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CBCT AND CT

COMPUTED TOMOGRAPHY - CT

� CT is a medical imaging method employing tomography created by

computer processing

� Digital geometry processing is used to generate a three-dimensional

image of the inside of an object from a large series of two-dimensional X-ray images taken around a single axis of rotation.

� Various applications:

� Medicine (including forensic and veterinary)

� Archeology

� Non-destructive object testing in industry

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RESEARCH BY PROF. URBANIK AND HIS

TEAM IN CRACOW, POLAND

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CT

� X-ray slice data is generated using an X-ray source that rotates around

the object; X-ray sensors are positioned on the opposite side of the circle from the X-ray source.

� Current sensors: scintillation systems based on photo diodes and modern scintillation materials with more desirable characteristics.

� Many data scans are progressively taken as the object is gradually passed through the gantry.

� The detectors measure the intensity of the X-ray beam emerging from the patient and convert this into digital data which are stored and can be manipulated by a computer.

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CT

� A patient lies down with the part of the body to be examined in the

cirucular opening in the part of a CT scanner called gantry.

� The gantry houses the X-ray tubehead and the detectors.

� The construction of gantry depends on the generation of a CT scanner.

� In the 4th generation scanners there is a fixed circular array of detectorand only the X-ray tube rotates. The patient is sequentially moved furtherinto the gantry and the next adjacent slice is imaged. The process is

repeated until the whole region of interest is scanned.

� Current scanners have more than one ring of detectors

� Most modern scanners are dual-source or dual energy scanners.

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PATIENT DURING CT EXAM

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gantry

Direction of spiral rotation of X-ray tube

Patient on

moving table

X-ray tube

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DUAL SOURCE/DUAL ENERGY CT

13Two X-ray tubes One X-ray tube

fast switchingof current voltage

One X-ray tube

Two layers of detectors14

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DUAL SOURCE CT

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CT

� Once the scan data has been acquired, the data must be processed using

a form of tomographic reconstruction, which produces a series of cross-sectional images

� The numerical information of attenuation of X-ray beam is converted intoa grey scale representing different tissue densities thus allowing a visualimage to be generated.

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CT

� Pixels in an image obtained by CT scanning are displayed in terms of

relative radiodensity.

� The pixel itself is displayed according to the mean attenuation of the

tissue(s) that it corresponds to on a scale from +3071 (most attenuating) to -1024 (least attenuating) on the Hounsfield scale.

� Pixel is a two dimensional unit based on the matrix size and the field of view. When the CT slice thickness is also factored in, the unit is known as a voxel, which is a three dimensional unit.

� Each voxel is given a CT numer or Hounsfield unit.

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VOXEL – „VOLUME PIXEL” – THE SMALLEST

ELEMENT OF CT SLICE

19width

height

thickness

RECONSTRUCTION OF CT IMAGE

MOST SIMPLE EXAMPLE

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X-rays

X-rays

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HOUNSFIELD UNITS

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CT

� CT produces a volume of data which can be manipulated, through a process known as „windowing”, in order to demonstrate various

bodily structures based on their ability to block the X-ray beam.

Although historically the images generated were in the axial or transverse plane, orthogonal to the long axis of the body, modern

scanners allow this volume of data to be reformatted in various

planes or even as volumetric (3D) representations of structures.

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CT

� Window level – this is the CT numer selected for the center of the range,

depending on whether the lesion under investigation is in soft tissue orbone.

� Window width – the range selected to view on the screen for the variousshades of grey, eg. a narrow range allows subtle differences between verysimilar tissues to be detected.

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SOFT TISSUE WINDOW

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BONE WINDOW

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CONTRAST MEDIA

� Iodine based

� Intravenous injection

� CT scanning before and after contrast enhancement

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CT PERFUSION – DEMONSTRATES

VASCULARISATION OF TISSUES AND ORGANS

brain abdomen

CT RECONSTRUCTIONS

� Multiplanar Reconstruction (MPR) is the simplest method of

reconstruction. A volume is built by stacking the axial slices. The software then cuts slices through the volume in a different plane (usually orthogonal). Optionally, a special projection method, such as maximum-

intensity projection (MIP) or minimum-intensity projection (mIP), can be used to build the reconstructed slices.

