Optimizing the tube potential for lumbar spine radiography with a flat-panel digital detector

Radiation dose reduction and image quality evaluation for lateral lumbar spine projection

Purpose

Optimization studies in digital radiology help to reduce the radiological risk to patients and maximize the benefits associated with their clinical purpose. The aim of this study was to assess the optimization of lateral lumbar spine projection via a combination of exposure parameters adjustments and additional filtration using a sectional anthropomorphic phantom.

Materials and methods

We evaluated the effects of peak voltage, tube loading, and low-cost filters made of copper, titanium, brass, and nickel on both the perceived and physical quality of 125 radiographs obtained in a computer radiography system. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) with their Figure of Merit (FOM), based on the entrance surface air kerma with backscatter (ESAK), was used to assess physical image quality.

Results

The standard image had a perceived image quality, SNR, FOMSNR, CNR, FOMCNR and ESAK of 3.4, 22.3, 386.4, 23.6, 433.7 and 1.28 mGy, respectively. Copper (90.3% purity) and titanium (95.0% purity) filters reduced ESAK by an average of 60% without compromising diagnostic quality, while brass and nickel filters increased dose under the conditions of the study.

Conclusions

Our findings show that optimizing lumbar spine projection can reduce radiation dose without compromising image quality. Low-cost copper and titanium filters can be valuable in resource-limited settings. Further research can explore additional strategies for radiological optimization.

An evaluation of the effect of tube potential on clinical image quality using direct digital detectors for pelvis and lumbar spine radiographs

INTRODUCTION

High kVp techniques, 15% or 10-kVp rules, are well-known dose reduction methods. Traditionally, the use of high tube potential (i.e. increased kVp) is associated with decreased radiographic contrast and overall image quality. Recent studies suggest contrast and image quality are not heavily reliant on kVp with digital systems. This study aims to assess the effects of the high tube potential technique on clinical radiographic image quality when using digital systems, to validate high kVp as a dose saving technique.

METHODS

A selection of comparable pelvis and lumbar spine radiographs were collected from the hospital's picture archiving and communication system (PACS), with technical factors recorded. All clinical radiographs were assessed by 5 senior radiographers using a 15-point visual grading analysis (VGA) rubric.

RESULTS

For 40 AP pelvis radiographs and 40 lateral lumbar spine radiographs, reduction in the dose area product (DAP) with higher kVp is seen. Average pelvis DAP at 75 kVp = 14.06 mGy.cm2 ; 85 kVp = 7.47 mGy.cm2 . Average lumbar spine DAP at 80 kVp = 15.76 mGy.cm2 ; 90 kVp = 14.83 mGy.cm2 . Image quality and contrast scores showed no statistically significant difference between the high and low kVp groups (z = 0.06 and 0.12, respectively). Average pelvis VGA score at 75 kVp = 11.26; 85 kVp = 12.55. Average lumbar spine VGA score at 80 kVp = 9.23; 90 kVp = 10.64.

CONCLUSIONS

The high tube potential techniques allowed for reduced patient radiation doses whilst showing no degradation of diagnostic image quality in a clinical setting. This study successfully validates the high kVp technique as a useful tool for reducing patient radiation doses whilst maintaining high diagnostic image quality for digital pelvis and lumbar spine radiography.

Optimisation of radiographic acquisition parameters for direct digital radiography: A systematic review

INTRODUCTION

The objective of this systematic review was to uncover and synthesise all available literature regarding appropriate acquisition parameters for direct digital radiography. It sought to either confirm current practices as optimal, or to uncover practices that may produce more optimised results.

METHODS

A comprehensive search of published and unpublished literature was undertaken to find studies that evaluated how adjustment of different acquisition parameters affected subjective image quality and patient radiation dose. Eight hundred and fifty-eight studies were retrieved for title and abstract screening. Eighty-nine studies were retrieved for full-text screening, and 23 were included for review and methodological quality screening.

RESULTS

Narrative synthesis of the 23 included studies revealed limited evidence to guide any potential change or acceptance of currently accepted best practice. Meta-analysis was unable to be performed for any of the included studies due to high levels of methodological heterogeneity. A key finding of this review was that the goals of optimisation research varied greatly across the included studies.

CONCLUSION

Significant methodological heterogeneity in the included studies limited the number of clinically relevant findings that would give evidence to an acceptance of, or suggest changes to, currently accepted best practice. Improving consistency in approach across future works of technique optimisation will ensure future systematic reviews will be able to provide strong evidence and meta-analysis will be able to be performed.

IMPLICATIONS FOR CLINICAL PRACTICE

This review highlights that in the literature, studies of optimisation of radiographic acquisition parameters have varying goals. This methodological heterogeneity limits the applicability of systematic reviews and precludes the use of meta-analysis. The authors recommend that a framework for optimisation research be produced as a priority to help improve homogeneity in future research.

