Spatial Resolution Of Computed Tomography Research Articles

A Subband-Specific Deconvolution Model for MTF Improvement in CT.

The purpose of this research is to achieve uniform spatial resolution in CT (computed tomography) images without hardware modification. The main idea of this study is to consider geometry optics model, which can provide the approximate blurring PSF (point spread function) kernel, which varies according to the distance from X-ray tube to each pixel. The FOV (field of view) was divided into several band regions based on the distance from X-ray source, and each region was deconvolved with different deconvolution kernels. Though more precise calculation for the PSF for deconvolution is possible as the number of subbands increases, we set the number of subbands to 11. 11 subband settings seem to be a balancing point to reduce noise boost, while MTF (modulation transfer function) increase still remains. As the results show, subband-wise deconvolution makes image resolution (in terms of MTF) relatively uniform across the FOV. The results show that spatial resolution in CT images can be uniform across the FOV without using additional equipment. The beauty of this method is that it can be applied to any CT system as long as we know the specific system parameters and determine the appropriate PSF for deconvolution maps of the system. The proposed algorithm shows promising result in improving spatial resolution uniformity while avoiding the excessive noise boost.

A distance-driven deconvolution method for CT image-resolution improvement

The purpose of this research is to achieve high spatial resolution in CT (computed tomography) images without hardware modification. The main idea is to consider geometry optics model, which can provide the approximate blurring PSF (point spread function) kernel, which varies according to the distance from the X-ray tube to each point. The FOV (field of view) is divided into several band regions based on the distance from the X-ray source, and each region is deconvolved with a different deconvolution kernel. As the number of subbands increases, the overshoot of the MTF (modulation transfer function) curve increases first. After that, the overshoot begins to decrease while still showing a larger MTF than the normal FBP (filtered backprojection). The case of five subbands seems to show balanced performance between MTF boost and overshoot minimization. It can be seen that, as the number of subbands increases, the noise (STD) can be seen to show a tendency to decrease. The results shows that spatial resolution in CT images can be improved without using high-resolution detectors or focal spot wobbling. The proposed algorithm shows promising results in improving spatial resolution while avoiding excessive noise boost.

LabPET II, an APD-based Detector Module with PET and Counting CT Imaging Capabilities

Computed tomography (CT) is currently the standard modality to provide anatomical reference for positron emission tomography (PET) in molecular imaging applications. Since both PET and CT rely on detecting radiation to generate images, using the same detection system for data acquisition is a compelling idea even though merging PET and CT hardware imposes stringent requirements on detectors. These requirements include large signal dynamic range with high signal-to-noise ratio for good energy resolution in PET and energy-resolved photon-counting CT, high pixelization for suitable spatial resolution in CT, and high count rate capability for reasonable CT acquisition time. To meet these criteria, the avalanche photodiode (APD)-based LabPET II module is proposed as the building block for a truly combined PET/CT scanner. The module is made of two monolithic $ 4\times 8$ APD pixel arrays mounted side-by-side on a custom ceramic holder. Individual APD pixels have an active area of $ 1.1\times 1.1~\hbox{mm}^{2}$ at a 1.2 mm pitch. The APD arrays are coupled to a 12-mm high, $8 \times 8$ LYSO scintillator array made of $1.12 \times 1.12~\hbox{mm}^{2}$ pixels also at a pitch of 1.2 mm to ensure direct one-to-one coupling to individual APD pixels. The scintillator array was designed with unbound specular reflective material between pixels to maximize the difference between refractive indices and enhance total internal reflection at the crystal side surfaces for better light collection, and the APD quantum efficiency was improved to $ \sim60\%$ at 420 nm to optimize intrinsic detector performance. Mean energy resolution was $20 \pm 1\%$ at 511 keV and $ 41\pm 4\%$ at 60 keV. The measured intrinsic spatial and time resolution for PET were respectively $0.81 \pm 0.04~\hbox{mm}~{\rm FWHM}/1.57 \pm 0.04~\hbox{mm}$ FWTM and $ 3.6\pm 0.3~\hbox{ns}$ FWHM with an energy threshold of 400 keV. Initial phantom images obtained using a CT test bench demonstrated excellent contrast linearity as a function of material density. With a magnification factor of 2, a CT spatial resolution of 0.66 mm FWHM/1.2 mm FWTM, corresponding to 1.18 lp/mm at ${\rm MTF}_{10\%}/0.67~\hbox{lp/mm}$ at ${\rm MTF}_{50\%}$ , was measured, allowing 0.75 mm air holes in an Ultra-Micro Hot Spot resolution phantom to be clearly distinguished.

