Estación de trabajo para registro 3D y fusión de imágenes para la planificación de radioterapia

Este trabajo presenta una estación de trabajo para registro tridimensional y fusión de imágenes orientada a la ayuda en la planificación y monitorización de terapias de radiación externa. El concepto de radioterapia adaptativa propone la realización de una planificación del tratamiento en cada una de las sesiones a las que acude el paciente, lo que supondría un decremento importante en la radiación que afecta a los tejidos sanos circundantes al tumor y por tanto, una mejora significativa en la evolución de estos pacientes. Para reducir el tiempo que conlleva la delineación manual de los volúmenes de interés en la realización de una nueva planificación en cada sesión, la herramienta en la que se debe basar la radioterapia adaptativa es el registro tridimensional deformable de estudios CT para radioterapia. El prototipo que se presenta en este artículo permite el registro de imágenes DICOM mediante algoritmos no rígidos, su visualización, la comparación cualitativa de los resultados mediante fusión de imágenes, selección de regiones de interés en las imágenes y el almacenamiento de resultados en formato DICOM, visualizables por cualquier otro lector. El empleo de esta estación de trabajo, en combinación con algoritmos de reconstrucción tridimensional y segmentación automática desarrollados dentro del grupo, supone una gran ayuda en los procesos previos de la planificación radioterápica

An open environment CT-US fusion for tissue segmentation during interventional guidance.

Therapeutic ultrasound (US) can be noninvasively focused to activate drugs, ablate tumors and deliver drugs beyond the blood brain barrier. However, well-controlled guidance of US therapy requires fusion with a navigational modality, such as magnetic resonance imaging (MRI) or X-ray computed tomography (CT). Here, we developed and validated tissue characterization using a fusion between US and CT. The performance of the CT/US fusion was quantified by the calibration error, target registration error and fiducial registration error. Met-1 tumors in the fat pads of 12 female FVB mice provided a model of developing breast cancer with which to evaluate CT-based tissue segmentation. Hounsfield units (HU) within the tumor and surrounding fat pad were quantified, validated with histology and segmented for parametric analysis (fat: -300 to 0 HU, protein-rich: 1 to 300 HU, and bone: HU>300). Our open source CT/US fusion system differentiated soft tissue, bone and fat with a spatial accuracy of ∼1 mm. Region of interest (ROI) analysis of the tumor and surrounding fat pad using a 1 mm(2) ROI resulted in mean HU of 68±44 within the tumor and -97±52 within the fat pad adjacent to the tumor (p<0.005). The tumor area measured by CT and histology was correlated (r(2) = 0.92), while the area designated as fat decreased with increasing tumor size (r(2) = 0.51). Analysis of CT and histology images of the tumor and surrounding fat pad revealed an average percentage of fat of 65.3% vs. 75.2%, 36.5% vs. 48.4%, and 31.6% vs. 38.5% for tumors <75 mm(3), 75-150 mm(3) and >150 mm(3), respectively. Further, CT mapped bone-soft tissue interfaces near the acoustic beam during real-time imaging. Combined CT/US is a feasible method for guiding interventions by tracking the acoustic focus within a pre-acquired CT image volume and characterizing tissues proximal to and surrounding the acoustic focus

Group-Slicer: A collaborative extension of 3D-Slicer

AbstractIn this paper, we describe a first step towards a collaborative extension of the well-known 3D-Slicer; this platform is nowadays used as a standalone tool for both surgical planning and medical intervention. We show how this tool can be easily modified to make it collaborative so that it may constitute an integrated environment for expertise exchange as well as a useful tool for academic purposes

A finite element evaluation of the talocrural join and the effects of ligament injury on joint mechanics

