A Look Inside: Next-Generation Multidetector CT

 Multidetector CT scanning is about to take the next step, with major vendors previewing their next-generation systems at radiology’s extravaganza—the Radiological Society of North America meeting in November. The newest innovations in CT scanning promise significant gains ranging from improved temporal and spatial resolution to new applications in stroke evaluation, and for all studies—less contrast media, shorter exam times and, across the board, lower radiation dose.

Four new systems are slated for availability in 2008. Toshiba America Medical Systems dominates on slice count with its AquilionONE 320-slice scanner; Philips Healthcare’s answer is the Brilliance iCT 256-slice scanner. Siemens Medical Solutions touts the SOMATOM Definition Adaptive Scanner (AS), an “adaptive” scanner available in 40-, 64- and 128-count configurations. And GE Healthcare is re-defining CT through High-Definition CT (HDCT) technology.

Health Imaging & IT spoke with a few early adopters of these technologies to gain some insight into the capabilities and see what the next generation has in store.

Clinically meaningful functional CT

Brigham and Women’s Hospital in Boston is an early adopter of Toshiba’s AquilionONE CT scanner. “The new system enables dynamic volume imaging,” says Frank Rybicki, MD, PhD, director of cardiac CT and vascular CT/ MRI. “Using the Aquilion-ONE, we can cover 16 cm in the cranio-caudal direction in a single gantry rotation, [thus] reinventing CT imaging and opening the door to new applications.”

Prior to the introduction of AquilionONE, 64-slice volumetric imaging entailed imaging of separate pieces or sub-volumes. Sub-volumes were stitched together after the scan, a process that produces artifacts, particularly when imaging a moving organ such as in coronary CT angiography (CTA). “Dynamic volume imaging eliminates the need to put the pieces back together and the problems associated with the approach. This is especially important when iodinated contrast is moving through the heart. With a sub-volume CT scanner, iodinated contrast is imaged at a different place in every sub-volume,” explains Rybicki.

Other major AquilionONE applications include CT angiography/venography and CT perfusion of the brain. With 320 x 0.5 mm slices, or 16 cm of coverage, radiologists can image the entire brain parenchyma in a single gantry rotation. The principle is similar to the heart, since whole brain scans capture the exact phase of the iodinated contrast as it tracks from the arteries to the brain parenchyma and then to the veins. “This provides vastly more information for stroke evaluation than current CT scanners,” states Rybicki, who predicts that after the clinical evidence is in, every stroke center will consider an investment in the scanner. Instead of using MRI to assess stroke, centers can potentially use CT in lieu of MRI to avoid the expense, complexity and acquisition time associated with MRI.  “With stroke, physicians constantly battle against the clock to initiate therapy. If time can be shaved from patient imaging, it represents a huge advance in care. Potentially, the entire CT acquisition including the non-contrast, angiography and perfusion maps could take 15 minutes,” notes Rybicki.

“This is clinically relevant functional CT,” continues Rybicki. The difference between 320 and 64 slices is that the new paradigm allows radiologists to view an entire organ rather than a sub-volume. “There are multiple new applications, such as the perfusion of tumors that we are just beginning to explore,” concludes Rybicki.

Deliveries of the AquilionONE are slated to begin this summer.

Cardiac scanning and beyond

MetroHealth in Cleveland, Ohio, deployed Philips Healthcare Brilliance iCT scanner in October and has scanned hundreds of patients with the 256-slice system. The new system produces superior cardiac images as its speed and coverage freezes the motion of the heart and produces a clear snapshot of the coronary arteries. But its benefits extend beyond cardiac and cardiovascular scanning.

“Higher slice [count], higher speed, larger coverage scanner are intended to deliver maximum benefits to cardiovascular and cardiac imaging; however, we’ve seen significant benefits from iCT’s higher resolution and speed in every scan we’ve acquired,” states Pedro Diaz, PhD, vice chair of imaging and informatics. For example, the department turned to iCT to complete a renal stone protocol on an uncooperative patient in tremendous pain. The four-second scan resulted in high-resolution diagnostic images. Radiologists see similar results for everything from trauma scans to routine chest, abdomen and pelvis protocols as well and expect to use the scanner for both routine imaging and emerging applications such as brain perfusion and cardiovascular imaging.

