First came computed tomography (CT) imaging, and it was good. Then came helical CT, or spiral, and it was better. This was followed by larger multislice CT, which garnered much acclaim, but the four- and 16-slice systems were not perfect. Now the medical imaging industry has 32-, 40-, and even 64-slice technology, and the resulting images are better than anything yet seen. However, CT technology continues to evolve toward an ideal not yet qualified. One company is working with a 256-slice prototype, while another has a scanner incorporating flat-panel technology.
Toshiba’s Aquilion 32-slice CT features a hybrid 64-row quantum detector to produce 32 slices of 0.5 mm or 1 mm with each gantry revolution, for a total z-axis coverage of 32 mm.
According to Sean McSweeney, product manager for CT at Toshiba America Medical Systems Inc (TAMS of Tustin, Calif), the four key drivers for the CT market are:
- desire to improve patient care;
- the need to increase productivity;
- demand for greater accuracy in diagnosis; and
- new applications.
Faster speeds and higher resolution images have contributed to improvements in all four areas. Studies are under way at leading CT companies to examine the use of the technology in the diagnosis and treatment of the nation’s three leading killers: heart disease, cancer, and stroke. Thus far, results have been positive.
McSweeney notes that CT has become the gold standard of abdominal imaging. He and others believe that use of CT for virtual colonoscopy and coronary angiography will soon become the norm. Other expectations for use include a role in stroke assessment and real-time surgical guidance. Until the next advances are clinically assessed, it is impossible to predict just what new applications they will have, but one thing is clear: The advancements will very likely be linked to higher speeds and greater resolution.
Eliminating Compromises
“There has always been a tradeoff between speed and resolution,” McSweeney says. “Traditionally, the more resolution desired in an image, the more time required to capture it. With multislice, and particularly 16-slice, there is no longer a need to compromise.”
The new high speeds are the equivalent of a freeze frame, says Jim Green, senior VP and general manager of business CT for Philips Medical Systems (Andover, Mass). “Everything in the body moves: the heart, the lungs, the organs. The heart, for example, performs 60–100 beats per minute. So the CT technology needs to sample faster than what’s moving.”
With technological advances, it is now possible to cover the entire chest region with just one breath hold, and the corresponding reproduction of images is more anatomically correct. But how does this benefit the patient, the facility, and the doctor?
Patients get faster and more accurate diagnosis, sometimes with less invasive procedures. Dominic Smith, LightSpeed global product manager for GE Healthcare (Waukesha, Wis), says, “CT has basically done away with exploratory surgery.”
Siemens’ SOMATOM Sensation 64 is awaiting FDA clearance, which the company expects to receive later this month.
In addition, reduced time on the examination table means less contrast needed and diminished radiation exposure. Murat Gungor, marketing manager for the SOMATOM Sensation scanner line at Siemens Medical Solutions USA (Malvern, Pa), claims that the company’s 64-slice scanner reduces this dose by 66%.
This faster and more accurate diagnosis improves patient care and comfort as well as provides the physician with more confidence in his selected treatment path, reducing the risk that the patient will need to return for additional treatment. Furthermore, the doctor now has the ability to see more patients. Green notes that this factor is especially beneficial for physicians in private practice or independent imaging centers.
Similarly, facilities can benefit from the increased productivity. Gungor notes that a cardiac angiogram can be completed in roughly 9 seconds, and a pulmonary embolism exam can be done in 5 seconds.
Of course, another benefit is being able to determine when a patient does not need to be admitted for further treatment, eliminating waste and freeing resources to treat those who do need care, points out McSweeney.
Expanding CT Applications
As the images produced become more detailed, CT’s clinical use expands. Its use for coronary angiography has proven so beneficial that it is expected to soon replace the catheterization procedure. “Traditionally, both diagnostic and therapeutic work for cardiac disease has been done in the catheter lab. This traditional diagnostic method is not only invasive, but also carries a high risk of vascular incidence and mortality,” McSweeney says.
A CT exam can produce the same, if not better, results with far less risk and much more comfort. Green notes that many sites already have adopted the procedure for diagnostic coronary angiogram.
