Additional Resources ❯ Multidetector CT ❯ MDCT: Syllabus: General: Effective and Efficient Delivery of 3D Visualization in the Clinical Environment

Effective and Efficient Delivery of 3D Visualization in the Clinical Environment

(10-2002. 9/16)

Elliot K. Fishman, M.D.
Professor of Radiology and Oncology
Johns Hopkins University School of Medicine

Three-dimensional imaging (3D) of CT datasets was introduced shortly after clinical CT scanning became a reality in the late 1970s. Whether through work done by Gabor Herman and associates at the University of Pennsylvania or Mike Vannier and associates at the Mallinckrodt Institute of Radiology, 3D imaging was viewed as a way of abstracting more information from a series of transaxial CT scan slices. Not suprisingly early applications involved bone especially in areas like the skull and craniofacial regions (regions of high CT attenuation and anatomic zones less affected by patient motion or breathing). Although most radiologists at the time were not enthusiastic about 3D reconstructions, our referring physicians found them extremely helpful in patient management decisions, especially in complex orthopedic cases. Over the next 15 or so years, 3D imaging continued to evolve with the introduction of faster computer processing times, lower priced workstations with better price/performance profiles, and new rendering algorithms (i.e., volume rendering). Yet, despite these and many other advances, 3D imaging continued to be a study performed in a select group of institutions for a limited set of applications.

It is debatable why the progress of 3D imaging that the radiologic environment was so slow but a number of reasons have been suggested including:

high cost of workstations ($100-250,000).
perceived notion that 3D had limited clinical applications.
3D was felt to be of value only to the referring physician but not to the radiologist.
difficulty in using 3D workstations due to poor system design and limited functionality
training of radiologists on system use has been defined as poor by nearly all radiologist.
a "killer app" (application) had not been developed to drive 3D imaging into the mainstream.
major equipment vendors like Siemens Medical Systems and GE did not push 3D as a mainstream product .
poor reimbursement for 3D studies (especially the professional component).

What really began to change the equation was the development of spiral CT and the ability to obtain true volume data sets which were ideal for 3D or volume imaging. With the continued development of spiral CT scanning from a technology where one could acquire 12 seconds of data to a technology that could acquire up to 100 seconds of data, things really began to change. New applications for CT began to develop based on these new technologies and capabilities. The role of 3D imaging was becoming more of a core function of CT and inseparable especially with applications like CT angiography and virtual endoscopy. The introduction of multidetector CT and its advances for vascular imaging continued this development cycle which has been driving 3D imaging to become more of a standard exam rather than a unique procedure. In fact, every scanner manufacturer now recommends or ships a workstation capable of 3D imaging with their high-end scanners (multidetector CT scanners (MDCT). Yet, there is still the feeling among some radiologists that 3D imaging is not yet suitable for their practice. This seeming contradiction may seem hard to explain but is based in great part on the resistance of radiology and radiologists to change as well as in part to the current shortage of radiologists.

In our experience, the biggest limitations to the use of 3D imaging (and other postprocessing tools) in the clinical environment include:
A lack of understanding of the advantages provided by these techniques both from a clinical and patient care perspective.
A lack of understanding of how to use these new techniques including a lack of understanding on how to use the workstation.
A lack of understanding how to merge new technologies into a busy clinical practice that already may be overwhelmed by the volume of work and/or a staffing shortage (both radiologists and technologists).
Resistance to change especially to changes in work distribution and workflow.
Resistance to new paradigms in image interpretation and management.

These limitations can be translated into a need for:

education
training
clarification of workflow issues
staffing

None of these problems however is insurmountable and in fact can be overcome with only change needed as the necessary ingredient. I believe that education can come from any of several sources including:

CME courses including courses with hands-on sessions. For example, the RSNA as part of its annual meeting has hands-on sessions on the use of computers including medical workstations. Major equipment vendors are providing more hands-on training both off-site (central training centers) and on-site.
Reading the radiologic literature (and pertinent literature from other subspecialties) and noting the clinical role of 3D imaging especially as it applies to CT angiography.
Getting information from the vendor of your workstation including detailed hands on training on the use of the workstation and better system documentation. Training needs to be continuous for both the radiologist and the radiologic technologists.
Web-based educational sites like www.CTISUS.c where all of the 3D protocols are available including a large teaching file of illustrated 3D cases. Web-based training needs to be expanded and is currently undergoing this expansion at several sites.

