FDG Uptake Patterns Research Articles

18F-fluorodeoxyglucose positron emission tomography/computed tomography and the relationship between fluorodeoxyglucose uptake and the expression of hypoxia-inducible factor-1 , glucose transporter-1 and vascular endothelial growth factor in thymic epithelial tumours

The objective of this study was to evaluate the usefulness of (18)F-fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT) and the relationships among the expressions of hypoxia-inducible factor-1α (HIF-1α), glucose transporter-1 (Glut-1) and vascular endothelial growth factor (VEGF), histological type, other clinical factors and FDG uptake in thymic epithelial tumours. Thirty-three patients who underwent FDG-PET/CT before treatment were reviewed. All types of tumours were reclassified into three subgroups: low-risk thymomas (types A, AB and B1), high-risk thymomas (types B2 and B3) and thymic carcinomas. Tumour contour, pattern of FDG uptake, tumour size and maximum standardized uptake value (SUVmax) were obtained. Expressions of HIF-1α, Glut-1 and VEGF were analysed immunohistochemically, and these expressions were evaluated using grading scales. FDG uptake was visually recognized in all (100%) tumours. A homogeneous pattern of FDG uptake was increasingly observed in the order of low-risk thymomas to high-risk thymomas to thymic carcinomas (P = 0.016). SUVmax for thymic carcinomas was significantly higher than that for thymomas (P = 0.008). With the optimal cut-off value of SUVmax of 5.6, the sensitivity, specificity and accuracy for diagnosing thymic carcinoma were 0.75, 0.80 and 0.79, respectively. Regarding the mean scoring of HIF-1α, Glut-1 and VEGF, increasing trends were observed in the order of low-risk thymomas to high-risk thymomas to thymic carcinomas. Tumour size revealed a significant correlation with SUVmax (r = 0.60, P < 0.001), and the expression of HIF-1α showed a moderate association, but the expression of Glut-1 showed no correlation with SUVmax. Regarding correlations between the expression of the three markers, there were moderate associations between HIF-1α and Glut-1, and HIF-1α and VEGF, and a significant correlation between Glut-1 and VEGF (r = 0.60, P < 0.001). In type B1 thymoma, HIF-1α and Glut-1 were partly expressed in non-neoplastic immature lymphocytes. FDG-PET/CT should be performed in patients with tumours in the anterior mediastinum because the pattern of FDG uptake and SUVmax are useful in the differential diagnosis of thymic epithelial tumours. Furthermore, the expressions of HIF-1α, Glut-1 and VEGF might be associated with malignancy of thymic epithelial tumours. In contrast, FDG uptake might be dependent on tumour size rather than Glut-1 overexpression.

Abstract 2672: Early evaluation of response to Vemurafenib treatment with FDG PET/CT in patients with metastatic melanoma.

Abstract Targeted therapy against the V600 mutated form of BRAF is a proven effective therapy for melanoma. Reduction of FDG accumulation on PET/CT studies occurs very rapidly in responding patients. This exploratory study aims to correlate early changes in FDG uptake patterns with treatment outcome in patients undergoing Vemurafenib treatment. Patients treated at our institution were evaluated with PET-CT at baseline and at day 7, 14 and 28 from the start of therapy. Maximal Standardized Uptake Value (SUVmax) and Total Lesion Glycolysis (TLG, mean SUV x lesion volume) were recorded and compared for single lesions in the 4 studies. Patients were then monitored for clinical, laboratory and imaging signs of progression and results correlated to the early PET/CT findings. Fifteen patients have been studied. A total of 87 lesions are available for comparative evaluation. A greater than 30% reduction in SUVmax compared to baseline was seen in 69 lesions at day 7, 76 at day 14 and 75 at day 28. Nineteen lesions showed a greater than 20% increase in FDG uptake between day 14 and 28. Similar results were found when comparing TLG values. Quantitative and visual analysis of PET/CT studies identified 5 patients showing signs of metabolic progression between day 14 and 28 likely indicating early signs of treatment resistance. Three of these patients showed signs of disease progression by other means within 4 months from the beginning of treatment while 2 are still in treatment with 3 months follow-up. Of the 10 patients not showing metabolic signs of progression at day 28, four have progressed between 2 and 9 months from the beginning of treatment, while the remaining 6 are still in treatment and progression free with 2 to 12 months of follow-up. In conclusion, our preliminary results suggest that PET/CT may be a powerful surrogate marker of treatment response to vemurafenib. Sequential monitoring of targeted therapy with PET/CT may be useful in early identification of treatment resistance, aid in tailoring alternative strategies and deserves further investigation. Citation Format: Luigi Aloj, Corradina Caracò, Francesca Di Gennaro, Antonio M. Grimaldi, Ester Simeone, Marcello Curvietto, Corrado Caracò, Nicola Mozzillo, Valter Torri, Paolo A. Ascierto, Secondo Lastoria. Early evaluation of response to Vemurafenib treatment with FDG PET/CT in patients with metastatic melanoma. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2672. doi:10.1158/1538-7445.AM2013-2672

