G K von Schulthess

University of Zurich, Zürich, Zurich, Switzerland

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Publications (296)1033.37 Total impact

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    ABSTRACT: The aim of this study was to investigate the registration accuracy of a newly developed patient shuttle system that can integrate different scanners by patient transfer without repositioning for 'hardware'-based image fusion. We aimed to assess the registration accuracy of image fusion in two different settings: a trimodality PET/CT+MR system and a SPECT+CT system.
    Nuclear Medicine Communications 10/2014; · 1.38 Impact Factor
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    ABSTRACT: (d)-(18)F-fluoromethyltyrosine (d-(18)F-FMT), or BAY 86-9596, is a novel (18)F-labeled tyrosine derivative rapidly transported by the l-amino acid transporter (LAT-1), with a faster blood pool clearance than the corresponding l-isomer. The aim of this study was to demonstrate the feasibility of tumor detection in patients with non-small cell lung cancer (NSCLC) or head and neck squamous cell cancer (HNSCC) compared with inflammatory and physiologic tissues in direct comparison to (18)F-FDG.
    Journal of nuclear medicine : official publication, Society of Nuclear Medicine. 09/2014;
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    ABSTRACT: Purpose To assess the diagnostic performance of whole-body non-contrast material-enhanced positron emission tomography (PET)/magnetic resonance (MR) imaging and PET/computed tomography (CT) for staging and restaging of cancers and provide guidance for modality and sequence selection. Materials and Methods This study was approved by the institutional review board and national government authorities. One hundred six consecutive patients (median age, 68 years; 46 female and 60 male patients) referred for staging or restaging of oncologic malignancies underwent whole-body imaging with a sequential trimodality PET/CT/MR system. The MR protocol included short inversion time inversion-recovery (STIR), Dixon-type liver accelerated volume acquisition (LAVA; GE Healthcare, Waukesha, Wis), and respiratory-gated periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER; GE Healthcare) sequences. Primary tumors (n = 43), local lymph node metastases (n = 74), and distant metastases (n = 66) were evaluated for conspicuity (scored 0-4), artifacts (scored 0-2), and reader confidence on PET/CT and PET/MR images. Subanalysis for lung lesions (n = 46) was also performed. Relevant incidental findings with both modalities were compared. Interreader agreement was analyzed with intraclass correlation coefficients and κ statistics. Lesion conspicuity, image artifacts, and incidental findings were analyzed with nonparametric tests. Results Primary tumors were less conspicuous on STIR (3.08, P = .016) and LAVA (2.64, P = .002) images than on CT images (3.49), while findings with the PROPELLER sequence (3.70, P = .436) were comparable to those at CT. In distant metastases, the PROPELLER sequence (3.84) yielded better results than CT (2.88, P < .001). Subanalysis for lung lesions yielded similar results (primary lung tumors: CT, 3.71; STIR, 3.32 [P = .014]; LAVA, 2.52 [P = .002]; PROPELLER, 3.64 [P = .546]). Readers classified lesions more confidently with PET/MR than PET/CT. However, PET/CT showed more incidental findings than PET/MR (P = .039), especially in the lung (P < .001). MR images had more artifacts than CT images. Conclusion PET/MR performs comparably to PET/CT in whole-body oncology and neoplastic lung disease, with the use of appropriate sequences. Further studies are needed to define regionalized PET/MR protocols with sequences tailored to specific tumor entities. © RSNA, 2014 Online supplemental material is available for this article.
    Radiology 08/2014; · 6.34 Impact Factor
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    ABSTRACT: The purpose of this study was to analyze whether diffusion-weighted imaging (DWI) adds significant information to positron emission tomography/magnetic resonance imaging (PET/MRI) on lesion detection and characterization in head and neck cancers.
    European journal of nuclear medicine and molecular imaging 08/2014; · 5.11 Impact Factor
  • Gustav K von Schulthess, Patrick Veit-Haibach
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    ABSTRACT: Many groups attempt to optimize imaging protocols on PET/MR imaging systems. Although research protocols may take as long as 60-90 min, much more efficient clinical workflows are needed to achieve cost-effective examination times of less than 1 h. Considering these difficulties, simultaneous PET/MR imaging is an intriguing research tool, but its clinical applications are uncertain or just beginning to emerge. However, unlike PET/CT, in which the options for various CT protocols are limited, the MR imaging portion of PET/MR imaging can be extended arbitrarily depending on the MR pulse sequences chosen. For PET/MR imaging to be complementary, feasible, and somewhat competitive with PET/CT, image acquisition times should ideally be limited to 30 min. The purposes of this article are to help the reader to understand the critical workflow issues in simultaneous PET/MR imaging in comparison with sequential PET/MR imaging and to learn how to optimize an imaging examination. Current knowledge toward this goal is summarized.
