Recently there has been considerable attention directed towards the increased risk for head injuries that athletes face while participating in high impact sports. Furthermore, there is also heightened interest in the asymptomatic sport related sub-concussive blows, commonly experienced during play, that possibly lead to long term neurological deficits. Purpose: The goal of this study was to investigate retired professional athletes of the Canadian Football League with a history of sport-related concussions, using several advanced MRI methods. The ultimate goal being the identification of any potential synergistic effects between a history of sport-related concussions, and exacerbated cognitive decline later on in life. Materials and Methods: Twenty former professional athletes of the Canadian Football League were scanned using a GE Discovery MR750 3T MRI with a 32-channel RF-coil. Axial FSPGR-3D images were used to define rs-BOLD and DTI scans. Seed based network analysis of the DMN was performed on rs-BOLD data. Voxel-wise tensor fitting of DTI data provided the means for estimating several tensor metrics. Results were normalized through comparison with a database of healthy controls. Potential associations between functional connectivity, white matter integrity, and cortical thickness measures were correlated with retired athlete position and years of professional play. Results: We found widespread cortical thinning in retired CFL subjects, alongside significant increases in axial and mean diffusivity in the corona radiata and splenium and genu of the corpus callosum compared to controls. Seed based correlation analysis of the DMN network revealed interrupted connectivity in retired athletes. Athlete age, po- sition, and number of years played appear to be factors in overall core white matter microstructural integrity. Conclusions: When compared to an age and sex matched control population, differences were observed both in functional and structural con- nectivity, suggesting that even years after retiring the brains of these former athletes still exhibit signs of damage. / Thesis / Master of Applied Science (MASc) / Sport-related concussions affect millions of athletes on a yearly basis in the United States alone. Concussions are often accompanied by short-lived neurological impairments, such as confusion, headaches, dizziness, nausea and memory loss. In addition, there is the potential for development of long term mental health and cognitive impairment. The goal of this work was to identify any neurological changes present in retired athletes of the Canadian Football League, through the use of advanced magnetic resonance imaging techniques evaluating thickness of brain structures, changes in brain activity, and alterations in core microstructure of the brain. Analyzing the results of these techniques revealed changes in a number of brain regions within the retired professional athlete population. These results suggest that a career of high impact sports may lead to short term, in addition to long-term neurological consequences.

For many decades the Boston University School of Medicine Department of Anatomy and Neurobiology has housed an unprovenienced collection of fetal specimens. At least ten percent of the 137 fetal specimens were lost due to drying out and other damage. The specimens were stored for many decades in individual fluid filled containers. There is no reliable information regarding the medical or curation histories of the human fetal specimens. Furthermore, there is concern that the fixative may have led some internal structures to shrink more than others. At issue was to determine whether the specimens had maintained or lost their relationships, and size amongst internal structures. In normal fetal development the cerebellum, the femur, and the foot all follow mostly positive linear growth with age. Therefore, the purpose of the present study was to assess whether these specimens demonstrate anatomical correlations that one might find within in utero fetuses. This prospective correlation study used MRI images of the cerebellum and femur as well as anthropometric measurements of each foot and mass to seek to answer this question. A blind, random sample of twenty-five specimens was selected from forty-eight specimens roughly grouped by size. The Boston University Institutional Review Board was notified and, assigned waiver status to the application because the specimens were unprovenienced fixed tissue. All specimens were magnetic resonance scanned at the Center for Biomedical Imaging at the Boston University School of Medicine using a 3.0T whole body scanner (Achieva, Philips Healthcare, Best, The Netherlands). All scans were acquired using the 8-channel high-resolution head coil made by Invivo for the Achieva 3T scanner. This study found that the measurements taken from the images, and the feet had good intra-rater reliability because paired t-tests did not show significant differences between the measurements (alpha (α) < 0.05, all p-values were > 0.17, t-values were less than t-critical, and R2 < 0.02). Pearson's correlation coefficient testing revealed strong positive correlation between all the mean measures comparing these three structures: transverse cerebellar diameter (TCD), femur length, and foot length (α < 0.05, r - values were > 0.91, p < 0.001, and R2 > 0.82). Leading us to conclude that the dimensions of the soft tissues - TCD; and bone tissues - femur and foot of the lower extremities were unlikely to have changed significantly in decades of storage.

