18F-fluorocholine PET/MRI versus ultrasound and sestamibi for the localization of parathyroid adenomas.

PURPOSE: Accurate preoperative localization is imperative to facilitate a minimally invasive parathyroidectomy (MIP) in primary hyperparathyroidism (pHPT). This study aims to compare the diagnostic value of standard-of-care localization techniques (ultrasound [US] and 99mTechnetium (99mTc) -sestamibi scintigraphy) to [F-18]-fluorocholine positron emission tomography/magnetic resonance imaging (FCH-PET/MRI) to determine the additional clinical usefulness of PET/MRI in a Canadian cohort. METHODS: We conducted a prospective, appropriately powered, study to compare the diagnostic value of -FCH PET/MRI to that of the US and 99mTc-sestamibi scintigraphy for localization of parathyroid adenomas in a patient with pHPT. The primary outcome was the per-lesion sensitivity and positive predictive value (PPV) of FCH-PET/MRI, US, and 99mTc-sestamibi scintigraphy. Intraoperative surgeon localization, parathormone levels, and histopathological findings were used as reference standards. RESULTS: Forty-one patients underwent FCH-PET/MRI of which 36 patients had parathyroidectomy. In these 36 patients, 41 parathyroid lesions were histologically confirmed as adenomas or hyperplastic glands. Per-lesion sensitivity of FCH-PET/MRI was 82.9% and of US and 99mTc-sestamibi scintigraphy combined at 50.0%, respectively. The sensitivity of FCH-PET/MRI was superior to that of US and 99mTc-sestamibi scintigraphy (p = 0.002). In the 19 patients in whom both US and 99mTc-sestamibi scintigraphy were negative, PET/MRI correctly identified the parathyroid adenoma in 13 patients (68%). CONCLUSIONS: FCH-PET/MRI is a highly accurate imaging modality for localization of parathyroid adenomas in a tertiary center in North America. It is a superior functional imaging modality to 99mTc-sestamibi scintigraphy alone and more sensitive for localization of parathyroid lesions than US and 99mTc-sestamibi scintigraphy combined. This imaging modality could become the most valuable preoperative localization study given its superior performance in localizing parathyroid adenomas.

WITHDRAWN: Evaluation and clinical quantification of neoplastic lesions and physiological structures in TOF-PET/MRI and non-TOF/MRI - a pilot study.

Ahead of Print article withdrawn by publisher.

Multi-slice SPECT/CT vs. lymphoscintigraphy and intraoperative gamma ray probe for sentinel node mapping in HNSCC.

To assess the diagnostic potential of multi-slice single-photon emission computed tomography/computed tomography (SPECT/CT) for preoperative sentinel node (SN) mapping in early stage head and neck squamous cell carcinoma (HNSCC). Retrospective case-control study including data of consecutive HNSCC patients treated between November 2011 and December 2015. The diagnostic accuracy of multi-slice SPECT/CT was assessed with regard to the gold standard intraoperative gamma ray detection probe, using McNemar's test and calculating the area under the ROC curve. Additionally, the hot spot yield of SPECT/CT and planar lymphoscintigraphy (LS) was compared. Compared to the intraoperative gold standard, SPECT/CT showed an overall positive predictive value of 60.3% [confidence interval (CI) 46.6-73.0%)], a negative predictive value of 96.3% (CI 93.6-98.1%), and an accuracy of 90.8% (CI 89.1-92.4%). SPECT/CT detected more hot spots than LS and provided detailed anatomical information as well as relevant additional findings with potential impact on further patient management. Sentinel lymph node biopsy proved to be a reliable and safe procedure with an excellent SN excision rate (97%). Multi-slice SPECT/CT is a highly accurate diagnostic test and matches the gold standard intraoperative gamma ray detection probe.

Multi-technique hybrid imaging in PET/CT and PET/MR: what does the future hold?

Integrated positron-emission tomography and computed tomography (PET/CT) is one of the most important imaging techniques to have emerged in oncological practice in the last decade. Hybrid imaging, in general, remains a rapidly growing field, not only in developing countries, but also in western industrialised healthcare systems. A great deal of technological development and research is focused on improving hybrid imaging technology further and introducing new techniques, e.g., integrated PET and magnetic resonance imaging (PET/MRI). Additionally, there are several new PET tracers on the horizon, which have the potential to broaden clinical applications in hybrid imaging for diagnosis as well as therapy. This article aims to highlight some of the major technical and clinical advances that are currently taking place in PET/CT and PET/MRI that will potentially maintain the position of hybrid techniques at the forefront of medical imaging technologies.

