Evaluation of the potential of PET-MRI fusion for detection of liver metastases in patients with neuroendocrine tumours

Interest of Integrated Whole-Body PET/MR Imaging in Gastroenteropancreatic Neuroendocrine Neoplasms: A Retro-Prospective Study

INTRODUCTION AND AIM

Simultaneous positron emission tomography/magnetic resonance imaging (PET-MRI) combines the high sensitivity of PET with the high specificity of MRI and is a tool for the assessment of gastroenteropancreatic neuroendocrine neoplasms (G-NENs). However, it remains poorly evaluated with no clear recommendations in current guidelines. Thus, we evaluated the prognostic impact of PET-MRI in G-NEN patients.

METHODS

From June 2017 to December 2021, 71 G-NEN patients underwent whole-body PET-MRI for staging and/or follow-up purposes. A whole-body emission scan with 18F-6-fluoro-L-dihydroxyphenylalanine (18FDOPA, n = 30), 18F-fluoro-2-deoxy-D-glucose (18FDG, n = 21), or 68Ga-(DOTA(0)-Phe(1)-Tyr(3))-octreotide (68Ga-DOTATOC, n = 20) with the simultaneous acquisition of a T1-Dixon sequence and diffusion-weighed imaging (DWI), followed by a dedicated step of MRI sequences with a Gadolinium contrast was performed. The patients underwent PET-MRI every 6-12 months during the follow-up period until death. Over this period, 50 patients with two or more PET-MRI were evaluated.

RESULTS

The mean age was 61 [extremes, 31-92] years. At the baseline, PET-MRI provided new information in 12 cases (17%) as compared to conventional imaging: there were more metastases in eight, an undescribed location (myocardia) in two, and an unknown primary location in two cases. G grading at the baseline influenced overall survival. During the follow-up (7-381 months, mean 194), clinical and therapy managements were influenced by PET-MRI in three (6%) patients due to new metastases findings when neither overall, nor disease-free survivals in these two subgroups (n = 12 vs. n = 59), were different.

CONCLUSION

Our study suggests that using PET/MRI with the appropriate radiotracer improves the diagnostic performance with no benefit on survival. Further studies are warranted to evaluate the cost-effectiveness of this procedure.

Comparison of 68Ga-DOTATATE Positron Emmited Tomography/Computed Tomography and Gadoxetic Acid-Enhanced Magnetic Resonance Imaging for the Detection of Liver Metastases from Well-Differentiated Neuroendocrine Tumors

This study aimed to compare the detection of neuroendocrine tumor liver metastases (NLMs) in hepatobiliary-specific contrast-enhanced MRI (pMR) versus 68Ga-DOTATATE PET/CT (DT-PET). This retrospective study cohort included 30 patients with well-differentiated neuroendocrine tumors who underwent both DT-PET and pMR. Two readers independently assessed NLMs count, SUVmax on DT-PET, and signal characteristics on pMR. A consensus review by two additional readers resolved discrepancies between the modalities. Results showed concordance between DT-PET and pMR NLM count in 14/30 patients (47%). pMR identified more NLMs in 12/30 patients (40%), of which 4 patients showed multiple deposits on pMR but only 0-1 lesions on DT-PET. DT-PET detected more in 4/30 patients (13%). Overall, pMR detected more metastases than DT-PET (p = 0.01). Excluding the four outliers, there was excellent agreement between the two methods (ICC: 0.945, 95%CI: 0.930, 0.958). Notably, pMR had a higher NLM detection rate than DT-PET, with correlations found between lesion size on pMR and DT-PET detectability, as well as diffusion restriction on pMR and SUVmax on DT-PET. In conclusion, in consecutive patients with well-differentiated NETs, the detection rate of NLM is higher with pMR than with DT-PET. However, when excluding patients whose tumors do not overexpress somatostatin receptors (13% of the cohort), high concordance in the detection of NLM is observed between DT PET and pMR.

PET/MRI imaging in neuroendocrine neoplasm

Molecular imaging plays a vital role in the management of neuroendocrine neoplasms (NENs). Somatostatin receptor (SSTR) PET is critical for evaluating NENs, ascertaining peptide receptor radionuclide therapy (PRRT) eligibility, and treatment response. SSTR-PET/MRI can provide a one-stop-shop multiparametric evaluation of NENs. The acquisition of complementary imaging information in PET/MRI has distinct advantages over PET/CT and MR imaging acquisitions. The purpose of this manuscript is to provide a comprehensive overview of PET/MRI and a current review of recent PET/MRI advances in the diagnosis, staging, treatment, and surveillance of NENs.

Evaluation of [68Ga]-DOTATOC PET/MRI in Patients with Meningioma of the Subcranial and Intraorbital Space

Meningiomas are known to express somatostatin receptor (SSTR) type 2 to a high degree. Therefore, radiolabeled somatostatin analogs, such as DOTATOC, have been introduced for PET imaging of meningiomas. However, the benefit of hybrid SSTR PET/MRI is still debated. Here, we report our experience with [⁶⁸Ga]-DOTATOC PET/MRI. Methods: PET/MRI was performed in 60 patients with suspected or diagnosed meningiomas of the skull plane and eye socket. Acquired datasets were reported by 2 independent readers regarding local tumor extent and signal characteristics. Histopathologic results and follow-up imaging served as the reference standard. SUVs of target lesions were analyzed according to the corresponding maximal tracer uptake. The diagnostic accuracy of PET/MRI and conventional MRI was determined independently and compared with the reference standard. Results: In total, 60 target lesions were identified, with 54 considered to be meningiomas according to the reference standard. Sensitivity and specificity of PET/MRI versus MRI alone were 95% versus 96% and 75% versus 66%, respectively. The McNemar test was not able to distinguish any differences between PET/MRI and the reference standard or MRI and the reference standard. No differences were found between the 2 modalities with respect to local infiltration. Conclusion: SSTR PET/MRI and MRI yielded similar accuracy for the detection of meningiomas of the skull base and intraorbital space. Here, sequential low-dose SSTR PET/CT might be helpful for the planning of radioligand therapy or radiotherapy.

Diagnostic performance of PET/CT in the detection of liver metastases in well-differentiated NETs

BACKGROUND

The aim of this retrospective study was to compare the diagnostic accuracy of somatostatin receptor (SSR)-PET/CT to liver MRI as reference standard in the evaluation of hepatic involvement in neuroendocrine tumors (NET).

