Tube Voltage Range Research Articles

Tube voltage in chest and abdomen DR imaging: Which settings return maximal non-prewhitening model observer with eye filter (NPWE) detectability?

The non-prewhitening computational model observer with eye filter (NPWE) has been shown to reasonably predict human observer performance in general radiography and is an appropriate substitute when real clinical trials are not feasible. In this study, the NPWE model observer is used to detect specific tasks (circular designer nodules) ranging between 1 and 30mm in diameter using chest and abdomen phantom images acquired across the diagnostic energy range (60-125 kVp) with and without an anti-scatter grid. The aim of this study was to derive tube voltage (kVp) settings that return maximal NPWE detectability (d') of designer nodules, for digital radiography (DR) chest and abdomen imaging. Images of a chest phantom (LucAl phantom) and a surrogate for an abdomen (18.5cm PMMA) were acquired across the diagnostic energy range (60-125 kVp) with matched effective dose (for the respective anatomies), with and without an anti-scatter grid, on a general x-ray system. Images were captured using an Agfa DX-D 40C wireless indirect caesium iodide (CsI) imaging panel. Modulation transfer function (MTF), normalized noise power spectrum (NNPS), and contrast (C) were measured in each image and the detectability index d' was calculated for circular designer nodules with diameters ranging from 1 to 30mm (in steps of 1mm). The calculated d' peaked at a nodule diameter of 3mm irrespective of tube voltage, for both chest and abdomen images. A tube voltage of 80kVp returned maximal d' for chest imaging across all nodule diameters both with and without an anti-scatter grid. A tube voltage of 70 kVp returned maximal d' for abdomen imaging. The NPWE observer model has been used to derive tube voltages (kVp) that return maximal detectability (d') of designer nodules for chest and abdomen radiography using a modern DR imaging system. This will provide the medical physicist with a starting point in the task of optimising tube voltage range for chest and abdomen imaging.

Influence of anode/filtration setup on X-ray multimeter energy response in mammography applications

Quality control and assurance of mammography X-ray generators include the use of solid-state detectors and/or ionization chambers calibrated in standard reference radiation fields. The IEC 61267:2005 standard defines reference mammography radiation fields for Mo/Mo anode/filtration, while various anode/filtration combinations are encountered in clinical mammography X-ray units. Not all Secondary Standard Dosimetry Laboratories have an X-ray generator with Mo/Mo radiation setup. Thus, traceability can be established only for the available anode/filter combinations, commonly limited to W/Al. In this study, W/Al radiation fields were established under laboratory conditions by performing half-value layer measurements. Then, four solid-state detectors were characterized. X-ray multimeter performance was evaluated in terms of energy response in the W/Al radiation fields. In the laboratory conditions, the energy response of the dosimeters had a large deviation from unity for dosimeters without appropriate anode/filter combination selected in the software settings, even though most of the dosimeters had a uniform relative response. The discrepancy in the response was further investigated by examining its variation induced by available detector software settings, and it was determined that the dosimeter response can vary up to 20 %. In a clinical setup, the half-value layer was determined, and detector performance was examined. Dosimeters were tested in clinical fields with Mo/Mo, Mo/Rh, W/Rh, W/Ag anode/filter combinations in the X-ray tube voltage range from 25 kV to 35 kV. For most clinical radiation fields, multi-element detectors had energy response deviation within ±5 %. The single-element detector had one software setting available and exhibited strong energy dependence. Extensive testing of detector response, such as presented in this paper. allows for correction factor interpolation based on the half-value layer.

An adult and pediatric size-based contrast administration reduction phantom study for single and dual-energy CT through preservation of contrast-to-noise ratio.

