Powering the Potential of CT Through Molecular Imaging
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CT has, obviously, made rapid strides in the last four to five years; but I would say that the best is still to come,” says Elliot K. Fishman, MD, professor of radiology and oncology at the Johns Hopkins Hospital in Baltimore and director of diagnostic imaging and body CT.
James K. Min, MD, of the Greenberg Division of Cardiology at Weill Cornell Medical College in New York City also believes the capabilities of CT technology are just beginning to be fully explored.
“The latest iterations of CT technology represent incremental advances in the field,” he says. “Increasing the number of detectors to permit whole-heart imaging in less than a heartbeat and improving temporal resolution with dual sources, or in the future stationary targets, will benefit imaging of coronary arteries that are in perpetual motion. Improving spatial resolution will be key for us to be able to differentiate accurately the exact percent of luminal diameter stenoses.”
Dushyant V. Sahani, MD, clinical instructor in radiology and director of CT imaging services at Massachusetts General Hospital in Boston, has been impressed by the advances made in CT over the past decade and feels these point to even more groundbreaking developments yet to come.
“We haven’t reached the limit for CT development at all,” Sahani notes. “Along with advances in hardware technology, there have been a lot of improvements in software technology. These improvements will continue as what they have generated is a demand and very high expectations among our clinical colleagues, which will continue to drive the growth and utilization of CT.”
Although improvements in CT are accelerating rapidly, concerns remain about radiation dose.
“If someone asked me the one feature I’d want in the next great scanner, I’d say the biggest feature is low radiation dose,” Fishman says. “Even if everything stayed the same, I’d like to see the dose be able to be dropped substantially—and substantially is probably a 50 to 80 percent level. I think the new scanners will combine very low dose, in the 10 to 30 percent range of where we are now, with improved spatial resolution and substantially improved temporal resolution.”
The relatively recent fusing of CT with PET and SPECT has allowed clinicians from a variety of medical specialties to exploit the potential of CT in combination with traditional nuclear modalities and improve patient care.
CT expands capability of PET
Marvin Burns, president of Las Vegas, Nev.-based healthcare market research firm Bio-Tech Systems, attributes much of the growth of PET imaging to the deployment of PET/CT systems.
“The overlap between PET and radiology, which was stimulated by the success of combined PET/CT systems, has allowed radiologists to promote the advantages of multi-modality imaging to both patients and investors in PET imaging facilities,” Burns says. “As the availability of PET increases and its capabilities become more visible to referring physicians, it will encourage procedure growth in oncology as well as cardiology and neurology.”
By combining CT and PET in a single system, the hybrid molecular imaging modality has been somewhat able to move beyond the traditional turf of nuclear medicine to be utilized by other clinical specialties, but is far from reaching its full potential in terms of being the standard of care in oncology for diagnosis, staging and restaging of disease.
“An important factor thus far in the success of PET/CT was that it introduced an image format familiar to radiologists, while adding important anatomic information regarding metabolically active tissue,” Burns notes. “The concept was originally sold to radiologists as CT imaging enhanced with PET as a contrast agent. One effect was that it brought radiologists and nuclear physicians closer together and also helped referring physicians understand the information conveyed by the images. This added confidence in the overall diagnostic workup.” This type of cooperation is ideal and when carried across the entire continuum, would provide patients with more efficient management of disease on the part of their providers.
Reimbursement for procedures has played a large role in the growth of PET/CT, according to Burns.
“Procedure volume also is increasing due to approvals of indications such as breast imaging, and expanded use of PET in diagnosing lung cancer, colon cancer, lymphoma, and melanoma,” he notes. “And although the dominant focus of PET is still in oncology, cardiology applications are expanding in diagnosing myocardial viability and follow-up to equivocal SPECT studies. Procedure volume also is being stimulated by the availability of PET/CT with multislice configurations suitable for cardiac imaging.”
Rondal Korn, MD, PhD, a board-certified radiologist and nuclear medicine physician, has recognized the potential for cardiac PET/CT and developed a program for his Phoenix area private practice, Scottsdale Medical Imaging.
“The value of PET/CT is that cardiac SPECT studies can be difficult to interpret because of artifacts, problems with image acquisition, and the build of the patient,” Korn says. “PET/CT helps clarify the equivocal SPECT.”
In addition to providing greater diagnostic certainty for cardiologists, PET/CT has the side benefit, through the CT portion of the exam, of capturing thoracic anatomic information. These images have allowed Korn, through his extensive radiological education and experience, to discover malignancies for which the patient did not present, also known as “incidentalomas.”
