- Email: [email protected]
Durham MED tester acceptance testing and calibration using EBT3 Gafchromic film
Physica Medica 42 (2017) 353–363
Contents lists available at ScienceDirect
Physica Medica journal homepage: http://www.physicamedica.com
Abstracts from the Irish Association of Physicists in Medicine 8th Annual Scientific Meeting Diagnostic Parallel Session 11:30–12:30 Effects of sampling frequency on the accuracy of phenomenological and pharmacokinetic parameters derived from dynamic contrast enhanced MRI data Silvin P. Knight a, Jacinta E. Browne b, James F. Meaney a, Andrew J. Fagan a a
National Centre for Advanced Medical Imaging (CAMI), St James’s Hospital/School of Medicine, Trinity College University of Dublin, Ireland b School of Physics & Medical Ultrasound Physics and Technology Group, Centre of Industrial Engineering Optics, FOCAS, Dublin Institute of Technology, Dublin 8, Ireland E-mail address: [email protected] (S P. Knight) The sampling frequencies (fs) at which dynamic contrast enhanced (DCE) MRI data are acquired is known to affects the accuracy of derived parameters. Phenomenological parameters empirically characterise the shape and structure of the signal-time curves, whereas pharmacokinetic approaches estimate physiologically relevant parameters from the concentration-time curves, such as the volume-transfer constant (Ktrans) and the extravascular-extracellular fractional volume (ve). Both of these approaches have shown promise in the detection of prostate cancer, however to date a method has been lacking to quantitatively compare MR-measured to known ‘ground truth’ parameter values. In the present work, a newly developed anthropomorphic DCE-MRI prostate phantom was utilised to this end. Precisely known ‘healthy’ and ‘tumorous’ curves were measured using a 3T scanner (Philips, Netherlands) and 32-channel detector coil (3D-SPGR, TR/TE = 4.3/1.4 ms, a = 10°, FOV = 224 224 80 mm3, voxels = 1 1 4 mm3) at fs = 0.5, 0.26, 0.19, 0.12, 0.061, and 0.041 Hz. Phenomenological analysis revealed that wash-in was measured with the lowest errors (<15%) at fs P 0.12 Hz, whereas wash-out gave comparatively higher errors (up to 27%) across this same range of fs. Lowest errors in time-to-peak (<11%) were measured using fs = 2 s and 8.1 s. Pharmacokinetic analysis using the Tofts model gave errors in Ktrans and ve values <14% and <10%, for acquisitions with fs P 0.12 Hz and fs P 0.061 respectively, with errors increasing dramatically (up to 172%) with fs < 0.061 Hz. Quantitative phantom-based approaches, such as the one used herein, offers the prospect of a standardisation in the way DCE-MRI is performed in the prostate, and possibly a wider acceptance of the technique for routine clinical use. Acknowledgement This work is funded by Irish Cancer Society Research Scholarship CRS13KNI (supported by Movember). https://doi.org/10.1016/j.ejmp.2017.05.006
Does magnification increase total unsharpness radiography? Eamon Loughman, Michael Rowan, Patrick Kenny
in
DR
Mater Misericordiae University Hospital, Ireland E-mail address: [email protected] (E. Loughman) In General Diagnostic Radiography it is generally assumed that an increase in magnification results in a non-linear increase in total unsharpness (Utot). Utot is the sum in quadrature of contributing sources of unsharpness, including geometrical/penumbra (Upen) and detector unsharpness (Udet). However, this assumption is based on traditional film/screen radiography where focal spot sizes of approximately one and two millimetres are considerably greater than the resolution of the film/screen detector. Therefore penumbra (or geometrical) unsharpness (Upen) dominated. However, modern Digital Radiography (DR) imaging systems combine smaller focal spot sizes (typically 0.6 & 1.0 mm), with lower resolution detectors having pixels sizes of approximately 0.15 mm. It is unclear how magnification affects total unsharpness in such systems. The purpose of this study is to record the total unsharpness for a range of imaging arrangements and verify that they are consistent with the calculated total unsharpness (Utot). Images of a Tantalum target in air, located at different distances from the detector, were recorded. Modulation Transfer Function (MTF) values were used to describe the total unsharpness obtained for a variety of focal spot sizes, detector pixel sizes and magnifications. A novel MTF parameter, % fill area below Nyquist, was used to estimate total unsharpness (Utot). The results obtained are surprising to the extent that many of the magnifications in conventional diagnostic radiography improved total unsharpness. This may have consequences in fluoroscopy. Finally, we verified that magnification, as used in mammography, reduces total image unsharpness. https://doi.org/10.1016/j.ejmp.2017.05.007
