Sinonasal mucosal melanoma treatment response assessment to immune checkpoint inhibitors using hybrid positron emission tomography imaging

The purpose of this retrospective study was to investigate response of sinonasal mucosal melanoma (SMM) patients to treatment with immune checkpoint inhibitors (ICI), using hybrid PET imaging. Fifteen SMM patients underwent hybrid PET imaging before and three months after initiation of ICI. The disease-specific survival (DSS) was calculated. Quantitative PET parameters of the primary tumor and their association with DSS and therapy response were investigated. Nine of the fifteen (60%) patients responded to ICI therapy. Patients with therapy response depicted on hybrid PET imaging had better DSS than those without (p = 0.0058). Quantitative PET parameters of the initial PET harbored no association with DSS or therapy response. However, these findings lack of sufficient statistical power and must be interpreted with caution. The first restaging PET-imaging after ICI initiation can help stratify patients with regard to DSS.

Outcome analysis in patients with metastatic gastroenteropancreatic neuroendocrine tumors receiving peptide receptor radionuclide therapy with Lu-177-DOTATATE

Background

Patients with neuroendocrine tumors (NET) of the gastroenteropancreatic tract (GEP-NET) were effectively treated with peptide receptor radionuclide therapy (PRRT) with Lu-177-DOTATATE in the NETTER-1 trial. The aim of this study was to assess the outcome of metastatic GEP-NET patients within a European Neuroendocrine Tumor Society (ENETS) certified center of excellence after this treatment.

Methods

A total of 41 GEP-NET patients who received PRRT with Lu-177-DOTATATE between 2012 and 2017 at a single center were included in this analysis. Data on pre- and post-PRRT treatments [selective internal radiation therapy (SIRT), somatostatin analogue therapy (SSA), blood parameters, patient symptomatic burden and overall survival] was extracted from patient records.

Results

Overall, PRRT was well tolerated and did not increase patient symptomatic burden. Blood parameters were not significantly affected by PRRT (means before and after therapy: hemoglobin: 125.4 vs. 122.3 mg/L, P=0.201; creatinine: 73.8 vs. 77.7 µmol/L, P=0.146), while leukocytes (6.6 vs. 5.6 G/L, P<0.01) and platelets (269.9 vs. 216.7 G/L, P<0.001) were significantly decreased yet without clinical significance in our study. Seven of 9 patients with SIRT treatment prior to PRRT were deceased (mortality odds ratio =4.083). The mortality odds ratio of patients with a pancreatic tumor and SIRT was 1.33 compared to patients with a different tumor origin. 6 of 15 patients (40%) with post-PRRT SSA were deceased (mortality odds ratio =0.429 without SSA after PRRT).

Conclusions

Patients with advanced GEP-NET might benefit from PRRT with Lu-177-DOTATATE as it can provide a valuable treatment modality in advanced disease stages. Safety profiles of PRRT were manageable without increasing the symptomatic burden. SIRT before PRRT or lack of SSA after PRRT seem to impair the response and reduce survival.

A descriptive analysis of the characteristics, treatment response and prognosis of hepatic dominant solid tumors undergoing selective internal radiation therapy (SIRT)

Background

Selective internal radiotherapy is widely used for liver dominant diseases of solid tumors. However, data about sequential treatment and prognostic factors are lacking.

Methods

We consecutively included all 209 patients who received a selective internal radiotherapy intervention between January 2015 and May 2019. A retrospective analysis of their electronic patient records was performed regarding diagnosis of cancer, previous therapies and applied radioactive activity. A multicenter follow-up at least 6 weeks after intervention to assess radiological response and irregular subsequent follow-ups to asses disease progression were conducted. In addition, subgroup analyses were carried out.

Results

The most frequently treated indications were hepatocellular carcinoma (37%), colorectal cancers (14%), neuroendocrine tumors (9%), and breast cancer (8%). In hepatocellular carcinoma, selective internal radiotherapy was most performed without prior systemic therapy (40%), and for the remaining indications, most often after surgery with systemic therapy in sequence. Local radiological response, defined as either regression or stable disease, was assessed at least 6 weeks after intervention and showed 52% across all indications. Hepatocellular carcinoma (59%) and breast cancer (67%) showed an excellent, colorectal cancers (29%) a particularly poor response rate. Neuroendocrine tumors showed the third longest median post-selective internal radiation therapy (SIRT) survival with 12.4 months and the second longest median progression-free time with 5.2 months. Hepatocellular carcinoma showed even better results with a post-SIRT survival of 15.7 months and a median progression-free time of 5.3 months. Pancreatic neuroendocrine tumors showed significantly worse outcomes than other neuroendocrine tumors, regarding median post-SIRT survival and median progression-free time. No relevant SIRT related differences among sexes were detected.

Conclusions

Patients with neuroendocrine tumors, breast cancer in late therapy lines and early-stage hepatocellular carcinoma seem to show better responses to SIRT than other entities. Colorectal cancers were mainly treated with SIRT in a second or third therapy line but with considerably weaker results than other entities.

Radiation dose reduction with deep-learning image reconstruction for coronary computed tomography angiography

Objectives

Deep-learning image reconstruction (DLIR) offers unique opportunities for reducing image noise without degrading image quality or diagnostic accuracy in coronary CT angiography (CCTA). The present study aimed at exploiting the capabilities of DLIR to reduce radiation dose and assess its impact on stenosis severity, plaque composition analysis, and plaque volume quantification.

