Advantage of delayed whole-body FDG-PET imaging for tumour detection

F-18 fluorodeoxyglucose uptake in leiomyomatous uterus

Leiomyomas of uterus are common disease in gynecology. It is important to differentiate leiomyoma from leiomyosarcoma at the decision of treatment methods, especially in the case of the conservative treatment for uterine leiomyoma. But the exact diagnosis of benign leiomyoma is often difficult due to the degeneration of myoma by imaging modalities including magnetic resonance imaging. Recently, whole-body positron emission tomography (PET) using F-18 fluorodeoxyglucose (FDG) has been used for a diagnosis of malignant tumors. There is a growing body of evidence for the use of FDG in differentiating malignant from benign disease. But optimal utilization in gynecology remains unclear. Our case represents increased uptake of FDG in myomatous uterus, which is pathologically confirmed benign leiomyoma by the hysterectomy. Immunohistochemical analysis of glucose transporter-1 showed positive in endometrial tissue and negative in leiomyoma. Our case indicates that myomatous uterus in premenopausal women shows the potential pitfall of a positive result of FDG-PET.

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.

Two cases of pulmonary paragonimiasis on FDG-PET CT imaging

Positron emission tomography (PET) using 18F-fluorodeoxyglucose (FDG) is useful in cancer diagnosis owing to its sensitivity to the differences in glucose metabolic rate between benign and malignant diseases, especially in the lung. One pitfall in PET imaging of lung disease, however, is the overlap in metabolic rate of inflammatory and neoplastic entities. Paragonimiasis is a food-borne parasitic disease that causes the pulmonary and pleural inflammation. We present two cases of pulmonary paragonimiasis that showed high uptake suggestive of tumor on FDG-PET CT images, both confirmed on histopathology by visualization of Paragonimus westermani eggs in the involved tissues.

Evaluation of delayed additional FDG PET imaging in patients with pancreatic tumour

AIM

To evaluate whether delayed fluorodeoxyglucose (FDG) positron emission tomography (PET) imaging is more helpful in differentiating between malignant and benign lesions and whether delayed FDG PET imaging can identify more lesions in patients in whom pancreatic cancer is suspected.

METHODS

The study evaluated 86 patients who were suspected of having pancreatic tumours. FDG PET imaging (whole body) was performed at 1 h (early) post-injection and repeated 2 h (delayed) after injection only in the abdominal region. Qualitative and semi-quantitative evaluation was performed. The semi-quantitative analysis was performed using the standardized uptake value (SUV), obtained from early and delayed images (SUVearly and SUVdelayed, respectively). Retention index (RI) was calculated according to the equation: (SUVdelayed-SUVearly)x100/SUVearly.

RESULTS

The final diagnosis was pancreatic cancer in 55 and benign disease in 31 patients. On visual and semi-quantitative analysis, the diagnostic accuracy of RI was the highest (88%). The differences between the SUVearly, SUVdelayed and RI value in both pancreatic cancer and benign disease were significant (P<0.01). The mean value of SUVdelayed was significantly higher than that of SUVearly (P<0.01) in pancreatic cancer. Furthermore, new foci of metastasis were seen in the liver in two patients and in the lymph node in one patient only on delayed images.

CONCLUSIONS

The RI values obtained using early and delayed FDG PET may help in evaluating pancreatic cancer. Furthermore, addition of delayed FDG PET imaging is helpful to identify more lesions in patients with pancreatic cancer.

Usefulness of FDG-microPET for early evaluation of therapeutic effects on VX2 rabbit carcinoma

PURPOSE

The aim of this study was to determine the potential use of high-resolution FDG-microPET for predicting the primary effects of radiotherapy and/or hyperthermia on tumor-bearing rabbits.

METHODS

Twenty-eight VX2 xenografts in the thighs of rabbits were divided into the following 5 treatment groups: radiotherapy at a single dose of 10, 20 or 30 Gy, hyperthermia (43 degrees Celsius, 1 hour), and the combination of radiotherapy and hyperthermia (10 Gy + 43 degrees Celsius, 1 hour). FDG-microPET images were obtained by using a microPET P4 system at pretreatment and at 24 hours and 7 days after treatment. For the evaluation by FDG-microPET, tumor/muscle (T/M) ratios, retention index [RI = (T/M ratio at 120 min - T/M ratio at 60 min) / T/M ratio at 60 min], and time activity curve (TAC) were acquired.

RESULTS

We divided the xenografts into a responder group (partial response + stable disease, n=14) and a non-responder group (progressive disease, n = 14). The T/M ratio at 24 hours after the treatment in the responder group was decreased remarkably with that at pre-treatment (p < 0.05), while in the non-responder group it showed no significant change between the time points. The RI and TAC patterns were comparable to T/M ratios in each treatment group. T/M ratios, RI, and TAC indicated marked changes at the time point of 24 hours in the responder group, although the tumors did not show any significant hange in volume at that time. Photomicrographs of sections showed that the number of viable tumor cells in the responder group decreased at 24 hours after treatment and that inflammatory cell infiltration was marked and almost all viable tumor cells had disappeared by day 7 after treatment.

CONCLUSION

These results suggest that early evaluation by FDG-microPET, especially 24 hours after treatment, is useful to predict the primary effects of the treatment. Histological analysis showed that inflammatory cell infiltration at 7 days after treatment was considered to be a cause of accumulation of FDG in the tumors that showed a significant decrease in tumor cell number. This false-positive should be noted when predicting tumor response by FDG accumulation.

Fluorine- 18-fluorodeoxyglucose positron emission tomography for assessment of patients with unresectable recurrent or metastatic lung cancers after CT-guided radiofrequency ablation: Preliminary results

OBJECTIVES

We compared the diagnostic value of fluorine-18-fluorodeoxyglucose positron emission tomography (FDG-PET) with that of computed tomography (CT) following radiofrequency ablation (RFA) of inoperable recurrent or metastatic cancers in the lung.

