Michael Sandborg - Academia.edu (original) (raw)
Papers by Michael Sandborg
Journal of Radiological Protection, Jul 28, 2022
Vascular x-ray guided interventions are complex and may result in high occupational doses to ioni... more Vascular x-ray guided interventions are complex and may result in high occupational doses to ionising radiation if staff do not take appropriate actions to minimise their exposure. In this prospective intervention study, ten staff members wore an extra personal dosimeter on the upper body above their regular protective clothing during four consecutive periods. Between each period either additional practical radiological protection training was given or a real-time direct display dosimeter were provided to the staff. Each staff’s personal dose equivalent, Hp(10) normalised to the total air kerma-area product for the procedures where each staff were involved, KAPt, was used as the dependent variable. A focus-group interview with the staff were performed about the usefulness of the training and real-time dose rate display system. Our aim was to investigate if the interventions (practical training or real-time dose rate display) did affect the staff doses in the short and long term (five months later). Significant (p < 0.05) reductions of staff doses Hp(10)/KAPt were found after practical radiological protection training, but not after using real-time dose rate displays. Significant reductions were maintained after five months without additional interventions. The results from the focus-group interview indicated that making radiation ‘visible’, during practical training and usage of real-time direct display dosimeter, made it easier to understand how to act to lower occupational doses.
Acta Radiologica, 1993
Conversion factors between the energy imparted to the patient in pediatric radiography and air co... more Conversion factors between the energy imparted to the patient in pediatric radiography and air collision kerma integrated over beam area are presented. The values have been derived from Monte Carlo calculations in soft tissue phantoms and extend results published earlier to cover children from early infancy to the age of 15 years. Variations related to phantom size as well as to focus-phantom distance, radiation field size, orientation of view (a.p., lateral), tube potential, and beam filtration are given. We show that the conversion factor increases with increasing half-value layer of the X-ray beam and the anterioposterior width of the simulated child. Increasing the focus-phantom distance increases the conversion factor, while increasing the field size decreases the factors due to more scattered radiation escaping laterally from the phantom.
Medical Physics, Oct 1, 2001
A computer program has been developed to model chest radiography. It incorporates a voxel phantom... more A computer program has been developed to model chest radiography. It incorporates a voxel phantom of an adult and includes antiscatter grid, radiographic screen, and film. Image quality is quantified by calculating the contrast ͑⌬OD͒ and the ideal observer signal-to-noise ratio (SNR I) for a number of relevant anatomical details at various positions in the anatomy. Detector noise and system unsharpness are modeled and their influence on image quality is considered. A measure of useful dynamic range is computed and defined as the fraction of the image that is reproduced at an optical density such that the film gradient exceeds a preset value. The effective dose is used as a measure of the radiation risk for the patient. A novel approach to patient dose and image quality optimization has been developed and implemented. It is based on a reference system acknowledged to yield acceptable image quality in a clinical trial. Two optimizations schemes have been studied, the first including the contrast of vessels as measure of image quality and the second scheme using also the signal-to-noise ratio of calcifications. Both schemes make use of our measure of useful dynamic range as a key quantity. A large variety of imaging conditions was simulated by varying the tube voltage, antiscatter device, screen-film system, and maximum optical density in the computed image. It was found that the optical density is crucial in screen-film chest radiography. Significant dose savings ͑30%-50%͒ can be accomplished without sacrificing image quality by using low-atomic-number grids with a low grid ratio or an air gap and more sensitive screen-film system. Dose-efficient configurations proposed by the model agree well with the example of good radiographic technique suggested by the European Commission.
DESCRIPTIONThis publication is aimed at students and teachers involved in programmes that train m... more DESCRIPTIONThis publication is aimed at students and teachers involved in programmes that train medical physicists for work in diagnostic radiology. It provides, in the form of a syllabus, a comprehensive overview of the basic medical physics knowledge required for the practice of modern diagnostic radiology. This makes it particularly useful for graduate students and residents in medical physics programmes. The material presented in the publication has been endorsed by the major international organizations and is the foundation for academic and clinical courses in both diagnostic radiology physics and in emerging areas such as imaging in radiotherapy.
