Estimation of the beta+ dose to the embryo resulting from 18F-FDG administration during early pregnancy.

Although 18F-FDG examinations are widely used, data are lacking on the dose to human embryo tissues in cases of exposure in early pregnancy. Although the photon component can easily be estimated from available data on the pharmacokinetics of 18F-FDG in female organs and from phantom measurements (considering the uterus as the target organ), the intensity of embryo tissue uptake, which is essential for deriving the beta+ dose, is not known. We report the case of a patient who underwent 18F-FDG PET/CT for tumor surveillance and who was later found to have been pregnant at the time of the examination (embryo age, 8 wk). METHODS: The patient received 320 MBq of (18)F-FDG. Imaging started with an unenhanced CT scan 1 h after the injection, followed by PET acquisition. PET images were used to compute the total number of beta+ emissions in embryo tissues per unit of injected activity, from standardized uptake value (SUV) measurements corrected for partial-volume effects. A Monte Carlo track structure code was then used to derive the beta+ self-dose and the beta+ cross-dose from amniotic fluid. The photon and CT doses were added to obtain the final dose received by the embryo. RESULTS: The mean SUV in embryo tissues was 2.7, after correction for the partial-volume effect. The mean corrected SUV of amniotic fluid was 1.1. Monte Carlo simulation showed that the beta+ dose to the embryo (self-dose plus cross-dose from amniotic fluid) was 1.8E-2 mGy per MBq of injected 18F-FDG. Based on MIRD data for the photon dose to the uterus, the estimated photon dose to the embryo was 1.5E-2 mGy/MBq. Thus, the specific 18F-FDG dose to the embryo was 3.3E-2 mGy/MBq (10.6 mGy in this patient). The CT scan added a further 8.3 mGy. CONCLUSION: The dose to the embryo is 3.3E-2 mGy/MBq of 18F-FDG. The beta+ dose contributes 55% of the total dose. This value is higher than previous estimates in late nonhuman-primate pregnancies.     

Is 18F-3'-fluoro-3'-deoxy-L-thymidine useful for the staging and restaging of non-small cell lung cancer?

The objective of this study was to compare 18F-3'-fluoro-3'-deoxy-L-thymidine (FLT) PET with clinical TNM staging, including that by 18F-FDG PET, in patients with non-small cell lung cancer (NSCLC). METHODS: Patients with NSCLC underwent whole-body 18F-FDG PET and whole-body 18F-FLT PET, using a median of 360 MBq of 18F-FDG (range, 160-500 MBq) and a median of 210 MBq of 18F-FLT (range, 130-420 MBq). 18F-FDG PET was performed 90 min after 18F-FDG injection, and 18F-FLT PET was performed 60 min after 18F-FLT injection. Two viewers independently categorized the localization and intensity of tracer uptake for all lesions. All 18F-FDG PET and 18F-FLT PET lesions were compared. Staging with 18F-FLT PET was compared with clinical TNM staging based on the findings of history, physical examination, bronchoscopy, CT, and 18F-FDG PET. From 8 patients, standardized uptake values (SUVs) were calculated. Maximal SUV and mean SUV were calculated. RESULTS: Sixteen patients with stage IB-IV NSCLC and 1 patient with strong suspicion of NSCLC were investigated. Sensitivity on a lesion-by-lesion basis was 80% for the 8 patients who received treatment before 18F-FLT PET and 27% for the 9 patients who did not receive pretreatment, using 18F-FDG PET as the reference standard. Compared with clinical TNM staging, staging by 18F-FLT PET was correct for 8 of 17 patients: 5 of 9 patients in the group with previous therapy and 3 of 8 patients in the group without previous therapy. The maximal SUV of 18F-FLT PET, at a median of 2.7 and range of 0.8-4.5, was significantly lower than that of 18F-FDG PET, which had a median of 8.0 and range of 3.7-18.8 (n = 8; P = 0.012). The mean SUV of 18F-FLT PET, at a median of 2.7 and range of 1.4-3.3, was significantly lower than that of 18F-FDG PET, which had a median of 6.2 and range of 2.8-13.9 (n = 6; P = 0.027). CONCLUSION: 18F-FLT PET is not useful for staging and restaging NSCLC.     

