In the PACS Equation: Nuclear Medicine & Image Management

Nuclear medicine has excelled in developing the image management tools it needs to acquire, store and transmit data in their original format so that nuclear medicine physicians can use modality workstations to reconstruct and reprocess images on the fly. However, the only way nuclear medicine can share these dynamic images with radiology is by sending 2D, screen-capture images to PACS. Physicians outside of the nuclear medicine department can not view beating images of the heart, nor can they view fused PET/CT studies on PACS workstations. Have PACS vendors left nuclear medicine behind?

"There is no doubt that nuclear medicine created its own [image management] solution way before MR, CT and digital x-ray PACS were being built," says George Zubal, PhD, technical director of nuclear medicine and associate professor of diagnostic imaging at Yale-New Haven Medical Center in Connecticut. "Nuclear medicine was the first modality to network and go digital. Our low-resolution images can be stored in fairly small matrices which means very little space on disk or very little data that need to be transferred."

Jerold Wallis, MD, professor of radiology, division of nuclear medicine, Mallinckrodt Institute of Radiology, Washington University Medical Center, agrees. "We have a long history of developing our own infrastructure, file formats and our ability to exchange data. These are pretty firmly entrenched and working fairly well within nuclear medicine," says Wallis.

Inside the nuclear medicine department, images are archived in their original format so they can be accessed by physicians for reconstruction, reprocessing and/or review. For access outside the department, nuclear medicine sends static, screen capture images to PACS because most systems can not adequately manage, display and transmit nuclear medicine, nuclear cardiology and PET data in their original format. Therefore, the images do not get presented on PACS workstations the same way they are displayed on modality workstations in nuclear medicine.


Dynamic images

Rather than looking at very high spatial resolution studies, nuclear medicine physicians are looking at physiology and function in the body. The image files are smaller when compared with CT and MR - except for PET/CT which can generate 200 MB to 300 MB of data per study. However, nuclear medicine images consist of four dimensions, use color to represent diagnostic information and require dynamic image display.

The complexity of nuclear medicine, nuclear cardiology and PET images is one reason the specialty has excelled at utilizing digital technology; it's also another reason why the specialty can not be fully integrated with conventional hospital-wide PACS used for CT, MR and digital x-ray.

"While providing the storage space is not an issue, being able to handle the images correctly and maintain the integrity of the data are a big issue," says Xiaoyi Wang, president of Thinking Systems, a PACS company focused on working with nuclear medicine, PET, ultrasound and cath lab images.

"Unlike with CT and MR, displaying nuclear medicine images as they are provides little diagnostic value to clinicians," says Wang. "There are eight nuclear medicine image types, and many processing and quantification protocols, depending on the acquisition protocol and body organ being imaged. The majority of the nuclear medicine scanners and workstations being used are either non-DICOM (Digital Imaging and Communications in Medicine) or not capable of receiving DICOM images. Therefore, sending images back to the modality workstation from PACS for processing and display is often not an option."

To make a PACS useful for nuclear medicine, Wang says it would need to provide the same tools found on a nuclear medicine modality workstation, such as cardiac image processing, cardiac quantification analysis, SPECT image processing, MUGA processing, and analysis of the lung, gallbladder and kidney, to name a few. These tools are not available today.


Half the pie

Mallinckrodt's division of nuclear medicine uses a home-built mini PACS with Unix-based workstations for physicians to read and review general nuclear medicine exams, and utilizes vendor supplied systems to manage nuclear cardiology and PET images. Each year, the department performs about 7,000 general nuclear medicine studies, 8,000 myocardial perfusion imaging studies and 3,000 PET exams.

"It's a high-volume department," says Wallis. "One thing that we have recognized is the need to store data both in a format that we can reload for processing back onto the original nuclear medicine dedicated equipment and also in a format that is easiest for viewing by referring clinicians. The decision we made was to archive internally all the data in its original format for reloading onto our processing equipment if we need to reload a study. But what we are sending to the general PACS is for the most part things that we think the referring physicians are going to want to look at, in a form that is easily interpretable."

For PET images, the entire data set is sent to PACS, as well as a selected screen-capture image that highlights the lesion a referring physician may have interest in seeing.

"Hopefully, in the future, our needs will be met by a single storage format, once vendors take full advantage of the various features included in the IHE [Integrating the Healthcare Enterprise] Nuclear Medicine Image profile, as well as other IHE profiles," Wallis says. "These features include better formatting of nuclear medicine images on PACS displays, better support for display of nuclear medicine image labels, and designation of key images to direct referring physicians to important images within a large data set. If we start asking for these IHE profiles when we go to purchase equipment, then vendors will be motivated to provide them." For more information on the IHE Nuclear Medicine profile, go to http://interactive.snm.org.

One of the biggest challenges facing the industry is the interconnectivity and image exchange between different vendors' systems. To integrate its nuclear medicine equipment in a harmonious environment, Yale-New Haven Medical Center installed Thinking Systems' PACS.

As soon as images are acquired and processed on the department's nuclear medicine scanners, images are automatically imported by Thinking Systems' DICOM gateway into an archive. Since the scanners are non-DICOM, the images are imported using proprietary protocols. The archive automatically forwards static screen-capture images to the hospital PACS. Nuclear medicine physicians read the studies on Thinking Systems PACS workstations equipped with special tools for image reconstruction, post-processing, quantitative analysis and image review. They also can bring other modality images from the hospital PACS for comparison.