Several cadaveric and in vivo biomechanical studies have looked at the effects that ligament injuries of the ankle joint complex have on the stability of the ankle joint and susceptibility to chronic degeneration of articular surfaces, but the re have been very few studies that use computer simulation and the finite element method to evaluate how a n ankle ligament injury affects stability, joint pressure, and potential subsequent failure points. Evidence shows that ankle instability is associated with excessive rotation of the talus in transverse plane, which contributes to articular surface degeneration. It has been documented that after disruption of the anterior talofibular ligament that additional load is placed on the posterior tibiotalar ligament, which leads to further rotational instability. Disruption of the interosseous talocalcaneal ligament creates a more complex instability that leads to chronic joint instability of both the talocrural and subtalar joints. A 3D model of the ankle joint was created using CT image data of a cadaver lower limb. A tetrahedral mesh was created and the bone modulus was assume d uniform. Tendons were represented by simple truss elements and surface to surface contact regions were established to facilitate joint motion. The tibia was fixed and internal rotation in the transverse plane was applied to the foot in the neutral position by means of a 5000 N-mm moment. Force displacement data was compared to experimental data collected using an MTS test frame on a cadaver specimen, and previously published data from an arthrometer study. The anterior talofibular ligament (ATFL) was then removed and compared to MTS and arthrometer load and displacement data. Joint pressures were calculated from the finite element model to evaluate potential lesion spots as well as ligament forces in the deep posterior tibiotalar ligament (DPTTL). Results show a correlation in the change in magnitude from intact to ATFL cut states in the FEA model to the in vitro testing methods. The model predicts a medial shift in contact pressures under internal rotation which has been shown to be a potential location for lesions in ankles with lateral instability. The model also predicts that the DPTTL carries a majority of the resistant forces in the ligaments in internal rotation when the ATFL has been compromised

Understanding mechanisms of stem cell tubulogenesis in PEGylated fibrin for improving neovascularization therapies

textStem cell-based therapies are an important developing technology for treating cardiovascular ischemic disease, including subsequent co-morbidities such as ulcerative wounds. Mesenchymal stem cells (MSCs) have a proven ability to augment wound healing and neovascularization processes and have been more recently investigated for their endothelial-like behavior. This doctoral work aims to understand mechanisms underlying matrix-driven MSC tubulogenesis within PEGylated fibrin gels, specifically (1) why this behavior occurs and (2) if this behavior has clinical utility. Briefly, a three-dimensional morphological quantification pipeline was first developed for analyzing the maturity of vascular networks (Chapter 2). This method was applied in later studies that examined the full spectrum of MSC behavior in PEGylated fibrin gels, linking biomaterial properties with network development (Chapter 3). Mechanisms underlying the cell-matrix relationship were more fully clarified through gain-of-function cell studies. These studies indicated that PEGylated fibrin promotes endothelial-like MSC behavior through a combination of hypoxic stress and bioactive fibrin cues (Chapter 4). Notably, this endothelial-like MSC behavior closely mirrored vasculogenic mimicry, a process whereby tumors establish non-endothelialized vasculature in response to hypoxic stress. The functionality of these tumor vessels suggests that mature endothelial differentiation of MSCs may not be necessary to achieve therapeutically beneficial tissue perfusion. This hypothesis opens up new mechanisms for exploitation in vascular tissue engineering strategies.Biomedical Engineerin

Computed tomography based talocrural joint motion capture for patient-specific external fixator design

