Accuracy of whole-body FDG-PET/CT for detecting brain metastases from non-central nervous system tumors

OBJECTIVE: Positron emission tomography (PET) using (18)F-fluoro-2-deoxy-D -glucose (FDG) has a limitation in detecting cerebral metastases; however, the feasibility of detection by inline PET/computed tomography (CT) system remains unknown. We evaluated the accuracy of FDG-PET/CT of body imaging protocol for the detection of cerebral metastases when compared with PET alone and CT alone. METHODS: Fifty patients underwent whole-body FDG-PET/CT scanning including the brain and contrast enhanced brain MR (magnetic resonance) scan. PET-only, CT-only, and the fused images were interpreted, and the confidence of presence of cerebral metastases was recorded using a five-point grading scale. Area under the receiver-operating characteristic (ROC) curve (Az) was calculated. Differences among the three modalities were tested with the Cochran-Q test, followed by multiple comparisons using the McNemar test with Bonferroni adjustment. RESULTS: Magnetic resonance imaging revealed 70 cerebral metastatic lesions in 20 patients. Patient-based analysis showed that the sensitivity, specificity, accuracy, and Az of PET-alone interpretation were 45%, 80%, 66%, and 0.6025, respectively, those of CT-alone interpretation were 50%, 97%, 78%, and 0.7158, respectively, and those of fused-image interpretation were 50%, 93%, 76%, and 0.7242, respectively. ROC analysis revealed significant differences among the three interpretation methods (P = 0.0238) and between PET and PET/CT (P = 0.0129). The sensitivity of PET, CT, and fused-image interpretation for detecting 70 lesions was 13%, 20%, and 20%, respectively. CONCLUSIONS: Even with an integrated PET/CT scanner of body imaging protocol, the sensitivity of cerebral metastases remained unsatisfactory. To assess intracranial lesions, MR scanning should still be considered.     

Screening for cerebral metastases with FDG PET in patients undergoing whole-body staging of non-central nervous system malignancy

PURPOSE: To compare fluorine 18 fluorodeoxyglucose (FDG) positron emission tomography (PET) with the current standard, magnetic resonance (MR) imaging, to determine the sensitivity and specificity of FDG PET for detection of cerebral metastases and to determine the factors that may affect lesion conspicuity. MATERIALS AND METHODS: Forty patients underwent brain PET and contrast material-enhanced brain MR imaging, with a maximum of 30 days between examinations. PET and MR images were each retrospectively reviewed by two independent readers who were blinded to the clinical history and results of the other technique. Presence of metastatic disease was recorded for each modality. Sensitivity and specificity of FDG PET were determined with MR imaging as the standard. Statistical analysis was performed with the Fisher exact test and the logistic regression model. RESULTS: Sixteen patients had cerebral metastases at MR imaging, and in 12 of these, PET scans were interpreted as showing metastatic disease (in four, scans were false-negative). Twenty-four patients had no cerebral metastases at MR imaging, and 20 of these had PET scans interpreted as normal (in four, scans were false-positive). For identification of patients with cerebral metastases, FDG PET had a sensitivity of 75% (12 of 16) and a specificity of 83% (20 of 24). Thirty-eight metastatic lesions were seen at MR imaging; 23 (61%) of these were identified at PET. Size was a statistically significant factor that influenced lesion detection at PET (P <.001). CONCLUSION: Only 61% of metastatic lesions in the brain were identified at PET. In particular, detection of small lesions was difficult.     

Gaucher disease in children: radiology of non-central nervous system manifestations

The radiological findings in paediatric Gaucher disease (GD) are reviewed and future challenges for radiology are discussed. This overview is based on a literature review and our experience of children with GD in one of two national institutions for paediatric GD in the UK. GD is known to progress more rapidly in childhood. Current imaging is mainly suitable for ascertaining the complications of GD. The UK recommendations for routine radiological surveillance are discussed. With enzyme replacement therapy (ERT), which dramatically modifies the course of the disorder, the challenge for radiology in the future is likely to be assessing treatment efficacy rather than the detection of disease complications. Disease manifestations are likely to change in those on ERT and the most notable recent alteration in the disease profile in childhood is the virtual disappearance of the acute bone crisis in this population.     