Global shortages of iodinated contrast media (ICM) during COVID-19 pandemic forced the imaging community to use ICM more strategically in CT exams. The purpose of this work is to provide a quantitative framework for preserving iodine CNR while reducing ICM dosage by either lowering kV in single-energy CT (SECT) or using lower energy virtual monochromatic images (VMI) from dual-energy CT (DECT) in a phantom study. In SECT study, phantoms with effective diameters of 9.7, 15.9, 21.1, and 28.5cm were scanned on SECT scanners of two different manufacturers at a range of tube voltages. Statistical based iterative reconstruction and deep learning reconstruction were used. In DECT study, phantoms with effective diameters of 20, 29.5, 34.6, and 39.7cm were scanned on DECT scanners from three different manufacturers. VMIs were created from 40 to 140keV. ICM reduction by lowering kV levels for SECT or switching from SECT to DECT was calculated based on the linear relationship between iodine CNR and its concentration under different scanning conditions. On SECT scanner A, while matching CNR at 120kV, ICM reductions of 21%, 58%, and 72% were achieved at 100, 80, and 70kV, respectively. On SECT scanner B, 27% and 80% ICM reduction was obtained at 80 and 100kV. On the Fast-kV switch DECT, with CNR matched at 120kV, ICM reductions were 35%, 30%, 23%, and 15% with VMIs at 40, 50, 60, and 68keV, respectively. On the dual-source DECT, ICM reductions were 52%, 48%, 42%, 33%, and 22% with VMIs at 40, 50, 60, 70, and 80keV. On the dual-layer DECT, ICM reductions were 74%, 62%, 45%, and 22% with VMIs at 40, 50, 60, and 70keV. Our work provided a quantitative baseline for other institutions to further optimize their scanning protocols to reduce the use of ICM.

Construction and validation of an infant chest phantom for paediatric computed tomography

Paediatric imaging protocols should be carefully optimised to maintain the desired image quality while minimising the delivered patient dose. A paediatric chest phantom was designed, constructed and evaluated to optimise chest CT examinations for infants. The phantom was designed to enable dosimetry and image quality measurements within the anthropomorphic structure. It was constructed using tissue equivalent materials to mimic thoracic structures of infants, aged 0–6 months. The phantom materials were validated across a range of diagnostic tube voltages with resulting CT numbers found equivalent to paediatric tissues observed via a survey of clinical paediatric chest studies. The phantom has been successfully used to measure radiation dose and evaluate various image quality parameters for paediatric specific protocols.

Effect of varying X-ray tube voltage and additional filtration on image quality and patient dose in digital radiography system

This study investigated the effect of varying x-ray tube voltage and additional filtration thicknesses on radiation dose and image quality in digital radiography system. The polymethylmethacrylate (PMMA) phantoms of different thicknesses simulating both the adult chest and abdomen and the pediatric patient's chest examinations were used. X-ray tube voltage range of 70–125 kVp was used for adult patient chest radiography, 70–100 kVp for adult patient abdominal radiography, and 50–70 kVp for pediatric 1-year-old chest examination. 0.1–0.3 mm Cu and 1.0 mm Al filters were used as additional filters. Patient doses were measured with an ionization chamber, considering the irradiation parameters recommended for radiographic examinations performed in radiology clinics in the EUR 16260 protocol. The Entrance Skin Dose (ESD) was calculated from the air kerma value measured at the entrance surface of the PMMA phantoms. Effective dose values were calculated by employing PCXMC 2.0 program. For image quality evaluations, CDRAD, LCD-4, Beam stop and Huttner test object used together with PMMA phantoms and Alderson RS-330 Lung/Chest phantom were used. Figure of Merit (FOM), which allows quantitative assessment in terms of image quality and patient dose, has been calculated. Based on the calculated FOM values were evaluated at the tube voltages and additional filter thicknesses recommended in the EUR 16260 protocol. Entrance Skin Dose and Inverse Image Quality Figure (IQFinv) value obtained from contrast detail analysis decreased with increasing filter thickness and tube voltage. Decrease in ESD and IQFinv with increasing tube voltage without additional filter was 56% and 21% for adult chest radiography, 69% and 39% for adult abdominal radiography and 34% and 6% for 1-year-old pediatric chest radiography. When calculated FOM values are examined, it can be recommended to use a 0.1 mm Cu filter at 90 kVp and a 0.1 mm Cu + 1.0 mm Al filter at 125 kVp for adult chest radiography. For adult abdominal radiography, 0.2 mm Cu filter at 70 and 80 kVp and 0.1 mm Cu filter at 90 and 100 kVp were found to be appropriate. It was determined that the appropriate additional filter at 70 kVp for 1-year-old chest radiography was 1.0 mm Al+0.1 mm Cu.

