Concurrent PET/CT with an Integrated Imaging System: Intersociety Dialogue from the Joint Working Group of the American College of Radiology, the Society of Nuclear Medicine, and the Society of Computed Body Tomography and Magnetic Resonance

Application of the long axial field-of-view PET/CT with low-dose [18F]FDG in melanoma

AIM

The recent introduction of long axial field-of-view (LAFOV) PET/CT scanners has yielded very promising results regarding image quality and sensitivity in oncological patients. We, herein, aim to determine an appropriate acquisition time range for the new long axial field of view Biograph Vision Quadra PET/CT (Siemens Healthcare) using low dose [¹⁸F]FDG activity in a group of melanoma patients.

METHODOLOGY

Forty-nine melanoma patients were enrolled in the study. All patients underwent total body PET/CT from the top of the head through the feet in two bed positions (field-of-view 106 cm) after i.v. injection of 2.0 MBq/kg [¹⁸F]FDG. The PET images of the first bed position (head to upper thigh; PET-10) were reconstructed and further split into 8-min (PET-8), 6-min (PET-6), 5-min (PET-5), 4-min (PET-4), and 2-min (PET-2) duration groups. Comparisons were performed between the different reconstructed scan times with regard to the visual evaluation of the PET/CT scans using the PET-10 images as reference and by calculating the 95%-CI for the differences between different time acquisitions. Moreover, objective evaluation of PET/CT image quality was performed based on SUV calculations of tumor lesions and background, leading to calculation of liver signal-to-noise ratio (SNR), and tumor-to-background ratio (TBR).

RESULTS

A total of 60 scans were evaluated. Concerning visual analysis, 49/60 (81.7%) PET-10 scans were pathological, while the respective frequencies were 49/60 (81.7%) for PET-8 (95%-CI: - 0.0602-0.0602), 49/60 (81.7%) for PET-6 (95%-CI: - 0.0602-0.0602), 48/60 (80%) for PET-5 (95%-CI: - 0.0445-0.0886), 46/60 (76.7%) for PET-4 (95%-CI: - 0.0132-0.1370), and 45/60 (75%) for PET-2 (95%-CI: 0.0025-0.1593). In 18 PET-10 scans, the extent of metastatic involvement was very large, rendering the accurate calculation of [¹⁸F]FDG-avid tumor lesions very complicated. In the remaining 42 PET-10 scans, for which the exact calculation of tumor lesions was feasible, a total of 119 tumor lesions were counted, and the respective lesion detection rates for shorter acquisitions were as follows: 97.5% (116/119) for PET-8 (95%-CI: 0-1), 95.0% (113/119) for PET-6 (95%-CI: 0-1), 89.9% (107/119) for PET-5 (95%-CI: 0-2), 83.2% (99/119) for PET-4 (95%-CI: 1-2), and 73.9% (88/119) for PET-2 (95%-CI: 2-4). With regard to objective image quality evaluations, as a general trend, the reduction of acquisition time was associated with a decrease of liver SNR and a decrease of TBR, although in lesion-based analysis the change in TBR and tumor SUV_mean values was non-significant up to 6 and 5 min acquisitions, respectively.

CONCLUSIONS

In melanoma, low-dose LAFOV PET/CT imaging is feasible and can reduce the total scan time from head to upper thigh up to 5 min providing comparable diagnostic data to standard lengths of acquisition. This may have significant implications for the diagnostic work-up of patients with melanoma, given the need for true whole-body imaging in this type of cancer.

Quantitative positron emission tomography imaging in the presence of iodinated contrast media using electron density quantifications from dual-energy computed tomography

PURPOSE

As preparation for future positron emission tomography (PET)/dual-energy computed tomography (DECT)T imaging modality and new possible clinical applications, the study aimed to evaluate the utility of clinically available spectral results from a DECT system for improving attenuation corrections of PET acquisitions in the presence of iodinated contrast media. The dependence of the accuracy of PET quantification values, reconstructed with conventional and spectral-based attenuation corrections, was examined as a function of the amount of iodine content and x-ray radiation exposure.

METHODS

Measurements were performed on commercial PET/CT and DECT systems, using a semi-anthropomorphic phantom with seven centrifuge tubes in its bore. Five different configurations of tube contents were scanned by both PET/CT and DECT. With the aim of mimicking clinically observed concentrations, in all phantom configurations the center tube contained a high concentration of radionuclide while the peripheral tubes contained a lower concentration of radionuclide. Iodine content was incrementally increased between phantom configurations by replacing iodine-free tubes with tubes that contained the original radionuclide concentration within a 10 mg/ml iodine dilution. DECT-based attenuation correction maps were generated by scaling electron density spectral results into corresponding 511 keV photon linear attenuation coefficients.