Durham MED tester acceptance testing and calibration using EBT3 Gafchromic film Michael Manley, Jackie McCavana St. Vincent’s University Hospital, Ireland E-mail address: [email protected] (M. Manley) The Hybec Durham Erythema MED tester is a hand held test device designed to measure the Minimal Erythema Dose for a patient receiving UVB phototherapy. It has a series of 10 apertures with a superimposed foil grid of varying attenuation so that 10 doses of UVB are delivered to a patient simultaneously in increments of 1.26. Several groups have researched this device and published results differ. A more optimum method of calibration is required. There are three challenges in the measurement of the output of the 9 mm diameter apertures: availability of a detector of appropri-
354
Abstracts / Physica Medica 42 (2017) 353–363
ate size, use of appropriate input optic for the ‘in contact’ geometry and the variation in bulb output with time. Calibrated EBT3 Gafchromic film is ideal for this application as it allows simultaneous measurement of all apertures and quantitative investigation in the patient exposure geometry. The EBT3 and a Bentham spectral radiometer were used to quantify the output characteristics of two handheld testers. Lamp stability, warm up characteristics, relative output at apertures and uniformity of bulbs were evaluated in simulated patient exposure geometry. Previous research was carried out with the tester free in air. Measurements carried out in this research demonstrate that the geometry has an influence on warm up and relative output of apertures, due to heating effects. Results allowed a treatment protocol to be established with revised warm-up time and modified relative aperture outputs. EBT3 is suitable for the commissioning and routine quality control of the device. https://doi.org/10.1016/j.ejmp.2017.05.008
Digital angiography: Moving with the times David Costello a, Patrick Kenny b, Mandy Lewis b
examine the effectiveness of their protection and determine the optimal transmission and design of protective aprons for future purchasing. Apron designs include full length, backless, skirt/vest aprons, both single panel and overlap. Measurements performed in narrow, broad and the recommended inverse-broad beam geometries (I.S. EN61331-1–2014) are compared with a 100% lead apron for a number of beam qualities. Aprons tested include Xenolite TB and NL, Safety First, Rayshield and Infab lead-free and bi-layer aprons, as well as a 100% lead Amray apron. Calibrated Harshaw TLD-100 and TLD100H dosimeters were placed on the aprons of several members of staff, including an IR radiologist and a Cardiology registrar, to measure the effectiveness of the apron at multiple sites in a clinical setting. Preliminary results show that for high throughput/high dose procedures, lead equivalence of 0.25 mm is inadequate. The extent of the overlap is not sufficient on some models of apron, particularly on the side of the apron closest to the tube. The suitability of backless aprons will also be discussed. Results will inform minimum requirements, such as the type and thickness of barrier material, apron design and extent of the overlap required for optimal protection. https://doi.org/10.1016/j.ejmp.2017.05.010
a
Mater Misericordiae University Hospotal, Ireland Mater Misericaordiae University Hospital, Ireland E-mail address: [email protected] (D. Costello) b
Low dose Angiography (LDA) systems rely on significant recursive filtration (AKA temporal averaging) to maintain image quality. In situations of rapid motion, such processing can have a detrimental effect on images obtained, producing motion blur and temporal ghosting. LDA enables the use of lower kV’s and mAs resulting in lower staff and patient doses. It also allows manufacturers to overcome output limitations when using smaller focal spots. While the benefits are clear very little work has been carried out in relation to the drawbacks of this approach. This work aims to examine the impact of recursive filtration on moving targets in LDA systems. Common test objects such as the Leeds Test Objects do not allow for the dynamic assessment of Image Quality. In this study, a NEMA Cardiology Phantom was modified to investigate the impact of Motion Unsharpness and Recursive Filtering on image quality in LDA. This investigation was carried out under conditions simulating normal clinical use. Systems assessed were: Philips Alura FD 20, Alura Clarity FD 10 and two Siemens Artis Zee systems. All systems using LDA demonstrated different levels of Temporal Ghosting. The Intensity and spacing of the ghost images was dependent on system type and pulse rate. When set to acquisition mode, the ghosting artefact was not present. However, an increase in motion unsharness as a result of longer pulse widths was observed. The impact of motion unsharpness and temporal ghosting impinges on the effective optimisation of clinical systems and should form of regular QC. https://doi.org/10.1016/j.ejmp.2017.05.009
