Faculty Bibliography

OBJECTIVES/OBJECTIVE:To evaluate the performance of radiomic features extracted from high-resolution computed tomography (HRCT) for the differentiation between cholesteatoma and middle ear inflammation (MEI), and to investigate the impact of post-reconstruction harmonization and data resampling. METHODS:One hundred patients were included in this retrospective dual-center study: 48 with histology-proven cholesteatoma (center A: 23; center B: 25) and 52 with MEI (A: 27; B: 25). Radiomic features (co-occurrence and run-length matrix, absolute gradient, autoregressive model, Haar wavelet transform) were extracted from manually defined 2D-ROIs. The ten best features for lesion differentiation were selected using probability of error and average correlation coefficients. A multi-layer perceptron feed-forward artificial neural network (MLP-ANN) was used for radiomics-based classification, with histopathology serving as the reference standard (70% of cases for training, 30% for validation). The analysis was performed five times each on (a) unmodified data and on data that were (b) resampled to the same matrix size, and (c) corrected for acquisition protocol differences using ComBat harmonization. RESULTS:Using unmodified data, the MLP-ANN classification yielded an overall median area under the receiver operating characteristic curve (AUC) of 0.78 (0.72-0.84). Using original data from center A and resampled data from center B, an overall median AUC of 0.88 (0.82-0.99) was yielded, while using ComBat harmonized data, an overall median AUC of 0.89 (0.79-0.92) was revealed. CONCLUSION/CONCLUSIONS:Radiomic features extracted from HRCT differentiate between cholesteatoma and MEI. When using multi-centric data obtained with differences in CT acquisition parameters, data resampling and ComBat post-reconstruction harmonization clearly improve radiomics-based lesion classification. KEY POINTS/CONCLUSIONS:• Unenhanced high-resolution CT coupled with radiomics analysis may be useful for the differentiation between cholesteatoma and middle ear inflammation. • Pooling of data extracted from inhomogeneous CT datasets does not appear meaningful without further post-processing. • When using multi-centric CT data obtained with differences in acquisition parameters, post-reconstruction harmonization and data resampling clearly improve radiomics-based soft-tissue differentiation.

Vaccination-associated adenopathy is a frequent imaging finding after administration of COVID-19 vaccines that may lead to a diagnostic conundrum in patients with manifest or suspected cancer, in whom it may be indistinguishable from malignant nodal involvement. To help the medical community address this concern in the absence of studies and evidence-based guidelines, this special report offers recommendations developed by a multidisciplinary panel of experts from three of the leading tertiary care cancer centers in the United States. According to these recommendations, some routine imaging examinations, such as those for screening, should be scheduled before or at least 6 weeks after the final vaccination dose to allow for any reactive adenopathy to resolve. However, there should be no delay of other clinically indicated imaging (eg, for acute symptoms, short-interval treatment monitoring, urgent treatment planning or complications) due to prior vaccination. The vaccine should be administered on the side contralateral to the primary or suspected cancer, and both doses should be administered in the same arm. Vaccination information-date(s) administered, injection site(s), laterality, and type of vaccine-should be included in every preimaging patient questionnaire, and this information should be made readily available to interpreting radiologists. Clear and effective communication between patients, radiologists, referring physician teams, and the general public should be considered of the highest priority when managing adenopathy in the setting of COVID-19 vaccination.

BACKGROUND:MR is an important imaging modality for evaluating musculoskeletal malignancies owing to its high soft tissue contrast and its ability to acquire multiparametric information. PET provides quantitative molecular and physiologic information and is a critical tool in the diagnosis and staging of several malignancies. PET/MR, which can take advantage of its constituent modalities, is uniquely suited for evaluating skeletal metastases. We reviewed the current evidence of PET/MR in assessing for skeletal metastases and provided recommendations for its use. METHODS:We searched for the peer reviewed literature related to the usage of PET/MR in the settings of osseous metastases. In addition, expert opinions, practices, and protocols of major research institutions performing research on PET/MR of skeletal metastases were considered. RESULTS:Peer-reviewed published literature was included. Nuclear medicine and radiology experts, including those from 13 major PET/MR centers, shared the gained expertise on PET/MR use for evaluating skeletal metastases and contributed to a consensus expert opinion statement. [18F]-FDG and non [18F]-FDG PET/MR may provide key advantages over PET/CT in the evaluation for osseous metastases in several primary malignancies. CONCLUSION/CONCLUSIONS:PET/MR should be considered for staging of malignancies where there is a high likelihood of osseous metastatic disease based on the characteristics of the primary malignancy, hight clinical suspicious and in case, where the presence of osseous metastases will have an impact on patient management. Appropriate choice of tumor-specific radiopharmaceuticals, as well as stringent adherence to PET and MR protocols, should be employed.

