RESUMEN
We provide a dedicated phase-correlated imaging procedure for respiratory gating in micro-CT imaging with automatic detection of the optimal data window providing the least amount of motion blurring. A rawdata-based motion function (kymogram) was used for synchronization purposes and for identification of the optimal data window used for phase-correlated image reconstruction. Measurements were performed on a dual-source micro-CT scanner. Projection data were acquired over ten rotations for multi-segment phase-correlated reconstruction. Visual assessment was performed on datasets of ten free-breathing subjects. The kymogram approach provided a reliable synchronization signal for phase-correlated image reconstruction. Also, it allowed for the identification of phase intervals of increased and decreased motion and the corresponding detection of the optimal reconstruction phase. Phase-correlated images showed a strong improvement with respect to motion blurring compared to standard image reconstruction. A reconstruction for the calculated optimal data window provided the least amount of motion blurring and even allowed for the assessment of small structures in the lung. The dedicated retrospective phase-correlated image reconstruction procedure for respiratory gating is a feasible approach for motion-free imaging. A subject-specific optimal reconstruction phase can minimize motion blurring and further improve image quality.
Asunto(s)
Artefactos , Aumento de la Imagen/métodos , Reconocimiento de Normas Patrones Automatizadas/métodos , Mecánica Respiratoria , Técnicas de Imagen Sincronizada Respiratorias/métodos , Tomografía Computarizada por Rayos X/métodos , Tomografía Computarizada por Rayos X/veterinaria , Algoritmos , Animales , Interpretación de Imagen Asistida por Computador/métodos , Masculino , Ratones , Ratones Endogámicos C57BL , Miniaturización , Reproducibilidad de los Resultados , Sensibilidad y EspecificidadRESUMEN
Image quality in pulmonary CT imaging is commonly degraded by cardiac motion artifacts. Phase-correlated image reconstruction algorithms known from cardiac imaging can reduce motion artifacts but increase image noise and conventionally require a concurrently acquired ECG signal for synchronization. Techniques are presented to overcome these limitations. Based on standard and phase-correlated images that are reconstructed using a raw data-derived synchronization signal, image-merging and temporal-filtering techniques are proposed that combine the input images automatically or interactively. The performance of the approaches is evaluated in patient and phantom datasets. In the automatic approach, areas of strong motion and static areas were well detected, providing an optimal combination of standard and phase-correlated images with no visible border between the merged regions. Image noise in the non-moving regions was reduced to the noise level of the standard reconstruction. The application of the interactive filtering allowed for an optimal adaptation of image noise and motion artifacts. Noise content after interactive filtering decreased with increasing temporal filter width used. We conclude that a combination of our motion-free merging approach and a dedicated interactive filtering procedure can highly improve pulmonary imaging with respect to motion artifacts and image noise.
Asunto(s)
Corazón/diagnóstico por imagen , Procesamiento de Imagen Asistido por Computador/métodos , Pulmón/diagnóstico por imagen , Algoritmos , Artefactos , Diagnóstico por Imagen/métodos , Electrocardiografía/métodos , Humanos , Modelos Estadísticos , Movimiento (Física) , Reconocimiento de Normas Patrones Automatizadas/métodos , Fantasmas de Imagen , Radiografía , Factores de TiempoRESUMEN
An individual balancing between spatial resolution and image noise is necessary to fulfil the diagnostic requirements in medical CT imaging. In order to change influencing parameters, such as reconstruction kernel or effective slice thickness, additional raw-data-dependent image reconstructions have to be performed. Therefore, the noise versus resolution trade-off is time consuming and not interactively applicable. Furthermore, isotropic resolution, expressed by an equivalent point spread function (PSF) in every spatial direction, is important for the undistorted visualization and quantitative evaluation of small structures independent of the viewing plane. Theoretically, isotropic resolution can be obtained by matching the in-plane and through-plane resolution with the aforementioned parameters. Practically, however, the user is not assisted in doing so by current reconstruction systems and therefore isotropic resolution is not commonly achieved, in particular not at the desired resolution level. In this paper, an integrated approach is presented for equalizing the in-plane and through-plane spatial resolution by image filtering. The required filter kernels are calculated from previously measured PSFs in x/y- and z-direction. The concepts derived are combined with a variable resolution filtering technique. Both approaches are independent of CT raw data and operate only on reconstructed images which allows for their application in real time. Thereby, the aim of interactively variable, isotropic resolution is achieved. Results were evaluated quantitatively by measuring PSFs and image noise, and qualitatively by comparing the images to direct reconstructions regarded as the gold standard. Filtered images matched direct reconstructions with arbitrary reconstruction kernels with standard deviations in difference images of typically between 1 and 17 HU. Isotropic resolution was achieved within 5% of the selected resolution level. Processing times of 20-100 ms per frame allow for interactive use.
Asunto(s)
Procesamiento de Imagen Asistido por Computador/métodos , Tomografía Computarizada por Rayos X/métodos , Estándares de ReferenciaRESUMEN
In order to achieve diagnostically useful CT (computed tomography) images of the moving heart, the standard image reconstruction has to be modified to a phase-correlated reconstruction, which considers the motion phase of the heart and generates a quasi-static image in one defined motion phase. For that purpose a synchronization signal is needed, typically a concurrent ECG recording. Commonly, the reconstruction phase is adapted by the user to the patient-specific heart motion to improve the image quality and thus the diagnostic value. The purpose of our work is to automatically identify the optimal reconstruction phase for cardiac CT imaging with respect to motion artifacts. We provide a solution for a patient- and heart rate-independent detection of the optimal phase in the cardiac cycle which shows a minimum of cardiac movement. We validated our method by the correlation with the reconstruction phase selected visually on the basis of ECG-triggering and used for the medical diagnosis. The mean difference between both reconstruction phases was 12.5% with respect to a whole cardiac motion cycle indicating a high correlation. Additionally, reconstructed cardiac images are shown which confirm the results expressed by the correlation measurement and in some cases even indicating an improvement using the proposed method.