Lowered social motivation is associated with adolescent attention deficit hyperactivity disorder and social anxiety symptoms.

BACKGROUND: Difficulties in social skills are highly prevalent in children and adolescents with attention deficit hyperactivity disorder (ADHD), however, the reasons for these social difficulties are poorly understood. This study aimed to understand social motivation in children (aged 5-8) and adolescents (aged 13-17) with and without ADHD, and the relationship between social anxiety and social motivation in youth with ADHD. METHOD: 204 parents of children and adolescents with and without ADHD completed online questionnaires on social motivation, social anxiety, and ADHD symptoms. RESULTS: Adolescents with ADHD had significantly lower social motivation than typically developing adolescents, and children with ADHD. Higher social anxiety significantly predicted lowered social motivation in participants with ADHD. CONCLUSIONS: These findings indicate a unique pattern of social motivation in ADHD, specifically a reduction during adolescence, reflecting social intervention inefficacy. Additionally, these findings establish a link between social motivation and social anxiety, suggesting that they may act as barriers to social intervention.

Prolonged Infant Crying: Caregiving Quality and Child Physical Abuse Risk.

Research suggests that prolonged infant crying may increase risk for child physical abuse (CPA). However, few studies have examined behavioral responses to infant crying among parents at risk for CPA. The present study sought to fill this gap by using a simulated infant to examine how mothers and fathers with varying degrees of CPA risk respond to prolonged infant crying. Specifically, a sample of 184 general population caregivers (107 mothers and 77 fathers) participated in a task that involved attempting to soothe a simulated infant that cried continuously for 30 min. The simulated infant sessions were video-recorded, and quality of caregiving behavior was coded in 5-min segments. Participants rated their negative affect (feelings of upset, distress, irritability) at the outset of the data collection session, before beginning the simulated infant task, and after the simulated infant task concluded. It was predicted that high-risk caregivers, compared to low-risk caregivers, would display lower quality caregiving, higher levels of negative affect, and that CPA risk group differences would increase over time. Gender differences were explored in relation to the aforementioned hypotheses. Over the course of the 30-min simulated infant task, the quality of caregiving behavior diminished among both high- and low-risk caregivers. As expected, high-risk caregivers, compared to low-risk caregivers, exhibited lower quality caregiving behaviors and were more likely to discontinue the simulated infant task early. In addition, high-risk, compared to low-risk, caregivers reported higher levels of negative affect throughout the data collection session, with the highest level of negative affect reported by high-risk caregivers after completing the simulated infant task. Overall, the quality of caregiving exhibited by men and women did not significantly differ. The present findings highlight the importance of early intervention designed to support caregivers' abilities to respond effectively to prolonged infant crying.

Impairments in Emotion Recognition and Positive Emotion Regulation Predict Social Difficulties in Adolescent With ADHD.

BACKGROUND: Emotional dysregulation, poor emotion recognition and impaired response inhibition have been highlighted as potential contributors to social difficulties in adolescents with attention-deficit/hyperactivity disorder (ADHD). It is currently unknown how these areas of impairment relate to one another; therefore, this study aims to identify the areas of emotion regulation which are associated with social difficulties in adolescents with ADHD, and determine whether emotion regulation mediates the relationship between deficits in response inhibition and emotion recognition, and social functioning, in this cohort. METHODS: Thirty Australian adolescents (Male = 21) with ADHD completed measures of response inhibition, emotion recognition, and emotion regulation. RESULTS: Positive emotion regulation was significantly associated with social difficulties. Although emotion recognition significantly predicted social difficulties, there was no relationship between emotion recognition and emotion regulation in this sample, ruling out emotion regulation as a mediator of emotion recognition and social difficulties. Whilst response inhibition was significantly correlated with positive emotion regulation, positive emotion regulation did not mediate the relationship between response inhibition and social difficulties. CONCLUSIONS: Difficulties recognising and regulating emotions appear to independently contribute to social difficulties in adolescents with ADHD. Interventions to increase emotional understanding and developing strategies to down-regulate positive emotions may be beneficial.

