OBJECTIVETo validate the efficiency and accuracy of an improved Demons deformable registration algorithm and evaluate its application in contour recontouring in 4D-CT.

METHODSTo increase the additional Demons force and reallocate the bilateral forces to accelerate convergent speed, we propose a novel energy function as the similarity measure, and utilize a BFGS method for optimization to avoid specifying the numbers of iteration. Mathematical transformed deformable CT images and home-made deformable phantom were used to validate the accuracy of the improved algorithm, and its effectiveness for contour recontouring was tested.

RESULTSThe improved algorithm showed a relatively high registration accuracy and speed when compared with the classic Demons algorithm and optical flow based method. Visual inspection of the positions and shapes of the deformed contours agreed well with the physician-drawn contours.

CONCLUSIONDeformable registration is a key technique in 4D-CT, and this improved Demons algorithm for contour recontouring can significantly reduce the workload of the physicians. The registration accuracy of this method proves to be sufficient for clinical needs.

Emerging technologies such as four-dimensional computed tomography (4D CT) is expected to allow clinicians to accurately model interfractional motion and to quantitatively estimate internal target volumes (ITVs) for radiation therapy involving moving targets. A need exists for a 4D radiation therapy quality assurance (QA) device that can incorporate and analyze the patient specific intrafractional motion as it relate to dose delivery and respiratory gating. We built a 4D RT prototype device and analyzed the patient-specific 4D radiation therapy QA for 2D dose distributions successfully. With more improvements, the 4D RT QA prototype device could be an integral part of a 4D RT decision process to confirm the dose delivery.
Four-Dimensional Computed Tomography ; Humans ; Polymethacrylic Acids

Multidetector-row computed tomography (MDCT) provides new opportunities and poses challenges for medical imaging to radiologists and physicians. Isotropic imaging (similar resolution in three dimensional directions) allows in-depth views of anatomy and disease. Ultra-fast scan enables whole-body volume imaging within a single breath hold and thus the reduction of contrast medium consumption. CT volume data sets can be used for threedimensional visualization of the whole body, with which the detailed and comprehensive interpretation of thoracic anatomy and specific disease location and extent is plausible. Moreover, four-dimensional CT imaging can be possible and therefore, we can observe and quantify cardiopulmonary functions without invasive procedures. The author reviews briefly the application of MDCT for the thoracic imaging.
Dataset ; Diagnostic Imaging ; Four-Dimensional Computed Tomography ; Multidetector Computed Tomography

For Stereotactic Radiosurgery of lung tumor, 4 dimensional CT was done during for free breathing of the patient. The movement of the treated target was measured in the CT images, and appropriate breathing cycle was selected for treatment. For patient A, the movement of the treatment target was 10.1 mm during full breathing cycle, and 5.4 mm for treated breathing cycle, 30~70%. For patient B, the movement was 13 mm, and 3.5 mm for full breathing cycle and treated breathing cycle, respectively.
Four-Dimensional Computed Tomography* ; Humans ; Lung Neoplasms* ; Lung* ; Radiosurgery* ; Respiration

PURPOSE : We propose the measurement method of tumor movement for respiratory gated therapy in lung cancer patient for stereotactic radiosurgery, contouring method of tumor for radiation treatment planning using measured tumor movement. And through phantom study, we ascertain that the tumor movement is properly reflected in determination of PTV, and the tumor is properly and safely treated in full respiration phases and respiratory gated therapy. MATERIALS AND METHODS : Lung cancer phantom and 1-dimensional moving phantom were made to evaluate respiratory gated radiation therapy for lung SRS. 4D CT scan was performed using these phantoms and 10 sets of CT images and post-processed MIP (Maximum Intensity Projection) images were used to measure the tumor movement. The measured tumor movement in 4D CT images and MIP images were compared. Also, during radiation exposure in full respiration phases and respiratory gated phases, tumor movement included in radiation exposure was measured using EPID image and compared with measured data in 4D CT images and MIP images. RESULTS : The tumor movement measured in full respiration phases was 28.8mm and 29.1 mm in 4D CT images and MIP images respectively, and in respiratory gated phases, 30~70% phases, was 12 mm and 12.2 mm respectively. The tumor contoured in each phase images and MIP images was well agreed in full respiration phases and respiratory gated phases. The tumor movement included in radiation exposure was 29.3 mm and 8.4 mm in full respiration phases and respiratory gated phases respectively. CONCLUSION : The tumor movement measured in 4D CT images and MIP images was well agreed, so we propose to use of MIP image for contouring of tumor in full respiration phases and respiratory gated phases. In full respiration radiation treatment and respiratory gated radiation therapy, the tumor movement included in radiation exposure was well agreed with measured tumor movement in 4D CT images or MIP images, so we ascertain though this phantom study we can exactly treat the tumor including tumor movement. In respiratory gated radiation therapy, the tumor movement included in radiation exposure was about 30% smaller than measured tumor movement in 4D CT images or MIP images, so we ascertain that we can safely treat the tumor including tumor movement in current provided technique
Four-Dimensional Computed Tomography ; Humans ; Lung Neoplasms* ; Lung* ; Radiosurgery* ; Respiration

