Anindita Saha

A Framework for Incorporating Patient Preferences Regarding Benefits and Risks into Regulatory Assessment of Medical Technologies.

BACKGROUND In response to 2012 guidance in which the US Food and Drug Administrations (FDA) Center for Devices and Radiological Health (CDRH) stated the importance of patient-centric measures in regulatory benefit-risk assessments, the Medical Device Innovation Consortium (MDIC) initiated a project. The project was used to develop a framework to help the Food and Drug Administration (FDA) and industry sponsors understand how patient preferences regarding benefit and risk might be integrated into the review of innovative medical devices. METHODS A public-private partnership of experts from medical device industry, government, academia and non-profits collaborated on development of the MDIC patient centered benefit-risk framework. RESULTS The MDIC Framework examines what patient preference information is and the potential use and value of patient preference information in the regulatory process and across the product development life cycle. The MDIC Framework also includes a catalog of patient preference assessment methods and an agenda for future research to advance the field. CONCLUSIONS This article discusses key concepts in patient preference assessment of particular importance for regulators and researchers that are addressed in the MDIC Framework for patient centered benefit-risk assessment as well as the unique public-private collaboration that led its development.

Evaluation of high‐resolution and mobile display systems for digital radiology in dark and bright environments using human and computational observers

— As digital display systems replace film traditionally used for reading radiographic images, resource-intensive acceptance testing must be performed to ensure that quality meets and maintains desired specifications. If machine observers can replace human readers, whose performances are highly variable, the results will be more consistent and less costly. To be effective, however, the automated observers must track human performance. An approach for a model observer, validated with human readers, for the evaluation of the visibility of low-contrast small targets in high-resolution and mobile displays under different ambient illumination, will be described. The displays were tested using CDMAM-like digital phantoms containing disks of varying diameters and contrasts on a flat background. For this task, we find the best indicator of display performance to be the displays ability to represent small luminance contrast, not resolution or pixel size. The results confirm that high-resolution systems perform better under low illumination while illuminance has a minor impact on the mobile-display performance. Finally, the results show that the machine observer tracks the performance of human readers. Machine observers with proper validation can replace humans in the acceptance testing procedures, saving the testers both time and money.

Color measurement methods for medical displays

— The effect of different measurement methods on the characterization of display color, maximum color difference, and luminance uniformity of medical liquid-crystal displays are reported. We use a telescopic colorimeter and a custom-designed collimated probe with an internal lens attached to a spectrometer. The maximum color-difference variations were found to be between 0.0047 to 0.0073, in the same range as variations among methods, displays, and screen locations.

Accurate color measurement methods for medical displays

PURPOSE The necessity for standard instrumentation and measurements of color that are repeatable and reproducible is the major motivation behind this work. Currently, different instrumentation and methods can yield very different results when measuring the same feature such as color uniformity or color difference. As color increasingly comes into play in medical imaging diagnostics, display color will have to be quantified in order to assess whether the display should be used for imaging purposes. The authors report on the characterization of three novel probes for measuring display color with minimal contamination from screen areas outside the measurement spot or from off-normal emissions. They compare three probe designs: A modified small-spot luminance probe and two conic probe designs based on black frusta. METHODS To compare the three color probe designs, spectral and luminance measurements were taken with specialized instrumentation to determine the luminance changes and color separation abilities of the probes. The probes were characterized with a scanning slit method, veiling glare, and a moving laser and LED arrangement. The scanning slit measurement was done using a black slit plate over a white line on an LCD monitor. The luminance was measured in 1 mm increments from the center of the slit to +/- 15 mm above and below the slit at different distances between the probe and the slit. The veiling glare setup consisted of measurements of the luminance of a black spot pattern with a white disk of radius of 100 mm as the black spot increases in 1 mm radius increments. The moving LED and laser method consisted of a red and green light orthogonal to the probe tip for the light to directly shine into the probe. The green light source was moved away from the red source in 1 cm increments to measure color stray-light contamination at different probe distances. RESULTS The results of the color testing using the LED and laser methods suggest a better performance of one of the frusta probes at shorter distances between the light sources, which translates to less contamination. The tails of the scans indicate the magnitude of the spread in signal due to light from areas outside the intended measurement spot. The measurements indicate a corresponding glare factor for a large spot of 140, 500, and 2000 for probe A, B1, and B2, respectively. The dual-laser setup suggests that color purity can be maintained up to a few tens of millimeters outside the measurement spot. CONCLUSIONS The comparison shows that there are significant differences in the performance of each probe design, and that those differences have an effect on the measured quantity used to quantify display color. Different probe designs show different measurements of the level of light contamination that affects the quantitative color determination.

