64-slice CT enters clinical practice realm

April 2, 2006

After installing a 64-slice CT system at Metroplex Hospital in Killeen, TX, radiologists invited asymptomatic referring physicians to undergo a free heart scan and experience the new technology firsthand. After a coronary CT angiogram, three of the doctors left with an appreciation for the new scanner- along with a diagnosis of heart disease.

After installing a 64-slice CT system at Metroplex Hospital in Killeen, TX, radiologists invited asymptomatic referring physicians to undergo a free heart scan and experience the new technology firsthand. After a coronary CT angiogram, three of the doctors left with an appreciation for the new scanner- along with a diagnosis of heart disease.

Metroplex, a small hospital that serves the community surrounding Fort Hood army base, is one of eight facilities contacted by Diagnostic Imaging about the practical impact of 64-slice technology on everything from system acquisition to applications and technical issues. The facilities operate equipment from a range of manufacturers in varying environments, including community and academic settings (see "64-slice CT survey: Early adopters offer advice," page 22)

In a short timeframe, Metroplex made the technological leap from a single-slice CT scanner to 32-slice and, ultimately, 64-slice systems. The purchases were mainly motivated by the promise of new CT angiography applications, as the hospital has a busy cardiology practice. Like other facilities included in this article, Metroplex is eager to realize the potential of the new scanner as a coronary artery screening tool and a noninvasive alternative to coronary angiography.

With 64-slice CT, it's possible to catch heart disease early, potentially preventing heart attacks, said Dr. Frederick Barnett, a radiologist at Metroplex. Coronary heart disease is the single largest killer of men and women in the U.S., with an annual cost to the healthcare system that averages $142.5 billion per year.

An estimated 25% to 30% of diagnostic cardiac catheterization procedures are normal, and another 30% to 40% find moderate disease that does not warrant surgical intervention. With a 97% to 99% negative predictive value, coronary CTA is poised to eliminate unnecessary procedures.

"One of these noninvasive studies provides reliable information quickly, improving overall patient care and reducing morbidity and costs. Coronary CT angiography should precede nearly every diagnostic cardiac catheterization," Barnett said.

Coronary artery screening can be done on a 16-slice or 32-slice CT system, but the 64-slice system provides consistently better exam quality and diagnostic capability, due to better temporal and spatial resolution, Barnett said.

Speed of scanning is another distinct advantage in imaging the heart. The 64-row detectors provide greater coverage, allowing fast scanning of the heart, brain, or lungs. A 64-slice system covers up to 40 mm in a single pass, compared with 20 to 32 mm on a 40-slice system and 8 to 12 mm on a 16-slice system. On a 64-slice system, the whole body can be scanned in about 30 seconds.

The breath-hold on a 64-slice or 32/40-slice scanner ranges from four to 10 seconds, compared with 20 to 40 seconds on a 16-slice scanner, said Dr. Jonas Rydberg, an associate professor of radiology at the Indiana University Hospital and Outpatient Center in Bloomington. This has obvious advantages for scanning certain patient groups, such as those who are very ill or elderly.

"It's easier for patients and easier for the technologists. It's a win-win situation," Rydberg said.

In moving organs in the chest, the results are consistently better on a 64-slice system compared with a 16-slice scanner, said Dr. Michael Vannier, a professor of radiology at the University of Chicago Medical Center.

At his site, virtually all cardiac and pulmonary embolism studies, as well as very sick patients, are scanned on either a 64-slice or a 40-slice scanner. The pace of technological change has been rapid, with single- and four-slice systems either replaced or complemented with 16-slice, then 32-slice, and ultimately 64-slice devices, Vannier said. When patients return after a few years following an initial assessment, it is possible to see pathology that was overlooked or misinterpreted on older scanners.

"You don't know what you are missing unless you use the scanners side by side or make a comparison with the same patient at two different points in time. It's not that we radiologists have grown smarter. The images are just so much better," he said.

Gating is being done not only for cardiac cases, but for a range of other studies, notably pulmonary embolism scans.

"I think gating is going to become mandatory for us in imaging virtually all vascular structures in the chest. We find and show things with such a great degree of confidence. The images are much more convincing and reliable," he said.

The facility is also routinely producing 3D reconstructions of the pancreas, pancreatic duct, and all adjacent structures to help plan surgery in oncology cases.

Some facilities have started with CT angiography and are planning to move on to other new procedures such as CT colonography and CT bronchoscopy.

"We have long way to go before we have utilized the technology to its full potential. The capabilities are phenomenal, and we have not even scratched the surface. In the beginning, we want to be master of a few instead of trying to be master of them all," Barnett said.

TRAINING REQUIREMENTS

Facilities approach training in 64-slice CT applications in a variety of ways. Most take advantage of vendor-sponsored training programs. Typically, they begin by training a few radiologists and technologists, and then gradually work toward educating the entire staff.

At the University of Washington Medical Center in Seattle, radiologists start with a four-day course (10 hours a day). They also read literature and textbooks and perform 40 cardiac CT studies under supervision.

At Atlantic Medical Imaging in Galloway, NJ, the radiologists' education begins with a weekend of hands-on training. They also receive extensive on-the-job training.

