Dual-time point FDG PET imaging in the evaluation of pulmonary nodules with minimally increased metabolic activity

Semiquantitative analysis using whole-body dynamic F-18 fluoro-2-deoxy-glucose-positron emission tomography to differentiate between benign and malignant lesions

OBJECTIVES

To investigate whether whole-body dynamic positron emission tomography (PET) is useful for differentiating benign and malignant lesions.

METHODS

In this retrospective study, data from a cohort of 146 lesions from 187 patients who consecutively underwent whole-body dynamic PET scans at our hospital for suspected lesions in the lung, lymph nodes, liver, bone, esophagus, and colon were analyzed. Patients with malignant lymphomas, accumulations > 5 cm in length along the long axis of the esophagus, or lesions in the colon in which the site of accumulation moved during the imaging period were excluded. Patients were administered 3.7 MBq/kg of fluorine-18-fluorodeoxyglucose (F-18 FDG), and dynamic imaging was initiated 60 min after administration. We defined the 60-65, 65-70, 70-75, and 75-80 min time mark as the first, second, third, and fourth pass, respectively. The static image is the summed average of all the four pass images. We measured the accumulation in the mean image of the whole-body dynamic PET scan, which was arithmetically similar to the maximum standardized uptake value (SUVmax) throughout the whole-body static images obtained during 20 min of imaging (S-SUVmax). The ratio of SUVmax in the dynamic first pass(60-65 min after FDG administration) and fourth pass(75-80 min after FDG administration) was calculated as R-SUVmax.

RESULTS

The S-SUVmax in the lung, lymph nodes, and bone did not differ significantly between the benign and malignant groups. However, there was a significant difference in R-SUVmax, which was > 1 in most malignant lesions indicating an increase in accumulation during routine scan time. Significant differences were observed between benign and malignant lesions of the liver in both S-SUVmax and R-SUVmax values, with the latter being > 1 in most malignant lesions.

CONCLUSIONS

Whole-body dynamic PET for 20 min starting 1 h after FDG administration improved the accuracy of malignant lesion detection in the liver, lymph nodes, lung, and bone. The incremental improvement was small, and the FDG dynamics in the distribution of values between benign and malignant overlapped. Additional information from whole-body dynamic imaging can help detect malignant lesions in these sites without increasing patient burden or prolonging imaging time.

Performance of digital PET/CT compared with conventional PET/CT in oncologic patients: a prospective comparison study

PURPOSE

Digital PET systems (dPET) improve lesion detectability as compared to PET systems with conventional photomultiplier tubes (cPET). We prospectively studied the performance of high-resolution digital PET scans in patients with cancer, as compared with high- and standard-resolution conventional PET scans, taking the acquisition order into account.

METHODS

We included 212 patients with cancer, who were referred for disease staging or restaging. All patients underwent FDG-PET/CT on a dPET scanner and on a cPET scanner in a randomized order. The scans were acquired immediately after each other. Three image reconstructions were generated: 1) standard-resolution (4 × 4 × 4 mm³ voxels) cPET, 2) high-resolution (2 × 2 × 2 mm³ voxels) cPET, and 3) high-resolution dPET. Two experienced PET readers visually assessed the three reconstructions side-by-side and ranked them according to scan preference, in an independent and blinded fashion.

RESULTS

On high-resolution dPET, the PET readers detected more lesions or they had a higher diagnostic confidence than on high- and standard-resolution cPET (p < 0.001). High-resolution dPET was preferred in 90% of the cases, as compared to 44% for high-resolution cPET and 1% for standard-resolution cPET (p < 0.001). However, for the subgroup of patients where dPET was made first (n = 103, 61 ± 10 min after FDG administration) and cPET was made second (93 ± 15 min after FDG administration), no significant difference in preference was found between the high-resolution cPET and dPET reconstructions (p = 0.41).

CONCLUSIONS

DPET scanners in combination with high-resolution reconstructions clinically outperform cPET scanners with both high- and standard-resolution reconstructions as the PET readers identified more FDG-avid lesions, their diagnostic confidence was increased, and they visually preferred dPET. However, when dPET was made first, high-resolution dPET and high-resolution cPET showed similar performance, indicating the positive effect of a prolonged FDG uptake time. Therefore, high-resolution cPET in combination with a prolonged FDG uptake time can be considered as an alternative.

Evaluation of dual time-point fluorodeoxyglucose PET/computed tomography imaging in gastric cancer

BACKGROUND

We aimed to evaluate the efficiency of dual time-point fluorodeoxyglucose (FDG) PET/computed tomography (CT) imaging in detecting primary and metastatic lesions in gastric cancer.

METHODS

Between May 2019 and January 2020, 52 patients with gastric carcinoma were prospectively involved in our study. And dual time-point FDG PET/CT imaging performed to the patients. Of detected primary and metastatic lesions, the ones that are better visualized or only appear in delayed imaging were visually identified. Also, maximum standardized uptake value (SUVmax) of the primary and metastatic lesions and the intact liver tissue were measured in early and delayed imaging. Acquired SUVmax values and SUVmax ratios were compared statistically.

RESULTS

In delayed images, lesions were better visualized in 32 patients (61.5%) and extra lesions were detected in 4 patients (7.7%). SUVmax of primary tumor, SUVmax of liver metastases, SUVmax of lymph node metastases, primary tumor SUVmax/liver SUVmax ratio and lymph node metastasis SUVmax/liver SUVmax ratio were significantly higher in delayed images (P < 0.001, P = 0.022, P < 0.001, P < 0.001, P < 0.001, respectively). However, SUVmax of liver parenchyma was significantly lower in delayed images (P < 0.001).

CONCLUSIONS

There is a visually and statistically significant increase in the number and detectability of lesions seen in delayed images and dual time-point FDG PET/CT imaging seems useful in detecting primary and metastatic lesions in gastric cancer.

Diagnostic accuracy of visual analysis versus dual time-point imaging with 18F-FDG PET/CT for the characterization of indeterminate pulmonary nodules with low uptake

OBJECTIVE

To determine the accuracy of visual analysis and the retention index (RI) with dual-time point ¹⁸F-FDG PET/CT for the characterization of indeterminate pulmonary nodules (IPN) with low FDG uptake.

MATERIALS AND METHODS

A retrospective analysis was performed on 43 patients (28 men, 64 ± 11 years old, range 36-83 years) referred for IPN characterization with ¹⁸F-FDG-PET/CT and maximum standard uptake value ≤ 2.5 at 60 minutes post-injection (SUV_max1). Nodules were analyzed by size, visual score for FDG uptake on standard (OSEM 2,8) and high definition (HD) reconstructions, SUV_max1, SUV_max at 180 minutes post-injection (SUV_max2), and RI was calculated. The definitive diagnosis was based on histopathological confirmation (n = 28) or ≥ 2 years of follow-up.

