By: Deborah R. Dakins

As the technique of choice for most cardiovascular cases, multidetector CT is earning accolades from early adopters of the latest 16-slice scanners. And while the device has been lauded for its cardiac imaging potential, users at sites around the country are identifying new CT frontiers beyond the heart. What some call a quantum leap in quality means that imaging will be faster and better in all parts of the body.

"The beauty of these new machines is that there are always areas that we don't anticipate," said Dr. Joseph Lee, chair of radiology at the University of North Carolina, Chapel Hill.

Often overlooked in the excitement about 16-slice CT's cardiac imaging capability is its value in trauma patients. The greatly accelerated diagnostic workup-a complete survey with 1.25-mm slices from head to pelvis completed in less than one minute of scanning-is the biggest clinical advantage of the new systems, according to Dr. Freidrich Knollmann, a professor of radiology at Humboldt University in Berlin.

The rapidity with which scans are conducted means that total time in the imaging suite for a typical complete trauma study is less than 10 minutes. Moreover, the accelerated protocol comprises all typical complications and has greatly improved diagnostic workflow in severe trauma patients.

Long Beach researchers reconstructed this image of a 95% stenosis in the right internal carotid artery. (Provided by J. Renner)

"At these fast speeds, we are increasingly able to convince our trauma surgeons that part of the conventional radiographic workup can either be delayed until after CT or replaced by the initial CT scan," he said.

Humboldt operates the largest university hospital system in Europe, the three-campus Charite, with a total of 2500 beds. The newest of these, Charite Virchow-Klinikum, was completed in 1988 and now boasts a 16-slice scanner. Installation of the scanner prompted workflow changes at Charite Virchow-notably, a transition to soft-copy reading.

"We automatically transfer all CT studies to a separate workstation capable of advanced 3D reconstruction and then review the images in cine mode, directly hopping to 3D reconstructions depending on the clinical problem and the axial image findings," Knollmann said.

Because Charite Virchow has no systemwide PACS installed, this process is used to speed integration of 3D techniques into the conventional reading process. For documentation, hard copies are generated with a larger slice thickness only, along with selected findings from the soft-copy reading session.

"We try to integrate 3D workup into our reading routine and are teaching residents how to use 3D tools to ensure that the diagnosis is not delayed," he said.

In both clinical and research projects, the new device offers dramatic potential. Clinically, the university has noted advantages ranging from cardiac investigations to an array of vascular applications. Specific benefits have also been found in pediatric CT and virtual endoscopy using 1.25-mm collimation. The same mode is beneficial for peripheral arterial runoff studies as well.

In research mode, 16-slice CT allows submillimeter imaging of entire anatomic compartments within a single breath-hold and with a single contrast bolus, Knollmann said.

"Many of the submillimeter protocols are still evolving, and the techniques leave ample room for future innovation and research," he said.

PEDIATRIC ADVANTAGE

Sixteen-slice CT offers numerous potential benefits for pediatric imagers, including dramatically improved resolution of the small anatomical structures found in infants and children. Along with the ability to scan faster, thus reducing the need for sedation in some children, resolution was a key selling point to Dr. John Renner, medical director of radiology at Long Beach Memorial Medical Center in Long Beach, CA.

The 750-bed hospital is linked to 200-bed Miller Children's Hospital, and the newly installed Toshiba Aquilion 16 scanner is the first multidetector unit onsite.

"We wanted to prove that we could scan with reduced dose, quicker scans, less sedation, and more accurate studies in children," Renner said. "That was one selling point. The other was the potential to perform CT angiography for peripheral and coronary applications."

University of Michigan researchers used 16-slice technology to obtain images of the mesenteric vessels in a patient with right lower quadrant pain (left) and the intrahepatic system in a living potential liver donor. (Provided by J. Platt)

The decision to purchase the scanner was just one step in a long line of firsts for Long Beach. The hospital's PACS was newly installed in September, just a month before the 16-slice scanner arrived.

The new scanner immediately assumed the lion's share of the more than 100 CT scans performed daily at the two facilities and is being pressed into service for a wide range of studies, according to Renner. The investment has proved so successful that Memorial has already purchased and scheduled delivery of a second 16-slice unit.

"Multidetector technology is a quantum leap forward from where we were before," he said. "We can do so much more, in fact, we are not even sure of all the applications yet. It's almost like learning CT all over again."

Based on the site's experience switching from nonspiral to spiral CT in the mid-1990s, Renner expects scan demand and volume to increase with the faster thin-slice device.

"Once word is out that you have this technology, people want to use it," he said. "When we switched to helical scanning, our volume went up threefold over the next two years. Now we expect it to take another jump-possibly by as much as 25%."

One unanticipated challenge is the amount of time spent by workstation-bound physicians processing 16-slice data of angiographic studies.

While more time has been spent on back-end processing, throughput is unquestionably faster.

"The fact that we can do some pediatric patients with little or no sedation has clearly improved our throughput and operational efficiency," he said.