Retro-orbital injection is an effective route for radiopharmaceutical administration in mice during small-animal PET studies

BACKGROUND AND AIM: Small-animal PET is acquiring importance for pre-clinical studies. In rodents, radiotracers are usually administrated via the tail vein. This procedure can be very difficult and time-consuming as soft tissue extravasations are very frequent and tail scars can prevent repeated injections after initial failure. The aim of our study was to compare the retro-orbital (RO) versus tail vein intravenous (i.v.) administration of (18)F-FDG and (11)C-choline in mice for small-animal PET studies. METHODS: We evaluated four healthy female ICR CD1 mice according to the following protocol. Day 1: each animal underwent an i.v. injection of 28 MBq of (11)C-choline. PET scan was performed after 10 min and 40 min. Day 2: each animal received an RO injection of 28 MBq of (11)C-choline. A PET scan was performed after 10 min and 40 min. Day 3: each animal received an i.v. injection of 28 MBq of (18)F-FDG. A PET scan was performed after 60 min and 120 min. Day 4: each animal received an RO injection of 28 MBq of (18)F-FDG. A PET scan was performed after 60 min and 120 min. Administration and image acquisition were performed under gas anaesthesia. For FDG studies the animals fasted for 2 h and were kept asleep for 20-30 min after injection, to avoid muscular uptake. Images were reconstructed with 2-D OSEM. For each scan ROIs were drawn on liver, kidneys, lung, brain, heart brown fat and muscles, and the SUV was calculated. We finally compared choline i.v. standard acquisition to choline RO standard acquisition; choline i.v. delayed acquisition to choline RO delayed acquisition; FDG i.v. standard acquisition to FDG RO standard acquisition; FDG i.v. delayed acquisition to FDG RO delayed acquisition. RESULTS: The RO injections for both (18)F-FDG and (11)C-choline were comparable to the intravenous injection of F-FDG for the standard and delayed acquisitions. CONCLUSION: The RO administration in mice represents a technical advantage over intravenous administration in being an easier and faster procedure. However, its use requires high specific activity while its value in peptides and other receptor-specific radiopharmaceuticals needs further assessment.     

Comparative evaluation of 18F-FDG PET and 67Ga scintigraphy in patients with sarcoidosis.

67Ga scintigraphy has been used for years in sarcoidosis for diagnosis and the extent of the disease. However, little information is available on the comparison of 18F-FDG PET and 67Ga scintigraphy in the assessment of sarcoidosis. The purpose of this study was to compare the uptake of 18F-FDG and 67Ga in the evaluation of pulmonary and extrapulmonary involvement in patients with sarcoidosis. METHODS: Eighteen patients with sarcoidosis were examined. 18F-FDG PET was performed at 1 h after injection of 185-200 MBq 18F-FDG. 67Ga whole-body planar and thoracic SPECT images were acquired 72 h after injection of 111 MBq 67Ga. We evaluated 18F-FDG and 67Ga uptake visually and semiquantitatively using standardized uptake values (SUVs) and the ratio of lesion to normal lumbar spine (L/N ratio), respectively. The presence of pulmonary and extrapulmonary lesions was evaluated histopathologically or by the radiologic findings. RESULTS: Five patients had only pulmonary lesions, 12 patients had both pulmonary and extrapulmonary lesions, and 1 patient had only an extrapulmonary lesion. Both 67Ga planar and SPECT images detected 17 of 21 (81%) clinically observed pulmonary sites. The mean +/- SD of the L/N ratio was 1.97 +/- 1.09. 67Ga planar images detected 15 of 31 (48%) clinically observed extrapulmonary sites. The mean +/- SD of the L/N ratio was 1.17 +/- 0.33. 18F-FDG PET detected all 21 (100%) clinically observed pulmonary sites. The mean +/- SD of the SUV was 7.40 +/- 2.48. 18F-FDG PET detected 28 of 31 (90%) clinically observed extrapulmonary sites. The mean +/- SD of the SUV was 5.90 +/- 2.75. CONCLUSION: The results of this clinical study suggest that 18F-FDG PET can detect pulmonary lesions to a similar degree as 67Ga scintigraphy. However, 18F-FDG PET appears to be more accurate and contributes to a better evaluation of extrapulmonary involvement in sarcoidosis patients.     

Grading of brain glioma with 1-11C-acetate PET: comparison with 18F-FDG PET

The objective of this study is to reevaluate the clinical significance of 1-11C-acetate (ACE) positron emission tomography (PET) in patients with brain glioma, in comparison with 18F-fluorodeoxyglucose (FDG) PET. METHODS: Ten patients with histologically proven glioma were included in this study. They underwent PET examination with both FDG and ACE on separate days. For ACE PET, 20-min data acquisition was performed just after the administration of 740 MBq of ACE; 10-20-min data were used for the analysis. FDG PET data acquisition for 10 min started 60 min postinjection of 370 MBq of FDG, approximately. Both reconstructed images were converted to standardized uptake value (SUV) images for patient body weight and injected dose. Regions of interest were placed on the tumor and the contralateral cerebral cortex, and SUV and tumor-to-cortex ratio (T/C) were calculated; these values were compared between high- and low-grade gliomas. RESULTS: SUV and T/C of ACE PET showed significant difference (SUV: 2.63+/-0.46 vs. 1.85+/-0.56, P=.03; T/C: 2.36+/-0.63 vs. 1.14+/-0.36, P=.02). In contrast, FDG PET revealed no significant difference in SUV or T/C between high- and low-grade gliomas (SUV: 7.13+/-4.31 vs. 4.71+/-1.27, P=.31; T/C: 0.98+/-0.55 vs. 0.62+/-0.09, P=.22). CONCLUSION: This preliminary study revealed that ACE PET is a promising tracer for the grading of brain glioma.     