Contrast Enhanced CT Radiogenomics in a Retrospective NSCLC Cohort: Models, Attempted Validation of a Published Model and the Relevance of the Clinical Context.

RATIONALE AND OBJECTIVE: To develop a radiogenomic predictive model for non-small cell lung cancer (NSCLC) patients studied through contrast enhanced chest computed tomography (CE-CT) targeting the most frequent gene alterations. M&M: A retrospective study of patients with NSCLC imaged with CE-CT before treatment and had their tumor genomics sequenced at our institution was performed. Data was gathered from their imaging studies, their electronic medical records and a web-based database search (cBioPortal.ca). All of the patient data was tabulated for analysis. Two predictive models (M1 & M2) were created using different approaches and a third model was extracted from the literature to also be tested in our population. RESULTS: Out of 157 patients, eighty were male (51%) and 124 (79%) had a history of smoking. The three most prevalent genes were KRAS, TP53 and EGFR. The M1 radiomics-only model median AUC were 0.61 (TP53), 0.53 (KRAS) and 0.64 (EGFR) and for M1 radiomics + clinical were 0.61 (TP53), 0.61 (KRAS) and 0.80 (EGFR). The M2 radiomics-only model median AUC were 0.63 (TP53), 0.60 (KRAS) and 0.65 (EGFR) and for M2 radiomics + clinical were 0.64 (TP53), 0.62 (KRAS) and 0.81 (EGFR). The external EGFR radiomic model showed an AUC of 0.69 and 0.86 for the radiomics-only and combined radiomics + clinical respectively. CONCLUSION: Our study was able to provide robust predictive radiomics model evaluation for the detection of TP53, KRAS and EGFR. We also compared our performance with an already published model and observed how impactful clinical variables can be on models' performance. CLINICAL RELEVANCE STATEMENT: Identifying tumor mutations in patients that can't undergo biopsy is critical for their outcomes. KEYPOINTS: • Tumor genomic profiling is critical for treatment selection • CE-CT radiomics produce robust predictive models comparable to those already published • Clinical variables should be considered/included in predictive models.

[SPECT/CT in diagnostics of the hand joint]. / SPECT/CT in der Handgelenkdiagnostik.

CLINICAL/METHODICAL ISSUE: Hand and wrist pain remains a diagnostic challenge, both for hand surgeons and for radiologists. Especially chronic wrist pain is often hard to localize clinically and further cross-sectional imaging is often indispensable. STANDARD RADIOLOGICAL METHODS: The well-established standard for non-invasive diagnostic imaging in chronic wrist pain is magnetic resonance imaging (MRI). METHODICAL INNOVATIONS: Recently, state-of-the-art single photon emission computed tomography/computed tomography (SPECT/CT) systems have been introduced into the diagnostic array for musculoskeletal conditions. Besides morphological data SPECT/CT also provides metabolic information. PERFORMANCE: SPECT/CT allows an exact detection and precise anatomical mapping of different pathologies of the wrist, which is often crucial for therapy. ACHIEVEMENTS: In patients with chronic wrist pain, SPECT/CT is more specific than MRI. It is also beneficial in patients with posttraumatic conditions and metal implants and may serve as a problem-solving tool in difficult cases. PRACTICAL RECOMMENDATIONS: It is considered that SPECT/CT imaging is useful if MRI results are equivocal or present no clearly leading pathology. A primary examination with SPECT/CT seems to be a reasonable option for patients with certain bone pathologies, metal implants and non-specific wrist pain.

[Importance of SPECT/CT for knee and hip joint prostheses]. / Stellenwert der SPECT/CT bei Knie- und Hüftgelenkprothesen.

