Strategies to Enhance Volumetric CT & Workflow

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Multislice CT facilities are overcoming the workflow challenges and near image-overload issues with a variety of efforts before, during and after the study, including powerful protocols, workstations, post-processing techniques such as 3D and multiplanar reconstruction and PACS.

Computed tomography examinations have become the cornerstone of modern radiology departments as studies that historically were performed using other modalities have migrated to this domain with the development of high speed, multislice, volumetric CT scanners.

Michael Vannier, MD, professor of radiology at the University of Chicago Hospitals, explains that utilizing the most modern CT scanners, in the same amount of time or less, at similar levels of reimbursement, clinicians can acquire more images at a lower radiation dose with greater image quality. Two to three years ago, the typical CT study generated approximately 300 images per exam, but with 16-slice scanners, it is not unusual to have 1,000 to 3,000 images produced for a single patient study.

Improvements to the scanners bring higher quality images in significantly less time. Most clinicians do not just look at slices, but use post-processing techniques to produce 3D volumetric image data sets for standard exams to enhance diagnostic capability in routine studies.

"It's gone a step further with scanners that are so fast and capable that you can look at moving structures, including the heart," says Vannier. "Now you can look at the beating heart with the kind of detail that we're accustomed to seeing with CT." The clarity of images provided by CT may surpass the details provided by other imaging modalities without requiring invasive procedures in cardiac catheterization, for example.

Given today's fastest scanners, clinicians can visualize coronary arteries in action using only an intravenous injection of contrast rather than threading a catheter from the patient's groin to heart that often necessitates an overnight hospital stay. The industry has moved from 4, 6 and 8 slice scanners up to 16 and 32 slice machines to the latest incarnations of this equipment featuring 40 to 64 slices that are in the process of release at this time.


MULTIFUNCTION MULTISLICE

Scott Lipson, MD, associate director of imaging at Long Beach Memorial Medical Center in California, uses the Toshiba America Medical Systems Aquilion 16 multislice scanner for their busy CT angiography practice, that includes several CTA exams every day as well as orthopedic imaging, brain, sinuses, chest exams and many trauma cases as well. He says the only study they do not perform is CT colonography in this active center that is the second largest private hospital on the West Coast.

Lipson believes that the work they did "up front" in establishing automated protocols for studies has made their workflow extremely efficient. They established comprehensive protocols to inform the technicians about not only how to perform the study, but how to manage the data after they are acquired.

"When I tell the CT techs I want an abdomen pancreas [scan] or a CTA of the carotid arteries, they can pull up a protocol that has all of the information they would need," says Lipson. "It has acquisition parameters, coverage, how to set up the scan, what type of contrast to use, and then it has all of the information about how to reconstruct [the images], what thickness, what planes, and where to send the reconstructed information: to the PACS, to the workstation, or both. All of our protocols have some sort of multiplanar reconstruction built-in." He says that typically they review thicker slice axial and multiplanar reconstructions even though they acquire their axial data set at 0.5 mm to 1 mm collimation.

Robert Herfkens, MD, professor of radiology at Stanford University, explains in using their GE Healthcare LightSpeed 16 slice scanner, that although the majority of the studies produce 700 to 800 images, it is not unusual for their studies to produce between 2,000 and 3,000 images, especially for cardiac-gated studies or some vascular exams. The Centricity PACS allows him to "cine-scroll" through these massive image data files to the point of interest he seeks.

The Centricity PACS used with a multislice scanner requires a dedicated standard 100-megabit network. The high-end algorithms pull the data at the precise time the user needs to see the data. Rather than pulling 1,000 slices to a PC and waiting for them to transfer, Centricity pulls just the data the clinician wishes to review onto the screen, and pulls all of the other images one by one on a second's notice. In other words, instead of transferring the massive file and waiting for it to display, Centricity pulls only the requested images and then loads the others as the clinician scrolls through them. Herfkens explains these functions are transparent to the end-user.

"It's amazing how efficient it can be at managing these large data setsâ?¦it's relatively seamless," says Herfkens. He describes depressing the shift key to cine-scroll to the appropriate location in the study, with the system loading specific images to the targeted area.


MORE, MORE, MORE IMAGES

Paul Nagy, PhD, director of radiology informatics laboratory at the Medical College of Wisconsin (MCW) in Milwaukee, where they have just installed the prototype GE Healthcare LightSpeed VCT 64-slice scanner, defines the size of CT files within that context. Each 512 X 512 image comprises 256,000 pixels, at one megabyte for every 2 images. Therefore 1,000 images are 500 megabytes, and 2,000 images would produce one gigabyte of data.

These immense image files present a number of challenges. First, the radiologist cannot possibly read 1,000 images or more per patient study. He or she may use a cine-stack to scroll through the files at three to four images per second, but Nagy says that most radiologists normally read 2.5 cm slice reconstructions. They may use some of the advance applications software on powerful workstations to produce post-processed images and use secondary screen shots of the results in their diagnostic process. MCW has five GE LightSpeed 16 CT scanners.

Nagy details two typical workflow patterns. The first involves the radiologist going to a dedicated, high-end viewing workstation to manipulate image data, pushing the resulting reconstructions to the PACS. This may not be the most efficient workflow because the radiologist is not in a central reading station, but must move to the modality workstation to manipulate images. The other approach involves sending all of the original image slices to the PACS workstation, which may or may not have imbedded advanced digitalization tools, and is incapable of accomplishing reformatting of thick slabs of data sets.

