It is important for all users of ClearCanvas Workstation (hereafter, the "software" or "Workstation") who will be involved in any capacity in the treatment or diagnosis of patients to fully read and understand these instructions. Failure to read these instructions and any other documentation cited in this section could result in incorrect usage of the software, which could ultimately affect patient outcome.
In general, before beginning any form of diagnosis or treatment, an assessment of whether or not the data presented is complete and correct should be performed by the user. If there is any question as to whether or not the data being presented is complete and correct, the user must take appropriate steps to ensure that it is before continuing. This may include, for example, verifying the number of images reported by the software versus the number on a PACS for the same imaging study and contacting a PACS administrator to resolve any discrepancy.
Hardware and Software
Make sure you follow all instructions in the Installation section of this guide, and only install the software on systems that meet or exceed the minimum system requirements. Display devices, including printers, must be clinical grade and must undergo evaluation in their intended configuration before being used. The evaluation, and any required calibration or maintenance steps, should be performed at regular intervals. Any changes to the display configuration should be followed by an immediate re-evaluation.
Exclusions from Diagnostic Use
This section discusses certain types of images that, although the software can display them, should not be used for diagnostic purposes.
Lossy Compressed Images
Lossy compressed images displayed by the software will show the text "LOSSY" in yellow on the text overlay, along with the compression ratio(s). Images can be lossy compressed generally for one of two reasons:
|1.||The modality that originally created them stored them in a lossy compressed format. In this situation, whether or not the images are appropriate for diagnosis is dependent on the intended use of the modality and the images it produces.|
|2.||The images have been lossy compressed by a storage device, such as a PACS system. Such images should never be used for diagnosis, but rather the original images should be used. This includes images that were originally lossy compressed, and have been compressed further by a storage device. This will be evident on the image text overlay, as there will be multiple compression ratios displayed.|
See "Indications for Use" on the Regulatory Notices
Measurements performed on images in the Workstation are entirely dependent on the calibration of the acquisition modality. If there is any question as to whether or not a modality has been properly calibrated, or it has not undergone regular quality control tests and maintenance, the images it produces should not be used for diagnostic purposes.
Manually Calibrated Images
Images whose pixel size have been altered from their original values, either from within the software or by some other means, should not be used for diagnosis. The ability to perform manual calibration exists within the software and is discussed in more detail in a later section. This operation, even with the use of fiducials in the image, is subject to human error and the reported values are to be used at the user's own risk.
Values reported by any measurement or Region of Interest (ROI) tools (e.g. Ruler, Ellipse, Rectangle, Polygon) use the pixel size in calculating the reported values, and hence when such tools are used with manually calibrated images, the reported values are to be used at the user's own risk.
Although the software is capable of creating and displaying PET-CT fusion images, and can measure the Standardized Uptake Value (SUV), it currently lacks some tools that are commonly used for primary diagnosis, such as Fusion MIP/MinIP; however, some acquisition modalities will include MIP/MinIP images in the studies. Therefore, it is up to the user to decide whether primary diagnosis can be performed with the tools that are available in the Workstation.
The software is capable of producing "key images" with burned in measurements and annotations that can be recalled later for review. For the purposes of diagnosis, key images should never be used, but rather the original images from which they were derived should be used. Although key images may contain "burned in" statistics for ROIs, these values are considered informational only, and any diagnosis should be done by performing such measurements on the source images.
Before attempting to use the DICOM Print feature, ensure you read and fully understand the documentation in this guide.
Images are rendered in the same manner as they are for display in the software (8 bit only) and no additional processing is applied before being sent to the printer. Image quality is dependent not only on the ClearCanvas Workstation software, but also on the physical printer itself and the media on which it prints images. For each printer in use, the proper configuration must be determined, and image quality thoroughly evaluated. Otherwise, printed images should not be used for diagnosis.
