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How to estimate the dose from a dental CT or CBCT scan
Physica Medica 32 (2016) 414–428
Contents lists available at ScienceDirect
Physica Medica j o u r n a l h o m e p a g e : h t t p : / / w w w. p h y s i c a m e d i c a . c o m
Abstracts from the Irish Association of Physicists in Medicine 6th Annual Scientific Meeting Diagnostic Parallel Session A study of the feasibility and reproducibility of measuring blood perfusion in the kidney using MRI without a contrast agent Andrew J. Fagan, Susie Clarke, James F. Meaney. National Centre for Advanced Medical Imaging (CAMI), St. James’s Hospital/ School of Medicine, Trinity College Dublin Introduction: MRI contrast agents are contra-indicated for patients with impaired renal function, and hence there is considerable interest in developing a non-contrast agent technique which can quantify blood perfusion, for example in transplant patients. Pseudo-continuous arterial spin labelling (pCASL) is a new technique which has recently been recommended for use in cerebral perfusion studies; however, its use in the torso/ abdomen regions is severely compounded by artefacts arising from respiratory motion and magnetic susceptibility inhomogeneities. This study aimed to optimise and assess the reproducibility of pCASL for renal perfusion. Methodology: 15 healthy controls were scanned using a 3T Philips scanner. A high spatial resolution pCASL sequence was optimised through careful tailoring of all acquisition parameters. 16 label/control image pairs were acquired in all cases, with the labelling plane positioned perpendicular to the aorta above the kidneys, and the image plane orientated coronallyoblique. Breath-hold acquisitions were used to minimise respiratory motion, and B-spline image registration was performed on all images prior to fitting to the standard pCASL perfusion model. Results: Image SNR of 56 ± 3 was achieved in images with: voxel resolution = 2.5 × 2.5 × 6 mm3, receiver bandwidth = 3037 Hz, label duration = 1500 ms, label delay = 1500 ms. Excellent contrast was achieved between medulla and cortex regions, with measured perfusion values of 293 ± 44 and 139 ± 20 ml/100 g/min respectively. Excellent intra- and intersession reproducibility was noted. Conclusions: It is possible to perform sensitive and reproducible measurements of blood perfusion in the kidney using the pCASL technique, with a spatial resolution sufficiently high to allow for separation of medulla from cortical regions. How to estimate the dose from a dental CT or CBCT scan Anthony Reynolds. IDT Ireland, Kinsale, Co. Cork Cone beam computed tomography (CBCT) scanners are now widely used in dentistry. Under current legislation, dental practitioners must balance the benefit to the patient against the radiation risk. Calculating exact values of dose (and hence risk) is time-consuming and requires specialist knowledge. This work shows a simple method of estimating the dose with sufficient accuracy for the task at hand. We estimate the effective dose from parameters stored in the DICOM header or displayed on the CT or CBCT screen. Database technology interpolates missing or incomplete data, and database tables can be refined as more information becomes available. Most modern equipment displays the Dose Length Product (DLP) or Dose Area Product (DAP). Published data can be used when machines do not provide this information. Multiplying the DLP (expressed in mGy.cm) by 2 for the maxilla or 3 for the mandible gives a rough estimate of the effective dose in microSieverts, within the context of an adult dental CT or CBCT scan. Results are accurate to within a factor of 2, which is sufficient for decisions regarding patient management. Trade-offs between dose and image quality can be complex, and are not always well understood. Selecting a smaller voxel size may improve the resolution, at the expense of greater noise, and operators may compensate by increasing the mAs. The additional patient
detriment must be justified on the basis of increased diagnostic information. Providing a method (however rough) of estimating the dose empowers dental practitioners to make an informed decision.
