What products are affected?

• All versions of ClearCanvas ImageServer
• All versions of ClearCanvas Workstation

What is the issue?

The ClearCanvas DICOM library utilized by the ClearCanvas Workstation and ClearCanvas ImageServer cannot decode DICOM unknown (UN) Value Representation (VR) attributes.  UN VR attributes typically occur for tags recently added to the DICOM standard when a message with those tags is passed through  a system that does not have knowledge of the attribute.  These attributes are left as UN VR, and applications using the DICOM library currently cannot decode the attributes.

There are two specific issues that have been caused by this functionality in the DICOM library:

• With the ImageServer if the tag "Lossy Image Compression" is encoded as UN VR, the ImageServer cannot compress the images within the study.
• With the Workstation, we have seen in the field the "Imager Pixel Spacing" tag in certain DR images being encoded as UN VR.  This causes subsequent measurements done by the Workstation to be reported in pixels instead of cm.  The error is obvious, so there's no risk of misdiagnosis, although the lack of ability to measure could be problematic.

What is the scope of this issue?

A specific set of circumstances must occur for a DICOM attribute to be encoded as UN VR.  The message must originate from a system that transfers the image as Implicit VR Little Endian where the VR of the tags are not encoded in the message. The message must then be changed to an Explicit VR transfer syntax by the system and transferred to another system, at which time the unknown tags are encoded as UN VR.  The problem may also occur  with studies stored on DICOM media, such as a CD, where files are typically stored as Explicit VR Little Endian.

Have people actually been affected by this issue?

Yes, both the issue with the ImageServer and with the Workstation have been seen in the field.

What do I need to do?

• Analyze the effect on yourselves and your users and take appropriate action.
• Install the new versions of ClearCanvas ImageServer and Workstation that corrects this problem when they become available.

What is ClearCanvas doing to address this issue?

We have made changes in the DICOM library to convert UN VR attributes to their proper VR, if it is known.  We have also written a number of regression tests to make sure this new functionality works properly.

Corrective Action Timelines

These problems will not be addressed until the next regularly scheduled releases of the ClearCanvas ImageServer and ClearCanvas Workstation, expected in the fall of 2010.

What products are affected?

• ClearCanvas ImageServer v.2.0 of the ClearCanvas RIS/PACS v.2.0
• ClearCanvas ImageServer v.1.5 of the ClearCanvas RIS/PACS v.1.5
• ClearCanvas Workstation v.2.0 SP1 of the ClearCanvas RIS/PACS v.2.0
• ClearCanvas Workstation v.1.5 SP1 of the ClearCanvas RIS/PACS v.1.5
• ClearCanvas Workstation v.1.5 of the ClearCanvas RIS/PACS v.1.5

What is the issue?

The value for Rescale Slope and Intercept will be truncated to 10 significant digits when an image is compressed or decompressed by the ImageServer or decompressed by the Workstation.  For example, if one of these tags were encoded as "10.000244140625", the value would be truncated in the DICOM file stored by the ImageServer to "10.00024414".

What is the scope of this issue?

During the act of compressing or decompressing a DICOM file, the DICOM library creates a copy of the Rescale Slope and Intercept.  When the copy is made, only 10 significant digits are preserved. 

From a practical perspective, this should not cause any issues due to there being 10 significant digits preserved.  However, there is still a loss of data since the original value from the modality is not preserved.

Have people actually been affected by this issue?

The issue was reported via our forums during testing by a customer.  We have no knowledge of this being a significant issue.

What do I need to do?

• Analyze the effect on yourselves and your users and take appropriate action.
• Install the new version of ClearCanvas ImageServer that corrects this problem when it becomes available.

What is ClearCanvas doing to address this issue?

We have already made the correction in the DICOM toolkit and have expanded our regression test suites to include some further testing for this issue.  We've also reviewed the affected code to look for other potential defects and have not found any issues.

Corrective Action Timelines

These problems will not be addressed until the next regularly scheduled releases of the ClearCanvas ImageServer and ClearCanvas Workstation, expected in the fall of 2010.

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.