PubMed, 1998
A model will be proposed for predicting the expected value and variance of the measured signal-le... more A model will be proposed for predicting the expected value and variance of the measured signal-level in collected radiographic images obtained with an image-intensifier-based X-ray radiography system. The model parameters are determined from both theoretical and experimental data and incorporate all parameters that can be varied by the system operator, except CCD-camera readout rate. The proposed model predicts the expected value and variance of the grey-level in the output image with high accuracy. It is also shown that it is very important to compensate for the inhomogeneous pixel sensitivity when comparing the variance of the signal-level in a pixel from sequentially collected images with the variance determined in a single image.
![Research paper thumbnail of [P244] Accuracy of ct numbers obtained by dira and monoenergetic plus algorithms in quantitative dual-energy computed tomography](https://attachments.academia-assets.com/107163732/thumbnails/1.jpg)
](Physica Medica, Aug 1, 2018
Rare earth materials instead of aluminium as added filter have been reported to reduce the mean a... more Rare earth materials instead of aluminium as added filter have been reported to reduce the mean absorbed dose in the patient. With these filters, the energy spectrum can be shaped to yield high ene ...
Radiation Protection Dosimetry, May 25, 2021
Automatic segmentation of bones in computed tomography (CT) images is used for instance in beam h... more Automatic segmentation of bones in computed tomography (CT) images is used for instance in beam hardening correction algorithms where it improves the accuracy of resulting CT numbers. Of special interest are pelvic bones, which-because of their strong attenuation-affect the accuracy of brachytherapy in this region. This work evaluated the performance of the JJ2016 algorithm with the performance of MK2014v2 and JS2018 algorithms; all these algorithms were developed by authors. Visual comparison, and, in the latter case, also Dice similarity coefficients derived from the ground truth were used. It was found that the 3D-based JJ2016 performed better than the 2D-based MK2014v2, mainly because of the more accurate hole filling that benefitted from information in adjacent slices. The neural network-based JS2018 outperformed both traditional algorithms. It was, however, limited to the resolution of 128 3 owing to the limited amount of memory in the graphical processing unit (GPU).
Catheterization and Cardiovascular Interventions, Feb 1, 2011
Objectives: We have developed a method using transthoracic echocardiography in establishing optim... more Objectives: We have developed a method using transthoracic echocardiography in establishing optimal visualization of the aortic root, to reduce the amount of contrast medium used in each patient. Background: During transcatheter aortic valve implantation, it is necessary to obtain an optimal fluoroscopic projection for deployment of the valve showing the aortic ostium with the three cusps aligned in the beam direction. This may require repeat aortic root angiograms at this stage of the procedure with a high amount of contrast medium with a risk of detrimental influence on renal function. Methods: We studied the conventional way and an echo guided way to optimize visualisation of the aortic root. Echocardiography was used initially allowing easier alignment of the image intensifier with the transducer's direction. Results: Contrast volumes, radiation/fluoroscopy exposure times, and postoperative creatinine levels were significantly less in patients having the echo-guided orientation of the optimal fluoroscopic angles compared with patients treated with the conventional approach. Conclusion: We present a user-friendly echo-guided method to facilitate fluoroscopy adjustment during transcatheter aortic valve implantation. In our series, the amounts of contrast medium and radiation have been significantly reduced, with a concomitant reduction in detrimental effects on renal function in the early postoperative phase. V
Radiation Protection Dosimetry, Mar 29, 2021
Traditional filtered back projection (FBP) reconstruction methods have served the computed tomogr... more Traditional filtered back projection (FBP) reconstruction methods have served the computed tomography (CT) community well for over 40 years. With the increased use of CT during the last decades, efforts to minimise patient exposure, while maintaining sufficient or improved image quality, have led to the development of model-based iterative reconstruction (MBIR) algorithms from several vendors. The usefulness of the advanced modeled iterative reconstruction (ADMIRE) (Siemens Healthineers) MBIR in abdominal CT is reviewed and its noise suppression and/or dose reduction possibilities explored. Quantitative and qualitative methods with phantom and human subjects were used. Assessment of the quality of phantom images will not always correlate positively with those of patient images, particularly at the higher strength of the ADMIRE algorithm. With few exceptions, ADMIRE Strength 3 typically allows for substantial noise reduction compared to FBP and hence to significant (≈30%) patient dose reductions. The size of the dose reductions depends on the diagnostic task.
