Medical Grade Displays in Radiation Oncology

In modern day medicine medical images are an integral part of clinical care. They are used in almost every clinical department from diagnosis to treatment and beyond. Medical images are viewed using electronic displays of various sizes, shapes, hardware, and software. Some clinical departments, like diagnostic radiology, require electronic displays with a large dynamic range, high contrast and high resolution. Other departments do not have any requirements and will use any commercially available display in their clinical workflow. Viewing the same medical image on different electronic displays with different hardware, software or calibration setup could influence how observers perceive and analyze these images. This occurs often when a patient is referred from diagnostic radiology to another clinical specialty department such as radiation oncology. In this case, the patient’s tumor would be diagnosed using a high-performance display while their treatment will be planned and delivered using a commercially available display. In this dissertation, at first, an experiment was design to examine and verify the visual contrast sensitivity of observers using the two types of displays used in the clinic. Observers were tasked with detecting a modulating bar pattern using each display under different background luminance levels and ambient room illumination. The luminance response of each display was also measured for proper comparison. Second, a set of visual experiments compared the image quality of both displays in the different sections of the radiation oncology workflow. Observers were tasked with comparing medical images viewed on both displays and ranking them on a rating scale. As part of the workflow, the observers used both displays to contour tumor and healthy tissue volumes, analyze and fuse two sets of images, verify and adjust patient’s treatment position in three degrees of motion. The results show a clear presence for the high-performance display over the commercial grade display in every step of the radiation oncology workflow. It was shown that better visualization of medical images can improve the accuracy and precision of treatment plan and treatment delivery of radiation oncology patients

Towards greater clarity for the analysis of imaging studies: Development & validation of an alternative to the area under the receiver-operator characteristic curve.

This thesis arose from a 2006 study performed by the author and his collaborators that attempted to gain regulatory approval for computer-assisted detection (CAD) software. The USA Food & Drug Administration (FDA) obliged us to use the change in the area under the receiver-operator characteristic curve (ROC AUC) as our primary outcome. Despite its wide dissemination in radiology research, we found implementation of ROC AUC very problematic. This thesis explores the hurdles we encountered and argues for an alternative approach. Chapter 1 describes the rationale for and against ROC AUC as a measure of diagnostic performance. An alternative analysis based on net benefit is proposed on the basis that it is more transparent and simpler to interpret. Chapter 2 uses the net benefit method to analyse a multi-reader multi-case (MRMC) study of CAD for CT colonography. The analysis requires an estimate of relative misclassification costs for false-negative versus false-positive diagnoses; “W”. This study used a conservative value for W, arrived at via consensus. In Chapter 3 an evidence-based value for W in the context of screening for colorectal cancer and polyps by CT colonography is arrived at via a discrete choice experiment (DCE) of patients and healthcare workers. Chapter 4 uses the value for W obtained in Chapter 3 in a net benefit analysis to compare observer performance in two MRMC studies of CAD for CT colonography. Chapter 5 obtains W by DCE for a different clinical context – detection of extracolonic pathology by CT colonography. Chapter 6 describes a systematic review that aims to determine whether reporting of MRMC ROC AUC methods in the radiological literature is comprehensive. Chapter 7 then provides guidelines for the comprehensive reporting of MRMC ROC AUC studies. The thesis finishes with a summary of the work performed and suggestions for further research