METHODS

Twelve patients (9 males and 3 females; 5 had recurrent lung cancer and the other 7 had metastatic nodules from a variety of primary cancers) were treated by RFA for 17 pulmonary nodules. FDG-PET was performed before and 2 months after RFA, and the mean standardized uptake value (SUV) was calculated. The response evaluation was based on the percent reduction relative to the baseline and the absolute values of SUV on FDG-PET performed at 2 months after RFA. We compared the response evaluations made based on findings of FDG-PET and CT at 2 and > or =6 months (mean 10.2) after RFA.

RESULTS

The percent reduction in uptake at 2 months was significantly lower in nodules considered progressive (69.6 +/- 18.6%) than nonprogressive disease (38.7 +/- 12.5%; p < 0.01) based on CT findings at > or =6 months after RFA. The absolute SUV at 2 months was significantly higher in nodules considered progressive (2.61 +/- 0.75) than nonprogressive disease (1.05 +/- 0.67; p < 0.01) based on CT findings at > or =6 months post-RFA.

CONCLUSION

Although our pilot study comprised few cases of various histopathological types of cancers in the lung, the results suggest that FDG-PET could predict regrowth on subsequent follow-up CT. Regrowth could be diagnosed earlier by FDG-PET than by CT, and nodules with residual uptake and with <60% reduction of uptake relative to baseline on FDG-PET at 2 months after ablation might require additional therapy.

Evaluation of pulmonary nodules: comparison of a prototype dual crystal (LSO/NAI) dual head coincidence camera and full ring positron emission tomography (PET)

PURPOSE

To determine the concordance of a prototype dual head coincidence camera (LSO-PS) and full ring PET (BGO-PET) using (18)F-fluorodeoxyglucose (FDG) in the evaluation of pulmonary nodules (PNs).

MATERIALS AND METHODS

Patients referred for evaluation of < or =3 PNs (< or =3 cm diameter) were prospectively studied on the same day with both BGO-PET and LSO-PS. Imaging was performed at 60 and 120 min after injection of 370MBq FDG, respectively. Images were independently interpreted by four observers with each observer blinded to the other modality for the same patient. Lesions were scored in terms of relative intensity versus background. Non-attenuation corrected (nonAC) BGO-PET was used as the reference test.

RESULTS

Forty-seven patients with 54 PNs (mean diameter 1.7 cm, S.D. 0.7) were included. Twelve nodules were in the < or =1.0 cm - 27 in the 1.1-2.0 cm - and 15 in the 2.1-3.0 cm range. Interobserver agreement was similar for both FDG imaging modalities. Using a sensitive assessment strategy with LSO-PS (> or = faint intensity deemed positive), there was a 97% (38/39, 95%CI 87-100%) concordance with BGO-PET and one false positive case with LSO-PS. Conservative reading (moderate or intense intensity deemed positive) resulted in a 92% (36/39, 95%CI 80-97%) concordance with BGO-PET, without false positives. The only lesion missed by LSO-PS using both assessment strategies involved a nodule 1.5 cm diameter that demonstrated moderate increased FDG uptake on BGO-PET.

CONCLUSION

Depending on the test positivity criteria, LSO-PS demonstrates a high concordance (92-97%) with nonAC BGO-PET for the characterization of pulmonary nodules.

Correlation of FDG-PET findings with histopathology in the assessment of response to induction chemoradiotherapy in non-small cell lung cancer

PURPOSE

The objective of this study was to evaluate the ability of FDG-PET to predict the response of primary tumour and nodal disease to preoperative induction chemoradiotherapy in patients with non-small cell lung cancer (NSCLC).

METHODS

FDG-PET studies were performed before and after completion of chemoradiotherapy prior to surgery in 26 patients with NSCLC. FDG-PET imaging was performed at 1 h (early) and 2 h (delayed) after injection. Semi-quantitative analysis was performed using the standardised uptake value (SUV) at the primary tumour. Percent change was calculated according to the following equation: [see text]. Based on histopathological analysis of the specimens obtained at surgery, patients were classified as pathological responders or pathological non-responders. The clinical nodal stage on the post-chemoradiotherapy PET scan was visually determined and compared with the final pathological stage.

RESULTS

Eighteen patients were found to be pathological responders and eight to be pathological non-responders. SUV(after) values from both early and delayed images in pathological responders were significantly lower than those in pathological non-responders. The percent change values from early and delayed images in the pathological responders were significantly higher than those in the pathological non-responders. The post-chemoradiotherapy PET scan accurately predicted nodal stage in 22 of 26 patients.

CONCLUSION

FDG-PET may have the potential to predict response to induction chemoradiotherapy in patients with NSCLC.

An experimental study onO-[18F]fluoromethyl-L-tyrosine for differentiation between tumor and inflammatory tissues

OBJECTIVE

O-[18F]fluoromethyl-L-tyrosine (18F-FMT) is a recently developed tumor-detecting agent with simple preparation and high radiochemical yields. The aim of this study was to assess the potency of 18F-FMT for differentiating tumor and inflammatory tissues using an animal model with an implanted tumor and experimentally induced inflammatory foci.

METHODS

An ascites hepatoma cell line, AH109A, turpentine oil and Staphylococcus aureus were inoculated subcutaneously into Donryu rats as a tumor model, aseptic inflammation model and bacterial infection model, respectively. The biodistribution of radioactivity was assessed in rats at 5, 10, 30, 60, and 120 min after injection with 18F-FMT. Dual tracer whole-body and macro autoradiographies were performed 60 min after injection with a mixture of 18F-FMT and 2-deoxy-D-[1-14C]glucose (14C-DG).

