Aim The aim of this study was to assess the agreement between predicted blood uptake values using 124I and actually measured 131I blood uptake values (reference) in patients with differentiated thyroid carcinoma receiving largely high therapeutic activities. Patients and methods Fourteen patients were analyzed retrospectively, who underwent a series of both pretherapeutic and intratherapeutic blood sampling using median 124I activities of 23 MBq and median therapy 131I activities of 10 GBq. Data of five blood samples from each patient were analyzed. Lin’s concordance correlation coefficient analysis was carried out to assess the kinetic agreement. The time-integrated 131I activity coefficient (TIAC) for the blood compartment and the effective 131I clearance time (ECT), expressed as effective 131I half-life on the basis of a monoexponential model, were ascertained. For each patient, the (intrapatient) percentage differences between pretherapeutic and intratherapeutic TIACs and ECTs were calculated. The (interpatient) difference in TIACs and ECTs between pretherapy and intratherapy groups was evaluated using the Mann–Whitney U-test. Results Lin’s concordance correlation coefficient was at least 0.97, indicating substantial kinetic agreement between pretherapeutic and intratherapeutic radioiodine kinetics. The mean (median)±SD (range) of the absolute percentage difference was 9% (11%)±7% (0.33–20%) for the TIAC and 11% (10%)±10% (0–23%) for the ECT. A slightly higher median TIAC was observed in intratherapy (2.8 vs. 3.3 h), but this was not statistically significant (P=0.15), whereas no remarkable ECT difference (P=0.62) was found. Conclusion The pretherapeutic blood kinetics derived from diagnostic 124I activities provides a reliable estimation of the intratherapeutic 131I blood kinetics in patients receiving largely high therapy activities, showing its potential for radioiodine treatment planning.

BACKGROUND The aim of this study was to evaluate whether 18F-fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT) is useful in the further characterization of sonographically suspicious and scintigraphically hypofunctional thyroid nodules. METHODS Sixty-five patients with sonographically suspicious thyroid nodules that were hypofunctional on 99m-Tc-pertechnetate scintigraphy (diameter >1 cm) were retrospectively analyzed. All patients underwent evaluation with FDG-PET/CT. Thyroid nodules were sonographically categorized by Thyroid Image Reporting and Data System (TIRADS) criteria. FDG uptake in the thyroid nodules was visually compared to the remainder of the thyroid tissue and categorized as pathological or non-pathological. In cases of pathologically increased uptake, maximum standardized uptake values (SUVmax) of the suspicious nodule and the perinodular thyroid tissue were determined. Depending on the results of the FDG-PET/CT, patients underwent thyroid surgery (pathological FDG uptake) or follow-up examinations (non-pathological FDG uptake). The endpoints for comparison with the FDG uptake were either histological results or sonographic follow-up examinations of at least five years. RESULTS In 18/65 (28%) patients, PET/CT showed visually pathological FDG uptake in the suspicious thyroid nodules (SUVmax 7.1 ± 4.6). Of these nodules, 3/18 (17%) were sonographically categorized as TIRADS 4a, 11/18 (61%) nodules as TIRADS 4b, 3/18 (17%) nodules as TIRADS 4c, and 1/18 (6%) nodule as TIRADS 5. The other nodules without pathological FDG uptake were categorized as TIRADS 4a in 24/47 (51%) patients, as TIRADS 4b in 18/47 (38%), and as TIRADS 4c in 5/47 (11%) patients. Twenty-three patients (18 FDG positive, 5 FDG negative) underwent surgery. The other patients underwent follow-up examinations with stability on observation over at least five years as a surrogate endpoint. Taking into consideration that FDG-PET/CT was rated as true negative in 42/47 patients with stability on sonographic follow-up, sensitivity, specificity, positive predictive value, and negative predictive value of FDG-PET/CT in detecting malignancy in the suspicious thyroid nodules were 100%, 87%, 61%, and 100%, respectively. CONCLUSION FDG-PET/CT allows stratification of patients with sonographically suspicious and scintigraphically hypofunctional thyroid nodules with a positive predictive value of 61% and negative predictive value of 100%. The absence of visually pathological FDG uptake in suspicious thyroid nodules may be useful for avoiding unnecessary thyroid surgery.

