Feasibility of simultaneous PET/MR imaging in the head and upper neck area

Tumor volume definitions in head and neck squamous cell carcinoma - Comparing PET/MRI and histopathology

BACKGROUND AND PURPOSE

In cancer treatment precise definition of the tumor volume is essential, but despite development in imaging modalities, this remains a challenge. Here, pathological tumor volumes from the surgical specimens were obtained and compared to tumor volumes defined from modern PET/MRI hybrid imaging. The purpose is to evaluate mismatch between the volumes defined from imaging and pathology was estimated and potential clinical impact.

METHODS AND MATERIALS

Twenty-five patients with head and neck squamous cell carcinoma were scanned on an integrated PET/MRI system prior to surgery. Three gross tumor volumes (GTVs) from the primary tumor site were delineated defined from MRI (GTV_MRI), PET (GTV_PET) and one by utilizing both anatomical images and clinical information (GTV_ONCO). Twenty-five primary tumor specimens were extracted en bloc, scanned with PET/MRI and co-registered to the patient images. Each specimen was sectioned in blocks, sliced and stained with haematoxylin and eosin. All slices were digitalized and tumor delineated by a head and neck pathologist. The pathological tumor areas in all slices were interpolated yielding a pathological 3D tumor volume (GTV_PATO). GTV_PATOwas compared with the imaging GTV's and potential mismatch was estimated.

RESULTS

Thirteen patients were included. The mean volume of GTV_ONCOwas larger than the GTV's defined from PET or MRI. The mean mismatch of the GTV_PATOcompared to the GTV_PET, GTV_MRIand GTV_ONCOwas 31.9 %, 54.5 % and 27.9 % respectively, and the entire GTV_PATO was only fully encompassed in GTV_ONCO in 1 of 13 patients. However, after the addition of a clinical 5 mm margin the GTV_PATO was fully encompassed in GTV_ONCO in 11 out of 13 patients.

CONCLUSIONS

Despite modern hybrid imaging modalities, a mismatch between imaging and pathological defined tumor volumes was observed in all patients.A 5 mm clinical margin was sufficient to ensure inclusion of the entire pathological volume in 11 out of 13 patients.

Intra-Individual Comparison of 124I-PET/CT and 124I-PET/MR Hybrid Imaging of Patients with Resected Differentiated Thyroid Carcinoma: Aspects of Attenuation Correction

Simple Summary

This study evaluates the qualitative and quantitative differences between 124-iodine PET/CT and PET/MR in oncologic patients with differentiated thyroid carcinoma after thyroidectomy. The impact of improved MR-based attenuation correction (AC) using a bone atlas was analysed in PET/MR data. Despite different patient positioning and AC methods PET/CT and PET/MR provide overall comparable results in a clinical setting. The overall number of detected ¹²⁴I-active lesions and the measured average SUV_mean values for congruent lesions were higher for PET/MR when compared to PET/CT. The addition of bone to the MR-based AC in PET/MR slightly increased the SUV_mean values for all detected lesions.

Abstract

Background: This study evaluates the quantitative differences between 124-iodine (I) positron emission tomography/computed tomography (PET/CT) and PET/magnetic resonance imaging (PET/MR) in patients with resected differentiated thyroid carcinoma (DTC). Methods: N = 43 ¹²⁴I PET/CT and PET/MR exams were included. CT-based attenuation correction (AC) in PET/CT and MR-based AC in PET/MR with bone atlas were compared concerning bone AC in the head-neck region. AC-map artifacts (e.g., dentures) were noted. Standardized uptake values (SUV) were measured in lesions in each PET data reconstruction. Relative differences in SUV_mean were calculated between PET/CT and PET/MR with bone atlas. Results: Overall, n = 111 ¹²⁴I-avid lesions were detected in all PET/CT, while n = 132 lesions were detected in PET/MR. The median in SUV_mean for n = 98 congruent lesions measured in PET/CT was 12.3. In PET/MR, the median in SUV_mean was 16.6 with bone in MR-based AC. Conclusions: ¹²⁴I-PET/CT and ¹²⁴I-PET/MR hybrid imaging of patients with DTC after thyroidectomy provides overall comparable quantitative results in a clinical setting despite different patient positioning and AC methods. The overall number of detected ¹²⁴I-avid lesions was higher for PET/MR compared to PET/CT. The measured average SUV_mean values for congruent lesions were higher for PET/MR.

The use of positron emission tomography/magnetic resonance imaging in dementia: A literature review

OBJECTIVES

Positron emission tomography-magnetic resonance imaging (PET/MRI) is an emerging hybrid imaging system in clinical nuclear medicine. Research demonstrates a comparative utility to current unimodal and hybrid methods, including PET-computed tomography (PET/CT), in several medical subspecialities such as neuroimaging. The aim of this review is to critically evaluate the literature from 2016 to 2021 using PET/MRI for the investigation of patients with mild cognitive impairment or dementia, and discuss the evidence base for widening its application into clinical practice.

METHODS

A comprehensive literature search using the PubMed database was conducted to retrieve studies using PET/MRI in relation to the topics of mild cognitive impairment, dementia, or Alzheimer's disease between January 2016 and January 2021. This search strategy enabled studies on all dementia types to be included in the analysis. Studies were required to have a minimum of 10 human subjects and incorporate simultaneous PET/MRI.

RESULTS

A total of 116 papers were retrieved, with 39 papers included in the final selection. These were broadly categorised into reviews (12), technical/methodological papers (11) and new data studies (16). For the current review, discussion focused on findings from the new data studies.

CONCLUSIONS

PET/MRI offers additional insight into the underlying anatomical, metabolic and functional changes associated with dementia when compared with unimodal methods and PET/CT, particularly relating to brain regions including the hippocampus and default mode network. Furthermore, the improved diagnostic utility of PET/MRI, as reported by radiologists, offers improved classification of dementia patients, with important implications for clinical management.

Imaging in head and neck cancers: Update for non-radiologist

Head and neck cancer (HNC) is the fifth most frequent cancer worldwide and associated with significant morbidity. Along with clinical examination and endoscopic evaluation, imaging plays an important role in pre- and posttherapeutic evaluation of patients with HNC. Cross-sectional Imaging techniques such as computed tomography (CT), magnetic resonance imaging (MRI) and positron emission tomography / computed tomography (PET/CT) are routinely used in the assessment of these patients. This review provides an overview of the various cross-sectional imaging modalities used in the evaluation of HNC and will give a short summary of the latest imaging technologies regarding head and neck cancer diagnosis.

