Rodney Elliott

Specialised Image Capture Systems for a DIET Breast Cancer Screening System

Digital Image-based Elasto-Tomography (DIET) is an emerging technology for non-invasive breast cancer screening. This technology actuates breast tissue and measures the surface motion using digital imaging technology. The internal distribution of stiffness is then reconstructed using Boundary Element or Finite Element Methods (FEM or BEM). However, obtaining accurate imaging at high frequency and high resolution in terms of numbers of pixels is challenging if enough accuracy is to be obtained in the motion sensing to deliver a useful result. The overall focus of such mechatronic and digitally centred systems is on providing a low-cost, radiation dose-free and portable screening system capable of screening numerous patients per day – in direct contrast to current low throughput, non-portable and high cost x-ray and MRI based approaches. Thus, DIET technology relies on obtaining high resolution images of a breasts surface under high frequency actuation, typically in the range of 50-100Hz. Off-the-shelf digital cameras and imaging elements are unable to capture images directly at these speeds. A method is presented for obtaining the required high speed image capture at a resolution of 1280x1024 pixels and actuation frequency of 100Hz. The prototype apparatus presented uses two imaging sensors in combination

A simple hybrid testing approach for dynamic analysis of civil structural control devices

This paper presents a simple and robust hybrid test system and outlines solutions to the major issues faced in developing any hybrid system. The overall approach is centred on the dSpace™ real-time control system development tool. The final system readily accommodates non-linear-single and multi-degree-of-freedom models and an operating bandwidth of 1 kHz. Experimental outcomes are based on studies of a linear single degree of freedom structure and a non-linear rocking wall system that includes impact loads and timing subject to random ground motions. The results illustrate the potential outcomes of full scale experiments but at a cost-effective level.

Peripheral venous blood oxygen saturation can be non-invasively estimated using photoplethysmography

Measurement of peripheral venous oxygen saturation (SvO2) is currently performed using invasive catheters or direct blood draw. The purpose of this study was to non-invasively determine SvO2 using a variation of pulse oximetry techniques. Artificial respiration-like modulations applied to the peripheral vascular system were used to infer regional SvO2 using photoplethysmography (PPG) sensors. To achieve this modulation, an artificial pulse generating system (APG) was developed to generate controlled, superficial perturbations on the finger using a pneumatic digit cuff. These low pressure and low frequency modulations affect blood volumes in veins to a much greater extent than arteries due to significant arterial-venous compliance differences. Ten healthy human volunteers were recruited for proof-ofconcept testing. The APG was set at a modulation frequency of 0.2 Hz (12 bpm) and 45-50 mmHg compression pressure. Initial analysis showed that induced blood volume changes in the venous compartment could be detected by PPG. Estimated arterial oxygen saturation (97% [IQR=96.1%-97.4%]) matches published values (95%-99%). Estimated venous oxygen saturation (93.2% [IQR=91.-93.9%]) agrees with reported ranges (92%-95%) measured in peripheral regions. The median difference between the two saturations was 3.6%, while the difference between paired measurements in each subject was statistically significant (p=0.002). These results demonstrate the feasibility of this method for real-time, low cost, non-invasive estimation of SvO2. Further validation of this method is warranted.

Assessing microcirculation condition in critical illness using the pulse oximeter's concept

Sepsis patients normally suffer microcirculatory dysfunction, which results in organ failure and increased risk of death [1]. Importantly, microcirculatory distress is the only independent factor for predicting patient outcome if it is not treated within 48 hours [2]. Therefore, analyzing oxygen transport and utilization can potentially assess microcirculation function and metabolic condition of an individual. In this study, a pulse oximeter is used to extract additional information signals due to absorption of red and infrared light. The IR signal is related to the overall blood volume, (HbO2 + Hb) and the R signal is related to the amount of reduced hemoglobin, (Hb). Differences between these two signals thus represent the amount of oxygenated hemoglobin, (HbO2). Unlike the standard pulse oximeter, the pulse oximeter used in this study provided the changes in red and infrared signals separately for analysis. In this study, a moderate physical exercise test has been conducted to validate the pulse oximeter concept. This test was done on healthy individuals to induce changes in extraction. This study and the use of this data was approved by the University of Canterbury Human Ethics Committee, Christchurch, New Zealand. In this test, AC R and IR signals were relatively higher during post-exercise periods compared to baseline, due to increases in heart rate. Median heart rate increases from 51 during rest to 83 beats per minute during post-exercise 1. Further exercise yielded median heart rates of 90, 90, 91 and 99 beats per minute. In addition, oxygen extraction was also changing during the post-exercise period, indicated by the difference in the AC IR signal to the R signal. Median oxygen extraction increases from 37.4% during rest to 41.2% during following intense exercise. For further (repeated) physical exercise tests yielded extraction of 37.9%, 36.6%, 39.4% and 40.4%. However, the increased rate varies across subjects showing significant inter-subject variability due to existing fitness levels. The pulse oximeter sensor concept used in this study is capable of extracting valuable information to assess metabolic condition. Thus, implementing this concept on ICU patients has the potential to aid sepsis diagnosis and provide more accurate tracking of patient state and sepsis status.