Cone beam computed tomography (or CBCT, also referred to as C-arm CT, cone beam volume CT, flat panel CT or Digital Volume Tomography (DVT)) is a medical imaging technique consisting of

X-ray computed tomography An X-ray (also known in many languages as Röntgen radiation) is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelength ran ...

where the X-rays are divergent, forming a cone. CBCT has become increasingly important in treatment planning and diagnosis in implant dentistry, ENT, orthopedics, and

interventional radiology Interventional radiology (IR) is a medical specialty that performs various minimally-invasive procedures using medical imaging guidance, such as Fluoroscopy, x-ray fluoroscopy, CT scan, computed tomography, magnetic resonance imaging, or ultraso ...

(IR), among other things. Perhaps because of the increased access to such technology, CBCT scanners are now finding many uses in dentistry, such as in the fields of

oral surgery Oral and maxillofacial surgery (OMFS) is a surgical specialty focusing on reconstructive surgery of the face, facial trauma surgery, the mouth, head and neck, and jaws, as well as facial plastic surgery including cleft lip and cleft palate ...

endodontics Endodontics () is the Specialty (dentistry), dental specialty concerned with the study and treatment of the dental pulp. Overview Endodontics encompasses the study (practice) of the basic and clinical sciences of normal dental pulp, the etiolo ...

and

orthodontics Orthodontics (also referred to as orthodontia) is a dentistry specialty that addresses the diagnosis, prevention, management, and correction of mal-positioned teeth and jaws, as well as misaligned bite patterns. It may also address the modificati ...

. Integrated CBCT is also an important tool for patient positioning and verification in image-guided radiation therapy (IGRT). During dental/orthodontic imaging, the CBCT scanner rotates around the patient's head, obtaining up to nearly 600 distinct images. For interventional radiology, the patient is positioned offset to the table so that the region of interest is centered in the field of view for the cone beam. A single 200 degree rotation over the region of interest acquires a volumetric data set. The scanning software collects the data and reconstructs it, producing what is termed a ''digital volume'' composed of three-dimensional

voxel In computing, a voxel is a representation of a value on a three-dimensional regular grid, akin to the two-dimensional pixel. Voxels are frequently used in the Data visualization, visualization and analysis of medical imaging, medical and scient ...

s of anatomical data that can then be manipulated and visualized with specialized software. CBCT shares many similarities with traditional (fan beam) CT however there are important differences, particularly for

reconstruction Reconstruction may refer to: Politics, history, and sociology *Reconstruction (law), the transfer of a company's (or several companies') business to a new company *''Perestroika'' (Russian for "reconstruction"), a late 20th century Soviet Union ...

. CBCT has been described as the gold standard for imaging the oral and maxillofacial area.

History

Oral and maxillofacial radiology

In the late 1990s, Dr Yoshinori Arai in Japan and Dr Piero Mozzo in Italy independently developed Cone Beam Computed Technology for oral and maxillofacial radiology. The first commercial system (the NewTom 9000) was introduced in the European market in 1996 and into the US market in 2001, by Italian company Quantitative Radiology. File:Prima Immagine Cone-Beam-1994-07-01 -1.jpg , Axial image obtained from the first Cone-Beam 3D Scan performed on July 1, 1994 File:Prima Immagine Cone-Beam-1994-07-02.jpg , Axial image obtained from the first Cone-Beam 3D Scan performed on July 1, 1994 File:Prima Immagine Cone-Beam-1994-07-01-3.jpg , Axial image obtained from the first Cone-Beam 3D Scan performed on July 1, 1994 File:Prima acquisizione totale 1994-07-01-pag1.jpeg , Original notes about the first Cone-Beam 3D Scan performed on July 1, 1994

Radiotherapy

Cone beam CT using kilovoltage

X-ray An X-ray (also known in many languages as Röntgen radiation) is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelength ran ...

s (as used for

diagnostic Diagnosis (: diagnoses) is the identification of the nature and cause of a certain phenomenon. Diagnosis is used in a lot of different academic discipline, disciplines, with variations in the use of logic, analytics, and experience, to determine " ...

, rather than therapeutic purposes) attached to a

linear accelerator A linear particle accelerator (often shortened to linac) is a type of particle accelerator that accelerates charged subatomic particles or ions to a high speed by subjecting them to a series of oscillating electric potentials along a linear ...

treatment machine was first developed in the late 1990s and early 2000s. Such systems have since become common on latest generation linacs. In the late 2010s CBCT also started to become available on-board particle therapy delivery systems.

