Browsing by Department "MRC/UCT Medical Imaging Research Unit"

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    Abnormal diastolic and systolic septal motion following pericardiectomy demonstrated by cine DENSE MRI
    (Clinics Cardive, 2008) Spottiswoode, Bruce; Russell, James B; Moosa, Sulaiman; Meintjes, Ernesta M; Epstein, Frederick H; Mayosi, Bongani M
    Constrictive pericarditis can lead to paradoxical interventricular septal motion. Displacement encoding with stimulated echoes (DENSE) magnetic resonance imaging (MRI) provides a method for quantifying myocardial motion and strain. A case of constrictive pericarditis is presented and the diastolic ‘septal bounce’ is clearly evident in both anatomical and DENSE ciné MRI images. (See video link to full-text electronic article). The postoperative systolic septal wall-motion abnormality of cardiac surgery is portrayed with greater precision by DENSE than anatomical ciné MRI images.
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    Open Access
    Assessing strain in arrhythmogenic right ventricular cardiomyopathy using cine DENSE MRI
    (BioMed Central Ltd, 2009) Ongori, Joash; Hendricks, Neil; Spottiswoode, Bruce; Meintjes, Ernesta; Epstein, Frederick; Mayosi, Bongani
    The kinematics of the right ventricle (RV) are not well understood due to its thin wall and asymmetric geometry. Cine displacement encoding with stimulated echoes (cine DENSE), which measures intramyocardial displacement and strain, has been adapted for RV analysis with encouraging preliminary results in normal subjects. This preliminary study evaluates cine DENSE MRI for detecting decreased myocardial strain in arrhythmogenic right ventricular cardiomyopathy (ARVC). ARVC is a unique heart muscle disease affecting predominantly the RV. The pathological hallmark of fibro-fatty replacement of the myocardium may result in localised aneurysms and wall motion abnormalities, detectable by cardiac magnetic resonance imaging.
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    Comparison of SNR efficiencies and strain for cine DENSE using conventional EPI, flyback EPI and spiral k-space trajectories
    (BioMed Central Ltd, 2011) Zhong, Xiaodong; Spottiswoode, Bruce; Meyer, Craig; Epstein, Frederick
    The original implementation of 2D cine DENSE (displacement encoding with stimulated echoes) employed a conventional EPI k-space trajectory for rapid data sampling. Follow-up studies used flyback EPI to reduce image artifacts. More recently a spiral k-space trajectory was utilized for improved SNR.
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    Comprehensive Cardiovascular magnetic resonance of myocardial mechanics in mice using three-dimensional cine DENSE
    (BioMed Central Ltd, 2011) Zhong, Xiaodong; Gibberman, Lauren; Spottiswoode, Bruce; Gilliam, Andrew; Meyer, Craig; French, Brent; Epstein, Frederick
    BACKGROUND: Quantitative noninvasive imaging of myocardial mechanics in mice enables studies of the roles of individual genes in cardiac function. We sought to develop comprehensive three-dimensional methods for imaging myocardial mechanics in mice. METHODS: A 3D cine DENSE pulse sequence was implemented on a 7T small-bore scanner. The sequence used three-point phase cycling for artifact suppression and a stack-of-spirals k-space trajectory for efficient data acquisition. A semi-automatic 2D method was adapted for 3D image segmentation, and automated 3D methods to calculate strain, twist, and torsion were employed. A scan protocol that covered the majority of the left ventricle in a scan time of less than 25 minutes was developed, and seven healthy C57Bl/6 mice were studied. RESULTS: Using these methods, multiphase normal and shear strains were measured, as were myocardial twist and torsion. Peak end-systolic values for the normal strains at the mid-ventricular level were 0.29 +/- 0.17, -0.13 +/- 0.03, and -0.18 +/- 0.14 for Err, Ecc, and Ell, respectively. Peak end-systolic values for the shear strains were 0.00 +/- 0.08, 0.04 +/- 0.12, and 0.03 +/- 0.07 for Erc, Erl, and Ecl, respectively. The peak end-systolic normalized torsion was 5.6 +/- 0.9degrees. CONCLUSIONS: Using a 3D cine DENSE sequence tailored for cardiac imaging in mice at 7 T, a comprehensive assessment of 3D myocardial mechanics can be achieved with a scan time of less than 25 minutes and an image analysis time of approximately 1 hour.