Arterial Spin Labeling (ASL) is a Magnetic Resonance Imaging (MRI) technique that is able to non-invasively quantify the rate of delivery of arterial blood to tissue, known as perfusion. In this thesis a method that uses Velocity Selective (VS) preparations to generate contrast between blood and tissue spins is investigated. The systematic errors associated with performing a VSASL experiment on imperfect hardware is first investigated. It is shown through simulations and experiments that some VS preparations will underestimate perfusion due to static and transmit magnetic field errors, and that eddy currents caused by switching of magnetic gradients lead to an overestimation of perfusion with VSASL by up to a factor 2. A novel VS preparation, BIR-8, is presented which is shown to be the most robust to these imperfections. The BIR-8 VSASL technique is then applied in brain tumours where it is found that significant VSASL signal can be detected in less than 5 minutes. However, in a comparison with a spatially selective ASL technique it is found that VSASL overestimates perfusion in these tumours, despite agreeing in Grey Matter. The systematic errors due to physiology are then modelled, and it is shown that both diffusion and bulk motion will systematically bias the VSASL measurement. A diffusion insensitive VSASL technique, VS-TILT, is then developed and it is found that a significant proportion of the VSASL signal originates from diffusion effects. Theoretical models for the shape of the bolus in vascular networks are also derived, and it is shown that an isotropic network of laminar vessels produces the most efficient saturation, but saturation is also achieved with plug flow. The diffusion insensitive VS preparation is then applied in an attempt to isolate the venous compartment in order to measure Oxygen Extraction Fraction. A kinetic model is derived in order to optimise the acquisition. However, it is found that accurate measurements of OEF would not be produced by this sequence in a clinically realistic time.

This thesis comprises three phases with a combined aim which was to investigate the effect of position on the lumbar intervertebral disc (IVD). The effect of position on the lumbar IVD in asymptomatic subjects and subjects with discogenic low back pain (DLBP) was explored using positional Magnetic Resonance Imaging (pMRI). Convenience samples of 11 asymptomatic and 34 DLBP subjects were recruited to have sagittal and axial pMRI scans performed in sitting (Neutral, Flexed and Extended), standing and lying (Supine and Prone extension) positions. The sagittal plane migration of the nucleus pulposus (NP) of each lumbar IVD in each position was measured from the sagittal and axial pMRI scans. Within and between group inferential analysis was performed using nonparametric tests. Both the asymptomatic and DLBP subjects’ demonstrated that position had statistically significant effects on the sagittal plane NP migration. Both groups demonstrated significantly greater posterior sagittal plane NP migration in Neutral and Flexed sitting positions compared to the other positions. However, between group comparisons identified that the asymptomatic subjects also demonstrated significantly greater posterior sagittal plane NP migration than the DLBP subjects. This pattern was more common in the upper lumbar IVDs (L1/2 and L2/3) between positions and less common in the lower IVDs (L4/5 and L5/S1) between positions. New knowledge regarding the behaviour of the lumbar IVD emerged from this research. The differences detected between the asymptomatic and DLBP subjects suggest that some current theories regarding DLBP may be incorrect. The results also support imaging of DLBP subjects in sitting positions as opposed to current supine positions. Although the limitations of the study reduce generalisation of the results, the implications for clinical practice, imaging and suggestions for further research from this work are important to improve understanding and conservative management of DLBP.

No description available.

Image-based quantifications of visceral adipose tissue (VAT) volumes from segmented VAT areas are increasingly considered for risk assessment in obese patients. The goal of this study was to determine the power of partial VAT areas to predict total VAT volume in morbidly obese patients (BMI > 40 kg/m2) as a function of gender, age and anatomical landmarks. 130 morbidly obese patients (mean BMI 46.5 kg/m2; 94 females) underwent IRB-approved MRI. Total VAT volumes were predicted from segmented VAT areas (of single or five adjacent slices) at common axial landmark levels and compared with the measured ones (VVAT-T, about 40 slices between diaphragm and pelvic floor). Standard deviations σ1 and σ5 of the respective VAT volume differences served as measures of agreement. Mean VVAT-T was 4.9 L for females and 8.1 L for males. Best predictions were found at intervertebral spaces L3-L4 for females (σ5 = 688 ml, σ1 = 832 ml) and L1-L2 for males (σ5 = 846 ml, σ1 = 992 ml), irrespective of age. In conclusion, VAT volumes in morbidly obese patients can be reliably predicted by multiplying the segmented VAT area at a gender-specific lumbar reference level with a fixed scaling factor and effective slice thickness.

