The 21st Century has arrived and with it the dawn of a new age in imaging technology. In a few short seconds, a heartbeat can be imaged or millimeters of tumor growth can be tracked. For the multislice CT market, the magic words are thinner, faster and sharper.
In the last year, the major players in multislice CT have greatly increased the power and functionality of their scanners. Multislice CT systems are becoming more popular than ever and physicians are now using them in clinical ways that were only just being explored a year ago. Faster scanning times mean more diagnostic accuracy and less motion artifacts when looking to discover the ailments of the human body.
The companies marketing multislice CT units — such as GE Medical Systems (GEMS of Waukesha, Wis.), Marconi Medical Systems Inc. (Highland Heights, Ohio), Philips Medical Systems North America (Shelton, Conn.), Siemens Medical Systems Inc. (Iselin, N.J.), and Toshiba America Medical Systems Inc. (Tustin, Calif.) — each are doing something slightly different, but their concentrations generally pare down into two categories: those that increase the efficiency and technology of their scanners, and those that focus on making new applications more commonplace in a clinical setting.
Among all of the applications of multislice scanners, cardiac CT has shown the most potential for becoming a routine practice, and many companies are marketing various cardiac CT packages that perform everything from cardiac scoring and gating to calcium measurements.
Thinner slices
Radiologists are seeking thinner slices in CT, and one millimeter slices are now the standard for multislice CT.
“I think that’s where the paradigm shift was,” says Mike Bonfit, an engineer on Siemens’ Volume Zoom. “Everyone thought multislice was going to be a fast single-slice CT, and truly it’s not. It brings some things clinically [to the market] that single-slice would have never brought.”
“I think the clear standard is you must have thin-slice acquisition, and the thinner the slice and the faster you can get them, the better it is. That’s the legacy of multislice,” says Bonfit. The Somatom Plus 4 Volume Zoom has half-second rotation speed, quarter-second scanning, and submillimeter slices.
Siemens has been concentrating on advanced applications, especially virtual colonoscopy. Bonfit says the capabilities of multislice CT to perform this procedure are not new, but the improved resolution of the images makes it more of a reality to use multislice as a screening tool for colon cancer and formidable substitute for colonoscopy. It shows a potential benefit for lung cancer detection and profusion CT as well.
At RSNA 2000, GEMS released its GE LightSpeed Plus multislice CT scanner, the newest generation of its LightSpeed QX/i. The scanner has a fast scan speed of 0.5 seconds, but also it allows technologists to use a feature called variable speed scanning to scan in 0.1 second increments from 0.5 to 1 second. GEMS says this capability is an advantage over other available scanners’ “jumps” of 0.25 second increments.
Cardiac scanning
More slices per second are useful in cardiac imaging for assessing the heart. Patients with heart rates of 50 to 120 beats per minute can be imaged using the variable speed scanning. More sophisticated software allows for the study of infractions of cardiac cycles, says Bill Radaj, GEMS’ Americas marketing manager of CT.
Screenings also can be performed on lungs and other organs to evaluate lesion size. Claudia Henschke, M.D., professor of radiology, is studying lung nodule assessment at Cornell University (Ithaca, N.Y.) in conjunction with GEMS. She has been performing screening tests and evaluating lung nodules since 1993, but multislice CT gives her a higher resolution and more accuracy.
Henschke explains that screenings were done on a single-slice CT in a breathhold at 10 millimeter slices with a low dose of radiation, then suspicious nodules were scanned again with a higher dose of radiation at one millimeter. The multislice CT scanner allows her to do low-dose scans in a breathhold at one-millimeter sections. Screenings can be conducted every few months to better detect if the nodule is growing, and if it is, the increase in size can be measured in millimeters.
Colonography also is an extention of clinical application from multislice CT, and there are currently studies being done at the Mayo Clinic in Rochester, Minn., and at Beth Israel Hospital (Boston). Radaj says different protocols are undergoing evaluation to see which is the most effective and accurate in diagnosis, while still remaining safe for the patient.
Toshiba’s Aquilion multislice CT scanner has a 0.5 second rotation, while its Asteion scanner has a full rotation every 0.75 seconds. A scan can be completed in 300 milliseconds, which is useful in freezing heart motion, says CT Product Manager Wes Strickland. Limiting motion artifacts has led to improved diagnostic accuracy and the increase of the Aquilion’s use in cardiac CT.
Toshiba’s helical scanning capabilities allow for characterization of the arterial and portal venous phases of blood flow in the patient. Forty percent more liver lesions were diagnosed in this manner than with a scan done in the axial plane. Similar results are seen with multislice CT and its quick rotation speed, says Strickland. Cardiac scoring can be done on the Aquilion and the Asteion with Toshiba’s specialized software.
Toshiba is conducting studies on coronary artery CT angiography with the aid of its cardiac-gating package, using an IV contrast bolus to evaluate the lumen of the vessel. Physicians can view both calcified and lipid plaque with this package. Creating a functional study of the heart is what Toshiba currently is focusing on, as it seeks a larger acquisition to image wall motion, ejection fraction and ejection volume.
Strickland says that he expects these advancements to carry over into renal and profusion applications in the future.
An improved CT fluoroscopy package also is available from Toshiba, and it is seeing more accuracy and less table time for the patient during the exam. The latest offering is a 24-frame-per-second package that can show three images simultaneously. The radiologist can visualize the tip of a needle for more accuracy in aspiration attempts, especially in critical locations, such as near the heart or an artery.
“This goes hand in hand with early detection,” says Strickland. “You know with early detection that we’re looking at smaller lesions, and with smaller lesions we need to be more accurate with our diagnosis, and this allows the interventional radiologist to do just that.”
To reduce the number of images read, Strickland says Toshiba’s systems have the ability to create structures and 3D volume sets and to couple thinner slices to view between two and five images at a time. Some customers are reading images in data sets of coronal or sagittal planes, rather than axial images. There also are soft-copy 2D workstations that allow the user to take the axial images and scroll through them, as well as many PACS (picture archiving and communications systems) for review and archival needs.
Please refer to the February 2001 issue for the complete story. For information on article reprints, contact Martin St. Denis
