Energy Subtraction Imaging Research Articles

The added value of contrast enhanced spectral mammography in identification of multiplicity of suspicious lesions in dense breast

ObjectiveTo evaluate the additive value of Contrast Enhanced Spectral Mammography (CESM) in the preoperative assessment of malignant lesions in dense breast parenchyma regarding multiplicity. Material and methodsThe study included 160 women having heterogeneous dense breast parenchyma (ACR c and d) with suspicious lesions identified on sono mammography examination. All patients performed contrast enhanced spectral mammography to confirm or exclude lesion multiplicity. The number of lesions was calculated in the contrast high energy subtraction images with the reference standard being histopathological analysis. ResultsAdding CESM to sono-mammography the accuracy in identifying multiple malignant lesion increased from 81.8% accuracy of sono-mammography up to 100% accuracy after adding CESM. ConclusionContrast enhanced spectral mammogram showed an added value in the preoperative assessment of breast masses increasing the accuracy of detection of lesions and multiplicity (multifocality and multi-centricity).

SU-G-JeP1-11: Feasibility Study of Markerless Tracking Using Dual Energy Fluoroscopic Images for Real-Time Tumor-Tracking Radiotherapy System

Purpose: The new real-time tumor-tracking radiotherapy (RTRT) system was installed in our institution. This system consists of two x-ray tubes and color image intensifiers (I.I.s). The fiducial marker which was implanted near the tumor was tracked using color fluoroscopic images. However, the implantation of the fiducial marker is very invasive. Color fluoroscopic images enable to increase the recognition of the tumor. However, these images were not suitable to track the tumor without fiducial marker. The purpose of this study was to investigate the feasibility of markerless tracking using dual energy colored fluoroscopic images for real-time tumor-tracking radiotherapy system. Methods: The colored fluoroscopic images of static and moving phantom that had the simulated tumor (30 mm diameter sphere) were experimentally acquired using the RTRT system. The programmable respiratory motion phantom was driven using the sinusoidal pattern in cranio-caudal direction (Amplitude: 20 mm, Time: 4 s). The x-ray condition was set to 55 kV, 50 mA and 105 kV, 50 mA for low energy and high energy, respectively. Dual energy images were calculated based on the weighted logarithmic subtraction of high and low energy images of RGB images. The usefulness of dual energy imaging for real-time tracking with an automated template image matching algorithm was investigated. Results: Our proposed dual energy subtraction improve the contrast between tumor and background to suppress the bone structure. For static phantom, our results showed that high tracking accuracy using dual energy subtraction images. For moving phantom, our results showed that good tracking accuracy using dual energy subtraction images. However, tracking accuracy was dependent on tumor position, tumor size and x-ray conditions. Conclusion: We indicated that feasibility of markerless tracking using dual energy fluoroscopic images for real-time tumor-tracking radiotherapy system. Furthermore, it is needed to investigate the tracking accuracy using proposed dual energy subtraction images for clinical cases.

胸部X線画像における肺腫瘤陰影の検出 -多重解像度フィルタ, エネルギー差分画像の利用と性能分析-

胸部X線画像における肺腫瘤陰影の検出 -多重解像度フィルタ, エネルギー差分画像の利用と性能分析-

Investigation of Energy-Dispersive X-ray Computed Tomography System with CdTe Scan Detector and Comparing-Differentiator and Its Application to Gadolinium K-Edge Imaging

An energy-dispersive (ED) X-ray computed tomography (CT) system is useful for carrying out monochromatic imaging by selecting optimal energy photons. CT is performed by repeated linear scans and rotations of an object. X-ray photons from the object are detected by the cadmium telluride (CdTe) detector, and event pulses of X-ray photons are produced using charge-sensitive and shaping amplifiers. The lower photon energy is determined by a comparator, and the maximum photon energy of 70 keV corresponds to the tube voltage. Logical pulses from the comparator are counted by a counter card through a differentiator to reduce pulse width and rise time. In the ED-CT system, tube voltage and current were 70 kV and 0.30 mA, respectively, and X-ray intensity was 18.2 µGy/s at 1.0 m from the source at a tube voltage of 70 kV. Demonstration of gadolinium K-edge CT for cancer diagnosis was carried out by selecting photons with energies ranging from 50.4 to 70 keV, and photon-count energy subtraction imaging from 30 to 50.3 keV was also performed.

