Dual-energy Subtraction Method Research Articles

Large-scale MV CT for cargo imaging: A feasibility study

Computed tomography (CT) has a major advantage over radiography in that it provides 3D imaging and resolves the structural overlap problem inherent to radiography. Since the early 1970s, CT evolved in parallel with radiography in many areas. As megavoltage (MV) cargo radiography is now in use, it is of interest to evaluate the feasibility of corresponding MV cargo CT. A feasibility study of MV cargo CT has been performed in this work. The MV cargo CT system has an imaging field of view of 3.25 m in diameter. The system design includes a compact X-ray source and detectors that are already used in existing MV cargo radiography systems. Although compact X-ray sources provide limited X-ray output, it is shown that this output is sufficient to perform CT imaging of large cluttered cargo contents for which MV radiography may be inconclusive. The scan time is 60 s at the X-ray dose levels lower than the permitted limit of 5 mGy. A steel tank phantom with 2 m diameter including different materials was used. The MV CT images were generated at 3.5 MV, 6 MV, and 9 MV beam energies. The materials were separated based on their CT numbers as well as using dual energy subtraction method. The materials with close densities and X-ray attenuations such as W and U were reliably separated and quantified based on their measured CT numbers. The boundary conditions for the system design were determined, including scan time, radiation dose, maximum object thicknesses, and spatial resolution. Based on the findings of this feasibility study, it is concluded that the MV cargo CT system with large field of view can be developed based on existing technology already used in MV cargo radiography. Such a CT system can be extremely useful when used adjunct to existing MV radiography on resolving the special cases that cannot be resolved conclusively with radiography alone.

Dual energy subtraction method for breast calcification imaging

The aim of this work was to present an experimental dual energy (DE) method for the visualization of microcalcifications (μCs). A modified radiographic X-ray tube combined with a high resolution complementary metal-oxide-semiconductor (CMOS) active pixel sensor (APS) X-ray detector was used. A 40/70kV spectral combination was filtered with 100 μm cadmium (Cd) and 1000 μm copper (Cu) for the low/high-energy combination. Homogenous and inhomogeneous breast phantoms and two calcification phantoms were constructed with various calcification thicknesses, ranging from 16 to 152 μm. Contrast-to-noise ratio (CNR) was calculated from the DE subtracted images for various entrance surface doses. A calcification thickness of 152 μm was visible, with mean glandular doses (MGD) in the acceptable levels (below 3mGy). Additional post-processing on the DE images of the inhomogeneous breast phantom resulted in a minimum visible calcification thickness of 93 μm (MGD=1.62mGy). The proposed DE method could potentially improve calcification visibility in DE breast calcification imaging.

듀얼 에너지 감산기법을 이용한 디지털 X-ray 영상 최적화에 관한 연구

듀얼 에너지 감산기법을 이용한 디지털 X-ray 영상 최적화에 관한 연구

Dual-energy subtraction radiography improves laryngeal delineation in patients with moderate to severe cervical spondylosis

To investigate the feasibility of dual-energy subtraction (DES) in patients with moderate-severe cervical spondylosis for improving delineation of the larynx on flat panel detector (FPD) radiography. For 118 patients, we graded conventional/DES anterior-posterior views for delineation of the vocal cords, subglottis, and pyriform sinus using a 5-point scale and lateral views from conventional laryngeal FPD radiography to determine cervical spondylosis severity on a scale from 0 (none) to 3 (severe). We compared the delineation of each anatomical structure in both groups of grades 0-1 and grades 2-3 of spondylosis severity between conventional and DES methods and the improved delineation rate for each anatomical structure by DES compared to the conventional method between both groups. With DES, the delineation of each anatomical structure was significantly better than with conventional radiography for both groups (P<0.0001). The improved delineation rate of the vocal cord and subglottis using DES was significantly higher in grades 2-3 than in grades 0-1 (P<0.05), although there was no significant difference in the delineation rate of the pyriform sinus between the groups (P=0.847). DES provides better delineation of the laryngeal anatomy than conventional FPD radiography predominantly in patients with moderate-severe cervical spondylosis.

Improving the Image Quality in Computed Tomographic Pulmonary Angiography With Dual-Energy Subtraction

The objectives of this study were to assess quantitative and subjective image quality in computed tomographic pulmonary angiography using dual-energy subtraction methods compared with those of the monochromatic images using optimal contrast-to-noise ratios and those of the routine polychromatic images and to select the best dual-energy subtraction method. A total of 1 routine polychromatic image, 3 sets of dual-energy subtraction images (DESIs), and 2 sets of monochromatic images with different optimal contrast-to-noise ratios from 30 patients were obtained. The signal intensity and noise were measured; signal-to-noise ratio and contrast-to-noise ratio (CNR) were calculated. The global subjective image quality was subjectively assessed. The DESI 3 got the highest CNR and the DESI 1 got the second highest CNR. The DESI 1 got the highest global subjective image quality score. The 3 subtraction image sets got the highest score in visualization of the pulmonary artery branches. Computed tomographic pulmonary angiography with dual-energy subtraction technique is feasible. The DESI 1 afforded the best balance between the quantitative analysis and the subjective evaluation.

