Patent Application
20250078696
To enable consistent and optimal contrast perception for the viewing of medical images, professional radiology standards apply to the displays on which such images are presented as well as to the ambient environments in which radiological reads are performed. For example, standards for display grayscale characteristics and standards for room lighting often apply.
With regard to greyscale display characteristics, computer monitors on which medical images are displayed typically undergo a calibration process that modifies an existing characteristic curve of the display. The characteristic curve (e.g., a curve representing a relationship between a Luminance Output (LO) and a Digital Driving Level (DDL) of each pixel) is modified such that each DDL is maximally distinguishable from that of the other pixels of the display throughout a luminance range. Such calibration processes are typically applied across all display equipment to ensure that the appearance of a medical image is consistent across similarly-calibrated displays and to ensure diagnostic quality.
A greyscale display calibration process can be performed manually or automatically. The calibration process typically involves the display of a test pattern on the computer monitor for visual inspection by a user, who is then able to adjust display parameters of the monitor, or for measurement by a photometer facing the monitor, with software providing for parameter adjustments based on photometer measurements.
Currently, there is no mechanism to calibrate digital displays found in extended reality head mounted displays for use in medical imaging. There exists a need for improved systems and methods for calibrating medical imaging displays in these types of devices.
Embodiments disclose systems and methods for calibration of head mounted displays, such as virtual reality headsets, augmented reality headsets, and mixed reality headsets. The systems and methods can be used to enable such head mounted displays to conform to medical imaging display standards.
An embodiment is directed toward a self-calibrating display system that includes a photosensor disposed at a digital display screen of a head-mounted display and a processor. The processor is configured to display a test pattern on the digital display screen, determine a correction factor based on luminance values as detected by the photosensor of at least a portion of the displayed test pattern, and apply the determined correction factor to adjust a display driving level of the digital display screen.
In an embodiment, the processor is further configured to compare a generated characteristic curve of the digital display screen with a standard display function to determine the correction factor. The standard display function may be a greyscale standard display function for medical imaging displays. Optionally, a calibration record can be generated. The calibration record may be generated to store information associated with the calibration of the display system and may include, for example, the calibration settings and/or calibration history for the sensor. The calibration record may be stored, for example, on the device. An advantage of generating and/or storing the calibration record is that the device may not need to be calibrated upon each use.
According to an embodiment, the head-mounted display is a virtual reality headset, augmented reality headset, or mixed reality headset. The digital display screen can include a lens-facing surface and a rear-facing surface (opposing surface), where the photosensor can be disposed at either or both surfaces. The photosensor can comprise one, two, or more photosensors, each of which can be associated with a distinct display screen (or distinct portion thereof) of the head-mounted display. The digital display screen can comprise one, two or more digital display screens, and each of the photosensors can be associated with a distinct one of the display screens.
In an embodiment, the processor can be further configured to determine a color correction factor based on color values as detected by the photosensor of at least a portion of the displayed test pattern and apply the determined color correction factor to adjust a color temperature of the digital display screen.
Another embodiment is directed toward a method for self-calibrating a display system that includes displaying a test pattern on a digital display screen of a head-mounted display and determining a correction factor based on luminance values as detected by a photosensor disposed at the digital display screen. The luminance values are detected from at least a portion of the displayed test pattern. The method further includes applying the determined correction factor to adjust a display driving level of the digital display screen. Optionally, the method can include generating a calibration record.
The method can further include comparing a generated characteristic curve of the digital display screen with a standard display function to determine the correction factor. The standard display function may be a greyscale standard display function for medical imaging displays.
In an embodiment, the head-mounted display is a virtual reality headset, augmented reality headset, or mixed reality headset. The digital display screen can include a lens-facing surface and a rear-facing surface, where the photosensor can be disposed at either or both surfaces. The photosensor can comprise one, two, or more photosensors, each of which associated with a distinct display (or a distinct portion of a display screen) of the head-mounted display. The digital display screen can comprise one, two, or more digital display screens, and each of the photosensors can be associated with a distinct one of the display screens.
The method can further include determining a color correction factor based on color values as detected by the photosensor of at least a portion of the displayed test pattern and applying the determined color correction factor to adjust a color temperature of the digital display screen.
The foregoing will be apparent from the following more particular description of example embodiments, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating embodiments.
A description of example embodiments follows.
Virtual reality (VR) systems, including extended reality (XR) and augmented reality (AR) systems, make use of head mounted displays (HMDs) to present a virtual, three-dimensional (3D) environment to a user. Recently, VR technologies have been adapted and extended to support various clinical applications, including medical imaging review procedures. Examples of systems and methods providing for virtual medical imaging reading room environments are described in International Pub. No. WO2022/047261A1, the entire teachings of which are incorporated herein by reference.
Traditionally, medical imaging review procedures are conducted in radiology read rooms, with images being presented on one or more computer monitors. The implementation of a read room environment in a virtual reality system can provide for several advantages. For example, whereas a read room is a physical location in which a reader must be present and requires a physical space large enough to accommodate not only the reader but also hardware consisting of computer workstations and monitors, a virtual reality system can effectively create a read room environment in any physical location and with a significantly more compact hardware footprint. Virtual reality can also provide for improved visualization and interaction with complex environments.
A challenge of implementing a read room environment in a virtual reality system is providing for virtual imaging displays that meet professional radiology standards, such as greyscale calibration requirements. Standard calibration devices and processes can be unsuitable for use with head-mounted displays. For example, standard hand-held calibration devices are physically adapted to be held up to a screen of a conventional computer monitor and include photosensors adapted to detect light from such larger-format displays. Similarly, photosensor devices configured to be attached to or integrated within a computer monitor are not capable of being attached to or integrated within a head-mounted display given physical format differences. Furthermore, head-mounted displays of virtual reality devices include display screens that are significantly smaller and disposed much closer to a user's eyes than conventional computer monitors. Such display screens are also configured to present a three-dimensional, 360° environment rather than a flat, two-dimensional presentation. As such, display characteristics affecting a user's perception can vary greatly between conventional displays and head-mounted displays.
