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1 Department of Radiology, University of Pittsburgh Medical Center, 200 Lothrop
St., Pittsburgh, PA 15213.
2 Departments of Psychiatry and Neurology, University of Pittsburgh Medical
Center, Pittsburgh, PA 15213.
Received November 1, 2004;
accepted after revision November 19, 2004.
Address correspondence to T. M. Blodgett. Todd Blodgett is a consultant and
speaker for PETNET Solutions.
Abstract
 Top Abstract IntroductionReasoning for This SupplementTrainingCT IssuesLegalInterpretation and ReportingClinical Utility of PET/CT...Additional Benefits of PET/CT...ConclusionReferences |
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CONCLUSION. Combining a PET tomography and CT scanner into a single unit amounts to advantages that are not merely additive, but synergistic. Even PET/CT skeptics will embrace the technology after becoming acquainted with the possibilities and will accept the reality that there is no return to PET only.
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TopAbstractIntroductionReasoning for This SupplementTrainingCT IssuesLegalInterpretation and ReportingClinical Utility of PET/CT...Additional Benefits of PET/CT...ConclusionReferences |
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As with most new imaging techniques, there are both software and hardware hurdles that continue to be examined; however, there has been a steady evolution in the design and implementation of the technique, with 16-MDCT (and greater) scanners and high-resolution PET scanners being incorporated into current commercial PET/CT devices. Referring clinicians have been eager to use PET/CT to evaluate their patients, not only because it promises superior diagnostic capabilities, but also because PET/CT offers imaging consolidation, faster scan times, and added advantages for radiation therapy planning that PET and CT separately simply do not offer. However, the variability in PET/CT protocols (particularly how the CT portion of the examination is performed), ways in which the scans are interpreted and by whom, and variability in reporting methods have led to many questions by referring clinicians, such as "I thought I had ordered a PET/CT, why do I need to order another CT scan?" "Why do I get two separate reports by two different interpreting physicians?" "What do you mean the CT is not a diagnostic CT?"
Nuclear medicine physicians and radiologists also are understandably excited about a new fusion imaging technique that has shown great promise in oncologic imaging, although their excitement is somewhat tempered by the complexities of successfully introducing this new technique into clinical practice, including where the scanner will reside (in radiology or nuclear medicine), and several difficult operational, educational, personnel, protocol, and legal issues. As a consequence, interpreting physicians ultimately have many questions, such as "where do I get the needed cross-training to read PET/CT?" "What amount of training is necessary?" "Does the CT portion of a PET/CT need to be interpreted?" "Are dual readouts between nuclear medicine physicians and radiologists necessary?" "Should I do CT with or without contrast?"
It is clear that the fusion of CT with PET represents not only a simple combination of anatomy (CT) with function (PET), but also a complex symbolic and real-life fusion of radiology with nuclear medicine, with the scanner serving as the catalyst for the inevitable union. Nuclear medicine has struggled for many years to establish PET in the mainstream of imaging, and through the many supporting studies over the past 20 years, PET has become the backbone of nuclear medicine, historically established in nuclear medicine departments; now, however, PET/CT threatens this stability.
With the increasing installation of PET/CT scanners in radiology departments, many radiologists are relying on consultation with their nuclear medicine colleagues and, at some institutions, there are joint readouts between nuclear medicine physicians and radiologists. Some will undoubtedly argue over whether PET/CT belongs in radiology or nuclear medicine but, certainly, the ultimate success of the technique will depend on the cooperation and collaboration of both disciplines. 18F-Flurodeoxyglucose (18F-FDG) is no more a simple contrast agent than a CT scan is a simple localization device that can serendipitously function as a method of performing attenuation correction.
The goal of this introductory article is to identify the most commonly encountered issues of combined PET/CT and show the wide variability in perceived possible solutions to the many issues surrounding PET/CT. This discussion will serve as a catalyst to stimulate discussion between experts in both radiology and nuclear medicine.
