Case Author(s): Scott Winner, M.D. and Henry Royal, M.D. , 2/14/97 . Rating: #D3, #Q4

Diagnosis: Moire effect

Brief history:

Quality control. Spatial resolution image obtained with a 4-quadrant bar pattern.

Images:

Bar phantom image

View main image(mm) in a separate image viewer

Full history/Diagnosis is available below

Diagnosis: Moire effect

Full history:

Utilizing a 128 x 128 matrix, the technician acquired this 4-quadrant bar pattern to evaluate the camera's external spatial resolution.

Radiopharmaceutical:

Cobalt-57 flood source

Findings:

There is distortion of the bar pattern image.

Discussion:

Spatial resolution determines the ability to see detail in an image and is one of the factors that determines the sharpness of edges. Variability in light collection, electronic noise in the photomultiplier tubes, crystal deterioration and collimator design can all cause decreased resolution. Therefore, spatial resolution must be checked on a regular basis (in general, weekly tests are recommended).

There are two common causes for Moire patterns. First, when a 4-quadrant bar pattern is used with the collimator in place, Moire patterns will be present due to the interplay between the bars of the test pattern and holes of the collimator. Due to the increased thickness of the septa, medium and high energy collimators are more likely to cause Moire patterns and are rarely used when acquiring a bar phantom image.

A second common cause for the Moire pattern is the use of too small of a matrix size while acquiring the image. Moire patterns can be prevented by the use of 512 x 512 or 1024 x1024 image matrices. The bar pattern shown in this case was obtained with a low energy collimator, but the techologist acquired this digital image with a 128 x 128 matrix. This large pixel size led to the Moire pattern observed.

ACR Codes and Keywords:

References and General Discussion of Bone Scintigraphy (Anatomic field:Skeletal System, Category:Normal, Technique, Congenital Anomaly)

Search for similar cases.

Edit this case

Add comments about this case

Read comments about this case

Return to the Teaching File home page.

Case number: bs072

Copyright by Wash U MO