Tube Current Modulation Technique Research Articles

Radiation dose reduction and image quality in pediatric paranasal sinus CT: with automatic tube current modulation and iterative reconstruction technique.

Our objective is to evaluate radiation dose and image quality in pediatric paranasal sinus computed tomography (CT) with automatic tube current modulation (ATCM) and sinogram-affirmed iterative reconstruction algorithm (SAFIRE). CT scans from 80 patients were divided into two groups: Group A [80 kVp, pitch 1.5, 40 mAs, the filtered back projection (FBP) algorithm] and Group B (70 kVp, pitch 3, ATCM with reference at 40 mAs, SAFIRE strengths 1-5). We have evaluated image quality and radiation dose. Group B demonstrated significantly lower volume computed tomography dose index, dose-length product, and effective dose than Group A (0.13±0.03 vs. 1.57±0.01mGy, 2.27±0.82 vs. 19.88±2.01mGy·cm, and 0.0081±0.0017 vs. 0.079±0.013mSv, respectively; P<.001). Increasing SAFIRE strengths correlated with noise reduction and SNR enhancement. Group B's noise and SNRsoft at SAFIRE strength 5 were comparable with Group A. Images reconstructed with SAFIRE strength 5 in Group B exhibit comparable image quality with FBP in Group A.

Fabrication and Evaluation of Thyroid Shield from Silicone Rubber-Cooper and its Comparison to Tube Current Modulation in CT Examination

This study aimed to fabricate thyroid shields made from Silicone Rubber (SR)-Cooper (Cu) material, analyze the effectiveness of SR-Cu shields in reducing radiation dose, and compare them with tube current modulation (TCM) in computed tomography (CT) examination. Thyroid shields were made from SR-Cu with Cu percentages of 0, 5, 10, 15, and 20%. The thyroid shields were positioned over the neck of the anthropomorphic phantom. Scanning was performed using a GE 128-slice CT scanner with fixed tube current of 150 mA and tube current modulation (TCM). The elatiscity of thyroid shields was tested using an universal testing machine (UTM). The ability of thyroid shields for dose reduction was measured using a 10X6-3CT Radcal detector, and quality of the resulted images was characterized with metric of signal-to-noise ratio (SNR) at the anterior, posterior, and lateral areas of the neck area of anthropomorphic phantom. It is found that the elasticity of the thyroid shields increased from 0.09 to 0.12 N/mm2 for Cu percentages from 0 to 20%. The measured dose decreased as the percentage of Cu increased. 20% of SR-Cu was able to reduce the dose by 32.4% for the fix tube current. In comparison, the TCM technique reduced the dose by 44.5%. Therefore, dose reduction using the developed shields is lower than using TCM approach. It is also found that implementation of the thyroid shields did not reduce image quality significantly. It is found that there were no apparent artifacts in the images. The highest SNR was found in the image with 20% SR-Cu, which was 3.84. In comparison, the SNR using the TCM approach was 3.59. In conclusion SR-Cu shields were successfully developed and they reduced dose with relatively consistent of image quality.

The Feasibility of Tube Current Modulation (TCM) to Reduce dose of the Surface Breast in Various Breast Sizes

This study aims to develop three sizes of breast phantoms from silicone rubber (SR) material and evaluate tube current modulation (TCM) to reduce surface doses of the developed breast phantoms. The in-house breast phantom has three sizes: small (cup 34), medium (cup 36), and large (cup 38). The cross-sectional areas of cup 34, 36, and 38 are 78.5, 113.04, and 153.87 cm2, respectively. The in-house phantom was attached to the adult anthropomorphic phantom for dose measurement. Dose measurement was performed using an Optically Stimulated Luminescence (OSL) dosimeter. Scans were performed with and without TCM technique. It was found that the TCM effectively reduce the radiation dose to the breast surface up to approximately 60%. However, the dose reduction was accompanied by a 66% increase in noise when using the TCM technique.

