Distribution Patterns of 18F-Labelled Fluoromethylcholine in Normal Structures and Tumors of the Head: A PET/MRI Evaluation

Mapping glioma heterogeneity using multiparametric 18 F-choline PET/MRI in childhood and teenage-young adults

OBJECTIVE

The heterogeneity of post-treatment imaging remains a significant challenge in children and teenagers/young adults (TYA) diagnosed with glioma. The aim of this study was to evaluate the utility of 18 F-choline PET/MRI in determining intratumoural heterogeneity in paediatric and TYA gliomas.

METHODS

Twenty-six patients (mean age 16 years, range 8-22 years) with suspected glioma disease progression were evaluated with 18 F-choline PET/MRI. Relative cerebral blood volume (rCBV), apparent diffusion coefficient (ADC) and maximum standardised uptake values (SUV max ) in enhancing (enh) and non-enhancing (ne) tumour volumes and normal-appearing white matter (wm) were calculated (rCBV enh , rCBV ne , rCBV wm , ADC enh , ADC ne , ADC wm , SUV enh , SUV ne and SUV wm ).

RESULTS

Significantly higher SUV enh and SUV ne compared with SUV wm were observed [SUV enh 0.89 (0.23-1.90), SUV ne 0.36 (0.16-0.78) versus SUV wm 0.15 (0.04-1.19); P  < 0.001 and P  = 0.004, respectively]. Equivalent results were observed for ADV and rCBV (ADC enh , ADC ne : P  < 0.001 versus ADC wm ; rCBV enh , rCBV ne : P  < 0.001 versus rCBV wm ). The highest values for mean SUV max [0.89 (0.23-1.90)] and mean rCBV [2.1 (0.74-5.08)] were in the enhancing component, while the highest values for ADC [1780 mm 2 /s (863-2811)] were in the necrotic component.

CONCLUSION

18 F-choline PET/MRI is able map imaging heterogeneity in paediatric and TYA gliomas, detecting post-treatment enhancing, non-enhancing, and necrotic tumour components equivalent to ADC and DSC-derived rCBV. This offers potential in the response assessment of diffuse non-enhancing gliomas and in selected cases such as posterior fossa tumours where quantitative MRI is technically difficult.

18F-Choline PET Detected the Third Ventricle Craniopharyngioma

ABSTRACT

Craniopharyngiomas are rare tumors of low histological malignancy (World Health Organization grade I) in the sellar and suprasellar region of the brain. We report a case of the third ventricular craniopharyngioma detected using 18F-choline PET/CT in a 43-year-old man. MRI of the brain revealed an intense gadolinium enhancement focus in the same area. Histology revealed characteristics of papillary craniopharyngioma. Our findings suggest that craniopharyngioma should be included in the differential diagnosis of 18F-choline-avid brain lesions.

Choroid Plexus Enlargement in Inflammatory Multiple Sclerosis: 3.0-T MRI and Translocator Protein PET Evaluation