Radioiodine therapy (RIT) is an integral component in the treatment of differentiated thyroid cancer (DTC). Patients usually undergo RIT as initial therapy or later in the case of recurrent or persistent disease. The most important requirement for a successful RIT is the ability of metastases and thyroid (remnant) tissue to accumulate radioiodine. In order to calculate the achievable absorbed radiation dose for a lesion, volume and iodine kinetics in the lesion need to be determined. Pretherapeutic imaging and dosimetry with 124I PET provide the methodology to answer these questions.

In a previous paper, we published the impact of initial [F-18]FDG PET/CT (FDG-PET/CT) in high-risk patients with differentiated thyroid cancer (DTC) and described the changes in therapy management. The aim of the present study was to evaluate the prognostic impact of the initial FDG-PET/CT on a patient's follow-up over three years and the rate of complete remission. Patients, methods: This study included 109 DTC patients who underwent radioiodine treatment (RIT), including post therapeutic whole-body scintigraphy with FDG-PET/CT and a follow-up over three years. The follow-up included high-resolution sonography of the neck and determination of serum Tg as well as Tg antibodies every six months. The results of initial FDG-PET/CT and whole-body scintigraphy were compared with the status after three years of follow-up. Results: 24/109 patients (22%) presented FDG-positive lesions, 22/109 patients (20%) only iodine-positive lesions, and 63/109 patients (58%) neither FDG-positive nor iodine positive lesions. After three years, 83/109 patients (76%) revealed full remission, 15/109 patients (14%) tumour persistence and 11/109 patients (10%) a progressive disease. The negative predictive value (NPV) was calculated for patients without FDG-positive lesions (NPV 85%) and patients without any lesions (NPV 91%) regarding full remission in the follow-up. Conclusion: FDG-PET/CT has a high NPV (85% to 91%) in DTC patients regarding recurrence-free follow-up after three years. The change in patient management in patients with iodine-negative lesions can lead to a higher rate of full remissions in the follow-up after additional surgery. Therefore, FDG-PET/CT should be performed in all high-risk DTC patients in the context of the first RIT to improve patient management and risk stratification.

UNLABELLED:The aim of this retrospective study was to assess the level of agreement between PET and scintigraphy using diagnostic amounts of (124)I and therapeutic amounts of (131)I, respectively, in detecting iodine-positive metastases in patients with differentiated thyroid carcinoma. METHODS:The study included patients who underwent PET /: CT 24 and 120 h after administration of approximately 25 MBq of (124)I and subsequently underwent imaging 5-10 d after administration of 1-10 GBq of (131)I. For each patient, the intratherapeutic (131)I imaging comprised a whole-body scintigraphy scan and a SPECT/CT scan of the neck to distinguish between metastatic and thyroid remnant tissues. Iodine uptake was rated as a metastatic focus if located outside the thyroid bed. Lesion- and patient-based analyses were performed. RESULTS:The study included 137 patients with 227 metastases iodine-positive on both functional imaging modalities. In the lesion-based analysis, (124)I PET and (131)I imaging detected 98% (223/227) and 99% (225/227) of the iodine-positive metastases, respectively; the level of agreement between (124)I PET and (131)I imaging was 97% (221/227). Four metastases (3 lymph node and 1 bone) in 4 patients were (124)I-negative but (131)I-positive, and 2 lymph node metastases in 2 patients were (131)I-negative but (124)I-positive. In the patient-based analysis, 61 of the 137 patients presented with iodine-positive metastases. (124)I PET and (131)I imaging detected at least one iodine-positive metastasis in 97% (59/61) and 98% (60/61) of the patients, respectively. The level of agreement was 95% (58/61). Both imaging modalities concordantly identified 76 of 137 patients without pathologic iodine uptake. CONCLUSION:Because of the high level of agreement, pretherapeutic (124)I PET/CT is an adequate methodology in the detection of iodine-positive metastases and can be used as a reliable tool for staging of thyroid cancer patients and individualized treatment planning.

