Magnetic resonance coronary vessel wall imaging with highly efficient respiratory motion correction

There is a need for a noninvasive imaging technique for use in longitudinal studies of sub-clinical coronary artery disease. Magnetic resonance (MR) can be used to selectively and non-invasively image the coronary wall without the use of ionising radiation. However, high-resolution 3D studies are often time consuming and unreliable, as data acquisition is generally gated to a small window of diaphragm positions around end-expiration which results in inherently poor and variable respiratory efficiency. This thesis describes the development and application of a novel technique (beat-to-beat respiratory motion correction (B2B-RMC)) for correcting respiratory motion in 3D spiral MR coronary imaging. This technique uses motion of the epicardial fat surrounding the artery as a surrogate for the motion of the artery itself and enables retrospective motion correction with respiratory efficiency close to 100%. This thesis first describes an assessment of the performance of B2B-RMC using a purpose built respiratory motion phantom with realistic coronary artery test objects. Subsequently, MR coronary angiography studies in healthy volunteers show that the respiratory efficiency of B2B-RMC far exceeds that of conventional navigator gating, yet the respiratory motion correction is equally effective. The performance and reproducibility of 3D spiral imaging with B2B-RMC for assessment of the coronary artery vessel wall is subsequently compared to that of commonly used 2D navigator gated techniques. The results demonstrate the high performance, reproducibility and reliability of 3D spiral imaging with B2B-RMC when data acquisition is gated to alternate cardiac cycles. Using this technique, a further in-vivo study demonstrates thickening of the coronary vessel wall with age in healthy subjects and these results are shown to be consistent with outward remodelling of the vessel wall. Finally, the performance of B2B-RMC in a variety of coronary vessel wall applications, including in a small cohort of patients with confirmed coronary artery disease, is presented

Analysis of first pass myocardial perfusion imaging with magnetic resonance

Early diagnosis and localisation of myocardial perfusion defects is an important step in the treatment of coronary artery disease. Thus far, coronary angiography is the conventional standard investigation for patients with known or suspected coronary artery disease and it provides information about the presence and location of coronary stenoses. In recent years, the development of myocardial perfusion CMR has extended the role of MR in the evaluation of ischaemic heart disease beyond the situations where there have already been gross myocardial changes such as acute infarction or scarring. The ability to non-invasively evaluate cardiac perfusion abnormalities before pathologic effects occur, or as follow-up to therapy, is important to the management of patients with coronary artery disease. Whilst limited multi-slice 2D CMR perfusion studies are gaining increased clinical usage for quantifying gross ischaemic burden, research is now directed towards complete 3D coverage of the myocardium for accurate localisation of the extent of possible defects. In 3D myocardial perfusion imaging, a complete volumetric data set has to be acquired for each cardiac cycle in order to study the first pass of the contrast bolus. This normally requires a relatively large acquisition window within each cardiac cycle to ensure a comprehensive coverage of the myocardium and reasonably high resolution of the images. With multi-slice imaging, long axis cardiac motion during this large acquisition window can cause the myocardium imaged in different cross- sections to be mis-registered, i.e., some part of the myocardium may be imaged more than twice whereas other parts may be missed out completely. This type of mis-registration is difficult to correct for by using post-processing techniques. The purpose of this thesis is to investigate techniques for tracking through plane motion during 3D myocardial perfusion imaging, and a novel technique for extracting intrinsic relationships between 3D cardiac deformation due to respiration and multiple ID real-time measurable surface intensity traces is developed. Despite the fact that these surface intensity traces can be strongly coupled with each other but poorly correlated with respiratory induced cardiac deformation, we demonstrate how they can be used to accurately predict cardiac motion through the extraction of latent variables of both the input and output of the model. The proposed method allows cross-modality reconstruction of patient specific models for dense motion field prediction, which after initial modelling can be use in real-time prospective motion tracking or correction. In CMR, new imaging sequences have significantly reduced the acquisition window whilst maintaining the desired spatial resolution. Further improvements in perfusion imaging will require the application of parallel imaging techniques or making full use of the information content of the ¿-space data. With this thesis, we have proposed RR-UNFOLD and RR-RIGR for significantly reducing the amount of data that is required to reconstruct the perfusion image series. The methods use prospective diaphragmatic navigator echoes to ensure UNFOLD and RIGR are carried out on a series of images that are spatially registered. An adaptive real-time re-binning algorithm is developed for the creation of static image sub-series related to different levels of respiratory motion. Issues concerning temporal smoothing of tracer kinetic signals and residual motion artefact are discussed, and we have provided a critical comparison of the relative merit and potential pitfalls of the two techniques. In addition to the technical and theoretical descriptions of the new methods developed, we have also provided in this thesis a detailed literature review of the current state-of-the-art in myocardial perfusion imaging and some of the key technical challenges involved. Issues concerning the basic background of myocardial ischaemia and its functional significance are discussed. Practical solutions to motion tracking during imaging, predictive motion modelling, tracer kinetic modelling, RR-UNFOLD and RR-RIGR are discussed, all with validation using patient and normal subject data to demonstrate both the strength and potential clinical value of the proposed techniques.Open acces