Methods

This prospective study includes 50 patients who underwent two sequential CCTA scans at normal-dose (ND) and lower-dose (LD). ND scans were reconstructed with Adaptive Statistical Iterative Reconstruction-Veo (ASiR-V) 100%, and LD scans with DLIR. Image noise (in Hounsfield units, HU) and quantitative plaque volumes (in mm³) were assessed quantitatively. Stenosis severity was visually categorized into no stenosis (0%), stenosis (< 20%, 20–50%, 51–70%, 71–90%, 91–99%), and occlusion (100%). Plaque composition was classified as calcified, non-calcified, or mixed.

Results

Reduction of radiation dose from ND scans with ASiR-V 100% to LD scans with DLIR at the highest level (DLIR-H; 1.4 mSv vs. 0.8 mSv, p < 0.001) had no impact on image noise (28 vs. 27 HU, p = 0.598). Reliability of stenosis severity and plaque composition was excellent between ND scans with ASiR-V 100% and LD scans with DLIR-H (intraclass correlation coefficients of 0.995 and 0.974, respectively). Comparison of plaque volumes using Bland–Altman analysis revealed a mean difference of − 0.8 mm³ (± 2.5 mm³) and limits of agreement between − 5.8 and + 4.1 mm³.

Conclusion

DLIR enables a reduction in radiation dose from CCTA by 43% without significant impact on image noise, stenosis severity, plaque composition, and quantitative plaque volume.

Key Points

•Deep-learning image reconstruction (DLIR) enables radiation dose reduction by over 40% for coronary computed tomography angiography (CCTA).

•Image noise remains unchanged between a normal-dose CCTA reconstructed by ASiR-V and a lower-dose CCTA reconstructed by DLIR.

•There is no impact on the assessment of stenosis severity, plaque composition, and quantitative plaque volume between the two scans.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00330-021-08367-x.

Comparison of MR Ultrashort Echo Time and Optimized 3D-Multiecho In-Phase Sequence to Computed Tomography for Assessment of the Osseous Craniocervical Junction

BACKGROUND

To assess changes of the craniocervical junction (CCJ), computed tomography (CT) is considered the reference standard. Recent advances in bone depiction on magnetic resonance imaging (MRI) enable high-quality visualization of osseous structures. Consequently, MRI may serve as an alternative to CT, without the use of ionizing radiation.

PURPOSE

To compare two MRI sequences optimized for bone visualization to the CT reference standard in the assessment of the osseous CCJ.

STUDY TYPE

Prospective.

POPULATION/SUBJECTS

Twenty-seven decedents and five healthy volunteers.

FIELD STRENGTH/SEQUENCE

3T/ultrashort-echo time gradient echo (UTE) and optimized 3D-multiecho in-phase gradient echo sequences (FRACTURE).

ASSESSMENT

All decedents were scanned with both MRI sequences and CT. Three observers rated degeneration to obtain a score for the upper (atlanto-dental and left/right atlanto-occipital joint) and for the lower part of the CCJ (left and right atlanto-axial joint). Two reader rated the following quantitative parameters: basion-axial-interval, atlanto-dental-interval, atlanto-occipital-interval, Powers-ratio, and signal/contrast-to-noise-ratio. As a proof of concept, five healthy volunteers were scanned with both MRI sequences.

STATISTICAL TESTS

Degeneration was assessed on a Likert scale by three independent observers. Interrater and intermodality reliability were calculated using an intraclass correlation coefficient. To compare distance measurements between examination methods, a Friedman test, between-degenerative ratings, and a Kruskal-Wallis test were performed.

RESULTS

Degenerative ratings of the CCJ between MRI sequences and CT showed a good interrater and intermodality agreement. MRI sequences tended to underestimate the degree of degeneration compared to CT, and this became more marked with increasing degeneration severity. There were no significant relationships between distance measurements and the degree of degeneration (P_CT = 0.62, P_UTE = 0.64, P_FRACTURE = 0.67). The in vivo examination proved the feasibility of both MRI methods in a clinical setting.

DATA CONCLUSION

Quantitative and qualitative ratings on MR images were comparable to CT images; thus, MRI may be a valid alternative to CT assessing the CCJ.

LEVEL OF EVIDENCE

1.

TECHNICAL EFFICACY STAGE

3.

Prognostic value of O-(2-[18F]-fluoroethyl)-L-tyrosine PET in relapsing oligodendroglioma

PURPOSE

To assess the relationship between F-18-fluoro-ethyl-tyrosine positron emission tomography (FET-PET) parameters of relapsing oligodendroglioma and progression-free survival.

MATERIAL AND METHODS

The relationship of clinical parameters, FET-PET parameters (SUV_max, TBR_max, BTV_, time-activity curves) and progression-free survival was analyzed using univariate and multivariate analysis in 42 adult patients with relapsing oligodendroglioma. Kaplan-Meier analysis was used to assess survival.

