Design of a generic method for single dual-tracer PET imaging acquisition in clinical routine

Using different tracers in PET imaging can bring complementary information on tumor heterogeneities. Ideally, PET images of different tracers should be acquired simultaneously to avoid the bias induced by movement and physiological changes between sequential acquisitions. Previous studies have demonstrated the feasibility of recovering separated PET signals or parameters of two or more tracers injected (quasi-)simultaneously in a single acquisition. In this study, a generic framework in the context of dual-tracer PET acquisition is proposed where no strong kinetic assumptions nor specific tuning of parameters are required. The performances of the framework were assessed through simulations involving the combination of [¹⁸F]FCH and [¹⁸F]FDG injections, two protocols (90 and 60-minute acquisition durations) and various activity ratios between the two injections. Preclinical experiments with the same radiotracers were also conducted. Results demonstrate the ability of the method both to extract separated arterial input functions (AIF) from noisy image-derived input function (IDIF) and to separate the dynamic signals and further estimate kinetic parameters.
The compromise between bias and variance associated with the estimation of net influx rateK_ishows that it is preferable to use the second injected radiotracer with twice the activity of the first for both 90-minute [¹⁸F]FCH+[¹⁸F]FDG and 60-minute [¹⁸F]FDG+[¹⁸F]FCH protocols. In these optimal settings, the weighted mean-squared-error of the estimated AIF was always less than 7%. TheK_ibias was similar to the one of single-tracer acquisitions; below 5%. Compared to single-tracer results, the variance ofK_iwas twice more for 90-minute dual-tracer scenario and four times more for the 60-minute scenario. The generic design of the method makes it easy to use for other pairs of radiotracers and even for more than two tracers. The absence of strong kinetic assumptions and tuning parameters makes it suitable for a possible use in clinical routine.

PET scatter estimation using deep learning U-Net architecture

Objective.Positron emission tomography (PET) image reconstruction needs to be corrected for scatter in order to produce quantitatively accurate images. Scatter correction is traditionally achieved by incorporating an estimated scatter sinogram into the forward model during image reconstruction. Existing scatter estimated methods compromise between accuracy and computing time. Nowadays scatter estimation is routinely performed using single scatter simulation (SSS), which does not accurately model multiple scatter and scatter from outside the field-of-view, leading to reduced qualitative and quantitative PET reconstructed image accuracy. On the other side, Monte-Carlo (MC) methods provide a high precision, but are computationally expensive and time-consuming, even with recent progress in MC acceleration.Approach.In this work we explore the potential of deep learning (DL) for accurate scatter correction in PET imaging, accounting for all scatter coincidences. We propose a network based on a U-Net convolutional neural network architecture with 5 convolutional layers. The network takes as input the emission and computed tomography (CT)-derived attenuation factor (AF) sinograms and returns the estimated scatter sinogram. The network training was performed using MC simulated PET datasets. Multiple anthropomorphic extended cardiac-torso phantoms of two different regions (lung and pelvis) were created, considering three different body sizes and different levels of statistics. In addition, two patient datasets were used to assess the performance of the method in clinical practice.Main results.Our experiments showed that the accuracy of our method, namely DL-based scatter estimation (DLSE), was independent of the anatomical region (lungs or pelvis). They also showed that the DLSE-corrected images were similar to that reconstructed from scatter-free data and more accurate than SSS-corrected images.Significance.The proposed method is able to estimate scatter sinograms from emission and attenuation data. It has shown a better accuracy than the SSS, while being faster than MC scatter estimation methods.

PET respiratory motion correction: quo vadis?

Positron emission tomography (PET) respiratory motion correction has been a subject of great interest for the last twenty years, prompted mainly by the development of multimodality imaging devices such as PET/computed tomography (CT) and PET/magnetic resonance imaging (MRI). PET respiratory motion correction involves a number of steps including acquisition synchronization, motion estimation and finally motion correction. The synchronization steps include the use of different external device systems or data driven approaches which have been gaining ground over the last few years. Patient specific or generic motion models using the respiratory synchronized datasets can be subsequently derived and used for correction either in the image space or within the image reconstruction process. Similar overall approaches can be considered and have been proposed for both PET/CT and PET/MRI devices. Certain variations in the case of PET/MRI include the use of MRI specific sequences for the registration of respiratory motion information. The proposed review includes a comprehensive coverage of all these areas of development in field of PET respiratory motion for different multimodality imaging devices and approaches in terms of synchronization, estimation and subsequent motion correction. Finally, a section on perspectives including the potential clinical usage of these approaches is included.

