Winkel-sensitive MRT zur nichtinvasiven Analyse belasteter Knorpelstruktur

Die Arthrose wird durch degenerative Veränderungen des Gelenkknorpels verursacht. Dabei sind die arthrotischen Veränderungen in späten Krankheitsstadien fast immer irreversibel. Nur gezielte therapeutische Maßnahmen gegen früh festgestellte Arthrose können diese progressive pathologische Entwicklung aufhalten.Gegenwärtig existieren jedoch keine etablierten nichtinvasiven Methoden zur frühen Arthrosediagnostik im Gelenkknorpel. Die konventionelle klinische Magnetresonanztomographie (MRT) kann weiches Gewebe nichtinvasiv darstellen, ist aufgrund der technischen Grenzen jedoch kaum zum Nachweis früharthrotischer Veränderungen geeignet.Eine erweiterte Methode – winkel-sensitive MRT (WS-MRT) – basiert auf der Orientierungsabhängigkeit der T2-Relaxation bei der MR-Bildgebung und bietet die Möglichkeit mit Hilfe eines analytischen Models Informationen über die Kollagenmatrixstruktur des Gelenkknorpels zu erhalten.Da die Arthrose die organisierte Ultrastruktur des Gelenkknorpels beeinflusst, verändern sich unter stetiger physiologischer Belastung auch seine biomechanischen Eigenschaften sowie das Deformationsverhalten der Kollagenmatrix. Erkennt man diese kaum wahrnehmbaren Veränderungen, könnten die frühen Arthrosestadien so detektiert werden.Aus diesem Grund basieren die Untersuchungen zur druckbedingten Deformation der Knorpelstruktur in dieser Arbeit auf der WS-MRT. Dafür wurden unbehandelte Knorpelproben aus Schafsknien entnommen und im hochauflösenden 7T MRT unter Druckbelastung untersucht. In den Versuchen wurde eine Verfahrensmodifizierung vorgenommen, welche sich durch Druckverteilung auf der gesamten Probenoberfläche mit Hilfe schnell härtenden Acryl-Harzes kennzeichnete. Dadurch konnten nicht nur elastomechanischen Eigenschaften des Gewebes gewonnen, sondern auch die druckbedingte Neigung von Kollagenfasern quantitativ erfasst werden. Diese Daten dienten der detaillierten Beobachtung der Matrixdeformation, einschließlich des Phänomens der Wellenbildung in der Faserform unter Druckbelastung.Die gewonnenen Erkenntnisse wurden zur WS-MRT-Analyse der Signalintensität herangezogen mit dem Ziel, die Möglichkeiten dieses Verfahrens für die klinische Praxis zu evaluieren. Diese Analyse ergab eine gute Übereinstimmung der modellierten Intensitäten mit den experimentell abgelesenen Daten. Das Resultat bietet gute Zukunftsaussichten ein inverses Problem zu lösen: Die druckbedingte Matrixdeformation könnte allein durch die Betrachtung der Signalintensität bei einem MRT-Belastungstest aufgeklärt werden. Dies erfordert jedoch weiterführende Studien, insbesondere grundlegende Untersuchungen am nativen und belasteten Knorpel in vivo

Targeting accuracy, procedure times and user experience of 240 experimental MRI biopsies guided by a clinical add-on navigation system: Targeting accuracy, procedure times and user experience of 240 experimental MRI biopsies guided by a clinical add-onnavigation system

Objectives: MRI is of great clinical utility for the guidance of special diagnostic and therapeutic interventions. The majority of such procedures are performed iteratively (\"in-and-out\") in standard, closed-bore MRI systems with control imaging inside the bore and needle adjustments outside the bore. The fundamental limitations of such an approach have led to the development of various assistance techniques, from simple guidance tools to advanced navigation systems. The purpose of this work was to thoroughly assess the targeting accuracy, workflow and usability of a clinical add-on navigation solution on 240 simulated biopsies by different medical operators. Methods: Navigation relied on a virtual 3D MRI scene with real-time overlay of the optically tracked biopsy needle. Smart reference markers on a freely adjustable arm ensured proper registration. Twenty-four operators – attending (AR) and resident radiologists (RR) as well as medical students (MS) – performed well-controlled biopsies of 10 embedded model targets (mean diameter: 8.5 mm, insertion depths: 17-76 mm). Targeting accuracy, procedure times and 13 Likert scores on system performance were determined (strong agreement: 5.0). Results: Differences in diagnostic success rates (AR: 93%, RR: 88%, MS: 81%) were not significant. In contrast, between-group differences in biopsy times (AR: 4:15, RR: 4:40, MS: 5:06 min: sec) differed significantly (p<0.01). Mean overall rating was 4.2. The average operator would use the system again (4.8) and stated that the outcome justifies the extra effort (4.4). Lowest agreement was reported for the robustness against external perturbations (2.8). Conclusions: The described combination of optical tracking technology with an automatic MRI registration appears to be sufficiently accurate for instrument guidance in a standard (closed-bore) MRI environment. High targeting accuracy and usability was demonstrated on a relatively large number of procedures and operators. Between groups with different expertise there were significant differences in experimental procedure times but not in the number of successful biopsies