This study evaluated the impact of 68Ga-DOTATOC PET/CT in detecting recurrence or metastases in differentiated thyroid carcinoma (DTC) patients with elevated serum thyroglobulin and both negative radioiodine imaging and negative 18F-FDG PET/CT. Methods: 68Ga-DOTATOC PET/CT (CT without contrast, low-dose) was performed on average 6 wk after negative 18F-FDG PET/CT (CT contrast-enhanced, full-dose) in 15 consecutive radioiodine-negative DTC patients with elevated and rising thyroglobulin. Visual assessment of 68Ga-DOTATOC PET/CT images used a 4-point scale for classification of lesions (0, no pathologic findings; 1, benign; 2, equivocal; 3, malignant). PET findings were correlated with the histologic subtype of tumor, levels of serum thyroglobulin, and morphologic findings on full-dose CT and neck ultrasound. Histology or clinical and imaging follow-up served as a reference standard. Analysis was performed on a patient and lesion basis. Results: 68Ga-DOTATOC PET/CT was true-positive in 5 patients (10 tumor lesions) and was false-positive in 1 patient. The rate of positive 68Ga-DOTATOC PET/CT was significantly higher in poorly differentiated/oxyphilic carcinomas (4/4 patients) than in papillary (1/5) or follicular (0/6) tumors. Thyroglobulin levels tended to be higher in patients with tumor localization on 68Ga-DOTATOC PET/CT, but differences were not significant. In 2 of 5 patients with true-positive findings on 68Ga-DOTATOC PET/CT, CT alone but not ultrasound identified 2 of 10 tumor lesions, but in both patients 68Ga-DOTATOC-PET/CT revealed further tumor lesions not detected on CT alone. Conclusion: 68Ga-DOTATOC PET/CT should be considered in the case of negative 18F-FDG PET/CT in radioiodine-negative DTC patients with elevated and rising thyroglobulin. Imaging with 68Ga-DOTATOC appears promising especially in poorly differentiated and oxyphilic subtypes of DTC.

Purpose: The aim of this study is to evaluate and compare the diagnostic potential of integrated whole body [18F]FDG-PETIMRI to [18F]FDG-PETICT for detection of a potential primary cancer and metastases in patients suspected for cancer of unknown primary (CUP).Methods: A total of 20 patients (15 male, 5 female, age 53 +/- 13 years) suspect for CUP underwent a dedicated head and neck & whole-body [18F]FDG-PETICT (Biograph mCT 128, Siemens Healthcare) and a subsequent simultaneous [18F]FDG-PETIMRI examination (Biograph mMR, Siemens Healthcare). Two readers rated the datasets (PET/CT; PET/MRI) regarding the detection of the primary cancer and metastases, lesion conspicuity (4-point ordinal scale) and diagnostic confidence (3-point ordinal scale). PET analysis comprised the assessment of maximum standardized uptake values (SUVmax) of all PET-positive lesions using volume of interest (VOI) analysis derived from the PET/CT and PET/MR datasets. All available data considering histology and imaging including prior and clinical follow-up examinations served as reference standard. Statistical analysis included comparison of mean values using Mann-Whitney U test and correlation of SUVmax using Pearson's correlation.Results: In 14 out of 20 patients 49 malignant lesions were present. The primary cancer could be correctly identified in 11/20 patients with both PET/CT and PET/MRI. PET/CT enabled the detection of a total 38 metastases, PET/MR respectively of 37 metastases (one lung metastasis <5mm was missed). PET/CT and PET/MRI showed comparably high lesion conspicuity (2.6 +/- 0.6 each), with superior assessment of cervical lesions in PET/MRI and an indicated superior assessment of pulmonary lesions in PET/CT. Diagnostic confidence was rated comparably high in PET/CT and PET/MRI (2.7 +/- 0.5 each). The mean values of SUVmax of all PET-positive lesions (PET/MRT 7.9 +/- 4.2 vs. PET/CT 7.2 +/- 3.5) showed a strong positive correlation between the SUVs derived from both hybrid imaging systems (Pearson's correlation r = 0.927).Conclusions: Both hybrid imaging techniques provide a comparable diagnostic ability for detection of primary cancer and metastases in patients with CUP, with comparably high lesion conspicuity and diagnostic confidence, offering superior assessment of cervical lesions in PET/MRI and potentially of pulmonary lesions in PET/CT. Furthermore, due to the significantly lower dose of ionizing radiation, PET/MRI may serve as a powerful alternative to PET/CT, particularly for therapy monitoring and/or surveillance considering the long-term cumulative dose. (C) 2016 Elsevier Ireland Ltd. All rights reserved.

