Dual-energy Subtraction Research Articles

Magnification Embossed Radiography Utilizing Image-Shifting Subtraction Program

We developed an image-shifting subtraction program and carried out magnification embossed radiography (MER) utilizing single- and dual-energy subtractions. In particular, dual-energy subtraction was carried out to decrease the absorption contrast of unnecessary regions. The contrast resolution of the target region was increased by the use of subtraction software and a linear-contrast system in a flat-panel detector (FPD). The X-ray generator had a 100-µm-focus tube, and the subtractions were performed at tube voltages of 40 and 70 kV, a tube current of 0.50 mA, and an X-ray exposure time of 5.0 s. MER images with threefold magnification were obtained using the FPD with a pixel size of 48×48 µm2, and the shifting dimensions of the imaged object in the horizontal and vertical directions ranged from 48 to 192 µm. At a shifting distance ranging from 48 to 144 µm, the spatial resolutions in the horizontal and vertical directions measured with a lead test chart were both 50 µm. In the MER of nonliving animals, we obtained high-contrast embossed images of fine bones, gadolinium oxide particles in blood vessels, and iodine-based microspheres in coronary arteries of approximately 100 µm diameter.

Bone images from dual-energy subtraction chest radiography in the detection of rib fractures

Objective To assess the sensitivity and image quality of chest radiography (CXR) with or without dual-energy subtracted (ES) bone images in the detection of rib fractures. Materials and methods In this retrospective study, 39 patients with 204 rib fractures and 24 subjects with no fractures were examined with a single exposure dual-energy subtraction digital radiography system. Three blinded readers first evaluated the non-subtracted posteroanterior and lateral chest radiographs alone, and 3 months later they evaluated the non-subtracted images together with the subtracted posteroanterior bone images. The locations of rib fractures were registered with confidence levels on a 3-grade scale. Image quality was rated on a 5-point scale. Marks by readers were compared with fracture localizations in CT as a standard of reference. Results The sensivity for fracture detection using both methods was very similar (34.3% with standard CXR and 33.5% with ES-CXR, p = 0.92). At the patient level, both sensitivity (71.8%) and specificity (92.9%) with or without ES were identical. Diagnostic confidence was not significantly different (2.61 with CXR and 2.75 with ES-CXR, p = 0.063). Image quality with ES was rated higher than that on standard CXR (4.08 vs. 3.74, p < 0.001). Conclusions Despite a better image quality, adding ES bone images to standard radiographs of the chest does not provide better sensitivity or improved diagnostic confidence in the detection of rib fractures.

Dual Energy Subtraction Digital Radiography Improves Performance of a Next Generation Computer-aided Detection Program

Computer-aided detection (CAD) has shown potential to assist physicians in the detection of lung nodules on chest radiographs, but widespread acceptance has been stymied by high false-positive rates. Few studies have examined the potential for dual energy subtraction (DES) to improve CAD performance. Institutional review board approval was obtained, the requirement for informed consent was waived because the study was retrospective, and practices conformed to Health Insurance Portability and Accountability Act regulations. The CAD program was applied retrospectively to dual energy posteroanterior (PA) chest radiographs of 36 patients (17 women, 19 men, mean age 69 y) with 48 pathology proven lung nodules. Results were analyzed to determine the stand-alone CAD program false-positive rates, and sensitivity by nodule subtlety and location. Statistical analysis was performed using the chi(2) or Fisher exact tests for independence of sensitivities between standard PA and DES radiography. Differences in the mean false-positives per image (FPPI) between radiographic modalities were determined using the paired Students t test, and bootstrap confidence intervals were obtained to confirm results. The sensitivity of the CAD program with the standard PA was 46% (22 of 48 nodules) compared with 67% (32 of 48 nodules) using the DES soft tissue or bone-subtracted view (P=0.064). The average number of FPPI identified by CAD was significantly lower using DES (FPPI(soft tissue) = 1.64) when compared with the standard PA chest radiograph (FPPI(PA) = 2.39) (P<0.01). DES has the potential to improve stand-alone CAD performance by both increasing sensitivity for certain subtle lung cancer lesions and decreasing overall CAD false-positive rates.

