Studies on the application of a low-voltage peak to the postsurgical follow-up CT scan in abdominal cancer patients in order to reduce the exposure of patients to radiation

This study examined the radiation dose, computed tomography (CT) number, contrast and image quality of patients requiring periodic follow-up abdominal CT examinations at various tube voltages. The subjects were divided into two groups. One group consisted of patients who underwent a clinical analysis and the other group was a phantom one. Somatom Sensation 16 (Siemens, Erlangen, Germany) was used. Twenty patients who underwent a periodic follow-up examination by CT were selected randomly. The tube current was fixed to 150 mA, and the tube voltage was adjusted according to the appropriate value of each examination. The computed tomography dose index (CTDI) values were measured. The CT number of each organ was measured by setting up a 1 cm diameter return on investment (ROI) in the abdominal organs at the same height of the first lumbar vertebra using images of the arterial phase. Two radiologists in consensus graded the quality of the abdominal images into three groups. An abdomen-shaped acrylic phantom was used in the phantom study. An ion chamber was inserted into the holes located at the center and periphery of the phantom, where the radiation dose was automatically displayed on the reader. Tube voltages of 80, 100, 120 and 140 kVp were applied to the phantom (diluted contrast medium with water at 1:10 ratio) and the phantom was scanned. The CT number was measured from a 1 cm diameter ROI at the center of the image. The CTDI value decreased by 36% at 100 kVp (7.50 mGy) compared with that at 120 kVp (11.70 mGy). According to the radiologists’ evaluation, there were 17 equivalent, 3 acceptable and 0 unacceptable levels in the group of 20 subjects. The radiation dose in the phantom study decreased with increasing tube voltages from 80 to 140 kVp. The peripheral and central doses decreased by 38% and 41%, respectively. The CT numbers at 80, 100, 120 and 140 kVp were 1365.9±4.4, 1046.1±3.7, 862.8±3.2 and 737.5±3.0 HU, respectively. In conclusion, in a follow-up observation for the detection of a recurrence or metastasis after surgery or patients with chronic abdominal diseases, the exposure doses can be reduced using a low-voltage peak CT examination without greatly changing the image quality.     

Evaluation of the radiation dose to a phantom for various X-ray exposure factors performed using the dose area product in digital radiography

The aim of this study is to measure the dose area product (DAP) in digital radiography by using a DAP meter to determine the X-ray exposure. Pediatric X-ray examinations can be obtained for any radiographic examinations using the selected radiographic examination parameters (kVp and mAs), the DAP information recorded. The best peak signal-to-noise ratio (PSNR) at a fixed tube voltage of 70 kVp was obtained at tube currents of 20 and 32 mA, whereas the best PSNR at a fixed tube current of 25 mA was obtained at a tube voltage of 73 kVp. The fixed tube voltage of 70 kVp and the fixed tube current of 25 mA could help to obtain the best image quality and depict the spatial resolution of an anthropomorphic torso phantom radiographic examination. The normalized data over the DAP were provided to determine the patient dose from radiography.     

Physical analysis of breast cancer using dual-source computed tomography

This study was aimed to analyze various physical characteristics of breast cancer using dual-source computed tomography (CT). A phantom study and a clinical trial were performed in order and a 64-multidetector CT device was used for the examinations. In the phantom study, single-source (SS) CT was set up with a conventional scanning condition that is usually applied for breast CT examination and implementation was done at tube voltage of 120?kVp. Dual-source CT acquired images by irradiating X-ray sources with fast switching between two kilovoltage settings (80 and 140?kVp). After scanning, Hounsfield Unit (HU) values and radiation doses in a region of interest were measured and analyzed. In the clinical trial, the HU values were measured and analyzed after single-source computed tomography (SSCT) and dual-source CT in patients diagnosed with breast cancer. Also, the tumor size measured by dual-source CT was compared with the actual tumor size. The phantom study determined that the tumor region was especially measured by dual-source CT, while nylon fiber and specks region were especially measured by SSCT. The radiation dose was high with dual-source CT. The clinical trial showed a higher HU value of cancerous regions when scanned by dual-source CT compared with SSCT.     