Case series of breast fillers and how things may go wrong: radiology point of view

INTRODUCTION: Breast augmentation is a procedure opted by women to overcome sagging breast due to breastfeeding or aging as well as small breast size. Recent years have shown the emergence of a variety of injectable materials on market as breast fillers. These injectable breast fillers have swiftly gained popularity among women, considering the minimal invasiveness of the procedure, nullifying the need for terrifying surgery. Little do they know that the procedure may pose detrimental complications, while visualization of breast parenchyma infiltrated by these fillers is also deemed substandard; posing diagnostic challenges. We present a case series of three patients with prior history of hyaluronic acid and collagen breast injections. REPORT: The first patient is a 37-year-old lady who presented to casualty with worsening shortness of breath, non-productive cough, central chest pain; associated with fever and chills for 2-weeks duration. The second patient is a 34-year-old lady who complained of cough, fever and haemoptysis; associated with shortness of breath for 1-week duration. CT in these cases revealed non thrombotic wedge-shaped peripheral air-space densities. The third patient is a 37‐year‐old female with right breast pain, swelling and redness for 2- weeks duration. Previous collagen breast injection performed 1 year ago had impeded sonographic visualization of the breast parenchyma. MRI breasts showed multiple non- enhancing round and oval shaped lesions exhibiting fat intensity. CONCLUSION: Radiologists should be familiar with the potential risks and hazards as well as limitations of imaging posed by breast fillers such that MRI is required as problem-solving tool

Characterization of alar ligament on 3.0T MRI: a cross-sectional study in IIUM Medical Centre, Kuantan

INTRODUCTION: The main purpose of the study is to compare the normal anatomy of alar ligament on MRI between male and female. The specific objectives are to assess the prevalence of alar ligament visualized on MRI, to describe its characteristics in term of its course, shape and signal homogeneity and to find differences in alar ligament signal intensity between male and female. This study also aims to determine the association between the heights of respondents with alar ligament signal intensity and dimensions. MATERIALS & METHODS: 50 healthy volunteers were studied on 3.0T MR scanner Siemens Magnetom Spectra using 2-mm proton density, T2 and fat-suppression sequences. Alar ligament is depicted in 3 planes and the visualization and variability of the ligament courses, shapes and signal intensity characteristics were determined. The alar ligament dimensions were also measured. RESULTS: Alar ligament was best depicted in coronal plane, followed by sagittal and axial planes. The orientations were laterally ascending in most of the subjects (60%), predominantly oval in shaped (54%) and 67% showed inhomogenous signal. No significant difference of alar ligament signal intensity between male and female respondents. No significant association was found between the heights of the respondents with alar ligament signal intensity and dimensions. CONCLUSION: Employing a 3.0T MR scanner, the alar ligament is best portrayed on coronal plane, followed by sagittal and axial planes. However, tremendous variability of alar ligament as depicted in our data shows that caution needs to be exercised when evaluating alar ligament, especially during circumstances of injury