Evaluation of Changes in Dose Estimation on Abdomen CT Scan with Automatic Tube Current Modulation Using In-House Phantom

This study evaluates the effect of the Automatic Tube Current Modulation (ATCM) technique on pitch and effective diameter variation in estimating dose values and noise levels for abdominal examination on Philips Ingenuity CT scan machine using in-house Phantoms. The in-house phantoms are oval in shape with three effective diameter sizes, namely 23.2 cm, 28.3 cm, and 33.3 cm to represent abdominal region. The three size Phantoms were scanned using an Ingenuity 128 Philips CT scan with the abdominal protocol exposure parameters of 120 kVp tube voltage, Dose Right Index (DRI) variations of 10,11,12,13, and 14, and pitch variations of 0.6; 0.8; 1.0; 1.2; and 1.49. The changes in mAs, CTDIvol, and noise to the Philips reference value were then verified (i.e. an addition of one DRI value increases mAs by 12 %). For evaluation, a metric to express the change in DRI is defined as ΔDRI. The study demonstrates that noise level is influenced by object size; size information of the object could be useful to predict the change of tube current and pitch due to ATCM with respect to selected DRI. The DRI value is proportional to the tube current, thus selecting the DRI at a certain pitch will directly determine tube current. The ΔDRI in general, according to Philips specifications, is verified to be approximately 10 % to 13 %, except for DRI 10 to 11 which is relatively high on average 15 % to 17 %. Increasing DRI increases the CTDIvol. The CTDI/mAs constantly ranges of 0.06 to 0.07. The value could serve as a characteristic parameter for quality assurance. The ATCM specifications of the Ingenuity 128 CT Scanner is according to Philips regulations.

Evaluation of Tube Current Modulation Profile on CT Image of 128 slices CT Scanner using The Borobudur Phantom

The purpose of this study is to evaluate the tube current profile of Siemens 128 slice CT scanner with tube current modulation (TCM) technique using the Borobudur phantom. Borobudur phantom was made from acrylic which has four different diameters of 8, 16, 24, and 32 cm. It was filled with distilled water. The phantom was scanned using a Siemens Somatom 128 slice CT Scanner. The CT scanner took a topogram image first to estimate the attenuation level of each diameter of the phantom. The phantom was scanned using tube voltage and quality reference variations. After the axial images of the phantom were obtained, the tube current information was extracted from digital imaging and communications in medicine (DICOM) header in each dataset using through IndoQCT software. It is found that as the phantom diameter increases, the tube current also increases. For variation of quality reference, the increasing value of quality reference will increase the tube current value. The results show that the tube current profile in the tube voltage variation shows insignificant changes with a statistical test p-value of 0.752. From this study, we conclude that TCM can be evaluated using Borobudur phantom and IndoQCT software.

Radiation Doses in Cardiovascular Computed Tomography.

We discussed the contemporary views on the effects of ionising radiation on living organisms and the process of estimating radiation doses in CT examinations and the definitions of the CTDI, CTDIvol, DLP, SSDE, ED. We reviewed the reports from large analyses on the radiation doses in CT examinations of the coronary arteries prior to TAVI procedures, including the CRESCENT, PROTECTION, German Cardiac CT Registry studies. These studies were carried out over the last 10 years and can help confront the daily practice of performing cardiovascular CT examinations in most centres. The reference dose levels for these examinations were also collected. The methods to optimise the radiation dose included tube voltage reduction, ECG-monitored tube current modulation, iterative and deep learning reconstruction techniques, a reduction in the scan range, prospective study protocols, automatic exposure control, heart rate control, rational use of the calcium score, multi-slices and dual-source and wide-field tomography. We also present the studies that indicated the need to raise the organ conversion factor for cardiovascular studies from the 0.014-0.017 mSv/mGy*cm used for chest studies to date to a value of 0.0264-0.03 mSv/mGy*cm.

Patient dose reduction for a localizer radiograph with an additional tin filter in chest-abdomen-pelvis, spine, and head computed tomography examinations.

