Imaging children suffering from lymphoma: an evaluation of different 18F-FDG PET/MRI protocols compared to whole-body DW-MRI

The Role of Whole-Body MRI in Pediatric Musculoskeletal Oncology: Current Concepts and Clinical Applications

Whole-body magnetic resonance imaging (WB-MRI) has gained importance in the field of musculoskeletal oncology over the last decades, consisting in a one-stop imaging method that allows a wide coverage assessment of both bone and soft tissue involvement. WB-MRI is valuable for diagnosis, staging, and follow-up in many oncologic diseases and is especially advantageous for the pediatric population since it avoids redundant examinations and exposure to ionizing radiation in patients who often undergo long-term surveillance. Its clinical application has been studied in many pediatric neoplasms, such as cancer predisposition syndromes, Langerhans cell histiocytosis, lymphoma, sarcomas, and neuroblastoma. The addition of diffusion-weighted sequences allows functional evaluation of neoplastic lesions, which is helpful in the assessment of viable tumor and response to treatment after neoadjuvant or adjuvant therapy. WB-MRI is an excellent alternative to fluorodeoxyglucose-positron emission tomography/computed tomography in oncologic children, with comparable accuracy and the convenience of being radiation-free, fast to perform, and available at a similar cost. The development of new techniques and protocols makes WB-MRI increasingly faster, safer, and more accessible, and it is important for referring physicians and radiologists to recognize the role of this imaging method in pediatric oncology. LEVEL OF EVIDENCE: 4 TECHNICAL EFFICACY STAGE: 2.

Recurrent prostate cancer: combined role for MRI and PSMA-PET in 68Ga-PSMA-11 PET/MRI

OBJECTIVES

To investigate the specific strengths of MRI and PET components in 68Ga-PSMA-11 PET/MRI for staging of patients with biochemically recurrent prostate cancer (PCa).

METHODS

Patients with biochemical recurrence of PCa and contrast-enhanced whole-body 68Ga-PSMA-11 PET/MRI including a dedicated pelvic multiparametric MRI were included in this retrospective study. Imaging datasets of MRI and PET were evaluated separately regarding local PCa recurrence (Tr), pelvic lymph node metastases (N1), distant lymph node metastases (M1a), bone metastases (M1b), and soft tissue metastases (M1c) according to PROMISE version 1. Data evaluation was performed patient- and region-/lesion-based. Cox regression revealed a PSA of 1.69 ng/mL as a cut-off for subgroup analysis. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy were evaluated for each image component. Differences in staging accuracy were assessed using the Wilcoxon and McNemar test.

RESULTS

Altogether 102 patients (mean aged 68 ± 8 years, median PSA 1.33 ng/mL) were included. PCa was found in 70/102 (68%) patients. Accuracy of MRI in the detection of Tr, N1, M + , M1a, and M1b was 100%, 79%, 90%, 97%, and 95% for PSA < 1.69 ng/mL and 100%, 87%, 87%, 91%, and 96% for PSA > 1.69 ng/mL. Accuracy of 68Ga-PSMA-11 PET was 93%, 97%, 93%, 98%, and 100% for PSA < 1.69 ng/mL and 87%, 91%, 96%, 100%, and 96% for PSA > 1.69 ng/mL.

CONCLUSIONS

Combined assessment of 68Ga-PSMA-11 PET/MRI improves tumor localization in men with biochemical recurrence. The MRI detected local recurrence of PCa more often whereas 68 Ga-PSMA-11 PET detected lymph node metastases more often, especially for PSA < 1.69 ng/mL.

CLINICAL RELEVANCE STATEMENT

This study gives a scientific baseline to improve the understanding and reading of 68Ga-PSMA-11 PET/MRI imaging in patients with biochemically recurrent PCa by showing the specific strength of each imaging component.