Background Choroid plexuses (CPs) have been suggested as a key gateway for inflammation in experimental autoimmune encephalitis, but in vivo evidence of their involvement in multiple sclerosis (MS) is lacking. Purpose To assess CP volumetric and inflammatory changes in patients with MS versus healthy control participants. Materials and Methods This was a secondary analysis of 97 patients (61 with relapsing-remitting MS [RRMS] and 36 with progressive MS) and 44 healthy control participants who participated in three prospective 3.0-T brain MRI studies between May 2009 and September 2017. A subgroup of 37 patients and 19 healthy control participants also underwent translocator protein fluorine 18 (¹⁸F)-DPA-714 PET for neuroinflammation. Relapses and disability scores were collected at baseline and over 2 years. CPs were manually segmented on three-dimensional T1-weighted images; other brain volumes were additionally segmented. Volumes were expressed as a ratio of intracranial volume. The ¹⁸F-DPA-714 distribution volume ratio was quantified in parenchymal regions, whereas standardized uptake value was used for CP inflammation. Multivariable linear regression analyses were performed to assess CP volumetric and inflammatory differences between patients with MS and healthy control participants and correlations between CP volume and lesion load, brain volumes, ¹⁸F-DPA-714 uptake, and annualized relapse rate. Results Ninety-seven patients with MS (mean age, 42 years ± 12 [standard deviation]; 49 women) and 44 healthy control participants (mean age, 39 years ± 14; 23 women) underwent MRI. Thirty-seven patients with MS and 19 healthy control participants underwent PET. CPs were 35% larger in patients with MS (mean value, 15.9 × 10^-4 ± 4.5) than in healthy control participants (mean value, 11.8 × 10^-4 ± 3.8; P = .004). Subgroup analysis confirmed greater CP volume in patients with RRMS (mean value, 15.5 × 10^-4 ± 4.6; P = .008) than in healthy control participants. CP enlargement was greater in patients with active lesions at MRI (mean volume, 18.2 × 10^-4 ± 4.9 in patients with lesions that enhanced with gadolinium vs 14.9 × 10^-4 ± 4 in patients with lesions that did not enhance with gadolinium; P < .001) and correlated with white matter lesion load (r = 0.39; 95% CI: 0.20, 0.55; P < .001) and ¹⁸F-DPA-714 binding in the thalami (r = 0.44; 95% CI: 0.22, 0.72; P = .04) and normal-appearing white matter (r = 0.5; 95% CI: 0.20, 0.71; P = .005). Moreover, it correlated with annualized relapse rate in patients with RRMS (r = 0.37; 95% CI: 0.1, 0.55; P = .005). Finally, patients with MS showed 18.5% higher CP ¹⁸F-DPA-714 uptake than control participants (mean value, 0.778 ± 0.23 vs 0.635 ± 0.15, respectively; P = .01). CP volume in patients with RRMS (r = 0.57; 95% CI: 0.37, 0.73; P = .009) correlated with higher ¹⁸F-DPA-714 uptake. Conclusion Choroid plexuses (CPs) are enlarged and inflamed in patients with multiple sclerosis (MS), particularly in those with relapsing-remitting MS with inflammatory profiles; CP volumetric analysis could represent an MS imaging marker. © RSNA, 2021 EudraCT no. 2008-004174-40; clinical trial registration nos. NCT02305264 and NCT01651520 Online supplemental material is available for this article.

Unusual uptakes on 18F-fluorocholine positron emission tomography/computed tomography (PET/CT): a retrospective study of 368 prostate cancer patients referred for a biochemical recurrence or an initial staging

Background

¹⁸F-fluorocholine positron emission tomography/computed tomography (F-choline PET/CT) is considered a cornerstone in the staging and restaging of patients with prostate cancer (PCa). The aim of this study was to retrospectively assess unusual uptakes in patients who underwent a F-choline PET/CT for the initial staging or for the restaging of a relapsing PCa.

Methods

Three hundred and sixty-eight PCa patients were staged or restaged using F-choline PET/CT. Unusual uptakes were defined as uptakes occurring outside the usual paths of diffusion of PCa or as uptake in bone with a clear morphological evidence of nonmetastatic lesion.

Results

We found unusual uptakes in 47/368 patients (12.8%). Among them, 41/47 presented with benign F-choline uptake, usually within lymph nodes, due to inflammatory processes (22/47). Other benign processes were found in: thyroid (3/47), adrenal gland (3/47), brain (2/47), liver (1/47), bowel (3/47), frontal sinus (1/47), lungs (4/47), parotid gland (1/47) and bone (1/47). The six remaining patients presented with a second cancer, including lymphoma (1/47), non-small cell lung cancer (4/47) and neuroendocrine tumor (1/47).

Conclusions

unusual uptakes on F-choline PET/CT are quite frequent and should be explored since they may correspond to non-PCa.

Prediction of Meningioma WHO Grade Using PET Findings: A Systematic Review and Meta-Analysis

BACKGROUND AND PURPOSE

World Health Organization (WHO) grading of meningiomas reflects recurrence rate and prognosis. Positron emission tomography (PET) investigates metabolic activity, allowing for distinction between low- and high-grade tumors. As preoperative suspicion for malignant meningioma will influence surgical strategy in terms of timing, extent of resection, and risks taken to achieve a total resection, we systematically reviewed the literature on PET-imaging in meningiomas and relate these findings to histopathological analysis.

METHODS

Searches in PubMed, EMBASE, and The Cochrane Library, from inception to September 2019, included studies of patients who had undergone surgery for a histologically verified intracranial meningioma, with a PET-scan prior to surgery and description of (semi)quantitative PET values for meningiomas from two different WHO groups. Studies comparing more than 1 patient per WHO group were included in the meta-analysis.