Why provision of clinical decision support (CDS) is not enough? Factors influencing the CDS adoption

Background

Clinical decision support (CDS) can improve the quality and efficiency of care by increasing access to evidence-based data at the point-of-care. However, CDS adoption is limited in clinical settings. The focus on the technical design have overlooked end-users’ perceptions, social and organisational factors that may influence uptake. Using the Unified Theory of Acceptance and Use of Technology (UTAUT) model, we aimed to identify different challenges and opportunities for CDSS adoption in clinical settings.

Methods

A cross-sectional online survey was conducted from June-October 2019 with general practitioners, physicians and surgeons in Australia. To measure the impact of UTAUT moderators (age, gender and experience) and care settings (primary care vs. hospitals) on perceived barriers and facilitators to CDS implementation, multivariate logistic regression was carried out. Qualitative data was thematically analysed for emerging patterns and themes.

Results

Many respondents indicated that CDS can promote evidence-based care (79%) and improve quality and safety (52%). Overall CDS adoption is dependent on factors such as effort expectancy (ease of use), performance expectancy and a facilitating environment for system use. Clinician perceptions of barriers and facilitators to uptake are associated with type of care setting. There was higher likelihood of perceiving ease of use (OR 1.39, 95% CI 1.15-2.07), time limitations (OR 1.95, 95%CI 1.10-3.77), patient' preferences (OR 2.17, 95% CI 1.14-3.37) and threat to professional autonomy (OR 2.15, 95%CI 1.39-3.41) as factors that influence adoption in primary care. Providing relevant information in right format at right time is critical for successful CDS use.

Conclusions

CDS implementation requires a holistic approach addressing users' perceptions and preferences determined through stakeholder consultation. The system design must be easy to use but also facilitated through the provision of on-site training and support.

Key messages

CDS adoption is determined by systems’ ease of use and provision of enabling environment. Users and setting characteristics are important moderators and must be considered in CDS implementation.

A strict requirement for LBP in the TNFα hyper-response of Propionibacterium acnes-sensitized mice to LPS

One important feature of the Propionibacterium acnes-induced hypersensitivity to LPS is the enhanced production of TNFα induced in the sensitized mice upon LPS challenge [Katschinski T., Galanos G., Coumbos A., Freudenberg M.A. Gamma interferon mediates Propionibacterium acnes-induced hypersensitivity to lipopolysaccharide in mice. Infect Immun 1992; 60: 1994-2001]. We investigated the role of LPS binding protein (LBP) in the TNFα response of normal and P. acnes-sensitized mice to LPS in LBP+/+ and LBP-/- mice. Treatment of LBP+/+ (BalbC and 129 Sv) mice with P. acnes enhanced their TNFα response to LPS by 75-200-fold compared to the non-treated controls. Unsensitized LBP-/- (129 Sv x BalbC) mice were also stimulated by LPS to produce low amounts of TNFα. These were enhanced by prior P. acnes treatment, however, only by a factor of 4. The characteristic TNFα hyper-response was absent suggesting that the enhanced activity of LPS in sensitized mice is expressed only in the presence of LBP. Evidence for this was obtained by showing that administration of exogenous LBP restored fully the inducibility of the TNFα hyper-response in P. acnes-sensitized LBP-/- mice. Their response to LPS was 1000-fold higher then that of sensitized controls without LBP. A similar LBP treatment of unsensitized LBP-/- mice increased the TNFα response by a factor of only 5. In an analogous experiment, also IFN-γ-sensitized LBP-/- mice exhibited a TNFα overproduction in response to LPS only in the presence of exogenous LBP.

Motion correction using anatomical information in PET/CT and PET/MR hybrid imaging