Medical Physics, Aug 26, 2004
The relationship and precision of four methods for measuring the low-contrast detail detectabilit... more The relationship and precision of four methods for measuring the low-contrast detail detectability in fluoroscopic imaging were studied. These included the physical measurement of the accumulation rate of the square of the signal-to-noise ratio (SNR rate 2), two-alternative forced-choice ͑2-AFC͒ experiments, sixteen-alternative forced-choice ͑16-AFC͒ experiments and subjective determination of the threshold contrast. The precision and sensitivity of the threshold contrast measurement were seen to be modest in the constancy testing of fluoroscopic equipment: only large changes in system performance could be reliably detected by that method. The measurement of the SNR rate 2 is suggested instead. The relationship between the results of the various methods were studied, and it was found that human performance can be related to SNR rate 2 by introducing the concept of the effective image information integration time (t eff). When measured for an unlimited observation time, it depicts the saturation of human performance in detecting a static low-contrast detail in dynamic image noise. Here, t eff was found to be about 0.6 s in 2-AFC tests and 0.3 s in 16-AFC tests.
The aim for this work was to study to what extent the detection of nodules is quantum noise limit... more The aim for this work was to study to what extent the detection of nodules is quantum noise limited, based on the combined results from a nodule-detection clinical trial and a Monte Carlo computational model of a digital chest imaging system. The Monte Carlo computer program computes measures of physical image quality such as image contrast, C and signalto-noise ratio, SNR for nodules of any size. A computed radiography (CR) imaging system used simulated. The patient anterior-posterior thickness was 25 cm and nodules with diameters between 1-40 mm were included. The image contrast and SNR was calculated for 1600 (40x40) positions in the chest image and averaged over five anatomical regions of interest (lateral pulmonary, retrocardial, hilar, lower-and upper mediastinal regions). Threshold contrasts for each region, C th , corresponding to A z =0.80 for detecting a 10 mm nodule, were deduced from the clinical trial. A threshold is also used for the quantum noise signal-to-noise ratio, SNR th. The model computes the diameter of a disk-shaped object that is required to comply with the two criteria: SNR≥SNR th and C≥C th. A system is said to be quantum noise limited when the nodule size required to fulfil both criteria is not limited by the contrast but by the SNR. The required nodule diameter is largest in the hilar region (25 mm) and smallest in the lateral pulmonary region (11 mm). When the threshold SNR th =25 is used, the lower mediastinal region is quantum noise limited already at low speed classes (S>100). The hilar region is never quantum noise limited at realistic speed classes (S<1000). The accuracy of this model will be tested in the future by more sophisticated modelling of anatomical background and noise in the SNR-expression. Purpose The aim for this work was to study to what extent the detection of nodules is quantum noise limited, based on the combined results from a nodule-detection clinical trial and a Monte Carlo computational model of a digital chest imaging system.
Research Square (Research Square), Aug 16, 2022
Objectives Images reconstructed with higher strengths of iterative reconstruction algorithms impa... more Objectives Images reconstructed with higher strengths of iterative reconstruction algorithms impair radiologists' subjective perception and diagnostic performance due to changes in the amplitude of different spatial frequencies of noise. The hypothesis was that there was a change in radiologists´ assessments towards a more positive attitude to the higher strengths of Advanced modeled iterative reconstruction algorithm (ADMIRE). Can radiologists learn to adapt to the unusual appearance of images produced by higher strengths of ADMIRE? Methods The present study is based on two ethical board, previously published, studies that evaluated the performance of ADMIRE in non-contrast and contrast-enhanced abdominal CT. Images from 25 (rst material) and 50 (second material) clinical examinations, were reconstructed with ADMIRE strengths 3, 5 and ltered back projection (FBP). These images were assessed by local radiologists using image criteria obtained from the European guidelines for quality criteria in CT. To ascertain if there was a learning effect as the reviews progressed, results from these two studies were used in the new analyses of existing data by introducing a time variable in the mixed-effects ordinal logistic regression model. Results For the highest strength (5) of the ADMIRE algorithm, the signi cant negative attitude for both liver parenchyma and overall image quality for diagnostic purposes, at the beginning of the reviews was strengthened during the progress of the reviews in both materials. For ADMIRE strength 3, an early positive attitude for the algorithm was perceived with no signi cant change over time for majority of the criteria except for one criterion, i.e., the overall image quality, where a signi cant negative trend over time was seen in the second material. Conclusions As the reviews in both materials progressed, an increasing dislike for ADMIRE 5 images was apparent for at least two image criteria. In the time perspective of weeks or months, no learning effect towards accepting the new algorithm could be demonstrated.