RESULTS

Tumor uptake of 18F-FMT was on average 1.27% injected dose per gram of tissue (%ID/g) and 1.43% ID/g at 30 min and 60 min, respectively and significantly higher than that in other normal tissues, except the pancreas (3.48% ID/g at 60 min). The uptakes in the aseptic and bacterial inflammatory tissues were very low and were not different from those of the background tissues. Dual tracer whole-body and macro autoradiographic studies showed that tumor uptake of 18F-FMT was clearly higher than uptake by the other tissues, while 18F-FMT accumulated much less both in aseptic and bacterial inflammatory tissues. In contrast, the 14C-DG images showed high accumulations not only in tumors but also in aseptic and bacterial inflammatory tissues.

CONCLUSION

18F-FMT seems to be a promissing tracer for the differentiation between tumor and inflammation because of higher specificity to tumor.

Factors influencing [F-18] 2-fluoro-2-deoxy-D-glucose (F-18 FDG) uptake in melanoma cells: the role of proliferation rate, viability, glucose transporter expression and hexokinase activity

Using human (SK-MEL 23, SK-MEL 24 and G361) and murine (B16) melanoma cell lines, the coregulatory potential of the uptake of the positron emission tomography (PET) tracer, [Fluorine-18] 2-fluoro-2-deoxy-D-glucose (F-18 FDG) has been investigated in relationship to tumor characteristics. Comparative studies among the four melanoma cell lines demonstrated that the lowest FDG uptake in SK-MEL 24 corresponded strongly to the data for DT (population doubling time) and MTT (tetrazolium salt) cell viability as well as hexokinase (HK) activity, but was not related to the glucose transporter 1 (GLUT 1) expression level. Furthermore, the FDG uptake in each melanoma cell line measured by cell cycle kinetics was significantly positively correlated to both the proliferation index (PI=S/G2M phase fractions) and the cell viability, though with one exception relating to the PI of the lowest FDG uptake cell line, SK-MEL 24. No positive correlation was found between the expression of GLUT 1 and FDG uptake in any individual cell line. However, the HK activities in SK-MEL 23 and 24 showed considerable positive relationships with FDG uptake. Our present study suggests that both the proliferation rate and the cell viability of melanoma cells may be key factors for FDG uptake and that HK activity, rather than GLUT 1 expression, seems to be a major factor.

Value of delayed 18F-FDG-PET imaging in the detection of hepatocellular carcinoma

BACKGROUND

18F-Fluorodeoxyglucose-positron emission tomography (18F-FDG-PET) is a very useful imaging technique and is the best modality for the evaluation of many kinds of tumour. However, in the evaluation of hepatocellular carcinoma (HCC), the diagnostic accuracy of routine 60 min static imaging is not satisfactory. Some authors have suggested that delayed 2 h imaging is a better 18F-FDG-PET protocol for tumour detection. However, the value of delayed 3 h imaging has not been clarified. In this study, we performed delayed 2 h and 3 h imaging on patients with HCC and compared their diagnostic accuracy with standard 60 min imaging.

METHODS

Twelve patients with HCC were enrolled in this study. Of these 12 patients, four had not been treated and eight had received transcatheter arterial embolization (TAE) therapy for more than 4 months before the PET study. One hour after injection of 18F-FDG, a whole-body scan was performed. In addition, delayed imaging focusing on the liver was also performed 2 h and 3 h after the injection. The standard uptake value (SUV) was calculated for the tumours in each image.

RESULTS

The twelve patients had 16 HCCs. Of the 16 HCCs, nine were detected by 18F-FDG-PET scans based on the 1 h images, whereas 10 HCCs were detected based on the 2 or 3 h images. The diagnostic sensitivity increased from 56.3% on the 1 h image to 62.5% on the 2 and 3 h images. In addition, the mean SUV increased from 3.63 at 1 h to 3.86 at 2 h and 3.99 at 3 h after the injection of 18F-FDG. On the other hand, the mean SUV in the normal liver tissue decreased slightly from 2.38 at 1 h to 2.33 at 2 h and 2.31 at 3 h. The tumour to normal liver tissue (T/N) ratio increased from 1.56 at 1 h to 1.68 at 2 h and 1.75 at 3 h.

CONCLUSION

In the evaluation of HCC, delayed 2 and 3 h imaging can detect more lesions than standard 1 h imaging. Imaging at 3 h has a better T/N ratio than imaging at 2 h, but does not increase the diagnostic sensitivity.

Nasopharyngeal carcinoma staging by (18)F-fluorodeoxyglucose positron emission tomography

PURPOSE

Nasopharyngeal carcinoma (NPC) has a high rate of neck lymph node and/or distant metastasis. We evaluated the value of (18)F-fluorodeoxyglucose positron emission tomography (FDG-PET) in staging NPC, especially in the detection of distant metastasis.

METHODS AND MATERIALS

A total of 95 patients, including 85 with primary and 10 with recurrent, NPC were enrolled. Dual-phase FDG-PET was used, in addition to the conventional workup. Eighty-one patients without distant metastases underwent repeat studies 3-4 months after initial radical treatment.

RESULTS

Of 14 patients with distant metastases, all had lesions detected by FDG-PET, and the conventional workup detected the metastases in only 4. Two patients had false-positive MRI findings for neck node metastasis, but the FDG-PET findings were accurate. Four patients without distant metastases on their initial workup were found to have new lesions on FDG-PET 3-4 months after initial treatment. Patients with advanced node disease had a significantly greater incidence of distant metastases on FDG-PET, especially for N3 disease. Of the 95 patients, the FDG-PET results for distant metastasis were true positive in 14 patients, false positive in 8, and true negative in 73. None of our patients had a false-negative result. For a patient base, the sensitivity and specificity of FDG-PET for distant metastasis was 100% and 90.1% (95% confidence interval 81.5-95.6%), respectively, in this study. The accuracy was 91.6% (95% confidence interval 84.1-96.3%), the positive predictive value was 63.6 (95% confidence interval 40.7-82.8%), and the negative predictive value was 100%.

CONCLUSION

FDG-PET stages N and M disease of NPC more accurately and sensitively than does the conventional workup. Patients with advanced node disease, particularly N3 disease, would benefit the most from FDG-PET.

