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Computers in Radiology |
1 Yale University School of Medicine, New Haven, CT 06519.
2 Department of Radiology, University of Michigan, 1500 E Medical Center Dr.,
TC-2910A, Ann Arbor, MI 48109-0326.
Received April 3, 2004; accepted after revision June 8, 2004.
Address correspondence to B. Desjardins
(benoitd{at}umich.edu).
OBJECTIVE. We describe a new tool to facilitate the creation and interactive display of stacks of images for scientific and educational presentations using Microsoft PowerPoint.
CONCLUSION. This new tool allows interactive scrolling through stacks of images. After a presentation is created, all elements required to display the stacks of images are embedded in the PowerPoint file. These presentations can be run on any computer (Macintosh or IBM-compatible versions) using PowerPoint with no other preinstalled software, making this tool useful for scientific and educational presentations at national and international meetings.
Since the advent of digital imaging, 3D data have become standard, particularly in CT and MRI. Most 3D data are represented by a series of stacked 2D images. In the modern digital environment of the PACS system, radiologists typically scroll back and forth through the stack of 2D images for a finding, systematically displaying the appearance of a finding or an organ throughout its anatomic extent in relation to surrounding structures. This scrolling has become the standard for radiologists reviewing digital images at workstations, whether formally interpreting a case, teaching students and house officers, or reviewing cases with physicians. PowerPoint (Microsoft), the standard tool for digital presentations at national and international radiology meetings [1–4], does not currently provide the basic functionality internally for easily displaying and interacting with stacks of 2D images. Thus, the effective representation of 3D information in radiologic presentations has remained difficult and does not reflect the interactivity used routinely in clinical practice.
Recently, a DICOM image viewer was proposed to incorporate interactive image stacks into PowerPoint presentations [5]. However, this DICOM viewer relies on technology that limits the portability and compatibility of the resulting presentation. For example, a presentation that contains the DICOM image viewer will not run on Macintosh computers. Also, because the DICOM application must first be installed on Windows (Microsoft) computers before a presentation, it is unlikely that the DICOM application can be used at major radiology meetings. Finally, the DICOM image viewer stores its images separately from the presentation file; therefore, transferring the presentation is cumbersome.
The application we describe, StackView, allows stacks of 2D images to be displayed interactively in PowerPoint presentations without compromising the portability or compatibility of the presentation (Fig. 1). It can be used with both Windows-based IBM-compatible versions and Mac Os X computers. StackView components are embedded directly into PowerPoint presentations when they are created; therefore, the presentations are easily portable because they require no installation before a PowerPoint presentation containing StackView components. Furthermore, the stacks of images can be loaded in any standard image format that is supported by PowerPoint.
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The portability of StackView makes it ideal for an educational setting, allowing presentations that contain image stacks to be downloaded from the Internet and viewed without any installation. The latest version of StackView can be downloaded free of charge [6].
Software
StackView is programmed in Visual Basic for Applications (Microsoft), the embedded macro language in PowerPoint. When StackView components are added to a presentation, embedded objects and commands are created in the PowerPoint presentation file. These objects are only visible within the Visual Basic Editor and are invisible to the typical PowerPoint user. They contain the code necessary to view and interact with stacks of images on any computer without requiring preinstalled add-in software in PowerPoint. Because Visual Basic for Applications varies among different versions of PowerPoint and different platforms, the process of displaying, editing, and creating stacks also varies slightly on different platforms. The more recent versions of PowerPoint for Windows allow additional features, whereas presentations on any version can be saved in the more basic Mac Os X–compatible format, which provides cross-platform portability. This article focuses on the Windows XP platform.
Creating and displaying StackView components requires macros to be enabled. The security settings to enable macros in PowerPoint are described in detail in the installation file of the software. Basically, a macro security level of medium or low is required in PowerPoint. If the security level is set to medium, the option Enable Macros must be selected. If a high security level is used or the option Disable Macros is selected, then the stacks of images will not respond. Instead, the user-selected default image will be displayed for each stack on a slide. Therefore, when using a computer provided at a meeting, the presenter must make certain that the computer running the presentation allows macros to execute.
Viewing and Formatting Image Stacks
In PowerPoint slideshow mode, any stack of images starts in the paused mode
on a slide. The visible image is initially the userselected default image at
stack creation. If the user comes back to a slide during a presentation, the
visible image is the most recently displayed image in the stack. By clicking
on the paused stack, the user unpauses the stack, and it becomes interactive.
Moving the cursor up and down over the image changes the displayed image in
the stack. There is a direct correspondence between the vertical position of
the cursor on the displayed image and the index of the displayed image in the
stack (Fig. 2). Moving the
cursor toward the very top of the visible image displays images earlier in the
stack, whereas moving the cursor toward the very bottom of the visible image
displays images later in the stack. Moving the cursor at the very top of the
image displays the first image in the stack, whereas moving the cursor at the
bottom of the image displays the last image in the stack. Finally, clicking
the mouse over the visible image pauses the stack once again. As an option, a
small oval can appear on the right side of a stack that has been paused to
provide a reminder of the position of the image in the stack.
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An image stack on a slide looks no different from a single image from the user's point of view (Fig. 1). In the PowerPoint edit mode, any standard formatting operation applied to the displayed image will apply to all images in the stack. Thus, a stack of images can be moved in a slide, resized, cropped, and brightness–contrast settings modified.
Creating Image Stacks
If a user plans only to view PowerPoint presentations that already have
embedded StackView components or simply to perform basic formatting operations
on image stacks already included in a presentation, there is no need to
preinstall anything in PowerPoint (besides Visual Basic for Applications,
which is usually part of the basic installation). If the user plans to create
PowerPoint presentations with his or her own stacks of images, the StackView
add-in must first be installed on the computer running PowerPoint. The
detailed steps for installation of the add-in on several platforms are
included in the installation file of the software.
When loaded, the StackView add-in creates a button in the Picture Toolbar that launches the StackView setup form (Fig. 3). This form guides the user through the process of creating and modifying stacks within the current presentation. The StackView setup form allows users to select a slide and then to create stacks in or remove stacks from that slide. Images can be added, removed, or sorted within a stack. When stacks are created, the first image in the stack becomes the visible image. Selecting an image name in the setup form makes that image visible in the slide and is the current approach to selecting the default image to be displayed in a stack.
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If two stacks contain the same number of images and are created on the same slide, then the two stacks can be linked (Fig. 3). Once linked, interacting with the one stack of images causes the other stack to respond identically. Thus, it is possible to scroll through two image stacks at the same time during a presentation. Scrolling is useful when presenting two different window settings of the same stack of images—for example a lung window and a soft-tissue window setting for a chest CT (Fig. 1) or two examinations separated in time to show disease evolution. Linking of stacks of images is determined by the user during creation of the stack and is only available on computers using the Microsoft Windows operating system.
Discussion
StackView adds the power of interactively displaying stacks of images in PowerPoint presentations, akin to scrolling at a PACS or advanced processing workstation, without compromising the portability or compatibility of presentations. Not only does StackView allow stacks to be created on Windows and Macintosh platforms, but StackView components created in PowerPoint for Windows can run on PowerPoint for Macintosh and vice versa, within the limitations of each platform. Combined with the power of saving the images seamlessly within the presentation file and requiring no installation before viewing presentations, StackView brings the power of representing 3D radiologic data to educational and scientific presentations.
Acknowledgments
We thank the numerous beta testers of the software in the Radiology Departments at the University of Michigan and at Yale University for providing useful feedback.
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