INDRODUCTION OF CT

INDRODUCTION OF CT

DISCOVERY OF CTDISCOVERY OF CT

MOTION IN ARTIFACTSMOTION IN ARTIFACTS

TYPES OF ARTIFACTS IN CT SCANTYPES OF ARTIFACTS IN CT SCAN

ADVANTAGES OF CTADVANTAGES OF CT

ARTIFACTS IN CT SCANARTIFACTS IN CT SCAN

METAL ARTIFACTSMETAL ARTIFACTS

BEAM HARDENING ARTIFACTSBEAM HARDENING ARTIFACTS

Beam-Hardening ImageBeam-Hardening Image

PARTIAL VOLUME ARTIFACTSPARTIAL VOLUME ARTIFACTS

Partial Volume ImagePartial Volume Image

RING ARTIFACTSRING ARTIFACTS

Blurring Artifacts (Volume Averaging)Blurring Artifacts (Volume Averaging)

Blurring Artifacts ImageBlurring Artifacts Image

Stair-Step ArtifactsStair-Step Artifacts

ImageImage

Created ByCreated By

EXIT

ARTIFACTS IN CT

PRESANTION PREPARED BY MASOOD AHMED (RADIOGRAPHER)

INDRODUCTION OF CT CT is a major technological break through

in radiology , especially neuroradiology. It provides images compariable to

anatomical slices (3-6 mm thick) of the brain.

Ct scanning helps in the diagnosis of exact location and size of the tumors, hemorrhage infraction and malformation including hydrocephalus.

DISCOVERY OF CT

The development of CT required the emergency of the digital computer and special mathematics.

Hounsfield demonstrated the first CT scanner in 1972, using Cormacks’s mathematics.

Godfrey Hounsfield, an engineer and Alan Cormark, a medical physicist, shared the 1979 Nobel Prize in medicine for the development of CT.

Houndsfields original attempts at CT used a gamma source-output too low, source too large.

ADVANTAGES OF CT

Better contrast resolution . No super imposition of tissue . Less scatter radiation. 3d imaging. Bone mineral assay.

ARTIFACTS IN CT SCAN

ARTIFACT Any artifact (man made)

product, any thing not naturally present but introduced by some external sourse.

An unwanted density or image on the radiograph.

CAUSED BY: It may be caused by operator

error, patient motion or equipment characteristic.

TYPES OF ARTIFACTS IN CT SCAN

1. Motion Artifacts2. Metal Artifacts3. Beam-Harding Artifacts4. Partial volume Artifacts 5. Ring Artifacts6. Stair-Step Artifacts7. Blurring Artifacts (Volume

Averaging)

MOTION IN ARTIFACTS

Voluntary and involuntary patient motion can result.

Appears as streaks or steps like patterns at high contrast edges.

Respiratory motion artifacts in Computed tomography angiography(CTA) can stimulate vascular steno sis or aneurysem

METAL ARTIFACTS

The x-rays absorption results in incomplete projection profiles.

Metal in tissue gives rise to steak and star shaped artifacts.

With penetration of cranial bone, the X-Rays beam is selectively filtered and “Hardened”

BEAM HARDENING ARTIFACTS

It appears as a dark ring in side cranial bone and cupping at the center of the image.

When an object (Calcification is not fully with in a slice thickness, the Ct number representing the object will be false.

Effective energy is shifted to higher value as the x-rays pass through an object.

Without correctionWith

correction

Beam-Hardening Artifacts

PARTIAL VOLUME ARTIFACTS

Partial volume artifacts arises when a voxel contains many types of tissue.

It can be reduced by overlapping scans but that increases patient dose.

Partial volume artifacts can be reduced in spiral Ct by moving plane of reconstruction.

Multiple reconstruction along z-axis during spiral Ct partial volume artifacts.

RING ARTIFACTS

It can be occur in third generation Ct imagers because of detector malfunction.

Pulsation artifacts is observed in CTA.

Pulsation artifacts can be reduced by using 360’ interpolation rather than 180’ interpolation .

Blurring Artifacts (Volume Averaging)

Causes• Large CT slice thickness and high contrast

structures only partially included• Finite source size• Finite sampling rates

Correction• Volume Artifact Reduction (VAR) mode• Deblurring

Blurring Artifacts (Volume Averaging)

Blurred DeblurredVolume averaging

Stair-Step Artifacts

Associated with inclined surfaces inreformatted slices

Causes• Large reconstruction interval• Asymmetric helical interpolation

Correction• Collimation and feed less than feature sizes,

and small reconstruction interval• Adaptive interpolation

Stair-step Artifacts

Stair-step artifact. (A) Axial CT shows central low attenuation in the right lower lobe pulmonary artery raising suspicion for pulmonary embolus (arrow). (B) Coronal reformatted image shows linear low attenuation across the vessel from data misregistration along z-axis.