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Computed tomography (CT) vendors have introduced several advancements in hardware and software in 2012.
“You want lower dose, better accuracy, and you also want more special and temporal resolution,” said Elliot Fishman, M.D., FSCCT, professor of radiology and oncology, director, diagnostic radiology and body CT, Johns Hopkins University, Baltimore, Md. He said all CT vendors have created next-generation CT scanners to accomplish these goals. New technologies include use of iterative reconstruction, more sensitive detectors that emit less electronic noise, and new software and hardware features to lower dose. New detectors have increased quantum detector efficiency (QDE). The higher QDE, the better the sensitivity of the detector to receive more photons, so lower radiation doses are needed, he explained.
New CT System Highlights
GE Healthcare introduced its Discovery CT750 HD FREEdom scanner, which offers a new type of detector for better signal-to-noise ratios and new reconstruction software to reduce stitching artifacts and noise of low-dose scans. It also offers the ability to perform dual energy scans using a single X-ray tube modulated every 0.5 milliseconds between 80 and 140 kVp.
The system addresses some of the main challenges of cardiac imaging, including coronary motion, calcium blooming, plaque composition and accurate myocardial perfusion. The system’s FREEdom (Fast Registered Energies and ECG) software offers intelligent motion correction via SnapShot Freeze, enhanced coronary visualization even in the presence of calcium, detailed plaque material composition assessment and accurate perfusion calculations. SnapShot Freeze is supposed to significantly reduce coronary motion and overcome the limitation of all hardware-only solutions. It precisely detects vessel motion and velocity, and determines actual vessel position and makes corrections.
Benchtop evaluation of the software shows it achieves a 58 msec equivalent gantry rotation speed, which is four to six times faster than hardware-only gantry rotation speed. This translates to a 29 msec effective temporal resolution, which achieves a CT temporal sampling similar to the frame rate of a cath lab.
“SnapShot Freeze will be a game changer by improving the effective temporal resolution, and from the initial images, I see significantly reduced motion artifacts and significantly improved image clarity,” said James Min, director of cardiac imaging research and co-director of cardiac imaging at Cedars Sinai Hospital and current president of Society of Cardiovascular Computed Tomography (SCCT). He is a principal investigator for the VICTORY trial, which is evaluating the diagnostic accuracy of SnapShot Freeze motion and stitching artifact correction.
Toshiba’s newest CT system is the Aquilion Prime, which is the replacement for its previous 64-slice system. It is an 80 detector row system that can generate 160 unique slices per rotation. It can also be configured with 40 detector rows, which can generate 80 unique slices per rotation. The system is field upgradable.
Toshiba is moving toward 0.5 mm slices for better resolution and using a larger detector than other vendors for more coverage. Its systems boast features to enable single-beat acquisition cardiac imaging. Its BEAT CTA software eliminates scan segments with arrhythmias to produce better quality scans without artifacts.
Earlier this year, Siemens introduced the new Stellar detector for its CT systems, which uses integrated, printed microcircuits instead of soldered circuit boards. This reduces the amount of electronic noise in scans by about 20 percent. The new detectors also overall improve image quality by reducing calcium and metal blooming, so it is easier to evaluate in-stent restenosis.
Siemens also offers CARE software to help reduce dose by offering the technologist an easy-to-use picture menu of scan protocols based on patient size and type of exam.
Philips Healthcare has introduced several new features. SmartShape increases beam hardness to reduce soft radiation when possible. IntelliBeam filters shape the beam inteligently based on the size of the object being scanned. The Nanpanel detector reduces electronic noise. A new collimator helps reduce radiation scatter.
Filtered back projection has traditionally been used to render nearly instantaneous images after a scan. However, with advances in computing power and speed, a more accurate reconstruction method, iterative reconstruction, is being introduced.
“Iterative reconstruction algorithms can lower dose and increase the signal-to-noise radiation and they also help reduce artifacts,” said Jeffrey Carr, M.D., MSc, FACR, Wake Forest School of Medicine, Winston-Salem, N.C. He said the software takes the raw image data and reconstructs it over and over in multiple iterations to create a more accurate, sharper rendering. Due to the computing power and time required to make these complex calculations, vendors have developed a mixed method of using filtered back projection and then adding a percentage of iterative reconstruction to enhance the image. This blending of the two methods reduces the time required to render images, from hours to seconds.
Iterative reconstruction also enables enhancement of lower-dose scans to achieve dose reductions of 30-50 percent without loss of image quality. itn