ABSTRACT
In order to suppress the geometrical artifacts caused by random jitter in ray source scanning, and to achieve flexible ray source scanning trajectory and meet the requirements of task-driven scanning imaging, a method of free trajectory cone-beam computed tomography (CBCT) reconstruction is proposed in this paper. This method proposed a geometric calibration method of two-dimensional plane. Based on this method, the geometric calibration phantom and the imaging object could be simultaneously imaged. Then, the geometric parameters could be obtained by online calibration method, and then combined with the geometric parameters, the alternating direction multiplier method (ADMM) was used for image iterative reconstruction. Experimental results showed that this method obtained high quality reconstruction image with high contrast and clear feature edge. The root mean square errors (RMSE) of the simulation results were rather small, and the structural similarity (SSIM) values were all above 0.99. The experimental results showed that it had lower image information entropy (IE) and higher contrast noise ratio (CNR). This method provides some practical value for CBCT to realize trajectory freedom and obtain high quality reconstructed image.
Subject(s)
Algorithms , Calibration , Cone-Beam Computed Tomography , Image Processing, Computer-Assisted , Phantoms, ImagingABSTRACT
Objective To execute geometric calibration and calibration phantom design to realize high-quality cone-beam Micro-CT image reconstruction. Methods The geometrical position parameters of cone-beam Micro-CT system were deduced by the data of the designed phantom projected on the detector by means of linear fitting and geometric relation,so as to realize the geometric calibration of the system.The calculation software and the simulation experiment were achieved by VC++programming language.Results The validity and feasibility of the calibration model and method were proved by the experimental simulation. Conclusion The geometric calibration method can accurately calculate the geometrical position parameter errors of the cone-beam Micro-CT system.It can effectively reduce the artifacts in the reconstructed image and further improve the imaging resolution by adjusting the geometric position parameters.[Chinese Medical Equipment Jour-nal,2018,39(5):29-34]
ABSTRACT
PURPOSE: Micro-pinhole SPECT system with conventional multiple-head gamma cameras has the advantage of high magnification factor for imaging of rodents. However, several geometric factors should be calibrated to obtain the SPECT image with good image quality. We developed a simplified geometric calibration method for rotating triple-head pinhole SPECT system and assessed the effects of the calibration using several phantom and rodent imaging studies. MATERIAL AND METHODS: Trionix Triad XLT9 triple-head SPECT scanner with 1.0 mm pinhole apertures were used for the experiments. Approximately centered point source was scanned to track the angle-dependent positioning errors. The centroid of point source was determined by the center of mass calculation. Axially departed two point sources were scanned to calibrate radius of rotation from pinhole to center of rotation. To verify the improvements by the geometric calibration, we compared the spatial resolution of the reconstructed image of Tc-99m point source with and without the calibration. SPECT image of micro performance phantom with hot rod inserts was acquired and several animal imaging studies were performed. RESULTS: Exact sphere shape of the point source was obtained by applying the calibration and axial resolution was improved. Lesion detectibility and image quality was also much improved by the calibration in the phantom and animal studies. CONCLUSION: Serious degradation of micro-pinhole SPECT images due to the geometric errors could be corrected using a simplified calibration method using only one or two point sources.
Subject(s)
Animals , Calibration , Gamma Cameras , Head , Imidazoles , Nitro Compounds , Radius , Rodentia , Tomography, Emission-Computed, Single-Photon , Track and FieldABSTRACT
According to improved radiation therapy technology such as IMRT and proton therapy, the accuracy of patient alignment system is more emphasized and IGRT is dominated research field in radiation oncology. We proposed to study the feasibility of cone-beam CT system using simple x-ray imaging systems for image guided proton therapy at National Cancer Center. 180 projection views (2,304x3,200, 14 bit with 127 micrometer pixel pitch) for the geometrical calibration phantom and humanoid phantoms (skull, abdomen) were acquired with 2degrees step angle using x-ray imaging system of proton therapy gantry room (360degrees for 1 rotation). The geometrical calibration was performed for misalignments between the x-ray source and the flat-panel detector, such as distances and slanted angle using available algorithm. With the geometrically calibrated projection view, Feldkamp cone-beam algorithm using Ram-Lak filter was implemented for CBCT reconstruction images for skull and abdomen phantom. The distance from x-ray source to the gantry isocenter, the distance from the flat panel to the isocenter were calculated as 1,517.5 mm, 591.12 mm and the rotated angle of flat panel detector around x-ray beam axis was considered as 0.25degrees. It was observed that the blurring artifacts, originated from the rotation of the detector, in the reconstructed toomographs were significantly reduced after the geometrical calibration. The demonstrated CBCT images for the skull and abdomen phantoms are very promising. We performed the geometrical calibration of the large gantry rotation system with simple x-ray imaging devices for CBCT reconstruction. The CBCT system for proton therapy will be used as a main patient alignment system for image guided proton therapy.