Respiratory and cardiac motion causes qualitative and quantitative inaccuracies in whole body multi-modality imaging such as positron emission tomography coupled with computed tomography (PET/CT) and positron emission tomography/magnetic resonance imaging (PET/MRI). Solutions presented to date include motion synchronized PET and corresponding anatomical acquisitions (four dimensional [4D] PET/CT, 4D PET/MR), frequently referred to as the gating approach. This method is based on the acquisition of an external surrogate using an external device (pressure belt, optical monitoring system, spirometer etc.), subsequently used to bin PET and CT or MR anatomical data into a number of gates. A first limitation of this method is the low signal to noise ratio (SNR) of the resulting motion synchronized PET frames, given that every reconstructed frame contains only part of the count statistics available throughout a motion average PET acquisition. Another limitation is that the complex motion of internal organs cannot be fully estimated, characterized and modelled using a mono-dimensional motion signal. In order to resolve such issues, many advanced techniques have been proposed which include three consecutive major steps. These are based on firstly acquiring an external or internal motion surrogate, estimating or modelling the internal motion using anatomical information extracted from 4D anatomical images (CT and/or MR) and finally correcting for motion either in the PET raw data space, the image space or incorporate it within the PET image reconstruction which is the most optimal based motion correction method in PET/CT and in PET/MR imaging. Current research efforts are concentrating on combining the last two steps within a joint motion estimation/motion correction approach, the exploitation of MRI specific motion characterization sequences and the combination of both respiratory and cardiac motion corrections. The goal of this review is to present and discuss the different steps of all these motion correction methods in PET/CT and PET/MR imaging for whole body applications.

Potential of [18F]-fluoromisonidazole positron-emission tomography for radiotherapy planning in head and neck squamous cell carcinomas

BACKGROUND AND PURPOSE

Positron-emission tomography (PET) with [(18)F]-fluoromisonidazole (FMISO) permits consideration of radiotherapy dose escalation to hypoxic volumes in head and neck cancers (HNC). However, the definition of FMISO volumes remains problematic. The aims of this study are to confirm that delayed acquisition at 4 h is most appropriate for FMISO-PET imaging and to assess different methods of volume segmentation.

PATIENTS AND METHODS

A total of 15 HNC patients underwent several FMISO-PET/computed tomography (CT) acquisitions 2, 3 and 4 h after FMISO injection. Three automatic methods of PET image segmentation were tested: fixed threshold, adaptive threshold based on the ratio between tumour-derived and background activities (R(T/B)) and the fuzzy locally adaptive Bayesian (FLAB) method. The hypoxic fraction (HF), which is defined as the ratio between the FMISO and CT volumes, was also calculated.

RESULTS

The R(T/B) for images acquired at 2, 3 and 4 h differed significantly, with mean values of 2.5 (1.7-2.9), 3 (2-4.5) and 3.4 (2.3-6.1), respectively. The mean tumour volume, as defined manually using CT images, was 39.1 ml (1.2-116 ml). After 4 h, the mean FMISO volumes were 18.9 (0.1-81), 9.5 (0.9-33.1) and 12.5 ml (0.9-38.4 ml) with fixed threshold, adaptive threshold and the FLAB method, respectively; median HF values were 0.47 (0.1-1.93), 0.25 (0.11-0.75) and 0.35 (0.14-1.05), respectively. FMISO volumes were significantly different.

CONCLUSION

The best contrast is obtained at the 4-hour acquisition time. Large discrepancies were found between the three tested methods of volume segmentation.

Role of lipopolysaccharide susceptibility in the innate immune response to Salmonella typhimurium infection: LPS, a primary target for recognition of Gram-negative bacteria

Lipopolysaccharide is an important recognition marker by virtue of which the innate immune system senses and reacts against Gram-negative bacteria invading the LPS susceptible host. This review deals with the factors affecting LPS susceptibility and with the role of the latter in the course and outcome of Salmonella typhimurium infection.

TNF-alpha hyper-responses to Gram-negative and Gram-positive bacteria in Propionibacterium acnes primed or Salmonella typhimurium infected mice

IFN-gamma-dependent hypersensitivity to LPS is inducible in mice by infection or pre-treatment with killed bacteria. Hypersensitive mice exhibit enhanced inflammatory responses to LPS, including the overproduction of TNF-alpha. Using Lps(n) BALB/c and Lps(d) BALB/c/l mice, primed with Propionibacterium acnes or infected with Salmonella typhimurium, we show that concurrently to hypersensitivity to LPS, a hypersensitivity to other constituents of killed Gram-negative or Gram-positive bacteria and to staphylococcal enterotoxin B (SEB) develops. The TNF-alpha hyper-responses in sensitized mice induced by different Gram-positive bacteria, are generally weaker than those by Gram-negative bacteria and vary significantly, due to the absence of a common, LPS-equivalent component. Using IFN-gamma R(-/-) and the respective wild-type mice, we demonstrate that although sensitization to LPS and killed Listeria monocytogenes is exclusively IFN-gamma-dependent, an IFN-gamma-independent, moderate sensitization to certain TNF-alpha-inducing constituents in bacteria may develop in parallel.

