Contrast is injected and monitored during a cardiac computed tomography angiography procedure using Toshiba America Medical System’s 64-slice Aquilion CT at Steinberg Diagnostic Medical Imaging Centers in Las Vegas.
Thanks to new, more intelligent interfacing capabilities based on new open software protocols, next-generation contrast injectors support more complex injection protocols and integrate with information systems, while keeping pace with increasing CT scanner speeds.
Not just a ‘power injector’
With more precise timing of contrast delivery, extravasation detection, and a more robust connection between injectors and scanners, next-generation contrast delivery systems are no longer just power injectors. “Contrast injectors are getting better, safer, and more programmable,” says Joel Platt, MD, head of the abdominal radiology division at the University of Michigan School of Medicine. “We want a power injector to be safe, reliable, and smart.”
Safety has improved with the ability to deliver only the contrast required. In the rare, but serious event of extravasation, a sensing system can detect a mild pooling of the blood before the extravasation becomes moderate or severe. Medrad just announced a new extravasation system that uses RF (radio frequency) to detect minor pooling of blood, stop injection, and notify the user. More precise timing also provides the ability to deliver only the needed amount of contrast, reducing the risk of contrast nephropathy in certain patients, and makes the CT procedure more comfortable with reduced scanning times. “Safety and reliability improve as contrast injectors get smarter and we get smarter about how to use them,” Platt says.
Dean Langwiser, CT technologist in the cardiac cath lab at University of California, Irvine, a show site for Medrad, will be one of the first to use Medrad’s new XDS extravasation detector. “We’re injecting 4ccs a second and we have a 10-second window from the start of the injection until we start scanning,” he explains. Halfway through the scan, the patient starts getting saline instead of contrast. “It’s a very different viscosity so it often builds up back pressure which prevents the patients from getting about 50ccs of saline.” That results in a lot of pain and the potential for compartment syndrome. Although that doesn’t happen as much as it used to, Langwiser says, it still occurs in about one in 50 patients. “To me, that’s a substantial number. It affects the scan. The discomfort causes the patient to move and it also prevents full washout of the right side of the heart.”
Langwiser says the new technology shouldn’t affect workflow at all. “It’s just a matter of putting a patch over the injection site. This is something I’ve always been hoping they’d come up with.”
Reliability has continued to improve with the better image quality that comes with consistent contrast medium delivery. In addition to the steady improvements in image quality provided by automated injection, better and faster scanners are reducing the window between contrast injection and the start of imaging, driving the need for faster, more precise contrast injection timing. Software-driven injection is particularly key for time-critical CT angiography (CTA) procedures.
In CT, injectors can manage the simultaneous injection of saline and contrast and help manage contrast attenuation to optimize visualization of the right and left heart. Injectors now provide multi-phase protocols that allow consistent opacification of the heart without causing artifacts that make it difficult to read the coronary arteries. The Stellant Dual Flow system from Medrad delivers contrast in three phases: first a contrast bolus, then a mixture of contrast and saline, and finally, an injection of 100 percent saline. Adding the middle phase reduces the contrast attenuation, providing matching opacification on both the right and left sides.
Robin Brothers, CT technologist at the Medical University of South Carolina in Charleston, uses Medrad’s CT interface device for Stellant CT Injection Systems (formerly known as iFlow) that, with the push of a button, starts both the scanner and the injector at the same time. Before the interface, one person had to be in the control room to start the scanner and someone else had to be in the room with the patient watching the IV. So, this helps improve throughput. Because multislice scanners capture images so quickly, having optimal contrast in the area of interest at the precise moment of the scan is critical and the interface helps improve the bolus timing necessary for coronary artery CTA imaging.
Since a technologist can remain at the patient’s side to monitor the injection site while maintaining the ability to control both scanner and injector, he or she can quickly handle any patient safety issues.
Communication: Injector to scanner
Yesterday’s power injector, with the ability to initiate contrast injection and scanning with the same button, is becoming an interfacing and data communications device, too. In February, the CiA (CAN in Automation) industry group announced the release of Version 2.0 of the CiA 425 CANOpen Device Profile for Contrast Injectors allowing “plug-and-play” interoperability between contrast delivery systems, and CT, MR and ultrasound scanners. The next step is more advanced data integration between the injector and scanner.
“It’s an exciting time for the manufacturers,” says Platt. They are working on a variety of approaches to customized contrast delivery protocols designed for specific clinical questions or patient characteristics.