RESULTS

Patients who did not undergo surgical resection of their relapsing tumor had significantly lower PFS if the tumor exhibited an SUV_max above 3.40 than those with an SUV_max below 3.40 (13.1 ± 2.3 months vs. 47.3 ± 6.0 months, respectively, p < .001). Patients who underwent surgery had similar PFS as the aforementioned non-operated patients with low SUV_max (53.6 ± 6.7 months, p = .948). The same was true for TBR_max using a threshold of 3.03 (PFS 12.5 ± 2.4 months vs. 44.0 ± 6.3 months / 53.6 ± 6.7 months, respectively; p < .001 / p = .825). Also, subjects with BTV below 10 cm³ that did not undergo surgery had a similar PFS as subjects who underwent surgery (40.2 ± 6.0 months vs. 52.4 ± 8.9 months, respectively, p = .587). Subjects with BTV above 10 cm³ and without surgery had a significantly worse PFS (13.8 ± 3.3 months, p < .001). Multivariate analysis showed that the prognostication by clinical parameters is improved by adding TBR_max to the model (AUC 0.945 (95% CI: 0.881-1.000), true classification rate 88.1%).

CONCLUSION

FET-PET may provide added value for the prognostication of relapsing oligodendroglioma in addition to clinical parameters.

Impact of different image reconstructions on PET quantification in non-small cell lung cancer: a comparison of adenocarcinoma and squamous cell carcinoma

OBJECTIVE:

Positron emission tomography (PET) using ¹⁸F-fludeoxyglucose (¹⁸F-FDG) is an established imaging modality for tumor staging in patients with non-small cell lung cancer (NSCLC). There is a growing interest in using ¹⁸F-FDG PET for therapy response assessment in NSCLC which relies on quantitative PET parameters such as standardized uptake values (SUV). Different reconstruction algorithms in PET may affect SUV. We sought to determine the variation of SUV in patients with NSCLC when using ordered subset expectation maximization (OSEM) and block sequential regularized expectation maximization (BSREM) in latest-generation digital PET/CT, including a subanalysis for adenocarcinoma and squamous cell carcinoma.

METHODS:

A total of 58 patients (34 = adenocarcinoma, 24 = squamous cell carcinoma) who underwent a clinically indicated ¹⁸F-FDG PET/CT for staging were reviewed. PET images were reconstructed with OSEM and BSREM reconstruction with noise penalty strength β-levels of 350, 450, 600, 800 and 1200. Lung tumors maximum standardized uptake value (SUV_max) were compared.

RESULTS:

Lung tumors SUV_max were significantly lower in adenocarcinomas compared to squamous cell carcinomas in all reconstructions evaluated (all p < 0.01). Comparing BSREM to OSEM, absolute SUV_max differences were highest in lower β-levels of BSREM with + 2.9 ± 1.6 in adenocarcinoma and + 4.0 ± 2.9 in squamous cell carcinoma (difference between histology; p-values > 0.05). There was a statistically significant difference of the relative increase of SUV_max in adenocarcinoma (mean + 34.8%) and squamous cell carcinoma (mean 23.4%), when using BSREM₃₅₀ instead of OSEM_TOF (p < 0.05).

CONCLUSION:

In NSCLC the relative change of SUV when using BSREM instead of OSEM is significantly higher in adenocarcinoma as compared to squamous cell carcinoma.

ADVANCES IN KNOWLEDGE:

The impact of BSREM on SUV may vary in different histological subtypes of NSCLC. This highlights the importance for careful standardization of β-value used for serial ¹⁸F-FDG PET scans when following-up NSCLC patients.

Magnetisation transfer as a biomarker for chronic airway fibrosis in a mouse lung transplantation model

Background

Chronic airway fibrosis (CAF) is the most prevalent complication in human lung transplant recipients. The aim of the study is to evaluate magnetisation transfer (MT) as a biomarker of developing CAF of lung transplants in a mouse model.

Methods

Lung transplantation was performed in 48 mice, applying major or minor histocompatibility mismatches between strains for the induction of CAF. MT measurements were performed in vivo with systematic variation of off-resonance frequencies and flip angle of the MT prepulse. MT ratios (MTRs) were compared for lungs showing CAF and without CAF.

Results

Seven out of 24 animals (29%) showed a pattern of CAF at histology. All mice developing CAF also showed signs of acute rejection, whereas none of the lungs showed signs of other post-transplant complications. After lung transplantation, pulmonary infiltration was a frequent finding (14 out of 24) exhibiting a higher MTR (24.8% ± 4.5%) compared to well-ventilated lungs (12.3% ± 6.9%, p = 0.001) at 8000 Hz off-resonance frequency, 3000° flip angle. In infiltrated lung tissue exhibiting CAF, lower MTR values (21.8% ± 5.7%) were found compared to infiltrated lungs showing signs of acute rejection alone (26.5% ± 2.9%, p = 0.028), at 8000 Hz, 3000° flip angle. The highest MTR values were observed at 3000° flip angle, using a 1000 Hz off-resonance frequency.

Conclusion

MTR might serve as a tool for the detection of CAF in infiltrated lung tissue.

Neer Award 2016: reduced muscle degeneration and decreased fatty infiltration after rotator cuff tear in a poly(ADP-ribose) polymerase 1 (PARP-1) knock-out mouse model

BACKGROUND

Disturbed muscular architecture, atrophy, and fatty infiltration remain irreversible in chronic rotator cuff tears even after repair. Poly (adenosine 5'-diphosphate-ribose) polymerase 1 (PARP-1) is a key regulator of inflammation, apoptosis, muscle atrophy, muscle regeneration, and adipocyte development. We hypothesized that the absence of PARP-1 would lead to a reduction in damage to the muscle subsequent to combined tenotomy and neurectomy in a PARP-1 knockout (KO) mouse model.

