Christian Rubbert

N staging of lung cancer patients with PET/MRI using a three-segment model attenuation correction algorithm: initial experience.

AbstractObjectivesEvaluate the performance of PET/MRI at tissue interfaces with different attenuation values for detecting lymph node (LN) metastases and for accurately measuring maximum standardised uptake values (SUVmax) in lung cancer patients.Materials and MethodEleven patients underwent PET/CT and PET/MRI for staging, restaging or follow-up of suspected or known lung cancer. Four experienced readers determined the N stage of the patients for each imaging method in a randomised blinded way. Concerning metastases, SUVmax of FDG-avid LNs were measured in PET/CT and PET/MRI in all patients. A standard of reference was created with a fifth experienced independent reader in combination with a chart review. Results were analysed to determine interobserver agreement, SUVmax correlation between CT and MRI (three-segment model) attenuation correction and diagnostic performance of the two techniques.ResultsOverall interobserver agreement was high (κ = 0.86) for PET/CT and substantial (κ = 0.70) for PET/MRI. SUVmax showed strong positive correlation (Spearman’s correlation coefficient = 0.93, P < 0.001) between the two techniques. Diagnostic performance of PET/MRI was slightly inferior to that of PET/CT, without statistical significance (P > 0.05).ConclusionsPET/MRI using three-segment model attenuation correction for LN staging in lung cancer shows a strong parallel to PET/CT in terms of SUVmax, interobserver agreement and diagnostic performance.Key Points•F18-FDG PET/MRI shows similar performance to F18-FDG PET/CT in lung cancer N staging. •PET/MRI has substantial interobserver agreement in N staging. •A three-segment model attenuation correction is reliable for assessing the mediastinum.

Qualitative and Quantitative Performance of 18F-FDG-PET/MRI versus 18F-FDG-PET/CT in Patients with Head and Neck Cancer

BACKGROUND AND PURPOSE: MR imaging and PET/CT are integrated in the work-up of head and neck cancer patients. The hybrid imaging technology 18F-FDG-PET/MR imaging combining morphological and functional information might be attractive in this patient population. The aim of the study was to compare whole-body 18F-FDG-PET/MR imaging and 18F-FDG-PET/CT in patients with head and neck cancer, both qualitatively in terms of lymph node and distant metastases detection and quantitatively in terms of standardized uptake values measured in 18F-FDG-avid lesions. MATERIALS AND METHODS: Fourteen patients with head and neck cancer underwent both whole-body PET/CT and PET/MR imaging after a single injection of 18F-FDG. Two groups of readers counted the number of lesions on PET/CT and PET/MR imaging scans. A consensus reading was performed in those cases in which the groups disagreed. Quantitative standardized uptake value measurements were performed by placing spheric ROIs over the lesions in 3 different planes. Weighted and unweighted κ statistics, correlation analysis, and the Wilcoxon signed rank test were used for statistical analysis. RESULTS: κ statistics for the number of head and neck lesion lesions counted (pooled across regions) revealed interreader agreement between groups 1 and 2 of 0.47 and 0.56, respectively. Intrareader agreement was 0.67 and 0.63. The consensus reading provided an intrareader agreement of 0.63. For the presence or absence of metastasis, interreader agreement was 0.85 and 0.70. The consensus reading provided an intrareader agreement of 0.72. The correlations between the maximum standardized uptake value in 18F-FDG-PET/MR imaging and 18F-FDG-PET/CT for primary tumors and lymph node and metastatic lesions were very high (Spearman r = 1.00, 0.93, and 0.92, respectively). CONCLUSIONS: In patients with head and neck cancer, 18F-FDG-PET/MR imaging and 18F-FDG-PET/CT provide comparable results in the detection of lymph node and distant metastases. Standardized uptake values derived from 18F-FDG-PET/MR imaging can be used reliably in this patient population.

Initial experience of MR/PET in a clinical cancer center.

Magentic Resonance/positron emission tomography (PET) has been introduced recently for imaging of clinical patients. This hybrid imaging technology combines the inherent strengths of MRI with its high soft‐tissue contrast and biological sequences with the inherent strengths of PET, enabling imaging of metabolism with a high sensitivity. In this article, we describe the initial experience of MR/PET in a clinical cancer center along with a review of the literature. For establishing MR/PET in a clinical setting, technical challenges, such as attenuation correction and organizational challenges, such as workflow and reimbursement, have to be overcome. The most promising initial results of MR/PET have been achieved in anatomical areas where high soft‐tissue and contrast resolution is of benefit. Head and neck cancer and pelvic imaging are potential applications of this hybrid imaging technology. In the pediatric population, MR/PET can decrease the lifetime radiation dose. MR/PET protocols tailored to different types of malignancies need to be developed. After the initial exploration phase, large multicenter trials are warranted to determine clinical indications for this exciting hybrid imaging technology and thereby opening new horizons in molecular imaging. J. Magn. Reson. Imaging 2014;39:768–780.

Amyloid PET/MRI in the differential diagnosis of dementia.

The potential of brain imaging has grown rapidly with new modalities, hybrid combinations of existing modalities, and novel metabolic tracers. F-florbetapir is an amyloid plaque-binding molecule labeled to F that allows positron imaging of the amyloid deposition in the brain. This protein deposition is known to be one of the features in Alzheimer disease and therefore can be of interest in the differential diagnosis of dementia. We present 2 cases combining the new hybrid imaging modality PET/MRI, which offers molecular and morphological information, with F-florbetapir in the differential diagnosis of dementia.

