Validation of echo planar imaging based diffusion-weighted magnetic resonance imaging on a 0.35 T MR-Linac.

Background and Purpose: The feasibility of acquiring diffusion-weighted imaging (DWI) images on an MR-Linac for quantitative response assessment during radiotherapy was explored. DWI data obtained with a Spin Echo Echo Planar Imaging sequence adapted for a 0.35 T MR-Linac were examined and compared with DWI data from a conventional 3 T scanner. Materials and Methods: Apparent diffusion coefficient (ADC) measurements and a distortion correction technique were investigated using DWI-calibrated phantoms and in the brains of seven volunteers. All DWI utilized two phase-encoding directions for distortion correction and off-resonance field estimation. ADC maps in the brain were analyzed for automatically segmented normal tissues. Results: Phantom ADC measurements on the MR-Linac were within a 3 % margin of those recorded by the 3 T scanner. The maximum distortion observed in the phantom was 2.0 mm prior to correction and 1.1 mm post-correction on the MR-Linac, compared to 6.0 mm before correction and 3.6 mm after correction at 3 T. In vivo, the average ADC values for gray and white matter exhibited variations of 14 % and 4 %, respectively, for different selections of b-values on the MR-Linac. Distortions in brain images before correction, estimated through the off-resonance field, reached 2.7 mm on the MR-Linac and 12 mm at 3 T. Conclusion: Accurate ADC measurements are achievable on a 0.35 T MR-Linac, both in phantom and in vivo. The selection of b-values significantly influences ADC values in vivo. DWI on the MR-Linac demonstrated lower distortion levels, with a maximum distortion reduced to 1.1 mm after correction.

Validation of daily 0.35 T diffusion-weighted MRI for MRI-guided glioblastoma radiotherapy.

BACKGROUND: MRI-Linac systems enable daily diffusion-weighed imaging (DWI) MRI scans for assessing glioblastoma tumor changes with radiotherapy treatment. PURPOSE: Our study assessed the image quality of echoplanar imaging (EPI)-DWI scans compared with turbo spin echo (TSE)-DWI scans at 0.35 Tesla (T) and compared the apparent diffusion coefficient (ADC) values and distortion of EPI-DWI on 0.35 T MRI-Linac compared to high-field diagnostic MRI scanners. METHODS: The calibrated National Institute of Standards and Technology (NIST)/Quantitative Imaging Biomarkers Alliance (QIBA) Diffusion Phantom was scanned on a 0.35 T MRI-Linac, and 1.5 T and 3 T MRI with EPI-DWI. Five patients were scanned on a 0.35 T MRI-Linac with a TSE-DWI sequence, and five other patients were scanned with EPI-DWI on a 0.35 T MRI-Linac and a 3 T MRI. The quality of images was compared between the TSE-DWI and EPI-DWI on the 0.35 T MRI-Linac assessing signal-to-noise ratios and presence of artifacts. EPI-DWI ADC values and distortion magnitude were measured and compared between 0.35 T MRI-Linac and high-field MRI for both phantom and patient studies. RESULTS: The average ADC differences between EPI-DWI acquired on the 0.35 T MRI-Linac, 1.5 T and 3 T MRI scanners and published references in the phantom study were 1.7%, 0.4% and 1.0%, respectively. Comparing the ADC values based on EPI-DWI in glioblastoma tumors, there was a 3.36% difference between 0.35 and 3 T measurements. Susceptibility-induced distortions in the EPI-DWI phantoms were 0.46 ± 1.51 mm for 0.35 MRI-Linac, 0.98 ± 0.51 mm for 1.5 T MRI and 1.14 ± 1.88 mm for 3 T MRI; for patients -0.47 ± 0.78 mm for 0.35 T and 1.73 ± 2.11 mm for 3 T MRIs. The mean deformable registration distortion for a phantom was 1.1 ± 0.22 mm, 3.5 ± 0.39 mm and 4.7 ± 0.37 mm for the 0.35 T MRI-Linac, 1.5 T MRI, and 3 T MRI scanners, respectively; for patients this distortion was -0.46 ± 0.57 mm for 0.35 T and 4.2 ± 0.41 mm for 3 T. EPI-DWI 0.35 T MRI-Linac images showed higher SNR and lack of artifacts compared with TSE-DWI, especially at higher b-values up to 1000 s/mm2. CONCLUSION: EPI-DWI on a 0.35 T MRI-Linac showed superior image quality compared with TSE-DWI, minor and less distortions than high-field diagnostic scanners, and comparable ADC values in phantoms and glioblastoma tumors. EPI-DWI should be investigated on the 0.35 T MRI-Linac for prediction of early response in patients with glioblastoma.

