Three-dimensional imaging has helped clinicians view anatomical structures with greater accuracy. In addition, advances in 4-D have instilled high resolution with movement, breathing life into fetal images and providing a dynamic representation of the cardiac cycle, among other visually compelling effects.
These capabilities, because of the obvious impact they will have on the quality of patient care, are driving the growth of the 3-D/4-D imaging market. In recent years, the technology has achieved a wider application, and continuing development of scanner and transducer technology-and the resulting increase in volume data sets-has led to increasing development of workstations and software with 3-D/4-D capabilities. More and more, the technology is being used in conjunction with ultrasound, CT, MRI, and intensity modulated radiation therapy (IMRT).
Options in Obstetrics
An area where 3-D/4-D technology perhaps has garnered the most attention and widest application is obstetrics. John Pellerito, MD, has called the interest and usage an “explosion.”
“The main focus has been the evaluation of the fetus,” says Pellerito, chief of the division of ultrasound, CT, and MRI, and director of the Peripheral Vascular Laboratory in the Department of Radiology at North Shore University Hospital (Manhasset, NY).
Used in combination with traditional 2-D ultrasound imaging, 3-D/4-D ultrasound provides a higher resolution image displayed as 3-D volume data in real time. “The image we see on the screen has been reconstructed in three dimensions, and 4-D gives it movement,” says Todd Rosen, MD, director of Atlantic Maternal Fetal Medicine, who uses 3-D/4-D ultrasound at both Morristown Memorial Hospital (NJ) and Overlook Hospital (Montclair, NJ).
This technology allows clinicians to see greater detail when a 2-D diagnosis indicates suspected structural abnormalities that need to be more closely scrutinized. Not only is the surface rendering more complete, but fetal activities not visible with 2-D scanning-such as finger movements, yawning, and swallowing-also are now apparent. For expectant mothers, such detail can be especially dramatic.
In recent years, such capabilities have given rise to US imaging centers whose main focus is to provide mothers with beautiful, in-the-womb “baby pictures.” However, because many of these centers operate unregulated, the FDA has considered taking actions (see “FDA says ‘Nay’ to Fetal Foto-Ops, below). At regulated clinics and hospitals, clinicians also provide mothers with such images, but only if it is part of a diagnostic study.
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| These live 4-D images of a 27-week healthy fetus (lower left) and a fetus with his foot in his mouth in the third trimester (lower right) were captured on Philips Medical Systems’ iU22 system (top) with the 3D6-2 transducer using XRES visualization technology. |
But 3-D/4-D fetal imaging has much more to it than cute baby pictures. “That’s what many end users and patients focus on, but clinicians are seeing dramatic uses of 3-D/4-D imaging data that are making some big changes in the modality,” says Jim R. Brown, director of clinical and technical marketing for Philips Medical Systems’ ultrasound group (Bothell, Wash).
The images generated help detect abnormalities, such as cleft lips and palates, as well as structural deformities of the hand, spine, and heart. The technology is not viewed as a replacement for traditional 2-D imaging; rather, it enhances diagnosis. Currently, 2-D ultrasound is the standard and serves as the basis for the more advanced 3-D/4-D techniques that are used when diagnosis is difficult. That is, 2-D scans are performed first, and when more detail is needed-as when an abnormality is suspected-3-D imaging and subsequent 4-D manipulation come into play to provide greater surface detail.
“The question really is, to what degree does 3-D ultrasound let me see things I could not see in 2-D?” suggests H. Frank Andersen, MD, medical director of maternal and fetal medicine at Baylor University Medical Center (Dallas). “Ninety-five percent of what we do, we still do in 2-D. Even if I want to evaluate a birth defect in 3-D, I’ll first look at it two dimensionally.”
Atlantic Maternal’s Rosen adds, “[3-D/4-D ultrasound] is not used as a first-line screening. It’s more of a secondary tool to help us clarify a diagnosis. If we have questions about the diagnosis, or if we think the imaging will provide additional information, we will use it.”