    Journal of Nuclear Medicine 05/2014; · 5.77 Impact Factor
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    ABSTRACT: Positron emission tomography (PET)/MRI combines the functional ability of PET and the high soft tissue contrast of MRI. The aim of this study was to assess contrast-enhanced (ce)PET/MRI compared to cePET/CT in patients with suspected recurrence of head and neck cancer (HNC). Eighty-seven patients underwent sequential cePET/CT and cePET/MRI using a trimodality PET/CT-MRI set-up. Diagnostic accuracy for the detection of recurrent HNC was evaluated using cePET/CT and cePET/MRI. Furthermore, image quality, presence of unclear (18)F-fluorodeoxy-D-glucose (FDG) findings of uncertain significance and the diagnostic advantages of use of gadolinium contrast enhancement were analysed. cePET/MRI showed no statistically significant difference in diagnostic accuracy compared to cePET/CT (91.5 vs 90.6 %). Artefacts' grade was similar in both methods, but their location was different. cePET/CT artefacts were primarily located in the suprahyoid area, while on cePET/MRI, artefacts were more equally distributed among the supra and infrahyoid neck regions. cePET/MRI and cePET/CT showed 34 unclear FDG findings; of those 11 could be solved by cePET/MRI and 5 by cePET/CT. The use of gadolinium in PET/MRI did not yield higher diagnostic accuracy, but helped to better define tumour margins in 6.9 % of patients. Our data suggest that cePET/MRI may be superior compared to cePET/CT to specify unclear FDG uptake related to possible tumour recurrence in follow-up of patients after HNC. It seems to be the modality of choice for the evaluation of the oropharynx and the oral cavity because of a higher incidence of artefacts in cePET/CT in this area mainly due to dental implants. However, overall there is no statistically significant difference.
    European Journal of Nuclear Medicine 02/2014; · 4.53 Impact Factor
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    ABSTRACT: Considering PET/MR imaging as a whole-body staging tool, scan time restrictions in a single body area are mandatory for the cost-effective clinical operation of an integrated multimodality scanner setting. It has to be considered that (18)F-FDG already acts as a contrast agent and that under certain circumstances MR contrast may not yield additional clinically relevant information. The concept of the present study was to understand which portions of the imaging information enhance the sensitivity and specificity of the hybrid examination and which portions are redundant. One hundred fifty consecutive patients referred for primary staging or restaging of head and neck cancer underwent sequential whole-body (18)F-FDG PET with CT-based attenuation correction, contrast-enhanced (ce) CT, and conventional diagnostic MR imaging of the head and neck in a trimodality PET/CT-MR system. Assessed were image quality, lesion conspicuity, diagnostic confidence, and the benefit of additional coronal and sagittal imaging planes in cePET/CT, PET/MR imaging with only T2-weighted fat-suppressed images (T2w PET/MR imaging), and cePET/MR imaging. In 85 patients with at least 1 PET-positive lesion, 162 lesions were evaluated. Similar robustness was found for CT and MR image quality. T2w PET/MR imaging performed similarly to (metastatic lymph nodes) or better than (primary tumors) cePET/CT in the morphologic characterization of PET-positive lesions and permitted the diagnosis of necrotic or cystic lymph node metastasis without application of intravenous contrast medium. CePET/MR imaging yielded a higher diagnostic confidence for accurate lesion conspicuity (especially in the nasopharynx and in the larynx), infiltration of adjacent structures, and perineural spread. The results of the present study provide evidence that PET/MR imaging can serve as a legitimate alternative to PET/CT in the clinical workup of patients with head and neck cancers. Intravenous MR contrast medium may be applied only if the exact tumor extent or infiltration of crucial structures is of concern (i.e., preoperatively) or if perineural spread is anticipated. In early assessment of the response to therapy, in follow-up examinations, or in a whole-body protocol for non-head and neck tumors, T2w PET/MR imaging may be sufficient for coverage of the head and neck. The additional MR scanning time may instead be used for advanced MR techniques to increase the specificity of the hybrid imaging examination.
