Masahito Aoyama

Automated computerized scheme for distinction between benign and malignant solitary pulmonary nodules on chest images

A novel automated computerized scheme has been developed to assist radiologists for their distinction between benign and malignant solitary pulmonary nodules on chest images. Our database consisted of 55 chest radiographs (33 primary lung cancers and 22 benign nodules). In this method, the location of a nodule was indicated first by a radiologist. The difference image with a nodule was produced by use of filters and then represented in a polar coordinate system. The nodule was segmented automatically by analysis of contour lines of the gray-level distribution based on the polar-coordinate representation. Two clinical parameters (age and sex) and 75 image features were determined from the outline, the image, and histogram analysis for inside and outside regions of the segmented nodule. Linear discriminant analysis (LDA) and knowledge about benign and malignant nodules were used to select initial feature combinations. Many combinations for subgroups of 77 features were evaluated as input to artificial neural networks (ANNs). The performance of ANNs with the selected 7 features by use of the round-robin test showed Az = 0.872, which was greater than Az = 0.854 obtained previously with the manual method (P= 0.53). The performance of LDA (Az = 0.886) was slightly improved compared to that of ANNs (P = 0.59) and was greater than that of the manual method (Az = 0.854) reported previously (P = 0.40). The high level of its performance indicates the potential usefulness of this automated computerized scheme in assisting radiologists as a second opinion for distinction between benign and malignant solitary pulmonary nodules on chest images.

Computerized scheme for determination of the likelihood measure of malignancy for pulmonary nodules on low-dose CT images

An automated computerized scheme has been developed for determination of the likelihood measure of malignancy of pulmonary nodules on low-dose helical CT (LDCT) images. Our database consisted of 76 primary lung cancers (147 slices) and 413 benign nodules (576 slices). With this automated computerized scheme, the location of a nodule was first indicated by a radiologist. The outline of the nodule was segmented automatically by use of a dynamic programming technique. Various objective features on the nodules were determined by use of outline analysis and image analysis, and the likelihood measure of malignancy was determined by use of linear discriminant analysis (LDA). The effect of many different combinations of features and the performance of LDA in distinguishing benign nodules from malignant ones were evaluated by means of receiver operating characteristic (ROC) analysis. The Az value (area under the ROC curve) obtained by the computerized scheme in distinguishing benign nodules from malignant ones was 0.828 when a single slice was employed for each of the nodules. However, the Az value was improved to 0.846 when multiple slices were used for determination of the likelihood measure of malignancy. The Az values obtained by the computerized scheme on LDCT images were significantly greater than the Az value of 0.70, which was obtained from our previous observer studies by radiologists in distinguishing benign nodules from malignant ones on LDCT images. The automated computerized scheme for determination of the likelihood measure of malignancy would be useful in assisting radiologists to distinguish between benign and malignant pulmonary nodules on LDCT images.

Optimal dose and injection duration (injection rate) of contrast material for depiction of hypervascular hepatocellular carcinomas by multidetector CT

PurposeThe aim of this study was to investigate the optimal dose and injection duration of contrast material (CM) for depicting hypervascular hepatocellular carcinomas (HCCs) during the hepatic arterial phase with multidetector row computed tomography (CT).Materials and methodsThe study population consisted of 71 patients with hypervascular HCCs. After unenhanced scans, the first (early arterial phase, or EAP), second (late arterial phase, or LAP), and third (equilibrium phase) scanning was started at 30, 43, and 180 s after injection of contrast material (CM). During a 33-s period, patients with a body weight ≤50 kg received 100 ml of non-ionic CM with an iodine concentration of 300 mg I/ml; patients whose body weight was >50 kg received 100 ml of CM with an iodine concentration of 370 mg I/ml. First, we measured enhancement in the abdominal aorta and tumor-to-liver contrast (TLC) during the EAP and LAP. Next, to investigate the relation between aortic enhancement and TLC during the LAP, two radiologists visually assessed the conspicuity of hypervascular HCCs during the LAP using a 3-point scale: grade 1, poor; grade 2, fair; grade 3, excellent. Finally, to examine the effect of the CM dose and injection duration on aortic enhancement during the EAP, we simulated aortic enhancement curves using test bolus data obtained for 10 HCC patients and the method of Fleischmann and Hittmair.ResultsA relatively strong correlation was observed between aortic enhancement during the EAP and TLC during the LAP (correlation coefficient r = 0.75, P < 0.001). The 95% confidence intervals for the population mean for aortic enhancement during EAP in patients with tumor conspicuity grades of 1, 2, and 3 were 188.5, 222.4; 228.8, 259.3; and 280.2, 322.5 HU (Hounsfield Unit), respectively. Thus, we considered the lower limit of the aortic enhancement value for excellent depiction of HCCs during EAP to be 280 HU. To achieve an aortic enhancement value of >280 HU for aortic enhancement simulations during EAP, the injection duration should be <25 s for patients receiving a CM dose of 1.7 ml/kg with 300 mg I/ml iodine and <30 s for those receiving 2.0 ml/kg.ConclusionsFor excellent depiction of hypervascular HCCs during the hepatic arterial phase, the injection duration should be <25 s in patients receiving a CM dose of 1.7 ml/kg with 300 mg I/ml iodine and <30 s for patients receiving 2.0 ml/kg.

