CT Advances Heart Disease Detection
|Robert Faberman, MD|
The 264-bed Caritas Norwood Hospital, of Norwood, Mass, provides emergency, cardiology, advanced surgical, cancer, OB/GYN, and Children’s Hospital Boston pediatric services. The acute care facility is a member of Caritas Christi Health Care, which is the second largest health care system in New England.
Last September, Caritas installed the LightSpeed VCT from GE to complement its cardiac catheterization lab. Medical Imaging discussed the hospital’s experience using the 64-slice CT scan technology with radiologist Robert Faberman, MD.
MI: Does the technology require more radiation dose? How does it work?
Faberman: The technology can result in a higher patient radiation dose than conventional cardiac catheterization or routine chest CT. However, available software can reduce the dose to below that of a conventional cardiac catheterization. This software allows images to be taken only during a specific phase of the cardiac cycle.
The technology involves x-rays passed through the patient as the patient travels through the CT scanner. Intravenous contrast is administered to opacify the coronary vessels. Very thin (submillimeter) slices are obtained and reconstructed to obtain 2D and 3D images of the heart and coronary vessels.
MI: Please explain the benefits this scanner offers, particularly the advantages of 3D over 2D.
Faberman: The scanner images a volume of data, which can be reconstructed in any plane to remove overlapping structures, as well as a 3D representation of the heart. Images can be obtained regardless of the patient’s anatomy and the ability to catheterize individual vessels. Coronary anomalies can also be assessed with ease. It requires only an intravenous injection of contrast, rather than an arterial puncture, as with conventional coronary angiography. There is no recuperation period. Cardiac function and cardiac morphology can also be assessed at the same sitting. In addition, the remainder of the chest is also imaged, including the lungs, mediastinum, and chest wall, as well as portions of the upper abdomen.
|Caritas Norwood Hospital staff with their 64-slice LightSpeed VCT from GE Healthcare.|
MI: What specific limitations does 2D possess, and how does 3D resolve those challenges?
Faberman: 2D imaging of the coronary arteries requires multiple projections (views) in order to adequately assess the coronary vessels. In 3D imaging, a volume of data is obtained, and the data can be reconstructed in any plane desired. Anomalies can be better assessed in 3D than with 2D. Convention 2D imaging is also invasive, requiring arterial puncture, with the risks of arterial dissection and induction of arrhythmias.
MI: Which patients are the best candidates for this kind of scan?
Faberman: Indications include patients with suspected coronary artery disease (the test is not for screening of asymptomatic patients), those with unexplained chest pain, and evaluation of bypass graft patency. The test has a high negative predictive value (a negative study excludes coronary disease) and is useful in assessing the need for conventional coronary angiography and in planning intervention.
Patients must have a heart rate of less than 65 beats per minute, and medications are often used to lower the heart rate. Patients must also have a regular heart rate. Patients with arrhythmias such as atrial fibrillation cannot be scanned.
Siemens Showcases MR Solutions at ISMRM
Siemens Healthcare presented its latest developments in magnetic resonance at the International Society for Magnetic Resonance in Medicine in Toronto.
Representing a new class of MRI technology that delivers high-field diagnostic imaging to a broader scope of patients, the MAGNETOM Verio aims to eliminate claustrophobia through a bore that is 70 cm in diameter. Furthermore, the average distance between a patient’s eyes and the magnet is 30 cm. Additionally, the wider space helps accommodate the needs of patients with kyphosis, limited mobility, and pain, as well as obese and pediatric patients.
“MR scanning for ICU patients is now easier than before on long-bore magnets,” said Dr Bernd J. Wintersperger, section chief, general radiology, Ludwig Maximilians University of Munich Hospitals Grobhadern. “Moreover, the wider bore enables us to a more patient-friendly positioning, especially in off-center scanning, like scanning with dedicated coils. This, overall, shortens the workflow and data acquisition.”
The MAGNETOM Verio, currently the shortest 3T MR system on the market, has the footprint of a 1.5T MRI system, according to Siemens. It is equipped with a lightweight, 6-ton magnet and total imaging matrix (TIM) technology. Because of the system’s smaller dimensions, installation costs are reduced. Moreover, due to the system’s zero Helium boil-off technology, operational costs are minimized.
Shipments of the MAGNETOM Verio began in April.
Siemens also showcased new multichannel coils designed to increase patient throughput and enhance image quality. Based on TIM technology, which the company says “set the trend in RF technology and coil workflow,” the new coils have up to 32 channels. Increased signal-to-noise ratio and higher imaging speed with higher acceleration factors in parallel imaging (iPAT) are achieved through the ultrahigh “density” of coil elements.
Developed for advanced neurology, the 32-channel head coil offers an open view that increases patient comfort and is ideal for visual stimulation experiments included in fMRI exams. Cardiac and abdominal imaging can be conducted in a single breath hold in all four dimensions.
Other applications demonstrated at the meeting included syngo Arterial Spin Labeling (ASL), syngo NATIVE, and syngo MapIt.
Allowing for a noninvasive and contrast-free assessment of blood flow in the brain, syngo ASL can be used for patients with stroke, cerebral tumors, or neurodegenerative diseases. Inline Subtraction enables fully automated processing of different image data sets and color-coded relative Cerebral Blood Flow (relCBF) maps of perfusion data.
As a solution for contrast-free MR angiography, syngo NATIVE contains protocols tailored for use in different body regions. Inline MIP provides 3D images of the vessels without user interaction, with Inline Subtraction simplifying the workflow.
Lastly, syngo MapIt lets radiologists detect subtle joint pathologies and determine courses of treatment for conditions such as osteoarthritis at an early stage. Used for biochemical imaging in joints, the liver, and other body regions, the application creates parametric maps for T1-, T2-, and T2 fully automatically and within minutes.