Gastric mucosa-associated lymphoid tissue (MALT) lymphoma responding to upfront treatment has an excellent outcome and no further therapy is recommended, even in the presence of residual disease. However, no data exist on the influence of initial depth of remission on progression-free survival (PFS). Methods: We investigated a correlation between PFS and depth of response, categorizing them as complete remission (CR), partial remission (PR) and stable disease (SD) in 137 consecutive patients at the Medical University Vienna. Results: All patients with Helicobacter pylori (H. pylori)-positive, localized disease received H. pylori eradication (70%, 96/137), while the remaining patients were treated with various modalities. The response rate was 67% for the entire collective and 58% for eradication only, with corresponding CR-rates of 48% and 38%. At a median follow-up of 56.2 months, the estimated PFS for the entire cohort was 34.2 months (95% Confidence Interval 16.0-52.4). Responding patients (=CR/PR) had a significantly longer PFS compared to SD (68.3 vs. 17.3 months, p < 0.001). This was also applicable to the eradication only cohort (49.0 vs. 17.3 months, p < 0.001) and remained significant after correction for MALT-IPI. Furthermore, CR significantly prolonged PFS over PR (p = 0.007 entire cohort, p = 0.020 eradication). Conclusions: Remission status correlated significantly with PFS, suggesting depth of remission as prognostic marker for long-term relapse-free survival.

BACKGROUND:Immune checkpoint inhibitors have become a valuable tool in the therapeutic strategy against metastasized non-small cell lung cancer (NSCLC) as they represent an effective and safe treatment option for many patients; however, the treatment response and side effects of this class of drugs can considerably differ compared to classical chemotherapeutics. The aim of this study was to highlight specific radiological pulmonary findings of NSCLC patients treated with immune checkpoint inhibitors. METHODS AND RESULTS/RESULTS:Medical records and images of prospectively collected data from 70 patients with advanced NSCLC, treated with immune checkpoint inhibitors, were reviewed. Of the patients two experienced an initial increase in tumor size, followed by a decrease in tumor size that was described as pseudoprogression. Another patient developed a sarcoid-like reaction accompanied by clinical improvements and radiological treatment response. A further two patients developed immune checkpoint-associated pulmonary injury that was clinically and radiologically classified as pneumonitis, which responded well to anti-inflammatory treatment. CONCLUSION/CONCLUSIONS:Management of patients with NSCLC using immune checkpoint inhibitors requires a knowledge of specific clinical and radiological findings. Both oncologists and radiologists have to be aware of the most common types, including atypical response patterns, such as a sarcoid-like reaction and pseudoprogression as well as of the pulmonary side effects that can encompass pneumonitis.

Biopsy is the standard for assessment of bone marrow involvement in mantle cell lymphoma (MCL). We investigated whether [18F]FDG-PET radiomic texture features can improve prediction of bone marrow involvement in MCL, compared to standardized uptake values (SUV), and whether combination with laboratory data improves results. Ninety-seven MCL patients were retrospectively included. SUVmax, SUVmean, SUVpeak and 16 co-occurrence matrix texture features were extracted from pelvic bones on [18F]FDG-PET/CT. A multi-layer perceptron neural network was used to compare three combinations for prediction of bone marrow involvement-the SUVs, a radiomic signature based on SUVs and texture features, and the radiomic signature combined with laboratory parameters. This step was repeated using two cut-off values for relative bone marrow involvement: REL > 5% (>5% of red/cellular bone marrow); and REL > 10%. Biopsy demonstrated bone marrow involvement in 67/97 patients (69.1%). SUVs, the radiomic signature, and the radiomic signature with laboratory data showed AUCs of up to 0.66, 0.73, and 0.81 for involved vs. uninvolved bone marrow; 0.68, 0.84, and 0.84 for REL ≤ 5% vs. REL > 5%; and 0.69, 0.85, and 0.87 for REL ≤ 10% vs. REL > 10%. In conclusion, [18F]FDG-PET texture features improve SUV-based prediction of bone marrow involvement in MCL. The results may be further improved by combination with laboratory parameters.