KEY POINTS

• Combining the individual modality strengths of 68Ga-PSMA-11 PET/MRI improves tumor localization in men with biochemical recurrence of prostate cancer. • MRI component of 68 Ga-PSMA-11 PET/MRI shows its strength in detecting local recurrence of prostate cancer, especially at PSA < 1.69 ng/mL. • 68 Ga-PSMA-11 PET component shows its strength in detecting local and distant lymph node metastases, especially at PSA < 1.69 ng/mL.

[18F]FDG PET/MRI in children suffering from lymphoma: does MRI contrast media make a difference?

OBJECTIVES

Evaluate the influence of an MRI contrast agent application on primary and follow-up staging in pediatric patients with newly diagnosed lymphoma using [18F]FDG PET/MRI to avoid adverse effects and save time and costs during examination.

METHODS

A total of 105 [18F]FDG PET/MRI datasets were included for data evaluation. Two different reading protocols were analyzed by two experienced readers in consensus, including for PET/MRI-1 reading protocol unenhanced T2w and/or T1w imaging, diffusion-weighted imaging (DWI), and [18F]FDG PET imaging and for PET/MRI-2 reading protocol an additional T1w post contrast imaging. Patient-based and region-based evaluation according to the revised International Pediatric Non-Hodgkin's Lymphoma (NHL) Staging System (IPNHLSS) was performed, and a modified standard of reference was applied comprising histopathology and previous and follow-up cross-sectional imaging. Differences in staging accuracy were assessed using the Wilcoxon and McNemar tests.

RESULTS

In patient-based analysis, PET/MRI-1 and PET/MRI-2 both determined a correct IPNHLSS tumor stage in 90/105 (86%) exams. Region-based analysis correctly identified 119/127 (94%) lymphoma-affected regions. Sensitivity, specificity, positive predictive value, negative predictive value, and diagnostic accuracy for PET/MRI-1 and PET/MRI-2 were 94%, 97%, 90%, 99%, 97%, respectively. There were no significant differences between PET/MRI-1 and PET/MRI-2.

CONCLUSIONS

The use of MRI contrast agents in [18F]FDG PET/MRI examinations has no beneficial effect in primary and follow-up staging of pediatric lymphoma patients. Therefore, switching to a contrast agent-free [18F]FDG PET/MRI protocol should be considered in all pediatric lymphoma patients.

CLINICAL RELEVANCE STATEMENT

This study gives a scientific baseline switching to a contrast agent-free [18F]FDG PET/MRI staging in pediatric lymphoma patients. This could avoid side effects of contrast agents and saves time and costs by a faster staging protocol for pediatric patients.

KEY POINTS

• No additional diagnostic benefit of MRI contrast agents at [18F]FDG PET/MRI examinations of pediatric lymphoma primary and follow-up staging • Highly accurate primary and follow-up staging of pediatric lymphoma patients at MRI contrast-free [18F]FDG PET/MRI.

Optimized Whole-Body PET MRI Sequence Workflow in Pediatric Hodgkin Lymphoma Patients

¹⁸F-FDG PET/MRI might be the diagnostic method of choice for Hodgkin lymphoma patients, as it combines significant metabolic information from PET with excellent soft-tissue contrast from MRI and avoids radiation exposure from CT. However, a major issue is longer examination times than for PET/CT, especially for younger children needing anesthesia. Thus, a targeted selection of suitable whole-body MRI sequences is important to optimize the PET/MRI workflow. Methods: The initial PET/MRI scans of 84 EuroNet-PHL-C2 study patients from 13 international PET centers were evaluated. In each available MRI sequence, 5 PET-positive lymph nodes were assessed. If extranodal involvement occurred, 2 splenic lesions, 2 skeletal lesions, and 2 lung lesions were also assessed. A detection rate was calculated dividing the number of visible, anatomically assignable, and measurable lesions in the respective MRI sequence by the total number of lesions. Results: Relaxation time-weighted (T2w) transverse sequences with fat saturation (fs) yielded the best result, with detection rates of 95% for nodal lesions, 62% for splenic lesions, 94% for skeletal lesions, and 83% for lung lesions, followed by T2w transverse sequences without fs (86%, 49%, 16%, and 59%, respectively) and longitudinal relaxation time-weighted contrast-enhanced transverse sequences with fs (74%, 35%, 57%, and 55%, respectively). Conclusion: T2w transverse sequences with fs yielded the highest detection rates and are well suited for accurate whole-body PET/MRI in lymphoma patients. There is no evidence to recommend the use of contrast agents.