ESTIMATES OF PATIENT DOSES AND KERMA-AREA PRODUCT MONITORING IN DIGITAL RADIOGRAPHY

The application of the kerma-area product (PKA) meter is increased rapidly in dosimetry. This study presents measurements of PKA in adherence to the International Atomic Energy Agency protocol for 300 adult patients in digital radiographic procedures. Effective doses (ED) were calculated from PKA measurements and conversion coefficients (E-103/PKA) obtained from the International Commission on radiological protection 103. In skull posteroanterior (PA), skull lateral (LAT), cervical spine anteroposterior (AP), cervical spine LAT, chest PA, abdomen AP, lumbar spine AP, pelvis AP and lumbar spine LAT, the third-quartile PKA values were found to be 0.2, 0.28, 0.33, 0.19, 0.26, 0.95, 0.93, 0.96 and 3.15 Gycm2, and estimated mean EDs were 0.005, 0.008, 0.056, 0.021, 0.037, 0.146, 0.165, 0.097 and 0.258 mSv, respectively. The third-quartile PKA values were suggested as local diagnostic reference levels (LDRLs). Results were compared with the diagnostic reference levels (DRLs) of the UK, the European Commission, previously published LDRLs in Greece and China by Metaxas et al. and Zhang and Chu, respectively. The PKA (third-quartile) value for cervical spine AP was 120% higher than UK 2010 DRLs, lumbar spine LAT was 123% higher than LDRLs given by Metaxas et al. and chest PA was 160% higher than UK 2010 DRLs and 225% higher than Metaxas et al. provided LDRLs. The PKA results were lower than the UK, and two studies in Greece by Metaxas et al. except for chest PA, cervical spine AP and lumbar spine LAT showed the need for further optimization. The LDRLs reported in this study may further contribute to establishing future national DRLs.

Image Quality Assessment of the Digital Radiography Units in Tabriz, Iran: A Phantom Study

Creating a high-quality image with the low patient dose is one of the most important goals in medical X-ray imaging. In this study, the image quality parameters of the digital radiographic units in Tabriz city were considered and compared with the international protocols. The image quality parameters were measured at 11 high workload digital radiography (DR) imaging centers in Tabriz city, and the results were compared to DINN 6868/58 standards. All centers equipped with the direct DR units passed the spatial resolution, low contrast detectability, contrast dynamic range, and noise tests, while the computed radiography (CR) units only could pass the two last tests. The highest spatial resolution was observed 3.2 lp/mm in the DR unit while the lowest one was 1.8 lp/mm in the CR unit. The highest noise was measured to be 0.03 OD that was observed in the DR unit. The most difference between the nominal and measured peak kilovoltage and mAs was 3.1% and 6.8%, respectively. The entrance surface air kerma in all units was obtained <0.63 mGy. The measured half-value layer range was between 2.4 and 3.54 mmAl. The physical parameters of image quality such as spatial resolution, contrast, and noise are robustness quantitative parameters for the assessment of the image quality performance of the units. Therefore, measurement and control of these parameters using two-dimensional phantoms are very critical.