Reduction in radiation dose with reconstruction technique in the brain perfusion CT

The principal objective of this study was to verify the utility of the reconstruction imaging technique in the brain perfusion computed tomography (PCT) scan by assessing reductions in the radiation dose and analyzing the generated images. The setting used for image acquisition had a detector coverage of 40 mm, a helical thickness of 0.625 mm, a helical shuttle mode scan type and a rotation time of 0.5 s as the image parameters used for the brain PCT scan. Additionally, a phantom experiment and an animal experiment were carried out. In the phantom and animal experiments, noise was measured in the scanning with the tube voltage fixed at 80 kVp (kilovolt peak) and the level of the adaptive statistical iterative reconstruction (ASIR) was changed from 0% to 100% at 10% intervals. The standard deviation of the CT coefficient was measured three times to calculate the mean value. In the phantom and animal experiments, the absorbed dose was measured 10 times under the same conditions as the ones for noise measurement before the mean value was calculated. In the animal experiment, pencil-type and CT-dedicated ionization chambers were inserted into the central portion of pig heads for measurement. In the phantom study, as the level of the ASIR changed from 0% to 100% under identical scanning conditions, the noise value and dose were proportionally reduced. In our animal experiment, the noise value was lowest when the ASIR level was 50%, unlike in the phantom study. The dose was reduced as in the phantom study.     

Dose assessment according to changes in algorithm in cardiac CT

The principal objective of this study was to determine the effects of the application of the adaptive statistical iterative reconstruction (ASIR) technique in combination with another two factors (body mass index (BMI) and tube potential) on radiation dose in cardiac computed tomography (CT). For quantitative analysis, regions of interest were positioned on the central region of the great coronary artery, the right coronary artery, and the left anterior descending artery, after which the means and standard deviations of measured CT numbers were obtained. For qualitative analysis, images taken from the major coronary arteries (right coronary, left anterior descending, and left circumflex) were graded on a scale of 1–5, with 5 indicating the best image quality. Effective dose, which was calculated by multiplying the value of the dose length product by a standard conversion factor of 0.017 for the chest, was employed as a measure of radiation exposure dose. In cardiac CT in patients with BMI of less than 25 kg/m², the use of 40% ASIR in combination with a low tube potential of 100 kVp resulted in a significant reduction in the radiation dose without compromising diagnostic quality. Additionally, the combination of the 120 kVp protocol and the application of 40% ASIR application for patients with BMI higher than 25 kg/m² yielded similar results.     

Optimal tube potential and tube current for radiation dose reduction in routine adult head computed tomography scanning

ABSTRACT

We proposed a new, optimised scanning parameter that can reduce the patient’s radiation dose while maintaining image quality in a head computed tomography (CT) scan. We evaluated the clinical CT scan parameters (tube voltage, tube current, slice thickness pitch, scan range, rotation time, and CT dose index) for brain CT examination in a total of 52 multi-detector row spiral CTs (SOMATOM Definition AS+, Siemens Healthcare, Germany). The data were analysed, and the range of valid scan parameters was determined clinically using quartile distribution within the 95% confidence interval. The American Association of Physicists in Medicine performance evaluation phantom was used to acquire images using these scan parameters, and new, optimised CT scan parameters were proposed by analysing CT number accuracy, noise, uniformity, spatial resolution, and contrast resolution. The new CT scan parameters proposed were determined as tube voltage 100?kVp and tube current 300?mAs. Compared with conventional clinical scan parameters, tube voltage was reduced by 16.7% and tube current was decreased by 33.3%. Loss in imaging accuracy and uniformity of CT number was less than 20%, loss in noise was less than 40%, and no change in resolution was observed. Conversely, the CT dose index and effective dose was 20%–50%. A new systematic method for clinically assessing the optimised CT scan parameters were proposed, and the effective dose was decreased, with changing exposure conditions.     

A generalized method of converting CT image to PET linear attenuation coefficient distribution in PET/CT imaging

The accuracy of attenuation correction in positron emission tomography scanners depends mainly on deriving the reliable 511-keV linear attenuation coefficient distribution in the scanned objects. In the PET/CT system, the linear attenu- ation distribution is usually obtained from the intensities of the CT image. However, the intensities of the CT image relate to the attenuation of photons in an energy range of 40 keV-140 keV. Before implementing PET attenuation correction, the intensities of CT images must be transformed into the PET 511-keV linear attenuation coefficients. However, the CT scan parameters can affect the effective energy of CT X-ray photons and thus affect the intensities of the CT image. Therefore, for PET/CT attenuation correction, it is crucial to determine the conversion curve with a given set of CT scan parameters and convert the CT image into a PET linear attenuation coefficient distribution. A generalized method is proposed for con- verting a CT image into a PET linear attenuation coefficient distribution. Instead of some parameter-dependent phantom calibration experiments, the conversion curve is calculated directly by employing the consistency conditions to yield the most consistent attenuation map with the measured PET data. The method is evaluated with phantom experiments and small animal experiments. In phantom studies, the estimated conversion curve fits the true attenuation coefficients accurately, and accurate PET attenuation maps are obtained by the estimated conversion curves and provide nearly the same correction results as the true attenuation map. In small animal studies, a more complicated attenuation distribution of the mouse is obtained successfully to remove the attenuation artifact and improve the PET image contrast efficiently.     