Relative clinical utility of simultaneous 18F-fluorodeoxyglucose PET/MRI and PET/CT for preoperative cervical cancer diagnosis

Objective

To investigate the utility of ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography/magnetic resonance imaging (PET/MRI) for the preoperative diagnosis of cervical cancer.

Methods

We retrospectively analyzed 114 patients who were diagnosed with cervical cancer and underwent PET/MRI (n = 59) or PET/computed tomography (PET/CT) (n = 65) before surgery. The maximal standardized uptake value (SUV_max) and mean SUV (SUV_mean) were determined for regions of interest in the resultant radiographic images.

Results

Relative to PET/CT, ¹⁸F-FDG PET/MRI exhibited higher specificity and sensitivity in defining the primary tumor bounds and higher sensitivity for detection of bladder involvement. The SUV_max and SUV_mean of PET/MRI were remarkably higher than those of PET/CT as a means of detecting primary tumors, bladder involvement, and the lymph node status. However, no significant differences in these values were detected when comparing the two imaging approaches as a means of detecting vaginal involvement or para-aortic lymph node metastasis.

Conclusions

These outcomes may demonstrate the capability of ¹⁸F-FDG PET/MRI to clarify preoperative cervical cancer diagnoses in the context of unclear PET/CT findings. However, studies directly comparing SUVs in different lesion types from patients who have undergone both PET/MRI and PET/CT scans are essential to validate and expand upon these findings.

Added value of [18F]FDG PET/MRI over MDCT alone in the staging of recurrent gastric cancer

OBJECTIVES

To investigate whether 2-[¹⁸F]fluoro-2-deoxy-D-glucose ([¹⁸F]FDG) positron emission tomography/magnetic resonance imaging (PET/MRI) can improve the diagnostic performance of TNM staging and help in making an accurate decision regarding resectability in patients with recurrent gastric cancer compared to multi-detector computed tomography (MDCT).

METHODS

Fifty patients with histologically (n = 31) or clinically (n = 19) confirmed recurrent gastric cancer underwent both MDCT and [¹⁸F]FDG PET/MRI. Two radiologists independently assessed TNM staging using MDCT with and without [¹⁸F]FDG PET/MRI and scored resectability using a 5-point confidence scale. Diagnostic performance as assessed by radiologists was compared using McNemar's test and receiver operating characteristic curve analysis.

RESULTS

Of the 50 patients, pathologic T and N staging was available in seven and six patients, respectively. Diagnostic accuracies for T and N staging were not significantly different between MDCT with and without [¹⁸F]FDG PET/MRI for both reviewers (p > 0.05). However, for M staging, diagnostic accuracy was significantly improved when ¹⁸F-FDG PET/MRI was added to MDCT alone (68.0% [34/50] to 90.0% [45/50] for reviewer 1 [p = 0.001] and 66.0% [33/50] to 96.0% [46/50] for reviewer 2 [p < 0.001]). Regarding the resectability of recurrent gastric cancers, the addition of [¹⁸F]FDG PET/MRI increased the area under the curve values for both reviewers (from 0.860 to 0.989 for reviewer 1 and from 0.778 to 0.898 for reviewer 2), with a statistical significance for reviewer 2 (p = 0.002).

CONCLUSION

Compared to MDCT alone, MDCT plus [¹⁸F]FDG PET/MRI can improve the diagnostic accuracy for evaluating preoperative M staging as well as resectability for recurrent gastric cancers.

KEY POINTS

• [¹⁸F]FDG PET/MRI can improve diagnostic accuracy for preoperative M staging in patients with recurrent gastric cancers. • [¹⁸F]FDG PET/MRI can improve diagnostic accuracy for determining resectability in patients with recurrent gastric cancers. • [¹⁸F]FDG PET/MRI can provide critical clues for management options for recurrent gastric cancers.

Are Gadolinium-Enhanced MR Sequences Needed in Simultaneous 18F-FDG-PET/MRI for Tumor Delineation in Head and Neck Cancer?

BACKGROUND AND PURPOSE

PET/MRI with ¹⁸F-FDG has demonstrated the advantages of simultaneous PET and MR imaging in head and neck cancer imaging, MRI allowing excellent soft-tissue contrast, while PET provides metabolic information. The aim of this study was to evaluate the added value of gadolinium contrast-enhanced sequences in the tumor delineation of head and neck cancers on ¹⁸F-FDG-PET/MR imaging.

MATERIALS AND METHODS

Consecutive patients who underwent simultaneous head and neck ¹⁸F-FDG-PET/MR imaging staging or restaging followed by surgery were retrospectively included. Local tumor invasion and lymph node extension were assessed in 45 head and neck anatomic regions using ¹⁸F-FDG-PET/MR imaging by 2 rater groups (each one including a radiologist and a nuclear medicine physician). Two reading sessions were performed, one without contrast-enhanced sequences (using only T1WI, T2WI, and PET images) and a second with additional T1WI postcontrast sequences. The results were compared with the detailed histopathologic analysis, used as reference standard. The κ concordance coefficient between the reading sessions and sensitivity and specificity for each region were calculated.

RESULTS

Thirty patients were included. There was excellent agreement between the contrast-free and postgadolinium reading sessions in delineating precise tumor extension in the 45 anatomic regions studied (Cohen κ = 0.96, 95% CI = [0.94-0.97], P < .001). The diagnostic accuracy did not differ between contrast-free and postgadolinium reading sessions, being 0.97 for both groups and both reading sessions. For the 2 rater groups, there was good sensitivity for both contrast-free (0.83 and 0.85) and postgadolinium reading sessions (0.88 and 0.90, respectively). Moreover, there was excellent specificity (0.98) for both groups and reading sessions.

CONCLUSIONS

Gadolinium chelate contrast administration showed no added value for accurate characterization of head and neck primary tumor extension and could possibly be avoided in the PET/MR imaging head and neck workflow.

