OMFPR 6: Advanced Imaging Modalities - CT, CBCT Technique and Application

False

T/F: Advanced imaging (3D) is routine form of imaging.

Tomographic Imaging

3D imaging techniques make a __________ image.

Tomographic image

Thin slice through tissue rather than a simple projection image

Projection image (PA) vs. tomographic image

Left vs. right

Axial

Coronal

Sagittal

3 spatial planes of tomographic images

Axial

Coronal

Sagittal

CBCT (cone beam computed tomography)

CT (computed tomography)

MRI

CT - fan shaped x-ray beam

Which imaging modality:

X-ray tube emits a fan shaped beam

Beam directed through a patient

Series of detectors arranged around the patient in a ring

Detectors measure the # of photons that exit the patient

Tissue density

For image display, each voxel is assigned a CT number representing _____ ______.

Attenuation of x-rays caused by the material by the material within that "voxel"

The CT number is proportional to the degree of...

+ 1000

Hounsfield number / CT number for bone

0

Hounsfield number / CT number for water

- 1000

Hounsfield number / CT number for air

Density of the anatomic structure in the image

Hounsfield number / CT number depends on...

CT scan

Which scan shows bone window + soft tissue window?

Soft tissue window

Lipoma: axial view

Uniform magnification

Lateral, coronal, and axial views available

Post acquisition reformatting may provide additional views

CT advantages

Limited availability

Expensive

Results in relatively high dose of radiation

Radiologist required for acquisition and interpretation

CT disadvantages

CT

What would be used for investigation of severe trauma?

CT

What would be used for evaluation of neoplasia?

CT

What would be used for assessment of chronic inflammation or infection?

CBCT (cone beam computed tomography)

3D imaging modality that uses x-ray beam that is "cone shaped" as opposed to "fan shaped" x-ray beam of traditional multi-slice CT

Hardware + software

Components of CBCT system

Rotating platform/gantry is fixed to x ray source and image detector

X-ray beam is cone shaped

X-ray source and detector rotate around a fulcrum fixed within the center of ROI (region of interest)

How does CBCT image acquisition work?

CT

CT or CBCT:

Fan shaped

CBCT

CT or CBCT:

Cone shaped

CT

CT or CBCT:

Multiple rotations of the gantry

CBCT

CT or CBCT:

Single rotation of the gantry

CT

CT or CBCT:

More dose

CBCT

CT or CBCT:

Poor contrast resolution - poor soft tissue detail

CBCT

CT or CBCT:

More scatter, due to a wide conical beam

CT

CT or CBCT:

More cost

CBCT

CT or CBCT:

Lower radiation exposure, higher spatial resolution, limited contrast resolution

CT

CT or CBCT:

Lower spatial resolution, superior contrast resolution

Voxels

Building blocks of 3D image volume

Voxel size

What is spatial resolution primarily dependent on?

Higher

Smaller voxel = ______ resolution

MPR

Axial, coronal, and sagittal is ___ view.

Ray rum vs. MIP

Left vs. right

Ray sum

The slice of orthogonal or MPR images can be "thickened" by increasing the # of adjacent voxels included in the display

Increasing the # of adjacent voxels included in the display

The slice of orthogonal or MPR images can be "thickened" by...

MIP (maximum intensity projection)

Achieved by evaluating each voxel volume along an imaginary projection ray from the observer's eyes within a particular volume of interest and representing only the highest value at the display value

Volume rendering

Allows visualization of volumetric data by selective display of voxels within a dataset

Image fusion

Fusion of CBCT data with photographic image sets

Metallic beam hardening

Patient motion

Floor of maxillary sinus

Nasopalatine canal

Inferior alveolar nerve canal (IAN)

Mental neurovascular canal and foramen

Landmarks that need to be avoided/prevented injury of in CBCT

CBCT

Useful for assessment of osseous components of TMJ

False; MRI

T/F: CBCT is useful for assessment of articular disk related issues.

MRI

Recommended for evaluation of soft tissue structures including articular disk of TMJs

CBCT

Useful in detecting missed canal during endodontic treatment

CBCT

Accessory neurovascular canals, anterior extension - these are best visualized with ____ images.

Labial undercut

Smooth depressions on the facial surface of the anterior maxilla that dental implants could perforate through the undercut during placement