TH-E-218-02: Deformable Registration Techniques for Dual Energy Imaging in Clinical Radiotherapy

Purpose: To demonstrate a deformable registration algorithm to reduce cardiac and respiratory motion artifacts in planar dual energy (DE) subtraction images obtained using a clinical on-board imaging (OBI) system. Methods: A Demons-based deformable registration algorithm was developed to reduce motion artifacts between sequential planar x-ray images obtained on the OBI. The algorithm was applied to paired (120 kVp and 60 kVp) chest x-rays, deforming the low energy image to the high energy image. To test the algorithm, a total of 20-paired scans were obtained from 6 lung cancer patients. All images were obtained using respiratory gating (RPM, Varian Medical Systems, Palo Alto, CA). In order to quantify the reduction in image artifacts, homologous landmarks were chosen using soft-tissue features on both sets of images. Landmarks were placed throughout the images to examine both cardiac and respiratory motion. The root-mean-square (RMS) difference between the individual points was calculated both before and after application of deformable registration. Results: A total of 160 landmarks were evaluated. Measurement of the RMS distances between the landmarks in the high and low energy deformed images showed improvement in all sectors. For points with < 2 mm RMS difference in original image, the deformation algorithm reduced the RMS residual by 36%. For points with > 2 mm RMS difference, the corresponding reduction was 64%. Qualitatively, DE images produced using Demons deformation showed fewer artifacts, and more defined tumor edges. Conclusions: The Demons algorithm reduced motion artifacts across all DE planar images. The greatest improvements were observed in regions near the diaphragm and the heart. In particular, artifacts due to cardiac motion showed the most improvement as these are not taken into account when performing respiratory gating. The iterative, matrix-based algorithm would greatly benefit from integration of GPU parallel-processing and will be implemented in future investigations. Supported by a grant from Varian Medical Systems.

SU-E-J-44: Dual Energy Subtraction Imaging to Improve Tumor Visibility at Oblique Angles.

To characterize the contrast improvement of simulated tumors in an anthropomorphic phantom using Dual Energy (DE) subtraction with a clinical on-board imager (OBI) at oblique angles. An Alderson lung/chest anthropomorphic phantom with simulated tumors in the thoracic cavity was imaged using a sequential DE imaging methodology. High (120kVp) and low (60kVp) planar images were obtained in pairs every 100 in a full (3600) rotation using the OBI (Varian Medical Systems, Palo Alto, CA). Optimal mAs settings for DE component images were determined byvarying the x-ray exposure time, while maintaining a constant tube current. DE images were created to best suppress the bone overlaying the simulated tumors. Tumor visibility in DE images was quantified using the Contrast-to-Noise Ratio (CNR). The ratio of the CNR from the DE image relative to a single image (standard protocol) was evaluated as a function of gantry angle. CNR was improved with DE imaging by an average ratio of 1.66 over all gantry angles. The greatest improvement occurred at gantry angles where the tumor was obstructed by the ribs alone. More modest improvements were observed where the tumor overlapped other soft tissue structures (such as the heart) or the dense spine, on a given projection. This study illustrates the feasibility of performing DE imaging at oblique gantry angles using a clinical on-board imaging system. Incorporating DE imaging into clinical practice may allow for verification of tumor position at oblique gantry angles, and may facilitate the development of markerless motion tracking techniques. Supported by a grant from Varian Medical Systems.

Dual-Energy Subtraction Imaging for Diagnosing Vocal Cord Paralysis with Flat Panel Detector Radiography

ObjectiveTo investigate the clinical feasibility of dual energy subtraction (DES) imaging to improve the delineation of the vocal cord and diagnostic accuracy of vocal cord paralysis as compared with the anterior-posterior view of flat panel detector (FPD) neck radiography.Materials and MethodsFor 122 consecutive patients who underwent both a flexible laryngoscopy and conventional/DES FPD radiography, three blinded readers retrospectively graded the radiographs during phonation and inspiration on a scale of 1 (poor) to 5 (excellent) for the delineation of the vocal cord, and in consensus, reviewed the diagnostic accuracy of vocal cord paralysis employing the laryngoscopy as the reference. We compared vocal cord delineation scores and accuracy of vocal cord paralysis diagnosis by both conventional and DES techniques using κ statistics and assessing the area under the receiver operating characteristic curve (AUC).ResultsVocal cord delineation scores by DES (mean, 4.2 ± 0.4) were significantly higher than those by conventional imaging (mean, 3.3 ± 0.5) (p < 0.0001). Sensitivity for diagnosing vocal cord paralysis by the conventional technique was 25%, whereas the specificity was 94%. Sensitivity by DES was 75%, whereas the specificity was 96%. The diagnostic accuracy by DES was significantly superior (κ = 0.60, AUC = 0.909) to that by conventional technique (κ = 0.18, AUC = 0.852) (p = 0.038).ConclusionDual energy subtraction is a superior method compared to the conventional FPD radiography for delineating the vocal cord and accurately diagnosing vocal cord paralysis.