18F-FDG PET/CT in Differentiating Acute Tuberculous From Idiopathic Pericarditis

The aim of this study was to evaluate retrospectively the diagnostic capability of F-FDG PET/CT in differentiating acute tuberculous from idiopathic pericarditis. FDG PET/CT findings were reviewed in 15 patients with acute tuberculous (n = 5) or idiopathic pericarditis (n = 10). The maximal thickness and SUVmax of the pericardium and the number, size, and SUVmax of the mediastinal and supraclavicular lymph nodes with increased FDG uptake were measured. All patients had small-to-large amount of pericardial effusion. The patients with acute tuberculous pericarditis (n = 5) showed diffuse (n = 3) or multifocal (n = 2) FDG uptake in the pericardia. The patients with acute idiopathic pericarditis (n = 10) showed diffuse (n = 6) or regional (n = 4) FDG uptake in the pericardia. The mean (SD) pericardial thickness and SUVmax of acute tuberculous pericarditis were significantly higher than those of acute idiopathic pericarditis (5.1 [1.0] vs 3.4 [0.9], P < 0.05; 13.5 [3.9] vs 3.0 [0.7], P < 0.05, respectively). A total of 69 mediastinal and supraclavicular lymph nodes with increased FDG uptake were observed in all 15 patients (44 in patients with acute tuberculous pericarditis and 25 in patients with acute idiopathic pericarditis). The mean (SD) SUVmax of mediastinal and supraclavicular lymph nodes of acute tuberculous pericarditis (5.3 [1.8]) was significantly higher than that of acute idiopathic pericarditis (2.8 [0.6], P < 0.05). There was no significant difference in the mean size of the mediastinal and supraclavicular lymph nodes between acute tuberculous and idiopathic pericarditis. The degrees of FDG uptake in the pericardium and the mediastinal and supraclavicular lymph nodes are useful for differentiating acute tuberculous from idiopathic pericarditis. Familiarity with the FDG uptake patterns of acute tuberculous and idiopathic pericarditis may be helpful for successful (especially timely) diagnosis and treatment.

Observer variation study of the assessment and diagnosis of incidental colonic FDG uptake