Diagnostic Accuracy and Confidence of [18F] FDG PET/MRI in comparison with PET or MRI alone in Head and Neck Cancer

The usefulness of PET/MRI in head and neck malignancy has not been fully elucidated. The purpose of our study was to evaluate the diagnostic accuracy and confidence of PET/MRI in comparison with PET or MRI alone. This study included 73 consecutive patients who underwent [18F] FDG PET/MRI in head and neck under the suspicion of malignancy. A neuroradiologist and a nuclear medicine specialist reviewed MRI and PET images, respectively and independently, followed by a consensus review of PET/MRI one month later. For 134 lesions, accuracy and confidence were compared among PET, MRI, and PET/MRI. For lesion base, PET/MRI had a sensitivity of 85.7%, a specificity of 89.1%, a PPV of 89.6%, a negative predictive value of 85.1%, and an accuracy of 87.3%. AUCs of PET/MRI per lesion (0.926) and per patient (0.934) for diagnosing malignancy were higher than PET (0.847 and 0.747, respectively) or MRI (0.836 and 0.798, respectively) alone (P < 0.05). More than 80% of the cases (111/134) showed diagnostic concordance between PET and MRI. PPV of PET/MRI was higher in malignant concordant cases (93.2%, 55/59) than in discordant cases (62.5%, 5/8) (p = 0.040). Confident scoring rate in malignant concordant cases was higher on PET/MRI (96.6%, 57/59) than on MRI (76.3%, 45/59) (p = 0.003). In conclusion, compared with PET or MRI alone, PET/MRI presents better diagnostic performance in accuracy and confidence for diagnosis of malignancy. PET/MRI is useful in patients with head and neck cancer.

18F-FDG-PET/CT Imaging in Advanced Glottic Cancer: A Tool for Clinical Decision in Comparison with Conventional Imaging

This study assessed the role of ¹⁸F-FDG PET-CT (PET/CT) to detect the cartilage and paraglottic infiltration in advanced glottic cancer comparing the results with those of conventional imaging (CI) (contrast-enhanced computed tomography and/or magnetic resonance). In addition, we assessed the prognostic value of quantitative parameters, measured on baseline PET/CT, in terms of event-free survival (EFS) and overall survival (OS). We retrospectively analyzed 27 patients with glottic squamous cell carcinoma stage III and IVA, treated in our institute between 2010 and 2016, comparing PET/CT, performed for staging and radiotherapy planning, and CI findings. Cohen's K was used to compare concordance between PET/CT and CI. Imaging findings were correlated with endoscopic evaluation and histological reports (gold standard (GS)). All lesions shown by CI were also detected by PET/CT imaging, and in 5 cases, a better definition of local infiltration was achieved with PET/CT than CI (5 CT). Sensitivity, specificity, and accuracy of PET/CT and CT were 95%, 86%, and 93% and 70%, 86%, and 74% for, respectively. MRI showed sensitivity and specificity of 100%. One false-negative (FN) cases and 1 false-positive (FP) case were observed with PET/CT with no difference compared to MRI (10 cases). Six FN cases and 1 FP case were observed with CT. Cohen's K was 0.60 (PET vs. CI) and 0.80 (PET vs. GS). Patients were followed-up for at least 24 months to calculate EFS and OS. 13 local recurrence and 7 deaths were recorded. Among quantitative PET parameters, baseline MTV was the most powerful predictor of outcome. Our data suggest a reliable sensitivity and accuracy of PET/CT in the evaluation of local extension, proving a useful method for initial local staging in addition to the well-established role in lymph-node and distant sites assessment. Furthermore, pretreatment MTV provides better prognostic information than other PET/CT parameters.

PET/MRI vs PET/CT in Head and Neck Imaging: When, Why, and How?

The increasing availability of hybrid PET/MRI systems has led to a breadth of new publications and opportunities for use of PET/MRI. While PET/CT has been a valuable tool for oncologic staging, including head and neck malignancy, there are several theoretical and practical advantages a PET/MRI system would have over PET/CT in head and neck imaging. This review article discusses the established role of PET/CT, early evidence for the role of PET/MRI, and protocol considerations for both PET/CT and PET/MRI as they apply to head and neck imaging.

Voxel-wise correlation of functional imaging parameters in HNSCC patients receiving PET/MRI in an irradiation setup

PURPOSE

The purpose of this study was to demonstrate the feasibility of voxel-wise multiparametric characterization of head and neck squamous cell carcinomas (HNSCC) using hybrid multiparametric magnetic resonance imaging and positron emission tomography with [¹⁸F]-fluorodesoxyglucose (FDG-PET/MRI) in a radiation treatment planning setup.

METHODS

Ten patients with locally advanced HNSCC were examined with a combined FDG-PET/MRI in an irradiation planning setup. The multiparametric imaging protocol consisted of FDG-PET, T2-weighted transverse short tau inversion recovery sequence (STIR) and diffusion-weighted MRI (DWI). Primary tumours were manually segmented and quantitative imaging parameters were extracted. PET standardized uptake values (SUV) and DWI apparent diffusion coefficients (ADC) were correlated on a voxel-wise level.

RESULTS

Images acquired in this specialised radiotherapy planning setup achieved good diagnostic quality. Median tumour volume was 4.9 [1.1-42.1] ml. Mean PET SUV and ADC of the primary tumours were 5 ± 2.5 and 1.2 ± 0.3 10^-3 mm²/s, respectively. In voxel-wise correlation between ADC values and corresponding FDG SUV of the tumours, a significant negative correlation was observed (r = -0.31 ± 0.27, p < 0.05).

CONCLUSION

Multiparametric voxel-wise characterization of HNSCC is feasible using combined PET/MRI in a radiation planning setup. This technique may provide novel insights into tumour biology with regard to radiation therapy in the future.

PET/MR Imaging in Head and Neck Cancer: Current Applications and Future Directions

Clinical PET/MR imaging is being implemented at institutions worldwide as part of the standard-of-care imaging for select oncology patients. This article focuses on oncologic applications of PET/MR imaging in cancers of the head and neck. Although current published literature is relatively sparse, the potential benefits of a hybrid modality of PET/MR imaging are discussed along with several possible areas of research. With the increasing number of PET/MR imaging scanners in clinical use and ongoing research, the role of PET/MR imaging in the management of head and neck cancer is likely to become more evident in the near future.