RESULTS

Twenty-two studies (432 patients) were included. 18fluor-fluorodesoxyglucose (18F-FDG) PET was mostly described to differentiate benign from malignant meningiomas. Pooled data showed differences in mean (95% CI) Standardized Uptake Value (SUV) for WHO II/III compared to WHO I of 2.51 (1.36, 3.66), and in tumor-to-normal (T/N) ratio (T/N ratio) for WHO II/III versus WHO I of .42 (.12, .73).

CONCLUSIONS

We found that SUV and T/N ratio in 18F-FDG PET may be useful to noninvasively differentiate benign from malignant meningiomas. T/N ratio seems to have a high specificity for the detection of high-grade meningiomas. Other PET tracers were studied too infrequently to draw definitive conclusions. Before treatment strategies can be adapted based on 18F-FDG PET, prospective studies in larger cohorts are warranted to validate the optimal T/N ratio cutoff point.

Imaging and Tissue Biomarkers of Choline Metabolism in Diffuse Adult Glioma: 18F-Fluoromethylcholine PET/CT, Magnetic Resonance Spectroscopy, and Choline Kinase α

The cellular and molecular basis of choline uptake on PET imaging and MRS-visible choline-containing compounds is not well understood. Choline kinase alpha (ChoKα) is an enzyme that phosphorylates choline, an essential step in membrane synthesis. We investigate choline metabolism through 18F-fluoromethylcholine (18F-FMC) PET, MRS, and tissue ChoKα in human glioma. Fourteen patients with a suspected diffuse glioma underwent multimodal 3T MRI and dynamic 18F-FMC PET/CT prior to surgery. Co-registered PET and MRI data were used to target biopsies to regions of high and low choline signal, and immunohistochemistry for ChoKα expression was performed. The 18F-FMC/PET differentiated WHO (World Health Organization) grade IV from grade II and III tumours, whereas MRS differentiated grade III/IV from grade II tumours. Tumoural 18F-FMC/PET uptake was higher than in normal-appearing white matter across all grades and markedly elevated within regions of contrast enhancement. The 18F-FMC/PET correlated weakly with MRS Cho ratios. ChoKα expression on IHC was negative or weak in all but one glioblastoma sample, and did not correlate with tumour grade or imaging choline markers. MRS and 18F-FMC/PET provide complimentary information on glioma choline metabolism. Tracer uptake is, however, potentially confounded by blood–brain barrier permeability. ChoKα overexpression does not appear to be a common feature in diffuse glioma.

18F-Fluorocholine PET/CT in the Prediction of Molecular Subtypes and Prognosis for Gliomas

AIM

To study the association of metabolic features of F-fluorocholine in gliomas with histopathological and molecular parameters, progression-free survival (PFS) and overall survival (OS).

METHODS

Prospective multicenter and nonrandomized study (Functional and Metabolic Glioma Analysis). Patients underwent a basal F-fluorocholine PET/CT and were included after histological confirmation of glioma. Histological and molecular profile was assessed: grade, Ki-67, isocitrate dehydrogenase status and 1p/19q codeletion. Patients underwent standard treatment after surgery or biopsy, depending on their clinical situation. Overall survival and PFS were obtained after follow-up. After tumor segmentation of PET images, SUV and volume-based variables, sphericity, surface, coefficient of variation, and multilesionality were obtained. Relations of metabolic variables with histological, molecular profile and prognosis were evaluated using Pearson χ and t test. Receiver operator caracteristic curves were used to obtain the cutoff of PET variables. Survival analysis was performed using Kaplan-Meier and Cox regression analysis.

RESULTS

Forty-five patients were assessed; 38 were diagnosed as having high-grade gliomas. Significant differences of SUV-based variables with isocitrate dehydrogenase status, tumor grade, and Ki-67 were found. Tumor grade, Ki-67, SUVmax, and SUVmean were related to progression. Kaplan-Meier analysis revealed significant associations of SUVmax, SUVmean, and multilesionaly with OS and PFS. SUVmean, sphericity, and multilesionality were independent predictors of OS and PFS in Cox regression analysis.

CONCLUSIONS

Metabolic information obtained from F-fluorocholine PET of patients with glioma may be useful in the prediction of tumor biology and patient prognosis.