MRI assessment of changes in adipose tissue parameters after bariatric surgery

Bariatric surgery and other therapeutic options for obese patients are often evaluated by the loss of weight, reduction of comorbidities or improved quality of life. However, little is currently known about potential therapy-related changes in the adipose tissue of obese patients. The aim of this study was therefore to quantify fat fraction (FF) and T1 relaxation time by magnetic resonance imaging (MRI) after Roux-en-Y gastric bypass surgery and compare the resulting values with the preoperative ones. Corresponding MRI data were available from 23 patients (16 females and 7 males) that had undergone MRI before (M0) and one month after (M1) bariatric surgery. Patients were 22-59 years old (mean age 44.3 years) and their BMI ranged from 35.7-54.6 kg/m(2) (mean BMI 44.6 kg/m(2)) at M0. Total visceral AT volumes (VVAT-T, in L) were measured by semi-automatic segmentation of axial MRI images acquired between diaphragm and femoral heads. MRI FF and T1 relaxation times were measured in well-defined regions of visceral (VAT) and subcutaneous (SAT) adipose tissue using two custom-made analysis tools. Average BMI values were 45.4 kg/m(2) at time point M0 and 42.4 kg/m(2) at M1. Corresponding VVAT-T values were 5.94 L and 5.33 L. Intraindividual differences in both BMI and VVAT-T were highly significant (p<0.001). Average relaxation times T1 VAT were 303.7 ms at M0 and 316.9 ms at M1 (p<0.001). Corresponding T1(SAT) times were 283.2 ms and 280.7 ms (p = 0.137). Similarly, FFVAT differences (M0: 85.7%, M1: 83.4%) were significant (p <0.01) whereas FFSAT differences (M0: 86.1, M1: 85.9%) were not significant (p = 0.517). In conclusion, bariatric surgery is apparently not only related to a significant reduction in common parameters of adipose tissue distribution, here BMI and total visceral fat volume, but also significant changes in T1 relaxation time and fat fraction of visceral adipose tissue. Such quantitative MRI measures may potentially serve as independent biomarkers for longitudinal and cross-sectional measurements in obese patients

Age and gender specific estimation of visceral adipose tissue amounts from radiological images in morbidly obese patients OPEN

Best predictions were found at intervertebral spaces L3-L4 for females (σ 5 = 688 ml, σ 1 = 832 ml) and L1-L2 for males (σ 5 = 846 ml, σ 1 = 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. Obesity is a worldwide increasing healthcare problem. In the United States, for example, over two thirds of the adult population are either overweight (33%, BMI: 25-30 kg/m 2 ), obese (35%, 30-40 kg/m 2 ) or morbidly obese (6%, &gt; 40 kg/m 2 ) 1 . While prevalence of obesity is still rising, in particular the morbid form 2 , more and more is known about its association with an increased overall mortality, often caused by cardiovascular diseases, diabetes or hypertension Quantification of abdominal VAT volumes by cross-sectional imaging, typically by computed tomography (CT) or magnetic resonance imaging (MRI), however, is generally time-consuming 7-9 . Various methods have already been proposed to estimate total VAT volumes from simple measurements on a limited number of slices. Studies using single or five slice VAT areas for VAT volume prediction have mainly focused on patients with BMI values below 40 kg/m 2 and data for the morbidly obese are lackin

Estimating steatosis and fibrosis: comparison of acoustic structure quantification with established techniques

To compare ultrasound-based acoustic structure quantification (ASQ) with established non-invasive techniques for grading and staging fatty liver disease

Estimating steatosis and fibrosis: comparison of acoustic structure quantification with established techniques

To compare ultrasound-based acoustic structure quantification (ASQ) with established non-invasive techniques for grading and staging fatty liver disease

Comparison of Two Mathematical Models of Cellularity Calculation

OBJECT: Nowadays, there is increasing evidence that functional magnetic resonance imaging (MRI) modalities, namely, diffusion-weighted imaging (DWI) and dynamic-contrast enhanced MRI (DCE MRI), can characterize tumor architecture like cellularity and vascularity. Previously, two formulas based on a logistic tumor growth model were proposed to predict tumor cellularity with DWI and DCE. The purpose of this study was to proof these formulas. METHODS: 16 patients with head and neck squamous cell carcinomas were included into the study. There were 2 women and 14 men with a mean age of 57.0 ± 7.5 years. In every case, tumor cellularity was calculated using the proposed formulas by Atuegwu et al. In every case, also tumor cell count was estimated on histopathological specimens as an average cell count per 2 to 5 high-power fields. RESULTS: There was no significant correlation between the calculated cellularity and histopathologically estimated cell count by using the formula based on apparent diffusion coefficient (ADC) values. A moderate positive correlation (r=0.515, P=.041) could be identified by using the formula including ADC and Ve values. CONCLUSIONS: The formula including ADC and Ve values is more sensitive to predict tumor cellularity than the formula including ADC values only

Mean Likert item scores on usability and workflow of navigation tool by 24 operators from three groups.

<p>* AR: attending radiologists, RR: resident radiologists, and MS: medical students</p><p>^† opposite item with reverse score, original item was negatively keyed</p><p>Mean Likert item scores on usability and workflow of navigation tool by 24 operators from three groups.</p

Mean Likert item scores on usability and workflow of navigation tool by 24 operators from three groups.

<p>* AR: attending radiologists, RR: resident radiologists, and MS: medical students</p><p>^† opposite item with reverse score, original item was negatively keyed</p><p>Mean Likert item scores on usability and workflow of navigation tool by 24 operators from three groups.</p