Air Kerma Calculation in Diagnostic Medical Imaging Devices Using Group Method of Data Handling Network

The air kerma, which is the amount of energy given off by a radioactive substance, is essential for medical specialists who use radiation to diagnose cancer problems. The amount of energy that a photon has when it hits something can be described as the air kerma (the amount of energy that was deposited in the air when the photon passed through it). Radiation beam intensity is represented by this value. Hospital X-ray equipment has to account for the heel effect, which means that the borders of the picture obtain a lesser radiation dosage than the center, and that air kerma is not symmetrical. The voltage of the X-ray machine can also affect the uniformity of the radiation. This work presents a model-based approach to predict air kerma at various locations inside the radiation field of medical imaging instruments, making use of just a small number of measurements. Group Method of Data Handling (GMDH) neural networks are suggested for this purpose. Firstly, a medical X-ray tube was modeled using Monte Carlo N Particle (MCNP) code simulation algorithm. X-ray tubes and detectors make up medical X-ray CT imaging systems. An X-ray tube's electron filament, thin wire, and metal target produce a picture of the electrons' target. A small rectangular electron source modeled electron filaments. An electron source target was a thin, 19,290 kg/m3 tungsten cube in a tubular hoover chamber. The electron source-object axis of the simulation object is 20° from the vertical. For most medical X-ray imaging applications, the kerma of the air was calculated at a variety of discrete locations within the conical X-ray beam, providing an accurate data set for network training. Various locations were taken into account in the aforementioned voltages inside the radiation field as the input of the GMDH network. For diagnostic radiology applications, the trained GMDH model could determine the air kerma at any location in the X-ray field of view and for a wide range of X-ray tube voltages with a Mean Relative Error (MRE) of less than 0.25%. This study yielded the following results: (1) The heel effect is included when calculating air kerma. (2) Computing the air kerma using an artificial neural network trained with minimal data. (3) An artificial neural network quickly and reliably calculated air kerma. (4) Figuring out the air kerma for the operating voltage of medical tubes. The high accuracy of the trained neural network in determining air kerma guarantees the usability of the presented method in operational conditions.

Unconventional High-Value Utilization of Metallurgical Iron-Bearing Dust as Shielding Composite for Medical X-rays

Iron-bearing dust is one of the main solid wastes in the metallurgical industry, and currently, it is mainly disposed of according to accumulation, which brings great environmental risks. Therefore, this paper proposes a method of preparing X-ray shielding materials by hot pressing using iron-bearing dust as the filler and polyimide resin powder as the matrix. A CT imaging system was used to test the X-ray shielding performance of the materials. The results demonstrated that shielding material I-95 had a shielding percentage of more than 95% at a tube voltage of 55 kVp and a tube current of 2 mA, and the thickness of the half-value layer was less than 0.68 mm. The shielding percentage and mass attenuation coefficient of the composites showed an increasing trend with increased filler addition, tube voltage, and tube current intensity, while the half-value layer thickness showed the opposite trend. Furthermore, the shielding percentage of composites with different fillers was affected by the voltage and hardly affected by the current variation. The dominant part of the shielding material interaction across the tested tube voltage range was photoelectric absorption. The prepared composite is a low-cost material and has high efficiency and is an ideal medical X-ray shielding material.