Usefulness of additional delayed regional F-18 Fluorodeoxy-Glucose Positron Emission Tomography in the lymph node staging of Non-Small Cell Lung Cancer patients

PURPOSE

In this study, we examined whether additional, delayed regional FDG PET scans could increase the accuracy of the lymph node staging of NSCLC patients.

MATERIALS AND METHODS

Among 87 patients who underwent open thoracotomy or mediastinoscopic biopsy under the suspicion of NSCLC, 35 (32 NSCLC and 3 infectious diseases) who had visible lymph nodes on both preoperative whole body scan and regional FDG PET scan were included. The following 3 calculations were made for each biopsy-proven, visible lymph node: maximum SUV of whole body scan (WB SUV), maximum SUV of delayed chest regional scan (Reg SUV), and the percent change of SUV between WB and regional scans (% SUV Change). ROC curve analyses were performed for WB SUVs, Reg SUVs and % SUV Changes.

RESULTS

Seventy lymph nodes (29 benign, 41 malignant) were visible on both preoperative whole body scan and regional scan. The means of WB SUVs, Reg SUVs and % SUV Changes of the 41 malignant nodes, 3.71+/-1.08, 5.18+/-1.60, and 42.59+/-33.41%, respectively, were all significantly higher than those of the 29 benign nodes, 2.45+/-0.73, 3.00+/-0.89, and 22.71+/-20.17%, respectively. ROC curve analysis gave sensitivity and specificity values of 80.5% and 82.8% at a cutoff of 2.89 (AUC 0.839) for WB SUVs, 87.8% and 82.8% at a cutoff of 3.61 (AUC 0.891) for Reg SUVs, and 87.8% and 41.4% at a cutoff of 12.3% (AUC 0.671) for % SUV Changes.

CONCLUSION

Additional, delayed regional FDG PET scans may improve the accuracy of lymph node staging of whole body FDG PET scan by providing additional criteria of Reg SUV and % SUV Change.

Fluorodeoxyglucose-PET in characterizing solitary pulmonary nodules, assessing pleural diseases, and the initial staging, restaging, therapy planning, and monitoring response of lung cancer

Fluorodeoxyglucose-PET imaging has secured an important role in the assessment and management of a multitude of pulmonary disorders, including solitary pulmonary nodules, lung cancer, and pleural diseases. While conventional imaging modalities such as chest radiography and CT are considered essential in these settings, FDG-PET can provide new information and complement structural imaging techniques in the evaluation of such disorders. In this review, the authors present a growing body of evidence that demonstrates and supports the utility of FDG-PET in the differentiation of benign and malignant pulmonary nodules, the assessment of lung cancer in various stages of disease, and the characterization of pleural diseases. In addition, new developments--such as prospects for potential utility of novel radiotracers and delayed imaging--that can further refine the role of FDG scans in the work-up of lung nodules and cancer and forecast the future place of PET in these common modalities are discussed.

Peripheral nerve schwannoma: two cases exhibiting increased FDG uptake in early and delayed PET imaging

We present two cases of peripheral nerve schwannoma which showed an increased accumulation of 2-deoxy-[(18)F] fluoro-D-glucose (FDG) in the tumors on positron emission tomography (PET) imaging acquired at both 1 h (early phase) and 2 h (delayed phase) after FDG injection. FDG-PET scans were performed with a dedicated PET scanner (HeadtomeV/ SET2400 W, Shimadzu, Kyoto, Japan) and the PET data analyzed the most metabolically active region of interest (ROI). We set the maximum standardized uptake value (SUV max) with a cut-off point of 3.0 to distinguish benign and malignant lesions. Although the mechanism responsible for the increased FDG uptake in benign schwannomas remains unknown, we discuss our findings in the context of tumor cellularity and briefly review other studies on the subject.

Utility of fluorodeoxyglucose-PET imaging in the management of patients with Hodgkin's and non-Hodgkin's lymphomas

FDG-PET imaging has a number of advantages in the management of patients with lymphoma. PET shows a functional metabolic status and gives quantitative information. In addition, PET provides whole-body images that give a comprehensive assessment of disease extent during the staging and followup. Based on the present literature, FDG-PET is at least equivalent to CT for the initial staging of lymphomas. The impact of new technologies of combined PET/CT and fast-scanning CT with contrast has yet to be evaluated in the management of lymphoma patients, however. At this point, FDG-PET and CT must be considered as giving complementary staging information. FDG-PET also has high diagnostic accuracy for restaging lymphoma after initial treatment. FDG-PET has shown high accuracy in the early prediction of response to chemotherapy and in the evaluation of residual masses after chemotherapy or radiation therapy. Therefore, PET is likely to play a major role in tailoring the intensity of the treatment to the individual patient. A pretreatment FDG-PET study is essential for accurate assessment of residual masses and early monitoring of response to the treatment. In addition, a baseline PET scan will help detect relapse or residual disease, because relapse occurs most often in the region of previous disease.

Quantification in PET

Quantification provides the link between the concentrations of radioactivity measured in tissue and the underlying physiologic processes occurring in the organ. It relates the rate at which radioactivity levels in the body change over time to quantitative parameters such as absolute rate glucose metabolism, regional blood flow, or concentrations of receptors or other binding sites. Absolute measurement of physiologic parameters generally requires accurate measurement of activity concentrations in arterial blood, which provides the input function to the kinetic model. Although absolute quantification can be a difficult process, simplifications of these invasive techniques, involving reference tissues or normalization approaches (eg, SUV), have been applied with some success. Any simplified model of tracer behavior must be validated against the full model to test for bias and systematic errors.

Recent advances in imaging hepatocellular carcinoma: diagnosis, staging and response assessment: functional imaging

Historically, nuclear medicine has had an important role in the differential diagnosis of liver tumors but has been largely superseded by other forms of conventional imaging, in particular computed tomographic portography. It remains helpful in difficult cases because it has characteristic features in both hepatocellular carcinoma (HCC) and benign conditions. 131I is an important therapeutic tool. FDG-PET is useful in certain cases, especially for finding metastases and monitoring response to therapy.

