Comparison of FDG-PET/CT and CT for evaluation of tumor response to nivolumab plus ipilimumab combination therapy and prognosis prediction in patients with unresectable malignant pleural mesothelioma.

OBJECTIVES: Results for malignant pleural mesothelioma (MPM) patients following first-line treatment with nivolumab plus ipilimumab obtained with immunotherapy-modified PERCIST (imPERCIST), shown by [18F]fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT), and modified RECIST (mRECIST), shown by CT, were compared for response evaluation and prognosis prediction. RESULTS: imPERCIST indicated nine progressive metabolic disease (PMD), eight stable metabolic disease (SMD), four partial metabolic response (PMR), and five complete metabolic response (CMR) cases. mRECIST showed nine with progressive disease (PD), nine stable disease (SD), seven partial response (PR), and one complete response (CR). Although high concordance was noted (κ = 0.827), imPERCIST correctly judged a greater percentage with CMR (15.4%). Following a median 10.0 months, 15 patients showed progression and eight died from MPM. With both, progression-free survival (PFS) and overall survival (OS) were significantly longer in patients without progression (CMR/PMR/SMD, CR/PR/SD, respectively) as compared to PMD/PD patients (imPERCIST p < 0.0001 and p = 0.015, respectively; mRECIST p < 0.0001 and p = 0.015, respectively). METHODS: Twenty-six patients (23 males, 3 females; median 73.5 years) with histologically proven MPM and no curative surgery received nivolumab plus ipilimumab combination therapy. FDG-PET/CT and diagnostic CT scanning at the baseline, and after 2-4 cycles (2 in three, 3 in 17, 4 in six patients) were performed. Therapeutic response findings evaluated using imPERCIST and mRECIST were compared. PFS and OS analyses were done using log-rank and Cox methods. CONCLUSION: For unresectable MPM patient examinations, FDG-PET and CT provide accurate findings for evaluating tumor response and also prognosis prediction following first-line nivolumab plus ipilimumab immunotherapy (approximately three cycles).

Imaging in pleural Mesothelioma: A review of the 16th International Conference of the International Mesothelioma Interest Group.

Imaging continues to gain a greater role in the assessment and clinical management of patients with mesothelioma. This communication summarizes the oral presentations from the imaging session at the 2023 International Conference of the International Mesothelioma Interest Group (iMig), which was held in Lille, France from June 26 to 28, 2023. Topics at this session included an overview of best practices for clinical imaging of mesothelioma as reported by an iMig consensus panel, emerging imaging techniques for surgical planning, radiologic assessment of malignant pleural effusion, a radiomics-based transfer learning model to predict patient response to treatment, automated assessment of early contrast enhancement, and tumor thickness for response assessment in peritoneal mesothelioma.

Predictive potential of MRI in differentiating the predominant component in biphasic pleural mesothelioma.

PURPOSE: To assess the potential of apparent diffusion coefficient (ADC) values derived from diffusion weighted (DW) MRI preoperatively to predict the predominant histologic component among biphasic pleural mesothelioma (PM) tumors. METHODS: ADC maps were generated from DW MRI scans. Histology and predominant component of biphasic PM were confirmed following surgical resection. Statistical analyses were done with R (R Foundation for Statistical Computing, Vienna, Austria). Average ADC values corresponding to epithelioid- and sarcomatoid-predominant tumors were compared. ADC thresholding was accomplished by recursive partitioning and confirmed with ROC analysis. RESULTS: Eighty-four patients with biphasic PM's, 69 (82 %) epithelioid-predominant (BE) and 15(18 %) sarcomatoid-predominant (BS) tumors were evaluated. Thirty-eight (45 %) patients underwent extrapleural pneumonectomy (EPP), 39 (46 %) had extended pleural decortication (ePDC) and 7 (8 %) had pleural decortication (PDC). ADC values ranged between 0.696 x 10-3 to 1.921 x 10-3 mm2/s. BE tumors demonstrated significantly higher ADC values than BS tumors (p = 0.026). ADC values above 0.94 x 10-3 mm2/s were associated with a significant increase of relative risk of being in group BE over group BS (relative risk: 1.47, 95 %CI: 1.05-2.06, p = 0.027) CONCLUSION: Average ADC values of BE tumors were higher than BS tumors and the two groups can be separated by a cut off value of 0.94 X 10-3 mm2/s.

18F-FDG and 68Ga-PSMA PET/CT in Paratesticular Mesothelioma.