Besides cleft lips and palates and finger malformations, 3-D/4-D ultrasound is helpful in identifying abnormalities of the bone, such as achondroplasia and spina bifida. It also has proved useful in examining the fetal heart, especially for studying the correlation between valves, chambers, and vessels; calculating heart cavity volume; and assessing valvular function and atrial and ventricular communication. In this way, heart defects can be diagnosed in the womb and appropriate treatments can be planned and then administered at birth.
Inside the System
In general, 3-D/4-D ultrasound systems include four main components: automatic acquisition, multi-planar display, volume rendering, and real-time imaging. Automatic acquisition represents a significant advance over the traditional 2-D slice-acquisition method that requires manual movement of the probe across a patient’s skin. In 2-D ultrasound, a technologist scans the patient by manually moving a probe over the abdomen. Now, with automatic acquisition, no manual movement is required; the probe remains still as data is acquired.
The 3-D multi-planar display reveals precise spatial relationships, which enable more accurate volume measurement calculations. Clinicians can see suspected abnormalities in three orthogonal scan planes-the sagittal (longitudinal), transverse, and horizontal (anterior and posterior). These planes can be rotated along three axes (x, y, and z) to obtain the best diagnostic view. The 4-D element provides the coronal view or an anterior to posterior view, creating a landscape perspective that helps with spatial positioning of pathology location and for looking at specific anatomical areas. The 3-D volume rendering component assembles the ultrasound image information into a 3-D image. Finally, the 4-D element essentially turns a static hologram into a 3-D moving image.
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| GE Healthcare’s Voluson 730 series offers real-time 4-D imaging as well as 3-D multi-planar display, 3-D power Doppler, and 3-D surface rendering. |
Baylor’s Andersen uses the Voluson 730 Expert from GE Healthcare (Waukesha, Wis), a system regarded as one of the most advanced on the market. The Voluson 730 displays up to 25 volume scans per second in 3-D planes, one of the highest rates available today. The system uses advanced signal processing and a probe that operates on 10 MHz. In addition to high resolution, the Voluson 730 offers spectral and color Doppler as well as advanced 3-D imaging. Automatic acquisition is accomplished with an electronic array that moves through the scanning transducer.
3-D/4-D: Advantages and Limitations
In combination with simplified 3-D acquisition and multi-planar views, 3-D/4-D ultrasound technology provides shorter study times and faster examinations. Further, fetal images, for example, can be shared with referring physicians and surgeons who will treat the baby after it is born.
But the technology has its limitations. Currently, viewing the face and body can be difficult if the amount of amniotic fluid is inadequate. Also, information can be hidden from view if the fetus is facing backward in the uterus. “If the baby is looking straight back, you just are not going to see that face; whatever information is there is going to be unobtainable,” Andersen says.
In addition, some of the detail provided can be misleading. “Although I can see a cleft lip better with 3-D, I’ve been misled as much as I’ve been helped doing 3-D of the lip, because you get funny little folds or shadows that can look like a cleft. So it is not that simple,” he reveals.
Movement artifacts present another challenge, depending on the software and the speed of the computer. “If the baby is moving faster than the frame rate of the ultrasound,” Andersen explains, “you can get some really bizarre images.”
Increasing Application, Healthy Market
Thinking that fetuses don’t need any photo opportunities, the FDA might take regulatory action on the numerous unregulated ultrasound centers that provide expectant mothers with ultrasound images of their unborn babies. These centers are using 3-D/4-D technology to provide what the agency calls “entertainment ultrasounds,” and the FDA points out that it is illegal to provide ultrasound for nonmedical purposes. Soon, such centers could be hit with injunctions, fines, and even equipment seizures. More important than the legal aspect, the high-frequency sound waves emitted by the advanced ultrasound technology could be harmful to developing fetuses. The American Institute of Ultrasound in Medicine (AIUM of Laurel, Md) worries that unregulated scans performed by unlicensed operators are longer and use more energy than clinical ultrasounds. The FDA indicates that some laboratory studies show that energy directed at tissue can produce physical effects. It’s not yet known for sure whether these effects are harmful, but both the FDA and the AIUM worry about future medical problems. The FDA reports that anecdotal studies in the United States and Europe have shown that it could negatively impact human development. Consumers also should be aware that not everyone who pays for this kind of ultrasound is going to get a pretty baby picture. Those “awwww”-inducing photos used in television commercials and print ads are fairly infrequent. “They’re really only 1 in 1,000,” reports H. Frank Andersen, MD, of Baylor University Medical Center. “Not every lady who walks through the door is going to get a beautiful picture of her baby.” -DH |
Despite these limitations and problems, observers are confident that 3-D/4-D technology will become a standard part of ultrasound imaging. Its application has spread well beyond the large institutions and into smaller clinics and doctors offices. “It’s becoming a commonplace mainstay of ultrasound,” says Philips’ Brown.
