Introduction: Advances and trends in image formation in X-ray computed tomography

Introduction to articles in a special focus series on CT imaging

Computerized 3-dimensional Localization of a Video Capsule in the Abdominal Cavity: Validation by Digital Radiography

Background: Video capsule endoscopy has become the gold standard for examining the small bowel and defining pathological lesions, however, localization of a specific lesion remains largely guesswork. We report the validation of a new 3D localization software using radiological localization in volunteers. Methods: 30 volunteers with no known prior history of gastrointestinal disease swallowed the EC-10 video capsule. A sensor array with six radiopaque markers was placed on the anterior abdominal wall. Once the capsule was visualized to be in the small intestine using a real time viewer, five sets of low dose x-rays were taken every thirty minutes. Distances between sensor points and the capsule were measured on the x-rays to provide X, Y, and Z coordinates and compared with the distances calculated by the software from the same points. Results: Data from 27 of the 30 subjects were suitable for analysis. There were three technical failures. Our study evaluated the accuracy of the “Capsule 3D Track function” which calculated the capsule position based on the signal strength received at the sensor array. The accuracy of the position was compared to the actual position of the capsule as determined by radiographic images obtained during the capsule’s transit through the small bowel. The average error for the software measurement for each of the three coordinates was: X -2.00 cm (SD 1.64 cm), Y -- 2.64 cm (SD 2.39 cm), and Z --2.51 cm (1.83 cm). Conclusion: The localization error reported here is comparable to the existing system for localization, however, it provides localization across all three spatial dimensions which has never been achieved before. The potential utility of this technology is yet to be seen, however, as it needs to now be studied in a prospective clinical trial for patients with suspected small bowel pathology

Calibration and Optimization of 3D Digital Breast Tomosynthesis Guided Near Infrared Spectral Tomography

Calibration of a three-dimensional multimodal digital breast tomosynthesis (DBT) x-ray and non-fiber based near infrared spectral tomography (NIRST) system is challenging but essential for clinical studies. Phantom imaging results yielded linear contrast recovery of total hemoglobin (HbT) concentration for cylindrical inclusions of 15 mm, 10 mm and 7 mm with a 3.5% decrease in the HbT estimate for each 1 cm increase in inclusion depth. A clinical exam of a patient\u27s breast containing both benign and malignant lesions was successfully imaged, with greater HbT was found in the malignancy relative to the benign abnormality and fibroglandular regions (11 μM vs. 9.5 μM). Tools developed improved imaging system characterization and optimization of signal quality, which will ultimately improve patient selection and subsequent clinical trial results

Photon-counting digital mammography: evaluation of performance under clinically relevant conditions

Comment on: Comparison of radiologist performance with photon-counting full-field digital mammography to conventional full-field digital mammography. [Acad Radiol. 2012

Modeling the performance characteristics of computed radiography (CR) systems

Computed radiography (CR) using storage phosphors is widely used in digital radiography and mammography. A cascaded linear systems approach wherein several parameter values were estimated using Monte Carlo methods was used to model the image formation process of a single-side read flying spot CR system using a granular phosphor. Objective image quality metrics such as modulation transfer function and detective quantum efficiency were determined using this model and show good agreement with published empirical data. A model such as that addressed in this work could allow for improved understanding of the effect of storage phosphor physical properties and CR reader parameters on objective image quality metrics for existing and evolving CR systems

X-ray phase contrast imaging of the breast: analysis of tissue simulating materials

PURPOSE: Phase contrast imaging, particularly of the breast, is being actively investigated. The purpose of this work is to investigate the x-ray phase contrast properties of breast tissues and commonly used breast tissue substitutes or phantom materials with an aim of determining the phantom materials best representative of breast tissues. METHODS: Elemental compositions of breast tissues including adipose, fibroglandular, and skin were used to determine the refractive index, n = 1 - delta + i beta. The real part of the refractive index, specifically the refractive index decrement (delta), over the energy range of 5-50 keV were determined using XOP software (version 2.3, European Synchrotron Radiation Facility, France). Calcium oxalate and calcium hydroxyapatite were considered to represent the material compositions of microcalcifications in vivo. Nineteen tissue substitutes were considered as possible candidates to represent adipose tissue, fibroglandular tissue and skin, and four phantom materials were considered as possible candidates to represent microcalcifications. For each material, either the molecular formula, if available, or the elemental composition based on weight fraction, was used to determine delta. At each x-ray photon energy, the absolute percent difference in delta between the breast tissue and the substitute material was determined, from which three candidates were selected. From these candidate tissue substitutes, the material that minimized the absolute percent difference in linear attenuation coefficient mu, and hence beta, was considered to be best representative of that breast tissue. RESULTS: Over the energy range of 5-50 keV, while the delta of CB3 and fibroglandular tissue-equivalent material were within 1% of that of fibroglandular tissue, the mu of fibroglandular tissue-equivalent material better approximated the fibroglandular tissue. While the delta of BR10 and adipose tissue-equivalent material were within 1% of that of adipose tissue, the tissue-equivalent material better approximated the adipose tissue in terms of mu. Polymethyl methacrylate, a commonly used tissue substitute, exhibited delta greater than fibroglandular tissue by approximately 12%. The A-150 plastic closely approximated the skin. Several materials exhibited delta between that of adipose and fibroglandular tissue. However, there was an energy-dependent mismatch in terms of equivalent fibroglandular weight fraction between delta and mu for these materials. For microcalcifications, aluminum and calcium carbonate were observed to straddle the delta and mu of calcium oxalate and calcium hydroxyapatite. Aluminum oxide, commonly used to represent microcalcifications in the American College of Radiology recommended phantoms for accreditation exhibited delta greater than calcium hydroxyapatite by approximately 23%. CONCLUSIONS: A breast phantom comprising A-150 plastic to represent the skin, commercially available adipose and fibroglandular tissue-equivalent formulations to represent adipose and fibroglandular tissue, respectively, was found to be best suited for x-ray phase-sensitive imaging of the breast. Calcium carbonate or aluminum can be used to represent microcalcifications