This study aimed to evaluate the dose reduction potential of adding a tin filter to localizer radiographs (LR) on computed tomography (CT) examinations in both phantom and clinical studies. LRs were performed using combinations of 120 kVp and 20mA (120/20), 100 kVp with a tin filter, and 50mA or 20mA (Sn100/50, Sn100/20). For the phantom experiment, entrance surface doses (ESD) of the LRs were evaluated for each protocol using an anthropomorphic phantom. This retrospective clinical study included 700 patients (300 for chest-pelvis, 200 for spine, and 200 for head CTs). The volume CT dose indices (CTDIvols) of the main CT scans were recorded and placed into one of three groups based on body mass index (BMI): underweight, normal-weight, and overweight, to evaluate the effect of LR acquisition conditions on the performance of the automatic tube current modulation technique of subsequent CT scans. The ESDs of all LRs with the Sn100/50 protocol were 0.03mGy, a decrease of more than 80% compared to those of the 120/20 protocol. Moreover, the Sn100/20 protocol reduced ESD to 0.02mGy. In chest-pelvis CT, there were no significant differences in the CTDIvol between with and without a tin filter for each BMI group. However, the lateral LRs with the tin filter on the spine CT slightly reduced the CTDIvol in normal-weight and overweight patients. Although there is room to optimize the acquisition conditions for larger patients, an additional tin filter for LR is a useful means to efficiently reduce ESDs.

Potential of Fluid Dynamic Bowtie Filter for Dose Reduction and Image Quality Improvement of Cone-Beam CT

Reducing radiation dose to patients without compromising imaging quality has been an important issue in the medical use of X-ray computed tomography (CT). In this study, based on the conceptual designs of different types of attenuation filters, the radiation doses to patients who undergo a typical head, thorax and abdomen scan using a cone-beam CT with different scanning protocols were simulated using the Monte Carlo method, and the isotropy of the noise power spectrum (NPS) of the reconstructed images was also calculated. Compared to the scanning protocol without attenuation and tube current modulation (TCM), the results showed that the fluid dynamic bowtie filter (FDB) combined with the TCM technique reduced the average organ dose by 70%, 34% and 60% for a typical head, thorax and abdomen scan, respectively, and the NPS isotropy of the reconstructed images was also significantly improved. Compared to most currently used static bowtie filters, the FDB has a higher potential to reduce the dose for patients undergoing CT scans. Further efforts are warranted to make the FDB technique clinically useful.

Individualized Scan Protocols in Abdominal Computed Tomography: Radiation Versus Contrast Media Dose Optimization.