The aim of this study was to evaluate the interpretations of incidental colonic 18F-FDG uptake made by 10 experienced readers and to more clearly identify the pattern of suspicious colonic FDG uptake. The potential contributions of delayed FDG-PET scanning and of immune fecal occult blood testing (FOBT) in making a diagnosis were also analyzed. Visual interpretations by 10 readers were made for 147 FDG uptake sites from 126 PET scans (cancer, 38 sites; adenoma, 43 sites; and no abnormality, 66 sites) with colonic FDG uptake. Assessments for the early FDG-PET images were (1) FDG uptake pattern, (2) FDG uptake degree, and (3) likelihood of malignancy. For the delayed images, the assessments were (1) change in the FDG uptake position, (2) change in FDG uptake degree, and (3) likelihood of malignancy. The results of FOBT were analyzed independently of the visual interpretations. Interobserver agreement (κ) was 0.501 for assessing FDG uptake patterns, while agreement on assessing changes in uptake degree and changes in uptake position between early and delayed imaging were low (κ = 0.213-0.229). Logistic regression analysis indicated that 'FDG uptake patterns' and 'FDG uptake degree' were significantly related to decide on the suspicion of malignancy (p < 0.001) and the final result (p < 0.001). "Small localized" and "large irregular localized" types had a high probability of a lesion regardless of either (1) FDG uptake degree or (2) variation in the uptake between the early and the delayed image. The delayed image decreased false-positive cases for some FDG uptake patterns, but it had little impact on distinguishing clearly between "cancer or adenoma" and "normal". The addition of FOBT had little impact on the diagnosis. There was highest agreement among readers with respect to the recognition of specified colonic FDG uptake patterns, and this pattern recognition had the most influence on the diagnosis. "Small localized" and "large irregular localized" types had a high probability of a lesion. The addition of delayed imaging and of FOBT results to the early imaging did not have much impact on the diagnosis.

18F-FDG PET/CT makes a significant contribution to diagnosis of malignancy in patients with cervical lymphadenopathy: a study using optimal scale regression tests

Background The specificity and precision of lymphadenopathy assessment using US, CT and MRI are generally unsatisfactory, while fluorodeoxyglucose-positron emission tomography/computed tomography (18F-FDG PET/CT) can support this process by providing additional information about the lymph node features. However, which image features of 18F-FDG PET/CT play the key role in the diagnosis and cutoffs of malignant cervical lymphadenopathy still needs to be determined by further studies. Our study aimed to identify 18F-FDG PET/CT abnormalities that would assist in making a reliable diagnosis of malignant cervical lymphadenopathy in enlarged cervical lymph nodes of patients with unknown primary diseases. Methods One hundred and ninety-one consecutive patients of cervical lymphadenopathy with unknown primary causes were examined by 18F-FDG PET/CT from May 2007 to October 2011 and a definite diagnosis was established by pathologic biopsy. 18F-FDG PET/CT images were evaluated to identify the relevant abnormalities. All image features were analyzed by optimal scale regression tests to determine the important factors that were predictive for the diagnosis of malignant cervical lymphadenopathy and the cutoffs. Results The factors studied in 18F-FDG PET/CT images for predicting malignant cervical lymphadenopathy were sex, age, node location, size, shape, margins, maximum standard uptake value (SUV), mean SUV, FDG uptake pattern and number of nodes. It was found that mean SUV, maximum SUV, FDG uptake pattern, location, size and margins were the important risk factors of cervical lymph nodes that could predict malignant cervical lymphadenopathy. Signs of mean SUV≥2.5 (or maximum SUV≥3.5), nodular FDG uptake pattern, location of IIA, III, IV, VB, VI and VII regions, size≥1.5 cm and vague margins had their optimal diagnostic accuracy (Ac) and Youden index (YI), further, combination of any three factors of these six important risk factors would led to the best diagnostic Ac of 96% and YI of 0.93. Conclusions Signs of mean SUV, maximum SUV, FDG uptake pattern, location, size and margins of node in 18F-FDG PET/CT imaging are important predictive factors of malignant cervical lymphadenopathy. A combination of multiple factors may yield a higher diagnostic efficacy.

When should we recommend use of dual time-point and delayed time-point imaging techniques in FDG PET?