Social difficulties in adolescent attention deficit hyperactivity disorder: Social motivation, social anxiety and symptom severity as contributing factors.

BACKGROUND: Many interventions have been developed to address the social difficulties commonly experienced by adolescents with attention-deficit/hyperactivity disorder (ADHD), yet they are largely ineffective. OBJECTIVE: This study examined social impairment among adolescents with and without ADHD, determining whether gender, social anxiety, age, and ADHD symptom type (inattention and hyperactivity/impulsivity) and severity are associated with social impairment. METHOD: Parents and primary caregivers of adolescents (aged 13-17) with (n = 76) and without ADHD (n = 36) completed the Strengths and Weaknesses of ADHD and Normal Behavior, Social Responsiveness Scale 2nd Edition, and Spence Children's Anxiety Scale. RESULTS: Adolescents with ADHD scored significantly higher than TD adolescents across social impairment domains. ADHD symptoms were associated with severity of impairment in all domains excluding Social Motivation. Hyperactivity/impulsivity and social anxiety predicted social impairment, whereas gender did not. CONCLUSION: Adolescents with ADHD are more likely to experience social impairment than TD adolescents, and interventions targeting symptom reduction and social anxiety may improve these social impairments.

Training inhibitory control in adolescents with elevated attention deficit hyperactivity disorder traits: a randomised controlled trial of the Alfi Virtual Reality programme.

INTRODUCTION: Attention deficit hyperactivity disorder (ADHD) is characterised by significant deficits in attention and inhibition. These deficits are associated with negative sequelae that emerge in childhood and often continue throughout adolescence. Despite these difficulties adolescents with ADHD often demonstrate poor treatment compliance with traditional interventions (eg, psychostimulant medication). Virtual reality (VR) presents an innovative means of delivering engaging cognitive interventions for adolescents with ADHD and offers the potential to improve compliance with such interventions. The current parallel, randomised controlled trial aims to evaluate the effects of a VR intervention (Alfi) designed to improve inhibition in adolescents with ADHD. METHODS AND ANALYSIS: A sample of 100 adolescents (aged 13-17) with elevated ADHD symptoms will be recruited from secondary schools and ADHD organisations located in the state of Victoria, Australia. Participants will be randomly assigned to either an 8-week VR intervention or a usual care control. The VR intervention involves the completion of 14 sessions, each 20 min in duration. Participants will complete computerised assessments of inhibition and risk-taking preintervention and immediately postintervention. Parents/guardians will complete online questionnaires about their child's ADHD symptoms and social functioning at each of these timepoints. The primary outcome is change in inhibition performance in adolescents who received the intervention from preintervention to postintervention compared with adolescents in the control condition. Secondary outcomes include change in risk-taking, ADHD symptoms and social functioning in adolescents who received the intervention from preintervention to postintervention compared with adolescents in the control condition. If the intervention is shown to be effective, it may offer a supplementary approach to traditional interventions for adolescents with ADHD experiencing inhibitory control difficulties. ETHICS AND DISSEMINATION: This trial has ethics approval from the Monash University Human Research Ethics Committee (HREC) (21530) and the Victorian Department of Education and Training HREC (2020_004271). Results will be disseminated through peer-reviewed journals, conference proceedings and community activities. Individual summaries of the results will be provided to participants on request. TRIAL REGISTRATION NUMBER: ACTRN12620000647932.

Accurate measurement of coronary artery calcium in cancer patients using the CT component of PET/CT scans.