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SKULL

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CHEST

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HEART AND CORONARY ARTERIES

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EXTREMITIES

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VIRTUAL COLONOSCOPY

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VIRTUAL BRONCHOSCOPY

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VIRTUAL AUTOPSY

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CT IN DENTOMAXILLOFACIAL

RADIOLOGY

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CHONDROSARCOMA

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MANDIBULAR HYPOPLASIA

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3D CEPHALOMETRICS

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http://orthostreams.com/2013/12/3-d-printing-for-patient-specific-medical-devices-will-reach-1b-by-2020/

THREE-DIMENSIONAL PRINTING

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SURGICAL GUIDE FOR DENTAL IMPLANTS

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STEREOLITOGRAPHY 3D SKULL

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STEREOLITOGRAPHY

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STEREOLITOGRAPHY

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THREE-DIMENSIONAL PRINTING IN FACE

TRANSPLANTATION – DONOR AND RECEPIENT

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VIRTUAL REALITY

THREE DIMENSIONAL GOOGLES

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MAIN INDICATIONS FOR CT IN THE HEAD

AND NECK

� Investigation of intracranial disease including tumors, haemorrhage and

infarcts

� Investigation of suspected intracranial and spinal cord damage following

trauma to the head and neck

� Assessment of maxillofacial fractures

� Tumor staging – assessment of the site, size and extent of tumors, bothbenign and malignant

� Investigation of osteomyelitis

� Investigation of bony structures of TMJ

� Preoperative assessment in implant placement

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ADVANTAGES OF CT OVER RADIOGRAPHY

� Very small amounts and differences in X-ray absorption can be detected

� Imaging of soft and hard tissues possible

� Images can be postprocessed

� Images can be enhanced by the use of intravenous contrast media

providing additional information.

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DISADVANTAGES OF CT

� Equipment is expensive

� Patient exposure dose is high

� Metallic objects such as fillings may produce marked artifacts across the CT image

� Intravenous administration of contrast media may cause adverse effects

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CBCT

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CBCT

� Cone-Beam Computed Tomography

� Cone Beam CT is a medical imaging modality, which has been applied in different fields of medicine (e.g. cardiac imaging, radiotherapy). Recently,

this technique has been applied to dental imaging.

� Other names:

� Dental Volumetric Tomography

� Dental Volumetric Imaging

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CBCT

� The principle behind this technique, as its name implies, is a cone-shaped

X-ray bundle, with the X-ray source and detector (Image Intensifier or Flat Panel Detector) rotating around a point (or field) of interest of the patient. The conical shape of the beam distinguishes this technique from helical

CT, which used a fan-shaped beam.

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Zoeller J.E., Neugebauer J. Quintessence Books, 2008

CBCT

� As a result of the acquisition of two-dimensional projections throughout

this rotation, only one rotation or less is needed to acquire a full (three-dimensional) dataset. The images received by the detector are then compiled by the computer into volumetric data (primary reconstruction).

This can then be visualized as two-dimensional multi-planar reformatted slices or in three dimensions by using surface reconstruction or volume rendering.

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CBCT

� By rotating the beam around a fixed point (isocentre) in the object of

interest and acquiring projections from many different angles, a (typically cylindrical) three-dimensional volume can be reconstructed. Typically, a few hundreds of projections are collected. Although a 360° rotation is

used in general, some devices have implemented a 180° or slightly greater rotation arc, which suffices for image reconstruction and leads to significant radiation reduction.

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CBCT

� The two-dimensional attenuation profiles obtained from all angles are then

reconstructed into a three-dimensional matrix, containing volume elements (voxels) each having a certain grey value which represents the average density within this volume element. The grey value for each voxel

is determined by the reconstruction algorithm, by combining the information from all obtained projections.