RESULTS

Twenty-four (56%) nodules were malignant. RI ≥ 10% on standard reconstruction detected 18 nodules that would have been considered negative using the standard SUV_max ≥ 2.5 criterion for malignancy. RI ≥ 10% had a sensitivity, specificity, PPV, NPV and accuracy of 75, 73.7, 78.3, 70, and 74.4%, respectively, while for FDG uptake > liver on HD these were 79.1, 63.2, 73.1, 70.6, and 72.1%, respectively. SUV_max1 ≥ 2, SUV_max2 > 2.5 and FDG uptake > liver on standard reconstruction had a PPV of 100%. FDG uptake > mediastinum on HD had a NPV of 100%.

CONCLUSIONS

RI ≥ 10% was the most accurate criterion for malignancy, followed by FDG uptake > liver on HD reconstruction. On standard reconstruction, SUV_max1 ≥2 was highly predictive of malignancy, as well as SUV_max2 > 2.5 and FDG uptake > liver. FDG uptake < mediastinum on HD was highly predictive of benign nodules.

The role of 18F-Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography (FDG PET/CT) in assessment of complex invasive fungal disease and opportunistic co-infections in patients with acute leukemia prior to allogeneic hematopoietic cell transplant

INTRODUCTION

Individuals diagnosed with acute lymphoid and myeloid malignancies are at significant risk of invasive fungal and bacterial infections secondary to their marked immunocompromised states with a significant high risk of mortality. The role of metabolic imaging with 18F-Fluorodeoxyglucose (FDG) Positron Emission Tomography/Computed Tomography (PET/CT) has been increasingly recognized in optimizing the diagnosis of invasive infection, monitoring the response to therapy and guiding the duration of antimicrobial therapy or need to escalate to surgical intervention.

METHODS

Two distinct cases of pulmonary co-infection of rare fungal and bacterial pathogens are explored in severely immunocompromised individuals where FDG PET/CT aided both patients to make a full recovery and transition to HCT. The first case explores mixed Scedosporium apiospermum and Rhizomucor pulmonary infection on a background of T cell/myeloid mixed phenotype acute leukemia ultimately warranting long-term antifungal therapy and lobectomy prior to HCT. The second case explores Fusarium and Nocardia pulmonary infection on a background of relapsed AML also warranting surgical resection with lobectomy and long-term antimicrobials prior to transition to HCT.

DISCUSSION

The cases highlight the utility of FDG PET/CT to support the diagnosis of infections, including the presence or absence of disseminated infection, and to provide highly sensitive monitoring of the infection over time. FDG PET/CT played a key role in directing therapy duration decisions and prompted the necessity for surgical intervention. Ultimately, the use of FDG PET/CT allowed for a successful transition to HCT highlighting its value in this clinical setting.

CONCLUSION

FDG PET/CT has an emerging role in the diagnostic and monitoring pathway for complex infections in high-risk immunocompromised patients.

Renal Medullary Carcinoma on Dual-Time Point FDG PET/CT Imaging

Renal medullary carcinoma is a rare and highly aggressive tumor seen almost exclusively in young individuals of African descent with sickle cell disease. Here, we describe a case of a 29-year-old man, who did not have sickle cell disease, with pathologically confirmed renal medullary carcinoma using dual-time FDG PET/CT.

Glucose-6-phosphatase Expression-Mediated [18F]FDG Efflux in Murine Inflammation and Cancer Models

PURPOSE

2-Deoxy-2-[¹⁸F]fluoro-D-glucose ([¹⁸F]FDG) accumulation in inflammatory lesions can confound the diagnosis of cancer. In this study, we investigated [¹⁸F]FDG accumulation and efflux in relation to the genes and proteins involved in glucose metabolism in murine inflammation and cancer models.

PROCEDURES

[¹⁸F]FDG accumulation and [¹⁸F]FDG efflux were measured in cancer cells (breast cancer, glioma, thyroid cancer, and hepatoma cells) and RAW 264.7 cells (macrophages) activated with lipopolysaccharide (LPS). The levels of mRNA expression were measured by real-time quantitative PCR (qPCR). The expression of glucose metabolism-related proteins was detected by western blotting. Dynamic [¹⁸F]FDG positron emission tomography-computed tomography (PET/CT) images were acquired for 2 h in tumor-bearing BALB/c nude mice and inflammatory mice induced by turpentine oil.

RESULTS

[¹⁸F]FDG accumulation in MDA-MB-231 (breast cancer) increased with time, but that of HepG2 (hepatoma) reached a constant level after 120 min. [¹⁸F]FDG efflux in HepG2 was faster than that in MDA-MB-231. HepG2 strongly expressed glucose-6-phosphatase (G6Pase) compared with MDA-MB-231. [¹⁸F]FDG accumulation increased with time, and [¹⁸F]FDG efflux accelerated after the activation of RAW 264.7 cells. The expression levels of G6Pase, glucose transporter1 and glucose transporter3 (GLUT1 and GLUT3), and hexokinase II (HK II) increased after the activation of RAW 264.7 cells. [¹⁸F]FDG efflux in activated macrophages was faster than that in MDA-MB-231 cancer cells. MDA-MB-231 strongly expressed HK II protein compared with the activated RAW 264.7. In murine models, [¹⁸F]FDG accumulation in MDA-MB-231 cancer and inflammatory lesions increased with time, but that in HepG2 tumor increased until 20-30 min (SUVmeans ± SD (tumor/muscle), 3.0 ± 1.3) and then decreased (2.1 ± 0.9 at 110-120 min).

CONCLUSIONS

There was no difference in the pattern of [¹⁸F]FDG accumulation with time in MDA-MB-231 tumors and inflammatory lesions. We found that [¹⁸F]FDG efflux accelerated in activated macrophages reflecting increased G6Pase expression after activation and lower expression of HK II protein than that in MDA-MB-231 cancer cells.

Concurrent Pancreatic Metastasis From Lung Adenocarcinoma and Primary Cholangiocarcinoma on FDG PET/CT Imaging

A 67-year-old man with a history of left upper lobe resection of poorly differentiated adenocarcinoma 1 year ago underwent FDG PET/CT for restaging. The images demonstrated a round cystic lesion with peripheral FDG uptake and centrally photopenic region. Additional focus of increased activity was detected in the left lobe of the liver. The patient underwent the Whipple and partial hepatectomy. The surgical pathology demonstrated concurrently the metastasis to the pancreas from the lung adenocarcinoma and a primary moderately differentiated cholangiocarcinoma.

Solitary pulmonary nodule evaluation in regions endemic for infectious diseases: Do regional variations impact the effectiveness of fluorodeoxyglucose positron emission tomography/computed tomography

BACKGROUND

Fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT) has become a preferred imaging modality for the evaluation of solitary pulmonary nodule (SPN), particularly in the developed world. Since FDG can concentrate in infective/inflammatory lesions, the diagnostic utility of FDG-PET can be questioned, particularly in regions endemic for infectious decisions.

AIM

To evaluate the accuracy of FDG-PET/CT in evaluation of SPNs in a population endemic for infectious disease and to assess if regional variations have an impact on its effectiveness.

