MRI - Prefi 3

Image artifact

An unwanted pattern or structure that does not represent the actual anatomy

Image artifact

A structure not normally present but visible as a result of a limitation or malfunction in the hardware or software of MRI device

Aliasing (wraparound)

Occurs when portions of the patient’s body are outside the prescribed field of view but within the area of RF excitation

Aliasing (wraparound)

FOV is smaller than body part being imaged

Chemical shift artifact

Refers to the difference in resonant frequency of protons due to local differences in chemical environment

Chemical shift artifact

This appear as a dark band on one side of the interface between fat and water and a bright band on the other side

Truncation artifact

Appears as multiple rings of regular periodicity or duplication at transitions between high- and low-intensity signals

Partial volume artifact

Occur when the image displayed demonstrates overlapping anatomic structures within the same pixel

Partial volume artifact

Caused by thickness too thick and voxel size too large

Motion artifact

Caused by movement of the object being imaged

Motion artifact

May result in fuzziness on the image or a lack of crispiness or detail

Magic angle artifact

Caused by angle about 55 deg to the main magnetic field

Magic angle artifact

Bright signal in tendons, ligaments, cartilage

Slice-overlap artifact (cross talk)

The loss of signal seen in an image from a multi-angle, multi-slice acquisition

Slice overlap artifact (cross talk)

Occurs when slice groups overlap or slices are positioned too closely

Slice overlap artifact (cross talk)

Commonly obtained in lumbar spine

Zipper/star artifact

System noise causes a bright signal at the isocenter or central reference point with a linear dashed pattern along the frequency axis

Zipper/star artifact

Cause by hardware or software problems

Cross cross/herringbone/rf spike artifact

Appears as a faint to gross herringbone fabric pattern throughout the image “Screen-door”

Cross cross/herringbone/rf spike artifact

Caused by Electromagnetic strikes by gradient coils, fluctuating power supply, RF pulse discrepancies

Zone 1

Includes all areas freely accessible to the general public where the magnet field poses no hazards, such as the entrance to the MR facility

Zone 2

Located between Zone I and the more restrictive Zone III

Zone 2

Often includes the reception area, dressing rooms and MRI screening rooms

Zone 3

Access-restricted by physical barriers such as doors with coded access

Zone 4

The room where the magnet is located

MR safe

Items that pose no known hazards in any MRI environment

MR conditional

Items that are safe under specific MRI conditions

MR unsafe

Items that pose hazards in all MRI environments

Noise

This checks for any random speckles or graininess in the image using a container field with a liquid

Uniformity

Ensures the image looks even across the whole scan by measuring signal consistency in a liquid bath

Contrast resolution

Measures how well the MRI can show differences between objects of different thicknesses

Linearity

Checks if straight lines in real life appear straight in the MRI using step-like objects or magnetic materials

Sensitivity profile

Examines how the MRI captures different levels of signal strength using a sloped wedge or rod

Slice continuity

Ensures that images taken in slices align properly using a ramp or spiral shape