OBJECTIVE: The aim of this study is to establish the correlation between a CAC score derived from the CT component of PET/CT scan (CAC-PET) using in-house software as compared to the conventional technique (CAC-Standard). In addition, the incidence of high CAC scores in asymptomatic cancer patients with low-to-intermediate cardiovascular risk will be determined. METHODS: 100 patients referred for oncologic PET/CT were prospectively recruited to have a conventional CAC score after their PET/CT. Patients with a history of cardiac disease were excluded. The nongated CT images from the PET/CT (CAC-PET) were analysed using validated in-house software with the results compared to those from gated CT analysed using the standard technique (CAC-Standard). RESULTS: The correlation of CAC scores between the two scan types was moderate [slope, 0.95; R2 = 0.91; limits of agreement (LOA) = 0.29-5.65]. Using a conventional categorical analysis, there was complete agreement in 73% of patients with one category difference in the remainder. [interclass correlation (ICC) = 0.90; Cohen's kappa = 0.63]. In total 28% of these asymptomatic low-to-intermediate-risk cancer patients had CAC scores over 300. CONCLUSION: Estimation of CAC from the CT component of PET/CT scans is a reliable method for the detection of significant CAC in cancer patients and correlates well with the standard method. This technique should permit the calculation of cardiovascular risk in cancer patients undergoing PET/CT without any additional radiation exposure. A significant number of asymptomatic low-to-intermediate-risk cancer patients were found to have a high risk of cardiovascular disease.

Oxytocin Receptor Signaling in Vascular Function and Stroke.

The oxytocin receptor (OXTR) is a G protein-coupled receptor with a diverse repertoire of intracellular signaling pathways, which are activated in response to binding oxytocin (OXT) and a similar nonapeptide, vasopressin. This review summarizes the cell and molecular biology of the OXTR and its downstream signaling cascades, particularly focusing on the vasoactive functions of OXTR signaling in humans and animal models, as well as the clinical applications of OXTR targeting cerebrovascular accidents.

OpenDose: Open-Access Resource for Nuclear Medicine Dosimetry.

Radiopharmaceutical dosimetry depends on the localization in space and time of radioactive sources and requires the estimation of the amount of energy emitted by the sources deposited within targets. In particular, when computing resources are not accessible, this task can be performed using precomputed tables of specific absorbed fractions (SAFs) or S values based on dosimetric models. The aim of the OpenDose collaboration is to generate and make freely available a range of dosimetric data and tools. Methods: OpenDose brings together resources and expertise from 18 international teams to produce and compare traceable dosimetric data using 6 of the most popular Monte Carlo codes in radiation transport (EGSnrc/EGS++, FLUKA, GATE, Geant4, MCNP/MCNPX, and PENELOPE). SAFs are uploaded, together with their associated statistical uncertainties, in a relational database. S values are then calculated from monoenergetic SAFs on the basis of the radioisotope decay data presented in International Commission on Radiological Protection Publication 107. Results: The OpenDose collaboration produced SAFs for all source region and target combinations of the 2 International Commission on Radiological Protection Publication 110 adult reference models. SAFs computed from the different Monte Carlo codes were in good agreement at all energies, with SDs below individual statistical uncertainties. Calculated S values were in good agreement with OLINDA/EXM 2.0 (commercial) and IDAC-Dose 2.1 (free) software. A dedicated website (www.opendose.org) has been developed to provide easy and open access to all data. Conclusion: The OpenDose website allows the display and downloading of SAFs and the corresponding S values for 1,252 radionuclides. The OpenDose collaboration, open to new research teams, will extend data production to other dosimetric models and implement new free features, such as online dosimetric tools and patient-specific absorbed dose calculation software, together with educational resources.

In vivo deposition study of a new generation nebuliser utilising hybrid resonant acoustic (HYDRA) technology.