MATERIALS AND METHODS

All patients who underwent an FDG/PET-CT with a clinico-radiological diagnosis of SPN categorized as indeterminate were included. Based on a maximum standardized uptake values (SUVmax) cut-off of 2.5, lesions were classified as benign (<2.5) or malignant (>2.5) and compared with gold standard histopathology. The diagnostic accuracy of PET-CT to detect malignancy was calculated. On the basis of final histopathology, lesions were grouped as (a) malignant nodules (b) infective/granulomatous nodules with a specific diagnosis and (c) nonspecific inflammatory nodules. The SUVmaxbetween these groups was compared using nonparametric statistical tests.

RESULTS

A total of 191 patients (129 males, 62 females) with a median age of 64 years (range: 36-83) were included. Totally, 144 nodules (75.3%) were malignant and 47 were benign (24.7%). Adenocarcinoma (n = 84) was the most common malignancy. Tuberculosis (n = 16) and nonspecific infections (n = 24) were the two most common benign pathologies. There was a significant overlap in the metabolic uptake of malignant (median SUVmax-11.2, range: 3.3-34.6) and tuberculous nodules (median SUVmax-10.3, range: 2.7-22.5) with no statistically difference between their SUVmaxvalues (P = 0.43). The false-positive rate was 65.2% and the false-negative rate was 5.5%. The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of FDG-PET/CT for detecting malignancy were 94.4%, 34.7%, 81.9%, 66.6%, and 79.5%, respectively.

CONCLUSIONS

Though FDG-PET scans show a very high sensitivity for malignant nodules, it has a high false-positive rate and reduced specificity when characterizing SPNs in an infectious endemic region. Physicians must be aware of this limitation in the workup of lung nodules, and regional variations must be considered before further management decisions are taken.

Normal Variants and Pitfalls Encountered in PET Assessment of Gynecologic Malignancies

Combined PET/computed tomography is used for oncological indications. PET/computed tomography benefits from the metabolic information of PET and the anatomic localization of computed tomography. The integrated scanner provides data with accurate registration of anatomy and molecular information. Many physiologic conditions, normal variants, and benign lesions within the pelvis and the body can cause confusion and uncertainty. False-negative results owing to low ¹⁸F-fluorodeoxyglucose uptake from the tumor can produce diagnostic challenges and inaccurate conclusions. This article reviews normal variants and potential pitfalls encountered in PET assessment of gynecologic malignancies to provide useful information for the referring and reporting physicians.

Prognostic significance of retention index of bone marrow on dual-phase 18F-fluorodeoxyglucose positron emission tomography/computed tomography in patients with diffuse large B-cell lymphoma

The purpose of this study was to determine the prognostic significance of F-18 fluorodeoxyglucose (FDG) uptake on a dual-phase positron emission tomography/computed tomography (PET/CT), focusing on the increment in maximal standardized uptake value (SUVinc) of tumor and bone marrow (BM) between initial and delayed phase images and retention index (RI) of tumor and BM, in patients with diffuse large B-cell lymphoma (DLBCL).From September 2009 to January 2013, 70 patients (37 males and 33 females, aged 60.6 ± 17.5 years) with DLBCL who had undergone dual-phase FDG PET/CT scans for pretreatment staging were enrolled. The patients subsequently received combination chemotherapy with rituximab. The dual-phase SUV, including SUVinc of tumor (SUVinc-t), RI of tumor (RI-t), SUVinc of BM, and RI of BM were measured. The clinical observation period was from September 2009 to December 2014. Both univariate and multivariate analyses were then used to assess the prognostic significance of SUVinc, RI, international prognostic index (IPI), gender, age, clinical stage, and laboratory tests.The median follow-up time was 35.5 months. The 3-year overall survival (OS) for patients with low/high SUVinc-t (cut-off 2.0) and for patients with low/high RI-t (cut-off 20) were 87.5%/ 62.1% (P = .08) and 83.3%/ 62.7% (P = .14), respectively. The 3-year OS for patients with SUVinc-i < 0.35 and for those with SUVinc-i ≥ 0.35 were 73.2% and 53.3%, respectively (P = .10). The 3-year OS for patients with RI-i < 45 and for those with RI-i ≥ 45 were 72.7% and 37.5%, respectively (P = .02). Subsequently, the Cox multivariate forward proportional hazards model revealed that a higher RI-i (hazard ratio: 4.49; 95% confidence interval: 1.64-12.32; P = .0035) and IPI were independent prognostic factors affecting OS.For patients with DLBCL, an elevated RI-i (≥45) was a predictor for shorter OS, independent of IPI score. It added to the value of pretreatment dual-phase FDG PET/CT scans.

18F-Fluoro-2-Deoxy-d-Glucose PET/Computed Tomography Evaluation of Lung Cancer in Populations with High Prevalence of Tuberculosis and Other Granulomatous Disease

Pulmonary tuberculosis infects one-third of world's population and is responsible for the high mortality and morbidity in developing countries. The presence of a high number of macrophages and lymphocytes in active tuberculosis granulomas is associated with high uptake of ¹⁸F-fluoro-2-deoxy-d-glucose on PET imaging mimicking lung cancer. In many cases, radiological features of pulmonary tuberculosis are undistinguishable from lung cancer, which makes the diagnosis difficult. Clinical history and computed tomographic (CT) findings on a hybrid PET/CT are as important as findings on a PET in the diagnosis of lung cancer.

Dual-time point 18F-FDG-PET and PET/CT for Differentiating Benign From Malignant Musculoskeletal Lesions: Opportunities and Limitations

In this review, we summarize the false-positive and false-negative results of standard ¹⁸F-FDG-PET/CT in characterizing musculoskeletal lesions and discussed the added value and limitations of dual-time point imaging (DTPI) and delayed imaging in differentiating malignant from benign musculoskeletal lesions, based on review of the peer-reviewed literature. The quantitative and semiquantitative parameters adopted for DTPI are standardized uptake value (mainly maximum standardized uptake value [SUVmax]) and retention index (RI), calculated as RI (%) = 100% × (SUV [maxD-Delayed] - SUV [maxE-Early])/SUV [maxE-Early], although the criteria and cutoff for diagnosing malignancy in studies have varied considerably. Also, there has been considerable heterogeneity in protocol (time point of delayed imaging), interpretation, and results in dual-time point (DTP) ¹⁸F-FDG-PET for differentiating malignant from benign musculoskeletal lesions in various research studies. The specificity of DTPI is a function of many factors such as the nature of the musculoskeletal lesion or malignancy in question, the prevalence of false-positive etiologies in the patient population, and the cutoff values (either SUVmax or RI) employed to define a malignancy. Despite the apparent conflicting reports on the performance, there have been certain common points of agreement regarding DTPI: (1) DTP PET increases the sensitivity of ¹⁸F-FDG-PET/CT due to continued clearance of background activity and increasing ¹⁸F-FDG accumulation in malignant lesions, when the same diagnostic criteria (as in the initial standard single-time point imaging) are used. Increased sensitivity for lesion detection can be viewed as a strong point of DTP and delayed-time point imaging. (2) The causes for false positives (such as active infectious or inflammatory lesions and locally aggressive benign tumors) and false negatives (eg, low-grade sarcomas) are the major hurdles accounting for reduced diagnostic value of the technique, with overlap of ¹⁸F-FDG uptake patterns between benign and malignant musculoskeletal lesions on DTPI. (3) DTPI, however, could still be potentially useful in increasing the confidence of interpretation such as differentiating malignancy from sites of inactive or chronic inflammation, post-treatment viable residue vs necrosis, and certain other benign lesions. (4) Consideration of diagnostic CT component of PET/CT and the patient's clinical picture can lead to increase in specificity of interpretation in a given case scenario. Further systematic research, adoption of uniform protocol, and interpretation criterion could evolve the specific indications and interpretation criteria of DTPI for improved diagnostic accuracy in musculoskeletal lesions and its clinical applications.