Phantom study to evaluate contrast‐medium‐enhanced digital subtraction mammography with a full‐field indirect‐detection system

This phantom study simulates contrast-medium-enhanced digital subtraction mammography (CEDM) and compares subtracted image quality and total mean glandular dose for two alternative spectral combinations available in a GE Senographe DS mammography unit. The first choice takes advantage of large iodine attenuation at low photon energies and uses traditionally available spectra (anode/filter combinations Mo/Mo at 25 kV and Rh/Rh at 40 kV, "Mo25-Rh40"). The second choice, selected from a previous analytical optimization, includes harder spectra obtained by adding external filtration to traditional beams (Rh/Rh at 34 kV and Rh/Rh+5 mm of Al at 45 kV, "Rh34-Rh45H"). Individual images of a custom-made phantom containing tubes of various diameters filled with water- or iodine-based contrast agent were acquired with both spectral combinations. The total breast entrance air kerma, considering subtraction of two images, was limited to 8.76 mGy (1 R). The results were compared to predictions obtained through an analytical formalism that assumes noise of stochastic origin. Individual images were evaluated and subtracted under five combinations of temporal and dual-energy modalities. Signal variance analysis in individual raw images showed important contributions of nonstochastic origin, associated with the software applied to raw images, the curved geometry, and strong attenuation of the phantom cylindrical iodine-filled tubes, causing experimental SNR to vary from 2.2 to 0.8 times the predictions from low to high values of SNR. Iodine contrast in the subtracted images was found to be mainly defined by the spectra, independent of exposure, and linearly dependent on the iodine mass thickness. The highest contrast was obtained with the combined dual-energy temporal subtraction with Rh34-Rh45H, its value was 7% larger than the highest value measured with Mo25-Rh40. As expected, temporal modalities (single and dual energy, any spectral choice) led to higher contrast-over-noise ratio (CNR) than nontemporal dual-energy subtraction, the latter being negligibly small with Mo25-Rh40. CNR for 4 mg iodine/cm2 imaged temporally in a dual-energy fashion with Rh34-Rh45H (iodine imaged at high energy) is about 1.7 times the optimum for Mo25-Rh40 (iodine imaged at low energy). Iodine thicknesses needed to fulfill Rose's criterion were 0.78 +/- 0.02 mg iodine/cm2 for Mo25-Rh40 and 0.54 +/- 0.17 mg iodine/cm2 for Rh34-Rh45H, both lower than the proposed biological concentration of iodine in breast tumors after contrast medium administration. Although similar dose levels were obtained with both spectral choices under dual-energy (temporal and nontemporal) subtraction, the dose obtained in single-energy temporal subtraction with the Mo25 spectrum was 1.2 mGy lower than the dose from the modality offering the highest CNR. In all results considered, the spectral choice Mo25-Rh40 was found to represent an interesting alternative to the use of high-energy hardened spectra for CEDM, particularly when performing dynamic studies of the contrast-agent uptake in breast lesions.

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.

Application of Dual-Energy K-Edge Subtraction Imaging to Assessment of Heat Treatments in Al-Cu Alloys

Dual-energy K-edge subtraction imaging technique has been employed to analyze the spatial distribution of copper and its change in three-dimensions quantitatively during a solution treatment. In order to realize it, some preliminary investigations on the verification and assurance of accuracy and repeatability have been performed. Inhomogeneous Cu concentration distribution is revealed even after the solution treatment for a sufficiently long period of time at a high temperature in an Al-Cu alloy. The present technique has a unique potential to realize four-dimensional chemical-concentration mapping.

Influence of high-temperature solution treatments on mechanical properties of an Al–Si–Cu aluminum alloy

It has been demonstrated that the strength of an Al–Si–Cu alloy is maximized by high-temperature solution treatment at 807 K, which is approximately 16 K higher than the ternary eutectic temperature. The dual-energy K-edge subtraction imaging technique has been employed to obtain the spatial distribution of copper and its change during its solution treatment in three dimensions quantitatively, providing interpretations of the improved mechanical properties in terms of age-hardenability and its spatial variation. It has been also confirmed that the occurrence of incipient local melting and the accompanying growth of micro pores adjacent to the melt regions lead to fractures caused by these defects. However, it can be inferred that the positive effects can outweigh the negative effects even above the eutectic temperature, thereby realizing the maximum strength at such relative high temperature levels.