Chapter 8 On the Horizon: Advanced Imaging Techniques to Improve Noninvasive Assessment of Cervical Lymph Nodes

Conventional imaging modalities are limited in the evaluation of lymph nodes as they predominantly rely on size and morphology, which have suboptimal sensitivity and specificity for malignancy. In this review we will explore the role of "on the horizon" advanced imaging modalities that can look beyond the size and morphologic features of a cervical lymph node and explore its molecular nature and can aid in personalizing therapy rather than use the "one-size-fits-all" approach.

[Molecular imaging of head and neck cancers : Perspectives of PET/MRI]

BACKGROUND

The (18)F-fluorodeoxyglucose positron emission tomography-computed tomography ((18)F-FDG-PET/CT) procedure is a cornerstone in the diagnostics of head and neck cancers. Several years ago PET-magnetic resonance imaging (PET/MRI) also became available as an alternative hybrid multimodal imaging method.

OBJECTIVE

Does PET/MRI have advantages over PET/CT in the diagnostics of head and neck cancers?

MATERIAL AND METHODS

The diagnostic accuracy of the standard imaging methods CT, MRI and PET/CT is depicted according to currently available meta-analyses and studies concerning the use of PET/MRI for these indications are summarized.

RESULTS

In all studies published up to now PET/MRI did not show superiority regarding the diagnostic accuracy in head and neck cancers; however, there is some evidence that in the future PET/MRI can contribute to tumor characterization and possibly be used to predict tumor response to therapy with the use of multiparametric imaging.

CONCLUSION

Currently, (18)F-FDG-PET/CT is not outperformed by PET/MRI in the diagnostics of head and neck cancers. The additive value of PET/MRI due to the use of multiparametric imaging needs to be investigated in future research.

PET/MRI: a novel hybrid imaging technique. Major clinical indications and preliminary experience in Brazil

In recent years, medical imaging with hybrid techniques has widely accepted and employed in clinical routine. PET/MRI offers significant advantages, including excellent contrast and resolution and reduced ionizing radiation, as compared to well-established PET/CT. Therefore, PET/MRI is a promising modality for oncologic imaging of some regions, such as brain, head and neck, liver and pelvis. This article set out to analyze clinical conditions that could benefit from PET/MRI imaging based on our caseload. The potential of PET/MRI to become the imaging modality of choice for assessment of neurologic and oncologic conditions associated with soft tissues is highlighted. Clinical aspects of PET/MRI and its application to clinical cases are illustrated with examples extracted from the authors’ preliminary experience.

Prospective comparison of 18F-NaF PET/CT versus 18F-FDG PET/CT imaging in mandibular extension of head and neck squamous cell carcinoma with dedicated analysis software and validation with surgical specimen. A preliminary study

BACKGROUND

The aim of this study is to propose a new method to quantify radioactivity with PET/CT imaging in mandibular extension in head and neck squamous cell carcinoma (HNSCC), using innovative software, and to compare results with microscopic surgical specimens.

PATIENTS AND METHODS

This prospective study enrolled 15 patients who underwent ¹⁸F-NaF and ¹⁸F-FDG PET/CT. We compared the delineations of bone invasions obtained with ¹⁸F-NaF PET/CT and ¹⁸F-FDG PET/CT with the results of histopathological analysis of mandibular resections (from right and left bone borders). A method for visualization and quantification of PET images was developed.

RESULTS

For all patients, a significant difference (p = 0.032 for right limits and p = 0.011 for left limits) was observed between ¹⁸F-FDG PET/CT imaging and histopathology results, and no significant difference (p = 0.88 for right limits and p = 0.55 for left limits) was observed between ¹⁸F-NaF PET/CT imaging and histopathology results. The right limits were less than 10 mm in 93% of patients, and the left limits were less than 10 mm in 86% of patients.

CONCLUSIONS

The dedicated software enabled the objective delineation of radioactivity within the bone. We can confirm that ¹⁸F-NaF is a precise and specific bone marker for the assessment of intraosseous mandibular extensions of head and neck cancers.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, III.

The Advents of Hybrid Imaging Modalities: A New Era in Neuroimaging Applications

Hybrid Imaging modalities have shown great potential in medical imaging and diagnosis. A more comprehensive and targeted view of neurological disorders can be achieved by blending the anatomical and functional perspectives through hybridization. With consistently improving technologies, there have been many developments in fused imaging techniques over the past few decades. This article provides an overview of various bimodal and trimodal hybrid imaging techniques being developed and explored for neuroimaging applications. Recent advancements and potentials are discussed for single photon emission computed tomography-computed tomography (SPECT-CT), positron emission tomography-CT (PET-CT), PET-magnetic resonance imaging (PET-MRI), electroencephalography-functional magnetic resonance imaging (EEG-fMRI), magnetoencephalography-fMRI (MEG-fMRI), EEG-near-infrared spectroscopy (EEG-NIRS), magnetic resonance-PET-EEG (MR-PET-EEG) and MR-PET-CT in the perspective of neuroimaging. A comparison of these hybrid approaches is provided on a single platform to analyze their performance on the basis of several common factors essential for imaging and analyzing neurological disorders and in vivo molecular processes. This article also provides an overview of recently developed advanced imaging technologies that are being hybridized with other imaging modalities and being explored as potential techniques for neuroscience. Novel approaches and clinical applications of hybrid neuroimaging are anticipated with inclusion of new technologies, better sensing capabilities, multimodal probes, and improved hybridization.