ABSTRACT: A 66-year-old man with local prostate adenocarcinoma underwent radical prostatectomy (Gleason score 3 + 4 = 7, pT2c) in 2016. Four years later, he presented with a hydrocele and cystic atypical change in the left scrotum and soft tissue in the left groin. Final histopathology revealed spermatic cord mesothelioma and left hemangiosis carcinomatosa. A bone biopsy of the sacrum revealed infiltrates of a prostatic adenocarcinoma with small cell neuroendocrine differentiation. Dual-tracer PET/CT imaging using 18F-FDG and 68Ga-PSMA was able to identify local recurrence of scrotal mesothelioma and differentiate metastases of prostate cancer from malignant mesothelioma.

The prognostic value of F18 Fluorothymidine positron emission tomography for assessing the response of malignant pleural mesothelioma to chemotherapy - A prospective cohort study.

INTRODUCTION: Malignant pleural mesothelioma is difficult to prognosticate. F18-Fluorodeoxyglucose positron emission tomography (FDG PET) shows promise for response assessment but is confounded by talc pleurodesis. F18-Fluorothymidine (FLT) PET is an alternative tracer specific for proliferation. We compared the prognostic value of FDG and FLT PET and determined the influence of talc pleurodesis on these parameters. METHODS: Overall, 29 prospectively recruited patients had FLT PET, FDG PET and CT-scans performed prior to and post one chemotherapy cycle; 10 had prior talc pleurodesis. Patients were followed for overall survival. CT response was assessed using mRECIST. Radiomic features were extracted using the MiM software platform. Changes in maximum SUV (SUVmax), mean SUV (SUVmean), FDG total lesion glycolysis (TLG), FLT total lesion proliferation (TLP) and metabolic tumour volume (MTV) after one chemotherapy cycle. RESULTS: Cox univariate analysis demonstrated FDG PET radiomics were confounded by talc pleurodesis, and that percentage change in FLT MTV was predictive of overall survival. Cox multivariate analysis showed a 10% increase in FLT tumour volume corresponded with 9.5% worsened odds for overall survival (P = 0.028, HR = 1.095, 95% CI [1.010, 1.187]). No other variables were significant on multivariate analysis. CONCLUSION: This is the first prospective study showing the statistical significance of FLT PET tumour volumes for measuring mesothelioma treatment response. FLT may be better than FDG for monitoring mesothelioma treatment response, which could help optimise mesothelioma treatment regimes.

Diagnostic value of computed tomography and magnetic resonance imaging in ovarian malignant mesothelioma.

OBJECTIVE: To investigate the diagnostic value of computed tomography (CT) and magnetic resonance imaging (MRI) in ovarian malignant mesothelioma (OMM). METHODS: The clinical and imaging data of 10 pathologically-confirmed OMM patients were analyzed retrospectively. RESULT: (1) The patients were 27 years to 70 years old, with an average age of 57.2 ± 15.4 years. Seven patients reported abdominal distension and pain, 1 reported lower abdominal discomfort and decreased appetite, and 2 patients had no symptoms. (2) Two cases of localized OMM with incomplete semi-annular "capsule" observed around the localized OMM tumors were reported while 8 cases had diffuse OMM in which the tumor parenchyma showed isointense or slightly hypointense on T1WI, inhomogeneous hyperintense on T2WI, and obviously hyperintense on DWI, with obvious inhomogeneous enhancement after enhancement. Diffuse OMM was not mainly composed of ovarian masses and was mainly characterized by mild ovarian enlargement, nodular and irregular thickening of the peritoneum, cloudy omentum, unclear fat gap, and reticular or irregular thickening, which can fuse into a "cake-shape". (3) All 10 patients underwent surgery, while 9 patients underwent systemic chemotherapy or immunotherapy after surgery. All patients with localized OMM survived. Out of the 8 diffuse-type patients, 5 died, 1 was lost to follow-up, and 2 survived. CONCLUSION: OMM has certain clinical and imaging characteristics. There is no liquefaction, calcification, or partition in the tumor. The ovarian enlargement in the diffuse lesion is not significant. The diffuse thickening of the peritoneum and omentum with early appearance of mural nodules and ascites in the upper abdomen, help the diagnosis of OMM.

18F-FDG PET/CT in Primary Mesothelioma of the Liver.