Relationship Between Dual Time Point FDG PET/CT and Clinical Prognostic Indexes in Patients with High Grade Lymphoma: a Pilot Study

Purpose

This study investigated the correlative relationship between metabolic parameters estimated from dual time point 2-deoxy-2-[¹⁸F] fluoro-D-glucose (¹⁸F-FDG) positron emission tomography/computerized tomography (PET/CT) and the clinical tools predicting the outcome of a lymphoma. We also measured metabolic and volumetric alterations between early and delayed ¹⁸F-FDG PET/CT in patients with high grade lymphoma (HGL).

Methods

The samples were 122 lymph nodes and extralymphatic lesions from 26 patients diagnosed with HGL. All patients were applied to the International Prognostic Index (IPI), Ann Arbor stage, and revised IPI as clinical prognostic parameters. ¹⁸F-FDG dual time point PET/CT (DTPFP) consisted of an early scan 1 h after ¹⁸F-FDG injection and a delayed scan 2 h after the early scan. Based on an analysis of DTPFP, we estimated the standardized uptake value (SUV) of tumors from the early and delayed scans, retention index (RI) representing the percentage change between early and delayed SUV, and metabolic volume different index (MVDI) calculated using metabolic tumor volumes (MTV).

Results

RI_max showed a multiple positive correlative relationship with stage and IPI in lesion-by-lesion analysis (p < 0.01). In the case of IPI, the high risk group exhibited higher RI_max than the low risk group (p = 0.004). In the case of revised IPI, the RI_max of the low risk group were significantly lower than the intermediate and high risk groups, respectively (p < 0.01). The MVDIs of the best outcome group were decreased in comparison to the moderate outcome group (p = 0.029). There was a significant negative correlative relationship between RI_max and MVDI, and the inclinations for decreased MVDIs were slightly associated with increased RIs.

Conclusions

RI_max extracted from DTPFP had a significant relationship to extranodal involvement, staging, IPI, and revised IPI. MVDI showed significant negative correlation with RI_max. Further large scale studies are warranted to support and extend these preliminary results.

Primary Pulmonary Artery Sarcoma on Dual-Time Point FDG PET/CT Imaging

A 59-year-old man presented cough, chest pain, and shortness of breath for 2 weeks and fever for 4 days. A contrast chest CT revealed a large right pulmonary artery filling defect, suggestive of pulmonary embolism that failed to respond to anticoagulation therapy. FDG PET/CT was performed to evaluate possible malignancy, which revealed intense activity in the right main pulmonary artery without any extrathoracic abnormality. The ratio of the SUVmax of this lesion to the liver was significantly increased in the delayed PET images. The pathological examination demonstrated primary pulmonary artery sarcoma.

The role of PET/CT as a prognosticator and outcome predictor in lung cancer

Positron emission tomography/computed tomography (PET/CT) is an important imaging tool for management of lung cancer and can be utilized in diagnosis, staging, restaging, treatment planning and evaluating treatment response. In the past decade PET/CT has proven to be beneficial for the prediction of prognosis and outcome. PET findings before and after treatment, the quantitative PET parameters such as standardized uptake value (SUV), metabolic tumor volume (MTV), and total lesion glycolysis (TLG) as well as delayed PET/CT imaging can be used to determine patient prognosis and outcome. Other tracers such as hypoxia and proliferation marker tracers may be used for prognostication. The prognostic factors derived from PET/CT imaging help early development of risk-adapted treatment strategies, which provides cost-effective treatment and leads to improved patient management. Here, we discuss findings of studies related to application of PET/CT in lung cancer as well as some technical updates on quantitative PET/CT in lung cancer.

Dual-time-point 18F-FDG PET/CT in the diagnosis of solitary pulmonary lesions in a region with endemic granulomatous diseases

OBJECTIVE

Granulomatous diseases (GDs) can be metabolically active and indistinguishable from lung cancer on ¹⁸F-fluorodeoxyglucose positron emission tomography (¹⁸F-FDG PET) imaging. Evaluation of solitary pulmonary lesions remains a diagnostic challenge in regions with endemic GD. This study sought to determine the efficacy of dual-time-point (DTP) ¹⁸F-FDG PET/computed tomography (CT) imaging in diagnosing solitary pulmonary lesions from such regions.

METHODS

A total of 50 patients with solitary pulmonary nodules or masses with confirmed histopathological diagnoses underwent DTP ¹⁸F-FDG PET/CT imaging at 1 and 3 h after tracer injection. The maximum standardized uptake value (SUV_max) on early and delayed scans (SUV_1h and SUV_3h, respectively) and retention index (RI) were calculated for each pulmonary lesion. Receiver operating characteristic analysis was performed to evaluate the discriminating validity of the parameters.

RESULTS

There were 37 malignant and 13 benign solitary pulmonary lesions. Eight of the 13 (62 %) benign lesions were GDs. The sensitivity/specificity/accuracy of SUV_1h, SUV_3h and RI were 84/69/80 %, 84/85/84 %, and 81/54/74 %, respectively. SUV_3h had the best diagnostic performance, especially regarding specificity. The values of SUV_1h and SUV_3h were significantly different between malignant lesions and GD, while the RI values of malignant lesions and GD were both high (18.6 ± 19.5 and 18.7 ± 15.3 %, respectively; P = not significant).

CONCLUSION

SUV_3h appeared to improve the diagnostic specificity of ¹⁸F-FDG PET/CT in evaluating solitary pulmonary lesions from regions with endemic GD.