CLINICAL/METHODICAL ISSUE: Complications, such as loosening or infections are common problems after hip or knee arthroplasty. STANDARD RADIOLOGICAL METHODS: If conventional X-rays are equivocal bone scintigraphy is the classical second-line imaging modality. METHODICAL INNOVATIONS: Single photon emission computed tomography/computed tomography (SPECT/CT) offers metabolic and morphologic information in one imaging step and is becoming increasingly more available in larger hospitals. PERFORMANCE: The SPECT/CT procedure is a promising method and is increasingly being used in daily routine to evaluate joint arthroplasty. The additional benefit compared with classical conventional bone scintigraphy has to be evaluated in further prospective studies. ACHIEVEMENTS: In our hospital SPECT/CT regularly gives important additional information regarding prosthetic joint complications. PRACTICAL RECOMMENDATIONS: SPECT/CT is increasingly being used as the second step imaging standard modality if conventional X-rays are equivocal.

[Importance of SPECT/CT for resolving diseases of the jaw]. / Stellenwert der SPECT/CT zur Abklärung von Kiefererkrankungen.

CLINICAL/METHODICAL ISSUE: Diseases of the jaw, such as osteomyelitis, condylar hyperactivity and tumors need adequate imaging to evaluate the extension and activity for therapy planning. STANDARD RADIOLOGICAL METHODS: Conventional planar scintigraphy, orthopantomography, computed tomography (CT) and magnetic resonance imaging (MRI) can be used for the evaluation of jaw diseases. METHODICAL INNOVATIONS: Single photon emission computed tomography/computed tomography (SPECT/CT) provides metabolic and morphologic information in one imaging step and is becoming increasingly more available in larger hospitals. PERFORMANCE: The SPECT/CT is superior to planar scintigraphy alone, CT and orthopantomography in the evaluation of the extension and activity of osteomyelitis and jaw tumors. ACHIEVEMENTS: In our hospital SPECT/CT has replaced the other imaging modalities in the evaluation of osteomyelitis and condylar hyperactivity. PRACTICAL RECOMMENDATIONS: If available SPECT/CT should be performed for the evaluation of osteomyelitis of the jaw.

Hodgkin's lymphoma in remission after first-line therapy: which patients need FDG-PET/CT for follow-up?

BACKGROUND: The purpose of the study was to evaluate the impact of 2-[fluorine-18]fluoro-2-deoxy-D-glucose-positron emission tomography (FDG-PET)/computed tomography (CT) during follow-up of patients with Hodgkin's lymphoma. PATIENTS AND METHODS: Patients in complete remission or an unconfirmed complete remission after first-line therapy who received FDG-PET/CT during their follow-up were analyzed retrospectively. Confirmatory biopsy was mandatory in case of recurrence. RESULTS: Overall, 134 patients were analyzed. Forty-two (31.3%) patients had a recurrence. The positive predictive value of FDG-PET/CT was 0.98. Single-factor analysis identified morphological residual mass [P = 0.0005, hazard ratio (HR) 3.4, 95% confidence interval (CI) 1.7-6.6] and symptoms (P < 0.0001, HR 4.9, 95% CI 2.4-9.9) as significant risk factors for relapse. By multivariate analysis, morphological residual mass was the only significant risk factor for early follow-up (<24 months) (P = 0.0019, HR 7.6, 95% CI 2.1-27.3). Advanced stage (P = 0.0426, HR 3.6, 95% CI 1.1-12.3) and the presence of symptoms (P = 0.0009, HR = 14.6, 95% CI 3.0-69.7) were found to be significant risk factors for later follow-up (>24 months). CONCLUSIONS: Asymptomatic patients without morphological residues and an early stage of disease do not need a routine FDG-PET/CT for follow-up. Asymptomatic patients with morphological residues should receive routine follow-up FDG-PET/CT for the first 24 months. Only patients with advanced initial stage do need a routine follow-up FDG-PET/CT beyond 24 months.

Risk-adapted FDG-PET/CT-based follow-up in patients with diffuse large B-cell lymphoma after first-line therapy.