Interventional radiology

While CBCT with X-ray image intensifiers was experimented with in the late 1990s, it was not until the adoption of flat-panel X-ray detectors, with improved contrast and spatial resolution, that CBCT became practical for clinical use in interventional radiology procedures. Many fixed, and even mobile, C-arm fluoroscopy systems are now capable of CBCT acquisitions, in addition to traditional planar fluoroscopy. CBCT aids image guidance during interventional radiology procedures treating various medical conditions including knee osteoarthritis, benign prostatic hyperplasia, and hepatocellular carcinoma.

Applications

Endodontics

The most significant advantage of the CBCT in Endodontics is that it can show critical root canal anatomical features that conventional intraoral or panoramic images cannot. According to the American Association of Endodontics, there are numerous specific situations in which 3D images produced by CBCT enhance diagnosis and influence treatment, and its use cannot be disputed over conventional intraoral radiology based on ALARA principles.

Implantology

A dental cone beam scan offers useful information when it comes to the assessment and planning of surgical implants. The American Academy of Oral and Maxillofacial Radiology (AAOMR) suggests cone-beam CT as the preferred method for presurgical assessment of dental implant sites.

Orthodontics

As a 3D rendition, CBCT offers an undistorted view of the

dentition Dentition pertains to the development of teeth and their arrangement in the mouth. In particular, it is the characteristic arrangement, kind, and number of teeth in a given species at a given age. That is, the number, type, and morpho-physiology ...

that can be used to accurately visualize both erupted and non-erupted teeth, tooth root orientation and anomalous structures, that conventional 2D radiography cannot. Processing example using x-ray data from a tooth model: File:DVT-scan-MagoCut-bild1-singlesample.jpg, single sampled (noisy) image File:DVT-scan-MagoCut-bild2-oversamplefocus.jpg, several samples overlay File:DVT-scan-MagoCut-bild3-panoramiomodejoined.jpg, joined images to panoramic File:DVT-scan-MagoCut-bild4-dvtreconstructed.jpg, algorithmic reconstruction File:CBCT image 03.png, in-vivo image

Orthopedics

The CBCT scanner offers undistorted views of the extremities. One advantage of orthopedic CBCT is the ability to take weight bearing images of the lower extremities. In the realm of the

foot The foot (: feet) is an anatomical structure found in many vertebrates. It is the terminal portion of a limb which bears weight and allows locomotion. In many animals with feet, the foot is an organ at the terminal part of the leg made up o ...

and

ankle The ankle, the talocrural region or the jumping bone (informal) is the area where the foot and the leg meet. The ankle includes three joints: the ankle joint proper or talocrural joint, the subtalar joint, and the inferior tibiofibular joint. The ...

particularly, weight bearing CBCT is gaining momentum due to its ability to combine 3 dimensional and weight bearing information which are of the utmost importance in diagnosis and surgical planning. The preferred term used for CBCT in the lower limb is thus WBCT for Weight Bearing CT following the first scientific publications on the subject.

Image-guided radiation therapy

Image-guided radiation therapy is a form of

external beam radiotherapy External beam radiation therapy (EBRT) is a form of radiotherapy that utilizes a high-energy collimated beam of ionizing radiation, from a source outside the body, to target and kill cancer cells. The radiotherapy beam is composed of particl ...

where the patient is positioned with the organs to be treated accurately matched in position to the treatment field, to reduce the dose to nearby organs which are not being treated. Many organs inside the body move by millimeters relative to the external skin surfaces, and a CBCT scanner mounted on the head of the radiotherapy unit is used immediately before treatment (and sometimes again during treatment) to ensure the patient's organs are in exactly the right position to match the treatment field, and to adjust the position of the treatment table if necessary. The images may also be used to check for other requirements of some types of treatment, such as full or empty bladder, empty rectum, etc. The same cone beam beam source and detector can alternatively be used to take simple X-ray positioning images if the organ shows particularly well on X-ray or if

Fiducial marker A fiducial marker or fiducial is an object placed in the field of view of an image for use as a point of reference or a measure. It may be either something placed into or on the imaging subject, or a mark or set of marks in the reticle of an opt ...

s have been inserted into the organ.