PATIENT DOSES IN COMMON DIAGNOSTIC X-RAY EXAMINATIONS

A local survey was conducted, to evaluate the radiation dose to adult patients who underwent diagnostic X-ray examinations. Patient-related and technical data were recorded, in 1504 patients, for each of the 11 individual projections, of the 7 most common examinations performed in an X-ray room, with 1 digital radiography system. The patient entrance surface air kerma (ESAK) and the effective dose (ED) were calculated based on the X-ray tube output and the exposure parameters, as well as utilisation of suitable conversion coefficients, respectively. The 75th percentiles of the distribution of the ESAK and kerma area product (KAP) values were also established. The mean, median and 75th percentiles were compared with the national reference levels and the most common values reported at the European level through the DOSE DATAMED II project. The corresponding ED values were also compared with the average values reported for all European countries. The mean ESAK, KAP and ED values along with the uncertainty U values for chest PA, chest LAT, cranium AP, cranium LAT, cervical spine AP, cervical spine LAT, lumbar spine AP, lumbar spine LAT, pelvis AP, abdomen AP, kidneys and urinary bladder (KUB) AP were 0.12 (0.001) mGy, 0.66 (0.023) mGy, 1.01 (0.034) mGy, 0.69 (0.098) mGy, 0.72 (0.014) mGy, 0.63 (0.011) mGy, 4.12 (0.050) mGy, 5.74 (0.082) mGy, 2.57 (0.024) mGy, 1.94 (0.017) mGy, 2.47 (0.073) mGy, and 0.09 (0.001) Gy cm2, 0.38 (0.012) Gy cm2, 0.32 (0.009) Gy cm2, 0.27 (0.052) Gy cm2, 0.17 (0.004) Gy cm2, 0.21 (0.006) Gy cm2, 1.18 (0.018) Gy cm2, 1.86 (0.023) Gy cm2, 1.41 (0.012) Gy cm2, 1.27 (0.010) Gy cm2, 1.28 (0.038) Gy cm2, as well as 0.01 (0.0001) mSv, 0.05 (0.0016) mSv, 0.02 (0.0006) mSv, 0.01 (0.0012) mSv, 0.03 (0.0008) mSv, 0.03 (0.0006) mSv, 0.26 (0.0038) mSv, 0.17 (0.0022) mSv, 0.20 (0.0016) mSv, 0.23 (0.0018) mSv, 0.23 (0.0068) mSv, respectively. The 75th percentiles along with the uncertainty U values for chest PA, chest LAT, cranium AP, cranium LAT, cervical spine AP, cervical spine LAT, lumbar spine AP, lumbar spine LAT, pelvis AP, abdomen AP, kidneys and urinary bladder (KUB) AP were 0.14 (0.006) mGy, 0.88 (0.031) mGy, 1.22 (0.049) mGy, 0.94 (0.098) mGy, 0.93 (0.027) mGy, 0.78 (0.013) mGy, 5.16 (0.073) mGy, 7.24 (0.134) mGy, 2.96 (0.047) mGy, 2.59 (0.036) mGy, 3.07 (0.116) mGy, as well as 0.10 (0.0006) Gy cm2, 0.51 (0.017) Gy cm2, 0.37 (0.020) Gy cm2, 0.33 (0.040) Gy cm2, 0.23 (0.007) Gy cm2, 0.26 (0.011) Gy cm2, 1.50 (0.036) Gy cm2, 2.26 (0.035) Gy cm2, 1.61 (0.023) Gy cm2, 1.67 (0.017) Gy cm2, 1.56 (0.069) Gy cm2, in terms of ESAK and KAP values, respectively. The results were significantly lower compared with the national reference levels, the most common DRL values reported at the European level and other previously reported dose values. Patient dose surveys could contribute towards optimising radiation protection for patients, therefore, highlighting the necessity to increase the awareness and knowledge of the radiation dose in conjunction with the required image quality.

Image quality and radiation dose in planar imaging - Image quality figure of merits from the CDRAD phantom

Purpose

A contrast‐detail phantom such as CDRAD is frequently used for quality assurance, optimization of image quality, and several other purposes. However, it is often used without considering the uncertainty of the results. The aim of this study was to assess two figure of merits (FOM) originating from CDRAD regarding the variations of the FOMs by dose utilized to create the x‐ray image. The probability of overlapping (assessing an image acquired at a lower dose as better than an image acquired at a higher dose) was determined.

Methods

The CDRAD phantom located underneath 12, 20, and 26 cm PMMA was imaged 16 times at five dose levels using an x‐ray system with a flat‐panel detector. All images were analyzed by CDRAD Analyser, version 1.1, which calculated the FOM inverse image quality figure (IQF_inv) and gave contrast detail curves for each image. Inherent properties of the CDRAD phantom were used to derive a new FOM h, which describes the size of the hole with the same diameter and depth that is just visible. Data were analyzed using heteroscedastic regression of mean and variance by dose. To ease interpretation, probabilities for overlaps were calculated assuming normal distribution, with associated bootstrap confidence intervals.

Results

The proportion of total variability in IQF_inv, explained by the dose (R²), was 91%, 85%, and 93% for 12, 20, and 26 cm PMMA. Corresponding results for h were 91%, 89%, and 95%. The overlap probability for different mAs levels was 1% for 0.8 vs 1.2 mAs, 5% for 1.2 vs 1.6 mAs, 10% for 1.6 vs 2.0 mAs, and 10% for 2.0 mAs vs 2.5 mAs for 12 cm PMMA. For 20 cm PMMA, it was 0.5% for 10 vs 16 mAs, 13% for 16 vs 20 mAs, 14% for 20 vs 25 mAs, and 14% for 25 vs 32 mAs. For 26 cm PMMA, the probability varied from 0% to 6% for various mAs levels. Even though the estimated probability for overlap was small, the 95% confidence interval (CI) showed relatively large uncertainties. For 12 cm PMMA, the associated CI for 0.8 vs 1.2 mAs was 0.1–3.2%, and the CI for 1.2 vs 1.6 mAs was 2.1–7.8%.

Conclusions

Inverse image quality figure and h are about equally related to dose level. The FOM h, which describes the size of a hole that should be seen in the image, may be a more intuitive FOM than IQF_inv. However, considering the probabilities for overlap and their confidence intervals, the FOMs deduced from the CDRAD phantom are not sensitive to dose. Hence, CDRAD may not be an optimal phantom to differentiate between images acquired at different dose levels.