Segmentation of gliomas in 18F-fluorocholine PET/CT. A multiapproach study

AIM

Our aim was two-fold, to study the interobserver agreement in tumour segmentation and to search for a reliable methodology to segment gliomas using ¹⁸F-fluorocholine PET/CT.

METHODS

25 patients with glioma, from a prospective and non-randomized study (Functional and Metabolic Glioma Analysis), were included.Interobserver variability in tumour segmentation was assessed using fixed thresholds. Different strategies were used to segment the tumours. First, a semi-automatic tumour segmentation was performed, selecting the best SUVmax-% threshold for each lesion. Next we determined a variable SUVmax-% depending on the SUVmax. Finally a segmentation using a fixed SUVmax threshold was performed. To do so, a sampling of 10 regions of interest (ROI of 2.8cm²) located in the normal brain was performed. The upper value of the sample mean SUVmax±3 SD was used as cut-off. All procedures were tested and classified as effective or not for tumour segmentation by two observer's consensus.

RESULTS

In the pilot segmentation, the mean±SD of SUVmax, SUVmean and optimal SUVmax-% threshold were: 3.64±1.77, 1.32±0.57 and 21.32±8.39, respectively. Optimal SUVmax-% threshold showed a significant association with the SUVmax (Pearson=-0.653, p=.002). However, the linear regression model for the total sample was not good, that supported the division in two homogeneous groups, defining two formulas for predicting the optimal SUVmax-% threshold. As to the third procedure, the obtained value for the mean SUVmax background+3 SD was 0.33. This value allowed segmenting correctly a significant fraction of tumours, although not all.

CONCLUSION

A great interobserver variability in the tumour segmentation was found. None of the methods was able to segment correctly all the gliomas, probably explained by the wide tumour heterogeneity on ¹⁸F-fluorocholine PET/CT.

The pituitary in nuclear medicine imaging

The pituitary is an endocrine gland with ability to uptake diverse radiopharmaceuticals and, therefore, susceptible to be investigated by nuclear medicine diagnostic procedures. Although this topic has been scarcely scrutinized, we have data indicating that somatostatin receptor scintigraphy with¹¹¹In-DTPA-D-Phe-octreotide or ^99mTc-EDDA/HYNIC-TOC may be of clinical utility in the diagnosis of some pituitary adenomas (PA). Only a few studies have evaluated the diagnostic performance of ^99mTc-MIBI and ^99mTc (V)-DMSA scintigraphy in pituitary disease. Scintigraphy using ¹²³I-methoxybenzamide (¹²³I-IBZM) might be useful in macroprolactinomas expressing dopamine D2 receptors. Pituitary gland does not usually accumulate 2-deoxy-2-[¹⁸F]fluoro-d-glucose (¹⁸F-FDG) and, therefore, it is not visualized on positron emission tomography (PET) imaging studies with this radiotracer. The pituitary uptake on¹⁸F-FDG PET/CT scans performed in the follow-up of oncological patients are uncommon. However, 60% of these incidental findings are due to PA, mainly non-functioning pituitary macroadenomas, and a small percentage to metastases or other pituitary lesions. Interestingly, ¹⁸F-FDG PET/CT may identify hypophysitis induced by different immunotherapeutic agents used in cancer patients. Positive ¹⁸F-FDG uptake has been reported in a high percentage of patients with PA, mainly macroadenomas and it seems that there is correlation between tumor size and SUVmax. ⁶⁸Ga-DOTA-TATE PET/CT may identify functioning and non-functioning PA, although this technique is more useful in the detection of remaining normal pituitary tissue after transsphenoidal adenomectomy, and in the confirmation of recurrence of functioning PA, such as thyrotroph-secreting PA. Furthermore, ⁶⁸Ga-DOTA-TATE uptake has potential therapeutic implications on molecular-targeted therapy. Lastly, other radiopharmaceuticals that have shown to be taken up in some patients with pituitary disease include ¹⁸F-DOPA (prolactinoma), ¹¹C-methionine (residual or recurrent PA), O-(2-¹⁸F-fluoroethyl)-l-tyrosine (metastasis), ¹⁸F-choline (silent adenoma, ectopic corticotropinoma), and ¹³N-ammonia (hypopituitarism).