Imaging of non-central nervous system primitive neuroectodermal tumours: diagnostic features and correlation with outcome

AIM: To document the varied radiological features before, during, and after treatment of non-Central Nervous System Primitive Neuroectodermal Tumours (PNETs), which are rare tumours of childhood.MATERIALS AND METHODS: Thirty-three children with PNETs have been treated at our institution between 1990 and 1999. Full radiological and clinical follow-up was obtained in 29 (17 females, 12 males). Imaging was retrospectively reviewed, with particular attention to Computed Tomography (CT) and Magnetic Resonance Imaging (MRI).RESULTS: Age range at diagnosis was 0-16 years old (mean 4.4 years). There were five main sites of tumour: head and neck (n = 7), scapula/axilla (n = 2), chest (n = 11), abdomen (n = 3), and spinal/paraspinal (n = 6). Overall mortality was 62%. Tumours of the scapula or paraspinal region appear to show better survival than other sites. Of 23 patients who had Tc99m-methylene diphosphonate (MDP) bone scans at diagnosis, four patients showed widespread distant metastases, seven showed focal increased uptake in an adjacent bone only, and 12 had normal examinations. CT was performed in 25 patients and MRI in 20, both at diagnosis and follow-up. Average size of tumours at presentation was 4.5 cm in the paraspinal, head and neck and scapular regions and 7.5 cm in the chest and abdomen. Tumours were typically of soft tissue density on CT with the larger (>5 cm) masses tending to be more heterogeneous in character. The lesions were slightly higher signal than muscle on T1-weighted (T1W) MRI and all masses were heterogeneous on T2W sequences. Calcification was uncommon (n = 6) and generally sparse. Tumours tended to displace adjacent soft tissue structures such as vessels and bronchi rather than invade or encase them. Tumours rarely crossed the midline. Local or bony invasion was seen in 12 patients at diagnosis. Metastases were identified in the lung (n = 5), pleura (n = 2), brain (n = 4), bone (n = 4), lymph nodes (n = 2), liver (n = 2), subcutaneous tissues (n = 2), kidney (n = 1) and peritoneum (n = 1).CONCLUSIONS: Imaging characteristics of non-CNS PNETs are described. Tumours tend to displace rather than encase adjacent structures; local invasion occurred in 43%. Tumour calcification is uncommon. Poor prognostic features included the presence of distant metastases at diagnosis (all four patients with distant metastases at diagnosis died), but even patients without metastatic disease have a relatively poor prognosis.     

Recurrence of colorectal tumors: PET evaluation

Positron emission tomography (PET) was used in the follow-up of patients with colorectal malignancies to differentiate between recurrent colorectal tumor and scar. Patients were examined with oxygen-15-labeled water and with fluorine-18-labeled deoxyglucose (FDG). FDG was injected intravenously to assess tumor metabolism. The tracer concentration was quantitatively evaluated by means of a region-of-interest technique and standardized for both injected dose and body volume. Of 29 patients, 21 had recurrent colorectal malignancy, and eight had a nonmalignant mass. All malignancies were seen on the PET cross sections. Nonmalignant lesions had a low FDG accumulation on images obtained 60 minutes after injection. While the tumor-soft tissue ratio was highest shortly after the intravenous injection of FDG, the tumor-scar ratio was highest 60 minutes after injection. It was possible to differentiate tumor from non-malignant tissue with FDG with the use of standardized concentration values and tumor-soft tissue ratios. Imaging with O-15-labeled water gave no additional information.     

Ultrafast MR imaging of the foetus: a study of 25 non-central nervous system anomalies