In contrast-enhanced abdominal computed tomography (CT), radiation and contrast media (CM) injection protocols are closely linked to each other, and therefore a combination is the basis for achieving optimal image quality. However, most studies focus on optimizing one or the other parameter separately. Reducing radiation dose may be most important for a young patient or a population in need of repetitive scanning, whereas CM reduction might be key in a population with insufficient renal function. The recently introduced technical solution, in the form of an automated tube voltage selection (ATVS) slider, might be helpful in this respect. The aim of the current study was to systematically evaluate feasibility of optimizing either radiation or CM dose in abdominal imaging compared with a combined approach. Six Göttingen minipigs (mean weight, 38.9 ± 4.8 kg) were scanned on a third-generation dual-source CT. Automated tube voltage selection and automated tube current modulation techniques were used, with quality reference values of 120 kVref and 210 mAsref. Automated tube voltage selection was set at 90 kV semimode. Three different abdominal scan and CM protocols were compared intraindividually: (1) the standard "combined" protocol, with the ATVS slider position set at 7 and a body weight-adapted CM injection protocol of 350 mg I/kg body weight, iodine delivery rate (IDR) of 1.1 g I/s; (2) the CM dose-saving protocol, with the ATVS slider set at 3 and CM dose lowered to 294 mg I/kg, resulting in a lower IDR of 0.9 g I/s; (3) the radiation dose-saving protocol, with the ATVS slider position set at 11 and a CM dose of 441 mg I/kg and an IDR 1.3 g I/s, respectively. Scans were performed with each protocol in arterial, portal venous, and delayed phase. Objective image quality was evaluated by measuring the attenuation in Hounsfield units, signal-to-noise ratio, and contrast-to-noise ratio of the liver parenchyma. The overall image quality, contrast quality, noise, and lesion detection capability were rated on a 5-point Likert scale (1 = excellent, 5 = very poor). Protocols were compared for objective image quality parameters using 1-way analysis of variance and for subjective image quality parameters using Friedman test. The mean radiation doses were 5.2 ± 1.7 mGy for the standard protocol, 7.1 ± 2.0 mGy for the CM dose-saving protocol, and 3.8 ± 0.4 mGy for the radiation dose-saving protocol. The mean total iodine load in these groups was 13.7 ± 1.7, 11.4 ± 1.4, and 17.2 ± 2.1 g, respectively. No significant differences in subjective overall image or contrast quality were found. Signal-to-noise ratio and contrast-to-noise ratio were not significantly different between protocols in any scan phase. Significantly more noise was seen when using the radiation dose-saving protocol (P < 0.01). In portal venous and delayed phases, the mean attenuation of the liver parenchyma significantly differed between protocols (P < 0.001). Lesion detection was significantly better in portal venous phase using the CM dose-saving protocol compared with the radiation dose-saving protocol (P = 0.037). In this experimental setup, optimizing either radiation (-26%) or CM dose (-16%) is feasible in abdominal CT imaging. Individualizing either radiation or CM dose leads to comparable objective and subjective image quality. Personalized abdominal CT examination protocols can thus be tailored to individual risk assessment and might offer additional degrees of freedom.

Effect of Body Mass Index in Coronary CT Angiography Performed on a 256-Slice Multi-Detector CT Scanner.

We aimed to investigate the effect of a patient’s body mass index (BMI) on radiation dose and image quality in prospectively ECG-triggered coronary CT angiography (CCTA) performed on a 256-slice multi-detector CT scanner. In total, 87 consecutive patients receiving CCTA examinations acquired with tube current modulation (TCM) and iterative reconstruction (IR) were enrolled in this study. The dose report recorded from the CT scanner console was used to derive the effective dose for patients. Subjective image quality scoring and objective noise measurements were conducted to quantify the impact of BMI on the image quality of CCTA. Because of the TCM technique, we expected tube current and radiation dose to increase as BMI increased. However, using TCM did not always guarantee sufficient radiation exposure to achieve consistent image quality for overweight or obese patients since the maximum X-ray tube output in milliamperes and kilovoltage peak was reached. The impact of photon starvation noise on image quality was not significant until BMI ≥ 27 kg/m2; this result could be due to IR’s noise reduction capability. Our results also suggest that using TCM with a noise index of 25 HU can reduce radiation dose without compromising image quality compared to images obtained based on the manufacturer’s default settings.

Relation between age and CT radiation doses: Dose trends in 705 pediatric head CT

PurposeTo evaluate the relationship between patient age and radiation doses associated with routine pediatric head CT performed with automatic tube potential selection and tube current modulation techniques. MethodsWe obtained patient demographics, scan parameters, and radiation dose descriptors (CT dose index volume -CTDIvol and dose length product -DLP) associated with consecutive routine head CT in 705 children (mean age 6.9 ± 5 years). Children were scanned on one of the three multidetector-row CTs (64–128 slices, Siemens) over 6 months period in a tertiary hospital. All head CT exams were performed in helical scan mode using automatic tube potential selection (Care kV) and automatic tube current modulation (Care Dose 4D) techniques. The information was obtained from a radiation dose monitoring software. Data were analyzed using linear correlation and analysis of variance. ResultsMost age-wise median CTDIvol (9−27 mGy; 703/705 pediatric head CT, >99 %) from our institution were lower than the European Diagnostic Reference Levels (EDRL, CTDIvol 24−50 mGy) but median DLP (151−586 mGy cm) from 201/705 children (28 %) was higher than the EDRL (DLP 300−650 mGy cm). Unlike the age-stratified EDRL, a combination of automatic tube potential selection and tube current modulation for pediatric head results in a significant linear correlation between radiation doses and patient age (r2 = 0.66, p < 0.001). ConclusionsRadiation doses for head CT change linearly with children's age. Despite lower CTDIvol and DLP for most children, longer scan length resulted in higher DLP for some pediatric head CT compared to the corresponding EDRL; this result underscores the need to promote clear guidelines for technologists operating CT.

