Motion correction

Question 1

Patient movement

Answer 1

• patient motion during data acquisition results in misalignment of projection frames
• causes various artifacts and a degradation of image quality
• some motion is unavoidable due to acquisition length
• must limit avoidable patient motion as much as possible

Question 2

Types of motion

Answer 2

• abrupt
• gradual
• other

Question 3

Detection of motion depends on…

Answer 3

• magnitude, timing, and number of events

Question 4

Correctable motion types

Answer 4

• translational
• includes y axis and x axis motion

Question 5

uncorrectable motion

Answer 5

• rotational motion

Question 6

methods of motion detection

Answer 6

• cine mode
• sinogram
• tracking of object center in frames
• projection summing
• frame-to-frame cross correlation

Question 7

Cine mode

Answer 7

• a method of watching moving data
• continuous loop
• can see shifts in object of interest

Question 8

Tracking

Answer 8

• object is centered in frame
• frame by frame tracking of the image can be done

Question 9

Sinogram

Answer 9

• created by taking the same row of image data from each projection and concentrating them in an image matrix
• 64 sinograms for a 64 x 64 matrix
• 32 sinograms for 2 rows summed
• counts/pixel of projection data vs. angle of the frame

Question 10

Sinogram in quality control

Answer 10

• used as a quality control tool after acquisition but before reconstruction
• used to detect: patient motion, skipped frames, collimator defects, image truncation, poor gating
• interruptions/discontinuities in activity

Question 11

Frame-to-frame correlation

Answer 11

• mathematical technique
• measures frame to frame differences
• best for abrupt and/or vertical motion

Question 12

technical methods to correct motion

Answer 12

• re alignment of the affected frames
• cross correlation
• diverging squares
• two-dimentional fit
• not always possible to correct motion

Question 13

Practical methods to correct motion

Answer 13

• make patient comfortable
• decrease time of acquisition
• assist patient in keeping still
• explain the significance of motion on image results
• prevention is best

Question 14

Motion Artifacts

Answer 14

• General blurring and decreased image quality
• ghost artifacts
• ray artifacts
• Cardiac artifacts

Question 15

Cardiac motion artifacts

Answer 15

• Hurricane sign: short axis horizontal motion
• smearing: long axis horizontal motion
• opposite side defect