METHODS

PARP-1 KO and wild-type C57BL/6 (WT group) mice were analyzed at 1, 6, and 12 weeks (total n = 84). In all mice, the supraspinatus and infraspinatus muscles of the left shoulder were detached and denervated. Macroscopic analysis, magnetic resonance imaging, gene expression analysis, immunohistochemistry, and histology were used to assess the differences in PARP-1 KO and WT mice.

RESULTS

The muscles in the PARP-1 KO group had significantly less retraction, atrophy, and fatty infiltration after 12 weeks than in the WT group. Gene expression of inflammatory, apoptotic, adipogenic, and muscular atrophy genes was significantly decreased in PARP-1 KO mice in the first 6 weeks.

DISCUSSION

Absence of PARP-1 leads to a reduction in muscular architectural damage, early inflammation, apoptosis, atrophy, and fatty infiltration after combined tenotomy and neurectomy of the rotator cuff muscle. Although the macroscopic reaction to injury is similar in the first 6 weeks, the ability of the muscles to regenerate was much greater in the PARP-1 KO group, leading to a near-normalization of the muscle after 12 weeks.

A Micro CT Study in Patients with Breast Microcalcifications Using a Mathematical Algorithm to Assess 3D Structure

PURPOSE

The aim of this study was to evaluate the relevance of the three-dimensional (3D) structure of breast microcalcifications (MC) as a predictor of malignancy using highly resolved micro-computed tomography (micro-CT) datasets of biopsy samples.

MATERIAL AND METHODS

The study included 28 women with suspicious MC in their mammogram undergoing vacuum-assisted biopsy. Directly after the intervention, the specimens were scanned in a micro-CT with an isometric spatial resolution of 9 μm. Datasets were analysed regarding the number, volume and morphology of suspicious non-monomorphic MC (fl-fine linear, fp-fine pleomorphic, ch-coarse heterogeneous) and the structure model index (SMI). Histological evaluation was performed according to the B-classification: normal tissue or benign (group A: B1, B2), unclear malignant potential or suspicious of malignancy (group B: B3, B4) and malignant lesions (group C: B5).

RESULTS

In all groups, suspicious non-monomorphic MC were found: group A exhibited fp MC in 38.5% of samples, no fl/ch; group B: fl 14.3%, fp 28.6%, ch 14.3%; group C always had at least one type of suspicious non-monomorphic MC (fl (57.1%) or fp (57.1%)) in each sample. The different histologic groups showed a similar mean SMI (benign: 2.97 ± 0.31, malignant: 3.02 ± 0.10, unclear: 2.90 ± 0.28). Between the three groups, no significant differences were found regarding number, volume or SMI value of MC.

CONCLUSION

3D structure based on the SMI of MC analysed with highest spatial resolution is not significantly associated with the B-classification of breast lesions. Thus, magnification views of MC may be omitted in the analysis of MC detected in mammograms.

Simultaneous multi-slice echo planar diffusion weighted imaging of the liver and the pancreas: Optimization of signal-to-noise ratio and acquisition time and application to intravoxel incoherent motion analysis

PURPOSE

To optimize and test a diffusion-weighted imaging (DWI) echo-planar imaging (EPI) sequence with simultaneous multi-slice (SMS) excitation in the liver and pancreas regarding acquisition time (TA), number of slices, signal-to-noise ratio (SNR), image quality (IQ), apparent diffusion coefficient (ADC) quantitation accuracy, and feasibility of intravoxel incoherent motion (IVIM) analysis.

MATERIALS AND METHODS

Ten healthy volunteers underwent DWI of the upper abdomen at 3T. A SMS DWI sequence with CAIPIRINHA unaliasing technique (acceleration factors 2/3, denoted AF2/3) was compared to standard DWI-EPI (AF1). Four schemes were evaluated: (i) reducing TA, (ii) keeping TA identical with increasing number of averages, (iii) increasing number of slices with identical TA (iv) increasing number of b-values for IVIM. Acquisition schemes i-iii were evaluated qualitatively (reader score) and quantitatively (ADC values, SNR).

RESULTS

In scheme (i) no differences in SNR were observed (p=0.321-0.038) with reduced TA (AF2 increase in SNR/time 75.6%, AF3 increase SNR/time 102.4%). No SNR improvement was obtained in scheme (ii). Increased SNR/time could be invested in acquisition of more and thinner slices or higher number of b-values. Image quality scores were stable for AF2 but decreased for AF3. Only for AF3, liver ADC values were systematically lower.

CONCLUSION

SMS-DWI of the liver and pancreas provides substantially higher SNR/time, which either may be used for shorter scan time, higher slice resolution or IVIM measurements.

