Now in its early 30s, CT technology is visibly maturing. It was only 1 decade ago when multi-slice technology entered the market with four slices. Now, CT manufacturers have commercially available equipment featuring 64-slice technology, and many of those who don’t have such a system for sale have one in development.
As the number of slices has increased, so has the number of procedures. “For the past 10 years, CT has doubled every three or four years, with 15 to 20 percent growth each year,” says Sean McSweeney, product manager at Toshiba America Medical Systems (TAMS of Tustin, Calif). Scott Schubert, global product manager of the LightSpeed VCT at GE Healthcare (Waukesha, Wis), notes that today, more than 50 million CT exams are performed annually in the United States; globally, that number is double.
The advances and increasing adoption have enabled CT technology to continually expand its clinical application throughout healthcare. “The proliferation of CT is due to the ability to explore the body at a high resolution,” Schubert says. As the speed and resolution of scans have improved, medical imagers have become able to virtually freeze motion. The technology’s use is quickly gaining acceptance in cardiac care and neurology; forecasters see CT’s increasing usefulness in virtual colonoscopy and lung cancer detection; and a rumor is circulating that CT angiography could possibly replace the cath lab.
Although experts agree that CT is a revolutionary tool in both cardiology and neurology, a lack of multicenter studies that prove its value in these disciplines is preventing a strong endorsement from the medical community. But the technology is being continuously applied in a range of applications, steadily gaining the confidence of the physicians who use it.
Improving With Age
CT technology has advanced in large leaps?and quickly. “Four-slice CT was introduced in 1998. Since then, the pace of innovation has accelerated,” Schubert says.
The hardware has evolved to support 64 detectors without sacrificing speed in the gantry rotation, without increasing the time needed to cool the equipment, and without increasing the radiation dose. Rather, manufacturers have reported improvements in one or more of these parameters.
The increase in the number of detectors (aka channels) allows greater image resolution, wider study views, and quicker exam times. The GE LightSpeed Volume CT (VCT), a 64-detector scanner, captures 64 slices of anatomy, each slightly less than 0.36 mm wide, for a study total near 40 mm of anatomy. Through reconstruction, this area can be viewed in a 3-D fashion.
According to GE Healthcare, the LightSpeed can capture any organ in 1 second, the heart and coronary arteries in less than 5 seconds, and the whole body in less than 10 seconds. “The speed with which the images are taken allows us to freeze motion, including blood flow and the heart,” Schubert notes.
The reduction in motion corresponds to a reduction in its artifact. Images are clearer. “Quick speed reduces motion artifact,” says James W. Green, senior VP for business unit CT at Philips Medical Systems (Bothell, Wash).
The improvements in resolution allow a reduction of other artifacts as well. “CT has been limited by its difficulty in scanning images with high-density pathology, such as calcified plaque or metallic implants. Better resolution reduces this artifact,” says Murat Gungor, marketing manager for the Somatom Sensation at Siemens Medical Solutions (Malvern, Pa). “It also reduces blooming artifact, which, at lower resolutions, can cause a small speck of calcium to appear 10 times larger than it actually is.”
The reduction in artifact permits physicians to more clearly see the anatomy of interest. “With 0.4-mm resolution, you can see more details and smaller objects,” says Loke-Gie Haw, manager of clinical marketing at Siemens Medical.
Time is saved not only during a scan but between scans as well. Nearly all manufacturers reported shorter cooling times for their equipment, eliminating related delays. “Even at maximum load, our new Straton X-ray tube cools down almost three times faster than a normal X-ray tube, virtually instantaneously, and in much less time than needed to initiate the next procedure,” Gungor says.
He adds that Siemens’ Straton tube is also smaller, allowing the gantry to rotate faster?at 330 ms. “CT hardware has achieved several milestones, but the software has advanced too. New programs and tools have been created, such as those for CT colonography, lung modules, and CAD versions,” Gungor says.
Trauma’s Modality of Choice
With CT’s recent advances, any application is improved; so is diagnostic confidence, especially with the reduction in artifact. The key applications to benefit are those that can take advantage of the high resolution and the ability to freeze motion, such as cardiology and neurology.
“CT is already the modality of choice for trauma in general, particularly head imaging,” McSweeney says. An emergency room adult patient can have a full-body scan in 30 seconds; a pediatric patient can be examined even more quickly, reducing the need for patient sedation and additional anxiety.
“You can apply CT technology to any organ, determining viability of tissue or ruling out conditions in a matter of seconds,” Green notes. This speed is especially valuable in treating ER patients complaining of chest pain or stroke symptoms. Patients are likely to experience improved outcomes with quicker diagnosis and treatment delivery with a CT scan.
Cath Lab: Here to Stay
The rumor that hospitals will be closing their cath labs is just that?a rumor. CT cannot replace the interventional value of the cath lab, but, by substituting for its diagnostic work, CT can help make the cath lab more profitable.
