Fluoroscopy is continuing to evolve, advancing over recent years from large and bulky image intensifiers into today’s sleek, flat devices with zero image distortion.
The advances in flat-panel technology used in fluoroscopy are not just due to the diligence of manufacturers, medical researchers, and medical developers. The advances also are due to improved low-noise, high-speed electronics; custom programmable chips; digital signal or image processing techniques; and flat-panel manufacturing equipment capable of processing large field-of-view formats and improved pixel architectures, according to Gary Okamoto, imaging products marketing manager at Varian Medical Systems (Salt Lake City).
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| This image was generated by Saori Tanaka, MD, at Osaka City University Hospital in Japan using a diagnostic imaging system incorporating Varian’s PaxScan digital X-ray image detector. It was used to assess damage to a patient’s pancreatic artery prior to surgery. The PaxScan detector operates in fluoroscopic mode at up to 60 frames per second-fast enough to enable physicians to track a moving tumor, observe blood flowing through a kidney, or carefully guide a catheter into a premature infant or a beating heart. |
What’s New?
The various components of a fluoroscopy system, such as the X-ray source, image intensifier, camera, gantry, flat-panel detector, display, image processor, and computer controller, all have their own technology trajectories. However, the latest digital technology that is present in the image sensor and camera greatly improves a system’s diagnostic ability.
“The latest in fluoroscopy today is scientific-grade, high-speed digital image capture,” explains Dave Litwiller, VP of corporate marketing and business development at DALSA Corp (Waterloo, Ontario). “This image-capture technology goes well beyond repurposed consumer imaging devices, typically from camcorders and security cameras. Employing scientific-grade digital imaging helps to deliver higher-quality images, as well as flexibility for higher frame rates, to improve diagnostic performance of fluoroscopy systems in clinical and research settings.”
Marc Levine, MD, is a professor of radiology and advisory dean at the University of Pennsylvania School of Medicine (Philadelphia), chief of the gastrointestinal radiology section at the Hospital of the University of Pennsylvania (Philadelphia), and immediate past president of the Society of Gastrointestinal Radiologists (Houston). He believes that the biggest innovation in fluoroscopy has been the transition from conventional to digital fluoroscopy.
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| This sequence of images highlights the extent to which a reference point on the lung moves over a 2-second period due to respiratory motion. |
“Only a few years ago, many practices were still using conventional fluoroscopy for GI [gastrointestinal] studies, necessitating the use of radiographic cassettes containing standard X-ray films. A new cassette had to be inserted into the fluoroscopy tower after every exposure, dramatically lengthening the time of the procedure. After the study was completed, the patient had to wait while the films were developed and reviewed by the radiologist in case additional films were needed,” he says. “With digital fluoroscopy, however, the exposures are obtained digitally with the press of a single button, so the examination can be performed in a fraction of the time required with conventional equipment. The fluoroscopist can then review the images immediately on a monitor in the control room to decide whether additional images are needed, and the patient can then be sent from the department without delay, dramatically increasing patient throughput and minimizing patient time in the department. The images from the study can be formally reviewed later in the day at a computer workstation on a departmental PACS.”
The use of digital fluoroscopy eliminates the need for actual film, decreasing the cost of the study as well as the long-term costs of film storage, as the images can now be saved in the department’s digital archives. The use of computer workstations for reviewing the images also enables radiologists to postprocess the images, altering the contrast, brightness, sharpness, and magnification to optimize their ability to detect abnormalities, according to Levine.
“For all of these reasons, in a relatively short period of time,” he adds, “digital fluoroscopy has, for the most part, supplanted conventional fluoroscopy at both academic centers and private practices in this country. In my mind, this has been the most dramatic change in GI fluoroscopic studies in the past decade.”
Okamoto notes that the main proponents of flat-panel detectors for use in medical diagnostic imaging are those folks at the forefront of discovering numerous benefits to be had with this technology.