BACKGROUND: The purpose of this study was to evaluate the impact of 2-[fluorine-18]fluoro-2-deoxy-D-glucose-positron emission tomography/computed tomography (FDG-PET/CT) during follow-up of patients with diffuse large B-cell lymphoma (DLBCL) being in complete remission or unconfirmed complete remission after first-line therapy. PATIENTS AND METHODS: DLBCL patients receiving FDG-PET/CT during follow-up were analyzed retrospectively. Confirmatory biopsy was mandatory in cases of suspected disease recurrence. RESULTS: Seventy-five patients were analyzed and 23 (30%) had disease recurrence. The positive predictive value (PPV) of FDG-PET/CT was 0.85. Patients >60 years [P = 0.036, hazard ratio (HR) = 3.82, 95% confidence interval (CI) 1.02-7.77] and patients with symptoms indicative of a relapse (P = 0.015; HR = 4.1; 95% CI 1.20-14.03) had a significantly higher risk for relapse. A risk score on the basis of signs of relapse, age >60 years, or a combination of these factors identified patients at high risk for recurrence (P = 0.041). CONCLUSIONS: FDG-PET/CT detects recurrent DLBCL after first-line therapy with high PPV. However, it should not be used routinely and if only in selected high-risk patients to reduce radiation burden and costs. On the basis of our retrospective data, FDG-PET/CT during follow-up is indicated for patients <60 years with clinical signs of relapse and in patients >60 years with and without clinical signs of relapse.

Value of combined 6-[18F]fluorodihydroxyphenylalanine PET/CT for imaging of neuroendocrine tumours.

BACKGROUND: Accurate knowledge of tumour presence and location is essential to treat neuroendocrine tumours (NETs). Standard imaging has been hampered by low sensitivity and lack of spatial resolution. This study assessed prospectively the diagnostic value and impact of combined 6-[18F]fluorodihydroxyphenylalanine positron emission tomography-computed tomography (18F-DOPA-PET/CT) in the management of NET. METHODS: 18F-DOPA-PET/CT findings in 61 patients with suspected NET were compared with a composite reference standard including somatostatin receptor scintigraphy (SRS), magnetic resonance imaging, computed tomography, histological examination and clinical follow-up. The impact on clinical management was estimated by calculating the proportion of patients whose treatment changed as a result of 18F-DOPA-PET/CT findings. RESULTS: 18F-DOPA-PET/CT correctly identified 32 of 36 patients with NET. The sensitivity and specificity of 18F-DOPA-PET/CT for the detection of NET were 91 and 96 per cent respectively. Sensitivity using SRS was significantly lower (59 per cent), whereas the specificity was similar (86 per cent). In 16 (26 per cent) of the 61 patients the management was altered as a result of new findings on 18F-DOPA-PET/CT. CONCLUSION: 18F-DOPA-PET/CT yields a high sensitivity and specificity in the detection of NET. The clinical impact was highly relevant as changes in therapy were observed in more than a quarter of the patients.

Limited value of 18F-FDG PET/CT and S-100B tumour marker in the detection of liver metastases from uveal melanoma compared to liver metastases from cutaneous melanoma.

PURPOSE: The objective of this study was to evaluate the value of (18)F-FDG PET/CT and S-100B tumour marker for the detection of liver metastases from uveal melanoma in comparison to liver metastases from cutaneous melanoma. METHODS: A retrospective evaluation was conducted of 27 liver metastases in 13 patients with uveal melanoma (UM) (mean age: 56.8, range: 30-77) and 43 liver metastases in 14 patients (mean age: 57.9, range: 40-82) with cutaneous melanoma (CM) regarding size and FDG uptake by measuring the maximum standardized uptake value (SUV(max)). S-100B serum tumour markers were available in 20 patients. Cytology, histology, additional morphological imaging and follow-up served as reference standard. In nine patients liver metastases were further evaluated histologically regarding GLUT-1 and S-100 receptor expression and regarding epithelial or spindle cell growth pattern. RESULTS: Of 27 liver metastases in 6 of 13 patients (46%) with UM, 16 (59%) were FDG negative, whereas all liver metastases from CM were positive. Liver metastases from UM showed significantly (p < 0.001) lower SUV(max) (mean: 3.5, range: 1.5-13.4) compared with liver metastases from CM (mean: 6.6, range: 2.3-15.3). In four of six (66.7%) patients with UM and liver metastases S-100B was normal and in two (33.3%) increased. All PET-negative liver metastases were detectable by morphological imaging (CT or MRI). S-100B was abnormal in 13 of 14 patients with liver metastases from CM. S-100B values were significantly higher (p = 0.007) in the CM patient group (mean S-100B: 10.9 microg/l, range: 0.1-115 microg/l) compared with the UM patients (mean: 0.2 microg/l, range: 0.0-0.5 microg/l). Histological work-up of the liver metastases showed no obvious difference in GLUT-1 or S-100 expression between UM and CM liver metastases. The minority (36%) of patients with UM had extrahepatic metastases and the majority (86%) of patients with CM had extrahepatic metastases, respectively. There was a close to significant trend to better survival of UM patients compared with CM patients (p = 0.06). CONCLUSION: FDG PET/CT and serum S-100B are not sensitive enough for the detection of liver metastases from UM, whereas liver metastases from cutaneous melanoma are reliably FDG positive and lead regularly to increased S-100B tumour markers. The reason for the lower FDG uptake in UM liver metastases remains unclear. We recommend to perform combined contrast-enhanced PET/CT in order to detect FDG-negative liver metastases from UM.