A point mutation in the IL-12R beta 2 gene underlies the IL-12 unresponsiveness of Lps-defective C57BL/10ScCr mice

Lps-defective C57BL/10ScCr (Cr) mice are homozygous for a deletion encompassing Toll-like receptor 4 that makes them refractory to the biological activity of LPS. In addition, these mice exhibit an inherited IL-12 unresponsiveness resulting in impaired IFN-gamma responses to different microorganisms. By positional cloning methods, we show here that this second defect of Cr mice is due to a mutation in a single gene located on mouse chromosome 6, in close proximity to the Igkappa locus. The gene is IL-12Rbeta2. Cr mice carry a point mutation creating a stop codon that is predicted to cause premature termination of the translated IL-12Rbeta2 after a lysine residue at position 777. The truncated beta2 chain can still form a heterodimeric IL-12R that allows phosphorylation of Janus kinase 2, but, unlike the wild-type IL-12R, can no longer mediate phosphorylation of STAT4. Because the phosphorylation of STAT4 is a prerequisite for the IL-12-mediated induction of IFN-gamma, its absence in Cr mice is responsible for their defective IFN-gamma response to microorganisms.

Inherited IL-12 unresponsiveness contributes to the high LPS resistance of the Lps(d) C57BL/10ScCr mouse

LPS(d) mouse strains are characterized by the presence of a defective LPS/tlr4 gene that make them refractory to the biological activity of LPS. One of the mouse strains commonly used to study LPS defects is the C57BL/10ScCr (Cr) strain. However, unlike other LPS(d) strains, the Cr strain also has a heavily impaired IFN-gamma response to micro-organisms. As a consequence, unlike other LPS(d) mouse strains, they do not acquire a partial LPS susceptibility when treated with sensitizing bacteria. Because IL-12 is important for the microbial induction of IFN-gamma, we investigated whether the production or function of IL-12 might be defective in Cr mice. IL-12 mRNA (p35 and p40) was present in the spleen of untreated Cr mice, IL-12p40 mRNA was inducible in mice injected with live or killed Salmonella typhimurium, and IL-12 (p70) was inducible in macrophages by bacteria. Thus, Cr mice exhibit normal IL-12 responses. In functional tests, splenocytes of untreated or of S. typhimurium-infected mice failed to produce IFN-gamma when stimulated with murine rIL-12 or with a combination of IL-12 and murine rIL-18 or Con A. Furthermore, Cr mice were identical with IL-12p35/p40 and IL-12 receptor beta(1) knockout mice in their impaired in vivo and in vitro IFN-gamma responses to bacteria. Thus, Cr mice carry a second genetic defect unrelated to the Lps/tlr4 mutation that underlies the IL-12 unresponsiveness and contributes to the LPS resistance and impaired innate immune response in this strain.

Bacterial induction of beta interferon in mice is a function of the lipopolysaccharide component

We investigated the reason for the inability of lipopolysaccharide (LPS)-resistant (Lps-defective [Lps(d)]) C57BL/10ScCr mice to produce beta interferon (IFN-beta) when stimulated with bacteria. For this purpose, the IFN-beta and other macrophage cytokine responses induced by LPS and several killed gram-negative and gram-positive bacteria in LPS-sensitive (Lps-normal [Lps(n)]; C57BL/10ScSn and BALB/c) and Lps(d) (C57BL/10ScCr and BALB/c/l) mice in vitro and in vivo were investigated on the mRNA and protein levels. In addition, double-stranded RNA (dsRNA) was used as a nonbacterial stimulus. LPS and all gram-negative bacteria employed induced IFN-beta in the Lps(n) mice but not in the Lps(d) mice. All gram-positive bacteria tested failed to induce significant amounts of IFN-beta in all four of the mouse strains used. As expected, all other cytokines tested (tumor necrosis factor alpha, interleukin 1alpha [IL-1alpha], IL-6, and IL-10) were differentially induced by gram-negative and gram-positive bacteria. Stimulation with dsRNA induced IFN-beta and all other cytokines mentioned above in all mouse strains, regardless of their LPS sensitivities. The results suggest strongly that LPS is the only bacterial component capable of inducing IFN-beta in significant amounts that are readily detectable under the conditions used in this study. Consequently, in mice, IFN-beta is inducible only by gram-negative bacteria, but not in C57BL/10ScCr or other LPS-resistant mice.