Radiation dose and image quality in K‐edge subtraction computed tomography of lung in vivo

K‐edge subtraction computed tomography (KES‐CT) allows simultaneous imaging of both structural features and regional distribution of contrast elements inside an organ. Using this technique, regional lung ventilation and blood volume distributions can be measured experimentally in vivo. In order for this imaging technology to be applicable in humans, it is crucial to minimize exposure to ionizing radiation with little compromise in image quality. The goal of this study was to assess the changes in signal‐to‐noise ratio (SNR) of KES‐CT lung images as a function of radiation dose. The experiments were performed in anesthetized and ventilated rabbits using inhaled xenon gas in O₂ at two concentrations: 20% and 70%. Radiation dose, defined as air kerma (K_a), was measured free‐in‐air and in a 16 cm polymethyl methacrylate phantom with a cylindrical ionization chamber. The dose free‐in‐air was varied from 2.7 mGy to 8.0 Gy. SNR in the images of xenon in air spaces was above the Rose criterion (SNR > 5) when K_a was over 400 mGy with 20% xenon, and over 40 mGy with 70% xenon. Although in human thorax attenuation is higher, based on these findings it is estimated that, by optimizing the imaging sequence and reconstruction algorithms, the radiation dose could be further reduced to clinically acceptable levels.     

A novel dosimetry system for computed tomography using phototransistor

Computed tomography (CT) dosimetry normally uses an ionization chamber 100 mm long to estimate the computed tomography dose index (CTDI), however some reports have already indicated that small devices could replace the long ion chamber to improve quality assurance procedures in CT dosimetry. This paper presents a novel dosimetry system based in a commercial phototransistor evaluated for CT dosimetry. Three detector configurations were developed for this system: with a single, two and four devices. Dose profile measurements were obtained with them and their angular responses were evaluated. The results showed that the novel dosimetry system with the phototransistor could be an alternative for CT dosimetry. It allows to obtain the CT dose profile in details and also to estimate the CTDI in longer length than the 100 mm pencil chamber. The angular response showed that the one device detector configuration is the most adequate among the three configurations analyzed in this study.     

Application of computed tomography images in the evaluation of magnetic nanoparticles biodistribution

In this work we evaluate the effectiveness of computed tomography images as a tool to determine magnetic nanoparticle biodistribution over biological tissues. For this purpose, tomography images for magnetic nanoparticles, composed of Fe₃O₄, coated with 2,3-dimercaptosuccinic acid (DMSA), were generated at several material concentrations. The comparison of CT numbers, calculated from these images generated at clinical conditions, with typical CT numbers for biological tissues, shows that the detection of nanoparticle in most tissues is only possible for high material concentrations.     

A study of photon interaction in some hormones

The effective atomic numbers (Z _eff) and electron density (N _el) of some hormones such as testosterone, methandienone, estradiol and rogesterone for total and partial photon interactions have been computed in the wide energy region 1 keV–100 GeV using an accurate database of photon-interaction cross sections and the WinXCom program. The computed Z _eff and N _el are compared with the values generated by XMuDat program. The computer tomography (CT) numbers and kerma values relative to air are also calculated and the computed data of CT numbers in the low-energy region help in visualizing the image of the biological samples and to obtain precise accuracy in treating the inhomogenity of them in medical radiology. In view of dosimetric interest, the photon absorbed dose rates of some commonly used gamma sources (Na-21, Cs-137, Mn-52, Co-60 and Na-22) are also estimated.     