PET/MRI: Applications in Clinical Imaging

PET/MRI is a new hybrid modality which is increasingly being used in clinical settings, although both clinical evaluation and technical optimization are still an ongoing process. Initial experience with this new imaging device proves promising for oncologic applications. Other clinical indications in the field of cardiac imaging and neuroimaging are also being explored. This article aims to review the current status of PET/MRI and its value in oncologic applications, and summarizes our own preliminary experience in this field.

Artifacts and diagnostic pitfalls in positron emission tomography-magnetic resonance imaging.

Introduction Positron emission tomography-magnetic resonance (PETMR) is a new hybrid imaging modality that has recently been introduced in clinical practice for oncologic imaging and is increasingly being used in various clinical indications. PET-MR unifies the complementary capabilities of magnetic resonance imaging (MRI) and PET in a single imaging modality. Excellent anatomical and morphologic information with high soft tissue resolution and contrast from MRI and the best possible molecular, functional, and physiological information fromPET are complementary andhave the potential to provide maximum diagnostic information in a single procedure. However, the incremental diagnostic value of PET-MRover the current standard imaging procedures in various clinical scenarios is still under investigation. Initial results indicate that PET-MR is particularly promising in oncologic diseases and is at least equivalent to PET-computed tomography (PETCT) in lesion detection. Besides the hope for improved clinical and diagnostic performance, there are further expected benefits of PET-MR over current conventional imaging techniques: PET-MR harbors the potential to improve the patients’ workflow and save the patient and the administrative organization the implications of numerous appointments for multiple imaging procedures. As such “one-stop-shop” imaging modality, PET-MRmaybemore time efficient than conventional imaging techniques, such as CT or even PET-CT. Furthermore, there is the potential to decrease the overall radiation exposure to the patient from diagnostic imaging; an issue that gains particular relevance in the world of pediatric patients and young adult patients with a need for repetitive imaging follow-up. Although, both PET and MRI have been well-established individual standalone imaging modalities for decades, the marriage of the 2 components in 1 device came along with significant hardware and software adjustments. Inherent to such adjustments is the risk and likelihood for new imaging effects and artifacts that need to be addressed to guarantee appropriate, reliable, and reproducible diagnostic interpretation. The fact that today’s commercially available models of PET-MR devices operate with significant vendor-dependent technical differences adds complexity to these systems. Differences in the technical approach to PET-MRI increases the necessity to identify, improve, or if not possible at least, describe technology-related imaging artifacts and effects and bring these effects to the attention of the ultimate user of this new technology. The present review first aims to provide an overview over the most common artifacts and pitfalls encountered with PET-MR. It describes their imaging characteristics and discusses the technical background and potential ways of mitigating these issues. It focuses on the potential clinical implications of these artifacts to increase the awareness of these challenges and helps avoid interpretation errors in the clinical use. Secondly, this review addresses the challenges in workflow and in setting up appropriate functional and practical imaging protocols for the use of this complex combined hybrid imaging modality. It will provide suggestions and examples of practical approaches.

The impact of orthopedic metal artifact reduction software on interreader variability when delineating areas of interest in the head and neck

PURPOSE Metal artifacts during computed tomography (CT) hinder the evaluation of diagnostic images and impair the delineation of tumor volume in treatment planning. Several solutions are available to minimize these artifacts. Our objective was to determine the impact of one of those tools on the interreader variability when measuring head and neck structures in the presence of metal artifacts. METHODS AND MATERIALS Eleven patients were retrospectively selected from an institutional review board-approved study based on the presence of metallic artifacts in the head and neck region. CT raw data were postprocessed using a metal artifact reduction tool. A single matching CT slice from the filtered backprojection and postprocessed data sets was selected in the region of the metal artifact. Areas of selected anatomical structures were measured by independent readers, including an anatomical structure selected from a CT slice with no metal artifact in each patient as control. The intraclass correlation coefficient was calculated. RESULTS Two extreme outliers were identified and the intraclass correlation coefficient was performed with and without them. The intraclass correlation on filtered backprojection, postprocessed, and control images was 0.903, 0.948, and 0.985 with outliers and 0.884, 0.971, and 0.989 without outliers, respectively, for all readers. On the other hand, the intraclass correlation on filtered backprojection, postprocessed, and control images for experienced readers was 0.904, 0.979, and 0.976 with outliers and 0.934, 0.975, and 0.990 without outliers, respectively. CONCLUSIONS The interreader variability of areas measured in the presence of metal artifact was greatly decreased by the use of the metal artifact reduction tool and almost matched the variability observed in the absence of the metal artifact.

Management and Organization of Positron Emission Tomography/Magnetic Resonance Imaging

Introduction The decision to install a positron emission tomography/ magnetic resonance imaging (PET/MRI) system within a health care organization requires an understanding of the mission and vision for using the PET/MRI system. A critical question to consider is if the PET/MRI system will be used for research, routine clinical imaging, or both purposes. If the primary purpose of PET/MRI system is research, then an appropriate funding infrastructure needs to be in place to operate and maintain it. For clinical applications, it is essential that adult and pediatric referring clinicians, including those from medical oncology, radiation oncology, neurology, and cardiology departments, be engaged in discussions about the potential use. Regardless of the purpose, it is important to recognize that, from a financial perspective, a facility should not expect ideal annual growth and increasing net revenue until PET/MRI system development and deployment is more mature. Continued adoption of the PET/MRI modality may take several years and additional peer-reviewed evidence in its support before it is clinically accepted in the United States. The physical location of the system within the radiology department must simultaneously satisfy the requirements of patient workflow, radiation safety, radioactive materials security, and MRI safety. The Philips Ingenuity TF PET/MR system was installed in the University Hospitals Seidman Cancer Center in Cleveland, OH, in December 2011. The installation was the first Food and Drug Administration–approved sequential system designed for use in a clinical environment