Significance of incidental focal fluorine-18 fluorodeoxyglucose uptake in colon/rectum,thyroid,and prostate:With a brief literature review

BACKGROUND Fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography(F-18 FDG PET/CT),a functional imaging method,is usually performed on the entire torso,and regions of unexpected suspicious focal hypermetabolism are not infrequently observed.Among the regions,colon,thyroid,and prostate were found to be the common organs in a recent umbrella review.Some studies reported that a high rate of malignancy was shown in incidentally identified focal hypermetabolic regions and suggested that further examinations should not be ignored.AIM To investigate the malignancy rate of incidental focal FDG uptake,useful PET parameters and their cutoffs in discrimination between malignant and benign lesions.METHODS Retrospectively,the final reports of 16510 F-18 FDG PET/CT scans performed at our hospital between January 2016 and March 2022 were reviewed to identify incidentally observed FDG uptake in the colon/rectum,thyroid,and prostate.The scans of patients with current or prior malignancies at each corresponding location,without the final reports of histopathology or colonoscopy(for colon and rectum)for the corresponding hypermetabolic regions,or with diffuse(not focal)hypermetabolism were excluded.Finally,88 regions of focal colorectal hypermetabolism in 85 patients(48 men and 37 women with mean age 67.0±13.4 years and 63.4±15.8 years,respectively),48 focal thyroid uptakes in 48 patients(12 men and 36 women with mean age 62.2±13.1 years and 60.8±12.4 years,respectively),and 39 focal prostate uptakes in 39 patients(mean age 71.8±7.5 years)were eligible for this study.For those unexpected focal hypermetabolic regions,rates of malignancy were calculated,PET parameters,such as standardized uptake value(SUV),capable of distinguishing between malignant and benign lesions were investigated,and the cutoffs of those PET parameters were determined by plotting receiver operating characteristic curves.RESULTS In the colon and rectum,29.5%(26/88)were malignant and 33.0%(29/88)were premalignant lesions.Both SUVmax and SUVpeak differentiated malignant/premalignant from benign lesions,however,no parameters could distinguish malignant from premalignant lesions.Higher area under the curve was shown with SUVmax(0.752,95%CI:0.649-0.856,P<0.001)and the cutoff was 7.6.In the thyroid,60.4%(29/48)were malignant.The majority were well-differentiated thyroid cancers(89.7%,26/29).The results of BRAF mutation tests were available for 20 of the 26 welldifferentiated thyroid cancers and all 20 had the mutation.Solely SUVmax differentiated malignant from benign lesions and the cutoff was 6.9.In the prostate,56.4%(22/39)were malignant.Only SUVmax differentiated malignant from benign lesions and the cutoff was 3.8.Overall,among the 175 focal hypermetabolic regions,60.6%(106/175)were proven to be malignant and premalignant(in colon and rectum)lesions.CONCLUSION Approximately 60%of the incidentally observed focal F-18 FDG uptake in the colon/rectum,thyroid,and prostate were found to be malignant.Of the several PET parameters,SUVmax was superior to others in distinguishing between malignant/premalignant and benign lesions.Based on these findings,incidental focal hypermetabolism should not be ignored and lead physicians to conduct further investigations with greater confidence.

Assessment of incidental focal colorectal uptake by analysis of fluorine-18 fluorodeoxyglucose positron emission tomography parameters

BACKGROUND Colon and rectal cancers are among the top five cancers worldwide in terms of their incidence and mortality rates.As the treatment options for cure include surgery even in specific advanced-stage cases,the early detection of lesions is important for applying active treatment methods.Fluorine-18 fluorodeoxyglucose(F-18 FDG)positron emission tomography/computed tomography(PET/CT)is an established imaging study for many types of cancers;however,physiologic uptake in the gastrointestinal tract is a frequent finding and may interfere with lesion identification.Nevertheless,as unexpectedly observed focal colorectal F-18 FDG uptake may harbor malignant lesions,further examination must not be avoided.AIM To assess the clinical implications of unexpected focal colorectal F-18 FDG uptake by analyzing FDG PET parameters.METHODS A total of 15143 F-18 FDG PET/CT scans performed at our hospital between January 2016 and September 2021 were retrospectively reviewed to identify incidentally observed focal colorectal FDG uptake.Finally,83 regions showing focal colorectal FDG uptake with final histopathological reports from 80 patients(45 men and 35 women with mean ages of 66.9±10.7 years and 63.7±15.3 years,respectively)were eligible for inclusion in the present study.Each focal hypermetabolic colorectal region was classified as malignant,premalignant,or benign according to the histopathological report.PET parameters such as maximum and peak standardized uptake value(SUVmax and SUVpeak),metabolic tumor volume(MTV),mean SUV of the metabolic tumor volume(mSUVmtv),and total lesion glycolysis(TLG)were measured or calculated for the corresponding hypermetabolic regions.Parametric and nonparametric statistical comparisons of these parameters were performed among the three groups.Receiver operating characteristic curves were plotted to identify cut-off values.RESULTS The detection rate of incidental focal colorectal uptake was 0.53%(80/15,143).Of the 83 regions with unexpected focal colorectal hypermetabolism,28.9%(24/83)were malignant,32.5%(27/83)were premalignant,and 38.6%(32/83)were benign.Overall,61.4% of the regions had malignant or premalignant lesions.SUVmax,SUVpeak,and mSUVmtv differentiated malignant and/or premalignant lesions from benign lesions with statistical significance(P<0.05).mSUVmtv3.5 differentiated malignant from benign lesions,with the largest area under the curve(AUC)of 0.792 and a cut-off of 4.9.SUVmax showed the largest AUC of 0.758 with a cut-off value of 7.5 for distinguishing between premalignant and benign lesions.Overall,SUVmax with a cut-off value of 7.6(AUC:0.770,95% confidence interval(CI):0.668-0.872;sensitivity,0.686;specificity,0.688)was a superior parameter for distinguishing between malignant/premalignant and benign lesions or physiologic uptake.No parameters differentiated malignant from premalignant lesions.Moderate or weak positive correlations were observed between the long diameter of the malignant lesions and PET parameters such as SUVpeak and some mSUVmtv.CONCLUSION Approximately two-thirds(61.4%)of incidental focal hypermetabolic colorectal regions were malignant/premalignant lesions,for which SUVmax was an independent diagnostic parameter.Unexpected suspicious focal colorectal FDG uptake should not be avoided and consideration for further evaluation is strongly recommended not to miss the two-thirds.