Interventional radiology

The CBCT scanner is mounted on a C-arm

fluoroscopy Fluoroscopy (), informally referred to as "fluoro", is an imaging technique that uses X-rays to obtain real-time moving images of the interior of an object. In its primary application of medical imaging, a fluoroscope () allows a surgeon to see t ...

unit in the

(IR) suite, which offers real time imaging with a stationary patient. This eliminates the time needed to transfer a patient from the

angiography Angiography or arteriography is a medical imaging technique used to visualize the inside, or lumen, of blood vessels and organs of the body, with particular interest in the arteries, veins, and the heart chambers. Modern angiography is perfo ...

suite to a conventional

computed tomography A computed tomography scan (CT scan), formerly called computed axial tomography scan (CAT scan), is a medical imaging technique used to obtain detailed internal images of the body. The personnel that perform CT scans are called radiographers or ...

scanner and facilitates a broad spectrum of applications of CBCT during IR procedures. The clinical applications of CBCT in IR include treatment planning, device or implant positioning and assessment, intra-procedural localization, and assessment of procedure endpoints. CBCT is useful as a primary and supplemental form of imaging. It is an excellent adjunct to DSA and

for

soft tissue Soft tissue connective tissue, connects and surrounds or supports internal organs and bones, and includes muscle, tendons, ligaments, Adipose tissue, fat, fibrous tissue, Lymphatic vessel, lymph and blood vessels, fasciae, and synovial membranes.� ...

and

vascular Vascular can refer to: * blood vessels, the vascular system in animals * vascular tissue Vascular tissue is a complex transporting tissue, formed of more than one cell type, found in vascular plants. The primary components of vascular tissue ...

visibility during complex procedures. The use of CBCT before fluoroscopy potentially reduces patient radiation exposure.

Clinical applications

* Chemoembolization for

Hepatocellular Carcinoma Hepatocellular carcinoma (HCC) is the most common type of primary liver cancer in adults and is currently the most common cause of death in people with cirrhosis. HCC is the third leading cause of cancer-related deaths worldwide. HCC most common ...

: CBCT with contrast confirms that the proper artery is selected to deliver the therapy. The contrast enhances the parenchyma supplied by the selected artery and therefore reveals if the vasculature also supplies the tumor. Post-treatment non-contrast CBCT confirms

lipiodol Iodized oil, also known as ethiodized oil, brand name Lipiodol, is a medication derived from poppyseed oil and iodine. When given by injection, it is a radio-opaque contrast agent that is used to outline structures in radiological investiga ...

staining of the tumor, which improves operator confidence of complete tumor coverage or further treatment. * Prostatic artery embolization for

benign prostatic hyperplasia Benign prostatic hyperplasia (BPH), also called prostate enlargement, is a noncancerous increase in size of the prostate gland. Symptoms may include frequent urination, trouble starting to urinate, weak stream, urinary retention, inability t ...

: CBCT provides the soft tissue detail needed to visualize prostatic enhancement, identify duplicated prostatic arteries, and avoid nontarget embolization. CBCT is superior to DSA for this therapy since the enhancement patterns on DSA can be difficult to discern due to the overlapping pelvic structures and variable arterial anatomy. *

Abscess An abscess is a collection of pus that has built up within the tissue of the body, usually caused by bacterial infection. Signs and symptoms of abscesses include redness, pain, warmth, and swelling. The swelling may feel fluid-filled when pre ...

drainage: CBCT confirms needle tip location after placement under ultrasound and confirms drain placement by revealing contrast injection into the desired location. * Adrenal Vein sampling for an

adenoma An adenoma is a benign tumor of epithelium, epithelial tissue with glandular origin, glandular characteristics, or both. Adenomas can grow from many glandular organ (anatomy), organs, including the adrenal glands, pituitary gland, thyroid, prosta ...

