Submission Date: 2020-07-14
Review Date: 2020-07-25
Pubblication Date: 2020-08-21
The purpose of this article is to compare three Cone Beam CT equipment used for 3D visualization of the foot and ankle, highlighting the advantages and disadvantages of each machine. Cone Beam Computed Tomography provides high resolution (3D) volumetric images with a particularly low dose.
Computed tomography was initially introduced with the advent of implantology, but its use has remained limited to a small number of specialists, due to its indications, access and radiation dose. At the end of the 90s, a new technology that used a conical or pyramidal beam and an alternative detector, which rotates around the patient 360 degrees and acquires the projected data in a single rotation, namely the Cone Beam Computed Tomography (CBCT), spreads in dentistry, making the perception of 3D easily acceptable for dentists and their patients by greatly reducing radiation exposure. The rays are acquired by a two-dimensional detector placed on the opposite side of the object with respect to the X-ray source. A process of data analysis and reconstruction follows, in order to obtain a series of diagnostically valid images on any observation plane. The source can emit continuous radiation during the scan, or pulsed, as occurs in most cases in order to limit the dose administered to the patient. The peculiarity of having a conical beam, instead of a “fan” as in CT tomographs, allows each exposure to cover the entire field of view and therefore in a single turn, instead of several spiral turns, acquire a series of images two-dimensional models of the anatomical part under examination, in the various projections.The CBCT models on the market can be divided into two groups, depending on the technology on which their detector is based: an image intensifier tube coupled with a charge-coupled device (IIT / CCD), or flat technology panel.The IIT / CCD (image intensifier tube / charge-coupled devices) configuration consists of an image intensifier, normally a vacuum tube, coupled to a circuit consisting of a row, or a grid, of semiconductor elements capable of accumulating an electric charge proportional to the intensity of the electromagnetic radiation that hits them. When the device receives a pulse, in this case in the form of X radiation, the vacuum tube converts the radiation into photons and multiplies them by projecting them onto the surface of the CCD. An electrical signal is obtained as a result of which it is possible to reconstruct the matrix of pixels that make up the image even with relatively low radiation levels. The direct flat panel detector instead consists of a scintillator (made of amorphous selenium, cadmium tellurite or mercury iodide) which converts the photon of X radiation into an electron allowing the acquisition and reconstruction of the image. This technology involves stability and memory problems resulting inadequate for the acquisition of real-time images.The indirect flat panel detector consists of a scintillator (normally made of gadolinium oxide or cesium iodide) that converts X radiation into photons concentrated with a matrix of lenses on the photosensor, normally composed of a CCD.Indirect flat panel detectors guarantee qualitatively higher performance and results than IIT / CCD technology.Image intensifiers can create geometric distortions, due to the path of electrons inside the tube, which must be corrected by post-processing software. Otherwise, flat panel detectors are not susceptible to this problem. However, the latter have some limitations due to the not always perfect linearity in response to the incident radiation spectrum, the not always optimal uniformity of the image and the possible presence of the so-called “bad pixels”. However, these defects can be reduced thanks to the frequent calibration of the machine and the help of software that correct the linearity and the presence of bad pixels.CBCT has revolutionized dental diagnostics, but it also finds applications in interventional radiology, in guided image radiotherapy, in mammography, in the study of the lower and upper joints. The present study aims to study three different Cone Beam CT machines for the limbs, especially the foot:
- Planned CT
- CARESTREAM OnSight 3D Extremity System
Methodology and materials
The PedCat is a Cone Beam CT machine that allows the 3D visualization of the foot and ankle under load, useful to provide specialists with the information they need to create complete treatment plans and to evaluate biomechanical spatial relationships and alignment of lower limbs. The patient stands in a completely natural way allowing to see the real physiological changes that occur. The dose is very low: the actual radiation dose of a 3D scan with pedCAT is comparable to a few hours of equivalent background radiation. The effective radiation dose with pedCAT scanning is at most about 6 micro-Sieverts, and the average person in the United States receives an effective radiation dose of around 3000 micro-Sieverts per year from naturally occurring radioactive materials and cosmic radiation coming from space. The scan time is one minute and the pedCAT automatically generates all standard radiographic views in addition to the full CT volume. Standing CT imaging has the advantage of showing specialists fractures, complications of the sole of the foot, thin injuries, flat feet, sprains, arthritis and complications related to diabetes. In addition, based on the diagnostic question, the pedCAT allows you to scan both or only one foot at a time, with the patient sitting (not under load) or the patient in orthostasis under load.