CT also is being touted as a new diagnostic tool in stroke assessment. McSweeney notes that of the three leading killers, stroke is the costliest in terms of debilitation. “There is a 6-hour window after an incident of stroke in which the physician must determine the path of care,” he says. “Profusion will provide information about the blood flow of the brain but not if a certain part of the brain is viable.”
However, with CT, the physician can look in the head to determine if a stroke has occurred and where, the size of the section of brain affected, and which parts are salvageable, Green adds. CT also can be used to follow the patient through the treatment process to determine its success.
With spatial resolution comparable to that of MRI, orthopedic and musculoskeletal work is possible as well. This similarity benefits everyone since the facility can avoid calling in an MR technician, McSweeney explains. Perhaps because CT was developed as a diagnostic tool nearly a decade before MRI, a technician is always on hand.
Considering the History of CT
EMI Laboratories Engineer Sir Godfrey Hounsfield is generally credited with having invented CT imaging, also known as computed axial tomography (CAT) scanning, in 1972. The original systems were designed to scan the head, but by the mid-1970s, whole-body systems were available.
These systems consisted of a rotating gantry, which spun around the examination table. An X-ray tube was mounted on one side, and on the other side were arc-shaped detectors, which measured the X-ray profile and, thus, captured the image of a small slice of the body. At the end of each 360? rotation, the gantry would stop and rotate in the opposite direction to capture another image slice. At the same time, the patient bed would be moved forward an inch or so to allow the equipment to produce an image of the next section.
The development of the power slip ring in the 1980s eliminated power-source issues and allowed the gantry to continuously rotate. This—combined with alterations to the path of the X-ray beam and constant movement of the examination table through the gantry—allowed spiral CT to gather continuous data with no gaps between the images.
But the speed and image quality needed improvements, and physicians wanted more coverage along the length of the patient, or the z-axis. The technology evolved to capture smaller slices of the body in less time. Known as multislice CT, it has advanced from four slices to 16 to 32 to 40, and now, Siemens is awaiting FDA clearance on the SOMATOM Sensation 64, its new 64-slice CT system. It is expected in late April, Gungor says.
Overcoming Technological Hurdles
These newer systems deliver more detailed images in less time, an achievement that has required advances in numerous technologies. Companies have had to overcome obstacles related to gantry size, power generation, detector systems, rotation technology, data capture, and information processing.
“Tremendous g-forces are involved in rotating a tube of that mass at subsecond speeds,” McSweeney notes. “In addition, you need a detector system capable of capturing thin slices, which allows the radiologist and physician to view smaller anatomical objects.”
Leon Kaufman, PhD, head of research at AccuImage Diagnostics Corp (San Francisco), agrees that improvements in detector materials and design have been important to the development of multislice CT. “The first generation used xenon gas detectors, which limited the size of the cells—they can only be so small,” he says. Newer generations use not only newer materials, but also more detectors. “With more rows of detectors,” Kaufman explains, “less time is required to capture the images.”
Indeed, new detector technology is one of the advances cited by Siemens’ Gungor that contributed to the development of the new 64-slice system. Its design is wider and uses more detectors, thereby providing 0.4-mm
resolution. The scanner also incorporates a new tube, developed by Siemens specifically for the system. “The Straton X-ray tube has a very low heat storage capacity and cools down almost instantaneously, so the scanner can be pushed to its limits,” Gungor notes. Technically speaking, the tube completes rotations in 0.37 seconds; cools in less than 20 seconds; and, using an advanced electromagnetic control system for X-ray focus, doubles the sampling density for an organ, resulting in higher resolution. Compare these numbers to those from an early CT prototype, which required roughly 4 minutes to capture a single image.
The Brilliance 40-slice CT from Philips Medical Systems features DoseWise technology, which offers dose efficiency without compromising image quality.
Even technology that doesn’t claim 64-slice capture can boast specifications far better than those of the original. Philips’ Brilliance 40-slice CT imaging equipment features 0.4-second gantry rotations and 40-mm coverage.
Green notes that in addition to the advances in the technology that captures the images, corresponding advances in high-speed electronics have permitted the company to break the 32-slice barrier. “Philips’ Tach technology was a breakthrough in very high-density mixed-signal, application-specific integrated circuits,” he says, “which permits the conversion of analog data into digital signals at high speeds and with ultralow noise.”