Lesion detectability of a gamma camera based coincidence system with FDG in patients with malignant tumors: A comparison with dedicated positron emission tomography

OBJECTIVE

The aim of this study was to investigate the lesion detectability of a gamma camera based coincidence detector system (c-PET system) in comparison to the dedicated PET system (d-PET system), and thereby clarify the feasibility of the clinical application of this system and also describe any factors influencing the lesion detectability of the c-PET system.

METHODS

We examined 74 patients including 19 with malignant lymphoma, 16 with lung cancer, 9 with primary malignant bone tumor, 7 with esophageal cancer, 6 with malignant melanoma, 3 with hepatocellular carcinoma, 3 with primary unknown cancer, 2 with breast cancer, 2 with colon cancer, and 7 with others. d-PET images were obtained using ECAT EXACT HR+ at 60 min, followed by c-PET imaging using ECAM at 120 min after the injection of 185 MBq of FDG. Each image was reconstructed without any attenuation correction. In the image interpretation, the whole body was classified into 16 regions (5 superficial regions and 11 deep regions). The FDG accumulation of the lesions was evaluated by visual grading based on the consensus of three nuclear medicine physicians, and the findings were classified into three grades; (++), (+), and (-). The lesions were also classified into 3 groups according to their size: large group (> or =2 cm), middle group (1 < or = <2 cm) and small group (<1 cm).

RESULTS

In 627 regions, the abnormal FDG uptake was detected in 109 regions by the d-PET system. Out of 109 regions, the c-PET system could detect the lesions in 91 regions and was false positive in 1 region. Therefore, the sensitivity, specificity, and accuracy of the c-PET system were 83.5%, 99.8% and 97.0%, respectively. Lesion detectability of the small group (54.5%) was significantly lower than that of the large group (97.9%) (p < 0.001) and that of the middle group (93.1%) (p < 0.001); however, the difference in lesion detectability between the large and middle groups was not significant. Neither the degree of FDG accumulation nor the location of the lesion markedly influenced the lesion detectability of the c-PET system. However, when we focused on the large and middle size lesions, the detectability of deep lesions tended to be lower than that of superficial lesions.

CONCLUSION

In conclusion, the lesion detectability of the c-PET system was inferior to that of the d-PET system, especially in the case of small lesions. Further examination is required to assess the clinical usefulness of the c-PET system.

FDG-PET delayed imaging for the detection of head and neck cancer recurrence after radio-chemotherapy: comparison with MRI/CT

In advanced head and neck cancer, an organ-sparing approach comprising radiation therapy combined with intra-arterial chemotherapy has become an important technique. However, the high incidence of residual masses after therapy remains a problem. In this study, we prospectively evaluated the use of 2-[18F]fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET) delayed imaging for the detection of recurrence of head and neck cancer after radio-chemotherapy, and compared the FDG-PET results with those of magnetic resonance imaging (MRI) or computed tomography (CT). Forty-three lesions from 36 patients with head and neck cancer suspected to represent recurrence after radio-chemotherapy (median interval from therapy, 4 months) were studied. PET was performed at 2 h after FDG injection, and evaluated. The results were compared to those of contrast studies with MRI or CT performed within 2 weeks of the PET study, and to histological diagnosis (in all patients suspected of having recurrence) or clinical diagnosis. The lesion-based sensitivity (visual interpretation) and negative predictive value of FDG-PET (88% and 91%, respectively) were higher than those of MRI/CT (75% and 67% respectively). The specificity, accuracy and positive predictive value of FDG-PET (78%, 81% and 70%, respectively) were significantly ( P<0.05) higher than those of MRI/CT (30%, 47% and 39% respectively). Three of six patients with false positive findings had post-therapy inflammation. Receiver operating characteristic (ROC) analysis showed that retrospective evaluation with the standardised uptake ratio yielded the best results (sensitivity 87.5%, specificity 81.5%), followed by visual interpretation and then the tumour/neck muscle ratio. An FDG-PET delayed imaging protocol yielded significantly better results for the detection of recurrence of head and neck cancer after radio-chemotherapy than MRI/CT. Because of the high negative predictive value of FDG-PET (91.3%), if PET is negative, further invasive procedures may be unnecessary.

FDG-PET scanning after radiation can predict tumor regrowth three months later

PURPOSE

Positron emission tomography (PET) with 2-[(18)F]fluoro-2-deoxy-D-glucose (FDG) is well known for providing excellent clinical information regarding malignant tumors. We investigated whether dual-time FDG-PET performed immediately post radiation could predict early regrowth of malignant tumors.

MATERIALS AND METHODS

Twenty patients with malignant tumors were included in this study. All patients received radiation, and each underwent FDG-PET before the initiation of therapy and within 10 days of completing their course of irradiation. PET images after irradiation were obtained at 60 min and 180 min post FDG injection. For 26 lesions in 20 patients, standardized uptake value (SUV) before and after treatment was calculated and then correlated with postradiation tumor response and outcome at 3 months status post irradiation.

RESULTS

Retention index [RI = (SUV on delayed image - SUV on early image)/SUV on early image] after irradiation showed a significant difference between patients with residual tumor and those without residual tumor at 3 months status post irradiation (p < 0.0025). All 9 lesions in 6 patients with residual tumors showed more than 0.1 of RI, whereas none of the lesions with less than 0.1 of RI revealed residual tumors.

CONCLUSIONS

Dual-time FDG-PET imaging just after irradiation is potentially useful for predicting early regrowth of malignant tumors.

Metabolic significance of the pattern, intensity and kinetics of 18F-FDG uptake in malignant pleural mesothelioma

BACKGROUND

Malignant pleural mesothelioma is an aggressive neoplasm with a highly variable course. This pilot study evaluated the significance of the pattern, intensity and kinetics of 18F-FDG uptake in mesothelioma in the context of histopathology and surgical staging.