    Journal of Nuclear Medicine 02/2014; · 5.77 Impact Factor
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    ABSTRACT: To compare the accuracy of PET/MR imaging with that of FDG PET/CT and to determine the MR sequences necessary for the detection of liver metastasis using a trimodality PET/CT/MR set-up. Included in this single-centre IRB-approved study were 55 patients (22 women, age 61 ± 11 years) with suspected liver metastases from gastrointestinal cancer. Imaging using a trimodality PET/CT/MR set-up (time-of-flight PET/CT and 3-T whole-body MR imager) comprised PET, low-dose CT, contrast-enhanced (CE) CT of the abdomen, and MR with T1-W/T2-W, diffusion-weighted (DWI), and dynamic CE imaging. Two readers evaluated the following image sets for liver metastasis: PET/CT (set A), PET/CECT (B), PET/MR including T1-W/T2-W (C), T1-W/T2-W with either DWI (D) or CE imaging (E), and a combination (F). The accuracy of each image set was determined by receiver-operating characteristic analysis using image set B as the standard of reference. Of 120 liver lesions in 21/55 patients (38 %), 79 (66 %) were considered malignant, and 63/79 (80 %) showed abnormal FDG uptake. Accuracies were 0.937 (95 % CI 89.5 - 97.9 %) for image set A, 1.00 (95 % CI 99.9 - 100.0 %) for set C, 0.998 (95 % CI 99.4 - 100.0 %) for set D, 0.997 (95 % CI 99.3 - 100.0 %) for set E, and 0.995 (95 % CI 99.0 - 100.0 %) for set F. Differences were significant for image sets D - F (P < 0.05) when including lesions without abnormal FDG uptake. As shown by follow-up imaging after 50 - 177 days, the use of image sets D and both sets E and F led to the detection of metastases in one and three patients, respectively, and further metastases in the contralateral lobe in two patients negative on PET/CECT (P = 0.06). PET/MR imaging with T1-W/T2-W sequences results in similar diagnostic accuracy for the detection of liver metastases to PET/CECT. To significantly improve the characterization of liver lesions, we recommend the use of dynamic CE imaging sequences. PET/MR imaging has a diagnostic impact on clinical decision making.
    European Journal of Nuclear Medicine 12/2013; · 4.53 Impact Factor
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    ABSTRACT: PURPOSE To assess and to compare the diagnostic accuracy of PET/CT and PET/MRI in primary and metastatic gynaecological malignancies. METHOD AND MATERIALS 13 patients (13 female, mean age: 64, range 55-76years) with different primary and recurrent gynaecological diseases underwent a contrast-enhanced tri-modality PET/CT-MRI examination (PET/CT D 690 and 3T MRI 750W, GE Healthcare). Patients were first injected with an average of 320 MBq F18-FDG and then rested for 30 minutes. Then, a full diagnostic, contrast-enhanced MRI of the abdomen and pelcis, based on the current guidelines, was acquired with the following sequences: coronal T2 SSFSE pelvis, axial T2 SSFSE liver, axial T1 LaveFlex whole abdomen, axial diffusion pelvis, sagittal/axial T2 propeller pelvis, sag/axial T1 LavaFlex post contrast whole abomden. After the MRI, patients were transferred on a dedicated shuttle to the PET/CT. Here, a standard PET/CT with /without intravenous contrast media was acquired (FOV mid-thigh to the vertex of the skull. CT: 50-79 mAs/slice, automated dose modulation 120 kVp, 3.75 mm slice thickness. PET: 3D mode, 2 minutes/bed, iterative reconstruction with 3 iterations, 18 subsets). All data were evaluated on a commercially available workstation and can be displayed as PET, CT, PET/CT and PET/MRI. PET/MRI and PET/CT were evaluated concerning detection and conspicuity of the primary tumor, lymph node metastases and distant metastases. Readers also evaluated if the PET/MRI revealed relevant additional information compared to PET/CT. RESULTS Acquisition of PET/CT-MRI and PET/CT vs. PET/MRI evaluation was feasible in all patients. Concerning the primary tumour, the PET/CT was superior in 2 cases, PET/MRI in 5 cases, concerning lymph nodes PET/CT was superior in 2 cases, PET/MRI in 2 cases, in abdominal metastases PET/CT was superior in 2 cases, PET/MRI in none. PET/CT overall showed additional relevant additional information in 9 cases mainly concerning distant metastases, while PET/MRI showed relevant additional information in 3 cases concerning the primary tumour. CONCLUSION PET/MRI is well feasible within a tri-modality PET/CT-MRI system. The PET/MRI shows mainly advantages concerning the evaluation of the pimary tumor/local pelvic situation while the PET/CT has advantages concerning distant metastases. CLINICAL RELEVANCE/APPLICATION PET/MRI might be eligible to replace PET/CT in the work-up of OB-Gyn cancers.