“Leading radiologists already have reported at RSNA in the United States and the JRC [Japan Radiology Conference] about significant dose reduction with better image quality compared to image intensifier-based systems within a specific modality, such as angiography and rotational DSA [digital subtraction angiography],” Okamoto says. “Another reason the flat-panel detector is becoming a ‘must-have’ feature for radiologists is the high image quality now achievable for DSA procedures as a direct result of the lack of image distortion common to flat-panel detectors. This feature is important when viewing second- and third-order veins and arteries. New and upcoming users in cardiology also are now adopting flat-panel detectors for their equipment for many of the same reasons: [Their] low profile allows for improved patient accessibility, better image quality, and longer overall life when compared to image intensifiers.”
Dick Hoffower, supervisor of diagnostic imaging at the Fallon Clinic (Boston), has noted many changes in fluoroscopy technology throughout his 20 years in radiology.
“I’ve seen a dramatic improvement in the image-processing technology. It used to be a direct image on the fluoroscopy screen; now we’re hooked up to a laser center and camera. The technology improvements are a combination of both the quality and the speed of imaging,” he says. “Today’s fluoroscopy systems require a much less radiation dose to the patient to produce an image. We can freeze the image or hold the image, which is useful for placing a needle or monitoring a contrast exam more easily. The images we take today are virtually available to radiologists.”
Who’s Using It?
“Fluoroscopy is primarily used for GI and GU [genitourinary] studies and for invasive procedures performed by interventional radiologists and angiographers under fluoroscopic guidance,” Levine explains. “The major GI studies include barium swallows, upper GI examinations, defecography, barium enemas, and small-bowel studies like small-bowel follow-throughs and, less frequently, small bowel enemas or enteroclysis.”
At the University of Pennsylvania, along with most major academic centers and many private practices, the GI fluoroscopic studies, especially the upper GIs and barium enemas, are performed as double-contrast studies rather than single-contrast studies, using high-density barium and air to optimize the diagnostic yield of these examinations.
“The double-contrast technique allows us to detect more subtle inflammatory and neoplastic abnormalities of the mucosa that cannot be visualized on single-contrast studies,” Levine says. “Major GU fluoroscopic studies include voiding cystograms, retrograde urethrographies, retrograde pyelograms, and hysterosalpingograms.”
Over the past 2 years in Japan, Hitachi Medical Systems America Inc (Twinsburg, Ohio) has installed more than 60 flat-panel detector systems, including over-the-tube radiography and fluoroscopy (R&F), multipurpose C-arm R&F, and C-arm angiography systems. Shigeyuki Ikeda is the key Hitachi Medical research and development engineer who helped develop all of the company’s new medical diagnostic fluoroscopy systems, which use the PaxScan 4030A flat-panel imager from Varian Medical Systems (Palo Alto, Calif). The three systems are the rotational DSA system, a universal angiography R&F system, and an R&F table. Hitachi Medical currently is the market leader in Japan in flat-panel?based medical digital fluoroscopy systems.
According to Ikeda, no distortion improves clinical images of neurosurgery with 3-D DSA, a cone-beam reconstruction technique, nonvascular interventional radiography (IVR), percutaneous transhepatic gallbladder drainage, and percutaneous transhepatic cholangio drainage. He also explains that large detecting areas contribute to the IVR technique for transbronchial lung biopsy, lower GI, transcatheter arterial chemo-embolization, and percutaneous ethanol injection. High-detector quantum efficiency – a measure of how well the flat-panel detector captures an analog image and reproduces it digitally with respect to spatial frequency – decreases the dose of a DSA technique by more than 30% compared to an image-intensifier system, Ikeda says. The image-intensifier system is a device used to focus and convert X-rays into visible light photons onto a small square area for readout by a charge-coupled device (CCD) digital video camera. The sizes for image intensifiers range from 4 to 16 inches in diameter.
Interventional radiologists perform a host of diagnostic and therapeutic procedures under fluoroscopic guidance. Musculoskeletal radiologists perform arthrography of various joints to evaluate the integrity of the joints and injury to ligamentous structures, cartilage, and menisci under fluoroscopic guidance. Chest radiologists occasionally perform biopsies of lung nodules and diagnostic fluoroscopy of the diaphragms to evaluate for diaphragmatic paralysis under fluoroscopy.
DALSA’s Litwiller notes that the low end of fluoroscopy usage is with mini C-arms utilized in emergency rooms and in orthopedic surgery applications.