Nagy describes their hybrid PACS solution that employs a gigabit network, and high-end RAID (Redundant Array of Independent Disks). They established hanging protocols that load the images as 2.5-centimeter slice reconstructions. On the worklist, the radiologist sees all images that are available, and can pull a sub-series of the study of interest.

Their PGP (Presentation of Grouped Procedures) protocol assigns correct borders to each series of images, not the entire stack of images. So in a chest/abdomen/pelvis study, if the radiologist only wants to see the chest images, that's all that's sent to the reading station. That way, radiologists can focus on the order of viewing images, as well as only work with one segment of the study at a time. Nagy recommends 64-bit processors that can handle more than 4 gigabytes of RAM.


SLICING IT THIN

Not only has the sheer quantity of images grown exponentially, but these latest scanners produce thinner and thinner slices. Scott Zimmerman, global manager of customer productivity for GE Healthcare, says that while clinicians used to complete 5mm slice studies, now the routine includes 0.625 mm images, which results in the huge increase in the number of slices.

Thomas Koonce, MD, director of imaging for the Hematology-Oncology Clinic of Little Rock (Arkansas) uses the Phillips' Brilliance 16 CT scanner to perform between 60 and 75 exams a day in addition to reading another 12 to 15 studies a day from a cardiology clinic nearby. He explains that most radiologists are accustomed to reading a certain number of studies per day, requiring a given amount of time to complete.

Just by adding a few minutes per study, the overload to the clinician can mean the difference between success and failure. Koonce says that he is impressed with the efficiency of their Brilliance Workspace workstation to provide answers to his diagnostic questions in a short enough time to enable him to complete his work in a timely manner.

Elliot K. Fishman, MD, professor of radiology at Johns Hopkins University in Baltimore, offers another perspective to the workflow challenge. He suggests that clinicians experience difficulty when they attempt to review axial slices as they did before, and that the 16-slice scanners (or above) facilitate 3D volumetric renderings that provide excellent clinical information for diagnostic activities and review with referring physicians and patients.

Using their Sensation 16 scanner from Siemens Medical Solutions coupled with InSpace 3D Medical Imaging Software, Fishman relates that by using interactive review of a combination of 3D images and multiplanar reconstructions, workflow is more efficient. Besides enhanced reading capabilities, the size of the reconstructed 3D files ranges from 3 to 5 megabytes, so storage is facilitated.

"You have to recognize that the way 16-slice is meant to be used is to change how you look at and think about the data, as volumes rather than slices," says Fishman. "Once you learn how to use the workstation and look at the volume, you can do that quickly, interactively and intuitively."

While advances to these imaging studies have improved clinical management, IT departments are charged with maintaining smooth flowing data streams of the resultant gigantic image files.


CONFIGURING THE NETWORK

Scott Lodoen, a consultant with Accession Consulting in Daytona, Fla., says they recommend a gigabit backbone for a network that will support multislice CT. Then they suggest that the PACS and modality components should all be on 100 megabit lines set up as a separate VLAN (Virtual Local Area Network) so that the PACS doesn't overrun all other departments competing for bandwidth. They would include certain network ports such as ICU, operating room or emergency department on the VLAN for high- quality workstations.

Lodoen notes that frequently institutions underestimate expected network loads and traffic that will be generated even by a conventional CT, let alone a multislice unit. Once the study is acquired, and sent to PACS, it may be pulled across the network several more times: to the QA station, to perhaps multiple reading physicians in other parts of the hospital, often including prior studies.

"They say, we'll do 100,000 exams per year and the average exam will be X megabytes, and they'll size their network on that, not considering how many times that study will go across the network," says Lodoen. "It's a common mistake."

Most radiology departments put their imaging networks behind a firewall to prevent contamination of the hospital network, notes Vannier of the University of Chicago. The other benefit to this approach is that images are not generally placed on a network that can be accessed from the Internet, not only for security reasons, but for performance reasons as well.

Koonce in Little Rock uses a 100-megabit backbone for their network, with a storage system design that includes 120 gigabits of active space online with 360 gigabits of deep archive that is readily available and then a DVD jukebox for long-term storage of studies. They distribute images to several workstations outside the radiology suite, where clinicians can perform all functions except 3D renderings. They burn CDs to send to the operating room, and digitize all incoming films so that the practice is completely filmless.

Rex Healthcare in Raleigh, N.C., is a 394-bed acute care hospital with several dedicated specialty clinics and is equipped with three Phillips' Brilliance 16-slice scanners.

"All of the images are managed by two servers, each with 3 Terabytes of SAN [Storage Area Network]," says Dave Bullamore, manager of systems integration. There is a third server that runs the database, using hierarchical storage management (HSM) software to direct the placement and movement of images. Most of their reading stations are on 100-megabit lines, but their dedicated PACS network is attached to their core network by a gigabit line.

"As we needed to access images in more areas of the hospital, it became easy to expand and upgrade the remainder of the network, so that no matter where you are, you can pull a PACS image and not worry about blowing out the rest of your network," Bullamore explains.


CONCLUSION

Given the current need for high levels of productivity in busy radiology departments, efficient workflow becomes a high priority for the IT department. Volumetric CT scanners, while offering excellent clinical images that enhance diagnostic capabilities, can produce nightmares on a network that is not configured to move images effectively.