Detection of simulated pulmonary nodules by single-exposure dual-energy computed radiography of the chest: effect of a computer-aided diagnosis system (Part 2)

Objective: To evaluate the performance of the computer-aided diagnosis (CAD) scheme on the detection of pulmonary nodules (PNs) in single-exposure dual-energy subtraction computed radiography (CR) images of the chest, and to evaluate the effect of this CAD scheme on radiologists' detectabilities. Methods and material: We compared the detectability by the CAD scheme with the detectability by 12 observers by using conventional CR (C-CR) and bone-subtracted CR (BS-CR) images of 25 chest phantoms with a low-contrast nylon nodule. Results: Both in the CAD scheme and for the observers, the detectability of BS-CR images was superior to that of C-CR images ( P<0.005). The detection performance of the CAD scheme was equal to that of the observers. The nodules detected by the CAD did not necessarily coincide with those by the observers. Thus, if observers can use the results of the CAD system as a ‘second opinion’, their detectabilities increase. Conclusion: The CAD system for detection of PNs in the single-exposure dual-energy subtraction method is promising for improving radiologists' detectabilities of PNs.

高度画像処理による胸部1回撮影エネルギー差分法の臨床的有用性の検討

高度画像処理による胸部1回撮影エネルギー差分法の臨床的有用性の検討

Single-Exposure Dual-Energy Chest Images with Computed Radiography

Dual-energy subtraction radiography using computed radiography (CR) can aid in the detection of pulmonary abnormalities such as nodules, but the subtracted image requires higher x-ray exposure than usual to reduce quantum mottle. To reduce quantum mottle without increasing x-ray exposure, a new dual-energy subtraction algorithm was investigated that included an edge-adaptive smoothing process and a subtraction process. The signal-to-noise ratio and the image quality of this new subtracted image was significantly superior to that of conventional subtracted images. Observer performance of the subtracted digital radiography in detecting simulated pulmonary nodules was compared with original CR images and conventional subtracted digital radiography of 50 patients. A combination of an original CR image and a new subtracted CR image was significantly superior to a single original CR image or a combination of an original CR image and a conventional subtracted CR image (P < .01). The single-exposure dual-energy subtraction method is superior to the conventional subtraction method in the detection of pulmonary nodules.

Improvement of detection in computed radiography by new single-exposure dual-energy subtraction.

It is reported that the use of the dual-energy subtraction method enhances the abnormal shadow detection capability. However, because the subtracted image is significantly inferior to the original in signal-to-noise ratio (SNR), the x-ray dosage normally used for chest x-rays has not yielded subtracted images with adequate SNRs. Under these circumstances, we focus on the fact that there is a correlation between the noise contents of bone-and soft-tissue-subtracted images although there is no correlation between the signal contents of these images. We propose an algorithm that improves SNRs of subtraction images by reducing the noise only.

Ｄｉｇｉｔａｌ ｒａｄｉｏｇｒａｐｈｙによる喉頭の画像診断

The author evaluated the usefulness of digital radiography in the radiographic diagnosis of laryngeal diseases, utilizing Fuji Computed Radiography (CR) system. Main distinctive features of CR are as follows; photostimulable phosphor is used as the memory material, X-ray energy pattern is converted into digital signals, and then image signals are processed digitally.As the result, three types of image processing of CR, i. e. contrast processing, spatial frequency enhancement, and image subtraction, were clinically useful methods. Especially, one shot dual energy subtraction method is a new technical procedure to extinguish both cervical spine and calcified cartilage shadows in plain antero-posterior laryngeal X-photograph. Although this method belongs to a kind of plain X-photography, the feature of the laryngeal soft structures can be clearly demonstrated without little mortion artifact during examination.Digital radiography has so high spatial resolution and various image processing systems that it is possible to replace this system for some of the conventional screen-film method in X-ray analysis of laryngeal diseases.

DSA画像における記録系の基礎的および臨床的検討

Digital Subtraction Angiography (DSA) digtizes conventional X-ray images produced by the image intensifier TV system, and shows analogue vascular images on the monitor simultaneously. This modality is more sensitive to a contrast medium than the conventional angiography and can visualize vessels filled with a low concentration of a contrast medium very clearly. About two years has passed since the Philips DSA unit (DVI-1) was installed in Osaka University Hospital. During this period, about 600 cases were examined using the DSA. Factors that influenced the quality of the DSA imagies were divided into three categories as follows. 1) X-ray system (x-ray dose, tube voltage) 2) Display and recording system (film, multiformat camera) 3) Clinical problems (e.g., patients movement during X-ray exposure) We studied the relation between these factors and quality of the DSA images in this report. The most adequate X-ray dose was about 2,500 μR and tube voltage was 60 to 80 kVp. The result of evaluation of the film was that the film with wide latitude gave goodimages, because the specificity of the images could be changed by adjusting the brightness and contrast of the multiformat camera to get the best image. The multiformat camera that we used in this report could not give satisfactory imagies and should be designed fit to the specificity of the DSA images. Misregistration was mostly caused by patient movement, in many cases ; the movement was caused because of an inadequate explanation of the DSA examination to the patients. However, the current DSA system is limited because of the temporal subtraction method. One of the solutions for the misregistration is to decrease the patient's heat sensation by using a contrast medium having a low osmotic pressure. The contrast medium having a low osmotic pressure seems to be warking well. The other way is to use the dual energy subtraction method to decrease the misregistration. This system will become popular in the future. We discussed the major problems and some solutions for the DSA images by using our clinical experience.