Fluorine-18 Fluorodeoxyglucose Positron Emission Tomography for Osteochondromas Utilizing a Triple-Time Point Protocol

Purpose: The purpose of this study was to assess solitary osteochondroma and hereditary multiple osteochondral exostoses (HMOCE) utilizing FDG PET and a triple time point protocol. Methods: Seven patients were consented and recruited for PET evaluation of presumed benign osteochondroma. Following injection of 15 mCi of FDG, the lesion(s) of interest was imaged with PET-CT at 45 minutes post injection, whole body at 50 minutes post, and lesion of interest at 95 minutes post injection. A maximum standardized uptake value (SUVmax) was obtained for the lesion(s) of interest at each time point, and an SUVΔ was calculated for each lesion of interest from the first time point to the third time point. Results: 16 lesions from 7 patients were included in the study. Mean SUVmax for all 3 time points was 1.04 with a standard deviation of 0.50 (range 0.3 - 2.2). The mean SUV was 0.096 with a range of 0 - 0.4. Among the 3 patients with histologically confirmed osteochondromas, mean SUVmax was 0.67, with standard deviation of 0.23 and range of 0.3 to 1.0. The mean SUVΔ13 was 0.081 (range 0 - 0.4), mean SUVΔ12 was 0.10 (0 - 0.3), and mean SUVΔ23 was 0.11 (range 0 - 0.4) (p = 0.74). Conclusion: Benign lesions were found to not have progressively increasing uptake on multiple time point FDG PET. Until chondrosarcomas are evaluated using triple time point 18FDG PET, its applicability in the evaluation of osteochondroma versus malignant change remains uncertain.

Potential of (18)~F-FDG-PET as a valuable adjunct to clinical and response assessment in rheumatoid arthritis and seronegative spondyloarthropathies

AIM: To evaluate the role of fluorine-18-labeled fluorodeoxyglucose positron emission tomography (18F-FDG PET) in various rheumatic diseases and its potential in the early assessment of treatment response in a limited number of patients. METHODS: This study involved 28 newly diagnosed patients, of these 17 had rheumatoid arthritis (RA) and 11 had seronegative spondyloarthropathy (SSA). In the SSA group, 7 patients had ankylosing spondylitis, 3 had psoriatic arthritis, and one had non-specific SSA. Patients with RA were selected as per the American College of Rheumatology criteria. One hour after FDG injection, a whole body PET scan was performed from the skull vertex to below the knee joints using a GE Advance dedicated PET scanner. Separate scans were acquired for both upper and lower limbs. Post-treatment scans were performed in 9 patients in the RA group (at 6-9 wk from baseline) and in 1 patient with psoriatic arthropathy. The pattern of FDG uptake was analysed visually and quantified as maximum standardized uptake value (SUVmax) in a standard region of interest. Metabolic response on the scan was assessed qualitatively and quantitatively and was correlated with clinical assessment. RESULTS: The qualitative FDG uptake was in agreement with the clinically involved joints, erythrocyte sedimentation rate, C-reactive protein values and the clinical assessment by the rheumatologist. All 17 patients in the RA group showed the highest FDG avidity in painful/swollen/tender joints. The uptake pattern was homogeneous, intense and poly-articular in distribution. Hypermetabolism in the regional nodes (axillary nodes in the case of upper limb joint involvement and inguinal nodes in lower limb joints) was a constant feature in patients with RA. Multiple other extra-articular lesions were also observed including thyroid glands (in associated thyroiditis) and in the subcutaneous nodules. Treatment response was better appreciated using SUVmax values than visual interpretation, when compared with clinical evaluation. Four patients showed a favourable response, while 3 had stable disease and 2 showed disease progression. The resolution of regional nodal uptake (axillary or inguinal nodes based on site of joint involvement) in RA following disease modifying anti-rheumatoid drugs was noteworthy, which could be regarded as an additional parameter for identifying responding patients. In the SSA group, uptake in the affected joint was heterogeneous, low grade and nonsymmetrical. In particular, there was intense tendon and muscular uptake corresponding to symptomatic joints. The patients with psoriatic arthritis showed intense FDG uptake in the joints and soft tissue. CONCLUSION: 18F-FDG PET accurately delineates the ongoing inflammatory activity in various rheumatic diseases (both at articular and extra-articular sites) and relates well to clinical symptoms. Different metabolic patterns on FDG-PET scanning in RA and SSA can have important implications for their diagnosis and management in the future with the support of larger studies. FDG-PET molecular imaging is also a sensitive tool in the early assessment of treatment response, especially when using quantitative information. With these benefits, FDG-PET could play a pivotal clinical role in the management of inflammatory joint disorders in the future.