Standardized Uptake Values from PET/MRI in Metastatic Breast Cancer: An Organ-based Comparison With PET/CT

Quantitative standardized uptake values (SUVs) from fluorine-18 (18F) fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) are commonly used to evaluate the extent of disease and response to treatment in breast cancer patients. Recently, PET/magnetic resonance imaging (MRI) has been shown to qualitatively detect metastases from various primary cancers with similar sensitivity to PET/CT. However, quantitative validation of PET/MRI requires assessing the reliability of SUVs from MR attenuation correction (MRAC) relative to CT attenuation correction (CTAC). The purpose of this retrospective study was to assess the utility of PET/MRI-derived SUVs in breast cancer patients by testing the hypothesis that SUVs derived from MRAC correlate well with those from CTAC. Between August 2012 and May 2013, 35 breast cancer patients (age 37-78 years, 1 man) underwent clinical 18F-FDG PET/CT followed by PET/MRI. One hundred seventy metastases were seen in 21 of 35 patients; metastases to bone in 16 patients, to liver in seven patients, and to nonaxillary lymph nodes in eight patients were sufficient for statistical analysis on an organ-specific per patient basis. SUVs in the most FDG-avid metastasis per organ per patient from PET/CT and PET/MRI were measured and compared using Pearson's correlations. Correlations between CTAC- and MRAC-derived SUVmax and SUVmean in 31 metastases to bone, liver, and nonaxillary lymph nodes were strong overall (ρ = 0.80, 0.81). SUVmax and SUVmean correlations were also strong on an organ-specific basis in 16 bone metastases (ρ = 0.76, 0.74), seven liver metastases (ρ = 0.85, 0.83), and eight nonaxillary lymph node metastases (ρ = 0.95, 0.91). These strong organ-specific correlations between SUVs from PET/CT and PET/MRI in breast cancer metastases support the use of SUVs from PET/MRI for quantitation of 18F-FDG activity.

Dual time-point (18)F-FDG PET/CT to assess response to radiofrequency ablation of lung metastases

AIM

To establish the usefulness of dual time-point PET/CT imaging in determining the response to radiofrequency ablation (RFA) of solitary lung metastases from gastrointestinal cancer.

MATERIALS AND METHODS

This prospective study included 18 cases (3 female, 15 male, mean age 71±15 yrs) with solitary lung metastases from malignant digestive tract tumors candidates for RFA. PET/CT images 1h after injection of 4.07MBq/kg of (18)F-FDG (standard images) were performed at baseline, 1 month, and 3 months after RFA. PET/CT images 2h after injection centered in the thorax at 1 month after RFA were also performed (delayed images). A retention index (RI) of dual time-point images was calculated as follows: RI=(SUVmax delayed image-SUVmax standard image/SUVmax standard image)*100. Pathological confirmation of residual tumor by histology of the treated lesion was considered as local recurrence. A negative imaging follow-up was considered as complete response.

RESULTS

Local recurrence was found in 6/18 lesions, and complete response in the remaining 12. The mean percentage change in SUVmax at 1 month and at 3 months showed a sensitivity and specificity for PET/CT of 50% and 33%, and 67% and 92%, respectively. The RI at 1 month after RFA showed a sensitivity and specificity of 83% and 92%, respectively.

CONCLUSIONS

Dual time point PET/CT can predict the outcome at one month after RFA in lung metastases from digestive tract cancers. The RI can be used to indicate the need for further procedures to rule out persistent tumor due to incomplete RFA.

Dual-time-point Imaging and Delayed-time-point Fluorodeoxyglucose-PET/Computed Tomography Imaging in Various Clinical Settings

The techniques of dual-time-point imaging (DTPI) and delayed-time-point imaging, which are mostly being used for distinction between inflammatory and malignant diseases, has increased the specificity of fluorodeoxyglucose (FDG)-PET for diagnosis and prognosis of certain diseases. A gradually increasing trend of FDG uptake over time has been shown in malignant cells, and a decreasing or constant trend has been shown in inflammatory/infectious processes. Tumor heterogeneity can be assessed by using early and delayed imaging because differences between primary versus metastatic sites become more detectable compared with single time points. This article discusses the applications of DTPI and delayed-time-point imaging.

Imaging observations of pulmonary inflammatory myofibroblastic tumors in patients over 40 years old

Pulmonary inflammatory myofibroblastic tumors (PIMTs) are extremely rare in adults. If occurring in patients >40 years old, PIMT should be rapidly distinguished from lung cancer. The present study aimed to characterize the imaging features of PIMT in patients >40 years old in order to improve the diagnosis of PIMT. The imaging data of 10 patients with PIMT were reviewed retrospectively. Of the patients, eight underwent computed tomography (CT), two underwent positron emission tomography (PET)/CT and four underwent single-photon emission computed tomography (SPECT). Unenhanced CT revealed 10 lesions with a maximum diameter ranging between 5 and 57 mm located in the lower (n=6) or upper (n=4) lobe, in a peripheral (n=9) or central (n=1) region, and that were well- (n=4) or ill-defined (n=6), and round to oval (n=5) or irregular (n=5) in shape. Calcification (n=3), necrosis (n=6), cavity (n=4), air bronchogram (n=6) and obstructive pneumonia (n=1) were also observed in the patients. Contrast-enhanced CT revealed six lesions with moderate to high contrast enhancement in the arterial and venous phases, including four lesions with delayed enhancement. PET/CT identified two lesions with increased tracer uptake that were homogeneous and heterogeneous and each exhibited a maximal standard uptake value (SUV_max) of 6.0 and 5.4, respectively. The delayed PET/CT revealed foci that each exhibited an increased SUV_max of 6.9 and 5.9, respectively. SPECT demonstrated no definitive bone metastases, but did reveal atypical hypertrophic pulmonary osteoarthropathy in one patient. The combined imaging methods may lead to a more precise evaluation of PIMT in patients >40 years old.

Positron emission tomography/computed tomography for bone tumors (Review)

The aim of the present study was to investigate positron emission tomography (PET)/computed tomography (CT) and its applications for the diagnosis and treatment of bone tumors. The advantages and disadvantages of PET/CT were also evaluated and compared with other imaging methods and the prospects of PET/CT were discussed. The PubMed, Medline, Elsevier, Wanfang and China International Knowledge Infrastructure databases were searched for studies published between 1995 and 2013, using the terms 'PET/CT', 'positron emission tomography', 'bone tumor', 'osteosarcoma', 'giant cell bone tumor' and 'Ewing sarcoma'. All the relevant information was extracted and analyzed. A total of 73 studies were selected for the final analysis. The extracted information indicated that at present, PET/CT is the imaging method that exhibits the highest sensitivity, specificity and accuracy. Although difficulties and problems remain to be solved, PET/CT is a promising non-invasive method for the diagnostic evaluation of and clinical guidance for bone tumors.

Tumour and lymph node uptakes on dual-phased 2-deoxy-2-[18F]fluoro-D-glucose positron emission tomography/computed tomography correlate with prognostic parameters in breast cancer

OBJECTIVES

To examine correlations between the uptake of 2-deoxy-2-[18F]fluoro-D-glucose (FDG) by primary tumours and axillary lymph nodes, and clinical and biological tumour prognostic parameters, in patients with newly diagnosed breast cancer.