Direct comparison of [11C] choline and [18F] FET PET to detect glioma infiltration: a diagnostic accuracy study in eight patients

Background

Positron emission tomography (PET) is increasingly used to guide local treatment in glioma. The purpose of this study was a direct comparison of two potential tracers for detecting glioma infiltration, O-(2-[¹⁸F]-fluoroethyl)-l-tyrosine ([¹⁸F] FET) and [¹¹C] choline.

Methods

Eight consecutive patients with newly diagnosed diffuse glioma underwent dynamic [¹¹C] choline and [¹⁸F] FET PET scans. Preceding craniotomy, multiple stereotactic biopsies were obtained from regions inside and outside PET abnormalities. Biopsies were assessed independently for tumour presence by two neuropathologists. Imaging measurements were derived at the biopsy locations from 10 to 40 min [¹¹C] choline and 20–40, 40–60 and 60–90 min [¹⁸F] FET intervals, as standardized uptake value (SUV) and tumour-to-brain ratio (TBR). Diagnostic accuracies of both tracers were compared using receiver operating characteristic analysis and generalized linear mixed modelling with consensus histopathological assessment as reference.

Results

Of the 74 biopsies, 54 (73%) contained tumour. [¹¹C] choline SUV and [¹⁸F] FET SUV and TBR at all intervals were higher in tumour than in normal samples. For [¹⁸F] FET, the diagnostic accuracy of TBR was higher than that of SUV for intervals 40–60 min (area under the curve: 0.88 versus 0.81, p = 0.026) and 60–90 min (0.90 versus 0.81, p = 0.047). The diagnostic accuracy of [¹⁸F] FET TBR 60–90 min was higher than that of [¹¹C] choline SUV 20–40 min (0.87 versus 0.67, p = 0.005).

Conclusions

[¹⁸F] FET was more accurate than [¹¹C] choline for detecting glioma infiltration. Highest accuracy was found for [¹⁸F] FET TBR for the interval 60–90 min post-injection.

Electronic supplementary material

The online version of this article (10.1186/s13550-019-0523-8) contains supplementary material, which is available to authorized users.

Ectopic Salivary Gland in a Patient With Prostate Cancer at 18F-Choline PET/CT: An Incidental Finding

A 65-year-old man with prostate cancer surgically treated in June 2016 underwent F-choline PET/CT in April 2017 for a biochemical recurrence of disease. PET/CT revealed a high tracer uptake in a solid nodulation near the left masseter muscle with a high SUVmax. The patient underwent both ultrasonography examination and fine needle aspiration cytology that confirmed the presence of an ectopic salivary gland. This case highlights that, in patients undergoing choline PET/CT, a careful analysis of the physiological biodistribution should be made by considering also the presence of accessory salivary glands.

PET/CT analysis of 21 patients with breast cancer: physiological distribution of 18F-choline and diagnostic pitfalls

Objectives

¹⁸F-choline is a useful tracer for detecting tumours with high lipogenesis. Knowledge of its biodistribution pattern is essential to recognise physiological variants. The aim of this study was to describe the physiologic distribution of ¹⁸F-choline and pitfalls in patients with breast cancer.

Methods

Twenty-one consecutive patients with breast cancer (10 premenopausal and 11 postmenopausal women; mean age, 52.82 ± 10.71 years) underwent ¹⁸F-choline positron emission tomography (PET)/computed tomography (CT) for staging. Whole-body PET/CT was acquired after 40 minutes of ¹⁸F-choline uptake. Acquired PET images were measured semiquantitatively.

Results

All patients showed pitfalls unrelated to breast cancer. These findings were predominantly caused by physiological glandular uptake in the liver, spleen, pancreas, bowels, axial skeleton (85%-100%), inflammation and benign changes (4.76%), appendicular skeleton (4.76%–19.049%), and site contamination (61.9%). In <1%, a concomitant metastatic neoplasm was found. The breast showed higher physiological uptake in premenopausal compared with postmenopausal woman (¹⁸F-choline maximum standardised uptake values [g/dL] of the right breast = 2.04 ± 0.404 vs 1.59 ± 0.97 and left breast = 2.00 ± 0.56 vs 1.93 ± 1.28, respectively).

Conclusion

¹⁸F-choline uptake was higher in premenopausal women. Physiological ¹⁸F-choline uptake was observed in many sites, representing possible pathologies.