The aim of this study was to evaluate integrated 18F-FDG PET/MRI as a one-stop diagnostic procedure in the assessment of (active) idiopathic retroperitoneal fibrosis (RPF)

PURPOSE:To evaluate the accuracy of integrated (18)F-FDG PET/MR imaging for locoregional tumour evaluation compared to (18)F-FDG PET/CT and MR imaging in initial tumour and recurrence diagnosis in histopathologically confirmed head and neck squamous cell carcinoma (HNSCC). METHODS:(18)F-FDG PET/CT and integrated (18)F-FDG PET/MR imaging were performed for initial tumour staging or recurrence diagnosis in 25 patients with HNSCC. MR, fused (18)F-FDG PET/CT and fused (18)F-FDG PET/MR images were analysed by two independent readers in separate sessions in random order. In initial tumour staging, T and N staging was performed while individual lesions were analysed in patients with suspected cancer recurrence. In T and N staging, histopathological results after tumour resection served as the reference standard while histopathological sampling as well as cross-sectional and clinical follow-up were accepted in cancer recurrence diagnosis. The diagnostic accuracy of each modality was calculated separately for T and N staging as well as for tumour recurrence, and compared using McNemar's test. Values of p <0.017 were considered statistically significant after Bonferroni correction. RESULTS:In 12 patients undergoing (18)F-FDG PET/CT and (18)F-FDG PET/MR for initial tumour staging, T staging was accurate in 50 % with MRI, in 59 % with PET/CT and in 75 % with PET/MR while N staging was accurate in 75 % with MRI, in 77 % with PET/CT and in 71 % with PET/MR in relation to the reference standard. No significant differences were observed in T and N staging among the three modalities (p > 0.017). In 13 patients undergoing hybrid imaging for cancer recurrence diagnosis, diagnostic accuracy was 57 % with MRI and in 72 % with (18)F-FDG PET/CT and (18)F-FDG PET/MR, respectively. Again, no significant differences were found among the three modalities (p > 0.017). CONCLUSION:In this initial study, no significant differences were found among (18)F-FDG PET/MR, (18)F-FDG PET/CT and MRI in local tumour staging and cancer recurrence diagnosis.

In a previous paper, we published the impact of initial [18F]FDG PET/CT (FDG-PET/CT) in high-risk patients with differentiated thyroid cancer (DTC) and described the changes in therapy management. The aim of the present study was to evaluate the prognostic impact of the initial FDG-PET/CT on a patient’s follow-up over three years and the rate of complete remission. Patients, methods: This study included 109 DTC patients who underwent radioiodine treatment (RIT), including post-therapeutic whole-body scintigraphy with FDG-PET/CT and a follow-up over three years. The follow-up included high-resolution sonography of the neck and determination of serum Tg as well as Tg antibodies every six months. The results of initial FDG-PET/CT and whole-body scintigraphy were compared with the status after three years of follow-up. Results: 24/109 patients (22%) presented FDG-positive lesions, 22/109 patients (20%) only iodine-positive lesions, and 63/109 patients (58%) neither FDG-positive nor iodine-positive lesions. After three years, 83/109 patients (76%) revealed full remission, 15/109 patients (14%) tumour persistence and 11/109 patients (10%) a progressive disease. The negative predictive value (NPV) was calculated for patients without FDG-positive lesions (NPV 85%) and patients without any lesions (NPV 91%) regarding full remission in the follow-up. Conclusion: FDG-PET/CT has a high NPV (85% to 91%) in DTC patients regarding recurrence-free follow-up after three years. The change in patient management in patients with iodine-negative lesions can lead to a higher rate of full remissions in the follow-up after additional surgery. Therefore, FDG-PET/CT should be performed in all high-risk DTC patients in the context of the first RIT to improve patient management and risk stratification.