Stroke of the Visual Cortex

Stroke is the leading cause of homonymous visual field defect (VFD), resulting from irreversible damage of the post-chiasmatic visual pathway. From 6 to 13% of ischaemic strokes affect the supply area of the posterior cerebral artery, including the visual cortex in the occipital lobe. Besides ischaemic injury, the visual cortex can be damaged by intracerebral haemorrhage (ICH), 10% of which reside in the occipital lobe. Since occipital stroke almost always disturbs vision but can leave motor and language functions untouched, it may remain unrecognised in the acute phase, withholding the patients from receiving recanalisation treatments. Moreover, only up to 25% of stroke-related VFD recover spontaneously, whereas the rest continue to hinder patients’ independence in daily living and quality of life. Despite rigorous efforts, no evidence-based rehabilitation method to restore vision after stroke has been established. The aim of this thesis was to study the recognition, clinical characteristics, rehabilitation, neural mechanisms, and outcome of occipital stroke patients with VFD. The retrospective part of the thesis consists of two cohorts. The first cohort comprised 245 occipital ischaemic stroke patients admitted to the neurological emergency department of Helsinki University Hospital due to visual symptoms in 2010‒2015. We investigated their prehospital recognition and diagnostic delays and analysed the obstacles in their access to acute stroke treatment. The second retrospective cohort was the Helsinki ICH Study registry of 1013 consecutive non-traumatic ICH patients treated at Helsinki University Hospital in 2005‒2010, among whom we searched for isolated occipital ICH patients and analysed their clinical characteristics, aetiology, outcome, and incidence of post-stroke epilepsy in comparison to ICHs of other location. The prospective part of the thesis was based on the multicentre, randomised, sham-controlled exploratory REVIS (Restoration of Vision after Stroke) trial that studied rehabilitation of persistent VFD after chronic occipital stroke with different methods of non-invasive electrical brain stimulation. Altogether 56 patients were included in three 10-day experiments in three centres. The centres examined: 1) repetitive transorbital alternating current stimulation (rtACS) vs transcranial direct current stimulation preceding rtACS (tDCS/rtACS) vs sham in Germany, 2) rtACS vs sham in Finland, and 3) tDCS vs sham in Italy. In a functional magnetic resonance imaging spin-off study, resting-state functional connectivity of occipital stroke patients receiving rtACS or sham was compared to healthy control subjects at baseline and to each other after intervention. We found out that the prehospital delay of occipital stroke patients ranged between 20 minutes and 5 weeks and only 20% were admitted within the 4.5-hour time window of intravenous thrombolysis. Consequently, only 6.5% received thrombolysis, which is the mainstay of acute stroke treatment. One fourth of the patients arrived through at least two points of care and as many were assessed by an ophthalmologist before entering the neurological care, even though acute stroke patients should be transported directly to the neurological emergency department. The diagnostic delay was primarily caused by the patients’ late contact to health care but was also attributed to poor recognition and misdiagnosis by health-care professionals. The incidence of isolated occipital ICH was 1.9% of all non-traumatic ICHs and 5.3% of lobar ICHs. The patients with occipital ICH were younger and had more often vascular malformations as an aetiology of the bleeding than the non-occipital lobar ICH patients. They presented with milder symptoms and longer delay, and over 60% of the patients suffered solely from visual focal symptom. The haematoma volume in the occipital lobe was smaller and grew less compared to the non-occipital lobar haemorrhages. All in all, the occipital location of ICH was independently associated with favourable outcome at discharge among the patients with lobar ICH. The majority of the occipital ICH patients were able to return to independent activities of daily living, including driving a car and working, within a follow-up of a year. However, post-stroke epilepsy was as frequent as after non-occipital lobar ICH. In the prospective REVIS