METHODS

An institutional database was screened for "SSR" imaging studies between 2006 and 2021. 1000 NET Patients (grade 1/2) with 2383 SSR-PET/CT studies and matching liver MRI in an interval of +3 months were identified. Medical reports of SSR-PET/CT and MRI were retrospectively evaluated regarding hepatic involvement and either confirmed by both or observed in MRI but not in SSR-PET/CT (false-negative) or in SSR-PET but not in MRI (false-positive).

RESULTS

Metastatic hepatic involvement was reported in 1650 (69.2%) of the total 2383 SSR-PET/CT imaging studies, whereas MRI detected hepatic involvement in 1685 (70.7%) cases. There were 51 (2.1%) false-negative and 16 (0.7%) false-positive cases. In case of discrepant reports, MRI and PET/CT were reviewed side by side for consensus reading. SSR-PET/CT demonstrated a sensitivity of 97.0% (95%CI: 96.0%, 97.7%), a specificity of 97.7% (95%CI: 96.3%, 98.7%), a PPV of 99.0% (95%CI: 98.4%, 99.4%) and NPV of 93.0% (95%CI: 91.0, 94.8%) in identifying hepatic involvement. The most frequent reason for false-negative results was the small size of lesions with the majority < 0.6 cm.

CONCLUSION

This study confirms the high diagnostic accuracy of SSR-PET/CT in the detection of hepatic involvement in NET patients based on a patient-based analysis of metastatic hepatic involvement with a high sensitivity and specificity using liver MRI imaging as reference standard. However, one should be aware of possible pitfalls when a single imaging method is used in evaluating neuroendocrine liver metastases in patients.

Neuroendocrine Tumor Diagnosis: PET/MR Imaging

Imaging plays a critical role in the diagnosis and management of neuroendocrine tumors (NETs). The initial workup of the primary tumor, including its characterization, local and distant staging, defines subsequent treatment decisions. Functional imaging using hybrid systems, such as PET combined with computed tomography, has become the gold standard. As NETs majorly arise from the gastrointestinal system and metastasize primarily to the liver, simultaneous PET and MR imaging with its high soft tissue contrast might be a valuable clinical one-stop-shop whole-body imaging tool. This review presents the current status and challenges of PET/MR imaging for diagnosis of NETs.

Detection of distant metastases and distant second primary cancers in head and neck squamous cell carcinoma: comparison of [18F]FDG PET/MRI and [18F]FDG PET/CT

PURPOSE

This prospective study aimed to compare the diagnostic performance of [¹⁸]FDG PET/MRI and PET/CT for the detection of distant metastases and distant second primary cancers in patients with head and neck squamous cell carcinoma (HNSCC).

METHODS

A total of 103 [¹⁸F]FDG PET/MRI examinations immediately followed by PET/CT were obtained in 82 consecutive patients for staging of primary HNSCC (n = 38), suspected loco-regional recurrence/follow-up (n = 41) or unknown primary HNSCC (n = 3). Histology and follow-up > 2 years formed the standard of reference. Blinded readers evaluated the anonymized PET/MRI and PET/CT examinations separately using a 5-point Likert score. Statistical analysis included: receiver operating characteristic (ROC) analysis, jackknife alternative free-response ROC (JAFROC) and region-of-interest (ROI)-based ROC to account for data clustering and sensitivity/specificity/accuracy comparisons for a score ≥ 3.

RESULTS

Distant metastases and distant second primary cancers were present in 23/103 (22%) examinations in 16/82 (19.5%) patients, and they were more common in the post-treatment group (11/41, 27%) than in the primary HNSCC group (3/38, 8%), p = 0.039. The area under the curve (AUC) per patient/examination/lesion was 0.947 [0.927-1]/0.965 [0.917-1]/0.957 [0.928-0.987] for PET/MRI and 0.975 [0.950-1]/0.968 [0.920-1]/0.944 [0.910-0.979] for PET/CT, respectively (p > 0.05). The diagnostic performance of PET/MRI and PET/CT was similar according to JAFROC (p = 0.919) and ROI-based ROC analysis (p = 0.574). Sensitivity/specificity/accuracy for PET/MRI and PET/CT for a score ≥ 3 was 94%/88%/89% and 94%/91%/91% per patient, 96%/90%/91% and 96%/93%/93% per examination and 95%/85%/90% and 90%/86%/88% per lesion, respectively, p > 0.05.

CONCLUSIONS

In HNSCC patients, PET/MRI and PET/CT had a high and similar diagnostic performance for detecting distant metastases and distant second primary cancers.

Multimodal Management of Grade 1 and 2 Pancreatic Neuroendocrine Tumors

Pancreatic neuroendocrine tumors (p-NETs) are rare tumors with a recent growing incidence. In the 2017 WHO classification, p-NETs are classified into well-differentiated (i.e., p-NETs grade 1 to 3) and poorly differentiated neuroendocrine carcinomas (i.e., p-NECs). P-NETs G1 and G2 are often non-functioning tumors, of which the prognosis depends on the metastatic status. In the localized setting, p-NETs should be surgically managed, as no benefit for adjuvant chemotherapy has been demonstrated. Parenchymal sparing resection, including both duodenum and pancreas, are safe procedures in selected patients with reduced endocrine and exocrine long-term dysfunction. When the p-NET is benign or borderline malignant, this surgical option is associated with low rates of severe postoperative morbidity and in-hospital mortality. This narrative review offers comments, tips, and tricks from reviewing the available literature on these different options in order to clarify their indications. We also sum up the overall current data on p-NETs G1 and G2 management.