Feasibility of a data-constrained prediction of hydrocarbon reservoir sandstone microstructures

Microstructures are critical for defining material characteristics such as permeability, mechanical, electrical and other physical properties. However, the available techniques for determining compositional microstructures through segmentation of x-ray computed tomography (CT) images are inadequate when there are finer structures than the CT spatial resolution, i.e. when there is more than one material in each voxel. This is the case for CT imaging of geomaterials characterized with submicron porosity and clay coating that control petrophysical properties of rock. This note outlines our data-constrained modelling (DCM) approach for prediction of compositional microstructures, and our investigation of the feasibility of determining sandstone microstructures using multiple CT data sets with different x-ray beam energies. In the DCM approach, each voxel is assumed to contain a mixture of multiple materials, optionally including voids. Our preliminary comparisons using model samples indicate that the DCM-predicted compositional microstructure is consistent with the known original microstructure under low noise conditions. The approach is quite generic and is applicable to predictions of microstructure of various materials.

Computed tomography commissioning programmes: how to obtain a reliable MTF with an automatic approach?

The purpose of this study was to assess the spatial resolution of a computed tomography (CT) scanner with an automatic approach developed for routine quality controls when varying CT parameters. The methods available to assess the modulation transfer functions (MTF) with the automatic approach were Droege's and the bead point source (BPS) methods. These MTFs were compared with presampled ones obtained using Boone's method. The results show that Droege's method is not accurate in the low-frequency range, whereas the BPS method is highly sensitive to image noise. While both methods are well adapted to routine stability controls, it was shown that they are not able to provide absolute measurements. On the other hand, Boone's method, which is robust with respect to aliasing, more resilient to noise and provides absolute measurements, satisfies the commissioning requirements perfectly. Thus, Boone's method combined with a modified Catphan 600 phantom could be a good solution to assess CT spatial resolution in the different CT planes.

Lumber value differences from reduced CT spatial resolution and simulated log sawing

In the past few years, computed tomography (CT) scanning technology has been applied to the detection of internal defects in hardwood logs for the purpose of obtaining a priori information that can be used to arrive at better log sawing decisions. Because sawyers currently cannot even see the inside of a log until the log faces are revealed by sawing, there is little perceived need to obtain scan images as detailed as those obtained in medical CT imaging. Yet, CT scanner speed and the usefulness of CT data for decision-making are dependent on the spatial resolution of scans. Spatial resolution is a function of three factors: physical pixel size, scan thickness, and scan frequency (pitch). A 3×2 3 factorial experiment was designed with two levels for each of these three factors, to test their effect on lumber values. Three hypothetical logs corresponding to three hardwood log grades were simulation-scanned, then simulation-sawed by a human operator using a modified Malcolm opening face heuristic. Log grade affected lumber value recovery as expected, although reduced spatial resolution (by doubling the pitch, thickness, and pixel size) exhibited no discernible pattern in our statistical tests for effects. Volume recovery for below grade boards was predicted very accurately by size, thickness, and pitch-size. The greatest opportunity for lumber value recovery improvement using information-augmented sawing appears to be in grade #2 logs.

MR Imaging of the Retroperitoneum

The diagnosis of retroperitoneal pathology has historically presented a challenge to physicians. The signs and symptoms of retroperitoneal diseases are myriad and often subtle. Cross-sectional imaging techniques have therefore had a major impact on retroperitoneal diagnosis. Computed tomography (CT) is currently the standard imaging technique for evaluating the retroperitoneum. Magnetic resonance (MR) imaging is also well suited for retroperitoneal imaging and has several advantages over CT. MR imaging is the preferred technique in patients with contraindications to iodinated contrast material due to renal dysfunction or allergy. It excels at evaluating the blood vessels, providing a reliable assessment of vessel patency, aneurysm, or dissection. The ability of MR imaging to acquire images without exposure to ionizing radiation facilitates imaging of obstetric and pediatric patients. The ability to acquire images in any plane is a distinct advantage for assessing the extent and origin of retroperitoneal pathology, although this can now be accomplished with spiral CT as well as MR imaging. The spatial resolution of CT is currently superior to MR imaging for most retroperitoneal studies, but this may change with continued technological advances such as improved phased array coil systems (Bidgood WD Jr, Schiebler ML. Retroperitoneum and mesentery. In: Ros PR, Bidgood WD Jr, eds. Abdominal magnetic resonance imaging. St. Louis: Mosby Year Book, 1993:310-47). Finally, MR imaging provides the flexibility to tailor each examination to the specific clinical question. With few exceptions, anything CT can do in the retroperitoneum, MR imaging can do as well or better.

The Use of Iodolipids in Hepatosplenic Computed Tomography

Iodolipids have been used as a contrast medium for hepatosplenic computed tomography (CT) in 148 patients. In all but two of these cases, the contrast material was injected by the intravenous route. The method appears to be safe due to the marked reduction of dosage in CT compared with conventional radiographic iodolipid hepatography. This decreased dosage is made possible by the improved density and spatial resolution of CT. Pictorial and histographic densitometric analysis of normal and abnormal liver after iodolipid administration yields considerable diagnostic improvement.