Individual refinement of attenuation correction maps for hybrid PET/MR based on multi-resolution regional learning

PET/MR is an emerging hybrid imaging modality. However, attenuation correction (AC) remains challenging for hybrid PET/MR in generating accurate PET images. Segmentation-based methods on special MR sequences are most widely recommended by vendors. However, their accuracy is usually not high. Individual refinement of available certified attenuation maps may be helpful for further clinical applications. In this study, we proposed a multi-resolution regional learning (MRRL) scheme to utilize the internal consistency of the patient data. The anatomical and AC MR sequences of the same subject were employed to guide the refinement of the provided AC maps. The developed algorithm was tested on 9 patients scanned consecutively with PET/MR and PET/CT (7 [¹⁸F]FDG and 2 [¹⁸F]FET). The preliminary results showed that MRRL can improve the accuracy of segmented attenuation maps and consequently the accuracy of PET reconstructions.

T-replete haploidentical allogeneic transplantation using post-transplantation cyclophosphamide in advanced AML and myelodysplastic syndromes

Unmanipulated haploidentical transplantation (Haplo-SCT) using post-transplantation cyclophosphamide (PT-Cy) represents an alternative for patients with high-risk diseases lacking HLA-identical donor. Although it provides low incidences of GVHD, the efficacy of Haplo-SCT is still questioned, especially for patients with myeloid malignancies. Thus, we analyzed 60 consecutive patients with refractory (n=30) or high-risk CR (n=30) AML or myelodysplastic syndromes (MDSs) who underwent PT-Cy Haplo-SCT. The median age was 57 years (22-73 years), hematopoietic cell transplantation comorbidity index was ⩾3 in 38 patients (63%) and Haplo-SCT was the second allogeneic transplantation for 10 patients (17%). Although most of patients received PBSC as graft source (n=48, 80%), we found low incidences of grade 3-4 acute (2%) and severe chronic GVHD (4%). Among patients with high-risk CR diseases, 1-year non-relapse mortality, cumulative incidence of relapse, progression-free and overall survivals were 20%, 32%, 47% and 62%, respectively. In patients with refractory disease, corresponding results were 34%, 35%, 32% and 37%, respectively. We conclude that PT-Cy Haplo-SCT could provide promising anti-leukemic effect even in the setting of very advanced diseases. Thus, it represents a viable alternative for high-risk AML/MDS patients without HLA-identical donor.

Motion correction strategies for integrated PET/MR

Integrated whole-body PET/MR facilitates the implementation of a broad variety of respiratory motion correction strategies, taking advantage of the strengths of both modalities. The goal of this study was the quantitative evaluation with clinical data of different MR- and PET-data-based motion correction strategies for integrated PET/MR.

METHODS

The PET and MR data of 20 patients were simultaneously acquired for 10 min on an integrated PET/MR system after administration of (18)F-FDG or (68)Ga-DOTANOC. Respiratory traces recorded with a bellows were compared against MR self-gating signals and signals extracted from PET raw data with the sensitivity method, by applying principal component analysis (PCA) or Laplacian eigenmaps and by using a novel variation combining the former and either of the latter two. Gated sinograms and MR images were generated accordingly, followed by image registration to derive MR motion models. Corrected PET images were reconstructed by incorporating this information into the reconstruction. An optical flow algorithm was applied for PET-based motion correction. Gating and motion correction were evaluated by quantitative analysis of apparent tracer uptake, lesion volume, displacement, contrast, and signal-to-noise ratio.

RESULTS

The correlation between bellows- and MR-based signals was 0.63 ± 0.19, and that between MR and the sensitivity method was 0.52 ± 0.26. Depending on the PET raw-data compression, the average correlation between MR and PCA ranged from 0.25 ± 0.30 to 0.58 ± 0.33, and the range was 0.25 ± 0.30 to 0.42 ± 0.34 if Laplacian eigenmaps were applied. By combining the sensitivity method and PCA or Laplacian eigenmaps, the maximum average correlation to MR could be increased to 0.74 ± 0.21 and 0.70 ± 0.19, respectively. The selection of the best PET-based signal for each patient yielded an average correlation of 0.80 ± 0.13 with MR. Using the best PET-based respiratory signal for gating, mean tracer uptake increased by 17 ± 19% for gating, 13 ± 10% for MR-based motion correction, and 18 ± 15% for PET-based motion correction, compared with the static images. Lesion volumes were 76 ± 31%, 83 ± 18%, and 74 ± 22% of the sizes in the static images for gating, MR-based motion correction, and PET-based motion correction, respectively.

