New scanner increases diagnostic power and speed, cuts radiation

New scanner increases diagnostic power and speed, cuts radiation

December 2, 2008

The first 256-slice "wide-area" computed tomography scanner in Illinois, with four times the capacity of the previous generation of multi-slice scanners, has been installed and is in clinical use at the University of Chicago Medical Center. The scanner, called the "Brilliance iCT" and manufactured by Philips Healthcare, combines power, speed and coverage to produce extremely high-resolution images with reduced radiation exposure.

With 128 rows of detectors, it can acquire cross-sectional images of the body more than 3 inches wide in a single rotation, which takes less than one-third of a second. A scan from head to toe can be acquired in about 10 seconds. This speed can be extremely important for time-critical exams for small children, trauma and areas of the body that move, such as the beating heart.

The scanner produces 256 slices of information during each rotation, which takes 0.27 seconds. It can reconstruct those slices for display at a rate of more than 100 slices a second.

"The pictures are breathtaking," said Michael Vannier, MD, professor of radiology at the University of Chicago, "cleaner and crisper than anything we had seen before. We can perform detailed analysis of very complex anatomy within seconds."

The scanner produces three-dimensional images of blood vessels within an organ, including the arteries that supply the heart, which have always been difficult to study because the heart's motion. It can take pictures fast enough to follow an injected dye that can be seen by x-rays, as it travels through the blood vessels.

The shift from earlier 4-, 8- or 16-slice scanners to 64-slice scanners, introduced in 2005, changed the way radiologists look at CT scans. Prior to that, physicians examined individual slices. "Now we look at reconstructed two-, three-, and four-dimensional views," Vannier said. "Doctors who send us patients insist on reconstructions. They won't tolerate a collection of slices anymore."

The move from the 64- to the 256-slice version could quickly have "a major impact on the diagnosis of heart disease," said Stephen Archer, MD, professor of medicine and section chief of cardiology at the University of Chicago Medical Center. "With the speed of this scanner, we can now provide completely noninvasive diagnosis and even risk assessment for coronary disease."

One recent study showed that images of the coronary arteries taken with a 64-slice scanner were "accurate in identifying coronary stenoses and characterizing disease severity in symptomatic patients." The more powerful 256-slice scanner provides better images and cuts the radiation dose almost in half. In some cases, the radiation exposure has been reduced by 80% compared to standard 64-slice cardiac CT exams.

It now takes about 5 seconds on the scanner, less than one second of x-ray exposure, to get detailed images of the heart and its coronary arteries. The speed of the 256-slice scanner makes the process easier for patients, who may have difficulty holding their breath during a scan. This scanner is fast enough to get motionless pictures of the heart despite heart rates of up to 100 beats per minute.

Dose reduction is also a significant benefit, said Vannier. Increased speed, detector size and sensitivity mean doctors can scan a heart, lung or brain with considerably less radiation than a scan with a 64-slice CT or a nuclear stress test. The 64-slice scanners required four to six heart beats to capture an image of the entire heart. The 256 can cover the distance in two heartbeats.

"I am particularly excited by the lower dose of radiation and contrast required," Archer said. "This improves patient safety without compromising the quality of the pictures."

Increasing the scanner's speed created several engineering challenges. The scanner's gantry, which holds more than a ton of electronics, x-ray generators and detectors, spins around the patient 220 times a minute, floating on 5 microns of air--a design exclusive to Philips. They also had to build a special x-ray tube sturdy enough to handle forces created by spinning so rapidly.

Speed and precision not only improve the image quality, but also "let us look at dynamic processes," Vannier explained. About 60 percent of CT scans at the Medical Center are for cancer patients. "Instead of just monitoring changes in tumor size, we can watch the perfusion of a contrast agent as it moves toward, around and through a tumor," Vannier said. "This can provide an early view of how a patient is responding to therapy. It helps us predict, rather than simply describe responses to treatment."

Neither speed nor radiation mattered to the first human studied with this scanner. The "patient," known only as Meresamun, came to the Medical Center from the University's Oriental Institute where, 3,000 years after her death, she is on display. A mummy, she had been scanned with standard CT in 1991. She came for an appointment with the 64-slice scanner last summer, but when the 256 arrived, Vannier called her back for a follow-up visit.

Despite having to peer through a wooden case, which has never been opened, and other trappings of the mummification process, both multi-slice scanners produced sharp, detailed images. Those from the newest scanner, however, were "significantly better," said Vannier. "We could see subtle things--wear patterns on the teeth, a clear view of the embalming incision, precise indications of her age--that were not apparent on the previous exam."

The Philips Brilliance iCT 256-slice scanner is one of about 20 such devices in the United States. The University of Chicago Medical Center entered a partnership with Philips in 2004 to serve as a clinical testing and development site for Philips' newest equipment. This brings Philips' most advanced imaging technologies to the University of Chicago. In exchange, the Medical Center's experts in computer detection and diagnosis help Philips test and improve their image-processing software.

The 256-slice CT has one more modification designed to meet the needs of today's radiologists. The gurney for previous scanners could accommodate patients up to 450 pounds. This newest scanner can handle a 650-pound patient. It has already been put to use.