Block selective redaction for minimizing loss during de-identification of burned in text in irreversibly compressed JPEG medical images

Abstract

Abstract. Deidentification of medical images requires attention to both header information as well as the pixel data itself, in which burned-in text may be present. If the pixel data to be deidentified is stored in a compressed form, traditionally it is decompressed, identifying text is redacted, and if necessary, pixel data are recompressed. Decompression without recompression may result in images of excessive or intractable size. Recompression with an irreversible scheme is undesirable because it may cause additional loss in the diagnostically relevant regions of the images. The irreversible (lossy) JPEG compression scheme works on small blocks of the image independently, hence, redaction can selectively be confined only to those blocks containing identifying text, leaving all other blocks unchanged. An open source implementation of selective redaction and a demonstration of its applicability to multiframe color ultrasound images is described. The process can be applied either to standalone JPEG images or JPEG bit streams encapsulated in other formats, which in the case of medical images, is usually DICOM.

Pseudonymization and Anonymization of Radiology Data

“…However, it can occur that images contain burned in text [3]. In case of acquisition devices that use video capture, storage of screen shots or secondary captures by the radiologist, or encapsulation of scanned documents, the image part of the DICOM file might contain patient identifiable information [4]. In these cases, the pixels of the image containing the identifiable information need to be blacked out or otherwise made unreadable before the images are considered to be deidentified.…”

Cybersecurity in PACS and Medical Imaging: an Overview

“…Robinson [ 44 ] provides an overview of literature and available tools for de-identification of DICOM images and discusses cases where patient identifying information may be present in the image pixel data, such as Ultrasound and Nuclear Medicine images, screen captures, scanned documents, post-processed images and the output of some computer-aided detection systems. Clunie et al [ 45 ] discuss the special case where patient identifying information is embedded in the image pixel data of images that have been subjected to an irreversible (lossy) image compression using the JPEG (Joint Photographic Expert Group) compression algorithm, something that is very common for example with Ultrasound cine-loops. In this situation the sequence of decompression, de-identification and re-compression would lead to a decrease in image quality, which is undesirable.…”