ABSTRACT: Primary malignant mesothelioma is a rarity among malignant liver tumors. We present the case of a 48-year-old woman presenting with increasing upper abdominal discomfort and inappetence accompanied by a weight loss of approximately 10 kg. CT and MRI revealed a highly suspicious mass lesion in the liver. 18F-FDG PET/CT performed for staging showed a pathological 18F-FDG uptake of the known liver tumor. Histology and immunohistochemistry indicated mesothelioma of the liver. Herein we present a rare case of primary mesothelioma in the liver with CT, MRI, and 18F-FDG PET/CT.

The efficacy of 18F-FDG PET/CT in monitoring disease progression in malignant pleural mesothelioma.

OBJECTIVE: In the event of suspicion of malignant pleural mesothelioma (MPM) progression, imaging plays an important role. We aimed to evaluate the efficacy of 18F-FDG PET/CT in monitoring disease progression by comparing it with CT, and estimate median overall survival (OS) according to progression status with CT and 18F-FDG PET/CT. MATERIALS AND METHODS: This was an observational, retrospective, single-institution study with MPM patients who had both 18F-FDG PET/CT and CT for monitoring disease progression from March 2009 to February 2020. Clinical features, radiological findings, and progression status according to CT [radiologic progression negative (RPN), radiologic progression positive (RPP)] and 18F-FDG PET/CT [metabolic progression negative (MPN), metabolic progression positive (MPP)] were recorded. The discrepancies and concordance between two methods were evaluated. The OS was estimated using the Kaplan-Meier method. RESULTS: A total of 56 patients were included. There were thirty-one (55.3%) RPN and 25 (44.7%) RPP, while there were 26 (46.5%) MPN and 30 (53.5%) MPP. All RPP patients were also found to be MPP, however, among RPN, 5 patients (8.9% of all patients) were evaluated as MPP. The concordance between two methods in monitoring disease progression was very good (K = 0.423; p < 0.01). The OS was 26 ±â€¯2.6 months in all patients. Kaplan-Meier curves between RPN and RPP, and between MPN and MPP did not show statistically significant differences (p = 0.56 and p = 0.25, respectively). CONCLUSIONS: Both methods are equally acceptable in monitoring disease progression in MPM, even though 18F-FDG PET/CT detected more progression than CT did.

68 Ga-FAPI-04 Versus 18 F-FDG PET/CT in Detection of Epithelioid Malignant Pleural Mesothelioma.

ABSTRACT: We describe 68 Ga-FAPI (fibroblast activation protein inhibitor)-04 and 18 F-FDG PET/CT findings in a case with epithelioid malignant pleural mesothelioma. Compared with 18 F-FDG PET/CT, 68 Ga-FAPI-04 PET/CT more clearly showed the pleural tumors and lymph node metastases and detected more pleural lesions because the tumors showed higher 68 Ga-FAPI-04 activity. This case indicates that 68 Ga-FAPI-04 PET/CT may be a promising new tool in evaluation of malignant pleural mesothelioma, which needs further investigation.

FDG PET/CT for Staging and Restaging Malignant Mesothelioma.

Malignant mesothelioma is an aggressive tumor originating from the mesothelial cells and presenting in general with a very poor prognosis. The pleural localization represents the prevailing disease site, while peritoneal involvement is commonly rare. The WHO classifies mesotheliomas into epithelioid, biphasic, and sarcomatoid histotypes, having diverse outcome with the sarcomatoid or biphasic forms showing the poorest prognosis. Given the peculiar rind-like pattern of growth, mesothelioma assessment is rather challenging for medical imagers. Conventional imaging is principally based on contrast-enhanced CT, while the role of functional and metabolic imaging is regarded as complementary. By focusing essentially on the staging and restaging role of [18F]FDG PET/CT in malignant mesotheliomas, the present review will summarize the available data present in literature and provide some hints on alternative imaging and future perspectives. Given the prevailing incidence of pleural disease, the majority of the information will be addressed on malignant pleural mesothelioma, although a summary of principal characteristics and imaging findings in patients with peritoneal mesothelioma will be also provided.

FDG PET/CT for Primary Staging of Lung Cancer and Mesothelioma.

Lung cancer is the leading cause of cancer-related mortality in the United States. Accurate staging at initial diagnosis determines appropriate treatment and is the most important predictor of survival. Since 2018, the 8th edition of the TNM staging system has been used to stage lung cancer based on local tumor extent (T), nodal involvement (N), and metastases (M). 18 F fluorodeoxyglucose (FDG) PET/CT, which combines functional and anatomic imaging, is the standard of care and an integral part of clinical staging of patients with lung cancer. Malignant pleural mesothelioma (MPM), the most common primary malignant pleural tumor affecting the pleura is staged with 8th edition of TNM staging for MPM. 18 F FDG PET/CT is indicated in select patients who are surgical candidates to identify locally advanced tumor, nodal metastases, or extrathoracic metastases, which may preclude surgery.

