Software Offers PET/CT/MR Image Fusion
As medical images continue to serve an increasing role in medical decision-making and treatment monitoring, there has been a louder call for image display and visualization tools in clinical practice. With today’s imaging modalities producing large, complex volumes of data, users look toward sophisticated rendering techniques to help them better understand physiological and anatomical findings.
Swiss researchers from the University Hospital of Geneva have developed open source software based on the OsiriX platform, a fully interactive image navigation and visualization software designed for the display and analysis of large data sets of 3D images. End users around the world and across the nation, such as the radiology departments of the University of California-Los Angeles, the University of Texas, the University of Michigan, and the University of Maryland, use OsiriX free of charge. In fact, more than 25,000 registered sites have been identified.
“More and more images are acquired today on hybrid scanners combining PET and CT or SPECT and CT and MR and PET images,” said Osman Ratib, MD, PhD, FAHA, professor and chair of radiology of the Department of Medical Imaging and Information Sciences at the University Hospital of Geneva. “Our goal was to provide a convenient platform for users to ‘navigate’ through multimodality images in three, four, and five dimensions—the fourth dimension being time for dynamic images and the fifth dimension being the metabolic images of PET or SPECT.”
With an ability to visualize fused, coregistered images, OsiriX is specifically designed to handle new generations of multimodality imaging data that combines both anatomical and metabolic images, such as PET/CT. Moreover, it features dynamic display for time-varying images, including cardiac motion or metabolic functional studies. The platform was developed to support peer-to-peer technology as an alternative to a centralized PACS architecture.
Ratib, along with Antoine Rosset, MD, and Joris Heiberger, designed an intuitive, user-friendly interface specifically for physicians who are not familiar with complex image-processing tools and manipulation techniques. Ratib explained that full control is given to the user, who can customize the interface and add or remove tools as needed. Furthermore, plug-in components can be easily added.
“We chose a simple pragmatic approach that allows users to either realign images visually, or by selecting a series of reference points in the selected image modalities and by matching the points, the program will realign one image set over the other,” Ratib said. The software can be downloaded from www.osirix-viewer.com.
Bright Ideas: MRI-Compatible Lighting
Sunnex Inc, Natick, Mass, is lighting the way for providers with its MRI-compatible lighting—a growing necessity as MR-guided procedures such as breast biopsies become increasingly commonplace.
“As stereotactic breast examination becomes the standard of care, people are finding that MRI-compatible lighting is a need,” said David Trinks, sales director at Sunnex. “It’s something that wasn’t as necessary before, but now it is. As MRIs get to be more specific and the imaging gets to be better, these lights will be useful in more and more clinical applications.” Even catheter insertion can be challenging in a dimly lit room, Trinks says. “Even with autoinjectors of contrast media, it’ll be a big help,” he said.
And there are economic benefits to investing in MRI-compatible lighting. “MRI rooms don’t generally have a lot of light in them,” he said. “Lights are difficult to maintain, like anything in the MR suite. If a light goes down, you have to shut down the MRI at a very high cost—losing thousands of dollars an hour.”
Trinks explains that the company’s lighting solutions are built entirely from nonferrous materials, including stainless steel, nylon, and various types of plastics. They come in two configurations, ceiling-mounted and mobile, each with its advantages and disadvantages.
“If you’re going to mount a light in the ceiling you need to be spec’ed in while the construction is being performed,” he said. “It’s cost-prohibitive to go back and retrofit a light into the ceiling. We have mobile units, but it’s not always preferable to have a light sitting next to the gantry.”
The mobile configuration is ideal for MR suites that have already been RF-shielded. “All that needs to happen is that a transformer box needs to be mounted a hundred feet outside the gaus line,” Trinks said. “It’s plug and play.”
Sunnex is one of two companies currently manufacturing MRI-safe lighting. Its models include the Celestial Star, which features unlimited positioning and wide vertical and horizontal reach to optimize functionality around the bore, and the PF Series, a high-intensity solution. The Celestial Star offers “no tool” service, and its compact design keeps work areas clear. It’s a 105-watt system, generating 64,500 lumens at a meter, ideal for stereotactic breast examinations. The PF Series is a 50-watt, halogen-based system designed for minor procedures like biopsies or catheter insertion.
“People love the lights,” Trinks said. “They’re easy to handle, they’re very compact, and they allow them to do things in a lighted field that they couldn’t ordinarily do. People are ecstatic that they can get a light into a room where they couldn’t before. They’re also very cost-effective. We’re finding a lot of success this past year installing them in MRI suites so mobile units don’t have to come into play.”
Sunnex’s lights are compatible up to 3T, and “we have a product out for testing at the University of Minnesota with a 9T magnet,” Trinks said. “We’re also hoping to get an LED version of the light out soon.”
Education Update: Contrast-Enhanced Neuroimaging
At the recent symposium of the American Society of Neuroradiology (ASNR), Oak Brook, Ill, Bracco Diagnostics Inc, Princeton, NJ, sponsored a “how-to” session on contrast media for neuroimaging. Consisting of three related presentations, the session looked at issues ranging from tips and techniques for contrast-enhanced neuroimaging to the safety of using gadolinium-based contrast agents.
