1. Tuesday Physics Case of the Day
Robert MacDougall, M.S.
Mark Supanich, Ph.D.
Donovan Bakalyar, Ph.D.
History: A radiograph of an AP projection of the pelvis acquired with a CR system demonstrates two sharp lines that span the length of the radiograph.
This artifact was most
likely caused by:
Improper use of edge enhancement
Black Surround Mask applied incorrectly
Misaligned Wedge Filter
Incorrect filter wheel position
Dirt on optical sensor of CR reader
Figure 1a: AP pelvis with line artifacts
Figure 1b: Magnified view of artifact

2. Answer (slide 1/3): The correct answer is b) Black Surround Mask applied incorrectly. Black Surround Masking is an image processing feature used to reduce viewing glare by applying a black mask outside the relevant anatomy. The placement of the mask typically corresponds to the position of the collimator blades. Image processing is performed within the area defined by the mask only (see Figures 1a and 1b).
Figure # 1a: Image with Black Surround Mask applied showing region of original processing.
Figure # 1b: Magnified view of black surround edge.

3. Answer (slide 2/3):
The correct answer is b) Black Surround Mask applied incorrectly. Black Surround Masking is an image processing feature used to reduce viewing glare by applying a black mask outside the relevant anatomy. The placement of the mask typically corresponds to the position of the collimator blades. Image processing is performed within the area defined by the mask only (see Figures 1a and 1b). In this case, the black surround mask was applied incorrectly by the software since there was no collimation (see Figure 2a). When the mask was removed to increase the visible anatomy after the image was processed, a sharp, sawtooth border remained as a result of the different image processing parameters inside and outside the masked region (see Figure 2b).
Figure # 2a: Initial image presentation – mask removed but not re-processed.
Figure # 2b: Magnified view of artifact with sawtooth pattern.

4. Answer (slide 3/3): The correct answer is b) Black Surround Mask applied incorrectly. Black Surround Masking is an image processing feature used to reduce viewing glare by applying a black mask outside the relevant anatomy. The placement of the mask typically corresponds to the position of the collimator blades. Image processing is performed within the area defined by the mask only (see Figures 1a and 1b). In this case, the black surround mask was applied incorrectly by the software since there was no collimation (see Figure 2a). When the mask was removed to increase the visible anatomy after the image was processed, a sharp, sawtooth border remained as a result of the different image processing parameters inside and outside the masked region (see Figure 2b). The artifact is not present in the unprocessed image (see Figure 3).
Incorrect Answers:
a) Improper use of edge enhancement
This can be ruled out by inspection of other edges within the masked region which are blurred.
c/d) Misaligned wedge filter or Incorrect filter wheel position
A filter would appear blurred in the image as a result of geometric distortion
e) Dirt on Optical Sensor of CR reader
The sharp, sawtooth nature of the line indicates the artifact is due to a post processing/digitization step.
Figure # 3: Raw, Unprocessed image with mask removed.
Reference
Kodak DirectView Help Guide, Version 2.0, September2007.