Protective aprons in Interventional Radiology and Cardiology: An assessment of minimum requirements Danielle Maguire, Eileen Seymour, Julie Lucey, Jackie McCavana St. Vincent’s University Hospital, Ireland E-mail address: [email protected] (D. Maguire) It has been shown that lead-free and lead-composite aprons do not perform as well as their 100% lead counterparts, and secondary fluorescent radiation can contribute to staff doses. The aim of this project is to measure the transmission through the current cohort of aprons in use in our Cardiology and Interventional Radiology departments, to
Personalised medicine – Dosimetry in radioiodine therapy for benign thyroid disease Jennie Cooke a, Maeve Masterson b, Isolda Frizelle c, Niamh Phelan a, Marie-Louise Healy a a
St. James’s Hospital, Ireland DIT Kevin Street, Ireland c AMNCH, Ireland E-mail address: [email protected] (J. Cooke) b
The EANM Guidelines for Dosimetry for Benign thyroid diseases [1] recommend two or more uptake measurements to estimate the residence time of I-131 in the thyroid, which when combined with the mass of the gland can be used to calculate the treatment activity. The guidelines also outline methods to estimate residence time using one early or one late uptake assessment, with subsequent loss of accuracy. The workup for therapy in our centre includes thyroid ultrasound and an I-131 uptake measurement. For patients with a solitary toxic nodule the uptake measurement combined with nodule size have been used to determine treatment activity. Patients with Grave’s disease and multinodular goitre were previously treated with fixed activities. Following a review of the treatment outcome for 130 patients we present a retrospective analysis which demonstrates that these fixed activities resulted in estimated thyroid doses which ranged over an order of magnitude. Subsequently we present our initial experiences of adopting the EANM Dosimetry guidelines using a minimum of two uptake measurements. For therapies such as I-131 therapy with high success rates (85%–90% in our centre), it has been difficult to justify the use of dosimetry in the past. However with the imminent implementation of the 97/43/ EURATOM and to optimise the therapeutic benefit to the patient, it is essential that we begin to utilize available dosimetry techniques.
Reference 1. Heribert Hänscheid et al. EANM Dosimetry Committee series on standard operational procedures for pre-therapeutic dosimetry II. Dosimetry prior to radioiodine therapy of benign thyroid diseases. EJNMMI 2013;40(7):1126–34. https://doi.org/10.1016/j.ejmp.2017.05.011
Contents lists available at ScienceDirect
Physica Medica journal homepage: http://www.physicamedica.com
Abstracts from the Irish Association of Physicists in Medicine 8th Annual Scientific Meeting Diagnostic Parallel Session 11:30–12:30 Effects of sampling frequency on the accuracy of phenomenological and pharmacokinetic parameters derived from dynamic contrast enhanced MRI data Silvin P. Knight a, Jacinta E. Browne b, James F. Meaney a, Andrew J. Fagan a a
National Centre for Advanced Medical Imaging (CAMI), St James’s Hospital/School of Medicine, Trinity College University of Dublin, Ireland b School of Physics & Medical Ultrasound Physics and Technology Group, Centre of Industrial Engineering Optics, FOCAS, Dublin Institute of Technology, Dublin 8, Ireland E-mail address: [email protected] (S P. Knight) The sampling frequencies (fs) at which dynamic contrast enhanced (DCE) MRI data are acquired is known to affects the accuracy of derived parameters. Phenomenological parameters empirically characterise the shape and structure of the signal-time curves, whereas pharmacokinetic approaches estimate physiologically relevant parameters from the concentration-time curves, such as the volume-transfer constant (Ktrans) and the extravascular-extracellular fractional volume (ve). Both of these approaches have shown promise in the detection of prostate cancer, however to date a method has been lacking to quantitatively compare MR-measured to known ‘ground truth’ parameter values. In the present work, a newly developed anthropomorphic DCE-MRI prostate phantom was utilised to this end. Precisely known ‘healthy’ and ‘tumorous’ curves were measured using a 3T scanner (Philips, Netherlands) and 32-channel detector coil (3D-SPGR, TR/TE = 4.3/1.4 ms, a = 10°, FOV = 224 224 80 mm3, voxels = 1 1 4 mm3) at fs = 0.5, 0.26, 0.19, 0.12, 0.061, and 0.041 Hz. Phenomenological analysis revealed that wash-in was measured with the lowest errors (<15%) at fs P 0.12 Hz, whereas wash-out gave comparatively higher errors (up to 27%) across this same range of fs. Lowest errors in time-to-peak (<11%) were measured using fs = 2 s and 8.1 s. Pharmacokinetic analysis using the Tofts model gave errors in Ktrans and ve values <14% and <10%, for acquisitions with fs P 0.12 Hz and fs P 0.061 respectively, with errors increasing dramatically (up to 172%) with fs < 0.061 Hz. Quantitative phantom-based approaches, such as the one used herein, offers the prospect of a standardisation in the way DCE-MRI is performed in the prostate, and possibly a wider acceptance of the technique for routine clinical use. Acknowledgement This work is funded by Irish Cancer Society Research Scholarship CRS13KNI (supported by Movember). https://doi.org/10.1016/j.ejmp.2017.05.006