Quantitative diffusion MRI of the abdomen and pelvis

Diffusion MRI has enormous potential and utility in the evaluation of various abdominal and pelvic disease processes including cancer and noncancer imaging of the liver, prostate, and other organs. Quantitative diffusion MRI is based on acquisitions with multiple diffusion encodings followed by quantitative mapping of diffusion parameters that are sensitive to tissue microstructure. Compared to qualitative diffusion-weighted MRI, quantitative diffusion MRI can improve standardization of tissue characterization as needed for disease detection, staging, and treatment monitoring. However, similar to many other quantitative MRI methods, diffusion MRI faces multiple challenges including acquisition artifacts, signal modeling limitations, and biological variability. In abdominal and pelvic diffusion MRI, technical acquisition challenges include physiologic motion (respiratory, peristaltic, and pulsatile), image distortions, and low signal-to-noise ratio. If unaddressed, these challenges lead to poor technical performance (bias and precision) and clinical outcomes of quantitative diffusion MRI. Emerging and novel technical developments seek to address these challenges and may enable reliable quantitative diffusion MRI of the abdomen and pelvis. Through systematic validation in phantoms, volunteers, and patients, including multicenter studies to assess reproducibility, these emerging techniques may finally demonstrate the potential of quantitative diffusion MRI for abdominal and pelvic imaging applications.

Imaging of neuroendocrine tumors: A pictorial review of the clinical value of different imaging modalities

Neuroendocrine tumors (NETs) are multifaceted tumors occurring in a variety of organs and often present as metastatic at the time of diagnosis. Accurate staging is the most significant factor in therapy planning, but it remains a challenge. Imaging is established as the cornerstone for disease detection/diagnosis, staging, and follow up. To accurately assess and monitor tumor burden in patients with NETs, various imaging techniques have been developed and optimized. Current recommendations for the imaging of patients with NETs include a combination of both morphologic (or anatomic) and molecular imaging, but a final choice can be puzzling for clinicians. Recognizing that there is no uniform sequence consensus on the "best" imaging test, and the heterogeneity of technologic availability at different centers, we hope to provide a pictorial review of the different imaging techniques and their role and utility in management of patients with NETs, aimed to provide a practical guide for all clinicians.

Imaging and its Impact on Defining the Oligometastatic State

Successful treatment of oligometastatic disease (OMD) is facilitated through timely detection and localization of disease, both at the time of initial diagnosis (synchronous OMD) and following the initial therapy (metachronous OMD). Hence, imaging plays an indispensable role in management of patients with OMD. However, the challenges and complexities of OMD management are also reflected in the imaging of this entity. While innovations and advances in imaging technology have made a tremendous impact in disease detection and management, there remain substantial and unaddressed challenges for earlier and more accurate establishment of OMD state. This review will provide an overview of the available imaging modalities and their inherent strengths and weaknesses, with a focus on their role and potential in detection and evaluation of OMD in different organ systems. Furthermore, we will review the role of imaging in evaluation of OMD for malignancies of various primary organs, such as the lung, prostate, colon/rectum, breast, kidney, as well as neuroendocrine tumors and gynecologic malignancies. We aim to provide a practical overview about the utilization of imaging for clinicians who play a role in the care of those with, or at risk for OMD.

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.

High Interobserver Agreement for the Standardized Reporting System SSTR-RADS 1.0 on Somatostatin Receptor PET/CT

Recently, a standardized framework system for interpreting somatostatin receptor (SSTR)-targeted PET/CT, termed the SSTR reporting and data system (RADS) 1.0, was introduced, providing reliable standards and criteria for SSTR-targeted imaging. We determined the interobserver reliability of SSTR-RADS for interpretation of ⁶⁸Ga-DOTATOC PET/CT scans in a multicentric, randomized setting. Methods: A set of 51 randomized ⁶⁸Ga-DOTATOC PET/CT scans was independently assessed by 4 masked readers with different levels of experience (2 experienced readers and 2 inexperienced readers) trained on the SSTR-RADS 1.0 criteria (based on a 5-point scale from 1 [definitively benign] to 5 [high certainty that neuroendocrine neoplasia is present]). For each scan, SSTR-RADS scores were assigned to a maximum of 5 target lesions (TLs). An overall scan impression based on SSTR-RADS was indicated, and interobserver agreement rates on a TL-based, on an organ-based, and on an overall SSTR-RADS score-based level were computed. The readers were also asked to decide whether peptide receptor radionuclide therapy (PRRT) should be considered on the basis of the assigned RADS scores. Results: Among the selected TLs, 153 were chosen by at least 2 readers (all 4 readers selected the same TLs in 58 of 153 [37.9%] instances). The interobserver agreement for SSTR-RADS scoring among identical TLs was good (intraclass correlation coefficient [ICC] ≥ 0.73 for 4, 3, and 2 identical TLs). For lymph node and liver lesions, excellent interobserver agreement rates were derived (ICC, 0.91 and 0.77, respectively). Moreover, the interobserver agreement for an overall scan impression based on SSTR-RADS was excellent (ICC, 0.88). The SSTR-RADS-based decision to use PRRT also demonstrated excellent agreement, with an ICC of 0.80. No significant differences between experienced and inexperienced readers for an overall scan impression and TL-based SSTR-RADS scoring were observed (P ≥ 0.18), thereby suggesting that SSTR-RADS seems to be readily applicable even for less experienced readers. Conclusion: SSTR-RADS-guided assessment demonstrated a high concordance rate, even among readers with different levels of experience, supporting the adoption of SSTR-RADS for trials, clinical routine, or outcome studies.

The impact of 18F-FDOPA-PET/MRI image fusion in detecting liver metastasis in patients with neuroendocrine tumors of the gastrointestinal tract

Background

This study assesses the value of image fusion using 18F-fluoro-L-DOPA (18F-DOPA) positron emission tomography (PET) and magnetic resonance imaging (MRI) for examining patients with neuroendocrine tumors (NETs) and a suspicion of metastasis of the liver.

Methods

Eleven patients (five women and six men aged between 20 and 81, with a mean age of 54.6 years) were included in the study. All patients underwent whole-body 18F-DOPA PET examinations and contrast-enhanced MRI with diffusion-weighted sequences (DWS). Image fusion was performed using a semiautomatic voxel-based algorithm. Images obtained using PET and MRI were assessed separately. Side-by-side evaluations of fused PET/MRI images were also performed.

Results

In total, 55 liver lesions (52 liver metastases and 3 benign lesions) were detected in the 11 patients. Sensitivity detection for liver lesions was higher when using PET/CT than when using contrast-enhanced MRI without DWSs and lower than using MRI with DWSs. The sensitivity of PET/MRI image fusion in the detection of liver metastasis was significantly higher than that of MRI with DWSs (P < 0.05).

