ClearCanvas Product Recall Notice: Non-Square Pixels

Updated: 2010-03-03

What product is affected?

ClearCanvas Workstation v.1.5  and v.1.5 SP1 of the ClearCanvas RIS/PACS v.1.5

What is the issue?

The Angle and Calibration tools malfunction when they are applied to images composed of pixels that are not square. Consequently all distances measured in cm or mm and all angles will be incorrect.

What is the scope of this issue?

The defect is limited to images where the pixels are not square in shape. That is, this problem will manifest only when the DICOM header of the image specifies Pixel Aspect Ratio, and the computed ratio is anything other than 1. If the Calibration tool is applied to such an image to calibrate the distance between pixels, all resulting distance and area measurements will be incorrect. For example, using the Line tool after applying the Calibration tool on an image with non-square pixels will result in an incorrect measurement of length.

Have people actually been affected by this issue?

No, not to our knowledge. This recall is a result of findings from internal testing.

What do I need to do?

• Please do not use the Calibration and Angle tools at all if you are not certain whether you routinely encounter images with non-square pixels.
  
  Modalities that produce images with non-square pixels are rare. Nonetheless, when viewing such an image, it is very unlikely that an unsuspecting user would be alerted to the fact that the image has this attribute, since in all other respects, the image is presented correctly.
  
  The safest course of action, then, is to refrain from using the above tools.
  
  To determine whether or not a modality produces images that are composed of non-square pixels, please refer to the modality's DICOM conformance statement and take note of any documentation on the Pixel Aspect Ratio tag. Any particular image's Pixel Aspect Ratio can also be ascertained by using the DICOM Dump tool in the ClearCanvas Workstation and examining the Pixel Aspect Ratio tag (0028,0034). If this tag doesn't exist in the header of the image file, then the pixels are square, since DICOM requires the presence of this tag only in the event that the pixels are non-square.

• Analyze the effect on yourselves and your users and take appropriate action.

• Install the new version of ClearCanvas Workstation that corrects this problem when it becomes available.

What is ClearCanvas doing to address this issue?

Firstly, out of an abundance of caution, we have elected to remove ClearCanvas Workstation 1.5 and 1.5 SP1 from our website so that new users will not be affected by the issue. While this may seem extreme, it reflects our deep commitment to our users and to our quality process. Even though our products are freely available, we recognize the impact that they can have on patient care. Because of that, we take quality very seriously.

Secondly, we are reviewing and improving our internal processes to reduce the likelihood of similar issues occurring in the future. This will include a thorough review of our regression test suites and implementation of new unit tests. Furthermore, new compiler technologies have already been implemented that will catch this type of error early in the design phase.

Thirdly, we are correcting this problem in our upcoming release.  We expect to make this available within three weeks of the issue date of this bulletin.

Corrective Action Timelines

The expected date of release of a new version of the ClearCanvas Workstation that corrects this problem is 2010-03-05.