METHODS

Sixteen consecutive patients with pleural disease on CT scan underwent 18F-FDG imaging. Imaging was performed with a dual detector gamma camera operating in coincidence mode. Semiquantitative image analysis was performed by obtaining lesion-to-background ratios (18F-FDG uptake index) and calculating the increment of 18F-FDG lesion uptake over time (malignant metabolic potential index (MMPi)).

RESULTS

Twelve patients had histologically proven malignant mesotheliomas (10 epithelial, two sarcomatoid). Thirty two lesions were positive for tumour. Patterns of uptake matched the extent of pleural and parenchymal involvement observed on CT scanning and surgery. Mean (SD) 18F-FDG uptake index for malignant lesions was 3.99 (1.92), range 1.5-9.46. Extrathoracic spread and metastases had higher 18F-FDG uptake indices (5.17 (2)) than primary (3.42 (1.52)) or nodal lesions (2.99 (1)). No correlation was found between histological grade and stage. The intensity of lesion uptake had poor correlation with histological grade but good correlation with surgical stage. 18F-FDG lesion uptake increased over time at a higher rate in patients with more advanced disease. The MMPi was a better predictor of disease aggressiveness than the histological grade.

CONCLUSIONS

This pilot study suggests that the pattern, intensity, and kinetics of 18F-FDG uptake in mesothelioma are good indicators of tumour aggressiveness and are superior to the histological grade in this regard.

Narrow time-window dual-point 18F-FDG PET for the diagnosis of thoracic malignancy

Dual time-point imaging has been proposed as a means of improving the accuracy of 2-[18F]fluoro-2-deoxy-D-glucose positron emission tomography (18F-FDG PET) for the diagnosis of malignant pulmonary nodules. The purpose of this study was to evaluate a dual time-point protocol that has a narrow time window between its initial and its delayed imaging sessions. All patients examined during a 16-month time period, either for the diagnosis of a radiographically indeterminate thoracic lesion or for the staging of non-small-cell carcinoma, were included in the study provided that they completed the dual-point protocol and had either biopsy evidence of malignancy, biopsy evidence of a benign condition involving the thoracic lesion of concern, or clinical and radiographic follow-up consistent with the absence of malignancy. The entire study population was further divided into a central subpopulation, whose index lesions were adjacent to or within the hilum or mediastinum, and a peripheral subpopulation, whose index lesions were non-central. The maximum standardized uptake value (SUV) was measured for each lesion, and various body surface areas (BSAs) and glucose corrections on the SUV were compared using discriminant analysis. BSA corrected SUVs for the initial (iSUV) and the delayed (dSUV) imaging sessions, along with their absolute difference (deltaSUV) and fractional difference (fSUV) were also compared using discriminant analysis and receiver operating characteristic (ROC) analysis. The study population consisted of 132 patients, of whom 81 had malignancy and 51 were classified as having a benign condition. Thirty-three index lesions were central and 99 were peripheral; 109 had visible uptake and 23 had such low uptake that they were not visible above background. The mean time (+/-SD) between initial and delayed imaging for the visible lesions was 31.1+/-9.4 min. With respect to the entire study population, the BSA replacement for body weight gave the best performance among the various SUV corrections examined. In addition, the BSA corrected delayed SUV (dSUV) gave a performance superior to either initial SUV (iSUV), absolute difference in SUV (deltaSUV) and fractional difference in SUV (fSUV) alone. Performance gains achieved by BSA correction and by dSUV appeared to derive primarily from the central subpopulation, thereby indicating that central lesions tend to behave differently to peripheral ones. For the central subpopulation, ROC analysis also demonstrated improved detection of malignancy from dual-point imaging. The best performance was achieved when the BSA corrected dSUV was at least 2.4, or when the fSUV showed at least a 5% increase from initial to delayed imaging. With the optimal combined dSUV/fSUV strategy, the area under the ROC curve was 0.99, as opposed to 0.96 for dSUV alone, or 0.93 for iSUV alone. The ability of 18F-FDG PET to discriminate between benign and malignant conditions of the central thorax can be improved by correcting the SUV for BSA and by increasing the 'incubation time' between 18F-FDG injection and imaging, or by performing narrow time-window dual-point imaging.

Optimal scan time for evaluating pancreatic disease with positron emission tomography using F-18-fluorodeoxyglucose

OBJECTIVE

Image interpretation in positron emission tomography (PET) using F-18-fluoro-2-deoxy-D-glucose (FDG) is usually performed for images obtained at 1 h postinjection (PI) of FDG, but it remains unknown whether this is the optimal time for imaging patients with pancreatic disease. The aim of this study was to assess the optimal scan time for FDG-PET for patients suspected of having pancreatic cancer.

PATIENTS AND METHODS

Forty-four patients with suspected pancreatic cancer underwent FDG-PET scans at both 1 h and 2 h PI. Tracer uptake in the pancreatic lesions and possible liver metastasis was interpreted qualitatively, using a 5-point grading system (0 = normal, 1 = probably normal, 2 = equivocal, 3 = probably abnormal, and 4 = definitely abnormal) by 4 nuclear medicine physicians independently, who were blind to all clinical information. Detection performance with each image was compared using receiver operating characteristic (ROC) analysis. An average score of the 4 readers for each patient was also defined as consensus average index (CAI) and compared between the two images.

RESULTS

ROC results indicated no significant differences in detection performance (Averaged areas under ROC curves of 1 h vs. 2 h were 0.92 vs. 0.90 for primary tumor, and 0.81 vs. 0.85 for liver metastases). There were no significant differences in CAIs between 1 h and 2 h PI images in interpreting primary tumor and positive liver metastases, but a significant difference was observed for cases without liver metastases (p < 0.05).