Radiation Protection Dosimetry, Jul 16, 2021
Dual-energy computed tomography (CT) can be used in radiotherapy treatment planning for the calcu... more Dual-energy computed tomography (CT) can be used in radiotherapy treatment planning for the calculation of absorbed dose distributions. The aim of this work is to evaluate whether there is room for improvement in the accuracy of the Monoenergetic Plus algorithm by Siemens Healthineers. A Siemens SOMATOM Force scanner was used to scan a cylindrical polymethyl methacrylate phantom with four rod-inserts made of different materials. Images were reconstructed using ADMIRE and processed with Monoenergetic Plus. The resulting CT numbers were compared with tabulated values and values simulated by the proof-of-a-concept algorithm DIRA developed by the authors. Both the Monoenergetic Plus and DIRA algorithms performed well; the accuracy of attenuation coefficients was better than about ±1% at the energy of 70 keV. Compared with DIRA, the worse performance of Monoenergetic Plus was caused by its (i) two-material decomposition to iodine and water and (ii) imperfect suppression of the beam hardening artifact in ADMIRE.
Information about each X-ray examination, in a modern digitized X-ray department is generated and... more Information about each X-ray examination, in a modern digitized X-ray department is generated and stored in a PACS. Appropriate conversion factors, e.g. E/DAP, can be applied to separate projections and summed to the total effective dose for each examination. The objectives of the work were (i) to investigate the accuracy and precision in the calculated effective dose (ii) to identify data for registration of (1) patient dose, (2) exposure data, and (3) patient information (iii) to make it possible to derive dose statistics on patient level for documentation of diagnostic standard doses, optimizations, constancy checks, and future epidemiological studies. The effective doses were calculated using Monte Carlo based computer programs or by using tabulations. Conversion factors were calculated for different levels of information and the individual effective dose was compared to the most precise estimation. The results suggest that the accuracy in the estimations of effective dose increases by added information about the patient (gender, size) and how the examination was performed.
Background: Reduced ventilation in lung regions affected by chronic obstructive pulmonary disease... more Background: Reduced ventilation in lung regions affected by chronic obstructive pulmonary disease (COPD), reflected as inhomogeneities in the single-photon emission computed tomography (SPECT) lung image, is correlated to disease advancement. An analysis method for measuring these inhomogeneities is proposed in this work. The first aim was to develop a quantitative analysis method that could discriminate between Monte Carlo simulated normal and COPD lung SPECT images. A second aim was to evaluate the ability of the present method to discriminate between human subjects with advanced COPD and healthy volunteers. Methods: In the simulated COPD study, different activity distributions in the lungs were created to mimic the healthy lung (normal) and different levels of COPD. Gamma camera projections were Monte Carlo simulated, representing clinically acquired projections of a patient who had inhaled 125 MBq 99m Tc-Technegas followed by a 10-min SPECT examination. Reconstructions were made with iterative ordered subset expectation maximisation. The coefficient of variance (CV) was calculated for small overlapping volumes covering the 3D reconstructed activity distribution. A CV threshold value (CV T) was calculated as the modal value of the CV distribution of the simulated normal. The area under the distribution curve (AUC), for CV values greater than CV T , AUC(CV T), was then calculated. Moreover, five patients with advanced emphysema and five healthy volunteers inhaled approximately 75 MBq 99m Tc-Technegas immediately before the 20-min SPECT acquisition. In the human study, CV T was based on the mean CV distribution of the five healthy volunteers. Results: A significant difference (p < 0.001) was found between the Monte-Carlo simulated normal and COPD lung SPECT examinations. The present method identified a total reduction of ventilation of approximately 5%, not visible to the human eye in the reconstructed image. In humans the same method clearly discriminated between the five healthy volunteers and five patients with advanced COPD (p < 0.05). Conclusions: While our results are promising, the potential of the AUC(CV T) method to detect less advanced COPD in patients needs further clinical studies.