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    Diffusion tensor imaging point to ongoing functional impairment in HIV-infected children at age 5, undetectable using standard neurodevelopmental assessments
    (2020-05-19) Ackermann, Christelle; Andronikou, Savvas; Saleh, Muhammad G; Kidd, Martin; Cotton, Mark F; Meintjes, Ernesta M; Laughton, Barbara
    Background Perinatal HIV infection negatively impacts cognitive functioning of children, main domains affected are working memory, processing speed and executive function. Early ART, even when interrupted, improves neurodevelopmental outcomes. Diffusion tension imaging (DTI) is a sensitive tool assessing white matter damage. We hypothesised that white matter measures in regions showing HIV-related alterations will be associated with lower neurodevelopmental scores in specific domains related to the functionality of the affected tracts. Methods DTI was performed on children in a neurodevelopmental sub study from the Children with HIV Early Antiretroviral (CHER) trial. Voxel-based group comparisons to determine regions where fractional anisotropy and mean diffusion differed between HIV+ and uninfected children were done. Locations of clusters showing group differences were identified using the Harvard–Oxford cortical and subcortical and John Hopkins University WM tractography atlases provided in FSL. This is a second review of DTI data in this cohort, which was reported in a previous study. Neurodevelopmental assessments including GMDS and Beery-Buktenica tests were performed and correlated with DTI parameters in abnormal white matter. Results 38 HIV+ children (14 male, mean age 64.7 months) and 11 controls (4 male, mean age 67.7 months) were imaged. Two clusters with lower fractional anisotropy and 7 clusters with increased mean diffusion were identified in the HIV+ group. The only neurodevelopmental domain with a trend of difference between the HIV+ children and controls (p = 0.08), was Personal Social Quotient which correlated to improved myelination of the forceps minor in the control group. As a combined group there was a negative correlation between visual perception and radial diffusion in the right superior longitudinal fasciculus and left inferior longitudinal fasciculus, which may be related to the fact that these tracts, forming part of the visual perception pathway, are at a crucial state of development at age 5. Conclusion Even directed neurodevelopmental tests will underestimate the degree of microstructural white matter damage detected by DTI. The visual perception deficit detected in the entire study population should be further examined in a larger study.
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    Elliptical Subject Specific model for respiratory motion
    (Biomed Central Ltd, 2012) Burger, Ian; Meintjes, Ernesta; Keegan, Jennifer; Firmin, David
    Respiratory motion of the heart poses a problem for high resolution cardiac MR imaging. Prospective slice following uses the navigator position immediately prior to the imaging segment to correct the slice positions throughout the segment [1]. The navigator is typically placed over the right hemi-diaphragm and a fixed correction factor is used to adjust for the difference to the motion of the heart. The relationship between the motion of the heart and the superior-inferior motion of the diaphragm is approximately linear although highly subject specific, with an element of hysteresis [2]. We investigated a more complex model to incorporate non rigid transformation of the heart as well as hysteresis.
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    Mapping right ventricular myocardial mechanics using 3D cine DENSE cardiovascular magnetic resonance
    (BioMed Central Ltd, 2012) Auger, Daniel; Zhong, Xiaodong; Epstein, Frederick; Spottiswoode, Bruce
    BACKGROUND: The mechanics of the right ventricle (RV) are not well understood as studies of the RV have been limited. This is, in part, due to the RV's thin wall, asymmetric geometry and irregular motion. However, the RV plays an important role in cardiovascular function. This study aims to describe the complex mechanics of the healthy RV using three dimensional (3D) cine displacement encoding with stimulated echoes (DENSE) cardiovascular magnetic resonance (CMR). METHODS: Whole heart 3D cine DENSE data were acquired from five healthy volunteers. Tailored post-processing algorithms for RV mid-wall tissue tracking and strain estimation are presented. A method for sub-dividing the RV into four regions according to anatomical land marks is proposed, and the temporal evolution of strain was assessed in these regions. RESULTS: The 3D cine DENSE tissue tracking methods successfully capture the motion and deformation of the RV at a high spatial resolution in all volunteers. The regional Lagrangian peak surface strain and time to peak values correspond with previous studies using myocardial tagging, DENSE and strain encoded CMR. The inflow region consistently displays lower peak strains than the apical and outflow regions, and the time to peak strains suggest RV mechanical activation in the following order: inflow, outflow, mid, then apex. CONCLUSIONS: Model-free techniques have been developed to study the myocardial mechanics of the RV at a high spatial resolution using 3D cine DENSE CMR. The consistency of the regional RV strain patterns across healthy subjects is encouraging and the techniques may have clinical utility in assessing disrupted RV mechanics in the diseased heart.
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    Paradoxical facilitation of working memory after basolateral amygdala damage
    (Public Library of Science, 2012) Morgan, Barak; Terburg, David; Thornton, Helena B; Stein, Dan J; van Honk, Jack
    Working memory is a vital cognitive capacity without which meaningful thinking and logical reasoning would be impossible. Working memory is integrally dependent upon prefrontal cortex and it has been suggested that voluntary control of working memory, enabling sustained emotion inhibition, was the crucial step in the evolution of modern humans. Consistent with this, recent fMRI studies suggest that working memory performance depends upon the capacity of prefrontal cortex to suppress bottom-up amygdala signals during emotional arousal. However fMRI is not well-suited to definitively resolve questions of causality. Moreover, the amygdala is neither structurally or functionally homogenous and fMRI studies do not resolve which amygdala sub-regions interfere with working memory. Lesion studies on the other hand can contribute unique causal evidence on aspects of brain-behaviour phenomena fMRI cannot "see". To address these questions we investigated working memory performance in three adult female subjects with bilateral basolateral amygdala calcification consequent to Urbach-Wiethe Disease and ten healthy controls. Amygdala lesion extent and functionality was determined by structural and functional MRI methods. Working memory performance was assessed using the Wechsler Adult Intelligence Scale-III digit span forward task. State and trait anxiety measures to control for possible emotional differences between patient and control groups were administered. Structural MRI showed bilateral selective basolateral amygdala damage in the three Urbach-Wiethe Disease subjects and fMRI confirmed intact functionality in the remaining amygdala sub-regions. The three Urbach-Wiethe Disease subjects showed significant working memory facilitation relative to controls. Control measures showed no group anxiety differences. Results are provisionally interpreted in terms of a 'cooperation through competition' networks model that may account for the observed paradoxical functional facilitation effect.