CONCLUSIONS

The certainty of excluding liver metastases was increased when the 2h image was used, although ROC analysis did not establish a difference between 1 h and 2 h imaging for differentiating malignant and benign lesions in primary pancreatic cancer or its liver metastases.

Diagnosis of pancreatic cancer using fluorine-18 fluorodeoxyglucose positron emission tomography (FDG PET) --usefulness and limitations in "clinical reality"

The present review will provide an overview of the literature concerning the FDG PET diagnosis of pancreatic cancer and a summary from our experience of 231 cases of pancreatic lesions. FDG PET can effectively differentiate pancreatic cancer from benign lesion with high accuracy. Newly-developed PET scanners can detect small pancreatic cancers, up to 7 mm in diameter, by their high resolution, which could make a great contribution to the early detection of resectable and potentially curable pancreatic cancers. FDG PET is useful and cost-beneficial in the pre-operative staging of pancreatic cancer because an unexpected distant metastasis can be detected by whole-body PET in about 40% of the cases, which results in avoidance of unnecessary surgical procedures. FDG PET is also useful in evaluation of the treatment effect, monitoring after the operation and detection of recurrent pancreatic cancers. However, there are some drawbacks in PET diagnosis. A relatively wide overlap has been reported between semiquantitative uptake values obtained in cancers and those in inflammatory lesions. As for false-positive cases, active and chronic pancreatitis and autoimmune pancreatitis sometimes show high FDG accumulation and mimic pancreatic cancer with a shape of focal uptake. There were 8 false negative cases in the detection of pancreatic cancer by FDG PET, up to 33 mm in diameter, mainly because of their poor cellularity in cancer tissues. In addition, there are 19% of cancer cases with a decline in FDG uptake from 1 hr to 2 hr scan. FDG PET was recently applied to and was shown to be feasible in the differential diagnosis of cystic pancreatic lesions, such as intraductal papillary mucinous tumor of the pancreas. Further investigations are required to clarify the clinical value of FDG PET in predicting prognosis of the pancreatic patients.

Limitations of PET for imaging lymphoma

The uptake of fluorine-18 fluorodeoxyglucose (FDG) is increased in processes with enhanced glycolysis, including malignancy. It is this property of FDG which is exploited in positron emission tomography (PET) imaging for lymphoma. FDG, whilst a good oncology tracer, is not perfect and there are limitations to its use. FDG may have low uptake in some types of lymphoma, predominantly low-grade lymphomas. High physiological uptake may occur within the bowel, urinary tract, muscle, salivary glands and lymphoid tissue. FDG is not specific for malignancy and increased uptake occurs in benign conditions with increased glycolysis such as infection, inflammation and granulomatous disease. Benign conditions usually have lower uptake than malignancy but there is overlap. These limitations of FDG mean that tumour may be 'missed', 'masked' or 'mimicked' by other pathology. These limitations are described in this article and methods to circumvent them where possible are discussed. These include performing baseline scans at presentation with lymphoma for comparison with post-treatment scans, simple manoeuvres to reduce physiological uptake such as administration of frusemide and diazepam and remaining alert to the possibility of alternative pathology in immunosuppressed patients. Patients with disease secondary to human immunodeficiency virus are a particular challenge in this regard as they often have dual or multiple pathology. One of the most important skills in PET reporting may be to recognise its limitations and be clear when a definitive answer cannot be given to the referring clinician's question. This may require using PET to direct the clinician to biopsy the site most likely to yield the correct diagnosis.

Value of whole-body FDG PET in management of lung cancer

18F-fluorodeoxyglucose (FDG) PET imaging provides physiologic and metabolic information that characterizes lesions that are indeterminate by CT. FDG PET imaging is sensitive to the detection of lung cancer in patients who have indeterminate lesions on CT, whereas low grade malignancy such as bronchioloalveolar carcinoma and carcinoid may be negative on FDG PET. The specificity of PET imaging is less than its sensitivity because some inflammatory processes, such as active granulomatous infections, avidly accumulate FDG. This possibility should be kept in mind in the analysis of PET studies of glucose metabolism aimed at differentiating malignant from benign solitary pulmonary nodules. FDG uptake is considered to be a good marker of cell differentiation, proliferative potential, aggressiveness, and the grade of malignancy in patients with lung cancer. FDG PET accurately stages the distribution of lung cancer. Several studies have documented the increased accuracy of PET compared with CT in the evaluation of the hilar and mediastinal lymphnode status in patients with lung cancer. Whole-body PET studies detect metastatic disease that is unsuspected by conventional imaging. Management changes have been reported in up to 41% of patients on the basis of the results of whole-body studies. Whole-body FDG PET is also useful for the detection of recurrence. Several studies have indicated that the degree of FDG uptake in primary lung cancer can be used as an independent prognostic factor. Thus, whole-body FDG PET is clinically very useful in the management of lung cancer.

Positron emission tomography in cancer research and treatment

Positron emission tomography (PET), the imaging of pharmaceuticals labeled with positron-emitting radionuclides, is a rapidly growing modality for the diagnosis and management of cancer. PET yields high-quality images characterizing substrate metabolism, cellular proliferation, receptor density, and other parameters that can be used to identify cancer and evaluate its response to therapies. The technique mainly utilized in cancer management is FDG-PET, which exploits the abnormal glucose metabolism of cancer cells first characterized by Warburg. We discuss the principles of PET, the currently available instrumentation and radiopharmaceuticals, the efficacy of FDG-PET in the management of cancer, and the prospects for near-term advances in cancer using PET.