Embodiments provide systems and methods for enabling automatic calibration of head-mounted displays. These systems and methods can be particularly advantageous for use in medical imaging review contexts.
In some embodiments, the head mounted displays 100a-100c illustrate example configurations in which an integrated photosensor 120a-120c is disposed at a rear-facing surface 103 of a display screen 102, relative to lenses 112, 114 of the display. The photosensor 120a-120c is associated with a portion of the display screen 102 presenting to a right lens 114 (see 100a
In some embodiments, the head-mounted displays of
The photosensor can also be disposed at one or more locations relative to lenses 112, 114. For example, as shown in
In yet further examples, a photosensor 120d can be disposed at a lens-facing surface 105 of the display screen 102 and at a location close to or associated with a right lens 114 of the device 100d, as shown in
It should be understood that photosensors can be included within a head-mounted display in any combination. For example, the photosensor configurations of any of
The photosensors (e.g., photosensors 120a-120f, 220a-220d, 222a-222d) can be configured to detect amounts of light emitted from the display screen (e.g., screen 104) to provide luminance values. A photosensor, as used herein, can comprise a plurality of discrete sensors capable of detecting light. For example, a “photosensor” can comprise an array of photodetection elements. Examples of suitable photodetection elements include photoelectric cells, photovoltaic cells, and photo voltaic transistors. The VR displays used in the HMD typically use a higher pixel density, and may use a smaller pixel pitch, than conventional liquid crystal displays (LCDs). Because the VR display in the HMD is a closed system, there are no ambient light scenarios to consider when calibrating the display. In contrast, for example, a radiologist viewing a diagnostic monitor in a reading room may need to consider the way the ambient light is affecting the display monitor when reading the radiology results. This is not a concern with the VR display in the HMD as it is an inherently isolated system.
As used herein, a “standardized display function,” is a function that defines a relationship between input values for pixels of a digital display and a desired output feature (e.g., luminance, color, etc.).
A standardized display function for the display of greyscale images is provided in Part 14 of the Standards for Digital Imaging and Communications in Medicine (DICOM). DICOM Part 14 was developed to provide for a quantitative method of modifying an existing characteristic curve of a display system (e.g., a curve representing a relationship between a Luminance Output (LO) and a Digital Driving Level (DDL) of each pixel) to the Grayscale Standard Display Function (GSDF). The standard provides for maximizing the Just Noticeable Differences (JND) between each DDL and is based on models of human perception. The standard describes a relationship between LO and DDL values such that a slope of a characteristic curve of the digital display (e.g., of contrast) is proportional to that associated with a JND based on the model.
A mechanism for human calibration for the JND for grayscale can be included. The human visual system can “see” a difference of 1 part in 1000; however, it can only discriminate around 7-8 bits of levels. The mechanism can be constructed to allow an individual user to create a value of interest (VOI) look up table (LUT) that can adjust luminance values so that the viewer can “see” all the varying grayscale patterns. A VOI LUT can transform the modality pixel values which are meaningful for the user or the application. For example, as a person ages, their ability to “see” variations in darkness diminishes. This person would then be able to adjust the luminance values to suit their ability.
The standardized display function utilized by a processor of the provided systems and methods can be, for example, the GSDF. Other standard display functions, including display functions for color display, can alternatively be applied. For example, other test patterns can be used, including but not limited to the Commission Internationale de l'Éclairage (CIE) L*a*b Colour Space display function, a log-linear luminance function, and the Color Standard Display Function (CSDF), an extension of the DICOM GSDF.
The test pattern displayed can vary depending upon the standard display function to be applied. Where the standard display function is the GSDF, the test pattern can be the monochrome test pattern published by the Society of Motion Picture and Television Engineers (SMPTE). Other suitable test patterns include the National Equipment Manufacturer Association's (NEMA) test patterns, from the American Association of Physicists in Medicine (AAPM), report “assessment” ASSESSMENT OF DISPLAY PERFORMANCE FOR MEDICAL IMAGING SYSTEMS.[1]
During self-calibration, luminance values are automatically measured from the testing area using a photosensor integrated within the HMD 518, and measured luminance values are processed by a calibration module 520. The calibration module compares the measured luminance values to expected values (e.g., based on a standardized displayed function) and calculates a correction factor 522. The correction factor is provided to the display controller 524, and luminance of the display is adjusted accordingly 526. The user may then either accept the autocalibration or move to a manual calibration process 528. If the autocalibration is accepted, a calibration record is stored 530.
The self-calibration process can include causing the display drivers of the digital display to step through a series of DDLs, for example, from minimum to maximum values. At each step, luminance measures can be obtained to generate a characteristic curve of the display. If the luminance measures, or other performance measures, of certain pixels in the display do not fall appropriately along the curve, a correction factor can be applied to those pixels. The correction factor can be calculated based on the difference between the standard display function and the pixels which need correction. These correction factors and the modifications can be determined based on the DICOM standards.[2]
The teachings of all patents, published applications and references cited herein are incorporated by reference in their entirety.
While example embodiments have been particularly shown and described, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the embodiments encompassed by the appended claims.
This application claims the benefit of U.S. Provisional Application No. 63/535,367,filed on Aug. 30, 2023. The entire teachings of the above application are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 63535367 | Aug 2023 | US |