Evaluation of an organ-based tube current modulation tool in pediatric CT examinations

ObjectivesTo investigate the effect of an organ-based tube current modulation (OTCM) technique on organ absorbed dose and assess image quality in pediatric CT examinations.MethodsFour physical anthropomorphic phantoms that represent the average individual as neonate, 1-year-old, 5-year-old, and 10-year-old were used. Standard head and thorax acquisitions were performed with automatic tube current modulation (ATCM) and ATCM+OTCM. Dose calculations were performed by means of Monte Carlo simulations. Radiation dose was measured for superficial and centrally located radiosensitive organs. The angular range of the OTCM exposure window was determined for different tube rotation times (t) by means of a solid-state detector. Image noise was measured as the standard deviation of the Hounsfield unit value in regions of interest drawn at selected anatomical sites.ResultsATCM+OTCM resulted in a reduction of radiation dose to all radiosensitive organs. In head, eye lens dose was reduced by up to 13% in ATCM+OTCM compared with ATCM. In thorax, the corresponding reduction for breast dose was up to 10%. The angular range of the OTCM exposure window decreased with t. For t = 0.4 s, the angular range was limited to 74° in head and 135° for thorax. Image noise was significantly increased in ATCM+OTCM acquisitions across most examined phantoms (p < 0.05).ConclusionsOTCM reduces radiation dose to exposed radiosensitive organs with the eye lens and breast buds exhibiting the highest dose reduction. The OTCM exposure window is narrowed at short t. An increase in noise is inevitable in images located within the OTCM-activated imaged volume.Key Points• In pediatric CT, organ-based tube current modulation reduces radiation dose to all major primarily exposed radiosensitive organs.• Image noise increases within the organ-based tube current modulation enabled imaged volume.• The angular range of the organ-based tube current modulation low exposure window is reduced with tube rotation time.

Calculation of Size-Specific Dose Estimation (SSDE) of The Pediatric’s Head for Tube Current Modulation (TCM) CT Examinations

Computed Tomography (CT) examinations in the pediatric patient are sensitive to the impact of ionizing radiation, which gives long-term risk. In addition, the actual radiation dose delivered during CT examinations has not been well-described mainly when using tube current modulation (TCM) technique. To quantified this effect, an algorithm for calculating radiation dose is needed. Therefore, this study aims to calculate and analyze the estimated effective dose of head examinations from 3D CT images, based on the equivalent water diameter (Dw)For the TCM technique. Four pediatric patients in the 0-6-year-old age groups were examinations using Somatom Definition Flash with variation in the number of slices. CTDIvol and Tube current values were obtained from the DICOM header. There are two main parts algorithm for Dw calculation. First, images of CT data were converted to Hounsfield units (HU). Then, Dw values based on the patients contour using the K-mean cluster and morphological gradient algorithm were calculated for every slice. The coefficient factor is obtained by American Association of Physicists in Medicine (AAPM) report 220. The values then multiplied by CTDIvolto acquire values of SSDE. The results showed that the relation between SSDE and tube current was strongly correlated with R2 values of 0.982.