Staging performance of whole-body DWI, PET/CT and PET/MRI in invasive ductal carcinoma of the breast

The aim of the present study was to evaluate the performance of whole-body diffusion-weighted imaging (WB-DWI), whole-body positron emission tomography with computed tomography (WB-PET/CT), and whole-body positron emission tomography with magnetic resonance imaging (WB-PET/MRI) in staging patients with untreated invasive ductal carcinoma of the breast. Fifty-one women with newly diagnosed invasive ductal carcinoma of the breast underwent WB-DWI, WB-PET/CT and WB-PET/MRI before treatment. A radiologist and a nuclear medicine physician reviewed in consensus the images from the three modalities and searched for occurrence, number and location of metastases. Final staging, according to each technique, was compared. Pathology and imaging follow-up were used as the reference. WB-DWI, WB-PET/CT and WB-PET/MRI correctly and concordantly staged 33/51 patients: stage IIA in 7 patients, stage IIB in 8 patients, stage IIIC in 4 patients and stage IV in 14 patients. WB-DWI, WB-PET/CT and WB-PET/MRI incorrectly and concordantly staged 1/51 patient as stage IV instead of IIIA. Discordant staging was reported in 17/51 patients. WB-PET/MRI resulted in improved staging when compared to WB-PET/CT (50 correctly staged on WB-PET/MRI vs. 38 correctly staged on WB-PET/CT; McNemar's test; p<0.01). Comparing the performance of WB-PET/MRI and WB-DWI (43 correct) did not reveal a statistically significant difference (McNemar test, p=0.14). WB-PET/MRI is more accurate in the initial staging of breast cancer than WB-DWI and WB-PET/CT, however, the discrepancies between WB-PET/MRI and WB-DWI were not statistically significant. When available, WB-PET/MRI should be considered for staging patient with invasive ductal breast carcinoma.

PET+MR versus PET/CT in the initial staging of head and neck cancer, using a trimodality PET/CT+MR system

PURPOSE

To compare the diagnostic accuracy of PET+MR with PET/CT in the initial staging of head and neck cancer.

MATERIALS AND METHODS

Contrast-enhanced PET/CT+MR was performed in 27 patients with newly diagnosed head and neck cancer. PET/CT and PET+MR were evaluated separately, and the TNM stage and factors influencing treatment were assessed.

RESULTS

The TNM staging by PET+MR was comparable to PET/CT (T: p=0.331, N: p=0.453, M: p=0.034). The sensitivity/specificity/accuracy of treatment-influencing factors by PET/CT and PET+MR were 0.68/0.99/0.97, and 1.00/1.00/0.99, respectively.

CONCLUSIONS

Whole-body staging with PET+MR yields at least equal diagnostic accuracy as PET/CT in head and neck cancer.

FDG Whole-Body PET/MRI in Oncology: a Systematic Review

The recent advance in hybrid imaging techniques enables offering simultaneous positron emission tomography (PET)/magnetic resonance imaging (MRI) in various clinical fields. ¹⁸F-fluorodeoxyglucose (FDG) PET has been widely used for diagnosis and evaluation of oncologic patients. The growing evidence from research and clinical experiences demonstrated that PET/MRI with FDG can provide comparable or superior diagnostic performance more than conventional radiological imaging such as computed tomography (CT), MRI or PET/CT in various cancers. Combined analysis using structural information and functional/molecular information of tumors can draw additional diagnostic information based on PET/MRI. Further studies including determination of the diagnostic efficacy, optimizing the examination protocol, and analysis of the hybrid imaging results is necessary for extending the FDG PET/MRI application in clinical oncology.

PET/MR in cancers of the head and neck

One early application of PET/MRI in clinical practice may be the imaging of head and neck cancers. This is because the morphologic imaging modalities, CT and MR, are recognized as similarly effective tools in cross-sectional oncological imaging of the head and neck. The addition of PET with FDG is believed to enhance the accuracy of both modalities to a similar degree. However, there are a few specific scenarios in head and neck cancer imaging where MR is thought to provide an edge over CT, including perineural spread of tumors and the infiltration of important anatomical landmarks, such as the prevertebral fascia and great vessel walls. Here, hybrid PET/MR might provide higher diagnostic certainty than PET/CT or a separate acquisition of PET/CT and MR. Another advantage of MR is the availability of several functional techniques. Although some of them might enhance the imaging of head and neck cancer with PET/MR, other functional techniques actually might prove dispensable in the presence of PET. In this overview, we discuss current trends and potential clinical applications of PET/MR in the imaging of head and neck cancers, including clinical protocols. We also discuss potential benefits of implementing functional MR techniques into hybrid PET/MRI of head and neck cancers.

Positive and Negative Predictive Value of PET-CT in Skull Base Lesions: Case Series and Systematic Literature Review

Objectives To study positive (PPV) and negative predictive value (NPV) of positron emission tomography with computed tomography (PET-CT) scans in determining malignancy in skull base lesions and perform a systematic literature review for optimal PET-CT interpretation. Design Retrospective case series and systematic literature review of the current English literature. Setting Tertiary referral academic medical center. Participants All patients with skull base lesions that underwent PET-CT and tissue biopsy from 2010 to 2013. Main Outcome Measures PPV and NPV of radiologist's report and standardized uptake value (SUV) cutoff of 2.5 and 3, biopsy with pathologic interpretation, clinical follow-up. Results A total of 31 PET-CT scans of 16 patients were studied; 10 PET-CT were performed upfront for diagnostic purposes and 21 were post-treatment surveillance scans. The PPV of radiologist's interpretation, SUV cutoff of 2.5, and SUV cutoff of 3.0 was 80%, 60%, and 68.4%, with a NPV of 100%, 83.3%, and 75%, respectively. Literature search yielded 500 abstracts; 7 studies met inclusion criteria for detailed review. No consensus or guidelines for optimal SUV cutoff value was found. Conclusions PET-CT based on SUV cutoff criteria alone has high NPV but low PPV in determining malignancy in skull base lesions. Interpretation by a radiologist experienced in nuclear medicine and neuroradiology, synthesizing clinical, SUV, and radiologic data are of superior value.

Standardized Uptake Values from PET/MRI in Metastatic Breast Cancer: An Organ-based Comparison With PET/CT

Quantitative standardized uptake values (SUVs) from fluorine-18 (18F) fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) are commonly used to evaluate the extent of disease and response to treatment in breast cancer patients. Recently, PET/magnetic resonance imaging (MRI) has been shown to qualitatively detect metastases from various primary cancers with similar sensitivity to PET/CT. However, quantitative validation of PET/MRI requires assessing the reliability of SUVs from MR attenuation correction (MRAC) relative to CT attenuation correction (CTAC). The purpose of this retrospective study was to assess the utility of PET/MRI-derived SUVs in breast cancer patients by testing the hypothesis that SUVs derived from MRAC correlate well with those from CTAC. Between August 2012 and May 2013, 35 breast cancer patients (age 37-78 years, 1 man) underwent clinical 18F-FDG PET/CT followed by PET/MRI. One hundred seventy metastases were seen in 21 of 35 patients; metastases to bone in 16 patients, to liver in seven patients, and to nonaxillary lymph nodes in eight patients were sufficient for statistical analysis on an organ-specific per patient basis. SUVs in the most FDG-avid metastasis per organ per patient from PET/CT and PET/MRI were measured and compared using Pearson's correlations. Correlations between CTAC- and MRAC-derived SUVmax and SUVmean in 31 metastases to bone, liver, and nonaxillary lymph nodes were strong overall (ρ = 0.80, 0.81). SUVmax and SUVmean correlations were also strong on an organ-specific basis in 16 bone metastases (ρ = 0.76, 0.74), seven liver metastases (ρ = 0.85, 0.83), and eight nonaxillary lymph node metastases (ρ = 0.95, 0.91). These strong organ-specific correlations between SUVs from PET/CT and PET/MRI in breast cancer metastases support the use of SUVs from PET/MRI for quantitation of 18F-FDG activity.