Evaluation of Cerium-Doped Lanthanum Bromide (LaBr3:Ce) Single-Crystal Scintillator’s Luminescence Properties under X-ray Radiographic Conditions

In the present study, the response of the crystalline scintillator LaBr3:Ce when excited with X-rays at tube voltages from 50 kVp to 150 kVp was investigated, for possible use in hybrid medical-imaging systems. A single crystal (10 × 10 × 10 mm3) was irradiated by X-rays within the aforementioned tube-voltage range, and the absolute efficiency (AE), as well as the detective quantum efficiency for zero spatial-frequency (DQE(0)), were measured. The energy-absorption efficiency (EAE), the quantum-detection efficiency (QDE) and the spectral compatibility with various optical photodetectors were also calculated. The results were compared with the published data for the LaCl3:Ce, Bi4Ge3O12 (BGO), Lu2SiO5:Ce (LSO), and CdWO4 single crystals of equal dimensions. The AE values of the examined crystal were found to be higher than those of the compared crystals across the whole X-ray tube-voltage range. Regarding the EAE, LaBr3:Ce demonstrated a comparatively better performance than the LaCl3:Ce crystal. The emitted-light spectrum of LaBr3:Ce was found to be compatible with various types of photocathodes and silicon photomultipliers. Moreover, the LaBr3:Ce crystal exhibited excellent performance concerning its DQE(0). Considering these properties, the LaBr3:Ce crystal could be considered as a radiation-detector option for hybrid medical-imaging modalities, such as PET/CT and SPECT/CT.

Experimental optimization of single-exposure dual-energy angiography with photon-counting x-ray detectors.

Photon-counting x-ray detectors may enable single-exposure dual-energy (DE) x-rayangiography. The purpose of this paper is to experimentally optimize the energy thresholds and tube voltage for single-exposure DE x-rayangiography. We optimized single-exposure DE x-ray angiography using the iodine signal-difference-to-noise ratio (SDNR) per root patient air kerma (κ) as a figureof merit. We measured the iodine SDNR by imaging an iodine stepwedge immersed in a water tank with a depth of 30cm in the direction of x-ray propagation. The stepwedge was imaged using tube voltages ranging from 90 to 150kV and a cadmium telluride (CdTe) x-ray detector with two energy bins and analog charge summing for charge sharing suppression. The energy threshold that separates the two energy bins was varied from approximately 35keV to approximately 75% of the maximum energy of the x-ray beam. Curve fitting was used to determine the threshold that maximized . The effect of scatter was determined from measurements of the scatter-to-primary ratios (SPRs) of the low-energy and high-energy images and a semi-empirical model of the relationship between SDNR and SPR. Using the optimal parameters, we imaged a phantom with vessel-simulating structures and backgroundclutter. The optimal energy thresholds increased monotonically from ∼50 to ∼85keV over the range of tube voltages considered. For tube voltages greater than 90kV, the optimal energy thresholds consistently allocated approximately two thirds of all detected primary photons to the low energy bin; this ratio was preserved without scatter. Consistent with prior modeling studies, increased monotonically with tube voltage from 90 to 150kV; at 150kV was approximately 38% higher than that at 90kV for an iodine area density of ∼50mg/cm2 . Scatter reduced SDNR by approximately 25% for SPRs of ∼1 and 0.4 in low-energy and high-energy images, respectively. Achieving optimal image quality in single-exposure DE angiography with photon-counting x-ray detectors will require high tube voltages (i.e.,>130kV) and, for thick patients, energy thresholds that allocate approximately two thirds of all primary photons to the low-energy image. Future work will compare the image quality of singe-exposure photon-counting and kV-switching approaches to DE x-rayangiography.

Efficiency Properties of Cerium-Doped Lanthanum Chloride (LaCl3:Ce) Single Crystal Scintillator under Radiographic X-ray Excitation