METHODS

Newly diagnosed breast cancer patients who had received a dual-phased FDG positron emission tomography/computed tomography scan for pretreatment staging were enrolled retrospectively. Maximal standardized uptake values at 1 h (SUV1), 2 h (SUV2), and retention indices (RI) of the tumours and ipsilateral axillary lymph nodes were measured. SUV and RI were compared with clinical and biological prognostic parameters.

RESULTS

A total of 32 patients participated in the study. Tumour FDG uptake correlated with histological grade and tumour size. FDG uptake in axillary lymph nodes correlated positively with lymph node status, metastasis status and clinical stage. RI values for the tumour and lymph nodes were significantly positively correlated with human epidermal growth factor receptor-2 positivity.

CONCLUSIONS

FDG uptake in tumours and lymph nodes showed correlations with some clinical and biological parameters, and may serve as a predictive marker of tumour biological behaviour in breast cancer.

Hepatoid adenocarcinoma of the stomach: dual-time-point (18)F-FDG PET/CT findings

Hepatoid adenocarcinoma of the stomach (HAS) is a rare distinct variant of gastric carcinoma with earlier metastases and worse prognosis compared to the more common intestinal types. It is often misdiagnosed as hepatocellular carcinoma, especially when primary HAS is insignificantly anatomically abnormal, produces high alpha-fetoprotein and develops early liver metastasis. In this case we show the significance of dual-time-point (18)F-fluorodeoxyglucose positron emission tomography (PET)/computed tomography (CT) in accurately diagnosing and staging HAS.

Predictive value of 18F-fluorodeoxyglucose positron emission tomography - computed tomography compared to postoperative pathological findings for patients with non-small-cell lung cancer

This study was conducted to investigate the predictive value of ¹⁸F-fluorodeoxyglucose positron emission tomography-computed tomography (¹⁸F-FDG PET-CT) in patients with non-small-cell lung cancer (NSCLC), compared to that of postoperative pathological findings, for T and N staging and the associations of the metabolic parameters of the primary tumor with histological type and differentiation. The preoperative contrast-enhanced CT and ¹⁸F-FDG PET-CT and postoperative pathological findings of 112 NSCLC patients treated with lobectomy or pneumonectomy combined with systematic mediastinal lymphadenectomy were retrospectively reviewed. Compared to the postoperative pathological findings, the effect of contrast-enhanced CT and ¹⁸F-FDG PET-CT on T and N staging were evaluated. The metabolic tumor volume (MTV) and maximum standardized uptake value (SUVmax) of the primary tumor were measured. The associations between these metabolic parameters and histological type and differentiation were also evaluated. The differences in the accuracy in overall staging and T staging between PET-CT and contrast-enhanced CT were significant (91.1 vs. 69.6%, P=0.000; and 92.9 vs. 76.8%, P=0.000, respectively). The sensitivity, specificity, positive predictive value, negative predictive value and accuracy of regional lymph node metastasis detection were 91.7, 93.0, 86.5, 95.8 and 92.6%, respectively, with PET-CT; and 71.3, 77.2, 60.6, 84.5 and 75.2%, respectively, with contrast-enhanced CT. The SUVmax (7.29±1.83 vs. 5.91±1.65, t=4.15, P=0.000) and MTV (48.20±22.47 vs. 30.21±19.72 cm³, t=4.48, P=0.000) were significantly higher for squamous cell carcinoma (SCC) compared to those for adenocarcinoma (AC). There was a positive correlation between the MTV and SUVmax of the primary tumor (Pearson's r=0.838, P=0.000). Significant differences were observed among differentiation subgroups in the SUVmax and MTV of the primary tumor for both SCC and AC. In conclusion, compared to the postoperative pathological findings, the predictive value of ¹⁸F-FDG PET-CT for T and N staging in NSCLC was higher compared to that of contrast-enhanced CT. The FDG uptake of the primary tumor was associated with histological type and differentiation and the difference was statistically significant. Therefore, the SUVmax and MTV of the primary tumor may be valuable indices to partly predict the histological type and grade of differentiation of NSCLC.

Serial changes of FDG uptake and diagnosis of suspected lung malignancy: a lesion-based analysis

OBJECTIVE

This study prospectively evaluates the serial change of FDG uptake and its diagnostic value in malignant versus benign lung lesions in patients with suspected lung cancer.

PATIENTS AND METHODS

Patients with suspected lung malignancy underwent whole-body FDG PET/CT at 1, 2, and 3 hours after an IV injection of F-FDG. The SUVs of FDG in lung nodules and hilar/mediastinal nodes at each time point were correlated with biopsy/surgical pathologic findings.

RESULTS

There were a total of 45 malignant lesions and 80 benign lesions from 43 patients with pathologic diagnosis that were included for analysis. The SUVmax had an average of 25.5% increase in all tumor-positive lesions from 1 to 2 hours (vs 1.6% decrease in all tumor-negative lesions, P < 0.0001) and an average of 39.1% increase from 1 to 3 hours (vs 4.5% increase in all tumor-negative lesions, P < 0.0001). The receiver operating characteristic analysis showed that the 2-hour and 3-hour SUVmax had similar area under the curve and outperformed the SUVmax on the 1-hour initial imaging or retention index (RI). The optimal cutoff values to differentiate malignancy from benign lesions were 3.24 for 1-hour SUVmax, 3.67 for 2-hour SUVmax, and 4.21 for 3-hour SUVmax, with 11.6% for 1- to 2-hour RI and 23.9% for 1- to 3-hour RI. The 3-hour delayed SUVmax of 4.21 provided the best overall performance (accuracy of 88.8%). The analysis of the lesion-to-background ratio revealed that delayed imaging improved the image quality significantly, leading to much easier detection of either malignant or benign lesions.

CONCLUSIONS

Multiple time point FDG PET/CT imaging moderately improves the diagnostic accuracy of lung cancer and significantly improves the image quality.

Imaging of solitary pulmonary nodule-a clinical review

Current widespread use of cross-sectional imaging has led to exponential rise in detection of solitary pulmonary nodules (SPNs). Whilst large numbers of these are benign 'incidentalomas', lung cancers presenting as SPNs are often early disease, which have good prognosis. Therefore, there is rising demand and expectation for more accurate, non-invasive, diagnostic tests to characterize SPNs, aiming to avoid missed or delayed diagnosis of lung cancer. There are wide differential diagnoses of benign and malignant lesions that manifest as SPNs. On conventional imaging, the morphological features supporting benignity include stable small nodule size, smooth demarcated margins, and calcifications. Lack of significant contrast enhancement is also more suggestive of benign nodules. With improved understanding of tumor biology, for instance neo-vascularization and increased vascular permeability, imaging techniques such as dynamic contrast-enhanced computed tomography (CT) provide details on contrast uptake and wash-out kinetics, which is more closely reflecting the physiological and pathological phenomena. Positron emission tomography (PET) using 18fluorine-fluoro-deoxyglucose ((18)F-FDG) is a well-established functional imaging technique, for which one of the most common indications is differentiating between benign and malignant SPNs. Combined PET-CT integrates the anatomical, morphological and metabolic aspects in a single examination, improving overall diagnostic accuracy. Semi-quantitative analysis in FDG-PET imaging is based on measurement of maximum standardized uptake values (SUVmax). SUVmax analysis may become more useful as an assessment of tumor biology in future risk stratification models for cancers. Dual-time point FDG-PET imaging, dual-energy CT, perfusion CT, magnetic resonance (MR) imaging using dynamic contrast enhancement or diffusion-weighted imaging (DWI) techniques, are among the growing armamentarium for diagnostic imaging of SPNs. Provided there is no unacceptably high procedural or operative risk, tissue diagnosis by resection or percutaneous biopsy of SPN should be advocated in those patients identified as at moderate or high risk of malignancy, based on clinical stratification.