CONCLUSION

Respiratory traces extracted from MR and PET data are comparable to those based on external sensors. The proposed PET-driven gating method improved respiratory signals and overall stability. Consistent results from MR- and PET-based correction methods enable more flexible PET/MR scan protocols while achieving higher PET image quality.

An SPM8-based approach for attenuation correction combining segmentation and nonrigid template formation: application to simultaneous PET/MR brain imaging

We present an approach for head MR-based attenuation correction (AC) based on the Statistical Parametric Mapping 8 (SPM8) software, which combines segmentation- and atlas-based features to provide a robust technique to generate attenuation maps (μ maps) from MR data in integrated PET/MR scanners.

METHODS

Coregistered anatomic MR and CT images of 15 glioblastoma subjects were used to generate the templates. The MR images from these subjects were first segmented into 6 tissue classes (gray matter, white matter, cerebrospinal fluid, bone, soft tissue, and air), which were then nonrigidly coregistered using a diffeomorphic approach. A similar procedure was used to coregister the anatomic MR data for a new subject to the template. Finally, the CT-like images obtained by applying the inverse transformations were converted to linear attenuation coefficients to be used for AC of PET data. The method was validated on 16 new subjects with brain tumors (n = 12) or mild cognitive impairment (n = 4) who underwent CT and PET/MR scans. The μ maps and corresponding reconstructed PET images were compared with those obtained using the gold standard CT-based approach and the Dixon-based method available on the Biograph mMR scanner. Relative change (RC) images were generated in each case, and voxel- and region-of-interest-based analyses were performed.

RESULTS

The leave-one-out cross-validation analysis of the data from the 15 atlas-generation subjects showed small errors in brain linear attenuation coefficients (RC, 1.38% ± 4.52%) compared with the gold standard. Similar results (RC, 1.86% ± 4.06%) were obtained from the analysis of the atlas-validation datasets. The voxel- and region-of-interest-based analysis of the corresponding reconstructed PET images revealed quantification errors of 3.87% ± 5.0% and 2.74% ± 2.28%, respectively. The Dixon-based method performed substantially worse (the mean RC values were 13.0% ± 10.25% and 9.38% ± 4.97%, respectively). Areas closer to the skull showed the largest improvement.

CONCLUSION

We have presented an SPM8-based approach for deriving the head μ map from MR data to be used for PET AC in integrated PET/MR scanners. Its implementation is straightforward and requires only the morphologic data acquired with a single MR sequence. The method is accurate and robust, combining the strengths of both segmentation- and atlas-based approaches while minimizing their drawbacks.

Systematic Comparison of the Performance of Integrated Whole-Body PET/MR Imaging to Conventional PET/CT for ¹⁸F-FDG Brain Imaging in Patients Examined for Suspected Dementia

Technologic specifications of recently introduced integrated PET/MR instrumentation, such as MR-based attenuation correction, may particularly affect brain imaging procedures. To evaluate the qualitative performance of PET/MR in clinical neuroimaging, we systematically compared results obtained with integrated PET/MR with conventional PET/CT in the same patients examined for assessment of cognitive impairment.

METHODS

Thirty patients underwent a single-injection ((18)F-FDG), dual-imaging protocol including PET/CT and integrated PET/MR imaging in randomized order. Attenuation and scatter correction were performed using low-dose CT for the PET/CT and segmented Dixon MR imaging data for the PET/MR. Differences between PET/MR and PET/CT were assessed via region-of-interest (ROI)-based and voxel-based statistical group comparison. Analyses involved attenuation-corrected (AC) and non-attenuation-corrected (NAC) data. Individual PET/MR and PET/CT datasets were compared versus a predefined independent control population, using 3-dimensional stereotactic surface projections.

RESULTS

Generally, lower measured PET signal values were obtained throughout the brain in ROI-based quantification of the PET signal for PET/MR as compared with PET/CT in AC and NAC data, independently of the scan order. After elimination of global effects, voxel-based and ROI-based group comparison still revealed significantly lower relative tracer signal in PET/MR images in frontoparietal portions of the neocortex but significantly higher relative signal in subcortical and basal regions of the brain than the corresponding PET/CT images of the AC data. In the corresponding NAC images, the discrepancies in frontoparietal portions of the neocortex were diminished, but the subcortical overestimation of tracer intensity by PET/MR persisted.