The aim of this study is to evaluate the suitability of crystalline scintillator LaCl3:Ce for possible use in hybrid medical imaging systems, such as PET/CT and SPECT/CT scanners. For this purpose, a single crystal (10 × 10 × 10 mm3) was irradiated by X-rays within the tube voltage range from 50 to 150 kVp, and the absolute efficiency (AE) was measured experimentally. The energy absorption efficiency (EAE), quantum detection efficiency (QDE), and the spectral compatibility with various optical detectors were also calculated with the use of mathematical formulas. The results were compared with published data for Bi4Ge3O12 (BGO), Lu2SiO5:Ce (LSO), and CdWO4 single crystals of equal dimensions, commonly used in medical imaging applications. The luminescence efficiency values of the examined crystal were found to be higher than those of LSO, BGO, and CdWO4 crystals, within the whole X-ray tube voltage range. In the matter of EAE, LaCl3:Ce demonstrated reduced performance with respect to LSO and CdWO4 crystals. The emission spectrum of LaCl3:Ce was found to be compatible with various types of photocathodes and silicon photomultipliers (SiPMs). Considering these properties, LaCl3:Ce crystal could be considered suitable for use in hybrid medical imaging systems.

Dose reduction potential in diagnostic single energy CT through patient-specific prefilters and a wider range of tube voltages.

Various studies have demonstrated that additional prefilters and/or reduced tube voltages have the potential to significantly increase the contrast-to-noise ratios at unit dose (CNRDs) and thereby to significantly reduce patient dose in clinical CT. An exhaustive analysis, accounting for a wide range of filter thicknesses and a wide range of tube voltages extending beyond the 70 to 150kV range of today's CT systems, including their specific choice depending on the patient size, is, however, missing. Therefore, this work analyzes the dose reduction potential for patient-specific selectable prefilters combined with a wider range of tube voltages. We do so for soft tissue and iodine contrast in single energy CT. The findings may be helpful to guide further developments of x-ray tubes and automatic filter changers. CT acquisitions were simulated for different patient sizes (semianthropomorphic phantoms for child, adult, and obese patients), tube voltages (35-150kV), prefilter materials (tin and copper), and prefilter thicknesses (up to 5mm). For each acquisition soft tissue and iodine CNRDs were determined. Dose was calculated using Monte Carlo simulations of a computed tomography dose index (CTDI) phantom. CNRD values of acquisitions with different parameters were used to evaluate dosereduction. Dose reduction through patient-specific prefilters depends on patient size and available tube current among others. With an available tube current time product of 1000mAs dose reductions of 17% for the child, 32% for the adult and 29% for the obese phantom were achieved for soft tissue contrast. For iodine contrast dose reductions were 57%, 49%, and 39% for child, adult, and obese phantoms, respectively. Here, a tube voltage range extended to lower kV isimportant. Substantial dose reduction can be achieved by utilizing patient-specific prefilters. Tube voltages lower than 70kV are beneficial for dose reduction with iodine contrast, especially for small patients. The optimal implementation of patient-specific prefilters benefits from higher tube power. Tin prefilters should be available in 0.1mm steps or lower, copper prefilter in 0.3mm steps or lower. At least 10 different prefilter thicknesses should be used to cover the dose optima of all investigated patient sizes and contrast mechanisms. In many cases it would be advantageous to adapt the prefilter thickness rather than the tube current to the patient size, that is, to always use the maximum available tube current and to control the exposure by adjusting the thickness of the prefilter.

Investigation of single-shot beam quality measurements using state of the art solid-state dosimeters for routine quality assurance applications in mammography

<h2>Abstract</h2><h3>Purpose</h3> To assess if single shot acquisitions with solid-state dosimeters as well as Robson's method could replace ionization chambers for tube output and HVL measurements, saving medical physicists time. <h3>Material and methods</h3> The energy responses of 4 solid-state dosimeters with automatic calculation of HVL were compared to ionization chamber measurements. Five anode/filter combinations were tested: Mo/Mo, Mo/Rh, Rh/Rh, W/Rh and W/Ag, from 24kVp to 35kVp. Tube output was measured free in air. HVL was measured using the solid-state dosimeters (single-shot acquisition), then manually with aluminum sheets and finally using the parametrization method of Robson. <h3>Results</h3> Deviations in tube output and HVL related to energy response in SSD were small in the 25–32 kVp range, and for tube output typically within 3%. Extrapolation using the Robson parametrization was within 5%, except for one device and for all W/Rh. Deviations of the HVL using the single shot approach were within 10% of the gold standard data. Larger deviations were found at the extreme tube voltages of 24kVp and 35kVp (maximum of 24%). <h3>Conclusion</h3> With the assumption that deviations in tube output of 5% and for HVL of 10% are acceptable, all tested solid state dosimeters met this criterion in the tube voltage range of 26kVp to 32kVp. Robson's method worked well for the spectra for which the method was developed, making both alternative approaches trustworthy for routine quality assurance purposes.