Innovations in imaging modalities for recurrent and metastatic prostate cancer: a systematic review

INTRODUCTION

The last decade has witnessed tremendous changes in the management of advanced and metastatic castration resistant prostate cancer. In the current systematic review, we analyze novel imaging techniques in the setting of recurrent and metastatic prostate cancer (PCa), exploring available data and highlighting future exams which could enter clinical practice in the upcoming years.

EVIDENCE ACQUISITION

The National Library of Medicine Database was searched for relevant articles published between January 2012 and August 2017. A wide search was performed including the combination of following words: "Prostate" AND "Cancer" AND ("Metastatic" OR "Recurrent") AND "imaging" AND ("MRI" OR "PET"). The selection procedure followed the Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA) principles and is presented using a PRISMA flow chart.

EVIDENCE SYNTHESIS

Novel imaging techniques, as multiparametric magnetic resonance imaging (MRI), whole-body MRI and Choline and prostate-specific membrane antigen (PSMA) PET imaging techniques are currently revolutioning the treatment planning in patients with advanced and metastatic PCa, allowing a better characterization of the disease. Multiparametric MRI performs well in the detection of local recurrences, with sensitivity rates of 67-98% and overall diagnostic accuracy of 83-93%, depending on the type of magnetic field strength (1.5 vs. 3T). Whole body MRI instead shows a high specificity (>95%) for bone metastases. PET imaging, and in particular PSMA PET/CT, showed promising results in the detection of both local and distant recurrences, even for low PSA values (<0.5 ng/mL). Sensitivity varies from 77-98% depending on PSA value and PSA velocity.

CONCLUSIONS

Whole body-MRI, NaF PET, Choline-PET/CT and PSMA PET/CT are flourishing techniques which find great application in the field of recurrent and metastatic PCa, in the effort to reduce treatment of "PSA only" and rather focus our therapies on clinical tumor entities. Standardization is urgently needed to allow adequate comparison of results and diffusion on a large scale.

18F-FCho PET and MRI for the prediction of response in glioblastoma patients according to the RANO criteria

PURPOSE

In this study, we investigated fluorine-18 fluoromethylcholine (F-FCho) PET and contrast-enhanced MRI for predicting therapy response in glioblastoma (GB) patients according to the Response Assessment in Neuro-Oncology criteria. Our second aim was to investigate which imaging modality enabled prediction of treatment response first.

MATERIALS AND METHODS

Eleven GB patients who underwent no surgery or debulking only and received concomitant radiation therapy (RT) and temozolomide were included. The gold standard Response Assessment in Neuro-Oncology criteria were applied 6 months after RT to define responders and nonresponders. F-FCho PET and MRI were performed before RT, during RT (week 2, 4, and 6), and 1 month after RT. The contrast-enhancing tumor volume on T1-weighted MRI (GdTV) and the metabolic tumor volume (MTV) were calculated. GdTV, standardized uptake value (SUV)mean, SUVmax, MTV, MTV×SUVmean, and percentage change of these variables between all time-points were assessed to differentiate responders from nonresponders.

RESULTS

Absolute SUV values did not predict response. MTV must be taken into account. F-FCho PET could predict response with a 100% sensitivity and specificity using MTV×SUVmean 1 month after RT. A decrease in GdTV between week 2 and 6, week 4 and 6 during RT and week 2 during RT, and 1 month after RT of at least 31%, at least 18%, and at least 53% predicted response with a sensitivity and specificity of 100%. As such, the parameter that predicts therapy response first is MR derived, namely, GdTV.

CONCLUSION

Our data indicate that both F-FCho PET and contrast-enhanced T1-weighted MRI can predict response early in GB patients treated with RT and temozolomide.

The usefulness of 18F-fluorocholine PET/CT in the detection of recurrence of central nervous system primary neoplasms

AIM

To study the usefulness of ¹⁸F-fluorocholine (FCH) in detecting the recurrence of primary brain tumours.

MATERIAL AND METHODS

A prospective study was conducted on brain PET/CT with FCH for compassionate use in 21 patients with suspected recurrence of a primary brain tumour. The distribution by pathology was: three grade ii astrocytomas, three grade iii astrocytomas, one grade ii oligodendroglioma, three grade iii oligodendrogliomas, one grade iii oligoastrocytoma, four glioblastoma multiform, one gliomatosis cerebri, and five meningiomas. Studies in which there was a visually significant uptake in the brain parenchyma were classified as positive.