FDG PET and PET/CT are now widely used in oncological imaging for tumor characterization, staging, restaging, and response evaluation. However, numerous benign etiologies may cause increased FDG uptake indistinguishable from that of malignancy. Multiple studies have shown that dual time-point imaging (DTPI) of FDG PET may be helpful in differentiating malignancy from benign processes. However, exceptions exist, and some studies have demonstrated significant overlap of FDG uptake patterns between benign and malignant lesions on delayed time-point images. In this review, we summarize our experience and opinions on the value of DTPI and delayed time-point imaging in oncology, with a review of the relevant literature. We believe that the major value of DTPI and delayed time-point imaging is the increased sensitivity due to continued clearance of background activity and continued FDG accumulation in malignant lesions, if the same diagnostic criteria (as in the initial standard single time-point imaging) are used. The specificity of DTPI and delayed time-point imaging depends on multiple factors, including the prevalence of malignancies, the patient population, and the cut-off values (either SUV or retention index) used to define a malignancy. Thus, DTPI and delayed time-point imaging would be more useful if performed for evaluation of lesions in regions with significant background activity clearance over time (such as the liver, the spleen, the mediastinum), and if used in the evaluation of the extent of tumor involvement rather than in the characterization of the nature of any specific lesion. Acute infectious and non-infectious inflammatory lesions remain as the major culprit for diminished diagnostic performance of these approaches (especially in tuberculosis-endemic regions). Tumor heterogeneity may also contribute to inconsistent performance of DTPI. The authors believe that selective use of DTPI and delayed time-point imaging will improve diagnostic accuracy and interpretation confidence in FDG PET imaging.

FDG PET/CT findings in rare sarcomas

The role of FDG PET/CT in management of soft tissue and bone sarcomas has been described in many studies up-to-date. However, contribution of PET/CT to diagnosis and treatment in some types of sarcomas that are seen with low incidence has not been identified properly yet. Clear cell sarcoma, synovial sarcoma of chest and myxoid lyposarcoma are rare types of sarcomas. We aimed to describe the FDG uptake patterns of these rare tumors and find out the role of FDG PET/CT in management of disease.

Differentiation of tumor recurrence from radiation-induced pulmonary fibrosis after stereotactic ablative radiotherapy for lung cancer: characterization of 18F-FDG PET/CT findings

Stereotactic ablative radiotherapy (SABR), also known as stereotactic body radiotherapy (SBRT), is now a standard treatment option for patients with stage I non-small cell lung cancer or oligometastatic lung tumor who are medically inoperable or medically operable but refuse surgery. When mass-like consolidation is observed on follow-up CT after SABR, it is sometimes difficult to differentiate tumor recurrence from SABR-induced pulmonary fibrosis. In this study, we evaluated the role of (18)F-fluorodeoxyglucose positron emission tomography combined with computed tomography (FDG-PET/CT) in differentiating tumor recurrence from radiation fibrosis after SABR. Between June 2006 and June 2009, 130 patients received SABR for stage I non-small cell lung cancer or metastatic lung cancer at our institution. Fifty-nine patients of them were imaged with FDG-PET/CT after SABR. There were a total of 137 FDG-PET/CT scans for retrospective analysis. The FDG uptake in the pulmonary region was assessed qualitatively using a 3-point scale (0, none or faint; 1, mild; or 2, moderate to intense), and the shape (mass-like or non mass-like) was evaluated. For semi-quantitative analysis, the maximum standardized uptake value (SUV(max)) was calculated. Sixteen of 59 patients had local failure. In recurrent tumor, the combination of intensity grade 2 and mass-like shape was most common (21/23; 91%). By contrast, in cases of radiation fibrosis, the combination of intensity grade 0 or 1 and non mass-like shape was most common (48/59; 81%). The SUV(max) of tumor recurrence after 12 months was significantly higher than that of radiation fibrosis (8.0 ± 3.2 vs. 2.1 ± 0.9, p < 0.001), and all tumor recurrence showed the SUV(max) > 4.5 at diagnosis of local failure. At ≥12 months after SABR, these two variables, the combination of intensity 2 and mass-like FDG uptake or SUV(max) > 4.5 acquired a significant high predictive value of local recurrence, finding sensitivity 100% and specificity 100% for both of them. The combination of FDG uptake patterns and SUV(max) was useful for distinguishing tumor recurrence from radiation fibrosis after SABR.

Is There Any Additional Benefit of Contrast-Enhanced CT as Part of Routine PET/CT Protocols for the Differentiation of Suspicious Incidental Gastrointestinal 2-Deoxy-18F-FDG Uptake?