Organ-based Tube-current Modulation Applied on Different MDCT Scanners: Reduction in the Radiation Dose to the Eye Lens at Head CT

Organ-based tube current modulation (OB-TCM) techniques, which are provided by three vendors, reduces the radiation dose to the lens of the eyes by decreasing the tube current, when the X-ray tube passes over the anterior surface of critical organs. However, the characteristics of dose modulation of these techniques are different. The purpose of this study was to understand the performance characteristics of OB-TCM technique of each computed tomography (CT) vendor at head CT. We used three CT scanners (SOMATOM Definition Flash; Siemens Healthcare, Revolution CT; GE Healthcare, and Aquilion ONE Genesis Edition; Canon Medical Systems). We measured the radiation dose to the lens surface as evaluation of radiation dose reduction and measured the image noise as index of image quality. We measured the radiation dose rate in the air for analysis of the characteristics of dose modulation in each OB-TCM. When applying OB-TCM, the radiation doses for the lens surface were decreased by 28%, 22%, and 25% for Siemens, GE, and Canon CT scanners, respectively, and the image noise level was increased by 5.6%, 8.5%, and 15.1% for Siemens, GE, and Canon CT scanners, respectively. The characteristics of dose modulation in each OB-TCM were also confirmed by measured the radiation dose rate. We confirmed that each OB-TCM has different influence on image quality and radiation doses for lens surface, due to the different characteristics of dose modulation for each CT vendor.

Effect of Arm Position on Image Quality and Radiation Dose in Multidetector Computed Tomography

Background: Abdominal CT using a tube-current modulation technique may result in artifacts due to changes in the position of the patient’s arms, resulting in poor image quality and excessive radiation exposure. To solve these problems, the patient’s arm is positioned mainly on the head or outside the examination area. Objectives: An optimization method to acquire high-quality images in CT examination by comparing the radiation dose and image according to the change in arm position and the use of the tube-current modulation method in CT examination. Materials and Methods: To analyze the CT images, the mean, standard deviation (SD), and coefficient of variation (COV) of the Hounsfield unit (HU) of the CT were obtained by measuring the pixel values of the heart, chest, lung, and bone using region of interest (ROI) manage. The dose of computed tomography dose index (CTDI) and dose length product (DLP) according to the position of the arm. Results: The arms up position of CTDIvol and DLP values were lower than the arms down position. In the z-axis thickness modulation (Z-DOM), the tube current increased in the shoulders, decreased in the lungs, and increased in the abdomen. There was no artifact when the arms were raised, but an artifact was present when the arm was lowered. The calculated peak signal-to-noise ratio (PSNR) for the Z-DOM application in the CT scan of the anthropomorphic phantom by applying automatic exposure control (AEC) was 38.21 dB. There was no significant difference between SD and COV using Z-DOM and the fixed tube current technique (P > 0.05). Noise in the image increased when the arm was raised, and dose increased in the thyroid and upper chest. Conclusion: The position of the upper arms directly affects the image in the MDCT imaging of the anthropomorphic phantom. Therefore, it is possible to increase the quality of the image by reducing the amount of artifacts and the amount of radiation by orienting the arms upward. This optimal test method could be used in clinical practice to achieve high image quality and low noise in the MDCT of trauma patients.

Effects of the Use of Automatic Tube Current Modulation on Patient Dose and Image Quality in Computed Tomography

Objectives:The frequency of abdominal computed tomography examinations is increasing, leading to a significant level of patient dose. This study aims to quantify and evaluate the effects of automatic tube current modulation (ATCM) technique on patient dose and image quality in contrast-enhanced biphasic abdominal examinations.Methods:Two different scan protocols, based on constant tube current and ATCM technique, were used on 64 patients who visited our radiology department periodically. For three patient groups with different patient size, results from two protocols were compared with respect to patient dose and image quality. Dosimetric evaluations were based on the Computed Tomography Dose Index, dose length product, and effective dose. For the comparison of image qualities between two protocols, Noise Index (NI) and Contrast to Noise Ratio (CNR) values were determined for each image. Additionally, the quality of each image was evaluated subjectively by an experienced radiologist, and the results were compared between the two protocols.Results:Dose reductions of 31% and 21% were achieved by the ATCM protocol in the arterial and portal phases, respectively. On the other hand, NI exhibited an increase between 9% and 46% for liver, fat and aorta. CNR values were observed to decrease between 5% and 19%. All images were evaluated by a radiologist, and no obstacle limiting a reliable diagnostic evaluation was found in any image obtained by either technique.Conclusion:These results showed that the ATCM technique reduces patient dose significantly while maintaining a certain level of image quality.