Conclusion

Images of the liver obtained using PET and MRI in patients with NETs exhibited characteristic features. These findings suggest that an appropriate combination of available imaging modalities can optimize patient evaluations.

[Neuroendocrine tumors of the stomach, duodenum and pancreas : Value of (hybrid) radiological diagnostics]

CLINICAL/METHODICAL ISSUE

Neuroendocrine tumors (NET) of the stomach, duodenum and pancreas are rare tumors with a low incidence but the exact tumor localization and staging diagnostics are of critical importance for further planning of treatment.

STANDARD RADIOLOGICAL METHODS

Standard primary diagnostic methods include multimodal imaging with computed tomography (CT) and magnetic resonance imaging (MRI) but in 20-50% of the cases the localization of the primary tumor cannot be identified.

METHODICAL INNOVATIONS

Modern hybrid imaging procedures combine radiological procedures and functional imaging, e.g. using somatostatin receptor (SSR) positron emission tomography CT (PET)/CT imaging. For the exact diagnostics of the primary tumor and distant metastases morphological and functional aspects can be combined for targeted diagnostics. For primary tumor staging a sensitivity of 80.0% and a specificity of 88.4% are given in the literature.

PERFORMANCE

The application of SSR PET/CT led to a change in patient management in 44% of all cases according to a recently published meta-analysis and therefore had a significant influence on the further procedure.

ASSESSMENT

The use of SSR PET/CT can provide critical information for further treatment and can lead to a significant change in treatment management in a relevant proportion of patients.

PRACTICAL RECOMMENDATIONS

Radiological imaging diagnostics and in particular hybrid functional imaging procedures using PET/CT will become increasingly more relevant for the diagnostics, treatment and follow-up of NET patients.

PET/MRI for neuroendocrine tumors: a match made in heaven or just another hype?

Purpose

To evaluate the current literature on technical feasibility and diagnostic value of PET/MRI in management of patients with neuroendocrine tumors (NETs).

Methods

A systematic literature search of the PubMed/MEDLINE database identified studies that evaluated the role of simultaneous PET/MRI for the evaluation of neuroendocrine tumors in human subjects. Exclusion criteria included studies lacking simultaneous PET/MRI, absence of other than attenuation-correction MRI pulse sequences, and case reports. No data-pooling or statistical analysis was performed due to the small number of articles and heterogeneity of the methodologies.

Results

From the 21 identified articles, five were included, which demonstrated successful technical feasibility of simultaneous PET/MRI through various imaging protocols in a total of 105 patients. All articles demonstrated equal or superior detection of liver lesions by PET/MRI over PET/CT. While one study reported superior detection of bone lesions by PET/MRI, two demonstrated favorable detection by PET/CT. Two studies demonstrated superiority of PET/CT in detection of nodal metastases; three studies reported the pitfall of PET/MRI in detection of lung lesion.

Conclusion

The current literature reports successful technical feasibility of PET/MRI for imaging of NETs. While whole-body PET/CT in conjunction with an abdominal MRI may serve as a comprehensive approach for baseline staging, follow up with PET/MRI may be preferred for those with liver-only disease. Another possible role for PET/MRI is to provide a multiparametric approach to follow up of response to treatment. With further advances in MRI imaging acquisitions and post-processing techniques, PET/MRI may become more applicable to a broader group of patients with NETs, and possibly the imaging modality of choice for this patient population.

Novel Functional Imaging of Neuroendocrine Tumors

Somatostatin receptor imaging constitutes an integral part in neuroendocrine tumor visualization and should, because of its vastly superior performance, use ⁶⁸Ga-DOTA-somatostatin analogue-PET/computed tomography rather than scintigraphy; it is particularly valuable for detecting metastases to lymph nodes, bone, peritoneum, and liver, which may be missed by morphologic imaging. ¹⁸FDG-PET/computed tomography is better suited for G3 and high-G2 neuroendocrine tumors. ¹⁸FDG-PET/computed tomography provides prognostic information. Alternative available PET tracers are ¹⁸F-DOPA and ¹¹C-5-hydroxytryptophan. To take full advantage of the technique PET/computed tomography should include diagnostic intravenous contrast-enhanced computed tomography. PET/MRI is currently mainly investigational.

PET/MRI for Gastrointestinal Imaging: Current Clinical Status and Future Prospects

Positron emission tomography (PET)/computed tomography (CT) with 2-deoxy-2-[¹⁸F]fluoro-d-glucose (FDG) has become the standard of care for the initial staging and subsequent treatment response assessment for numerous gastrointestinal malignancies. However, it is often supplemented by magnetic resonance imaging (MRI) for local tumor staging. Hybrid PET/MRI scanners, which acquire PET data and MRI data simultaneously, have the potential to provide accurate whole-body staging in a single examination. Furthermore, to address certain limitations of FDG, many new PET tracers have been developed to probe distinctive aspects of tumor biology.

Preoperative 68Ga-DOTA-Somatostatin Analog-PET/CT Hybrid Imaging Increases Detection Rate of Intra-abdominal Small Intestinal Neuroendocrine Tumor Lesions

Background

Small intestinal neuroendocrine tumors (SI-NETs) are the most common form of neoplasm in the small bowel. Radiological identification of primary tumors (PT), which may be multiple, is difficult, and therefore palpation of the entire small bowel is routinely performed during laparotomy. The aim was to determine detection rates of PT and peritoneal carcinomatosis (PC) with ⁶⁸Ga-DOTATOC/TATE-PET/CT in comparison with i.v. contrast-enhanced computed tomography (CE-CT) and thus to clarify whether modern functional imaging can mitigate the need for palpation of bowel during surgery enabling oncologically adequate laparoscopic resection.

Methods

A total of 28 patients with SI-NET who preoperatively underwent both ⁶⁸Ga-DOTATOC/TATE-PET/CT and CE-CT were included. The detection rates of PT and PC for PET/CT and CE-CT were compared to the findings in the surgical and histopathological reports. Appropriate statistical tests were used, and significance was set to p < 0.05.

Results

Out of 82 PT, 43 PT were not detected by any imaging modality. More PT lesions were detected with PET/CT (n = 39 [47.5%]) than with CE-CT (n = 10 [12.2%], p < 0.001). Also, PET/CT identified significantly more PC lesions than CE-CT (78 and 38%, p = 0.004, respectively).