New MR Scanner Targets Novices, Experts
A complete liver exam in 15 minutes. A complete breast exam in two sequences. A routine fMRI with shorter paradigms and greater activation. A new innovation from GE Healthcare is making it all possible, efficiently and easily.
At the International Society of Magnetic Resonance in Medicine meeting in Toronto last month, GE announced FDA clearance of the newest addition to its Signa family of MR systems: the Signa MR750 3.0T.
“We’re combining the most powerful MR scanner in the world with the most advanced clinical applications that are very easy to use,” said David Handler, general manager, global MR marketing, GE. “We’ve taken emerging applications for MR, which has tremendous clinical value and safety, and made them accessible to everyone—the patient, the referring physician, and the MR department.”
Focusing on improving productivity, the Signa MR750 brings together the industry’s most powerful gradients, user-friendly workflow features, and GE’s advanced Thermal Management System. The MR scanner delivers up to 60% additional anatomical coverage and resolution unit per time and allows for up to five times the imaging performance over previous generations. It also boasts a newly designed RF Transmit system that maximizes performance with a 17% gain in scanning efficiency.
|GE’s new Signa MR750 delivers up to 60% additional anatomical coverage and up to five times the imaging performance over previous generations.|
Handler points out that the system features the only detachable patient table in the industry, which leads to a number of benefits. For example, customers who work in high-volume environments can purchase two tables—one for scanning and one for positioning. Furthermore, users have the ability to do future upgrades with third-party technology that works exclusively with GE’s docking system.
Moreover, the system is equipped with GE’s exclusive Optical RF Technology, which adds up to 27% higher signal-to-noise ratio over conventional, nonoptical MR receivers. “In the past, you would have to take the signal from the patient exam, digitize it, and transmit that information from the computer,” Handler said. “We’ve moved the digitization right next to the patient. There is no noise introduced anywhere along the chain.”
The optical chain, in conjunction with GE’s use of high-density surface coils, represents a critical path for ensuring clear signal reception and data analysis. To maintain the high-density approach, the scanner’s architecture is scalable to 128 channels of simultaneous data acquisition.
Additionally, the Signa MR750 features a newly developed technique aimed to improve full-body imaging. Arc, or Auto Calibrating Reconstruction for Cartesian imaging, allows for auto-calibration, which helps avoid collecting external sensitivity map. It also makes it possible for less sensitivity to field-of-view positioning with a tight FOV, clinically practical reconstruction times for continuous scanning, and workflow simplification that can be integrated into sequences without necessitating separate calibration scans.
Experts and new users alike will be able to streamline their clinical workflow through automated acquisition tools based on the concept of touch-and-go protocols, as well as utilize the first-ever in-room operator console, Handler said. As a result, the Signa 750 3.0T allows them to focus more of their attention on the patient, he continued.
New advanced applications offered by the MR technology include LAVA-IDEAL, a dual-echo acquisition technique that provides detailed, 3D abdominal images in one breath hold; VIBRANT-IDEAL, which allows for fat-free breast imaging with high spatio-temporal resolution; and PROPELLER 2.0, which uses the No Phrase Wrap technique to produce virtually ghost-artifact-free, motion-immune scans in sagittal, coronal, axial, and oblique planes.
Choosing Mastectomy: MRI False-Positives or Other Factors?
omen at high genetic risk of developing breast cancer were only slightly more likely to choose prophylactic mastectomy after receiving a false-positive MRI result for the disease than women who did not receive a false-positive, according to a study conducted in the Netherlands.
The study, based on a survey of 196 women, was published in the April issue of the Annals of Oncology. In 83% of incidents where an MRI exam showed breast cancer in a patient who was part of the survey, the MRI finding turned out to be a false-positive.
“We doctors will have to tell our patients that there are so many false-positives,” said Nicoline Hoogerbrugge, MD, the lead author of the study. “But we don’t have to be afraid that it will change their minds in another direction that they don’t want for themselves.”
The women surveyed all had genetic mutations that put their chances of eventually developing breast cancer as high as 80%. In the group that expressed a prior preference for mastectomy to guard themselves from breast cancer, 89% of women who had received a false-positive MRI result went through with the surgical procedure. But 66% of women who did not receive a false-positive result also went through with the procedure.
The difference between those numbers was not significant, said Hoogerbrugge, who heads the Hereditary Cancer Clinic of the Radboud University Nijmegen Medical Center in the Netherlands. That is especially true because the survey followed up with the women for less than 3 years, so more of the second group of women may have opted for prophylactic mastectomy after the study ended, she said.
Among women who had a prior preference for surveillance, instead of prophylactic mastectomy, 15% who received a false-positive MRI changed their minds and opted for mastectomy. In the same group with a prior preference for surveillance, 11% who did not receive a false-positive MRI ended up having prophylactic mastectomy performed.
The study shows that women at a high risk of breast cancer can handle the shock of receiving a false-positive MRI result for breast cancer, and that they will not automatically opt for an irreversible mastectomy, Hoogerbrugge said. “They just have a few bad days, and then they go on with their lives, exactly as they would before,” she said.
The study also showed that imaging by mammography and MRI had a sensitivity of 71% and a specificity of 90%. “The combination of mammography and MRI is the best you can have,” Hoogerbrugge said.
The high number of false-positive breast cancer results generated in MRI imaging is the result of the emphasis that physicians place on not missing any cancers, Hoogerbrugge said.
“What I want to underline is that MRI is good; we don’t miss relevant cancers,” she said. “That’s very important, so people can feel safe when they use MRI, as long as they know there are many false-positives.”
In 2004, the most recent year for which statistics are available, 186,772 women in the United States were diagnosed with breast cancer and 40,954 women died from the disease, according to the federal Centers for Disease Control and Prevention.