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TopAbstractIntroductionReasoning for This SupplementTrainingCT IssuesLegalInterpretation and ReportingClinical Utility of PET/CT...Additional Benefits of PET/CT...ConclusionReferences |
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There is little or no debate that the best outcome for patient care is a true collaborative effort by both nuclear medicine and radiology. To assess the variability in perceived possible solutions to the many issues addressed at the ARRS meeting, a survey was constructed by participants of the PET/CT consensus panel. Standardized surveys were distributed to radiologists, nuclear medicine physicians, and dually trained physicians with experience in PET/CT interpretation at several academic institutions, community imaging centers, and outpatient PET centers to gather information on the current opinions and range of possible solutions to the many complex issues surrounding PET/CT. Although these data previously were unpublished, the range of responses to some of the most commonly asked questions will be included in this first article to show the need for ongoing discussion and cooperative consensus recommendations.
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TopAbstractIntroductionReasoning for This SupplementTrainingCT IssuesLegalInterpretation and ReportingClinical Utility of PET/CT...Additional Benefits of PET/CT...ConclusionReferences |
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The first section of the multiinstitutional survey focused on training issues. Because there is a lack of programs designed to offer comprehensive training to either radiologists or nuclear medicine physicians seeking to acquire skills in PET/CT, the first set of questions addressed respondents' perceptions of reasonable training requirements and what would be reasonable training curricula for future trainees. The "reasonable PET training requirements" (days of training and supervised scan interpretations) for radiologists ranged from 3 days to a full year of PET fellowship and 25-500 supervised scans. The "reasonable cross-sectional CT training requirements" for nuclear medicine physicians ranged from 3 months to a 4-year radiology residency. Answers were biased based on the background training of the physicians. To complicate matters, there are no current training guidelines, recommendations, or certification programs for either nuclear medicine physicians or radiologists for PET/CT. Although there are several 1-day to 2-week PET and PET/CT courses for radiologists to improve their PET skills, there are few yearlong PET and PET/CT fellowships and, only more recently, are there courses aimed at teaching nuclear medicine physicians pertinent cross-sectional CT anatomy. These programs, however, have no established curricula or certification requirements. Clearly, training recommendations from experts in both fields with overview and support by professional societies are warranted. Although nothing has been published, training recommendations currently are under consideration by a joint committee including the Society of Nuclear Medicine and the American College of Radiology.
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TopAbstractIntroductionReasoning for This SupplementTrainingCT IssuesLegalInterpretation and ReportingClinical Utility of PET/CT...Additional Benefits of PET/CT...ConclusionReferences |
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Among the survey respondents, 55% felt that all CT scans performed as part of a PET/CT should be with oral and IV contrast. As might be expected, radiologists recommended the use of contrast more often than nuclear medicine physicians did, although there were several nuclear medicine physicians who recommended routine use of contrast. Eighty percent of dually trained physicians polled recommended routine use of oral and IV contrast, which suggests that when nuclear medicine physicians have additional training in radiology, they generally prefer contrast. Compared with nuclear medicine physicians in the community setting, those at academic institutions also suggested the routine use of oral and IV contrast. However, many of the community-based nuclear medicine physicians commented that the main reason they did not perform contrast-enhanced studies was a lack of medical coverage.
Among the interpreting physicians at academic institutions who thought the scans should be done with contrast, 58% also thought that additional CT protocol considerations, such as timing/rate of the contrast bolus and additional hepatic artery phase or delayed CT scans for certain tumors would likely add additional information that could prove helpful in making a diagnosis by PET/CT.
For unenhanced CT scans, there are generally two methods currently in use: full dose (140 mA) and low dose (as low as 40 mA). Some centers are using low-dose CT, occasionally referred to as "nondiagnostic CT," for attenuation correction and localization purposes, and are including a disclosure that the scan is not being performed for diagnostic purposes. However, there are several legal and logistical concerns with this technique; these are described in more detail in other articles within this supplement series. As with many of the training issues, it is clear that there is wide variability in the perceived right way or best way to do the CT portion of a PET/CT examination.
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TopAbstractIntroductionReasoning for This SupplementTrainingCT IssuesLegalInterpretation and ReportingClinical Utility of PET/CT...Additional Benefits of PET/CT...ConclusionReferences |
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Additional legal concerns involved the opinions regarding the Stark Law, which is legislation that forbids entrepreneurial ownership of CT scanners by making it unlawful to bill for such examinations. However, nuclear medicine devices in general, and PET in particular, do not fall under the Stark Law, making it possible for a physician or group of physicians to own a PET or PET/CT scanner, provided the CT portion of the examination is not billed. There are several potential ethical concerns given the current way the law is written, and quality assurance issues. Certainly, the potential for self-referral is present in the case of an oncologist or group of oncologists who have a financial interest in the success of a PET or PET/CT center. There also is a potential conflict of interest for a group of interpreting and referring clinicians to have ownership interests. Clearly, discussion of these legal issues is imperative to protect patients and physicians alike.
