The literature that has recently been coming out of nuclear medicine indicates that two really are better than one, at least for imaging modalities. “The literature is beginning to show that PET/CT is the ideal way to do a lot of things already being done but to decrease the confusion in doing it,” said Robert E. Henkin, MD, FACNP, FACR, with UNM, Ltd in Lombard, Ill.

PET/CT combines the two modalities to image anatomic structures and metabolic information simultaneously. PET/CT hybrid units have been found to be superior to either modality alone or combined using fusion technology or side-by-side comparisons. Advantages include co-registration, faster scanning, and better attenuation.

Henkin recently completed a review of relevant articles and found that in studies of older technologies, positive rates for lesions were close to 50%. With PET/CT, they dropped significantly, primarily through the elimination of false positives. “PET/CT produces just a small improvement in finding lesions but a big improvement in specificity,” said Henkin.

Unfortunately, it comes at a price. PET/CT units are more expensive than single modalities, and shrinking reimbursement rates mean longer periods to realize a return on investment. The resulting economics can create difficulties justifying the cost, but expanded volumes and applications may help to provide some justification. As physicians realize the value provided by the hybrid modality, they often order more PET/CT scans.

Although PET/CT can be expected to follow a normal technological adoption curve, which eventually plateaus, the hybrid modality is still in its adoption phase and has not yet crested its popularity. The use of PET/CT can be expected to increase as more PET units are replaced with hybrid devices and more PET/CT applications are developed.

Ahead of the Curve

According to a report by the IMV Medical Information Division in Des Plaines, Ill, an estimated 1,129,000 clinical PET studies were performed in the United States in 2005. These included exams completed using PET/CT devices, PET alone, mobile units, and nuclear medicine cameras with coincidence detection.

Although the proportion of these exams was not determined, the report did find an increase in the acquisition of hybrid PET/CT machines. The study quotes IMV’s senior director of market research, Lorna Young, who noted that the proportion of PET/CT scanners, versus PET alone, that had been installed up until 2005 was approximately 55%, but that in 2005, more than 90% of the units installed were PET/CT.

“PET/CT technology has been in commercial use for just 5 to 6 years, but more hybrid units are being installed now than stand-alone PET,” said Amjad Ali, MD, professor of diagnostic radiology and nuclear medicine at Rush University in Chicago. He suggests the medical community may reach a point in the next few years where PET-only scanners are ordered solely for research needs and no longer for clinical settings.

Peeyush Bhargava, MD, chief of nuclear medicine at the Michael E. DeBakey VA Medical Center in Houston, has found the use of PET/CT tends to vary by facility. “In my previous position at St Luke’s-Roosevelt Hospital Center [New York], we performed about 10 to 15 PET/CT scans a day, most for oncologic indications. Results were presented at tumor boards, and images were sent to reference physicians, which created a lot of awareness. At [the DeBakey center], we do not currently have a PET/CT scanner. Patients are sent for scans on a fee basis, but the technology is underutilized,” said Bhargava.

That can be expected to gradually change since the facility has plans to add a PET/CT scanner within the next few months. Its presence will likely lead to an increase in the hybrid modality’s use, mirroring the community at large. Most expect the use of PET/CT to expand—to new facilities (the IMV report found 1,725 sites in the United States performing PET/CT) and to new applications.

Not Just Oncology

Most of this use occurs in oncology, but the proportion is expected to expand as new uses are researched and found to be efficacious. The IMV report found that 93% of patient studies performed on PET or PET/CT were for oncologic indications with the remaining 7% applied to cardiac and neurological indications.

Ali notes this statistic is accurate. “Right now, oncology represents about 90% to 95% of the work being done, but the numbers can differ depending on a practice and its typical patients,” said Ali.