Chronic liver disease is a worldwide health problem, and hepatic fibrosis (HF) is one of the hallmarks of the disease. Pathology diagnosis of HF is based on textural change in the liver as a lobular collagen network that develops within portal triads. The scale of collagen lobules is characteristically on order of 1mm, which close to the resolution limit of in vivo Gd-enhanced MRI. In this work the methods to collect training and testing images for a Hotelling observer are covered. An observer based on local texture analysis is trained and tested using wet-tissue phantoms. The technique is used to optimize the MRI sequence based on task performance. The final method developed is a two stage model observer to classify fibrotic and healthy tissue in both phantoms and in vivo MRI images. The first stage observer tests for the presence of local texture. Test statistics from the first observer are used to train the second stage observer to globally sample the local observer results. A decision of the disease class is made for an entire MRI image slice using test statistics collected from the second observer. The techniques are tested on wet-tissue phantoms and in vivo clinical patient data.

Objective: Chronic recurrent multifocal osteomyelitis/ chronic non-bacterial osteomyelitis (CRMO/CNO) is a rare auto-inflammatory disease and typically manifests in terms of musculoskeletal pain. Because of a high frequency of musculoskeletal disorders in children/ adolescents, it can be quite challenging to distinguish CRMO/ CNO from nonspecific musculosketetal pain or from malignancies. The purpose of this study was to evaluate the visibility of CRMO lesions in a whole-body diffusion-weighted imaging (WB-DWI) technique and its potential clinical value to better characterize MR-visible lesions. Materials and methods: Whole-body imaging at 3T was performed in 16 patients (average: 13 years) with confirmed CRMO. The protocol included 2D Short Tau Inversion Recovery (STIR) imaging in coronal and axial orientation as well as diffusion-weighted imaging in axial orientation. Visibility of lesions in DWI and STIR was evaluated by two readers in consensus. The apparent diffusion coefficient (ADC) was measured for every lesion and corresponding reference locations. Results: A total of 33 lesions (on average 2 per patient) visible in STIR and DWI images (b = 800 s/mm2 and ADC maps) were included, predominantly located in the long bones. With a mean value of 1283 mm2/s in lesions, the ADC was significantly higher than in corresponding reference regions (782 mm2/s). By calculating the ratio (lesion to reference), 82% of all lesions showed a relative signal increase of 10% or higher and 76% (25 lesions) showed a signal increase of more than 15%. The median relative signal increase was 69%. Conclusion: This study shows that WB-DWI can be reliably performed in children at 3T and predominantly, the ADC values were substantially elevated in CRMO lesions. WB-DWI in conjunction with clinical data is seen as a promising technique to distinguish benign inflammatory processes (in terms of increased ADC values) from particular malignancies.