Accurate, repeatable, and geometrically precise diffusion-weighted imaging on a 0.35 T magnetic resonance imaging-guided linear accelerator.

Background and purpose: Diffusion weighted imaging (DWI) allows for the interrogation of tissue cellularity, which is a surrogate for cellular proliferation. Previous attempts to incorporate DWI into the workflow of a 0.35 T MR-linac (MRL) have lacked quantitative accuracy. In this study, accuracy, repeatability, and geometric precision of apparent diffusion coefficient (ADC) maps produced using an echo planar imaging (EPI)-based DWI protocol on the MRL system is illustrated, and in vivo potential for longitudinal patient imaging is demonstrated. Materials and methods: Accuracy and repeatability were assessed by measuring ADC values in a diffusion phantom at three timepoints and comparing to reference ADC values. System-dependent geometric distortion was quantified by measuring the distance between 93 pairs of phantom features on ADC maps acquired on a 0.35 T MRL and a 3.0 T diagnostic scanner and comparing to spatially precise CT images. Additionally, for five sarcoma patients receiving radiotherapy on the MRL, same-day in vivo ADC maps were acquired on both systems, one of which at multiple timepoints. Results: Phantom ADC quantification was accurate on the 0.35 T MRL with significant discrepancies only seen at high ADC. Average geometric distortions were 0.35 (±0.02) mm and 0.85 (±0.02) mm in the central slice and 0.66 (±0.04) mm and 2.14 (±0.07) mm at 5.4 cm off-center for the MRL and diagnostic system, respectively. In the sarcoma patients, a mean pretreatment ADC of 910x10-6 (±100x10-6) mm2/s was measured on the MRL. Conclusions: The acquisition of accurate, repeatable, and geometrically precise ADC maps is possible at 0.35 T with an EPI approach.

Designing Improved Safer Gambling Messages for Race and Sports Betting: What can be Learned from Other Gambling Formats and the Broader Public Health Literature?

Safer gambling messages are one potential input to a public health approach toward reducing gambling-related harm, and yet there is no strong evidence supporting current messages such as "gamble responsibly" or "keep the fun in the game". Furthermore, sports betting is increasing in popularity in multiple jurisdictions, such as Australia and the US, increasing the need to design effective messaging campaigns for race and sports betting. Compared to other gambling formats, such as electronic gambling machines, the level of potential skill involved in race and sports betting may raise unique issues regarding the design of effective messages. This review first highlights research from the related public health domains of alcohol and tobacco. Then, five potential areas for further messaging-based research in race and sports betting are discussed: teaching safer gambling practices, correcting gambling misperceptions, boosting conscious decision making, norm-based messages, and emotional messages. A broad approach to message design is encouraged, given the potential for individual differences in message receptivity, and for frequently-repeated messages to be ignored or cause negative psychological reactance.

Legacy gambling harms: What are they and how long do they last?

Background and aims: Legacy gambling harms are negative consequences of gambling that extend past periods of low risk, moderate risk and problem gambling. Gambling harm is typically measured within a 12-month timeframe and is often restricted to examining harm amongst active gamblers. The present research aimed to explore whether people experienced gambling harms 12 months or more after the resolution of at-risk or problem gambling, and how long these legacy harms lasted. Methods: An online survey was conducted in New Zealand with past and current gamblers and concerned significant others (CSOs) of gamblers, N = 1,240 (50.8% female), that asked them about both past and current gambling harms. Results: A majority of both gamblers and CSOs of gamblers indicated that they still suffered from gambling harm even after most of their behavioural issues with gambling had been resolved, 12+ months ago. Legacy gambling harms reduced over time, with harms diminishing most quickly in the early years, and having an average half-life of 4 years. Harms involving community-relationships, church involvement, and domestic and other violence resolved more quickly than others. Discussion and conclusions: Legacy harms are common among ex-problem gamblers and should be considered in any full accounting of the impacts of gambling. Conclusion: Understanding the time course and persistence of legacy harms from gambling can provide gamblers, treatment professionals and public health experts with insights into how to address gambling's long-term consequences.

