Performance evaluation of a dedicated computed tomography scanner used for virtual simulation using in-house fabricated CT phantoms (original) (raw)
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CT scanner quality control using a quality assurance phantom and a PMMA phantom
Background: The American Association of Physics in Medicine recommends using a specific phantom for quality control and to evaluate the operation of the CT scanner. The current studies' objectives were to determine the multi- slice Philips CT scanner's performance through rigorous quality control testing. Image quality was estimated using a quality assurance CT phantom and radiation dose was assessed using a PMMA head and a PMMA body phantom with a 100mm pencil chamber. The image quality performance parameters that were tested were CT image noise, uniformity, CT number accuracy, and resolution. The radiation dose performance parameters that were evaluated were volume computed tomography dose index (CTDIvol), and dose length product (DLP).Result: The results of the present study were all image quality and CT dose index parameters tested within the acceptable standard limits. The CT radiation dose parameter and image quality test were accepted because they were within the tole...
Dosimetric characteristics of a 16-slice computed tomography scanner
European Radiology, 2006
Standard CT dose measurements were performed on a Siemens Sensation 16 scanner. CT dose indices, free-in-air (CTDI F ) and weighted (CTDI W ), were measured in all available axial and helical beam collimations of the head and body scanning modes. The effect of tube current, high voltage, rotation time, beam collimation and pitch on the CT doses was investigated. CT doses increased as a power function of high voltage. The kVp exponent n varied with beam collimation from 2.7 to 3.1 for CTDI W , and from 2.4 to 2.6 for CTDI F . Automatic change of the focal spot size increased radiation doses up to a factor of 1.18. Measured smallfocus CTDI W values differed from those displayed at the console from -24 to 14%. Peripheral doses in the head phantom were higher compared to the body phantom by a factor of 1.5 to 2. Central doses are 2.7 to 4.1 times higher. Differences in beam collimation resulted in 50% variation in the CTDI W in the body phantom and 60% in the head phantom. In conclusion, our study has confirmed the great impact of technique factors and acquisition parameters on CT doses. The provided comprehensive dosimetric data will facilitate the dose-effective use of the scanner studied.
e-Journal of Nondestructive Testing, 2023
The lack of traceability to meter of X-ray Computed Tomography (CT) measurements still hinders a more extensive acceptance of CT in coordinate metrology and industry. To ensure traceable, reliable, and accurate measurements, the determination of the task-specific measurement uncertainty is necessary. The German guideline VDI/VDE 2630 part 2.1 [1] describes a procedure to determine the measurement uncertainty for CT experimentally by conducting several repeated measurements with a calibrated test specimen. However, this experimental procedure is cost and effort intensive. Therefore, the simulation of dimensional measurement tasks conducted with X-ray computed tomography can close these drawbacks. Additionally, recent developments towards a resource and cost-efficient production ("smart factory") motivate the need for a corresponding numerical model of a CT system ("digital twin") as well. As there is no standardized procedure to determine the measurement uncertainty of a CT system by simulation at the moment, the project series CTSimU was initiated, aiming at this gap. Concretely, the goal is the development of a procedure to determine the measurement uncertainty numerically by radiographic simulation. The first project (2019-2022), "Radiographic Computed Tomography Simulation for Measurement Uncertainty Evaluation-CTSimU" developed a framework to qualify a radiographic simulation software concerning the correct simulation of physical laws and functionalities [2-6]. The most important outcome was a draft for a new guideline VDI/VDE 2630 part 2.2, which is currently under discussion in the VDI/VDE committee. The follow-up project CTSimU2 "Realistic Simulation of real CT systems with a basic-qualified Simulation Software" will deal with building and characterizing a digital replica of a specific real-world CT system. The two main targets of this project will be a toolbox including methods and procedures to configure a realistic CT system simulation and to develop tests to check if this replica is sufficient enough. The result will be a draft for a follow-up VDI/VDE guideline proposing standardized procedures to determine a CT system's corresponding characteristics and test the simulation (copy) of a real-world CT system which we call a "digital twin".
Construction and Evaluation of a Multipurpose Performance Check Phantom for Computed Tomography
Atom Indonesia, 2020
The use of computed tomography (CT) has become a common practice in medical diagnosis in Indonesia. Its number, however, is not matched by the availability of dedicated-performance-check phantoms. This paper aims to describe the design, construction, and evaluation of an in-house phantom for CT performance check that accommodates both radiation dose measurement and image quality performance checks. The phantom is designed as laser-cut polymethyl methacrylate (PMMA) slabs glued together to form a standard cylindrical shape, with spaces to place dose measurement and image quality modules. In this paper, measurement results on both aspects are discussed and compared with standard phantoms and other works. For dose measurement, the constructed phantom exhibited the greatest absolute discrepancy against the reference standard phantom of 8.89 %. Measurement of the CT number linearity and modulation transfer function (MTF) yielded, at most, 7.51 % and 5.07 % discrepancies against Catphan 604, respectively. Meanwhile, although found to be more linear in the phantom-based contrast linearity test, the use of the in-house phantom for clinical image contrast threshold determination requires further study. For noise power spectrum (NPS) measurement, accurate results were obtained within a limited range of spatial frequency.