Improved detection of pulmonary nodules on energy-subtracted chest radiographs with a commercial computer-aided diagnosis software: comparison with human observers

To retrospectively analyze the performance of a commercial computer-aided diagnosis (CAD) software in the detection of pulmonary nodules in original and energy-subtracted (ES) chest radiographs. Original and ES chest radiographs of 58 patients with 105 pulmonary nodules measuring 5-30 mm and images of 25 control subjects with no nodules were randomized. Five blinded readers evaluated firstly the original postero-anterior images alone and then together with the subtracted radiographs. In a second phase, original and ES images were analyzed by a commercial CAD program. CT was used as reference standard. CAD results were compared to the readers' findings. True-positive (TP) and false-positive (FP) findings with CAD on subtracted and non-subtracted images were compared. Depending on the reader's experience, CAD detected between 11 and 21 nodules missed by readers. Human observers found three to 16 lesions missed by the CAD software. CAD used with ES images produced significantly fewer FPs than with non-subtracted images: 1.75 and 2.14 FPs per image, respectively (p = 0.029). The difference for the TP nodules was not significant (40 nodules on ES images and 34 lesions in non-subtracted radiographs, p = 0.142). CAD can improve lesion detection both on energy subtracted and non-subtracted chest images, especially for less experienced readers. The CAD program marked less FPs on energy-subtracted images than on original chest radiographs.

A Preliminary Investigation of Dual Energy (DE) Subtraction Imaging for Improved Soft-Tissue Localization in the Pelvis

A Preliminary Investigation of Dual Energy (DE) Subtraction Imaging for Improved Soft-Tissue Localization in the Pelvis

A Preliminary Investigation of Dual Energy Subtraction Imaging for Improved Target Localization in the Thorax

A Preliminary Investigation of Dual Energy Subtraction Imaging for Improved Target Localization in the Thorax

TU‐D‐L100J‐07: The Use of CT Dual‐Energy Subtraction Imaging to Detect Kidney Stones Amid Iodinated Contrast Material

Purpose: Iodinated contrast excreted into the renal collecting systems and ureters is of similar CT attenuation as kidney stones, making stones difficult or impossible to detect in contrast‐enhanced CT scans. This necessitates precontrast imaging for kidney stone work‐up. Our purpose was to determine the ability of CT dual‐energy subtraction imaging to selectively remove iodine signal while preserving the signal from kidney stones. Method and Materials: A phantom containing twenty kidney stones with different composition (calcium oxalate monohydrate, calcium hydroxyapatite, uric acid) and size (2 – 6 mm) was scanned with the stones surrounded by water or an iodine/water solution (500, 1000, 1400, 1900, 2300 HU at 120 kV) using a dual‐source CT system (Siemens Definition) and 80/140 kV tube potentials. Iodine calibration curves were generated to determine the CT‐number ratio between the low and high‐kV images and energy subtraction images created. Patients with known stone disease were scanned using the same radiation dose as for single‐energy CT as part of clinically‐indicated examinations. Subtraction images were created and compared to images of the known stone location. Results: Image subtraction performed using the empirical calibration curves was successful in removing iodine signal and preserving stone signal for all evaluated stones. One calibration factor to remove iodine signal was successful for all concentrations below the saturation limit, demonstrating independence of the technique on iodine concentration. In initial patient studies, the stone(s) remained visible after subtraction of the iodine signal, demonstrating the potential of the technique in vivo. Conclusion: Dual energy CT can successfully remove iodine while preserving the signal associated with renal stones. This capability may allow the elimination of the non‐contrast phase of CT urogram studies, which may decrease the radiation dose to the patient by 50%. Conflict of Interest: Partial research support from Siemens Medical Solutions.