PURPOSE: The aim of this paper is to suggest Magnetic Resonance (MR) Imaging as a useful tool in prenatal diagnosis. Although ultrasonography (US) is the imaging technique of choice for prenatal screening, in cases of complex malformations US findings may be sub-optimal and give rise to diagnostic difficulties requiring further investigation. Our study is focused on non-central nervous system (CNS) abnormalities of the foetus imaged using the ultrafast sequence EXPRESS. MATERIALS AND METHODS: 38 women whose foetuses were between 21-34 gestational age were studied. Indications for the examinations included the evaluation of non-CNS abnormalities in 25 cases. Foetal MR imaging was performed on a 1.5 T system (Edge, Marconi Medical System Italia SpA, Vimercate, MI) with the half-Fourier, single-shot, fast spin-echo EXPRESS sequence. Mild maternal and foetal sedation was obtained by oral administration of benzodiazepine (1 mg). RESULTS: In the 25 foetuses investigated for non-CNS pathologies the abnormalities were localised in the chest (9), abdomen (15) and extremities (1). The MR imaging diagnoses were: in the chest - congenital diaphragmatic hernia (CDH) (5), congenital cystic adenomatoid malformation (CCAM) (1), hydrothorax (1), cystic lymphangioma (1), Jeune syndrome (1); in the abdomen - 10 cases of urinary tract diseases - polycystic kidney (4), crossed renal ectopia (2), unilateral renal agenesis (1), solitary pelvic kidney (1), bilateral stenosis of ureteropelvic junction (1), duplex collecting system in association with controlateral hydroureteronephrosis (1)#151;5 cases of non-urinary tract pathologies#151;cystic lymphangioma of the liver (1), abdominal cystic lymphangioma (1), gastroschisis (1), gastric duplication (1), cavernous haemangioma of the liver (1); in the extremities - longitudinal hemimelia (1). CONCLUSIONS: In our experience MR is to be considered a useful though adjunct study to prenatal US particularly in the evaluation of lung parenchyma, congenital diaphragmatic viscera herniation, thoracic masses, pleural effusion, abdominal cystic masses, and urinary tract malformations. The ultrafast EXPRESS sequence enables a complete study to be performed in a very short time; as a consequence the examination is well tolerated by the patient. Currently there is no legislation which regulates the use of magnetic fields in MR, only a series of recommendations based on studies on animal embryos and foetuses, on pregnant women exposed to magnetic fields and follow-up studies of children exposed to MR during gestation. Therefore the decision to proceed with foetal MR should be made on a case-by-case basis in close consultation with the referring obstetrician. Considering the results, in our opinion the potential of MR in the evaluation of a wide variety of non-CNS foetal diseases will increase in the near future.     

PET评价骨转移瘤

肿瘤骨转移会产生顽固性骨痛和脊髓受压等严重并发症,并对分期、治疗和判断预后产生深远的影响,因而探测骨转移是制定治疗计划的重要部分。骨转移瘤发现频率因原发肿瘤的类型和所用检查手段不同而不同,虽然目前核素骨扫描是探测骨转移瘤最常用的手段,但其对骨转移瘤的诊断效能仍有一定限度。与99mTc-亚甲基二膦酸盐(99mTc-MDP)骨显像相比,18F-氟化钠(18F-NaF)和18F-氟代脱氧葡萄糖(18F-FDG) PET是分别从骨转移瘤产生的成骨反应和骨转移瘤本身的代谢活性角度进行评价的两种正电子示踪剂,结合PET的高度空间分辨率,特别是最近迅速应用于临床的PET-CT技术,使得正电子体层显像在全身骨骼恶性疾病评价上的准确性进一步提高。     

动态18F-FDG PET定量分析用于骨病变鉴别诊断

目的 评价^18F-脱氧葡萄糖（FDG）PET在骨骼病变中的诊断价值。谅研究对象为40例原发性骨骼病变患者。所有患者在注射示踪剂后立即开始动态PET采集，持续60min。对动态PET图像进行半定量分析，分别计算平均和最大标准摄取值（SUVaver和SUVmax)，病灶SUV／肌肉SUV比值（T／M），病灶60min SUV/30min SUV比值（SUVaver60/30min和SUVmax60/30min）等。采用Patlak作图分析法对动态图像数据进行拟合计算，得出摄入常数（Ki），计算FDG代谢率（MRFDG）。根据接受器工作特性曲线（ROC）确定各定量指标的诊断阈值，并比较其鉴别良恶性病变的灵敏度和特异性。结果 经病理检查证实恶性病变21例，良性病变19例。恶性病变的MRFDG和SUV值高于良性病变，但各种指标的数值分布均存在交叉重叠。SUVaver与MRFDG呈正相关（r=0.67)。以SUV值≥1.8作为阈值时，鉴别良恶性病变的灵敏度和特异性分别为85．0％和82．4％，以MRFDG（1．1）为阈值时的灵敏度（82．4％）与SUV相近，而特异性（92．9％）较高。同时采用SUV（1．8）和SUVaver60/30min(1.1)作为鉴别标准时，较之单独有用SUV特异性可改善为93．3％，灵敏度略有降低（81．3％）。结论 骨骼良恶性病变之间存在葡萄糖代谢率差异。单用静态FDG PET获取SUV值不能很好鉴别骨骼良恶性病变。动态显像定量分析可提供更有价值的信息。根据动态图像进行半定量分析获取可反映动态过程的摄取指标，可能是一种较简便和有价值的鉴别方法。     

