The use of micro-computed tomography in the diagnosis of dental and oral disease in rabbits
© Sasai et al.; licensee BioMed Central Ltd. 2014
Received: 18 September 2013
Accepted: 28 August 2014
Published: 5 September 2014
The aim of this study was to investigate the use of a newly developed micro-computed tomography (micro-CT) system for the diagnosis of oral pathologies in small animals, using the rabbit as a model. The diagnosis of dental diseases in rabbits is usually based on oral endoscopy and radiographic imaging, but detailed pathological diagnosis using these methods is frequently difficult. Micro-CT was used in this study to address this challenge.
This study was conducted using 50 privately owned rabbits, presented to our hospital due to loss of appetite or difficulty feeding. Image recording times were 18 s in normal mode and 120 s in fine mode. The animals were maintained in the required position for scanning via the administration of sedatives. Micro-CT captured with a slice thickness of 60-120 mm has excellent spatial resolution, and is suitable for the clinical diagnosis of dental diseases in rabbits weighing 1-3 kg.
Micro-CT can yield more detailed data than radiography or conventional CT. This study determined that this novel imaging modality can be utilized for the accurate assessment of dental and oral diseases in rabbits.
Dental diseases and associated complications, including apical abscesses of the maxilla and mandible, are common in pet rabbits. These conditions can become quite severe, leading to a loss of the ability to feed, and even death if left untreated . In rabbits, the diagnosis of dental diseases is based on clinical signs and symptoms, oral endoscopy, and radiography of the head ,. Radiography is a useful diagnostic modality in rabbits suspected of having dental diseases. Due to superimposition, making an accurate diagnosis requires multiple radiographic projections .
Micro-computed tomography (micro-CT) has remarkable space resolution, and a shorter capture time than cone beam computed tomography (CBCT). By coupling it with highly developed image reconstruction technology, it is possible to actively conduct imaging examinations in laboratory animals and other small animals . CBCT has been used in the image-based evaluation of medical conditions in dogs and cats , and in anatomical studies on rabbits and guinea pigs ,-. In most cases, its clinical applications have been limited by low resolution, or an excessively long image processing time -.
Radiographic evaluation of the skull, teeth, and soft tissues of the head requires capturing multiple images from various angles. Endoscopy is limited to the crowns. Not all types of CT imaging require the use of various positions, as is the case with radiography. The shortest possible implementation time is 18 s, and the time needed for image reconstruction is 1 minute. Thus, image reconstruction can be performed while scanning, reducing the overall time required for scanning, image processing, and performing the assessments required for diagnosis.
With each owner’s consent, micro-CT was used while performing clinical examinations and prognostic evaluations of 50 rabbits (mean age 4.7 ± 2.6 years), which were presented to our clinic due to loss of appetite or difficulty feeding, resulting from dental diseases. The study included 36 males and 14 females, and the breeds presented included Netherland dwarfs (n = 8), Holland lop-eared rabbits (n = 8), mini-rabbits (n = 10), and other breeds (n = 24). The diagnoses included mandibular abscesses and osteolysis (n = 24), maxillary tooth root growth lesions (n = 11), excessively long molar apices (n = 12), excessively long molar crowns (n = 25), excessively long incisors (n = 5), periapical infection of incisors (n = 4), maxillary abscesses (n = 4), and orbital abscesses (n = 3).
CT device and image acquisition conditions
An X-ray tube with 5-μm focus and a 2-dimensional (2D) flat panel detector was used to acquire 512 slice images, in a cylindrical range with a diameter of 60 ± 60 mm or 73 ± 60 mm in 18 s with one rotation of the rotating arm. In whole-body scan mode, 512 ± 2 slice images were acquired in a cylindrical range of 60 ± 120 mm or 73 ± 120 mm. These were used as appropriate for the size of the rabbit’s skull.
CT images (minimum: 10 mm pixel) were visualized with the number of pixels set to 512 × 512 × 512 (voxel = 10 × 10 × 10 μm) where the imaging time was 18 s, or 512 × 512 × 512 (voxel = 100 × 100 × 100 μm) where the imaging time was 120 s. Volume data was obtained from a cylindrical area 73 mm in diameter and 60-120 mm based on the height of the animal. For animals scanned under anesthesia, the scanning plane was vertical because complete positioning was possible. The acquisition of micro-CT images does not require a vertical plane however, so we were able to perform the procedure without anesthesia in cases where the animal’s behavior was conducive to doing so and the scanning time was 18 s.
We modified a previously reported approach to micro-CT used in laboratory guinea pigs and rats -, to perform the diagnostic evaluations of the pet rabbits in this study. Notably, since it is equipped with software that synchronizes images with respiration, as well as 2 and 3-dimensional (2D/3D) image processing software, the device is extremely easy to use -.
The 3D images clearly depicted alterations and deformities in the upper jawbone and teeth, as well as the absence, excessive length, or curvature of premolars and molars, and facilitated determination of the 3D positional relationship.
Rabbit oral cavity pathology as observed by endoscopy and micro-CT imaging
Endoscopy revealed traumatic ulcers in the buccal mucosa. Accurate diagnosis by endoscopy requires positioning using a suitable device in conjunction with sedation, and is thus associated with an anesthetic risk. In contrast, it is often possible to use micro-CT to capture images without anesthesia.
