Computer-assisted detection (CAD) software to analyze lung imaging studies is steadily gaining ground, improving in sensitivity and specificity as a increasingly reliable second pair of trained eyes to aid radiologists in the detection of pulmonary nodules. While more radiologists are championing the technology, the lack of PACS integration is a stumbling block for widespread adoption. At the same time, what first emerged as a tool for detection is transforming into a tool for characterization and possible diagnosis, while expanding its utilization beyond pulmonary diseases and lung cancer.
A second reader that makes sense
Lung CAD software was developed primarily for the detection of pulmonary nodules, which can be overlooked by radiologists reading chest x-rays and lung CTs. The software has been refined over the last few years, overcoming initial speculation regarding its efficacy with recent clinical studies that have validated its performance.
“Chest x-ray CAD makes sense—it helps to find nodules in the lungs on an x-ray that has superimposed soft tissues, skeletal structures, mediastinal structures—the problem is that it seems to be oversensitive in areas of overlapping bones such as the anterior rib and posterior rib crossings,” says Judith K. Amorosa, MD, clinical professor, radiology at Robert Wood Johnson School of Medicine in Piscataway, N.J., who uses the IQQA-Chest CAD enterprise solution from EDDA Technologies.
Lung CT CAD finds nodules which need to be distinguished from blood vessels and pleural reflections. It also can be useful for less experienced readers for confirmation of a possible finding. Used by less-experienced readers, CAD for chest x-rays (CXRs) will likely lead to more chest CTs, however, it is less expensive than a second reader, Amorosa notes.
Achieving a high level of sensitivity and specificity with the actual software, at a level where radiologists find it helpful in their day-to-day work, has been a challenge, adds Heber MacMahon, MB, BCh, professor of radiology at the University of Chicago and director, section of thoracic imaging.
Using the OnGuard lung CAD system from Riverain Technologies, MacMahon and colleagues sought to determine the sensitivity and number of false-positive marks for identifying lung cancers that were detected but misinterpreted on chest radiographs by radiologists. The OnGuard system marked 35 percent of lung cancers that had been previously overlooked, according to the study results that appeared in Radiology (January 2008).
Despite its sensitivity, the software tends to have a relatively high number of false positives, marking not only the nodules but also parts of normal anatomy which becomes distracting and time-consuming for the radiologist, he says, stressing the importance of reducing the number of false positives while maintaining sensitivity so tool aids radiologists rather than slowing them down.
Another bone of contention is determining not when the software should be applied, but how. Lung CAD might have started as a means of detection but systems are now being developed to diagnose and characterize lung nodules, offering temporal comparisons to give growth rate and doubling time. Some systems also offer tools that address density, borders and the overall appearances of the nodule, says Heidi Roberts, associate professor of radiology, University Health Network in Toronto.
“The benefit to temporal characterization that will quantify these features is ultimately an improvement in workflow and patient management,” Roberts adds. For example, in a patient with interstitial lung disease, lung CAD can be helpful in characterizing the disease, with the radiologist and pulmonologist being able to assess whether the patient is responding to treatment.
“Every CAD software has its strengths and weaknesses—the question that is difficult to answer is, do we only need CAD for lung nodule detection or do we want it for additional disease detection?” she notes, adding that lung CAD software vendors are looking outside nodule detection to other pulmonary diseases such as emphysema quantification or other airway diseases. Further studies, however, remain to be done to validate usage beyond lung nodule detection.
While some radiologists are believers in widespread lung CAD applications for digital chest x-rays or lung CTs, others are more selective. Regardless of what side of the fence you are on, the ubiquity of lung CAD utilization could primarily be hindered by one thing—integration with PACS.
There are programs currently available that radiologists would use but they aren’t simply because they are not integrated into the PACS. Instead, the software is available on a separate dedicated CAD workstation, a set up that is not practical given the reality of a radiologist’s workflow. “It needs to be highly integrated into PACS and once it happens, it is going to have a big impact on utilization,” MacMahon comments.
Roberts concurs, recommending that the software be centralized on a server and available across all workstations within the department, and ideally, it should be integrated into existing reading software.
Integration is something the University of Munich is familiar with. They are using Siemens Healthcare’s syngo CAD Manager as an enabler for syngo Lung CAD and syngo Chest X-ray (CXR) CAD to network the multiple sites within the university. The syngo CXR CAD, which is not available for sale in the United States, is used to detect lung nodules in digital chest x-ray studies that are integrated with the syngo CAD Manager for viewing CAD results on PACS workstations, according to Peter Herzog, MD, fellow of radiology, at the Institute for Clinical Radiology.
Hospitals, departments and practices must consider their infrastructure and workflow to choose a product that best supports their needs, he says, adding that it must be easy and convenient to use, otherwise it will not be used in all cases. For large institutions with more than one scanner and more than one reading room, Herzog says lung CAD software needs to be server-based with results available on PACS, whereas for a small practice with one scanner and one reading station, a dedicated CAD workstation might make practical sense.
Meanwhile, other facilities are trying to filter lung CAD utilization through the high volume of patients being scanned, as is the case at the Hospital Peset in Valencia, Spain. For the last year, radiologists have been using the LMS Lung CAD from Median Technologies for chest CT analysis—specifically for serendipitous findings of pulmonary nodules in a regular CT, or for lung cancer screenings for heavy smokers, says Jose Vilar, MD, chairman of the radiology department.
Additionally, they have seen a great impact in oncology and pulmonology, mainly because it is easier to identify lung nodules, obtain objective measurements and see the growth and how treatment is affecting the nodules, Vilar says. Additional sophistication could possibly include structured reports in oncology that could come from lung CAD classifying items, adds Vilar.
Herzog adds that using lung CAD for scans performed for other indications than cancer, such as trauma or to rule out pulmonary emboli, has produced results regarding the clinical outcome or change in regime for these patients.
What the future holds
While many clinical users feel that lung CAD utilization will increase even more once reimbursement picks up in the United States, MacMahon speculates that its future doesn’t necessarily hinge on attaining reimbursement. “The hope is that if these systems become sophisticated enough and accurate enough, then radiologists will just simply want to use them for the greater level of assurance they can provide.”