Embossed radiography utilizing an image-shifting subtraction program

We developed an image-shifting subtraction program and carried out embossed radiography (ER) utilizing single- and dual-energy subtractions. In particular, dual-energy subtraction was carried out to decrease the absorption contrast of unnecessary regions. The contrast resolution of a target region was increased using the subtraction program and a linear-contrast system in a flat panel detector (FPD). The X-ray generator had a 100 μm-focus tube, and the subtractions were performed at tube voltages of 40 and 70 kV, a tube current of 0.50 mA, and an X-ray exposure time of 5.0 s. ER was achieved with cohesion imaging using the FPD with pixel sizes of 48×48 μm 2, and the shifting dimension of an object in the horizontal and vertical directions ranged from 48 to 96 μm. At a shifting distance of 96 μm, the spatial resolutions in the horizontal and vertical directions measured with a lead test chart were both 83 μm. In ER of animal phantoms, we obtained high-contrast embossed images of fine bones, gadolinium oxide particles in blood vessels, iodine-based microspheres in coronary arteries approximately 100 μm in diameter.

Dual-energy CT angiography of pelvic and lower extremity arteries: dual-energy bone subtraction versus manual bone subtraction

To analyse the effect of dual-energy bone subtraction (DEBS) on the image quality of peripheral computed tomography (CT) angiograms. Twenty patients underwent dual-energy CT angiography of the pelvic and lower extremity arteries using commercially available equipment. Two different methods of image processing were employed for each CT angiographic dataset: (1) DEBS, and (2) manual bone subtraction (MBS). Effects on vessel visibility and artificial vessel alterations were compared. Bone removal, and the resultant visibility of vessel segments, were significantly better with DEBS than with MBS (p=0.011). The overall frequency of vessel-related alterations was lower in MBS compared with DEBS (p=0.001). Specifically, in the 249 vessel segments with calcified plaques, MBS generated fewer vessel alterations than DEBS (p<0.001). In the 309 vessel segments without calcified plaques, there was no difference in vessel alteration between the two techniques (p=0.22). DEBS facilitates bone removal in peripheral CT angiography, but generates more vessel alterations, particularly in the presence of calcified plaque.

Projection x-ray imaging with photon energy weighting: experimental evaluation with a prototype detector

The signal-to-noise ratio (SNR) in x-ray imaging can be increased using a photon counting detector which could allow for rejecting electronics noise and for weighting x-ray photons according to their energies. This approach, however, was not feasible for a long time because photon counting x-ray detectors with very high count rates, good energy resolution and a large number of small pixels were required. These problems have been addressed with the advent of new detector materials, fast readout electronics and powerful computers. In this work, we report on the experimental evaluation of projection x-ray imaging with a photon counting cadmium–zinc–telluride (CZT) detector with energy resolving capabilities. The detector included two rows of pixels with 128 pixels per row with 0.9 × 0.9 mm2 pixel size, and a 2 Mcount pixel−1 s−1 count rate. The x-ray tube operated at 120 kVp tube voltage with 2 mm Al-equivalent inherent filtration. The x-ray spectrum was split into five regions, and five independent x-ray images were acquired at a time. These five quasi-monochromatic x-ray images were used for x-ray energy weighting and material decomposition. A tissue-equivalent phantom was used including contrast elements simulating adipose, calcifications, iodine and air. X-ray energy weighting improved the SNR of calcifications and iodine by a factor of 1.32 and 1.36, respectively, as compared to charge integrating. Material decomposition was performed by dual energy subtraction. The low- and high-energy images were generated in the energy ranges of 25–60 keV and 60–120 keV, respectively, by combining five monochromatic image data into two. X-ray energy weighting was applied to low- and high-energy images prior to subtraction, and this improved the SNR of calcifications and iodine in dual energy subtracted images by a factor of 1.34 and 1.25, respectively, as compared to charge integrating. The detector energy resolution, spatial resolution, linearity, count rate, noise and image uniformity were investigated. The limitations of this technology were emphasized and possible solutions were discussed.