The additional value of CT images interpretation in the differential diagnosis of benign vs. malignant primary bone lesions with 18F-FDG-PET/CT.

OBJECTIVE: To evaluate the value of a dedicated interpretation of the CT images in the differential diagnosis of benign vs. malignant primary bone lesions with 18 fluorodeoxyglucose-positron emission tomography/computed tomography (18F-FDG-PET/CT). MATERIALS AND METHODS: In 50 consecutive patients (21 women, 29 men, mean age 36.9, age range 11-72) with suspected primary bone neoplasm conventional radiographs and 18F-FDG-PET/CT were performed. Differentiation of benign and malignant lesions was separately performed on conventional radiographs, PET alone (PET), and PET/CT with specific evaluation of the CT part. Histology served as the standard of reference in 46 cases, clinical, and imaging follow-up in four cases. RESULTS: According to the standard of reference, conventional 17 lesions were benign and 33 malignant. Sensitivity, specificity, and accuracy in assessment of malignancy was 85%, 65% and 78% for conventional radiographs, 85%, 35% and 68% for PET alone and 91%, 77% and 86% for combined PET/CT. Median SUV(max) was 3.5 for benign lesions (range 1.6-8.0) and 5.7 (range 0.8-41.7) for malignant lesions. In eight patients with bone lesions with high FDG-uptake (SUV(max) >or= 2.5) dedicated CT interpretation led to the correct diagnosis of a benign lesion (three fibrous dysplasias, two osteomyelitis, one aneurysmatic bone cyst, one fibrous cortical defect, 1 phosphaturic mesenchymal tumor). In four patients with lesions with low FDG-uptake (SUV(max) < 2.5) dedicated CT interpretation led to the correct diagnosis of a malignant lesion (three chondrosarcomas and one leiomyosarcoma). Combined PET/CT was significantly more accurate in the differentiation of benign and malignant lesions than PET alone (p = .039). There was no significant difference between PET/CT and conventional radiographs (p = .625). CONCLUSION: Dedicated interpretation of the CT part significantly improved the performance of FDG-PET/CT in differentiation of benign and malignant primary bone lesions compared to PET alone. PET/CT more commonly differentiated benign from malignant primary bone lesions compared with conventional radiographs, but this difference was not significant.

Highly iodinated intravenous contrast material for PET/CT - a feasibility study.

PURPOSE: Intravenous contrast materials (CM) are of benefit in PET/CT imaging. However, CM may influence tracer quantification and may cause artifacts when using the CT data for PET attenuation correction. The aim of the study was to assess the feasibility of applying a highly concentrated CM (HCCM, 400 mg iodine/ml) in PET/CT in comparison to a lower concentrated CM (LCCM, 300 mg iodine/ml). MATERIALS AND METHODS: In 60 whole-body FDG PET/CT scans (30 scans each with HCCM and LCCM), tracer uptake (maximal standardized uptake value - SUVmax) and CT attenuation (Hounsfield Units) were quantified at 16 positions in different vessels and parenchyma. The number of potential PET artifacts was documented. The Mann-Whitney-Wilcoxon Test was performed for statistical assessment (p < 0.05). RESULTS: HCCM did not cause a significant increase in the SUVmax (p > 0.05) or the number of PET artifacts (p = 0.69) while simultaneously significantly increasing CT attenuation (p = 0.002) as compared to LCCM in 11 / 16 positions. CONCLUSION: The application of HCCM seems feasible in PET/CT and should be considered in future protocols.