Whole-body magnetic resonance/diffusion-weighted sequence with background signal suppression (WB-MR/DWIBS) vs. 18F-FDG PET/CT in diagnosis of lymphoma

Background

The purpose of this study was to compare the performance of whole-body magnetic resonance/diffusion-weighted imaging with background signal suppression (WB-MR/DWIBS) method, with that of 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG-PET/CT), for lesion detection and initial staging of patients with lymphoma using the histopathologically diagnosis as a reference standard.

Results

Thirty-two patients with newly pathologically proven lymphoma were enrolled in this prospective study from May 2018 to January 2020 (27 males, 5 females). All patients underwent PET/CT followed by WB-MR/DWIBS as an attempt to compare the performance of both methods for lesion detection and initial staging in patients with lymphoma.

The overall sensitivity, specificity, PPV, NPV, and accuracy of 18F-FDG-PET/CT vs WB-MR/DWIBS in correlation with reference standard data in detection of lymphoma were calculated for PET/CT 96%, 100%, 100%, 80%, and 97% while those of WB-MR/DWIBS were 93%, 76%, 96%, 61%, and 91%, respectively.

Conclusion

18F-FDG PET/CT remains the standard reference of imaging in evaluation of lymphoma due to its higher sensitivity and specificity over WB-MR/DWIBS. Future studies with larger cohorts are necessary for better evaluation of the role of WB-MR/DWIBS in lymphoma patients. The current study highlights the potential complementary role of WB-MRI/DWIBS in the context of bone marrow involvement evaluation omitting unnecessary bone marrow biopsy.

PET/MR in Head and Neck Cancer - An Update

In academic centers, PET/MR has taken the road to clinical nuclear medicine in the past 6 years since the last review on its applications in head and neck cancer patients in this journal. Meanwhile, older sequential PET + MR machines have largely vanished from clinical sites, being replaced by integrated simultaneous PET/MR scanners. Evidence from several studies suggests that PET/MR overall performs equally well as PET/CT in the staging and restaging of head and neck cancer and in radiation therapy planning. PET/MR appears to offer advantages in the characterization and prognostication of head and neck malignancies through multiparametric imaging, which demands an exact preparation and validation of imaging modalities, however. The majority of available clinical PET/MR studies today covers FDG imaging of squamous cell carcinoma arising from a broad spectrum of locations in the upper aerodigestive tract. In the future, specific PET/MR studies are desired that address specific histopathological tumor entities, nonepithelial malignancies, such as major salivary gland tumors, squamous cell carcinomas arising in specific locations, and malignancies imaged with non-FDG radiotracers. With the advent of digital PET/CT scanners, PET/MR is expected to partake in future technical developments, such as novel iterative reconstruction techniques and deviceless motion correction for respiration and gross movement in the head and neck region. Owing to the still comparably high costs of PET/MR scanners and facility requirements on the one hand, and the concentration of multidisciplinary head and neck cancer treatment mainly at academic centers on the other hand, a more widespread use of this imaging modality outside major hospitals is currently limited.

PET in Pediatric Lymphoma

Although fluorodeoxyglucose PET/MR imaging is a promising new modality, there is not yet enough data to support its routine use for staging or surveillance of children with lymphoma. PET/MR imaging protocols are still under development, and its availability globally is limited. The cost-benefit of using PET/MR imaging has not yet been established, especially because annual post-treatment surveillance imaging with fluorodeoxyglucose PET is not necessary in most patients with lymphoma. Further research into the use of PET/MR imaging in pediatric oncology patients is needed with continued collaborations among institutions.

