Artificial intelligence (AI) has been able to gain deeper insights from patient examination and trial data, thereby improving diagnostic capabilities and enhancing predictive and trend analysis capabilities. The next step is to migrate AI driven medical testing and sample analysis from the laboratory to doctors' offices, clinics, or homes. This bedside (PoC) monitoring method can quickly assess medical conditions, reduce patient burden, and enable more frequent testing to provide more refined data and detect worrying trends faster.
To achieve AI driven PoC, it is necessary to use a multifunctional application optimized IC with advanced analog front-end (AFE) to interface with various biosensors for necessary data acquisition and measurement. These ICs must meet the unique characteristic requirements of complex electrochemical, biological, and related measurements, including accuracy, low power consumption, and highly integrated functionality. They must also rely on advanced security technologies to ensure data privacy.
This article will explore the trend of PoC transformation and its impact on design, then describe widely used AFE measurement scenarios, and introduce example solutions of Analog Devices that can meet PoC measurement and security requirements.
Why do we need PoC now?
The driving factors for increasing PoC detection and sample processing include: the demand for more and better medical diagnoses to improve individual health conditions; Develop insights into the needs of population based aging, diseases, and disease changes. Regulatory regulations encourage or even require more testing, which must be done at lower costs and reduce testing and waiting times. In addition, there is a trend to establish more local PoC in clinics or homes to minimize interference and costs for patients, which requires simple yet powerful instruments.
At the same time, AI is rapidly developing, enabling these data to be used for deeper analysis and prediction.
These comprehensive factors create a demand and opportunity for complex IC based circuits that need to be optimized according to the unique requirements of medical testing data acquisition and management. This type of IC is the front-end interface that connects the patient's bodily fluids with the system, responsible for capturing and recording data from various sensors, evaluating it, and reporting the final data (Figure 1).
Key interface diagram between patient vital signs and body fluids and related PoC instruments and data systems (click to enlarge)
Figure 1: Simulation and related electronic devices serve as important communication interfaces between patient vital signs and body fluids, as well as related PoC instruments and data systems. (Image source: Analog Devices)
Application oriented diversified ICs should be able to address various challenges
We can use some examples to clearly illustrate this situation:
Example 1: Pulse oximetry and heart rate monitor:
Blood oxygen saturation (SpO2) and heart rate are important basic health measurement indicators. The first parameter provides the most vivid example of how optical and electronic technologies can change the expectations of PoC. The only way to measure SpO2 has always been for nurses to take blood samples and send them to the laboratory for testing.
Now, with the well-established electronic optical technology from decades ago, LEDs, light sensors, and algorithms on fingertips can provide fast DIY readings in seconds. In addition, the same arrangement of LED photoelectric sensors can also provide heart rate information.
The more advanced LED and photoelectric sensor system provides us with more performance and functionality. There are some ICs specifically designed for these applications, such as MAX86171 (Figure 2, top), which is an ultra-low power optical data acquisition system with transmission and reception channels. Despite its internal complexity, only a few discrete components need to be configured in applications (Figure 2, bottom).
MAX86171 multi-channel, ultra-low power, optical data acquisition system from Analog Devices (click to enlarge)
Figure 2: The MAX86171 multi-channel, ultra-low power, optical data acquisition system (top image) simplifies external wiring and the need for passive auxiliary components with its highly integrated internal functions (bottom image). (Image source: Analog Devices)
On the transmitter side, MAX86171 is equipped with 9 programmable LED driver output pins, each connected to 3 high current 8-bit LED drivers. On the receiver side, the MAX86171 is equipped with two low-noise, charge integration front-end and ambient light cancellation (ALC) circuits, forming an optical based, highly integrated high-performance data acquisition system.
In addition to SpO2 and heart rate data, this IC can also evaluate heart rate variability, body hydration, muscle and tissue oxygen saturation (SmO2 and StO2), and maximum oxygen consumption (VO2 max).
Please note that the performance indicators and priorities of medical applications are different from non-medical situations. Due to the relatively low light level, the absolute background noise of the optical front-end is a key parameter, rather than the signal-to-noise ratio (SNR).
Although in the biomedical field, signal bandwidth and sampling rate are usually very low because the relevant parameters do not change at a rate of several kilohertz, the complex analog properties of patients and signals require different priority orders in terms of specifications. These features include high sensitivity, wide dynamic range, and low noise to successfully cope with constantly changing non fixed environments. In this environment, the patient's skin and internal organs will constantly move, and even slight movements can cause changes in the contact area and contact force. In addition, these characteristics are also affected by various interferences, noise, and changes, making the problem more complex.
To meet application requirements, the dynamic range of MAX86171 is between 91 and 110 decibels (dB), depending on the test layout. Its resolution is 19.5 bits, dark current noise is less than 50 picoamps (pA) (effective value), and the ambient light suppression coefficient at 120 hertz (Hz) is better than 70 dB.
Example 2: Potentiometric method, current analysis method, volt ampere measurement method, and impedance measurement:
Nowadays, electrical engineers can proficiently measure voltage, current, impedance, and their interrelationships using various standard instruments. However, these measurements have unique requirements and limitations in chemical and biological environments, and present different measurement scenarios:
Potentiometric method: using a potentiostat to measure the potential between two electrodes to determine the concentration of substances in a solution
Current analysis method: using a current measuring device to detect ions in a solution based on current or changes in current
Voltammetric method: Apply a specific voltage curve that varies over time to the working electrode and measure the current generated by the system, usually using a potentiostat for measurement
Impedance: Measuring the voltage current relationship between the skin and the body
To evaluate these parameters, AD5940 offers multiple functionalities and interface options in a 56 ball WLCSP package measuring 3.6 × 4.2 millimeters (mm) (Figure 3). This low-power AFE has multiple functions and interfaces, designed specifically for portable applications that require high-precision electrochemical measurement techniques such as ampere, volt ampere, or impedance measurements.