3.1 Advantages of beagles as animal models
Animal models are an indispensable in medical research, especially for operations with trauma or uncertain safety, which therefore cannot be directly carried out on the human body in clinical research. Thus, using an animal model to carry out preliminary research to verify safety and efficacy is the best choice. The Beagle breed is the only standard experimental canine recognized in the world because of its gentle temperament, stable genetic gene profile, repeatability of anatomic structures, and stable physiological index. Compared with rats and other small experimental animals, the Beagle canine is closer to human in the research model of skeletal and blood vessel structure, which is critical for comparison of research results.
In the study of scoliosis, Hou et al. observed that the Beagle animal model was close to clinical cases, and obtained typical scoliosis performance when establishing a scoliosis model, which completely achieved the purpose of simulating clinical scoliosis, and the modeling operation was simple, the success rate was high, and the damage to the accessory structure around the spine was minimal.
Li et al. used the Beagle canine model in the study of hip joint stress by fixing one side of the forelimb, and then increasing the load of the hind limb of the canine in order to simulate the load-bearing walking state of the human. Three-dimensional gait analysis was conducted to show that the changes of the mechanical parameters of the hind limb of the Beagle conform to the biomechanical changes of the human hip joint. The study highlights that the Beagle animal model is used to study the related diseases of the human hip joint.
Kim et al.[9-10] studied a new type of internal fixation materials, and found that the bone shape and specification of Beagles are close to the human body, and therefore can be used to test standard size screw and steel plates. Furthermore, they found that the Beagle has a muscle strength load that can reach that of a human, and approximates well the stress simulation and stability.
In the research field of osteonecrosis of the femoral head and revision of the hip joint, Omoto et al.[11-12] put forward that the hip joint and surrounding tissue of beagles are suitable for human body simulation. They claim the modeling operation is simple, the success rate is high, the imaging examination results are clear, the local bone mineralization rate after operation is similar, and the biological consistency is good. In a follow-up osteotomy experiment in this study, Beagles served as a more satisfactory bone model than small animals, so as to better recapitulate simulation and visualization of the operation.
The author’s opinion is that compared with sheep, orangutan and other animals, beagles are the best animal model for this field of research, particularly for better representing operation procedures and mimicking skeletal, nervous and vascular structures.
3.2 Operation and interference factors of DSA
DSA is a combination of angiography and computer technology. It refers to the contrast agent scanning and developing of X-ray, by digital processing, which removes unnecessary tissues from the image, and finally presents a clear vascular morphology. At present, DSA technology mainly includes step-by-step technology and segmentation technology. The step-by-step technology realizes the acquisition of a complete image and a dynamic image by controlling the movement and exposure of the working bed, while the segmentation technology is to inject the contrast agent and collect the image iteratively; the step-by-step Technology has the advantages of low contrast agent consumption and short exposure duration. The technique used in this study is step-by-step technique for DSA.
DSA is regarded as the "gold standard" for the diagnosis of vascular diseases internationally, especially in the diagnosis and treatment of peripheral arterial diseases, such as diabetic foot and lower extremity arteritis. Accurate angiography of arterial circulation is an important basis for diagnosis, reconstruction of blood circulation and prognosis [14-16].
Yoshinori et al.  performed DSA of the hepatic artery for the diagnosis and treatment of liver tumor diseases. Due to its good imaging quality, we can clearly observe the morphology of the hepatic artery and its branches, the morphology and number of proliferative vessels in a tumor, which provides a more intuitive treatment support for tumor tissue disconnection and final resection.
Blagojevic et al. [18-20] highlighted the clinical diagnosis, treatment and research of lower extremity artery disease that DSA technology can accurately reflect its blood circulation and define the location of disease occurrence and accumulated tissue area. These capabilities play an indispensable role in the formulation of treatment plans, even in the case of amputation, since DSA can provide a more reliable reference standard, thus reducing the amount of amputation, allowing as much limb function to be preserved as possible.