Conventional nebulisation has the disadvantages of low aerosol output rate and potential damage to macromolecules due to high shear (jet nebulisation) or cavitation (ultrasonic nebulisation). HYDRA (HYbriD Resonant Acoustics) technology has been shown to overcome these problems by using a hybrid combination of surface and bulk sound waves to generate the aerosol droplets. We report the first in vivo human lung deposition study on such droplets. Twelve healthy adult subjects inhaled saline aerosols radiolabelled with technetium-99 m complexed with diethylene triamine penta-acetic acid (99mTc-DTPA). The distribution of the aerosolised droplets in the lungs was imaged by single photon emission computed tomography combined with low dose computed tomography (SPECT/CT). The volume median diameter and geometric standard deviation of the droplets were 1.32 ± 0.027 µm and 2.06 ± 0.040, respectively. The mean delivery efficiency from the nebuliser into the body was 51.2%. About 89.1 ± 4.3% and 2.3 ± 1.4% of the inhaled radiolabelled dose deposited in the lungs and oropharynx, respectively. The deposition was symmetrical and diffusive between the two lungs, with a mean penetration index of 0.82. Thus, the prototype HYDRA nebuliser showed excellent in vivo aerosol deposition performance, demonstrating its potential to be further developed for clinical applications.

Training attention in children with acquired brain injury: a study protocol of a randomised controlled trial of the TALI attention training programme.

INTRODUCTION: Childhood inattention has been linked with poor academic outcomes, and increased lifetime social, occupational and psychiatric morbidity. Children with an acquired brain injury (ABI) are particularly susceptible to attention deficits and may benefit from interventions aimed at enhancing attention. The primary objective of this study is to evaluate the short-term efficacy of the TALI Train programme, compared with a placebo, on the outcome of attention in children with ABI. METHODS AND ANALYSIS: The study is a parallel, double-blind, randomised controlled trial. Participants will consist of 80 children with a diagnosis of ABI aged 4-9 years 11 months. Participants will be randomly allocated to either (1) TALI Train (intervention group), an adaptive game-based attention training programme, or (2) a non-adaptive placebo programme (control group). Both programmes are delivered on a touchscreen tablet, and children complete five 20 min sessions per week for a 5-week period at home. Assessment of selective, sustained and executive attention (primary outcomes), and behavioural attention, working memory, social skills and mathematics ability (secondary outcomes) will occur at baseline, post-training, and at 3-month and 6-month follow-up to assess immediate and long-term efficacy of TALI Train compared with placebo. Assessments will be completed at the Royal Children's Hospital in Melbourne, Australia. All assessments and analyses will be undertaken by researchers blinded to group membership. Latent growth curve modelling will be employed to examine primary and secondary outcomes. ETHICS AND DISSEMINATION: Ethics approval has been obtained from the Royal Children's Hospital Human Research Ethics Committee (HREC) (38132) and the Monash University HREC (17446). Results will be disseminated through peer-reviewed journals, conference presentations, media outlets, the internet and various community/stakeholder activities. TRIAL REGISTRATION NUMBER: ACTRN12619000511134.

Locus Coeruleus Degeneration Induces Forebrain Vascular Pathology in a Transgenic Rat Model of Alzheimer's Disease.

Noradrenergic locus coeruleus (LC) neuron loss is a significant feature of mild cognitive impairment and Alzheimer's disease (AD). The LC is the primary source of norepinephrine in the forebrain, where it modulates attention and memory in vulnerable cognitive regions such as prefrontal cortex (PFC) and hippocampus. Furthermore, LC-mediated norepinephrine signaling is thought to play a role in blood-brain barrier (BBB) maintenance and neurovascular coupling, suggesting that LC degeneration may impact the high comorbidity of cerebrovascular disease and AD. However, the extent to which LC projection system degeneration influences vascular pathology is not fully understood. To address this question in vivo, we stereotactically lesioned LC projection neurons innervating the PFC of six-month-old Tg344-19 AD rats using the noradrenergic immunotoxin, dopamine-ß-hydroxylase IgG-saporin (DBH-sap), or an untargeted control IgG-saporin (IgG-sap). DBH-sap-lesioned animals performed significantly worse than IgG-sap animals on the Barnes maze task in measures of both spatial and working memory. DBH-sap-lesioned rats also displayed increased amyloid and inflammation pathology compared to IgG-sap controls. However, we also discovered prominent parenchymal albumin extravasation with DBH-sap lesions indicative of BBB breakdown. Moreover, microvessel wall-to-lumen ratios were increased in the PFC of DBH-sap compared to IgG-sap rats, suggesting that LC deafferentation results in vascular remodeling. Finally, we noted an early emergence of amyloid angiopathy in the DBH-sap-lesioned Tg344-19 AD rats. Taken together, these data indicate that LC projection system degeneration is a nexus lesion that compromises both vascular and neuronal function in cognitive brain areas during the prodromal stages of AD.