: contrast-enhanced CBCT shows perfusion of the

adrenal gland The adrenal glands (also known as suprarenal glands) are endocrine glands that produce a variety of hormones including adrenaline and the steroids aldosterone and cortisol. They are found above the kidneys. Each gland has an outer adrenal corte ...

to confirm catheter placement for obtaining a satisfactory sample. *

Stent In medicine, a stent is a tube usually constructed of a metallic alloy or a polymer. It is inserted into the Lumen (anatomy), lumen (hollow space) of an anatomic vessel or duct to keep the passageway open. Stenting refers to the placement of ...

placement: CBCT improves the visualization of

intracranial The cranial cavity, also known as intracranial space, is the space within the skull that accommodates the brain. The skull is also known as the cranium. The cranial cavity is formed by eight cranial bones known as the neurocranium that in human ...

and extracranial stents compared to conventional DSA and digital radiography by providing a better depiction of the relationship of the stents to nearby structures (i.e. vascular walls and

aneurysm An aneurysm is an outward :wikt:bulge, bulging, likened to a bubble or balloon, caused by a localized, abnormal, weak spot on a blood vessel wall. Aneurysms may be a result of a hereditary condition or an acquired disease. Aneurysms can also b ...

lumen). * Lung

nodule Nodule may refer to: * Nodule (geology), a small rock or mineral cluster * Manganese nodule, a metallic concretion found on the seafloor *Nodule (medicine), a small aggregation of cells *Root nodule Root nodules are found on the roots of plants, ...

percutaneous {{More citations needed, date=January 2021 In surgery, a percutaneous procedurei.e. Granger et al., 2012 is any medical procedure or method where access to inner organs or other tissue is done via needle-puncture of the skin, rather than by using ...

transthoracic needle biopsy: CBCT guides needle placement and demonstrated a diagnostic accuracy, sensitivity, and specificity of 98.2%, 96.8%, and 100%, respectively. Diagnostic accuracy was unaffected by technically challenging conditions. * Vascular Anomalies: After correction of

arteriovenous malformation An arteriovenous malformation (AVM) is an abnormal connection between arteries and veins, bypassing the capillary system. Usually congenital, this vascular anomaly is widely known because of its occurrence in the central nervous system (usually ...

s with coiling, CBCT sensitively detects small infarcts in tissue that has been "sacrificed" during the procedure to prevent further shunting. The infarcted tissue appears as a small area of contrast retention. * Peripheral Vascular Interventions * Biliary Interventions * Spinal Interventions * Enterostomy Interventions

Industrial applications

Cone beam CT is used for material analysis,

metrology Metrology is the scientific study of measurement. It establishes a common understanding of Unit of measurement, units, crucial in linking human activities. Modern metrology has its roots in the French Revolution's political motivation to stan ...

, and

nondestructive testing Nondestructive testing (NDT) is any of a wide group of analysis techniques used in science and technology industry to evaluate the properties of a material, component or system without causing damage. The terms nondestructive examination (NDE), n ...

in the manufacturing sector. Cone beam CT is also inspect and detect defects of tiny sizes, such as internal pitting corrosion or cracks of an object in

quality control Quality control (QC) is a process by which entities review the quality of all factors involved in production. ISO 9000 defines quality control as "a part of quality management focused on fulfilling quality requirements". This approach plac ...

Reconstruction

Cone beam reconstruction algorithms are similar to typical

tomographic reconstruction Tomographic reconstruction is a type of multidimensional inverse problem where the challenge is to yield an estimate of a specific system from a finite number of projection (linear algebra), projections. The mathematical basis for tomographic imag ...

algorithms, and methods such as filtered backprojection or

iterative reconstruction Iterative reconstruction refers to Iteration, iterative algorithms used to reconstruct 2D and 3D reconstruction, 3D images in certain Digital imaging, imaging techniques. For example, in computed tomography an image must be reconstructed from pro ...

may be used. However, since the reconstruction is three-dimensional, modifications such as the FDK algorithm may be needed.

Risks

Oral and maxillofacial radiology

Total radiation doses from 3D dental CBCT exams are 96% lower than conventional CT exams, but deliver 5-16x more radiation than standard dental 2D x-ray (OPG). The time of exposure in CBCT is also comparatively less when compared to conventional CT. CBCT use is only lightly regulated in the US. The recommended standard of care is to use the smallest possible field of view (FOV), the smallest

size, the lowest mA setting and the shortest exposure time in conjunction with a pulsed exposure mode of acquisition. International organisations such as the

World Health Organization The World Health Organization (WHO) is a list of specialized agencies of the United Nations, specialized agency of the United Nations which coordinates responses to international public health issues and emergencies. It is headquartered in Gen ...

and ICRP, as well as many local bodies and legislation, encourage the idea of justification for all medical exposures, where risks and benefits must be weighed up before a procedure goes ahead.

Disadvantages

Oral and maxillofacial radiology

There are a number of drawbacks of CBCT technology over that of CT scans, such as increased susceptibility to movement artifacts (in first generation machines) and to the lack of appropriate bone density determination.