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FIELD OF VIEW - FOV

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Small FoV

Medium FoV

Large FoV

Image volume

consists of volume elementscalled voxelsof different sizes

Voxel

0.125 mm

Volume

Ø 60 mm

x 60 mm

Volume

Ø 40 mm

x 40 mm

„STITCHING” – FUSION OF 3 SEPARATE

SMALL VOLUMES INTO 1 MEDIUM FOV

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JAW-SHAPED FIELD OF VIEW

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CBCT

� After a gradual introduction of this modality into dental radiology, the use

of CBCT has steadily increased, and the market has been growing with a wide range of CBCT devices.

� These devices, although based on the same principle, exhibit great differences regarding exposure parameters and other quality factors, requiring an objective analysis of the performance of these devices, and

an optimized implementation into dental practice.

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Higher resolution in smaller volumes

Lower resolution in larger volumes

TYPES OF CBCT MACHINES

PATIENT SITTING, LYING SUPINE OR STANDING

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CBCT

� The latest CBCTs are patient friendly, the scan time is decreased, as well

as the effective patient dose compared to medical CT and the provided resolution is getting higher. High resolution means that image quality is improved.

� Furthermore, the latest CBCT systems need some seconds to take and reconstruct the images. Combined with sophisticated software programs

they provide us with images in 3 orthogonal planes (axial, sagittal andcoronal).

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CBCT

� CBCT is a useful tool for imaging the craniofacial area that produces more

realistic images that facilitate interpretation.

� All the previous conventional and digital intraoral and extraoral

procedures, as they were two dimensional (2D) projections, suffer from several limitations. These limitations were magnification, distortion, superimposition and misrepresentation of structures. CBCT has achieved

a transition of dental imaging from 2D to 3D images

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CBCT

� Moreover, the application of sophisticated software, contribute to the

reestablishment of imaging sciences role. Now dentomaxillofacialradiology has been expanding from the diagnosis field to image guidance of operative and surgical procedures. As a consequence the treatment

outcome is enhanced

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MAIN INDICATIONS FOR CBCT IN HEAD AND

NECK REGION

� Preoperative assessment in virtual implant planning

� Dental anomalies (eg. impacted teeth, supernumerary teeth)

� Odontogenic tumors

� Maxillofacial cysts

� Endodontics – eg. vertical root fractures, periapical lesions not visible in plain radiography, demonstration of atypical root morphology

� Prior to surgical extraction of teeth eg. third molars

� 3D evaluation of periodontal vertical bone defects

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MAIN INDICATIONS FOR CBCT IN HEAD AND

NECK REGION

� Maxillofacial developmental abnormalities

� Orthognathic surgery planning and follow-up

� Diseases of paranasal sinuses

� Assessment of middle and inner ear pathologies

� Evaluation of bony structures of the TMJ

� Evaluation of air spaces of oral cavity and pharynx

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ADVANTAGES OF CBCT OVER PLAIN

RADIOGRAPHY

� Allows three-dimensional evaluation of teeth and bonewithout superimposition of other structures

� Allows imaging in thin slices thus increasing sensitivity

and specificity of diagnostics

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Disdvantages of CBCT in comparison with plain radiography

� Exposure dose in CBCT is slightly higher than that of

radiographs

� CBCT equipment is more expensive

� CBCT volumes must be reported by qualified

practitioners

ADVANTAGES OF CBCT OVER CT� Allows imaging in thinner slices than in CT

� Exposure dose in CBCT is at least 10 times lower than in CT

� CBCT machines are cheaper than CT scanners and can be installed in dental offices, while CT scanners are mostlyhospital-based

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Disdvantages of CBCT in comparison with CT

� Image contrast is lower in CBCT than in CT

� Estimation of Hounsfield units in CBCT is less precise

than in CT

� It is almost not possible to diagnose soft tissue lesions in

CBCT

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