The advent of spiral CT and fast MRI, advances in computer processing capacity, software, and speed, and a new generation of high-technology graphic techniques from the companies that created special effects for Star Wars and Toy Story are beginning to revolutionize the way diagnostic imaging displays anatomy. The era of 3-D has begun.

Although 3-D reconstruction of CT, MRI, and ultrasound data has been performed in a handful of universities and large teaching and research hospitals for years, technical and economic barriers have prevented the display technology from achieving its full potential. As diagnostic imaging prepares to enter the next century, new applications will likely be approved and 3-D imaging will take on new importance.


When experts began exploring the possibilities inherent in 3-D imaging, it became apparent that slices of CT data could not be acquired thinly or quickly enough with conventional imagers to permit the reconstruction of anything but choppy 3-D surface volume renderings.

The time it took investigators to create 3-D images was also a barrier, according to Joel Neuman, MD, chief of the Department of Radiology in the eastern region of Penn State Geisinger Health System, Wilkes-Barre, Pa.

“Five years ago I attended a meeting where they showed us these wonderful fly-throughs in and around the heart, looking at the vascular system,” he reports. “This very short movie required 2 days of continuous processing to produce. To show you how far we’ve come, we can now do that same movie in 15-20 minutes.”

Nor were inadequate volumetric data sets and lengthy reconstruction time the only significant problems. Prior to the development of spiral CT in the early 1990s, conventional scanning often took too long to permit optimal imaging with contrast media of vascular structures.

“You couldn’t inject a patient and scan during the arterial phase in the aorta or during the arterial phase in the brain,” Neuman explains, “unless you wanted to use 600 mL of contrast.”

Thus, the invention of spiral CT was a watershed in bringing 3-D imaging from the laboratory to the imaging department because it enabled physicians to acquire a large body of volumetric data in a very short time. Spiral CT scan data alone, however, were insufficient to create smooth 3-D images of clinical value. The problems of stair-step artifact and choppy image motion had to be addressed.

Manufacturers and researchers devised elaborate interpolation software to correct the problem by filling the space between spirals with artificial data points derived from the slices above and below each gap. The resulting volume data sets could then be reprocessed into 3-D images that could be viewed on workstations and high-end PCs as volume renderings, surface shaded renderings, or maximum intensity projections.

While 3-D image data could be rapidly acquired with spiral CT, reprocessing time remained unacceptably long through the 1980s. Workstations were expensive and too slow. During the last 5 years, however, the computer industry has responded with new generations of processors, disk drives, and monitors with the necessary power and speed. Equally significant is the fact that manufacturing efficiencies and competition have drastically reduced prices so that many facilities can participate in the 3-D revolution.

“Viewing clinical CT and MR data in the conventional manner — in cross-sectional slices — is time-consuming and laborious,” notes David J. Vining, MD, associate professor of radiology at Wake Forest University School of Medicine, Winston-Salem, NC. “But with the new 3-D techniques and the speed and power of computers, we have a new vehicle with which to visualize that information,” he explains. “It’s like driving a sports car on the Information Highway.”

Assessing the value of 3-D imaging requires an understanding of how the unique perspectives that it provides can be fit into clinical care. Elliot K. Fishman, MD, professor of radiology and oncology at Johns Hopkins University Medical Center in Baltimore, has worked with 3-D since 1985, beginning with orthopedic applications. He acknowledges that viewing a fractured pelvis in 3-D as opposed to 2-D does not alter the diagnosis, nor is it supposed to, he indicates. Rather, seeing a 3-D display may alter the physician’s approach to managing the fracture.

“We found that when we provided 3-D images of acetabular fractures to orthopedic surgeons, it enabled them to sense the personality of the fracture,” Fishman explains, “and this had significant importance to them in patient management.”

Fishman and his colleagues have studied the clinical utility of 3-D images to orthopedists. In one study, experienced orthopedic surgeons altered their management of trauma and reconstructive surgery patients approximately 30% of the time after comparing 2-D images with 3-D displays. That result did not come as a surprise to Fishman because the value of 3-D imaging often derives from helping physicians view anatomy in new ways, occasionally revealing additional information that would be unobtainable or equivocal if viewed in 2-D.

“When we first began working with Pixar and LucasFilms, it took 24-26 hours to do one study or even one part of one study,” Fishman recalls. “Inadequate volumetric data were problematic until spiral scanners became available to make high-resolution fast scanning a reality. After that, CT exams that formerly required more than 10 minutes could be performed in 40-50 seconds.”

According to Fishman and other 3-D experts, cost was a big consideration in the 1980s. The Pixar computer initially cost $250,000. Although computer costs gradually began to decrease in the late 1980s, workstations still cost $130,000 to $250,000. Add the cost of a high-end computer and workstation to a new $900,000 spiral CT scanner, and 3-D imaging became prohibitively expensive for all but the larger hospitals and universities.