Comparison of lesion-to-cerebellum uptake ratios and standardized uptake values in the evaluation of lung nodules with 18F-FDG PET

OBJECTIVE: To evaluate the clinical performance of the lesion-to-cerebellum uptake ratio (LCR), a semiquantitative index for differentiating malignant from benign lung nodules with [F]fluorodeoxyglucose positron emission tomography (F-FDG PET). METHODS: Thirty-six patients (16 females, 20 males; median age, 73 years; range, 41-87 years) with 42 known or suspected malignant lung nodules underwent whole-body PET imaging after an intravenous injection of a mean dose of 543+/-69 MBq (14.7+/-1.9 mCi) of F-FDG. The standardized uptake value (SUV) and the LCR were calculated for each nodule and receiver operating characteristic (ROC) curves were analysed using the ROCKIT 0.9B software package. RESULTS: Surgical pathology and follow-up with serial computed tomography scans for at least 24 months revealed 18 malignant lung lesions and 24 benign lesions less than 3.0 cm in size. The mean LCR was 0.70+/-0.40 for malignant nodules and 0.23+/-0.12 for benign nodules (P<0.001, two-tailed test). The area under the estimated ROC curve was 0.8660 for SUV data and 0.9197 for LCR data (P=0.2408, two-tailed test). CONCLUSIONS: The LCR method appears to be a valuable semiquantitative index for the evaluation of malignancy in pulmonary nodules with F-FDG PET, which is simple to perform clinically and does not require accurate measurements of body weight or the residual activity in the syringe utilized for F-FDG injection.     

Optimisation of the OS-EM algorithm and comparison with FBP for image reconstruction on a dual-head camera: a phantom and a clinical <Superscript>18</Superscript>F-FDG study

Iterative reconstruction algorithms, such as the ordered subsets expectation maximisation (OS-EM), are a promising alternative to filtered backprojection (FBP). The aims of this study were first to optimise the OS-EM algorithm in terms of iteration number and to study the usefulness of post-filtering, and second to compare OS-EM and FBP for image reconstruction on a fluorine-18 fluorodeoxyglucose (¹⁸F-FDG) dual-head camera (DHC). These two goals were addressed using phantom acquisitions. The performances of these algorithms were also studied in patient acquisitions performed on a DHC and a PET on the same day. Phantom experiments were performed on a DHC using a Jaszczak phantom containing six spheres filled with ¹⁸F-FDG, two background levels (0.95, 6.80 kBq/ml) and three object contrasts (5.9, 3.7, 2.7). The reconstruction algorithms were FBP with a Gaussian filter (FWHM 0.5–2 pixel width) and OS-EM using 8–128 equivalent iterations (equivalent to the ML-EM algorithm) with and without Gaussian post-filtering [OS-EM (iterations, pixel width)]. Contrast recovery coefficient (CRC) and noise characteristics were assessed. Twenty-two patients (21 male, one female; age 55±15 years) with lung cancer underwent, on the same day, PET (1 h post injection of 37 MBq/kg ¹⁸F-FDG) and DHC acquisitions (3 h post injection). DHC data were reconstructed using six methods: FBP (1), OS-EM (16), (40), (40,1), (64) and (64,1). These sets were evaluated by two observers and compared to PET reconstructed with OS-EM (16). The number of detected lesions and the visual quality were assessed. A marked improvement in CRC was observed with OS-EM as compared with FBP when more than 24 iterations were used. The CRC increased markedly from 8 to 40 iterations and then reached a plateau. The noise was stable until 40 iterations and then increased. The best compromise was obtained for OS-EM (32) and OS-EM (40,1). For the patient study, OS-EM provided images of better visual quality, but with no significant difference in detection sensitivity. OS-EM was superior to FBP in terms of contrast recovery and noise level. The optimal compromise between contrast recovery and noise was obtained for OS-EM (32) and (40,1) on the phantom study. The clinical study showed that OS-EM yielded images of better visual quality but with no improvement in terms of detection of lung cancer.     

18F-FDG PET/CT显像正常腹部消化器官的标准摄取值分析

目的分析^18F-脱氧葡萄糖（FDG）PET/CT显像正常腹部消化器官标准摄取值（SUV）的变化范围.方法60例要求行PET/CT检查的健康人,按体重7.77 MBq/kg静脉注射^18F-FDG,PET采集为三维模式,每个床位3 min.对腹部肝、胆囊、脾、胰腺、胃、盲肠、结肠和直肠进行半定量分析,各器官的SUV由横断面测量,准确定位时参考同机CT.结果正常腹部消化器官^18F-FDG摄取有较大差异,其中摄取较高者SUV平均值（SUVavg）依次为直肠、肝、乙状结肠、回盲部和脾、升结肠,SUV最大值（SUVmax）依次为直肠、乙状结肠、肝、回盲部、升结肠、脾.结论PET/CT显像能较好地识别腹部消化器官;熟悉正常腹部消化器官^18F-FDG摄取的差异,对判读图像十分重要.     