Peri-Infarct Upregulation of the Oxytocin Receptor in Vascular Dementia.

Vascular dementia (VaD) is cognitive decline linked to reduced cerebral blood perfusion, yet there are few therapeutic options to protect cognitive function following cerebrovascular accidents. The purpose of this study was to profile gene expression changes unique to VaD to identify and characterize disease relevant changes that could offer clues for future therapeutic direction. Microarray-based profiling and validation studies of postmortem frontal cortex samples from VaD, Alzheimer disease, and age-matched control subjects revealed that the oxytocin receptor (OXTR) was strongly and differentially upregulated in VaD. Further characterization in fixed tissue from the same cases showed that OXTR upregulation occurs de novo around and within microinfarcts in peri-infarct reactive astrocytes as well as within vascular profiles, likely on microvascular endothelial cells. These results indicate that increased OXTR expression in peri-infarct regions may be a specific response to microvascular insults. Given the established OXTR signaling cascades that elicit antioxidant, anti-inflammatory, and pro-angiogenic responses, the present findings suggest that de novo OXTR expression in the peri-infarct space is a tissue-protective response by astroglial and vascular cells in the wake of ischemic damage that could be exploited as a therapeutic option for the preservation of cognition following cerebrovascular insults.

Maternal positive responses to a distressed infant simulator predict subsequent negative affect in infants.

Existing evidence indicates that maternal responses to infant distress, specifically more sensitive and less inconsistent/rejecting responses, are associated with lower infant negative affect (NA). However, due to ethical and methodological constraints, most existing studies do not employ methods that guarantee each mother will be observed responding to infant distress. To address such limitations, in the current study, a distressed infant simulator (SIM), programmed to be inconsolable, was employed to ensure that mothers (N = 150; 4 months postpartum) were observed responding to infant distress. Subsequently, maternal report of infant NA and an early aspect of regulatory capacity, sootheability, were collected at eight-months postpartum, and observational assessments of infant fear and frustration, fine-grained aspects of NA, were collected at 12-months of age. After controlling for infant sex, the proportion of time mothers spent using soothing touch during the SIM task was related to less overall maternal reported NA and sadness at eight-months postpartum. Similarly, greater use of touch was associated with less fear reactivity, and greater maternal use of vocalizations was related to lower infant frustration, at 12-months postpartum. Specific maternal soothing behaviors were not related to infant soothability at 8 months postpartum. Total time spent interacting with the SIM was not related to infant temperament, suggesting that type of soothing, not quantity of interactions with distressed infants, is important for reducing infant NA. The implications of these findings and important future directions are discussed.

Parameters of visual processing abnormalities in adults with body image concerns.