Cervical lymph node metastases of unknown origin: primary tumor detection with whole-body positron emission tomography/computed tomography.

BACKGROUND: Identification of primary tumor in patients with cervical lymph node metastasis of unknown primary (MUO) has a great impact on therapy approach and potentially on patient prognosis. PURPOSE: To assess the diagnostic accuracy of combined positron emission tomography(PET)/computer tomography (CT) for primary tumor detection in cervical metastases of unknown origin compared to PET, CT, and PET+CT side-by-side evaluation. MATERIAL AND METHODS: 39 consecutive patients (eight women, 31 men; mean age 59.9 ± 11.2 years) with MUO were enrolled in this study. PET/CT images were obtained 1 hour after injection of 350 MBq of fluorodeoxyglucose. Oral and intravenous contrast agents were administered in all patients to ensure diagnostic CT data. Fused PET/CT data were evaluated for primary tumor detection. Diagnostic accuracy was calculated and compared with CT alone, PET alone, and side-by-side PET+CT evaluation.Statistical analysis of differences in diagnostic performance between the different imaging procedures was based on the McNemar test. RESULTS: Fused PET/CT depicted the primary tumor in 11 of 39 (28%) patients. In 28(72%) patients, the primary tumor remained occult. CT revealed the primary in five(13%), PET alone in 10 (26%), and side-by-side evaluation of PET+CT in 10 (26%) of 39 patients. Statistical analysis showed no significant differences between the imaging modalities. CONCLUSION: PET, side-by-side PET+CT, and PET/CT revealed similar detection rates for primary tumors in cervical MUO patients. Therefore, cervical metastases of an unknown primary may be assessed with either of these imaging modalities. Detection rates with CT were substantially lower. Thus, inclusion of functional data for assessment of cervical MUO patients must be recommended.

18FDG-PET-CT improves specificity of preoperative lymph-node staging in patients with intestinal but not diffuse-type esophagogastric adenocarcinoma.

INTRODUCTION: The accuracy of preoperative lymph-node staging in patients with adenocarcinoma of the esophagogastric junction (AEG) or gastric cancer (GC) is low. The aim of this study was to assess the accuracy of [18F]fluorodeoxyglucose positron emission tomography/computed tomography (PET-CT) for lymph-node staging in patients with AEG or GC, with or without neoadjuvant treatment. PATIENTS AND METHODS: 221 consecutive patients with GC (n = 88) or AEG (n = 133) were evaluated. Initial staging included endoscopic ultrasound (EUS), multidetector spiral CT (MDCT) and PET-CT. PET-CT was performed for restaging in patients after neoadjuvant treatment (n = 94). Systematic lymphadenectomy was routinely performed with histopathological assessment of individual mediastinal and abdominal lymph-node stations. Preoperative staging from EUS, MDCT, and PET-CT was correlated with histopathological results. RESULTS: PET-CT showed a high specificity (91%) and positive predictive value (89%) for the preoperative detection of lymph-node metastases. In comparison, EUS was more sensitive (73% versus 50%, P < 0.01) but less specific (60%, P < 0.01). In patients with intestinal/mixed-type tumors, PET-CT improved the detection of extra-regional lymph-node metastases (P = 0.01) and distant metastases (P = 0.01) compared to CT alone. In contrast, lymph-node assessment by PET/CT after neoadjuvant treatment (32%, P < 0.01) and in diffuse-type cancers (24%, P < 0.01) is futile because of low sensitivities. CONCLUSION: PET-CT does not improve the overall accuracy of N staging, but does improve specificity compared to EUS and MDCT in AEG and GC. We do not recommend routine PET-CT for the initial staging in patients with diffuse-type cancer or for restaging of lymph nodes after neoadjuvant treatment.

Stability of radiomic features in CT perfusion maps.

