PACS for the Developing World

Digital imaging is now firmly ensconced in the developed world. Its widespread adoption has enabled instant access to images, remote viewing, remote consultation, and the end of lost or misplaced film. Unfortunately, the current paradigm of Picture Archiving and Communication System (PACS), with advanced technology inseparable from high complexity, high purchase costs, and high maintenance costs, is not suited for the low-income developing world. Like the simple, easy to repair, 1950’s American cars still running on the streets of Havana, the developing world requires a PACS (DW-PACS) that can perform basic functions and survive in a limited-resource environment. The purpose of this article is to more fully describe this concept and to present a blueprint for PACS tailored to the needs and resources of the developing world. This framework should assist both users looking for a vendor-supplied or open-source solutions and developers seeking to address the needs of this emerging market

Introduction to Grayscale Calibration and Related Aspects of Medical Imaging Grade Liquid Crystal Displays

Consistent presentation of digital radiographic images at all locations within a medical center can help ensure a high level of patient care. Currently, liquid crystal displays (LCDs) are the electronic display technology of choice for viewing medical images. As the inherent luminance (and thereby perceived contrast) properties of different LCDs can vary substantially, calibration of the luminance response of these displays is required to ensure that observer perception of an image is consistent on all displays. The digital imaging and communication in medicine (DICOM) grayscale standard display function (GSDF) defines the luminance response of a display such that an observer’s perception of image contrast is consistent throughout the pixel value range of a displayed image. The main purpose of this work is to review the theoretical and practical aspects of calibration of LCDs to the GSDF. Included herein is a review of LCD technology, principles of calibration, and other practical aspects related to calibration and observer perception of images presented on LCDs. Both grayscale and color displays are considered, and the influence of ambient light on calibration and perception is discussed

Defining Acceptable Colour Tolerances for Identity Branding in Natural Viewing Conditions

Graphic arts provide the channel for the reproduction of most brand communications. The reproduction tolerances in the graphic arts industry are based on standards that aim to produce visually acceptable outcomes. To communicate with their target audience brands, use a set of visual cues that may include the definition of a single or combinations of them to represent themselves. The outcomes are often defined entirely by their colour specification without an associating it to target parameters or suitable colour thresholds. This paper researches into the feasibility of defining colour tolerances for brand graphical representations. The National Health Service branding was used as a test case borne out of a need to resolve differences between contracted suppliers of brand graphics. Psychophysical evaluation of colour coded navigation used to facilitate wayfinding in hospitals under the varying illuminances across the estate was found to have a maximum acceptable colour difference threshold of 5ΔE00. The simulation of defined illumination levels in hospitals, between 25-3000 lux, resulted in an acceptable colour tolerance estimation for colour coded navigation of 3.6ΔE00. Using ICC media relative correction an experiment was designed to test the extent to which substrate white points could be corrected for colour differences between brand proofs and reproductions. Branded stationery and publications substrate corrections to achieve visual matches had acceptable colour difference thresholds of 9.5ΔE*ab for solid colours but only 2.5ΔE*ab. Substrate white point corrections on displays were found to be approximately 12ΔE*ab for solids and 5ΔE*ab for tints. Where display media were concerned the use of non-medical grade to view medical images and branded content was determined to be inefficient, unless suitable greyscale functions were employed. A STRESS test was carried out, for TC 1-93 Greyscale Calculation for Self-Luminous Devices, to compare DICOM GSDF with Whittle’s log brightness. Whittle’s function was found to outperform DICOM GSDF. The colour difference formulas used in this research were tested, using near neutral samples 2 judged by observers using estimated magnitude differences. The CIEDE2000 formula was found to outperform CIELAB despite unexpected outcomes when tested using displays. CIELAB was outperformed in ΔL* by CIEDE2000 for displays. Overall it was found that identity branding colour reproduction was mostly suited to graphic arts tolerances however, to address specific communications, approved tolerances reflecting viewing environments would be the most efficient approach. The findings in this research highlights the need for brand visualisation to consider the adoption of a strategy that includes graphic arts approaches. This is the first time that the subject of defining how brands achieve tolerances for their targeted visual communications has been researched

Repeatability and reproducibility of visual field tests in people with established visual field loss

The thesis investigated the repeatability of the Esterman Visual Field Test (EVFT) on the Humphrey Field Analyser (HFA), and the reproducibility of the EVFT on the HFA and Henson Pro 5000 Perimeter. The reproducibility of the Ring of Sight (ROS) 24-2 full threshold (FT) examination was also evaluated. These were investigated with participants with established visual field loss (VFL) using case control studies. The reduced sensitivity that influences test-retest variability in those with VFL and differences within the perimeter methodologies, including the influence of background luminance were considered. Agreement in sensitivity threshold values or the Esterman Efficiency Scores (EES) between perimeters were analysed and pointwise analysis was undertaken. Any change in fitness-to-drive status or ability to determine/rule out disease was investigated. Principal Findings: The EVFT possesses poor repeatability and reproducibility for individuals with VFL with significant change in EES on test-retest at different sessions and significant lack of agreement when comparing EES on the HFA and the Henson Pro 5000 Perimeter. The EVFT possesses good repeatability and reproducibility in fitness-to-drive status. The significant variation in EES and location of defect in those with VFL does not impact upon on an individual’s fitness-to-drive status. It is recommended that a repeat examination is performed on the HFA for those with VFL who fails the EVFT on initial examination to account for variability of test-retest and the significantly lower EES recorded by the Henson Pro 5000 Perimeter. There is a large proportion of those with VFL (33.33%) who are unable to see a target, which is required to be seen, in order to conduct a visual field test on the ROS. There is significant lack of agreement in defect depth, defect location, mean deviation and sensitivity threshold values found on the ROS 24-2 FT examination compared to the SITA Standard 24-2 examination performed on the HFA. The ROS possesses a sensitivity value of 33.33%