Purpose:To develop an easily-implemented technique with free publicly-available analysis software to measure the modulation transfer function (MTF) and noise-power spectrum (NPS) of a clinical computed tomography (CT) system from images acquired using a widely-available and standardized American College of Radiology (ACR) CT accreditation phantom. Methods: Images of the ACR phantom were acquired on a Siemens SOMATOM Definition Flash system using a standard adult head protocol: 120 kVp, 300 mAs, and reconstructed voxel size of 0.49 mm × 0.49 mm × 4.67 mm. The radial (axial) MTF was measured using an edge method where the boundary of the third module of the ACR phantom, originally designed to measure uniformity and noise, was used as a circular edge. The 3D NPS was measured using images from this same module and using a previously-described methodology that quantifies noise magnitude and 3D noise correlation. Results: The axial MTF was radially symmetrical and had a value of 0.1 at 0.62 mm −1 . The 3D NPS shape was consistent with the filter-ramp function of filtered-backprojection reconstruction algorithms and previously reported values. The radial NPS peak value was ∼115 HU 2 mm 3 at ∼0.25 mm −1 and dropped to 0 HU 2 mm 3 by 0.8 mm −1 . Conclusions:The authors have developed an easily-implementable technique to measure the axial MTF and 3D NPS of clinical CT systems using an ACR phantom. The widespread availability of the phantom along with the free software the authors have provided will enable many different institutions to immediately measure MTF and NPS values for comparison of protocols and systems.

The drag force on thoracic stent grafts is high. A significant change in stent-graft diameter occurs after endovascular repair for type B dissections, which is associated with an increase in hemodynamic drag force. These stent grafts may be subjected to a higher risk of distal migration, and continuing surveillance is mandatory.

This paper presents a visual-based dimension estimation method for vehicle type classification. Our method extracts moving vehicles from traffic image sequences and fits them with a simple deformable vehicle model. Using a set of coordination mapping functions derived from a calibrated camera model and relying on a shadow removal method, vehicle's width, length and height are estimated. Our experimental tests show that the modeling method is effective and the estimation accuracy is sufficient for general vehicle type classification.

Endovascular aortic stent-graft is a new, minimally invasive procedure for treating thoracic aortic diseases, and has quickly evolved to be one of the standard treatments subject to anatomic constraints. This procedure involves the placement of a self-expanding stent-graft system in a high-flow thoracic aorta. Stent-graft deployment in the thoracic aorta, especially close to the aortic arch, normally experiences a significant drag force which might lead to the risk of stent-graft failure. A comprehensive investigation on the biomechanical factors affecting the drag force on a stent-graft in the thoracic aorta is thus in order, and the goal is to perform an in-depth study on the contributing biomechanical factors. Three factors affecting the deployed stent-graft are considered, namely, the internal diameter of the vessel, the starting position of the graft and the diameter of curvature of the aortic arch. Computational fluid dynamic techniques are applied to model the blood flow. The inlet velocity and outlet pressure are assumed to be pulsatile. The three-dimensional continuity equation and the time-dependent Navier-Stokes equations for an incompressible fluid were solved numerically. The drag force due to the change of momentum within the stent-graft and the shear stress were calculated and analyzed. The drag force on a stent-graft will depend critically on the internal diameter and the starting position of stent-graft deployment. Larger internal diameter leads to larger drag force and the stent-graft deployed at the more distal position may be associated with significantly diminished drag force. Smaller diameter of curvature of the aortic arch probably results in a decline of the drag force on the stent-graft, even though this factor merely causes only a modest difference. These findings may have important implications for the choice and design of stent-grafts in the future.

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