Adaptive scanning at a glance

Medical University of South Carolina (MUSC) in Charleston, S.C., installed Siemens Medical Solutions Somatom Definition Dual Source (DS) CT scanner in September 2006 and plans to deploy the Somatom Definition AS early this year after evaluating the new scanner for several months. The system is pending FDA clearance.

The new system helps answer shifting clinical needs, says U. Joseph Schoepf, MD, associate professor of radiology and medicine. “In the last three years, clinical needs have evolved in a way that makes adding slices and detector rows a lower priority than in the past,” opines Schoepf. Current-generation 16-slice scanners, the workhorses of many radiology departments, adequately answer nearly all routine clinical applications in body imaging including pulmonary embolism detection and full-body trauma scans. Sixty-four slice scanners can be used for body imaging, but the additional slices add minimal clinical value to body scans, says Schoepf. In fact, in some cases like peripheral runoff studies and acute trauma scans, techs must curb 64-slice scanner speed because the scan outruns the bolus.

But when it comes to cardiac imaging, 64-slice systems are a valuable clinical and operational asset. “The heart and coronary arteries are minute and fast-moving targets. Successful imaging solely depends on temporal resolution,” explains Schoepf. With a single detector row, temporal resolution is a function of the single row; however, the addition of a second detector row improves temporal resolution by a magnitude of two. “[By improving temporal resolution] Definition DS expands cardiac imaging applications,” says Schoepf.

Radiology needs to move away from rigid slice numbers as the sole determinant of a CT scanner’s utility and consider factors such as overall, versatility and usefulness of a system, says Schoepf. Definition AS fits the new niche by enabling sites to adapt to changing and emerging clinical needs. For example, the system fits in an 18m2 space, allowing hospitals short on real estate to shoehorn the system into spaces previously too small to house a CT suite. At the same time, the table and gantry accommodate patients weighing up to 650 pounds. On the clinical front, Definition AS is a good fit for the expansion of perfusion imaging in CT. Physicians can use the scanner for perfusion imaging of the entire brain, which could be a valuable tool in the early detection of stroke. Schoepf also envisions using the new system to detect changes in tumor morphology and tumor perfusion and thus assess a patient’s response to chemotherapy. CT will play an increasingly key role in facilitating techniques such as radiofrequency ablation, cryoablation, targeted chemotherapy and brachytherapy, says Schoepf. These minimally invasive therapies require image guidance, and Definition AS offers the speed and resolution necessary to enable them.

CT meets HD

Last summer, Medical College of Wisconsin in Milwaukee, Wis., began exploring the next-generation of CT scanners. Dennis Foley, MD, director of imaging, and his colleagues are evaluating GE Healthcare’s new HDCT technologies on a modified LightSpeed VCT scanner. Comprising a front-to-back redesign, HDCT enables dual-energy imaging and improved registration in conjunction with iterative reconstruction. A modified garnet gemstone scintillator improves x-ray conversion speed. The clinical upshot? “It produces very sharp images of the coronary arteries and abdominal visceral arteries,” says Foley.

Projection-based, dual-energy data processing reduces beam hardening artifacts. In addition, the scanner tackles one of the primary impediments in coronary imaging. That is, it is expected to subtract out coronary calcium in images. Calcium can obscure diagnosis in cardiac cases, so the ability to subtract it should enhance diagnostic capabilities. Other potential clinical applications include iodine separation, accurate auto-bone removal in 3D assessments and material decomposition. Dual-energy CT should improve body imaging, too, providing increased sensitivity with less contrast media. The new technology also overhauls software and enables iterative reconstruction for improved image quality.

GE expects to file for FDA clearance in the first half of 2008.

CT: The next stage

Radiology is re-inventing CT imaging. The newest scanners prove that CT will continue to play a central role in the clinical arena, opening new applications ranging from CT-guided interventions to brain perfusion imaging and improving standard exams by providing superior resolution.