Calvin Huntzinger, senior product marketing manager at Varian Medical, explains that the company’s On-Board Imager digital imaging system, which is mounted on a linear accelerator, can operate in a fluoroscopic mode. This device is used to confirm that a patient is positioned correctly and to localize the targeted tumor prior to treatment.
“Fluoroscopy is an effective tool for verifying, just before treatment, that the patient’s respiration is stable, that Varian’s RPM [real-time position management] Respiratory Gating System is operating properly, and that the treatment field encompasses the full range of residual target motion,” he explains. “The therapist makes sure that the gating system is operating properly and that the patient is stabilized. Just before treatment, hypofractionation allows a quick confirmation that the patient’s position is stable. It helps the therapist to quickly visualize that treatment is set up right and that normal tissue is minimized, all with hypofractionation, which was not possible before.”
What’s Coming?
Litwiller notes that future fluoroscopy systems will integrate easier with PACS. He adds that the basic dimensions upon which people would like to improve are “always the same: improved image quality, greater flexibility, reduced size, reduced cost, and lower X-ray dosage.”
According to Okamoto, advances in electronics, combined with real-time operating systems and software, have allowed companies like Varian to pioneer the use of flat-panel detectors in future cone-beam systems as well as on-board imaging and patient positioning for oncology systems.
Levine adds, “I think attempts will continue to be made by the various fluoroscopy unit manufacturers to develop equipment that generates lower doses of radiation for the patient. One technique is so-called pulsed fluoroscopy, which lowers the amount of radiation during these procedures. By pulsing the fluoroscopy so that it is intermittent rather than continuous [when the fluoroscopy is on], the patient receives a smaller radiation dose. The tradeoff is that this [process] affects the quality of the fluoroscopic image. I also anticipate that the transition toward digital fluoroscopy will continue until virtually all fluoroscopic systems are taking advantage of this technology, and conventional fluoroscopy becomes obsolete.”
The Newest in Fluoroscopy Technology |
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Varian Medical Systems (Palo Alto, Calif) is at the forefront of new advances in fluoroscopy. The company manufactures the PaxScan flat-panel digital imager, an amorphous-silicon digital imager that can be used for digital radiography and fluoroscopy. Another new development is a device for image-guided radiation therapy, the On-Board Imager accessory. Using digital kV X-ray imaging technology to help clinicians deliver radiation therapy treatments more accurately, this device incorporates one of Varian’s flat-panel imagers. The company recently introduced an 11-inch diagonal PaxScan 2020 flat-panel detector to fulfill a need in the high-end cardiac and cost-competitive C-arm markets. The PaxScan 4030 CB also was introduced recently, which is a 20-inch diagonal flat-panel detector for the emerging cone-beam diagnostic imaging market.
“All of our flat-panel detectors are exclusively air-cooled imaging components, making the overall integration process simple for the system designer, less prone to field failure for the service technician, and dependable for the radiologist and patient,” explains Gary Okamoto of Varian Medical Systems. “Varian provides all of its flat-panel detectors with corrected image output to the OEM’s workstation. Typically, the image corrections required involve compensating for slight variations in signal levels from channel to channel and certain pixel or line imperfections that have been known to create small image artifacts.” Last summer, Varian received FDA 510(k) clearance for an additional feature to the On-Board Imager that uses fluoroscopy to verify what the company calls “gated treatment plans,” which are radiotherapy treatment plans for respiratory gating. The fluoroscopic mode of the On-Board Imager will enable physicians to see the patient’s internal anatomy as it moves due to respiration as well as verify that the gated treatment delivery is going to adequately compensate for the tumor motion.
Recently, InfiMed (Liverpool, NY) introduced the newest members of its cardiology product portfolio: PlatinumOne Cardiac, PlatinumOne Combo, and PlatinumOne EP. The PlatinumOne Cardiac is an in-room digital-acquisition system that provides advanced imaging capabilities for complex interventional procedures. New features include an expanded DICOM 3.0 interface and enhanced image quality using InfiMed’s newly designed CCD camera system. The system also offers left ventricular analysis and quantitative coronary analysis, which allow results to be saved as photo files for ease of archive and review; customizable physician preferences that allow each user to select his/her own settings for acquisition and review; and thumbnail displays, which allow for quick identification of available images.