Diffusional kurtosis MRI of the lower leg: changes caused by passive muscle elongation and shortening

Diffusional kurtosis MRI (DKI) quantifies the deviation of water diffusion from a Gaussian distribution. We investigated the influence of passive elongation and shortening of the lower leg muscles on the DKI parameters D (diffusion coefficient) and K (kurtosis). After approval by the local ethics committee, eight healthy volunteers (age, 29.1 ± 2.9 years) underwent MRI of the lower leg at 3 T. Diffusion-weighted images were acquired with 10 different b values at three ankle positions (passive dorsiflexion 10°, neutral position 0°, passive plantar flexion 40°). Parametrical maps of D and K were obtained by voxel-wise fitting of the signal intensities using a non-linear Levenberg-Marquardt algorithm. D and K were measured in the tibialis anterior, medial and lateral gastrocnemius, and soleus muscles. In the neutral position, D and K values were in the range between 1.66-1.79 × 10(-3) mm(2) /s and 0.21-0.39, respectively. D and K increased with passive shortening, and decreased with passive elongation, which could also be illustrated on the parametrical maps. In dorsiflexion, D (p < 0.01) and K (p = 0.036) were higher in the tibialis anterior than in the medial gastrocnemius. In plantar flexion, the opposite was found for K (p = 0.035). DKI parameters in the lower leg muscles are significantly influenced by the ankle joint position, indicating that the diffusion of water molecules in skeletal muscle deviates from a Gaussian distribution depending on muscle tonus. Copyright © 2016 John Wiley & Sons, Ltd.

Separation of collagen-bound and porous bone-water longitudinal relaxation in mice using a segmented inversion recovery zero-echo-time sequence

PURPOSE

Cortical bone mechanical properties are related to the collagen-bound water (CBW) and pore water (PW) components of cortical bone. The study evaluates the feasibility of zero-echo-time imaging in mice in vivo for longitudinal relaxation time (T1) measurements in cortical bone and separation of CBW and PW components.

METHODS

Zero-echo-time data were acquired at 4.7 Tesla in six mice with 14 different inversion times (0-2,600 ms). Region-of-interest analysis was performed at level of femur diaphysis. The T1 of cortical bone and of CBW (T1cbw) and PW (T1pw) as well as the CBW fraction (cbwf) was computed using a mono-exponential and a bi-exponential fitting approach, respectively. The sum of the squared residuals (Res) to the fit was provided for both approaches.

RESULTS

For the mono-exponential model, mean T1 ± standard deviation (SD) was 1,057 ± 160 ms. The bi-exponential approach provided a reliable separation of two different bone-water components, with a mean T1cbw of 213 ± 95 ms, T1pw of 2,152 ± 894 ms, and cbwf of 7.4 ± 2.7 %. Lower Res was obtained with bi-exponential approach (P < 0.001), and Res mean values ± SD were 0.016 ± 0.007 (bi-exponential) and 0.033 ± 0.016 (mono-exponential).

CONCLUSION

Zero-echo-time imaging allows for longitudinal relaxation measurements of cortical bone in vivo in mice models, with a reliable separation of PW and CBW components using a bi-exponential curve fitting approach. Magn Reson Med 77:1909-1915, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Antagonizing the Hedgehog Pathway with Vismodegib Impairs Malignant Pleural Mesothelioma Growth In Vivo by Affecting Stroma

An autocrine-driven upregulation of the Hedgehog (Hh) signaling pathway has been described in malignant pleural mesothelioma (MPM), in which the ligand, desert Hh (DHH), was produced from tumor cells. However, our investigation revealed that the Hh pathway is activated in both tumor and stroma of MPM tumor specimens and an orthotopic immunocompetent rat MPM model. This was demonstrated by positive immunohistochemical staining of Glioma-associated oncogene 1 (GLI1) and Patched1 (PTCH1) in both tumor and stromal fractions. DHH was predominantly expressed in the tumor fractions. To further investigate the role of the Hh pathway in MPM stroma, we antagonized Hh signaling in the rat model of MPM using a Hh antagonist, vismodegib, (100 mg/kg orally). Daily treatment with vismodegib efficiently downregulated Hh target genes Gli1, Hedgehog Interacting Protein (Hhip), and Ptch1, and caused a significant reduction of tumor volume and tumor growth delay. Immunohistochemical analyses revealed that vismodegib treatment primarily downregulated GLI1 and HHIP in the stromal compartment along with a reduced expression of previously described fibroblast Hh-responsive genes such as Fibronectin (Fn1) and Vegfa Primary cells isolated from the rat model cultured in 3% O2 continued to express Dhh but did not respond to vismodegib in vitro However, culture supernatant from these cells stimulated Gli1, Ptch1, and Fn1 expression in mouse embryonic fibroblasts, which was suppressed by vismodegib. Our study provides new evidence regarding the role of Hh signaling in MPM stroma in the maintenance of tumor growth, emphasizing Hh signaling as a treatment target for MPM. Mol Cancer Ther; 15(5); 1095-105. ©2016 AACR.

Whole-Body Diffusion Imaging Applying Simultaneous Multi-Slice Excitation

PURPOSE

The purpose of this study was to examine the feasibility of a fast protocol for whole-body diffusion-weighted imaging (WB-DWI) using a slice-accelerated echo-planar sequence, which, when using comparable image acquisition parameters, noticeably reduces measurement time compared to a conventional WB-DWI protocol.

MATERIALS AND METHODS

A single-shot echo-planar imaging sequence capable of simultaneous slice excitation and acquisition was optimized for WB-DWI on a 3 T MR scanner, with a comparable conventional WB-DWI protocol serving as the reference standard. Eight healthy individuals and one oncologic patient underwent WB-DWI. Quantitative analysis was carried out by measuring the apparent diffusion coefficient (ADC) and its coefficient of variation (CV) in different organs. Image quality was assessed qualitatively by two independent radiologists using a 4-point Likert scale.