Optimizing imaging quality and radiation dose by the age-dependent setting of tube voltage in pediatric chest digital radiography

Objective

The quality and radiation dose of different tube voltage sets for chest digital radiography (DR) were compared in a series of pediatric age groups.

Materials and Methods

Forty-five hundred children aged 0-14 years (yr) were randomly divided into four groups according to the tube voltage protocols for chest DR: lower kilovoltage potential (kVp) (A), intermediate kVp (B), and higher kVp (C) groups, and the fixed high kVp group (controls). The results were analyzed among five different age groups (0-1 yr, 1-3 yr, 3-7 yr, 7-11 yr and 11-14 yr). The dose area product (DAP) and visual grading analysis score (VGAS) were determined and compared by using one-way analysis of variance.

Results

The mean DAP of protocol C was significantly lower as compared with protocols A, B and controls (p < 0.05). DAP was higher in protocol A than the controls (p <0.001), but it was not statistically significantly different between B and the controls (p = 0.976). Mean VGAS was lower in the controls than all three protocols (p < 0.001 for all). Mean VGAS did not differ between protocols A and B (p = 0.334), but was lower in protocol C than A (p = 0.008) and B (p = 0.049).

Conclusion

Protocol C (higher kVp) may help optimize the trade-off between radiation dose and image quality, and it may be acceptable for use in a pediatric age group from these results.

Comparison of visual grading and free-response ROC analyses for assessment of image-processing algorithms in digital mammography

OBJECTIVE

To compare two methods for assessment of image-processing algorithms in digital mammography: free-response receiver operating characteristic (FROC) for the specific task of microcalcification detection and visual grading analysis (VGA).

METHODS

The FROC study was conducted prior to the VGA study reported here. 200 raw data files of low breast density (Breast Imaging-Reporting and Data System I-II) mammograms (Novation DR, Siemens, Germany)-100 of which abnormal-were processed by four image-processing algorithms: Raffaello (IMS, Bologna, Italy), Sigmoid (Sectra, Linköping, Sweden), and OpView v. 2 and v. 1 (Siemens, Erlangen, Germany). Four radiologists assessed the mammograms for the detection of microcalcifications. 8 months after the FROC study, a subset (200) of the 800 images was reinterpreted by the same radiologists, using the VGA methodology in a side-by-side approach. The VGA grading was based on noise, saturation, contrast, sharpness and confidence with the image in terms of normal structures. Ordinal logistic regression was applied; OpView v. 1 was the reference processing algorithm.

RESULTS

In the FROC study all algorithms performed better than OpView v. 1. From the current VGA study and for confidence with the image, Sigmoid and Raffaello were significantly worse (p<0.001) than OpView v. 1; OpView v. 2 was significantly better (p=0.01). For the image quality criteria, results were mixed; Raffaello and Sigmoid for example were better than OpView v. 1 for sharpness and contrast (although not always significantly).

CONCLUSION

VGA and FROC discordant results should be attributed to the different clinical task addressed.

ADVANCES IN KNOWLEDGE

The method to use for image-processing assessment depends on the clinical task tested.

Visual grading regression: analysing data from visual grading experiments with regression models

For visual grading experiments, which are an easy and increasingly popular way of studying image quality, hitherto used data analysis methods are often inadequate. Visual grading analysis makes assumptions that are not statistically appropriate for ordinal data, and visual grading characteristic curves are difficult to apply in more complex experimental designs. The approach proposed in this paper, visual grading regression (VGR), consists of an established statistical technique, ordinal logistic regression, applied to data from single-image and image-pair experiments with visual grading scores selected on an ordinal scale. The approach is applicable for situations in which, for example, the effects of the choice of imaging equipment and post-processing method are to be studied simultaneously, while controlling for potentially confounding variables such as patient and observer identity. The analysis can be performed with standard statistical software packages using straightforward coding of the data. We conclude that the proposed statistical technique is useful in a wide range of visual grading studies.

Digital radiography: the balance between image quality and required radiation dose

Although the transition from conventional screen-film imaging to digital image acquisition has been almost completed during the last couple of years, examination parameters, such as tube voltage, tube current, and filtration have been adopted from screen-film technology without further adjustments. Digital systems, however, are characterised by their flexibility: the acquisition dose can be reduced at the expense of image quality and vice versa. The imaging parameters must be optimised according to the best performance of a particular system. The traditional means of dose containment, such as positioning and collimation, are as valid for digital techniques as they were for conventional techniques. Digital techniques increasingly offer options for dose reduction. At the same time, there is a risk of substantially increasing the patient dose, possibly unawares, due to the lack of visual control. Therefore, implementation of dose indicators and dose monitoring is mandatory for digital radiography. The use of image quality classes according to the dose requirements of given clinical indications are a further step toward modern radiation protection.