Whole-Body Diffusion-Weighted MRI Compared to 18 FFDG PET/CT in Initial Staging and Therapy Response Assessment of Hodgkin Lymphoma in Pediatric Patients

PURPOSE

The aim of our study was to compare whole-body diffusion-weighted MRI (WB-DWI-MRI) to fluoro-2-deoxyglucose positron emission tomography/computed tomography (FDG-PET/CT) in the assessment of initial staging and treatment response in pediatric patients with Hodgkin lymphoma.

MATERIALS AND METHODS

This prospective study comprised 11 children with Hodgkin lymphoma. Whole-body DWI-MRI and FDG-PET/CT were obtained at baseline and after 2 cycles of chemotherapy. Two radiologists measured the apparent diffusion coefficient (ADC) values of the sites of involvement agreed upon in consensus and 1 nuclear medicine physician assessed the PET/CT. Reliability of radiologists' ratings was assessed by intraclass correlation coefficients (ICC_2,1). The sensitivity and positive predictive value (PPV) of DW-MRI relative to PET/CT were calculated for nodal and extranodal sites. The patients were staged according to both modalities. Association of treatment responses was assessed through the Pearson correlation between the ADC ratios and the change standardized uptake value (SUV) between baseline and follow-up.

RESULTS

There was good agreement between the raters for nodal and extranodal ADC measurements. The sensitivity and PPV of DW-MRI relative to PET/CT of nodal disease was 0.651 and 1.0, respectively, at baseline, and 0.697 and 0.885 at follow-up. The sensitivity and PPV of extranodal disease were 0.545 and 0.6 at baseline, and 0.167 and 0.333 at follow-up. Diffusion-weighted MRI determined correct tumor stage in 8 of 11 examinations. There was poor correlation between the ADC ratios and the absolute change in SUV between baseline and follow-up (0.348).

CONCLUSION

Our experience showed that WB-DWI-MRI is inferior to PET/CT for initial staging and assessment of treatment response of Hodgkin lymphoma in pediatric patients.

Comparison of FDG PET/MRI and FDG PET/CT in Pediatric Oncology in Terms of Anatomic Correlation of FDG-positive Lesions

The aims of our study were to compare F-18 fluorodeoxyglucose (FDG) positron-emission tomography/magnetic resonance imaging (PET/MRI) and PET/computed tomography (CT) in pediatric oncology patients in terms of anatomic correlation of FDG-positive lesions, and also to compare diffusion-weighted imaging (DWI) with PET to assess the correlation between apparent diffusion coefficient (ADC) values and standardized uptake value (SUV). Sequential PET/CT and PET/MRI images and/or whole-body DWI and ADC mapping in 34 pediatric patients were retrospectively analyzed. FDG-positive lesions were visually scored for CT, T1-weighted, T2-weighted, and DWI images separately in terms of anatomic correlation of FDG-avid lesions. Correlation analysis was performed for SUV parameters and ADC values. Among 47 FDG-positive lesions identified concurrently on PET/CT and PET/MRI, 37 were positive on CT and 46 were positive on at least one MRI sequence (P=0.012). Among 32 FDG-positive lesions for which DWI were available, 31 could be clearly depicted on DWI, resulting in significant difference compared with CT alone in the detection of FDG-positive lesions. No correlation was found between ADC and SUV. FDG PET/MRI exhibits better performance than PET/CT in terms of anatomic correlation of FDG-avid lesions. Therefore, PET/MRI may be more advantageous than PET/CT, not only due to reduced ionizing radiation dose but also for a better depiction of FDG-avid lesions in pediatric PET imaging.

Summary of the First ISMRM-SNMMI Workshop on PET/MRI: Applications and Limitations

Since the introduction of simultaneous PET/MRI in 2011, there have been significant advancements. In this review, we highlight several technical advancements that have been made primarily in attenuation and motion correction and discuss the status of multiple clinical applications using PET/MRI. This review is based on the experience at the first PET/MRI conference cosponsored by the International Society for Magnetic Resonance in Medicine and the Society of Nuclear Medicine and Molecular Imaging.

