Already in the early days of CAN, it was used in medical devices as embedded network. Still nowadays, CAN is because of its reliability and robustness a preferred network technology in healthcare.

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The complete article is published in the December issue of the CAN Newsletter magazine 2022. This is just an excerpt.

CAN has been used in medical devices since a long time. Today, CAN networks are used also in intensive care units including patient beds, in operating rooms, and in other healthcare equipment. Most of these CAN networks are embedded or even deeply embedded. Open networks are used for example to connect medical imaging systems to contrast media injectors. CAN is used in medical devices such as X-ray machines, magnetic resonators, angiographs, computer tomographs, and others.

These devices may implement cascaded CAN networks for embedded and deeply embedded control applications. Sub-systems with a standardized CANopen interface include collimators and dosemeters. Also, medical imaging devices may be connected to contrast media injectors by an open CANopen-based network. CAN networks can also connect all devices and units inside operating rooms to enable fast and monitored plugging together of operating gear so as to avoid any omissions and to check on the functionality of all devices. Intensive care units (ICU) are another use case for CAN in healthcare. CAN is used as deeply embedded network for internal control purposes. The interconnection of ICUs via CAN networks is a further application area. Some sophisticated patient beds use an embedded CAN control system for the motion controllers and the different user interfaces.

Collimator coordinate system, whereby the individual coordinates are as seen from a front view (Source: CiA)

The beds additionally provide a CAN interface to connect for example a blood-pressure monitor. Philips Medical Systems was one of the early adopters of CAN communication in X-ray devices, computer tomography, and other medical devices. As an early CAN in Automation (CiA) member, the healthcare company supported the development of the CAN Application Layer (CAL) released by CiA in 1993. It was a pure application layer (layer-7) approach, which was the predecessor of the CANopen application layer and communication profile. In 1993, Siemens implemented CAN networks with proprietary higher-layer protocols in its computer tomography systems.

CAL was also used by Karl Storz, a Swiss company, for its endoscopy devices. Mid of the 90ties, endoscopy pioneer Richard Wolf, a German company, connected its products via embedded CANopen networks. Additionally, the company linked operating (OR) tables, surgical lights, and other devices from third-party suppliers by means of a second CAN interface.

CANopen profiles for medical devices

With the introduction of CANopen, Siemens (nowadays Siemens Healthineers) and GE Healthcare migrated from proprietary CAN-based embedded networks to this application layer. CiA members developed CANopen profiles for automatic X-ray collimators (CiA 412-2) and dose measurement systems (CiA 412-6). The CiA 412 CANopen profiles for medical devices specify general definitions (Part 1), the CANopen interface for automatic X-ray collimators (Part 2) as well as for dose measurement systems (Part 6).

Network topology example with a permanently installed medical diagnostic device (Source: CiA)

Using standardized CANopen interfaces, device manufacturers may supply diverse markets with medical devices implementing the same electronic interface according to CiA 412 and can simply vary the appropriate application software. A system designer may choose between CANopen devices from different manufacturers implementing the same profile-compliant functionality. For development, analysis, and maintenance of the devices, CANopen tools can be used.

The CiA 412-2 document for automatic X-ray collimators, represents the CANopen device profile for generic X-ray collimators, and as such describes the generic subset of collimator functionality. A collimator has three basic functions for which the profile specifies the appropriate configuration, application, and diagnostic parameters. The main function limits (or collimates) the X-ray beam (e.g. rectangular collimation) issued by an X-ray emitting source (X-ray tube) to a defined (receptor) format. Filters may be applied to influence spectral characteristics of the X-ray beam. The visual simulation of the X-ray beam is the third specified functionality. Some automatic X-ray collimators support local control functionality. The defined collimator functionality coordinates (X, Y, s, ω, D) may be controlled either in position or velocity mode. Devices compliant to this profile are required to support the emergency message (CiA 301). The defined device errors are sorted in warnings, recoverable errors, and non-recoverable errors.

The introduced collimator device FSA (finite state automaton) specifies the application behavior as well as the corresponding state transitions of the collimators. As a collimator is usable with local control even when the CAN network does not work properly, the communication FSA (CANopen NMT server FSA, CiA 301) and the collimator FSA are very loosely coupled. Also defined is a coordinate FSA applicable for the symmetric rectangular collimation sets, the quadrangle collimation sets, the circular collimation sets, as well as the spatial filter sets. The third specified FSA (homogeneous filter FSA) has the same states as the coordinate FSA with a different definition for some states. In addition, the X-ray visualization FSA is defined. Further, the profile provides some use case scenarios e.g. coordinate motion between the defined limits, changes of the SID (source image distance) value, etc. The CiA 412-2 pre-defines one RPDO containing the collimator command and the target x-y-position value as well as one TPDO providing the collimator state and the actual x-y-position value.

Injector state machine; FSA (finite state automaton) (Source: CiA)

The CANopen dose measurement system (CiA 412-6) measures the X-ray dose and the dose area product. In addition, the dose area product rate, dose rate, RD (reference distance) entrance/skin dose, RD entrance/skin dose rate, MD (measured distance) entrance/skin dose, MD entrance/skin dose rate, irradiation time, chamber temperature, as well as the air pressure values are measured. The actual measured values (called field values) are converted to values with a real physical dimension (called process values). The profile specifies all required objects to fulfill this conversation and to represent the mentioned values in a standardized manner. Additionally, CiA 412-6 introduces an FSA for the dose measurement systems.

The profile defines one RPDO and two TPDOs respectively transferring the control word (RPDO1) and the status word (TPDO1) as well as the current process value (TPDO2). Profiles for X-ray generators (Part 3), patient tables (Part 4), and X-ray stands (Part 5) are also intended in the future. Nowadays, many of the medical device suppliers use CANopen as embedded network for different purposes in X-ray machines, in computer tomography, and angiography. This includes United-Imaging Healthcare, a Chinese CiA member, which has equipped its products with CANopen networks to integrate devices from several suppliers, especially motion controllers and I/O modules.

If you would like to read the full article, you can download it free of charge or you download the entire magazine.

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