CBCT Basics

Interpretation of images in Cone Beam CT

Introduction

Cone beam CT is a tomographic scanning technology that can scan and acquire a specified volume of the patient head and generate a 3D data set at much lower radiation doses than their medical CT counterparts. In effect, Cone Beam CT represents the latest generation in medical imaging scanning machines ascending from conventional x-ray to panoramic and cephalometric x-ray to medical spiral CT. It provides numerous advantages over the other imaging modalities in favor for its accuracy, speed and safety. Above all, its an economical and cost effective system that can supplant to a huge extent the existing modalities to be the standard of health care.

Cone Beam CT scanners have been employed in clinical practice for several years till now and mostly it is used for diagnosis and treatment planning in diverse dental specialties such maxillofacial surgery, implantology and oral pathology. Up till now, however, no single system has been developed to illustrate the radiographic appearance of anatomical landmarks in Cone Beam CT images. And thus, it is the scope of this module to teach you how to identify and describe the anatomical landmarks as they appear on the maxilla and mandible when examining them on MPR (Multi-planar reformatted, Surface and Volume rendered).


A movie showing how a cone beam CT scan looks like

Principle of action

Image reconstruction: The end result of the acquisition process is a stack of 360 images or exposures that are compiled into a volume of data called volumetric data set through a computer process known as the primary reconstruction.

The data volume generated from the primary reconstruction process is then converted into a patient-study where, by using the CBCT system accompanying software, any number of diagnostic images can be generated.

The compiled volumetric data set can then be visualized in standardized 2D trans-axial, multi-planar reformatted or by using 3D visualization techniques such as surface reconstruction and volume rendering or any combination of 2D and 3D visualization techniques. Also, the data set can be exported in standardized 2D or 3D file formats for visualization and further processing in 3D party software.





Cone Beam CT versus spiral CT

A movie showing how a spiral CT scan looks like

CT scanner utilizes a narrowly collimated, fan shaped x-ray beam that is projected through a limited thickness slice through the human body. Then, these projections will be detected through a linear array of detectors and the patient has to be advanced through the gantry while the x-ray tube and the detectors are rotating around the patient. Based on the specific system configuration, both of the x-ray tube and the detectors’ array may be rotating around the patient, alternatively, the detectors’ array can be static while only the x-ray tube is rotating. Still, the fundamental variation between cone beam ct and spiral ct is that cone beam CT utilizes a cone shaped and an area detector and that it acquires a full volume of images in a single rotation with no need for patient movement. While, spiral ct utilizes a narrowly collimated, fan-shaped x-ray beam and a linear array of detectors and the patient has to be advanced continuously while the x-ray beam rotates around the patient.