In Colour Management, an ICC profile is a set of data that characterizes a colour input or output device, or a colour space, according to standards that are widely used by the International Colour Consortium (ICC). Complete accuracy and standardisation across a scanner portfolio are achieved by each individual scanner deploying a unique ICC profile with unique corrective ratios. ICC profiles that are produced by PathQA’s Sierra technology are DICOM and ISO 15076-1 compliant and meet the FDA Guidance of 2016.

Any Whole Slide Imaging (WSI) scanner or device.

Delta E (CIEDE2000) is a unit of measure defined by the International Commission on Illumination (CIE), that calculates and quantifies in CIELAB space the difference between two colours, one being a reference colour, the other a sample colour that attempts to match it.

Colour calibration with Sierra corrects Delta E values from averages in the range of 15-25 to below 2. Defined by the CIE, a Delta E value of 1 is approximately a just-noticeable colour difference to a person trained in colour analysis where different colours are directly adjacent to each other – average observers, including pathologists and cytologists, are unable to reliably differentiate colour differences below values of 2-3.

Many literature sources suggest that a delta E of 5 or below is acceptable for diagnosis. Therefore, device-specific Sierra ICC profiles computed from achievable Delta E values that average below 2 ensure the highest colour fidelity for validated digital pathology and digital cytology diagnosis.

The Sierra slide is formatted to the same specifications as standard glass tissue slides for WSI scanners. The slide incorporates 55 patches of a material that mimics the way stains bind to tissue, which when stained using common histology and cytology stains from across the colour gamut of pathology creates an accurate measure of ground truth colour as found in histological and cytological samples.

With the colour truth of the slide captured, the Sierra slide can be scanned on the WSI device to be analysed with the resultant image containing the colour errors introduced by digitization.

Using the ground truth slide measurements and the scanned colour with errors, the colour difference introduced by WSI is calculated, represented as Delta E values using the CIEDE2000 formula accredited by ISO11664-6. From this data, an ICC profile is computed to correct the image displayed to the user when displayed on a monitor using the integrated viewer or in other scenarios may be presented to an AI platform.

Please contact us to discuss the integration of Sierra technology into your work flow. Each workflow and architecture can differ, and we can scope out a bespoke solution of colour management of all WSI, diagnostic and AI workflows.

The analysis displays inherent errors in current WSI device images and therefore inclusion in onwards assessment and diagnosis by human or AI. The analysis shows the magnitudes by which these errors can be corrected, to what accuracy systems and their data can be validated, how QA and standardisation requirements can be met in an interoperable format and provides the framework for meeting FDA/GLP auditing and reporting requirements.

Importantly, Sierra calibration creates an end-to-end process that can be trusted, as it can also be tested – the ground-truth colour input can be matched closely to the ground-truth colour displayed. This means that once integrated into workflow, the cytologist or pathologist can work from coloured images that are standardized across any calibrated WSI device and are accurate to the actual, ground truth colour of the real slide.

It can be shown that diagnosis can occur on images that have all the benefits of digitization without the colour artefacts that otherwise may invalidate analysis comparative to the actual stained sample. Sierra VSA is a tool that allows the user to establish quantitative current and target colour differences within their WSI systems and qualitative visual confirmation of the effect of applying Sierra ICC profiles to tissue, and provides a framework on which to consider elements of integration and FDA/GLP auditing pipelines before further investment in an advanced solution and deployment.

The integrated viewer takes a scanner-specific ICC profile and applies the corrective colour values to the raw tissue image collected from the same WSI scanner to be analysed as it is input to the viewer, alongside the colour space of the display to be used. VSA assumes sRGB and a suggested rendering intent as default, for the purposes of demonstration, however other colour spaces are possible and potentially preferred in medical imaging. The ICC profile acts as metadata tagged to the raw image – nothing about the raw image and its original image quality is changed, instead it is displayed exactly as captured but with exception of improved colour accuracy.
It is Important to Note: This Software is for Research Use Only (RUO) and has not been validated for In vitro Diagnostics (IVD).

The slide should always be stored in the container it was supplied in when not in use.

Supported image file formats used in the VS-A and VS-P applications are based on the OpenSlide Library capabilities. It may be possible to use software from 3rd parties to convert currently unsupported vendor formats to generic TIFF containing a pyramid of resolution levels that could then be analysed by the VS-A and VS-P applications, however this capability has not been verified for all currently unsupported vendor formats.

If the FAQs above haven’t provided you with the information you are looking for, please contact us for further assistance, we will endeavour to respond to your request within two working days at enquiries@pathqa.co.uk.