Detection of Klatskin's tumor in extrahepatic bile duct strictures using delayed 18F-FDG PET/CT: preliminary results for 22 patient studies.

Detection of cholangiocarcinoma in extrahepatic bile duct strictures is a continuing challenge in clinical practice because brush cytology taken at endoscopic retrograde cholangiography has an average sensitivity of 50%. The aim of this study was to evaluate the effectiveness of dual-modality PET/CT using (18)F-FDG for noninvasive differentiation of extrahepatic bile duct strictures. METHODS: Twenty-two PET/CT studies were performed on 20 patients (10 women, 10 men; mean age +/- SD, 63 +/- 14 y) with extrahepatic bile duct strictures on endoscopic retrograde cholangiography. PET imaging was started 101 +/- 22 min after injection of 369 +/- 48 MBq of 18F-FDG. Blood glucose was 100 +/- 20 mg/dL. PET images were reconstructed iteratively with attenuation correction based on a rescaling of the CT image. CT was performed within 1 min before the PET study, with the patient in the same position. CT was used to place a volume of interest 5 cm in diameter at the liver hilus for quantitative evaluation of PET images by means of standardized uptake values (SUVs). RESULTS: Final diagnosis was histologically proven cholangiocarcinoma in 14 cases and benign causes of strictures in 8 cases without evidence of malignancy during a follow-up of 18 +/- 3 mo. All patients with cholangiocarcinoma presented with focal increased uptake in the liver hilus with an SUV of 6.8 +/- 3.3 (range, 3.9-15.8), compared with 2.9 +/- 0.3 (range, 2.5-3.3) in patients with benign causes of strictures (P = 0.003). There was a clear cutoff SUV of 3.6 for detection of malignancy in the liver hilus. CONCLUSION: 18F-FDG PET/CT provided high accuracy for noninvasive detection of perihilar cholangiocarcinoma in extrahepatic bile duct strictures.     

18F-FDG PET全身显像时颈背部肌肉对称性浓聚分析

目的 分析^18F-脱氧葡萄糖(FDG) PET全身显像时部分患者颈部及胸椎两旁肌肉局限性代谢增高的显像特点及规律。方法 回顾性分析行^18F-FDG PET全身显像者1600例。受检者禁食4h后，按体重5．55MBq／kg静脉注入^18F-FDG，坐位松弛状态下休息50min后，用Siemens ECAT EXACTHR’PET仪进行采集。结果 1600例受检者中，共有9例10次显示双侧颈根部及双侧锁骨上区对称性放射性浓聚，同时均伴有胸椎两侧对称性点状浓聚。1例5d后行镇静剂介入显像，颈锁部及胸椎旁高代谢灶基本消失。结论 肌肉紧张可使少数患者颈部及胸椎两旁肌肉局限性^18F-FDG摄取增高。认识其显像特征有利于避免误诊。     

Dual-time-point 18F-FDG PET for the evaluation of gallbladder carcinoma.

Conventional imaging techniques such as ultrasonography, CT, and MRI are able to detect gallbladder abnormalities but are not always able to differentiate a malignancy from other disease processes such as cholecystitis. The purpose of the present study was to evaluate the efficacy of dual-time-point (18)F-FDG PET for differentiating malignant from benign gallbladder disease. METHODS: The study evaluated 32 patients who were suspected of having gallbladder tumors. (18)F-FDG PET (whole body) was performed at 62 +/- 8 min (early) after (18)F-FDG injection and was repeated 146 +/- 14 min (delayed) after injection only in the abdominal region. We evaluated the (18)F-FDG uptake both visually and semiquantitatively. Semiquantitative analysis using the standardized uptake value (SUV) was performed for both early and delayed images (SUV(early) and SUV(delayed), respectively). The retention index (RI) was calculated according to the equation (SUV(delayed) - SUV(early)) x 100/SUV(early). The tumor-to-liver ratio was also calculated. Results: The final diagnosis was gallbladder carcinoma in 23 patients and benign disease in 9 patients. For visual analysis of gallbladder carcinoma, delayed (18)F-FDG PET images improved the specificity of diagnosis in 2 patients. When an SUV(early) of 4.5, SUV(delayed) of 2.9, and RI of -8 were chosen as arbitrary cutoffs for differentiating between malignant and benign conditions, sensitivity increased from 82.6% to 95.7% and 100% for delayed imaging and combined early and delayed imaging (i.e., RI), respectively. With the same criteria, specificity decreased from 55.6% to 44.4% for delayed imaging and combined early and delayed imaging, respectively. The specificity of (18)F-FDG PET improved to 80% in the group with a normal level of C-reactive protein (CRP) and decreased to 0% in the group with an elevated CRP level. For gallbladder carcinoma, both SUV and tumor-to-liver ratios derived from delayed images were significantly higher than the ratios derived from early images (P < 0.0001). CONCLUSION: Delayed (18)F-FDG PET is more helpful than early (18)F-FDG PET for evaluating malignant lesions because of increased lesion uptake and increased lesion-to-background contrast. However, the diagnostic performance of (18)F-FDG PET depends on CRP levels.     