    Radiological Society of North America 2013 Scientific Assembly and Annual Meeting; 12/2013
  • Gustav K von Schulthess
    Journal of Magnetic Resonance Imaging 09/2013; · 2.57 Impact Factor
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    ABSTRACT: OBJECTIVES: The purpose of this study was to evaluate if positron emission tomography (PET)/magnetic resonance imaging (MRI) with just one gradient echo sequence using the body coil is diagnostically sufficient compared with a standard, low-dose non-contrast-enhanced PET/computed tomography (CT) concerning overall diagnostic accuracy, lesion detectability, size and conspicuity evaluation. METHODS AND MATERIALS: Sixty-three patients (mean age 58 years, range 19-86 years; 23 women, 40 men) referred for either staging or restaging/follow-up of various malignant tumours (malignant melanoma, lung cancer, breast cancer, Hodgkin's lymphoma, non-Hodgkin's lymphoma, CUP, gynaecology tumours, pleural mesothelioma, oesophageal cancer, colorectal cancer, stomach cancer) were prospectively included. Imaging was conducted using a tri-modality PET/CT-MR set-up (full ring, time-of-flight Discovery PET/CT 690, 3 T Discovery MR 750, both GE Healthcare, Waukesha, WI). All patients were positioned on a dedicated PET/CT- and MR-compatible examination table, allowing for patient transport from the MR system to the PET/CT without patient movement. In accordance with RECIST 1.1 criteria, measurements of the maximum lesion diameters on CT and MR images were obtained. In lymph nodes, the short axis was measured. A four-point scale was used for assessment of lesion conspicuity: 1 (>25 % of lesion borders definable), 2 (25-50 %), 3 (50-75 %) and 4 (>75 %). For each lesion the corresponding anatomical structure was noted based on anatomical information of the spatially co-registered PET/CT and PET/MRI image sections. Additionally, lesions were divided into three categories: "tumour mass", "lymph nodes" and "lesions". Differences in overall lesion detectability and conspicuity in PET/CT and PET/MRI, as well as differences in detectability based on the localisation and lesion type, were analysed by Wilcoxon signed rank test. RESULTS: A total of 126 PET-positive lesions were evaluated. Overall, no statistically significant superiority of PET/CT over PET/MRI or vice versa in terms of lesion conspicuity was found (p = 0.095; mean score CT 2.93, mean score MRI 2.75). A statistically significant superiority concerning conspicuity of PET/CT over PET/MRI was found in pulmonary lesions (p = 0.016). Additionally, a statistically significant superiority of PET/CT over PET/MRI in "lymph nodes" regarding lesion conspicuity was also found (p = 0.033). A higher mean score concerning bone lesions were found for PET/CT compared with PET/MRI; however, these differences did not achieve statistical significance. CONCLUSION: Overall, PET/MRI with body coil acquisition does not match entirely the diagnostic accuracy of standard low-dose PET/CT. Thus, it might only serve as a back-up solution in very few patients. Overall, more time needs to be invested on the MR imaging part (higher matrix, more breath-holds, additional surface coil acquired sequences) to match up with the standard low-dose PET/CT. MAIN MESSAGES : • Evaluation of whether PET/MRI with one sequence using body coil is diagnostically sufficient compared with PET/CT • PET/MRI with body coil does not match entirely the diagnostic accuracy of standard low-dose PET/CT • PET/MRI might only serve as a backup solution in patients.