Imaging of central nervous system tumors

Magnetic resonance imaging has been used increasingly in the staging and evaluation of neoplasia of the brain and leptomeninges. In the classification of gliomas, the MR accuracy rate approaches that of pathologic diagnosis. Contrast-enhanced MR imaging has improved specificity in evaluating brain tumors in children and is now the preferred modality for evaluating leptomeningeal metastases of the brain and spine. MR imaging in children has also increased the specificity of histologic diagnosis in hypothalamic hamartoma and juvenile pilocytic astrocytoma. Gadolinium enhancement is most useful in patients older than 35 years of age who have focal neurologic complaints and certain disease histories. The expense of gadolinium contrast material is the major drawback to its routine use. In patients with seizure disorder, MR imaging is more sensitive than CT for detecting abnormalities such as mesial temporal sclerosis, tumors, and vascular malformations. Gadolinium enhancement may be useful in differentiating tumors from mesial temporal sclerosis. Recent reports on the use of MR spectroscopy for evaluating brain metabolism and tumors demonstrate that differences in metabolites exist. A correlation was found in epidermoid tumors between high signal on T1-weighted images and high lipid content, and several studies have shown a positive correlation between glioma grade and glycolytic activity as determined on 18F-2-fluoro-2-deoxy-D-glucose positron emission tomography.     

Brain metastases detectability of routine whole body (18)F-FDG PET and low dose CT scanning in 2502 asymptomatic patients with solid extracranial tumors

As fluorine-18-fluorodesoxyglucose positron emission tomography/computed tomography ( (18)F-FDG PET/CT) is gaining wider availability, more and more patients with malignancies undergo whole body PET/CT, mostly to assess tumor spread in the rest of the body, but not in the brain. Brain is a common site of metastatic spread in patients with solid extracranial tumors. Gold standard in the diagnosis of brain metastases remains magnetic resonance imaging (MRI). However MRI is not routinely indicated and is not available for all cancer patients. Fluorine-18-FDG PET is considered as having poor sensitivity in detecting brain metastases, but this may not be true for PET/CT. The aim of our study was to assess the value of (18)F-FDG PET/CT in the detection of brain metastases found by whole body scan including the brain, in patients with solid extracranial neoplasms. A total of 2502 patients with solid extracranial neoplasms were studied. All patients underwent a routine whole body (18)F-FDG PET/CT scan with the whole brain included in the scanned field. Patients with known or suspected brain metastases were preliminary excluded from the study. Hypermetabolic and ring-like brain lesions on the PET scan were considered as metastases. Lesions with CT characteristics of brain metastases were regarded as such irrespective of their metabolic pattern. Lesions in doubt were verified by MRI during first testing or on follow-up or by operation. Our results showed that brain lesions, indicative of and verified to be metastases were detected in 25 out of the 2502 patients (1%), with lung cancer being the most common primary. Twenty three out of these 25 patients had no neurological symptoms by the time of the scan. The detection rate of brain metastases was relatively low, but information was obtained with a minimum increase of radiation burden. In conclusion, whole body (18)F-FDG PET/CT detected brain metastases in 1% of the patients if brain was included in the scanned field. Brain scanning as a part of whole body scan cannot replace routine imaging techniques, but in case of positive findings provides early and crucial information for further patient management, especially in asymptomatic patients.     

Congenital tumors of the central nervous system

Congenital tumors of the central nervous system (CNS) are often arbitrarily divided into “definitely congenital” (present or producing symptoms at birth), “probably congenital” (present or producing symptoms within the first week of life), and “possibly congenital” (present or producing symptoms within the first 6 months of life). They represent less than 2% of all childhood brain tumors. The clinical features of newborns include an enlarged head circumference, associated hydrocephalus, and asymmetric skull growth. At birth, a large head or a tense fontanel is the presenting sign in up to 85% of patients. Neurological symptoms as initial symptoms are comparatively rare. The prenatal diagnosis of congenital CNS tumors, while based on ultrasonography, has significantly benefited from the introduction of prenatal magnetic resonance imaging studies. Teratomas constitute about one third to one half of these tumors and are the most common neonatal brain tumor. They are often immature because of primitive neural elements and, rarely, a component of mixed malignant germ cell tumors. Other tumors include astrocytomas, choroid plexus papilloma, primitive neuroectodermal tumors, atypical teratoid/rhabdoid tumors, and medulloblastomas. Less common histologies include craniopharyngiomas and ependymomas. There is a strong predilection for supratentorial locations, different from tumors of infants and children. Differential diagnoses include spontaneous intracranial hemorrhage that can occur in the presence of coagulation factor deficiency or underlying vascular malformations, and congenital brain malformations, especially giant heterotopia. The prognosis for patients with congenital tumors is generally poor, usually because of the massive size of the tumor. However, tumors can be resected successfully if they are small and favorably located. The most favorable outcomes are achieved with choroid plexus tumors, where aggressive surgical treatment leads to disease-free survival.     

