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THEORY OF OPERATION

How it all works & why it is
revolutionary to the medical imaging industry.

INTRODUCTION TO THE VIRTUAL C SYSTEM & MACHINE VISION COLLIMATOR

At its core, the Virtual C System is a mobile imaging system that acquires, processes & displays both static radiographic images & dynamic radiographic images, such as multi-rad and fluoroscopy. What sets the Virtual C apart from traditional imaging systems and methods utilizing a physical C- or U-arm, is that the Virtual C allows for dynamic image acquisition without the limitations of a mechanical linkage between the X-ray source and X-ray detector.

  • Currently, physical C- or U-arms are used to ensure the alignment of imaging components during image acquisition; the physical linkage of the components has proven problematic in a number of use scenarios, often putting critical care patients at a disadvantage due to the machine’s physical limitations.

  • PortaVision’s Virtual C system instead relies on our novel collimator, featuring built-in X-ray source-to-detector alignment software, called Machine Vision Collimator (MVC).

  • The MVC software, in combination with PortaVision’s proprietary alignment system, come together to create the Virtual C System & eliminate the restrictions and obstacles of traditional C-arm imaging.

Utilizing four independent shutters to automatically position the radiation beam, the MVC ensures the area of exposure always remains within the confines of the active area of the detector, eliminating the need to physically link the components. A visual display provides real-time video of the patient, with a shaded area appearing on the video image to indicate the location and size of the radiation beam with respect to the patient. Additionally, the angle and inclination of the X-ray source is displayed to the operator on the display as well.   

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Use Cases
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USE CASES

There exist numerous medical applications for dynamic imaging where the use of a mobile C-arm or traditional, fixed-

install fluoroscopic systems are not only impractical, but potentially harmful to critical care patients.

  • Life-saving catheter and line placement in neonatal intensive care units

    • These procedures are typically performed with a radiographic mobile system where X-ray exposures are taken repeatedly to verify placement, exposing the neonate to additional and unnecessary radiation.

  • Barium swallow studies performed in nursing homes

    • The weight of the Virtual C System is significantly less than a traditional mobile C-arm; this increases the overall maneuverability of the machine, making it easier and more practical to perform such tests in the nursing home itself, instead of having to transport fragile or immobile patients to an imaging center.

  • Contrast injections for MRI exams

    • The Virtual C System is vastly more cost-effective than a R&F table, as it does not require a dedicated room to house, or additional patient supports.

MACHINE VISION COLLIMATOR (MVC) 

The mobile X-ray system and detector of the Virtual C System is comprised of products that are already available in the marketplace with the appropriate certifications required for use with class II medical devices.

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FIGURE 1: The Machine Vision Collimator (MVC)

MAJOR COMPONENTS & HOW IT WORKS

The Machine Vision Collimator (MVC) is comprised of the following components:

  • Four independent motorized shutters

  • Motorized rotating filter disc

  • Video Camera

  • Touchpanel display

  • Inertial Measuring Unit (IMU)

  • Lidar measuring device (SOD)

  • Computer

The MVC comprise a computer, a touchscreen display, four motorized independent shutters, a motorized rotating filter disc, a video camera, an inertial measuring unit (IMU) to provide degree of angulation, and a Lidar measuring device to provide distance between the x-ray source and patient (SOD). The four independent motorized shutters allow not only to determine the size of the radiation beam but also the location of the radiation beam. This allows the collimator computer to position the radiation beam to any location within the active area of the detector. The rotating filter disc contains predetermine radiation filters. The filters are selected by the workstation APR stations, the filter reduce radiation dose for the selected patient size and anatomic region to be examined. The display screen shows video images from the video camera of the patient seen from the perspective of the collimator and show the area of the radiation beam indicated by the shaded area (virtual collimator). The x-ray source/detector alignment system compares an alignment image to the alignment reference image. The alignment system also compares the size, and shape of the alignment image to the alignment reference image.  From this data, it is possible to calculate the location of the x-ray source relative to the detector in 3 dimensions. Once the location of the x-ray source to the detector has been determine, the MVC then automatically reposition the collimator shutters until the radiation beam is aligned to the detector. The size of the alignment image reveals the source image distance (SID) and the shape of the alignment image reveals the degree of angulation between the x-ray source and the detector by the shape of the trapezoid produced.  Once the radiation beam is aligned to the detector if the user determines that the size or location of the radiation beam is not aligned to the anatomic region to be examined. The user with the use of the touchscreen can readjust the size and reposition the location of the radiation beam by typical pinch and zoom as well as pan by swipe. Pinch and zoom will define the shutter opening as far as the output size. Pan by swipe will move the shutter opening about a range of motion of the collimator shutters while maintaining the desired shutter opening. Once the x-ray source is aligned and the collimated area is adjusted for the anatomic region to be examined, then the system is ready to acquire fluoroscopic images using the techniques associated with the selected protocol.