Free-breathing radial magnetic resonance elastography of the liver in children at 3 T: a pilot study.

BACKGROUND: Magnetic resonance (MR) elastography of the liver measures hepatic stiffness, which correlates with the histopathological staging of liver fibrosis. Conventional Cartesian gradient-echo (GRE) MR elastography requires breath-holding, which is challenging for children. Non-Cartesian radial free-breathing MR elastography is a potential solution to this problem. OBJECTIVE: To investigate radial free-breathing MR elastography for measuring hepatic stiffness in children. MATERIALS AND METHODS: In this prospective pilot study, 14 healthy children and 9 children with liver disease were scanned at 3 T using 2-D Cartesian GRE breath-hold MR elastography (22 s/slice) and 2-D radial GRE free-breathing MR elastography (163 s/slice). Each sequence was acquired twice. Agreement in the stiffness measurements was evaluated using Lin's concordance correlation coefficient (CCC) and within-subject mean difference. The repeatability was assessed using the within-subject coefficient of variation and intraclass correlation coefficient (ICC). RESULTS: Fourteen healthy children and seven children with liver disease completed the study. Median (±interquartile range) normalized measurable liver areas were 62.6% (±26.4%) and 44.1% (±39.6%) for scan 1, and 60.3% (±21.8%) and 43.9% (±44.2%) for scan 2, for Cartesian and radial techniques, respectively. Hepatic stiffness from the Cartesian and radial techniques had close agreement with CCC of 0.89 and 0.94, and mean difference of 0.03 kPa and -0.01 kPa, for scans 1 and 2. Cartesian and radial techniques achieved similar repeatability with within-subject coefficient of variation=1.9% and 3.4%, and ICC=0.93 and 0.92, respectively. CONCLUSION: In this pilot study, radial free-breathing MR elastography was repeatable and in agreement with Cartesian breath-hold MR elastography in children.

Accelerated k-space shift calibration for free-breathing stack-of-radial MRI quantification of liver fat and R2∗.

PURPOSE: To develop an accelerated k-space shift calibration method for free-breathing 3D stack-of-radial MRI quantification of liver proton-density fat fraction (PDFF) and R2∗ . METHODS: Accelerated k-space shift calibration was developed to partially skip acquisition of k-space shift data in the through-plane direction then interpolate in processing, as well as to reduce the in-plane averages. A multi-echo stack-of-radial sequence with the baseline calibration was evaluated on a phantom versus vendor-provided reference-standard PDFF and R2∗ values at 1.5T, and in 13 healthy subjects and 5 clinical subjects at 3T with respect to reference-standard breath-hold Cartesian acquisitions. PDFF and R2∗ maps were calculated with different calibration acceleration factors offline and compared to reference-standard values using Bland-Altman analysis. Bias and uncertainty were evaluated using normal distribution and Bayesian probability of difference (P < .05 considered significant). RESULTS: Bland-Altman plots of phantom and in vivo data showed that substantial acceleration was highly feasible in both through-plane and in-plane directions. Compared to the baseline calibration without acceleration, Bayesian analysis revealed no significant differences on biases and uncertainties of PDFF and R2∗ measurements with all acceleration methods in this study, except the method with through-plane acceleration equaling slices and averages equaling 20 for PDFF and R2∗ (both P < .001) for the phantom. A six-fold reduction in equivalent calibration acquisition time (time saving ≥25 s and ≥80.7%) was achieved using recommended acceleration factors for the in vivo protocols in this study. CONCLUSION: This proposed method may allow accelerated calibration for free-breathing stack-of-radial MRI PDFF and R2∗ mapping.

Free-breathing 3D stack-of-radial MRI quantification of liver fat and R2* in adults with fatty liver disease.