PURPOSE:F]FDG PET/x-ray computed tomography (CT) for detection of distant metastatic disease in patients with malignant melanoma. PROCEDURES:F]FDG dual-imaging protocol that included whole-body PET/CT and subsequent whole-body PET/MRI for staging or restaging purposes in a prospective setting. Images from both modalities were analyzed by two rater teams for the presence of metastatic lesions. PET/CT-PET/MRI overall agreement as well as region-based accuracies, sensitivities (Se), and specificities (Sp) were computed. RESULTS:Between July 2014 and December 2018, 22 patients were enrolled. Interrater agreement and overall accuracy (consensus reading) were 78.8 % (95 % CI 71-84.9) and 96.1 % (95 % CI 92.3-98) for PET/MRI and 78 % (70.2-84.3) and 97.4 % (95 % CI 93.7-98.9) for PET/CT, respectively (P = 0.42). PET/MRI reached a region-based Se of 89.1 % (95 % CI 79.4-94.5) and a Sp of 100 %, whereas PET/CT showed a region-based Se of 92.7 % (95 % CI 84-96.9) and a Sp of 100 % for the detection of metastatic disease in malignant melanoma. CONCLUSIONS:F]FDG-PET/CT for lesion detection in patients with malignant melanoma.

The role of MRI differs considerably between the three main groups of hematological malignancies: lymphoma, leukemia, and myeloma. In myeloma, whole-body MRI (WB-MRI) is recognized as a highly sensitive test for the assessment of myeloma, and is also endorsed by clinical guidelines, especially for detection and staging. In lymphoma, WB-MRI is presently not recommended, and merely serves as an alternative technique to the current standard imaging test, [¹⁸ F]FDG-PET/CT, especially in pediatric patients. Even for lymphomas with variable FDG avidity, such as extranodal mucosa-associated lymphoid tissue lymphoma (MALT), contrast-enhanced computed tomography (CT), but not WB-MRI, is presently recommended, despite the high sensitivity of diffusion-weighted MRI and its ability to capture treatment response that has been reported in the literature. In leukemia, neither MRI nor any other cross-sectional imaging test (including positron emission tomography [PET]) is currently recommended outside of clinical trials. This review article discusses current clinical applications as well as the main research topics for MRI, as well as PET/MRI, in the field of hematological malignancies, with a focus on functional MRI techniques such as diffusion-weighted imaging and dynamic contrast-enhanced MRI, on the one hand, and novel, non-FDG PET imaging probes such as the CXCR4 radiotracer [⁶⁸ Ga]Ga-Pentixafor and the amino acid radiotracer [¹¹ C]methionine, on the other hand. Level of Evidence: 5 Technical Efficacy Stage: 3 J. Magn. Reson. Imaging 2020;51:1325-1335.

Radiomics is a rapidly evolving field of research concerned with the extraction of quantitative metrics-the so-called radiomic features-within medical images. Radiomic features capture tissue and lesion characteristics such as heterogeneity and shape and may, alone or in combination with demographic, histologic, genomic, or proteomic data, be used for clinical problem solving. The goal of this continuing education article is to provide an introduction to the field, covering the basic radiomics workflow: feature calculation and selection, dimensionality reduction, and data processing. Potential clinical applications in nuclear medicine that include PET radiomics-based prediction of treatment response and survival will be discussed. Current limitations of radiomics, such as sensitivity to acquisition parameter variations, and common pitfalls will also be covered.