A Role for PET/CT in Response Assessment of Malignant Pleural Mesothelioma.

Malignant pleural mesothelioma is a rare type of cancer, whose incidence, however, is increasing and will presumably continue to rise in the coming years. Key features of this disease comprise its mantle-shaped, pleura-associated, often multifocal growth, which cause diagnostic challenges. A growing number of mesotheliomas are being treated with novel immunotherapies for which no image derived general response criteria have been established. However, recent studies indicate that FDG-PET/CT could be superior for response assessment compared to CT-based criteria. This article aims at providing an overview of response assessment criteria dedicated to malignant pleural mesothelioma, such as mRECIST, iRECIST, and PERCIST. In addition, the potential future role of PET/CT in the management of malignant pleural mesothelioma will also be discussed.

Dynamic contrast-enhanced MRI in malignant pleural mesothelioma: prediction of outcome based on DCE-MRI measurements in patients undergoing cytotoxic chemotherapy.

BACKGROUND: The malignant pleural mesothelioma (MPM) response rate to chemotherapy is low. The identification of imaging biomarkers that could help guide the most effective therapy approach for individual patients is highly desirable. Our aim was to investigate the dynamic contrast-enhanced (DCE) MR parameters as predictors for progression-free (PFS) and overall survival (OS) in patients with MPM treated with cisplatin-based chemotherapy. METHODS: Thirty-two consecutive patients with MPM were enrolled in this prospective study. Pretreatment and intratreatment DCE-MRI were scheduled in each patient. The DCE parameters were analyzed using the extended Tofts (ET) and the adiabatic approximation tissue homogeneity (AATH) model. Comparison analysis, logistic regression and ROC analysis were used to identify the predictors for the patient's outcome. RESULTS: Patients with higher pretreatment ET and AATH-calculated Ktrans and ve values had longer OS (P≤.006). Patients with a more prominent reduction in ET-calculated Ktrans and kep values during the early phase of chemotherapy had longer PFS (P =.008). No parameter was identified to predict PFS. Pre-treatment ET-calculated Ktrans was found to be an independent predictive marker for longer OS (P=.02) demonstrating the most favourable discrimination performance compared to other DCE parameters with an estimated sensitivity of 89% and specificity of 78% (AUC 0.9, 95% CI 0.74-0.98, cut off > 0.08 min-1). CONCLUSIONS: In the present study, higher pre-treatment ET-calculated Ktrans values were associated with longer OS. The results suggest that DCE-MRI might provide additional information for identifying MPM patients that may respond to chemotherapy.

Conspicuity of malignant pleural mesothelioma in contrast enhanced MDCT - arterial phase or late phase?

BACKGROUND: To determine if late phase is superior to arterial phase intraindividually regarding conspicuity of MPM in contrast enhanced chest MDCT. METHODS: 28 patients with MPM were included in this retrospective study. For all patients, chest CT in standard arterial phase (scan delay ca. 35 s) and abdominal CT in portal venous phase (scan delay ca. 70 s) was performed. First, subjective analysis of tumor conspicuity was done independently by two radiologists. Second, objective analysis was done by measuring Hounsfield units (HU) in tumor lesions and in the surrounding tissue in identical locations in both phases. Differences of absolute HUs in tumor lesions between phases and differences of contrast (HU in lesion - HU in surrounding tissue) between phases were determined. HU measurements were compared using paired t-test for related samples. Potential confounding effects by different technical and epidemiological parameters between phases were evaluated performing a multiple regression analysis. RESULTS: Subjective analysis: In all 28 patients and for both readers conspicuity of MPM was better on late phase compared to arterial phase. Objective analysis: MPM showed a significantly higher absolute HU in late phase (75.4 vs 56.7 HU, p < 0.001). Contrast to surrounding tissue was also significantly higher in late phase (difference of contrast between phases 18.5 HU, SD 10.6 HU, p < 0.001). Multiple regression analysis revealed contrast phase and tube voltage to be the only significant independent predictors for tumor contrast. CONCLUSIONS: In contrast enhanced chest-MDCT for MPM late phase scanning seems to provide better conspicuity and higher contrast to surrounding tissue compared to standard arterial phase scans.

Diaphragm reconstruction by GORE DUALMESH in patients undergoing resection for thoracic malignancies.