PURPOSE: To investigate the agreement, intra-session repeatability, and inter-reader agreement of liver proton-density fat fraction (PDFF) and R2* quantification using free-breathing 3D stack-of-radial MRI, with and without self-gated motion compensation, compared to reference breath-hold techniques in subjects with fatty liver disease (FLD). METHODS: In this institutional review board-approved prospective study, thirty-eight adults with FLD and/or iron overload (24 male, 58 ± 12 years) were imaged at 3T using free-breathing stack-of-radial MRI, breath-hold 3D Cartesian MRI, and breath-hold single-voxel MR spectroscopy (SVS). Each sequence was acquired twice in random order. To assess agreement compared to reference breath-hold techniques, the dependency of liver PDFF and/or R2* quantification on the sequence, radial sampling factor, and radial self-gating temporal resolution was assessed by calculating the Bayesian mean difference (MDB) of the posteriors. Intra-session repeatability and inter-reader agreement (two independent readers) were assessed by the coefficient of repeatability (CR) and intraclass correlation coefficient (ICC), respectively. RESULTS: Thirty-five participants (21 male, 57 ± 12 years) were included for analysis. Both free-breathing radial MRI techniques (with and without self-gating) achieved ICC ≥ 0.92 for quantifying PDFF and R2*, and quantified PDFF with MDB < 1.2% compared to breath-hold techniques. Free-breathing radial MRI required self-gating to accurately quantify R2* (MDB < 10s-1 with self-gating; MDB < 50s-1 without self-gating). The radial sampling factor affected PDFF and R2* quantification while the radial self-gating temporal resolution only affected R2* quantification. Repeated self-gated free-breathing radial MRI scans achieved CR < 3% and CR < 27 s-1 for PDFF and R2*, respectively. CONCLUSION: A free-breathing stack-of-radial MRI technique with self-gating demonstrated agreement, repeatability, and inter-reader agreement compared to reference breath-hold techniques for quantification of liver PDFF and R2* in adults with FLD.

Deep Learning-Based Parameter Mapping with Uncertainty Estimation for Fat Quantification using Accelerated Free-Breathing Radial MRI.

Deep learning has been applied to remove artifacts from undersampled MRI and to replace time-consuming signal fitting in quantitative MRI, but these have usually been treated as separate tasks, which does not fully exploit the shared information. This work proposes a new two-stage framework that completes these two tasks in a concerted approach and also estimates the pixel-wise uncertainty levels. Results from accelerated free-breathing radial MRI for liver fat quantification demonstrate that the proposed framework can achieve high image quality from undersampled radial data, high accuracy for liver fat quantification, and detect uncertainty caused by noisy input data. The proposed framework achieved 3-fold acceleration to <1 min scan time and reduced the computational time for signal fitting to <100 ms/slice in free-breathing liver fat quantification.

Free-Breathing Volumetric Liver R2* and Proton Density Fat Fraction Quantification in Pediatric Patients Using Stack-of-Radial MRI With Self-Gating Motion Compensation.

BACKGROUND: Stack-of-radial multiecho gradient-echo MRI is promising for free-breathing liver R2* quantification and may benefit children. PURPOSE: To validate stack-of-radial MRI with self-gating motion compensation in phantoms, and to evaluate it in children. STUDY TYPE: Prospective. PHANTOMS: Four vials with different R2* driven by a motion stage. SUBJECTS: Sixteen pediatric patients with suspected nonalcoholic fatty liver disease or steatohepatitis (five females, 13 ± 4 years, body mass index 29.2 ± 8.6 kg/m2 ). FIELD STRENGTH/SEQUENCES: Stack-of-radial, and 2D and 3D Cartesian multiecho gradient-echo sequences at 3T. ASSESSMENT: Ungated and gated stack-of-radial proton density fat fraction (PDFF) and R2* maps were reconstructed without and with self-gating motion compensation. Stack-of-radial R2* measurements of phantoms without and with motion were validated against reference 2D Cartesian results of phantoms without motion. In subjects, free-breathing stack-of-radial and reference breath-hold 3D Cartesian were acquired. Subject inclusion for statistical analysis and region of interest placement were determined independently by two observers. STATISTICAL TESTS: Phantom results were fitted with a weighted linear model. Demographic differences between excluded and included subjects were tested by multivariate analysis of variance. PDFF and R2* measurements were compared using Bland-Altman analysis. Interobserver agreement was assessed by the intraclass correlation coefficient (ICC). RESULTS: Ungated stack-of-radial R2* inside moving phantom vials showed a significant positive bias of 64.3 s-1 (P < 0.00001), unlike gated results (P > 0.31). Subject inclusion decisions for statistical analysis from two observers were consistent. No significant differences were found between four excluded and 12 included subjects (P = 0.14). Compared to breath-hold Cartesian, ungated and gated free-breathing stack-of-radial exhibited mean R2* differences of 18.5 s-1 and 3.6 s-1 . Mean PDFF differences were 1.1% and 1.0% for ungated and gated measurements, respectively. Interobserver agreement was excellent (ICC for PDFF = 0.99, ICC for R2* = 0.90; P < 0.0003). DATA CONCLUSION: Stack-of-radial MRI with self-gating motion compensation seems to allow free-breathing liver R2* and PDFF quantification in children. LEVEL OF EVIDENCE: 2 TECHNICAL EFFICACY STAGE: 2.