18F-FLT PET for visualization of laryngeal cancer: comparison with 18F-FDG PET.

The feasibility of (18)F-3'-fluoro-3'-deoxy-L-thymidine PET (FLT PET) for detecting laryngeal cancer was investigated and compared with (18)F-FDG PET. METHODS: Eleven patients diagnosed with or strongly suspected of having recurrent laryngeal cancer and 10 patients with histologically proven primary laryngeal cancer underwent attenuation-corrected (18)F-FLT PET imaging 60 min after injection of a median of 213 MBq (range, 175-400 MBq) (18)F-FLT and attenuation-corrected (18)F-FDG PET imaging 90 min after injection of a median of 340 MBq (range, 165-650 MBq) (18)F-FDG. All patients were staged by endoscopy and CT according to the Union Internationale Contre la Cancer TNM staging system. All patients underwent biopsy of the laryngeal area after imaging. Lesions seen on (18)F-FDG PET and (18)F-FLT PET were compared with histopathologic results. Mean SUVs, maximum SUVs, and tumor-to-nontumor (TNT) ratios were calculated for (18)F-FLT and (18)F-FDG. Wilcoxon nonparametric testing was used for comparison of (18)F-FDG with (18)F-FLT uptake. The Spearman correlation coefficient was used to correlate mean SUVs, maximum SUVs, and TNT ratios of (18)F-FDG PET and (18)F-FLT PET. Two-tailed P values < 0.05 were considered significant. RESULTS: (18)F-FDG PET and (18)F-FLT PET detected laryngeal cancer correctly in 15 of 17 patients. One lesion judged as positive on (18)F-FDG PET turned out to be normal tissue. Of 2 lesions judged as positive on (18)F-FLT PET, 1 turned out to be inflammation and the other to be normal tissue. Maximum SUVs were 3.3 (range, 1.9-8.5) for (18)F-FDG and 1.6 (range, 1.0-5.7) for (18)F-FLT (P < 0.001). Mean SUVs were 2.7 (range, 1.5-6.5) for (18)F-FDG and 1.2 (range, 0.8-3.8) for (18)F-FLT (P < 0.001). TNT was 1.9 (range, 1.3-4.7) for (18)F-FDG and 1.5 (range, 1.1-3.5) for (18)F-FLT (P < 0.05). CONCLUSION: The numbers of laryngeal cancers detected with (18)F-FLT PET and (18)F-FDG PET were equal. In laryngeal cancer, the uptake of (18)F-FDG is higher than that of (18)F-FLT.     

Correcting tumour SUV for enhanced bone marrow uptake: retrospective 18F-FDG PET/CT studies

PURPOSE: The concentration of F-FDG in the bone marrow is usually low. One common cause of high uptake is due to bone marrow stimulating drugs administered in conjunction with chemotherapy or radiation therapy. It has been hypothesized that the sequestration of F-FDG to the bone marrow may reduce the standardized uptake value (SUV) of a tumour. We tested this hypothesis by quantifying total F-FDG uptake in the bone marrow of patients with visibly enhanced bone marrow uptake and computing its effect on tumour SUV. METHODS: Total F-FDG in bone marrow was measured in two groups of PET/CT studies: one (n=19) with visibly enhanced bone marrow, the other (n=5), a baseline group with 'normal' levels of uptake. To measure the F-FDG in bone marrow, the entire skeleton in the CT was segmented from surrounding tissue, and the resulting volume applied to the PET image. Using kinetic analysis we show that the predicted correction factor to tumour SUV is given by (1-q0/Q)/(1-q/Q), where Q is the injected dose, and q and q0 are enhanced and baseline bone marrow uptake (MBq). RESULTS: The enhanced bone marrow uptake averaged 8.9+/-3.2% of injected dose (15.2% max) vs. 4.2+/-0.4% (4.6% max) at baseline. This resulted in a predicted artificial decrease in tumour SUV of up to 11.5% (4.9+/-4.3%, on average). CONCLUSION: Enhanced bone marrow uptake is predicted to reduce tumour SUVs by as much as 11.5% in our patient group and is a potential confounding factor in using SUV for monitoring tumour response to therapy.     

