Medical Imaging : X-ray


Frame-by-Frame 3-D Reconstruction of Dynamic Catheter Device

UW–Madison researchers have developed a method to obtain frame-by-frame 3-D representations of a TAVR valve or other interventional device in a patient using bi-plane X-ray imaging.

Specifically, they developed a new pose estimation technique to compare measured X-ray images to forward projections of a dynamic 3-D model, which can assume different states of expansion and deformation. The model is defined by a limited set of parameters (ex., in the case of an expanding TAVR valve these include pitch, yaw, roll, proximal and distal diameter of the device) as well as a priori knowledge such as predictable changes in shape.

Other technologies have been developed based on a similar concept, but they assume a rigid, static object with a shape that has been fully characterized prior to X-ray imaging.

Angiography Technique Integrates Blood Flow Information

The researchers have now developed a method for integrating flow information with 4-D DSA images. The method involves generating a series of 3-D time-resolved vascular volumes and calculating blood velocity by tracking a contrast agent.

Time-Resolved 3-D Angiography Captures Blood Flow, Vessel Dynamics

UW–Madison researchers have developed a system and method for integrating 4-D DSA with physiological information (blood flow, velocity) derived via MRI or ultrasound. More specifically, the image processing system receives angiographic data and flow data to generate a combined data set. The resulting images display time-resolved, color-coded flow information.

The new process can be referred to as 7-D DSA.

X-Ray Phase Contrast Imaging Using Standard Equipment

A UW–Madison researcher has developed a method for generating X-ray phase contrast images from conventional X-ray attenuation data.

First, calibration factors are obtained using a phantom. The patient or object then is X-rayed to acquire attenuation data at two different energy levels. Images are reconstructed at the different energy levels to produce spatial maps. Based on the calibration factors and spatial maps, a phase contrast image can be produced.

Statistical Noise Map for Reducing X-Ray Exposure

UW–Madison researchers have developed a system and method for estimating a statistical noise map from a single X-ray exposure. This map accounts for noise acquired with X-ray imaging systems, including computed tomography (CT), tomosynthesis and C-arm systems.

The method reconstructs an image from acquired data using any standard filtered back projection (FBP) algorithm. This image is used as a baseline to estimate a noise standard distribution map. The raw projection data represents a typical measurement among many repeated measurements under the same experimental conditions. Therefore, this data can be used to generate several (e.g., 20 or more) noisy data sets.

These data sets are used to reconstruct noisy images that can be subtracted from the original image, resulting in a statistical noise map. This map accounts for a physical model of noise.

Range Adjusted Dynamic Image Construction Algorithm (RADICAL) Method to Suppress Artifacts in X-Ray Imaging

A UW–Madison researcher has developed a method for substantially suppressing streak artifacts in images produced with an X-ray imaging system without significant loss of information. The Range Adjusted Dynamic Image Construction Algorithm (RADICAL) approach reconstructs an image by weighting the coefficient values of highly attenuating regions so that values above a user specified threshold contribute less to a given location in the image than those below the threshold. This method removes much of the metal artifacts on CT imaging, resulting in a more accurate reconstructed image. In addition, it may limit other inconsistent data artifacts.

Improved Highly Constrained Image Reconstruction (HYPR) Method

UW-Madison researchers have developed an improvement to the HYPR process in which a higher quality composite image may be produced when subject motion is present during the scan. The composite image is produced by accumulating data from a series of acquired image frames, and the number of image frames used is determined by the amount and nature of subject motion. Subject motion is determined on a pixel-by-pixel basis, and the integration of each pixel with the composite image is based on the detected motion. This adaptation allows the best image possible to be produced when the subject moves during the scan.

The method can be applied to digital subtraction angiography (DSA) and X-ray fluoroscopy by acquiring a series of image frames as a contrast agent flows into the area being imaged. The improved HYPR method then is used to form the composite image on a region-by-region basis.

Ultra Low Radiation Dose Computed Tomography Scanner for X-ray Mammography

A UW–Madison researcher has developed a line scan X-ray cone beam CT scanner system and method with an ultra low radiation dose to provide high in-plane spatial resolution and excellent low contrast resolution. The system is made up of an x-ray cone beam source and a 2-D X-ray detector array. Both move linearly on opposing sides of the breast in opposite directions to capture data from various angles. They do not move in a circular pattern around the breast.

An image is reconstructed with the data from a limited amount of angles, which results in a significantly lower X-ray dose to the patient. The cone beam data is converted into a parallel beam projection data set to create an image using a novel image reconstruction method. This method determines the image quality by using a determined metric to measure it against with the image quality continually increased until a preset quality is met. The limited number of angles required for this method leads to an approximate 20- fold reduction in radiation dose.

Improved Portal Imaging During Radiation Therapy Using a Modulated Treatment Beam

High-energy treatment beams always include lower energy components, however, and a UW-Madison researcher has now devised a way to modulate the beam, without affecting patient treatment, so that only low-energy X-rays contribute to portal images. The device, which includes multiple filters and bandwidth-narrowed detection, can create quality images at a rate of approximately 10 per second. The filters modulate the low-energy X-rays already present in the treatment beam. The detector then screens out all un-modulated, high-energy beam components to create clear, quality images strictly from low-energy, non-interacting X-rays.

X-Ray System for Use in Image-Guided Procedures

UW-Madison researchers have developed an x-ray imaging system that provides angiograms depicting a subject’s vasculature along with parametric images that indicate perfusion of tissues. The system consists of a moveable x-ray source and an opposed, two-dimensional detector. It moves in a first scan path to acquire data from which a three-dimensional digital subtraction angiogram of the subject’s vasculature is reconstructed. During the inflow of a contrast agent into the vasculature, the x-ray system moves in a second scan path to acquire images that indicate blood perfusion in the subject’s tissue.