Fig. 1,2 – From left: Ped Cat to patient under load in orthostasis; patient seated not under load.
Planmed Verity CT uses Cone Beam Computed Tomography (CBCT) technology to provide high resolution (3D) volumetric images of the extremities and maxillofacial area with a particularly low dose. It is capable of imaging seated, supine and standing patients and is designed to detect subtle limb fractures on the first visit to the clinic – the types of fractures that are most difficult to find using only 2D radiographs. The Planmed Verity limb scanner is a unique solution to the problem of timely 3D imaging at the point of care. It is designed for pre and postoperative imaging and boasts improved patient resolution and adaptability, as well as a significantly lower radiation dose than full body computed tomography. Unlike other 3D imaging devices, Planmed Verity also allows you to perform limb imaging under load. Compact, autonomous and mobile, Planmed Verity adapts to any existing X-ray room and can easily support other imaging equipment.
Equipped with dedicated lasers for patient positioning and a soft adjustable stand, Planmed Verity offers the patient a versatile positioning and optimized comfort. It has both a fixed and mobile configuration, it connects to a standard wall socket ensuring an integrated workstation with touch screen. CBCT technology provides up to 10 times lower radiation dose than conventional MDCT scanners. The scattered radiation is low; depending on local regulations, protection equivalent to 1 mm Pb is recommended. The Planmed Verity limb scanner can also be equipped with an integrated radiation protection to protect the patient during the scan. Planmed Verity is fully compatible with hospital workstation information systems and software and is therefore a flexible tool for all imaginable work environments.
Fig. 3,4,5 – From left: patient sitting comfortably, patient under load and in the last patient under load resting on support handles.
Fig. 8,9 – From left: maxillofacial imaging and wrist imaging
CARESTREAM OnSight 3D Extremity System ensures an accurate diagnosis of the upper 3D extremities and the lower extremities under load, optimizing both performance and productivity.
- Provides high resolution 3D exams that can show subtle occult fractures that are difficult to see in a traditional CT scan.
- Allows continuous 3D studies to facilitate an accurate assessment of the fracture that heals over time.
- It offers convenient access to the patient and simplifies the work flow thanks to its easy-to-open door thus allowing the execution of studies under load that cannot be performed with traditional CT.
- Allows three-dimensional adjustment of height, inclination and rotation to facilitate patient positioning.
- A secondary monitor allows patients to view scan progress.
- It features an auto-positioning system and a large touchscreen monitor that allow you to work quickly and effectively and a simplified user interface to guide the technician in each exam.
- Improves anatomical and diagnostic visibility thanks to the reconstructions allowing you to also view ligaments and tendons.
- Uses three X-ray sources to reduce artifacts and improve the field of view, to capture the entire area of interest in a single scan.
- Uses advanced dispersion and metal artifact reduction algorithms (CMAR) in order to improve the visibility of the patient’s anatomy and reduce the disturbances given by metal implants.
- Features optional administrative analysis and reporting software to provide a digital dashboard: a centralized management tool for viewing average and maximum exam exposure levels, the number of exams rejected by technology, and more.
- Uses low dose images compared to traditional CT images – while still providing excellent images. Unlike total body CT, only the part of the target body receives radiation. And it is compatible with NEMA XR-29 CT, which provides safeguards for patient radiation safety.
- Advanced algorithms for correcting metal artifacts.
- Isotropic spatial resolution.
- Three X-ray sources and a wide field of view.
- Provides high resolution 3D images.
Results and discussion
The 3 technologies differ from each other by presenting advantages and disadvantages.
The pedCAT has the advantage of offering comfortable access to the patient, and allows the study of both feet at the same time but has the disadvantage of being a machine dedicated only to the study of the foot and ankle.
Planmed CT instead has the possibility of being used for both the lower and upper extremities and for the maxillofacial area. It is equipped with a laser for positioning the patient who can be in the supine position, sitting or in orthostasis. A disadvantage of this machine is the non-opening door, the patient must insert the limb inside the machine and it is possible to study only one limb at a time.
OnSight 3D Extremity System allows the study of the lower and upper extremities and has the advantage of having a door that is easy to open manually which facilitates patient access. One of the disadvantages is that this machine offers the possibility of studying one limb at a time and is not equipped with a laser for positioning but allows the three-dimensional adjustment of the height, inclination and rotation to facilitate patient positioning. It is able to improve anatomical and diagnostic visibility thanks to the reconstructions allowing also to visualize ligaments and tendons.
It is limited in the study of the foot as it allows the scanning of feet with a maximum size of 37.
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