Journal of Radiological Protection, Jul 28, 2022
Vascular x-ray guided interventions are complex and may result in high occupational doses to ioni... more Vascular x-ray guided interventions are complex and may result in high occupational doses to ionising radiation if staff do not take appropriate actions to minimise their exposure. In this prospective intervention study, ten staff members wore an extra personal dosimeter on the upper body above their regular protective clothing during four consecutive periods. Between each period either additional practical radiological protection training was given or a real-time direct display dosimeter were provided to the staff. Each staff’s personal dose equivalent, Hp(10) normalised to the total air kerma-area product for the procedures where each staff were involved, KAPt, was used as the dependent variable. A focus-group interview with the staff were performed about the usefulness of the training and real-time dose rate display system. Our aim was to investigate if the interventions (practical training or real-time dose rate display) did affect the staff doses in the short and long term (five months later). Significant (p < 0.05) reductions of staff doses Hp(10)/KAPt were found after practical radiological protection training, but not after using real-time dose rate displays. Significant reductions were maintained after five months without additional interventions. The results from the focus-group interview indicated that making radiation ‘visible’, during practical training and usage of real-time direct display dosimeter, made it easier to understand how to act to lower occupational doses.
Acta Radiologica, 1993
Conversion factors between the energy imparted to the patient in pediatric radiography and air co... more Conversion factors between the energy imparted to the patient in pediatric radiography and air collision kerma integrated over beam area are presented. The values have been derived from Monte Carlo calculations in soft tissue phantoms and extend results published earlier to cover children from early infancy to the age of 15 years. Variations related to phantom size as well as to focus-phantom distance, radiation field size, orientation of view (a.p., lateral), tube potential, and beam filtration are given. We show that the conversion factor increases with increasing half-value layer of the X-ray beam and the anterioposterior width of the simulated child. Increasing the focus-phantom distance increases the conversion factor, while increasing the field size decreases the factors due to more scattered radiation escaping laterally from the phantom.
Medical Physics, Oct 1, 2001
A computer program has been developed to model chest radiography. It incorporates a voxel phantom... more A computer program has been developed to model chest radiography. It incorporates a voxel phantom of an adult and includes antiscatter grid, radiographic screen, and film. Image quality is quantified by calculating the contrast ͑⌬OD͒ and the ideal observer signal-to-noise ratio (SNR I) for a number of relevant anatomical details at various positions in the anatomy. Detector noise and system unsharpness are modeled and their influence on image quality is considered. A measure of useful dynamic range is computed and defined as the fraction of the image that is reproduced at an optical density such that the film gradient exceeds a preset value. The effective dose is used as a measure of the radiation risk for the patient. A novel approach to patient dose and image quality optimization has been developed and implemented. It is based on a reference system acknowledged to yield acceptable image quality in a clinical trial. Two optimizations schemes have been studied, the first including the contrast of vessels as measure of image quality and the second scheme using also the signal-to-noise ratio of calcifications. Both schemes make use of our measure of useful dynamic range as a key quantity. A large variety of imaging conditions was simulated by varying the tube voltage, antiscatter device, screen-film system, and maximum optical density in the computed image. It was found that the optical density is crucial in screen-film chest radiography. Significant dose savings ͑30%-50%͒ can be accomplished without sacrificing image quality by using low-atomic-number grids with a low grid ratio or an air gap and more sensitive screen-film system. Dose-efficient configurations proposed by the model agree well with the example of good radiographic technique suggested by the European Commission.
DESCRIPTIONThis publication is aimed at students and teachers involved in programmes that train m... more DESCRIPTIONThis publication is aimed at students and teachers involved in programmes that train medical physicists for work in diagnostic radiology. It provides, in the form of a syllabus, a comprehensive overview of the basic medical physics knowledge required for the practice of modern diagnostic radiology. This makes it particularly useful for graduate students and residents in medical physics programmes. The material presented in the publication has been endorsed by the major international organizations and is the foundation for academic and clinical courses in both diagnostic radiology physics and in emerging areas such as imaging in radiotherapy.