ObjectiveSuspicious incidental gastrointestinal FDG uptake during positron-emission tomography/computed tomography (PET/CT) examinations can be caused by different diseases, including malignancies. However, differentiation with PET alone is difficult. The aim of this study was to investigate the potential of PET alone, contrast-enhanced CT (ceCT), and low-dose CT (ldCT) in routine PET/CT protocols for differentiation of incidental gastrointestinal lesions.Materials and MethodsSixty patients with incidental gastrointestinal lesions who underwent a routine PET/CT protocol with ldCT and ceCT were retrospectively analysed. The PET lesions were evaluated regarding their FDG uptake patterns and the standard uptake value. The anatomical correlates in both CT protocols were compared in regard to the correct lesion classification with the reference standard endoscopy.ResultsSixty-two lesions were found in 60 patients (17 malignant, 10 premalignant, 5 benign, 13 inflammatory, 17 physiological). The differentiation of the FDG uptake patterns did not enable reliable lesion classification. The positive predictive value for pathology was 0.81 for ceCT in PET/CT and 0.70 for ldCT. Malignancies were detected in 100% of the patients by ceCT vs. 29.4% by ldCT. The false negative rate of ceCT for all pathologies was 31.1%, vs. 68.9% for ldCT. False positive results (17/62) could not be excluded sufficiently by either CT protocol.ConclusionPET/ceCT protocols provide additional benefit especially in detecting gastrointestinal malignancies as a cause of suspicious incidental gastrointestinal FDG uptake. However, since follow-up endoscopy cannot be forgone due to the considerable false negative rate even with ceCT, the addition of ceCT to a routine PET/ldCT protocol cannot be recommended for this purpose.

Intratumoral Heterogeneity of 64Cu-ATSM Uptake is a Prognostic Indicator in Patients with Cervical Cancer

Introduction: Intratumoral heterogeneity determined by FDG-PET is a poor prognostic factor in cervical cancer. Cu- ATSM has been used to evaluate hypoxia in cervical cancer. In this study, FDG and 64Cu-ATSM uptake patterns were compared and the prognostic significance of 64Cu-ATSM heterogeneity was determined. Methods: 15 patients with cervical cancer who underwent pretreatment 64Cu-ATSM- and FDG-PET/CT were included. The 64Cu-ATSM- and FDG-PET/CT images were co-registered and tumor volumes were autocontoured for each image set in 10% increments of the SUVmax ranging from 40% to 80%. The hypoxic fraction defined by 64Cu-ATSM uptake was determined. Concordance between 64Cu-ATSM and FDG uptake was determined by Dice’s coefficient. Heterogeneity of 64Cu-ATSM and FDG uptake was calculated as the variance of the 40-80% isothreshold volumes. The association between heterogeneity of 64Cu-ATSM uptake with tumor-specific factors and outcomes was determined. Results: The hypoxic fraction ranged from 0.773 ± 0.013 to 0.087 ± 0.010 as defined by the 40% to 80% Cu-ATSM isothreshold volumes, respectively. Dice’s similarity coefficients for the FDG and 64Cu-ATSM 40 to 80% isothreshold volumes ranged from 0.476 ± 0.012 to 0.112 ± 0.017. Greater 64Cu-ATSM heterogeneity was associated with increased risk of lymph node metastasis at diagnosis (p<0.01), persistent disease after therapy, (p<0.01), and decreased median progression-free survival (11 months vs. not reached, p=0.03). Conclusion: Significant fractions of cervical tumors are hypoxic. Regions of highest 64Cu-ATSM and FDG uptake were discordant. Elevated 64Cu-ATSM heterogeneity may predict for increased risk of lymph node metastases, decreased responsiveness to treatment, and decreased progression-free survival.