The option to print "True Size" is also dependent on the capabilities of the printer, in that it must properly support the "Requested Image Size" DICOM attribute. Before using the "True Size" option in the treatment of patients, a thorough evaluation of accuracy should be performed. Even after evaluation, it is highly recommended that the image scale overlay not be turned off when printing "True Size" images, and the user should verify that the images are indeed true size by measuring the distance between the scale's minor tick marks on the printed film. The distance between minor tick marks is exactly 1cm.
Image Storage and Retrieval
This section discusses parts of the software that have to do with image storage and retrieval. Although these functions should operate as expected under normal conditions, it is possible for errors to occur in transport of images across the network, or on import into the Workstation's local store. Users should never assume that these operations have completed successfully, but rather they should verify the success of the operation before beginning any form of diagnosis or treatment involving the use of patient imaging studies.
When a patient study is sent to the Workstation from another DICOM device (e.g. via a PACS auto-route), the Workstation is unable to determine whether or not it received all the images, due to limitations in DICOM.
In the situation where a user has manually initiated a retrieval of one or more imaging studies from another DICOM device to the Workstation, it is important to check the Activity Monitor for any errors that may have occurred during transfer. For each study retrieved, there will be one work item for the retrieve operation which, if successful, will indicate the number of images retrieved, along with the number expected; these numbers should be the same. There will be another work item for importing received images into the local store. If both work items completed successfully, and the number expected, received and imported are all the same, then the entire study has been retrieved successfully. Note, however, that the number expected comes from the remote device, which Workstation has no control over. If this number is not accurately provided by the remote device, then the behaviour is unknown.
Workstation allows the user to retrieve select series within a study, which will result in a partial study in the local store, possibly leading to patient misdiagnosis due to incomplete information. It is very important that this feature be used with care, and if there is every any doubt about whether or not retrieving part of a study is the right thing to do, then the entire study should be retrieved.
The user is ultimately responsible for ensuring that all necessary images have been successfully received and imported before using them for treatment or diagnosis. Studies opened for viewing before they have been completely received remain incomplete; they are not updated as new images are received or imported.
When sending studies to another device, it is important to make sure the entire study was sent successfully, as the receiving device has no way to verify this, due to limitations in DICOM.
Work items for studies being sent to remote devices can be cancelled in the Activity Monitor. However, it is important that the operation either be restarted and allowed to complete successfully, or the study should be manually deleted from the destination device. Cancelling a send operation will result in a partial study on the destination device, which could lead to patient misdiagnosis due to incomplete information.
Select series in a study can also be sent to a remote device, which will result in a partial study on the destination device. It is important to use this function carefully, and if there is ever any doubt as to whether sending a partial study is the correct thing to do, then the entire study should be sent.
When importing images into the local store, the user should always check the Activity Monitor to ensure that the import completed successfully, and the number of images imported is correct.
Select series can be deleted from studies in Workstation's local store. This function should be used carefully as it can result in a partial study, which could cause patient misdiagnosis due to incomplete information. Also, in DICOM, studies are sent/received to/from many different devices, and deleting series from a study in Workstation does not mean they were deleted permanently. For example, Workstation will automatically send newly created key images and PDF attachments to remote devices (see publishing) in an effort to keep the study synchronized. It is important to consult a knowledgeable PACS professional when modifying the contents of a study.
Automatic Study Deletion
Workstation can be configured to delete studies a specific period of time after receipt/import. When configuring automatic study deletion, it is important to make sure study deletion times will be appropriate for the intended use of Workstation. For example, if Workstation is being used as a semi-permanent archive, it is important to make sure the configuration satisfies all legal/regulatory concerns.
Workstation will stop importing and receiving DICOM images if the maximum disk usage is reached. Work items in progress (in the Activity Monitor) when this occurs may fail, leaving one or more partial studies in the local store. Once the disk usage problem has been resolved, these work items should be restarted to ensure the affected studies are completely received/imported. Note that unsolicited receive operations, such as auto-routes coming from other devices, cannot be restarted from within Workstation; they must be restarted at the sending device.