Thorough training in cardiac studies is essential, according to Dr. Anthony Mancuso, chair of radiology at Shands Healthcare (affiliated with the University of Florida) in Gainesville.

"This part of the body is very critical. If you misinterpret a heart study, a patient can die very quickly," he said.

In June 2005, the ACR published a clinical statement on noninvasive cardiac imaging to offer guidance until official practice guidelines are developed. According to this statement, physicians should supervise and interpret 75 cardiac CT cases, excluding those performed for calcium scoring, within a 36 month-period in order to become proficient (see "Association devises stringent training guidelines for cardiac CT," page 28).

The ACR statement also advises that the dose be as low as can be reasonably achieved without compromise to the images. As a general rule, multislice CT scans of the heart should not result in a volume CT dose index greater than 60 mGy or an effective dose of greater than 13 mSv, the statement indicates.

Separately, the American College of Cardiology Foundation (ACCF) and the American Heart Association (AHA) have published a statement on cardiac CT and MR that outlines three levels of physician competence. In order to interpret exams independently, physicians must reach Level 2, which requires a minimum of 150 exams under supervision.

Shands Healthcare has a formal training program in place. Radiologists must follow both sets of guidelines (ACR and ACCF/AHA) and therefore will not be interpreting exams independently until they have performed 150 studies under supervision, according to Mancuso.

"We are targeting satisfaction of the most rigorous guidelines in our educational goals," he said.

Radiologists need to learn more about the physiology of the heart in order to perform cardiac CT studies, but some may find that cardiac CT does not carry a big learning curve. It is actually easier to learn than other types of diagnostic imaging exams, Rydberg said "If you are a well-trained chest radiologist, the conversion to reading cardiac studies will not be difficult," he said.

DETERMINING NEEDS

It's not necessary to be an early adopter to know that the main clinical value of 64-slice CT is in cardiac applications. Media hype has surrounded the new systems, and even Oprah Winfrey televised a demonstration of the technology. This has led some hospitals to invest in advanced technology that they may not even need, a number of sources say.

After purchase, these facilities may use the 64-slice systems as if they were 16-slice or smaller units. A 64-slice scanner offers an advantage in applications that primarily relate to coverage of a large area or when rapid acquisition has value, said Dr. Chris Ullrich, medical director of radiology at the Carolinas Medical Center in Charlotte, NC. For example, 64-slice CT is better for cardiac CTA because of temporal resolution and spatial coverage, but it does not offer as much of an advantage for cardiac calcium scoring.

While 16- and 64-slice scanners are equivalent for routine brain CT, the 64-slice is advantageous for simultaneous CTA of the neck and head because of greater speed and coverage. The same is true for CTA of the abdomen and leg runoff CTA. CT brain perfusion studies are also better on the 64-slice scanner because greater geographic coverage can be obtained, he said.

Sources say that a 64-slice scanner makes sense for facilities furnishing a new emergency room, as the technology enables rapid, thorough coverage of trauma patients. If a scan of the chest, abdomen, and pelvis is taken, the spine and hips are automatically included in the same study, Rydberg said.

Conversely, with a 16-slice scanner, it may be necessary to scan the same patient several times.

At the Carolinas Medical Center, one of the busiest, largest trauma centers in North Carolina, the 64-slice machine is used for rapid evaluation of trauma patients, including coverage of the entire spine, Ullrich said.

"This is a Level 1 trauma center-we care for the sickest of the sick. We have a high need for CT angiography and for rapid evaluation of trauma patients," he said. "The 64-slice system really shines when you do full-body scanning for multitrauma initial assessment."

Facilities that see few trauma patients and lack high volumes of cardiac cases should consider buying a 16-slice or eight-slice system instead, he said.

"The number of cases where a 64-slice system truly produces unique value for a patient is a small percentage of the total cases you do in [general] radiology practice. Is that worth the cost of the system?" Ullrich said.

SCAN VOLUME

Some facilities are justifying the 64-slice expense based on projections for new scan volume. The University of Washington Medical Center installed three new 64-slice systems to replace its single-slice, four-slice, and eight-slice scanners. Prior to the purchase, the center had a busy CT schedule, was losing referrals to other facilities, and had a relatively poor technological image, according to Dr. William Shuman, director of radiology.

Originally, the department did 48 patients a day on CT and had a one-week backlog. It is now scanning about 110 cases per day with no waiting list. It typically scans nearly five patients per hour on each scanner and would like to increase this rate to six.

The biggest use of the new technology lies in evaluating patients who have atypical chest pain and multiple risk factors, such as diabetes and a family history of cardiac disease, Shuman said.

To generate new volume, the center hired a dedicated marketing person and focused on increasing awareness about the 64-slice installations among referring physicians and in the community. As part of this awareness-raising campaign, brochures promoting the new systems were mailed to 9000 referring physicians in the area. Shuman says the center's business plan indicates that systems will pay for themselves in a relatively short period of time.

Due to the speed of scanning, the department is planning to build four prep rooms at a cost of about $1 million.

"We realized we needed more prep rooms to make sure these machines are operating at full capacity," Shuman said.

