INTRODUCTION TO THE VIRTUAL C-ARM SYSTEM & MACHINE VISION COLLIMATOR
At its core, the Virtual C-arm 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-arm apart from traditional imaging systems and methods utilizing a physical C- or U-arm, is that the Virtual C-arm 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-arm 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-arm 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.
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-arm 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-arm 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.
PRODUCTS & PATENTS
The mobile X-ray system and detector of the Virtual C-arm System is comprised of products that are already available in the marketplace with the appropriate certifications required for use with class II medical devices.
The alignment system is the subject of three issued US patents and one EU patent.
Patent nos. 9,693,746, 9,788,810, 9,918,684, EU 2840973B1
The patent-pending Machine-Vision Collimator (MVC) was designed and tested to meet all the requirements for fluoroscopic imaging stated under FDA 21 CFR 1020.32.
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
Inertial Measuring Unit (IMU)
Ultrasound distance measuring device
The four independent motorized shutters allow for the user to determine both the size of the radiation beam, as well as the location of the radiation beam. This feature allows the collimator computer to position the radiation beam to any location within the perimeter of the detector.
The rotating filter disc contains predetermined filters and an alignment exposure aperture—the filters reduce the radiation dose based on the selected patient size and the anatomic region being examined. Both the filter and aperture settings are selected and set by the workstation APR to each patient’s particular needs. The alignment exposure aperture only allows for a small, ½” x ¾” alignment radiation beam to strike the patient when completing the alignment process. Although an initial alignment exposure is required to verify the alignment conditions between the X-ray source and the detector, the incremental dose area product (DAP) exposure is extremely low.
Using the video camera, the touchpanel display screen shows video of the patient from the perspective of the collimator, with a shaded area appearing on the video, indicating the area of the radiation beam (“virtual collimator”). The inertial measuring unit (IMU) provides the X-ray source degree of angulation, while the ultrasound measuring unit provides the distance between the X-ray source and the patient (SOD).
The alignment system then compares the ½”x ¾” alignment image to the alignment reference image, while also comparing the size and shape of the two—the size of the alignment image reveals the source image distance (SID) while the shape of the alignment image reveals the degree of angulation between the X-ray source and the detector by analyzing the shape of the trapezoid produced. Using this data, the MVC is able to calculate the location of the X-ray source, relative to the detector, in three dimensions. Once the location of the X-ray source in relation to the detector has been determined, the MVC automatically repositions the collimator shutters until the radiation beam is aligned to the detector.
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
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, each frame of the image is analyzed to determine if the exposed area of the detector touches any of its borders (i.e.- exposes the last row or column of pixels on any outer edge). If not, image acquisition remains enabled and the next frame of the image will be acquired and captured. In the event the image area approaches or touches the detector borders, the MVC will attempt to reposition the radiation beam towards the center of the detector. If repositioning of the radiation beam cannot satisfy the border constraints due to the mechanical limitations of the MVC, the radiation exposure is immediately terminated, as not to expose the patient to additional, unnecessary radiation. In this event, an error message is displayed, along with the last frame of captured fluoroscopic data. The user is finally instructed to realign the X-ray source or detector in order to continue.
The alignment application employs a series of interlocks that prevents radiation exposure in the event the area to be examined is not confined within the area of the detector before or during the emission of radiation—by utilizing an inscribed border zone, the MVC validates alignment with every pulse of X-ray. This feature provides a degree of exposure safety to the patient that is unprecedented. Over-collimation or misalignments with traditional C-arm systems are virtually impossible to detect by the user, and are often only noticed and corrected during an annual inspection of the system, resulting in excessive and unnecessary radiation exposure. The inscribed border parameters ensure any misalignments or over-collimation are immediately identified, and radiation stopped, thus providing a considerably higher degree of patient safety.
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.
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.