Simulation of subtle lung nodules in projection chest radiography
TL;DR: The radiologic pattern of subtle lung nodules is poorly simulated by nodule phantoms with simple spherical or disk shapes, but the nodulePhantoms in this study produce realistic radiographic patterns with an energy-dependent attenuation equivalent to that of tissue.
Abstract: PURPOSE: To measure the radiologic characteristics of subtle lung nodules and develop nodule phantoms that simulate these characteristics. MATERIALS AND METHODS: From a database of chest radiographs, 16 radiographs that showed confirmed subtle lung nodules were selected. The optical density values surrounding each nodule were obtained, and the radiologic characteristic of the nodules were evaluated. A set of Teflon nodule phantoms with similar x-ray transmission and variability was designed and fabricated. The contrast characteristics of the images of the nodule phantoms were measured. RESULTS: Most of the subtle nodules appeared to have diffuse edges with Gaussian-like contrast profiles. The contrast and size characteristics of the nodule phantom images fulfilled the design criteria within a 4% deviation. CONCLUSION: The radiologic pattern of subtle lung nodules is poorly simulated by nodule phantoms with simple spherical or disk shapes. The nodule phantoms in this study produce realistic radiographic pa...
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TL;DR: The detection of subtle lung nodules on chest radiographs is limited by anatomic noise, and the findings generally agreed with the signal-to-noise ratio calculations based on statistical observer models.
Abstract: PURPOSE: To assess the relative influence of quantum mottle and structured lung patterns (anatomic noise) on the detection of subtle lung nodules on chest radiographs. MATERIALS AND METHODS: Sixty 8 × 8-cm lung pattern images were extracted from digital chest radiographs in healthy individuals. Sixty quantum mottle images of the same size and quantum noise level were extracted from uniformly exposed digital radiographs. Simulated nodules with various peak contrast-diameter products (CD) that emulated subtle tissue-equivalent lung nodules were numerically superimposed at the center on three-fourths of the images. Printouts were independently viewed and scored by five experienced radiologists. The area under the receiver operating characteristic curve (Az) was estimated as a measure of the detectability of the nodules. RESULTS: At a fixed observer performance level (eg, Az = 0.8), much smaller and lower-contrast nodules were detected on quantum mottle images (1-mm diameter, CD = 0.01 mm), compared with thos...
242 citations
TL;DR: The effect of acquisition parameters on lesion detectability depends on signal size, and increasing the angular scan range increased detectability for all signal sizes.
Abstract: Purpose: Tomosynthesis is a promising modality for breast imaging. The appearance of the tomosynthesis reconstructed image is greatly affected by the choice of acquisition and reconstruction parameters. The purpose of this study was to investigate the limitations of tomosynthesis breast imaging due to scan parameters and quantum noise. Tomosynthesis image quality was assessed based on performance of a mathematical observer model in a signal-known exactly (SKE) detection task.
Methods: SKE detectability (d′) was estimated using a prewhitening observer model. Structured breast background was simulated using filtered noise. Detectability was estimated for designer nodules ranging from 0.05 to 0.8 cm in diameter. Tomosynthesis slices were reconstructed using iterative maximum-likelihood expectation-maximization. The tomosynthesis scan angle was varied between 15° and 60°, the number of views between 11 and 41 and the total number of x-ray quanta was ∞, 6×105, and 6×104. Detectability in tomosynthesis was compared to that in a single projection.
Results: For constant angular sampling distance, increasing the angular scan range increased detectability for all signal sizes. Large-scale signals were little affected by quantum noise or angular sampling. For small-scale signals, quantum noise and insufficient angular sampling degraded detectability. At high quantum noise levels, angular step size of 3° or below was sufficient to avoid image degradation. At lower quantum noise levels, increased angular sampling always resulted in increased detectability. The ratio of detectability in the tomosynthesis slice to that in a single projection exhibited a peak that shifted to larger signal sizes when the angular range increased. For a given angular range, the peak shifted toward smaller signals when the number of views was increased. The ratio was greater than unity for all conditions evaluated.
