CT Image Quality Assessment: From Phantom Development to Human Observer Studies

Purpose: To assess the Computed Tomography (CT) image quality by: first, developing custom phantoms with variable, controllable and repeatable texture features for the assessment of high-resolution CT scanners; second, applying the dynamic Fluence Field Modulation (FFM) technique and validating its efficacy by conducting a human observer study. Methods: Procedural routines for texture generation were developed based on constrained sphere packing within specified volumes. Repeatability in phantom production was investigated by printing ensembles phantoms of the same design. They were scanned and registered for assessment of measures across different prints, permitting computation of standard deviation volumes and various radiomic measures to quantify variability. Tissue contrast control was achieved by immersing these phantoms in potassium phosphate solutions with varying concentrations. Dynamic FFM was achieved by combining view-dependent Tube Current Modulation (TCM) and spatially modulating the X-ray beam through the Moiré patterns produced by the relative motion of Multiple Aperture Devices (MADs). Three different FFM imaging protocols were designed, and a 9 Alternative Forced Choice (9AFC) human observer study was to be conducted to evaluate their imaging performances. Results: All texture inserts being developed exhibited great similarity with respect to the corresponding anatomical textures. The textures further depended on the 3D printer nozzle size: smaller nozzle resulted in higher printing quality and precision but with higher variability. Although biased from the ground truth, the low standard deviations of the radiomics and the standard deviation maps indicated high repeatability of the texture features. Results for the assessment of different FFM imaging protocols via the human observer study are ongoing pending Institutional Review Board (IRB) review. Conclusion: The 3D printed texture phantoms offer a highly repeatable and flexible method to probe the ability of high-resolution CT to reproduce textures in reconstructed images. With increasing focus on task-based image quality and radiomics, such custom phantoms have the potential to play an increasing role in imaging performance assessments. The observer study with different FFM strategies helps to evaluate the detectability of certain texture features in CT scans. In summary, both the procedural phantom generation and the human observer study are effective methods for probing CT image quality

Anthropomorphic liver phantom with flow for multimodal image-guided liver therapy research and training

Purpose The objective of this study was to develop a multimodal, permanent liver phantom displaying functional vasculature and common pathologies, for teaching, training and equipment development in laparoscopic ultrasound and navigation. Methods Molten wax was injected simultaneously into the portal and hepatic veins of a human liver. Upon solidification of the wax, the surrounding liver tissue was dissolved, leaving a cast of the vessels. A connection was established between the two vascular trees by manually manipulating the wax. The cast was placed, along with different multimodal tumor models, in a liver shaped mold, which was subsequently filled with a polymer. After curing, the wax was melted and flushed out of the model, thereby establishing a system of interconnected channels, replicating the major vasculature of the original liver. Thus, a liquid can be circulated through the model in a way that closely mimics the natural blood flow. Results Both the tumor models, i.e., the metastatic tumors, hepatocellular carcinoma and benign cyst, and the vessels inside the liver model, were clearly visualized by all the three imaging modalities: CT, MR and ultrasound. Doppler ultrasound images of the vessels proved the blood flow functionality of the phantom. Conclusion By a two-step casting procedure, we produced a multimodal liver phantom, with open vascular channels, and tumor models, that is the next best thing to practicing imaging and guidance procedures in animals or humans. The technique is in principle applicable to any organ of the body.publishedVersio

Development and validation of a hybrid surgical simulator for ultrasound guided laparoscopic common bile duct exploration

This thesis investigates using 3D printing for developing a low-cost, quick, and simple fabrication method for the surgical simulation of the basic skills needed in a laparoscopic common bile duct exploration using ultrasound. This is achieved through a human-centred design methodology where each step of the development is guided by interactions or evaluations with the end users. The specifications are defined by using interviews to understand the needs of surgeons in a simulation practice and to characterise the experience of performing surgery, including the embodied knowledge of surgeons when they manipulate soft tissues. Using an action research methodology combining qualitative and quantitative evaluations in an iterative process, commonly used materials in simulation are thoroughly investigated to identify the most suitable synthetic materials for each type of soft tissue. The synthetic materials identified are silicones because of their tactile properties; moreover, two augmented reality techniques are implemented in addition to the physical model. The first one is style transfer, which aims to improve the appearance of the physical simulator when it is viewed through the laparoscopic camera. The style transfer algorithm used during this research can successfully modify the appearance of the simulator to replicate the diversity of real life. The second technique is marker tracking, which is used to simulate the laparoscopic ultrasound step by overlaying pre-recorded ultrasound images onto the physical model. This technique allows surgeons to practice reading laparoscopic ultrasound images and identifying key anatomical features during the surgery. Through consultations with the surgeons, the outcomes of this research are evaluated using face, content, and construct validations. Throughout this thesis, the research methods and results are explained and discussed to provide a basis for further research. These findings can be used as a framework for future development of surgical simulators