    Insights into imaging. 05/2013;
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    ABSTRACT: Although clinical positron emission tomography (PET)/computed tomography (CT) applications were obvious and have completely replaced PET in oncology, clinical applications of PET/magnetic resonance (MR) are currently not clearly defined. This is due to the lack of clinical data, which is mainly because PET/MR technology is not clinically mature at this point. Open issues are technical and concern ease of obtaining PET attenuation correction maps, dealing with, for example, MR surface coil metal in the PET field-of-view and appropriate workflows leading to a cost-effective examination. All issues can be circumvented by using a shuttle-connected PET/CT-MR system, but the penalty is that simultaneous PET and MR imaging are not possible and potential motion between examinations may occur. Clinically, some systems installed worldwide start to have a reasonable bulk of clinical data. Preliminary results suggest that in oncology, PET/MR may have advantages over PET/CT in head and neck imaging. In liver imaging, more PET-positive lesions are seen on MR than on CT, but that does not mean that PET/MR is superior to PET/CT. Possibly in some settings where a contrast-enhanced PET/CT is needed to be diagnostic, PET/MR can be done without contrast media. Although PET/CT has virtually no role in brain imaging, this may be an important domain for PET/MR, particularly in dementia imaging. The role of PET/MR in the heart is as yet undefined, and much research will have to be done to elucidate this role. At this point, it is also not clear where the simultaneity afforded by a fully integrated PET/MR is really needed. Sequential data acquisition even on separate systems and consecutive software image fusion may well be appropriate. With the increasing installed base of systems, clinical data will be forthcoming and define more clearly where there is clinical value in PET/MR at an affordable price.
    Seminars in nuclear medicine 01/2013; 43(1):3-10. · 3.96 Impact Factor
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    ABSTRACT: OBJECTIVE: The objective of this study was to prospectively compare the detection rate, the location, and the size of pulmonary nodules in low-dose computed tomography (CT) and in magnetic resonance (MR) imaging with a 3-dimensional (3D) dual-echo gradient-echo (GRE) pulse sequence using a trimodality positron emission tomography (PET)/CT-MR setup. METHODS: Forty consecutive patients (25 men and 15 women; mean [SD] age 64 [12] years) referred for staging of malignancy were prospectively included in this single-center, Institutional Review Board-approved study. Imaging using trimodality PET/CT-MR setup (full ring, time-of-flight PET/CT and 3-T whole-body MR imager) comprised PET, low-dose CT for anatomic referencing/attenuation correction of PET, and MR imaging with 3D dual-echo GRE pulse sequence, allowing the reconstruction of water-only (WO) and in-phase (IP) images. Two blinded and independent readers assessed all images randomly for the presence, the location, and the size of pulmonary nodules. Detection rates, defined as the proportion of screened participants with at least 1 pulmonary nodule, were compared between low-dose CT and MR imaging including both WO and IP images. RESULTS: Inter-reader agreements were high regarding the location (k = 0.93-0.98) and the size of pulmonary nodules (intraclass correlation analysis = 0.94-0.98) in CT and in MR imaging. Computed tomographic scans revealed 66 pulmonary nodules in 34 of the 40 patients (85%), whereas WO and IP images showed 56 and 58 pulmonary nodules in 33 of the 40 patients (83%), respectively. The detection rates of CT and MR imaging were similar (P's > 0.05) regarding all nodules, 18F-Fluordesoxyglucose-positive pulmonary nodules, and 18F-Fluordesoxyglucose-negative pulmonary nodules. The size of pulmonary nodules was significantly smaller on WO (P < 0.05; mean difference, 3 mm; 95% confidence interval, - 13 to 18 mm) and IP images (P < 0.001; mean difference, 4 mm; 95% confidence interval, -5 to 12 mm) compared with in CT. CONCLUSIONS: Our study indicates that a 3D Dixon-based, dual-echo GRE pulse sequence might be suitable for lung imaging in clinical whole-body PET/MR examinations. Although the detection rates were lower, there was no statistically significant difference on a patient-based evaluation concerning detection rates of pulmonary nodules compared with low-dose CT. Assessment of nodule location can be performed equally well with MR imaging.
    Investigative radiology 10/2012; · 4.85 Impact Factor
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    ABSTRACT: Tri-modality PET/CT-MRI includes the transfer of the patient on a dedicated shuttle from one system into the other. Advantages of this system include a true CT-based attenuation correction, reliable PET-quantification and higher flexibility in patient throughput on both systems. Comparative studies of PET/MRI versus PET/CT are readily accomplished without repeated PET with a different PET scanner at a different time point. Additionally, there is a higher imaging flexibility based on the availability of three imaging modalities, which can be combined for the characterization of the disease. The downside is a somewhat higher radiation dose of up to 3 mSv with a low dose CT based on the CT-component, longer acquisition times and potential misalignment between the imaging components. Overall, the tri-modality PET/CT-MR system offers comparative studies using the three different imaging modalities in the same patient virtually at the same time, and may help to develop reliable attenuation algorithms at the same time.