RESULTS

Mean SUV values obtained from the nominal PET reconstruction, using conventional CT images as input for the attenuation correction, demonstrate a monotonic increase of 8.6% when the water and radionuclide mixtures were replaced by iodine, water, and radionuclide (same level of activity) mixture. Mean SUV values obtained from the DECT-based reconstruction, in which the attenuation correction utilizes electron density values as input, demonstrate different, more stable behavior across all iodine insert configurations, with a standard deviation to mean ratio of less than 1%. This observed behavior was independent of the area size used for measurement. A minor radiation dose dependency of the electron density values (below 0.5%) was observed. This resulted in consistent (iodine independent) PET quantification behavior, which persisted even at the lowest radiation dose levels tested in our experiment, that is, 25% of the radiation dose utilized for CT acquisition in the clinical PET/CT protocol.

CONCLUSIONS

Utilization of DECT-generated electron density estimations for attenuation correction benefit PET quantification consistency in the presence of iodine and at nominal and low DECT radiation exposure levels. The ability to correctly account for iodinated contrast media in PET acquisitions will allow the development of new clinical applications that rely on the quantitative capabilities of spectral CT technologies and modern PET systems.

ACR Practice Parameter for the Performance of Gallium-68 DOTATATE PET/CT for Neuroendocrine Tumors

Radiopharmaceuticals targeting cell surface expression of somatostatin receptors (SSTRs) are particularly useful in the evaluation of neuroendocrine tumors. Gallium-68 DOTA-Tyr-octreotatate (Ga-DOTATATE) primarily binds to SSTR type 2 receptors. Ga DOTATATE PET/CT is proven to have high impact on the management of neuroendocrine patients compared to traditional anatomical imaging as well as provides additional information over that of conventional nuclear medicine studies (indium-III DTPA-octreotide). It can result in change in management of approximately 75% of patients with neuroendocrine tumors. Ga DOTATATE and F FDG PET/CT imaging are complementary, with the degree of uptake varying depending on the degree of differentiation of the tumor. Well-differentiated tumors maintain their SSTRs and are positive on Ga DOTATATE PET/CT scan, while dedifferentiated tumors are less likely to demonstrate uptake of Ga DOTATATE but will demonstrate uptake with F FDG PET/CT. In addition, Ga DOTATATE PET/CT identifies patients with SSTR expression in their tumors, who have progressed on somatostatin analog therapy, for treatment with Lu DOTATATE.

ACR-ACNM Practice Parameter for the Performance of Fluorine-18 Fluciclovine-PET/CT for Recurrent Prostate Cancer

The American College of Radiology (ACR) and American College of Nuclear Medicine (ACNM) collaborated to develop a clinical practice document for the performance of fluciclovine positron-emission tomography (PET) / computed tomography (CT) in the evaluation of patients with suspected prostate cancer recurrence based on the elevation of prostate-specific antigen (PSA) level (biochemical recurrence) after prior therapy. Prostate cancer is the third leading cause of cancer death in the United States. Up to 50% of patients diagnosed with prostate cancer will develop biochemical failure after initial therapy. The differentiation of local from extraprostatic recurrence plays a critical role in patient management. The use of functional imaging targeting features of cancer metabolism has proven highly useful in this regard. Amino acid transport is upregulated in prostate cancer. Fluciclovine (anti-1-amino-3-F-18-fluorocyclobutane-1-carboxylic acid, FACBC, Axumin™) is an artificial amino acid PET tracer which demonstrates utility in the diagnosis of recurrent prostate cancer with significant added value to conventional imaging.

Gene Regulation and Targeted Therapy in Gastric Cancer Peritoneal Metastasis: Radiological Findings from Dual Energy CT and PET/CT