This study aimed to identify a set of stable radiomic parameters in CT perfusion (CTP) maps with respect to CTP calculation factors and image discretization, as an input for future prognostic models for local tumor response to chemo-radiotherapy. Pre-treatment CTP images of eleven patients with oropharyngeal carcinoma and eleven patients with non-small cell lung cancer (NSCLC) were analyzed. 315 radiomic parameters were studied per perfusion map (blood volume, blood flow and mean transit time). Radiomics robustness was investigated regarding the potentially standardizable (image discretization method, Hounsfield unit (HU) threshold, voxel size and temporal resolution) and non-standardizable (artery contouring and noise threshold) perfusion calculation factors using the intraclass correlation (ICC). To gain added value for our model radiomic parameters correlated with tumor volume, a well-known predictive factor for local tumor response to chemo-radiotherapy, were excluded from the analysis. The remaining stable radiomic parameters were grouped according to inter-parameter Spearman correlations and for each group the parameter with the highest ICC was included in the final set. The acceptance level was 0.9 and 0.7 for the ICC and correlation, respectively. The image discretization method using fixed number of bins or fixed intervals gave a similar number of stable radiomic parameters (around 40%). The potentially standardizable factors introduced more variability into radiomic parameters than the non-standardizable ones with 56-98% and 43-58% instability rates, respectively. The highest variability was observed for voxel size (instability rate >97% for both patient cohorts). Without standardization of CTP calculation factors none of the studied radiomic parameters were stable. After standardization with respect to non-standardizable factors ten radiomic parameters were stable for both patient cohorts after correction for inter-parameter correlations. Voxel size, image discretization, HU threshold and temporal resolution have to be standardized to build a reliable predictive model based on CTP radiomics analysis.

Combined PET/MRI: from Status Quo to Status Go. Summary Report of the Fifth International Workshop on PET/MR Imaging; February 15-19, 2016; Tübingen, Germany.

This article provides a collaborative perspective of the discussions and conclusions from the fifth international workshop of combined positron emission tomorgraphy (PET)/magnetic resonance imaging (MRI) that was held in Tübingen, Germany, from February 15 to 19, 2016. Specifically, we summarise the second part of the workshop made up of invited presentations from active researchers in the field of PET/MRI and associated fields augmented by round table discussions and dialogue boards with specific topics. This year, this included practical advice as to possible approaches to moving PET/MRI into clinical routine, the use of PET/MRI in brain receptor imaging, in assessing cardiovascular diseases, cancer, infection, and inflammatory diseases. To address perceived challenges still remaining to innovatively integrate PET and MRI system technologies, a dedicated round table session brought together key representatives from industry and academia who were engaged with either the conceptualisation or early adoption of hybrid PET/MRI systems. Discussions during the workshop highlighted that emerging unique applications of PET/MRI such as the ability to provide multi-parametric quantitative and visual information which will enable not only overall disease detection but also disease characterisation would eventually be regarded as compelling arguments for the adoption of PET/MR. However, as indicated by previous workshops, evidence in favour of this observation is only growing slowly, mainly due to the ongoing inability to pool data cohorts from independent trials as well as different systems and sites. The participants emphasised that moving from status quo to status go entails the need to adopt standardised imaging procedures and the readiness to act together prospectively across multiple PET/MRI sites and vendors.

MR-driven metal artifact reduction in PET/CT.

Among the proposed system architectures capable of delivering positron emission tomography/magnetic resonance (PET/MR) datasets, tri-modality systems open an interesting field in which the synergies between these modalities can be exploited to address some of the problems encountered in standalone systems. In this paper we present a feasibility study of the correction of dental streak artifacts in computed tomography (CT)-based attenuation correction images using complementary MR data. The frequency and severity of metal artifacts in oncology patients was studied by inspecting the CT scans of 152 patients examined at our hospital. A prospective correction algorithm using CT and MR information to automatically locate and edit the region affected by metal artifacts was developed and tested retrospectively on data from 15 oncology patients referred for a PET/CT scan. In datasets without malignancies, the activity in Waldeyer's ring was used to measure the maximum uptake variation when the proposed correction was applied. The measured bias ranged from 10% to 30%. In datasets with malignancies on the slices affected by artifacts, the correction led to lesion uptake variations of 6.1% for a lesion 3 cm away from the implant, 1.5% for a lesion 7 cm away and <1% for a lesion 8 cm away.