Does magnification increase total unsharpness radiography? Eamon Loughman, Michael Rowan, Patrick Kenny
in
DR
Mater Misericordiae University Hospital, Ireland E-mail address: [email protected] (E. Loughman) In General Diagnostic Radiography it is generally assumed that an increase in magnification results in a non-linear increase in total unsharpness (Utot). Utot is the sum in quadrature of contributing sources of unsharpness, including geometrical/penumbra (Upen) and detector unsharpness (Udet). However, this assumption is based on traditional film/screen radiography where focal spot sizes of approximately one and two millimetres are considerably greater than the resolution of the film/screen detector. Therefore penumbra (or geometrical) unsharpness (Upen) dominated. However, modern Digital Radiography (DR) imaging systems combine smaller focal spot sizes (typically 0.6 & 1.0 mm), with lower resolution detectors having pixels sizes of approximately 0.15 mm. It is unclear how magnification affects total unsharpness in such systems. The purpose of this study is to record the total unsharpness for a range of imaging arrangements and verify that they are consistent with the calculated total unsharpness (Utot). Images of a Tantalum target in air, located at different distances from the detector, were recorded. Modulation Transfer Function (MTF) values were used to describe the total unsharpness obtained for a variety of focal spot sizes, detector pixel sizes and magnifications. A novel MTF parameter, % fill area below Nyquist, was used to estimate total unsharpness (Utot). The results obtained are surprising to the extent that many of the magnifications in conventional diagnostic radiography improved total unsharpness. This may have consequences in fluoroscopy. Finally, we verified that magnification, as used in mammography, reduces total image unsharpness. https://doi.org/10.1016/j.ejmp.2017.05.007
Durham MED tester acceptance testing and calibration using EBT3 Gafchromic film Michael Manley, Jackie McCavana St. Vincent’s University Hospital, Ireland E-mail address: [email protected] (M. Manley) The Hybec Durham Erythema MED tester is a hand held test device designed to measure the Minimal Erythema Dose for a patient receiving UVB phototherapy. It has a series of 10 apertures with a superimposed foil grid of varying attenuation so that 10 doses of UVB are delivered to a patient simultaneously in increments of 1.26. Several groups have researched this device and published results differ. A more optimum method of calibration is required. There are three challenges in the measurement of the output of the 9 mm diameter apertures: availability of a detector of appropri-
354
Abstracts / Physica Medica 42 (2017) 353–363
ate size, use of appropriate input optic for the ‘in contact’ geometry and the variation in bulb output with time. Calibrated EBT3 Gafchromic film is ideal for this application as it allows simultaneous measurement of all apertures and quantitative investigation in the patient exposure geometry. The EBT3 and a Bentham spectral radiometer were used to quantify the output characteristics of two handheld testers. Lamp stability, warm up characteristics, relative output at apertures and uniformity of bulbs were evaluated in simulated patient exposure geometry. Previous research was carried out with the tester free in air. Measurements carried out in this research demonstrate that the geometry has an influence on warm up and relative output of apertures, due to heating effects. Results allowed a treatment protocol to be established with revised warm-up time and modified relative aperture outputs. EBT3 is suitable for the commissioning and routine quality control of the device. https://doi.org/10.1016/j.ejmp.2017.05.008
Digital angiography: Moving with the times David Costello a, Patrick Kenny b, Mandy Lewis b
examine the effectiveness of their protection and determine the optimal transmission and design of protective aprons for future purchasing. Apron designs include full length, backless, skirt/vest aprons, both single panel and overlap. Measurements performed in narrow, broad and the recommended inverse-broad beam geometries (I.S. EN61331-1–2014) are compared with a 100% lead apron for a number of beam qualities. Aprons tested include Xenolite TB and NL, Safety First, Rayshield and Infab lead-free and bi-layer aprons, as well as a 100% lead Amray apron. Calibrated Harshaw TLD-100 and TLD100H dosimeters were placed on the aprons of several members of staff, including an IR radiologist and a Cardiology registrar, to measure the effectiveness of the apron at multiple sites in a clinical setting. Preliminary results show that for high throughput/high dose procedures, lead equivalence of 0.25 mm is inadequate. The extent of the overlap is not sufficient on some models of apron, particularly on the side of the apron closest to the tube. The suitability of backless aprons will also be discussed. Results will inform minimum requirements, such as the type and thickness of barrier material, apron design and extent of the overlap required for optimal protection. https://doi.org/10.1016/j.ejmp.2017.05.010