MRI and PET/MRI in hematologic malignancies

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, [¹⁸F]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 [⁶⁸Ga]Ga‐Pentixafor and the amino acid radiotracer [¹¹C]methionine, on the other hand.

Level of Evidence: 5

Technical Efficacy Stage: 3

J. Magn. Reson. Imaging 2020;51:1325–1335.

DW-MRI for esophageal squamous cell carcinoma, correlations between ADC values with histologic differentiation and VEGF expression: A retrospective study

The aim of the present study was to assess the correlations between diffusion-weighted magnetic resonance imaging (DW-MRI) features with the histologic differentiation and the expression of vascular endothelial growth factor (VEGF) in esophageal squamous cell carcinoma (ESCC). A total of 52 patients with ESCC included in the present study received radiotherapy, and all patients underwent contrast enhanced MRI and DW-MRI prior to and following radiotherapy. The diffusion sensitivity coefficient (b value) was set as 800 s/mm². Apparent diffusion coefficient (ADC) values were automatically computed. VEGF expression was evaluated by immunohistochemical staining. The results demonstrated that the pathological grading of ESCC was positively correlated with ADC values (r=0.635, P=0.0007), and the VEGF expression was inversely correlated with ADC values (r=−0.321, P=0.008). However, no correlation was identified between the pathological grading and the VEGF expression (r=0.178, P=0.284). All patients were categorized as complete response (CR) or partial response (PR) and the ADC values were increased significantly following radiotherapy. The mean ADC values in the CR group were higher than the PR group prior to radiotherapy (t=5.156, P=0.0004). Therefore, we concluded that the DWI with ADC value measurement may represent the grade of tumor histologic differentiation and the degree of VEGF expression, and may also serve as a useful marker to predict radiotherapy and anti-VEGF response in ESCC. ADC value may be a substitution for assessing tumor angiogenesis and novel prognostic factor and contribute to the treatment of ESCC.

Feasibility of diffusion-weighted imaging with DWIBS in staging Hodgkin lymphoma in pediatric patients: comparison with PET/CT

Objective

The aim of the study was to evaluate feasibility of diffusion-weighted whole-body imaging with background body signal suppression (DWIBS) method in diagnosing Hodgkin lymphoma in pediatric patients and to compare it with 18F-FDG PET/CT as a gold standard.

Materials and methods

Eleven patients (median age 14) with newly diagnosed Hodgkin lymphoma were examined with 18F-FDG PET/CT and MRI including whole-body DWIBS sequence (b = 0, 800 s/mm²), before the oncologic treatment. About 26 locations of lymphatic tissues were evaluated visually and quantitatively using ADC_mean (DWIBS) and SUV_max (18F-FDG PET/CT), respectively.

Results

All affected lymph node regions (n = 134) diagnosed in 18F-FDG PET/CT were found with DWIBS, presenting decreased diffusion. Significant correlation was found between ADC and SUV values (R² = − 0.37; p = 0.0001). Nevertheless, additional 33 regions were recognized only by DWIBS. They were significantly smaller than regions diagnosed by both methods.

Discussion

Agreement between DWIBS and 18F-FDG PET/CT for detection and staging of malignant lymphoma is high. DWIBS can be used for the evaluation of pediatric Hodgkin lymphoma.

Whole-Body MR Imaging: The Novel, "Intrinsically Hybrid," Approach to Metastases, Myeloma, Lymphoma, in Bones and Beyond

Whole-body MR imaging (WB-MR imaging) has become a modality of choice for detecting bone metastases in multiple cancers, and bone marrow involvement by multiple myeloma or lymphoma. Combination of anatomic and functional sequences imparts an inherently hybrid dimension to this nonirradiating tool and extends the screening of malignancies outside the skeleton. WB-MR imaging outperforms bone scintigraphy and CT and offers an alternative to PET in many tumors by time of lesion detection and assessment of treatment response. Much work has been done to standardize procedures, optimize sequences, validate indications, confirm preliminary research into new applications, rendering clinical application more user-friendly.