|Volume rendered 3-D image of mesentric and renal arterial system in a patient with a cystic renal cell carcinoma. The image was produced on a PC platform, and CT data was acquired using a helical CT scanner. Courtesy of Matthew A. Barish, MD.
The use of 3-D imaging by radiologists has been previously limited to major academic imaging departments and usually performed for research rather than clinical purposes. The reasons for this are multi–factorial and consist of a series of barriers to the routine implementation of 3-D imaging. Recent advances in the fields of computer science and image acquisition have removed several of these barriers. For example, the cost of performing 3-D reconstructions was a significant barrier to the widespread use of this technology. Workstations were major capital expenses usually tied to the purchase of CT or MRI scanners. Due to the high cost of the technology, most departments purchased only a single workstation, which limited access. In addition, the user interfaces were difficult to understand, requiring training of special personnel, typically technologists, which further increased cost. The recent advances in computer processing power, data storage, and software rendering algorithms now make it possible to develop 3-D imaging workstations on a PC platform. Several vendors of imaging workstations have adopted the PC platform, which allows for the production of affordable 3-D workstations. Many of these workstations developed on PC platforms will be on display at the Radiological Society of North America annual meeting.
A discussion of the cost of 3-D imaging without a review of the reimbursement is only half of the equation. The production of 3-D images is reimbursed under the CPT code 76375 (multiplanar reconstructions [MPR], sagittal, coronal, axial, holographic, 3-D, or other), which is added to the CPT code for either CT or MRI. The global reimbursement depends on the contractual agreements with the individual third-party payors; typical global reimbursement ranges between $130 and $200. If one bills separately for technical and professional charges, the professional charge is approximately 5-10% of the global fee and the technical charge is approximately 90-95%. This method of reimbursement assumes the major cost of supplying 3-D imaging services is borne by the institution providing the technical component such as the 3-D imaging equipment and the technologists. As the technology moves from the single large workstation to the radiologist’s desktop PC or picture archiving and communications system (PACS) review station, the radiologist will be the primary person performing the 3-D reconstructions. The professional charges must be increased to reflect this transfer of work from the technologist to the radiologist. In those centers that bill globally, 3-D imaging is now becoming a revenue resource primarily due to the reduced cost of the hardware and software as well as the reduced time required to produce high-quality images. In addition, many imaging centers are now advertising their 3-D imaging capability to referring physicians in an effort to gain a competitive advantage over other imaging centers without this advanced technology.
A second former barrier to the implementation of 3-D imaging included limited access to quality image data acceptable for postprocessing. The widespread installation of helical and multidetector CT scanners, modern MRI scanners, and PACS systems allows for the acquisition and distribution of high-resolution, thin-slice data, which are necessary for the production of diagnostic high-quality 3-D reconstructions. In fact, the newer multidetector CT scanners acquire such a large number of slices that conventional methods of image review become obsolete. For example, a scan of a patient’s chest, abdomen, and pelvis may generate more than 800 images. Attempting to print these images onto film would be cost prohibitive. In addition, the amount of time that would be necessary to review these images is also unrealistic. Future PACS image review workstations with 3-D capability for reviewing multidetector CT is likely to become the norm.
Advances in 3-D imaging software and hardware as well as advances in the image acquisition technologies such as MRI and multidetector CT have led to the development of several unique clinical applications for 3-D imaging. The evaluation of complex bony fractures has long been accepted as a role for 3-D imaging. Newer rendering techniques such as volume rendering have replaced previous methods such as surface rendering or summation projections. Perhaps the most accepted clinical role for 3-D imaging is in the area of MR and CT angiography. Previously, the only method available to visualize the lumen of the blood vessels required the direct puncture of a vessel with a needle followed by the insertion of a catheter and injection of an iodine contrast agent. Noninvasive techniques such as contrast-enhanced MR angiography have replaced catheter angiography in many areas. The images acquired by MR are reviewed both as individual slices and as postprocessed images, which use 3-D MIP (maximum intensity pixel projection) postprocessing to simulate conventional angiography. The advances in CT technology now allow CT-based angiography techniques (CTA) to compete with MRI. The major advances have been in the speed of image acquisition and in the acquisition of thinner slices. CT angiography is now used routinely to evaluate thoracic and abdominal aortic aneurysms. Many centers have also adopted CTA to evaluate the intracranial vessels in patients with cerebral aneurysms or vascular malformations. CTA is also being used for preoperative planning in patients undergoing laparoscopic nephrectomy either for tumor resection or as a means of organ donation.
The drive to replace invasive diagnostic methods with noninvasive alternatives continues to promote radiologic research. One such area of intense investigation of 3-D imaging is in the field of virtual colonoscopy. The term virtual colonoscopy is used to describe the technique of acquiring thin-slice helical CT of the well-distended (air insufflated) cleansed colon followed by 3-D postprocessing to produce images similar to those obtained by conventional fiber-optic colonoscopy. The hope is that this method of visualizing the colon will replace conventional colonoscopy as a means of screening for colorectal polyps. Researchers from around the world recently met for a 2-day conference in Boston to discuss the future of the technology (2nd International Symposium on Virtual Colonoscopy, October 16-17, www.virtualcolonoscopy.net). The recent advancements that have made this technique possible are the development of helical CT scanners and fast real-time production of perspective volume rendered images. This method of 3-D postprocessing uses perspective to give a sense of depth perception. The addition of light and shadows can further highlight surface abnormalities. Researchers have reported results very similar to those of conventional colo-noscopy for the clinically significant-sized polyp. Further refinements in software will make virtual colonoscopy an economically and clinically feasible tool in the fight against colorectal cancer in the near future.
As 3-D imaging becomes more available, inexpensive, and easier to use, one can expect that the generation of 3-D images will become part of the routine work flow of image interpretation. The widespread installation of multidetector CT scanners is likely to require the fusion of 2-D and 3-D workstations for all soft-copy CT reading stations, further increasing the use of 3-D images.
Matthew A. Barish, MD, is assistant professor of radiology, Boston University School of Medicine, and vice chairman of radiology; section head, body imaging; and director, Virtual Colonoscopy Imaging Center, Boston Medical Center, Boston.