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For other articles and previous issues click here. August 30, 2004 CT
Evolution The latest 40- and 64-slice scanners are now in clinical use. Here’s a look at how clinicians are using them—and how they might. It seems like only yesterday that 16-slice scanners represented the state-of-the-art CT technology. The next incremental advancement was eagerly awaited but still only in research and development. But something happened on the way to the 32-slice system. A logical exponential step in the progression seemed to have been skipped. Some product manufacturers leapfrogged over the 32-channel systems and forged ahead into the 40- and 64-slice realms. Not that anyone’s complaining. In making the leap, the manufacturers sought to improve z-axis resolution, allow greater coverage per rotation, increase imaging speed, shorten scan times, and allow submillimeter resolution. They’ve developed systems with the kind of speed and image quality that are especially useful when scanning regions of the body containing moving organs. Their efforts may prove invaluable to clinical areas such as cardiology, neurology, and angiography. The new systems are enhancing complex applications such as organ perfusion studies, coronary artery imaging, and pulmonary imaging that require visualization of very small structures. They’re also aiding in stroke assessment and improving critical and trauma care through increased acquisition speeds and faster reconstruction capabilities. The technology can be used on just about any patient. “We don’t need to do any patient selection,” says Nathan Peled, MD, head of the department of radiology at Lady Davis Carmel Medical Center in Haifa, Israel, the first facility to use Philips Medical Systems’ Brilliance CT 40-slice scanner. “We can scan any patient from the emergency room and intensive care unit, postoperative patients, unconscious patients, and uncooperative patients. The only patients we can’t scan are those with renal failure because they can’t have any contrast agent.” He describes the system’s speed and accuracy as critical in detecting problem areas, providing the best diagnoses, and determining the best treatments for acutely ill and injured patients. Peled says the studies are easy to perform. As high-end slice configurations open the door to more research opportunities, he believes the system’s clinical applications will broaden. Despite expectations that the next generation of high-end scanner technology would have 32 slices, manufacturers felt compelled to go even higher. “About 18 months ago, we reached a critical juncture in the development [of our scanner],” says Scott Schubert, CT global product manager for GE Healthcare of Waukesha, Wis. At that crossroads, the company had to determine whether it wanted its next product to be a 32- or 64-slice scanner. After analyzing feedback from dozens of advisory boards and hundreds of customers, the message—and which path to take—became clear. “Our customers were looking for a breakthrough technology, not something that just incrementally provided more slices than a 16-slice scanner,” recalls Schubert. “So we made the product and business decision to leapfrog the 32-slice scanner to go straight to our LightSpeed VCT, a 64-channel system.” The new wave of products indeed represent breakthroughs. Speaking at a recent conference cohosted by Philips and the American Roentgen Ray Society, Jonas Rydberg, MD, an abdominal radiologist with Indiana Radiology Partners and associate professor of radiology at the Indiana University School of Medicine, which recently purchased a Brilliance scanner, says the technology will change how routine CT work is performed. First 40-Slice in the United
States “In general, the thinner the slice, the better,” says Peled, who was the first physician to use the Brilliance 40-slice configuration in a clinical setting (for cardiovascular imaging, CT angiography, and peripheral angiography). “It makes your diagnoses better and more precise.” In addition, he points out that for the first time, the entire body can be covered in a thin-slice mode, which was not possible in the 16-slice mode. “So this is a major change because you can get now anything in the body in slices of 1-millimeter to 1.5-millimeter slices, and you can very look at very tiny detail in the entire body,” he says. At Indiana Hospital, the system will be used primarily to study cardiac patients and scan the chest and abdomen, which are particularly challenging to image because of the motion from the heart and patient breathing. The system addresses these challenges with its increased coverage and data acquisition, which allows for shorter breath holds and enables physicians to digitally freeze motion, which the developers believe will make it helpful for examining the vascular system and early detection of cardiac problems. The shorter breath holds are more comfortable for patients and reduce the need for rescanning. Further, the system is more versatile in terms of patient selection. The necessity of long breath holds was a big problem with earlier CT scanners, Peled says. Some patients, especially older ones, had trouble holding their breath for long periods of time. “With the 40 slice, we’ve managed to reduce the scan time for cardiac CT to an average of 10 seconds compared to an average of 20 seconds on a 16-slice scanner, and this makes it possible for any patient to pass the examination,” he says. Because of the shorter scan times, less contrast can be used, which enables the scanning of some patients with borderline renal function. It is also helpful in pediatric studies, unconscious trauma patients, and uncooperative emergency department patients. “With the ultrafast scan mode, you just put the patient on the table and you can cover the chest and abdomen within five to six seconds and the chest in two to five seconds, and you get superb images,” says Peled. 