Re-index File Store
The user should never simply assume that the re-index operation has completed successfully, but rather should always check the Activity Monitor to make sure no failures have occurred. Although the user is able to continue using the Workstation while a re-index is occurring, it is not advisable to perform any diagnostic activities during this time as studies may be incomplete if opened for viewing while a re-index is in progress. Such studies opened in the viewer will not be updated with newly re-indexed images as the re-index proceeds; the user must wait for the study to be complete in "My Studies" before opening the study for viewing.
Image Viewer Functions
This section discusses specific functions within the Image Viewer portion of the software that may require additional explanation in order to be used safely and effectively. However, it is important for the user to read the entire contents of this manual in order to fully understand the software and its functions.
The display of mammography images is automatically normalized with respect to flips and rotations depending on the laterality and patient orientation of the anatomy regardless of how the pixel data is stored. For lateral views (including MLO and LMO), the standard display is with the head towards the top and the posterior either towards the left (for the left breast) or towards the right (for the right breast). For cranial-caudal views, the standard display is with the patient's arms towards the top, the patient's median towards the bottom, and the posterior either towards the left or right (again, left and right breast, respectively). Additionally, overlay text will be positioned in the corners opposite the posterior to avoid occluding anatomy.
Despite these functions, it remains imperative that the standardized and consistent positioning of physical lead markers be used as part of the imaging protocol in order to ensure correct viewing of the images. The ACR requirements are for this marker to be placed near the patient's axilla (armpits), which translates to a position near the top of the images when displayed according to the previously described normalized views. Extreme discretion should be exercised if there is any discrepancy between this placement and the display of the image and/or the text overlay, as it indicates the presence of errors in the laterality and/or patient orientation information encoded in the image.
Pixel size information stored in the image headers are used by the Workstation to support features like ROI measurements and true size printing. In cross-sectional modalities (e.g. CT, MR, PT, etc.), these values will correspond to the actual anatomical size. In projection modalities (e.g. CR, DX, MG, etc.), these values value may represent either the physical size of detector elements (i.e. in the plane of the detector), or the anatomical size after some form of correction (either by assuming the anatomy of interest is at a particular depth, or by using fiducials located at the same depth as the anatomy of interest). Therefore, when making measurements on such images, it is imperative that the text overlay be consulted to determine which calibration method, if any, was used by the modality. Discretion should be exercised if the calibration method is unknown.
If the pixel size has not been specified by the modality, the Measurement Calibration function may be used to manually set the pixel size. Once this is done, the user can then make other measurements within the image and statistics will be reported in physical units (cm) rather than pixels. It is important to note that:
|•||Even within the same series/display set, each image must be calibrated separately. The calibration will not be applied to other images because it is unreasonable for the software to assume that every image in the series has the same pixel size.|
|•||For an image that has been calibrated, the calibration will apply everywhere that image appears, but only within a single viewing session. Calibration is a temporary function, and the underlying DICOM images are not modified in any way.|
Multi-planar reconstruction images that are slabbed are created by extracting a number of slices in a sub-volume and creating a 2-dimensional projection using a maximum, minimum or average intensity projection. The sub-volume slices contain interpolated values, and may not precisely reflect the absolute maximum, minimum or average intensities in the original data from which the data was extracted. Furthermore, statistics shown in regions of interest drawn on these images will be based on the projected pixel values; for example, the mean value reported in an area ROI on a MIP slab will be the mean value of the projected maximums. Therefore, these images should not be used for any quantitative analysis, but rather only for visual interpretation and guidance.
Images are fused by first constructing a volume from the PET series and re-slicing it at the same location within the patient for each CT image on which a PET image is to be overlaid. The software does not perform any kind of image registration in order to fuse images, but rather it relies entirely on the information provided in the image headers with regards to the position and orientation of images in the patient space. Therefore, it is very important to make sure the modality is accurately calibrated.