trial, rtACS was mostly ineffective in vision rehabilitation according to behavioural vision tests. Neither did it affect resting-state functional connectivity in comparison to sham. Transcranial DCS alone increased the monocular visual field measured with standard automated perimetry. The combined tDCS/rtACS propelled some improvements in the secondary visual outcome measures but did not differ from the sham stimulation. All the stimulation modalities were tolerated well. The functional connectivity of the chronic occipital stroke patients with VFD did not differ from the healthy control subjects when the whole brain network was considered in the analyses. However, a few occipital regions close to the infarct expressed lower local connectivity to the highly connected regions of the network according to the network graph metrics, whereas a lateral occipital region in the damaged hemisphere had higher network connectivity. These findings support the view that chronic ischaemic damage of the visual cortex affects functional connectivity within the visual network but leaves global connectivity unchanged. In conclusion, occipital stroke patients are insufficiently recognised, and thus the awareness of visual stroke symptoms should be raised especially among the public but also among health-care professionals to provide the patients with timely acute treatment and to prevent permanent disability. Occipital ICH patients have relatively favourable outcomes, but a structural cause of bleeding should be searched. Non-invasive electrical brain stimulation with the examined modalities does not cause robust improvement in vision or functional connectivity of the brain networks after a 10-day treatment, but further experiments with tDCS-based methods, potentially in combination with vision training, may be worth pursuing.Ihmisen näköaivokuori sijaitsee pääosin takaraivolohkossa ja sen vaurio johtaa tyypillisesti molempien silmien toispuoleiseen näkökenttäpuutokseen. Yleisin syy vaurioon on aivoverenkiertohäiriö: joko aivovaltimon tukoksesta johtuva infarkti tai verisuonen repeämästä aiheutuva aivoverenvuoto. Näkökenttäpuutos alentaa toiminta-, työ- ja ajokykyä ja heikentää elämänlaatua. Alle neljäsosa näkökenttäpuutoksista paranee täysin, eikä niiden kuntouttamiseksi ole kliiniseen käyttöön vakiintunutta menetelmää. Väitöskirjatyössä tutkittiin näköaivokuoren aivoverenkiertohäiriöiden tunnistamista, kliinistä kuvaa, kuntoutusta ja ennustetta. Tutkimuksessa selvisi, että ainoastaan 20,8 % HUS:in neurologian päivystyksessä vuosina 2010–2015 hoidetuista, näköoirein ilmenneen takaraivolohkon infarktin saaneista potilaista tuli hoitoon liuotushoidon mahdollistavassa aikaikkunassa ja vain 6,5 % sai liuotuksen. Viiveen yleisin syy oli potilaiden hidas hakeutuminen hoitoon, mutta kolmasosassa tapauksista myöskään terveydenhuoltohenkilökunta ei aluksi tunnistanut oireiden johtuvan aivoverenkiertohäiriöstä. Takaraivolohkoon rajautuvia aivoverenvuotoja esiintyi 1,9 %:lla HUS:issa 2005–2010 hoidetusta 1013 aivoverenvuotopotilaasta. Potilaat olivat nuorempia ja lieväoireisempia kuin muut vuotopotilaat, ja heidän vuotonsa johtuivat useammin verisuoniepämuodostumista. Vuodon sijainti takaraivolohkossa ennusti parempaa toimintakykyä sairaalasta kotiutuessa, ja suurin osa potilaista toipui vuoden sisällä päivittäistoiminnoissa itsenäisiksi. Epilepsian ilmaantuvuus ei eronnut pitkäaikaisseurannassa muista aivoverenvuotopotilaista. Satunnaistetussa, lumekontrolloidussa REVIS-monikeskustutkimuksessa selvitettiin kajoamattomien, heikkoa sähkövirtaa hyödyntävien stimulaatiomenetelmien tehoa takaraivolohkon aivoinfarktin aiheuttaman kroonisen näkökenttäpuutoksen kuntoutuksessa. Hoitokokeessa tasavirtastimulaatio (tDCS) pienensi vaurion vastapuoleisen silmän näkökenttäpuutosta verrattuna lumehoitoon, kun taas vaihtovirtastimulaatio (rtACS) oli tehotonta. Myöskään näiden yhdistelmällä (tDCS/rtACS) tulokset eivät eronneet lumeesta. Lisäksi toiminnallisella magneettikuvauksella tutkittiin 16 takaraivolohkon aivoinfarktipotilaan lepohermoverkostojen toiminnallista kytkeytyvyyttä verrattuna terveisiin koehenkilöihin. Tutkimus paljasti paikallisia muutoksia kytkeytyvyydessä potilaiden näköinformaation käsittelyyn osallistuvilla aivoalueilla, mutta laajemmin verkostojen toiminta ei eronnut verrokeista. Vaihtovirtastimulaatio ei muuttanut toiminnallista kytkeytyvyyttä