CONCLUSION

Considerable region-dependent differences were observed between brain imaging data acquired on the PET/MR, compared with corresponding PET/CT images, in patients evaluated for neurodegenerative disorders. These findings may only in part be explained by inconsistencies in the attenuation-correction procedures. The observed differences may interfere with semiquantitative evaluation and with individual qualitative clinical assessment and they need to be considered, for example, for clinical trials. Improved attenuation-correction algorithms and a PET/MR-specific healthy control database are recommended for reliable and consistent application of PET/MR for clinical neuroimaging.

Impact of flexible body surface coil and patient table on PET quantification and image quality in integrated PET/MR

AIM

The surface coils of the Biograph mMR integrated PET/MR system were optimised for PET, but are otherwise unaccounted for. The patient table is still more massive than those of PET/CT devices. The goal was to assess those hardware effects on quantification, count statistics, image quality and scan time both with phantoms and in patients and to investigate their clinical relevance.

PATIENTS, MATERIAL, METHODS

PET phantom data were acquired with and without the patient table. Image noise was expressed as relative standard deviation and compared to a state-of-the-art PET/CT scanner. Protocols of the phantom/patient study regarding the surface coils were similar. Thoraces/abdomens of 11 patients were scanned with and without a coil (1 BP, 4 min). Mean uptake and standard deviation in a cubical VOI were derived and expressed as SUV.

RESULTS

The patient table reduced the number of true coincidences (trues) by 19% (PET/MR) and by 11% (PET/CT). The scan duration for the mMR had to be increased by approximately 30% to achieve a noise level comparable to that of the PET/CT. Decreased SUVs with coil observed in the phantom were confirmed by the patient study. By removing the coil, the mean liver SUV increased by (6 ± 2)%. With (+3 ± 14)%, the average change was similar in lesions, but exceeded 20% in almost one fifth of them. The number of trues grew by (6 ± 1)% for the patients and by 7% for the phantom.

CONCLUSION

Due to the additional attenuation caused by MR hardware, PET scan durations would have to be increased compared to current PET/CTs to provide similar image noise levels. The effect of the coils is mostly in the order of statistical fluctuations. In tumour lesions, it is more pronounced and shows a larger variability. Therefore, coils should be included in the attenuation correction to ensure accurate quantification and thus comparability across PET/MR and PET/CT scanners and within patient populations.

Self-gated radial MRI for respiratory motion compensation on hybrid PET/MR systems

Accurate localization and uptake quantification of lesions in the chest and abdomen using PET imaging is challenging due to the respiratory motion during the exam. The advent of hybrid PET/MR systems offers new ways to compensate for respiratory motion without exposing the patient to additional radiation. The use of self-gated reconstructions of a 3D radial stack-of-stars GRE acquisition is proposed to derive a high-resolution MRI motion model. The self-gating signal is used to perform respiratory binning of the simultaneously acquired PET raw data. Matching mu-maps are generated for every bin, and post-reconstruction registration is performed in order to obtain a motion-compensated PET volume from the individual gates. The proposed method is demonstrated in-vivo for three clinical patients. Motion-corrected reconstructions are compared against ungated and gated PET reconstructions. In all cases, motion-induced blurring of lesions in the liver and lung was substantially reduced, without compromising SNR as it is the case for gated reconstructions.

Performance of whole-body integrated 18F-FDG PET/MR in comparison to PET/CT for evaluation of malignant bone lesions

Because of its higher soft-tissue contrast, whole-body integrated PET/MR offers potential advantages over PET/CT for evaluation of bone lesions. However, unlike PET/CT, PET/MR ignores the contribution of cortical bone in the attenuation map. Thus, the aims of this study were to evaluate the diagnostic performance of whole-body integrated (18)F-FDG PET/MR specifically for bone lesions and to analyze differences in standardized uptake value (SUV) quantification between PET/MR and PET/CT.

METHODS

One hundred nineteen patients with (18)F-FDG-avid primary malignancies underwent a single-injection, dual-imaging protocol using (18)F-FDG on a PET/CT scanner and a subsequent PET/MR scan with a T1-weighted volumetric interpolated breath-hold examination (VIBE) Dixon sequence for attenuation correction and an unenhanced coronal T1-weighted turbo spin-echo (TSE) sequence for bone analysis. Three sets of images (CT with PET [from PET/CT; set A], T1-weighted VIBE Dixon with PET [set B], and T1-weighted TSE with PET [both from PET/MR; set C]) were analyzed. Two readers rated every lesion using a 4-point scale for lesion conspicuity on PET, a 4-point scale for anatomic allocation of PET-positive lesions, and a 5-point scale for the nature of every lesion based on its appearance on morphologic imaging and uptake on PET. For all lesions and for representative regions of normal bone, SUV analysis was performed for PET/MR and PET/CT.