Dual-energy contrast-enhanced digital breast tomosynthesis – a feasibility study

Contrast-enhanced digital breast tomosynthesis (CE-DBT) is a novel modality for imaging breast lesion morphology and vascularity. The purpose of this study is to assess the feasibility of dual-energy subtraction as a technique for CE-DBT (a temporal subtraction CE-DBT technique has been described previously). As CE-DBT evolves, exploration of alternative image acquisition techniques will contribute to its optimisation. Evaluation of dual-energy CE-DBT was conducted with Institutional Review Board (IRB) approval from our institution and in compliance with federal Health Insurance Portability and Accountability Act (HIPAA) guidelines. A 55-year old patient with a known malignancy in the right breast underwent imaging with MRI and CE-DBT. CE-DBT was performed in the medial lateral oblique view with a DBT system, which was modified under IRB approval to allow high-energy image acquisition with a 0.25 mm Cu filter. Image acquisition occurred via both temporal and dual-energy subtraction CE-DBT. Between the pre- and post-contrast DBT image sets, a single bolus of iodinated contrast agent (1.0 ml kg(-1)) was administered, followed by a 60 ml saline flush. The contrast agent and saline were administrated manually at a rate of approximately 2 ml s(-1). Images were reconstructed using filtered-back projection and transmitted to a clinical PACS workstation. Dual-energy CE-DBT was shown to be clinically feasible. In our index case, the dual-energy technique was able to provide morphology and kinetic information about the known malignancy. This information was qualitatively concordant with that of CE-MRI. Compared with the temporal subtraction CE-DBT technique, dual-energy CE-DBT appears less susceptible to motion artefacts.

SYNCHROTRON‐BASED ANGIOGRAPHY FOR INVESTIGATION OF THE REGULATION OF VASOMOTOR FUNCTION IN THE MICROCIRCULATION IN VIVO

1. Real-time imaging of the vascular networks of any organ system in vivo is possible with synchrotron radiation (SR) angiography. In this review, we discuss the advantages of SR angiography over clinical X-ray imaging and other non-ionizing imaging modalities. Current limitations are also described. 2. The usefulness of dual-energy and temporal subtraction approaches to K-edge iodine imaging are compared. 3. High-resolution images of the microcirculation in small animals are now being collected routinely by multiple research groups through public access research programmes at synchrotrons worldwide. Such images are permitting unrivalled insights into vasomotor regulation deep within intact organ systems, such as the brain, kidney, lung and heart. For example, recent observations indicate changes in vascular control mechanisms in pulmonary hypertension that are specific to certain branching segments of the pulmonary circulation. 4. New possibilities for non-iodinated contrast agents in SR angiography are briefly described. 5. High-resolution angiography in vivo using SR will now allow us to identify vessels with localized or non-uniform vasoconstriction in states such as diabetes or to characterize the extent of endothelial dysfunction in the circulation following hypertension or ischaemic-reperfusion injury. In the near future, this research is expected to reveal the contribution of resistance vessel dysfunction to diverse pathophysiological states, such as stroke, hypertension and ischaemic heart disease.

Embossed radiography utilizing energy subtraction

Currently, it is difficult to carry out refraction-contrast radiography by using a conventional X-ray generator. Thus, we developed an embossed radiography system utilizing dual-energy subtraction for decreasing the absorption contrast in unnecessary regions, and the contrast resolution of a target region was increased by use of image-shifting subtraction and a linear-contrast system in a flat panel detector (FPD). The X-ray generator had a 100-microm-focus tube. Energy subtraction was performed at tube voltages of 45 and 65 kV, a tube current of 0.50 mA, and an X-ray exposure time of 5.0 s. A 1.0-mm-thick aluminum filter was used for absorbing low-photon-energy bremsstrahlung X-rays. Embossed radiography was achieved with cohesion imaging by use of the FPD with pixel sizes of 48 x 48 microm, and the shifting dimension of an object in the horizontal direction ranged from 100 to 200 microm. At a shifting distance of 100 mum, the spatial resolutions in the horizontal and vertical directions measured with a lead test chart were both 83 microm. In embossed radiography of non-living animals, we obtained high-contrast embossed images of fine bones, gadolinium oxide particles in the kidney, and coronary arteries approximately 100 microm in diameter.