“CT technology has taken a huge leap, and healthcare needs time to adapt its clinical applications,” says W. Dennis Foley, MD, professor of radiology at the Medical College of Wisconsin (Milwaukee) and chief of digital imaging at the Medical College’s Froedtert Hospital. “We could be on the verge of a major paradigm change.”
|The newest CT technology enables imagers to freeze motion, allowing physicians to reach diagnoses quicker than before.
According to Schubert, many physicians say time is of the essence in trauma, especially for chest pain. Doctors need to rule out causes and determine the root nature of the problem. Physicians can rule out the three most life-threatening causes of chest pain?heart attacks, pulmonary embolisms, and aortic dissections or tears?with one scan.
“The VCT can get this scan in 10 seconds with one breath hold and one contrast injection. This is more cost effective and time efficient than using three or four different studies to reach the same diagnosis,” Schubert says. If a trauma patient was indicated for cardiac disease via CT, he or she would proceed to the cardiac cath lab for intervention, skipping the diagnostic portion. “There is no definitive proof CT will replace cath labs, which have two primary functions: diagnosis of cardiovascular disease and interventional treatments, such as angioplasty. CT will never handle the interventional portion, but its diagnostic capabilities are much quicker than the 60-minute cath lab exam and are not invasive,” he adds.
CT can rule out significant disease more quickly than a catheter angiography, which is invasive and, therefore, riskier. Approximately 40% of cath diagnostic exams are ruled normal. CT can save these patients from an unnecessary procedure.
CT also can save money. “Cath is expensive,” McSweeney says. “Leaving a patient in ICU is expensive, and stress tests are expensive. CT, as an option, saves time and money, and it improves patient care.”
Because it is a better diagnostic option, CT can complement the cath lab, liberating its resources for additional interventional procedures, which typically earn the facility more money. “Hospitals can’t replace the cath lab because it also provides interventional value, but there is great motivation to replace diagnostic cath,” Haw says. “Unfortunately, no multicenter study yet proves the outcome; and until this is done, the cath lab cannot be eliminated.”
Taking Freeze Frames
CT angiography isn’t just an improvement over the cath lab; the 64-slice technology also has shown clear advances over previous CT systems. “The biggest breakthrough has been the ability to freeze the motion of the heart,” Schubert explains. “With a 16-slice scanner, 10 to 30 percent of studies can’t be completed because the patient can’t hold his or her breath, or the heartbeat changes too much. With a 32-channel detector, it will still take 10 to 12 seconds to acquire an exam.”
Data degrades as it is collected over a greater number of heartbeats. “High heart rates and variable heart rates still can pose significant challenges,” says McSweeney, citing cases where the heart beats 150 times per minute. TAMS’ SureCardio software ensures successful examinations up to 100 beats per minute by automatically selecting successful acquisition parameters, including reconstruction mode, pitch, and rotation time, based on the patient’s heart rate.
According to McSweeney, cardiac care has been one of the biggest drivers for CT technology during the past few years. TAMS offers software packages, such as SureCardio, to assist with routine cardiac care. “We recently received FDA clearance for SurePlaque, a program that enables the quantification of soft plaque in the arteries. Instead of a risk measurement, physicians can look at actual lesions, which have the potential to rupture or break loose and cause sudden cardiac arrest,” he says.
SureSubstration is a digital substration angiography (DSA) program. “Calcified vessels are difficult to see, but if you subtract the plaque, you can see an occlusion that might have been missed before and that can affect the course of treatment,” McSweeney says. He also suggests that CT can help avoid sending patients home with an existing problem, reducing the potential for patient injury and hospital liability.
Foley adds, “CT is a potentially rapid test for indeterminate-origin chest pain. You can use techniques to view the coronary, pulmonary, and thoracic aorta in one exam. You can change the way these patients are diagnosed. But first, comparative studies must be finished.”
Making Viability Visible
Neurology applications are still new enough to lack definitive data as well, but CT has shown great value in brain studies, particularly in the diagnosis of stroke. Treatment of the condition, which typically presents in the ER, depends on whether the cause of the symptoms is due to a blockage or a hemorrhage. Because of the opposite natures of these conditions, the treatments for the two are incompatible and can increase patient risk significantly if delivered in error.
“There is about a six-hour window in which to complete intervention. A CT exam can speed the process and, subsequently, its success,” says McSweeney, suggesting that brain perfusion offers the major value that CT has been promising.
Physicians can freeze the blood flow in the brain and characterize how much of the flow is reaching the organ. They can scan for aneurysms and see small structures over a wide area. Green notes that perfusion studies can identify regions that might be salvageable. “You can see the functionality with perfusion maps,” he says.
Gungor adds, “We can now scan the entire anatomy from the aortic arch in the chest to the top of the head in 6 seconds with a resolution that allows identification of structures, such as tiny aneurysms or clots.” He notes that Siemens Medical’s newest Somatom CT scanner can identify vessels less than 1 mm in size.
On the Horizon
Schubert says that adopters in the primary buying cycle have shown interest in the ability to see three conditions: small aneurysms, lesions, and/or plaque buildup in blood vessels. But other applications are in development as well.