18F-FDG PET/CT oncologic imaging at extended injection-to-scan acquisition time intervals derived from a single-institution 18F-FDG-directed surgery experience: feasibility and quantification of 18F-FDG accumulation within 18F-FDG-avid lesions and background tissues

Background

¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography/computed tomography (PET/CT) is a well-established imaging modality for a wide variety of solid malignancies. Currently, only limited data exists regarding the utility of PET/CT imaging at very extended injection-to-scan acquisition times. The current retrospective data analysis assessed the feasibility and quantification of diagnostic ¹⁸F-FDG PET/CT oncologic imaging at extended injection-to-scan acquisition time intervals.

Methods

¹⁸F-FDG-avid lesions (not surgically manipulated or altered during ¹⁸F-FDG-directed surgery, and visualized both on preoperative and postoperative ¹⁸F-FDG PET/CT imaging) and corresponding background tissues were assessed for ¹⁸F-FDG accumulation on same-day preoperative and postoperative ¹⁸F-FDG PET/CT imaging. Multiple patient variables and ¹⁸F-FDG-avid lesion variables were examined.

Results

For the 32 ¹⁸F-FDG-avid lesions making up the final ¹⁸F-FDG-avid lesion data set (from among 7 patients), the mean injection-to-scan times of the preoperative and postoperative ¹⁸F-FDG PET/CT scans were 73 (±3, 70-78) and 530 (±79, 413-739) minutes, respectively (P < 0.001). The preoperative and postoperative mean ¹⁸F-FDG-avid lesion SUV_max values were 7.7 (±4.0, 3.6-19.5) and 11.3 (±6.0, 4.1-29.2), respectively (P < 0.001). The preoperative and postoperative mean background SUV_max values were 2.3 (±0.6, 1.0-3.2) and 2.1 (±0.6, 1.0-3.3), respectively (P = 0.017). The preoperative and postoperative mean lesion-to-background SUV_max ratios were 3.7 (±2.3, 1.5-9.8) and 5.8 (±3.6, 1.6-16.2), respectively, (P < 0.001).

Conclusions

¹⁸F-FDG PET/CT oncologic imaging can be successfully performed at extended injection-to-scan acquisition time intervals of up to approximately 5 half-lives for ¹⁸F-FDG while maintaining good/adequate diagnostic image quality. The resultant increase in the ¹⁸F-FDG-avid lesion SUV_max values, decreased background SUV_max values, and increased lesion-to-background SUV_max ratios seen from preoperative to postoperative ¹⁸F-FDG PET/CT imaging have great potential for allowing for the integrated, real-time use of ¹⁸F-FDG PET/CT imaging in conjunction with ¹⁸F-FDG-directed interventional radiology biopsy and ablation procedures and ¹⁸F-FDG-directed surgical procedures, as well as have far-reaching impact on potentially re-shaping future thinking regarding the “most optimal” injection-to-scan acquisition time interval for all routine diagnostic ¹⁸F-FDG PET/CT oncologic imaging.

Multiple organ metastases from ameloblastoma detected by FDG PET/CT imaging

A 74-year-old patient was admitted to our hospital with recurrent ameloblastoma of the right mandible. Multiple lung nodules were noted during the presurgical evaluation. FDG PET/CT was subsequently performed to assess the nature of the nodules and search the possible primary tumors. The images showed abnormal FDG activity not only in the lung nodules but also in the lumbar vertebral body and the liver. Pathologic examination after hepatic biopsy demonstrated metastases from ameloblastoma.

Routine use of dual time ¹⁸F-FDG PET for staging of preoperative lung cancer: does it affect clinical management?

OBJECTIVE

The objective of this study was to compare the diagnostic accuracy of dual-time-point 18F-fluorodeoxyglucose ((18)F-FDG) positron emission tomography (PET) to single-time-point (18)F-FDG PET for staging of preoperative lung cancer.

METHODS

Between November 2008 and December 2009, 107 patients who were diagnosed as having lung cancer or strongly suspected of having lung cancer were enrolled. They underwent dual-time-point (18)F-FDG PET following conventional imaging. Dual-time-point (18)F-FDG PET imaging (whole body) was performed at 1-h (early) post-FDG injection and repeated (2 h delayed) after injection. The diagnostic accuracy of pre-PET staging and post-PET staging was retrospectively evaluated, and the diagnostic accuracy of dual-time-point (18)F-FDG PET was compared to that of single-time-point (18)F-FDG PET.

RESULTS

In 100 patients, the early (18)F-FDG PET scan resulted in upstaging of the tumor in ten (10 %) and down-staging of the tumor in five (5 %) compared to the conventional scan. The delayed phase of (18)F-FDG PET provided no additional information on staging for lung cancer patients. The remaining seven patients were diagnosed as not having lung cancer.

CONCLUSION

This study confirmed that dual-time-point (18)F-FDG PET is useful for differential diagnosis between benign and malignant lesions, but has no major impact on staging and therapeutic management of patients with pathologically proven lung cancer.

Value of delayed 18F-FDG PET in the diagnosis of solitary pulmonary nodule

Performing dual point 18F-FDG PET scans of solitary pulmonary nodules at an initial SUV (max) <2.5 is a useful technique. However, prolonging second image acquisition from 120 to 180 min does not appear to improve accuracy. Dual time 18F-FDG PET is not useful in differentiating benign and malignant pulmonary nodules with an initial mean SUV ≤2.5 in parts of the world where granulomatous disease is prevalent. Prolonged imaging on PET scanners is expensive particularly where availability if these scanners is limited. Further prospective research is required to define the potential benefits of dual time point 18F-FDG PET imaging, before recommending routine use of the technique.

Elevated 99mTc 3PRGD2 activity in benign metastasizing leiomyoma

PET/CT scan was performed in a 43-year-old woman to evaluate pulmonary nodules/masses. The images showed that there was only minimal FDG activity in the masses. However, these soft tissue masses in the lungs had significantly elevated (99m)Tc 3PRGD(2) activity. Pathological examination demonstrated that this patient suffered benign metastasizing leiomyoma.

Dual-time-point FDG PET/CT for the evaluation of pediatric tumors

OBJECTIVE

The utility of dual-time-point (18)F-FDG PET/CT in differentiating benign from malignant processes in pediatric patients was assessed.