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PET/CT’s usefulness in oncology is extensive, particularly because of the metabolic capabilities of PET. The University of Maryland Medical Center, Baltimore, reports that PET is considered particularly effective in the detection, staging, treatment, and recurrence monitoring for cancer. Its use covers a wide range of malignancies, including lung (“particularly non-small cell lung cancer,” said Bhargava), brain, cervical, colorectal, esophageal, head and neck, lymphoma, and thyroid.

The ability to measure metabolism alongside anatomy also has been found to have indications in neurology and cardiology. PET/CT can help to characterize brain activity, detecting the presence of disease, differentiating among potential neurological conditions, and localizing diseased areas. In the heart, the modality has been found to measure perfusion in addition to the metabolic rate, providing information on blood flow, muscle damage, and myocardial viability.

Shrinking Reimbursement

Piece By Piece

Segmentation is a tool pulled from the CT toolbox that helps physicians identify and measure anatomical structures. Traditionally, the work is done by a specialist, who spends significant time outlining structures and performing manual calculations. Naturally, a more automatic process, such as that provided through software, can reduce the time and increase the reproducibility of the results.

“Automated features allow clinicians to arrive at an answer faster and without having to eyeball reproducibility,” said Doug Hussey, an application specialist with Merge Healthcare in Toronto, parent company of Cedara Software.

In the PET/CT toolbox, segmentation can be used to determine the standardized uptake value (SUV) or whole volume of tumors. “Volume is the best indicator of size but not always the most reliable, since the calculations are so time-consuming and complicated. To repeat them over and over manually is difficult,” said Hussey. Subsequently, physicians will rely on measurement of the diameter of the tumor’s longest proportion. “But if the process is automated, whole volume gets easier,” said Hussey.

Manual outlining of the desired segment and the calculations lie at one end of the scale; at the other end is software that brings structures out automatically. The trade-offs impact time and accuracy. “Radiologists will save time with software that performs these functions automatically, but they will have to make sure that they are looking at what they want to see,” said Hussey.

Many of the more common protocols have been approved by the Centers for Medicare and Medicaid Services (CMS) for PET, but none have been approved for reimbursement of PET and CT reported together despite the increased cost of the hybrid modality. PET/CT devices cost more than PET-only machines, and facilities can find it difficult to justify the extra cost.

In the 2005 edition of Basics of PET Imaging: Physics, Chemistry, and Regulations, Gopal B. Saha estimates the total capital cost for a $1.5 million PET scanner, along with PET room construction and/or renovation, a hot lab, and radiation safety equipment, can run $1.7 million. That cost climbs for hybrid machines. Saha notes PET/CT devices start at $1.7 million and can run as much as $2.5 million, meaning initial capital costs could be as much as $2.7 million.

CMS’s reimbursement policy, however, does not compensate for this extra cost. In addition, the organization has been decreasing the dollar amount reimbursed for PET exams. “If reimbursements continue to decline, it could slow the adoption of PET/CT,” said Ali.

“When a hospital or practice evaluates the expected return on investment for PET/CT, it finds that the return for a PET scanner can be realized more quickly. Institutions that already have PET are looking at it and saying, ‘I really want PET/CT, but how can I justify it economically when the differential in reimbursement is so small?'” said Henkin, suggesting this can influence the likelihood of making the acquisition.

Asked why Medicare might implement such a policy, Henkin theorizes the reason is tied to the quality of the CT scan acquired by hybrid PET/CT devices. “Traditionally, the CT scan acquired with a PET/CT device is not the equivalent of a full diagnostic CT scan because it has been performed for anatomic correlation. Medicare therefore views the CT portion of PET/CT as a less valuable exam and won’t reimburse it in the same way. However, newer hybrid technologies are now incorporating full diagnostic CT scans, eliminating that concern,” said Henkin.

Despite this, Henkin does not expect CMS to revisit the issue in the near future, particularly in view of the organization’s cost-cutting behavior. Many in radiology are closely watching where the DRA goes next. Therefore, many, like Henkin and Ali, see cost as becoming prohibitive to PET/CT, though Henkin holds out hope that the technology can be “redescribed” in the future. “But that is a longer-term issue,” Henkin said.