RESULTS

In total, 98 bone lesions were identified in 33 of 119 patients, and 630 regions of normal bone were analyzed. Visual lesion conspicuity on PET was comparable for PET/CT (mean rating, 2.82 ± 0.45) and PET/MR (2.75 ± 0.51; P = 0.3095). Anatomic delineation and allocation of suggestive lesions was significantly superior with T1-weighted TSE MRI (mean rating, 2.84 ± 0.42) compared with CT (2.57 ± 0.54, P = 0.0001) or T1-weighted VIBE Dixon MRI (2.57 ± 0.54, P = 0.0002). No significant difference in correct classification of malignant bone lesions was found among sets A (85/90), B (84/90), and C (86/90). For bone lesions and regions of normal bone, a highly significant correlation existed between the mean SUVs for PET/MR and PET/CT (R = 0.950 and 0.917, respectively, each P < 0.001). However, substantially lower mean SUVs were found for PET/MR than for PET/CT both for bone lesions (12.4% ± 15.5%) and for regions of normal bone (30.1% ± 27.5%).

CONCLUSION

Compared with PET/CT, fully integrated whole-body (18)F-FDG PET/MR is technically and clinically robust for evaluation of bone lesions despite differences in attenuation correction. PET/MR, including diagnostic T1-weighted TSE sequences, was superior to PET/CT for anatomic delineation and allocation of bone lesions. This finding might be of clinical relevance in selected cases--for example, primary bone tumors, early bone marrow infiltration, and tumors with low uptake on PET. Thus, a diagnostic T1-weighted TSE sequence is recommended as a routine protocol for oncologic PET/MR.

Comparison of integrated whole-body [11C]choline PET/MR with PET/CT in patients with prostate cancer

PURPOSE

To evaluate the performance of conventional [(11)C]choline PET/CT in comparison to that of simultaneous whole-body PET/MR.

METHODS

The study population comprised 32 patients with prostate cancer who underwent a single-injection dual-imaging protocol with PET/CT and subsequent PET/MR. PET/CT scans were performed applying standard clinical protocols (5 min after injection of 793 ± 69 MBq [(11)C]choline, 3 min per bed position, intravenous contrast agent). Subsequently (52 ± 15 min after injection) PET/MR was performed (4 min per bed position). PET images were reconstructed iteratively (OSEM 3D), scatter and attenuation correction of emission data and regional allocation of [(11)C]choline foci were performed using CT data for PET/CT and segmented Dixon MR, T1 and T2 sequences for PET/MR. Image quality of the respective PET scans and PET alignment with the respective morphological imaging modality were compared using a four point scale (0-3). Furthermore, number, location and conspicuity of the detected lesions were evaluated. SUVs for suspicious lesions, lung, liver, spleen, vertebral bone and muscle were compared.

RESULTS

Overall 80 lesions were scored visually in 29 of the 32 patients. There was no significant difference between the two PET scans concerning number or conspicuity of the detected lesions (p not significant). PET/MR with T1 and T2 sequences performed better than PET/CT in anatomical allocation of lesions (2.87 ± 0.3 vs. 2.72 ± 0.5; p = 0.005). The quality of PET/CT images (2.97 ± 0.2) was better than that of the respective PET scan of the PET/MR (2.69 ± 0.5; p = 0.007). Overall the maximum and mean lesional SUVs exhibited high correlations between PET/CT and PET/MR (ρ = 0.87 and ρ = 0.86, respectively; both p < 0.001).

CONCLUSION

Despite a substantially later imaging time-point, the performance of simultaneous PET/MR was comparable to that of PET/CT in detecting lesions with increased [(11)C]choline uptake in patients with prostate cancer. Anatomical allocation of lesions was better with simultaneous PET/MR than with PET/CT, especially in the bone and pelvis. These promising findings suggest that [(11)C]choline PET/MR might have a diagnostic benefit compared to PET/CT in patients with prostate cancer, and now needs to be further evaluated in prospective trials.