    MAGMA Magnetic Resonance Materials in Physics Biology and Medicine 10/2012; · 1.86 Impact Factor
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    ABSTRACT: PURPOSE: PET/MR has the potential to become a powerful tool in clinical oncological imaging. The purpose of this prospective study was to evaluate the performance of a single T1-weighted (T1w) fat-suppressed unenhanced MR pulse sequence of the abdomen in comparison with unenhanced low-dose CT images to characterize PET-positive lesions. METHODS: A total of 100 oncological patients underwent sequential whole-body (18)F-FDG PET with CT-based attenuation correction (AC), 40 mAs low-dose CT and two-point Dixon-based T1w 3D MRI of the abdomen in a trimodality PET/CT-MR system. PET-positive lesions were assessed by CT and MRI with regard to their anatomical location, conspicuity and additional relevant information for characterization. RESULTS: From among 66 patients with at least one PET-positive lesion, 147 lesions were evaluated. No significant difference between MRI and CT was found regarding anatomical lesion localization. The MR pulse sequence used performed significantly better than CT regarding conspicuity of liver lesions (p < 0.001, Wilcoxon signed ranks test), whereas no difference was noted for extrahepatic lesions. For overall lesion characterization, MRI was considered superior to CT in 40 % of lesions, equal to CT in 49 %, and inferior to CT in 11 %. CONCLUSION: Fast Dixon-based T1w MRI outperformed low-dose CT in terms of conspicuity and characterization of PET-positive liver lesions and performed similarly in extrahepatic tumour manifestations. Hence, under the assumption that the technical issue of MR AC for whole-body PET examinations is solved, in abdominal PET/MR imaging the replacement of low-dose CT by a single Dixon-based MR pulse sequence for anatomical lesion correlation appears to be valid and robust.
    European Journal of Nuclear Medicine 09/2012; · 4.53 Impact Factor
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    ABSTRACT: This study compares the frequency and distribution of increased activity on 18 F-fluoride PET/CT with the presence of bone marrow edema on whole-body MR imaging in the spine and sacroiliac joints (SIJ) of patients with active ankylosing spondylitis (AS). Ten patients (6 men and 4 women), between 30 and 58 years old (median 44) with active AS, were prospectively examined with both whole-body MRI and 18 F-fluoride PET/CT. Patients fulfilled modified NY criteria and had a Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) of at least 4. Increased radiotracer uptake in PET/CT and bone marrow edema in whole-body MRI of spine and SIJ was evaluated independently by two blinded observers for each modality. Kappa statistics were used to compare interobserver agreement as well as scores of consensus reading of the two imaging modalities. Analysis of interobserver agreement for PET/CT yielded a kappa value of 0.68 for spinal lesions and of 0.88 for SIJ lesions. The corresponding kappa values for the MRI modality were 0.64 and 0.93, respectively. More spinal lesions were detected by MRI in comparison to PET/CT (68 vs. 38), whereas a similar number of SIJ quadrants scored positive in both modalities (19 vs. 17). Analysis of agreement of lesion detection between both imaging modalities yielded a kappa value of only 0.25 for spinal lesions and of 0.64 for SIJ lesions. Increased 18 F-fluoride uptake in PET/CT is only modestly associated with bone marrow edema on MRI in the spine and SIJ of patients with AS, suggesting different aspects of bone involvement in AS.
    EJNMMI research. 07/2012; 2(1):38.
