USB3 Arrives for Medical Imaging
By John Phillips
Pleora Technologies
Thanks primarily to its ease of use USB has become the backbone for wired data connectivity in
a wide range of medical electronics devices. In particular, portable and home-based health
monitoring devices have benefitted from the “plug-and-play” simplicity of USB connections.
One clear exception is medical imaging, where previous versions of USB failed to deliver the
bandwidth required to support real-time image delivery. This changed thanks to the raw speed
offered by USB 3.0 and the development of the USB3 Vision standard. For medical imaging
system manufacturers, USB3 Vision delivers clear design, cost, and performance advantages.
Real-Time Image Transfer
As part of the continuing evolution toward home-based care, a growing number of USB-enabled
medical devices allow patients to monitor and manage their own health and wellness. Personal or
prescribed monitoring devices record and store data until they’re simply plugged into the USB
port of a computer, where information can be displayed, analyzed, or transmitted to a healthcare
provider.
For the majority of these applications, there’s no real-time requirement for data delivery. The
few seconds its takes to transmit historic data from the device to a computer does not impact a
patient’s ability to monitor their response to treatment.
The same is not true for advanced medical imaging systems, where high-resolution images must
be transferred in real-time, and with low, consistent latency (or delay). A medical telepresence
robot, for example, requires instantaneous transfer of imaging data from a camera to a processor
to precisely navigate its environment. The visual, auditory, and tactical technologies must all
work together at near-zero latency to reproduce a level of care for a remote patient that rivals an
in-person visit. Similarly, microscopy and surgical applications requiring live analysis demand
real-time visual data for display and analysis.
A key component to ensure instantaneous image transfer is the video interface – the hardware
and software used to format image data and transmit it to a computer or display. Video interfaces
in medical imaging systems are often based on standards developed for other industries, such as
LVDS commonly used in telecom and consumer communications, HD-SDI from the broadcast
industry, and Camera Link from the machine vision market.
With each of these standards, imaging system designers must often balance cost, ease-of-design,
and performance. While they provide the bandwidth required for high-resolution sensors and fast
frame rates, the trade-off is complexity and cost. With Camera Link, for example, each camera
or sensor requires a PCIe or PC card frame grabber at the computing endpoint to capture data.
This limits the types of computers that can be used, drives up component costs, and increases
complexity.
Alternatively, some medical imaging system manufacturers have designed their own custom
video interface. This approach has issues as well. Custom interfaces are often costly to develop
and maintain, introduce integration challenges in multi-vendor systems, and can sidetrack
internal R&D resources from more valuable core projects.
Recognizing these limitations, medical imaging system designers are increasingly adopting
industry standards initially developed to support higher performance, more flexible, and less
costly machine vision systems. Building on the concepts introduced with the widely adopted
GigE Vision standard, in combination with the release of the “super speed” USB 3.0, USB3
Vision provides a framework for transmitting video and control data over more flexible USB
cabling.
The Basics of USB3 Vision
USB interfaces have been widely adopted in consumer, PC, and home-based medical devices,
but the bandwidth supported by earlier versions of the standard was insufficient for imaging
applications requiring uncompressed, raw data for real-time image analysis. This changed with
the third major version of the USB standard – USB 3.0 or SuperSpeed USB – which provides 10
times the bandwidth of USB 2.0 while addressing power, processing usage, and multi-camera
capabilities.
The USB3 Vision standard provides a framework for designers to address performance, cost, and
usability requirements in real-time imaging systems. Data is transmitted directly to existing ports
on a computer with sustained throughputs approaching 3 Gb/s, surpassing the performance of
Camera Link Base configurations and rivalling Medium configuration, but without requiring
specialized frame grabbers at endpoints to capture data. By eliminating the need for frame
grabber cards, designers can choose from a wider range of computing platforms, including
laptops, tablets, and embedded processors.
USB 3.0 video interfaces deliver advantages beyond speed and connectivity to help lower costs
and boost performance. The flexible, lighter USB cables cost less and are simpler to install than
the bulky cabling and connectors of legacy interfaces. Video, control data, and power are
transmitted over a single cable. This simplifies cabling and eliminates the need for an external
power supply for cameras, lowering both system footprint and bill of material. Multiple active
copper and optical cabling solutions are now available that extend the distance between imaging
sources and processing units far beyond the initial five meter range described in the USB3
Vision standard
Per-frame metadata, such as data and time of acquisition and imaging equipment used, is
transmitted with the images over the USB3 link for easy integration with DICOM-compliant
software and hardware in a medical imaging system.
USB3 Vision and Medical Imaging
As USB3 Vision gains wider adoption, an increasing number of standards-compliant video
interface products are becoming available as off-the-shelf solutions. For retrofit projects, external
frame grabbers make it relatively straightforward for designers to convert feeds from existing
cameras into more manageable USB3 Vision-compliant video. For new projects, embedded
hardware products allow manufacturers to integrate USB3 Vision-compliant video connectivity
directly into cameras and imaging systems, including custom sensors and smart camera heads for
specialty applications.
The simplified cabling and plug-and-play usability of USB 3.0 can deliver cost, performance,
and reliability advantages in a wide range of medical imaging applications. In microscopy
applications (Diagram 1), an external frame grabber allows designers to retain existing cameras,
sensors, and optics while leveraging the ubiquitous computing platform support and simplified
cabling of USB 3.0.
Microscopy systems often use a Camera Link camera to transmit microscopic images to a
computer for analysis and observation. With an external frame grabber, the image feed from a
Camera Link microscopy camera can be converted into USB3 Vision-compliant video. The
uncompressed video is transmitted with low, consistent latency over a USB 3.0 cable directly to
an existing USB 3.0 port on a laptop used for analysis and display. The thinner, lighter USB 3.0
cable is easier to route than bulky Camera Link cables and connects with “plug-and-play” ease,
allowing faster setup and teardown of inspection stations.
Increasingly, robotics manufacturers are migrating to embedded processing to help deliver
footprint, weight, and power-saving advantages. However, as form factors shrink there is no
room for an internal frame grabber. USB3 Vision-compliant external frame grabbers or
embedded hardware can be deployed to simplify the design of robots used for medical service or
telepresence applications (Diagram 2).
In this example, images from block cameras used for inspection and navigation in a medical
service robot are converted to USB3 Vision-compliant video streams by external frame grabbers.
Alternatively, embedded video interface hardware provides system and camera manufacturers
with a straightforward way to integrate USB 3.0 video connectivity directly into their products.
Video, power, and control data is transmitted over high-bandwidth, flexible, low-cost USB
cables directly to ports on an integrated single-board computing platform. By eliminating PCIe
frame grabbers within the robot, designers can reduce system complexity, component count, and
costs. In addition, decreasing the weight and power consumption of the robot extends battery
life, translating into more patient visits between charges.
The medical industry has long recognized the benefits of USB to simply and easily transfer data
between devices. With the evolution towards faster data rates, and the introduction of a vision
standard that guides performance and assures interoperability, these benefits can now be realized
for advanced imaging applications. Microscopy and robotics are two obvious applications where
the cabling flexibility and computing platform choice supported by USB 3.0 video interfaces are
delivering cost, performance, and ease-of-use advantages. As technologies continue to evolve,
USB 3.0 will become the video interface of choice for an even wider range of medical imaging
applications.
Cut lines
Diagram 1: In a microscopy application, a USB3 Vision external frame grabber allows designers
to retain existing cameras, sensors, and optics while leveraging the ubiquitous computing
platform support and simplified cabling of USB 3.0.
Diagram 2: USB3 Vision video interfaces simplify the design and lower the cost of telepresence
by enabling the use of embedded processing.