Principles of CBCT Imaging

A Brief History of Computed Tomography

1950’s EMI (Electrical and Musical Industries) an Industrial Research Company employ Godfrey Hounsfield who is doing computer research for the company

1962 EMI sign the Beatles

EMI sell the Computer Division (losing money)

1960’s EMI continue to fund Godfrey Hounsfield’s research with money generated through Beatles success

1972 EMI and Godfrey Hounsfield announce first medical CT scanner

1979 Godfrey Hounsfield shares Nobel Prize in Medicine with Alan Cormack who developed the image reconstruction mathematics used in CT imaging

Principles of CBCT Imaging

A Brief History of Computed Tomography

1972 10 cm CT of the head takes approximately 40 minutes

1982 Cone-beam CT technology developed for angiography

Early 1990’s Multi-slice helical CT scanner developed

Late 1990’s Dental/Maxillofacial cone-beam CT available

Current Full body CT takes about 20 seconds

Principles of CBCT Imaging

CONE-BEAM CT vs MSCT

CONE-BEAM CT Multi-Slice CT

Miracle AC, Mukherji SK. Conebeam CT of the head and neck, Part 1: Physical principles. AJNR 2009;30:1088-1094.

Principles of CBCT Imaging

CONE-BEAM CT• X-ray source and detector panel

rotate around patient head.

• Detectors are either flat panel detector or image intensifier/CCD combination

• Many cephalometric exposures are made in rapid succession as the machine rotates.

• Each exposure is called a basis image.

• The set of basis images is called projection data.

Principles of CBCT Imaging

Miracle AC, Mukherji SK. Conebeam CT of the head and neck,

Part 1: Physical principles. AJNR 2009;30:1088-1094.

CONE-BEAM CT

• Complex mathematics creates a 3-D data set from the projection data. (Primary Reconstruction)

• The 3-D data set divides the patient anatomy into small cubes called voxels.

• The surface of a voxel is called a pixel.

• The smaller the voxel the better the image resolution.

• For a given size, the more pixels, the clearer the image.

Miracle AC, Mukherji SK. Conebeam CT of the head and neck, Part 1:

Physical principles. AJNR 2009;30:1088-1094.

Principles of CBCT Imaging

Principles of CBCT Imaging

Miracle AC, Mukherji SK. Conebeam CT of the head and neck, Part 1:

Physical principles. AJNR 2009;30:1088-1094.

CONE-BEAM CT

CONE-BEAM CT - DISPLAY

The volumetric data is typically reconstructed and displayed in standard, anatomical orthogonal planes

Principles of CBCT Imaging

Axial Sagittal Coronal

CONE-BEAM CT - DISPLAY

• The voxels in CBCT are cubic (isotropic) and this allows non-orthogonal reconstruction

• Oblique

• Curved Planar

Principles of CBCT Imaging

CONE-BEAM CT

Artifacts

Beam Hardening

As x-rays travel through matter, low energy photons are

Preferentially absorbed, compared to high energy photons.

Cupping

Streaks/Dark Bands

Patient Motion

Partial Volume Averaging

One voxel contains both hard and soft tissue. The resultant

pixel will be a density somewhere between the two.

Undersampling

Noise / Aliasing

Principles of CBCT Imaging

CONE-BEAM CT

Artifacts – Beam Hardening

http://aadmrt.com/static.aspx?content=currents/lee_summer_08

Principles of CBCT Imaging

CONE-BEAM CT

Metal Streak Artifact

Beam Hardening

Aliasing

Artifacts

Principles of CBCT Imaging