RESULTS

Using our proposed protocol, the scan time of the WB-DWI measurement was reduced by up to 25.9 %. Both protocols, the slice-accelerated protocol and the conventional protocol, showed comparable image quality without statistically significant differences in the reader scores. Similarly, no significant differences of the ADC values of parenchymal organs were found, whereas ADC values of brain tissue were slightly higher in the slice-accelerated protocol.

CONCLUSION

It was demonstrated that slice-accelerated DWI can be applied to WB-DWI protocols with the potential to greatly reduce the required measurement time, thereby substantially increasing clinical applicability.

KEY POINTS

•Whole-body diffusion-weighted imaging (WB-DWI) using simultaneous multi-slice and blipped-CAIPIRINHA reduces the measurement time strongly without having a significant impact on image quality. •The reduction in measurement time might strongly contribute to the clinical applicability of WB-DWI. •However, further refinement of the slice-accelerated EPI sequence, and the WB-DWI protocol applying this sequence type seems necessary; and the value of such WB-DWI protocols for assessment of systemic oncological diseases needs to be investigated in further clinical studies.

Functional Characterization of Germline Mutations in PDGFB and PDGFRB in Primary Familial Brain Calcification

Primary Familial Brain Calcification (PFBC), a neurodegenerative disease characterized by progressive pericapillary calcifications, has recently been linked to heterozygous mutations in PDGFB and PDGFRB genes. Here, we functionally analyzed several of these mutations in vitro. All six analyzed PDGFB mutations led to complete loss of PDGF-B function either through abolished protein synthesis or through defective binding and/or stimulation of PDGF-Rβ. The three analyzed PDGFRB mutations had more diverse consequences. Whereas PDGF-Rβ autophosphorylation was almost totally abolished in the PDGFRB L658P mutation, the two sporadic PDGFRB mutations R987W and E1071V caused reductions in protein levels and specific changes in the intensity and kinetics of PLCγ activation, respectively. Since at least some of the PDGFB mutations were predicted to act through haploinsufficiency, we explored the consequences of reduced Pdgfb or Pdgfrb transcript and protein levels in mice. Heterozygous Pdgfb or Pdgfrb knockouts, as well as double Pdgfb^+/-;Pdgfrb^+/- mice did not develop brain calcification, nor did Pdgfrb^{redeye/redeye} mice, which show a 90% reduction of PDGFRβ protein levels. In contrast, Pdgfb^ret/ret mice, which have altered tissue distribution of PDGF-B protein due to loss of a proteoglycan binding motif, developed brain calcifications. We also determined pericyte coverage in calcification-prone and non-calcification-prone brain regions in Pdgfb^ret/ret mice. Surprisingly and contrary to our hypothesis, we found that the calcification-prone brain regions in Pdgfb^ret/ret mice model had a higher pericyte coverage and a more intact blood-brain barrier (BBB) compared to non-calcification-prone brain regions. While our findings provide clear evidence that loss-of-function mutations in PDGFB or PDGFRB cause PFBC, they also demonstrate species differences in the threshold levels of PDGF-B/PDGF-Rβ signaling that protect against small-vessel calcification in the brain. They further implicate region-specific susceptibility factor(s) in PFBC pathogenesis that are distinct from pericyte and BBB deficiency.

Accelerated magnetic resonance diffusion tensor imaging of the median nerve using simultaneous multi-slice echo planar imaging with blipped CAIPIRINHA

PURPOSE

To investigate the feasibility of MR diffusion tensor imaging (DTI) of the median nerve using simultaneous multi-slice echo planar imaging (EPI) with blipped CAIPIRINHA.

MATERIALS AND METHODS

After federal ethics board approval, MR imaging of the median nerves of eight healthy volunteers (mean age, 29.4 years; range, 25-32) was performed at 3 T using a 16-channel hand/wrist coil. An EPI sequence (b-value, 1,000 s/mm(2); 20 gradient directions) was acquired without acceleration as well as with twofold and threefold slice acceleration. Fractional anisotropy (FA), mean diffusivity (MD) and quality of nerve tractography (number of tracks, average track length, track homogeneity, anatomical accuracy) were compared between the acquisitions using multivariate ANOVA and the Kruskal-Wallis test.

RESULTS

Acquisition time was 6:08 min for standard DTI, 3:38 min for twofold and 2:31 min for threefold acceleration. No differences were found regarding FA (standard DTI: 0.620 ± 0.058; twofold acceleration: 0.642 ± 0.058; threefold acceleration: 0.644 ± 0.061; p ≥ 0.217) and MD (standard DTI: 1.076 ± 0.080 mm(2)/s; twofold acceleration: 1.016 ± 0.123 mm(2)/s; threefold acceleration: 0.979 ± 0.153 mm(2)/s; p ≥ 0.074). Twofold acceleration yielded similar tractography quality compared to standard DTI (p > 0.05). With threefold acceleration, however, average track length and track homogeneity decreased (p = 0.004-0.021).

CONCLUSION

Accelerated DTI of the median nerve is feasible. Twofold acceleration yields similar results to standard DTI.

KEY POINTS

• Standard DTI of the median nerve is limited by its long acquisition time. • Simultaneous multi-slice acquisition is a new technique for accelerated DTI. • Accelerated DTI of the median nerve yields similar results to standard DTI.