Current Status of Hybrid PET/MRI in Oncologic Imaging

OBJECTIVE

This review article explores recent advancements in PET/MRI for clinical oncologic imaging.

CONCLUSION

Radiologists should understand the technical considerations that have made PET/MRI feasible within clinical workflows, the role of PET tracers for imaging various molecular targets in oncology, and advantages of hybrid PET/MRI compared with PET/CT. To facilitate this understanding, we discuss clinical examples (including gliomas, breast cancer, bone metastases, prostate cancer, bladder cancer, gynecologic malignancy, and lymphoma) as well as future directions, challenges, and areas for continued technical optimization for PET/MRI.

Clinical applications of PET/MRI: current status and future perspectives

Fully integrated positron emission tomography (PET)/magnetic resonance imaging (MRI) scanners have been available for a few years. Since then, the number of scanner installations and published studies have been growing. While feasibility of integrated PET/MRI has been demonstrated for many clinical and preclinical imaging applications, now those applications where PET/MRI provides a clear benefit in comparison to the established reference standards need to be identified. The current data show that those particular applications demanding multiparametric imaging capabilities, high soft tissue contrast and/or lower radiation dose seem to benefit from this novel hybrid modality. Promising results have been obtained in whole-body cancer staging in non-small cell lung cancer and multiparametric tumor imaging. Furthermore, integrated PET/MRI appears to have added value in oncologic applications requiring high soft tissue contrast such as assessment of liver metastases of neuroendocrine tumors or prostate cancer imaging. Potential benefit of integrated PET/MRI has also been demonstrated for cardiac (i.e., myocardial viability, cardiac sarcoidosis) and brain (i.e., glioma grading, Alzheimer's disease) imaging, where MRI is the predominant modality. The lower radiation dose compared to PET/computed tomography will be particularly valuable in the imaging of young patients with potentially curable diseases.However, further clinical studies and technical innovation on scanner hard- and software are needed. Also, agreements on adequate refunding of PET/MRI examinations need to be reached. Finally, the translation of new PET tracers from preclinical evaluation into clinical applications is expected to foster the entire field of hybrid PET imaging, including PET/MRI.

Simultaneous whole-body time-of-flight 18F-FDG PET/MRI: a pilot study comparing SUVmax with PET/CT and assessment of MR image quality

PURPOSE

The recent introduction of hybrid PET/MRI scanners in clinical practice has shown promising initial results for several clinical scenarios. However, the first generation of combined PET/MRI lacks time-of-flight (TOF) technology. Here we report the results of the first patients to be scanned on a completely novel fully integrated PET/MRI scanner with TOF.

MATERIALS AND METHODS

We analyzed data from patients who underwent a clinically indicated F FDG PET/CT, followed by PET/MRI. Maximum standardized uptake values (SUVmax) were measured from F FDG PET/MRI and F FDG PET/CT for lesions, cerebellum, salivary glands, lungs, aortic arch, liver, spleen, skeletal muscle, and fat. Two experienced radiologists independently reviewed the MR data for image quality.

RESULTS

Thirty-six patients (19 men, 17 women, mean [±standard deviation] age of 61 ± 14 years [range: 27-86 years]) with a total of 69 discrete lesions met the inclusion criteria. PET/CT images were acquired at a mean (±standard deviation) of 74 ± 14 minutes (range: 49-100 minutes) after injection of 10 ± 1 mCi (range: 8-12 mCi) of F FDG. PET/MRI scans started at 161 ± 29 minutes (range: 117 - 286 minutes) after the F FDG injection. All lesions identified on PET from PET/CT were also seen on PET from PET/MRI. The mean SUVmax values were higher from PET/MRI than PET/CT for all lesions. No degradation of MR image quality was observed.

CONCLUSION

The data obtained so far using this investigational PET/MR system have shown that the TOF PET system is capable of excellent performance during simultaneous PET/MR with routine pulse sequences. MR imaging was not compromised. Comparison of the PET images from PET/CT and PET/MRI show no loss of image quality for the latter. These results support further investigation of this novel fully integrated TOF PET/MRI instrument.

Locoregional tumour evaluation of squamous cell carcinoma in the head and neck area: a comparison between MRI, PET/CT and integrated PET/MRI

PURPOSE

To evaluate the accuracy of integrated (18)F-FDG PET/MR imaging for locoregional tumour evaluation compared to (18)F-FDG PET/CT and MR imaging in initial tumour and recurrence diagnosis in histopathologically confirmed head and neck squamous cell carcinoma (HNSCC).

METHODS

(18)F-FDG PET/CT and integrated (18)F-FDG PET/MR imaging were performed for initial tumour staging or recurrence diagnosis in 25 patients with HNSCC. MR, fused (18)F-FDG PET/CT and fused (18)F-FDG PET/MR images were analysed by two independent readers in separate sessions in random order. In initial tumour staging, T and N staging was performed while individual lesions were analysed in patients with suspected cancer recurrence. In T and N staging, histopathological results after tumour resection served as the reference standard while histopathological sampling as well as cross-sectional and clinical follow-up were accepted in cancer recurrence diagnosis. The diagnostic accuracy of each modality was calculated separately for T and N staging as well as for tumour recurrence, and compared using McNemar's test. Values of p <0.017 were considered statistically significant after Bonferroni correction.