The PlatinumOne Combo system adds real-time digital subtraction for interventional vascular procedures as well as full cardiac functionality. And the PlatinumOne EP system is designed to provide advanced imaging features and low-dose pulsed fluoroscopic acquisition required for electrophysiology procedures. DALSA Corp has a full range of image sensors and cameras that cover fluoroscopy applications from cardiology up to general fluoroscopy, including mobile C-arms. In the near future, the company expects to add new image sensors to its offerings that will further extend fluoroscopy trends with excellent image quality, higher frame rates, and a competitive price/performance level. |
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-LG |
Safety Issues with Fluoroscopy |
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The FDA (Rockville, Md) has reports of occasional and sometimes severe radiation-induced burns to patients from fluoroscopically guided, invasive procedures, and has issued recommendations to avoid these types of injuries. Procedures that typically involve extended fluoroscopic exposure time are vascular embolization; stent and filter placement; radio-frequency cardiac catheter ablation; percutaneous transluminal angioplasty; thrombolytic and fibrinolytic procedures; percutaneous transhepatic cholangiography; transjugular intrahepatic portosystemic shunt; and percutaneous nephrostomy, biliary drainage, or urinary/biliary stone removal. “The major safety issue is minimizing radiation exposure to the patient,” explains Marc Levine, MD, from the University of Pennsylvania School of Medicine, the Hospital of the University of Pennsylvania, and the Society of Gastrointestinal Radiologists. “Equipment manufacturers and fluoroscopists are always taking steps to keep this exposure as low as possible. For example, the radiologist always tries to use as little fluoroscopy as possible during the examination and to fluoroscope the patient intermittently to minimize the radiation dose.” Many fluoroscopic X-ray systems used for invasive procedures have modes of operation, which result in dose rates that significantly exceed the usual dose rate. Many fluoroscopically guided procedures involve image recording, or fluorography, that requires using film or digital means to permanently record images. The recording modes usually involve much higher dose rates than fluoroscopy, and the contributions from fluorography also must be included in assessing total absorbed dose to the skin.1 “As an imaging-component supplier, the safety issues that we recognize and have taken measures to safeguard against are those related to image quality and field reliability,” says Gary Okamoto of Varian Medical Systems. “Image quality can be known to be affected by slight imperfections created during the TFT [thin-film transistor] manufacturing process, resulting in inactive pixels or blemishes. Varian is unique in that we have provided-ever since the introduction of the fluoroscopy flat-panel detector, the PaxScan 2520-a command processor, or image processing subsystem with corrected image output for each of our flat-panel detectors. “In response to field reliability,” he continues, “we conducted accelerated life and environmental tests, and we made and continue to make improvements to the design or manufacturing processes to address potential field issues. We also work closely with our customers to develop safeguards on the system level to provide the end-user with backup image display features and calls when necessary for routine maintenance, many of which are now capable through a dedicated Ethernet connection to our command processor.” The FDA recommends that:
The FDA also recommends that a qualified medical physicist be enlisted to help implement these principles so as not to compromise the clinical objectives of each procedure. Dave Litwiller of DALSA Corp points out that two subjects arise when discussing safety:
“In higher end fluoroscopy systems, the operator typically will be shielded by a lead screen when the system is energized, so that operator safety is addressed,” he explains. “Safety for the patient is met by reducing the amount of X-ray energy to achieve a given image quality and [having the patient] wear a lead-lined apron during exams. In lower-end flouro systems, such as mini C-arms, the operator and the patient might both be exposed, especially in orthopedic surgery applications. The goal in low-end systems is also to reduce the X-ray power level, ideally to the point that the X-ray dosage is not significantly different from what one would experience in daytime sunshine outdoors.” From a digital image capture standpoint, the contribution to improving safety is to continually advance the performance of image sensors and cameras so that neither the sensor nor the camera degrades the acquired image, according to Litwiller. He adds, “The physics of image formation in the X-ray source, patient, and conversion medium should be the constraints on image quality, with any degradation or noise contribution from the image sensor and camera at inconsequential levels.” |
-LG |
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Laura Gater is a contributing writer for Medical Imaging.
