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.
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