Intraoperative MR/OR Allows Imaging in the Surgical Arena
Cardiac MRI Technique Can Demonstrate Arterial Blockage Without Surgery
Running the Numbers
Recent Paper Stresses Importance of Ferromagnetic Detection
MRI Systems Evaluated by ECRI
Intraoperative MR/OR Allows Imaging in the Surgical Arena
In the summer of 2005, Children’s Hospital Boston opened the doors to its new suite of operating rooms (ORs), designed by Shepley Bulfinch Richardson and Abbott (Boston) and featuring one particularly specialized space—one of the nation’s first intraoperative MR/OR of its kind.
Children’s Hospital Boston’s MR/OR features a mobile MR system suspended from the ceiling; the magnet is a 1.5T MRI scanner manufactured by Siemens Medical Solutions (Malvern, Pa), mounted on a transport assembly manufactured by Innovative Magnetic Resonance Imaging Systems (Winnipeg, Manitoba). The MRI scanner is safely garaged during the majority of the surgical procedure, but allows for MRI image acquisition during the surgery to determine whether further surgery is required. “The neurosurgery operating room can be transformed into a state-of-the-art imaging suite in a couple of minutes,” said Charles Osborne, senior associate of health care planning and design at Shepley Bulfinch. “First, the room is cleared of equipment, and booms are swung into their parked position; the magnet is brought into the room, where the patient is positioned on a hydraulically powered, cantilevered operating table.” After the imaging is complete, the magnet is moved back to its garage, and the doors are closed. Aided by the high-quality images, the surgeons and radiologists can decide whether further surgical interventions are required before completing the operation.
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| The MR/OR at Children?s Hospital Boston can be moved into place after a surgical procedure (above right) to safely enable MR imaging. |
Safe inclusion of the magnet was the foremost concern in the designers’ minds. “The magnet is located in a bay adjacent to the OR so that it does not become an obstacle during surgery,” Osborne said. “The sliding doors of the docking bay and the ceiling-mounted mobile MR are very high tech.” Design of the MR/OR room required that several factors be taken into consideration: structure to support the 7.4-ton magnet; containment of the fringe magnetic fields associated with the scanner within the room; isolation of vibration and sound; and accommodation of adjacent spaces not typically found in ORs, such as the docking and control rooms. Secured entry and provisions for ease of circulation for the patient, equipment, and different types of clinicians involved in the intraoperative procedure also were important factors.
“We started with a prototypic general-purpose operating room,” Osborne said. “Then, we modified it as a subspecialty OR for neurosurgery. After that, we added the requirements for introducing the MR into the room, thus merging surgery and radiology. Our design process is a technologically adaptable approach. In the clinical building expansion, we knew we were going to be incorporating new technologies into the health care process. We worked in partnership with Children’s Hospital Boston, pioneers in providing advanced treatments and innovation in pediatric health care.”
Keith Strauss, MSc, director of radiology physics and engineering at Children’s Hospital Boston, concurred. “This is technology that the neurosurgeons requested to support their surgical procedures,” he said. “The design allows you to remove the MRI scanner from the operating arena, so the surgeons can use their normal surgical tools and still have high-quality imaging at appropriate points during the procedure. Normal surgical tools cannot be safely used in the immediate environment of an MRI scanner because of the attraction of these tools to the scanner’s large magnetic fields.”
The challenges of introducing an MR/OR system do not stop with design, Strauss noted. “It takes a lot of interdepartmental coordination to operate this kind of system safely in the middle of a busy OR environment,” he said. “It involves nurses, radiologic technologists, surgeons, anesthesiologists, imaging scientists, and support engineers to maintain the imaging equipment in a safe environment for patients and staff.”
Safety was tantamount in the minds of clinicians and support staff at Children’s Hospital Boston as they worked to write comprehensive guidelines for implementation of the system. “A lot of people were involved in writing policies and procedures,” Strauss said. “If you correctly identify a potential problem, it takes a finite amount of effort to identify a solution. Problems can occur later when you forget to ask an important question during the planning of operations. We had to get enough people involved with a sufficiently broad range of experience to be sure all questions related to patient and staff safety had been identified. That’s probably the biggest operational challenge we faced.”
The purchase of the MR/OR system was made possible by a grant from the Klarman Family Foundation.
—C. Vasko
Cardiac MRI Technique Can Demonstrate Arterial Blockage Without Surgery
More than 13 million Americans suffer from coronary artery disease (CAD), the top killer in the Western hemisphere. Coronary angiography is currently the standard method for CAD detection, but new cardiac MRI techniques show promise for the detection of arterial blockage without invasive surgery. In the July issue of Radiology, a study1 by researchers in Boston and Brazil demonstrates the efficacy of one such method.
The purpose of the study—which was led by Ricardo Cury, MD, director of clinical cardiac MRI at Massachusetts General Hospital (Boston), and which also included researchers from Harvard Medical School (Boston) and Beneficencia Portugueasa Hospital (Sao Paulo, Brazil)—was to determine the accuracy of a combination of stress first-pass perfusion imaging followed by delayed-enhancement imaging at detecting clinically significant coronary artery stenosis.