Developments in radiography and fluoroscopy

Digital technologies will eventually supersede film–screen radiography and image intensifier-based fluoroscopy.Software developments deliver advanced applications in digital imaging, including dual energy subtraction imaging, tomosynthesis, computer aided detection (CAD) and 3D volumetric imaging.Improved clinical detail is demonstrated in chest imaging, mammography and neuroimaging, amongst others.Clinical images are readily available and can be transferred to diverse locations via PACS (Picture Archive and Communication System) or a teleradiology system for remote diagnosis.The time commitment required for training in the use of the digital imaging equipment, workstations and extra routine quality assurance (e.g. as required for image display monitors) is a concern in the busy hospital imaging department.

New contrast media designed for x-ray energy subtraction imaging in digital mammography.

In contrast-enhanced dual-energy subtraction imaging 2 images acquired postcontrast media administration at different energies are subtracted to highlight structures hidden in the absence of contrast media. X-ray spectra of the newly developed digital full-field mammography units (GE Senographe 2000 D) are dominated by the emission lines of the Mo or Rh anodes. The K-edge of Zirconium (Zr) is flanked by these 2 emission lines. Thus, the attenuation of Zr should experience a pronounced change of attenuation in parallel with a change of anodes. Under clinically relevant conditions, the contrasting behavior of Zr should be compared with that of other elements having K-edge energies outside the window spanned by the 2 anode emission lines. Solutions containing the contrasting elements Br, Y, Zr, I, and Gd were investigated for dual-energy subtraction in digital mammography with the 2 anode/filter settings (Mo/Mo and Rh/Rh). These solutions were investigated in phantom studies in the energy range conventionally used in mammography. Additionally, the contrasting behavior of Zr and I was compared in an in vivo study in rats. The sweeping over the K-edge by alternating between the Mo and Rh anodes increases the detection of Zr in energy subtraction imaging at constant high voltage. This procedure does not lead to sufficient contrast enhancement for iodine-based contrast media which become detectable by increasing the high voltage to 40-49 kV. The instrumental and physical data outlined predestine Zr as contrasting element with a high potential for energy subtraction imaging in digital mammography in the energy range conventionally applied.

Image quality analysis for dual energy subtraction imaging with a femtosecond laser-based hard X-ray source

We present a study of image quality for dual energy subtraction imaging using an iodinated contrast agent and a femtosecond laser-based hard X-ray source. The INRS CPA laser (400 fs pulse focused on solid targets in a 3 /spl mu/m spot at 4 /spl times/ 10/sup 18/ W cm/sup -2/) was used to create a bright hard X-ray source (conversion efficiency of 10/sup -5/ in the characteristic K/sub /spl prop// line emission, 12 /spl mu/m X-ray source diameter). A model of image quality has been developed and been benchmarked with specific experiments using specially made angiography phantoms.

Quantification of Volumetric Coronary Blood Flow With Dual-Energy Digital Subtraction Angiography

As a solution to the well-documented problems associated with visual interpretation of coronary arteriograms, more physiological methods of assessing coronary artery stenosis are being investigated. Volumetric coronary blood flow (BF) can be a valuable aid in the analysis of functional significance of arterial obstruction. The left anterior descending coronary artery (LAD) of 15 anesthetized pigs (40 to 50 kg) was dissected free from the epicardium in its proximal portion, and a transmit-time ultrasound flow probe of the appropriate size was applied. A vascular occluder was positioned distal to the flow probe for flow adjustments. Contrast injections (2 to 4 mL/s for 3 seconds) were made into the left main coronary artery during image acquisition with a motion-immune dual-energy digital subtraction angiography (DE DSA) system. Tissue-suppressed energy-subtracted images were used to generate time-density curves. BF measurements were made in the LAD vascular bed with use of the time-density curve, with consideration that blood was momentarily replaced with contrast during the injection. In 19 comparisons, the mean BF, measured with the use of DE DSA, correlated extremely well with the mean ultrasound flow (DE DSA=0.90 ultrasound+3.10 mL/min, r=.96). Also, contrast injection increased the BF by an average of only 15% during the image-acquisition time interval. Accurate BF measurements can be made with motion-immune DE DSA. The BF measurements can be completed before the onset of significant changes in BF due to contrast injection. Furthermore, it is possible to make the BF measurements during routine coronary arteriography.