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TopAbstractIntroductionReasoning for This SupplementTrainingCT IssuesLegalInterpretation and ReportingClinical Utility of PET/CT...Additional Benefits of PET/CT...ConclusionReferences |
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There are also several different reporting options. These will depend largely on how the study is performed (particularly how the CT is performed and whether it will be charged), by whom the study will be interpreted, and by the development of dual ICD/CPT codes, which may narrow the possible methods for reporting. Seventy-four percent of survey respondents thought that a single report was the most useful, both for optimizing patient care and for the benefit of referring clinicians. However, many interpreting physicians fear that reimbursement may be negatively affected by dual CPT or billing codes by disallowing the ability to bill for both PET and CT. There are many potential problems with a dual interpretation/reporting method, the most extreme being the presence of discordant CT and PET reports in situations where the findings have not been corroborated by both the nuclear medicine physician and radiologist. Until dual codes are implemented, it is likely that insurance companies also will dictate to a degree the reporting methods used, with most currently requiring separate reports for CT and PET when both are charged to third party payers.
Clinical Utility of PET/CT Imaging
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TopAbstractIntroductionReasoning for This SupplementTrainingCT IssuesLegalInterpretation and ReportingClinical Utility of PET/CT...Additional Benefits of PET/CT...ConclusionReferences |
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There are alternatives to hardware fusion imaging, such as the software-based approaches that have been developed over the past 15 years or more [1-7]. Retrospective image registration by software is useful for certain applications, particularly when examining rigid structures, such as the brain, where it is relatively easy to attain accurate coregistration of images because the brain is a fixed structure within the cranial vault. These retrospective registration programs tend to be less useful for nonrigid applications, particularly in the neck and abdominopelvic regions where there is much greater potential for differences in patient positioning and organ movement. Reliance on accurate coregistration is nowhere more apparent than with lesions that are not visible on CT. This is precisely when reliance on accurate image coregistration is so important, and in these instances, it is impossible to be completely confident in localized software coregistration.
Other obvious benefits of performing combined PET/CT over PET and CT done separately include consolidation of the patient's imaging procedures, faster scan times and increased patient throughput (by not having to do a separate PET transmission scan), and the ability to use the technique for radiation therapy planning.
The most noticeable clinical benefit of combined PET/CT is improved lesion localization, with several authors reporting significant changes and improvement in lesion localization when comparing the PET portion of a PET/CT with full access to the fused PET/CT images [8-12]. One of the most frustrating aspects of FDG PET alone is the lack of anatomic detail and the uncertainty in localizing many areas of FDG accumulation. It is often difficult or impossible to differentiate specific areas of FDG uptake as physiologic or pathologic. By providing the ability to fuse accurately coregistered PET and CT data sets, PET/CT significantly reduces the magnitude of mislocalization of FDG uptake and improves the confidence level of the interpreting physicians in precisely localizing potential lesions. Many authors have also published case reports and case series describing how visualizing the fused images helped resolve potential misinterpretation of benign processes as malignant [13-22].
In addition, PET/CT has been reported to affect patient management, particularly in radiation therapy evaluation and planning [8, 23-28]. Patients undergoing radiation therapy planning have traditionally had their planning based solely on anatomic information from a CT scan performed with an approved radiation therapy immobilization pallet. With PET/CT, which can accommodate such radiation therapy pallets, both the CT and PET (fused) data sets can be exported from the acquisition workstation and imported into most planning software systems. The majority of these software packages have available up-grades with the ability to do fusion of one or more DICOM data sets. Contouring then can be performed, taking into consideration not only the anatomic information but also the metabolic data. This is particularly important when there are lesions that do not show any definite anatomic abnormality. When the lesion cannot be identified on the CT portion of the examination, radiation oncologists must rely on the metabolic or PET data for their contouring.