The Dose Question
Radiation dose is in the international spotlight, especially after the recent New England Journal of Medicine article that showed CT scans could be responsible for as much as 2 percent of all cancers in the United States in the next 20 to 30 years due the radiation exposure. The importance is compounded by the great increase in CT scans, with study authors David Brenner, PhD, DSc, and Eric J. Hall, DPhil, DSc, of Columbia University estimating “that more than 62 million CT scans are currently obtained each year in the United States, as compared with about 3 million in 1980.”

Thus, hospitals and imaging centers are attempting to devise strategies to minimize radiation dose to patients while maximizing imaging benefits. Vendors are on the same path—with all four multidetector CT vendors projecting dose reductions to patients in the range of 80 percent with their next-generation systems compared with current-generation scanners. Here’s how the majors address the dose challenge with their newest solutions.
  • GE Healthcare’s High-Definition (HD) CT technologies employ iterative reconstruction to extract additional image clarity, suppress noise and allow reduced dose.
  • Philips Healthcare’s Brilliance iCT scanner employs a new Eclipse collimator that eliminates all wasted radiation, and a step-and-shoot cardiac protocol uses one-third of the conventional radiation dose by imaging the coronaries during a single phase of the heart.
  • Siemens Medical Solutions Somatom Definition AS incorporates Adaptive Dose Shield, which dynamically blocks unnecessary dose before and after the spiral scan, ensuring the patient receives a clinically relevant dose only.
  • Toshiba America Medical Systems AquilionONE slashes scan time to 0.5 second; the shorter exposure minimizes radiation dose to the patient.

The IT Angle
 CT’s newest crop certainly yield exquisite images, but how do the scanners impact storage and network capacity? There’s good news here.

The IT impact is not as bad as one might think, says Pedro Diaz, PhD, vice chair of imaging and informatics at MetroHealth in Cleveland, Ohio, an early adopter of Philips Healthcare’s Brilliance iCT scanner.

Bread-and-butter scans like chest, abdomen and pelvis protocols comprise 90 percent of the CT business at MetroHealth; the number of slices for these studies is the same on the 256-slice system as it is on 64- and 16-slice scanners. The difference, says Diaz, is the iCT acquires the 300 slices faster and with better spatial resolution.

On the other hand, emerging applications such as brain perfusion imaging and cardiac and cardiovascular scans can generate 10,000 slices, which does represent an IT challenge. Still, Diaz waxes positive. Storage is ever-cheaper, and sites need not save every acquired slice.

Difficult Decisions Demystified
The wider array of CT scanners is a boon to health imaging; however, the new diversity in the market does present a challenge. How do sites decide which scanner best meets their needs? Here are a few pointers to guide hospitals and imaging centers through that tough call.

Determine the budget and any financial constraints. Can the scanner be shared with another department—such as radiology and cardiology—to offset expense?

Evaluate the structural environment and scanner suite. Verify the footprint of the suite; some space-strapped sites can house water-cooled systems only, says U. Joseph Schoepf, MD, associate professor of radiology and medicine, at Medical University of South Carolina (MUSC) in Charleston, S.C.

The most important factor in the decision, says Schoepf, is the analysis of the facility’s clinical needs. Hospitals eyeing the cardiovascular market may want to tap into a dual-source or higher slice-count scanner that provides a solid foundation for cardiac imaging. Hospitals with stroke centers should review the brain perfusion capabilities of various systems. Even facilities looking for a bread-and-butter CT solution may opt for higher-slice systems, says Schoepf. That’s because a state-of-the-art system is the best way to avoid obsolescence. Plus, a high-end system provides a means of differentiating a practice from local competitors. Hospitals and imaging centers that can not afford a top-of-the-line CT scanner, but anticipate growth over the next three to five years, should inquire about upgradeability and ensure that the new system facilitates future uncomplicated upgrades. Finally, scanners destined for siting outside of radiology in areas like the ED, interventional radiology or radiation oncology should fit the clinical needs of the “home base.”