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    ABSTRACT: Accurate attenuation correction (AC) is essential for quantitative analysis of PET tracer distribution. In MR, the lack of cortical bone signal makes bone segmentation difficult and may require implementation of special sequences. The purpose of this study was to evaluate the need for accurate bone segmentation in MR-based AC for whole-body PET/MR imaging. In 22 patients undergoing sequential PET/CT and 3-T MR imaging, modified CT AC maps were produced by replacing pixels with values of >100 HU, representing mostly bone structures, by pixels with a constant value of 36 HU corresponding to soft tissue, thereby simulating current MR-derived AC maps. A total of 141 FDG-positive osseous lesions and 50 soft-tissue lesions adjacent to bones were evaluated. The mean standardized uptake value (SUVmean) was measured in each lesion in PET images reconstructed once using the standard AC maps and once using the modified AC maps. Subsequently, the errors in lesion tracer uptake for the modified PET images were calculated using the standard PET image as a reference. Substitution of bone by soft tissue values in AC maps resulted in an underestimation of tracer uptake in osseous and soft tissue lesions adjacent to bones of 11.2 ± 5.4% (range 1.5-30.8%) and 3.2 ± 1.7% (range 0.2-4%), respectively. Analysis of the spine and pelvic osseous lesions revealed a substantial dependence of the error on lesion composition. For predominantly sclerotic spine lesions, the mean underestimation was 15.9 ± 3.4% (range 9.9-23.5%) and for osteolytic spine lesions, 7.2 ± 1.7% (range 4.9-9.3%), respectively. CT data simulating treating bone as soft tissue as is currently done in MR maps for PET AC leads to a substantial underestimation of tracer uptake in bone lesions and depends on lesion composition, the largest error being seen in sclerotic lesions. Therefore, depiction of cortical bone and other calcified areas in MR AC maps is necessary for accurate quantification of tracer uptake values in PET/MR imaging.
    European Journal of Nuclear Medicine 04/2012; 39(7):1154-60. · 4.53 Impact Factor
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    ABSTRACT: Reliable 18F-fluorodeoxyglucose (FDG) uptake quantification is crucial for cancer treatment monitoring. While interobserver variability has been found to be lower for a maximum standard uptake value (SUV)max than for an averaged SUV (SUVmean), the repeatability has not been investigated yet. In this study, we determined the repeatability of SUV values in two sequential measurements 5 min apart. Positron emission tomography data of malignant chest tumors were acquired dynamically during 45 min in 20 patients. SUV values were derived from the hottest (SUVmax), the mean of the 5 (SUV5) and 10 (SUV10) hottest voxels and the mean of a volume of interest (SUVmean). The repeatability of the SUV measurements was determined as the standard deviation of the difference between the values at 40 and 45 min and represented as Bland-Altman graphs. The standard deviation of the difference between the two sequential scans for SUVmax, SUV5, SUV10 and SUVmean was 1.01, 0.53, 0.37 and 0.28. The repeatability of SUV is markedly increased by deriving the value from multiple voxels. Compared to SUVmax, the variability in SUV measurements is reduced by a factor of 2.7 (2.7=1.01/0.37) if 10 voxels are pooled.
    Nuclear Medicine and Biology 02/2012; 39(5):666-70. · 2.52 Impact Factor
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    ABSTRACT: PURPOSE Increasing interest in hybrid PET/MR has led to the recent introduction of 3 different types of imaging systems from major vendors: sequential PET/MR, integrated PET/MR and sequential MR-PET/CT. In this MR-PET/CT study, we compare the diagnostic utility of PET/MR versus PET/CT in the abdomen. METHOD AND MATERIALS Nineteen oncologic patients (mean age 55) were examined on a TOF-PET/CT (unenhanced low dose CT)- and 3T MR platform (GE Discovery 690 & 750, respectively) integrated by a shuttle system. A connecting patient transfer table allowed torso coil application (GE) after PET/CT, in order to avoid coil-induced CT and PET AC artefacts while maintaining unaltered patient position. Subsequently, a T1w 3D GRE acquisition (LAVA, 32 sec) of the abdomen without contrast enhancement was obtained. PET/MR and PET/CT data were analysed independently by two double board certified radiologists/nuclear physicians using commercial software (AW4.5) to characterize PET-positive lesions while using 3-point scale to grade lesion conspicuity in CT and MR. Cohen κ statistics were calculated for interobserver agreement and the Wilcoxon rank-sum test was employed for intraobserver conspicuity grading. RESULTS A total of 27 PET positive lesions were evaluated at PET/CT and PET/MR in the liver (n=12), bone (n=4), bowel (n=3), pleura (n=2), lung (n=2), fat (n=2), pancreas (n=1) and epidural (n=1). Lesions were characterized and graded based on conspicuity in CT and MR with moderate (κ=0.59) and good (κ=0.70) interobserver agreement, respectively. In the overall lesion-based comparison, no significant difference was found, although a tendency for MR to outperform CT is apparent (p=0.11 & 0.08). However, in comparing liver lesions, MR performed significantly better than CT (p<0.01 for both readers). CONCLUSION In preliminary data, PET/MR tends to outperform PET/CT in abdominal lesion characterisation and conspicuity when using unenhanced CT and MR, although this difference falls short of statistical significance. In the liver, however, the difference is significant. While requiring confirmation, these results nonetheless suggest the potential utility of integrated PET/MR over PET/CT in the abdomen. CLINICAL RELEVANCE/APPLICATION PET/MR tends to outperform PET/CT in terms of lesion conspicuity and characterisation in the abdomen, particularly in the liver, suggesting the potential utility of integrated PET/MR over PET/CT.