Conclusion

PET/CT detected more PT and PC lesions than CE-CT. Some PTs and PC lesions were only detected by one of the modalities, and CT performed in conjunction with PET/CT should therefore be performed as a fully diagnostic CE-CT for optimal results. Palpation of the small bowel remains crucial during surgery in these patients because several PTs escaped detection by both PET/CT and CE-CT.

The utility of 68Ga-DOTATATE positron-emission tomography/computed tomography in the diagnosis, management, follow-up and prognosis of neuroendocrine tumors

Neuroendocrine tumors (NETs) are rare neoplasms that emerge mainly from the GI tract, pancreas and respiratory tract. The incidence of NETs has increased more than sixfold in the last decades. NETs typically express somatostatin receptors on their cell surface, which can be targeted by 'cold' somatostatin analogs for therapy or by 'hot' radiolabeled somatostatin analogs for tumor localization and treatment. 68-Gallium-DOTA peptides (DOTATATE, DOTATOC, DOTANOC) positron emission tomography/computed tomography is a highly accurate imaging modality for NETs that has been found to be more sensitive for NET detection than other imaging modalities. In the current review, we will discuss the clinical utility of 68-Gallium-DOTATATE positron emission tomography/computed tomography for the diagnosis and management of patients with NETs.

The Role of PET/MR Imaging in Precision Medicine

Fluorodeoxyglucose PET and PET/computed tomography have gained acceptance in the evaluation of disease. Nontargeted tracers have been used in the diagnosis of certain malignancies but may not be sensitive or specific enough to become standard of care. Newer targeted PET tracers have been developed that target disease-specific biomarkers, and allow accurate and sensitive detection of disease. Combined with the capabilities of MR imaging to evaluate soft tissue, precision imaging with PET/MR imaging can change the diagnosis. This article discusses specific areas in which precision imaging with nontargeted and targeted diagnostic agents can change the diagnosis and treatment.

Current evidence for the diagnostic value of gadoxetic acid-enhanced magnetic resonance imaging for liver metastasis

A variety of imaging techniques, including ultrasonography (US), multidetector computed tomography (MDCT), magnetic resonance imaging (MRI) and positron emission tomography combined with CT scan (PET/CT), are available for diagnosis and treatment planning in liver metastasis. Contrast-enhanced MDCT is a relatively non-invasive, widely available and standardized method for hepatic work-up. Gadoxetic acid (gadolinium-ethoxybenzyl-diethylenetriamine pentaacetic acid; EOB Primovist®]) is a recently developed liver-specific hepatobiliary MR contrast agent that offers both dynamic imaging as well as liver-specific static hepatocyte imaging, referred to as the hepatobiliary phase. Following contrast injection, this technique reveals dynamic vascular phases (arterial, portal venous and delayed phases), in addition to the hepatobiliary phase upon uptake by functional hepatocytes. The overall sensitivity of gadoxetic acid-enhanced MRI was significantly higher than that of contrast-enhanced CT. Specifically, the higher sensitivity of gadoxetic acid-enhanced MRI was observed in lesions smaller than 1 cm in diameter. Gadoxetic acid-enhanced MRI is considered an extremely useful tool for the diagnosis of liver metastases. Future studies will focus on diagnostic algorithms involving combinations of modalities such as MRI, MDCT and/or (18) F-fluorodeoxyglucose PET/CT, which may impact the treatment plan for these patients.

Multimodality fusion imaging in abdominal and pelvic malignancies: current applications and future perspectives

Medicine is evolving toward personalized care and this development entails the integration, amalgamation, and synchronized analysis of data from multiple sources. Multimodality fusion imaging refers to the simultaneous visualization of spatially aligned and juxtaposed medical images obtained by two or more image modalities. PET/MRI scanners and MMFI platforms are able to improve the diagnostic workflow in oncologic patients and provide exquisite images that aid physicians in the molecular profiling and characterization of tissues. Advanced navigation platforms involving real-time ultrasound are promising tools for guiding personalized and tailored mini-invasive interventional procedures on technically challenging targets. The main objective of the present essay was to describe the current applications and future perspectives of multimodality fusion imaging for both diagnostic and interventional purposes in the field of abdominal and pelvic malignancies. We also outlined the technical differences between fusion imaging achieved by means of simultaneous bimodal acquisition (i.e., integrated PET/MRI scanners), retrospective co-registration, and multimodality fusion imaging involving ultrafast or real-time imaging modalities.

Gastroenteropancreatic neuroendocrine tumours (GEP-NET) - Imaging and staging

Detection of gastroenteropancreatic neuroendocrine tumours (GEP-NETs) and monitoring of treatment response relies mainly on morphological imaging such as computed tomography (CT) and magnetic resonance imaging (MRI). Molecular imaging techniques also in combination with CT (hybrid imaging) greatly benefit patient management, including better localization of occult tumours and better staging. Somatostatin receptor scintigraphy (SRS) and somatostatin receptor (SSTR) positron emission tomography (PET) play a central role in the diagnostic work-up of patients with well-differentiated GEP-NETs. SSTR PET/CT is superior to SRS and should be used whenever available. (18)F-DOPA and (18)F-FDG PET/CT is inferior to SSTR PET/CT at least in patients with well-differentiated GEP-NETs. Both SSTR PET/CT and SRS have limitations, such as relatively low detection rate of benign insulinomas, poorly differentiated GEP-NETs and liver metastases. New innovations such as SSTR PET/MRI, radiolabelled SSTR antagonists and glucagon-like peptide-1 receptor (GLP-1R) agonists might further improve imaging of GEP-NETs.

[Combined PET-MRI of the abdomen]

The first fully integrated combined positron emission tomography-magnetic resonance imaging (PET-MRI) scanners have been clinically available since 2010. Large prospective studies regarding indications and diagnostic accuracy of this new modality are not yet available; however, preliminary studies have shown a higher diagnostic accuracy and confidence compared to PET-computed tomography (PET-CT) in regions where MRI is known to be superior to CT, such as the liver. The benefit of MRI in accurate lesion characterization and the additional value of diffusion-weighted imaging (DWI) as a complementary functional modality by means of the apparent diffusion coefficient (ADC) is apparent in entities with low tracer uptake (e.g. due to small size) and a decreased or absent accumulation pattern on PET.