Effect of graft source on mismatched unrelated donor hemopoietic stem cell transplantation after reduced intensity conditioning

This retrospective report compared the results of graft source on outcome after allogeneic stem cell transplantation (allo-SCT) in patients with hematologic malignancies receiving a reduced intensity conditioning (RIC) regimen. A total of 152 patients received either a RIC allo-SCT using a 9/10 mismatched unrelated donor (MisMUD, n=42) or a double unrelated umbilical cord blood (dUCB, n=110) graft. With a median follow-up of 30.3 months, the cumulative incidence of non-relapse mortality was 26% in the dUCB group versus 24% in the MisMUD group (P=0.95). Grade 3-4 acute graft-versus-host disease (GVHD) incidence was 19.7% in the dUCB group versus 21.4% in the MisMUD group (P=0.83). The cumulative incidence of extensive chronic GVHD at 2 years was 6.4% in the dUCB group versus 21.4% in the MisMUD group (P=0.02). The Kaplan-Meier estimate of overall survival at 2 years was comparable between both groups (52.3% (95% confidence interval (CI), 42.1-61.5%) in the dUCB group versus 47.9% (95% CI, 31.6-62.4%) in the MisMUD group, P=0.55). Progression-free survival at 2 years was 43.3% (95% CI, 33.7-52.5%) in the dUCB group versus 38.3% (95% CI, 23.2-53.3%) in the MisMUD group (P=0.55). These data suggest that dUCB is a valid alternative graft source with significantly less chronic GVHD compared with MisMUD in the setting of RIC allo-SCT.

PET/MR: a paradigm shift

More than a decade ago, multimodality imaging was introduced into clinical routine with the development of the positron emission tomography (PET)/computed tomography (CT) technique. Since then, PET/CT has been widely accepted in clinical imaging and has emerged as one of the main cancer imaging modalities. With the recent development of combined PET/magnetic resonance (MR) systems for clinical use, a promising new hybrid imaging modality is now becoming increasingly available. The combination of functional information delivered by PET with the morphologic and functional imaging of MR imaging (e.g., diffusion-weighted imaging, dynamic contrast-enhanced MR imaging and MR spectroscopy) offers exciting possibilities for clinical applications as well as basic research. However, the differences between CT and MR imaging are fundamental. This also leads to distinct differences between PET/CT and PET/MR not only regarding image interpretation but also concerning data acquisition, data processing and image reconstruction. This article provides an overview of the principal differences between PET/CT and PET/MR in terms of scanner design and technology, attenuation correction, speed, acquisition protocols, radiation exposure and safety aspects. PET/MR is expected to show advantages over PET/CT in clinical applications in which MR is known to be superior to CT due to its high intrinsic soft tissue contrast. However, as of now, only assumptions can be made about the future clinical role of PET/MR, as data about the performance of PET/MR in the clinical setting are still limited. The possible future clinical use of PET/MR in oncology, neurology and neurooncology, cardiology and imaging of inflammation is discussed.

TLI in refractory chronic GVHD

Refractory chronic GVHD (cGVHD) remains a major cause of morbidity after transplantation. Many drugs are used but there is no consensus on the standard of care. We investigated the efficacy of TLI in corticosteroid-refractory cGVHD. We analyzed retrospectively 31 patients receiving one or more TLI session for refractory cGVHD from 2000 to 2007. The main objective was to evaluate the response rate after TLI. Decreased corticosteroid doses and/or discontinued immunosuppressive agents were considered to be surrogate markers of response. All but one patient presented with severe cGVHD at the time of TLI. The median number of previous immunosuppressive treatment lines was 3 (range: 2-4). Fourteen patients (45%) achieved an objective response after TLI and 8 (25%) were cGVHD free at long-term follow-up. In all, 5 (29%) of the 17 nonresponsive patients did not show the features of progressive cGVHD and could decrease the amount of immunosuppressive drugs taken. Response after TLI significantly improved 5-year GVHD-related mortality (14% vs 42%, P=0.038) but not OS (58%vs 64% P=0.27). Regarding the promising response rate in this heavily pretreated population, we reasoned that TLI could be an alternative treatment for corticosteroid-refractory cGVHD.