RESULTS

A total of 17 patients were classified as positive, with the results being confirmed by histology (10 cases) or clinical follow-up and imaging, with no false positives or negatives. The mean SUVmax for positive patients was 8.02 and 0.94 for the negative ones, which was significantly different (P=.003) CONCLUSION: PET/CT with FCH shows encouraging results in the evaluation of patients with suspected recurrence of primary brain neoplasms.

Brain Tumors: An Update on Clinical PET Research in Gliomas

A previous review published in 2012 demonstrated the role of clinical PET for diagnosis and management of brain tumors using mainly FDG, amino acid tracers, and ¹⁸F-fluorothymidine. This review provides an update on clinical PET studies, most of which are motivated by prediction of prognosis and planning and monitoring of therapy in gliomas. For FDG, there has been additional evidence supporting late scanning, and combination with ¹³N ammonia has yielded some promising results. Large neutral amino acid tracers have found widespread applications mostly based on ¹⁸F-labeled compounds fluoroethyltyrosine and fluorodopa for targeting biopsies, therapy planning and monitoring, and as outcome markers in clinical trials. ¹¹C-alpha-methyltryptophan (AMT) has been proposed as an alternative to ¹¹C-methionine, and there may also be a role for cyclic amino acid tracers. ¹⁸F-fluorothymidine has shown strengths for tumor grading and as an outcome marker. Studies using ¹⁸F-fluorocholine (FCH) and ⁶⁸Ga-labeled compounds are promising but have not yet clearly defined their role. Studies on radiotherapy planning have explored the use of large neutral amino acid tracers to improve the delineation of tumor volume for irradiation and the use of hypoxia markers, in particular ¹⁸F-fluoromisonidazole. Many studies employed the combination of PET with advanced multimodal MR imaging methods, mostly demonstrating complementarity and some potential benefits of hybrid PET/MR.

Pitfalls and Artifacts in the Use of PET/CT in Oncology Imaging

Accurate reporting of combined PET/CT imaging requires a thorough understanding of the normal and variant physiological distribution of tracers as well as common incidental findings and technical artifacts. We describe these pitfalls and artifacts, what action may help to mitigate them in clinical practice, and what further action may be appropriate. This review presents these in a region-based approach, in order to closely mimic clinical practice, and focuses on technical artifacts followed by a description of two commonly used oncologic tracers: FDG and choline.

(18)F-fluoromethylcholine (FCho), (18)F-fluoroethyltyrosine (FET), and (18)F-fluorodeoxyglucose (FDG) for the discrimination between high-grade glioma and radiation necrosis in rats: a PET study

INTRODUCTION

Discrimination between (high-grade) brain tumor recurrence and radiation necrosis (RN) remains a diagnostic challenge because both entities have similar imaging characteristics on conventional magnetic resonance imaging (MRI). Metabolic imaging, such as positron emission tomography (PET) could overcome this diagnostic dilemma. In this study, we investigated the potential of 2-[(18)F]-fluoro-2-deoxy-D-glucose ((18)F-FDG), O-(2-[(18)F]-fluoroethyl)-L-tyrosine ((18)F-FET), and [(18)F]-Fluoromethyl-dimethyl-2-hydroxyethylammonium ((18)F-fluoromethylcholine, (18)F-FCho) PET in discriminating high-grade tumor from RN.

METHODS

We developed a glioblastoma (GB) rat model by inoculating F98 GB cells into the right frontal region. Induction of RN was achieved by irradiating the right frontal region with 60 Gy using three arcs with a beam aperture of 3×3 mm (n=3). Dynamic PET imaging with (18)F-FDG, (18)F-FET, and (18)F-FCho, as well as (18)F-FDG PET at a delayed time interval (240 min postinjection), was acquired.

RESULTS

MRI revealed contrast-enhancing tumors at 15 days after inoculation (n=4) and contrast-enhancing RN lesions 5-6 months postirradiation (n=3). On (18)F-FDG PET, the mean lesion-to-normal ratio (LNRmean) was significantly higher in GB than in RN (p=0.034). The difference in the LNRmean between tumors and RN was higher on the late (18)F-FDG PET images than on the PET images reconstructed from the last time frame of the dynamic acquisition (this is at a conventional time interval). LNRs obtained from (18)F-FCho PET were not significantly different between GB and RN (p=1.000). On (18)F-FET PET, the LNRmean was significantly higher in GB compared to RN (p=0.034).