The influence of tube voltage, X-ray exposure rate and thickness of filter material on image quality with dual-energy subtraction imaging in chest diagnostics

Digital luminescent radiography enables dual-energy subtraction imaging, because this computed system allows susbtraction of imaging data and image post processing, as for example special windowing or edge enhancement. In a special cassette a copper filter is placed between two imaging plates for energy separation by a single X-ray exposure. Image post-processing with subtraction of imaging data permits the elimination of either skeleton or soft tissue structures. The influence of filter thickness, tube voltage and the X-ray exposure dosage on image quality is examined by the use of an anthropomorphic quality is examined by the use of an anthropomorphic phantom of the chest. According to our initial results dual energy subtraction imaging in one-shot-technique seems to be useful in the diagnostics of skeletal lesions and especially pulmonary nodules.

Quantification of coronary arterial calcium by dual energy digital subtraction fluoroscopy

Clinical studies of the heart with fluoroscopy have shown that fluoroscopic visualization of calcium in the coronary arteries is strongly associated with coronary artery disease. However, fluoroscopic detection is limited by its low sensitivity, which is partly due to the interfering background tissue structures and image quantum noise. Moreover, quantification of the absolute amount of calcium in an arterial segment has not been possible. A real-time dual-energy subtraction technique has been investigated as a possible solution to the above problem. In this energy subtraction technique, the kVp and filtration are switched at 30 Hz. In order to assess the potential utility of this videodensitometric technique to quantitate coronary artery calcium, arterial phantoms and excised segments of diseased human arteries were imaged. The low- and high-energy images were corrected for scatter and veiling glare before subtraction. Calcium measurements were made using the tissue-suppressed energy-subtracted images. The estimated calcium phosphate and ashed weights of the calcified arterial segments (N = 20) were highly correlated (slope = 1.04, Intercept = -0.33 mg, r = 0.92).

Iodine K-edge dual-energy imaging for subtraction angiography using synchrotron radiation and a 2-dimensional detector

A 2-dimensional energy-subtraction imaging system using synchrotron radiation has been improved in a number of ways; especially the energy-switching mechanism in which a monochromator crystal is oscillated trapezoidally has been improved. These improvements have led to real-time imaging of the right coronary artery in a rabbit after an intravenous injection of a contrast agent. This artery has a diameter of about 0.5 mm. However, this system has limitations concerning the energy difference between two component exposures and the total time of acquiring two images. We have tested a new method. Since the crystal was too heavy to oscillate quickly, the next step was to make the energy switching faster than in the previous method by the use of lighter moving parts. An iodine filter is used in the new method. Filter-chopping of the X-ray beam switches the dual-energy imaging energies, because the iodine filter selectively absorbs high-energy X-rays rather than K-edge energy X-ray. Moreover, by the use of the iodine filter, the energy difference between two exposures can be decreased to less than half of that in the previous method. Preliminary studies on the new method were performed in rats.

162. ファクターアナリシスによるエネルギーサブトラクションイメージング(第 46 回総会学術大会会員研究発表予稿)

162. ファクターアナリシスによるエネルギーサブトラクションイメージング(第 46 回総会学術大会会員研究発表予稿)

Two interpolating filters for scatter estimation.

We have previously reported on a dual-measurement sample-and-estimate technique for scatter correction. In this paper, we present a scatter-correction technique that uses the previous sampling scheme but a different method of estimation. To provide samples of the scatter directly, an array of small, uniformly spaced lead disks is placed immediately before the object during only the first measurement. Interpolating from these samples we form an estimate of the scatter. We subtract this estimate from the second measurement to form a scatter-corrected image. Previously, we used least-squares interpolation to estimate the scatter. Because the samples are uniformly spaced, classical sampling theory motivated the investigation of interpolating filters for scatter estimation. To form the scatter image, we convolved the sample set with two different interpolating filters--a sinc function from classical sampling theory and a jinc function because the scatter function is radially symmetric. Using phantoms as objects, we applied both filters for scatter correction in vessel imaging and energy-subtraction imaging. Initial corrected images contained an artifact attributed to aliasing. We modified the filter widths to reduce the aliasing. Although improvements in image quality were measured and the artifact was less pronounced, the artifact was still present. We present the phantom results obtained with this class of filters and discuss methods for its improved performance.