Simplified “on-couch” daily quality assurance procedure for CT simulators
Journal of Applied Clinical Medical Physics, 2009
For most computed tomography (CT) simulators, radiation therapists must remove the flat couch top to perform daily CT quality assurance (QA), and then use separate tools to perform localization-laser QA. This process wastes time and effort and creates the opportunity for accidents to occur. In this study, we tested a simple yet comprehensive daily QA program and phantom that we designed for CT simulators used in radiation oncology that would enable us to use only one tool to perform laser and imaging QA on a flat couch. To construct a modified QA phantom, we attached three adjustable legs and fastened two metric scales (one vertically and one horizontally) to a commercial CT QA phantom. The adjustable legs helped to position the phantom conveniently in the needed position. The two metric scales were used for localization-laser QA, while the phantom body was used for CT imaging QA. We used five different scanners with their designated couches from two manufacturers to evaluate this phantom. Since the couch was scanned with the phantom, we evaluated the couch's effect on image quality. We found that the presence of the couch top changed the uniformity of water's CT number but did not change the visual image resolution; it also produced different, yet reproducible, effects on image quality. The effects were greatest in the section of the phantom closest to the couch top. For a commercial carbon fiber couch top, the variation was within 3 Hounsfield Unit (HU). The effect was couch- and scanner-specific and could be incorporated into the QA acceptability criteria for each CT scanner. By using the proposed program and phantom, we have been able to implement a more thorough QA program while decreasing the amount of effort and time the simulation therapists spend performing laser and imaging QA.
Medical Physics, 2003
The purpose of this document is to provide the medical physicist with a framework and guidance for establishment of a comprehensive quality assurance ͑QA͒ program for computed-tomography-͑CT͒ scanners used for CTsimulation, CT-simulation software, and the CT-simulation process. The CT-simulator is a CT scanner equipped with a flat tabletop and, preferably, external patient positioning lasers. The scanner is accompanied with specialized software which allows treatment planning on volumetric patient CT scans in a manner consistent with conventional radiation therapy simulators. 1-12 The CT scanner used in the CTsimulation process can be located in the radiation oncology department or in the diagnostic radiology department. Depending on the CT-scanner location and primary use, acceptance testing, commissioning, and QA can be the responsibility of a therapy medical physicist, diagnostic physicist, or a joint responsibility of diagnostic and therapy physicists. The commissioning and periodic QA of the accompanying software and the QA of the CT-simulation process is always the responsibility of the therapy physicist. This report does not address each of the two scenarios individually ͑scanner located in diagnostic radiology or radiation oncology͒, but rather establishes a set of QA procedures that are applicable to scanners used for CT-simulation regardless of their location and primary purpose. It is the responsibility of the respective diagnostic and therapy physicists to determine how the QA program is implemented and how the responsibilities are assigned. The primary responsibility for implementation of recommendations for QA of scanners used for CTsimulation in this document rests with the radiation oncology Quality Assurance Committee ͑QAC͒ as specified by the AAPM Task Group 40. 13 Further discussion of QA program responsibilities is provided in Appendix A. If the scanner is located in the radiation oncology department, a therapy medical physicist can perform QA of the CT-scanner and of the simulation process independently. It is recommended that the therapy physicist solicit help from a diagnostic physicist for the establishment of a QA program and scanner commissioning if he or she has limited CT experience. Likewise, if the CT-scanner is located in the diagnostic radiology department, the primary responsibility for the scanner QA rests with the diagnostic physicist. It is then the responsibility of the radiation oncology physicist to assure that the recommendations of this task group are implemented by either diagnostic radiology or the radiation oncology physicist or a designate.