RESULTS

In 12 patients undergoing (18)F-FDG PET/CT and (18)F-FDG PET/MR for initial tumour staging, T staging was accurate in 50 % with MRI, in 59 % with PET/CT and in 75 % with PET/MR while N staging was accurate in 75 % with MRI, in 77 % with PET/CT and in 71 % with PET/MR in relation to the reference standard. No significant differences were observed in T and N staging among the three modalities (p > 0.017). In 13 patients undergoing hybrid imaging for cancer recurrence diagnosis, diagnostic accuracy was 57 % with MRI and in 72 % with (18)F-FDG PET/CT and (18)F-FDG PET/MR, respectively. Again, no significant differences were found among the three modalities (p > 0.017).

CONCLUSION

In this initial study, no significant differences were found among (18)F-FDG PET/MR, (18)F-FDG PET/CT and MRI in local tumour staging and cancer recurrence diagnosis.

Pulmonary Nodule Detection in Patients with a Primary Malignancy Using Hybrid PET/MRI: Is There Value in Adding Contrast-Enhanced MR Imaging?

Purpose

To investigate the added value of post-contrast VIBE (volumetric-interpolated breath-hold examination) to PET/MR imaging for pulmonary nodule detection in patients with primary malignancies.

Materials and Methods

This retrospective institutional review board–approved study, with waiver of informed consent, included 51 consecutive patients who underwent ¹⁸F-fluorodeoxyglucose (FDG) PET/MR followed by PET/CT for cancer staging. In all patients, the thorax was examined with pre-and post-contrast VIBE MR with simultaneous PET acquisition. Two readers blinded to the patients’ data independently recorded their level of suspicion for pulmonary nodules based on PET, pre-contrast VIBE, and fused PET/MR images (first session), and reassessed them 4-weeks later after addition of post-contrast VIBE (second session). Jackknife alternative free-response receiver-operating-characteristic (JAFROC) analysis was performed, with PET/CT as the reference standard.

Results

A total of 151 pulmonary nodules (44 FDG-avid, 107 non-FDG-avid nodules) were detected on PET/CT, including 62 nodules≥5mm in diameter and 89 nodules<5mm. In the first session, the average nodule detection rate was 53.3% for all nodules, 97.7% for FDG-avid, 35.0% for non-FDG-avid nodules, 87.9% for nodules≥5mm and 29.2% for nodules<5mm. In the second session, the average detection rate was 53.3% for all nodules, 97.7% for FDG-avid, 35.0% for non-FDG-avid nodules, 85.5% for nodules≥5mm and 30.9% for nodules<5mm. The average JAFROC figure-of-merit was 0.837 in the first session and 0.848 in the second session. There were no significant differences in detection performance between sessions (P=0.48).

Conclusion

The addition of post-contrast VIBE to hybrid PET/MR imaging provided no additional value in the detection of pulmonary nodules.

Simultaneous PET/MR head-neck cancer imaging: Preliminary clinical experience and multiparametric evaluation

PURPOSE

To evaluate the role of simultaneous hybrid PET/MR imaging and to correlate metabolic PET data with morpho-functional parameters derived by MRI in patients with head-neck cancer.

METHODS

Forty-four patients, with histologically confirmed head and neck malignancy (22 primary tumors and 22 follow-up) were studied. Patients initially received a clinical exam and endoscopy with direct biopsy. Next patients underwent whole body PET/CT followed by PET/MR of the head/neck region. PET and MRI studies were separately evaluated by two blinded groups (both included one radiologist and one nuclear physician) in order to define the presence or absence of lesions/recurrences. Regions of interest (ROIs) analysis was conducted on the primary lesion at the level of maximum size on metabolic (SUV and MTV), diffusion (ADC) and perfusion (K(trans), Ve, kep and iAUC) parameters.

RESULTS

PET/MR examinations were successfully performed on all 44 patients. Agreement between the two blinded groups was found in anatomic allocation of lesions by PET/MR (Primary tumors: Cohen's kappa 0.93;

FOLLOW-UP

Cohen's kappa 0.89). There was a significant correlation between CT-SUV measures and MR (e.g., CT-SUV VOI vs.

MR-SUV VOI

ρ=0.97, p<0.001 for the entire sample). There was also significant positive correlations between the ROI area, SUV measures, and the metabolic parameters (SUV and MTV) obtained during both PET/CT and PET/MR. A significant negative correlation was observed between ADC and K(trans) values in the primary tumors. In addition, a significant negative correlation existed between MR SUV and ADC in recurrent tumors.

CONCLUSION

Our study demonstrates the feasibility of PET/MR imaging for primary tumors and recurrent tumors evaluations of head/neck malignant lesions. When assessing HNC, PET/MR allows simultaneous collection of multiparametric metabolic and functional data. This technique therefore allows for a more complete characterization of malignant lesions.

Reproducibility of (18)F-FDG PET uptake measurements in head and neck squamous cell carcinoma on both PET/CT and PET/MR

OBJECTIVE

To investigate reproducibility of fluorine-18 fludeoxyglucose ((18)F-FDG) uptake on (18)F-FDG positron emission tomography (PET)/CT and (18)F-FDG PET/MR scans in patients with head and neck squamous cell carcinoma (HNSCC).

METHODS

30 patients with HNSCC were included in this prospective study. The patients were scanned twice before radiotherapy treatment with both PET/CT and PET/MR. Patients were scanned on the same scanners, 3 days apart and according to the same protocol. Metabolic tumour activity was measured by the maximum and peak standardized uptake value (SUVmax and SUVpeak, respectively), and total lesion glycolysis from the metabolic tumour volume defined from ≥50% SUVmax. Bland-Altman analysis with limits of agreement, coefficient of variation (CV) from the two modalities were performed in order to test the reproducibility. Furthermore, CVs from SUVmax and SUVpeak were compared. The area under the curve from cumulative SUV-volume histograms were measured and tested for reproducibility of the distribution of (18)F-FDG uptake.

RESULTS

24 patients had two pre-treatment PET/CT scans and 21 patients had two pre-treatment PET/MR scans available for further analyses. Mean difference for SUVmax, peak and mean was approximately 4% for PET/CT and 3% for PET/MR, with 95% limits of agreement less than ±20%. CV was small (5-7%) for both modalities. There was no significant difference in CVs between PET/CT and PET/MR (p = 0.31). SUVmax was not more reproducible than SUVpeak (p = 0.09).