64-Slice Clinical Work Werner Bautz, MD, the radiology institute’s director, trumpets the system’s image quality, high level of temporal and spatial resolution, and speed. “The ability to see the smallest of details can improve early diagnosis and better determine treatment options,” he says. The Sensation 64’s speed and level of spatial and temporal resolution aid the visualization of the smallest intracranial, pulmonary, mesenteric, and peripheral vessels in less than 10 seconds without motion artifacts. It has an isotropic spatial resolution of 0.4 millimeters and provides 64-slice submillimeter imaging per rotation and a gantry rotation time at 0.37 seconds. “With its gantry rotation time, the system provides up to 76.8-millimeter-per-second table feed with submillimeter collimation,” says Bautz. “Thus, isotropic 0.4-millimeter resolution goes hand in hand with considerably reduced scan times.” Like the Brilliance system, the Somatom can increase patient throughput, broaden patient selection, and reduce the amount of contrast material needed. Bautz says the institute is exploring the new range of clinical applications and protocols, as well as studying how the system changes clinical workflow. The system’s capabilities are facilitated by Siemens’ z-Sharp technology, which combines rapid movement of the x-ray source in the Straton tube with the 64-channel UltraFastCeramic detector design. “The z-Sharp technology enables a significant reduction of spiral artifacts, which especially improves cranial CT exams considering brain stem imaging and evaluation of skull adjacent pathology,” comments Bautz. As for applications, Bautz says the scanner speed and resolution offer new opportunities for cardiac and vascular imaging and oncological applications. “Compared to previous systems, we can now run true arterial phases—for example, of the arteria carotis—without running into the venous phase,” he says. “For the first time, true arterial phase imaging of the entire carotid artery and the Circle of Willis can be performed with 0.4-millimeter spatial resolution. A CT angiography of the supra-aortic vessels requires only a five-second scan acquisition time for a scan range of 350 millimeters.” Even more, the institute has experienced a significant increase in image quality while focusing on coronary arteries. “Blooming of stent struts and calcified lesions has decreased tremendously, whereas we can see a new level in plaque detail, especially when it comes to delineation from the wall and plaque composition,” comments Bautz. “Volume” CT Clinical use includes cardiac, trauma, angiography, and pulmonary applications that require the combination of the system’s speed, submillimeter resolution, and wider coverage capacity. But it can also improve imaging in neurology, oncology, and other fields. The high speed allows for easy capture of dynamic events. Schubert says this has some significant ramifications, particularly for clinical imaging applications that need to freeze anatomical motion, such as respiratory, cardiac, or circulatory. The quicker imaging process can help with hard-to-handle children or trauma patients who may move a lot. GE installed its first beta unit of the scanner at Froedtert Hospital in Milwaukee. Schubert reports the system will be commercially available toward the end of 2004. GE refers to the LightSpeed VCT as a new generation of technology that they call volume CT scanners, or VCT. With four times the coverage (40 millimeters per rotation) of 16-slice scanners, 73% more coverage per second than currently projected from 32- and 40-slice scanners, and the highest possible resolution (0.35-millimeter micoVoxel), VCT represents a paradigm shift in terms of speed and the ability to cover the whole body and organ anatomy in virtually seconds, says Schubert. “We are going from imaging organs or patients in a breath hold to imaging in a second,” he says. GE was able to leapfrog over the 32- or 40-slice designs and move into the next generation of scanners via its new detector technology: the V-Res. “The detector is the platform for how we’ll get wider volume coverage and higher resolution in the future,” Schubert says. “It’s the world’s first true 64-channel detector. The number of slices on a CT system has always been defined by the number of simultaneous channels acquired by the detector. The V-Res follows that same historical definition of slices. Some systems are called 64 slices, but they don’t have the true 64 detector.” According to the company, creating a detector strong enough to acquire 64 channels of data while spinning at less than 0.4 seconds per rotation was the largest-ever single research and development initiative for its CT technology. Future Expansion Clinical testing of the system has led to new applications, including complete coronary angiograms within five heartbeats, determining the potentially life-threatening causes of chest pain via one noninvasive scan, and making stroke workup more routine. GE has identified at least 20 other clinical applications where its capabilities should prove useful. A partial list includes whole-body angiography, perfusion studies, and contrast injection. Toshiba Aquilion “Toshiba’s Aquilion 64-slice CT is the world’s first FDA-cleared true 64-slice system providing the industry’s best low-contrast detector and isotropic-slice resolution at 2 millimeters and .35 millimeter,” says Doug Ryan, director of Toshiba America Medical Systems’ CT business unit. “CT can now be used on a greater range of patients to more accurately visualize soft plaque and measure coronary stenosis.” The Aquilion 64-slice system will be available for U.S. delivery in 2005. Existing Aquilion 32 systems can be upgraded to a 64-slice system. At the heart of the Aquilion 64-slice CT is its Quantum detector, which enables the Aquilion CT scanner to acquire 64 simultaneous slices of 0.5 millimeter with each 400-millisecond gantry revolution for a total Z-axis coverage of 48 millimeters per rotation. The result is precise isotropic imaging of any region of the body during a breath hold under 10 seconds. “With the volumetric imaging of the Aquilion 64-slice CT, our sites are capturing and seeing more anatomical information than previously thought possible. The coverage and speed of the Aquilion 64-slice CT expands noninvasive capabilities for a wider range of patients,” says Ryan. The Quantum detector design also enables minimal dose due to a highly efficient ceramic material, according to the company. This material allows for the lowest noise and highest dose efficiency available on the market, which is reflected in the outstanding low-contrast performance of the Aquilion. Toshiba developed the SUREWorkflow applications
suite to ensure clinical accuracy and productivity by automating
complex CT studies. The Aquilion 64-slice CT automatically acquires
scan data, reconstructs images, and sends the results to the selected
review station. Advanced applications in the SUREWorkflow suite
include the following: What’s Ahead for 16 and
32? “We believe that in the next few years, this generation and the next generation of scanners will completely change the way we deal with coronary patients, as we witnessed in the evaluation of the body arterial tree [aorta, carotids, renal arteries, and peripheral arteries],” Peled says. “I believe we’re going to do most of the diagnostic studies noninvasively with CT or MRI and use conventional angiography only for selected cases and, of course, for intervention. The change we are going to see because of the relative ease of performing these exams is far beyond imaging only. We are going to diagnose patients in an earlier stage of their disease, detect life-threatening lesions and anomalies in an asymptomatic patient, and hopefully prevent irreversible damage and save lives.” — Dan Harvey is a frequent contributor to Radiology Today. |
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