BACKGROUND: We used GORE DUALMESH for the reconstruction of diaphragms in patients with thoracic malignancies. Here, we report the results. METHODS: Between July 2015 and August 2017, diaphragm reconstruction using 2-mm GORE DUALMESH was performed in 7 patients undergoing surgical resection for thoracic malignancies. After resection of the diaphragm, the mesh was trimmed to the size of defect and placed with the smooth surface facing the chest cavity and the rough surface facing the abdomen. It was fixed with interrupted sutures consisting of synthetic monofilament nonabsorbable 1-0 to 2 threads. RESULTS: Indications for resection were malignant pleural mesothelioma and primary lung cancer in 5 and 2 patients, respectively. Patients with malignant pleural mesothelioma underwent pleurectomy with decortication; patients with primary lung cancer underwent lung lobectomy. Right and left diaphragm reconstruction was performed for 4 and 3 patients, respectively. Neither complications related to diaphragm reconstruction nor displacement of mesh occurred during a follow-up period ranging from 11 days to 37 months. CONCLUSIONS: GORE DUALMESH is a good synthetic material for diaphragm reconstruction, because its smooth surface prevents adhesions to the lung and its rough surface allows adherence to abdominal tissue.

The role of volumetric method in the assessment of chemotherapy response and predicting survival in malignant pleural mesothelioma.

BACKGROUND: Malignant pleural mesothelioma (MPM) is a pleural tumor with high mortality rate and short-term survival expectancy after diagnosis. Assessment of the response to chemotherapy, which is the first choice in treatment of MPM, is important for the transition to alternative chemotherapy protocols and immunotherapy. There is no clarity in the response to chemotherapy treatment. OBJECTIVE: Our study aims to compare the assessment of chemotherapy response using the Modified Response Evaluation Criteria in Solid Tumors (mRECIST) criteria and volumetric measurements and to correlate with median survival. MATERIALS AND METHODS: Thirty-two patients (16 females and 16 males) were included in the study, and their ages ranged from 28 to 78 years. Chemotherapy response was determined by both mRECIST and volumetric approach. Tumor volume was measured by linear interpolation and semi-automatic segmentation. Log-rank multiple cutoff analysis was used to determine appropriate cutoff values of volumetric response criteria. RESULTS: According to both mRECIST and volumetric approach, median survival times in partial response, stable disease, and progressive disease groups were 24, 15, and 9 months, respectively. The survival times of the three groups were different (logrank: 17.76; P < 0.001) by mRECIST. The survival of the progressive disease group was shorter than that of the other groups (logrank: 18.91; P < 0.001) by volumetric approach. CONCLUSIONS: In the assessment of chemotherapy response, even though classifications obtained according to the mRECIST criteria and volumetric measurements are statistically compatible, we think that the measurement of the volumetric values will increase the standardization. In our study, threshold values for volumetric measurements were determined; however, these values should be supported by large-scale multicenter studies.

Impact of CT convolution kernel on robustness of radiomic features for different lung diseases and tissue types.

OBJECTIVES: In this study, we aimed to assess the impact of different CT reconstruction kernels on the stability of radiomic features and the transferability between different diseases and tissue types. Three lung diseases were evaluated, i.e. non-small cell lung cancer (NSCLC), malignant pleural mesothelioma (MPM) and interstitial lung disease related to systemic sclerosis (SSc-ILD) as well as four different tissue types, i.e. primary tumor, largest involved lymph node ipsilateral and contralateral lung. METHODS: Pre-treatment non-contrast enhanced CT scans from 23 NSCLC, 10 MPM and 12 SSc-ILD patients were collected retrospectively. For each patient, CT scans were reconstructed using smooth and sharp kernel in filtered back projection. The regions of interest (ROIs) were contoured on the smooth kernel-based CT and transferred to the sharp kernel-based CT. The voxels were resized to the largest voxel dimension of each cohort. In total, 1386 features were analyzed. Feature stability was assessed using the intraclass correlation coefficient. Features above the stability threshold >0.9 were considered stable. RESULTS: We observed a strong impact of the reconstruction method on stability of the features (at maximum 26% of the 1386 features were stable). Intensity features were the most stable followed by texture and wavelet features. The wavelet features showed a positive correlation between percentage of stable features and size of the ROI (R2 = 0.79, p = 0.005). Lymph node radiomics showed poorest stability (<10%) and lung radiomics the largest stability (26%). Robustness analysis done on the contralateral lung could to a large extent be transferred to the ipsilateral lung, and the overlap of stable lung features between different lung diseases was more than 50%. However, results of robustness studies cannot be transferred between tissue types, which was investigated in NSCLC and MPM patients; the overlap of stable features for lymph node and lung, as well as for primary tumor and lymph node was very small in both disease types. CONCLUSION: The robustness of radiomic features is strongly affected by different reconstruction kernels. The effect is largely influenced by the tissue type and less by the disease type. ADVANCES IN KNOWLEDGE: The study presents to our knowledge the most complete analysis on the impact of convolution kernel on the robustness of CT-based radiomics for four relevant tissue types in three different lung diseases. .