Evaluation of delayed18F-FDG PET in differential diagnosis for malignant soft-tissue tumors

OBJECTIVE: Positron emission tomography (PET) with 2-deoxy-2-[18F]fluoro-D-glucose (18F-FDG) has been used for the evaluation of soft-tissue tumors. However, the range of accumulation of 18F-FDG for malignant soft-tissue lesions overlaps with that of benign lesions. The aim of this study is to investigate the usefulness of delayed 18F-FDG PET imaging in the differentiation between malignant and benign soft-tissue tumors. METHODS: Fifty-six patients with soft-tissue tumors underwent whole body 18F-FDG PET scan at 1 hour (early scan) and additional scan at 2 hours after injection (delayed scan). The standardized uptake value (SUV(max)) of the tumor was determined, and the retention index (RI) was defined as the ratio of the increase in SUV(max) between early and delayed scans to the SUV(max) in the early scan. Surgical resection with histopathologic analysis confirmed the diagnosis. RESULTS: Histological examination proved 19 of 56 patients to have malignant soft-tissue tumors and the rest benign ones. In the scans of all 56 patients, there was a statistically significant difference in the SUV(max) between malignant and benign lesions in the early scan (5.50 +/- 5.32 and 3.10 +/- 2.64, respectively, p < 0.05) and in the delayed scan (5.95 +/- 6.40 and 3.23 +/- 3.20, respectively, p < 0.05). The mean RI was not significantly different between malignant and benign soft-tissue tumors (0.94 +/- 23.04 and -2.03 +/- 25.33, respectively). CONCLUSIONS: In the current patient population, no significant difference in the RI was found between malignant and benign soft-tissue lesions. Although the mean SUV(max) in the delayed scan for malignant soft-tissue tumors was significantly higher than that for benign ones, there was a marked overlap. The delayed 18F-FDG PET scan may have limited capability to differentiate malignant soft-tissue tumors from benign ones.     

Prevalence, challenges, and solutions for (18)F-FDG PET studies of obese patients: a technologist's perspective

Obesity has reached epidemic proportions in the United States; hence, it is frequently encountered in patients undergoing (18)F-FDG PET studies. The purpose of the current study was to present a technologist's perspective on the prevalence of obesity and the challenges and solutions in imaging obese patients in our PET facility. METHODS: From October 2002 to October 2003, whole-body (18)F-FDG PET was performed on 1,164 patients with a known or suspected malignancy. Images were acquired 45-60 min after (18)F-FDG injection (7.4 MBq [0.2 mCi]/kg, with a maximum of 925 MBq [25 mCi]) on a PET scanner using a 4-min emission and 3-min transmission time per bed position. A database was maintained of patient height and weight, and body mass index (BMI) was calculated. Patient obesity was classified as overweight (BMI > or = 25 kg/m(2)), obese (BMI > or = 30 kg/m(2)), or malignantly obese (BMI > or = 40 kg/m(2)). In addition, PET technologists recorded any problems and attempted solutions related to the patient weight. RESULTS: BMI calculations showed that 528 patients (45.4%) were overweight or obese (322 men and 206 women; mean age, 55 y). Of those, 201 (38%) were overweight, 270 (51%) were obese, and 57 (11%) were malignantly obese. Problems encountered in these patients included difficult intravenous access (15%), difficult patient positioning (10%), patient motion (7%), an incomplete study (emission only) (1%), and potentially higher radiation exposure to the technologist because of extra time spent near the patient. Attempted solutions included adjusting the schedule to allow more time per patient, adjusting the dose based on body weight, using varied positioning techniques, dividing the study to allow a respite between different image combinations, and dividing time spent with obese patients among the technologists involved. CONCLUSION: Excessive body weight and related problems have commonly been encountered in our PET facility. (18)F-FDG PET studies of obese patients represent an ongoing challenge, which requires patient-tailored solutions to avoid compromising image quality and risking higher radiation exposure to the technologists.     

Reproducibility of standardized uptake value measurements determined by 18F-FDG PET in malignant tumors

18F-FDG PET is increasingly being used to monitor the early response of malignant tumors to chemotherapy. Understanding the reproducibility of standardized uptake values (SUVs) is an important prerequisite in estimating what constitutes a significant change. METHODS: Twenty-six patients were studied on 2 separate occasions (mean interval +/- SD, 3 +/- 2 d; range, 1-5 d). A static PET/CT scan was performed 94 +/- 9 min after the intravenous injection of 383 +/- 15 MBq of 18F-FDG. Mean and maximum SUVs (SUVmean and SUVmax, respectively) were determined for regions of interest drawn around the tumor on the first study and for the same regions of interest transferred to the second study. RESULTS: SUVmean in tumors ranged from 1.49 to 17.48 and SUVmax ranged from 2.99 to 24.09. The correlation between SUVmean determined on the 2 separate visits was 0.99; the mean difference between the 2 measurements was 0.01 +/- 0.27 SUV. The 95% confidence limits for the measurements were +/-0.53. For SUVmax, the mean difference was -0.05 +/- 1.14 SUV. CONCLUSION: Our study demonstrates that repeated measurements of SUVmean performed a few days apart are highly reproducible. A decrease of 0.5 in the SUV is statistically significant.     