Comparison of in vitro breast cancer visibility in analyser‐based computed tomography with histopathology,mammography, computed tomography and magnetic resonance imaging

High‐resolution analyser‐based X‐ray imaging computed tomography (HR ABI‐CT) findings on in vitro human breast cancer are compared with histopathology, mammography, computed tomography (CT) and magnetic resonance imaging. The HR ABI‐CT images provided significantly better low‐contrast visibility compared with the standard radiological images. Fine cancer structures indistinguishable and superimposed in mammograms were seen, and could be matched with the histopathological results. The mean glandular dose was less than 1 mGy in mammography and 12–13 mGy in CT and ABI‐CT. The excellent visibility of in vitro breast cancer suggests that HR ABI‐CT may have a valuable role in the future as an adjunct or even alternative to current breast diagnostics, when radiation dose is further decreased, and compact synchrotron radiation sources become available.     

X‐ray fluorescence computed tomography with absorption correction for biomedical samples

To obtain accurate distributions of trace elements in biomedical samples nondestructively, the problems on absorption correction and radiation dose are confronted in X‐ray fluorescence computed tomography. In this paper, the absorption‐corrected ordered subsets expectation maximization (AC‐OSEM) algorithm is developed to solve these problems. Simulation results show that the AC‐OSEM‐based X‐ray fluorescence computed tomography is accurate when only the incident X‐ray attenuation map is known and relatively fewer projections are provided. In addition, for the biomedical samples, the simplified approximate expression of the fluorescence attenuation map is practicable. Experiments on the biomedical samples were also carried out to evaluate the applicability of the AC‐OSEM algorithm to soft tissues, which demonstrates that the distribution of the trace element Fe in the pathological liver could be clearly revealed. Copyright © 2014 John Wiley & Sons, Ltd.     

Radiation dose reduction by using low dose CT protocol of thorax

CT makes up to 67% of radiation from medical sources. Therefore emphasizes is especially on the importance of reducing doses and the introduction of procedures with the lowest possible dose received by the patient. The so called low dose CT protocol was studied for some chest diagnosis however it was not investigated for the patients with lymphoproliferative diseases. Lymphoproliferative diseases, including most lymphomas involve a large number of younger and middle age patients i.e. patients in the reproductive period of life. A CT exam of these patients is indispensable method for the diagnosis, and later for long life monitoring of the effectiveness of therapy. The aim of this work was to compare the patient doses between two different CT protocols of thorax in patients with this diagnosis. The entrance surface doses were measured and compared using standard CT protocol of thorax which implies 120 kV and 160 mA conditions and low dose CT protocol using 120 kV and 30 mA conditions while maintaining image quality. The study involved 60 patients. Each patient underwent two different CT thorax protocols during regular follow up of the disease. The doses were measured using LiF:Mg,Ti (TLD-100) thermoluminescent (TL) and GD-352M radiophotoluminescent (RPL) dosimeters on the thyroid, eye lens, sternum and gonads. The results showed that low dose protocol yielded with the reduction of doses by the factor of 1.8–15 on the eye lens, 1.0–9.1 on the thyroid, 2.5–7.0 on sternum and 0.3–12.8 on gonads, respectively. The doses were significantly lower using low dose CT protocol while the image quality for lymph node presentation was satisfactory according to European criteria. Therefore the use of low dose CT protocol as a standard for patients with lymphoproliferative disorders is highly recommended.     

基于稀疏优化的计算机断层成像图像不完全角度重建综述

计算机断层成像(computed tomography,CT)技术在医学和工业无损检测中都具有非常广泛的应用,CT重建算法是其中的核心,而不完全角度重建问题则是实际应用中重建算法研究领域的一个热点和难点问题.近年来,随着稀疏优化理论与算法的飞速发展,基于稀疏优化的重建算法已经在不完全角度重建问题中得到了较广泛的应用,且表现出了良好的精度与速度性能.本文首先对稀疏优化的基本理论结论与常用算法进行了介绍;而后对稀疏优化理论在CT图像不完全角度重建中的应用进行归纳,分类介绍了其主要研究成果及稀疏优化所发挥的作用;最后对基于稀疏优化的不完全角度重建研究进行了展望.     