With this method, researchers injected patients with contrast material and then performed MRI at regular intervals, checking for heart muscle ischemia attributable to coronary artery blockage and to see whether there was damage to the tissue that would indicate a prior heart attack. “While MRIs focus on functional and hemodynamic evaluation of a significant stenosis by assessing myocardium perfusion defects during drug-induced stress (first-pass MRI), cardiac CTs focus on anatomic detection of coronary obstruction,” Cury said. “Thus, stress-perfusion MRI is more comparable to nuclear imaging techniques, such as SPECT and PET. Moreover, cardiac MRI and cardiac CT can be complementary.” The team worked with a 1.5T CVi MR scanner from GE Healthcare (Waukesha, Wis).
“We have shown that cardiac MRI can be used reliably as an alternative to other more invasive detection techniques due to its high diagnostic accuracy; its comprehensive evaluation of cardiac function, perfusion and viability; and the lack of radiation exposure,” Cury said. “More information is gained through the evaluation of function, stress perfusion, and viability of the myocardium than using 64-slice CT.”
A total of 47 patients scheduled for coronary angiography were enrolled; 33 were suspected of having CAD, and 14 had experienced a previous myocardial infarction and were suspected of having new lesions. Coronary angiography demonstrated significant stenosis in 30 patients. Stress first-pass perfusion MR imaging and delayed-enhancement imaging yielded sensitivity of 0.87, specificity of 0.89, and accuracy of 0.88, leading the researchers to conclude that the new diagnostic method “is an accurate method to depict significant coronary stenosis in patients suspected of having or known to have CAD.”
In certain patient populations, the accuracy rate was even higher—in those with only one diseased vessel, accuracy jumped to 0.96; and in those who had previously undergone bypass graft surgery, the rate came in at 0.90.
The new MRI technique potentially could be used to enhance clinical decision-making and to guide disease management. “In addition to diagnostic accuracy, cardiac MRI is safe,” Cury noted. “It can provide information about the anatomy, function, blood flow, and damage that the heart has sustained. MRI also can be used to assess the blood vessels in the body.”
—C. Vasko
Reference
- Cury RC, Cattani CA, Gabure LA, et al. Diagnostic performance of stress perfusion and delayed-enhancement MR imaging in patients with coronary artery disease. Radiology. 2006;240(1):39-45. Available at: radiology.rsnajnls.org/cgi/content/abstract/240/1/39. Accessed August 3, 2006.
Running the Numbers
60% reduction in radiation dose can be achieved for pediatric patients undergoing abdominal CT by using a new technique developed by Soroosh Mahboubi, MD, et al, at the Children?s Hospital of Philadelphia, who presented results of their study at the May meeting of the American Roentgen Ray Society. By modulating the tube current to account for body symmetry, an average 15% reduction can be achieved over the typical weight-adjusted dose. Dose reduction from combining the two techniques ranged from 14% to 85%, depending on weight, for an average 60% reduction.
Recent Paper Stresses Importance of Ferromagnetic Detection
The Society for Medical Innovation and Technology (SMIT of Gelsenkirchen, Germany) held its 2006 international conference May 11?14 in Monterey, Calif. Kopp Development Inc (Jensen Beach, Fla) contributed a scientific paper to the Symposium on MRI Safety called “Impact of Ferromagnetic Detection on MRI Safety.”
Presented by Keith Kopp, president, Kopp Development, the paper reviews current and future magnet designs and their effect on projectile risk, with particular attention to the role of the static magnetic-field spatial gradient. “Recent information has indicated that ferromagnetic projectiles are a significant, if not the most significant, cause of serious injuries,” according to the paper. “A number of factors, including the MR magnet design and operational procedures, have caused these risks to increase.”
Ferromagnetic projectiles can cause costly damage to MRI equipment. The risk of injury from ferromagnetic objects left in the MRI suite has gained special attention in recent years, owing in part to a widely publicized incident in 2001 in which a boy was killed after being struck by an oxygen tank during an MRI scan.
The paper concludes that ferromagnetic detection systems, as a supplement to comprehensive screening procedures, can reduce the risk of a projectile incident significantly.
Kopp Development manufactures and markets electronic sensors such as the FerrAlert system, which detects ferromagnetic objects before they are carried into close proximity of an MR scanner.
—C. Vasko
MRI Systems Evaluated by ECRI
A recent evaluation of three 1.5T MRI systems has been published by ECRI (Plymouth Meeting, Pa), an independent, nonprofit health services research agency. It provides information on selection criteria, product specifications, and results and analysis from ECRI’s testing of the scanners.
The report specifically looks at the Signa 1.5 HD from GE Healthcare (Waukesha, Wis), the Avanto from Siemens Medical Solutions (Malvern, Pa), and the Vantage from Toshiba America Medical Systems (Tustin, Calif). “We invited all major manufacturers to participate—GE, Toshiba, Siemens, and Philips. Philips declined our invitation,” ECRI Evaluator Jason Launders told DOTmed News. “We chose the 1.5 Tesla, which represents most of the systems sold today, and we chose the most technologically advanced from each of those manufacturers.”
Offering guidance on such factors as field strengths, gradient systems, coils, channels, and specialized imaging features, the report in ECRI’s Health Devices journal also rates systems based on both inpatient and outpatient imaging. Systems are also evaluated and rated according to their ability to meet the needs of breast, cardiac, and functional MR imaging. DOTmed News also reported that ECRI assessed baseline image quality—signal-to-noise ratio, resolution, uniformity, and other technical measures, and that testing took place at the manufacturers’ facilities. The company also surveyed users to judge things like patient comfort and throughput, according to DOTmed News.
To purchase the June issue of Health Devices, visit www.ecri.org.