    Radiological Society of North America 2011 Scientific Assembly and Annual Meeting; 11/2011
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    ABSTRACT: PURPOSE Shuttle systems have been developed to integrate PET/CT and MR scanners permitting to transfer patients without patient repositioning between scans. The systems were designed such that MR surface coils can be installed and removed without moving the patient. Thus surface coil-induced CT beam-hardening and PET attenuation-artefacts are avoided. The purpose of this study was to assess the registration accuracy of this tri-modality PET/CT+MR system based on MR to CT registration analysis. METHOD AND MATERIALS In this prospective study, 14 patients underwent sequential PET/CT and 3T abdominal MRI using a dedicated torso surface coil. Either a custom built side-loading shuttle system (n = 9) or a front-loading system (n = 5) were used to transfer patients from a time-of-flight PET/CT system (Discovery PET/CT 690) to a 3T MR imaging system (Discovery MR750, both GE Healthcare) installed in an adjacent room. Rigid 3D image registration of abdominal CT and MR images was done using dedicated registration software (Integrated Registration, Advantage Workstation, GE Healthcare). Axial T1w fast dual gradient echo MR images were used for registration. The best match between CT (reference) and MR images was found by manual repositioning of MR images using anatomical landmarks. Offsets were recorded in X- (lateral), Y- (anterior-posterior) and Z-axis (cranio-caudal). RESULTS The mean offset between CT and MR images in all patients was 7 ± 7.5 mm in the X-axis, 4.9 ± 4 mm in the Y-axis and 3.6 ± 4.9 mm in the Z-axis. The front-loading system performed better than the side-loading system with corresponding mean offsets of 1.5 ± 1.5 mm vs. 10.1 ± 7.8 mm in the X-axis, 0.9 ± 1.1 mm vs. 7.2 ± 3.1 mm in the Y-axis and 4.4 ± 4.4 mm vs. 3.2 ± 5.4 mm in the Z axis, respectively. CONCLUSION Sequential PET/CT and MR imaging using dedicated patient transporter systems typically result in only sub-centimeter offsets between CT and MR data sets. Accurate correction of these patient transfer offsets using dedicated registration software was successful in all study patients. Minor shuttle system modifications can further improve registration accuracy. CLINICAL RELEVANCE/APPLICATION Sequential PET/CT and MRI acquisition using dedicated patient transporter systems allows accurate registration of multi-modality PET/CT and MR imaging data sets.
    Radiological Society of North America 2011 Scientific Assembly and Annual Meeting; 11/2011

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8k Citations
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Institutions

  • 1986–2014
    • University of Zurich
      • • Center for Integrative Human Physiology
      • • Department of Pediatric Orthopaedics
      • • Internal Medicine Unit
      Zürich, Zurich, Switzerland
  • 2008
    • Department of Nuclear Medicine
      Nyitra, Nitriansky, Slovakia
  • 2005
    • Schulthess Klinik, Zürich
      Zürich, Zurich, Switzerland
  • 2002
    • University of Wisconsin, Madison
      • Department of Medical Physics
      Madison, MS, United States
    • Universitätsspital Basel
      • Klinik für Allgemeinchirurgie
      Bâle, Basel-City, Switzerland
  • 1999
    • Universität Bern
      • Department of Geriatric Psychiatry
      Bern, BE, Switzerland
  • 1993
    • University of Cologne
      Köln, North Rhine-Westphalia, Germany
    • Psychiatrische Universitätsklinik Zürich
      Zürich, Zurich, Switzerland
  • 1987
    • ETH Zurich
      Zürich, Zurich, Switzerland