Analyzing the Sea of Data
Of course, once the data has been captured, it still must be analyzed. The new technology captures an overwhelming amount of information. “A 16-slice machine capturing 0.5-mm slices can generate almost 500 images in 15 seconds. A technologist can’t analyze that data conventionally. It’s too much,” explains John Zimmer, VP of marketing at TAMS.
Green agrees, noting that technology now fuses the many images together to produce one view, which the radiologist can zoom in on to better regard an area of interest.
Software can help create specific studies. “The radiologist has a lot more to look at, so he needs ways to manipulate data presentation,” says Kaufman, noting that the software provided with AccuImage’s machines provides various options, such as 3-D views and slide throughs.
GE Healthcare’s LightSpeed line offers software that expands the imaging possibilities, allowing views of the body without certain obstacles, such as the vessels or bones. “AutoBone allows the physician to remove the bones from the 3-D image to provide an unobstructed view of the vessels,” says GE Healthcare’s Smith.
Naturally, technologists, radiologists, and physicians require some training on the new equipment—though many companies utilize the same user interfaces, making the software easier to master with upgrades. The real change in culture comes with the original switch to multislice, Gungor says. The procedures change, within workflow, patient preparation, and analysis.
McSweeney adds, “The client needs to set up protocols to send specific information to the workstation and to storage.”
Capturing Market Share
The benefits well outweigh the need for training, as evidenced by the fact that multislice CT has penetrated even smaller facilities. “Eighty percent of everything we sell is spiral CT,” Smith says, estimating the market at $2.5 billion to $3 billion.
According to Zimmer, 75% of the market is utilizing six-slice CT. “We’ve sold multislice CT to 30-bed hospitals that purchased the equipment to fulfill the role they play in the community. They might need to refer patients to larger facilities, but can send them with their scans, avoiding the need to rerun tests,” he adds.
Other rural facilities might care for a large patient population and can improve their business model by having patients referred to them for the tests, Green notes. And as the clinical applications of CT expand, Gungor adds, other small centers see them as revenue generators.
Acquiring the equipment need not be hindered by cost. Kaufman says that as high-end institutions upgrade, their machines filter down through the system. “Smaller centers can now buy four- and eight-slice CT scanners for lower prices,” he says.
Typically, the high-end scanners are found in large hospitals or university and research settings. Because these facilities generally have the money and need to justify their purchases, they’re the same institutions where studies examining the impact of the equipment take place.
Looking to the Horizon
Studies provide hints as to where the CT market is headed. Kaufman predicts that slices will be made thinner, permitting isotropic resolution, which, in turn, will allow physicians to look at a subject from any dimension. And of course, the increase in slices will continue; GEMS, for example, also has a 64-slice CT in development.
Industry experts believe that more protocols will continue to move to CT, eliminating invasive procedures and producing more accurate diagnoses. The resulting impact will include a migration of diagnostic work to the emergency room as well as shorter or no hospital stays for some patients.
It’s also likely that CT will become a tool for actual interventions. Its ability to capture images in real time can be an asset during surgery, providing operational guidance.
According to Gungor, Siemens is working on the project already. “We are now focused on a flat-panel CT prototype in place at Massa-chusetts General Hospital [Boston]. It offers improvements in coverage and detail, attaining a new resolution by scanning an organ with one rotation. Though clinical trials are 4 to 5 years down the road, it’s expected to have a high value in interventional studies and perfusion,” he says.
TAMS also is working with a prototype, currently running in Japan, that can capture up to 256 slices. “We’ve seen a greater ability to image the coronary arteries, to determine viable brain sections after stroke, and even to analyze polyps at an early stage of lung cancer by working with computer-aided diagnosis, or CAD,” McSweeney says.
He notes that when looking ahead, it’s important to consider those four drivers of the market—improved patient care, increased productivity, greater diagnostic accuracy, and new applications. Each new advance in the technology brings surprises in its usefulness.
“When we launched the 64-slice 2 years ago, we didn’t expect so many advantages,” Gungor says. Similarly, new applications for the equipment in the pipeline won’t be fully realized until it’s available.
Renee DiIulio is a contributing writer for Medical Imaging.