Analysis of18F-fluorodeoxyglucose positron emission tomography findings in patients with pituitary lesions

Background/AimsAlthough magnetic resonance imaging (MRI) is a good visual modality for the evaluation of pituitary lesions, it has limited value in the diagnosis of mixed nodules and some cystic lesions. We evaluated the usefulness of 18F-fluorodeoxyglucose positron emission tomography (FDG PET) for patients with pituitary lesions.Methods18F-FDG PET and MRI were performed simultaneously in 32 consecutive patients with pituitary lesions. The relationships between FDG uptake patterns in PET and MRI findings were analyzed.ResultsOf 24 patients with piuitary adenomas, 19 (79.2%) showed increased uptake of 18F-FDG in the pituitary gland on PET scans. All patients with pituitary macroadenomas showed increased 18F-FDG uptake on PET scans. Meanwhile, only five (50%) of the 10 patients with pituitary microadenomas showed positive PET scans. Interestingly, of two patients with no abnormal MRI findings, one showed increased 18F-FDG uptake on PET. For positive 18F-FDG uptake, maximum standardized uptake values (SUVmax) > 2.4 had 94.7% sensitivity and 100% specificity. In addition, SUVmax increased in proportion to the size of pituitary adenomas. Most cystic lesions did not show 18F-FDG uptake on PET scans.ConclusionsAbout 80% of pituitary adenomas showed positivity on PET scans, and SUVmax was related to the size of the adenomas. PET may be used as an ancillary tool for detection and differentiation of pituitary lesions.

FDG Uptake Pattern on PET/CT Imaging in Non-Infectious Graft of a Patient with Operated Abdominal Aortic Aneurysm

Positron emission tomography using fluorodeoxyglucose is a well known diagnostic tool for routine assessment of the patients with carcinoma. Fluorodeoxyglucose uptake, as a marker of glucose metabolism, is increased in malignant conditions as well as infectious and inflammatory processes. In this case report, findings of postoperative changes in the graft on FDG PET/CT were presented in a patient on follow-up for operated renal cell carcinoma and aortic aneurysm graft surgery. The importance of the FDG uptake pattern has been pointed out for differential diagnosis of infectious and non-infectious conditions.Conflict of interest:None declared.

Impact of molecular imaging on the diagnostic process in a memory clinic

Background[11C]Pittsburgh compound B ([11C]PIB) and [18F]-2-fluoro-2-deoxy-D-glucose ([18F]FDG) PET measure fibrillar amyloid-β load and glucose metabolism, respectively. We evaluated the impact of these tracers on the diagnostic process in a memory clinic population. MethodsOne hundred fifty-four patients underwent paired dynamic [11C]PIB and static [18F]FDG PET scans shortly after completing a standard dementia screening. Two-year clinical follow-up data were available for 39 patients. Parametric PET images were assessed visually and results were reported to the neurologists responsible for the initial diagnosis. Outcome measures were (change in) clinical diagnosis and confidence in that diagnosis before and after disclosing PET results. Results[11C]PIB scans were positive in 40 of 66 (61%) patients with a clinical diagnosis of Alzheimer’s disease (AD), 5 of 18 (28%) patients with frontotemporal dementia (FTD), 4 of 5 (80%) patients with Lewy body dementia, and 3 of 10 (30%) patients with other dementias. [18F]FDG uptake patterns matched the clinical diagnosis in 38 of 66 (58%) of AD patients, and in 6 of 18 (33%) FTD patients. PET results led to a change in diagnosis in 35 (23%) patients. This only occurred when prior diagnostic certainty was <90%. Diagnostic confidence increased from 71 ± 17% before to 87 ± 16% after PET (p < .001). Two-year clinical follow-up (n = 39) showed that [11C]PIB and [18F]FDG predicted progression to AD for patients with mild cognitive impairment, and that the diagnosis of dementia established after PET remained unchanged in 96% of patients. ConclusionsIn a memory clinic setting, combined [11C]PIB and [18F]FDG PET are of additional value on top of the standard diagnostic work-up, especially when prior diagnostic confidence is low.