Journal of Applied Clinical Medical Physics, 2022
PurposeTo investigate the operation principles of the automatic tube current modulation (ATCM) of a CT scanner, using a dedicated phantom and the CT dosimetry index (CTDI) phantom.Material and methodsThe Mercury 4.0 phantom and three different configurations of the CTDI dosimetry phantom were employed. A frequently used clinical scanning protocol was employed as a basis for the acquisitions performed with all phantoms, using both scanning directions. Additional acquisitions with different pitch and examination protocols were performed with Mercury phantom, to further explore their effect on ATCM and the resulting image quality. Different software named DICOM Info Extractor, ImageJ, and imQuest, were used to derive CTDIvol and table position, image noise, and water equivalent diameter (WED) of each phantom CT image, respectively. ImQuest was also used to derive the detectability index (d’) of five different materials (air, solid water, polystyrene, iodine, and bone) embedded in the Mercury phantom.ResultsIt was exhibited with all four phantoms that the scanning direction greatly affects the modulation curves. The fitting of the dose modulations curves suggested that for each table position what determines the CTDIvol value is the WED values of the phantom structures laying ahead towards the scanning direction, for a length equal to the effective width of the X‐ray beam. Furthermore, it was also exhibited that ATCM does not fully compensate for larger thicknesses, since images of larger WED phantom sections present more noise (larger SD) in all four phantoms and in Mercury 4.0 phantom smaller detectability (d’).ConclusionMercury 4.0 is a dedicated phantom for a complete and in‐depth evaluation of the ATCM operation and the resulting image quality. However, in its absence, different CTDI configurations can be used as an alternative to investigate and comprehend some basic operation principles of the CT scanners’ ATCM systems.
Performance evaluation of the General Electric eXplore CT 120 micro-CT using the vmCT phantom
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2011
The eXplore CT 120 is the latest generation micro-CT from General Electric. It is equipped with a high power tube and a flat panel detector. It allows high resolution and high contrast fast CT scanning of small animals. The aim of this study was to compare the performance of the eXplore CT 120 with the one of the eXplore Ultra, its predecessor for which the methodology using the vmCT phantom was already described [1]. The phantom was imaged using typical rat (fast scan or F) or mouse (in vivo bone scan or H) scanning protocols. With the slanted edge method, a 10% modulation transfer function (MTF) was observed at 4.4 (F) and 3.9-4.4 (H) mm-1 corresponding to 114 µm resolution. A fairly larger MTF was obtained with the coil method with the MTF for the thinnest coil (3.3 mm-1) equal to 0.32 (F) and 0.34 (H). The geometric accuracy was better than 0.3%. There was a highly linear (R 2 > 0.999) relationship between measured and expected CT numbers for both the CT number accuracy and linearity sections of the phantom. A cupping effect was clearly seen on the uniform slices and the uniformity-to-noise ratio ranged from 0.52 (F) to 0.89 (H). The air CT number depended on the amount of polycarbonate surrounding the area where it was measured: a difference as high as approximately 200 HU was observed. This hindered the calibration of this scanner in HU. This is likely due to the absence of corrections for beam hardening and scatter in the reconstruction software. However in view of the high linearity of the system, the implementation of these corrections would allow a good quality calibration of the scanner in HU. In conclusion, the eXplore CT 120 achieved a better spatial resolution than the eXplore Ultra (based on previously reported specifications) and future software developments to include beam hardening and scatter corrections will make the new generation CT scanner even more promising.
Verification of CT number to density conversion for a simulator-CT attachment
Australasian Physics & Engineering Sciences in Medicine, 2002
The calculation and verification of a CT number to density conversion table for a simulator-CT attachment known as Scanvision, which provides CT images for radiotherapy treatment planning, is presented. While the linear fit for CT-number-to-density is similar to most conventional doughnut gantry CT scanners, an offset of approximately 178 Hounsfield units was found for air using a polyethylene normalisation, and approximately 262 for air using air normalisation. The offset continues for other low-density samples. Results show that the simulator-CT reproducibly measures CT numbers. However a separate calibration line needs to be entered into the radiotherapy planning computer to ensure accurate CT-number-to-density conversion.
Scanner and kVp dependence of measured CT numbers in the ACR CT phantom
Journal of applied clinical medical physics / American College of Medical Physics, 2013
Quality control testing of CT scanners in our region includes a measurement of CT numbers in the American College of Radiology (ACR) CT phantom using a standardized protocol. CT number values are clinically relevant in determining the composition of various tissues in the body. Accuracy is important in the characterization of tumors, assessment of coronary calcium, and identification of urinary stone composition. Effective quality control requires that tolerance ranges of CT number values be defined: a measured value outside the range indicates the need for further investigation and possible recalibration of the scanner. This paper presents the results of CT number measurements on 36 scanners (25 GE, 10 Siemens and 1 Toshiba) at each available kVp. Among the five materials (solid water, air, polyethylene, acrylic, bone-equivalent) the measured CT numbers exhibit manufacturer and kVp dependence, which should be taken into account when defining tolerances. With this scan protocol, air...