Morphologic and Functional Imaging of Non-Colorectal Liver Metastases

Liver metastases are the most frequent malignant liver lesions. Besides colorectal carcinoma, gastric carcinoma, pancreatic carcinoma, breast cancer, lung cancer, and neuroendocrine tumors are the most common entities that metastasize to the liver. The morphology of these metastases depends on the primary tumor. For morphologic and functional imaging of non-colorectal liver metastases, multiple imaging techniques such as ultrasonography, computed tomography (CT), magnetic resonance imaging (MRI), and positron emission tomography coupled with CT or MRI are available. This review summarizes morphologic and functional characteristics of different non-colorectal liver metastases.

Somatostatin receptor PET/CT in restaging of typical and atypical lung carcinoids

Background

To assess the role of somatostatin receptor (SR) PET/CT using Ga-68 DOTATOC or DOTATATE in staging and restaging of typical (TC) and atypical (AC) lung carcinoids.

Methods

Clinical and PET/CT data were retrospectively analyzed in 27 patients referred for staging (N = 5; TC, N = 4; AC, N = 1) or restaging (N = 22; TC, N = 8; AC, N = 14). Maximum standardized uptake value (SUVmax) of SR-positive lesions was normalized to the SUVmax of the liver to generate SUVratio; SR PET was compared to contrast-enhanced (ce) CT. The classification system proposed by Rindi et al. (Endocr Relat Cancer. 2014;21(1):1-16, 2014) was used for classification of patients in TC and AC groups.

Results

Only 18/27 patients were found to have metastases on PET/CT. Of the 186 lesions, 101 (54.3 %) were depicted on both PET and CT, 53 (28.5 %) lesions only on CT, and 32 (17.2 %) only on PET. SUVratio of lesions was significantly higher in AC as compared to TC (p < 0.001). In patients referred for restaging, additional findings on PET lead to upstaging with change in management strategy in 5/22 (22.7 %) patients (AC, N = 5; TC, N = 1). In four patients (all AC) referred for restaging and in one patient (TC) referred for staging, additional findings on CT missed on PET lead to correct staging.

Conclusions

Typical and atypical carcinoid patients have complex patterns of metastases which make it necessary to combine functional SR PET and contrast-enhanced CT for appropriate restaging. In patients referred for restaging SR, PET may have a relevant impact on treatment strategy in up to 22.7 of patients with typical and atypical lung carcinoids.

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.

PET tracers for somatostatin receptor imaging of neuroendocrine tumors: current status and review of the literature

Neuroendocrine tumors have shown rising incidence mainly due to higher clinical awareness and better diagnostic tools over the last 30 years. Functional imaging of neuroendocrine tumors with PET tracers is an evolving field that is continuously refining the affinity of new tracers in the search for the perfect neuroendocrine tumor imaging tracer. (68)Ga-labeled tracers coupled to synthetic somatostatin analogs with differences in affinity for the five somatostatin receptor subtypes are now widely applied in Europe. Comparison of sensitivity between the most used tracers - (68)Ga-DOTA-Tyr3-octreotide, (68)Ga-DOTA-Tyr3-octreotate and (68)Ga-DOTA-l-Nal3-octreotide - shows little difference and expertise on the specific tracer used, and knowledge regarding physiological uptake might be more important than in vitro-proven differences in affinity. Using isotopes such as (18)F or (64)Cu might improve these PET tracers further.

PET/MRI in Oncological Imaging: State of the Art

Positron emission tomography (PET) combined with magnetic resonance imaging (MRI) is a hybrid technology which has recently gained interest as a potential cancer imaging tool. Compared with CT, MRI is advantageous due to its lack of ionizing radiation, superior soft-tissue contrast resolution, and wider range of acquisition sequences. Several studies have shown PET/MRI to be equivalent to PET/CT in most oncological applications, possibly superior in certain body parts, e.g., head and neck, pelvis, and in certain situations, e.g., cancer recurrence. This review will update the readers on recent advances in PET/MRI technology and review key literature, while highlighting the strengths and weaknesses of PET/MRI in cancer imaging.

[Gastroenteropancreatic endocrine tumors]

CLINICAL/METHODICAL ISSUE

Gastroenteropancreatic neuroendocrine tumors (GEP-NET) are a rare, heterogeneous group of neoplasms. Only 2% of gastrointestinal tumors belong to the group of neuroendocrine neoplasms.

STANDARD RADIOLOGICAL METHODS

A wide spectrum of diagnostic imaging modalities is available: apart from ultrasound not only computed tomography (CT) but also magnetic resonance imaging (MRI) and positron emission tomography CT (PET-CT) play an important role in detection and staging of GEP-NETs.

METHODICAL INNOVATIONS

The PET-CT technique with somatostatin analogues is used for staging as well as for evaluation and monitoring of treatment with peptide radionuclide radiation therapy.

PERFORMANCE

According to the literature NETs of the small bowel with a size over 3 cm can be detected with a sensitivity of 84.7% and a specificity of 96.6% using CT enteroclysis and MR enteroclysis provides the detection of NETs of the small bowel in 93.3% of cases. 'The sensitivity of MRI in detection of pancreatic NETs is between 74% and 100% and is, therefore, higher than CT. Detection of small primary tumors is carried out using PET-CT and seems to be the most sensitive imaging modality to identify the exact location. On the other hand MRI has to be regarded as the best imaging modality for detection of liver metastases compared to CT and PET-CT.

ACHIEVEMENTS

The role of diagnostic imaging is to identify the exact location of the primary tumor and possible metastases, to define an appropriate therapy and to monitor treatment effects; however, the choice of the most appropriate diagnostic imaging modality varies depending on the location and type of the primary tumor.

PRACTICAL RECOMMENDATIONS

The GEP-NETs are predominantly well-vascularized; therefore, dual-phase CT/MR imaging with the arterial and venous phases after contrast media injection is mandatory for detection and localization of primary tumors and metastases. For whole body staging CT and PET-CT should be performed.

Qualitative and quantitative image analysis of CT and MR imaging in patients with neuroendocrine liver metastases in comparison to (68)Ga-DOTATOC PET

PURPOSE

To compare lesion conspicuity in patients with liver metastases arising from gastroenteropancreatic neuroendocrine tumors (GEP-NETs) using MRI, PET and CT.