Training gamblers to re-think their gambling choices: How contextual analytical thinking may be useful in promoting safer gambling.

BACKGROUND AND AIMS: Harmful gambling has been associated with the endorsement of fallacious cognitions that promote excessive consumption. These types of beliefs stem from intuitively derived assumptions about gambling that are fostered by fast-thinking and a lack of objective, critical thought. The current paper details an experiment designed to test whether a four-week online intervention to strengthen contextual analytical thinking in gamblers is effective in changing gamblers cognitions and encouraging safer gambling consumption. METHODS: Ninety-four regular gamblers who reported experiencing gambling-related harm were randomly allocated to either an experimental (n = 46) or control condition (n = 48), including 45 males, ranging from 19 to 65 years of age (M = 36.61; SD = 9.76). Following baseline measurement of gambling beliefs and prior week gambling consumption, participants in the experimental condition were required to complete an adaption of the Gamblers Fallacy Questionnaire designed to promote analytical thinking by educating participants on common judgement errors specific to gambling once a week for four weeks. Post-intervention measures of beliefs and gambling consumption were captured in week five. RESULTS: The experimental condition reported significantly fewer erroneous cognitions, greater endorsement of protective cognitions, and reduced time spent gambling post-intervention compared to baseline. The control group also reported a reduction in cognitions relating to predicting and controlling gambling outcomes. CONCLUSION: Cognitive interventions that encourage gamblers to challenge gambling beliefs by reflecting on gambling involvement and promoting critical thinking may be an effective tool for reducing the time people invest in gambling activities.

Characterization of Uterine Motion in Early Gestation Using MRI-Based Motion Tracking.

Magnetic resonance imaging (MRI) is a promising non-invasive imaging technique that can be safely used to study placental development and function. However, studies of the human placenta performed by MRI are limited by uterine motion and motion in the uterus during MRI remains one of the major limiting factors. Here, we aimed to investigate the characterization of uterine activity during MRI in the second trimester of pregnancy using MRI-based motion tracking. In total, 46 pregnant women were scanned twice (first scan between 14 and 18 weeks and second scan between 19 and 24 weeks), and 20 pregnant subjects underwent a single MRI between 14 and 18 weeks GA, resulting in 112 MRI scans. An MRI-based algorithm was used to track uterine motion in the superior-inferior and left-right directions. Uterine contraction and maternal motion cases were separated by the experts, and unpaired Wilcoxon tests were performed within the groups of gestational age (GA), fetal sex, and placental location in terms of the overall intensity measures of the uterine activity. In total, 22.3% of cases had uterine contraction during MRI, which increased from 18.6% at 14-18 weeks to 26.4% at 19-24 weeks GA. The dominant direction of the uterine contraction and maternal motion was the superior to the inferior direction during early gestation.

Beliefs About Gambling Mediate the Effect of Cognitive Style on Gambling Problems.

Problem gambling is often accompanied by a range of irrational cognitions that promote excessive gambling. The cognitive basis for these beliefs has been largely overlooked in the gambling literature. Dual process theory suggests there are two parallel cognitive processing systems, an intuitive and an analytic system, and that there are potential individual differences in preference for one or the other cognitive style. The current study explored whether people's cognitive styles are an important factor in the development of specific beliefs about gambling that in-turn contribute to gambling problems. The sample consisted of 1168 regular gamblers (539 female, ranging from 18 to 78 years of age; M = 35.47, SD = 10.78) recruited via Mechanical Turk. Participants completed a survey assessing cognitive style, problem gambling severity, and measures of protective and erroneous beliefs. In a path model, greater analytical thinking and lower intuitive thinking was associated with fewer erroneous gambling beliefs, which in turn were related to fewer gambling problems. A second model showed that protective beliefs also mediated the relationship between cognitive style and gambling, demonstrating that greater analytical thinking and lower intuitive thinking was associated with protective beliefs that similarly reduced problem gambling severity. Results suggest that a person's cognitive style influences peoples gambling by contributing to the endorsement of irrational or unsafe beliefs about gambling. Encouraging people to think more analytically may be useful in reducing erroneous beliefs about gambling that promote problematic gambling behaviour.