Analysis of low-dose radiation shield effectiveness of multi-gate polymeric sheets

Computed tomography (CT) uses a high dose of radiation to create images of the body. As patients are exposed to radiation during a CT scan, the use of shielding materials becomes essential in CT scanning. This study was focused on the radiation shielding materials used for patients during a CT scan. In this study, sheets were manufactured to shield the eyes and the thyroid, the most sensitive parts of the body, against radiation exposure during a CT scan. These sheets are manufactured using silicone polymers, barium sulfate (BaSO₄) and tungsten, with the aim of making these sheets equally or more effective in radiation shielding and more cost-effective than lead sheets. The use of barium sulfate drew more attention than tungsten due to its higher cost-effectiveness. The barium sulfate sheets were coated to form a multigate structure by applying the maximum charge rate during the agitator and subsequent mixing processes and creating multilayered structures on the surface. To measure radiation shielding effectiveness, the radiation dose was measured around both eyes and the thyroid gland using sheets in three different thicknesses (1, 2 and 3 mm). Among the 1 and 2 mm sheets, the Pb sheets exhibited greater effectiveness in radiation shielding around both eyes, but the W sheets were more effective in radiation shielding around the thyroid gland. In the 3 mm sheets, the Pb sheet also attenuated a higher amount of radiation around both eyes while the W sheet was more effective around the thyroid gland. In conclusion, the sheets made from barium sulfate and tungsten proved highly effective in shielding against low-dose radiation in CT scans without causing ill-health effects, unlike lead.     

A modified equally sloped algorithm based on the total variation algorithm in computed tomography for insufficient data

Computed tomography (CT) has become an important technique for analyzing the inner structures of material, biological and energy fields. However, there are often challenges in the practical application of CT due to insufficient data. For example, the maximum rotation angle of the sample stage is limited by sample space or image reconstruction from the limited number of views required to reduce the X‐ray dose delivered to the sample. Therefore, it is difficult to acquire CT images with complete data. In this work, an iterative reconstruction algorithm based on the minimization of the image total variation (TV) has been utilized to develop equally sloped tomography (EST), and the reconstruction was carried out from limited‐angle, few‐view and noisy data. A synchrotron CT experiment on hydroxyapatite was also carried out to demonstrate the ability of the TV‐EST algorithm. The results indicated that the new TV‐EST algorithm was capable of achieving high‐quality reconstructions from projections with insufficient data.     

Application of computed tomography to microgravity combustion

This paper describes applications of computed tomography (CT) to combustion phenomena under microgravity conditions. Infrared Thermography (IT) has been considered as a promising method for two-dimensional measurement of flames. We have applied IT to CT for a butane flame under microgravity conditions. The method joining spectroscopy to CT for diffusion flame of hydrogen has also been carried out. Intensity of chemical luminescence, which is originated from combustion-chemical reaction in the flame, can be measured by scanning a spectrometer with collimator. The effectiveness of the CT applications to microgravity combustion has been confirmed from two method.     

An advanced fully 3D OSEM reconstruction for positron emission tomography

A fully 3D OSEM reconstruction method for positron emission tomography （PET） based on symmetries and sparse matrix technique is described. Great savings in both storage space and computation time were achieved by exploiting the symmetries of scanner and sparseness of the system matrix. More reduction of storage requirement was obtained by introducing the approximation of system matrix. Iteration-filter was performed to restrict image noise in reconstruction. Performances of simulation data and phantom data got from Micro-PET （Type： Epuls-166） demonstrated that similar image quality was achieved using the approximation of the system matrix.     

Shadow effects in simulated ultrasound images derived from computed tomography images using a focused beam tracing model

Simulation of ultrasound images based on computed tomography (CT) data has previously been performed with different approaches. Shadow effects are normally pronounced in ultrasound images, so they should be included in the simulation. In this study, a method to capture the shadow effects has been developed, which makes the simulated ultrasound images appear more realistic. The method using a focused beam tracing model gives diffuse shadows that are similar to the ones observed in measurements on real objects. Ultrasound images of a cod (Gadus morhua) were obtained with a BK Medical 2202 ProFocus ultrasound scanner (BK Medical, Herlev, Denmark) equipped with a dedicated research interface giving access to beamformed radio frequency data. CT images were obtained with an Aquilion ONE Toshiba CT scanner (Toshiba Medical Systems Corp., Tochigi, Japan). CT data were mapped from Hounsfield units to backscatter strength, attenuation coefficients, and characteristic acoustic impedance. The focused beam tracing model was used to create maps of the transmission coefficient and scattering strength maps. Field II was then used to simulate an ultrasound image of 38.9 × 55.3 × 4.5 mm, using 10(6) point scatterers. As there is no quantitative method to assess quality of a simulated ultrasound image compared to a measured one, visual inspection was used for evaluation.