a
Mater Misericordiae University Hospotal, Ireland Mater Misericaordiae University Hospital, Ireland E-mail address: [email protected] (D. Costello) b
Low dose Angiography (LDA) systems rely on significant recursive filtration (AKA temporal averaging) to maintain image quality. In situations of rapid motion, such processing can have a detrimental effect on images obtained, producing motion blur and temporal ghosting. LDA enables the use of lower kV’s and mAs resulting in lower staff and patient doses. It also allows manufacturers to overcome output limitations when using smaller focal spots. While the benefits are clear very little work has been carried out in relation to the drawbacks of this approach. This work aims to examine the impact of recursive filtration on moving targets in LDA systems. Common test objects such as the Leeds Test Objects do not allow for the dynamic assessment of Image Quality. In this study, a NEMA Cardiology Phantom was modified to investigate the impact of Motion Unsharpness and Recursive Filtering on image quality in LDA. This investigation was carried out under conditions simulating normal clinical use. Systems assessed were: Philips Alura FD 20, Alura Clarity FD 10 and two Siemens Artis Zee systems. All systems using LDA demonstrated different levels of Temporal Ghosting. The Intensity and spacing of the ghost images was dependent on system type and pulse rate. When set to acquisition mode, the ghosting artefact was not present. However, an increase in motion unsharness as a result of longer pulse widths was observed. The impact of motion unsharpness and temporal ghosting impinges on the effective optimisation of clinical systems and should form of regular QC. https://doi.org/10.1016/j.ejmp.2017.05.009
Protective aprons in Interventional Radiology and Cardiology: An assessment of minimum requirements Danielle Maguire, Eileen Seymour, Julie Lucey, Jackie McCavana St. Vincent’s University Hospital, Ireland E-mail address: [email protected] (D. Maguire) It has been shown that lead-free and lead-composite aprons do not perform as well as their 100% lead counterparts, and secondary fluorescent radiation can contribute to staff doses. The aim of this project is to measure the transmission through the current cohort of aprons in use in our Cardiology and Interventional Radiology departments, to
Personalised medicine – Dosimetry in radioiodine therapy for benign thyroid disease Jennie Cooke a, Maeve Masterson b, Isolda Frizelle c, Niamh Phelan a, Marie-Louise Healy a a
St. James’s Hospital, Ireland DIT Kevin Street, Ireland c AMNCH, Ireland E-mail address: [email protected] (J. Cooke) b
The EANM Guidelines for Dosimetry for Benign thyroid diseases [1] recommend two or more uptake measurements to estimate the residence time of I-131 in the thyroid, which when combined with the mass of the gland can be used to calculate the treatment activity. The guidelines also outline methods to estimate residence time using one early or one late uptake assessment, with subsequent loss of accuracy. The workup for therapy in our centre includes thyroid ultrasound and an I-131 uptake measurement. For patients with a solitary toxic nodule the uptake measurement combined with nodule size have been used to determine treatment activity. Patients with Grave’s disease and multinodular goitre were previously treated with fixed activities. Following a review of the treatment outcome for 130 patients we present a retrospective analysis which demonstrates that these fixed activities resulted in estimated thyroid doses which ranged over an order of magnitude. Subsequently we present our initial experiences of adopting the EANM Dosimetry guidelines using a minimum of two uptake measurements. For therapies such as I-131 therapy with high success rates (85%–90% in our centre), it has been difficult to justify the use of dosimetry in the past. However with the imminent implementation of the 97/43/ EURATOM and to optimise the therapeutic benefit to the patient, it is essential that we begin to utilize available dosimetry techniques.
Reference 1. Heribert Hänscheid et al. EANM Dosimetry Committee series on standard operational procedures for pre-therapeutic dosimetry II. Dosimetry prior to radioiodine therapy of benign thyroid diseases. EJNMMI 2013;40(7):1126–34. https://doi.org/10.1016/j.ejmp.2017.05.011