Brain glucose and acetoacetate metabolism: a comparison of young and older adults

The extent to which the age-related decline in regional brain glucose uptake also applies to other important brain fuels is presently unknown. Ketones are the brain's major alternative fuel to glucose, so we developed a dual tracer positron emission tomography protocol to quantify and compare regional cerebral metabolic rates for glucose and the ketone, acetoacetate. Twenty healthy young adults (mean age, 26 years) and 24 healthy older adults (mean age, 74 years) were studied. In comparison with younger adults, older adults had 8 ± 6% (mean ± SD) lower cerebral metabolic rates for glucose in gray matter as a whole (p = 0.035), specifically in several frontal, temporal, and subcortical regions, as well as in the cingulate and insula (p ≤ 0.01, false discovery rate correction). The effect of age on cerebral metabolic rates for acetoacetate in gray matter did not reach significance (p = 0.11). Rate constants (min⁻¹) of glucose (Kg) and acetoacetate (Ka) were significantly lower (−11 ± 6%; [p = 0.005], and −19 ± 5%; [p = 0.006], respectively) in older adults compared with younger adults. There were differential effects of age on Kg and Ka as seen by significant interaction effects in the caudate (p = 0.030) and post-central gyrus (p = 0.023). The acetoacetate index, which expresses the scaled residuals of the voxel-wise linear regression of glucose on ketone uptake, identifies regions taking up higher or lower amounts of acetoacetate relative to glucose. The acetoacetate index was higher in the caudate of young adults when compared with older adults (p ≤ 0.05 false discovery rate correction). This study provides new information about glucose and ketone metabolism in the human brain and a comparison of the extent to which their regional use changes during normal aging.     

Utility of F-18 fluorodeoxyglucose pos?tron em?ss?on tomography/computed ?n carc?noma of unknown primary

Carcinoma of unknown primary (CUP) is a heterogeneous group of tumors with various clinical features causing diagnostic and therapeutic challenges. The aim of this study was to evaluate the ability of F-18 FDG PET/CT for localizing the primary tumor, disclosing additional metastases, and changing the treatment in patients with CUP. One hundred and twelve metastatic patients (female = 40, male = 72, median age = 60.5 years) in whom conventional diagnostic work-up failed to disclose the primary tumor were included in the study. F-18 FDG PET/CT imaging was performed in a standard protocol (patient supine, arms on patient’s side, vertex to thigh, 369.3 MBq (296-444 MBq) F-18 FDG, a 60-minute uptake period, 6-7 bed position). Histopathology was taken as the only reference standard. F-18 FDG PET/CT correctly detected primary tumor in 37 of 112 (33.03%) patients. The most common site of primary tumor detected by F-18 FDG PET/CT was lung (n = 18), which was followed by nasopharynx (n = 7), pancreas (n = 5), tonsil (n = 2), breast (n = 2), thyroid (n = 1), uterus (n = 1) and colon/rectum (n = 1). F-18 FDG PET/CT imaging disclosed additional previously undetected metastases in 32 (28.5%) and changed the treatment in 33 (29.4%) of 112 patients. There were false positive F-18 FDG PET/CT results in 21 (18.5%) patients. F-18 FDG PET/CT is able to disclose the primary tumor, disclose new metatases and change the treatment in about one third of patients with CUP.     

FDG PET显像在判断鼻咽癌放疗后鼻咽病灶复发中的临床价值

目的 探讨脱氧葡萄糖正电子发射断层扫描(FDG PET)在鼻咽癌放射治疗后随诊中的临床价值以及与CT、MRI的互补作用.方法 回顾性分析放射治疗后6～8个月、CT和MRI检查考虑鼻咽病灶复发的6例鼻咽癌患者,随后行FDG PET检查,并均作病理活检.结果 6例CT和MRI提示肿瘤复发的鼻咽癌患者,PET显示其中2例有局灶性FDG代谢明显增高,经病理活检,证实仅2例FDG摄取浓聚的病变为肿瘤复发.结论 与CT和MRI检查相比,FDG PET在鼻咽癌放射治疗后肿瘤复发的定性诊断上具有明显优势,若结合CT或MRI的影像结果分析,取得局部病变的结构与代谢改变复合信息,对后期局部复发病灶的精确适形放射治疗具有重要意义.     