Philips offers the iU22, which scans 30 volumes per second. This “flagship” product is the first premium ultrasound system to have fully integrated 2-D, 3-D, and real-time 4-D imaging modes as well as multi-planer reconstruction resolution. “It has the most powerful architecture ever put in an ultrasound system,” Brown says. “It’s designed for current applications as well as future applications.”
The significant benefits of 3-D/4-D imaging have been recognized throughout the medical field, and it is increasingly being used in other areas, such as obstetric and gynecological applications and prostate cancer diagnosis and treatment. For prostate cancer, 3-D/4-D technology helps increase the accuracy of ultrasound-guided biopsies by revealing needle movements in three planes. The practical applications for gynecology include detection of uterine fibroids, ovarian tumors, and endometrial polyps.
Meanwhile, 3-D echocardiography has developed to the point where it can provide a more complete picture of cardiac structure and cycle. “It’s a whole new way to visualize the heart,” Brown explains. “You’re basically taking the organ and cropping into it to see structures you really couldn’t appreciate with conventional 2-D imaging.”
This evolution, he says, has opened up new areas of where echocardiography can be used, such as interventional procedures and cardiac resynchronization therapy. Surgeons also are finding this technology helpful in preoperative planning and postsurgical follow-up.
In this area, Philips offers the Sonos 7500, a cardiac ultrasound system with Live 3-D Echo. It features the company’s xMatrix technology, which Brown describes as a completely electronic, fully sampled array. “It’s the first of its kind and has allowed us to generate real-time images of the heart in three dimensions,” he says.
In addition, North Shore University Hospital’s Pellerito indicates that the market is not restricted to ultrasound. Increasingly, it is being applied to CT and MRI. He reports that in the Peripheral Vascular Laboratory, 3-D is being used in vascular studies, such as evaluation of the carotid arteries and abdominal aortic aneurysms, as well as for planning endograft placement. “Now that [3-D] is becoming easier to use, we’ve started using it for more applications,” he says. “We’ve seen it used for bone applications, for cardiac applications, and we will use it to look at tumors.”
In the area of radiation therapy, 2 years ago, the NOMOS Corp (Cranberry Township, Pa), introduced real-time ultrasound guidance for radiation therapy with its ImageSync system, an ultrasonic, real-time imaging/positioning technology used as a treatment localization tool. The system provides a continuous stream of ultrasound images that can be used in real time to localize cancer targets before radiation therapy treatment. With it, clinicians can move and align structure sets to ensure accuracy and precision required for IMRT as well as conventional treatment. The result is greater accuracy with reduced complications of treatment.
The Research Realm
One of the most compelling examples where 3-D has been beneficial to research is at the Surgery and Planning Laboratory (SPL), a part of the MRI division of the department of radiology at Brigham and Women’s Hospital (Boston). There, staff members have developed advanced imaging methods that can be applied to interventional radiology and surgery. The efforts have led to the development of new tools and techniques. Since 1991, SPL researchers have been working on 3-D reconstructions for intraoperative displays.
Recently, SPL neurosurgeons developed a surgical technique that enables them to successfully remove brain tumors that were previously inoperable. To develop the technique, the SPL has relied on data storage and information technology developed by Sun Microsystems Inc (Santa Clara, Calif). “That was certainly an enabling technology,” says Ron Kikinis, MD, director of the SPL. “Some of what we are doing would not have been possible if we had taken a different approach.”