In the study of animal models, McCollough et al.  performed contrast examination on beagles’ hearts by injecting contrast agent into the central vein. According to the density of the contrast agent before and after the same cycle and the volume difference, the volume and ejection fraction of the ventricles can be quantitatively measured. The author pointed out that DSA technology has the advantages of objectivity, simple operation and repeatability.
Anesthesia and contrast agents are the two most important factors affecting the final image quality of DSA.[22-23] When DSA is performed, it is required that the examinee keep absolutely static relative to the working bed. Good anesthesia can play a role of sedation and analgesia, and ensure smooth operation. A large dose of anesthesia will lead to deep inhibition or even death of the canine, so that normal and effective observation images cannot be obtained. However, a shallow degree of anesthesia will lead to shaking of the canine due to pain stimulation during operation, resulting in mobility artifacts affecting the image quality. In this study, 1 ml of intramuscular anesthesia with 1:1 ratio of Shutai and shumianxin II was used. The degree of anesthesia was appropriate, and the effective time of anesthesia was about 40 min, which could meet the smooth operation.
The influence of contrast agent on the image quality of DSA mainly includes the concentration, dose and flow rate. Too high of a concentration will cause shaking and artifacts due to the stimulation of blood vessels in canines; too low concentration will cause poor development of small blood vessels. In this study, the contrast agent used was lipanol injection (300 g / L). During the initial operation, the contrast agent was not diluted, resulting in the irritant shaking of the hind limbs of the canine during the injection, and the quality of the collected image was therefore poor. Afterwards, the concentration was diluted by a ratio of 2:1 between lipanol and normal saline, and there was no obvious shaking in the operation of the canine, and the collected image also met the experimental requirements. In addition, proper flow rate is also an important factor to ensure the image quality. For example, if the flow rate of contrast medium is too slow, it will be diluted by the high-speed arterial blood in the artery; and if the flow rate is too fast, it will cause huge pressure on the blood vessel, and even cause the rupture of the blood vessel. In this study, 30 ml syringe was used for manual injection, and the diluted 30 ml contrast agent was pushed into the artery at a constant speed within 10 seconds, with an average flow rate of about 3 ml/s. During the operation, the flow of contrast agent in the artery was tracked and captured well, and the quality of the collected image was satisfactory.
In this study, a 18 G vein indwelling needle instead of a catheter can directly puncture the femoral artery through the skin, which avoids the process of crossing the iliac artery in the routine operation. This approach has minimal stimulation and damage to the blood vessel, is convenient to operate, and saves a lot in cost; but in the process of puncture,The first beagle shook when administered with the bolus of contrast agent, resulting in a poor quality angiographic image. To obtain high quality images, the canine limbs were fixed in position and a diluted concentration of the contrast agent was used. We should master the puncture tool, adjust the concentration of contrast agent and control the injection speed of contrast agent to avoid possible massive bleeding and Beagle tremor. It should be noted that there is a risk that the success of the experiment will be affected by the accidental removal of the needle. The image obtained by this method shows the shape of blood vessels clearly, the display of small blood vessels is good, and the image quality completely meets the requirements of research and design. In addition, all dogs in this study had three repeated arteriography over a two month period, with good repeatability. At the same time, some shortcomings in this experiment can also provide reference for this kind of experimental study.
Beagle, as the only standard experimental canine breed, provides ideal conditions for disease models and is a very suitable for large animal experiments. The DSA has a clear effect in the angiography of the canine's lower extremity artery. It can display the shape and density of the lower extremity artery very clearly, and the image quality can fully meet the experimental requirements, and recapitulates well the simulation research and operation of similar diseases. Moreover, the DSA technology is simple in operation and repeatable, and thus can be used to simulate the lower extremity artery diseases in canines. The verification of related theories is of great significance. However, appropriate measures should be taken during preoperative preparation, intraoperative anesthesia and immobilization, contrast agent control and image processing to ensure the quality of the final DSA image meets the experimental requirements.