Airway wall thickness (AWT) is an important bio-marker for evaluation of pulmonary diseases such as chronic
bronchitis, bronchiectasis. While an image-based analysis of the airway tree can provide precise and valuable airway size
information, quantitative measurement of AWT in Multidetector-Row Computed Tomography (MDCT) images involves
various sources of error and uncertainty. So we have developed an accurate AWT measurement technique for small
airways with three-dimensional (3-D) approach. To evaluate performance of these techniques, we used a set of acryl
tube phantom was made to mimic small airways to have three different sizes of wall diameter (4.20, 1.79, 1.24 mm) and
wall thickness (1.84, 1.22, 0.67 mm). The phantom was imaged with MDCT using standard reconstruction kernel
(Sensation 16, Siemens, Erlangen). The pixel size was 0.488 mm × 0.488 mm × 0.75 mm in x, y, and z direction
respectively. The images were magnified in 5 times using cubic
B-spline interpolation, and line profiles were obtained
for each tube. To recover faithful line profile from the blurred images, the line profiles were deconvolved with a point
spread kernel of the MDCT which was estimated using the ideal tube profile and image line profile. The inner diameter,
outer diameter, and wall thickness of each tube were obtained with full-width-half-maximum (FWHM) method for the
line profiles before and after deconvolution processing. Results show that significant improvement was achieved over the
conventional FWHM method in the measurement of AWT.
Hessian matrix is the square matrix of second partial derivatives of a scalar-valued function and is well known for object
recognition in computer vision and medical shape analysis. Previous curvature based polyp detection algorithms generate
myriad of false positives. Hessian-matrix based method, however, is more sensitive to local shape features, so easily
reduce false positives. Calculation of Hessian matrix on 3D CT data and Eigen decomposition of the matrix gives three
Eigen values and vectors at each voxel. Using these Eigen values, we can figure out which type of intensity structures
(blob, line, and sheet-like) is on the given voxel. We focus on detecting blob-like object automatically. In the inner
colonic wall structures, blob-like, line-like, and sheet-like objects represent polyps, folds and wall, respectively. In
addition, to improve the performance of the algorithm, Gaussian blurring factor and shape threshold parameters are
optimized. Before Hessian matrix calculation, smoothing the given region using Gaussian kernel with small deviation is
necessary to enhance local intensity structures. To optimize the parameters and validate this method, we have produced
anthropomorphic pig phantoms. Fourteen phantoms with 103 polyps (16 polyps <6mm, 87 >= 6mm) were used. CT scan
was performed with 1mm slice thickness. Our detection algorithm found 84 polyps (81.6%) correctly. Average number
of false positives is 7.9 at each CT scan. This results show that our algorithm is clinically applicable for polyp detection,
because of high sensitivity and relatively low false positive detections.
The purpose of this study is to determine a stable sampling rate not to be affected by sampling shift for reducing radiation exposure with time sampling and interpolation in cerebral perfusion CT examination. Original images were obtained every 1 second for 40 time series from 3 patients, respectively. Time sampling was performed with sampling intervals (SI) from 2 to 10 seconds. Sampling shift was applied from +1 to SI-1 for each sampling rate. For each patient, 30 tissue concentration time-course data were collected, and arterial input curves were fitted by gamma-variate function. The sinc function was introduced for interpolation. Deconvolution analysis based on SVD was performed for quantifying perfusion parameters. The perfusion values through time-varying sampling and interpolation were statistically compared with the original perfusion values. The mean CBF values with increase of sampling interval and shift magnitude from the collected data had a wider fluctuation pattern centering around the original mean CBF. The mean CBV values had a similar tendency to the mean CBF values, but a relatively narrower deviation. The mean MTT values were fluctuated reversely to the trend of the mean CBF values. The stable sampling interval for quantifying perfusion parameters with lower radiation exposure was statistically acceptable up to 4 seconds. These results indicate that sampling shift limits sampling rate for acquiring acceptable perfusion values. This study will help in selecting more reasonable sampling rate for low-radiation-dose CT examination.
Computer-aided characterization of a breast ultrasound lesion involves two steps: first, extracting features from the lesion whose boundary is pre-defined on the images, and then converting the features into mathematical models. Most methods assume that the boundaries of the lesions are pre-selected or outlined by sonographers or operators, because automated delineation of lesion boundary is not trivial and is a challenging task. The purpose of this study was to develop and evaluate an automated lesion boundary segmentation method that is based on texture-based, multi-resolution image analysis. One hundred ninety-seven breast ultrasound images containing solid breast lesions from 172 women (age 24-89 years, mean 38 years) were studied. Fifty-five of the 197 images were from 40 women with malignant lesions, and the remaining 142 were from 132 patients with benign lesions. Each breast lesion was identified by an operator who placed a rectangular region of interest (ROI) to widely encompass the lesion. The resolution of the image was compressed, at variable ratios depending on the ROI size, to reduce noise. Texture momentum was computed. A binary image was generated from the texture and pixel intensity parameters. Initial seed boundary was segmented from the binary image and then expanded to the original resolution using the boundary pixel intensity gradient information. The boundary of each breast lesion was delineated by a breast-imaging radiologist who was blinded to the computer-detected lesion boundary. The 'area match ratio' between the manually drawn boundaries and the automatically detected boundaries was computed. This ratio is equal to or less than unity (unity indicates that the areas match exactly). Overall, good agreement was seen between the multi-resolution segmentation method and the radiologist’s manual delineation. The mean area match ratio was 0.87 ±0.02. We have developed a multi-resolution, texture-based method to segment the boundary of breast lesions. This method will facilitate full automation for the characterization of breast ultrasound lesions.
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