The main challenges that the researchers sought to address with Sun’s technology included the visualization of complex and delicate vascular and neural structures to preserve healthy surrounding tissues while precisely locating tumor tissue for removal; display of 3-D models of internal structures that would aid doctors in surgical planning and image-guided neurosurgery; and the “real-time” processing of enormous amounts of data. Moreover, the system had to possess the utmost reliability crucial to such complex surgery. “You don’t want to have to reboot your system in the middle of a surgery,” says Jane Wasson, Sun’s senior product manager for desktop business solutions.
To meet these challenges, the SPL upgraded from a previous Sun platform to one that included the Sun Fire 6800 server and Sun Blade 1500 workstations equipped with Sun XVT Graphics.
During a procedure, data collected from MRI scans taken during the surgery is processed on the Sun Fire server and sent to the Sun Blade workstations equipped with Sun Expert 3-D graphics cards. This provides surgeons with 3-D models and views of the brain. The upgrade greatly reduced processing time and enabled surgeons to view results of previous surgical steps as an aid in subsequent surgical stages-something they weren’t able to do before.
The versatility that comes with 3-D/4-D technology is remarkable. It has proven beneficial in such diverse areas as presurgical planning, intraoperative surgery, echocardiography, and perinatology. Because it is multifaceted, many market observers feel 3-D/4-D technology will become a standard part of diagnostic imaging.
Dan Harvey is a contributing writer for Medical Imaging.
CT in 3-D
The advancement of 3-D imaging techniques coupled with recent developments in CT have enabled the modality to be used in a variety of ways to stage or treat various types of cancer. Spiral CT. Helical CT, also known as spiral CT, can provide high-resolution 3-D images of the lungs that could lead to earlier detection of cancer. The technique is about 10 times faster than conventional CT scanning, as it can scan entire regions of the body during a single breath hold of about 20 seconds. The technique is more sensitive than conventional chest X-rays, which cannot detect lung nodules smaller than 10 mm in diameter; spiral CT can detect nodules as small as 5 mm. Because of the improved specificity, as well as the lower radiation dose, spiral CT is viewed by many as an effective way to detect lung cancer at an earlier stage in high-risk, asymptomatic subjects. Earlier detection could lead to longer survival. During a scan, the patient lies on an examination table as the table moves through the scanner frame. An X-ray tube rotates around the patient, emitting X-rays that form a spiral path through the patient. The X-rays are picked up by detectors located inside the gantry. A data set is produced that is reconstructed by a computer into a high-resolution 3-D image of remarkable detail. Multi-detector CT (MDCT). Representing a significant advancement over conventional CT in the diagnosis of pancreatic cancer, MDCT involves multi-detector systems that allow the acquisition of multiple slices in the time traditionally used to acquire a single volume of data. MDCT enables clinicians to image the entire pancreas in 1-mm slices that can be reconstructed as 3-D models. It also can be used to screen for peripheral lung cancer. CT and Radiation Therapy. Three-dimensional conformal radiation therapy (3-DCRT) improves tumor localization and minimizes doses to surrounding, healthy tissue. In this way, 3-DCRT has made it possible to improve local tumor control by escalating dosage to the targeted area. IMRT is an advanced form of 3-DCRT that precisely shapes the high-dose radiation volume to cancerous areas and sculpts it around adjacent normal tissues, making it possible to deliver even higher doses to tumors without increasing side effects. Treatment planning involves acquiring a volumetric CT while the patient is immobilized in a position that will be identical to the one used for radiation treatment. Scans usually occur in intervals of 3-5 mm in the region of interest and are then reconstructed and displayed on a virtual simulation computer that re-creates a 3-D image. The CT information is transferred to a 3-D treatment planning workstation where clinicians can design highly complex radiation therapy treatment plans. Both 3-DCRT and IMRT have been proven effective in treating prostate cancer. Researchers are currently studying its effectiveness on cancers of the head and neck area, brain, liver, breast, and lung. -DH |