Aim: A theoretical dosimetry-based model was applied to estimate the lowest effective radioiodine activity for thyroid remnant ablation of low-risk differentiated thyroid cancer patients. Patients, methods: The model is based on the distribution of the absorbed (radiation) dose per administered radioiodine activity and the absorbed dose threshold of 300 Gy for thyroid remnants, the level believed to destroy most thyroid remnants. For this purpose, 124I PET/CT images of 49 thyroidectomised patients were retrospectively analysed to measure the distribution of the (average) absorbed doses to thyroid remnant per administered 131I activity. The fraction of thyroid remnants that received at least 300 Gy was determined for standard activities between 0.37 and 5.55 GBq. The lower activity was considered to be equally effective to that obtained with higher activity if the (absolute) fraction difference was below 5%. Results:A total of 62 thyroid remnants were included. The medians and ranges (in parentheses) for the absorbed dose per unit 131I activity were 359 Gy/GBq (34 to 1825 Gy/GBq). The fractions of thyroid remnants receiving more than 300 Gy at different therapy activities (within parentheses) were 60% (1.11 GBq), 76% (1.85 GBq), 79% (2.22 GBq), and 81–82% for activities between 2.59 and 3.70 GBq. The therapy activity of 1.11 GBq is considerably less effective than that of 1.85 or 2.22 GBq; therapy activities were equally effective in the range between 2.22 to 3.70 GBq. Conclusion: On the basis of the model and the patients’ data included, the lowest effective therapy activity appears to be approximately 2.2 GBq to ablate thyroid remnants. The results of this study may help to guide the design of prospective clinical studies.

Background Overall survival (OS) of patients with hepatic metastases of uveal melanoma is strongly linked with hepatic tumor control. Due to the lack of an effective systemic chemotherapy, locoregional therapies like radioembolization should play an increasingly important role. Purpose To report complications and response rates of radioembolization as salvage therapy for hepatic uveal melanoma metastases. Material and Methods Between October 2006 and January 2014, eight patients (age, 59.1 ± 15.3 years; 5 men) with histologically proven uveal melanoma and hepatic metastases received radioembolization with glass microspheres at a single center. All patients had been heavily pretreated with multiple systemic/locoregional therapies resulting in a long median interval between diagnosis of hepatic metastases and radioembolization (17.1 months; range, 6.4–23.2 months). Follow-up consisted of clinical assessment, laboratory tests and tri-phasic computed tomography (CT) before and 1, 3, 6, 9, and 12 months after radioembolization. Response to therapy was evaluated by CT using RECIST version 1.1 and by survival time. Safety (laboratory and clinical toxicity) was rated according to Common Terminology Criteria for Adverse Events 4.03. Using Kaplan-Meier analysis time to progression of hepatic metastases (hTTP) and OS were calculated. Results One month after radioembolization 50% of patients presented with stable and 50% with progressive disease. Median hTTP and OS after radioembolization were 4.3 weeks (range, 3.4–28.6 weeks) and 12.3 weeks (range, 3.7–62.6 weeks), respectively. Median OS after diagnosis of hepatic metastases was 19.9 months (range, 7.3–31.4 months). Radioembolization was tolerated well in all patients without toxicity higher than grade 2. Conclusion Radioembolization is a safe salvage therapy even in heavily pretreated hepatic metastases of uveal melanoma.

Purpose Selective Internal Radiation Therapy (SIRT) with 90yttrium (Y-90) is an increasingly used therapeutic option for unresectable liver malignancies. Nontarget embolization of extrahepatic tissue secondary to vascular shunting can lead to SIRT associated complications. Our aim was to assess whether extrahepatic shunts can reliably be diagnosed based on hepatic digital subtraction angiography (DSA) or whether subsequent SPECT/CT data can provide additional information. Materials and Methods 825 patients with hepatocellular carcinoma (n = 636), hepatic metastases (n = 158) or cholangiocellular carcinoma (n = 31) were retrospectively analyzed. During hepatic DSA 128 arteries causing shunt flow to gastrointestinal tissue were coilembolized (right gastric artery n = 63, gastroduodenal artery n = 29; branches to duodenum / pancreas n = 36). Technectium-99m-labeled human serum albumin (HSA) was injected in all 825 patients. SPECT/CT data was used to identify additional or remaining shunts to extrahepatic tissue. Results An unexpected uptake of HSA in extrahepatic tissue was found by SPECT/CT in 54/825 (6.5%) patients (located in stomach n = 13, duodenum n = 26, distal bowel segments n = 12, kidney n = 1, diaphragm n = 2). These patients underwent repeated DSA and newly identified shunt vessels were coilembolized in 22/54 patients, while in 12/54 patients a more distal catheter position for repeat injection of HSA was chosen. In 20/54 patients the repeated SPECT/CT data still revealed an extrahepatic HSA uptake. These patients did not receive SIRT. Conclusion Most extrahepatic shunts can be identified on DSA prior to Y-90 therapy. However, SPECT-CT data helps to identify additional shunts that were initially not seen on DSA.