Reduction of motion artefacts in non-gated dual-energy radiography

The objective of this work was to reduce motion artefacts in non-gated dual-energy subtraction radiography whilst preserving the contrast-to-noise ratio (CNR) in regions with low motion. Dual-energy radiography provides material-selective information (soft-tissue and bone images) that may be used for improved detection of calcifications in lung nodules. The weighted logarithmic dual-energy subtraction of thoracic images performed without electrocardiogram gating results in motion-induced artefacts. The low-energy image was acquired at the usual dose setting at 60 kV. To obtain the high-energy (120 kV) information, a series of consecutive images at a time interval of 30 ms were made. The series integral dose was equivalent to the dose of a single conventional high-energy image. A motion-free merging technique was introduced that combines standard images yielding low image noise with phase-selective images yielding motion artefact-free image regions which are used for dual-energy subtraction. Evaluations of the method were performed with simulations and measurements using a C-arm system (Axiom Artis; Siemens AG, Germany) equipped with a flat detector of 40 x 30 cm(2). The merging approach conserved standard image noise levels and the CNR in areas without cardiac motion, whereas image noise in pericardial lung regions and in the heart was increased compared with standard images. Motion artefacts in the heart and in the lung areas close to the heart are significantly reduced in the material-selective images when compared with a standard non-gated subtraction.

Energy-resolved computed tomography: first experimental results

First experimental results with energy-resolved computed tomography (CT) are reported. The contrast-to-noise ratio (CNR) in CT has been improved with x-ray energy weighting for the first time. Further, x-ray energy weighting improved the CNR in material decomposition CT when applied to CT projections prior to dual-energy subtraction. The existing CT systems use an energy (charge) integrating x-ray detector that provides a signal proportional to the energy of the x-ray photon. Thus, the x-ray photons with lower energies are scored less than those with higher energies. This underestimates contribution of lower energy photons that would provide higher contrast. The highest CNR can be achieved if the x-ray photons are scored by a factor that would increase as the x-ray energy decreases. This could be performed by detecting each x-ray photon separately and measuring its energy. The energy selective CT data could then be saved, and any weighting factor could be applied digitally to a detected x-ray photon. The CT system includes a photon counting detector with linear arrays of pixels made from cadmium zinc telluride (CZT) semiconductor. A cylindrical phantom with 10.2 cm diameter made from tissue-equivalent material was used for CT imaging. The phantom included contrast elements representing calcifications, iodine, adipose and glandular tissue. The x-ray tube voltage was 120 kVp. The energy selective CT data were acquired, and used to generate energy-weighted and material-selective CT images. The energy-weighted and material decomposition CT images were generated using a single CT scan at a fixed x-ray tube voltage. For material decomposition the x-ray spectrum was digitally spilt into low- and high-energy parts and dual-energy subtraction was applied. The x-ray energy weighting resulted in CNR improvement of calcifications and iodine by a factor of 1.40 and 1.63, respectively, as compared to conventional charge integrating CT. The x-ray energy weighting was also applied to low- and high-energy CT projections used for material decomposition. This improved the CNR in images of decomposed calcification and iodine by a factor of 1.57 and 1.46, respectively, as compared to conventional charge integrating CT. Some limitations were observed due to hole trapping in CZT and charge sharing between the detector pixels. First experimental results demonstrate that energy-resolved CT is coming close to its practical applications. Although hole trapping and charge sharing in CZT deteriorates x-ray spectrum and limits CNR improvement with energy weighting and detector count rate, this problem has a feasible solution, which is discussed in this paper and is a matter of ongoing research.