Best Protocols

Finances, however, are not the modality’s only limitation. Bhargava suggests that the community is still trying to maximize PET/CT technology, particularly through the determination of specific protocols. “In terms of protocol patterns, we can ask whether the PET or CT scan is more important? Whether contrast should be used? If so, whether it should be administered orally or through an IV?” asks Bhargava.

Some of the answers depend on who will read the exam. “A radiologist would most likely prefer to read a contrast-enhanced CT in correlation with PET, while a specialist in nuclear medicine would choose to read PET with a correlation to CT,” said Bhargava.

Even so, Bhargava suggests that the best protocol is the one that is indicated. “For instance, patients with abdominal malignancies, including colon and lung cancers, would need IV contrast for the CT portion of the scan,” said Bhargava.

New protocols are in development for the evaluation of infections and inflammation, “including fever of unknown origin,” said Bhargava. And there is much room for growth in the fields of neurology and cardiology. Protocols and economics may, therefore, drive the future development of the hybrid technology. “How these machines look might be different in 4 or 5 years,” suggests Henkin.

That PET/CT will be around is no longer hotly contested. “PET/CT has proven its clinical place, and its applications will continue to expand. Up to now, PET/CT has gone where PET went and shown it could do a better job, but we haven’t yet shown what it can do that PET can’t do at all,” said Henkin. The research can be expected to reveal even more reasons why two are better than one.

Renee Diiulio is a contributing writer for Axis Imaging News. For more information, contact

Reimbursement Reality

The Centers for Medicare and Medicaid Services (CMS) lists the following reimbursement protocols for PET:

  • Characterization of solitary pulmonary nodules;
  • Diagnosis, staging, and restaging of lung cancer;
  • Staging and restaging of particular breast cancers;
  • Adjunct to standard imaging modalities for staging of specified patients and the monitoring of tumor response in specific women with breast cancer.
  • Diagnosis, staging, and restaging of colorectal cancer, as well as determination of the location of tumors if rising CEA levels suggest recurrence;
  • Diagnosis, staging, and restaging of esophageal cancer;
  • Diagnosis, staging, and restaging of head and neck cancers, excluding CNS and thyroid;
  • Diagnosis, staging, and restaging of lymphoma, as well as the staging and restaging of lymphoma when PET is used as an alternative to a gallium scan,
  • Diagnosis, staging, and restaging of melanoma (noncovered for evaluating regional node), as well as the evaluation of recurrence prior to surgery as an alternative to a gallium scan;
  • Restaging of particular thyroid cancers;
  • Primary or initial diagnosis of myocardial viability, as well as following inconclusive SPECT;
  • Presurgical evaluation of refractory seizures; and
  • Noninvasive imaging of perfusion of the heart using rubidium 82 tracer and ammonia N-13 tracer.

MR in the Mirror?

If PET/CT is catching on, can PET/MR be far behind?

Too hard to say, according to experts Axis Imaging News spoke with. Development of the two hybrid technologies is completely unrelated, but if PET/MR proves as useful as PET/CT, it’s likely to find its way to market. At least one research prototype already exists.

  • “Just because we can do something, doesn’t mean it’s good. We need to know if PET/MR offers anything more diagnostically than what we have today,” said Robert E. Henkin, MD, FACNP, FACR, UNM, Ltd, Lombard, Ill. Specifications for applications rather than speculation will help to clarify the modality’s capability.
  • Peeyush Bhargava, MD, chief of nuclear medicine at the Michael E. DeBakey VA Medical Center in Houston, believes the technology will come to market, but that it will require “time to find its niche.”
  • Amjad Ali, MD, professor of diagnostic radiology and nuclear medicine at Rush University in Chicago, cites cost as an impeding factor in commercialization. “PET and MR are already expensive modalities. Added together, cost becomes an even bigger issue,” said Ali. He suspects it could take another decade before PET/MR makes a commercial entry.