Fortunately, the price of computing power and speed has continued to decline. Neuman estimates that good workstations now cost $40,000 to $80,000 and that a spiral CT system can be purchased for $400,000 to $800,000. Using current performance standards as a yardstick, it is hard to believe that 40 MIPS (million instructions per second) made the Pixar system state-of-the-art in the late 1980s. Current systems process more, cost less, and operate more reliably. Consequently, 3-D images can be reconstructed and displayed with remarkable clarity in near-real time.

“We do all of our 3-D virtually in real time,” Fishman agrees. “The technology has become so straightforward that we perform the studies ourselves in just minutes.”


In terms of reimbursement, physicians who perform their own 3-D studies may be paid for both the professional and technical components of the examination. Current Procedural Terminology (CPT) codes have long existed for CT studies of specific organs as well as for image reconstruction.

“We charge for the body part, the area covered, and then we charge for reconstruction,” Neuman explains, noting that several codes are routinely aggregated. “The CPT code for the professional component is 76375; it is 0950 for the technical component. Then we charge for the body part with contrast. We have been doing this for 5 years and no claims have been rejected.” The codes Neuman uses most frequently in reconstruction are 70460, CT head w/contrast; 71260, CT chest w/contrast; 74160, CT abdomen w/contrast; 72193, CT pelvis w/contrast; 72126, CT neck w/contrast; and 76375, the CT reconstruction charge.

Fishman points out that the lion’s share of reimbursement for 3-D imaging still falls within the technical component rather than the professional fee — which is why he and his colleagues perform their own reconstructions rather than having technologists do so.

“If your hospital receives the technical fee, cut a deal to give you a percentage of that component as well,” he advises.

That is good advice, according to Vining, because reimbursement varies regionally and from carrier to carrier. “Medicare reimbursement for 3-D reconstruction of CT data in my state, North Carolina, is $107, which is not bad. The professional fee, however, is only $7.”


The combination of next-generation scanners and the availability of affordable workstations and sophisticated 3-D reconstruction software is leading to new clinical applications for 3-D reconstruction, primarily utilizing CT and MR data. Technological barriers continue to hamper the development of 3-D ultrasound.

CT angiography (CTA), on the other hand, represents one of the fastest growing applications. “Our goal is not to replace conventional angiography with CTA or even make them equivalent,” Neuman says. “Rather, our intention is to provide physicians with diagnostic vascular images so that appropriate intervention or treatment can be performed as safely and quickly as possible. Approximately 95% of our renal artery stenosis screening is done with CTA rather than conventional or even MR angiography. We do CTA on all patients with subarachnoid hemorrhage to look for aneurysms. During the past 3 years, 100% of those patients have gone on to surgery without an angiogram and there has been 100% correlation.”

Fishman reports that CTA costs about one-third to one-quarter of conventional angiography without the risk to the patient. Studies take 30-40 seconds and the patient is on the table for 5 minutes instead of an hour, key benefits in terms of best practices.

“It is equivalent to angiography in accuracy,” Fishman states. “It is noninvasive, it is much cheaper, and it is easier on the patient.”

Michael Mawad, MD, professor of radiology, neurosurgery, neurology, and ophthalmology at Baylor College of Medicine in Houston, is pursuing another approach to vascular imaging: 3-D rotational angiography.

“Although rotational angiography has been approved by the Food and Drug Administration, the new 3-D software is still investigational,” Mawad explains.

Also director of neuroradiology and endovascular neuroradiology at Methodist Hospital in Houston, Mawad is convinced that 3-D imaging improves patient care as well as outcome.

“As an interventionalist, it gives me a better and clearer understanding of the anatomy of an aneurysm,” Mawad states. “Since we began our 3-D angiography research studies several months ago, we have found ourselves treating aneurysms that we would have considered untreatable when evaluated in 2-D. Rotational angiography allows us to use less contrast because image acquisition is so much faster. We have cut 20 to 30 minutes from a 3.5-hour procedure.

“Currently, we obtain 3-D angiography pre- and post-treatment to assess for adequacy of coiling or endovascular results,” he continues. “I believe that we will soon be able to perform 3-D angiography on the fly in real time to visualize coil placement as it occurs.”


Embarking on 3-D capability for most facilities requires only the addition of the right workstation and reconstruction software. Most are already DICOM-compatible. Thus, experts around the country have begun exploring 3-D reconstruction for new applications, ranging from arterial studies of potential kidney and liver transplant donors to the evaluation of aneurysms within the brain and abdominal aorta and the staging of pancreatic cancer and tumors. An array of virtual procedures may prove to be among the most spectacular in 3-D imaging, especially virtual colonoscopy, potentially a noninvasive alternative to an uncomfortable and risky physical procedure.

