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  • Technology Cuts Radiation Exposure

    February 01, 2014

    Spectral CT is among techniques that improves efficiency, lower radiation dose.

    Daily Bulletin coverage of RSNA 2013 is available at RSNA.org/bulletin.

    Recent technological advances have contributed to the development of photon-counting detectors (PCD), which are now able to discriminate between photons based on energy level, providing information about the composition of an object in a single scan.

    “PCDs are the next big thing in CT,” said Radin A. Nasirudin, Dipl.-Ing, of the Department of Diagnostic and Interventional Radiology, Technische Universitat München, Munich, Germany, in an RSNA 2013 presentation.

    Incorporating photon-counting detector technology into CT—a technique called spectral CT—not only relays this additional information in a single scan, but due to quantum efficiency, noise can be drastically reduced. This means that better image quality can be achieved with lower radiation dose, Nasirudin said. “Current estimates on dose reduction suggest a decrease by a factor of two or more,” he said.

    In his study, “Application of Photon-counting CT: Metal Artifact Reduction,” Nasirudin and colleagues investigated the advantages this technique provides in reducing metal artifacts.

    “Artifacts caused by metal objects are common and can significantly reduce the diagnostic quality in daily clinical practice,” Nasirudin said. “Although there are many well-established methods for metal artifact reduction, most involve segmentation and thresholding for detection of the metal object, which is prone to reintroduce new artifacts.”

    With this in mind, Nasirudin and colleagues developed an algorithm—spectral-driven iterative reconstruction (SPIR)—that utilizes spectral information to reduce metal artifact in CT.

    Researchers used a Monte Carlo simulator to simulate spectral CT projection data of a jaw phantom consisting of bone, soft tissue, teeth and gold implants. The resulting spectral projection data were decomposed to determine the spatial location and density of the gold. That information was then incorporated into a penalized maximum likelihood iterative reconstruction algorithm.

    “The results from our investigation into the reduction of metal artifacts are promising,” Nasirudin said. “The material decomposition technique is able to detect the metal implant from other components of the phantom.”

    When compared to a known shape, the error from detecting the implant by material decomposition is less than 2 pixels, he said, which “strongly suggests” the technique is able to accurately detect the spatial location and density of any dental implant.

    Use of the technique resulted in a reduction of streaking artifacts without compromising any other anatomical information, Nasirudin said. When visually compared to other techniques like filtered-back projection or standard penalized maximum likelihood iterative reconstruction, “our method delivers superior image quality while preserving the details around the metal implant,” he said.

    It’s significant that this technique seems to work well with any shape of dental implant, he said. For example, researchers first used the technique with a jaw phantom that had a circle-shaped metal implant, but later tested the algorithm with more realistic dental implants that produced images with high diagnostic quality.

    In addition, he said the parameters for the iterative reconstruction (such as number of iterations and the strength of the penalty) didn’t change from one shape to another, indicating that “our method can be extended to other parts of the body such as the lower extremity or the spine.”

    The study demonstrates that information provided by spectral CT “will be a central key to overcoming image quality issues in current clinical CT,” Nasirudin said. “We foresee that the clinical introduction of spectral CT will lead to more clinically relevant applications while possibly reducing radiation exposure to the general population.”

    Marco J. Van Strijen, M.D.
    Marco J. Van Strijen, M.D.

    New Angiography Platform Reduces Dose, Maintains Quality

    Daily Bulletin coverage of RSNA 2013 is available at RSNA.org/bulletin.

    A new angiographic imaging platform can reduce radiation dose by 83 percent without compromising image quality, according to RSNA 2013 presenters.

    “Over the past 10 years we have seen a large increase in the use of radiation for medical imaging,” said Marco J. Van Strijen, M.D., of the Department of Radiology, St. Antonius Ziekenhuis in Nieuwegein, the Netherlands. “Minimal invasive innovative therapies in interventional radiology and cardiology rely on high-quality imaging, but also lead to longer procedure times and often in younger patient groups.”

    A further hindrance, Dr. Van Strijen said, is the fact that many patients undergoing interventional procedures are obese, which “poses an additional problem to the dose we are using for getting optimal image quality,” and that procedures are getting more complex and at closer range, which also contributes to larger dose exposure.

    Therefore research in this area has been necessary to find new techniques to reduce dose for both individual patients and staff during these procedures, and to verify claims of particular vendors regarding the ability of their devices to reduce dose, he said.

    According to Dr. Van Strijen, the availability of increased computer power has led to the development of real-time imaging reconstruction algorithms that—combined with technical improvements in imaging equipment—are capable of reducing the needed radiation dose while maintaining image quality.

    The platform his group studied—a system from Philips Healthcare called AlluraClarity—can adjust more than 500 system parameters in real time, thereby reducing the radiation dose necessary for adequate imaging during interventional procedures.

    “The important part of the system is the flexible digital imaging pipeline,” Dr. Van Strijen said, adding that it enables the operator to make adjustments in functions such as pixel shifting, image enhancement or noise correction depending on the anatomical area of interest, and all in real time.

    In this study, the researchers acquired two angiographic runs for each of 50 patients scheduled for iliac interventions. One run was acquired using a conventional imaging platform while the other was acquired using the new platform. Air kerma (kinetic energy released per unit mass) and dose area product values were recorded in all acquisitions and at the end of the procedure.

    “As the definition of ‘adequate imaging’ is difficult to describe, we asked several non-affiliated experienced interventional radiologists across Europe to compare the results in a blinded way,” Dr. Van Strijen said.

    The researchers found that the radiation dose in all procedures showed a mean reduction of radiation dose of 83 percent. The imaging technology was used in the entire procedure for all 50 patients since the image quality was considered to be sufficient for performing the intervention.

    In addition, the qualitative image assessment by the non-affiliated interventional radiologists found that the run using the low-dose platform was usually of equivalent or better image quality as compared to the conventional imaging platform. According to Dr. Van Strijen, the blinded review comparison found that the lower dose technique provided better image quality in 14 cases, similar image quality in 32 cases, and worse image quality in two cases.

    “Results suggest that the technology will provide ‘enormous’ future radiation dose reduction benefits for both patients and staff during interventional procedures,” Dr. Van Strijen said.

    Radin A. Nasirudin, Dipl.-Ing
    Radin A. Nasirudin, Dipl.-Ing
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