Sequential dual-energy subtraction technique with a dynamic flat-panel detector (FPD): primary study for image-guided radiation therapy (IGRT)

A sequential dual-energy subtraction technique for image-guided radiation therapy (IGRT) was developed. Here, we report on a computerized method for creating sequential soft-tissue images and the accuracy of tracking targets on the images obtained, in comparison to conventional fluoroscopic images. Two sets of sequential chest images during respiration of a normal subject were obtained with X-rays of different energy separately with a flat-panel detector (FPD). Sequential soft-tissue images were created from the two sets of sequential images consisting of real-time images and reference template images, respectively. The creation of sequential soft-tissue images consisted of three steps: one-to-one image correspondence of the two sequential images, image registration, and image subtraction in each frame. Motion tracking of lung vessels was then performed by the template-matching technique. For evaluation of the accuracy of motion tracking on the sequential soft-tissue images, the results were compared with those on the original sequential images. Sequential soft-tissue images provided more accurate tracking than the original images (P < 0.01). There was no significant error throughout all frames in the soft-tissue images, whereas the rib shadow introduced a tracking error in the original images. The maximum errors were 4.1 +/- 0.3 mm in the sequential soft-tissue images and 28.1 +/- 20.0 mm in the original images. In conclusion, sequential soft-tissue images were helpful for tracking of a target affected by respiratory motion. Dual-energy subtraction has the potential to improve the accuracy of IGRT without implanted markers.

SU‐GG‐J‐93: Feasibility Study On Artifact Reduction Using Dual Energy Digital Tomosynthesis

Purpose: We propose a simulation study to examine the feasibility of incorporating dual energy (DE) subtraction with digital tomosynthesis (DTS) to help reduce DTS reconstruction artifacts. Method and Materials: We have previously investigated the incorporation of DTS into radiation therapy for patient localization and found the initial results promising. Due to the limited sampling of the Fourier space, high contrast signals, such as bone, tend to bleed into other slices of the reconstruction. These artifacts could be misconstrued or reduce the conspicuity of low‐contrast signals, especially in the lungs. For this simulation study, an advanced 4D NURBS based Cardiac‐Torso (NCAT) phantom, which includes a detailed whole‐body anatomy of organs including the lungs, airway tree, heart, and vessels, was used. When combined with advanced models of the imaging process, the NCAT phantom can produce realistic imaging data. For this study, a unique x‐ray projection algorithm developed specifically for the NCAT phantom was used to generate limited angle projection data for DTS reconstruction. 81 images were acquired over a 40 degree arc. The breathing cycle was set to simulate breath‐hold imaging. Data sets were generated using spectra of 80 and 120 kVp. For this study, dual energy subtraction (DES) was performed on these two sets of limited angle images to remove the overlying bony anatomy. The resulting images were then reconstructed using a modified filtered back projection technique. This DE‐DTS volume was then visually compared to a standard DTS reconstruction of the 120 kVp data set. Results: The removal of the overlying bony anatomy of the chest in the DE‐DTS images helps to reduce the high contrast artifacts present in the standard DTS reconstruction. Conclusion: This feasibility study demonstrates that DE‐DTS imaging may provide increased visualization of low contrast regions in the chest by reducing high contrast DTS reconstruction artifacts.

TH‐C‐332‐06: Optimization and Calibration Procedures of a Contrast‐Medium Based Subtraction Technique in Digital Mammography

