Multislice Computed Tomography (MSCT) has generated excitement among radiologists and other clinicians across the country and around the world as CT evolved from single-slice to 16-slice detectors over the course of a few years. Sophisticated new CT scanners are designed to enhance image acquisition and analysis while improving visualization of three-dimensional anatomic structures. New clinical applications have been developed to take advantage of technologic advances in the equipment that balances speed, image quality, and reduced radiation dose to patients.

>Variety Is the Spice of Life
Major vendors have approached multislice scanner design to offer a range of configurations with different application packages to meet specific clinical needs.

In its line of multislice scanners, Philips Medical Systems (Bothell, Wash) offers CTs with detector arrays capable of producing two, six, 10, and 16 slices per rotation. Based on more than 11 years delivering multislice CT systems and customer feedback, Philips introduced the six-slice version earlier this year.

“The customer benefit is that they can directly upgrade performance from six- to 10- or 16-slice systems without a gantry swap, saving time, saving lives, and improving patient outcomes,” says Chuck Armstrong, vice president of CT Marketing in North America at Philips.    

Armstrong believes that this year is when the market will take full advantage of 16-slice systems.

“Our sites enjoy cardiac exam success rates in the high 90% range, without the use of Beta Blockers to regulate heart rate. Stroke and trauma assessment, improved workflow, and the ability to see results almost instantaneously will continue to be the Philips difference,” he concludes.

Siemens Medical Solutions USA Inc (Malvern, Pa) offers three different product lines for single and multislice CT scanners: Smile, Emotion, and Sensation, the latter of which is the company’s high-end product line. Each group of scanners is manufactured in a choice of slice configurations that culminate in the Sensation 16-slice CT.

Siemens released its SOMATOM Emotion 6 keeping the tight siting issues of emergency rooms in mind.

Given the current multislice trend, the company sees development toward such new areas as dedicated emergency room scanners, where there are tight siting issues. With this need in mind, Siemens released its Emotion 6 scanner, capable of producing images at a maximum rotation time of 0.6 seconds. The first install of this system was accomplished in June of this year at the University of Iowa Hospitals and Clinics (Iowa City). Siemens expects this scanner to offer an affordable option for many customers who want the benefits that a multislice scanner provides.

The Siemens SOMATOM Sensation 16’s image reconstruction engines are capable of rendering six images per second.

Rapid image reconstruction is critical functionality for these systems. Siemens Sensation 16 offers image reconstruction engines capable of rendering six images per second. Since the image data sets are extremely large, speed in reconstruction becomes a major issue for productivity. Markus B. Lusser is the segment manager in radiology for computed tomography at Siemens. He explains that the company’s powerful workstations are capable of producing “real-time CT” because within a few seconds following a scan, high-resolution 3D images from any angle or plane are produced while the patient is still on the table.

GEMS’ Light Speed Pro16 CT scanner features SmartmA, a dose-reduction tool that modulates the X-ray beam.

General Electric Medical Systems (GEMS of Waukesha, Wis) released its Light Speed Pro16 CT scanner in June of this year. Peter Arduini, general manager of GEMS’ Global Computed Tomography, explains that the company spent a great amount of engineering design time in determining the particular slice profile it believes maximizes image quality while reducing radiation dose to the patient. Thin slices improve the spatial resolution but increase the radiation dose, which led GEMS to adopt a 3D automatic dose modulation capability.

“With the Light Speed Pro16, physicians are able to conduct extremely fast, detailed exams while caring for patients with responsible dose management,” Arduini says.

SmartmA is another dose reduction feature that automatically modulates the X-ray beam, depending on the portion of patient anatomy being scanned. This capability has been retrofit into all LightSpeed products in customers’ installed base at no additional charge.

On the scout view, the system is able to predict the quantity of milliAmperes (mA) required for each slice, depending on the specific anatomic region of the scan. For example, imaging through a person’s shoulders includes a large proportion of bone, while a lung scan would be less dense and, therefore, require a lower dose of radiation to produce the same image quality. Rather than maintaining a static setting throughout the scan, the dose would decrease as the scanner passes over the lung field.

The Aquilion 16 CFX Multislice CT scanner is the latest evolution of its platform for Toshiba America Medical Systems (Tustin, Calif). The gantry for this system was specifically designed to accommodate multislice technology. Douglas Ryan, director of the CT business unit, says the company’s system does not require a chiller, which reduces the cost of installation and long-term costs associated with running the system.