Cell cycle arrest in ovarian cancer cell lines does not depend on p53 status upon treatment with cytostatic drugs

Human ovarian cancer cell lines with different p53 status were investigated for p53-dependency of cell cycle arrest upon treatment with cytostatic drugs. For this purpose commonly used anti-cancer drugs and a novel anti-cancer drug, gemcitabine, were applied. Cell cycle arrest was dependent on the drug dose used, as observed for all anti-cancer drugs applied, but not related to functional p53. With the exception of the etoposide-effected G2/M arrest at high concentrations, which seems to depend on functional p53, since it did not occur in cells with inactive p53. Only in cells with wt p53 and quasi-wild-type, p53 accumulated in the nucleus upon drug treatment with all anti-cancer agents applied. The level of accumulation was drug dose-dependent for each drug tested. The accumulated p53 was biochemically active, as measured in a transient transfection assay upon treatment with gemcitabine, cisplatin, etoposide, and Taxol. Activity was dependent on the drug dose applied and proportional to the level of accumulated p53, except for Taxol-induced p53 accumulation which correlated inversely with p53 biochemical activity. Apoptosis was estimated by in situ end labeling by biotinylated dUTP with the terminal deoxyribonucleotidyl transferase assay. Apoptosis occured after arrest at the various phases of the cell cycle in all cell lines tested, depending on the drug and the drug dose used. Nevertheless, cells with wt p53 exhibited the highest fraction of apoptotic cells.

Reduced susceptibility of methicillin-resistant Staphylococcus aureus to cetylpyridinium chloride and chlorhexidine

Sensitivities of 120 strains of Staphylococcus aureus to methicillin, cetylpyridinium chloride (CPC) and chlorhexidine (CH) were measured by the agar dilution technique. The MICs for CPC and CH were < or = 2 micrograms/ml in 93 and 83% of methicillin-sensitive S. aureus, respectively, and > 2 micrograms/ml in 81 and 83% of methicillin-resistant S. aureus (MRSA), respectively. Overall, the MICs for CPC and CH were 5-10 times greater in the methicillin-resistant than in the methicillin-sensitive strains (p < 0.001). The MICs for CPC and CH also predicted the relative susceptibilities of S. aureus strains to the bactericidal action of these agents in growth and time-kill studies. The possibility that antiseptics and disinfectants contribute to the selection and maintenance of multiply resistant MRSA is considered.

CD5-negative cell mediated experimental hypersensitivity pneumonitis

Experimental hypersensitivity pneumonitis (EHP) can be transferred to Strain 2 guinea pigs by peripheral lymph node (PLN) cells cultured in vitro with antigen. The phenotype of the active cells has not been delineated. In addition, it is not known if cultured lung-associated lymph node (LALN) cells can transfer EHP. PLN and LALN cells from donor animals were cultured with a soluble extract of Micropolyspora faeni (10 micrograms/ml), and blast cells were isolated by centrifugation over Percoll gradients. Cultured PLN cells were passed through nylon wool columns, and the adherent and nonadherent fractions were tested for their ability to transfer EHP. PLN blast cell populations were depleted of CD5+ cells by treatment with monoclonal anti CD5 antibody (8BE6) and complement. Syngeneic recipients received media or LALN or PLN blast cells treated with antibody plus complement, media, or complement intravenously. Recipients were challenged intratracheally with M. faeni 48 h after the cell transfer, and they were killed 4 days later. The nonadherent PLN cell population was enriched for CD5+ (T) cells and depleted of surface immunoglobulin-positive (SIg+) cells. Treatment of the PLN blast cell population with 8BE6 and complement decreased CD5+ cells from 25 to 4% and increased SIg+ cells from 62 to 80%. All animals were maintained in HEPA-filtered air. Randomly selected microscopic fields of the lung (250/animal) were judged to be normal or abnormal without knowledge of treatment. There was a low level of pulmonary response to an intratracheal challenge of M. faeni in media recipients. There was a substantial increase (p less than 0.01) of the extent of pulmonary abnormalities in the animals receiving cultured PLN cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Inoculation of blood culture bottles with ascitic fluid. Improved detection of spontaneous bacterial peritonitis

The observation that only 42% of the cases of suspected spontaneous bacterial peritonitis at the University of New Mexico, Albuquerque, had positive cultures prompted a change in ascitic fluid culture technique such that a large volume (10 mL in toto) of ascitic fluid was inoculated into blood culture bottles at the bedside. This new method of culture increased the percentage of cases with positive cultures to 91% and decreased the interval between inoculation of the culture and detection of bacterial growth. This is a more sensitive method of culture than the conventional method in detecting spontaneous bacterial peritonitis.