Conclusion: The effect of acquisition parameters on lesion detectability depends on signal size. Tomosynthesis scan angle had an effect on detectability for all signals sizes, while quantum noise and angular sampling only affected the detectability small-scale signals.
181 citations
TL;DR: The frequency-dependent detective quantum efficiency DQE (f) of the 4k mode was slightly better than that for the 2k mode by about 0.02 due primarily to its better noise characteristics.
Abstract: The purpose of this study was to compare the image quality for a digital storage phosphor system using 1760 x 2140 (2k) and 3520 x 4280 (4k) image arrays. Measurements were made on a chest radiography system (Fuji FCR-9501) with special provisions to be operated in both 2k (standard) and 4k (HQ) modes. Presampled modulation transfer functions (MTF) were measured using an edge method. Noise power spectra (NPS) were determined for different input exposures by two-dimensional Fourier analysis. These measures along with exposure measurements and an x-ray spectral model were used to determine the frequency-dependent detective quantum efficiency DQE (f) of the system for the 4k and the 2k modes. The magnitude of the NPS for the 4k mode was about 1/2 that of the 2k mode. A MTF value of 0.5 was found at 1.25 cycles/mm for the 4k system and 1.50 cycles/mm for the 2k system. The 4k images had an extended MTF of 0.1 at 4.5 cycles/mm in the plate-scan direction. Overall, the DQE (f) of the 4k mode was slightly better than that for the 2k mode by about 0.02 due primarily to its better noise characteristics.
140 citations
TL;DR: The methods offer a set of common testing procedures that can be utilized towards the optimal clinical utilization of CT imaging devices, benchmarking across varying systems and times, and a basis to develop future performance-based criteria for CT imaging.
Abstract: Background The rapid development and complexity of new x-ray computed tomography (CT) technologies and the need for evidence-based optimization of image quality with respect to radiation and contrast media dose call for an updated approach towards CT performance evaluation. Aims This report offers updated testing guidelines for testing CT systems with an enhanced focus on the operational performance including iterative reconstructions and automatic exposure control (AEC) techniques. Materials and methods The report was developed based on a comprehensive review of best methods and practices in the scientific literature. The detailed methods include the assessment of 1) CT noise (magnitude, texture, nonuniformity, inhomogeneity), 2) resolution (task transfer function under varying conditions and its scalar reflections), 3) task-based performance (detectability, estimability), and 4) AEC performance (spatial, noise, and mA concordance of attenuation and exposure modulation). The methods include varying reconstruction and tube current modulation conditions, standardized testing protocols, and standardized quantities and metrology to facilitate tracking, benchmarking, and quantitative comparisons. Results The methods, implemented in cited publications, are robust to provide a representative reflection of CT system performance as used operationally in a clinical facility. The methods include recommendations for phantoms and phantom image analysis. Discussion In line with the current professional trajectory of the field toward quantitation and operational engagement, the stated methods offer quantitation that is more predictive of clinical performance than specification-based approaches. They can pave the way to approach performance testing of new CT systems not only in terms of acceptance testing (i.e., verifying a device meets predefined specifications), but also system commissioning (i.e., determining how the system can be used most effectively in clinical practice). Conclusion We offer a set of common testing procedures that can be utilized towards the optimal clinical utilization of CT imaging devices, benchmarking across varying systems and times, and a basis to develop future performance-based criteria for CT imaging.
128 citations
TL;DR: A method to generate medical textures that are fully defined by a set of adjustable parameters and a random number generator, and which statistical properties are analytically tractable is proposed.
Abstract: Realistic anatomical images are useful for assessment and improvement of medical image quality. The use of synthesized images has the advantage of providing the user with a large number of independent samples, in a controlled environment. We propose a method to generate medical textures that are fully defined by a set of adjustable parameters and a random number generator, and which statistical properties are analytically tractable. This method, called the “clustered lumpy background”, is a generalization of the original lumpy background described by Rolland and Barrett (1992). A detailed application of the method in the case of mammography is presented. It is shown that the synthesized images are visually very similar and that their first and second order statistics can be considered as being equivalent.
120 citations