This study was approved by the Animal Ethical Committee of Seoul National University Bundang Hospital (code of approval: BA1708-230/075-01) and was performed in accordance with the Guide for the Care and Use of Laboratory Animals from the Institute of Laboratory Animals Resources [16].
Design of the passive robot
The robotic mechanism consisted of a 7-degree of freedom (DoF) passive arm and 1-DoF needle holding assembly as shown in Fig. 1a. The three-dimensional model of the robotic mechanism is shown in Fig. 1b. We employed a 7-DoF commercially available passive arm (MA60003, NOGA Engineering & Technology, Nazareth, Israel). All 7 DoF of the passive arm could be locked at once by locking the knob.
To operate the device without exposing the physician’s hand, a needle holding assembly was designed. The needle holding assembly consisted of a platform, a linear stage for needle insertion, a needle holding aluminium rod, and a roller driving the needle. This device enabled the physician to move the needle easily without exposing herself/himself to x-rays. After positioning the needle to the target blood vessel, the roller could be operated at different configurations to give the physician ease in manoeuvring the needle tip.
The linear stage provided forward and backward motion. Needle holding aluminium rod was attached to the linear stage. The hub of the needle was attached to the needle holder assembly by bolts in such a way that the needle remained fixed to the holder during the interaction of the needle with the skin. The needle holder was designed in such a way so that different types of needles can be attached to the holder. Two sideways bolts for needle attachment also helped the physician in accurately aligning the needle to the targeted blood vessel during fluoroscopy-guided arterial puncturing. The third bolt tightened the hub of the needle firmly. For the insertion of a guidewire tool in the hub of the needle, a small groove had been carved out inside the needle holder assembly (Fig. 2). The guidewire was inserted inside the tool. The guidewire insertion tool was designed in such a manner that it would not allow the flexible end of the guidewire to bend. Buckling of the flexible tip of the guidewire could be avoided if the tip of the guidewire insertion tool was inserted properly into the hub of the needle. When the needle was inserted to the targeted blood vessel, blood came out from the hub, indicating the proper insertion of the needle tip. After the insertion of the guidewire, the needle could be removed easily by retracting the 7-DoF passive articulated arm. The base of the device was designed in such a way that it could be easily attached to the patient’s bed with the help of a clamp. It could also be attached to the table next to the bed according to the ease of the physician.
Figure 3a shows the position of the operator’s hand without the device while Fig. 3b shows the position of the operator’s hand with the device. The use of the device allowed the operator to keep his hand away from the x-ray source.
Animal preparation
The day before the experiment, male crossbred swine (n = 15; weight, from 17 to 35 kg) were fed with aspirin (300 mg) and clopidogrel (300 mg). On the experiment day, the swine were premedicated with atropine sulphate (0.05 mg/kg, intramuscularly) and subsequently anaesthetised with Zoletil (5 mg/kg) and Xylazine (4.4 mg/kg) intramuscularly, intubated, and ventilated with room air and isoflurane. We inserted a 6-Fr sheath via the right carotid artery by ultrasound-guided puncture. The animals received heparin (5000 U) intravenously prior to femoral artery digital subtraction angiography.
Fluoroscopy-guided femoral arterial puncture
A total of 30 fluoroscopy-guided punctures were performed, 15 using the robotic device and 15 without the device by an interventional cardiologist with a 10-year experience, targeting both femoral arteries in the 15 pigs. The mobile fluoroscopy system was Philips BV Pulsera (Philips Medical Systems, Bothell, USA). We selected both femoral arteries with a diagnostic catheter (Judkins right 4, Gifu, Japan) via the right carotid artery and performed angiography to guide the femoral puncture using the Seldinger technique.
Details on the use of the passive robotic device have been described in the previous section describing the design of the passive robot.
Measurement of radiation exposure
The radiation dose was measured using dosimeters that were attached to the different unprotected parts of the operating physician (Ray 3000, Kedian, Jining, China), and was used to measure the radiation. The dosimeters were attached to the dominant hand, dominant arm, and head of both the operating physician and the assistant animal technician (nurse). In this study, all the dose rates were measured in mSv per hour.
Two parameters were selected to analyse the effectiveness of the device: the success rate of the insertion procedure and the complication level, the latter including three sub-categories which were haematoma (collection of blood outside the vessel); dissection (tear of the vessel wall, which allows blood to separate the wall layers); and occlusion (a blockage of the vessel, usually by a clot or a severe dissection).
Statistical analysis
Continuous variables were described as mean ± standard deviation (SD), taking into consideration their normal or near normal distribution, confirmed by Shapiro-Wilk test (p = 0.9003). As a consequence, the comparison between the means of the two groups was evaluated by Student’s t test. A two-sided probability value of < 0.05 was considered indicative of a statistically significant difference. The success rates were presented as percentages with their 95% confidence intervals, calculated according to the binomial distribution. Statistical analysis was performed using R program version 3.1.0.