Our findings demonstrated that the micro-CT approach used in this study can be utilized for diagnosis in clinical settings. The equipment facilitated the collection of accurate data, as well as a rapid image processing time and reconstruction time (approximately 1 minute). Because the micro-CT device allows for reconstruction of images derived from slice image data with pixel sizes ranging from 120 μm2 to 150 μm2, the images are precise, and objects are very clear in comparison to those from conventional CT. The same performance has also been achieved with the imaging of laboratory animals. ,, While the bone structure and detailed morphological aspects of teeth in rabbits have been difficult to visualize with conventional CT, which is designed for humans, because of the inherently small size of the rabbits’ skull and teeth they are clearly depicted by micro-CT.
In this study, we attempted to compare the diagnostic utility of 2D and 3D images. 2D images allowed for a comparative study of the length, thickness, and curvature angles of teeth via numerical evaluations. These data were obtained by conducting imaging only once, minimizing the animals’ exposure to radiation. However, osteolysis and bone hyperplasia were difficult to identify with 2D imaging, hence we also utilized 3D images. Another advantage of this device is that the images generated are digitally processed in conjunction with every CT scan; consequently, they can be rotated in three dimensions, facilitating an enhanced understanding of the physical presentation of diseases or abnormalities evident in the images.
The excellent imaging capability of micro-CT allowed for the visualization of pathological images associated with diseases specific to rabbits. In the evaluation of each of the individual sites investigated, 2D images enabled the assessment of dentition in the X, Y, and Z-axes on a planar surface, and 3D images enabled the assessment of 3D structure. Thus, the advantages of the micro-CT scanning include the following: (1) Overall assessment of dentition and occlusion, and evaluation of the morphology of the upper and lower jaw, as well as abnormalities in terms of their length and angle (including abnormal angulation against the maxilla/mandible, which can worsen as the teeth continuously grow). (2) Evaluation of deformity, excessive length, and occlusion in the clinical crown. (3) Correlation between the alveolar bone and excessive elongation in the dental apices or deformities of the dental apices. (4) Changes in resorption due to bacterial infection of the dental apex, proliferative changes, fracture-related deformities, and occlusal changes in the upper and lower jaw. Furthermore, the changes identified included dental, skeletal, anatomical, and pathological abnormalities, excessive elongation, and internal and external deviation of the orientations of upper and lower jaw molars, which were difficult to detect by radiography.
The device described in this study allowed for comprehensive assessments via clear imaging of lesions such as those associated with changes in the dental apices and alveolar bones in a variety of disease contexts, including animals with chronic severe diseases. These evaluations can result in more accurate prognoses. The clear image data obtained via micro-CT facilitated the provision of informative explanations to the owners, and was extremely useful with regard to obtaining informed consent for subsequent procedures. Furthermore, the data obtained from the imaging device was useful for educating the owners about the importance of conducting routine monitoring for changes such as a refusal to eat food, spilling of food, reduced amount of stool, drooling, and nasal discharge .
According to Brodbelt et al. , the incidence rates of anesthetic and sedation-related death in healthy animals were 0.05% in dogs, 0.11% in cats, and 0.73% in rabbits. These increased to 1.33%, 1.40%, and 7.37%, respectively, in diseased animals. With regard to rabbits, it has been found that they usually remain still and calm when a net is placed over them in the manner shown in Figure 1. It was possible to acquire most of the images in this study without anesthesia. It was also possible to apply this method to rabbits with reduced cardiopulmonary function and respiratory function, for which death due to anesthesia was a distinct possibility. Also, the methods used were effective in cases where the owner agreed to CT image diagnosis but not anesthesia. Since the risk of adverse events related to anesthesia and sedation is increased in sick rabbits, it is considered an advantage that images could be acquired without anesthesia.
While dental diseases in rabbits develop gradually, we have diagnosed cases in which a failure to treat the condition during the acute phase caused the animal’s condition to deteriorate severely. To avoid such cases, the diagnosis needs to be made as early as possible. The positioning device described in this study is useful to this end, as it can be used to conduct diagnostic procedures while avoiding the risks associated with the use of anesthetics during endoscopic examination of the rabbit’s deep and narrow oral cavity.
Micro-CT can provide new and accurate image data that have not been possible to obtain fully with conventional diagnostic methods, and are important for the definitive diagnosis of significant dental and oral lesions in rabbits. We have determined that tests performed using this device can be utilized to accurately diagnose and elucidate the details of dental diseases in rabbits.
We describe the diagnostic capabilities of a modified micro-CT scanning approach for the evaluation and treatment planning of oral pathologies, including malocclusion and abscesses, in a sample of 50 rabbits exhibiting symptoms consistent with these abnormalities. Our imaging regimen was streamlined, and minimally invasive as described in our “Materials and methods” section. Furthermore, the quality of the scan data we obtained during this investigation permitted differential diagnosis and clinically meaningful resolution of oral malformations that are typically difficult to visualize using methods such as oral endoscopy and X-ray radiography.
This project was supported by the Rigaku Corporation in Tokyo.
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