Η απεικόνιση μαγνητικού συντονισμού (MRI) βασίζεται στο φυσικό φαινόμενο του πυρηνικού μαγνητικού συντονισμού (NMR). Ενώ το φαινόμενο αυτό είναι γνωστό από το 1950, η πρώτη μαγνητική τομογραφία σε άνθρωπο διενεργήθηκε μόλις το 1977. Η δεκαετία του '80 ήταν η δεκαετία που τα συστήματα MRI άρχισαν να εξελίσσονται ταχύτατα και η εξέλιξη αυτή συνεχίζεται ακόμη και σήμερα. Στις μέρες μας, τα σύγχρονα συστήματα MRI κάνουν πολύ περισσότερα από απλή απεικόνιση, με τη μαγνητική τομογραφία διάχυσης, τη φασματοσκοπία και τη λειτουργική μαγνητική τομογραφία να αποτελούν νέες και πολλά υποσχόμενες εφαρμογές. Τα συστήματα MRI δεν χρησιμοποιούν ιοντίζουσα ακτινοβολία, αλλά μαγνητικά πεδία και ηλεκτρομαγνητικά κύματα στην περιοχή των ραδιοσυχνοτήτων. Αυτός είναι πιθανώς ο λόγος για τον οποίο τα συστήματα MRI δεν είχαν τύχει τόσης προσοχής όπως τα συστήματα υπολογιστικής τομογραφίας, όσον αφορά τους κανονισμούς που διέπουν την ασφάλεια της χρήσης τους για χρήση σε εξετάσεις ασθενών. Ωστόσο, δεδομένου ότι η απεικόνιση χρησιμοποιείται για τη διάγνωση και μια λανθασμένη διάγνωση μπορεί να οδηγήσει σε λανθασμένη θεραπεία ή την απουσία θεραπείας, τα οποία με τη σειρά τους μπορεί να οδηγήσουν σε μη αναστρέψιμη βλάβη για την υγεία των ασθενών ή ακόμα και στο θάνατο, η Αμερικανική Ένωση Φυσικών Ιατρικής (AAPM) είχε προτείνει μεθόδους για τον έλεγχο της ποιότητας εικόνας από τις αρχές της δεκαετίας του 1990. Το Αμερικανικό Κολλέγιο Ακτινολογίας (ACR), είχε επίσης συμβάλει στην προσπάθεια αυτή από την αρχή της νέας χιλιετίας, προτείνοντας μεθόδους ελέγχου της ποιότητας εικόνας για τη δημιουργία ενός προγράμματος πιστοποίησης για τις εγκαταστάσεις MRI. Το 2010 η AAPM δημοσίευσε μια έκθεση (AAPM report No. 100) με τίτλο «Έλεγχοι αποδοχής και διαδικασίες διασφάλισης ποιότητας για εγκαταστάσεις απεικόνισης μαγνητικής τομογραφίας», το οποίο περιγράφει τις διαδικασίες για τον έλεγχο της απόδοσης των μαγνητικών τομογράφων, αλλά και τις διαδικασίες που αφορούν άλλα ζητήματα ασφάλειας για τους ασθενείς και το προσωπικό. Στην Ελλάδα μέχρι πρόσφατα, οι εγκαταστάσεις MRI - σε αντίθεση με τους υπολογιστικούς τομογράφους και όλα τα άλλα ακτινολογικά συστήματα - ήταν εκτός της εποπτείας της Ελληνικής Επιτροπής Ατομικής Ενέργειας (Ε.Ε.Α.Ε.) και της Ένωσης Φυσικών Ιατρικής Ελλάδος (Ε.Φ.Ι.Ε.). Ωστόσο, από τις αρχές του 2013, η E.E.A.E. έχει προτείνει ένα πρόγραμμα διαπίστευσης (με βάση την έκθεση AAPM Νο. 100) που πρέπει να εφαρμόζεται σε όλες τις καινούριες εγκαταστάσεις MRI. Αυτό το πρόγραμμα πιστοποίησης σταδιακά θα εφαρμοστεί και σε παλαιότερες εγκαταστάσεις. Ο στόχος είναι μέσα σε 5 χρόνια το πολύ, όλες οι εγκαταστάσεις MRI να είναι διαπιστευμένες όπως ισχύει εδώ και πολλά χρόνια για τις εγκαταστάσεις υπολογιστικής τομογραφίας. Ο σκοπός αυτής της διπλωματικής εργασίας είναι να συνοψίσει το βασικό θεωρητικό υπόβαθρο πάνω στο οποίο στηρίζεται η απεικόνιση μαγνητικού συντονισμού, για να βοηθήσει τους Φυσικούς Ιατρικής οι οποίοι δεν έχουν εξειδικευτεί στα συστήματα αυτά, να κατανοήσουν τις αρχές της λειτουργίας τους, ιδίως εκείνες που σχετίζονται με τον τρόπο δημιουργίας των διαγνωστικών εικόνων. Στο επόμενο κεφάλαιο, παρουσιάζεται η AAPM report No. 100 (μεταφρασμένη στα Ελληνικά), προκειμένου να θέσει τις βάσεις για την κατανόηση των διαδικασιών που χρησιμοποιούνται για τους ποιοτικούς ελέγχους (QC), αλλά και άλλα θέματα που αφορούν στην ασφάλεια λειτουργίας των συστημάτων MRI. Στο τελευταίο κεφάλαιο, παρουσιάζεται η εφαρμογή αυτών των διαδικασιών σε μια υπάρχουσα εγκατάσταση MRI, ως ένα παράδειγμα του τρόπου με τον οποίο εκτελούνται οι διαδικασίες QC και του τρόπου με τον οποίο οι εικόνες που προκύπτουν αξιολογούνται προκειμένου να εξαχθούν μετρήσιμες ποσότητες. Αυτές οι ποσότητες χρησιμοποιούνται ως δείκτες απόδοσης και ο Φυσικός Ιατρικής συγκρίνοντάς τις με καθορισμένα όρια, μπορεί να διαπιστώσει εάν το ελεγχόμενο σύστημα MRI πληροί τα καθορισμένα κριτήρια (κάτι που υποδηλώνει μια ικανοποιητική λειτουργία και ποιότητα απεικόνισης) ή εάν υπάρχουν ένα ή περισσότερα προβλήματα που οδηγούν σε μη αποδεκτή ποιότητα απεικόνισης και ως εκ τούτου απαιτούνται διορθωτικές ενέργειες. Στην τελευταία περίπτωση, ο έλεγχος που ανέδειξε το πρόβλημα θα πρέπει να επαναλαμβάνεται μετά από την όποια επισκευή, προκειμένου