A Forensic Disassembly of the BIS Monitor.
A Forensic Disassembly of the BIS Monitor.
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DOI：
10.1213/ane.0000000000005220
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发表时间：
2020-12
影响因子：
5.7
通讯作者：
Connor CW
中科院分区：
文献类型：
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作者：
Connor CW
BIS监视器已用于临床二十多年，并对麻醉学的学术活动产生了巨大的影响，有三千多篇文章引用了双谱指数。尽管试图通过外部观察推断其算法，但与其他商业上不太成功的麻醉下脑电图（EEG）活动监测仪的算法相比，其操作仍然未被描述。随着某些关键专利的到期，通过仔细拆卸，然后提取和检查其内部软件来检查监视器的运行情况的时机已经成熟。在二级市场上购买了一台A-2000 BIS监视器（枪金属蓝色外壳，琥珀色单色显示器）。在确定了主要的数据处理和存储组件后，使用一套免费或廉价的工具来检索和拆卸监视器的板载软件。该软件主要在ARMv7微处理器（Sharp/NXP LH77790B）和数字信号处理器（Texas Instruments TMS320C32）上执行。设备软件可以通过使用调试接口直接从监视器的硬件中检索，这些接口从最初的开发中保留下来。关键数值参数，如频谱边缘频率（SEF）、总功率和BIS值，从设备串行端口的外部传输回溯到提取软件中的计算点。在此过程中，确定了关键算法的位置。为了证明该技术的有效性，对SEF和总功率算法进行了分解、全面注释，并与理论理想行为进行了比较。在设备的SEF算法实现中发现了一个错误，这可以由完美等电脑电图引起。本文论证了A-2000 BIS监视器的电子设计不存在任何不可逾越的障碍，可以直接从主板上以十六进制机器码形式检索其设备软件。该软件可以通过反汇编和反编译进行逆向工程，以揭示BIS Monitor实现其算法的方法，这些算法最终必须形成其功能的明确声明。在不进一步泄露任何可能被视为商业秘密的算法的情况下，鼓励BIS监视器的制造商以其原始格式发布设备软件，以便为BIS相关的学术文献奠定坚实的理论基础，并促进脑电图监测算法的进一步学术发展。
The BIS Monitor has been available for clinical use for more than twenty years and has had an immense impact on academic activity in Anesthesiology, with more than three thousand articles referencing the bispectral index. Despite attempts to infer its algorithms by external observation, its operation has nevertheless remained undescribed, in contrast to the algorithms of other less commercially successful monitors of electroencephalogram (EEG) activity under anesthesia. With the expiration of certain key patents, the time is therefore ripe to examine the operation of the monitor on its own terms through careful dismantling, followed by extraction and examination of its internal software. An A-2000 BIS Monitor (gunmetal blue case, amber monochrome display) was purchased on the secondary market. After identifying the major data processing and storage components, a set of free or inexpensive tools was used to retrieve and disassemble the monitor’s onboard software. The software executes primarily on an ARMv7 microprocessor (Sharp/NXP LH77790B) and a digital signal processor (Texas Instruments TMS320C32). The device software can be retrieved directly from the monitor’s hardware by using debugging interfaces that have remained in place from its original development. Critical numerical parameters such as the Spectral Edge Frequency (SEF), Total Power and BIS values were retraced from external delivery at the device’s serial port back to the point of their calculation in the extracted software. In doing so, the locations of the critical algorithms were determined. To demonstrate the validity of the technique, the algorithms for SEF and Total Power were disassembled, comprehensively annotated and compared to their theoretically ideal behaviors. A bug was identified in the device’s implementation of the SEF algorithm, which can be provoked by a perfectly isoelectric EEG. This article demonstrates that the electronic design of the A-2000 BIS Monitor does not pose any insuperable obstacles to retrieving its device software in hexadecimal machine code form directly from the motherboard. This software can be reverse engineered through disassembly and decompilation to reveal the methods by which the BIS Monitor implements its algorithms, which ultimately must form the definitive statement of its function. Without further revealing any algorithms that might be considered trade secrets, the manufacturer of the BIS Monitor should be encouraged to release the device software in its original format in order to place BIS-related academic literature on a firm theoretical foundation and to promote further academic development of EEG-monitoring algorithms.