Body dysmorphic disorder (BDD), at the extreme end of the body image concern (BIC) spectrum, is thought to be associated with a local (detail-focussed) visual processing bias. Given that the inversion of a stimulus disrupts holistic processing and demands detail-specific attention, this perceptual bias is characterised by superior processing of such inverted stimuli. This study examined the processing bias, via a body-inversion discrimination task, of 26 participants with non-clinical, high-BIC (Dysmophic Concern Questionnaire (DCQ) scores between 11-19) and 26 participants with low-BIC (DCQ scores between 0-4). This study also explored the impact of varying stimuli presentation durations and discrimination difficulties during the inversion task on visual processing. As hypothesised, compared to those with low-BIC, participants with high-BIC demonstrated superior accuracy when discriminating between images of inverted bodies, indicating a local processing bias. Also as hypothesised, this local processing bias selectively manifested only when stimuli were presented for longer durations and at higher discrimination difficulties, revealing the parameters of this, potentially conscious, processing tendency. Consistent with previous research, this study identified a local processing bias in those with high BIC, which may be a predisposing factor for developing BDD. In turn, identifying the parameters (stimulus exposure and stimulus complexity) in which the local bias manifests has implications for future interventions aiming to reverse this perceptual abnormality.

Do emotion regulation difficulties explain the association between executive functions and child physical abuse risk?

This study examined the associations between executive functioning problems, emotion regulation difficulties, and risk for perpetrating child physical abuse (CPA). It was hypothesized that: (a) poor executive functions (i.e., working memory problems and inhibition/switching problems) would be associated with higher levels of emotion regulation difficulties and CPA risk; (b) emotion regulation difficulties would be positively associated with CPA risk; and (c) emotion regulation difficulties would partially explain the association between executive functions (i.e., working memory problems and inhibition/switching problems) and CPA risk. To examine these predictions, a sample of 133 general population parents (31% fathers) completed self-report measures of CPA risk, emotion regulation difficulties, working memory problems, and a performance-based measure of inhibition/switching skills. Results revealed that executive functioning problems were linked with emotion regulation difficulties, which in turn were associated with CPA risk. Moreover, emotion regulation difficulties explained the relationship between executive functions (working memory, inhibition/switching) and CPA risk. The final model accounted for 41% of the variance in CPA risk. Although additional research is needed, the present findings suggest that enhancing parents' executive functioning and teaching them effective emotion regulation skills may be important targets for CPA prevention efforts.

Multi-Infarct Dementia: A Historical Perspective.

BACKGROUND: Multi-infarct dementia (MID), a prominent subtype of vascular dementia (VaD), has only achieved recognition in the last 4 decades. Since its original description, the characterization, etiological understanding, and therapeutic direction of MID and other VaD subtypes has progressed at an astounding rate. SUMMARY: This paper divides the landmark discoveries and emergence of new research strategies for MID into decade-defining patterns so that a condensed picture of the total history of MID and its eventual inclusion as a VaD subtype emerges. This paper follows the first descriptive decade, a shift to a preventative focus, a renewed interest coinciding with timely advances in research technology, and a hopeful return to treatment possibilities for VaD. KEY MESSAGE: Concisely tracing the historical lineage of the modern understanding of MID, both as a singular entity and as part of the VaD con-stellation of disorders, provides a novel perspective on the foundation upon which future advances in combating vascular contributions to dementia will be based.

Sympathetic nervous system contributes to enhanced corticosterone levels following chronic stress.

Exposure to chronic stress often elevates basal circulating glucocorticoids during the circadian nadir and leads to exaggerated glucocorticoid production following exposure to subsequent stressors. While glucocorticoid production is primarily mediated by the hypothalamic-pituitary-adrenal (HPA) axis, there is evidence that the sympathetic nervous system can affect diurnal glucocorticoid production by direct actions at the adrenal gland. Experiments here were designed to examine the role of the HPA and sympathetic nervous system in enhancing corticosterone production following chronic stress. Rats were exposed to a four-day stress paradigm or control conditions then exposed to acute restraint stress on the fifth day to examine corticosterone and ACTH responses. Repeated stressor exposure resulted in a small increase in corticosterone, but not ACTH, during the circadian nadir, and also resulted in exaggerated corticosterone production 5, 10, and 20min following restraint stress. While circulating ACTH levels increased after 5min of restraint, levels were not greater in chronic stress animals compared to controls until following 20min. Administration of astressin (a CRH antagonist) prior to restraint stress significantly reduced ACTH responses but did not prevent the sensitized corticosterone response in chronic stress animals. In contrast, administration of chlorisondamine (a ganglionic blocker) returned basal corticosterone levels in chronic stress animals to normal levels and reduced early corticosterone production following restraint (up to 10min) but did not block the exaggerated corticosterone response in chronic stress animals at 20min. These data indicate that increased sympathetic nervous system tone contributes to elevated basal and rapid glucocorticoid production following chronic stress, but HPA responses likely mediate peak corticosterone responses to stressors of longer duration.