Training reflects more on the ability to obtain technical expertise on a 3D imaging system. Although every workstation vendor provides some form of hands-on training it usually is but two-day duration and this may be unsatisfactory for either the radiology technologist or radiologist. It is not suprising that the most common complaint about a workstation and its use is lack of sufficient training. This problem can be solved by either the 3D vendors providing enhanced training (including through web-based training) on or off-site or for the interested parties to go to sites with similar equipment and learn in a more hands-on method. Unless there is improvement in the training available the use of 3D imaging will continue to lag other technologies.

Workflow issues and staffing are both separate but closely intertwined problems. The decision as to who does the 3D imaging (radiologist vs. technologist) and where the workstation is located are decisions that are made by individual institutions. Although my experience is one where the radiologists do the actual 3D imaging (including creating the images and filming them), other sites have found a dedicated technologist (with radiologist supervision) to be an ideal strategy. The advantages of the radiologist only works in cases where the radiologist(s) is dedicated to committing the necessary time and effort to the enterprise.

This is becoming more of an issue where most institutions are understaffed and trying to cope with the clinical load without adding new studies. However, this is shortsighted as using a technique like CT angiography will decrease the staffing (both radiologist and technologist) needed for more invasive procedures like classic angiography. In addition, our view that the future of imaging revolves around direct 3D viewing replacing axial CT scanned based imaging, which will require primary radiologist participation. One factor that will increase the radiologist's willingness to be the primary person for the 3D-image analysis is the availability of true real-time volume rendering. The real-time rendering of several new 3D systems allows the radiologist to analyze even the most complicated cases in a matter of minutes.

Other sites have found that a dedicated technologist can perform most of the routine studies and the radiologist works in a more supervisory role as well as doing the more difficult/complex cases. Advantages of this workflow relate to less of a commitment of the radiologist’s time and may provide more continuity especially in those groups where a radiologist is not based at any one hospital or office. In this model selection of the technologist is critical as they should be an individual who is willing to learn what the purpose of each study is and is committed to continuing education. The person must be self-motivated and committed to the project. The technologist will also need people-skills to deal with both the radiologist and the referring physician. This workflow issue is critical to the success of any 3D program and will need to be decided on a case to case basis.

Although it would be ideal to have multiple workstations connected over a high-speed network capable of doing 3D imaging this is rarely the case today. The decision as to where to physically place the workstation is therefore critical. I have found that it is ideal to have the workstation away from the scanner suite in a separate room or office. This allows consultation with referring physicians without interrupting the primary function of the CT scanner which is to scan patients. This separate 3D suite or lab allows for the centralization of function especially when a number of different scanners and/or modalities are networked to a single workstation. For example, at Hopkins our 3D lab is connected by a 100 megabyte backbone to scanners in the hospital, the adjacent outpatient center, the adjacent oncology center, the emergency room and a remote site 10 miles away. All images seamlessly reach the workstation for postprocessing. However, with our 3D volumes increasing to over 15 cases per day as well as the need for rapid image turnaround (minutes rather than days), the location of the workstation will soon have to be closer to the scanners and reading room.

Workflow issues are obviously a critical factor in the success of a 3D operation. The timely performance of a CT scan will be negated if there is a time lag until the 3D images are generated. Although many 3D studies do not require an immediate turnaround, other applications are very time-sensitive. These applications include acetabular fracture repair (in select cases), suspected mesenteric ischemia, and suspected aortic dissection. Training of enough staff members to cover these off-hours cases is needed to provide the 24/7 coverage demanded today. The use of 3D imaging in the acute setting is rapidly increasing.

Another problem with placing a workstation in a single central location as 3D visualization becomes a primary interpretation tool that it would need to be located in the scanner suite or in the area where films are interpreted. This would potentially require a number of workstations, which would be cost-effective if used to enhance the primary interpretation. Implementation of this paradigm is beginning especially with the new design of PC-based systems including laptop systems.

One potentially interesting new paradigm is that introduced by Terarecon of a server-thin client enterprise That is, a central server using proprietary hardware and software that can service 10 remote sites. Although the server still is expensive, the costs become more acceptable when divided by 10. The system also promises to provide the ability to consult with up to four users at different workstations. The idea of remote consultation allows the radiologists to keep a close interaction with the referring physician, and yet, does not need the radiologist's physical presence. Remember that one of the concerns with PACS is that it has been shown in several articles that physician consultations decrease between 70-80%. This may seem like a blessing some days to all of us, but in the long run, it is a danger to radiology. Only through consultation will we maintain our expertise and provide our true value.