Towards standardization of x-ray beam filters in digital mammography and digital breast tomosynthesis: Monte Carlo simulations and analytical modelling

In digital breast tomosynthesis and digital mammography, the x-ray beam filter material and thickness vary between systems. Replacing K-edge filters with Al was investigated with the intent to reduce exposure duration and to simplify system design. Tungsten target x-ray spectra were simulated with K-edge filters (50 microm Rh; 50 microm Ag) and Al filters of varying thickness. Monte Carlo simulations were conducted to quantify the x-ray scatter from various filters alone, scatter-to-primary ratio (SPR) with compressed breasts, and to determine the radiation dose to the breast. These data were used to analytically compute the signal-difference-to-noise ratio (SDNR) at unit (1 mGy) mean glandular dose (MGD) for W/Rh and W/Ag spectra. At SDNR matched between K-edge and Al filtered spectra, the reductions in exposure duration and MGD were quantified for three strategies: (i) fixed Al thickness and matched tube potential in kilovolts (kV); (ii) fixed Al thickness and varying the kV to match the half-value layer (HVL) between Al and K-edge filtered spectra; and, (iii) matched kV and varying the Al thickness to match the HVL between Al and K-edge filtered spectra. Monte Carlo simulations indicate that the SPR with and without the breast were not different between Al and K-edge filters. Modelling for fixed Al thickness (700 microm) and kV matched to K-edge filtered spectra, identical SDNR was achieved with 37-57% reduction in exposure duration and with 2-20% reduction in MGD, depending on breast thickness. Modelling for fixed Al thickness (700 microm) and HVL matched by increasing the kV over (0,4) range, identical SDNR was achieved with 62-65% decrease in exposure duration and with 2-24% reduction in MGD, depending on breast thickness. For kV and HVL matched to K-edge filtered spectra by varying Al filter thickness over (700, 880) microm range, identical SDNR was achieved with 23-56% reduction in exposure duration and 2-20% reduction in MGD, depending on breast thickness. These simulations indicate that increased fluence with Al filter of fixed or variable thickness substantially decreases exposure duration while providing for similar image quality with moderate reduction in MGD

Large-angle x-ray scatter in Talbot-Lau interferometry for breast imaging

Monte Carlo simulations were used to investigate large-angle x-ray scatter at design energy of 25 keV during small field of view (9.6 cm x 5 cm) differential phase contrast imaging of the breast using Talbot-Lau interferometry. Homogenous, adipose and fibroglandular breasts of uniform thickness ranging from 2 to 8 cm encompassing the field of view were modeled. Theoretically determined transmission efficiencies of the gratings were used to validate the Monte Carlo simulations, followed by simulations to determine the x-ray scatter reaching the detector. The recorded x-ray scatter was classified into x-ray photons that underwent at least one Compton interaction (incoherent scatter) and Rayleigh interaction alone (coherent scatter) for further analysis. Monte Carlo based estimates of transmission efficiencies showed good correspondence [Formula: see text] with theoretical estimates. Scatter-to-primary ratio increased with increasing breast thickness, ranging from 0.11 to 0.22 for 2-8 cm thick adipose breasts and from 0.12 to 0.28 for 2-8 cm thick fibroglandular breasts. The analyzer grating reduced incoherent scatter by ~18% for 2 cm thick adipose breast and by ~35% for 8 cm thick fibroglandular breast. Coherent scatter was the dominant contributor to the total scatter. Coherent-to-incoherent scatter ratio ranged from 2.2 to 3.1 for 2-8 cm thick adipose breasts and from 2.7 to 3.4 for 2-8 cm thick fibroglandular breasts