Pilon-murtumat ovat vaikeita, välitöntä ortopedistä hoitoa vaativia nilkan traumoja. Trauman jälkeen nilkka on tuettava, mutta ravintoaineiden ja veren virtauksen parantamiseksi nilkan olisi suotavaa saada liikkua kontrolloidusti, esimerkiksi yhden akselin ympäri. Tätä varten on kehitetty kääntyviä, ulkoisia nilkkatukia. Ainetta lisäävän valmistuksen keinoin on mahdollista luoda jokaiselle potilaalle yksilöllinen tuki, joka seuraa potilaan nilkan luonnollista liikerataa. Tätä varten on selvitettävä potilaan ylemmän nilkkanivelen kääntöakselin paikka sekä suunta eri vaiheissa nilkan koukistusta ja ojennusta. Tässä diplomityössä suunniteltiin ja toteutettiin tietokonetomografiaan perustuva mittausmenetelmä. Koehenkilöitä oli kaksi: ensimmäisen nilkka kuvattiin kartiokeila-TT-laitteella kolmessa asennossa (äärikoukistus, neutraali, ääriojennus), ja toisen viidessä (edellä mainitut asennot, sekä puolittainen koukistus ja puolittainen ojennus). Tämän jälkeen kuvista segmentoitiin sääriluu sekä telaluu. Kahden peräkkäisen asennon (ääriojennus-puolittainen ojennus, puolittainen ojennus-neutraali, jne.) luut kohdennettiin toistensa suhteen. Nämä kohdennukset tuottivat kaksi muunnosmatriisia, joiden avulla laskettiin liikkeen kunkin vaiheen kääntöakselin (finite helical axis, FHA) paikka sekä suunta. Menetelmä tuotti järkeviä tuloksia, joten lisäkehitystä suositellaan. Tekniikan oikea tarkkuus on selvitettävä esimerkiksi toistokokein, mutta näitä rajoittaa tietokonetomografiakuvaukseen liittyvä säderasitus.Pilon fracture is a severe ankle trauma, which demands instant orthopedic treatment. After the trauma, the ankle needs to be shielded from load, but to maximize the flows of blood and nutrients, ankle should also be allowed to move in a controlled fashion, e.g. around one axis. External, rotating fixators exist for this purpose. Utilizing additive manufacturing techniques, a patient-specific fixator can be designed. It aims to mimic the natural range of motion, and thus minimize the motion resistance. Prior to the fixator fabrication, the location and orientation of the talocrural joint axis in different phases of the motion needs to be determined. In this thesis, a computed tomography based measurement method was developed and piloted. Two subjects were scanned with a cone-beam CT device: the first subject in three stances (full dorsiflexion, neutral, full plantarflexion), and the second one in five stances (aforementioned three, and in addition, half plantarflexion and half dorsiflexion). After this, the tibia and talus bones were segmented. The corresponding bones in two consecutive poses (full dorsiflexion-half dorsiflexion, half dorsiflexion-neutral, etc.) were registered in respect to each other. These registrations produced two transform matrices, which were used to calculate the finite helical axis (location and orientation) of each phase of the motion. The technique yielded sensible results, thus further development is recommended. The actual accuracy remains unknown, and needs to be determined e.g. by larger patient pool. This is complicated by the radiation burden involved with CT imaging

Segmentation of the Cerebrospinal Fluid from MRI Images for the Treatment of Disc Herniations

About 80 percent of people are affected at some point in their lives by lower back pain, which is one of the most common neurological diseases and reasons for long-term disability in the United States. The symptoms are primarily caused by overly heavy lifting and/or overstretching of the back, leading to a rupture and an outward bulge of an intervertebral disc, which puts pressure on and pinches the nerve fibers of the spine. The most common form is a lumbar disc herniation between the fourth and fifth lumbar vertebra and between the fifth lumbar vertebra and the sacrum. In recent years the diagnosis of lower back pain has improved, mainly due to enhanced imaging techniques and imaging quality, but the surgical therapy remains hazardous. Reasons for this include low visibility when accessing the lumbar area and the high risk of causing permanent damage when touching the nerve fibers. A new approach for increasing patient safety is the segmentation and visualization of the cerebrospinal fluid in the lower lumbar region of the vertebral column. For this purpose a new fully-automatic and a semi-automatic approach were developed for separating the cerebrospinal fluid from its surroundings on T2-weighted MRI scans of the lumbar vertebra. While the fully-automatic algorithm is realized by a model-based searching method and a volume-based segmentation, the semi-automatic algorithm requires a seed point and performs the segmentation on individual axial planes through a combination of a region-based segmentation algorithm and a thresholding filter. Both algorithms have been applied to four T2-weighted MRI datasets and are compared with a gold-standard segmentation. The segmentation overlap with the gold-standard was 78.7 percent for the fully-automatic algorithm and 93.1 percent for the semi-automatic algorithm. In the pathological region the fully-automatic algorithm obtained a similarity of 56.6 percent, compared to 87.8 percent for the semi-automatic algorithm