COMPARISON OF CONVENTIONAL HAND EXAMINATION ON SIX OPTIMISED DR SYSTEMS.

The purpose of this study was to investigate the challenges in comparing digital radiography (DR) systems from different vendors for various combinations of exposure factors in posterior–anterior hand radiographs. Image quality was evaluated for a range of tube voltages and tube current-time products using a technical contrast-detail (CDRAD) phantom and an anthropomorphic hand phantom. 900 technical CDRAD images were analysed providing quality figures of merit (IQFinv) and two experienced reporting radiographers using visual grading analysis (VGA) scored 108 anthropomorphic images. This study demonstrates the differences between the DR systems included. When compensating for variations in dose, Canon showed superior results for technical image quality and Fuji for visual image quality for a standard dose point at DR hand examination (ln(DAP) 1.1, 50 kV and 2.5 mAs).

Assessment of Bone Mineral Density From a Computed Tomography Topogram of Photon-Counting Detector Computed Tomography-Effect of Phantom Size and Tube Voltage.

The aim of this study was to assess the accuracy and impact of different sizes and tube voltages on bone mineral density (BMD) assessment using a computed tomography (CT) topogram acquired with photon-counting detector CT in an osteopenic ex vivo animal spine. The lumbar back of a piglet was used to simulate osteopenia of the lumbar spine. Five fat layers (each with a thickness of 3 cm) were consecutively placed on top of the excised spine to emulate a total of 5 different sizes. Each size was repeatedly imaged on (A) a conventional dual-energy x-ray absorptiometry scanner as the reference standard, (B) a prototype photon-counting detector CT system at 120 kVp with energy thresholds at 20 and 70 keV, and (C) the same prototype system at 140 kVp with thresholds at 20 and 75 keV. Material-specific data were reconstructed from spectral topograms for B and C. Bone mineral density was measured for 3 lumbar vertebrae (L2-L4). A linear mixed-effects model was used to estimate the impact of vertebra, imaging setup, size, and their interaction term on BMD. The BMD of the lumbar spine corresponded to a T score in humans between -4.2 and -4.8, which is seen in osteoporosis. Averaged across the 3 vertebrae and 5 sizes, mean BMD was 0.56 ± 0.03, 0.55 ± 0.02, and 0.55 ± 0.02 g/cm2 for setup A, B, and C, respectively. There was no significant influence of imaging setup (P = 0.7), simulated size (P = 0.67), and their interaction term (both P > 0.2) on BMD. Bone mineral density decreased significantly from L2 to L4 for all 3 setups (all P < 0.0001). Bone mineral density was 0.59 ± 0.01, 0.57 ± 0.01, and 0.52 ± 0.02 g/cm2 for L2, L3, and L4, respectively, for setup A; 0.57 ± 0.02, 0.55 ± 0.01, and 0.53 ± 0.01 g/cm2 for setup B; and 0.57 ± 0.01, 0.55 ± 0.01, and 0.53 ± 0.01 g/cm2 for setup C. A single CT topogram acquired on photon-counting detector CT with 2 energy thresholds enabled BMD quantification with similar accuracy compared with dual-energy x-ray absorptiometry over a range of simulated sizes and tube voltages in an osteopenic ex vivo animal spine.

Investigation of Tube Voltage Range using Dose Comparison based on Effective Detector Exposure Index in Chest Radiography

Investigation of Tube Voltage Range using Dose Comparison based on Effective Detector Exposure Index in Chest Radiography

Optimisation of tube voltage range (kVp) for AP abdomen, pelvis and spine imaging of average patients with a digital radiography (DR) imaging system using a computer simulator.