Emanuel Kanal, MD, a neuroradiologist at the University of Pittsburgh Medical Center, gave a talk titled “Safety Update on MR Contrast Use in Patients with Chronic Kidney Disease.” His presentation compared the safety of FDA-approved gadolinium-based contrast agents and looked at how best to minimize the risk of a patient developing nephrogenic systemic fibrosis (NSF).
“The prevailing theory—and I will stress that it’s a theory and nothing more—is that there’s a dissociation occurring between the gadolinium and the ligand molecule used to chelate that gadolinium,” Kanal said. “If they dissociate, that could cause the gadolinium ion to be released, which may in some way lead to the development of the problems that we associate with NSF.”
Kanal proceeded to explain that different contrast agents have different dissociation constants; those with a cyclic chelate structure appear to have higher stability. In addition, the agents can differ from one another in their relaxivities as well. “In the US, there’s one drug with a notable higher relaxivity than the others, and that’s MultiHance [a product of Bracco Diagnostics],” he said.
Kanal explains that while the FDA’s black box warning on gadolinium-based contrast agents covers all five US versions equally, the European equivalent does not. “The Europeans have singled out Omniscan and Optimark as seeming to have a higher incidence of NSF, and have more recently added Magnevist to that list,” he said.
A possible advantage in terms of safety is not the only benefit to this type of agent, however, explains copresenter Howard Rowley, MD, professor of neuroradiology at the University of Wisconsin, Madison. His talk, “Are There Real Differences Among the Gadolinium Agents for Contrast Enhanced Neuroimaging?” looked at chelate structure and relaxivity as functions of imaging quality. The answer to the question posed by his presentation’s title? A resounding yes.
“MultiHance has improved relaxivity properties that seem to give it an edge in the clinical world, not just in the test tube,” Rowley said. “This particular molecule has an extra side chain that’s lipophilic, which is thought to influence its relaxation behavior because it very weakly, but transiently, binds to proteins like albumen. Once it’s in the bloodstream, this very weak interaction slows its micromolecular tumbling rate.”
Rowley recently conducted a blind study comparing MultiHance to Omniscan. Patients with known or suspected brain lesions were imaged with both contrast agents; then blinded neuroradiologists compared the images and were asked which, to their thinking, offered superior enhancement. “All three blinded readers strongly favored MultiHance over Omniscan when a preference was expressed,” Rowley said. “In only a handful of cases was Omniscan preferred.”
Kanal notes that the risks posed by commonly used agents like Omniscan are extremely minimal. “If you don’t have severe renal disease or acute kidney injury, you’re probably not going to get NSF,” he stressed. However, he added, “By definition, the bloodwork for acute kidney injury will not detect an acute renal failure. Blood test-based eGFR values are fine if the patient has chronic kidney disease, but not if they’re in acute renal failure. So for clinical decision-making on patients with significant renal disease, at the University of Pittsburgh Medical Center we utilize either macrocyclic agents or lower doses of higher relaxivity agents in the hope that they are safer, as far as the likelihood of developing NSF is concerned, in case the gadolinium-dissociation theory proves correct.”
Rowley concurs: “All of these agents have been terrific adjuncts to our MR imaging protocols, and compared to most things in medicine they have an excellent overall safety record,” he said. “But when you look at the hard science of which agent actually produces the best contrast enhancement, MultiHance has a distinct advantage.”
Reducing Dose, Not Image Quality
The employment of dose-modulation techniques for neuroradiology CT exams subjects patients to significantly lower doses without decreasing the quality of the resulting images, according to a new study out of the University of California, San Francisco.
In an effort to retrospectively quantify the effect of systematic use of tube current modulation for neuroradiology CT protocols on patient dose and image quality, a team of researchers headed by Alice B. Smith, MD, evaluated the effect of dose modulation on adult and pediatric brain CT scans performed without contrast material (unenhanced), adult cervical spine CT, and adult cervical and intracranial CT angiography.
The clinicians examined three series of 100 consecutive studies for each type of CT exam. On the 16-slice scanner, 100 studies were performed without dose modulation and another 100 studies were performed with z-axis dose modulation. Using the 64-slice system, yet another 100 studies were conducting with x-y-z-axis dose modulation.
In each exam, the weighted volume CT dose index (CTDIvol) and dose-length product (DLP) were recorded and noise was measured. Continuous variables (CTDIvol, DLP, noise) were compared by using t tests, and categorical variables (image quality) were compared by using Wilcoxon rank-sum tests.
Each study was reviewed for image quality. The investigators found that using dose-modulation techniques resulted in significant reductions in radiation dose to adults and children by as much as 60.9% (P < 0.001). They also report that image quality and noise were unaffected by the use of either z-axis or x-y-z-axis dose modulation (P > 0.05).
Full results of the HIPAA-compliant study, “Radiation Dose Reduction Strategy for CT Protocols: Successful Implementation in Neuroradiology Section,” are published in the May issue of the journal Radiology (2008;247:499-506).
“Implementation of dose modulation requires a fine-tuning process to identify optimal signal-to-noise level for each type of CT study performed,” the authors write in the report, adding that they “recommend routine use of dose modulation for neuroradiology CT examinations because this approach affords a significant dose reduction while preserving image quality.”