A CT scan makes use of computer-processed combinations of many X-ray measurements taken from different angles to produce cross-sectional (tomographic) images (virtual. Cone beam computed tomography (or CBCT, also referred to as C-arm CT, cone beam volume CT, or flat panel CT) is a medical imaging technique consisting of X-ray. Three- dimensional imaging techniques: A literature review. Abstract. Imaging is one of the most important tools for orthodontists to evaluate and record size and form of craniofacial structures. Computed tomography (CT) CT imaging, also called computerized axial tomography (CAT) imaging, uses special X-ray equipment to generate cross-sectional images of the body. · Intensity modulated radiotherapy (IMRT) is widely used in clinical applications in developed countries, for the treatment of malignant and non-malignant. Orthodontists routinely use 2- dimensional (2. D) static imaging techniques, but deepness of structures cannot be obtained and localized with 2. D imaging. Three- dimensional (3. D) imaging has been developed in the early of 1. The aims of this literature review are to summarize the current state of the 3. D imaging techniques and to evaluate the applications in orthodontics. Keywords: 3. D imaging, 3. D scanning, orthodontic diagnosis, treatment planning. INTRODUCTIONOver the years, orthodontic and dentofacial orthopedic diagnosis and treatment planning have relied essentially upon technological and mechanical supports such as imaging, jaw monitoring, and functional analyses. The goals of these techniques are to replicate or describe the anatomic and physiological facts exactly and to display the three- dimensional (3. D) anatomy precisely.[1]Imaging is one of the most important tools for orthodontists to evaluate and record size and form of craniofacial structures.[2] Orthodontists routinely use 2- dimensional (2. D) static imaging techniques to record the craniofacial anatomy, but deepness of structures cannot be obtained and localized with 2. D imaging. 3. D imaging has been developed in the early of 1. In 3. D diagnostic imaging, a series of anatomical data is gathered using certain technological equipment, processed by a computer and later showed on a 2. D monitor to present the illusion of deepness.[3]Facial soft and hard tissues and dentition are 3 main sections, also named as triad, in orthodontics and orthognatic surgery.[4] The triad has a significant function in planning of orthodontic treatment. Therefore, imaging of these structures is one of useful diagnostic tools for clinicians to make decision treatment modality.[5] 3. D imaging for orthodontic purposes contain pre- and post- treatment evaluation of dentoskeletal and craniofacial relationships and facial appearance and beauty, inspecting treatment results in terms of soft and underlying hard tissues, and 3. D treatment predictions. D dental, facial, and skeletal records for making diagnostic decisions and planning treatment are the other benefits of using 3. D imaging in orthodontics.[6]A large number of diagnostic methods have been developed to display facial structures and the dentition,[7,8,9] most of which were abandoned due to their various drawbacks. The most popular method of current medicine is possibly 3. D imaging techniques giving detailed and problem- oriented information about soft and hard tissues, such as Computerized Tomography (CT), Cone Beam Computerized Tomography (CBCT), Micro Computerized Tomography (MCT), 3. D laser scanning, structured light technique, sterophotogrametry or 3. D surface imaging systems (3d. MD), 3. D facial morphometry (3. DFM), Tuned- Aperture Computed Tomography (TACT), and Magnetic Resonance Imaging (MRI).[1. The aims of this literature review are to present current state of the 3. D imaging techniques and to evaluate the applications in orthodontics. HISTORICAL BACKGROUNDIn 1. X- rays by W. C. Roentgen opened a new era in medicine and dentistry. Thirty- six years later, standardized methods for the production of cephalometric radiographs were introduced to the dental specialists by Broadbent and Hofrath simultaneously and independently,[1. Broadbent emphasized the importance of the position and distance arrangements to achieve distortion- free radiographs when taking the lateral and posteroanterior cephalometric radiographs.[1. Cephalograms have been widely used in clinical implementations and as an investigation technique to evaluate growth and treatment responses. However, there are several disadvantages of 2- dimensional cephalometry as a scientific method. The fact that a conventional head films reduce 3. D objects to 2- dimensional view is first and the most important reason. When 3. D objects are displayed in a 2- dimension, structures displace as vertically and horizontally in proportion to their distance from the film.[1. Secondly, cephalometric analyses are based on an excellent superimposition of the left and right sides at mid- sagittal plane, but such superimposition is rarely observed because facial symmetry is infrequent. Third reason is that manual data collection and processing in cephalometric analysis have been shown to have low correctness and precision.[2. Finally, major errors in cephalometric measurements are associated with uncertainties in locating anatomical landmarks due to the deficiency of well- defined outlines, hard edges, and shadows as well as patient position.[1. Beside these limitations, lots of cephalometric analyses have been developed to help diagnose skeletal and dental malocclusions and dentofacial deformities.[2. The quantitative errors associated with traditional 2. D cephalometry have been substantial enough to make orthodontic diagnosis and treatment planning.[1. Following the introduction of 3. D imaging, clinicians have had great opportunity to evaluate anatomic structures 3- dimensionally in orthodontic practice. Several investigators conducted 3. D imaging researches, and Singh and Savara[2. D analysis about growth changes in maxilla. Computer softwares helped to collect and analyze 3. D coordinates directly from digital cephalometric images, so that tracing manually and digitizing with mouse on screen were abandoned.[3. D imaging technique has been improved to use in different areas of health sciences. Being improved old photogrammetric techniques, stereophotogrammetry has been introduced to provide a more extensive and accurate assessments of the captured things. Using one or more converging pairs of views, a 3. D model can be constructed and monitored from any perspectives and measured from any directions. In 1. 94. 4, Thalmann- Degan recorded facial differences after orthodontic treatment. This was the earliest clinical report about stereophotogrammetry.[2. Computerized stereophotogrammetry has come into market as parallel to computer developments and has provided faster, more comprehensive and correct taking and constructing sequences.[3. The first CT scanning device was developed around 4. After a short time, a stack of CT sectional images was used to obtain 3. D information. At the beginning of 1. D imaging in craniofacial deformities. For craniofacial surgical needs, first simulation software was introduced in 1. Then, the principles and applications of 3. D CT- and MRI- based imaging in medicine were published. A specific discipline was established on 3. D imaging, dealing with different types of imaging, manipulation, and analysis of multi- dimensional medical structures.[3. D IMAGING METHODSComputed tomography (CT)CT imaging, also called computerized axial tomography (CAT) imaging, uses special X- ray equipment to generate cross- sectional images of the body. CT devices are divided into 2 groups: Cone beam and fan beam.[3. Using conventional fan beam CT devices, the X- ray source and detectors with the circular metal frame rotate around the patient. Patients are placed in a horizontal position on a table when CT scanner works. The table slowly passes through the center of a large X- ray machine. The procedure causes no pain, but some tests require a contrast material to make some parts of body appear better in the image. CT scanner works as follows: The patient is moved into circular opening of the CT imaging by a motorized table. When the patient is ready, the operator starts the CT imaging system, and a complete rotation of X- ray source and detector lasts about 1 second. The CT device generates a narrow, fan- shaped beam of X- rays scanning a section of the patient's body. A “snapshot” image was recorded and collected by a detector opposite from the X- ray source. The obtained data are transmitted to a computer for each turn of the scanner and detector. One or multiple cross- sectional images of the body parts were reconstructed. The patient is usually scanned in the axial plane sections taken in succession; the desired image appears when these sections combined. CT can achieve 6. CT at a one time. The system is most expensive because the image is obtained by increasing number of sensors. However, this system can perform in less time and at a low dose shooting.[3. In this technique, due to the sectioning of tissues, organs are not superposed on each other.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. Archives
October 2017
Categories |