Positron emission tomography imaging in nonmalignant thoracic disorders

The role of the fluorodeoxyglucose (FDG) technique positron emission tomography (PET) is well established in the management of patients with lung cancer. Increasingly, it is becoming evident that FDG-PET can be effectively employed to diagnose a variety of benign pulmonary disorders. Knowledge of such applications further expands the domain of this powerful modality and further improves the ability to differentiate benign from malignant diseases of the chest. We describe pertinent technical factors that substantially contribute to optimal imaging of the thoracic structures. Particularly, the complementary role of attenuation correction (AC) to that of non-AC images is emphasized. We further outline the need for and the state of the art for co-registration of PET and anatomic images for diagnostic and therapeutic purposes. We then review patterns of physiologic uptake of FDG in thoracic structures, including the lung, the heart, the aorta and large arteries, esophagus, thymus, trachea, thoracic muscles, bone marrow, and joints and alterations following radiation therapy to the thorax. A great deal of information is provided with regard to differentiating benign from malignant nodules and in particular, we emphasize the role of dual time point imaging and partial volume correction for accurate assessment of such lesions. Following a brief review of the diagnostic issues related to the assessment of mediastinal adenopathies, the role of FDG-PET imaging in environment-induced lung diseases, including pneumoconiosis, smoking, and asthma are described. A large body of information is provided about the role of this technology in the management of patients with suspected infection and inflammation of the lungs such as acquired immunodeficiency syndrome, fever of unknown origin, sarcoidosis, chronic granulomatous disease and monitoring the disease process and response to therapy. Finally, the value of FDG-PET in differentiating benign from malignant diseases of the pleura including asbestosis-related disorders is described at the conclusion of this comprehensive review.

Positron emission tomography in lung cancer

Carcinoma of the lung is one of the most frequent malignancies and a major cause of mortality. The use of positron emission tomography (PET) has been extensively investigated in patients with carcinoma of the lung and has established clinical utility and cost-effectiveness in characterization of solitary pulmonary nodules and preoperative staging of carcinoma of the lung. Evolving applications in carcinoma of the lung include detection of recurrence, assessment of treatment response, radiotherapy planning, and prognosis. In addition, there is developing interest in combined anatomic/metabolic imaging and new tracer techniques, in particular gene expression imaging. This review aims to present existing data supporting the use of PET in carcinoma of the lung and to explore the evolving indications and future prospects of PET and lung cancer.

The usefulness of 18F-FDG PET images obtained 2 hours after intravenous injection in liver tumor

Liver tumors, especially hepatocellular carcinomas (HCCs), often exhibit no contrast with surrounding non-tumorous liver tissue in F-18-fluoro-2-deoxy-2-fluoro-D-glucose (FDG) positron emission tomography (PET) images obtained at the usual interval of one hour after intravenous FDG injection. We evaluated the usefulness of FDG PET studies of liver tumors performed 2 hours after intravenous injection.

METHODS AND MATERIALS

Fifteen pretherapeutic patients with 33 liver tumors were studied, including 11 patients with 18 HCCs, and 4 patients with 15 metastatic liver tumors (METAs) from 3 colorectal carcinomas and 1 esophageal carcinoma. After transmission scans, emission scans were obtained 45-55 minutes and 115-125 minutes after intravenous injection of 185-370 MBq FDG as early images and delayed FDG PET images, respectively. Visual analysis of early and delayed images was performed, and the FDG uptake in the tumor to that in nontumorous liver ratio (T/N ratio), the FDG uptake in tumor to that in soft-tissue ratio (T/S ratio) and the FDG uptake in non-tumorous liver to that in soft-tissue ratio (N/S ratio) were calculated for each image.

RESULTS

In visual analysis, visual improvement seen in images was observed in 6 of 18 HCC lesions and all 15 META lesions. In quantitative analysis, the mean T/S ratio and T/N ratio of HCCs in early images were 4.97 and 1.90, respectively, and those in delayed images were 6.24 and 2.20, respectively. The mean T/S ratio and T/N ratio of METAs in early images were 5.97 and 2.21, respectively, and those in delayed images were 6.99 and 3.80, respectively. The T/S ratio of HCCs and T/S ratio and T/N ratio of METAs were significantly higher in delayed images than in early images. The mean N/S ratios of HCC cases were 2.58 in the early images and 2.57 in the delayed images, but the ratio showed no constant tendency in the images. All N/S ratios of META cases were decreased in delayed images, although the significance of the difference between early and delayed images in N/S ratios was not analyzed because of the small number of cases.

CONCLUSION

FDG PET studies performed 2 hours after intravenous injection were useful for clear visualization of liver tumors, especially metastatic liver tumors.

From tumor biology to clinical Pet: a review of positron emission tomography (PET) in oncology

Cancer cells show increased metabolism of both glucose and amino acids, which can be monitored with 18F-2-deoxy-2-fluoro-D-glucose (FDG), a glucose analogue, and 11C-L-methionine (Met), respectively. FDG uptake is higher in fast-growing than in slow-growing tumors. FDG uptake is considered to be a good marker of the grade of malignancy. Several studies have indicated that the degree of FDG uptake in primary lung cancer can be used as a prognostic indicator. Differential diagnosis of lung tumors has been studied extensively with both computed tomography (CT) and positron emission tomography (PET). It has been established that FDG-PET is clinically very useful and that its diagnostic accuracy is higher than that of CT. Detection of lymph node or distant metastases in known cancer patients using a whole-body imaging technique with FDG-PET has become a good indication for PET. FDG uptake may be seen in a variety of tissues due to physiological glucose consumption. Also FDG uptake is not specific for cancer. Various types of active inflammation showed FDG uptake to a certain high level. Understanding of the physiological and benign causes of FDG uptake is important for accurate interpretation of FDG-PET. In monitoring radio/chemotherapy, changes in FDG uptake correlate with the number of viable cancer cells, whereas Met is a marker of proliferation. Reduction of FDG uptake is a sensitive marker of viable tissue, preceding necrotic extension and volumetric shrinkage. FDG-PET is useful for the detection of recurrence and for monitoring the therapeutic response of tumor tissues in various cancers, including those of the lung, colon, and head and neck. Thus, PET, particularly with FDG, is effective in monitoring cancer cell viability, and is clinically very useful for the diagnosis and detection of recurrence of lung and other cancers.