Static images may be adequate for radiologists in some cases, but more dynamic images, particularly nuclear cardiology, are not as meaningful when viewed in 2D and grayscale. "The movie of a beating heart should really go to the central archive and be stored there the same way that MR, CT and other modalities store their data," says Zubal. "What we are doing is taking a piece of what should be a complete PACS and making it work within our own department instead of having that as part of the centralized PACS."


The DICOM impact

"Historically, a lot of nuclear medicine file exchange was based on a thing called Interfile, which was a common file format that all vendors supported," says Wallis. "It was developed in Europe as a way to exchange quality control data between cameras. It evolved into a way to exchange patient data as well. There are many departments in the country that are still using Interfile.
"But Interfile does not talk to the rest of radiology," continues Wallis. "Then DICOM in nuclear medicine came along. The first attempt at a DICOM format for nuclear medicine was not well regarded. It did not correspond well with the way we did our studies. That DICOM format was actually retired and a new DICOM format for nuclear medicine was brought in its place. What we are using today are descendants of that format."

Wallis relays that most of the major nuclear medicine vendors offer DICOM as part of their camera purchase. "Many of the vendors do not use DICOM as the native file format; that is when an image is acquired and it is stored in a local format. It's converted to DICOM on the way out and converted back into local format on the way back in again. Getting everything to flow smoothly can be a little tricky," he says.

Most nuclear medicine images can be transferred outside the department, but whether they will be fully understood by the receiver is another question. "One type of study that is still in limbo and does not have a clearly defined format is processed data from cardiovascular nuclear medicine studies," says Wallis. "They can be captured as a static image, but getting vendors to implement processed data in a more dynamic fashion is still in progress. We are trying to improve the cooperation between nuclear medicine systems and general radiology PACS through Integrating the Healthcare Enterprise (IHE).

"I think that a lot of radiology display systems are not familiar with the best way to display nuclear medicine data," continues Wallis. "That's one of the goals of the IHE Nuclear Medicine Image Profile. We have gone through various types of nuclear medicine images and tried to describe for the PACS vendors various display techniques that might be useful for [specific image types]. We boiled it down to a set of capabilities that a display system must meet if they are going to meet the display portion of the nuclear medicine profile. For example, when looking at a gated blood pool study, we typically look at three cine views simultaneously. A nuclear medicine system can do this. A PACS can only display one cine view at a time."


Adding PET

PET, in combination with CT, is one of the fastest growing nuclear medicine applications. It is used to diagnosis, stage and plan treatment for cancer, evaluate cardiac viability, and diagnose neurological conditions such as epilepsy and Alzheimer's disease.

"PET has played a major role in the advancement of nuclear medicine in general," says Edward Coleman, MD, director of the division of nuclear medicine at Duke University Medical Center. "We are now able to evaluate patients in a manner that we had not been able to do before PET became clinically widely used.

"PET images are relatively high resolution compared with other nuclear medicine images," continues Coleman. "When we combine PET and CT, which is the standard of care these days, then we have extremely high-resolution CT scans combined with the PET scans and we have very large amounts of data to be displayed and stored."

Vendors have equipped nuclear medicine physicians with the tools they need to co-register multimodality images such as PET/CT on the fly, but if the images are stored in the hospital-wide PACS, radiologists can only view transverse slices side by side. In almost all facilities, large or small, clinicians must make a trip to the nuclear medicine department to read fused images.

"Some systems have trouble storing the PET dataset and many PACS when they try to display it on a regular PACS viewer will show two entirely different exams," says Mallinckrodt's Wallis. "They won't be fused and aligned the way they would be if they were viewed on a dedicated nuclear medicine station. Trying to get the data displayed on the radiology PACS in a way that the referring physician can point to a lesion and then look back at the CT and say 'that lesion is here' is a challenge that we have yet to meet for the most part."


Making friends: nuke med & PACS

Both nuclear medicine and radiology will benefit once nuclear medicine, nuclear cardiology, PET and PET-CT images can be fully integrated with PACS. When it will happen is debatable. "I am sure it will happen sometime; I wish that it would happen next year," says Zubal. "It might be four years at the rate it's been going. It really is happening too slow for our comfort."

Once it does, clinicians will have enterprise-wide access to nuclear medicine and PET images and will be able to read them on PACS workstations the same way nuclear medicine reads them on high-end modality workstations. Mallincrodt's Wallis points out that in the long run, it may be more cost effective for nuclear medicine to store its images on a general radiology PACS.
Thinking Systems' Wang points out that there is a possibility of providing world-wide web access to nuclear medicine, PET and PET-CT images once PACS and nuclear medicine is integrated. "Clinicians will be able to go to any Windows-based computer on the enterprise network or the internet and will be able to perform securely the tasks they would do on the PACS workstations, such as image processing, quantitative analysis and image fusion. For instance, an oncologist can log onto the web server from his or her desktop computer and view and manipulate the PET/CT fusion images, instead of reading hardcopy printouts. The oncologist also will be able to confer online with radiologists or nuclear medicine physicians on cases.

"It also will prolong the lifespan of the existing investment," continues Wang. "Nuclear medicine gamma camera technology has not changed much in the last decade or so. A significant portion of the gamma cameras in use today are probably 15 to 20 years old. If these cameras are maintained well, they should still acquire very good images. What has changed a lot are the processing workstations. Many facilities replace their gamma cameras with newer ones, hoping that the new ones will be PACS-compatible. Unfortunately this has not been the case. If the PACS can interface with the cameras and replace the antiquated processing workstations, it will extend the lifespan of the cameras by many years."