PubMed, 1998
A model will be proposed for predicting the expected value and variance of the measured signal-le... more A model will be proposed for predicting the expected value and variance of the measured signal-level in collected radiographic images obtained with an image-intensifier-based X-ray radiography system. The model parameters are determined from both theoretical and experimental data and incorporate all parameters that can be varied by the system operator, except CCD-camera readout rate. The proposed model predicts the expected value and variance of the grey-level in the output image with high accuracy. It is also shown that it is very important to compensate for the inhomogeneous pixel sensitivity when comparing the variance of the signal-level in a pixel from sequentially collected images with the variance determined in a single image.
Physica Medica, Aug 1, 2018
Rare earth materials instead of aluminium as added filter have been reported to reduce the mean a... more Rare earth materials instead of aluminium as added filter have been reported to reduce the mean absorbed dose in the patient. With these filters, the energy spectrum can be shaped to yield high ene ...
Radiation Protection Dosimetry, May 25, 2021
Automatic segmentation of bones in computed tomography (CT) images is used for instance in beam h... more Automatic segmentation of bones in computed tomography (CT) images is used for instance in beam hardening correction algorithms where it improves the accuracy of resulting CT numbers. Of special interest are pelvic bones, which-because of their strong attenuation-affect the accuracy of brachytherapy in this region. This work evaluated the performance of the JJ2016 algorithm with the performance of MK2014v2 and JS2018 algorithms; all these algorithms were developed by authors. Visual comparison, and, in the latter case, also Dice similarity coefficients derived from the ground truth were used. It was found that the 3D-based JJ2016 performed better than the 2D-based MK2014v2, mainly because of the more accurate hole filling that benefitted from information in adjacent slices. The neural network-based JS2018 outperformed both traditional algorithms. It was, however, limited to the resolution of 128 3 owing to the limited amount of memory in the graphical processing unit (GPU).
Catheterization and Cardiovascular Interventions, Feb 1, 2011
Objectives: We have developed a method using transthoracic echocardiography in establishing optim... more Objectives: We have developed a method using transthoracic echocardiography in establishing optimal visualization of the aortic root, to reduce the amount of contrast medium used in each patient. Background: During transcatheter aortic valve implantation, it is necessary to obtain an optimal fluoroscopic projection for deployment of the valve showing the aortic ostium with the three cusps aligned in the beam direction. This may require repeat aortic root angiograms at this stage of the procedure with a high amount of contrast medium with a risk of detrimental influence on renal function. Methods: We studied the conventional way and an echo guided way to optimize visualisation of the aortic root. Echocardiography was used initially allowing easier alignment of the image intensifier with the transducer's direction. Results: Contrast volumes, radiation/fluoroscopy exposure times, and postoperative creatinine levels were significantly less in patients having the echo-guided orientation of the optimal fluoroscopic angles compared with patients treated with the conventional approach. Conclusion: We present a user-friendly echo-guided method to facilitate fluoroscopy adjustment during transcatheter aortic valve implantation. In our series, the amounts of contrast medium and radiation have been significantly reduced, with a concomitant reduction in detrimental effects on renal function in the early postoperative phase. V
Radiation Protection Dosimetry, Mar 29, 2021
Traditional filtered back projection (FBP) reconstruction methods have served the computed tomogr... more Traditional filtered back projection (FBP) reconstruction methods have served the computed tomography (CT) community well for over 40 years. With the increased use of CT during the last decades, efforts to minimise patient exposure, while maintaining sufficient or improved image quality, have led to the development of model-based iterative reconstruction (MBIR) algorithms from several vendors. The usefulness of the advanced modeled iterative reconstruction (ADMIRE) (Siemens Healthineers) MBIR in abdominal CT is reviewed and its noise suppression and/or dose reduction possibilities explored. Quantitative and qualitative methods with phantom and human subjects were used. Assessment of the quality of phantom images will not always correlate positively with those of patient images, particularly at the higher strength of the ADMIRE algorithm. With few exceptions, ADMIRE Strength 3 typically allows for substantial noise reduction compared to FBP and hence to significant (≈30%) patient dose reductions. The size of the dose reductions depends on the diagnostic task.