“With the Aquilion 16 CFX, we are capable of doing 16 0.5mm slices with every 0.4 msec rotation,” Ryan explains. “That gives us isotropic imaging in the smallest field of view on the market. With 0.5mm isotropic imaging, we get excellent depiction of blood vessels in any plane with no stairstep artifact on the edges.”

As image acquisition volume increases with thinner slices, computer-processing capabilities must be augmented to accommodate larger data sets. Toshiba has established a working relationship with Vital Images Inc (Plymouth, Minn) to use its Vitrea 2 systems for volumetric renderings on the Aquilion CT scanners.

>It’s All in the Applications
Julia R. Fielding, MD, chief of abdominal imaging and associate professor of radiology, University of North Carolina at Chapel Hill, explains that multislice CT imaging systems require clinicians to make some decisions about settings for the scanner.

“We can either obtain very thin slices of an area that we might want to look at very closely, or we can cover a very long region in a short amount of time,” explains Fielding, who uses the Siemens Sensation 16. For example, in a study of a pancreatic tumor, detailed views of vascular anatomy are needed to determine whether or not the tumor can be resected. By careful timing of the bolus of IV contrast material, users obtain an arteriogram of the area of interest. On the other hand, for a trauma patient, users might want to scan head to toe, and a 16-slice scanner enables them to accomplish that study within a few minutes. With a standard of scanning patients within 20 minutes of the time they reach the facility’s Level 1 Trauma Unit, Fielding is pleased to be able to accomplish a CT scan so quickly.

With trauma patients, one of the other benefits that a 16-slice scanner provides is the ability to look at different sections of the anatomy produced by a single scan.

The Philips Mx8000 series of multislice scanners can produce up to 16 slices per rotation. (Left: the Mx8000 Quad;   right: the Mx8000-6.)

Steven Primack, MD, vice chairman of the Department of Radiology at the Oregon Health and Science University in Portland, uses a Philips Mx8000 16-slice CT scanner. Although the first viewing of the films of a trauma patient might be to review the abdomen for injury to such soft tissue organs as the liver, spleen, or kidneys, the images also can be reconstructed to provide detailed views of the spine without re-scanning the patient.

“The quality of images is better than we were getting with targeted studies of the spine on a conventional scanner,” Primack explains.

In addition to the University’s trauma applications, Primack describes its busy renal transplant service. The facility now acquires all of its renal donor studies on the CT, and with the use of a Philips 16-slice detector, users obtain better-quality images of the renal arteries. Surgeons benefit from improved arterial imaging for pre-operative planning of transplant surgery.

“We are poised on a revolution in non-invasive vascular imaging,” says Scott Lipson, MD, associate director of the department of radiology at Long Beach Memorial Medical Center in California, which uses Toshiba’s Aquilion 16. “With the new scanners, the quality of vascular imaging is so good, and the images can be acquired so easily, that I think it is going to revolutionize how we evaluate carotid arteries, renal arteries, the aorta and peripheral runoff studies,” he says. Lipson also believes that CT angiography will prove superior to magnetic resonance angiography, and will eventually replace conventional angiography.

Although the Center has had its Aquilion 16 for only a brief time, Lipson has used it for several patients to triage the patient to an appropriate therapy: surgery or medical treatment or an interventional procedure, such as angioplasty and stent placement. The other value of the CT scan is that it can provide planning information to the interventional radiologist to inform decisions about how long a stent should be and precisely where it should be placed prior to beginning the procedure.

Stephen E. Koch, MD, medical director and senior radiologist of Imaging Heart and Imaging for Life (New York City), explains that both centers are in the process of developing coronary CT angiography capabilities. Using the Siemens Sensation 16, users have begun performing these studies to assist cardiologists in making better clinical decisions for each patient.

Koch anticipates a subgroup of asymptomatic patients, with high cholesterol levels and normal stress tests, would be good candidates for coronary CT angiography.

“With stress testing, you need to have a fairly high-grade stenosis, usually 75% to 80% narrowing for that test to be positive,” Koch explains. “But the true risky soft plaque usually causes between 30% and 60% stenosis, and nuclear stress testing would not diagnose this.” Early atherosclerotic plaque development can lead to a rupture in the plaque producing a massive clot that could obstruct a major coronary artery, leading to an unexpected heart attack.

In addition, the centers use coronary CT angiography to manage patients who have required stent placements or bypass surgery. Normally, these patients would be followed with multiple post-operative conventional angiograms to determine the patency of their grafts. With the centers’ 16-slice CT and IV contrast study, researchers monitor the progression of recurrent disease in bypass graft patients. Depending on the size of the stents, those same researchers can evaluate whether or not the stent remains functional.