Patient's respiration can have an effect on movement of tumor range and peripheral organs. Therefore, the respiratory signal was acquired by relation between external markers and movement of patient's abdomen during radiational therapy in order to minimize the effect of respiration. Based on this technique, many studies of rational therapy to irradiate at particular part of stable respiratory signals have executed and they have been clinically applied. Nevertheless, the phase-based method is preferred to the amplitude-based method for the rational therapy related to respiration. Because stabilization of the respiratory signal are limited. In this study, a in-house respiratory signal analysis program was developed for the phase reassignment and the analysis of the irregular respiratory signals. Various irregular respiratory patterns was obtained from clinical experimental volunteers. After then, the in-house program analyzed the factors affecting to phase assignment which is directly related to irradiated sector. Subsequently, accuracy of phase assignment was improved with removement of irregular signals by self-developed algorithm. This study is considered to be useful for not only image reconstruction and elevation of irradiating accuracy through phase assignment of RPM system but also analysis of respiratory signals. Moreover, development of 4D CT image is planed with phantom researches or clinical experiments based on this program.
Abdomen ; Four-Dimensional Computed Tomography ; Image Processing, Computer-Assisted ; Respiration

In this study, we evaluated accuracy and usefulness of CyberKnife Respiratory Tracking System (SynchronyTM, Accuray, USA) about a moving during stereotactic radiosurgery. For this study, we used moving phantom that can move the target. We also used Respiratory Tracking System called Synchrony of the Cyberknife in order to track the moving target. For treatment planning of the moving target, we obtained an image using 4D-CT. To measure dose distribution and point dose at the moving target, ion chamber (0.62 cc) and gafchromic EBT film were used. We compared dose distribution (80% isodose line of prescription dose) of static target to that of moving target in order to evaluate the accuracy of Respiratory Tracking System. We also measured the point dose at the target. The mean difference of synchronization for TLS (target localization system) and Synchrony were 11.5+/-3.09 mm for desynchronization and 0.14+/-0.08 mm for synchronization. The mean difference between static target plan and moving target plan using 4D CT images was 0.18+/-0.06 mm. And, the accuracy of Respiratory Tracking System was less 1 mm. Estimation of usefulness in Respiratory Tracking System was 17.39+/-0.14 mm for inactivity and 1.37+/-0.11 mm for activity. The mean difference of absolute dose was 0.68+/-0.38% in static target and 1.31+/-0.81% in moving target. As a conclusion, when we treat about the moving target, we consider that it is important to use 4D-CT and the Respiratory Tracking System. In this study, we confirmed the accuracy and usefulness of Respiratory Tracking System in the Cyberknife.
Four-Dimensional Computed Tomography ; Prescriptions ; Radiosurgery ; Track and Field

Super-resolution image reconstruction techniques play an important role for improving image resolution of lung 4D-CT. We presents a super-resolution approach based on fast sub-pixel motion estimation to reconstruct lung 4D-CT images. A fast sub-pixel motion estimation method was used to estimate the deformation fields between "frames", and then iterative back projection (IBP) algorithm was employed to reconstruct high-resolution images. Experimental results showed that compared with traditional interpolation method and super-resolution reconstruction algorithm based on full search motion estimation, the proposed method produced clearer images with significantly enhanced image structure details and reduced time for computation.
Algorithms ; Four-Dimensional Computed Tomography ; Humans ; Image Enhancement ; Lung ; anatomy & histology ; Motion ; Tomography, X-Ray Computed

Restriction by hardware caused the very low projection number at a single phase for 4-dimensional cone beam (4D-CBCT) CT imaging, and reconstruction using conventional reconstruction algorithms is thus constrained by serious streak artifacts and noises. To address this problem, we propose an approach to reconstructing 4D-CBCT images with multi-phase projections based on the assumption that the image at one phase can be viewed as the motion-compensated image at another phase. Specifically, we formulated a cost function using multi-phase projections to construct the fidelity term and the TV regularization method. For fidelity term construction, the projection data of the current phase and those at other phases were jointly used by reformulating the imaging model. The Gradient-Projection-Barzilai-Line search (GPBL) method was used to optimize the complex cost function. Physical phantom and patient data results showed that the proposed approach could effectively reduce the noise and artifacts, and the introduction of additional temporal correlation did not introduce new artifacts or motion blur.
Algorithms ; Artifacts ; Cone-Beam Computed Tomography ; Four-Dimensional Computed Tomography ; Models, Theoretical ; Motion ; Phantoms, Imaging

In pediatric thoracic CT, respiratory motion is generally treated as a motion artifact degrading the image quality. Conversely, respiratory motion in the thorax can be used to answer important clinical questions, that cannot be assessed adequately via conventional static thoracic CT, by utilizing four-dimensional (4D) CT. However, clinical experiences of 4D thoracic CT are quite limited. In order to use 4D thoracic CT properly, imagers should understand imaging techniques, radiation dose optimization methods, and normal as well as typical abnormal imaging appearances. In this article, the imaging techniques of pediatric thoracic 4D CT are reviewed with an emphasis on radiation dose. In addition, several clinical applications of pediatric 4D thoracic CT are addressed in various thoracic functional abnormalities, including upper airway obstruction, tracheobronchomalacia, pulmonary air trapping, abnormal diaphragmatic motion, and tumor invasion. One may further explore the clinical usefulness of 4D thoracic CT in free-breathing children, which can enrich one's clinical practice.
Airway Obstruction ; Artifacts ; Child* ; Four-Dimensional Computed Tomography ; Humans ; Thorax ; Tomography, X-Ray Computed ; Tracheobronchomalacia