CONCLUSIONS

Unlike (18)F-FCho, (18)F-FDG and (18)F-FET PET were effective in discriminating GB from RN. Interestingly, in the case of (18)F-FDG, delayed PET seems particularly useful.

ADVANCES IN KNOWLEDGE AND IMPLICATIONS FOR PATIENT CARE

Our results suggest that (delayed) (18)F-FDG and (18)F-FET PET can be used to discriminate GB (recurrence) from RN. Confirmation of these results in clinical studies is needed.

Incidental uptake of (18)F-fluorocholine (FCH) in the head or in the neck of patients with prostate cancer

Background

Positron emission tomography-computed tomography (PET/CT) with ¹⁸F-fluorocholine (FCH) is routinely performed in patients with prostate cancer. In this clinical context, foci of FCH uptake in the head or in the neck were considered as incidentalomas, except for those suggestive of multiple bone metastases.

Results

In 8 patients the incidental focus corresponded to a benign tumour. The standard of truth was histology in two cases, correlative imaging with MRI in four cases, ^99mTc-SestaMIBI scintigraphy, ultrasonography and biochemistry in one case and biochemistry including PTH assay in one case. The final diagnosis of benign tumours consisted in 3 pituitary adenomas, 2 meningiomas, 2 hyperfunctioning parathyroid glands and 1 thyroid adenoma.

Malignancy was proven histologically in 2 other patients: 1 papillary carcinoma of the thyroid and 1 cerebellar metastasis.

Conclusions

To the best of our knowledge, FCH uptake by pituitary adenomas or hyperfunctioning parathyroid glands has never been described previously. We thus discuss whether there might be a future indication for FCH PET/CT when one such tumour is already known or suspected: to detect a residual or recurrent pituitary adenoma after surgery, to guide surgery or radiotherapy of a meningioma or to localise a hyperfunctioning parathyroid gland. In these potential indications, comparative studies with reference PET tracers or with ^99mTc-sestaMIBI in case of hyperparathyroidism could be undertaken.

Biodistribution and radiation dosimetry of deuterium-substituted 18F-fluoromethyl-[1, 2-2H4]choline in healthy volunteers

(11)C-choline and (18)F-fluoromethylcholine ((18)F-FCH) have been used in patients to study tumor metabolic activity in vivo; however, both radiotracers are readily oxidized to respective betaine analogs, with metabolites detectable in plasma soon after injection of the radiotracer. A more metabolically stable FCH analog, (18)F-fluoromethyl-[1,2-(2)H4]choline ((18)F-D4-FCH), based on the deuterium isotope effect, has been developed. We report the safety, biodistribution, and internal radiation dosimetry profiles of (18)F-D4-FCH in 8 healthy human volunteers.

METHODS

(18)F-D4-FCH was intravenously administered as a bolus injection (mean ± SD, 161 ± 2.17 MBq; range, 156-163 MBq) to 8 healthy volunteers (4 men, 4 women). Whole-body (vertex to mid thigh) PET/CT scans were acquired at 6 time points, up to 4 h after tracer injection. Serial whole-blood, plasma, and urine samples were collected for radioactivity measurement and plasma radiotracer metabolites. Tissue (18)F radioactivities were determined from quantitative analysis of the images, and time-activity curves were generated. The total numbers of disintegrations in each organ normalized to injected activity (residence times) were calculated as the area under the curve of the time-activity curve normalized to injected activities and standard organ volumes. Dosimetry calculations were performed using OLINDA/EXM 1.1.

RESULTS

The injection of (18)F-D4-FCH was well tolerated in all subjects, with no radiotracer-related serious adverse event reported. The mean effective dose averaged over both men and women (± SD) was estimated to be 0.025 ± 0.004 (men, 0.022 ± 0.002; women, 0.027 ± 0.002) mSv/MBq. The 5 organs receiving the highest absorbed dose (mGy/MBq) were the kidneys (0.106 ± 0.03), liver (0.094 ± 0.03), pancreas (0.066 ± 0.01), urinary bladder wall (0.047 ± 0.02), and adrenals (0.046 ± 0.01). Elimination was through the renal and hepatic systems.

CONCLUSION

(18)F-D4-FCH is a safe PET radiotracer with a dosimetry profile comparable to other common (18)F PET tracers. These data support the further development of (18)F-D4-FCH for clinical imaging of choline metabolism.