Not all radiologists are doing coronary angiogram studies, and Koch explains that his group has spent six months developing the protocols to ensure reproducible results. In their practices, cardiologists are involved to administer beta-blockers to the patients as well as read the studies with the radiologist. CT angiography is reimbursed by Medicare as a diagnostic study.

Toshiba’s Aquilion 16 CFX CT scanner was designed specifically for the multislice market.

Kieran J. Murphy, MD, associate professor of radiology and neurologic surgery at Johns Hopkins Medical Institutions (Baltimore, Md), uses a Toshiba Aquilion 16 for a number of neurologic applications.

“We use it every day for diagnostic neuroradiology, and also use it as guidance for procedures in its CT fluoroscopy mode,” Murphy says. In fluoro mode, the system captures up to 39 frames per second of continuous axial images. He runs the scanner from the bedside to check the position of a shunt catheter in the ventricle, or to do radiofrequency ablation of a tumor. In addition, Johns Hopkins is using this technique to improve the design of cerebral ventricular shunts, placing them under CT fluoroscopy guidance.

In regular CT mode, Johns Hopkins uses its Aquilion 16 scanner in the evaluation of stroke victims. Murphy explains that usually, only a small fraction of patients with acute stroke are treated. The CT scans provide diagnostic evaluation of stroke patients prior to administering TPA to dissolve blood clots that block blood vessels in the brain and cause brain damage secondary to reduced oxygenation. Knowing whether a stroke is caused by a clot or by hemorrhage is extremely important prior to administering TPA.

The speed of a CT scanner proves invaluable for pediatric patients who need a scan of their heads. Prior to the ultrafast multislice CT, these patients would require general anesthetic to obtain studies. With the high-speed scanner, a cerebral study takes only seven seconds, and the children no longer need to be sedated.

The Philips Mx8000-6, the company’s newest CT system.

Oncology applications benefit from multislice CT imaging studies as well. William D. Boswell, MD, chief of radiology at the University of Southern California Norris Cancer Center in Los Angeles relates that its patients have remarked about how much faster their current scans are accomplished on the Philips Mx8000 16 slice scanner. He says that the center now provides as many as half of its studies with multiplanar 3D image reconstructions. Formerly, the Center did these reconstructions on about 10% of its scans because of the time required to complete this image manipulation.

The Mx8000 speeds up the scanning process, according to the University of Southern California Norris Cancer Center, Los Angeles.

Referring physicians visit the radiology department to see the images now that they are rendered in 3D, Boswell says. These image reconstructions prove valuable for surgeons in their planning, and for radiation oncologists who are better able to visualize the volume of a tumor to be treated. Prior to installing a 16-slice scanner, users would scan one patient a day for radiation therapy planning; now they accomplish three studies in a day.

Just as with trauma patients, the ability to visualize more anatomy proves beneficial to this population. A single body scan provides soft tissue analysis as well as a spinal view to look for metastases.

From a departmental standpoint, Boswell says his group has increased its productivity by 20% to 25% and continues to look for more ways to enhance patient throughput.

“The more you prepare patients outside the room, the more patients you can do,” he says. “Since 90% of our patients are scheduled, when there is an urgent case, we can squeeze them in, and they don’t have to wait until the next day.”

Dr. Julia Fielding agrees that there are issues of re-engineering a department when a 16-slice scanner is installed. She reorganized her support staff to make sure they completed all of the necessary paperwork and started IVs in a timely manner to keep patient flow moving smoothly. Training the technicians took two weeks with an applications specialist from the vendor. The department might need to add more computer memory and workstations to review images. New protocols were devised to take advantage of the features of the more powerful scanner.

When it came to setting up the scanner, Fielding says it took longer for the construction to prepare the room than the actual installation of their Siemens Sensation 16. Although it was a new product, she says that this machine is a finished product without “bugs” to work out. Once the machine was installed, Fielding was performing scans within 2 days.

Finally, the radiologist needs to plan for an increase in the number of studies to read. In one recent busy weekend, Fielding read 102 CT scans from Friday afternoon until Monday morning.

“You have to plan not only to use the scanner to its full ability, but also to use your department to its full ability,” she notes. Fielding has found that her technicians are re-invigorated because they have many new techniques to try and new ways to think of imaging patients. Three-dimensional reconstruction creates fascinating images that are interesting for both physicians-in-training and technicians who work in the department.

>Sixteen Is Better than One
The benefits of 16-slice scanners are notable across clinical specialties. Image clarity, speed, and dose reduction are just three reasons this CT technology is so enthusiastically embraced by those who use it. As the technology is refined and more applications are developed, this imaging modality will most likely increase in popularity.