Clinical effects of electroconvulsive therapy in severe depression and concomitant changes in cerebral glucose metabolism—An exploratory study

ObjectiveElectroconvulsive therapy (ECT) is an effective mode of treatment—especially for severe depression and for depression refractory to pharmacotherapy, nevertheless the mode of action of ECT is far from being fully understood. This study assessed the effects of a series of ECT in depressive subjects on cerebral glucose metabolism measured by FDG–PET scans pre- and post-therapy in thus far the largest group of 12 patients. MethodsOur analysis included careful repeated evaluation of clinical changes in mood and behaviour by standardised questionnaires, which allowed testing for a potential correlation between clinical and cerebral metabolic changes. PET scanning was done within a predefined time window and we used predefined ROIs with counts normalized to the pons activity. ResultsWe observed few changes in cerebral glucose metabolism over time. There was a marginal increase in the left temporal and a trend for a decrease in left frontobasal areas subsequent to treatment in our sample. FDG uptake patterns remained remarkably stable in all the other predefined ROIs pre- and post-treatment. There were no significant correlations between changes in relative metabolic rates and changes in depression scores and parameters derived from neurocognitive testing. ConclusionsOur study thus cannot support the view that FDG–PET can assess the functional brain changes that are likely to occur subsequent to ECT in such a scenario, but this may be related to limited sensitivity given the sample size. Future studies thus might wish to challenge this notion in larger patient samples to clarify this issue.

Apparent Relative Hypermetabolism of Selective Brain Areas in Huntington Disease and Importance of Reference Region for Analysis

We investigated the pattern of reduced and increased metabolism in symptomatic Huntington chorea (HD) patients and assessed the influence of intensity normalization method. FDG brain PET was performed in 11 manifest HD patients and 11 age-matched controls. Images underwent statistical parametric mapping analysis after global normalization or with white matter or pons as reference region. Region of interest analysis of FDG uptake ratios was also performed using total region or white matter as reference. Correlation between regional uptake ratios to that of the caudate was evaluated by linear regression analysis. Although statistical parametric mapping analysis identified striatal hypometabolism and thalamic hypermetabolism in HD patients with all methods, substantially different FDG uptake patterns were shown depending on the method of intensity normalization. Global normalization displayed large areas of relative normalized hypermetabolism across the cerebral cortex and cerebellum. With white matter as reference, relative normalized hypermetabolism was observed in the thalamus and a much more limited area of the cortex. With pons as reference, relative normalized hypermetabolism was largely confined to the thalamus and a small area of the cerebellum. These results demonstrate apparent relative normalized hypermetabolism in selective brain regions in manifest HD patients. Furthermore, the choice of reference region for intensity normalization is critical for accurate monitoring of this metabolic change with FDG PET.

Four Chamber FDG Uptake in the Heart

A 57-year-old-male presented for whole-body PET with CT for restaging of lung cancer. Besides revealing postradiation changes, we noticed an unusual pattern of FDG uptake in the myocardium, with prominent metabolic uptake involving 4 chambers of the heart. Later that day, the patient was referred to the emergency department for increased heart rate, but otherwise asymptomatic. CT angiography was performed, which showed scattered filling defects in bilateral pulmonary arteries consistent with pulmonary embolism. The finding of prominent FDG uptake involving all cardiac chambers in this patient is likely related to heart strain caused by acute pulmonary embolism.

Clinical Significance of Incidental Colonic 18F-FDG Uptake on PET/CT Images in Patients with Gastric Adenocarcinoma

Background and ObjectivesWe assessed the ability of positron emission tomography–computed tomography (PET/CT) to detect synchronous colonic pathology and determined the significance of 18F-fluorodeoxyglucose (18F-FDG) activity in the colon of gastric cancer patients. MethodsA total of 239 gastric cancer patients who underwent PET/CT and colonoscopy preoperatively were included. FDG uptake patterns on PET/CT were classified as (1) group A, focal; (2) group B, diffuse; and (3) group C, no uptake. The PET/CT findings were compared with the results of concurrent colonoscopy. ResultsIn group A, a total of 123 polyps of >0 mm were observed. Of these, nine polyps were colonic adenocarcinomas and six were high-grade dysplasia. The incidence of colonic adenocarcinomas was significantly higher in group A than in the other two groups (p = 0.037). There was a significant correlation between SUVmax values and incidence of colonic polyps of >10 mm (r = 0.471, p = 0.04). The distribution pattern of SUVmax in polyps with adenoma (>10 mm) was less homogenous than in polyps (>10 mm) with adenocarcinoma. ConclusionsThe focal colonic FDG uptake in PET/CT requires colonoscopic confirmation. The suspicion of colonic malignancy increased in the presence of polyps >10 mm that showed a positive correlation with the SUVmax.