SUBJECTS AND METHODS

Twenty-one patients (13 girls and eight boys; age range, 1-17 years) with suspected malignancy underwent dual-time-point FDG PET/CT. Scan 1 was performed at approximately 60 minutes after i.v. injection of 5.18 MBq/kg of FDG, and scan 2 was performed at 121 ± 43 minutes after the first scan. Regions of interest were overlaid onto each non-attenuated-corrected image, and semiquantitative analysis was performed using the standardized uptake value (SUV) obtained from early and delayed images. A retention index was calculated according to the following equation: [(delayed SUV - early SUV) / early SUV] × 100. Results were compared prospectively in relation to pathologic examination or other conventional radiologic imaging or clinical follow-up. A retention index of 10% or higher was chosen as a cutoff for differentiating malignant from benign entities.

RESULTS

For patients with malignant disease, the average SUV increased from 7.3 ± 1.2 to 10.9 ± 2.7 between the two time points, whereas the SUV changed from 4.5 ± 0.8 to 4.2 ± 1.0 for patients with benign lesions. The average retention index was 37.1% ± 10.8% for patients with malignant lesions versus -9.9% ± 7.1% for benign lesions (p < 0.01). With a cutoff value of 10% or higher for the retention index, the sensitivity and specificity of dual-time-point FDG PET/CT were 77% and 80%, respectively.

CONCLUSION

These data show that dual-time-point FDG PET/CT is useful in distinguishing malignant from benign processes in pediatric patients.

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

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

Potential value of dual-time-point ¹⁸F-FDG PET compared with initial single-time-point imaging in differentiating malignant from benign pulmonary nodules: a systematic review and meta-analysis

We performed a meta-analysis to assess the potential value of dual-time-point (DTP) imaging as compared with initial single-time-point (STP) scanning with 18F-fluorodeoxyglucose (18F-FDG) PET in differentiating malignant from benign single pulmonary nodules. Data on the performance of DTP 18F-FDG PET imaging in assessing lung nodules were extracted from articles of prospective or retrospective original research published between January 2001 and April 2010. The Quality Assessment of Diagnostic Accuracy Studies (QUADAS) tool was used to assess the quality of study methodology. Heterogeneity in the results of the studies was assessed, and summary receiver operating characteristic (SROC) curves were constructed. Eleven studies comprising a total of 788 patients who underwent initial scanning, 778 of whom also underwent DTP imaging, were included in the final analysis. The quality of study methodology was judged to be moderate. Substantial heterogeneity in the results of the studies, with inconsistency (I2) index values above 85%, reflected important differences in study methods and populations, including varying lesion sizes, 18F-FDG avidity, uptake interval for delayed imaging, and threshold for positive result on DTP imaging. SROC curve analysis revealed a statistically nonsignificant trend toward higher sensitivity with DTP imaging, at moderate levels of specificity, when compared with initial STP scanning. The area under the curve (SE) values for DTP and initial STP imaging were 0.839 (0.079) and 0.757 (0.074), respectively. Although the results of our analysis do not support the routine use of DTP imaging with 18F-FDG PET in the differential diagnosis of pulmonary nodules, this technique may provide additional information in selected cases with equivocal results from initial scanning. Further prospective research is required to better define the potential benefits of DTP 18F-FDG PET imaging.

The value of delayed (18)F FDG-PET imaging in diagnosis of solitary pulmonary nodules: A preliminary study on 28 patients

OBJECTIVE

The aim of this study was to investigate whether adding delayed phase imaging can improve diagnostic ability of (18)F-fluorodeoxyglucose ((18)F-FDG) positron emission tomography (PET) in evaluating solitary pulmonary nodules (SPNs).

MATERIALS AND METHODS

28 patients with SPNs received dual-phase (18)F-FDG PET at 1h and 2h after (18)F-FDG injection during Feb 2009 to Jun 2011were included in this retrospective study. Their final diagnosis was confirmed by pathological examination in 27 cases and clinical follow-up in 1 case. The standardized uptake value (SUV) of early and delayed phases of all lesions was measured.

RESULTS

The 28 SPNs included 9 benign lesions and 19 malignant lesions. Using SUV ≥2.5 as a criteria for malignancy, the sensitivity, specificity, and accuracy were 52.6%, 55.6% and 53.6% respectively at early phase; 68.4%, 55.6% and 64.3% respectively at early and delayed phases combined. Combined early and delayed phase scans combined picked up 3 additional malignant lesions from the 14 lesions with an initial SUV value less than 2.5, and there was no additional false positive result with the benign lesions.

CONCLUSION

Adding delayed phase scanning resulted in correct diagnosis of three malignant lesions with an initial SUV value less than 2.5. Delayed phase scanning can be recommended in the SPNs with SUV less than 2.5 at early phase.

Evaluation for local failure by 18F-FDG PET/CT in comparison with CT findings after stereotactic body radiotherapy (SBRT) for localized non-small-cell lung cancer

PURPOSE

Stereotactic body radiotherapy (SBRT) is the standard care for medically inoperable early non-small-cell lung cancer (NSCLC). However, it can be difficult to differentiate local recurrence from non-recurrence radiation-induced lung opacity. We retrospectively assessed (18)F-FDG PET/CT to detect local recurrence after SBRT for NSCLC.

METHODS

Between 2005 and 2011, 273 NSCLCs in 257 patients were treated with SBRT. Prescribed doses were 50Gy and 40Gy per 5 fractions for peripheral and central lesions, respectively. Tri-monthly follow-up CT scans were acquired. (18)F-FDG PET/CT scans were scheduled for screening at one year after SBRT or when recurrence was highly suspected. The dual-time-point maximum standardized uptake values (SUVmaxs) and their retention indexes (RIs) were obtained.

RESULTS

A total of 214 (18)F-FDG PET/CT scans were obtained for 164 localized NSCLC tumors in 154 patients. The median follow-up period was 24.9 months (range: 6.3-72.1). Among these, 21 scans of 17 tumors were diagnosed as local recurrence. The median SUVmaxs on early and late images of recurrence and their RI were 5.0 (range: 3.2-10.7), 6.3 (range: 4.2-13.4), and 0.20 (range; 0-0.41), respectively. These were significantly higher than the respective values of non-recurrence images of 1.8 (range: 0.5-4.6), 1.7 (range: 0.5-6.1), and 0.00 (range: -0.37-0.41) (all p<0.05). For SUVmaxs on early and late images, optimal thresholds were identified as 3.2 and 4.2. Using each threshold, the sensitivity and specificity were 100% and 96-98%, respectively. CT findings were classified into ground-glass opacity (N=9), scar or fibrotic change (N=96), consolidation with air-bronchogram (N=34), consolidation only (N=22), and nodule (N=17); the respective numbers of recurrence were 0, 0, 1, 3, and 17.

CONCLUSION

SUVmaxs of (18)F-FDG PET/CT could detect local recurrence after SBRT for localized NSCLC. In contrast, CT scan results had a limited ability to diagnose local recurrence.