Medical Physics, Aug 26, 2004
The relationship and precision of four methods for measuring the low-contrast detail detectabilit... more The relationship and precision of four methods for measuring the low-contrast detail detectability in fluoroscopic imaging were studied. These included the physical measurement of the accumulation rate of the square of the signal-to-noise ratio (SNR rate 2), two-alternative forced-choice ͑2-AFC͒ experiments, sixteen-alternative forced-choice ͑16-AFC͒ experiments and subjective determination of the threshold contrast. The precision and sensitivity of the threshold contrast measurement were seen to be modest in the constancy testing of fluoroscopic equipment: only large changes in system performance could be reliably detected by that method. The measurement of the SNR rate 2 is suggested instead. The relationship between the results of the various methods were studied, and it was found that human performance can be related to SNR rate 2 by introducing the concept of the effective image information integration time (t eff). When measured for an unlimited observation time, it depicts the saturation of human performance in detecting a static low-contrast detail in dynamic image noise. Here, t eff was found to be about 0.6 s in 2-AFC tests and 0.3 s in 16-AFC tests.
The aim for this work was to study to what extent the detection of nodules is quantum noise limit... more The aim for this work was to study to what extent the detection of nodules is quantum noise limited, based on the combined results from a nodule-detection clinical trial and a Monte Carlo computational model of a digital chest imaging system. The Monte Carlo computer program computes measures of physical image quality such as image contrast, C and signalto-noise ratio, SNR for nodules of any size. A computed radiography (CR) imaging system used simulated. The patient anterior-posterior thickness was 25 cm and nodules with diameters between 1-40 mm were included. The image contrast and SNR was calculated for 1600 (40x40) positions in the chest image and averaged over five anatomical regions of interest (lateral pulmonary, retrocardial, hilar, lower-and upper mediastinal regions). Threshold contrasts for each region, C th , corresponding to A z =0.80 for detecting a 10 mm nodule, were deduced from the clinical trial. A threshold is also used for the quantum noise signal-to-noise ratio, SNR th. The model computes the diameter of a disk-shaped object that is required to comply with the two criteria: SNR≥SNR th and C≥C th. A system is said to be quantum noise limited when the nodule size required to fulfil both criteria is not limited by the contrast but by the SNR. The required nodule diameter is largest in the hilar region (25 mm) and smallest in the lateral pulmonary region (11 mm). When the threshold SNR th =25 is used, the lower mediastinal region is quantum noise limited already at low speed classes (S>100). The hilar region is never quantum noise limited at realistic speed classes (S<1000). The accuracy of this model will be tested in the future by more sophisticated modelling of anatomical background and noise in the SNR-expression. Purpose The aim for this work was to study to what extent the detection of nodules is quantum noise limited, based on the combined results from a nodule-detection clinical trial and a Monte Carlo computational model of a digital chest imaging system.
Research Square (Research Square), Aug 16, 2022
Objectives Images reconstructed with higher strengths of iterative reconstruction algorithms impa... more Objectives Images reconstructed with higher strengths of iterative reconstruction algorithms impair radiologists' subjective perception and diagnostic performance due to changes in the amplitude of different spatial frequencies of noise. The hypothesis was that there was a change in radiologists´ assessments towards a more positive attitude to the higher strengths of Advanced modeled iterative reconstruction algorithm (ADMIRE). Can radiologists learn to adapt to the unusual appearance of images produced by higher strengths of ADMIRE? Methods The present study is based on two ethical board, previously published, studies that evaluated the performance of ADMIRE in non-contrast and contrast-enhanced abdominal CT. Images from 25 (rst material) and 50 (second material) clinical examinations, were reconstructed with ADMIRE strengths 3, 5 and ltered back projection (FBP). These images were assessed by local radiologists using image criteria obtained from the European guidelines for quality criteria in CT. To ascertain if there was a learning effect as the reviews progressed, results from these two studies were used in the new analyses of existing data by introducing a time variable in the mixed-effects ordinal logistic regression model. Results For the highest strength (5) of the ADMIRE algorithm, the signi cant negative attitude for both liver parenchyma and overall image quality for diagnostic purposes, at the beginning of the reviews was strengthened during the progress of the reviews in both materials. For ADMIRE strength 3, an early positive attitude for the algorithm was perceived with no signi cant change over time for majority of the criteria except for one criterion, i.e., the overall image quality, where a signi cant negative trend over time was seen in the second material. Conclusions As the reviews in both materials progressed, an increasing dislike for ADMIRE 5 images was apparent for at least two image criteria. In the time perspective of weeks or months, no learning effect towards accepting the new algorithm could be demonstrated.