Assessment of colour Doppler sensitivity of a range of early pregnancy ultrasound systems Browne JE a, Cournane S b, Fagan AJ c. a School of Physics & Medical Ultrasound Physics & Technology Group, IEO, FOCAS Institute, Dublin Institute of Technology; b Medical Physics and Bioengineering, St James’s Hospital, Ireland; c Centre for Advanced Medical Imaging, St James’s Hospital & Trinity College Dublin, Ireland Background: Foetal cardiac activity is well documented as the earliest proof of a viable pregnancy. Ultrasound imaging, particularly Doppler imaging using a transvaginal (TV) probe, has become the main diagnostic means of examining the health and development of the foetus [1–4]. The aim of this study was to evaluate the colour Doppler sensitivity and detectability of ultrasound systems used in early pregnancy evaluation using a commercially available flow phantom and to devise an objective measure of signal-to-noise ratio. Methods: An evaluation of colour Doppler sensitivity for a range of ultrasound systems with both transvaginal and curvilinear transducers was carried out using a Mini-Doppler Flow Phantom (Gammex-RMI). The change in Doppler sensitivity and detectability was evaluated by using additional layers of highly attenuating fat mimicking material (FMM-attenuation = 1 dB/ cm/MHz and a speed of sound = 1490 m/s) placed on top of the imaged region. The quality of the colour Doppler signal was analysed in terms of the signal-to-noise (SNR) ratio using an in-house developed program (Matlab). Results: The use of the phantom alone did not sufficiently challenge any of the systems, however incorporation of the highly attenuating FMM layer produced a significant challenge, reducing the achievable penetration depth and quality of the signal. The Doppler detectability and sensitivity results for this range of ultrasound systems will be presented. Conclusions: The evaluation of colour Doppler Sensitivity and detectability using this commercial flow phantom can be evaluated by incorporating an FMM layer and through the SNR analysis of the colour Doppler signal. Acknowledgements: IPEM funding (Research and Innovation Award 2013) References [1] Jauniaux E., Johns J., Burton G.J. The role of ultrasound imaging in diagnosing and investigating early pregnancy failure. Ultrasound in obstetrics & gynecology 2005;25:613–24. [2] Blaas H-G., Eik-Nes S.H., Kiserud T., Hellevik L.R. Early development of the abdominal wall, stomach and heart from 7 to 12 weeks of gestation: a longitudinal ultrasound study. Ultrasound in Obstetrics & Gynecology 1995;6:240–9. [3] Condous G., Okaro E., Bourne T. The conservative management of early pregnancy complications: a review of the literature. Ultrasound in obstetrics & gynecology 2003;22:420–30. [4] Mitra A.G., Laurent S.L., Moore J.E., et al. Transvaginal versus transabdominal Doppler auscultation of fetal heart activity: A comparative study. American journal of obstetrics and gynecology 1996;175:41–4.
Examining the feasibility of daylight PDT in Ireland and comparing with other PDT sources Michael Manley, Jackie McCavana, Linda Gray, Susan O’Gorman, Paul Collins. St. Vincent’s University Hospital
Contents lists available at ScienceDirect
Physica Medica j o u r n a l h o m e p a g e : h t t p : / / w w w. p h y s i c a m e d i c a . c o m
Abstracts from the Irish Association of Physicists in Medicine 6th Annual Scientific Meeting Diagnostic Parallel Session A study of the feasibility and reproducibility of measuring blood perfusion in the kidney using MRI without a contrast agent Andrew J. Fagan, Susie Clarke, James F. Meaney. National Centre for Advanced Medical Imaging (CAMI), St. James’s Hospital/ School of Medicine, Trinity College Dublin Introduction: MRI contrast agents are contra-indicated for patients with impaired renal function, and hence there is considerable interest in developing a non-contrast agent technique which can quantify blood perfusion, for example in transplant patients. Pseudo-continuous arterial spin labelling (pCASL) is a new technique which has recently been recommended for use in cerebral perfusion studies; however, its use in the torso/ abdomen regions is severely compounded by artefacts arising from respiratory motion and magnetic susceptibility inhomogeneities. This study aimed to optimise and assess the reproducibility of pCASL for renal perfusion. Methodology: 15 healthy controls were scanned using a 3T Philips scanner. A high spatial resolution pCASL sequence was optimised through careful tailoring of all acquisition parameters. 