Dose optimization in computed tomography of brain using CARE kV and CARE Dose 4D

Background: Computed Tomography (CT) scan of brain is the most widely used CT examination. Latest CT scanners have the potential to deliver very low radiation dose by utilizing tube potential and tube current modulation techniques. We aim to determine the application of CARE kV (tube potential modulation) and CARE Dose4D (tube current modulation) in CT scan of brain. Both CARE kV and CARE Dose4D are well-established innovative technology of Siemens Medical Solutions.&#x0D; Methodology: A prospective hospital-based study was conducted during four months at Tribhuvan University Teaching Hospital (TUTH). The data were collected on a Siemens Somatom Definition Edge 128 slices CT scanner. Non-random purposive sampling technique was employed. Ethical approval and consent to participate were taken for every participant. Non-contrast (NC) CT images were acquired without using CARE kV and CARE Dose4D, whereas during contrast-enhanced (CE) investigation, both were turned on keeping other scanning parameters constant for each individual.&#x0D; Results: A total of 72 patients, 42 males and 28 females - mean age 41y (range 16-87y) participated in this study. The Body Mass Index (BMI) was 22.0, range 20.1-25.0. The mean value of Computed Tomography Dose Index (CTDI), Dose Length Product (DLP) and Effective Dose (ED) before and after switching on both CARE kV and CARE Dose4D were 58.19±0.35 and 39.67±3.59 milli-Gray (mGy), 946.67 and 652.58 mGy-cm, and 1.98 and 1.36 milli-Sievert (mSv) respectively.&#x0D; Conclusion: CARE kV and CARE Dose4D can reduce radiation dose in CT scan of brain without loss of image quality.

58. Dosimetric changes with Computed Tomography Automatic Tube Current Modulation techniques

Purpose The objective of the study is the verification of dose changes for a Computed Tomography (CT) Automatic Tube Current Modulation (ATCM) technique. In particular, the work aims to verify that (1) previsions of the CT scanner console (in terms of CTDIvol and DLP) are reflected in the dose distribution within the patient and (2) the experimental results coincide with the predictions of the noise theory on which the technique is based. For this purpose, an anthropomorphic Alderon RANDO (AR) phantom and Gafchromic® XR-QA2 films were used. Methods Radiochromic films were cut to shape the AR phantom in two anatomical regions (shoulders and mid-chest). Since the ATCM algorithm used is based on the Noise Index (NI) parameter, three thorax exam protocols were chosen: reference (NI = 13), lower (NI = 10) and higher (NI = 16) noise. All other acquisition parameters during the three scans were maintained unchanged. CTDIvol and DLP values reported by the CT console were recorded after each exam to compare theoretical and experimental measurements. After dose calibration of the films, dose maps were normalized to the reference map (NI = 13) to obtain percentage variations. Experimental results were compared to the relative variations obtained from CT console and quantum noise theory. Results The results showed that the information reported by the CT console in terms of CTDIvol and DLP variation are in agreement, on average, with experimental measurements. The dose distribution, however, is not uniform and CT console dose reports are purely indicative. Variations, in fact, are calculated by considering a uniform water phantom that does not represent the actual composition of the patient, as shown in Fig. 1. The values reported by the CT console are also in agreement with the prediction by the quantum noise theory. Conclusions The study allowed to verify the dose information reported by the CT scanner console for an ATCM technique. The CTDIvol and DLP values represent, on average, the experimentally measured variation in the AR phantom. Although this evaluation represents an estimate, this method can be a starting point for further studies.