Assessment of Mobile Technologies for Displaying Medical Images

We compared the characteristics of state-of-the-art mobile display systems based on reflective and transmissive liquid crystal displays (LCDs) and an organic light-emitting display with respect to physical characterization metrics and observer studies. Physical performance factors provided information on the differences among display technologies. Observer studies resulted in different system ranking between the task-based performance and user-preference approaches. The results of the physical characterization and preference study showed that the reflective LCD ranked lower. We also found that ambient illumination played a lesser role than previously seen in large-format workstation displays. The methodology developed in this study provides an initial insight into the comparison of alternative technologies for display of diagnostic images in small portable devices.

Display methods for adjustable grayscale and luminance depth

We explore the calibration of a high luminance range, dual-layer, liquid crystal display (LCD) prototype. The operation of the prototype is done by splitting a high luminance resolution image (graylevel > 28) into two 8-bit depth components and sending these images to the two liquid crystal panels stacked over the backlight module. By interpolation of a small set of luminance data gathered using a specialized luminance probe, the look-up table of graylevel pairs of front/back layer LCD and the corresponding luminance values can be generated. To display images, we fit an extended DICOM model to the interpolated luminance table which is adjustable for graylevel and luminance depth. A dynamic look up table is generated in which for each luminance there are several graylevel pair candidates. We show results for one possible calibration strategy involving the pair selection criterion. By selecting the pair that maximizes back-layer smoothness, the images with arbitrary graylevel and luminance depth can be then displayed with equal perceptual distance between luminance levels, while minimizing parallax effects. Other possible strategies that minimize glare and noise are also described. The results can be used for high luminance range display performance characterization and for the evaluation of its clinical significance.

Working with the Food and Drug Administration's Center for Devices to Advance Regulatory Science and Medical Device Innovation.

Within the US Food and Drug Administration (FDA), the mission of the Center for Devices and Radiological Health (CDRH) is to protect and promote public health by assuring that patients have timely and continued access to medical devices that are both safe and effective. Inherent in this mission is an obligation to facilitate innovation so that better medical devices can be developed and utilized as quickly as possible (1–3). To accomplish this goal, CDRH is actively engaged in advancing “regulatory science” for use in the product development and review process. Regulatory science research and practices provide industry and FDA with scientifically based assessment tools and approaches that can assist in the development, manufacture, and evaluation of new devices and technologies, as well as the creation of more efficient regulatory pathways (4,5). Most of the 1600 CDRH staff members (which include scientists, engineers, clinicians, statisticians, and public health specialists) support regulatory science processes by: (i) developing new standardized test methods and computational modeling techniques through laboratory-based device research; (ii) analyzing premarket bench, animal, and clinical trial testing and data for new devices; (iii) improving surveillance and epidemiological methods for monitoring and studying devices already on the market; (iv) preparing regulatory-based information and guidance documents to assist industry; and (v) bringing together interested parties and experts to address challenges in device development and assessment. With the fast-paced advances in science and the increasing complexity of new devices and technology, CDRH strives to collaboratively work with external stakeholders to continually update its regulatory science knowledge base. To enable this effort, CDRH has several initiatives by which private industry, the medical community, patient groups, and academia can partner with federal scientists to exchange information and remove barriers that may impede medical device development, thus fulfilling our collective goal of providing patients access to better devices. In the text of this article, we present several of the current CDRH programs and pathways that foster scientific collaboration and regulatory interaction, promote medical device innovation, and welcome your participation. A summary of all available programs (presented under three general categories including: Collaborative Research and Support Programs, Advancing Regulatory Science Expertise and Information Exchange, and Streamlining Regulatory Review Pathways) appears in Table 1 and includes website links to find more information.

Validation of simulated point response of columnar phosphor screens

Typical methods to measure the resolution properties of x-ray detectors use slit or edge devices. However, complete models of imaging systems for system optimization require knowledge of the point-response function of the detector. In this paper, we report on the experimental methods developed for the validation of the point-response function of an indirect columnar CsI:Tl detector predicted by Monte Carlo using mantis. We describe simulation results that replicate experimental resolution measurements using edge and pinhole devices. The experimental setup consists of a high-resolution CCD camera with a 1-to-1fiber optic faceplate that allows measurements for different scintillation screens. The results of these experiments and simulations constitute a resource for the development and validation of the columnar models of phosphor screens proposed as part of previous work with mantis. We compare experimental high-resolution pinhole responses of two different CsI(Tl) screens to predictions from mantis. The simulated response matches reasonably well the measurements at normal and off-normal x-ray incidence angle when a realistic pinhole is used in the simulation geometry. Our results will be combined with results on Swank factors determined from Monte Carlo pulse-height spectra to provide a comprehensive validation of the phosphor models, therefore allowing their use for in silico system optimization.

9.2: Temporal and Color Measurements in Medical Displays

We report on the accurate characterization of temporal response, maximum color difference and luminance uniformity in medical liquid crystal displays. We find that the variability among results from different methods can be larger than measured color differences, and that poor response time estimates occur for transitions between neighboring gray levels.