να διαπιστωθεί εάν το σύστημα MRI είναι κατάλληλο να χρησιμοποιηθεί για διάγνωση. / Magnetic Resonance Imaging (MRI) is based on the physical phenomenon of Nuclear Magnetic Resonance (NMR). While this phenomenon has been known since the 1950s, the first MRI scan was performed on a human being just in 1977. The 80’s was the decade that MRI systems started to evolve rapidly and this evolution still goes on. Nowadays, modern MRI systems do so much more than simple imaging, with diffusion MRI, MRI spectroscopy and functional MRI being the new promising applications. MRI scanners do not use ionizing radiation but magnetic fields and electromagnetic waves in the range of radiofrequencies. This is probably the reason why the MRI scanners did not attract so mach attention as CT scanners did, in terms of regulations regarding the safety of their use for patient scanning. However, since imaging is used for diagnosis and a wrong diagnosis can result to a wrong therapy or no therapy at all, which in turn may result to irreversible damage in the patient health or even to death, the American Association of Physicists in Medicine (AAPM) had proposed methods for testing the image quality from the early 1990s , . The American College of Radiology (ACR) has also contributed to this effort in the beginning of the new millennium, proposing image quality control methods to establish an accreditation program for MRI facilities , . In 2010 the AAPM published a report (AAPM REPORT NO. 100) with title “Acceptance Testing and Quality Assurance Procedures for Magnetic Resonance Imaging Facilities”, which describes procedures for testing the performance of MRI scanners, but also procedures concerning other safety issues for the patients and the personnel. In Greece until recently, MRI facilities – in contrast to CT scanners and all the other radiological equipment - were beyond the supervision of the Greek Atomic Energy Commission (Ε.Ε.Α.Ε.) and the Greek Association of Physicist in Medicine (Ε.Φ.Ι.Ε.). However, from the beginning of 2013, E.E.A.E. has proposed an accreditation program (based on the AAPM report No. 100) to be applied in all new MRI facilities. This accreditation program will progressively applied in older MRI facilities as well. The goal is within 5 years at most, all MRI facilities be accredited in the same way that CT scanners are. The purpose of this MSc thesis was to review the basics of MRI theory, to help Medical Physicists which are not experts in MRI, understand the principles of its operation, especially those related to the production of diagnostic images. In the next chapter the AAPM No. 100 report is presented (translated in Greek), in order to set the foundations for understanding the procedures used for quality control (QC) purposes but also other MRI operation safety issues. In the last chapter, an application of these procedures to an existing MRI installation is presented, as an example of the way that QC procedures are performed and the way that the resulting images are evaluated to result to measurable quantities. These quantities are used as performance indices and when compared to established limits, may inform the Medical Physicist whether the tested MRI systems satisfies the established criteria indicating an acceptable performance or whether one or more problems exist that result to suboptimal image quality and therefore corrective actions should be taken. In the latter case the failed test should be repeated after the field service engineers have corrected the problem, in order to ascertain that the MRI system is eligible to be used for medical diagnosis.

Δεδομένης και της χρήσης της τεχνικής SPECT, ο σκοπός της παρούσας διπλωματικής εργασίας είναι η διερεύνηση του κατά πόσο μπορούν, συνδυαστικά, οι 5 αυτές τεχνικές να δείξουν μία πιο σαφή εικόνα στη διαφορική διάγνωση όγκων του ΚΝΣ. Συνδυάζοντας τα δεδομένα που θα ληφθούν από τις μετρήσεις θα δημιουργηθεί μια μικρή βάση δεδομένων η οποία ως απώτερο στόχο θα έχει τη διεύρυνσή της στο μέλλον και συνεπώς την εξαγωγή ασφαλέστερων συμπερασμάτων. / Combination and evaluation of advanced MR techniques (MRS, DWI, DTI, PWI) and Scintigraphy in the differential diagnosis of Central Nervous System tumors.