TestDose: A nuclear medicine software based on Monte Carlo modeling for generating gamma camera acquisitions and dosimetry.

PURPOSE: The TestDose platform was developed to generate scintigraphic imaging protocols and associated dosimetry by Monte Carlo modeling. TestDose is part of a broader project (www.dositest.com) whose aim is to identify the biases induced by different clinical dosimetry protocols. METHODS: The TestDose software allows handling the whole pipeline from virtual patient generation to resulting planar and SPECT images and dosimetry calculations. The originality of their approach relies on the implementation of functional segmentation for the anthropomorphic model representing a virtual patient. Two anthropomorphic models are currently available: 4D XCAT and ICRP 110. A pharmacokinetic model describes the biodistribution of a given radiopharmaceutical in each defined compartment at various time-points. The Monte Carlo simulation toolkit gate offers the possibility to accurately simulate scintigraphic images and absorbed doses in volumes of interest. The TestDose platform relies on gate to reproduce precisely any imaging protocol and to provide reference dosimetry. For image generation, TestDose stores user's imaging requirements and generates automatically command files used as input for gate. Each compartment is simulated only once and the resulting output is weighted using pharmacokinetic data. Resulting compartment projections are aggregated to obtain the final image. For dosimetry computation, emission data are stored in the platform database and relevant gate input files are generated for the virtual patient model and associated pharmacokinetics. RESULTS: Two samples of software runs are given to demonstrate the potential of TestDose. A clinical imaging protocol for the Octreoscan™ therapeutical treatment was implemented using the 4D XCAT model. Whole-body "step and shoot" acquisitions at different times postinjection and one SPECT acquisition were generated within reasonable computation times. Based on the same Octreoscan™ kinetics, a dosimetry computation performed on the ICRP 110 model is also presented. CONCLUSIONS: The proposed platform offers a generic framework to implement any scintigraphic imaging protocols and voxel/organ-based dosimetry computation. Thanks to the modular nature of TestDose, other imaging modalities could be supported in the future such as positron emission tomography.

A software tool for specifying voxel models for dosimetry estimation.

Many dose estimation problems can be conveniently formulated in terms of finding the energy emitted and absorbed by a set of homogeneous volume elements (voxels) arranged in a rectilinear grid. The solution of these problems requires an accurate model of the source and target geometry to be established, whereupon conventional Monte Carlo simulation of radiation transport can be employed to determine energy deposition. A software application ("MrVoxel") has been developed to assist in the specification of the source and target models. This application includes tools for image segmentation and image registration (2D and 3D, intra- and inter-modality, interactive, and automatic). It employs a plug-in architecture to facilitate customization and future expansion: plug-ins can be written to perform image import and export as well as to implement specialized image processing routines. Using plug-ins, the package can, for example, import DICOM 3.10 files and export input files for a voxel-based Monte Carlo package. Standard dosimetric tools such as the geometric mean method, transmission based attenuation correction, and MIRD-style voxel dose kernel convolution are also implemented as plug-ins. MrVoxel was implemented on a Macintosh computer using a commercial software framework to produce a conventional document-centric application. Hence it includes useful features such as the ability to undo an operation or to save a processed image set at any point. This latter feature enables the production of a processing trail, to allow post-hoc auditing of the analysis process. This paper describes the MrVoxel application and its role in the analysis of a particular dosimetry problem.