Gamble with Your Head and Not Your Heart: A Conceptual Model for How Thinking-Style Promotes Irrational Gambling Beliefs.

Dual process theory suggests that people use two processing systems to filter information and form judgments that direct a course of action: an intuitive and an analytic system. While the intuitive system is necessary for efficient and effective daily functioning, reliance on fast, intuitive thinking when gambling is likely to result in biased or flawed decision-making. Those who gamble tend to endorse an array of fallacious or irrational beliefs that contribute to risky decision-making and excessive gambling. This paper argues that gambling beliefs may be developed and reinforced through underlying cognitive mechanisms described by dual process theory. More specifically, gamblers tend to apply assumptions and theories developed based on their understanding of the natural world to artificial gambling contexts where such rules do not apply. As a result, gamblers develop biased interpretations and understandings for how gambling works, which tend to align with personal schemas, experiences and gambling motivations. These beliefs are used in future gambling contexts to inform decision-making. Gamblers are often unlikely or unwilling to reflect on the veracity of beliefs as they are often used to justify gambling behaviours. Educating gamblers on how they make decisions and encouraging them to think more analytically may help to reduce the strength with which erroneous beliefs about gambling are endorsed, resulting in safer gambling decisions.

Mobile EGM Games: Evidence That Simulated Games Encourage Real-Money Gambling.

Electronic gaming machines (EGMs) and other gambling-themed simulators are a popular sub-genre of video-games or "apps" played on mobile devices (King et al. in Comput Hum Behav 31(Supplement C):305-313, 2014). Qualitative evidence suggests that some people use gambling-themed simulators in an attempt to limit their real-money expenditure (Thorne et al. in J Gambl Issues 34:221-243, 2016), although playing such games might also encourage gambling due to anticipated enjoyment or profit. To test the potential relationship between use of simulated mobile gambling products and real-money gambling, a study was devised to explore current and retrospective accounts, as well as a prospective trial of how weekly play on EGM simulators might influence subsequent gambling. A total of 736 EGM gamblers (421 male) completed an initial scoping survey on their current and retrospective use of simulated and real-money gambling products. By invitation, 556 people (314 male) from the initial survey also volunteered in a 24 weeks follow-up study where approximately half (48.2%) were randomly assigned to play a simulated game, "Lucky Lolly Slots", for at least 5 min each week. Simulated gambling sessions were recorded for both Lucky Lolly Slots and any other gambling apps played by the participants. Results showed that people who had played gambling-themed EGM apps at some point in their lifetime had a higher frequency of play on real-money EGMs and were more likely to admit to current gambling problems. In addition, those people who played a simulated EGM app prior to age 13 nominated an earlier age at which they "gambled the most" in adolescence. In the 24 weeks trial, people's app play (number of sessions) in 1 week reliably predicted increases in real-money gambling the following week. We found no evidence that people who were trying to reduce their expenditure were contrarily influenced to gamble less as a result of their app play, with their app-sessions similarly being related to increases in expenditure. The present results suggest that gamblers who play simulated games are likely to be influenced to gamble more on real-money forms of gambling as a result of their use. The study raises particular concerns about the widespread availability and popularity of such gambling-themed simulators amongst children and adolescents.

Encouraging Gamblers to Think Critically Using Generalised Analytical Priming is Ineffective at Reducing Gambling Biases.

Gambling has been associated with an array of fallacious beliefs that foster risky gambling decisions. Research into other belief systems suggests that the endorsement of non-evidence based beliefs, such as the paranormal or conspiracy theories, can be reduced when people think more analytically. The purpose of this study was to explore whether an intervention designed to elicit analytical thinking was effective in altering the gambling beliefs and simulated gambling behaviour of 178 regular electronic gaming machine (EGM) gamblers (102 males, 76 female). Participants were randomly allocated to complete either an analytic or a neutral priming task, followed by completion of belief measures (erroneous and protective) and play on a simulated EGM game. Results failed to show that priming for analytical thinking changed betting on an EGM; including features of bet size, bet change, persistence and theoretical losses. Contrary to expectations, results suggest that priming analytical thinking using generalised interventions does not appear to be effective in altering peoples' simulated gambling involvement or gambling beliefs. In fact, priming people to think more critically might be counterproductive by contributing to greater positive expectations about gambling outcomes. The results further suggested that the number of times a player alters their bet is a good indicator of theoretical gambling losses and is associated with irrational gambling cognitions. Interventions designed to promote safer thinking in gamblers should be implemented with care, as results from our study suggest that encouraging critical thinking in at-risk or problem gamblers may not be effective in reducing risky gambling.