“I can find most colon polyps just by looking at axial CT images,” Vining says. “When I find a spot I am unsure of, I go into the 3-D mode to help me determine with confidence whether it is a polyp or an artifact. It provides me with a road map to convey clinical information to the surgeon and gastroenterologist.”

Vining predicts that virtual colonoscopy will become one of the first mass applications of 3-D imaging. He and his associates recently completed their 200th case comparison of virtual and real colonoscopy.

“Our results are quite good,” he reports. “We are finding that we can get the same data with fewer risks. It is all coming of age, except for reimbursement. In that respect, we’re still in the Dark Ages.

“When I do a virtual colonoscopy, my charges reflect CPT codes for CT of the abdomen, pelvis, and for reconstruction for a total of $577. Will that make virtual colonoscopy competitive with its conventional counterpart as a screening procedure? Not likely.”

One key to reimbursement, experts agree, is to convince the Health Care Financing Administration (HCFA) and other third-party payors that 3-D imaging may substitute for accepted procedures in certain circumstances rather than duplicating them. CT angiography is one example and virtual colonoscopy may prove to be another.

While advanced technology has enabled physicians to reconstruct CT and MR data into three dimensions, ultrasound continues to lag behind, according to R. Brooke Jeffrey, MD, professor of radiology and chief of abdominal imaging at Stanford University Medical Center, Stanford, Calif.

“The trouble with ultrasound is that it is a handheld technology,” Jeffrey explains. “You manually scan a region of interest with a transducer, and that makes it difficult to acquire a stack of perfectly registered 2-D images necessary for 3-D reconstruction.”


Aside from the technical difficulty of producing 3-D images from ultrasound data, it is not entirely clear what the most appropriate clinical applications might be. Most of the work to date has focused on fetal anatomy in the belief that 3-D images might prove diagnostically useful. Furthermore, ultrasound is limited in some anatomic regions by the presence of bowel gas.

“The added value of 3-D versus 2-D in ultrasound has not been clearly documented, and I think that will take some further work,” Jeffrey indicates. “Experience with CT and MRI has demonstrated that the benefits will likely be there once the technical challenges are overcome. The human body is a three-dimensional structure, and we expect that there are going to be some areas of anatomic complexity where 3-D ultrasound can play an important role.”

While Jeffrey expects fetal imaging to be the first area to receive major attention in 3-D ultrasound, he anticipates that gynecologic applications — uterine anomalies, fibroids, and related issues — will closely follow. There is interest, for example, in using 3-D ultrasound to potentially replace x-ray hysterosalpingography for studying fallopian tube patency. The application of 3-D ultrasound to carotid artery screening especially intrigues him.

“We are attempting to develop a 3-D screening technique that will rapidly survey patients to see if they have occlusive vascular disease of the carotid bifurcation, which is a major cause of stroke,” he notes. “The best way to capture the information is to do so in 3-D, using either a 3-D color Doppler or perhaps some sort of velocity mapping. At present, a complete bilateral carotid examination takes 30-40 minutes. We are hoping to reduce that to less than 5 minutes.”

Although acquiring 3-D ultrasound technology costs substantially less than CT and MR, the prototype 3-D systems used by Jeffrey and other investigators do require specialized transducers and reconstruction software, making them more expensive than conventional machines.

Jeffrey and his coworkers foresee yet another benefit of 3-D visualization: it may soon be possible to link intelligent software to the analysis of 3-D carotid artery images.

“The display would initially be reviewed by an artificially intelligent system,” he explains, “like a computer-analyzed ECG. If the ultrasound image is normal, a radiologist may glance only briefly at it. To find the 2% of the population that really has occlusive disease, we want a spell-checker, an intelligent system that says, ‘This is moderately abnormal, there is a little bit of plaque here. You had better look at it.'”

As with CTA and rotational angiography, virtual colonoscopy and other virtual procedures, 3-D imaging makes it possible to fly through the interior of a vessel or other hollow structures to detect disease or delineate damage. The actual display of 3-D data takes the form of volume renderings, surface shaded renderings, or maximum intensity projections, depending on the workstation and physician preference. Each display approach has advantages and disadvantages (see related article) according to whether the region of interest is soft tissue, vessel, bone, or stent.


Evidence that 3-D imaging adds value to diagnosis and clinical care continues to mount. Manufacturers upgrade the reconstruction and display software yearly, increasing their speed, improving image quality, and enhancing user-friendliness. Achieving better reimbursement — especially if new CPT codes are to be created — will require education as well as evidence, according to Fishman, who will soon join colleagues to present the collective body of knowledge on 3-D imaging to HCFA on behalf of the American College of Radiology. Success there could lead to greater reimbursement by managed care organizations and insurers as well as Medicare, while potentially making it easier for this exciting technology to continue its evolution into routine diagnostic imaging.


Sheldon M. Stern is a medical writer in Irvine, Calif, and a contributing writer for Decisions in Axis Imaging News.