Whether centers see dramatically increased volume depends on what type of scanner the 64-slice system is replacing, and how the technology will be used, Rydberg said. For example, if a site is moving from a single-slice to 64-slice system, throughput could dramatically increase. However, the total number of patients scanned is roughly the same with 16-, 32/40-, and 64-slice systems.

At Rydberg's hospital, run-of-the mill brain cases are scanned on the 16-slice scanner, while the 64-slice system is reserved for more advanced cases, particularly in cardiac work. For complex cardiac cases, it might only be possible to scan two patients per hour on a 64-slice scanner, he said.

After the scan, image postprocessing may take time. In comparison with chest, abdomen, and brain studies, which can be performed in seconds, postprocessing of cardiac studies on 64-slice systems can be time-consuming, Barnett said. Images are typically sent to a specialized workstation where they are reconstructed by technologists into 3D format for viewing.

"The workstations are much more user-friendly, but postprocessing is still very cumbersome-it can easily take an hour. We need to continue to work with CT and workstation vendors to promote automation of 3D isotropic volume data," Barnett said.

More automation of image processing is definitely needed, according to Dr. Richard Morin, chair of the Society for Computer Applications in Radiology.

In the community setting, for example, with a high volume of normal cases, it would be very useful if computers could separate the normal from abnormal studies, much in the way Pap smears are handled, Morin said.

"We are still using humans in the same way we did with film. The machines are not doing much. The machine needs to do more processing so the human does not have to spend as much time going through the data set," he said.

MANAGING IMAGE LOADS

Compared with older CT systems, a typical cardiac study on a 64-slice system might include four or five times the number of images. Whole-body scans are particularly challenging, as they can easily generate from 3000 to 5000 images.

The industry is just starting to realize the tremendous impact such technological developments have on radiologist workload, Morin said.

"Sixty-four-slice scanners have not been available for very long, and they bring a real difference from what we had a generation before. Not only do they produce a lot of images but they do so very quickly," Morin said.

Because the technology is so new, not much standardization exists. Departments are approaching data management in different ways. Some go with thicker slices on the first pass, and if nothing catches their eye, they are satisfied. Others want to see all of the original data in thin slices, Morin said.

Most of the departments interviewed by Diagnostic Imaging have rewritten their image protocols to avoid image overload. This is particularly important for large trauma studies.

"People buying 64-slice or 40-slice scanners need to develop image handling algorithms so they are not showered by all the thin slices," Rydberg said.

Shands Healthcare has also taken a limiting approach. In the past, technologists took axial images, made sagittal and coronal images, and sent all the images to the PACS for the radiologist.

With 64-slice scanners, such a practice would have a huge impact on the network, said Janice Honeyman, director of radiology informatics at Shands.

Sagittal and coronal images can easily and quickly be created on the fly at PACS workstations, so it is only necessary to send axial images, she said.

"We cut two-thirds of the images out by only sending the coronals and sagittals if someone requests them. Physicians don't need to be burdened with all the extra images from technologists," Honeyman said.

Despite the image management challenges, two facilities contacted for this article are operating 64-slice systems without a PACS. Studies are stored on CDs and DVDs. Both facilities are planning to implement a PACS within the year. But operating a 64-slice system without a PACS can sap personnel resources-most informatics specialists don't recommend this approach.

"The advent of these large data sets is going to drive people to PACS much sooner," Mancuso said.

Facilities with PACS are very careful about which images they store to avoid overload of the network and archive. At the University of Indiana, for example, only 25% of the images taken are stored on PACS.

It's important to consider the potential for additional scan volume through new applications and determine if the image archive can handle the demand. IT changes made in conjunction with the acquisition of a 64-slice system could range from $200,000 to $1 million, depending on the local department configuration and workflow, Morin said.

To ensure IT success with a new 64-slice scanner, Morin concludes that it is best to seek guidance earlier rather than later in the purchasing process.

"It's a very good idea to involve PACS team early on with these new modalities," he said.

Ms. Hayes is feature editor of Diagnostic Imaging.

Association Devises Stringent Training Guidelines for Cardiac CT

American College of Radiology cardiac CT guidelines

The radiologist should meet the following criteria for supervising and interpreting cardiac CT, not including studies performed for calcium scoring only:

- Board certification and supervised and interpreted 75 cardiac CT cases, excluding those done for calcium scoring only, in the past 36 months, or

- Completed an Accreditation Council for Graduate Medical Education (ACGME)-approved radiology residency program and supervised and interpreted 75 cardiac CT cases, excluding those performed exclusively for calcium scoring, in the past 36 months, and

- Completed at least 40 hours of Category 1 continuing medical education in cardiac imaging, including cardiac CT, anatomy, physiology, and/or pathology or documented equivalent supervised experience in a center actively performing CT.

Maintenance of competence

Minimum 75 examinations, excluding those performed exclusively for calcium scoring, every three years.

Continuing medical education:

Radiologists should be meeting ACR practice guideline for CME, 150 hours every three years, including CME in general and cardiac CT, as appropriate to needs of the practice.

Source: American College of Radiology statement (Radiology 2005;235:723-727)