Volumetric PET Response Assessment Outperforms Conventional Criteria in Patients Receiving High-Dose Pembrolizumab for Malignant Mesothelioma.

Fixed-dose pembrolizumab (200 mg absolute, day 1, every 3 wk) for the treatment of malignant pleural mesothelioma did not result in survival benefit in the phase 3 PROMISE-meso trial compared with second-line chemotherapy. Because of lack of validated imaging response criteria, responder subgroups with potential survival benefit have not yet been identified. Here, we administered high-dose pembrolizumab (10 mg/kg, day 1, every 2 wk) considering the KEYNOTE-028 trial and assessed the prognostic value of PET metabolic response in patients with chemotherapy-resistant malignant mesothelioma of the pleura or peritoneum. Methods: Data from 27 patients with baseline and follow-up 18F-FDG PET/CT imaging were retrospectively analyzed. RECIST, version 1.1; modified RECIST; and PERCIST using both tumor lesion metabolic activity in a 1 cm3 spheric region of interest of up to 5 target lesions (PERCISTSULpeak) and metabolic tumor volume PERCIST (PERCISTMTV) were applied separately to categorize responders in CT and PET imaging studies. Progression-free survival (PFS) and overall survival (OS) were compared between responders and nonresponders using Kaplan-Meier and log-rank analyses. Programmed cell death protein 1 ligand expression status was assessed, and its association with outcome was investigated. Results: Twenty-seven patients had 18F-FDG PET/CT imaging at baseline and after at least 4 cycles pembrolizumab. Median PFS and OS were 3.4 and 15.1 mo, respectively. Response rates were 7%, 7%, 30%, and 30% based on RECIST, modified RECIST, PERCISTSULpeak, and PERCISTMTV response criteria, respectively. Response according to PERCISTMTV predicted prolonged OS or PFS (P < 0.01), whereas all other imaging criteria and programmed cell death protein 1 ligand expression did not. Conclusion:18F-FDG PET metabolic volume response predicts survival in patients with malignant mesothelioma receiving high-dose pembrolizumab. These results should prompt inclusion of PET response assessment in future phase 3 clinical trials.

Delayed-Phase Enhancement for Evaluation of Malignant Pleural Mesothelioma on Computed Tomography: A Prospective Cohort Study.

BACKGROUND: Radiologic assessment of malignant pleural mesothelioma (MPM) on computed tomography (CT) imaging can be limited by similar attenuations of MPM and adjacent tissues. This can result in inaccuracies in defining the presence and extent of pleural tumor burden. We hypothesized that increasing the time delay for pleural enhancement will optimize discrimination between MPM and noncancerous tissues on CT. Here we conduct a prospective observational study to determine the optimal time delay for imaging MPM on CT. PATIENTS AND METHODS: Adult MPM patients (n = 15) were enrolled in this prospective exploratory imaging trial. Patients with < 1 cm MPM thickness, prior pleurectomy, pleurodesis, pleural radiotherapy, or antiangiogenic therapy were excluded. All patients underwent a dynamically-enhanced CT with multiple time delays (0 - 10 minutes) after intravenous contrast administration. Tumor tissue attenuation was measured at each phase of enhancement. A qualitative assessment of tumor enhancement kinetics was also performed. The optimal phase of enhancement based on qualitative lesion conspicuity and quantitative tumor enhancement was then compared. RESULTS: MPM tumor enhancement was quantitatively and qualitatively increased at time delays beyond the conventional time delay for thoracic CT imaging (40-60 seconds). Patient tumor enhancement kinetics, displayed as the fraction of maximal tumor tissue attenuation as a function of time, revealed an optimal time delay of 230 to 300 seconds after intravenous contrast administration. There was an association between degree of tumor enhancement and subjective lesion conspicuity. CONCLUSION: Optimal MPM contrast enhancement occurs at a later phase than typically acquired with conventional thoracic CT imaging.