In the last 3 years, several reports have also emerged demonstrating the improved performance and incremental value of PET/CT over PET, CT, or PET and CT performed separately for staging patients with both Hodgkin's and non-Hodgkin's lymphoma, and lung and colorectal cancer [28-34].
One of the most beneficial applications of combined PET/CT is in restaging patients who have undergone extensive surgery or who have had significant levels of radiation, both of which tend to distort normal anatomy and cause inflammatory changes. The importance and utility of PET/CT in the restaging of several malignancies, including head and neck, colorectal, thyroid, ovarian cancer, and lymphoma also have been reported [29, 32, 35-42].
Additional Benefits of PET/CT In Terms of Lesion Localization
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TopAbstractIntroductionReasoning for This SupplementTrainingCT IssuesLegalInterpretation and ReportingClinical Utility of PET/CT...Additional Benefits of PET/CT...ConclusionReferences |
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PET Lesions Obscured by CT Artifacts
It has become essential for interpreting PET physicians to have some type
of correlative anatomic imaging to corroborate identified abnormalities.
Occasionally, the lesion may not be seen due to overlying or obscuring
artifacts. Artifacts such as streak or beam hardening can make it difficult or
impossible to see a small lymph node or an area of soft-tissue abnormality.
Before PET/CT, an interpreting PET physician would describe the general
location of the abnormality and usually convey that further precision was not
possible due to an overlying artifact. Although detecting the presence of and
localizing a lesion to a particular region can be helpful for the referring
clinician, surgeons generally need localization that is more precise. Using
combined PET/CT, provided the coregistration is accurate, the precise
localization of lesions obscured by artifacts is possible
(Fig. 2).
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Identification of Normal-Sized Malignant Nodes
There are general size criteria for characterizing a lymph node as abnormal
depending on its location and, in general, normal-sized lymph nodes range in
size from less than 1 cm up to about 1.5 cm. In addition, necrosis generally
suggests a pathologic process. However, many malignant lymph nodes appear
normal in size and do not show abnormal enhancement or necrosis, particularly
in the early stages of disease. In these cases, PET is very useful for
detecting the presence of tumor within a node, as long it is larger than the
spatial resolution of the scanner (typically > 6 mm). PET/CT typically is
more useful in cases where there is more than one normalsized lymph node in
close proximity, but only one or two of them are hypermetabolic
(Fig. 3). In these cases, it is
possible to identify and convey to a surgeon which lymph nodes that appear
normal are actually involved with tumor. Before PET or PET/CT, these patients
often were followed with serial CT until the nodes grew large enough to be
confidently called malignant or until there was visible necrosis.
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Improved Biopsy Localization Information
To increase the chances of making an accurate diagnosis with a positive
biopsy, it is important to direct the biopsy to the most metabolically active
portion of the mass, or if there are two nodules or masses in the same
vicinity, the more metabolically active lesion should be targeted for
sampling. With PET/CT, accurate biopsy sampling is possible by examining the
fused PET/CT images and directing the biopsy to the area of highest metabolic
activity (Fig. 4). However,
because contrast typically is not used for CT-guided biopsies, it often will
be necessary to print representative fused images for reference during the
biopsy procedure.
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Exclusion of Suspicious Lesions on Other Imaging
PET and PET/CT offer metabolic data not obtainable via anatomic imaging
techniques that can be used to evaluate further suspicious or equivocal
lesions found via other imaging techniques. By confirming or excluding the
presence of tumor in these patients, patient management often is affected.
Before PET/CT, patients might undergo additional surgical resection or at
least biopsy sampling to determine whether areas appearing suspicious on CT or
MRI were definitely involved with tumor. Clearly, PET/CT will have an
increasing role in differentiating posttreatment changes or anatomic variants
from residual or recurrent tumor, particularly before surgery.
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TopAbstractIntroductionReasoning for This SupplementTrainingCT IssuesLegalInterpretation and ReportingClinical Utility of PET/CT...Additional Benefits of PET/CT...ConclusionReferences |
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TopAbstractIntroductionReasoning for This SupplementTrainingCT IssuesLegalInterpretation and ReportingClinical Utility of PET/CT...Additional Benefits of PET/CT...ConclusionReferences |
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