Image Quality Performance of Virtual Single-Source CT Using Dual-Source Computed Tomography

The aim of this study is to analyze the image quality provided by a dual-source (DS) data set and a single-source (SS) data set at the same radiation exposure, in order to evaluate a dose splitting method for dual-source scanning protocols. A 192-slice dual-source third generation CT (Somatom Force; Siemens Healthcare, Forchheim, Germany) was used to image a Catphan phantom (Catphan503; The Phantom Laboratory, Salem, New York) utilizing different X-ray tube voltages from 70 to 120 kVp with an organ-based tube-current modulation technique (X-CARE; Siemens Healthcare, Forchheim, Germany). In order to keep the radiation dose (given by volume computed tomography dose index) in a clinically relevant range, different X-ray tube time-current products ranging from 80 to 300 mAs were selected. The data sets by each X-ray tube voltage were collected using a single-source as well as a dual-source mode. The measurements in the dual-source mode were performed with five different tube currents of the X-ray tube A and B. Thereby, the tube current ratios were 50%|50% (DS 0.5), 60%|40% (DS 0.6), 70%|30% (DS 0.7), 80%|20% (DS 0.8), and 90%|10% (DS 0.9). The images were reconstructed by the use of a filter-back projection (Br40) and an advanced mode led iterative reconstruction algorithms (advanced modeled iterative reconstruction algorithms [ADMIRE]; Siemens Healthcare, Forchheim, Germany) with a strength range of 1-5. The image quality was evaluated in terms of noise, contrast-to-noise ratio (CNR), low-contrast detectability expressed as the structural similarity index (SSIM) and spatial resolution quantified by the full width at half maximum of the line-spread function. Image noise decreased by the use of the dual-source mode, which led to improvement of their CNR compared to the single-source mode. SSIM showed an almost constant behavior by both modes. The spatial resolution indicated a lower trend by the dual-source mode in comparison to the single-source mode. However, the loss of the spatial resolution performance was lower than 5% for the dual-source modes. The presented phantom study demonstrated that SSIM and spatial resolution performance obtained by dual-source CT protocols showed a negligible variation to those by the single-source CT. However, the noise and CNR displayed an improvement for the dual-source CT. Therefore, the use of the dual-source CT enables to split the radiation dose between X-ray tubes and to compare the data sets with different radiation dose levels without loss in the image quality.

Craniocervical computed tomography angiography with adaptive iterative dose reduction 3D algorithm and automatic tube current modulation in patients with different body mass indexes.

The aim of this study was to investigate the feasibility of head and neck computed tomography angiography (CTA) using the 80-kV tube voltage and the adaptive iterative dose reduction (AIDR) 3D algorithm in patients with different body mass indexes (BMIs).From November 2016 to January 2017, 128 consecutive patients scheduled for head and neck CTA examinations were randomized into the 100-kV group (n = 60) and the 80-kV group (n = 68). Both groups used the automatic tube current modulation technique and the AIDR 3D algorithm. The patients were further grouped as slender (BMI < 22 kg/m2), normal weight (22 kg/m2≤BMI < 25 kg/m2), and overweight (BMI ≥25 kg/m2). The image quality and the radiation dose of each subgroup were analyzed.The images of the head and neck vessels and the brain tissue obtained with 100 kV were all of diagnostic quality. Slender and normal weight patients imaged with 80 kV also produced images of diagnostic quality. However, 80 kV in the overweight patients failed to produce images of diagnostic quality. The radiation dose in the patients imaged with 80 kV was significantly decreased in comparison with those imaged with 100 kV. The effective dose was 0.36 ± 0.06 and 0.41 ± 0.05 mSv in the slender and normal weight patients imaged with 80 kV.Head and neck CTA scanning with 80 kV, automatic tube current modulation, and AIDR 3D algorithm can produce high quality images with reduced radiation dose in slender or normal weight patients.