UNLABELLED:In high-activity radioiodine therapies for differentiated thyroid cancer, blood dosimetry has been developed to estimate the maximum tolerable activity (MTA) of (131)I that can be safely administered without leading to toxic effects. The reference protocol involves a series of both blood sampling (BS) and whole-body counting (WC) over a period of several days. The aim of this retrospective study was to identify simplified protocols without an appreciable loss of accuracy. METHODS:Data from 211 thyroid cancer patients who received (124)I blood dosimetries were retrospectively analyzed. BS and WC acquired at approximately 1-2, 4, 24, 48, and 96 h or longer after (124)I administration were included. This dataset was used to determine the reference MTA and estimations based on a reduced number of combined data from BS and respective WC. MTA estimates were also determined on the basis of either BS or WC alone using some simplifying assumptions in the dosimetry approach. A simplified protocol was considered equivalent to the reference protocol if the estimates of 95% of the MTAs were within the ±20% range and the absolute maximum percentage deviation did not exceed the limit of 30% in a few cases. Lin's concordance correlation analysis was applied to assess the protocol's agreements. RESULTS:Two equivalent protocols were identified that included both BS and respective WC acquired at only 3 time points (1-2, 24 or 48, and ≥96 h). Further equivalent protocols with only 3 blood samples drawn at similar time points were discovered for patients, who had undergone at least 1 radioiodine therapy. For all equivalent protocols, deviations of the mean absolute percentage MTA were below 9% and Lin's concordance correlation coefficients of 0.95 or greater were found, indicating almost excellent agreement (according to Partik's criteria). CONCLUSION:The pretherapy blood dosimetry protocol can be substantially shortened and may be beneficial to patients and patient management while reducing the radiation exposure to medical staff.

Purpose: To compare the utility of gadolinium ethoxybenzyl diethylenetriamine penta-acetic acid (Gd-EOB-DTPA), a liver-specific magnetic resonance (MR) imaging contrast agent, versus gadobutrol for treatment response evaluation of hepatocellular carcinoma (HCC) after radioembolization.Materials and Methods: This prospective study included 50 patients with HCC undergoing radioembolization. All patients underwent contrast-enhanced computed tomography (CT) and MR imaging with gadobutrol and Gd-EOB-DTPA on 2 consecutive days before radioembolization and 30 days, 90 days, 180 days, and 270 days after radioembolization. The standard of reference indicating tumor progression was CT combined with either alpha-fetoprotein or gamma-glutamyltransferase. Gadobutrol-enhanced MR imaging, Gd-EOB-DTPA-enhanced MR imaging without late phase imaging (Gd-EOB-DTPA), and Gd-EOB-DTPA-enhanced MR imaging with late phase imaging (Gd-EOB-DTPA+) were evaluated by 2 radiologists in consensus using a 4-point scale: 1 = definitely no tumor progression; 2 = probably no tumor progression; 3 = probably tumor progression; 4 = definitely tumor progression. Diagnostic accuracy was assessed with receiver operating characteristic analysis.Results: Tumor progression was detected in 14 of 82 study visits according to the reference standard. Pairwise comparison of the area under the curve showed a tendency toward a larger area under the curve for Gd-EOB-DTPA+ compared with gadobutrol (P = .056). Sensitivity and specificity were higher in Gd-EOB-DTPA+ (0.929 and 0.971) than in Gd-EOB-DTPA- (0.786 and 0.941) or gadobutrol (0.643 and 0.956). In 2 cases, tumor progression was detected by Gd-EOB-DTPA+ and by an increase in alpha-fetoprotein, but not by CT, gadobutrol, or Gd-EOB-DTPA.Conclusions: Gd-EOB-DTPA+ MR imaging was not inferior to gadobutrol-enhanced MR imaging in therapy response evaluation after radioembolization and may allow a more accurate detection of early HCC recurrence in single cases.