CONCLUSION

(18)F-FDG uptake in PET/CT and PET/MR is highly reproducible and we found no difference in reproducibility between PET/CT and PET/MR.

ADVANCES IN KNOWLEDGE

This is the first report to test reproducibility of PET/CT and PET/MR.

Integrated whole body MR/PET: where are we?

Whole body integrated magnetic resonance imaging (MR)/positron emission tomography (PET) imaging systems have recently become available for clinical use and are currently being used to explore whether the combined anatomic and functional capabilities of MR imaging and the metabolic information of PET provide new insight into disease phenotypes and biology, and provide a better assessment of oncologic diseases at a lower radiation dose than a CT. This review provides an overview of the technical background of combined MR/PET systems, a discussion of the potential advantages and technical challenges of hybrid MR/PET instrumentation, as well as collection of possible solutions. Various early clinical applications of integrated MR/PET are also addressed. Finally, the workflow issues of integrated MR/PET, including maximizing diagnostic information while minimizing acquisition time are discussed.

Diagnostic value of retrospective PET-MRI fusion in head-and-neck cancer

Background

To assess the diagnostic value of retrospective PET-MRI fusion and to compare the results with side-by-side analysis and single modality use of PET and of MRI alone for locoregional tumour and nodal staging of head-and-neck cancer.

Methods

Thirty-three patients with head-and-neck cancer underwent preoperative contrast-enhanced MRI and PET/CT for staging. The diagnostic data of MRI, PET, side-by-side analysis of MRI and PET images and retrospective PET-MRI fusion were systematically analysed for tumour and lymph node staging using receiver operating characteristic (ROC) analysis. The results were correlated to the histopathological evaluation.

Results

The overall sensitivity/specificity for tumour staging for MRI, PET, side-by-side analysis and retrospective PET-MRI fusion was 79%/66%, 82%/100%, 86%/100% and 89%/100%, respectively. The overall sensitivity/specificity for nodal staging on a patient basis for MRI, PET, side-by-side analysis and PET-MRI fusion was 94%/64%, 94%/91%, 94%/82% and 94%/82%, respectively. MRI, PET, side-by-side analysis and retrospective image fusion were associated with correct diagnosis/over-staging/under-staging of N-staging in 70.4%/18.5%/11.1%, 81.5%/7.4%/11.1%, 81.5%/11.1%/7.4% and 81.5%/11.1%/7.4%, respectively.

ROC analysis showed no significant differences in tumor detection between the investigated methods. The Area Under the Curve (AUC) for MRI, PET, side-by-side analysis and retrospective PET-MRI fusion were 0.667/0.667/0.702/0.708 (p > 0.05). The most reliable technique in detection of cervical lymph node metastases was PET imaging (AUC: 0.95), followed by side-by-side analysis and retrospective image fusion technique (AUC: 0.941), which however, was not significantly better then the MRI (AUC 0.935; p > 0.05).

Conclusions

We found a beneficial use of multimodal imaging, compared with MRI or PET imaging alone, particular in individual cases of recurrent tumour disease. Side-by-side analysis and retrospective image fusion analysis did not perform significantly differently.

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 (18)F-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 (18)F-FDG-PET/MR imaging and (18)F-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 (18)F-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 (18)F-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 (18)F-FDG-PET/MR imaging and (18)F-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, (18)F-FDG-PET/MR imaging and (18)F-FDG-PET/CT provide comparable results in the detection of lymph node and distant metastases. Standardized uptake values derived from (18)F-FDG-PET/MR imaging can be used reliably in this patient population.

FDG-PET/CT pitfalls in oncological head and neck imaging

OBJECTIVES

Positron emission tomography-computed tomography (PET/CT) with fluorine-18-fluorodeoxy-D-glucose (FDG) has evolved from a research modality to an invaluable tool in head and neck cancer imaging. However, interpretation of FDG PET/CT studies may be difficult due to the inherently complex anatomical landmarks, certain physiological variants and unusual patterns of high FDG uptake in the head and neck. The purpose of this article is to provide a comprehensive approach to key imaging features and interpretation pitfalls of FDG-PET/CT of the head and neck and how to avoid them.

METHODS

We review the pathophysiological mechanisms leading to potentially false-positive and false-negative assessments, and we discuss the complementary use of high-resolution contrast-enhanced head and neck PET/CT (HR HN PET/CT) and additional cross-sectional imaging techniques, including ultrasound (US) and magnetic resonance imaging (MRI).

RESULTS

The commonly encountered false-positive PET/CT interpretation pitfalls are due to high FDG uptake by physiological causes, benign thyroid nodules, unilateral cranial nerve palsy and increased FDG uptake due to inflammation, recent chemoradiotherapy and surgery. False-negative findings are caused by lesion vicinity to structures with high glucose metabolism, obscuration of FDG uptake by dental hardware, inadequate PET scanner resolution and inherent low FDG-avidity of some tumours.

CONCLUSIONS

The interpreting physician must be aware of these unusual patterns of FDG uptake, as well as limitations of PET/CT as a modality, in order to avoid overdiagnosis of benign conditions as malignancy, as well as missing out on actual pathology.

TEACHING POINTS

• Knowledge of key imaging features of physiological and non-physiological FDG uptake is essential for the interpretation of head and neck PET/CT studies. • Precise anatomical evaluation and correlation with contrast-enhanced CT, US or MRI avoid PET/CT misinterpretation. • Awareness of unusual FDG uptake patterns avoids overdiagnosis of benign conditions as malignancy.

From PET/CT to PET/MRI: advances in instrumentation and clinical applications

Multimodality imaging of positron emission tomography/computed tomography (PET/CT) provides both metabolic information and the anatomic structure, which is significantly superior to either PET or CT alone and has greatly improved its clinical applications. Because of the higher soft-tissue contrast of magnetic resonance imaging (MRI) and no extra ionizing radiation, PET/MRI imaging is the hottest topic currently. PET/MRI is swiftly making its way into clinical practice. However, it has many technical difficulties to overcome, such as photomultiplier tubes, which cannot work properly in a magnetic field, and the inability to provide density information on the object for attenuation correction. This paper introduces the technique process of PET/MRI and summarizes its clinical applications, including imaging in oncology, neurology, and cardiology.