Gastric cancer remains fourth in cancer incidence worldwide with a five-year survival of only 20%-30%. Peritoneal metastasis is the most frequent type of metastasis that accompanies unresectable gastric cancer and is a definitive determinant of prognosis. Preventing and controlling the development of peritoneal metastasis could play a role in helping to prolong the survival of gastric cancer patients. A non-invasive and efficient imaging technique will help us to identify the invasion and metastasis process of peritoneal metastasis and to monitor the changes in tumor nodules in response to treatments. This will enable us to obtain an accurate description of the development process and molecular mechanisms of gastric cancer. We have recently described experiment using dual energy CT (DECT) and positron emission tomography/computed tomography (PET/CT) platforms for the detection and monitoring of gastric tumor metastasis in nude mice models. We have shown that weekly continuous monitoring with DECT and PET/CT can identify dynamic changes in peritoneal metastasis. The sFRP1-overexpression in gastric cancer mice models showed positive radiological performance, a higher FDG uptake and increasing enhancement, and the SUVmax (standardized uptake value) of nodules demonstrated an obvious alteration trend in response to targeted therapy of TGF-β1 inhibitor. In this article, we described the detailed non-invasive imaging procedures to conduct more complex research on gastric cancer peritoneal metastasis using animal models and provided representative imaging results. The use of non-invasive imaging techniques should enable us to better understand the mechanisms of tumorigenesis, monitor tumor growth, and evaluate the effect of therapeutic interventions for gastric cancer.

Nuclear medicine at a crossroads

The growth of molecular imaging heightens the promise of clinical nuclear medicine as a tool for individualization of patient care and for improvement of health-care outcomes. Together with greater use of integrated structure-function imaging, clinical nuclear medicine reaches beyond traditional specialty borders into diagnostic radiology and oncology. Yet, there are concerns about the future of nuclear medicine, including progressively declining reimbursement, the competitive advantages of diagnostic radiology, limited translation of research accomplishments to clinical diagnostic imaging and patient care, and an insufficient pool of incoming highly qualified nuclear medicine clinicians. Thus, nuclear medicine views itself as being at a critical crossroads. What will be important is for nuclear medicine to be positioned as the quintessential molecular imaging modality more centrally within medical imaging and for the integration of nuclear medicine with primary care specialties to be driven more by patient needs than by specialty needs. In this way, the full potential of nuclear medicine as an effective and efficient tool for improving patient outcomes can be realized.

Image-based biomarkers in clinical practice

The growth of functional and metabolically informative imaging is eclipsing anatomic imaging alone in clinical practice. The recognition that magnetic resonance (MR) and positron emission tomography (PET)-based treatment planning and response assessment are essential components of clinical practice and furthermore offer the potential of quantitative analysis being important. Extracting the greatest benefit from these imaging techniques will require refining the best combinations of multimodality imaging through well-designed clinical trials that use robust image-analysis tools and require substantial computer based infrastructure. Through these changes and enhancements, image-based biomarkers will enhance clinical decision making and accelerate the progress that is made through clinical trial research.

18F-FDG PET/CT of patients with cancer: comparison of whole-body and limited whole-body technique

OBJECTIVE

Use of the routine field of view for whole-body (18)F-FDG PET/CT can lead to underestimation of the true extent of the disease because metastasis outside the typical base of skull to upper thigh field of view can be missed. The purpose of this study was to evaluate the incremental added value of true whole-body as opposed to this limited whole-body PET/CT of cancer patients.

MATERIALS AND METHODS

True whole-body FDG PET/CT, from the top of the skull to the bottom of the feet, was performed on 500 consecutively registered patients. A log was kept of cases of suspected malignancy outside the typical limited whole-body field of view. Suspected lesions in the brain, skull, and extremities were verified by correlation with surgical pathologic or clinical follow-up findings.

RESULTS

Fifty-nine of 500 patients had PET/CT findings suggestive of malignancy outside the limited whole-body field of view. Thirty-one of those patients had known or suspected malignancy outside the limited whole-body field of view at the time of the true whole-body study. Among the other 28 patients, follow-up data were not available for two, six had false-positive findings, and new cancerous involvement was confirmed in 20. Detection of malignancy outside the limited whole-body field of view resulted in a change in management in 65% and in staging in 55% of the 20 cases.

CONCLUSION

Our study showed that 20 of 500 (4.0%) of patients had previously unsuspected malignancy outside the typical limited whole-body field of view. Detection of such malignancy resulted in a change in management in 13 of 500 cases (2.6%). We propose that adopting a true whole-body field of view in the imaging of cancer patients may lead to more accurate staging and restaging than achieved with the routinely used limited whole-body field of view.

Global trends in hybrid imaging

At the 2009 Scientific Assembly and Annual Meeting of the Radiological Society of North America, a special session was devoted to global trends in hybrid imaging. This article expands on the key points of the session, focusing primarily on positron emission tomography/computed tomography. Global trends in hybrid imaging equipment acquisition, usage, and image interpretation practices are reviewed, and emerging requirements for training and clinical privileging are discussed. Also considered are the current benefits of hybrid imaging for patient care and workflow and the potential of hybrid imaging for advancing drug development and personalized medicine.