Significance of 18F-FDG PET/CT in Characterization of Equivocal Lesions in High-Risk Testicular Carcinoma in Restaging Setting

Objectives: The present study aims to evaluate the role of Positron emission tomography (PET) -computed tomography (CT) with 18F-fluorodeoxyglucose (18F-FDG) in the restaging of high-risk testicular cancer. Methods: Forty-five patients (mean age of 38.1±11.3 years and range 23-81 years) with testicular carcinoma, underwent 18F-FDG PET-CT during their clinical course were prospectively selected. PET positivity was defined as a site of abnormal 18F-FDG uptake in tissue histologically proven or clinically or radiographically suspected to represent tissue involvement. The sites of disease were characterized as either nodal or extranodal. All patients were followed-up for at least 12 months with a diagnostic and/or functional imaging modality. Results: Of the 45 patients 38 (84%) patient presented with seminoma and 7 (16%) were Non-seminomatous germ cell tumors. Analysis of secondary disease spectrum showed nodal involvement in 65%, osseous involvement in 23% and mixed visceral/soft tissue lesions in 12% of patients. Nineteen (42%) were negative for any metastatic disease. All negative patients remain disease free in the follow-up of one year. Out of the positive 26/45 patients, PET-CT showed progressive disease in 3/26, stable disease 1/26 and partial response in 2/26 and complete metabolic resolution in 20/26 patients. 18F-FDG PET-CT was able to characterize all patients leading to significant change of primary decision of wait and watch to go for treatment and vice versa. Conclusion: 18F-FDG PET-CT scan is potentially an excellent tool for characterization of equivocal lesions on CT scan in the restaging settings and follow up of high-risk testicular cancer patients.     

18F-FDG分子符合探测成像在肿瘤诊断中的临床价值

目的　探讨18F FDG分子符合探测 (MCD)肿瘤代谢显像应用和评价其临床价值。方法　对经组织学证实的 44例原发性肿瘤、18例转移性肿瘤和 10例肺部良性病变进行氟化脱氧葡萄糖 (18F FDG)MCD显像 ,将显像与组织学结果进行比较分析。结果　 62例肿瘤患者中 ,5 9例FDG影像示单个或多处呈不同程度异常FDG浓聚灶 ,3例未见异常FDG浓聚灶。 10例肺部良性病变FDG影像中 ,3例肺部可见异常摄取增高 ,7例未见异常FDG浓聚影。本组研究的敏感度95 .2 % ,特异性 70 % ,阳性预测值 95 .5 % ,阴性预测值 70 % ,诊断准确率 92 .1%。结论　FDGMCD/AC显像对肿瘤良恶性鉴别、分期和分级、疗效预测和预后判断具有一定优势     

Oral contrast medium in PET/CT: should you or shouldn’t you?

Purpose It has been suggested that the use of computed tomography (CT) positive contrast agents has led to attenuation-induced artefacts on ¹⁸F-fluorodeoxyglucose positron emission tomography (¹⁸F-FDG PET/CT) systems. Consequently, centres may withhold the use of such agents. Whilst there is theoretical evidence to support the aforementioned claim, the clinical relevance of the induced artefacts has not been widely established. Moreover, the potential benefits of bowel enhancement on PET/CT have yet to be formally evaluated. We therefore prospectively examined PET/CT studies to assess whether the use of oral contrast medium induces clinically relevant artefacts and whether the use of these agents is diagnostically helpful.Methods Over a 2-month period, ¹⁸F-FDG PET/CT images were prospectively reviewed from 200 patients following Gastrografin administration 2 h prior to examination. Both a radiologist and a nuclear medicine physician reviewed the images for contrast medium-mediated clinically relevant artefacts. Artefacts were sought on the CT attenuation-corrected images and were compared with the appearance on non-attenuated-corrected images. The number of examinations in which the oral contrast aided image interpretation was also noted.Results There were no oral contrast medium-induced clinically significant artefacts. In 38 of the 200 patients, oral contrast aided image interpretation (owing to differentiation of mass/node from bowel, discrimination of intestinal wall from lumen or definition of the anatomy of a relevant site). In 33 of these 38 patients, the anatomical site of interest was the abdomen/pelvis.Conclusion The use of oral contrast medium in ¹⁸F-FDG PET studies should not be withheld as it improves image interpretation and does not produce clinically significant artefacts.     

Cold tuberculous abscess identified by FDG PET

We report FDG PET of two cases of cold abscess due to Mycobacterium tuberculosis. Case 1 had colon cancer; FDG PET showed high FDG uptake in the colon lesion and low uptake in the inguinal lesion. The latter was a tuberculous cold abscess confirmed by CT/MRI and biopsy. Case 2 received radiotherapy for lung cancer and presented with suspected vertebral metastasis. Further studies revealed tuberculosis of the vertebra and a tuberculous cold abscess in the iliopsoas muscle. FDG PET showed moderate uptake in the third lumbar spine and low uptake in the abscess center of iliopsoas lesion. Both tuberculous cold abscesses showed moderate FDG uptake in the capsule and low uptake in the center. These features are unique compared with non-tuberculous abscess and typical tuberculosis lesions, which are characterized by high FDG uptake. Pathologically, tuberculous cold abscess is not accompanied by active inflammatory reaction. Our findings suggested that the FDG uptake by tuberculous lesion varies according to the grade of inflammatory activity. The new diagnostic features of tuberculous cold abscess may be useful in the evaluation of such lesions by FDG PET.