The CiA protocol for the injector/scanner interface is based on CAN (Controller Area Network), a serial, asynchronous communication protocol for connecting electronic control modules. It provides a more robust interface between the injector and scanner that can improve timing to keep pace with faster scanners for CT. Originally developed for automotive applications in the 1980s, the protocol supports applications that need high level data integrity and data rates up to 1 Mbits. Like TCP/IP for local area networks, CAN specifies a protocol for sending and receiving messages from the contrast injector to the image processing diagnostic device—such as CT, MR or ultrasound. Messaging is transparent to the user.
In February, the CiA (CAN in Automation) industry group announced the release of Version 2.0 of the CiA 425 CAN Open Device Profile for Contrast Injectors allowing “plug-and-play” interoperability between contrast delivery systems, and CT, MR and ultrasound scanner. The next step is more advanced data integration between the injector and scanner.
Embedded as a serial bus system in microprocessors, CAN also provides error signaling, and re-transmission of erroneous frames, which provides increased data integrity for injector/scanner messaging. CAN provides a multi-master hierarchy, that allows manufacturers to provide redundant network nodes for devices on the CAN bus. All devices on the CAN bus receive the same message, which guarantees data integrity.
First, the protocol supported the physical connection between the contrast injector and scanner, allowing users to initiate the injection and scan with a single button. This provided better image quality with more precise timing of the release of contrast and the start of scanning. The recent version supports the physical connection between injector and scanner plus support for easy connections to scanners for CT, MR, angiography and ultrasound open the way toward more sophisticated protocols and radiology informatics.
The CiA device profile specification was jointly developed by imaging devices vendors GE Healthcare, Philips Medical Systems, Siemens Medical Solutions, and Toshiba America Medical Systems, and injector manufacturers including Acist Medical Systems, E-Z-EM, Mallinckrodt, Medrad, Medtron AG and ulrich medical.
Smarter contrast delivery also includes the new extravasation detection technology. The Stellant CT Injection System uses a pressure sensor to detect mild pooling of blood under the skin before the extravasation becomes moderate or severe. When the system detects the start of an extravasation, it stops injecting contrast until the clinician can examine the patient. “Extravasation technology is not new,” says Platt. There has been some reluctance to use it because of false positives and the cost/benefit considerations of implementing it for every case. “They must work reliably all the time for all patients in order to be incorporated into existing workflow,” says Platt. The real test will be to put these into use all the time, for all patients. Platt’s department handles about 100 cases per day.
Toward patient specific medicine
Today, intelligent contrast delivery means better timing for optimum imaging of the heart and coronary arteries. With a more robust injector-scanner interface, the latest contrast delivery systems are much smarter. “A more sophisticated approach is to deliver the best bolus for the patient,” says Harold Litt, section chief of cardiovascular imaging at the Hospital of the University of Pennsylvania. “If you have a protocol that allows you to change the contrast parameters for a particular patient, you can include such simple things as height, weight and body surface area. You can then determine the circulating blood volume and calculate contrast you would need.” This would allow calculation of not only the amount of contrast, but also the rate of delivery, if there should be a mix of contrast and saline.” The first efforts to include these parameters started with the need to enhance imaging. “More recent efforts allow you to keep the same degree of enhancement, but reduce the amount of contrast significantly,” Litt says.
Litt and his colleagues are using mathematical models of contrast flow rates that might serve as the basis for algorithms to calculate the optimum contrast delivery. This software could reside on a PC next to the scanner, or it could be on board the injector, Litt says. After entering the specific parameters, the software would propose an optimized protocol. These developments are “not that far down the road,” he says. Of course, he adds, with software control, there will be regulatory review. In addition, such innovations will significantly affect the current workflow.
More comprehensive patient information
The injector-scanner software interface has far-reaching implications for the use of IT in practice. With better integration between injectors and scanners, and interfaces between scanners and PACS, real-time actual flow rates, scan rates, dual flow rates, and peak pressures can be captured and stored with the image and as part of the patient report. “I am cautiously optimistic about integration into the workflow,” says Platt. Like many IT applications, the new data capabilities must be incorporated into the existing workflow in a way that does not interfere with patient safety and staff efficiency. “These technologies are designed to supplement the things we do every day,” says Litt, “not replace them.” Rather than removing control, they provide an additional set of tools for the clinician.
Contrast delivery systems no longer just offer power in contrast injection, they are smart, too. Microprocessor control now provides a more robust interface between the injector and scanner, bringing the possibility of customized protocols and integration of injector data into the cardiovascular information system, radiology information system and PACS. “Those who’ve resisted upgrading to this technology because ‘it’s just a power injector’ may find themselves at a disadvantage in a rapidly changing multidetector CT world” says Platt.