Multidetector CT is probably the final brick that will push 3D imaging into the mainstream. Although I will not discuss the specific clinical advantages of MDCT, it is easy to conclude that any 3D application that could be done previously can be done better due to a combination of factors including narrower collimation, higher resolution imaging and faster scan times.

MDCT also has resulted in many new applications for CT now becoming a clinical reality. These include topics like mesenteric angiography for ischemia, coronary artery angiography and peripheral CT angiography. However, even more than that is the practical reality of MDCT. While in the prespiral era, a scan sequence of 35-50 images were the rule, with multidetector spiral CT a typical study may be anywhere from 150-600 slices. Even if film cost and storage were not an issue, the radiologist may become fatigued from looking at so many images. 3D imaging or volume imaging may prove to be an alternative. Viewing the entire data set as a volume with an interactive 3D real time display may be ideal. The ability to interactively segment out organs or organ systems will help with more accurate detection of disease as well as quantification of disease volumes. The use of an interactive mode will also speed up the viewing process for both the radiologist and the referring physician. Another practical factor is that studies like CT angiography cannot be truly evaluated as axial images. The CT display must be more like a classic angiogram and display the vessels in the format that show the vessels in a true vascular map. Volume rendering is ideal for this task and provides breath-taking images with the next generation of 16 slice MDCT scanners producing routine .5-.75 mm scan collimation and up to 130 scans per second there will be choice but to move toward volume viewing.

Although a detailed analysis of specific 3D applications is beyond the scope of the article, a brief listing of the direction we are going will give you the feel of how 3D imaging will become not only mainstream but a central part of imaging in the 21^st century. Although classic 3D imaging tended to focus on orthopedic imaging like acetabular fractures or tibial plateau fractures the hottest areas of interest focus on vascular imaging. The applications include:

Oncologic imaging - 3D mapping of tumor for better staging of disease as well as for surgical planning. Specific applications include staging pancreatic cancer, renal cell carcinoma, primary liver tumors as well as lung cancer.
Vascular imaging - in addition to the evaluation of aortic aneurysms and dissection we are now doing CT angiograms for mesenteric ischemia and to look at bowel activity in Crohns disease. Evaluation of carotid or renal artery stenosis are two other strong applications. CT is at least 40% cheaper than a conventional angiogram.
Organ donor imaging - 3D CT angiography is the gold standard for the preoperative evaluation of potential renal donors. It is also our study of choice for evaluating patients who are potential living related liver donors or transplant recipients.

Conclusion

The modification of an established workflow pattern is difficult and at times will seem impossible to change. This is especially true if the old system worked well and its members are satisfied with its performance. To paraphrase an old saying "everyone wants progress but no one wants change." It is only when the system becomes unworkable or unsatisfactory does the window for change open. The introduction of MDCT and the new real-time capabilities and functionality of real-time imaging will provide the impetus by creating an environment where a new paradigm will be needed. We look forward to these changes and the potential innovative solutions that will be its result.

TABLE 1

The factors, which are driving 3D imaging into the realm of a commonly used and accepted clinical study (by the radiologic community) include:

better understanding of the clinical value added of 3D imaging.
the growth of CT angiography and the demand for clinical studies by the referring physicians.
better reimbursements for 3D.
wealth of supporting data in the radiologic literature.
easier to use 3D workstations.

TABLE 2

3D CT Imaging: WorkFlow Issues. Where Should the 3D Image Processing be Done?

a dedicated 3D lab.
anywhere there is space to put a workstation.
in the CT reading area.
in the referring physicians office, clinic and/or the O.R.
near the CT scanner.

TABLE 3

The biggest limitations to the use of 3D imaging and other post-processing tools are:

a lack of understanding of the advantages provided by these techniques.
a lack of understanding of how to use these new techniques.
a lack of understanding how to merge new technologies into a busy clinical practice that already may be overwhelmed by the volume of work and/or a staffing shortage (both radiologists and technologists).

References

www.CTisus.com contains all the CT protocols for single and multidetector CT as well as complete references for all of the clinical applications.