As discussed in the Image Fusion section, sometimes PET and CT images will indicate that the images were acquired in different frames of reference, usually because they are actually acquired by different physical devices that have simply been configured to work together. The software will still fuse such images, but there will be a yellow indicator on the text overlay of fused images indicating that the two Frames of Reference don't match. It is up to whomever is responsible for the configuration and maintenance of the acquisition devices to ensure they are properly calibrated. Otherwise, fused images will not appear correctly in the Workstation.
Standardized Uptake Value (SUV)
SUV is used to measure the concentration of a radiotracer in a defined region of interest on PET or PET-CT images. The accuracy of SUV is dependent on many factors, most of which are outside the control of ClearCanvas Workstation. Some of these factors are: image noise/background activity, attenuation correction and patient motion artefacts, partial volume effects, patient size, the timing of the scan post-injection, among others. ClearCanvas Workstation uses a simple, but widely accepted method for calculating SUV; however before using the SUV feature for diagnosis or treatment of patients, you should conduct an independent evaluation of the SUV values reported by ClearCanvas Workstation with studies from all the PET acquisition devices at your facility, under typical acquisition conditions.
Note also that SUV measurements on a PET-CT fusion image may be slightly different than a measurement performed on the corresponding PET image for the same anatomy. This is because the PET overlay for the fusion image is extracted from a volume and may have been interpolated, perhaps from more than one of the original PET images. The difference will be minimal, but if you ever have any doubt about which one is correct, always use the measurement from the PET image(s).
A Hanging Protocol automatically selects display sets from the study that was opened for viewing as well as any prior studies that are available for the same patient. It is very important to note that only studies that occur on the same day as, or prior to, the study that was opened for viewing are considered by the protocol. This is because matching of studies is time-based in relation to the study opened, and defining protocols that reference studies in the future is not intuitive and does not necessarily make sense in typical radiology workflow. Therefore, it is important to make sure you open the correct study, which is usually the patient's most recent (or current) study.
Also, because Hanging Protocols are based on simple filters, it is entirely possible that a valid prior study, or an image or series within it, will not be selected by a Protocol simply because the data within the study was not a match for a filter. Similarly, it is also possible for an older prior study to be selected instead of a more recent one simply because the older study matched the filter(s). This can happen especially often when there is no consistency in the DICOM headers of similar studies. As such, it is very important to standardize how various types of studies are described within your institution.
Finally, because Hanging Protocols can never be a replacement for human decision-making, it is the responsibility of the user to be aware of the patient's history, to make sure all the required studies are available and complete, and to make sure that everything presented by the Protocol is complete and correct before performing any kind of diagnosis or treatment. It is also highly recommended that care be taken to thoroughly test each Hanging Protocol for typical scenarios encountered within your institution to insure they will work as expected.
Study attachments allows the user to associate PDF reports and other documentation with a patient's study by creating and adding an Encapsulated PDF document DICOM file. There is an increased risk to patient safety and/or confidentiality if the wrong document (e.g. a report for a different patient) is attached to the study. The Workstation does not verify the contents of the PDF documents. It is strongly recommended that the user take advantage of the automatic document preview feature to ensure that the correct report is being attached to the study.
Study attachments are also automatically published back to your PACS server by default. In the event that you have accidentally attached a report to the wrong study, you cannot simply delete the study from Workstation's local store. Your PACS admin must find the study on your PACS, and any other servers to which it may have been published, and delete the attachment from the study. You must then delete the study from Workstation's local store (if it was stored locally), and redo the attachment.
When you open a study for viewing, prior studies are automatically found for the same patient, and they become available automatically in the viewer. See the section on prior studies for more details on how this feature works. In the event that one of your priors servers cannot be contacted, the software will warn you once that some prior studies may not be available and it will not warn you again until after the next time your server has been queried successfully.
In general, it is the responsibility of the user to be aware of the patient's history and to make sure all the required studies are available and complete before performing any kind of diagnosis or treatment.
ClearCanvas Workstation, Personal - User's Guide
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