“The same patients who are at risk for coronary artery disease because of smoking or other bad habits are also at risk for lung cancer,” he notes. “We’ve found in about 1 to 2 percent of our population an incidental finding that required aggressive evaluation for cancer.”
Paul D. Shreve, MD, also has found the pairing of CT and PET to be of significant clinical value due to the combination of CT’s anatomical imaging strengths with PET’s functional imaging capabilities.
“Adding molecular imaging probes such as FDG to CT imaging has been of great clinical importance,” says Shreve, medical director of the PET Medical Imaging Center at Advanced Radiology Services in Grand Rapids, Mich., and medical director for PET/CT at the West Michigan Cancer Center in Kalamazoo.
He also notes that the hybrid modality offers the capability for practices to expand their service lines beyond traditional CT imaging.
“Many facilities operating PET/CT systems bolster their return on investment for the technology by using it as a dedicated CT scanner when they’re not using it for PET/CT studies,” he says.
With the recent publication of results from the National Oncologic PET Registry (NOPR) providing evidence-based data that PET/CT delivers considerable benefits for patient care and management, the technology is poised for more widespread deployment. Fishman notes that PET/CT is an imaging modality with potential yet to be fully explored.
“I think you’ll see continued growth in the whole area of PET/CT,” he says. “One can look at it not as PET/CT, but as CT/PET. What PET really is, is just one more contrast agent for CT. [In the future,] we will have more-specific contrast agents that light up at certain sites, whether it’s for Alzheimer’s or for different types of tumors, and CT will be able to take significant advantage of that.”
SPECT gains clinical clarity with CT
Since its commercial introduction, SPECT/CT has been steadily winning converts as the technology increases its deployment. The response from clinicians conducting studies with the equipment, as well as their referrers, has been nothing short of enthusiastic.
Nuclear medicine physicians utilizing SPECT/CT no longer have to hear the old bromide about “unclear medicine;” the anatomic detail of CT paired with the functional capabilities of SPECT is delivering exams that are increasing diagnostic certainty, reducing the need for additional imaging procedures, and providing precise roadmaps for surgical interventions.
One of the greatest advantages to using SPECT/CT is that the specificity of the diagnoses from the department has been greatly enhanced, says Jean Luc Urbain, MD, PhD, chief and chair of nuclear medicine at the University of Western Ontario, Schulich School of Medicine and Dentistry in London, Ontario.
“Now that we have the capability to view the functional and anatomic aspects of the exam together, we are very confident about the localization of what we see,” he notes. “Overall, it has improved tremendously our ability to diagnose accurately.”
Stephen Scharf, MD, chief of nuclear medicine at Lenox Hill Hospital in New York City, performs a wide range of oncologic and musculoskeletal exams with SPECT/CT.
“The utilization of SPECT/CT has improved our diagnostic capabilities in patients presenting with thyroid cancer,” says Hemalatha Rao, MD, chair of nuclear medicine at Coney Island Hospital, a multi-site community medical center serving southern Brooklyn. “Before, we were able to determine that something was in the neck; but now we can tell specifically if it is in the thyroid gland, the lymph node, the muscle, or the bone.”
Molecular expansion of CT?
While the molecular imaging industry has seen tremendous growth from the addition of CT capabilities to PET and SPECT modalities, in fact almost completely driving out the existence of PET scanners without a CT, this hybrid technology has only successfully driven radiology and molecular imaging specialists together on a small scale. The benefits have been obvious in molecular imaging, but can they extend into radiology? Can CT continue to advance without the convergence of molecular technology? The capabilities of CT have grown exponentially, but axial slice capabilities will eventually have diminishing returns. The power of CT needs to be revved up and there are some who think this is just the tip of the iceberg.
“I think we’re at the beginning of where CT is going to take us as a diagnostic tool,” says Daniel S. Berman, MD, president of the SCCT and professor at the University of California, Los Angeles School of Medicine and chief of cardiac imaging and nuclear cardiology at the S. Mark Taper Foundation Imaging Center at Cedars-Sinai Medical Center in Los Angeles.
“When we think we’ve reached the maximum, the next year we turn around and we realize that something better has come out,” Berman says. “For example, the dual-source CT cut the temporal resolution in half and a 320-slice scanner can scan the entire heart in one heartbeat.”
As it stands, even the most exquisite CT images leave unanswered clinical questions and could benefit from the addition of molecular contrast to add metabolic information piece that’s missing in traditional CT imaging. The potential for CT continues to expand, and this expansion might be as close as the molecular imaging department.