Effect of respiratory motion on free-breathing 3D stack-of-radial liver R2∗ relaxometry and improved quantification accuracy using self-gating.

PURPOSE: To develop an accurate free-breathing 3D liver R2∗ mapping approach and to evaluate it in vivo. METHODS: A free-breathing multi-echo stack-of-radial sequence was applied in 5 normal subjects and 6 patients at 3 Tesla. Respiratory motion compensation was implemented using the inherent self-gating signal. A breath-hold Cartesian acquisition was the reference standard. Proton density fat fraction and R2∗ were measured and compared between radial and Cartesian methods using Bland-Altman plots. The normal subject results were fitted to a linear mixed model (P < .05 considered significant). RESULTS: Free-breathing stack-of-radial without self-gating exhibited signal attenuation in echo images and artifactually elevated apparent R2∗ values. In the Bland-Altman plots of normal subjects, compared to breath-hold Cartesian, free-breathing stack-of-radial acquisitions of 22, 30, 36, and 44 slices, had mean R2∗ differences of 27.4, 19.4, 10.9, and 14.7 s-1 with 800 radial views, and they had 18.4, 11.9, 9.7, and 27.7 s-1 with 404 views, which were reduced to 0.4, 0.9, -0.2, and -0.7 s-1 and to -1.7, -1.9, -2.1, and 0.5 s-1 with self-gating, respectively. No substantial proton density fat fraction differences were found. The linear mixed model showed free-breathing radial R2∗ results without self-gating were significantly biased by 17.2 s-1 averagely (P = .002), which was eliminated with self-gating (P = .930). Proton density fat fraction results were not different (P > .234). For patients, Bland-Altman plots exhibited mean R2∗ differences of 14.4 and 0.1 s-1 for free-breathing stack-of-radial without self-gating and with self-gating, respectively, but no substantial proton density fat fraction differences. CONCLUSION: The proposed self-gating method corrects the respiratory motion bias and enables accurate free-breathing stack-of-radial quantification of liver R2∗ .

A variable flip angle golden-angle-ordered 3D stack-of-radial MRI technique for simultaneous proton resonant frequency shift and T1 -based thermometry.

PURPOSE: To develop and evaluate a variable-flip-angle golden-angle-ordered 3D stack-of-radial MRI technique for simultaneous proton resonance frequency shift (PRF) and T1 -based thermometry in aqueous and adipose tissues, respectively. METHODS: The proposed technique acquires multiecho radial k-space data in segments with alternating flip angles to measure 3D temperature maps dynamically on the basis of PRF and T1 . A sliding-window k-space weighted image contrast filter is used to increase temporal resolution. PRF is measured in aqueous tissues and T1 in adipose tissues using fat/water masks. The accuracy for T1 quantification was evaluated in a reference T1 /T2 phantom. In vivo nonheating experiments were conducted in healthy subjects to evaluate the stability of PRF and T1 in the brain, prostate, and breast. The proposed technique was used to monitor high-intensity focused ultrasound (HIFU) ablation in ex vivo porcine fat/muscle tissues and compared to temperature probe readings. RESULTS: The proposed technique achieved 3D coverage with 1.1-mm to 1.3-mm in-plane resolution and 2-s to 5-s temporal resolution. During 20 to 30 min of nonheating in vivo scans, the temporal coefficient of variation for T1 was <5% in the brain, prostate, and breast fatty tissues, while the standard deviation of relative PRF temperature change was within 3°C in aqueous tissues. During ex vivo HIFU ablation, the temperatures measured by PRF and T1 were consistent with temperature probe readings, with an absolute mean difference within 2°C. CONCLUSION: The proposed technique achieves simultaneous PRF and T1 -based dynamic 3D MR temperature mapping in aqueous and adipose tissues. It may be used to improve MRI-guided thermal procedures.