To investigate via computer simulation, an optimised tube voltage (kVp) range for caesium iodide (CsI)-based digital radiography (DR) of the abdomen, pelvis and lumbar spine. Software capable of simulating abdomen, pelvis and spine radiographs was used. Five evaluators graded clinical image criteria in images of 20 patients at tube voltages ranging from 60 to 120 kVp in 10 kVp increments. These criteria were scored blindly against the same patient reconstructed at a specific reference kVp. Linear mixed effects analysis was used to evaluate image scores for each criterion and test for statistical significance. Score was dependent on tube voltage and image criteria; both were statistically significant. All criteria for all anatomies scored very poorly at 60 kVp. Scores for abdomen, pelvis and spine imaging peaked at 70, 70 and 100 kVp, respectively, but other kVp values were not significantly poorer. Results indicate optimum tube voltages of 70 kVp for abdomen and pelvis (with an optimum range 70-120 kVp), and 100 kVp (optimum range 80-120 kVp) for lumbar spine. There are no recommendations for optimised tube voltage parameters for DR abdomen, pelvis or lumbar spine imaging. This study has investigated and recommended an optimal tube voltage range.

Relative response of dosimeters to variations in scattered X-ray energy spectra encountered in interventional radiology

PurposeThe new lower eye lens dose limit is of relevance in interventional radiology, where higher dose procedures result in increased scattered radiation to staff. The eye lens dose may be monitored using the directional dose equivalent at 3 mm depth, Hp(3), or through Hp(10) or Hp(0.07) measurements and using conversion factors. However, there are a considerable range of factors which contribute to measurement uncertainties, one of which is the incident photon energy. This study investigated the energy spectra of scattered radiation in interventional radiology, and the dosimetry accuracy of dosimeter types, evaluating their energy dependence. MethodsScatter X-ray energy spectra were recorded under varied conditions in a fluoroscopy imaging suite. Dosimetry accuracy of eye dosimeters, including TLDs (100 s, 100Hs), Landauer Hp(3), John Caunt ED3 and Electronic Personal dosimeters (EPDs) were compared to air kerma measurements across a range of tube voltages. ResultsThe variation of energy spectra with changing phantom thickness, spectrometer angulation and filtration are presented. The 100 and 100H TLDs, and EPDs showed a consistent air kerma response (within 10%) with changes in energy. The real-time silicon diode detectors showed a variable over response of between 10 and 25% across the energies investigated while Landauers dedicated Hp(3) eye dosimeters showed considerable variation between dosimeters for similar conditions, a 17% variation at 50 kVp. ConclusionThe work aimed to validate the scattered energy spectra typically encountered in interventional radiology and to further determine the accuracy of eye dosimeters in relation to energy response variations.

Use of a computer simulator to investigate optimized tube voltage for chest imaging of average patients with a digital radiography (DR) imaging system.

The aim of this study was to investigate via computer simulation a proposed improvement to clinical practice by deriving an optimized tube voltage (kVp) range for digital radiography (DR) chest imaging. A digitally reconstructed radiograph algorithm was used which was capable of simulating DR chest radiographs containing clinically relevant anatomy. Five experienced image evaluators graded clinical image criteria, i.e. overall quality, rib, lung, hilar, spine, diaphragm and lung nodule in images of 20 patients at tube voltages across the diagnostic energy range. These criteria were scored against corresponding images of the same patient reconstructed at a specific reference kVp. Evaluators were blinded to kVp. Evaluator score for each criterion was modelled with a linear mixed effects algorithm and compared with the score for the reference image. Score was dependent on tube voltage and image criteria in a statistically significant manner for both. Overall quality, hilar, diaphragm and spine criteria performed poorly at low and high tube voltages, peaking at 80-100 kVp. Lung and lung nodule demonstrated little variation. Rib demonstrated superiority at low kVp. A virtual clinical trial has been performed with simulated chest DR images. Results indicate mid-range tube voltages of 80-100 kVp are optimum for average adults. There are currently no specific recommendations for optimized tube voltage parameters for DR chest imaging. This study, validated with images containing realistic anatomical noise, has investigated and recommended an optimal tube voltage range.