Quantitative imaging in oncology patients: Part 1, radiology practice patterns at major U.S. cancer centers

OBJECTIVE

The objective of our study was to examine radiologists' opinions and practice patterns concerning tumor measurements in cancer patients.

MATERIALS AND METHODS

An electronic mail survey was sent to 565 abdominal imaging radiologists at 55 U.S. National Cancer Institute (NCI)-funded cancer centers. The survey contained questions about departmental demographics, procedures for interpretation of imaging in oncologic patients, and opinions concerning the role of radiologists in using the Response Evaluation Criteria in Solid Tumors (RECIST) system for tumor measurements.

RESULTS

Two hundred ninety-six responses (52%) were received. The distribution of the size of the respondents' abdominal imaging groups was as follows: 1-5 (16/295, 5%), 6-10 (112/295, 38%), 11-15 (77/295, 26%), and > 20 (73/295, 25%). Most respondents dictate some but not all tumor measurements in the first clinical scan (236/270, 87%). For follow-up imaging, 95% (255/268) of respondents dictate tumor measurements for selected index lesions. Most respondents believe inclusion of tumor measurements in the first scan is the responsibility of the radiologist (248/262, 95%). Ninety percent of respondents (235/261) believe inclusion of several index lesion measurements is satisfactory to document disease activity. Eighty-two percent (214/260) of respondents were familiar with RECIST. Forty-two percent (110/262) of respondents' departments have a centralized process for approval of industry-sponsored oncologic trials in which imaging is an important component of the protocol end point.

CONCLUSION

Most oncologic imaging at NCI-sponsored cancer centers includes tumor measurements on initial and follow-up imaging. Very few radiology departments have a centralized process for approval of clinical trial protocols that require imaging.

Unexpected findings at imaging: predicting frequency in various types of studies

OBJECTIVE

: The objective was to evaluate the prevalence and associated variables of unsuspected findings from imaging tests in clinical practice.

MATERIAL AND METHODS

: Cross-sectional study of patients referred for an imaging test in 2006. Two independent radiologists classified the imaging tests according to the presence or absence of an unexpected finding in relation with the causes that prompted the test (kappa=0.95). A thorough chart review of these patients was carried out as a quality control.

RESULTS

: Out of 3259 patients in the study, 488 revealed unsuspected findings (15.0%). The prevalence of abnormal findings varied according to age: from 20.4% (150/734) in the over 74-group to 9.0% (76/847) in the under 43-group. The largest prevalence was in the category of infectious diseases (14/49, 28.6%) and in CT (260/901, 28.9%) and ultrasound (138/668, 20.7%). Studies showing moderate clinical information on the referral form were less likely to show unexpected findings than those with null or minor information (OR 0.51; 95% CI 0.36-0.73).

CONCLUSION

: Clinicians should expect the frequency of diseases detectable by imaging to increase in the future. Further research with follow-up of these findings is needed to estimate the effect of imaging technologies on final health outcomes.

Incidental Findings on Integrated PET/CT That Do Not Accumulate18F-FDG

OBJECTIVE

The purpose of this study was to report the prevalence of abnormalities that do not show increased 18F-FDG uptake on the CT component of integrated PET/CT in patients with non-small cell lung cancer.

MATERIALS AND METHODS

Images from all PET/CT studies performed consecutively between April and October 2003 on patients with non-small cell lung cancer were retrospectively reviewed. All abnormalities present on the CT component of the PET/CT scans that did not show abnormally increased 18F-FDG uptake were documented.

RESULTS

Three hundred twenty-one patients with non-small cell lung cancer (179 men, 142 women; mean age, 67 years; age range, 38-91 years) underwent initial staging (198/321 [62%]) or restaging (123/321 [38%]) PET/CT imaging during the study period. In 263 (82%) of the patients, CT showed 1,231 abnormalities that were not 18F-FDG avid. The abnormalities were located in the thorax (n = 650), abdomen and pelvis (n = 444), head and neck (n = 69), and bony skeleton (n = 68). In total, 298 (24%) of the abnormalities that were not 18F-FDG avid were located outside the range of a standard thoracic CT scan. The clinical importance of these abnormalities was classified as major (n = 48 [4%]), moderate (n = 465 [38%]), or minor (n = 718 [58%]). Four (1%) of the patients had findings of major clinical importance that did not show increased 18F-FDG uptake and were previously unsuspected.

CONCLUSION

Among patients with non-small cell lung cancer undergoing PET/CT, there is a high prevalence of CT abnormalities that do not show correlative 18F-FDG avidity but that may be clinically important.