18F-FDOPA PET imaging of brain tumors: comparison study with 18F-FDG PET and evaluation of diagnostic accuracy.

We evaluated the amino acid and glucose metabolism of brain tumors by using PET with 3,4-dihydroxy-6-(18)F-fluoro-l-phenylalanine ((18)F-FDOPA) and (18)F-FDG. METHODS: Eighty-one patients undergoing evaluation for brain tumors were studied. Initially, 30 patients underwent PET with (18)F-FDOPA and (18)F-FDG within the same week. Tracer kinetics in normal brain and tumor tissues were estimated. PET uptake was quantified by use of standardized uptake values and the ratio of tumor uptake to normal hemispheric tissue uptake (T/N). In addition, PET uptake with (18)F-FDOPA was quantified by use of ratios of tumor uptake to striatum uptake (T/S) and of tumor uptake to white matter uptake. The accuracies of (18)F-FDOPA and (18)F-FDG PET were determined by comparing imaging data with histologic findings and findings of clinical follow-up of up to 31 mo (mean, 20 mo). To further validate the accuracy of (18)F-FDOPA PET, (18)F-FDOPA PET was performed with an additional 51 patients undergoing brain tumor evaluation. RESULTS: Tracer uptake in tumors on (18)F-FDOPA scans was rapid, peaking at approximately 15 min after intravenous injection. Tumor uptake could be distinguished from that of the striatum by the difference in peak times. Both high-grade and low-grade tumors were well visualized with (18)F-FDOPA. The sensitivity for identifying tumors was substantially higher with (18)F-FDOPA PET than with (18)F-FDG PET at comparable specificities, as determined by simple visual inspection, especially for the assessment of low-grade tumors. Using receiver-operating-characteristic curve analysis, we found the optimal threshold for (18)F-FDOPA to be a T/S of greater than 1.0 (sensitivity, 96%; specificity, 100%) or a T/N of greater than 1.3 (sensitivity, 96%; specificity, 86%). The high diagnostic accuracy of (18)F-FDOPA PET at these thresholds was confirmed with the additional 51 patients (a total of 81 patients: sensitivity, 98%; specificity, 86%; positive predictive value, 95%; negative predictive value, 95%). No significant difference in tumor uptake on (18)F-FDOPA scans was seen between low-grade and high-grade tumors (P = 0.40) or between contrast-enhancing and nonenhancing tumors (P = 0.97). Radiation necrosis was generally distinguishable from tumors on (18)F-FDOPA scans (P < 0.00001). CONCLUSION: (18)F-FDOPA PET was more accurate than (18)F-FDG PET for imaging of low-grade tumors and evaluating recurrent tumors. (18)F-FDOPA PET may prove especially useful for imaging of recurrent low-grade tumors and for distinguishing tumor recurrence from radiation necrosis.     

Brain tumors: MR imaging with gadolinium-DTPA

Magnetic resonance (MR) imaging was performed on 40 patients with intracranial tumors, before and after intravenous administration of gadolinium-DTPA (Gd-DTPA). Precontrast studies included a comprehensive protocol of spin-echo sequences. Tumors were visualized on precontrast images either directly or indirectly by anatomic distortion caused by the mass. However, differentiation of the tumor from adjacent tissues was possible in only 17 of 40 cases. Delineation of the tumor was best on precontrast, T2-weighted images. After administration of Gd-DTPA (0.1 mmol/kg), increased signal intensity from the tumor was observed in all patients. The localized increase in signal intensity in the tumor considerably improved the tumor delineation in 36 of 40 patients. Whereas most of the meningiomas, neuromas, and adenomas could be delineated prior to administration of contrast material if appropriate pulse sequences were applied, glioblastomas and intracranial metastases required Gd-DTPA administration for diagnostically sufficient tumor display.