Radiation Protection Dosimetry, Jul 16, 2021
Dual-energy computed tomography (CT) can be used in radiotherapy treatment planning for the calcu... more Dual-energy computed tomography (CT) can be used in radiotherapy treatment planning for the calculation of absorbed dose distributions. The aim of this work is to evaluate whether there is room for improvement in the accuracy of the Monoenergetic Plus algorithm by Siemens Healthineers. A Siemens SOMATOM Force scanner was used to scan a cylindrical polymethyl methacrylate phantom with four rod-inserts made of different materials. Images were reconstructed using ADMIRE and processed with Monoenergetic Plus. The resulting CT numbers were compared with tabulated values and values simulated by the proof-of-a-concept algorithm DIRA developed by the authors. Both the Monoenergetic Plus and DIRA algorithms performed well; the accuracy of attenuation coefficients was better than about ±1% at the energy of 70 keV. Compared with DIRA, the worse performance of Monoenergetic Plus was caused by its (i) two-material decomposition to iodine and water and (ii) imperfect suppression of the beam hardening artifact in ADMIRE.
Information about each X-ray examination, in a modern digitized X-ray department is generated and... more Information about each X-ray examination, in a modern digitized X-ray department is generated and stored in a PACS. Appropriate conversion factors, e.g. E/DAP, can be applied to separate projections and summed to the total effective dose for each examination. The objectives of the work were (i) to investigate the accuracy and precision in the calculated effective dose (ii) to identify data for registration of (1) patient dose, (2) exposure data, and (3) patient information (iii) to make it possible to derive dose statistics on patient level for documentation of diagnostic standard doses, optimizations, constancy checks, and future epidemiological studies. The effective doses were calculated using Monte Carlo based computer programs or by using tabulations. Conversion factors were calculated for different levels of information and the individual effective dose was compared to the most precise estimation. The results suggest that the accuracy in the estimations of effective dose increases by added information about the patient (gender, size) and how the examination was performed.
Background: Reduced ventilation in lung regions affected by chronic obstructive pulmonary disease... more Background: Reduced ventilation in lung regions affected by chronic obstructive pulmonary disease (COPD), reflected as inhomogeneities in the single-photon emission computed tomography (SPECT) lung image, is correlated to disease advancement. An analysis method for measuring these inhomogeneities is proposed in this work. The first aim was to develop a quantitative analysis method that could discriminate between Monte Carlo simulated normal and COPD lung SPECT images. A second aim was to evaluate the ability of the present method to discriminate between human subjects with advanced COPD and healthy volunteers. Methods: In the simulated COPD study, different activity distributions in the lungs were created to mimic the healthy lung (normal) and different levels of COPD. Gamma camera projections were Monte Carlo simulated, representing clinically acquired projections of a patient who had inhaled 125 MBq 99m Tc-Technegas followed by a 10-min SPECT examination. Reconstructions were made with iterative ordered subset expectation maximisation. The coefficient of variance (CV) was calculated for small overlapping volumes covering the 3D reconstructed activity distribution. A CV threshold value (CV T) was calculated as the modal value of the CV distribution of the simulated normal. The area under the distribution curve (AUC), for CV values greater than CV T , AUC(CV T), was then calculated. Moreover, five patients with advanced emphysema and five healthy volunteers inhaled approximately 75 MBq 99m Tc-Technegas immediately before the 20-min SPECT acquisition. In the human study, CV T was based on the mean CV distribution of the five healthy volunteers. Results: A significant difference (p < 0.001) was found between the Monte-Carlo simulated normal and COPD lung SPECT examinations. The present method identified a total reduction of ventilation of approximately 5%, not visible to the human eye in the reconstructed image. In humans the same method clearly discriminated between the five healthy volunteers and five patients with advanced COPD (p < 0.05). Conclusions: While our results are promising, the potential of the AUC(CV T) method to detect less advanced COPD in patients needs further clinical studies.