Abstract: A remote control product for reagent dispensing, dilution, and preparation based on an industrial control computer was developed. This product is particularly suitable for the dilution and preparation of radioactive reagents. It utilizes a pneumatic device and a stepper motor with precise control to drive a peristaltic pump to complete the transfer, dilution, and dispensing of reagents. The remote operation capability of the industrial control computer overcomes the radiation hazards to operators in traditional manual radioactive reagent dilution and preparation operations. Methods such as overall calibration and liquid deviation processing ensure accurate measurement. Practical application results show that the system is characterized by low pollution, high efficiency, and high precision, meeting the requirements of practical applications.
Keywords: reagent dilution; preparation; radionuclides
1. Introduction
With the development of society, medical imaging, industrial flaw detection, nuclear scales, level gauges and other radiation devices and radionuclides have been continuously applied. Radiation technology is increasingly widely used in all walks of life, and the number of radiation workers has increased accordingly. Doing a good job in radiation protection and preventing and controlling the hazards of occupational diseases has become an important direction for the development of medical equipment[1].
Although radionuclide diagnostic and therapeutic technologies are widely used in clinical medicine, the dilution and preparation of radionuclide sources, both domestically and internationally, are still primarily done manually. This results in low precision in radionuclide dilution and dispensing, affecting diagnostic or therapeutic outcomes and potentially causing unnecessary harm to patients. Furthermore, medical personnel engaged in radionuclide dilution and dispensing are exposed to radiation for extended periods, causing significant health damage. Therefore, there is an urgent need for equipment capable of remote and precise dilution and preparation of radionuclides.
2. System Hardware Components
To meet the needs of drug dilution and preparation, we developed this system. The system hardware mainly consists of mechanical actuators and an electrical control system.
2.1 The mechanical actuator includes an air source, a robotic arm, a cylinder, a needle assembly, a peristaltic pump, etc. (as shown in Figure 1).
This system partially uses a high-pressure air source as power to drive each cylinder to complete the action of moving the medicine source. The cylinder movement is a two-position operation, which is characterized by simple operation, less risk of jamming due to gear and lead screw transmissions, and small wear and movement error.
The drug transfer process mainly consists of several parts: cap removal, needle insertion, liquid transfer, and return to the designated position. After the drug source, along with its protective bottle, is placed on the work platform, a robotic arm, driven by a cylinder, grasps the protective bottle cap. The work platform then moves to its final position. Since the completion of this step is crucial for subsequent processes, a position sensor is used for confirmation. Once the drug source bottle is in position, the needle assembly, driven by a cylinder, descends and inserts the needle into the bottle. This needle assembly, specifically designed for this system's drug transfer, consists of high and low-position dual-needle assemblies. The solvent used for dilution is pumped in through the high-position needle orifice by a peristaltic pump, increasing the pressure inside the bottle and forcing the drug out. As the transfer process continues, the concentration of the drug solution in the bottle gradually decreases, effectively flushing the bottle and ensuring complete drug transfer.
The liquid dispensing mechanism of this system is a peristaltic pump. Its dispensing accuracy depends on the step distance of the pressure roller and the inner diameter of the latex tubing. The step distance is determined by the step angle of the stepper motor and the outer diameter of the pressure roller. The peristaltic pump motor is a two-phase four-step stepper motor with a step angle of 0.9°. The latex tubing is a high-wear-resistant latex tubing with an inner diameter of 0.5 mm. The outer diameter of the pressure roller in the peristaltic pump head is 45 mm. Therefore, its accuracy is approximately 0.278 mm³, which is far higher than the accuracy requirements for dispensing oral radionuclides in medical applications. During the drug transfer process, the system automatically calculates the required amount of solvent based on the concentration requirements and the input drug source information, thereby determining the appropriate amount of solvent to be pumped in by the peristaltic pump.
This dispensing device has two sets of radiation-proof lead containers, used for the preparation and storage of high- and low-concentration drug solutions, respectively. The high-concentration solution is prepared by mixing the drug source (pressurized from the drug source bottle) with the solvent pumped in by a peristaltic pump. The low-concentration solution is prepared automatically by the industrial control computer based on the original data and entered preparation requirements. The low-concentration solution uses the high-concentration solution as the stock solution; the required amount of solvent is calculated by the system and pumped in by the peristaltic pump. After each injection of a certain dose, the solenoid valve at the front end of the peristaltic pump switches to allow air to be introduced, pumping out a portion of the tubing and any remaining liquid in the drug source bottle.