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    Semi-automated left ventricular segmentation based on a guide point model approach for 3D cine DENSE cardiovascular magnetic resonance
    (2014-01-14) Auger, Daniel A; Zhong, Xiaodong; Epstein, Frederick H; Meintjes, Ernesta M; Spottiswoode, Bruce S
    Abstract Background The most time consuming and limiting step in three dimensional (3D) cine displacement encoding with stimulated echoes (DENSE) MR image analysis is the demarcation of the left ventricle (LV) from its surrounding anatomical structures. The aim of this study is to implement a semi-automated segmentation algorithm for 3D cine DENSE CMR using a guide point model approach. Methods A 3D mathematical model is fitted to guide points which were interactively placed along the LV borders at a single time frame. An algorithm is presented to robustly propagate LV epicardial and endocardial surfaces of the model using the displacement information encoded in the phase images of DENSE data. The accuracy, precision and efficiency of the algorithm are tested. Results The model-defined contours show good accuracy when compared to the corresponding manually defined contours as similarity coefficients Dice and Jaccard consist of values above 0.7, while false positive and false negative measures show low percentage values. This is based on a measure of segmentation error on intra- and inter-observer spatial overlap variability. The segmentation algorithm offers a 10-fold reduction in the time required to identify LV epicardial and endocardial borders for a single 3D DENSE data set. Conclusion A semi-automated segmentation method has been developed for 3D cine DENSE CMR. The algorithm allows for contouring of the first cardiac frame where blood-myocardium contrast is almost nonexistent and reduces the time required to segment a 3D DENSE data set significantly.
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    Short emergency department length of stay attributed to full-body digital radiography - a review of 3 paediatric cases
    (2006) Koning, Lizanne; Douglas, Tania S; Pitcher, Richard; Van As, A B
    Multiple casualties strain the resources of emergency departments. Two polytraumatised patients arriving simultaneously can overwhelm a small community hospital, while the capacity of a large urban emergency department does not extend beyond the treatment of 3 - 4 severely injured patients at the same time using the routine trauma protocol.1 Emergency department overcrowding because of multiple casualties leads to increased length of stay and can have an adverse effect on patient outcome. Variations from the norm in trauma management, particularly during the initial assessment and resuscitation phase of care, during a multiple casualty incident, has been associated with 10% and 9% incidence of preventable morbidity and mortality, respectively.2 Inadequate evaluation may contribute to up to 30% of early deaths in children with polytrauma.3
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    Virtual reality exposure therapy as treatment for pain catastrophizing in fibromyalgia patients: proof-of-concept study (Study Protocol)
    (BioMed Central Ltd, 2011) Morris, Linzette; Grimmer-Somers, Karen; Spottiswoode, Bruce; Louw, Quinette
    BACKGROUND: Albeit exercise is currently advocated as one of the most effective management strategies for fibromyalgia syndrome (FMS); the implementation of exercise as a FMS treatment in reality is significantly hampered by patients' poor compliance. The inference that pain catastrophizing is a key predictor of poor compliance in FMS patients, justifies considering the alteration of pain catastrophizing in improving compliance towards exercises in FMS patients. The aim of this study is to provide proof-of-concept for the development and testing of a novel virtual reality exposure therapy (VRET) program as treatment for exercise-related pain catastrophizing in FMS patients. METHODS: Two interlinked experimental studies will be conducted. Study 1 aims to objectively ascertain if neurophysiological changes occur in the functional brain areas associated with pain catastrophizing, when catastrophizing FMS subjects are exposed to visuals of exercise activities. Study 2 aims to ascertain the preliminary efficacy and feasibility of exposure to visuals of exercise activities as a treatment for exercise-related pain catastrophizing in FMS subjects. Twenty subjects will be selected from a group of FMS patients attending the Tygerberg Hospital in Cape Town, South Africa and randomly allocated to either the VRET (intervention) group or waiting list (control) group. Baseline neurophysiological activity for subjects will be collected in study 1 using functional magnetic resonance imaging (fMRI). In study 2, clinical improvement in pain catastrophizing will be measured using fMRI (objective) and the pain catastrophizing scale (subjective).DISCUSSION:The premise is if exposing FMS patients to visuals of various exercise activities trigger the functional brain areas associated with pain catastrophizing; then as a treatment, repeated exposure to visuals of the exercise activities using a VRET program could possibly decrease exercise-related pain catastrophizing in FMS patients. Proof-of-concept will either be established or negated. The results of this project are envisaged to revolutionize FMS and pain catastrophizing research and in the future, assist health professionals and FMS patients in reducing despondency regarding FMS management.TRIAL REGISTRATION:PACTR201011000264179