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FIGURE 2: MVC Screen Interface

STEP-BY-STEP USAGE EXAMPLE

1.)  For a typical procedure, the operator selects the “Fluoro” option on the touchpanel workstation display           monitor, then selects an APR station for the patient size and anatomic region to be examined.

2.)  Next, the operator places the detector under the patient and visually aligns the detector to the anatomic        region to be examined.

3.)  Then, the X-ray source is positioned over the patient, and visually aligned to the intended region by                  observing the live video image feed of the patient and the shaded virtual collimator area.

4.)  The operator then initiates the alignment X-ray exposure, which is limited to a ½” x ¾” radiation beam;           the beam passes through the patient to strike the detector.

5.)  The workstation computer, in communication with the detector, transmits the alignment image to the             MVC; the MVC calculates the present location of the X-ray source with respect to the detector.

6.)  The MVC then automatically repositions the shutters to align the radiation beam to the detector, and the         size of the collimated area is adjusted for the anatomic region being imaged.

7.)  At this point, manual manipulations of the beam size and location can be performed using the “pinch”             and “swipe” touchpanel actions—“pinching” the touchpanel, as you would to zoom in or out on a                       smartphone, will define the shutter opening relative to the beam output size, while “swiping” will move

       the shutter openings, adjusting the location of the beam itself while maintaining the desired shutter

       opening.

8.)  Now that the X-ray source is aligned, and the collimated area is adjusted for the anatomic region to the           examined, the system is ready to acquire fluoroscopic images using the techniques associated with the         selected protocol.

SAFETY & ACCURACY MEASURES

During fluoroscopic image acquisition the MVC maintain the radiation beam within the perimeter of the detector borders. If the imaging area does approach the detector borders due to intentional or unintentional movement of the x-ray source or detector the collimator computer will attempt to reposition the radiation beam towards the center of the detector, if repositioning the radiation beam cannot correct the image approaching or touching the border due to the mechanically limitations of the collimator, then fluoroscopic image acquisition is halted by disabling output from the x-ray source.  An error message is displayed along with the last frame of captured fluoroscopic data. The operator is then instructed to realign the x-ray source or detector.

The alignment application employs a series of interlocks that prevents radiation exposure if the exposure area is not confined within the area of the detector at any time before or during emission of radiation. This provides a degree of radiation exposure safety to the patient that is unprecedented. Over collimation or miss- alignments with traditional C-Arm systems are virtually impossible to detect by the user and are only noticed and corrected during annual inspection. Utilizing an inscribed border zone validates alignment with every pulse of x-ray. This ensures any miss alignments or over collimations are identified immediately and radiation is stopped, thus providing a considerably higher degree of safety. An illustration of how this works is shown in Figures 3 and 4 below. Figure 3 shows a typical frame of a fluoroscopic image loop. As shown, the collimator is nominally closed to provide a small border of collimated area around the perimeter of the detector. The  actual dimensions of this border can be user defined and based on their comfort level as to how much margin for error they want for degree of misalignment..

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FIGURE 3: Fluoro Frame with Border INTACT

Figure 3 (above) shows a typical frame of a fluoroscopic image loop; as shown, the collimator is nominally closed to provide a small border of collimated area around the perimeter of the detector.

The actual dimensions of this border can be user defined, based on their comfort level as to how great of a margin of error they wish to account for in the degree of misalignment.​

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FIGURE 4: Fluoro Frame with Border EXPOSED

Figure 4 (above) shows a frame of the fluoroscopic image loop where the collimated radiation beam has become misaligned with the detector, exposing the left border of the detector.

As this fluoro loop frame is processed, the border alignment error will be generated, the fluoroscopic exposures will be terminated, and a message will be displayed, instructing the operator to realign the X-ray source and/or the detector.

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