16 label/control image pairs were acquired in all cases, with the labelling plane positioned perpendicular to the aorta above the kidneys, and the image plane orientated coronallyoblique. Breath-hold acquisitions were used to minimise respiratory motion, and B-spline image registration was performed on all images prior to fitting to the standard pCASL perfusion model. Results: Image SNR of 56 ± 3 was achieved in images with: voxel resolution = 2.5 × 2.5 × 6 mm3, receiver bandwidth = 3037 Hz, label duration = 1500 ms, label delay = 1500 ms. Excellent contrast was achieved between medulla and cortex regions, with measured perfusion values of 293 ± 44 and 139 ± 20 ml/100 g/min respectively. Excellent intra- and intersession reproducibility was noted. Conclusions: It is possible to perform sensitive and reproducible measurements of blood perfusion in the kidney using the pCASL technique, with a spatial resolution sufficiently high to allow for separation of medulla from cortical regions. How to estimate the dose from a dental CT or CBCT scan Anthony Reynolds. IDT Ireland, Kinsale, Co. Cork Cone beam computed tomography (CBCT) scanners are now widely used in dentistry. Under current legislation, dental practitioners must balance the benefit to the patient against the radiation risk. Calculating exact values of dose (and hence risk) is time-consuming and requires specialist knowledge. This work shows a simple method of estimating the dose with sufficient accuracy for the task at hand. We estimate the effective dose from parameters stored in the DICOM header or displayed on the CT or CBCT screen. Database technology interpolates missing or incomplete data, and database tables can be refined as more information becomes available. Most modern equipment displays the Dose Length Product (DLP) or Dose Area Product (DAP). Published data can be used when machines do not provide this information. Multiplying the DLP (expressed in mGy.cm) by 2 for the maxilla or 3 for the mandible gives a rough estimate of the effective dose in microSieverts, within the context of an adult dental CT or CBCT scan. Results are accurate to within a factor of 2, which is sufficient for decisions regarding patient management. Trade-offs between dose and image quality can be complex, and are not always well understood. Selecting a smaller voxel size may improve the resolution, at the expense of greater noise, and operators may compensate by increasing the mAs. The additional patient
detriment must be justified on the basis of increased diagnostic information. Providing a method (however rough) of estimating the dose empowers dental practitioners to make an informed decision.
Assessment of colour Doppler sensitivity of a range of early pregnancy ultrasound systems Browne JE a, Cournane S b, Fagan AJ c. a School of Physics & Medical Ultrasound Physics & Technology Group, IEO, FOCAS Institute, Dublin Institute of Technology; b Medical Physics and Bioengineering, St James’s Hospital, Ireland; c Centre for Advanced Medical Imaging, St James’s Hospital & Trinity College Dublin, Ireland Background: Foetal cardiac activity is well documented as the earliest proof of a viable pregnancy. Ultrasound imaging, particularly Doppler imaging using a transvaginal (TV) probe, has become the main diagnostic means of examining the health and development of the foetus [1–4]. The aim of this study was to evaluate the colour Doppler sensitivity and detectability of ultrasound systems used in early pregnancy evaluation using a commercially available flow phantom and to devise an objective measure of signal-to-noise ratio. Methods: An evaluation of colour Doppler sensitivity for a range of ultrasound systems with both transvaginal and curvilinear transducers was carried out using a Mini-Doppler Flow Phantom (Gammex-RMI). The change in Doppler sensitivity and detectability was evaluated by using additional layers of highly attenuating fat mimicking material (FMM-attenuation = 1 dB/ cm/MHz and a speed of sound = 1490 m/s) placed on top of the imaged region. The quality of the colour Doppler signal was analysed in terms of the signal-to-noise (SNR) ratio using an in-house developed program (Matlab). Results: The use of the phantom alone did not sufficiently challenge any of the systems, however incorporation of the highly attenuating FMM layer produced a significant challenge, reducing the achievable penetration depth and quality of the signal. The Doppler detectability and sensitivity results for this range of ultrasound systems will be presented. Conclusions: The evaluation of colour Doppler Sensitivity and detectability using this commercial flow phantom can be evaluated by incorporating an FMM layer and through the SNR analysis of the colour Doppler signal. Acknowledgements: IPEM funding (Research and Innovation Award 2013) References [1] Jauniaux E., Johns J., Burton G.J. The role of ultrasound imaging in diagnosing and investigating early pregnancy failure. Ultrasound in obstetrics & gynecology 2005;25:613–24. [2] Blaas H-G., Eik-Nes S.H., Kiserud T., Hellevik L.R. Early development of the abdominal wall, stomach and heart from 7 to 12 weeks of gestation: a longitudinal ultrasound study. Ultrasound in Obstetrics & Gynecology 1995;6:240–9. [3] Condous G., Okaro E., Bourne T. The conservative management of early pregnancy complications: a review of the literature. Ultrasound in obstetrics & gynecology 2003;22:420–30. [4] Mitra A.G., Laurent S.L., Moore J.E., et al. Transvaginal versus transabdominal Doppler auscultation of fetal heart activity: A comparative study. American journal of obstetrics and gynecology 1996;175:41–4.
Examining the feasibility of daylight PDT in Ireland and comparing with other PDT sources Michael Manley, Jackie McCavana, Linda Gray, Susan O’Gorman, Paul Collins. St. Vincent’s University Hospital