Evaluation of tube current modulation programms for the optimization of scan protocols in computed tomography

Computed tomography (CT) is commonly associated with relatively high patient doses. In order to keep the patient doses from the CT examinations on the acceptable level it is necessary to apply the principle of optimization. An essential part of optimization is the achievement of the compromise between the patient dose reduction and the maintenance of the image quality that provides accurate diagnostic information. The aim of the study was to determine the relations between the patient doses, CT image quality and the parameters of the tube current modulation program (Auto mA, CareDose and DoseRight) for the examination of the chest. The study was performed on the three most common modern tomographs in Russia: Ingenuity Core 128, Philips; Optima 64, General Electric; Definition AS, Siemens. The anthropomorphic phantom Lungman (Kyoto Kagaku CO., LTD) was used in the study. In order to assess the tube current modulation for the range of tube voltage (80–120 kV), the reference mA∙s (ref. mAs), Noise Index (NI) and Dose Right Index (DRI) were changed for the CareDose (Siemens), Auto mA (GE) and RightDose (Philips), respectively. Estimation of the effective dose was performed using the method from Methodical guidance 2.6.1.2944-11 (MU 2.6.1.2944-11). In order to evaluate the image quality, the noise of a CT image in the mediastinum was selected as the most homogenous for chest region. It was estimated, that for the GE units with Auto mA, the noise of CT image had a liner relationship with NI; the patient dose decreased with the increase of NI. For the Siemens units with CareDose, the noise of CT image decreased with the ref.mAs for the range of tube voltage (80–120 kV); the patient dose was directly proportional to the ref.mAs and increased with the tube voltage. For the Philips units with DoseRight, the noise of CT image decreased with the DRI for the range of tube voltage (80–120 kV); the patient dose was directly proportional to the DRI and had no dependence on the tube voltage. The tube current modulations are proprietary for each manufacturer; it is necessary to consider them for the protocol development. The obtained dependences could be useful for optimization of CT protocols.

Evaluation of the dose reduction capabilities in digital radiography of the chest using contrast-detail phantom

Assessment of the quality of the images obtained using optimized (low-dose) protocols is the inherent part of the optimization in X-ray diagnostics. To perform the objective quantitative image quality assessment one can use dedicated test-objects, including several components for the simultaneous measurement of the different physical image characteristics (contrast and spatial resolution). The use of such test objects allows estimating and assessing the relations between the patient dose, parameter of the X-ray examination and image quality. That is especially important for the optimization of the digital radiographic examinations performed with automated exposure control. The aim of the current study was to evaluate the possibilities of the patient dose reduction using “contrast-detail” test-object for the digital radiography of the chest in posterior-anterior projection performed with automated exposure control. The study was performed in St-Petersburg Mariinsky hospital on a digital X-ray unit “ARC-Electron” with a flat-panel detector. The combination of a test-object and a tissue-equivalent phantom were imaged on a range of chest X-ray protocols: on a 60–150 kV tube voltage range with automated exposure control; and using fixed 90 kV tube voltage on a range of 2–100 mAs tube current-exposure time product. Dose-area product (cGy×cm2) was measured for each exposure; effective dose (mSv) was estimated for each exposure based on dose-area product. A dedicated software was developed for the automated image quality assessment. The results of the study indicate that the use of a high tube voltage (140–150 kV) with current automated exposure control settings would lead to 60% and 95% reduction of the dose-area product and effective dose, respectively, compared to the standard protocol. The adjustment of the current automated exposure control settings with the reduction of the tube current-exposure time product from 11,2 mAs to the 4,2 mAs for the tube voltage of 90 kV would lead to the reduction of both the dose-area product and effective dose up to a factor of three, compared to the standard protocol. For both scenarios image quality characteristics decreased by less than 15%. The proposed low-dose protocols are under the clinical approbation at Mariinsky hospital. The proposed method of image quality assessment and development of low-dose protocols is recommended for inclusion in the quality assurance program for the radiography examinations.