MATERIALS AND METHODS

16 patients with GEP-NETs were evaluated using non-contrast MRI, contrast-enhanced (CE) MRI using Gd-EOB-DTPA and CE-(68)Ga-DOTATOC PET. Quantitative analyses were performed by two blinded readers using ROI-analyses quantifying contrast ratios (CR) between normal liver-tissue and GEP-NET-metastases. Qualitative analyses were performed evaluating primary visibility and spatial detectability of all lesions.

RESULTS

103 of the same liver metastases were detected on all modalities. Qualitatively, lesion conspicuity was superior on CE-MRI imaging compared to non-contrast MR-sequences (T2, DWI, fl2D, fl3D), as well as arterial- and portal-venous phase CT. Concerning detectability of lesions, CE-MRI was superior to all other modalities. The quantitative ROI-analysis demonstrated improved CR for DWI compared to all other non-contrast MR-sequences (p<0.001). CE-MRI presented with higher CR-values compared to CE-(68)Ga-DOTATOC PET/CT (p<0.001).

CONCLUSIONS

Anatomic imaging using non contrast MRI with fl2D-and fl3D-sequences in combination with the molecular imaging modality (68)Ga-DOTATOC PET is optimal for the assessment of liver lesions in GEP-NET-patients. Even though CE-MRI was superior to non-contrast MRI, non-contrast MRI is sufficient to detect and quantify liver metastases in daily routine, especially in combination with DW-Imaging.

Searching for primaries in patients with neuroendocrine tumors (NET) of unknown primary and clinically suspected NET: Evaluation of Ga-68 DOTATOC PET/CT and In-111 DTPA octreotide SPECT/CT

Background

To evaluate the clinical efficacy of In-111 DTPA octreotide SPECT/CT and Ga-68 DOTATOC PET/CT for detection of primary tumors in patients with either neuroendocrine tumor of unknown primary (NETUP) or clinically suspected primary NET (SNET).

Patients and methods.

A total of 123 patients were included from 2006 to 2009, 52 received Ga-68 DOTATOC PET/CT (NETUP, 33; SNET, 19) and 71 underwent In-111 DTPA octreotide SPECT/CT (50; 21). The standard of reference included histopathology or clinical verification based on follow-up examinations.

Results

In the NETUP group Ga-68 DOTATOC detected primaries in 15 patients (45.5%) and In-111 DTPA octreotide in 4 patients (8%) (p < 0.001); in the SNET group, only 2 primaries could be detected, all by Ga-68 DOTATOC. In patients with NETUP, primary tumors could be found significantly more often than in patients with SNET (p = 0.01). Out of these 21 patients 14 patients were operated.

Conclusion

Ga-68 DOTATOC PET/CT is preferable to In-111 DTPA octreotide SPECT/CT when searching for primary NETs in patients with NETUP but should be used with caution in patients with SNET.

[(18)F]FDG PET/MRI vs. PET/CT for whole-body staging in patients with recurrent malignancies of the female pelvis: initial results

PURPOSE

To evaluate the diagnostic potential of PET/MRI with [(18)F]FDG in recurrent ovarian and cervical cancer in comparison to PET/CT.

METHODS

A group of 19 patients with suspected recurrence of pelvic malignancies (ovarian cancer, 11 patients; cervical cancer, 8 patients) scheduled for an [(18)F]FDG PET/CT were subsequently enrolled for a PET/MRI. The scan protocol comprised: (1) a T1-W axial VIBE after contrast agent adminstration, (2) an axial T2-W HASTE, (3) a coronal TIRM, (4) an axial DWI, and dedicated MR sequences of the female pelvis including (5) a T1-W VIBE before contrast agent adminstration, (6) a sagittal T2-W TSE, and (7) a sagittal T1-W dynamic VIBE. The datasets (PET/CT, PET/MRI) were rated separately by two readers regarding lesion count, lesion localization, lesion conspicuity (four-point scale), lesion characterization (benign/malignant/indeterminate) and diagnostic confidence (three-point scale). All available data (histology, prior examinations, PET/CT, PET/MRI, follow-up examinations) served as standard of reference. Median values were compared using the Wilcoxon rank sum test.

RESULTS

Metastatic lesions were present in 16 of the 19 patients. A total of 78 lesions (malignant, 58; benign, 20) were described. Both PET/CT and PET/MRI allowed correct identification of all malignant lesions and provided equivalent conspicuity (3.86 ± 0.35 for PET/CT, 3.91 ± 0.28 for PET/MRI; p > 0.05). Diagnostic confidence was significantly higher for PET/MRI in malignant (p < 0.01) and benign lesions (p < 0.05).

CONCLUSION

Both PET/CT and PET/MRI offer an equivalently high diagnostic value for recurrent pelvic malignancies. PET/MRI offers higher diagnostic confidence in the discrimination of benign and malignant lesions. Considering the reduced radiation dose and superior lesion discrimination, PET/MRI may serve as a powerful alternative to PET/CT in the future.

Detection of neuroendocrine tumours in the small intestines using contrast-enhanced multiphase Ga-68 DOTATOC PET/CT: the potential role of arterial hyperperfusion

Background

Interpretation of small intestinal neuroendocrine tumours (NETs) by Ga-68 DOTATOC PET/CT can be difficult. The potential benefit of arterial hyperperfusion for the detection of NETs was evaluated.

Methods

Between 2006 and 2009, 320 consecutive Ga-68 DOTATOC PET/CT examinations, performed for NETs, revealed 40 lesions suggesting intestinal NETs in 25 patients. Two groups of lesions were distinguished: epigastric lesions evaluable in the arterial and venous CT scan (Group 1) and hypogastrial lesions evaluable in the venous CT scan only (Group 2). Lesions were jointly rated by two radiologists and a nuclear medicine physician. Maximum standard uptake values (SUVmax) of lesions and background were assessed. The reference standard was histology (available for 28 lesions) or follow-up (for a mean of 22.9 months).

Results

PET detected all suspicious lesions but was false positive in 3 lesions. In Group 1 the arterial scan performed significantly better than the venous scan (p = 0.008). Diagnostic performance was better in Group 1 than in Group 2 (p < 0.001). SUVmax of true positive lesions were significantly higher than background SUVmax (p < 0.001) and SUVmax of false positive lesions (p = 0.005).