Spinal interaction between the highly selective μ agonist DAMGO and several δ opioid receptor ligands in naive and morphine-tolerant mice

Since the discovery of opioid receptor dimers their possible roles in opioid actions were intensively investigated. Here we suggest a mechanism that may involve the μ-δ opioid heterodimers. The exact role of δ opioid receptors in antinociception and in the development of opioid tolerance is still unclear. While receptor up-regulation can be observed during the development of opioid tolerance no μ receptor down-regulation could be detected within five days. In our present work we investigated how the selective δ opioid receptor agonists and antagonists influence the antinociceptive effect of the selective μ receptor agonist DAMGO in naïve and morphine-tolerant mice. We treated male NMRI mice with 200 μmol/kg subcutaneous (s.c.) morphine twice daily for three days. On the fourth day we measured the antinociceptive effect of DAMGO alone and combined with delta ligands: DPDPE, deltorphin II (agonists), TIPP and TICPψ (antagonists), respectively, administered intrathecally (i.t.) in mouse tail-flick test. In naive control mice none of the δ ligands caused significant changes in the antinociceptive action of DAMGO. The treatment with s.c. morphine resulted in approximately four-fold tolerance to i.t. DAMGO, i.e. the ED₅₀ value of DAMGO was four times as high as in naive mice. 500 and 1000 pmol/mouse of the δ₁ selective agonist DPDPE enhanced the tolerance to DAMGO while 1000 pmol/mouse of the δ₂ selective agonist deltorphin II did not influence the degree of tolerance. However, both δ antagonists TIPP and TICPψ potentiated the antinociceptive effect of i.t. DAMGO, thus they restored the potency of DAMGO to the control level. The inhibitory action of DPDPE against the antinociceptive effect of DAMGO could be antagonized by TIPP and TICPψ. We hypothesize that during the development of morphine tolerance the formation of μδ heterodimers may contribute to the spinal opioid tolerance. δ ligands may affect the dimer formation differently. Those, like DPDPE may facilitate the dimer formation hence inhibit the antinociceptive effect of DAMGO by causing virtual μ receptor down-regulation. Ligands that do not affect the dimer formation do not influence antinociception either but ligands with the presumed capability of disconnecting the dimers may decrease the spinal tolerance to DAMGO.

Tandem autologous-allo-SCT is feasible in patients with high-risk relapsed non-Hodgkin's lymphoma

Allo-SCT is used to exploit GVL effect in high-risk relapsed non-Hodgkin's lymphoma (NHL). Here, we retrospectively analyzed 34 high-risk NHL patients who underwent auto-SCT followed closely by reduced-intensity allo-SCT ('tandem auto-allo') from January 2002 to November 2010. The search for an allogeneic donor was started at the beginning of salvage regimen. Median patients' age was 47 (27-68) years; histotypes were: diffuse large B-cell n=5, follicular n=14, transformed follicular n=4, mantle-cell n=5, plasmocytoid lymphoma n=1, anaplastic large T-cell n=2, peripheral T-cell n=3. Donors were HLA-identical siblings (n=29) or 10/10-matched unrelated individuals (n=5). Median interval between auto-SCT and allo-SCT was 77 days (36-197). At a median follow-up of 46 (8-108) months since allo-SCT, 5-year OS is 77% (61-93) and PFS is 68% (51-85). Disease relapse or progression occurred in six patients, 100-day TRM was 0%, 2-year TRM incidence was 6%. In conclusion, tandem transplantation is feasible in high-risk NHL patients having a HLA-identical donor. This approach could represent a suitable therapeutic option for those patients with high-risk NHL potentially benefitting from further therapy after auto-SCT. Donor searches should be started promptly whenever such an approach is chosen.

First clinical experience with integrated whole-body PET/MR: comparison to PET/CT in patients with oncologic diagnoses

The recently introduced first integrated whole-body PET/MR scanner allows simultaneous acquisition of PET and MRI data in humans and, thus, may offer new opportunities, particularly regarding diagnostics in oncology. This scanner features major technologic differences from conventional PET/CT devices, including the replacement of photomultipliers with avalanche photodiodes and the need for MRI-based attenuation correction. The aim of this study was to evaluate the comparability of clinical performance between conventional PET/CT and PET/MR in patients with oncologic diseases.

METHODS

Thirty-two patients with different oncologic diagnoses underwent a single-injection, dual-imaging protocol consisting of a PET/CT and subsequent PET/MR scan. PET/CT scans were performed according to standard clinical protocols (86 ± 8 min after injection of 401 ± 42 MBq of (18)F-FDG, 2 min/bed position). Subsequently (140 ± 24 min after injection), PET/MR was performed (4 min/bed position). PET images of both modalities were reconstructed iteratively. Attenuation and scatter correction as well as regional allocation of PET findings were performed using low-dose CT data for PET/CT and Dixon MRI sequences for PET/MR. PET/MR and PET/CT were compared visually by 2 teams of observers by rating the number and location of lesions suspicious for malignancy, as well as image quality and alignment. For quantitative comparison, standardized uptake values (SUVs) of the detected lesions and of different tissue types were assessed.