Figure 1 System structure diagram
2.2 Electrical Control Section
The electrical control section of this system consists of an industrial computer system and a drive control board, as shown in Figure 2. The industrial computer and the sub-assembly system are located in the control room and the sub-assembly room, respectively, about 15 meters apart, and use ribbon cables, twisted-pair cables and coaxial cables for signal transmission.
Figure 2 Circuit control schematic diagram
The industrial control computer system consists of an industrial computer and various control cards. The MPC01 control card, based on the ISA bus, is the upper-level control unit for the stepper motors. It forms a master-slave control structure with the industrial computer. The industrial computer manages the human-machine interface and controls various system operations, while the MPC01 control card handles the detailed tasks. Each MPC01 control card can control three-axis stepper motors and supports multiple cards sharing. It can also connect external position, speed, and limit signals to achieve functions such as position detection and protection. Various switch signals are automatically detected and responded to by the MPC01 control card. The MPC01 control card has a powerful motion function library, allowing users to easily perform secondary development using C/C++ or Visual Basic programming languages. This system uses three two-phase four-step stepper motors, each equipped with one MPC01 control card.
The PCL724 digital I/O card has 32-bit digital output and 32-bit digital input. This system uses its digital input/output ports to control relays via opto-isolation [2].
An incremental photoelectric encoder is used to provide speed feedback on the movement of the peristaltic pump and to detect the movement of the stepper motor.
The SDK-2000 video card is a high-speed video acquisition unit based on the PCI bus. It provides two video signal inputs simultaneously and features a rich library of DLL dynamic libraries, OCX controls, and function libraries, allowing for easy secondary development using programming languages such as VC or VB. This system uses cameras to monitor the drug transfer process to ensure accuracy. Due to the need for panoramic monitoring of the drug distribution room, an external camera is installed for monitoring drug dispensing and administration. The system uses two cameras in total. Considering the system resources and cost of the microcomputer and the need for dedicated system addresses and interrupt numbers for each card, only one video card is used. Image display is controlled by the digital output of the PCI-724 card, which controls the corresponding relays for display conversion. The terminal control unit includes a stepper motor driver, position switches, various control relays, and a video head. The stepper motor driver subdivides and assigns phase sequence to the pulses from the microcomputer system and amplifies the current to drive the stepper motor. The position switches limit the movement of parts, providing protection.
3. System Software Design
The software of the automatic dispensing instrument mainly includes several parts: drug source transfer, dilution, dispensing of high and low concentration drug solutions, and database management. The basic structure of the software is shown in Figure 3.
The software uses the DDL dynamic link library and various functions provided by the board manufacturer to implement the design of the automatic packaging device using the Visual C++ programming language [3].
Figure 3. System main functional structure block diagram
During the preparation of high-concentration solutions, the program controls the robotic arm and cylinders to move sequentially, achieving functions such as opening the lid, shifting the worktable, inserting the needle, and automatically calculating the required solvent volume based on drug source information and the concentration requirements input by the operator. This calculation is then converted into a control signal to control the peristaltic pump, directly pumping the drug into the radiation-proof lead container to prepare a high-concentration solution for treatment. The preparation process simultaneously displays data information within the concentrated drug solution lead container and the current volume of solvent pumped in.
The dilution process automatically calculates the required volume of high-concentration solution and the required amount of solvent based on the operator's input of the desired radioactivity level and concentration, taking into account the remaining amount of drug in the lead container at the current concentration. The software then controls the corresponding peristaltic pump to dispense the solution. Due to the decay of the radionuclide, the remaining amount of drug is automatically recalculated based on the half-life of the selected radionuclide, and the displayed values are all the current values after decay.
The database for this control system is an Excel spreadsheet. Database management primarily involves patient data management, including the entry, modification, deletion, and querying of basic patient information; and medication information management, including the current dosage of medication in radiation-proof lead containers and the amount after decay. We closely integrate the database with commonly used operations to record each patient's medication usage and print the patient's medication order immediately. In addition, the system also records the use and transfer of radioactive nuclide solutions in detail, serving as documentation for law enforcement agencies.
