here to diagnose soft tissue condition. The technique is applied, in vitro, to samples of excised prostate gland affected by benign prostate hyperplasia and/or prostate cancer. Particular attention is paid to the relationship between the histological structure of the tissue and the dynamic mechanical properties in an attempt to separate patient-specific aspects from histopathological condition (i.e. prostate cancer or benign prostate hyperplasia). The technique is of clinical interest because it is potentially deployable in vivo. Prostate samples were obtained from a total of 36 patients who had undergone transurethral resection of the prostate to relieve prostatic obstruction and 4 patients who had undergone radical cystoprostatectomy for bladder cancer. Specimens (chips) recovered from transurethral resection of the prostate were of nominal size 5 mm × 8 mm and thicknesses between 2 and 4 mm, whereas those from the cystoprostatectomy were in the form of transverse slices of thickness approximately 6 mm. Specimens were mechanically tested by a controlled strain cyclic compression technique, and the resulting dynamic mechanical properties expressed as the amplitude ratio and phase difference between the cyclic stress and cyclic strain. After mechanical testing, the percentage areas of glandular and smooth muscle were measured at each probe point. Good contrast between the dynamic modulus of chips from benign prostate hyperplasia and prostate cancer patients was demonstrated, and absolute values similar to those published by other authors are reported. For the slices, modulus values were considerably higher than for chips, and good in-patient mechanical contrast was revealed for predominantly nodular and predominantly stromal areas. Extending this classification between patients required pattern recognition techniques. Overall, the study has demonstrated that dynamic mechanical properties can potentially be used for diagnosis of prostate condition using in vivo measurements.