TH‐C‐213AB‐09: State‐Driven Mathematical Model Simulations of Tumor Response to Radiotherapy: How Does High FDG Uptake Relate to Classical Radiobiological Principles?

Purpose: High FDG‐PET tracer tumor uptake is well‐established to correlated to increased local failures and shorter overall survival. However, the relationship between uptake and classical radiobiological mechanisms is unclear. We explore the potential relationship between FDG‐PET uptake and classical radiobiolocial mechanisms using a mathematical framework. Methods: Tumor response was simulated using a novel, state‐driven tumor response model, including proliferating, hypoxic, and intermediate cell sub‐populations. Different potential relationships between FDG uptake and these cell populations were simulated. The uptake of FDG was assumed to be associated either with (1) the total number of viable cells, (2) the number of proliferative cells or (3) the number of intermediate cells. The predicted tumor doses for 50% control (TD50) in 2 Gy/fx were estimated for all possible initial conditions and correlated with the FDG uptake level for each assumption. Results: When the FDG uptake pattern was assumed to reflect the level of proliferation, the TD50 decreased with high FDG uptake. When the FDG was assumed to reflect the fraction of viable cells, only a weak positive correlation was observed between FDG uptake and TD50. As a surrogate of metabolically‐viable hypoxic cells, FDG uptake exhibited a strong positive correlation with TD50, consistent with clinical observations. Conclusions: Several different FDG uptake patterns were simulated using the model. Given the established clinical fact that FDG uptake correlates to a requirement of higher dose to achieve local control, the results support a potential avidity of FDG for cells in the intermediate stress state between being well‐oxygenated (and proliferating) and very poorly oxygenated (extremely hypoxic). Supported by the Enid A. Haupt Endowment for Medical Physics

Honda Sign On 18-FDG PET/CT in a Case of Lymphoma Leading to Incidental Detection of Sacral Insufficiency Fracture

Sacral insufficiency fracture (SIF) is an important and treatable cause of low back pain in at-risk groups and the elderly. We report rare demonstration of ‘Honda sign’ in fluoro-deoxy-glucose positron emission tomography-computed tomography (FDG PET-CT) in a case of lymphoma, which led to incidental diagnosis of SIF. Honda sign, which is classically described in bone scans in cases of SIF, was found in FDG PET-CT in our case. This suggests SIF should be suspected when similar FDG uptake pattern is encountered and may help in early detection and management of SIF.

A Patient with Psoriatic Arthritis Imaged with FDG-PET/CT Demonstrated an Unusual Imaging Pattern with Muscle and Fascia Involvement: A Case Report.

We describe the case of a patient with known history of psoriasis that presented with 1 year of unexplained fever, muscle weakness and marked weight loss, suspicious for B symptoms of a malignant origin. [(18)F]-Fluorodeoxyglucose positron emission tomography-computed tomography (FDG-PET/CT) scans demonstrated an unusual serpiginous pattern of uptake in the fascia and muscles as well as lymph node activity. Multiple histological samples, including a final PET-probe guided lymph node surgical resection, excluded malignancy and confirmed the diagnosis of reactive inflammatory changes, with a plausible diagnosis of autoimmune lymphoproliferative syndrome with associated lymphadenitis, fasciitis and myositis, possibly mediated by tumor necrosis factor (TNF) inhibitor. To our knowledge, there is no evidence of a previously reported FDG uptake pattern of fascia and muscle involvement in psoriatic arthritis.