Free-breathing 3-D quantification of infant body composition and hepatic fat using a stack-of-radial magnetic resonance imaging technique.

BACKGROUND: Body composition and hepatic fat correlate with future risk for metabolic syndrome. In children, many conventional techniques for quantifying body composition and hepatic fat have limitations. MRI is a noninvasive research tool to study body composition and hepatic fat in infants; however, conventional Cartesian MRI is sensitive to motion, particularly in the abdomen because of respiration. Therefore we developed a free-breathing MRI technique to quantify body composition and hepatic fat in infants. OBJECTIVE: In infants, we aimed to (1) compare the image quality between free-breathing 3-D stack-of-radial MRI (free-breathing radial) and 3-D Cartesian MRI in the liver and (2) determine the feasibility of using free-breathing radial MRI to quantify body composition and hepatic proton-density fat fraction (PDFF). MATERIALS AND METHODS: Ten infants ages 2-7 months were scanned with free-breathing radial (two abdominal; one head and chest) and Cartesian (one abdominal) MRI sequences. The median preparation and scan times were reported. To assess feasibility for hepatic PDFF quantification, a radiologist masked to the MRI technique scored abdominal scans for motion artifacts in the liver using a 3-point scale (1, or non-diagnostic, to 3, or no artifacts). Median visceral adipose tissue (VAT), subcutaneous adipose tissue (SAT) and brown adipose tissue (BAT) volume and PDFF, and hepatic PDFF were measured using free-breathing radial MRI. We assessed repeatability of free-breathing radial hepatic PDFF (coefficient of repeatability) between back-to-back scans. We determined differences in the distribution of image-quality scores using McNemar-Bowker tests. P<0.05 was considered significant. RESULTS: Nine infants completed the entire study (90% completion). For ten infants, the median preparation time was 32 min and scan time was 24 min. Free-breathing radial MRI demonstrated significantly higher image-quality scores compared to Cartesian MRI in the liver (radial scan 1 median = 2 and radial scan 2 median = 3 vs. Cartesian median = 1; P=0.01). Median measurements using free-breathing radial were VAT=52.0 cm3, VAT-PDFF=42.2%, SAT=267.7 cm3, SAT-PDFF=87.1%, BAT=1.4 cm3, BAT-PDFF=26.1% and hepatic PDFF=3.4% (coefficient of repeatability <2.0%). CONCLUSION: In this study, free-breathing radial MRI in infants achieved significantly improved liver image quality compared to Cartesian MRI. It is feasible to use free-breathing radial MRI to quantify body composition and hepatic fat in infants.

Free-breathing Magnetic Resonance Imaging Assessment of Body Composition in Healthy and Overweight Children: An Observational Study.

OBJECTIVE: Conventional, breath-holding magnetic resonance imaging (MRI) assesses body composition by measuring fat volumes and proton density fat fraction (PDFF). However, breath-holding MRI is not always feasible in children. This study's objective was to use free-breathing MRI to quantify visceral and subcutaneous fat volumes and PDFFs and correlate these measurements with hepatic PDFF. METHODS: This was an observational, hypothesis-forming study that enrolled 2 groups of children (ages 6-17 years), healthy children and overweight children with presumed nonalcoholic fatty liver disease. Free-breathing MRI was used to measure visceral and subcutaneous fat volumes and PDFFs, and hepatic PDFF. Imaging biomarkers were compared between groups, and correlations coefficients (r) and coefficients of determination (R) were calculated. RESULTS: When compared with the control group (n = 10), the overweight group (n = 9) had greater mean visceral (1843 vs 329 cm, P < 0.001) and subcutaneous fat volumes (7663 vs 893 cm, P < 0.001), as well as greater visceral (80% vs 45%, p < 0.001) and subcutaneous fat PDFFs (89% vs 75%, P = 0.003). Visceral fat volume (r = 0.79, P < 0.001) and PDFF (r = 0.92, P < 0.001) correlated with hepatic PDFF. In overweight subjects, for each unit increase in visceral fat PDFF, hepatic PDFF increased by 2.64%; visceral fat PDFF explained 54% of hepatic PDFF variation (R = 0.54, P = 0.02). CONCLUSIONS: In this study, we used free-breathing MRI to measure body composition in children. Future studies are needed to investigate the possible value of subcutaneous and visceral fat PDFFs, and validate free-breathing MRI body composition biomarkers.