UNLABELLED:The aim of this study was to systematically assess the quantitative and qualitative impact of including point-spread function (PSF) modeling into the process of iterative PET image reconstruction in integrated PET/MR imaging. METHODS:All measurements were performed on an integrated whole-body PET/MR system. Three substudies were performed: an (18)F-filled Jaszczak phantom was measured, and the impact of including PSF modeling in ordinary Poisson ordered-subset expectation maximization reconstruction on quantitative accuracy and image noise was evaluated for a range of radial phantom positions, iteration numbers, and postreconstruction smoothing settings; 5 representative datasets from a patient population (total n = 20, all oncologic (18)F-FDG PET/MR) were selected, and the impact of PSF on lesion activity concentration and image noise for various iteration numbers and postsmoothing settings was evaluated; and for all 20 patients, the influence of PSF modeling was investigated on visual image quality and number of detected lesions, both assessed by clinical experts. Additionally, the influence on objective metrics such as changes in SUVmean, SUVpeak, SUVmax, and lesion volume was assessed using the manufacturer-recommended reconstruction settings. RESULTS:In the phantom study, PSF modeling significantly improved activity recovery and reduced the image noise at all radial positions. This effect was measurable only at a high number of iterations (>10 iterations, 21 subsets). In the patient study, again, PSF increased the detected activity in the patient's lesions at concurrently reduced image noise. Contrary to the phantom results, the effect was notable already at a lower number of iterations (>1 iteration, 21 subsets). Lastly, for all 20 patients, when PSF and no-PSF reconstructions were compared, an identical number of congruent lesions was found. The overall image quality of the PSF reconstructions was rated better when compared with no-PSF data. The SUVs of the detected lesions with PSF were substantially increased in the range of 6%-75%, 5%-131%, and 5%-148% for SUVmean, SUVpeak, and SUVmax, respectively. A regression analysis showed that the relative increase in SUVmean/peak/max decreases with increasing lesion size, whereas it increases with the distance from the center of the PET field of view. CONCLUSION:In whole-body PET/MR hybrid imaging, PSF-based PET reconstructions can improve activity recovery and image noise, especially at lateral positions of the PET field of view. This has been demonstrated quantitatively in phantom experiments as well as in patient imaging, for which additionally an improvement of image quality could be observed.

2007 Objectives Analysis of the impact of CT-based attenuation correction on visualization of pulmonary embolism (PE) in lung perfusion SPECT-CT. Methods Lung perfusion SPECT-CT (Symbia T2, Siemens) studies of 45 patients with confirmed PE were analyzed. Comparative quantitative analysis of perfusion defect contrast was performed in attenuation corrected (AC) and non-attenuation corrected (NAC) SPECT data. The lesion-to-background ratio (LBR) of each PE lesion was calculated using the ratio of its average pixel counts to that of adjacent normal lung, each from AC and NAC data (LBRAC and LBRNAC). The AC benefit ratio (ACBR) was defined as the ratio of LBRNAC/LBRAC. The results of each lesion were correlated with the degree of SPECT-CT misalignment (Euclidian distance of misalignment in 3 dimensions, EDM) and with the lesion depth (distance-to-body surface, DBS). Results In total, 94 PE lesions were analyzed. The mean LBR of all lesions was higher for the NAC (0.31 ±0.17) than for the AC images (0.27 ±0.15), p 20 mm) was not lower than that of the remaining lesions (1.24± 0.27 vs. 1.23± 0.37, p=0.929). Conclusions This first systematic set of data on contribution of CT-derived attenuation correction to PE lesion contrast indicates that AC is associated with a better lesion-to-background ratio than NAC. This seems largely independent from the degree of misalignment between SPECT and CT acquisition or the distance-to-body surface.