Conclusions

The arterial phase of multiphase Ga-68 DOTATOC PET/CT might improve the localization of intestinal NETs and, thereby, improve the overall diagnostic accuracy of this modality in the assessment of intestinal NETs by adding information about lesion perfusion not available when only venous CT is performed.

Diagnostic accuracy of dynamic gadoxetic-acid-enhanced MRI and PET/CT compared in patients with liver metastases from neuroendocrine neoplasms

PURPOSE

To evaluate the diagnostic accuracy of dynamic-contrast-enhanced (DCE) MRI in comparison to both (18)F-FDG- and (68)Ga-DOTATATE-PET/CT in patients with liver metastases of neuroendocrine neoplasms (NEN).

MATERIALS AND METHODS

Thirty-two patients with hepatic metastases from NEN were examined both in DCE-MRI and positron emission tomography/computed tomography (PET/CT), using either (18)F-fluorodeoxyglucose ((18)F-FDG) or (68)Ga-DOTATATE as tracer. DCE-MRI was performed at 3 Tesla with Gd-EOB-DTPA acquiring 48 slices every 2.2 s for 5 min. Three regions of interest (ROIs) representing liver background and liver metastases were defined in fat-saturated T1w three-dimensional GRE MRI sequences in the hepatobiliary phase. Corresponding ROIs were then defined in the DCE-MRI- and in the PET/CT-dataset. Area under the curve (AUC) was calculated for the differentiation between metastases and liver background for DCE-MRI and PET-CT parameters.

RESULTS

AUC was very high for SUVmean (mean standardized uptake value) derived from (68)Ga-DOTATATE- (AUC = 0.966), and (18)F-FDG-PET/CT (AUC = 0.989). For DCE-MRI parameters, arterial flow fraction and intracellular uptake fraction showed the highest AUCs (AUC = 0.826, AUC = 0.819, respectively). The combination of those two had an AUC of 0.949. The combination of DCE-MRI and PET-CT parameters resulted in the highest AUC.

CONCLUSION

Both PET/CT parameters and DCE-MRI perfusion parameters show a high diagnostic accuracy in the distinction between liver metastases and liver tissue. Our data suggest that both modalities provide complementary information.

Prospective of ⁶⁸Ga-radiopharmaceutical development

Positron Emission Tomography (PET) experienced accelerated development and has become an established method for medical research and clinical routine diagnostics on patient individualized basis. Development and availability of new radiopharmaceuticals specific for particular diseases is one of the driving forces of the expansion of clinical PET. The future development of the ⁶⁸Ga-radiopharmaceuticals must be put in the context of several aspects such as role of PET in nuclear medicine, unmet medical needs, identification of new biomarkers, targets and corresponding ligands, production and availability of ⁶⁸Ga, automation of the radiopharmaceutical production, progress of positron emission tomography technologies and image analysis methodologies for improved quantitation accuracy, PET radiopharmaceutical regulations as well as advances in radiopharmaceutical chemistry. The review presents the prospects of the ⁶⁸Ga-based radiopharmaceutical development on the basis of the current status of these aspects as well as wide range and variety of imaging agents.

Depiction and characterization of liver lesions in whole body [¹⁸F]-FDG PET/MRI

OBJECTIVES

To assess the value of PET/MRI with [(18)F]-FDG using a whole body protocol for the depiction and characterization of liver lesions in comparison to PET/CT.

METHODS

70 patients (31 women, 39 men) with solid tumors underwent [(18)F]-FDG PET/CT and followed by an additional PET/MRI using an integrated scanner. Two readers rated the datasets (PET/CT; PET/MRI) regarding conspicuity of hepatic lesions (4-point ordinal scale) and diagnostic confidence (5-point ordinal scale). Median scores for lesion conspicuity and diagnostic confidence were compared using Wilcoxon's rank sum test. Prior examinations, histopathology and clinical follow-up (116 ± 54 days) served as standard of reference.

RESULTS

36 of 70 (51%) patients showed liver lesions. Using PET/CT and PET/MRI all patients with liver metastases could correctly be identified. A total of 97 lesions were found (malignant n=26; benign n=71). For lesion conspicuity significantly higher scores were obtained for PET/MRI in comparison to PET/CT (p<0.001). Significantly better performance for diagnostic confidence was observed in PET/MRI, both for malignant as for benign lesions (p<0.001).

CONCLUSIONS

PET/MRI, even in the setting of a whole body approach, provides higher lesion conspicuity and diagnostic confidence compared to PET/CT and may therefore evolve as an attractive alternative in oncologic imaging.

Somatostatin receptor PET/CT in neuroendocrine tumours: update on systematic review and meta-analysis

PURPOSE

Neuroendocrine tumours (NET) are uncommon and may be localized in many different places in the body. Traditional imaging has mainly been performed with CT and somatostatin receptor scintigraphy (SRS). Recently, it has become possible to use somatostatin receptor PET/CT (SMSR PET) instead, which might improve diagnostic quality. To evaluate the diagnostic quality of SMSR PET we performed a meta-analysis as an update of a previous study published in 2012.

METHODS

A literature search was performed searching MEDLINE, Embase and five other databases with a combination of the expressions "PET", "positron emission tomography", "neuroendocrine" and "NET". The search was updated to 31 December 2012. Studies were selected which evaluated the sensitivity and specificity of SMSR PET for NET in the thorax or abdomen with a study size of at least eight patients. The methodological quality of the included studies was evaluated with QUADAS-2.

RESULTS

Eight studies fulfilled the inclusion criteria and were selected for final analysis, and 14 articles from a previous meta-analysis were added for a total of 22 articles. A total of 2,105 patients were included in the studies, an increase from 567 in the previous meta-analysis. The pooled sensitivity was 93 % (95 % CI 91 - 94 %) and specificity 96 % (95 % CI 95 - 98 %). The area under the summary ROC curve was 0.98 (95 % CI 0.95 - 1.0). In the previous meta-analysis the pooled sensitivity was 93 % (95 % CI 91 - 95 %) and specificity 91 % (95 % CI 82 - 97 %).

CONCLUSION

SMSR PET has good diagnostic performance for evaluation of NET in the thorax and abdomen, better than SRS which has been the previous standard method. This meta-analysis gives further support for switching to SMSR PET.