The system calibration section is directly related to the accuracy of dispensing and dilution, and is an important part to ensure accurate measurement. Since the stepper motor step distance is proportional to the amount of medicine pumped out by the peristaltic pump, the pumping amount per step distance can be used for measurement. However, since the pumping amount per step distance is difficult to obtain accurately, and the output of tens of thousands of control pulses will amplify this error, this system calibration adopts an overall calibration method, that is, the average step distance output is calculated based on the large dose output, which can be used for more accurate measurement. This system uses a closed pipeline to deliver the liquid medicine or solvent. Liquid medicine is only output after a certain amount of air is pumped out of the pipeline, resulting in a certain offset. The length and inner diameter of the pipeline determine the magnitude of this offset. The calibration process uses large-dose testing and average step output to determine the offset. After initially determining the offset, the test program is run to adjust this offset, with the critical dispensing value used as the final offset value. Error handling addresses the residual drug in the pipeline by taking measures to ensure accuracy. Reverse evacuation of the pipeline ensures the same offset each time. Due to the surface tension of the water film inside the pipeline, the water will re-aggregate into a small column after evacuation. Repeated evacuation significantly reduces error. Through these measures, actual testing shows that the error for small-dose dispensing (1-3 ml) is approximately 2%, and the error for large-dose dispensing is approximately 1%.
4. Conclusion
This automated dilution and preparation system employs technologies such as remote control via industrial computer, precision peristaltic pump liquid dispensing control, and radiation shielding. It solves problems related to radiation contamination, radioactive irradiation, and inaccurate metering during the dispensing of radioactive nuclides. The use of cylinders and peristaltic pumps greatly simplifies the mechanical structure, making the system safer and more reliable. It achieves the following functions:
(1) Transfer and repackaging of drug sources, and inputting product information of drug sources into the database.
(2) Automatic conversion of radiopharmaceutical dosage and display of remaining drug information.
(3) Preparation and dilution: High and low concentration solutions can be prepared and stored simultaneously according to different needs. The concentration can be set arbitrarily as needed.
(4) Video monitoring and intercom functions.
(5) Safety protection and fault handling functions: The drug solution of this system is diluted and stored in a 3.5cm thick radiation-proof lead container to prevent radionuclide contamination of the environment. Remote control is used to keep operators away from radiation sources; the mechanical mechanism is sequentially locked to reduce misoperation; and possible accidents during operation are judged and corresponding fault handling is performed. Fault handling can also be carried out under manual intervention.
(6) Automatic cleaning function of the system: The system can clean the pipelines and vessels when there is no medicine in the two radiation protection tanks, so as to reduce cross-contamination of different solutions.
Tests show that the dispensing system has good safety protection performance, high degree of automation, simple operation, high dispensing accuracy, and complete functions. It is a pharmaceutical dilution and preparation system suitable for practical requirements.
The author's innovation lies in developing an intelligent device with completely independent intellectual property rights that can meet the requirements of dilution and preparation of hazardous drugs by utilizing modern robotic arms, pneumatic machinery, precision peristaltic pumps, and industrial control computers. This device enables automatic opening of the lid by the robotic arm, drug dilution and preparation under sealed conditions, and batch preparation of drugs, solving long-standing problems in the dilution and preparation of hazardous drugs such as highly toxic pollution, radioactive irradiation pollution, and inaccurate measurement.
This system can be used for single-dose and batch dilution and packaging of hazardous agents (highly induced, highly toxic, and radioactive), and is also suitable for the packaging of ordinary pharmaceuticals and chemical agents. Regarding the dilution and packaging of hazardous agents alone, there is a demand for this product from approximately 3,000 hospitals and over 300 biological research institutes nationwide. If the device is priced at 100,000 yuan with a 30% profit margin, and if more than one-tenth of these institutions (over 330 institutions) purchase one unit each, the resulting output value would be nearly 33 million yuan and the profit 9.9 million yuan.
References
[1] Li Qiang, Wei Zengquan. Application of radionuclides in biomedicine. Nuclear Technology, 2002, 25(1): 71-77.
[2] Lü Xiafu, Luo Qinlin. Automatic dilution and source separation system for radioactive isotopes. Medical and Health Equipment 2004, 6: 23-25.
[3] Liu Fucai, Zhang Hailiang. Design of a Modem Distributed Remote Monitoring System Based on VC. Microcomputer Information, 2006, 9-1: 100-103.