McSweeney notes a dramatic rise in musculoskeletal imaging, particularly for fixation devices and spinal hardware. Also, virtual colonoscopy has become a reality and is winning supporters. Widespread acceptance is expected to drive its adoption. Says Green, “Everyone is excited about being able to reduce the more invasive exam.”
A newer application for CT is the early detection of lung cancer, though no studies offer evidence of the technology’s value in this area. However, the earlier that cancer of any kind is detected, the better a patient’s chances for survival. A CT scan can assist with identification of lung cancer through accurate measurement of the growth of suspicious nodules. “With the improved resolution, a low-dose lung scan will identify nodules less than 1 mm in size. A follow-up three to six months later can provide insight into the rate of growth through volumetric measurement,” Gungor says.
Of course, with each new application, physicians need to be brought up to speed. “There is always a physician learning curve with new technology and interpretation,” Foley says. But they’ll get the hang of it. And as CT technology continues to mature?like a fine wine, a tasty cheese, or a young artist’s painting?its potential has yet to be fully realized.
Compare and Contrast
Which multi-slice CT scanner will work best for your facility depends on needs, goals, and budget. To help make a decision, use this chart for comparing the most advanced systems currently on the market (ordered alphabetically by manufacturer).
Product: LightSpeed VCT
Detector/Slice Number: 64/64
Resolution: 0.35 mm
Rotation Rate: 0.35 seconds
Reconstruction Time: 16 images/second
Tube Power: 100kW
Philips Medical Systems
Product: Brilliance 64
Detector/Slice Number: 64/64
Resolution: 0.34 mm
Rotation Rate: 0.40 seconds
Reconstruction Time: 40 images/second
Tube Power: 60kW
Siemens Medical Solutions
Product: Somatom Sensation 64
Detector/Slice Number: 32/64
Resolution: 0.34 mm
Rotation Rate: 0.33 seconds
Reconstruction Time: 20 images/second
Tube Power: 80kW
Toshiba America Medical Systems
Product: Aquilion 64
Detector/Slice Number: 64/64
Resolution: 0.35 mm
Rotation Rate: 0.40 seconds
Reconstruction Time: 16 images/second
Tube Power: 60kW
Reducing the Health Hazard
Many mixed messages have been circulating about the risk of exposure from radiation resulting from a CT exam. Some cite low danger about equal to that of a day in the sun; others think the risk is somewhat greater than that. Whatever the danger, the physician decides whether it is outweighed by the risk of not treating the patient with CT.
The risk, however, can be reduced through hardware modifications and software protocols. Most manufacturers offer some technique to reduce the dose and have designed their systems to decrease risk.
Safety in Design
Some manufacturers start with the materials. According to Sean McSweeney of Toshiba America Medical Systems (TAMS), the company focused on finding a detector substance sensitive enough to X-rays that it would absorb more of them, requiring a reduced dose.
James W. Green is with Philips Medical Systems, which uses filters. The company employs an active titanium filter to remove lower-power photons from the X-ray beam. “These photons never make it through the body, but are instead absorbed by the skin. If you filter them out before they ever reach the patient, you can deliver 40 percent less absorbable dose,” he says.
GE Healthcare also uses filters and has introduced a new bow-tie filter for cardiac studies on its LightSpeed VCT. “The bow-tie filter is a physical piece of graphite that sits between the X-ray tube and the patient. It’s tuned to provide the optimal dose of radiation for a specific exam,” says Scott Schubert of GE Healthcare, citing dose reduction between 15% and 30%.
Reducing Risk With Software Protocols
Protocols and software also can be used effectively to maximize exposure and reduce risk. “Modulation schemes are being developed and perfected,” notes W. Dennis Foley, MD, of the Medical College of Wisconsin and Froedtert Hospital. Most manufacturers offer a variety of protocols.
At GE Healthcare, Schubert notes that with the move to the volumetric CT scanner, new technology in place reduces dose by up to 20% compared to 16-slice scanners.
At Siemens Medical Solutions, radiation exposure is modulated with its CARE (combined applications to reduce exposure) programs. CARE Dose4D can reduce the dose for an average adult patient up to 66% through real-time, automatic exposure control. HandCARE turns off the X-ray beam at three different positions to prevent direct exposure to the clinician’s or surgeon’s hand, which, according to Murat Gungor of Siemens Medical, can reduce staff exposure by 70%.
TAMS reduces dose by as much as 30% through SureExposure, which automatically adjusts the tube current with every rotation of the gantry and bases that exposure on an initial view of the patient’s anatomy.
Pediatric protocols reduce the exposure for children and were some of the first developed. Many take into account the patient’s age and size. “Dynamic dose modulation reduces the power applied to the tubes based on patient size and the study being completed, and then it’s done dynamically during a scan,” Green notes.
These methods aim to make sure that the clearest image possible is captured with the least amount of radiation necessary, maximizing benefit and minimizing harm.
Wren Davis is a contributing writer for Medical Imaging.