Renner is eager to tackle CT coronary angiography, a clinical frontier that had been out of his reach.

"While our outpatient facility did have a four-slice unit on which we could do coronary calcium screening, we really could not perform good coronary angiography," he said. "Nor could we do good CT abdomen, pelvis, or runoff angios before-it was just too much coverage. Now we can image with 1-mm slices in less than 30 seconds, from the diaphragm to the ankles, with very good quality."

20/20 VISION

In the 20 years since he penned the first textbook on CT, Lee has seen his share of new developments in radiology. But few are as exciting as 16-slice CT.

"As a resident in St. Louis during the era of the EMI 5000, I literally witnessed the birth of body CT," Lee said. "Most of my current faculty are too young to even know what the EMI 5000 was-18 seconds for a single slice, then two and a half minutes for reconstruction of one image. Twenty years ago, no one could have envisioned what we would be able to do."

Using 0.5-mm imaging, a 16-slice scanner can depict tendons in the ankle. (Provided by Toshiba)

Today, six months after installing a 16-slice scanner, Lee and colleagues are using it for everything from vascular imaging to bread-and-butter studies.

"Sixteen-slice is very straightforward for all of the vascular structures, pulmonary embolism, abdominal aortic aneurysms, and intracranial vessels," he said. "But the speed of 16-slice also makes it excellent for trauma cases, C-spines, and musculoskeletal indications."

Indeed, the quality of thin-slice imaging could bolster CT as a substitute for MR in musculoskeletal imaging, particularly joint imaging, where spatial resolution is crucial. In addition, because 16-slice provides good resolution equally in all three imaging planes, patients with musculoskeletal injuries may not have to be placed in painful positions during scanning.

In addition to these established uses, Lee has set his sights on identifying and exploring some of the lesser known frontiers of 16-slice CT.

"We're actively trying to figure out various aspects of the body where people have not been able to use CT as effectively," he said. "Just like a fine bottle of wine, our research targets are not quite mature enough to release. There are lots of exciting things going on and lots of ideas at all the sites that now have 16-slice. Everybody will pick a niche and explore it."

In the near term, having 16-slice on hand means that UNC is able to tackle more complex clinical cases than in the past, particularly in the vascular realm. In a department already well known for its endovascular grafts and interventional and neuroradiology procedures, UNC has made headway in collecting data to establish 16-slice CT as a substitute for invasive preoperative imaging of intracranial aneurysms.

"One of these days, we may not need to do angiograms before embolizing intracranial aneurysms," Lee said. "It still needs to be proven, but the diagnosis is straightforward, and the quality is very good."

To prepare for 16-slice installation, UNC rescaled the resident PACS and added dedicated 3D workstations. The department has a protocol for image storage, wherein only the reconstructed data are saved.

"If we saved the raw data, we would literally saturate our PACS," he said.

Having seen the birth and gradual evolution of CT over the years, Lee believes that the modality is finally giving MRI a run for its money.

"Because of the vascular applications, the musculoskeletal, C-spines, and trauma uses, 16-slice is really phenomenal," he said. "There is now a real horse race between MRI and CT. While CT has always been an anatomical technique, it is beginning to verge on functional imaging status."

PLACES IN THE HEART

For months prior to installation of a 16-slice scanner at the University of Michigan, Ann Arbor, Dr. Joel Platt had heard all the hyperbole about the dazzling cardiac capabilities of the new device. But he wasn't prepared for the hype to be true.

"When we were told that this might be the cardiac machine everyone has been waiting for, we were skeptical," said Platt, a professor of radiology who specializes in body CT. "We did a few cases, and we're not skeptical anymore."

Platt had logged thousands of studies on the university's four- and eight-slice machines and thought he knew what to expect.

"Sixteen slices really seems to make a difference," he said. "At least in the case of our vendor, it seems to be the first foray into isotropic CT imaging."

Other early adopters have noted how the thin slices create excellent spatial resolution in all three imaging planes. The resulting isotropic voxels of 16-slice CT capture fine detail and create 3D renderings of arteries that wind in and out of the imaging plane.

"I can tell a case that was performed using a 16-slice scanner from one acquired with a four- or eight-slice scanner just by the way the images look," Platt said. "It's a noticeable difference. That surprised us. The other surprise was that it really could do heart vessels and very small vessels, such as the kidney and liver."

He was also pleased by the scanner's ability to deliver many of the cardiac imaging requirements needed to challenge invasive imaging with a noninvasive form. The value of the noninvasive form remains to be seen, however, and he expects it to be the topic of studies done over the next several years.

Platt is hopeful that 16-slice is not just another technological benchmark for CT, a critical-but not final-upgrade. Even though the device has been lauded for its cardiac capabilities, he sees much more potential for it. Sixteen-slice is applicable to numerous vascular applications beyond the heart.

"In the old days, we were taught that you had to choose between coverage and resolution, because you could not have both with CT," he said. "You can have them both now."

Ms. Dakins is a freelance writer in Ben Lomond, CA.