Dynamic intravoxel incoherent motion imaging of skeletal muscle at rest and after exercise

The purpose of this work was to demonstrate the feasibility of intravoxel incoherent motion imaging (IVIM) for non-invasive quantification of perfusion and diffusion effects in skeletal muscle at rest and following exercise. After IRB approval, eight healthy volunteers underwent diffusion-weighted MRI of the forearm at 3 T and eight different b values between 0 and 500 s/mm(2) with a temporal resolution of 57 s per dataset. Dynamic images were acquired before and after a standardized handgrip exercise. Diffusion (D) and pseudodiffusion (D*) coefficients as well as the perfusion fraction (FP ) were measured in regions of interest in the flexor digitorum superficialis and profundus (FDS/FDP), brachioradialis, and extensor carpi radialis longus and brevis muscles by using a multi-step bi-exponential analysis in MATLAB. Parametrical maps were calculated voxel-wise. Differences in D, D*, and FP between muscle groups and between time points were calculated using a repeated measures analysis of variance with post hoc Bonferroni tests. Mean values and standard deviations at rest were the following: D*, 28.5 ± 11.4 × 10(-3) mm(2) /s; FP , 0.03 ± 0.01; D, 1.45 ± 0.09 × 10(-3) mm(2) /s. Changes of IVIM parameters were clearly visible on the parametrical maps. In the FDS/FDP, D* increased by 289 ± 236% (p < 0.029), FP by 138 ± 58% (p < 0.01), and D by 17 ± 9% (p < 0.01). A significant increase of IVIM parameters could also be detected in the brachioradialis muscle, which however was significantly lower than in the FDS/FDP. After 20 min, all parameters were still significantly elevated in the FDS/FDP but not in the brachioradialis muscle compared with the resting state. The IVIM approach allows simultaneous quantification of muscle perfusion and diffusion effects at rest and following exercise. It may thus provide a useful alternative to other non-invasive methods such as arterial spin labeling. Possible fields of interest for this technique include perfusion-related muscle diseases, such as peripheral arterial occlusive disease.

ZTE imaging with long-T2 suppression

Three-dimensional radial zero echo time (ZTE) imaging enables efficient direct MRI of tissues with rapid transverse relaxation. Yet, the feature of capturing signals with a wide range of T2 and T2 * values is accompanied by a lack of contrast between the corresponding tissues. In particular, the targeted short-T2 tissues may not be easily identified, and various approaches have been proposed to generate T2 contrast by reducing the long-T2 signal of water and/or fat. The aim of this work was to provide efficient long-T2 suppression for selective direct MRI of short-T2 tissues using the ZTE technique. For magnetization preparation, suppression pulses for water and fat were designed to provide both good T2 selectivity and off-resonance performance. To obtain high efficiency at short TRs, the pulses were applied in a segmented sequence scheme with minimized timing overhead, thus leading to a quasi-steady state of magnetization. The sequence timing was adjusted for optimal tissue contrast in musculoskeletal applications by means of simulations and experiments, incorporating both T2 and T1 of the involved tissues. The developed technique was employed for imaging of a lamb joint sample at 4.7 T. ZTE images were obtained with effective suppression of signals from tissues with long-T2 water, such as muscle or articular spaces, and fat. Hence, primarily short-T2 tissues were visible, such as bone and tendon. The MR image intensity of bone showed strong similarity with bone density imaged with micro-computed tomography.

Hybrid PET/MR imaging: an algorithm to reduce metal artifacts from dental implants in Dixon-based attenuation map generation using a multiacquisition variable-resonance image combination sequence

It was the aim of this study to implement an algorithm modifying Dixon-based MR imaging datasets for attenuation correction in hybrid PET/MR imaging with a multiacquisition variable resonance image combination (MAVRIC) sequence to reduce metal artifacts.

METHODS

After ethics approval, in 8 oncologic patients with dental implants data were acquired in a trimodality setup with PET/CT and MR imaging. The protocol included a whole-body 3-dimensional dual gradient-echo sequence (Dixon) used for MR imaging-based PET attenuation correction and a high-resolution MAVRIC sequence, applied in the oral area compromised by dental implants. An algorithm was implemented correcting the Dixon-based μ maps using the MAVRIC in areas of Dixon signal voids. The artifact size of the corrected μ maps was compared with the uncorrected MR imaging μ maps.

RESULTS

The algorithm was robust in all patients. There was a significant reduction in mean artifact size of 70.5% between uncorrected and corrected μ maps from 697 ± 589 mm(2) to 202 ± 119 mm(2) (P = 0.016).

CONCLUSION

The proposed algorithm could improve MR imaging-based attenuation correction in critical areas, when standard attenuation correction is hampered by metal artifacts, using a MAVRIC.

Evaluation of imaging techniques for the assessment of tumour progression in an orthotopic rat model of malignant pleural mesothelioma†

OBJECTIVES

An orthotopic rat tumour recurrence model for malignant pleural mesothelioma (MPM) provides clinical similarity to patients and is useful for drug testing combined with surgical intervention. Importantly, a reliable imaging method is required allowing for noninvasive and repetitive evaluation of the tumour load. We compared the tumour load assessed by bioluminescence and magnetic resonance imaging (MRI) to the macroscopic tumour volume as a reference standard.