Imaging proliferation in brain tumors with 18F-FLT PET: comparison with 18F-FDG.

3'-Deoxy-3'-(18)F-fluorothymidine ((18)F-FLT) is a recently developed PET tracer to image tumor cell proliferation. We characterized (18)F-FLT PET of brain gliomas and compared (18)F-FLT with (18)F-FDG PET in side-by-side studies of the same patients. METHODS: Twenty-five patients with newly diagnosed or previously treated glioma underwent PET with (18)F-FLT and (18)F-FDG on consecutive days. Three stable patients in long-term remission were included as negative control subjects. Tracer kinetics in normal brain and tumor were measured. Uptake of (18)F-FLT and (18)F-FDG was quantified by the standardized uptake value (SUV) and the tumor-to-normal tissue (T/N) ratio. The accuracy of (18)F-FLT and (18)F-FDG PET in evaluating newly diagnosed and recurrent gliomas was compared. More than half of the patients underwent resection after the PET study and correlations between PET uptake and the Ki-67 proliferation index were examined. Patients were monitored for a mean of 15.4 mo (range, 12-20 mo). The predictive power of PET for tumor progression and survival was analyzed using Kaplan-Meier statistics. RESULTS: (18)F-FLT uptake in tumors was rapid, peaking at 5-10 min after injection and remaining stable up to 75 min. Hence, a 30-min scan beginning at 5 min after injection was sufficient for imaging. (18)F-FLT visualized all high-grade (grade III or IV) tumors. Grade II tumor did not show appreciable (18)F-FLT uptake and neither did the stable lesions. The absolute uptake of (18)F-FLT was low (maximum-pixel SUV [SUV(max)], 1.33) but image contrast was better than with (18)F-FDG (T/N ratio, 3.85 vs. 1.49). (18)F-FDG PET studies were negative in 5 patients with recurrent high-grade glioma who subsequently suffered tumor progression within 1-3 mo. (18)F-FLT SUV(max) correlated more strongly with Ki-67 index (r = 0.84; P < 0.0001) than (18)F-FDG SUV(max) (r = 0.51; P = 0.07). (18)F-FLT uptake also had more significant predictive power with respect to tumor progression and survival (P = 0.0005 and P = 0.001, respectively). CONCLUSION: Thirty-minute (18)F-FLT PET 5 min after injection was more sensitive than (18)F-FDG to image recurrent high-grade tumors, correlated better with Ki-67 values, and was a more powerful predictor of tumor progression and survival. Thus, (18)F-FLT appears to be a promising tracer as a surrogate marker of proliferation in high-grade gliomas.     

Prevalence and patterns of physiologic muscle uptake detected with whole-body 18F-FDG PET

Recently, the use of 18F-FDG PET has progressed rapidly as a standard diagnostic imaging tool in many types of cancer. The purpose of this study was to evaluate the patterns and prevalence of muscle uptake as a result of muscle activity shortly before the 18F-FDG injection or during the uptake phase. METHODS: From October 2002 to October 2003, whole-body 18F-FDG PET scans (4-min emission and 3-min transmission per bed position) were performed on 1,164 patients with known or suspected malignancy. Images were acquired on a dedicated PET scanner 45-60 min after an intravenous injection of a weight-adjusted dose of 7.4 MBq/kg (0.2 mCi/kg) with a maximum of 925 MBq (25 mCi) 18F-FDG. A log of any nonphysiologic muscle activity during the uptake phase or reported excessive muscle activity the day before scanning was kept by the technologists. In addition, PET scans were reviewed retrospectively to evaluate any undesirably increased muscle uptake. RESULTS: A total of 146 of 1,164 patients (12.5%) had excessively increased muscle uptake detected on the PET scan that corresponded to the technologists' notes of muscle activity during the uptake phase or before 18F-FDG injection. Encountered patterns of muscle uptake due to muscle activity included uptake in neck, secondary to neck strain from being on a stretcher; masseter, secondary to chewing gum; vocal cords, secondary to speaking; chest wall, secondary to labored breathing; forearms and hands, secondary to reading; and lower extremities, secondary to nervous tapping of the feet. CONCLUSION: Undesirably increased physiologic muscle uptake is frequently encountered on 18F-FDG PET scans. In this study, 12.5% of patients were affected. It is prudent to instruct the patient to avoid any excessive physical activity at least 48 h before injection as well as to not exert muscle activity during the uptake phase. Furthermore, a record should be kept by the technologist of any observed excessive muscle activity during the uptake phase and reported to the reading physician-thus, eliminating a potential source of false-positive findings on interpreting PET scans.     