RESULTS

Simultaneous PET/MR acquisition was feasible with high quality in short acquisition time (≤ 20 min). No significant difference was found between the numbers of suspicious lesions (n = 80) or lesion-positive patients (n = 20) detected with PET/MR or PET/CT. Anatomic allocation of PET/MR findings by means of the Dixon MRI sequence was comparable to allocation of PET/CT findings by means of low-dose CT. Quantitative evaluation revealed a high correlation between mean SUVs measured with PET/MR and PET/CT in lesions (ρ = 0.93) and background tissue (ρ = 0.92).

CONCLUSION

This study demonstrates, for what is to our knowledge the first time, that integrated whole-body PET/MR is feasible in a clinical setting with high quality and in a short examination time. The reliability of PET/MR was comparable to that of PET/CT in allowing the detection of hypermetabolic lesions suspicious for malignancy in patients with oncologic diagnoses. Despite different attenuation correction approaches, tracer uptake in lesions and background correlated well between PET/MR and PET/CT. The Dixon MRI sequences acquired for attenuation correction were found useful for anatomic allocation of PET findings obtained by PET/MR in the entire body. These encouraging results may form the foundation for future studies aiming to define the added value of PET/MR over PET/CT.

Relative contributions of peripheral versus supraspinal or spinal opioid receptors to the antinociception of systemic opioids

The contribution of supraspinal, spinal or peripheral mu-opioid receptors (MORs) to the overall antinociception of systemic centrally penetrating versus peripherally restricted opioids has not been thoroughly investigated. Therefore, we examined paw pressure thresholds in Wistar rats with complete Freund's adjuvant hindpaw inflammation following different doses of intraplantar (i.pl.) as well as intravenous (i.v.) fentanyl (6.25-50 μg/kg), morphine (1-7.5 mg/kg) or loperamide (1-7.5 mg/kg). Antagonism of the i.v. mu-opioid agonists by intracerebroventricular (i.c.v.), intrathecal (i.t.) or i.pl. naloxone-methiodide (NLXM) revealed the relative contributions of supraspinal, spinal and peripheral MOR to the overall antinociceptive effects. In parallel, the MOR density at these three levels of pain transmission was assessed by radioligand binding. Antinociceptive effects of i.v. fentanyl and morphine, but not of the peripherally restricted loperamide were two- to threefold greater and longer lasting compared with their i.pl. administration. I.c.v. but not i.pl. NLXM significantly antagonized fentanyl's and morphine's antinociception by 70-80%, whereas i.t. NLXM reduced it by 20-30%. In contrast, antinociception of i.v. loperamide was abolished by i.pl. but not by i.c.v. or i.t. NLXM. In parallel, a respective 32- and sixfold higher MOR density in supraspinal and spinal versus peripheral sensory neurons was detected. In conclusion, in comparison with supraspinal and spinal opioid receptors, peripheral opioid receptors do not significantly contribute to the antinociception of systemic fentanyl and morphine during inflammatory pain. Antinociception of their i.v. administration was superior over both i.v and i.pl. loperamide, acting exclusively via peripheral MOR. These findings may guide the future development of novel peripherally restricted opioids.

[Psychotic and non-psychotic denial of pregnancy]

We report about two patients with denial of pregnancy. While the first patient was free of psychopathological symptoms besides denial of pregnancy until rupture of the membranes, and was able to accomodate the new born, the second patient with psychotic denial of pregnancy could not accomodate the child because of the schizophrenia, so that an adoption was necessary. On the basis of the two cases aetiological, epidemiological, clinical und prognostic implications of psychotic and non-psychotic denial of pregnancy are discussed.

Performance measurements of the Siemens mMR integrated whole-body PET/MR scanner

The recently released Biograph mMR is the first commercially available integrated whole-body PET/MR scanner. There are considerable advantages to integrating both modalities in a single scanner that enables truly simultaneous acquisition. However, there are also concerns about the possible degradation of both PET and MR performance in an integrated system. This paper evaluates the performance of the Biograph mMR during independent and simultaneous acquisition of PET and morphologic MR data.