Low-dose contrast protocol using the test bolus technique for 64-detector computed tomography coronary angiography

PurposeWe evaluated low-contrast injection protocols for coronary computed tomography angiography (CTA) using a 64-detector scanner and the test bolus technique.Materials and methodsWe randomly assigned 60 patients undergoing coronary CTA to one of two contrast material (CM) injection protocols. For the lowcontrast dose protocol (Plow), the patients received injections of iohexol-350 [0.7 ml/kg body weight (BW)] during 9 s, and the test-bolus technique was used. Under the conventional protocol (Pconv), they received iohexol-350 (1.0 ml/kg BW) during 15 s, and bolus tracking was used. We compared the protocols for attenuation values in the ascending aorta and coronary arteries and for the amount of CM required.ResultsThere was no significant difference in the mean CT attenuation of the ascending aorta and coronary arteries between the Plow and Pconv groups. The amount of CM was significantly less with Plow than with Pconv [49.7 ± 6.4 ml (main bolus: 39.7 ± 6.4 ml) vs. 57.0 ± 10.1 ml, P < 0.01].ConclusionWith 64-detector CTA of the heart, the low-dose and short-injection-duration protocol with the test-injection technique provides vessel attenuation comparable to that obtained with the standard-dose protocol with the bolus-tracking technique.

Calibration of a 3D endoscopic system based on active stereo method for shape measurement of biological tissues and specimen.

For endoscopic medical treatment, measuring the size and shape of the lesion, such as a tumor, is important for the improvement of diagnostic accuracy. We are developing a system to measure the shapes and sizes of living tissue by active stereo method using a normal endoscope on which a micro pattern projector is attached. In order to perform 3D reconstruction, estimating the intrinsic and extrinsic parameters of the endoscopic camera and the pattern projector is required. Particularly, calibration of the pattern projector is difficult. In this paper, we propose a simultaneous estimation method of both intrinsic and extrinsic parameters of the pattern projector. This simplifies the calibration procedure required in practical scenes. Furthermore, we have developed an efficient user interface to intuitively operate the calibration and reconstruction procedures. Using the developed system, we measured the shape of an internal tissue of the soft palate of a human and a biological specimen.

Collimation Detection in Digital Radiographs Using Plane Detection Hough Transform

In medical X-ray examinations, X-ray collimators are frequently employed to shield the body parts from unnecessary X-ray exposure and to improve the image quality. The confined regions (collimations) are not regarded as diagnostically important. And it has been pointed out that the presence of collimations may impair diagnosis of subtle lesions due to dazzle. For efficient image compression, it is desirable that the collimations are accurately detected. The purpose of this study is to develop a computerized method to correctly identify collimations in digital radiographs. In this study, we propose a method of applying plane detection Hough transform where digital radiographs are regarded as three-dimensional data by adding one-dimension of the brightness direction, in order to detect the boundaries between collimations and irradiation fields as planes. Therefore, we describe a validity of the plane detection by modeling the collimation boundaries. In addition, the effectiveness in compressing the data of a processed images greater than the original ones.

Table form document analysis based on the document structure grammar

Structure analysis of table form documents is an important issue because a printed document and even an electronic document do not provide logical structural information but merely geometrical layout and lexical information. To handle these documents automatically, logical structure information is necessary. In this paper, we first analyze the elements of the form documents from a communication point of view and retrieve the grammatical elements that appear in them. Then, we present a document structure grammar which governs the logical structure of the form documents. Finally, we propose a structure analysis system of the table form documents based on the grammar. By using grammar notation, we can easily modify and keep it consistent, as the rules are relatively simple. Another advantage of using grammar notation is that it can be used for generating documents only from logical structure. In our system, documents are assumed to be composed of a set of boxes and they are classified as seven box types. Then the box relations between the indication box and its associated entry box are analyzed based on the semantic and geometric knowledge defined in the document structure grammar. Experimental results have shown that the system successfully analyzed several kinds of table forms.

Proposal on 3-D endoscope by using grid-based active stereo

In this paper, we propose a novel 3-D endoscope system by using grid-based active stereo. In the proposed system, projection of a waved-grid pattern that consists of vertical and horizontal sinusoidal lines realizes accurate shape acquisition in sub-pixel accuracy. We develop a small pattern projector implementable to a head of a ready-made endoscope, and examine 3-D shape reconstruction by actual equipment. As the result of the measurement for a known-shaped object, which is a hexagonal cylinder, the error of length measurement is below 0.9% and the error of angle measurement is below 2.2%. We make a measurement of animal organ meat, and confirm that the system can reconstruct a 3-D shape of the organ surface.

Extraction and Visualization of Cardiac Beat by Grid-Based Active Stereo

We propose a method to observe cardiac beat from 3D shape information of body surface by using grid-based active stereo, and report preliminary experiments to evaluate validities of the proposed method. By comparing results of our proposed with those of electrocardiogram ECG, we confirmed sufficient correspondences between peak intervals of inter-frame depth changes measured by the active stereo and R-R intervals measured by ECG. We tried the visualization of the spatial distribution of inter-frame depth change plotted on the 3D shape of chest region. And, the shape change by cardiac beat is mainly found on the left side of the chest region.

Mixing Paints for Generating Metamerism Art under 2 Lights and 3 Object Colors

Metamerism is a phenomenon where two objects recognized as having different colors under one light are also recognized as having the same color under another light. This research proposes technology for actualizing artistic illusion that exploits metamerism. Specifically, the purpose of the research relates to automatic calculation of blending ratios of oil paints that cause metamerism to occur under specific light sources. We entails metamerism occurring between three types of object colors under two types of light sources. Also, we utilize plausible reflection model for the mixture of oil paints.