METHODS

A total of 500,000 syngeneic rat MPM cells transfected with luciferase were implanted underneath the parietal pleura of immunocompetent rats (n=13). From the second day after implantation, bioluminescence measurements of the tumour load expressed as the maximum bioluminescent intensity (photon/second) were performed daily after intraperitoneal injection of the luciferase substrate, d-luciferin, to observe the first occurrence of tumour. Six days after the first detection of tumour, bioluminescence, MRI and macroscopic tumour volume measurement were conducted. For MRI, a 4.7-Tesla small animal imager equipped with a 1H whole-body rat coil was employed using T2-weighted fast spin-echo sequences. Tumour burden (mm3) was quantified from magnetic resonance transverse images by two independent readers by manual segmentation. Finally, the tumour burden assessed by bioluminescence and MRI was correlated (Pearson's correlation) with the macroscopic measurement of tumour (ellipsoid) volume.

RESULTS

In all rats, a single tumour nodule was found at the inoculation site with a median macroscopic volume of 46 mm3 (18-377 mm3). For tumour burden quantification of MRIs, we observed good interobserver correlation (R2=0.81, P<0.0001) as well as significant association with the macroscopic tumour volume (R2=0.59, P=0.002). However, the signal intensity of bioluminescence did not correspond to the macroscopic tumour volume (R2=0.01, P=0.76).

CONCLUSIONS

MRI is a reliable and reproducible noninvasive in vivo imaging method for MPM tumour burden assessment for the present MPM model.

Characterization of trabecular bone density with ultra-short echo-time MRI at 1.5, 3.0 and 7.0 T--comparison with micro-computed tomography

The goal of this study was to test the potential of ultra-short echo-time (UTE) MRI at 1.5, 3.0 and 7.0 T for depiction of trabecular bone structure (of the wrist bones), to evaluate whether T2* relaxation times of bone water and parametric maps of T2* of trabecular bone could be obtained at all three field strengths, and to compare the T2* relaxation times with structural parameters obtained from micro-computed tomography (micro-CT) as a reference standard. Ex vivo carpal bones of six wrists were excised en bloc and underwent MRI at 1.5, 3.0 and 7.0 T in a whole-body MR imager using the head coil. A three-dimensional radial fat-suppressed UTE sequence was applied with subsequent acquisitions, with six different echo times TE of 150, 300, 600, 1200, 3500 and 7000 µs. The T2* relaxation time and pixel-wise computed T2* parametric maps were compared with a micro-computed-tomography reference standard providing trabecular bone structural parameters including porosity (defined as the bone-free fraction within a region of interest), trabecular thickness, trabecular separation, trabecular number and fractal dimension (Dk). T2* relaxation curves and parametric maps could be computed from datasets acquired at all field strengths. Mean T2* relaxation times of trabecular bone were 4580 ± 1040 µs at 1.5 T, 2420 ± 560 µs at 3.0 T and 1220 ± 300 µs at 7.0 T, when averaged over all carpal bones. A positive correlation of T2* with trabecular bone porosity and trabecular separation, and a negative correlation of T2* relaxation time with trabecular thickness, trabecular number and fractal dimension, was detected (p < 0.01 for all field strengths and micro-CT parameters). We conclude that UTE MRI may be useful to characterize the structure of trabecular bone, comparable to micro-CT.

Rapid and robust pulmonary proton ZTE imaging in the mouse

Pulmonary MRI is challenging because of the low proton density and rapid transverse relaxation in the lung associated with microscopic magnetic field inhomogeneities caused by tissue-air interfaces. Therefore, low signal is obtained in gradient and spin echo proton images. Alternatively, non-proton MRI using hyperpolarized gases or radial techniques with ultrashort or zero TE have been proposed to image the lung. Also with the latter approach, the general challenge remains to provide full coverage of the lung at sufficient spatial resolution, signal-to-noise ratio (SNR) and image quality within a reasonable scan time. This task is further aggravated by physiological motion and is particularly demanding in small animals, such as mice. In this work, three-dimensional (3D) zero echo time (ZTE) imaging is employed for efficient pulmonary MRI. Four protocols with different averaging and respiratory triggering schemes are developed and compared with respect to image quality and SNR. To address the critical issue of background signal in ZTE images, a subtraction approach is proposed, providing images virtually free of disturbing signal from nearby hardware parts. The protocols are tested for pulmonary MRI in six mice at 4.7 T, consistently providing images of high quality with a 3D isotropic resolution of 313 µm and SNR values in the lung between 8.0 and 18.5 within scan times between 1 min 21 s and 4 min 44 s. A generally high robustness of the ZTE approach against motion is observed, whilst respiratory triggering further improves the SNR and visibility of image details. The developed techniques are expected to enable efficient preclinical animal studies in the lung and will also be of importance for human applications. Further improvements are expected from radiofrequency (RF) coils with increased SNR and reduced background signal.

Economics of youth drug use, addiction and gateway effects

The use of illicit drugs by American youth rose dramatically during the 1990s. Reducing these trends is an important policy objective. However, for policies to be effective it is important to understand the key causal links that lead to substance use and abuse. Policy makers must understand whether attempts to reduce the demand for one drug have impacts on the current and future use of other drugs. This paper overviews an economic approach to modeling drug use, addiction and gateway effects, emphasizing the potential of this method for identifying causal links in consumption. The paper demonstrates how this multi-substance theory of drug use leads to empirical specifications that can identify the impact of consumption of one drug on the contemporaneous and future consumption of other drugs. This is followed by a discussion of what types of data would be needed to estimate these effects.