Purpose: To optimize radiological and clinical parameters for the application of a contrast‐medium‐based subtraction technique in digital mammography and to evaluate its clinical feasibility using a commercial mammography unit without any external or internal hardware modification. Method and Materials: This is a two‐stage project. Firstly, an extension of Lemacks' analytical formalism was implemented in order to maximize contrast‐to‐noise ratios (CNR) in simulated applications of dual‐energy and temporal subtraction modalities, and combinations of them. The formalism was validated by imaging tubular structures with an iodine‐based contrast medium embedded in a PMMA phantom. Once two optimized techniques were defined, calculations were performed to obtain exposure values limiting the total glandular dose to 2.5 mGy in a dynamical study of 1 mask + 3 post‐contrast images. Secondly, these parameters were used to calibrate the gray level in subtracted images as function of contrast medium iodine concentration contained in a multi‐well PMMA‐phantom. Optimized subtraction techniques are being applied in a clinical study which shall include 20 patients. Results: Experimental CNR results surpass Rose's criterion (CNR=5) and validate the predicted advantage of temporal techniques. Dual energy temporal subtraction, with iodine administered in the low energy image arises as the optimum subtraction technique, instead of the predicted advantage of contrast medium administration during the high‐energy acquisition. With respect to the calibration, relations between CNR and iodine concentration were found to be approximately linear beyond 8 mg/ml, although for lower concentrations, CNR is undetectable. Conclusion: The advantage of temporal over dual energy subtraction in terms of CNR has been validated, particularly of dual energy temporal subtraction. Furthermore, concentrations below 8 mg/ml do not satisfy the detection criterion.

SU‐GG‐J‐94: Feasibility Study On the Efficacy of Dual Energy Cine Imaging in Radiation Therapy for Lung Cancer

Purpose: Modern IMRT plans have necessitated improved image localization techniques. In the lungs, internal target volumes (ITVs) are often generated from 4DCT images; however, the patient must be properly localized daily for this to work effectively. In this simulation study, we investigate the efficacy of dual energy cine (DEC) imaging in radiation therapy (RT). Method and Materials: An advanced 4D NURBS (nonuniform rational b‐splines) based Cardiac‐Torso (NCAT) phantom, which includes a detailed whole‐body anatomy of organs including the lungs, airway tree, heart, and vessels, was used for this study. This model allows for the insertion of a lung nodule of any size, shape, contrast, and location. The NCAT phantom also incorporates realistic 4D modeling of periodic cardiac and respiratory motion. The NCAT includes an x‐ray projection algorithm that can accurately generate x‐ray images in 4D. This algorithm was used to generate cine images of the chest with an embedded lung nodule. Images were generated using spectra of 80 and 120 kV. Dual energy subtraction was performed on these two sets of cine images to remove the overlying bony anatomy. The resulting images were visually examined to determine if the lung nodule motion could be better visualized in the DEC images then in the 120 kV images. Results: The removal of the overlying bony anatomy of the chest allowed the DEC images to demonstrate superior visualization of the temporo‐spatial motion of the nodule. Conclusion: This feasibility study demonstrates that DEC imaging may provide increased visualization of lung nodules for RT treatment. Daily DEC imaging would allow for proper treatment portal placement for thoracic plans using ITVs and IMRT. Additionally, this technique shows much promise to be used in conjunction with dynamic adaptive radiation therapy, where nodule tracking is a necessity.

TH‐C‐332‐07: Dual Energy Contrast‐Enhanced Breast Computed Tomography: A Phantom Study

Purpose: To investigate lesion enhancement with iodinated contrast material using dual energy breast computed tomography (CT). Method and Materials: The dual energy cone‐beam breast CT system consisted of a flat panel detector and an x‐ray tube installed on an optical bench. The x‐ray tube voltage and x‐ray beam filtration were switched at 30 Hz between 50 kVp (2.0‐mm Al filter) and 120 kVp (2.0‐mm Al + 0.8‐mm Ag filtration). A cylindrical breast phantom was constructed from polymethylmethacrylate (PMMA) and filled with oil and shredded PMMA. Five known concentrations of iodine (0.5, 1, 2, 4, 8 mgI/ml) were embedded in the phantom. The images were reconstructed with a Feldkamp filtered‐back‐projection algorithm. Dual energy subtraction was used to eliminate the contrast of oil and PMMA to enhance iodine signals. Results: The low energy scan could not distinguish PMMA and iodine concentrations of 0.5 and 1 mgI/ml. The high energy image could not distinguish PMMA and iodine concentration of 8 mgI/ml. After subtracting the PMMA, all five concentrations of iodine could be clearly visualized on the dual energy CT image. The dual energy iodine signal (CTDE) and the iodine concentration (CI) were related by (R = 0.998 and SEE=15.26) Conclusion: Dual energy contrast‐enhanced breast CT can potentially improve lesion.