METHODS

The NEMA NU 2-2007 protocol was followed for studying the PET performance. The following measurements were performed: spatial resolution; scatter fraction, count losses, and randoms; sensitivity; accuracy of the correction for count losses and randoms; and image quality. The quality control manual of the American College of Radiology was followed for studying the MR performance. The following measurements were performed: geometric accuracy, spatial resolution, low-contrast detectability, signal-to-noise ratio, static field (B(0)) homogeneity, radiofrequency field (B(1)) homogeneity, and radiofrequency noise.

RESULTS

An average spatial resolution of 4.3 mm in full width at half maximum was measured at 1 cm offset from the center of the field of view. The system sensitivity was 15.0 kcps/MBq along the center of the scanner. The scatter fraction was 37.9%, and the peak noise-equivalent count rate was 184 kcps at 23.1 kBq/mL. The maximum absolute value of the relative count rate error due to dead-time losses and randoms was 5.5%. The average residual error in scatter and attenuation correction was 12.1%. All MR parameters were within the tolerances defined by the American College of Radiology. B(0) inhomogeneities below 1 ppm were measured in a 120-mm radius. B(1) homogeneity and signal-to-noise ratio were equivalent to those of a standard MR scanner. No radiofrequency interference was detected.

CONCLUSION

These results compare favorably with other state-of-the-art PET/CT and PET/MR scanners, indicating that the integration of the PET detectors in the MR scanner and their operation within the magnetic field do not have a perceptible impact on the overall performance. The MR subsystem performs essentially like a standalone system. However, further work is necessary to evaluate the more advanced MR applications, such as functional imaging and spectroscopy.

Image-guided tumor-selective radioiodine therapy of liver cancer after systemic nonviral delivery of the sodium iodide symporter gene

We reported the induction of tumor-selective iodide uptake and therapeutic efficacy of (131)I in a hepatocellular carcinoma (HCC) xenograft mouse model, using novel polyplexes based on linear polyethylenimine (LPEI), shielded by polyethylene glycol (PEG), and coupled with the epidermal growth factor receptor-specific peptide GE11 (LPEI-PEG-GE11). The aim of the current study in the same HCC model was to evaluate the potential of biodegradable nanoparticle vectors based on pseudodendritic oligoamines (G2-HD-OEI) for systemic sodium iodide symporter (NIS) gene delivery and to compare efficiency and tumor specificity with LPEI-PEG-GE11. Transfection of HCC cells with NIS cDNA, using G2-HD-OEI, resulted in a 44-fold increase in iodide uptake in vitro as compared with a 22-fold increase using LPEI-PEG-GE11. After intravenous application of G2-HD-OEI/NIS HCC tumors accumulated 6-11% ID/g (123)I (percentage of the injected dose per gram tumor tissue) with an effective half-life of 10 hr (tumor-absorbed dose, 281 mGy/MBq) as measured by (123)I scintigraphic gamma camera or single-photon emission computed tomography computed tomography (SPECT CT) imaging, as compared with 6.5-9% ID/g with an effective half-life of only 6 hr (tumor-absorbed dose, 47 mGy/MBq) for LPEI-PEG-GE11. After only two cycles of G2-HD-OEI/NIS/(131)I application, a significant delay in tumor growth was observed with markedly improved survival. A similar degree of therapeutic efficacy had been observed after four cycles of LPEI-PEG-GE11/(131)I. These results clearly demonstrate that biodegradable nanoparticles based on OEI-grafted oligoamines show increased efficiency for systemic NIS gene transfer in an HCC model with similar tumor selectivity as compared with LPEI-PEG-GE11, and therefore represent a promising strategy for NIS-mediated radioiodine therapy of HCC.

The chemical and pharmacological importance of morphine analogues

The object of this review is to summarize the efforts which resulted in the discovery of therapeutically useful morphine-like drugs. The search for new analgesics can be divided into three stages: (a) search for analgesics with high efficacy and reduced unwanted side-effects; (b) understanding of structure-activity relationships; (c) studies on the mechanism of pain perception and its alleviation by investigation of the pharmacology of opioids. An immense body of literature has been produced on the syntheses of thousands of new compounds which resulted in the development of detailed structure-activity relationships. The physical and psychologic dependence of opioid analgesics also facilitated investigators to solve the problem of the separation of strong analgesia from addiction liability. In the past decades more mixed agonist-antagonist analgesics, pure antagonists devoid of agonist action and potent opioids like the 6,14-ethenomorphinan derivatives were developed. Naloxone, Naltrexone, Buprenorphine and Pentazocine are the outstanding representatives which are introduced into clinical therapy.