Bone density and the Hounsfield scale

The

Hounsfield scale The Hounsfield scale ( ), named after Sir Godfrey Hounsfield, is a quantitative scale for describing radiodensity. It is frequently used in CT scans, where its value is also termed CT number. Definition The Hounsfield unit (HU) scale is a linear t ...

is used to measure

radiodensity Radiodensity (or radiopacity) is opacity to the radio wave and X-ray portion of the electromagnetic spectrum: that is, the relative inability of those kinds of electromagnetic radiation to pass through a particular material. Radiolucency or hypod ...

and, in reference to

CT scans A computed tomography scan (CT scan), formerly called computed axial tomography scan (CAT scan), is a medical imaging technique used to obtain detailed internal images of the body. The personnel that perform CT scans are called radiographers or ...

, can provide an accurate absolute density for the type of tissue depicted. The radiodensity, measured in Hounsfield Units (HU, also known as CT number) is inaccurate in CBCT scans because different areas in the scan appear with different

greyscale In digital photography, computer-generated imagery, and colorimetry, a greyscale (more common in Commonwealth English) or grayscale (more common in American English) image is one in which the value of each pixel is a single sample repres ...

values depending on their relative positions in the organ being scanned, despite possessing identical densities, because the image value of a

of an organ depends on the position in the image volume. HU measured from the same anatomical area with both CBCT and medical-grade CT scanners are not identical and are thus unreliable for determination of site-specific, radiographically-identified bone density for purposes such as the placement of dental implants, as there is "no good data to relate the CBCT HU values to bone quality." Although some authors have supported the use of CBCT technology to evaluate bone density by measuring HU, such support is provided erroneously because scanned regions of the same density in the skull can have a different grayscale value in the reconstructed CBCT dataset. Dental CBCT systems do not employ a standardized system for scaling the grey levels that represent the reconstructed density values and, as such, they are arbitrary and do not allow for assessment of bone quality. In the absence of such a standardization, it is difficult to interpret the grey levels or impossible to compare the values resulting from different machines. While there is a general acknowledgment that this deficiency exists with CBCT systems (in that they do not correctly display HU), there has been little research conducted to attempt to correct this deficiency. See also this linear method adapted to different machines (in & citations); and a comparatively unusual

neural network A neural network is a group of interconnected units called neurons that send signals to one another. Neurons can be either biological cells or signal pathways. While individual neurons are simple, many of them together in a network can perfor ...

approach (in & citations). With time, further advancements in CBCT reconstruction algorithms will allow for improved area detectors, and this, together with enhanced postprocessing, will likely solve or reduce this problem. A method for establishing attenuation coefficients with which actual HU values can be derived from CBCT "HU" values was published in 2010 and further research is currently underway to perfect this method ''

in vivo Studies that are ''in vivo'' (Latin for "within the living"; often not italicized in English) are those in which the effects of various biological entities are tested on whole, living organisms or cells, usually animals, including humans, an ...

''.

Interventional radiology

While the practicality of CBCT fosters its increasing application in IR, technical limitations hinder its integration into the field. The two most significant factors that affect successful integration are image quality and time (for set up, image acquisition, and image reconstruction). Compared to multidetector computed tomography (MDCT), the wider collimation in CBCT leads to increased scatter radiation and degradation of image quality as demonstrated by artifacts and decreased

contrast-to-noise ratio Contrast-to-noise ratio (CNR) is a measure used to determine image quality. CNR is similar to the metric signal-to-noise ratio (SNR), but subtracts a term before taking the ratio. This is important when there is a significant bias in an image, s ...

. The temporal resolution of cesium iodide detectors in CBCT slows data acquisition time to approximately 5 to 20 seconds, which increases motion artifacts. The time required for image reconstruction takes longer for CBCT (1 minute) compared to MDCT (real time) due to the computationally demanding cone beam reconstruction algorithms.

History

Oral and maxillofacial radiology

Radiotherapy

Interventional radiology

Applications

Endodontics

Implantology

Orthodontics

Orthopedics

Image-guided radiation therapy

Interventional radiology

Clinical applications

Industrial applications

Reconstruction

Risks

Oral and maxillofacial radiology

Disadvantages

Oral and maxillofacial radiology

Bone density and the Hounsfield scale

Interventional radiology

See also

References

Further reading