Imaging of atherosclerotic aorta of rabbit model by detection of plaque inflammation with fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography

Abstract：Background Atherosclerotic plaque rupture is the primary mechanism of thrombosis which plays a key role in the onset of acute coronary syndromes. Detection of these plaques prone to rupture （vulnerable plaque） could be clinically significant for prevention of cardiac events. It has been shown that high metabolism cells have a high uptake of fluorine-18 fluorodeoxyglucose （18F-FDG）. The objective of this study was to investigate the correlation of FDG uptake and the immuno-histochemistry parameters of plaques, and the effect of atorvastatin on vulnerable atherosclerotic plaque in a rabbit model.Methods Ten male New Zealand White rabbits were divided into three groups as follows： （1） normal control group （n=2,C group）： the animals were fed a standard diet at 120 g/d and were given water ad labium; （2） atherosclerosis group （n=4,As group）： animals were fed with high fat diet for 5 months after aortic endothelia damage; （3） treatment group （atherosclerosis ＋ atorvastatin, n=4, Statin group）： animals were fed with high fat diet for 5 months and then changed into normal chow plus atorvastatin （2.5 mg·d-1·kg-1） treatment for another 4 months. Then these four rabbits were imaged with fluorine-18 fluorodexyglucose positron emission tomography/computed tomography （PET/CT） and sacrificed for pathohistologic studies. FDG uptake by the aorta was expressed as target-to-background ratio （TBR）. Maximal standardized uptake value （SUV） was measured over the thoracic and abdominal aortas. The aortic smooth muscle cell （SMC） number, CD-14 antibody positive cell （macrophage） number and the ratio of the thickness of fibrous cap to the thickness of lipid core （cap-to-core ratio） in atherosclerotic plaques were analyzed.Results As group showed significantly higher uptake of FDG than C group （SUVs： 0.746±0.172 vs. 0.286±0.073, P 〈0.001）. After 4 months of atorvastatin treatment and the modification of diet, SUVs decreased significantly （Statin group：0.550±0.134, compared to As group, P 〈0.001）. However, no marked difference was found in TBR, the number of macrophages, the number of SMC and the cap-to-core ratio in the aortic segments between Statin group and As group.The correlation of aortic FDG uptake with SMC assessed by histopathology was negatively significant （r=0.57, P〈0.001）. When aortic FDG uptake was expressed as TBR, it correlated significantly （r=0.69, P 〈0.001） with the macrophage number, and also correlated significantly （r=0.78, P 〈0.001） with the cap-to-core ratio.Conclusion 18F-FDG PET/CT might serve as a useful non-invasive imaging technique for detection of atherosclerotic plaque and potentially permit monitoring of relative changes in inflammation within the atherosclerotic lesion.

Early PET/CT after radiofrequency ablation in colorectal cancer liver metastases： is it useful？

Background Morphologic imaging after radiofrequency ablation （RFA） of liver metastases is hampered by an inflammatory response in the ablation margin, making the identification of local tumor progression （LTP） difficult. The aim of this study was to evaluate the efficacy of early ^18F-FDG PET/CT scanning to monitor the effectiveness of RFA in colorectal liver metastases. Methods Twelve patients with 20 metastases were treated with RFA for colorectal liver metastases. They underwent PET/CT within 2 weeks before RFA and within 24 hours after RFA （so termed ＂early PET/CT＂）. PET/CT was repeated at 1, 3, and 6 months, and then every 6 months after ablation. The standard of reference was based on available clinical and radiological follow-up data. Results Early PET/CT revealed total photopenia in 16 RFA-treated metastases, which were found to be without residual tumor on the final PET/CT scan. Three RFA-treated metastases with focal uptake were identified as local tumor progression, which necessitated further treatment. One RFA-treated metastasis with rim-shaped uptake was regarded as inflammation. The results of the early PET/CT scanning were consistent with the findings of the final follow-up. Conclusions PET/CT performed within 24 hours after RFA can effectively detect whether residual tumor exists for colorectal cancer liver metastases. The results can guide further treatment, and may improve the efficacy of RFA.