Whole-body tumor imaging using PET and 2-18F-fluoro-L-tyrosine: preliminary evaluation and comparison with 18F-FDG.

18F-FDG PET imaging is now established as a valuable tool for evaluating cancer patients. However, a limitation of (18)F-FDG is its absence of specificity for tumor. Both protein synthesis and amino acid transport are enhanced in most tumor cells, but their metabolism is less affected in inflammation. We therefore decided to evaluate the ability of PET with 2-(18)F-fluoro-L-tyrosine ((18)F-TYR) to visualize cancer lesions in patients compared with (18)F-FDG PET. METHODS: (18)F-FDG PET and (18)F-TYR PET were performed on 23 patients with histologically proven malignancies (11 non-small cell lung cancers (NSCLCs), 10 lymphomas, and 2 head and neck carcinomas). Fully corrected, whole-body PET studies were obtained on separate days. (18)F-FDG studies were performed after routine clinical fashion. (18)F-TYR studies were started 36 +/- 6 min after tracer injection and a second scan centered over a reference lesion was acquired after completion of the whole-body survey-on average, 87 min after injection. Standardized uptake values (SUVs) were calculated for all abnormal foci and for various normal structures. Results were compared with pathologic or correlative studies. RESULTS: (18)F-FDG PET correctly identified 54 malignant lesions, among which 36 were also visualized with (18)F-TYR (67%). (18)F-TYR did not detect any additional lesion. Tumor SUVs (SUV(bw), 5.2 vs. 2.5), tumor-to-muscle (7.4 vs. 2.7), and tumor-to-mediastinum activity ratios (3 vs. 1.4) were higher with (18)F-FDG than with (18)F-TYR. Two of 11 NSCLCs and 4 of 10 lymphomas were understaged with (18)F-TYR compared with (18)F-FDG. Although the NSCLC lesions missed by (18)F-TYR PET were small, several large lymphoma lesions did not accumulate the tracer. In 4 patients, (18)F-TYR-positive lesions coexisted with (18)F-TYR-negative lesions. There was a high physiologic (18)F-TYR uptake by the pancreas (average SUV(bw), 10.3) and the liver (average SUV(bw), 6.3). Muscle and bone marrow uptakes were also higher with (18)F-TYR than with (18)F-FDG: average SUV(bw), 1 versus 0.7 and 2.6 versus 1.8, respectively. There was no change over time in the (18)F-TYR uptake by the tumors or the normal structures. CONCLUSION: (18)F-TYR PET is not superior to (18)F-FDG PET for staging patients with NSCLC and lymphomas.     

Early prediction of response to chemotherapy in metastatic breast cancer using sequential 18F-FDG PET.

Chemotherapy is currently the treatment of choice for patients with high-risk metastatic breast cancer. Clinical response is determined after several cycles of chemotherapy by changes in tumor size as assessed by conventional imaging procedures including CT, MRI, plain film radiography, or ultrasound. The aim of this study was to evaluate the use of sequential 18F-FDG PET to predict response after the first and second cycles of standardized chemotherapy for metastatic breast cancer. METHODS: Eleven patients with 26 metastatic lesions underwent 31 (18)F-FDG PET examinations (240-400 MBq of 18F-FDG; 10-min 2-dimensional emission and transmission scans). Clinical response, as assessed by conventional imaging after completion of chemotherapy, served as the reference. 18F-FDG PET images after the first and second cycles of chemotherapy were analyzed semiquantitatively for each metastatic lesion using standardized uptake values (SUVs) normalized to patients' blood glucose levels. In addition, whole-body 18F-FDG PET images were viewed for overall changes in the 18F-FDG uptake pattern of metastatic lesions within individual patients and compared with conventional imaging results after the third and sixth cycles of chemotherapy. RESULTS: After completion of chemotherapy, 17 metastatic lesions responded, as assessed by conventional imaging procedures. In those lesions, SUV decreased to 72% +/- 21% after the first cycle and 54% +/- 16% after the second cycle, when compared with the baseline PET scan. In contrast, 18F-FDG uptake in lesions not responding to chemotherapy (n = 9) declined only to 94% +/- 19% after the first cycle and 79% +/- 9% after the second cycle. The differences between responding and nonresponding lesions were statistically significant after the first (P = 0.02) and second (P = 0.003) cycles. Visual analysis of 18F-FDG PET images correctly predicted the response in all patients as early as after the first cycle of chemotherapy. As assessed by 18F-FDG PET, the overall survival in nonresponders (n = 5) was 8.8 mo, compared with 19.2 mo in responders (n = 6). CONCLUSION: In patients with metastatic breast cancer, sequential 18F-FDG PET allowed prediction of response to treatment after the first cycle of chemotherapy. The use of 18F-FDG PET as a surrogate endpoint for monitoring therapy response offers improved patient care by individualizing treatment and avoiding ineffective chemotherapy.