Carlijn Roozemond

Ciaran Bench, Vivek Desai, Carlijn Roozemond et al.

Feature embeddings acquired from pretrained models are widely used in medical applications of deep learning to assess the characteristics of datasets; e.g. to determine the quality of synthetic, generated medical images. The Fréchet Inception Distance (FID) is one popular synthetic image quality metric that relies on the assumption that the characteristic features of the data can be detected and encoded by an InceptionV3 model pretrained on ImageNet1K (natural images). While it is widely known that this makes it less effective for applications involving medical images, the extent to which the metric fails to capture meaningful differences in image characteristics is not obviously known. Here, we use Monte Carlo dropout to compute the predictive variance in the FID as well as a supplemental estimate of the predictive variance in the feature embedding model's latent representations. We show that the magnitudes of the predictive variances considered exhibit varying degrees of correlation with the extent to which test inputs (ImageNet1K validation set augmented at various strengths, and other external datasets) are out-of-distribution relative to its training data, providing some insight into the effectiveness of their use as indicators of the trustworthiness of the FID.

Alistair Mackenzie, Mark Halling-Brown, Ruben van Engen et al.

In this report a framework for the collection of clinical images and data for use when training and validating artificial intelligence (AI) tools is described. The report contains not only information about the collection of the images and clinical data, but the ethics and information governance processes to consider ensuring the data is collected safely, and the infrastructure and agreements required to allow for the sharing of data with other groups. A key characteristic of the main collection framework described here is that it can enable automated and ongoing collection of datasets to ensure that the data is up-to-date and representative of current practice. This is important in the context of training and validating AI tools as it is vital that datasets have a mix of older cases with long term follow-up such that the clinical outcome is as accurate as possible, and current data. Validations run on old data will provide findings and conclusions relative to the status of the imaging units when that data was generated. It is important that a validation dataset can assess the AI tools with data that it would see if deployed and active now. Other types of collection frameworks, which do not follow a fully automated approach, are also described. Whilst the fully automated method is recommended for large scale, long-term image collection, there may be reasons to start data collection using semi-automated methods and indications of how to do that are provided.